HHtinhthe_P2

7/24/2019 HHtinhthe_P2

1/151

Csha hc tinh th

NXB i hc quc gia H Ni 2006.

Tr 141 188.

Tkho: Tinh ththc, c im cu trc, ng hnh, a hnh, bin dng do.

Ti liu trong Th vin in tH Khoa hc Tnhin c thc sdng cho

mc ch hc tp v nghin cu c nhn. Nghim cm mi hnh thc sao chp, in

n phc vcc mc ch khc nu khng c schp thun ca nh xut bn v

tc gi.

Mc lc

Chng 5 C IM CU TRC TINH THTHC .................................... 3

5.1 CC LOI SAI HNG TRONG TINH THTHC.............................. 3

5.1.1 Sai hng im.................................................................................... 3

5.1.2 Sai hng ng.................................................................................. 45.1.3 Sai hng mt ...................................................................................... 4

5.2 NG HNH.......................................................................................... 6

5.2.1 Vectthay th.................................................................................... 7

5.2.2 ng cu trc .................................................................................. 10

Chng 1. c im cu trc tinh ththc

Trnh Hn

Ngy Tuyt Nhung


2/151

5.3.3 a dng ........................................................................................... 20

5.3.4 Metamict ......................................................................................... 215.3.5 Khong vt khng kt tinh............................................................... 22

5.3.6 Gihnh........................................................................................... 22

5.4 BIN DNG DO TRONG KHONG VT TO ........................ 22

5.4.1 Olivin .............................................................................................. 24

5.4.2 Disten (kyannit) ............................................................................... 25

5.4.3 Enstatit ............................................................................................ 25

5.4.4 Amphibol......................................................................................... 26

5.4.5 Mica ................................................................................................ 26

5.4.6 Plagioclas ........................................................................................ 26

5.4.7 Thch anh........................................................................................ 27

5.4.8 Carbonat .......................................................................................... 28

5.5 C TNH HO L CA TINH THLIN QUAN VI CU TRC

CA CHNG....................................................................................... 315.5.1 c tnh ho l lin quan vi dng lin kt ho hc trong tinh th..... 31

5.5.2 Tnh cht in.................................................................................. 34

5.5.3 Tnh cht quang ............................................................................... 35

5.5.4 Tnh rn c ca kim loi .............................................................. 37

5.5.5 Tnh ct khai.................................................................................... 38

5.5.6 Cc hsco c, gin nhit............................................................... 39

5.5.7 cng v nhit nng chy........................................................ 40

5.5.8 nh hng ca dng lin kt hydro n cc tnh cht ho l............. 43

5.5.9 Hiu ng chn ca ion ..................................................................... 44

5.5.10 ho tan................................................................................... 45

5.5.11 Ttrng ....................................................................................... 48


3/151

3

Chng 5

C IM CU TRC TINH THTHC

Theo lun thuyt hnh hc ca cu trc tinh th, cht kt tinh l mt kin trc khnggian ba chiu, u n, tun hon ca ht vt cht (nguyn t, ion, phn t). iu ng

vi trng hp l tng, rt qu v rt cn bn ca cht kt tinh; nhng y ch l mttrong nhng khnng ca t rt t. So vi tinh th l tng, mng tinh ththc thngcha nhiu loi sai hng khc nhau.

5.1 CC LOI SAI HNG TRONG TINH THTHC

Nghin cu c im vt l ca tinh ththc, tnhin hay nhn to, cho thy nhngvt thy lun c nhng sai hng cp nguyn ttrong cu trc ca chng. Sai hng

loi ny tc ng ln nhiu c im ca cht kt tinh nhbn, dn, bin dng chc v mu sc. Sai hng trong cu trc bao gm sai hng im, sai hng ng v saihng mt [13].

5.1.1 Sai hng im

Trong mng c nhng vtr btrng vn dnh cho ht vt cht no (sai hng imkiuSchottky). Pyrrhotin vn l mt khong vt vi thnh phn ho hc khng c mt tlng xc nh: Fe1XS; st lun thiu ht mt lng no ; Fe

2+ lun btrng mt svtr ca n trong khoang bt din do lu hunh (S2xp theo lut ABABAB) to nn.Phn thiu ht in tch dng to thun li cho mt sFe3+ vo thay Fe2+ (xem loi cutrc nickelin, 4.3.2,d v dung dch cng khuyt tt, 5.2.3).

Mt khi nt trng xut hin, in tc th lp vo lm ny sinh tm mu. y ltrng hp ca khong vt fluorit, khi anion fluor ri bvtr khin in tch m ti chbthiu ht. in tddng bht vo (hnh 5.16 v li gii thch).

Khi ion ri bvtr ca n, n nm xen gia cc nt dnh cho ion khc slm nn

sai hng kiu Frenkel. Sai hng loi ny xy n vi cation thng xuyn hn so vianion; vi kch thc thng nh, cation dch chuyn c phn d dng hn. Sai hngFrenkel lm cho tinh thtrnn dn in tt; ion t rng buc vn ng trong mng dinh hng ca in trng. V d, trong AgCl cation bc bt u di chuyn khi nhit t 146C.

Sai hng tp cht cng l sai hng im, khi ion ngoi lai xen vo gia cc nt mng


4/151

4

ht, ti lp vo , n sbli ng sau mt nt trng mi. Nguyn txen c thkhngging nguyn tca nt mng; vi nhng tc ng vho hc tinh th(khc vkch thcht, khc vho tr), chng c thnh hng ti tnh do ca tinh th. Sc mt ca nctrong thch anh c chiu hng lm tng tnh do bng tc dng thuphn i vi lin ktSiO.

5.1.2 Sai hng ng

y l stp trung sai hng dc theo chui mng; n to ra mt sgin on trongcu trc, gi l lch mng.Khi mt mt mng trong cu trc bgin on thay v ko di

lin tc song song vi cc mt mng khc, l lch mng bin haylch bin (hnh 5.1,a).Lch bin thhin bng du ; vch ng chhng mt mng bgin on, vch ngangbiu thmt trt. Giao im ca 2 vch l ni ng lch mng l ra; l cnh bin, nigin on ca mt mng d, ni cu trc mng bbin ng mnh nht.

Nhlch bin m mt trong hai na ca mng ddng dch chuyn song song vi mttrt di tc ng ca mt lc (theo hng ca vch ngang). Cng vi strt y, lchbin sdch chuyn (theo kiu su o) dn tng on thng schui, cng chiu vi lctc ng, cho n khi thot hn ra ngoi.

Hnh 5.1,b cho thy hnh nh ca mt lch mng xon/lch xon; cc nguyn txungquanh ng D phn btrn mt ng xon. Di tc dng ca ng sut, lch xon dchchuyn dn theo hng vung gc vi vectca lc, ri cng thot ra ngoi.

5.1.3 Sai hng mt

Bin dng n hi ca mng xung quanh mt lch mng to nn trng ng sut tichvi ni nng tng cao. Bng khnng dch chuyn ca chng, cc lch mng ri rc

trong mng thng tp hp, sp xp li theo hnh thu n. Khi ni nng trnn thpnht, hnh th ny mang tn vch lch mng. y l mt trong nhng biu hin ca saihng mt, ni tp trung cc lch mng cng loi (lch bin hoc lch xon). Cc vch nychia ct ht thnh nhng min nh(hnh 5.1,c). Cc min nm hai bn vch lch mng vinhau, c thny xoay mt gc nhquanh mt trc so vi c thkia.y chnh l cu trcbn vng ca tinh ththc: vic xoay mng hai bn vch khin cho lch mng cc loi cthcng tn ti trong mt trt tkhng hon ho (gi l kin trc khm/mosaic) ca tinhth.

Song tinh

Theo nh ngha, song tinh l lin kt i c quy lut ca tinh th cng bin thahnh. Trong mt song tinh, mng khng gian ca hai c ththng lin quan vi nhau vnh hng tinh thhc, cthho bng cc lut song tinh, tc l bng yu ti xngca song tinh, nhmt gng hay trc xoay bc hai. Cc yu ti xng ny phi songsong vi mt mng hay chui mng Trong trng hp n gin cu trc ca mt trong


5/151

5

hp vi mng khng gian ca c hai pha; chng u thuc v cc chui mng v mtmng ca chng. Tuy nhin, vcu trc vi m, mt song tinh v vng ln cn thhin mtdng sai hng mt.

Hnh 5.1.Smt ssai hng trong cu trc tinh tha) Lch bin vi mt mng gin on (d). b) Lch xon.

c) Sai hng mt chia ct tinh ththnh cc min lch nhau.) Song tinh vi mt ranh gii (130) v siu mng do mt phn nguyn t(mu en) ca hai c thto nn

Mng song tinh l mng bao qut chung cho hai c th. Trn hnh 5.1, mng song tinhthhin bng cc nt en, tnh lin tc ca n biu thbng = 0(l nghing songtinh, gc gia tia php ca mt song tinh v mng song tinh, gc ny bin thin trongkhong t0n khong 6): tia php ca mt song tinh (310) cng l chui [310]ca chai c thv trng vi mt trong cc chui ca mng song tinh. Tnh lin tc ca mng

song tinh l iu kin cn bn ca tnh n nh song tinh; nghing ca n cng nh,tn sut gp cng ln.

Vngun gc, shnh thnh song tinh c ba trng hp (Buerger, 1945).

Song tinh pht sinh trong qu trnh pht trin ca tinh thkhong vt. Sphttrin hon thin ca mt tinh thl tng thng tun thmt trnh tu n.Nm trong dung dch bo ho hay trong dung th, a din tinh th tng trng


6/151

6

V d, trn hnh 5.1,d, mt (310) c thxem nhdu vt ca mt trong nhng mt catinh thbn tri (nguyn thu). Trong khi n ang tng trng, mt ht c thtip cn vtr ng vi trt t ca mng tinh th ny. y l trng hp tinh th pht trin bnhthng, cu trc nguyn thukhng bgin on. Trong trng hp ht tip cn mng tinhthbn phi th tinh thtri ngng pht trin; bin c ny cho cu trc song tinh. y l

song tinh nguyn sinh, ngun pht sinh phn ln cc song tinh tip xc v song tinh mcxen.

Song tinh hnh thnh sau chuyn pha. Thch anh nhit cao (hnh 5.5,b) vinhm khng gian P6222 chng hn, sau khi chuyn sang pha nhit thpP3221 (hnh 5.5,c) th cu trc phn li thnh hai phn lin quan vi nhau bngphp quay 180quanh trc chnh 32. l song tinh lut Dauphin. Bt nngth song tinh bin mt v thch anh nhit cao khng song tinh c phc hi.Mt v d khc, Kfeldspat gm sanidin (C2/m) pha nhit cao, orthoclas(C2/m) pha nhit trung bnh v microclin pha nhit thp (C1 ). Trongbc chuyn tpha mt nghing sang ba nghing, cc yu ti xng ca mtnghing bin mt. Nhng vng microclin (ba nghing) xut hin, lin kt vinhau bng cc lut song tinh albit v periclin; y l song tinh mng li quenthuc trong microclin (xem thm 6.11.3).

Song tinh bin dng sinh ra do lc chc. Nu lc tc dng khng ln ph vcu trc th n c thlm cho cc mt mng trt song song vi nhau vtheo hng ca lc chc. Song tinh bin dng ny thng gp trong kim loiv trong vi; chng hn song tinh lin phin rt thng gp trong calcit (hnh5.8 v mc 5.4.8).

Sai hng mc khc nhau bt gp trong cu trc tinh thhu nhthng xuyn.Kin trc khm c Laue M. ni n (nm 1913), sau khi pht hin trong fluorit. Kin

trc ny lm gim bn chc ca vt kt tinh; theo Stranski I., ht tinh thcng lncng km bn vng. Chng hn, tinh thhalit vi mt ct ngang 105cm2bph vdilc nngn bng gi trl thuyt tnh cho NaCl hon thin. Vi mt ct ngang 1000 ln lnhn tinh thddng bph vchvi mt lc 100 ln nhhn.

Nhvy, khi nh gi tinh thmt cht khng chlu c im tinh thhc v hohc ca n, m ccht lng, tc l mc hon thin ca cu trc.

5.2 NG HNH

Nhng cu trc sai hng cn c thxut hin khi hnh thnh tinh thhp cht phctp, m c im ca chng lin quan ti khi nim ng hnh, do Mitscherlich E. (nm1819) a ra ln u. Theo ,cht ng hnh l nhng cht khc nhau vho hc, kttinh thnh a din ging nhau hay gn ging nhau, khi ng nhn thy cp hp chtKH2PO4v KH2AsO4 kt tinh thnh cng mt dng a din. Chng u l hnh ghp ca


7/151

7

nguyn tny bng nguyn tkhc, thng gn ging nhau, nhng i khi khc nhau vbn cht. Mt v dkhc, trong khi cp hp cht CaSO4 v SrSO4, tng tvho hc,khng bc lnng lc ng hnh, th hai cp CaSO4NaClO4 v SrSO4KClO4 li c nnglc y. Trong nhng trng hp ny kch thc ca cc n vcu trc tng ng ngmt vai tr nht nh. Tinh thca hai mui xy dng tcation v anion phc, nhcc cptrn, c thl nhng cht ng cu trc v ng hnh vi iu kin anion ca chng gnnhau vkch thc v vtlbn knh gia cation vi anion, khng phthuc ho trvc im nguyn t.Bn knh ca Sr2+ 1,27 ln hn hn ca Ca2+ 1,04 ; Sr thay cho Casph v sbn vng ca cu trc sulfat v dn n shnh thnh cu trc mi. AnionClO4

c cng dng tdin v cng kch thc nhSO42, ion Na+ (0,98) gn vi Ca2+ v

ln; mc du ho trkhc nhau, CaSO4 v NaClO4 l cp ng hnh. Ion K+ (1,33) lnhn hn ion Na+ lm cho n khng th i vo cu trc NaClO4; nhng ng hnh caSrSO4 v KClO4 l c tht.

Trong thay thng hnh bn cht ca lin kt ho hc cng c ngha ln v n xcnh loi cu trc v do cdng tinh th. V d, periclas MgO v zincit ZnO thot nhnc thcoi l ng cu trc; bn knh hu hiu ca Mg v Zn kh gn nhau (0,78 v 0,83).Nhng lin kt ion chim u thtrong periclas cn trong zincit l lin kt cng ho tr. Vvy, cu trc ca chng ln lt thuc loi halit v vurzit.

5.2.1 Vectthay th

Phng thc hiu qum tsthay thng hnh l vic sdng khi nim vectthay th (theo F.S. Spear, 1993) hay vect trao i. Ging nh vect trong khng gianx,y,z, vectthay thcng c hng v ln: hng chsthay thnguyn tny bngnguyn tkhc, ln xc nh s lng nguyn t(b) thay th. nhn vectgia 2im trong khng gian x, y, z, hy ly ta im u tri toim cui. Cng vy,

mun c vectthay thgia 2 thnh phn khong vt, cng ly thnh phn ca 2 khongvt trcho nhau. Chng hn, vectthay thgia orthoclas v albit l:

KAlSi3O8 (orthoclas)

NaAlSi3O8 (albit)

= K Na = KNa1

Schnh lch gia orthoclas v albit l KNa, m theo php k hiu ca vect thayth, hiu ny vit thnh: KNa1. Du trsau Na c ngha l khi mt nguyn tkali i vo

thay th, th mt nguyn tnatri sby ra.Vectthay thNaK1 cp strao i tng t, nhng theo chiu ngc li. Vect

thay thtrnh by mt thc thho hc; n cho thy skhc nhau gia 2 cng thc khongvt hu quan.

Thut ngcchthay thhay cchtrao i cng phbin trong vn liu. Sthay


8/151

8

CaAl2Si2O8 (anorthit)

= NaSi CaAl = NaSiCa1Al1

Trong sthay thkp trn, Na+ v Ca2+ c trng thi ho trkhc nhau; chng khngththay thtrc tip cho nhau (nhtrong thay thn), v cn duy tr tnh trung ho inca tinh th. Vy, Na+ v Si4+ cp i vi nhau v thay thcho cp Ca2+ v Al3+; in tchtng ca mi cp u bng +5.

Bng 5.1 gii thiu nhng vectthay thhay nhng cchthay thphbin, bt gptrong khong vt to . C l, ph bin nht l vect trao i FeMg1, li thng gptrong mi khong vt cha st v magnesi. S thay th ny gn nh l tng v thngdng trong a nhit k. Thng thng, nhng khong vt giu magnesi c bn nhitcao hn so vi nhng dng giu st. FeMn1cng phbin, nhng chc trong st mitrng to khong; bi v cc loi giu mangan cng him. Granat l bit lng ch ,n cha khi lng kh ln thnh phn mangan (spesartin) trong cc bin cht bc thp.

Nhng vectthay thbao hm calci (CaMg1, CaFe1, CaMn1) thng phbin trongpyroxen, amphibol, granat v carbonat. Ni chung, chng khng hon ho v trong nhiutrng hp thng c min gin on. V d: Trong hai cp khong vt:

- diopsitclinoenstatit (CaMgSi2O6Mg2Si2O6) v- tremolitMg-cummingtonit (Ca2Mg5Si8O22(OH)2Mg2Mg5Si8O22(OH)2),

u bc lmin gin on. Mt solvus tng tcng tng gp trong granat:

gia grosular (Ca3Al2Si3O12) v pyrop (Mg3Al2Si3O12).

Chai trng hp CaMg1 v CaFe1 u c min gin on, nhng trong dung dchcng thnht min gin on rng hn so vi trng hp thhai: vkch thc th calci

v st gn nhau hn so vi calci v magnesi.Mt vecttrao i khc cng bc lsolvus l Fe3+Al1. Cchthay thny thc hin

trong cp granat grosularandradit; granat vi thnh phn ny thng c lp lnh ngscv/hay d hng v tnh cht quang hc. Nguyn nhn l sphn r (xem di) dungdch cng (Hira v Nakazawa, 1986). Epidot cng thuc vectthay thny v cng chamin gin on vng nhit thp. Min gin on cn phbin trong nhiu cp thaythkhc. Thng gp nht l trao i kiu plagioclas NaSiCa1Al1 vi vi ba min ginon.

Bng 5.1.

Bng lit k nhng vecttrao i phbin trong khong vt to

Vecttrao i Khong vt tiu biu V d Ghi ch

KNa1Feldspat, feldspathoid,mica, amphibol

KAlSi3O8

NaAlSi3O8Mi nhm khong uc min gin on.


9/151

9

Bng 5.1.

Bng lit k nhng vecttrao i phbin trong khong vt to

Vecttrao i Khong vt tiu biu V d Ghi ch

FeMn1Ging nhca FeMg1.

c bit trong granat.

Fe3Al2 (SiO4)3 Mn3Al2(SiO4)3

AlmandinSpesartin

Rt ph bin trong giu Mn.

Dung dch cng gnnhlin tc.

CaMg1Olivin (thyu), pyroxen,amphibol, granat,carbonat.

Ca3Al2(SiO4)3

Mg3Al2(SiO4)3

GrosularPyrop

Ph bin trong hu htcc nhm khong. Mingin on rng gptrong a snhm.

CaFe1

Olivin (thyu),

pyroxen, amphibol,

granat, carbonat.

CaFeSi2O6

Fe2Si2O6

Hedenbergit

Ferosillit

Min gin on khngln nhCaMg1

Fe3+Al1

Zoisit, epidot, granat,

pyroxen, amphibol,

spinel.

Ca2Al3Si3O12OH

Ca2AlFe2Si3O12OH

Clinozoisitpistacid

Rt c thc min ginon trong epidot,granat, v.v

Cr3+Al1 Granat, spinel MgCr2O4 MgAl2O4Cromitspinel

F(OH)1

Cl(OH)1

Mica, amphibol, talc,topaz,v.v

Mg3Si4O10F2

Mg3Si4O10F2(OH)2

Fluorotalctalc

Gp trong mi trnggiu Cl, F.

AlVIAlIVMg1Si1Thay th kiutschermak

Pyroxen, amphibol, mica,talc, chlorit,serpentin,v.v

CaAlAlSiO6

CaMgSi2O6

Al-diopsitdiopsit

Al thay th l ch yutrong hu ht silicat. Clkhng lin tc.

NaAlIV1Si1

Thay th kiuedenit

Amphibol, mica.NaCa2Mg5AlSi7O22

Ca2Mg5AlSi8O22

Edenittremolit.

Kim loi kim thay thtrong amphibol haymica.

NaSiCa1Al1IV

Thay th kiuplagioclas

Plagioclas, pyroxen,

amphibol, jadeit.

NaAlSi3O8

CaAl2Si2O8

Albitanorthit

Nhiu min gin on; p sut cao

NaSi bn vng hnCaAl.

NaAlVICa1Mg1Thay th kiu

jadeit hayglaucophan

Pyroxen, amphibol.NaAlSi2O6

CaMgSi2O6

Jadeitdiopsit

Khng lin tc. NaAl bnvng p sut cao.

TiAl2Mg1Si2

Thay th kiutitan tschermak

Pyroxen, mica,

amphibol, v.v

CaTiAl2O6

CaMgSi2O6

Ti t h k di it

Thay th titan trongsilicat.


10/151

10

y cng l s thay th gia jadeit v Ca-tschermak trong pyroxen, glaucophan vtschermakit trong amphibol, cng nhparagonit v margarit trong mica. Mi nhm khong

vt ny u cho thy nhng min gin on dc vectny. y l kiu trao i c ngha,bi v ni chung, NaSi thng thay thCaAl khi p sut tng. Mt cp thay thquan trngkhc l ca kiu tschermak (AlVIAlIVMg1Si1) v phin bn ca n (Al

VIAlIVFe1Si1).

Qu trnh thay thny xy ra trong nhiu silicat, nhpyroxen, amphibol, mica, chlorit,serpentin v cordierit.

Thay thkiu edenit NaAlIV1Si1c mt trng. Amphibol v mica u c thc trng ti vtr ca nguyn tkim loi kim; vy khong vt ca chai nhm u c kiu

thay thny. Mc du vy, sthay thvi trng c thcho thy mt khong vt bt k.Trong amphibol v mica, min gin on thng thy dc vect thay th kiu edenit.Chng hn, gia actinolit v edenit, muscovit (hay paragonit) v pyrophyllit, cng nhgia biotit (hay Na-phlogopit) v talc. Trong Caamphibol, thay thkiu edenit thng kthp vi thay thkiu tschermak tskhong 1 : 1 (mc du tsny thay i tuthucloi v mi trng PT) cho vectthay thkiu pargasit

NaAlIV1Si1 + AlVIAlIVMg1Si1 = NaAl

VIAlIV21Mg1Si2

Bnh thng, amphibolit p sut trung bnh (80 90% tnh a dng ho hc ca Ca-amphibol) l nm gia actinolit v hornblend dc vectthay thkiu pargasit (hay phinbn Fe ca n l NaAlVIAlIV1Fe1Si2).

Bng 5.1 c hai vectthay th: kiu titantschermak

TiAlIV2Mg1Si2v TiFe2+Fe3+2. Titan him khi c nhiu trong silicat (mc du, n l

nguyn tchyu trong cc oxit nhrutil v ilmenit); tuy vy, n l nguyn tquan trng:lng titan thay thddng bin i theo nhit . Nhiu cng trnh nghin cu thc a

v trong phng th nghim u chng t mi tng quan trong amphibol, mica vpyroxen. Hiu ng ny s c p dng lm a nhit k. TiFe2+Fe3+2 l vect giailmenit v hematit v xy ra trong oxit. Nhng khnng khc cho sthay thtitan c thl cchTi trng bt din: TiMg2 quan st c trong mica, v TiAl1(OH/F)1trong titannit (sphen).

Mt vectquan trng khc l thay thkiu glaucophan hay jadeit: NaAlVICa1Mg1.Sthay thny xy ra gia diopsit v jadeit trong pyroxen v gia tremolit v glaucophantrong amphibol. y l sthay thrt quan trng, n din bin cng vi sgia tng ca p

sut, bi v glaucophan v jadeit u l nhng khong vt p sut cao. Vectthay thnycha mt hay hai min gin on trong chai nhm pyroxen v amphibol. N c thsuy rat2 vectthay thkiu plagioclas v kiu tschermak:

NaAlVICa1Mg1 = NaSiCa1Al1 AlVIAlIVMg1Si1


11/151

11

Nhng tinh thgi l ng cu trc hay cng loi cu trc, khi cc nguyn tthnhphn chim nhng v tr tinh th hc tng t trong mng ca chng, bt k bn knh

nguyn thay dng lin kt trong mng khc nhau nhthno. Kch thc tng i canguyn tcc loi trong hp cht l yu tquan trng hng u i vi phi tr ca chngv do loi cu trc. Chng hn, tt ccc tinh ththuc nhm khng gian Fm3m, trong nguyn tcc loi vi cng phi tr 6 v u c cng slng trong cng thc, th uthuc loi cu trc halit NaCl. Mt lot khong vt thnh phn khc nhau nhsylvin KCl,periclas MgO, bunsenit NiO, galen PbS, alabandit MnS, chlorargyrit AgCl v osbornit TiNu chung loi cu trc ny.

Hai khong vt stishovit SiO2 (bin tha hnh p sut cao ca silica) v rutil TiO2cng ng cu trc, c cng nhm khng gian P42/mnm v cation trong c2 khong vt(Si4+ hay Ti4+) u c phi tr bt din. Trong mi bin th bit ca silica (kcthchanh), cng nhtt ccc silicat trong vTri t, silic u c phi tr tdin.

5.2.3 Dung dch cng

Dung dch cng l mt cu trc khong vt trong mt vtr (him quy tc) bchim bi hai hay nhiu nguyn t(hay nhm nguyn t) ho hc khc nhau nhng t

lng thay i. Sthay thng hnh trong cu trc tinh thphthuc nhng yu tsau: Kch thc so snh ca cc ion, nguyn tthay thnhau.Ni chung, schnh

lch vkch thc gia cc ion hay nguyn tnhhn 15% m bo khnngthay thrng ln. Nu bn knh ca hai nguyn tkhc nhau t15 n 30%, thsthay thshn chv him c; nu schnh lch vt 30% th sthay thng hnh gn nhkhng xy ra.

in tch cc ion thay thnhau. Nu in tch nh nhau, Mg2+ v Fe2+ chnghn, th khi xy ra thay thcu trc vn trung ho in tch. Nu cc ion khngcng ho tr, nhtrng hp Al3+thay thSi4+, mt sthay thbsung sphixy ra trong cu trc nhm duy tr trung ho cho in tch tng.

Nhit khi xy ra thay thng hnh. Nhit tng cao lm cho dao ngnhit ca cu trc trnn mnh mhn, vtr nguyn tcng trnn rng mhn, dung sai sln hn i vi sthay thng hnh. Vy, nhit cao cthmong i mt thnh phn ho hc a dng hn cho cu trc so vi khi nhit thp.

Di y, hy cp n cc loi dung dch cng.a) Dung dch cng thay th

Sthay thcationcation hoc anionanion l thay thn gin nht. Trong mthp cht ion dng A+X, A+ c thb thay th tng phn hay ton bbi B+ m ho trkhng thay i. Chng hn, Rb+ nm ti vtr ca K+ trong KCl hoc biotit. Anion Yc


12/151

12

tc ca anion nm gia hai hp cht KCl v KBr l th dkhc vdung dch cng. Kchthc ca chng thay i trong khong 10% cho php hai anion thay th lin tc tCl

sang Brv ngc li.

Nu trong cng thc tng A2+X2cation B3+thay thcho A2+ th mt trong nhng giiphp nhm duy tr in tch tng l cation C+ cng i vi B3+: 2A2+= 1B3++1C+. Sthayth kp loi ny th hin trong cu trc ca saphir; Fe2+ v Ti4+ th chn 2Al3+ trongcorindon -Al2O3. Dy dung dch cng plagioclas nm gia hai thnh phn u cui lalbit Na[AlSi3O8] v anorthit Ca[Al2 Si2O8] th hin bng thay th kp sau: Na

1+Si4+ =Ca2+Al3+.

Ca2+ thay thNa+ trong cu trc plagioclas, Si4+ sbAl3+ thchn trong khung SiO. ng thc cho thy in tch tng ca chai vu nhnhau; chng tcu trc vntrung ho. Mt th dvthay thkp hu hn l dung dch cng ca hai pyroxen, diopsitCaMgSi2O6v jadeit NaAlSi2O6. ng thc thay thkp vit nhsau: Ca

2+Mg2+=Na+Al3+.

b) Dung dch cng xen k

Khc vi dung dch cng thay th, trong cu trc ca dung dch cng xen knguyn tca nguyn tny khng thay thnguyn tthuc nguyn tkia, m phn bkhong

khng gian gia chng. Tiu biu ca dung dch cng loi ny l tinh ththp dung dchca carbon trong st. Khi C ho tan trong -Fe vi cu trc xp cu lp phng, th dungdch nhn c l thp austenit. Trong qu trnh ti, nhit hchm ti 700C n chuynthnh phapelit lhn hp ca ferit v cementit.Ferit l dung dch cng xen kca C trong-Fe v -Fe vi hm lng carbon ti a 0,06%. Cn cementit l hp cht ho hc cast v carbon, Fe3C. Nu tr hon qu trnh chuyn pha ca austenit n 150C th nhitny qu trnh din bin theo hng khc. Loi thp cng hnh thnh y l martensit.Pha ny l dung dch qu bo ho ca C trong -Fe vi 1,6% C; tinh ththuc hbn

phng vi tsc/a = 1,07.Trong v dtrn, dung dch khng cha nhiu phi kim trong cu trc kim loi. Nhiu

trng hp, nguyn tho tan nm ti khoang trng loi no ca lut xp cu (thngcht nht) ca nguyn tkim loi. Lc ny, tng quan gia cc nguyn tthnh phn thhin bng tlng n gin; theo c im cu trc, pha tinh thny khng khc hp chtho hc thng thng. Chng c gi l cu trc xen k. Trong ScN chng hn, nguyntkim loi phn btheo lut xp cu lp phng, nguyn tphi kim nm ti khoang btdin ging loi cu trc halit. Do nh hng ca nguyn tphi kim khch trong cu trc

xen k, kim loi ch i khi phi thay i cu trc c th. Kim loi tantal chng hn, nvn kt tinh theo mng lp phng tm khi; nhng trong cu trc xen kTaC, sc mtca nguyn tcarbon lm cho nguyn ttantal thay i cch phn b; chuyn sang lutxp cu lp phng tm mt. Phi chng y l trng hp c o ca a hnh.

i khi, khoang trng gia cc nguyn t kim loi li do nhm nguyn t phi kimchim. Cu trc xen k ca trng hp ny tng ng vi thnh phn MeX2, v d: LaC2,


13/151

13

ca Ca trong CaTiO3b trng trng hp oxit volfram. Nguyn tNa kim loi thmnhp vo ch trng ny; nu chng chim ht cc v tr y, dung dch c thnh phn

NaWO3 v trthnh mt hp cht ho hc ging CaTiO3. Trong nhng trng hp trunggian, khi Na chim tng phn cc vtr y, dung dch nhn c sl nhng pha vi thnhphn bin i; theo , ho trca volfram bin i theo, tng phn tng ng ca nguyntvolfram ho trsu schuyn sang ho trnm.

Nhvy, cng vi shnh thnh cc dung dch cng xen kny, c thxut hin schuyn di lin tc ( trng dn dn b lp cho n ht) ca cu trc t loi ny (WO3)sang loi khc (CaTiO3). cng l s chuyn di lin tc v thnh phn gia hai hpcht ho hc. y l hin tng mi trong ho hc, m bn cht ca n chtrnn sng tnhspht trin ca ho hc tinh th. Khgia cc nguyn t, ion thc sl nhng chtrng trong cu trc. Khi chng b lp bng nhng ion v nguyn tkhc th pha kt tinhmi sra i; l dung dch cng xen k.

Trong mt scu trc, nhberyl Be3Al2[Si6O18], chtrng ny rng mthnh dngng, do cc nhm chc vng su [Si6O18]chng ln nhau to nn. Cc kt qunghin cuberyl chng tmt lng ng kca K+, Rb+, Cs+,H2O v CO2 trong knh dng ng lcgic y. Phn tH2O v CO2gn vi cc nguyn toxy bn trong vng su bng lin kt

yu. Cc ion c ln, ho tr mt ca kim loi kim R

+

, nhkali, rubidi, cesi cng nmtrong , nhng chng c gn kt vng chc hn nhiu. l do cch thay thkpsau y: Si4+ = Be2++ 2R+v Si4+= Al3++ R+. Theo ng thc u, hai cation kim loikim ho trmt vo trong vng su; cn trong ng thc sau, chmt cation R+ti .

Dung dch cng loi ny cn bt gp trong nhm zeolit. Nhm khong vt ny thucphlp silicat khung, trong cc tdin (SiO4) v (AlO4) kt thnh khung. Trong khungy, nhng hang rng v nhng knh di c ng knh t2 n 7. Chng mng chosthm nhp ddng vo trong tinh th, v chng cng cha cphn tnc. Nh lin

kt hydro, cc phn tny gn vi khung AlSi. Nhit tng nh cng y chngkhi vtr xen km khng gy bin dng khung silicat. Khi c sn nc v nhit chophp, zeolit li nhim cc phn tnc vo khe hm t chng ra i.

Sau cht, hy ni i iu vskhc nhau gia dung dch cng thay thv dung dchcng xen k. Nu dung dch loi mt khng thphn bit dung mi v cht ho tan (nuc thni nhvy), th trong loi hai hai khi nim ny ginguyn gi tr. Ti th dvzeolit nhim nc nhng lng thay i th, mt iu tng nhnghch l, nc khngng vai dung mi, m trthnh cht ho tan. Skhc nhau thhai l chcht chv

cht thay thphi cng chung dng lin kt trong dung dch cng thay th; cn trong dungdch cng xen kdng lin kt ca hai thnh tc thhon ton khc nhau.

c) Dung dch cng khuyt tt

Dung dch cng khuyt tt hnh thnh khi mt cation ho trcao vo thay cho nhiucation ho trthp hn nhm gicn bng in tch. Sthay thny chxy ra trong mt

d khi b2+ h h +


14/151

14

1. Gii ho hc tng a ra nhiu cng thc nhFe6 S7 hay FenOn +1 nhm nhn mnh iudthng ny. Phng php Roentgen tinh thhc cho thy trong khong vt pyrrhotin,

nguyn tlu hunh phn btheo lut xp cu su phng, nguyn tst c phi tr suvi lu hunh. Nu mi khoang bt din u b chim, th cng thc ca pyrrhotin lFeS (loi cu trc NiAs). Nhng vtr trong khoang bt din bkhuyt mt phn, thnh racng thc ca khong vt vit thnh Fe1XS,vi x bin thin t0 n 0,2.

Khong vtnhpyrrhotin l dung dch khuyt tt, bi v trong cu trc ca n mt him quy tc khng c chim ht. Khi Fe2+ thiu vng trong mt skhoang bt din, mmng lu hunh vn nguyn vn, cu trc skhng trung ho in. Rt c th, trong sionst c mt sc ho trba b p s thiu ht in tch. Nu quvy, cng thc capyrrhotin trung ho in tch vit thnh: Fe2+13X Fe3+2XX S; trong l v tr cacation bbtrng. Nu x bng 0,1 th ng vi 0,1 chtrng sc 0,7 Fe2+ v 0,2 Fe3+ trongcu trc ca pyrrhotin. Ni cch khc, st ba thm nhp cu trc bng sthay thnhsau:Fe2++ Fe2+ + Fe2+ =Fe3++ Fe3++.

Mt th dkhc ca dung dch cng khuyt tt l maghemit -Fe2O3, mt sn phmoxy ho ca magnetit Fe3O4 (Fe

2+Fe3+2O4). Maghemit cng l spinel thiu st, trong vtr tdin v bt din ca cation bthiu ht ng k. Thnh phn ca khong vt thhin

bng cng thc sau: Fe

3+

Fe

3+

1,67

0,33O4, trong

cho thy sthiu ht st ho trba.Tthay thng hnh

Khuyt tt v cu trc khuyt tt khng chbc lnhng khong trng vng nguyntngay ti vtr dnh cho chng. Hy xem xt cu trc cc hp cht spinel MgAl2O4 lmth d. Mt nghch l trong cu trc ca chng l chbt din l khoang trng ln thcha ion cnh(bn knh ca Al3+0,57 so vi ca Mg2+0,74); khoang trng tdinnh li cha Mg ln. Trong Ga-spinel MgGa2O4 (rGa = 0,62), mt s (c th ti 50%)nguyn tgali ri vtr bt din, ti nm trong khoang tdin cng vi magnesi. Ti y,

ion thuc hai nguyn tchim khoang tdin theo quy lut ngu nhin, hon ton gingnhcc nguyn tthchn nhau trong cu trc ca dung dch cng thay th. Theo thnhphn ho hc th nhng pha ny thc sl nhng hp cht ho hc, cn vcu trc chngli ging nhdung dch cng thay th. C thgi chng l dung dch cng tthay thhaycht tng hnh (xem thm 6.13.6).

5.2.4 Sphn r ca dung dch cng

Trong shnh thnh dung dch cng nu c sthay thgia hai nguyn t(hay ion)vi kch thc chnh lch nhau nhiu, th iu ny chxy ra mc hn ch. Tuy nhin,nhit cao lm cho cu trc gin n, nguyn tdao ng vi bin ln hn; cc vtrca nguyn tvn khng ging nhau, nay trnn bt phn bit hn. Kt qu, sthay thgia cc ion ny tr nn bt kh khn, trong nguyn tkhc loi hon v nhau theocch ngu nhin.


15/151

15

dch cng gia hai pha u v cui: Na[AlSi3O8] v K[AlSi3O8]. Khong vt nhit caony vn ng nht, nhng v cha cc cation khc bit nhau vkch thc, nn khi lm

vo iu kin nhit thp n strnn khng bn vng v bphn r (hnh 5.2,b).

y l qu trnh xy n vi mt dung dch cng; khin n btch ra thnh hai (hoc

c thnhiu hn) pha rn khc nhau; mc du khng c vt liu mang n hoc mang i.Ni cch khc, khng c sbin ng vthnh phn trong h.

Di knh hin vi in t phn gii cao c thquan st cc phin dy c 1m caamphibol, cc phin tch t khong vt chu c cng mt hng tinh th hc. Phinhornblend u song song vi (001) trn nn khong vt chgrunerit, phin grunerit tch ratpha chhornblend th theo hng (100). Trong feldspat kim c thquan st hin tngphn r dung dch cng bng mt thng: phin feldspat giu natri gn song song vi(100) trong khong vt chfeldspat kali. Smc xen mang tnperthit ny cn bt gp

thang nhhn, phi dng n knh hin vi thm ch k thut nhiu xRoentgen mipht hin c.

Loi mc xen c quy lut sinh ra do phn r dung dch cng ny bt gp trong nhiuhkhong vt: felspat kim, amphibol, pyroxen v oxit st.

Xut xca kin trc (mc xen) phn r thy r trn gin TX hnh 5.4,a). Trc


16/151

16

Dung dch cng gia hai khong vt thnh to nhit T1. Ti vng nhit thphn c mt min solvus, cc mi tn dc ng bin cho thy sthay i vthnh phn

ca khong vt ng sinh khi nhit h thp. Hnh 5.4,b l s lt mng cc pha kttinh (vi thnh phn Xi) vi mt trnh txut hin. Ln lt ttrn xung, trc ht l phang nht, dung dch cng hnh thnh nhit T1. Sau l ht cha cc phin li khaisong song vi (001) sinh ra nhit T2. Di cng, ngoi cc phin th hn dc (001),trn ht khong vt mt lot phin song song vi (100) xut hin nhit T4.

Hai silicat ginh ny c thbt gp trong basalt. Lot dung dch cng lin tc c

ththy trong vi thnh phn tng tv bn vng nhit T1. Vng nm gia T1 vT4 ca gin trng thi cho thy minsolvus. l trng TX trong sho tan giahai cu tgim u tnhit cao xung nhit thp. Mi thnh phn nm trong minng vi hai pha cng tn ti, thay cho mt pha ng nht pha trn min.

Hy ly thnh phn X1lm v d. Ti vng pha trn min solvus, nhit T1, cutrc silicat cn trng thi nng lng cao cho php ion A v B (d kch thc chnh lchti 25%) phn btrong cng him quy tc mt cch ngu nhin. Thnh phn ny clm ngui rt chm, khi t nhit T2th cu trc khng cn ddng cho php cation A

v B phn bhon ton ngu nhin c na. Nhng ng sut xut hin trong cu trc, dochnh lch kch thc ca cation, gy nn skhuch tn ca ion A sn sinh ra nhngmin silicat giu A. Skhuch tn ng thi ca ion Bcng lm xut hin nhng mingiu Btrong cu trc (xem li hnh 5.2,b).

Ti y bt u qu trnh phn r dung dch cng: mt khong vt vn ng nht phn li


17/151

17

phn X3. Mc du sphn li ion bn trong cu trc silicat bt u T2 l qu trnh phc tp

thang nguyn t, n pht sinh chyu do cu trc khng nng lc vt qua skhc bit vkch thc ion. Nhit hlm cho nng lng ca cu trc gim theo.

Hnh 5.4.Gin T X ca pyroxen/amphibol

Qu trnh phn r dung dch cng l skhuch tn nguyn txy ra trng thi rn.Nhit tng (ng nng cng tng theo) lm cho nguyn tdao ng nhiu hn v tngthm chi cho chng bt khi nguyn tvy quanh, di chuyn ti vtr mi. Nhvy,tc khuch tn phthuc nhiu vo nhit . Khi nhit hxung, s lu ng ca

nguyn tt rnn hn ch; thnh ra qu trnh khng tht n pha cui vi thnh phntinh khit. Kch thc cc tm mc xen c thbin ng theo nhiu thang , nh nitrn, v phthuc vo tc hnhit ca hthng. Nhit hchm th thi gian dnhcho nguyn tkhuch tn cng c nhiu; kin trc mc xen phn r sc ht th hn.Nhng ngui nhanh c thbo tn c kin trc ng nht nhit cao ca chng,mc d l trng thi gibn. Nu nhit hvi tc trung bnh, kin trc phn rdung dch cng pht trin c thl cc tm mc xen vi tinh.

5.3 A HNHa hnh l nng lc ca mt hp cht ho hc kt tinh theo nhiu loi cu trc (tu

thuc sthay i nhit v p sut). Nhng cu trc khc nhau ca mt nguyn thohc hay mt hp cht ho hc gi l ccbin tha hnh.

5 3 1 M bi h h h


18/151

18

Phbin nht trong bin cht l thch anh. Trong iu kin bnh thng ca vTrit, thch anh thng tri qua sbin i pha: gia -thch anh (nhit thp) v -thch

anh (nhit cao). Tt cthch anh tn ti iu kin nhit v p sut ca kh quynu l -thch anh, sn phm bin i a hnh ca -thch anh do s hgim nhit (xung thp hn 537C, p sut kh quyn), phn ng xy ra cng vi sthay i gc hotrSiOSi, nhanh chng v c tho ngc. Phn ng loi ny khng i hi ph bcutrc cng cc mi lin kt, khng cn n sthay i ln vni nng.

Hnh 5.5.Cu trc tinh thca cc bin tha hnh SiO2chiu trn mt (0001)a) Tridymit; b) Thch anh nhit cao; c) Thch anh nhit thp

Bng 5.2.

Mt skhong vt a hnh tiu biu

Thnh phn Tn khong vtHv nhm khng

giancng Ttrng

Kim cng Lp phng Fd3m 10 3,52C Graphit Su phng P63/mmc 1 2,23

Pyrit Lp phng Pa3 6 5,02FeS2

Marcasit Trc thoi Pnnm 6 4,89

Calcit Su phng R c 3 2,71CaCO3


19/151

19

Coesit Mt nghing C2/c 7,5 3,01

Stishovit Bn phng P42/mnm 4,3

Hnh 5.6.

Biu trng thi P-T ca cc bin tha hnh SiO2p sut o bng kilobar = 1000 bar; 1 bar = 0.987 at (Theo Cornelis K.v nnk,1993)

Cristobalit v tridymit hnh thnh trong iu kin nhit cao v p sut tng ithp, nhtrong dng dung nham giu SiO2. Theo bng 5.2, ttrng ca chng u t gitrthp nht (2,20) trong scc bin thca SiO2. Mt khc, cristobalit v tridymit u lnhng bin thgibn trong iu kin kh quyn. Chai khong vt u phong ph trongdung nham lc nguyn c. Nhng chng cy cho thy rng, phi cn n mt nng lngphn ng cao c thbin i mng tinh thca cristobalit (hay tridymit) sang trt tniti kiu thch anh nhit thp.

Coesit v stishovit bn vng p sut cao n rt cao (xem biu PT, hnh 5.6),thng bt gp ti cc hthin thch. Coesit tn ti di dng bao thtrong granat v cckhong vt eclogit vng Alp (Chopin v nnk, 1991). Chng cng c ttrng cao v rt cao,nu so snh vi cc bin thSiO2khc. Vi phi tr cao dthng ca silic, stishovit ccoi nhsn phm ca phn ng nng lng cao ca sbin i tcu trc vi phi tr tdin v vi dng lin kt cng ho trl chnh sang cu trc vi phi tr bt din ca silic


20/151

20

5.3.2 Trt t khng trt ta hnh lin quan vi bin i trt tkhng trt tthng quan st thy trong hp

kim v trong khong vt. Trt thon ho ch gp im khng tuyt i (0K tngng 273,15C). trng thi ny cc nguyn ttrong cu trc sp t trn vtr tinh thhc ring, tc l ti him quy tc xc nh. Nhit tng ko theo dao ng nhit caht trong cu trc, trt thon ho bri lon; cho n khi t n mt nhit cao no, th sthu c trng thi hon ton ri lon,khng trt thon ton. Gia hai thi cc

ny l cc trng thi khng xc nh, v d: feldspat kali (KAlSi3O8). Khung ca nhmchc (AlSi3O8) c cu trc gm nhng vng bn tdin trong Al chim (1/4) v tr

trong khoang tdin ging nhca Si; v n thchn silic trong khong vt.

Sanidin l bin thnhit caovi nhm khng gian C2/m. Nguyn tnhm ca nphn bngu nhin (hon ton khng trt t) trong cu trc khung ca alumo-silicat ny.Nhvy, Al3+c tn sut gp bng nhau cho c4 tdin (ca vng bn); ni cch khc,n chia u cho 4 tdin (cc hnh 6.29 v 6.30): tnh bnh qun mi tdin cha 1/4 ionnhm. Vng bn sc i xng ring l 2/m. Vi trt tthp nht, cng thc ho tinh

thca sanidinvit thnh:K[(Al,Si)4O8]

Microclin l bin thnhit thp ca K-feldspat. Vi nhm khng gian C1 bin thny c trt tcao nht. Mi ion nhm phn b(mt Al3+/vng bn) ti mt tdin xcnh ca vng bn, 3 tdin cn li l ca silic. Vng ny khng cn gic i xngcv cng thc ho tinh thvit nhsau:

K[AlSi3O8]

Orthoclas l bin thtrung gian.N cng chim vtr trung gian cvtrt t. Ionnhm chphn bti 2/4 tdin ca vng bn, mi ion nhm chia u cho 2 tdin ny.i xng ca vng bn chcn l trc xoay bc hai. Bin thny c cng thc ho tinhth:

K[(Al,Si)2Si2O8]

5.3.3 a dng

a dng (politypism) l trng hp ring ca a hnh, p dng i vi tng bin tha hnh (vn chmt thnh phn ho hc); trt tnguyn tca bin thchduy tr theohai chiu khng gian, tc l theo tng lp. Cc cu trc ca bin thy chkhc nhau cchphn bcc lp, tc l gi trthng sca chui thng gc vi mt lp.

Carbur silic SiC, vurtzit ZnS, mica v cc silicat lp u c hin tng a dng. Ring


21/151

21

nguyn t lu hunh xp theo lut lp phng, tc l ABCABC). Loi cu trc vikch thc cca csca cc dng vurtzit lit k nhsau:

Loi cu trc Thng sc, Loi cu trc Thng sc,

4H 12,46 6H 18,73

8H 24,96 10H 31,20

(H : Hsu phng)

Bdy ca cc lp csny l 3,12 . Bng lit k cho thy ln ca cc thng sc u l bi ca gi trny.

Cu trc ca mica v silicat lp khc u bao gm cc lp csTO hoc TOT vi ixng ring thuc h mt nghing (T l l tdin silicoxy, O l l bt din kiu brucitMg(OH)2 hay gibbsit Al(OH)3). Cc lp ny xp song song trong silicat theo cc trt tkhc nhau. i xng ca vng su quanh nhm OH l su phng; nhng khi cc lp csxp chng ln nhau, cc vng su ny khng i din nhau, m lch nhau, trt tngi mt vectvi ln n nh l a/3 (a l thng smng) theo ba phng cch nhau120. Mi phng c cp vectngc nhau.

Mt sloi cu trc ca mica c gii trnh di y.

a) Nu cc lp lch nhau lun theo mt chiu, tc l trt theo 1 vect[1], cu trcnhn c sginguyn cu trc mt nghing vi nhm khng gian C2/m : loi cu trc1M.

b) Nu cc lp lch nhau theo 2 vectngc nhau [1,I]th loi cu trc l 2O thuc htrc thoi vi nhm khng gian Ccm21.

c) Nu cc lp lch nhau theo hai vectcch nhau 120, chng hn [1,2]th l cutrc vi i xng mt nghing C2/c, l loi cu trc 2M1.

d) Khi lp cstrch nhau theo cba vect, nh[1,2,3], sc loi cu trc 3T, vinhm khng gian P3112 hay P3212.

Cc loi cu trc mica phbin nht l 1M (2/m), 2M1 (C2/c) v 3T (P3112) (hnh 6.27).

5.3.4 Metamict

Khong vt gi l metamict khi cu trc tinh th bphn humc khc nhau,

mc du nhiu khi n vn cn gic hnh dng a din ca n. Tt ccc khong vtmetamict u cha trong cu trc nguyn thuca n nhng nguyn tphng x, nhuranv thori, ngun pht sinh bc xalpha gy phn hui vi khong vt ch. Nguyn tphng xc thloi bhon ton trt ttun hon quanh n. Tuy vy, hin tng ny cphn kh hiu bi v mt s khong vt cha nguyn t phng x cha ti 0,5% vn bmetamict ho. Trong khi nhiu c thkhc cha nguyn tphng xnhiu hn li duy tr


22/151

22

Khong vt cha bmetamict ho c thc ct khai tt, sn phm metamict ho skhng bc ltnh cht y, thay vo l vt vvs. Nhiu khong vt metamict c dng

a din tinh th v nh th chng cho thy dng gi hnh (xem di y). Khi nung,khong vt metamict c thhi phc trng thi kt tinh v tng ttrng ca n.

5.3.5 Khong vt khng kt tinh

Theo nh ngha, khong vt thng c trng thi trt tcao trong sphn bnguynt. Mc du vy, vn thng gp cc dng khong vt vi trt tthay i, mt snhkhong vt keo v thutinh, xp loi v nh hnh. Khong vt keo hnh thnh trong iukin nhit thp, p sut thp v thng trong qu trnh phong ho. V dmng , ct trong cc hang ng. Limonit FeO.OH.nH2O v alophan (silicat nhm ngm nc) lnhng khong vt v nh hnh thng gp.

Thutinh giu silica thng c trong vt liu phun tro, chng c trt ttm gn ctrng. Mc du Si4+ v Al3+ trong cu trc vn duy tr phi tr tdin, ging trong silicatkt tinh.

Opal c mc v nh hnh thp hn. Thnh phn ho hc ca n c th lSiO2.nH2O vi cha nc trung bnh khong 4 n 9% trng lng. Trn nh hin vi

in tqut opal mu trng phn cho thy n cu to tnhng ht silica ng knh xp x3000; chng xp kht theo lut su phng ABABAB bng lin kt yu. Trongphm vi cc ht cu y, opal duy tr c trt tsp xp cc tdin SiO2.

5.3.6 Gihnh

Khong vt gi lgihnh khi n tn ti di hnh thi a din ca mt khong vtkhc. Mt bin thgihnh c thvn bo tn hnh thi a din nguyn thuca n, tuy

cu trc tinh thv thnh phn ho hc bn trong bin i. Bn trong a din tinh thca pha ny c th l thnh phn ho hc v cu trc tinh thca pha khc. V d, pyritFeS2 c thbin i n limonit FeO.OH.nH2O, nhng vn ginguyn c mi nt hnhthi ca pyrit. Khong vt ny c m tl bin thgihnh ca limonit theo pyrit.

Gihnh c thhnh thnh bng cc cch sau y:

a) Thay th. Trong qu trnh ny ng thi vi s chuyn i tun t ca vt liunguyn thul sthay thtng ng ca vt liu mi; mc du gia chng khng xy raphn ng ho hc. V d, silica thay thsi gcho gho hay mc thch. Thch anh c

ththay thfluorit to v bc quanh khi lp phng fluorit.b)Bin i. Trong shnh thnh ca gihnh loi ny vic vt liu cchuyn i hoc

vic vt liu mi chuyn n chng vai tr th yu. l do cc vt liu ny c thkhng khc nhau lm vthnh phn ho hc; ngoi ra, y c scan thip ca cc qutrnh sn c trong iu kin kh quyn nhhydrat ho, oxy ho, v.v... Chng hn, anhydrit


23/151

23

trng si ng, y bin cca lng t. Ngay ttrong qu trnh sinh thnh v pht trin,chng lun hm cha nhng tim n; sai hng v khuyt tt thng xuyn c nguy cxut

hin. Trn y, u chng ni n cc sai hng cc loi.Hy bt u tnhng sai hng im, phn nhiu lin quan n cu trc. Bn cnh ,

cu trc tinh thcn c sai hng im do tp cht, do nguyn txen k. Khc vi nguyntca mng, cc nguyn txen kny nh hng khng tt ti tnh do ca tinh th, binhng hiu ng mang tnh cu trc (kch thc khc nhau) v hiu ng in (in tchkhc nhau). Ngc li, sc mt ca phn tnc trong mng tinh ththch anh chnghn, c xu hng lm tng tnh do, bi tc dng thuphn i vi lin kt Si O.

Do hot ng trt do, trong lng tinh thc thtn ti min lch mng; ti , mngtinh ththiu slin tc vn c ca n vi vng xung quanh. Min ny gii hn bng vnhng bin khp kn (hnh 5.7) gi l ng lch mng hn hp (vung gc vi nglch mng hn hp ny l vectca lch bin v cn vectsong song vi n l lch xon).Di tc dng ca ng lc trt ct n(cn gi l vectBurgers biu thbng mi tn)mng dch chuyn v min ny mrng. Ti tt ccc im , ng lch mng hn hpc vect lun xin gc vi n v c thphn tch thnh hai thnh phn: thnh phn lchbin vung gc v thnh phn lch xon song song vi ng.

ln ca vectBurgers thhin mc bin dng ca mng, tng ng vi thngschui trong hng trt, tc l hng ca lch xon. Dc theo ng lch mng hnhp, vect lm vi n mt gc thay i tim ny sang im khc. Nhng ln vphng (n khng c ngha vchiu) ca n th lun khng i. Do , vectBurgers lmt hng s ca lch mng, thhin nng lng ti thiu vn dng cho mt bc dchchuyn (bc trt) cs([9], Tr.283293).

Trong mi cu trc xc nh chc mt skhng nhiu vectBurgers bn vng, n

tng ng vi thng snhnht, hay vi lin kt ho hc mnh nht ca mng tinh th.Cn mt trt th song song vi mt mng vi mt ht ln nht (do , n trnh ct quacc lin kt ho hc mnh).

Song tinh bin dng hay song tinh chc l mt trong nhng kiu bin dng do. Ns tr nn ng quan tm khi song tinh c mt s h trt, chng hn trng hp caf ld t h l it


24/151

24

song tinh) v dc theo hng trt1. Bc trt ct n S l mt hng sca song tinhv tnh bng biu thc S = 2tg(/2) (hnh 5.8).

Do bc trt n S, hnh cu bin thnh elipsoit v mi mt u xoay trhai tit dintrn ca elipsoit (cng l tit din chung ca hai hnh): l mt K1 v mt K2.Song tinhcng c th hnh thnh nh bc trt n S song song vi mt trt K2 v dc theohng trt 2.Mt stc gichuyn xl kha cnh tinh thhc ca song tinh xc nhhsong tinh bng 4 yu tK1 K2 1 2. Di y, trong khi ni n cc trng hp cth,

hsong tinh c sdng sgm mt song tinh K1, hng song tinh 1 v bc trt nS (Klassen-Nekliudova, 1964).

Di y l slc vbin dng trt trong mt skhong vt.

5.4.1 Olivin

mng cs: a [100] = 4,76

b [010] = 10,21c [001] = 5,99

Vect trt ct n dc b[010] ng vi nng lng ng lc 4 ln ln hn so vihng a [100] hay c [001], bi v nng lng ny t lthun vi bnh phng ln cavect.

Cu trc tinh th ca olivin ly lut xp cu hai lp ca anion oxy lm c s. Mt(0001) ca n ng vi (100) ca mng trc thoi (theo Poirier, 1975). Ngoi (100), mt

mng dy c nht (c thl mt trt) l (011) v (010), ng vi cc mt lng trca lutxp cu su phng (hnh 6.2).

Tuy nhin, cu trc ca olivin gm cc tdin SiO4 c lp vi lin kt Si-O m mttrt khng thct qua. Nhvy, tr(010) tt ccc mt mng dy c ca xp cu suphng u khng phi l mt trt. Tgc ho hc tinh thc thni (010) l mttrt ca olivin


25/151

25

Bng 5.3.

Cc htrt chnh trong olivin

(+ phbin; khng phbin)Nhit thp Nhit cao

(100) [001]+ {110}[001]

{110}[001]+ (010) [100]+

(100) [010] {0kl}[100]+

(001) [100]

{101}[010]

5.4.2 Disten (kyannit)

Disten l bin thba nghing ca Al2SiO4O. Cu trc tinh thc tdin SiO4 c lpv nhng nguyn toxy khng lin kt vi Si. Hnh 6.8,a l scu trc tinh thcadisten. Cc nguyn tnhm u phi tr bt din, mt na sa din ny gn vi nhau quacnh chung to nn chui song song vi [001]. Cc chui ny li kt vi nhau nhcc btdin cn li v cc tdin SiO4. Nhng quan st ho hc tinh thcho php dbo mt

trt thun li c thl (100) v n song song vi chui dy c nguyn toxy dc [001]v vectBurgers ngn nht ng vi b = 4,57 . Trn thc t, Mugge (1883) v Friedel(1964) tm ra mt trt (100) ny cho disten. Ngoi vic khng inh iu ny bng thcnghim, Raleigh (1965) i n kt lun rng [001] l hng trt thun li ca disten.

Hnh 5.9.

(a) Song tinh (lut) albit: Hng song tinh 1 v chiu dng ca n, mi mi tnng vi mt thnh phn plagioclas (hm lng anorthit). (010) l mt song tinh K1.

(b) Song tinh periclin: Hng song tinh 1 = [010] v chiu dng ca n, vtr camt song tinh K1 ng vi mi thnh phn plagioclas (hm lng anorthit) K1 l mt


26/151

26

hng thun li cn bi v n song song vi chui ca thng sc = 5,2 ngn nht. Ngoira, hng [010] vi b = 8,9 l mt gi vmt mng (100) thun li vmt nng lng,

bi v n song song vi hai hng trn.Mugge (1898) quan st mt (100) un cong quanh trc [010] trong tinh thpyroxen

trc thoi tnhin v i n kt lun vstn ti ca htrt (100) [001]. Nhng quanst y c khng nh vsau bng cc thc nghim tin hnh c lp ca Turner et al(1960), Griggs et al (1960), Raleigh (1965), Green v Radcliffe (1972), Coe v Muller(1973) v sau cng l Kohlstedt v van der Sande (1973). c bit, hai tc giny cngnm quan st bin dng vi vectBurgers song song vi [010].

5.4.4 Amphibol

Cu trc tinh thca tt ccc amphibol vi thnh phn ho hc thay i thng cchui kp c trng do tdin SiO4ghp li (hnh 6.17). Nhth, amphibol lin quan chtch vi pyroxen m nhm chc chui cng l nt c trng. Hornblend Ca2(Mg,Fe

2+)3(Al,Fe3+,Ti)2 (Si3AlO11)2 (OH)2 l amphibol duy nht c nghin cu tnh do.

Cng nhi vi pyroxen, c thdbo htrt ca cu trc sl (100)[001] khngct qua bt clin kt SiO no. Bng thc nghim tin hnh trn hornblend v sdng

thm kt quthc nghim ca Turner, Rooney v Riecker (1969, 1973) khng nh htrt dbo trn.

5.4.5 Mica

Hai khong vt to chnh ca mica l biotit K2(Mg,Fe)6(Si6Al2O20)(OH)4 vmuscovit K2Al4(Si6Al2O20)(OH)4.

Chng thuc h mt nghing v c cu trc lp vi nhm chc dng l do t din

SiO4 kt li (hnh 6.24, 6.25 v 6.26). Cu trc gisu phng ca hai l tdin to nncc lp TOT, ri cc lp cation kali kt ni chng vi nhau. C thsuy on rng trt dosddng xy ra dc theo mt mng (001), v lin kt ion ti y c thbph b. Hngtrt c thc l dc theo mt mng dy c kali, tc l [100] vi khong K-K ngn nhtv [110] ng vi hng [1120 ] ca li tdin gisu phng.

Mgge (1898) sau nhng thc nghim trn mica kt lun vhtrt l (001) [100]v (001) [110]. Nhng nghin cu vsau chng tngoi (001) mica khng cn mt trtno khc (Brg v Handin, 1966; Horz v Arhens, 1969; Horz, 1970; Schneider, 1972;

Etheridge et al, 1973). Cc hng trt cng c khng nh l [100] (Brg vHandin, 1966) hay l [100] v [110] (Etheridge et al, 1973).

5.4.6 Plagioclas

27


27/151

27

Theo Borg v Heard (1969, 1970), nhit trong khong t50 n 800oC v p sutt5 n 10kB, mi thnh vin ca dy plagioclas u bc ltnh do mt cch tng t.

Seifert (1965) quan st mt trt trong albit tnhin. n tinh thalbit nhit thp nhit 800oC v 10kB cho thy mt trt (010) v hng trt [001].

Plagioclas bc lsong tinh vnh cu trong thc nghim vbin dng trt (Brg vHandin, 1966, Brg v Heard, 1969, 1970). Trong khi tin hnh thc nghim vbin dngStarkey (1964) nhn thy nhng hsong tinh chc ng vi lut albit v periclin (bng5.4, hnh 5.9). Tt ccc plagioclas trong dy tAn30 n An95 trAn44 u cho thy songtinh albit v periclin.

Bng 5.4.

Song tinh albit v periclin trong plagioclas

Lut song tinh Mt song tinh Hng songtinh

ng sut (An55)

Albit

(lut vung gc)

K1 = (010) 1 = v t

(xem hnh 5.9)

S = 750

Periclin

(lut song song)

K1 = v t,

gn vi (001)

1 = [010] S = 750

5.4.7 Thch anh

Thch anh SiO2 l silicat c cu trc khung gm cc tdin SiO4kt ni nhau quanh. Chng c hai bin tha hnh bn vng nhng trng P-T khc nhau (hnh 5.6).

Thch anh (nhit thp) kt tinh hba phng (hnh 5.5,c) c i xngphi tri tuthuc sphn bca tdin silicoxy quanh cc trc xon i xngbc ba.

Thch anh (nhit cao) l bin thbn vng nhit trn 573C v psut kh quyn (hnh 5.5,b). Thch anh c i xng su phng; s chuynho tsang khi nung l qu trnh xy ra cng vi sdch chuyn hn chca nguyn t, khng gy ra sgin on lin kt ho hc. i xng phi trivn bo tn trong thch anh .

Trt do trong thch anh i hi ph blin kt cng ho trmnh SiO v hnh nhrt kh thc hin.

Bng 5.5.

28


28/151

28

Lng trbc mt {1010 }[0001]+ Nhit cao

Lng trbc mt{1010 }[1210 ]

+ Nhit cao

Lng trbc mt {1010 }[1213 ] Nhit cao

Lng trbc hai {1120 }[0001] Nhit cao

Thp bc hai {1212 }[1123 ] Nhit cao

Thc ra, thch anh lun cha mt lng nc nht nh. Vi cha H2O ti0,0015% trng lng (104 H/Si) thch anh gi l kh (Griggs, 1967). Tinh ththch anh

nhn to vi hm lng nc ti 8,8.10

3

H/Si c th bin dng trn nhit ti hn380C, di ng sut 10 n 20 ln thp hn so vi thch anh tnhin kh (theo Griggsv Blacic, 1965). Cc tc giny cn cho rng khi lin kt SiO bthuphn th tnh lung ca bin dng sc tng cng. Nhth, khng thtin hnh thc nghim vbindng ca thch anh nu khng bit cha nc ca mu (xc nh bng phhp phtiahng ngoi).

Di p sut kh quyn v nhit trn 600C, bin dng trt do xut hin trongthach anh vi htrt y {0001}[1120 ]. Nhit t 700C l lc c trt do vi h

trt lng tr(bng 5.5), v d: {1010 }[0001].Thch anh kh chc trt do theo h{0001}[1120 ]nhit gn 750C v theo

h{1010 }[0001]trn 750C. Trt do theo mt lng trc thkm theo trt do dcmt thp (vi chsMiller thp). Thch anh cng c chung nhng htrt ca thch anh.

5.4.8 Carbonat

Calcit CaCO3 v dolomit CaMg(CO3)2 l hai carbonat to chnh. Ngoi chng ra,khng mt carbonat no c xem xt y. Cn aragonit, vn cha c s liu no vbin dng do ca n; mc du bin tha hnh ca carbonat calci ny c thc mt trongqu trnh bin cht p sut rt cao (trn 8 10kB 400C).

Cu trc tinh th

Calcit v dolomit u thuc hba phng (xem thm hnh 4.18). Cu trc c 4 n vcng thc trong mng mt thoi vi cnh [100], [010]v [001]trng vi cc cnh ct khai

hon ton. Hnh 5.10 cng cho thy mng thhai ca calcit/dolomit di gp i vi dunglng chbng mt na. Chai mng u ly [111]lm hng chung.

Cu trc c th kho st theo php nh trc su phng, vi cc quy c sau: c[0001]ng vi [111](trc chnh i xng bc ba), {1011 }NG VI {100}(MT CTKHAI). MI MT C THK HIU BNG 4 CHSBRAVAIS-MILLER ( hkil ) vi i

29


29/151

29

Hnh 5.10.

Cu trc tinh th calcit. Quan h gia ctkhai mt thoi v mng csmt thoi

Hnh 5.11.

Cc mt mng trong calcit. Mi mt c hai k hiu: bachsMiller (HKL) v bn chsBravais Miller ( hk il )

Htrt

Calcit. Htrt trong n tinh thcalcit v trong hoa c nghin cu rt chi tit(Turner, Griggs v cng s, 1951, 1953, 1954, 1956, 1960, 1970, 1972; Mugnier, 1973,Braillon et al, 1974 v nhiu ngi khc). Bng 5.6 lit k nhng htrt bit, trong c hai hchnh l r = (100)[011]vf = (111) [101]xc lp trn n tinh th(Turner et al,1954) bin dng bng thc nghim di p sut thutnh v nhit thay i.

Bng 5.6.

Cc htrt trong calcit

Mt trt k hiu bng ch(Hnh 5.11), bng 4 chsBravais-Miller v 3 chsMillertheo mng ct khai. Hng trt k hiu bng giao tuyn ca cc mt trt.

Mt trt Hng trtSh

tng ngGhi ch

r1

(1011 ) (100)

[r1 : f2]

[(1011) : (2021)]

[011]

3 Phbin

f1

(2021 )(111)

[r2 : f3], [r3 :f1]

[(1011) : (0221)]

[(0111):(2021 )]

[101], [011]

6

a2

(1210 )

[r1:f2]

[(1011) (2201)]

6 Rt him

30


30/151

30

Hnh 5.12.

Song tinh trong calcit

Mi tn chchiu ca trt ct n

Hnh 5.13.

Song tinh trong dolomit

Mi tn chchiu ca trt ct n

Dolomit.Htrt duy nht c bit trong dolomit l htrt y (0001) [1120]. Kt

quny do Johnsenl ngi u tin t c, Higgs v Handin (1959) nghin cu y hn trn tinh thn, nhit 25 500C v 5kB. Trong cc mu nh hng thun li(i vi hng trt song song [f1 :f3]hay vung gc vi r), duy nht h trt y nyxut hin nhit di 400C. 400C song tinh f xut hin v khong 500C thhon ton nhng chcho htrt y.

Song tinh bin dng

Calcit. Song tinh trn mt e = { 012} ph bin nht trong calcit. Ngay nhit

trong phng, c thnhn c song tinh ny di lc nn vung gc [0001](Turner et al,1954). Gi trcao ca ng lc S = 2tg1915/= 0,694 tng ng vi khnng ti a trongthc nghim, t c bng lc ko song song trc C (hnh 5.12, bng 5.7).

Mt song tinh k hiu bng ch(hnh 5.11), bng 4 chsBravais-Miller v 3 chsMiller theo mng ct khai. Hng song tinh k hiu bng giao tuyn ca cc mt.

Bng 5.7.

Hsong tinh trong calcit

Mt song tinh Hng songtinh Shtng ng

e1

( 012)

(011)

[e1 : a2]

[( 012):( 2 0)]

[100]

3

[ f ] 3

31


31/151

31

(111) [211]

Dolomit.Song tinh chc pht hin ln u tin trn mu tnhin (Fairbairn v Hawks,1941). l song tinhf (hnh 5.13, bng 5.7) v ng lc S = 2tg1622= 0,587.

5.5 C TNH HO L CA TINH TH LIN QUAN VI CUTRC CA CHNG

Gia cu trc ca tinh thv cc tnh cht ho l ca chng c mi lin quan cht ch.Mt stnh cht nhy cm vi cu trc, lin quan nhiu n loi n vcu trc, cch spxp cc nguyn t; bao gm cc tnh cht chc nhtnh ct khai, cng, hoc nhhnh

thi tinh th, song tinh. Mt s tnh cht vt l khc li chu nh hng chyu ca cuhnh in tca nguyn tv dng lin kt ho hc, nhtnh dn in, tnh dn nhit, gin nhit. V d, dn in cao ca kim loi sinh ra nhstn ti ca cc in ttdo,tnh cht ny thhin khng chkhi kim loi trng thi rn m ckhi nng chy.

Tuy nhin, a scc tnh cht lin quan ng thi vi c im phn bcc n vcu trc ln dng lin kt gia chng. Cc bin tha hnh (kim cng v graphit, calcit varagonit, disten v silimanit) cho thy nhng bng chng r nht vvai tr quyt nhca loi cu trc v dng lin kt ti tnh cht ho l ca cht kt tinh. V dsau vccbin tha hnh ca carbon thhin r rng mi lin quan (bng 5.8, hnh 5.14).

Bng 5.8.

Tnh cht ca ba bin thcarbon

Bin thSphi

trDng lin kt

v loi cu trcTnh cht Vng dn, eV

Kim cng 4 ng cc, ba chiu Rt cng, trong sut, cch in 6

Graphit 3 ng cc/van der Waals,

lp

Mm, khng thu quang, mu

en, tnh kim loi

0

C60 3 van der Waals, phn t Mm, mu en, bn dn ~1

32


32/151

Hng lot cc tnh cht vt l, trong c tnh cht nhit, tnh cht c, tnh cht in(v d, dn in, dn nhit ca kim loi) ph thuc ch yu vo dng lin kt ho

hc.bn vng ca cc tinh ththng c nh gi theo cch n gin nht qua tnh

cht nhit v tnh cht cca chng. Tinh thcng cng, nhit nng chy cng cao cngha l tinh thcng bn vng. Khi nghin cu cc cht c cng loi cu trc, ngi tanhn thy c sbin i song song ca cng v nhit nng chy cng vi s thayi thnh phn ho hc. V th, mt stnh cht cv nhit thng c xem xt ngthi. Cc tinh thc mi lin kt ion thng c trng bi ttrng v cng trung bnh,nhit nng chy cao, dn nhit v dn in thp. dn in ca cc tinh th ion

km, v cc ion rt bn vng, chng khng ddng thu np electron hoc y chng i.Cc tinh thc mi lin kt ng cc thng c cng cao, chu nhit, cch in.

cng cao lin quan vi lc rt mnh ca mi lin kt ng cc. Tri li, cc cht vimi lin kt kim loi c dn in cao, nhng cng thng thp n trung bnh. Linkt tn d (van der Waals) c lc lin kt yu, v th cc tinh th vi mi lin kt nythng mm, i khi do, nhit nng chy thp. nh hng ca dng lin kt ti mt stnh cht ho l ca tinh thc thhin trong bng 5.9.

Cc hp cht tnhin thng chu schi phi ht sc phc tp ca qu trnh v mitrng thnh to; v th, rt him khi chng cha mt dng lin kt, a phn l hai hocnhiu dng lin kt cng tn ti. Trong cc hp cht dlin kt ny, cc tnh cht chu nhhng ca mi dng lin kt bn trong. Thng thng tnh cht c hng rt r. V d,trong khong vt graphit, mi lin kt ng cc rt mnh gn cc nguyn tcarbon thnhtng lp mng; cc lp gn vi nhau bng mi lin kt van der Waals yu, v thmt ctkhai c hng song song vi mt lp (hnh 5.15).

Bng 5.9.

Mt stnh cht c trng cho cc dng lin kt (L.K.)

Tnh cht L.K. ion L.K. cng ho tr L.K. kim loiL.K.van der Waals

Lc Mnh Rt mnhDao ng,

thng trung bnhYu

C

cng trung bnhn cao tuthuckhong cch ion

v in tch, rn

cng cao

cng thp ntrung bnh, rnc, un c, ddt mng

Mm, i khi do

inDn in km khi thrn, dn in ttkhi thlng

Cch in khi thrn v nngchy

Dn in ttCch in khi thrn v lng

Nhit*Tnc trung bnh ncao tuthuckhong cch ion v

Tnc cao, Dn thp.dng nguyn t,phn tkhi nng

Tnc v Dn daong. dngnguyn tkhi nng

Tnc thp, Dn cao.dng phn tkhi nng chy

33


33/151

Cu trcKhng hng, cutrc c i xng v

sphi tr cao

C hng, cutrc c tnh ixng v sphi tr

thp

Khng hng, cutrc c i xng v

sphi tr cao

Khng hng,i xng thp linquan vi hnh

dng phn t

V dHalit NaCl, fluoritCaF2, phn lnkhong vt

Kim cng C,sphalerit ZnS,phn tO2, phntcht hu c,graphit (mi linkt mnh)

ng Cu, bc Ag,electrum (Au, Ag),phn ln kim loi

Sulfur (mi linkt yu), hpcht hu c,graphit (mi linkt yu)

Tnh cht L.K. ion L.K. cng ho tr L.K. kim loiL.K.van der Waals

Lc Mnh Rt mnh Dao ng,thng trung bnh

Yu

C

cng trung bnhn cao tuthuckhong cch ion

v in tch, rn

cng cao

cng thp ntrung bnh, rnc, un c, ddt mng

Mm, i khi do

inDn in km khi thrn, dn in ttkhi thlng

Cch in khi thrn v nngchy

Dn in ttCch in khi thrn v lng

Nhit*Tnc trung bnh ncao tuthuckhong cch ion vin tch, Dn thp

Tnc cao, Dn thp.dng nguyn t,phn tkhi nngchy

Tnc v Dn daong. dngnguyn tkhi nngchy

Tnc thp, Dn cao.dng phn tkhi nng chy

ho tanHo tan trong dungmi phn cc thnhdung dch cha ion

Kh ho tan

Khng ho tan, trtrong acid hoctrong dung dchkim nhphn ngho hc

Ho tan trongdung mi hu cthnh dung dch

Cu trcKhng hng, cutrc c i xng vsphi tr cao

C hng, cutrc c tnh ixng v sphi trthp

Khng hng, cutrc c i xng vsphi tr cao

Khng hng,i xng thp linquan vi hnhdng phn t

V dHalit NaCl, fluoritCaF2, phn lnkhong vt

Kim cng C,sphalerit ZnS,phn tO2, phntcht hu c,graphit (mi linkt mnh)

ng Cu, bc Ag,electrum (Au, Ag),phn ln kim loi

Sulfur (mi linkt yu), hpcht hu c,graphit (mi linkt yu)

Ch thch: * Tnc l nhit nng chy, Dn l hsgin nhitTrong nhiu trng hp, mt cht cng tn ti nhiu dng lin kt, c thmt vi

tnh cht chphthuc vo mt dng lin kt. V d, tnh cht cca cht hu cchphthuc vo mi lin kt yu nht, khng chu nh hng ca mi lin kt thhai l ngcc. Ngc li, tnh cht quang hc ca chng li phthuc vo cc lc lin kt bn trong

34


34/151

Hnh 5.15.

Mt ct khai song song vi mt lp trong khong vtgraphit lin quan vi mi lin kt van der Waals yugia cc lp

Hnh 5.16.

M hnh cu trc khuyt tt ca fluorit CaF2Mt electron lp vo ltrng do ion fluor li, tora mt tm mu

c im lin kt ion c thquan st c nhiu mui, trong c cc halogenurca kim loi kim, chng bphn li thnh ion khi ho tan trong dung mi phn cc. Tuynhin, nu mt cht khng ho tan khng c ngha l lin kt ca n khng phi lin ktphn cc lin kt ion. Tht vy, chng hn i vi cc oxit, nng lng lin kt gia ccion trong oxit ln hn trong cc halogenur kim v ln n mc hng sin mi ca n-c khng bt cc ion ra khi tinh th.

Ngoi ra, mt shp cht, thng c mi lin kt ng cc, di nh hng ca hngsin mi ln ca dung mi phn cc, c thphn li thnh cc ion trong dung dch, mcd trng thi kt tinh chng khng phi l hp cht ion (v dHCl, HBr).

5.5.2 Tnh cht in

S tn ti ca nhng in t tdo trong mng tinh th to cho kim loi nhng tnhcht vt l c bit: dn in, dn nhit, khng thu quang, nh kim (nng lc phn quangcao). Cc in tdi chuyn tdo trong kim loi, nhng khng thbt ra ngoi mng do bngng th nng chn li. vt qua ngng th nng ny, in t cn tiu th mtcng. Nu khi dng nng lng ca tia sng th hiu ng bt in tgi l hiu ngquang in. Hiu ng tng tc thquan st thy cc hp cht vi lin kt ng cc.

in t, sau khi bt khi quo, vn li bn trong tinh th to nn dn in chocc cht ny (hiu ng quang in bn trong). Trong iu kin bnh thng (khng cchiu x) cc cht nhvy khng phi l cht dn in, kckhi trng thi kt tinh lnkhi nng chy.

Trong cc tinh thion cng quan st thy hiu ng quang in bn trong, nng lng

35


35/151

thuc cu trc loi sphalerit v vurtzit. Bin thnhit cao vi cu trc khuyt tt bnvng nhit t145,6C n nhit nng chy 552C. Cc nguyn t(anion) iod phn

btheo cc nt mng lp phng tm khi, cn cc nguyn t(cation) bc nm trong ccl trng. Do s l trng nhiu hn sht bc, cc cation c thdch chuyn khp trongmng ging nhcht lng hoc cht kh.

c im ny ca cu trc dn n nhng tnh cht c bit ca cht. dn in cabin thAgI loi ZnS gn nhit nng chy (142,4C) bng 0,00033cm2/mol. Vic chuyni AgI tbin thnhit thp sang bin thnhit cao dn n s nhy vt dnin ln vi nghn ln (1,31 146,5C). Stng nhit tip tc km theo stng dnin, khi n gn nhit nng chy, dn in t gi trl 2,64. iu th vl i l-

ng ny cn vt ln trn dn in ca cht trng thi nng chy (2,36 552C).

5.5.3 Tnh cht quang

Tnh cht quang hc rt nhy cm vi i xng. Ph thuc vo h i xng, mtquang sut c hnh dng v tnh cht khc nhau; da vo c thddng don nhngbiu hin ca tinh thdi nh sng phn cc. Mc d phn ln cc tnh cht quang hcchu nh hng mnh ca thnh phn ho hc, mt strong chng nhchschit sut,

lng chit sut, quang du li ph thuc nhiu vo c im cu trc. Ch schit sutphthuc vo mt ht ca cu trc, n thng c gi trthp cu trc khung. Lngchit sut cao hoc rt cao c coi l du hiu pht hin cc khong vt c cu trcmch hoc lp. Cc cu trc cha khuyt tt l nguyn nhn gy mu mt skhong vtnhfluorit, thch anh. Trong cu trc cc khong vt ny, cc tm mu c thhnh thnhdo sthiu ht ion hoc nguyn tmt nt mng hoc sxut hin ion hay electron dtha khong gia cc nt mng (hnh 5.16 v 5.17).

Di tc dng ca bc x, mt trong cp in tca oxy bbt ra; lm xut hin m

tm mu dng l trng. Tnh cht quang hc cng ph thuc rt nhiu vo dng lin ktho hc. Cc hp cht ion c tnh cht quang hc khng thay i, d trng thi kt tinhhay dung dch. Hp phn in ca tia ti lm bin dng lp v in tca ion. khc xca tng ion l thc o bin dng (phn cc) ca chng, tng t lthun vi kchthc ion v tlnghch vi bn vng ca lp vin t. Trong cc hp cht ion, anionng vai tr quyt nh ti khc xv gi tr ny tng t l thun vi in tch (xembng 5.10).

36


36/151

Bng 5.10.

Sphthuc ca khc xvo kch thc v in tch ca ion

Ion F O2 Cl Br I Ne Na+ Mg2+

Bn knh,

khc x, cm3

1,33

2,5

1,36

7,0

1,81

9,0

1,96

12,6

2,20

19,0

1,60

1,00

0,98

0,5

0,74

0,3

Trong cu trc i xng (phi tr) cng nhtrong dung dch, khc xion l kt qutng hp ca tt ccc ion bphn cc. i vi cu trc khng i xng, khc xcngc quyt nh bi sbin dng ca ion; nhng hin tng ny gy ra khng chdo hp

phn in ca tia sng m cn do in trng ca cc ion kbn to ra sphn cc mtchiu. Hin tng ny c dng trong ho tinh thxt on cu trc tinh th. Cc tinhthion, trmui ca cc kim loi chuyn tip v nguyn tt him, thng trong sut vkhng mu.

Cht ng cc (vi lin kt cng ho tr) khc hn cc cht ion vtnh cht quang hcdo chng c nhng in tng thi thuc hai nguyn t. Tuy nhin, bn vng ca milin kt li dao ng rt ln: cc bn kim cng, yu hn silic hoc ZnS, thic yun mc cht ny c nhiu tnh kim loi. Sgim bn vng ca mi lin kt ko theo

shp thphnh sng bc sng di. nhng cht ny, tnh quang dn xut hin khichng c chiu bi nhng nhng tia c bc sng tng ng vi di phhp thcachng. Kim cng c tnh quang in trong vng phcc tm, silic - nh sng nhn thy,ring thic c c trng bi dn kim loi.

Hp cht ng cc c gi trchit sut cao, tng ng vi nh kim cng (theo phnloi trong khong vt hc). Chng thng c mu v khng trong sut. Trong dung dch,c im phn bin tkhc hn trong tinh th, v vy tnh cht quang hc cng khchn. y chnh l c im cbn m hp cht ng cc khc vi hp cht ion.

i vi cc cht c mi lin kt trung gian ion - ng cc th mc chuyn tip nhhng n gi trchit sut (bng 5.11).

Hp cht phn tc tnh cht quang hc gn nhkhng i khi cc trng thi khcnhau: rn, lng, kh. Cc hp cht vi mi lin kt van der Waals thng trong sut, khngmu. Nu cu trc gm cc phn t dng si (phn ln parafin) hoc dng tm (n-dichlorobenzen) th tinh th c tnh d hng quang hc r rng vi quang tnh dngtrong trng hp thnht v quang tnh m trong trng hp thhai.

Tnh cht quang hc ca tinh thc sdng rng ri xc nh vtr cc phn tkhng ng thc trong cu trc.

Bng 5.11.

S h th hit t ti h th li kt i

37


37/151

KI

CsCl

48

} = 22

26

1,667

} = 0,133

1,534LiBr

RbF

43

} = 40

3

1,784

} = 0,388

1,396

LiI

CsF

54

} = 52

2

1,955

} = 0,507

1,448

MgS

CaO

65

} = 4619

2,271

} = 0,4331,838

CaTe

BaS

75

} = 54

21

2,510

} = 0,355

2,155

Hp cht % mi lin kt ng cc Gi tr chit sut

KBr

RbCl

36

} = 8

28

1,559

} = 0,065

1,494

KI

CsCl

48

} = 22

26

1,667

} = 0,133

1,534

LiBr

RbF

43

} = 40

3

1,784

} = 0,388

1,396

LiI

CsF

54

} = 52

2

1,955

} = 0,507

1,448

MgS

CaO

65

} = 46

19

2,271

} = 0,433

1,838

CaTe

BaS

75

} = 54

21

2,510

} = 0,355

2,155

5.5.4 Tnh rn c ca kim loi

Kim loi c tnh rn c nu n chu c bin dng do. Bin dng do l khnngtng phn ring lca tinh thc thtrt tng i so vi nhau khi c lc tc dng t

38


38/151

Cc sn phm kim loi thng l tp hp tinh thnhphn bkhng trt t. Khi cn c mt yu tcu trc thhai rt quan trng, quyt nh n khnng bin dng do

ca kim loi, l s lng cc hng vung gc vi mt xp kht cc qucu (hngphn lp). Nu mi ht tinh thc shng phn lp cng ln th hai ht tinh thknhaucng c nhiu hng trt song song hoc gn song song vi nhau. Nhvy, xc sut xyra bin dng do cng ln. Bi v strt phi i qua mt slng ln cc tinh th.

Trong trng hp ny c th thy r s khc nhau gia cu trc chng kht suphng v chng kht lp phng. Trong cu trc chng kht hai lp ch c mt hngphn lp, cn trong cu trc chng kht ba lp c n bn hng phn lp trng vi bntrc bc ba. Nhvy, bin dng do bt u tmt ht tinh thkim loi c kiu xp cu

su phng, c thbchn li ti ranh gii vi ht tinh thkhc; v t c khnng ccht knhau c mt xp cu trng hoc gn trng nhau. Tri li, stn ti ca bn hngphn lp trong tinh thkim loi c cu trc chng kht lp phng lm tng ln rt nhiuxc sut trng hoc gn trng ca cc mt xp cu trong hai tinh thknhau. Nhvy, cththy, cc kim loi c cu trc chng kht lp phng l kim loi c tnh rn c caonht.

5.5.5 Tnh ct khai

Ngi u tin thgii thch hin tng ct khai trong tinh th l O. Bravais. Xutpht thc thuyt mng tinh thng xut githuyt l mt ct khai {hkl}ssong songvi mt c mt mng ln nht, hay nhng mt mng nm cch xa nhau nht, tc l cdhkl ln nht. tng l chnh xc nu nhcc n v cu trc trong tinh th l ccphn tng thc nhBravais githit. Trong trng hp , r rng l khong cch cci s tng ng vi lc lin kt yu nht v to iu kin cho mt ct khai i qua. Tuynhin cch gii thch gin n nhvy cho hin tng ct khai chng vi nhng trnghp khng phc tp, v di vi graphit.

Nhng th nghim nhm kim tra hc thuyt cu trc tinh th xc minh rng trongtinh thca a scc cht v cthiu vng cc phn t. Cc tinh thny c cu to tcc nguyn tring lkhng gn vi nhau theo nhm thnh phn tv v thkhng thxem chng nhcc nt mng. Cc nguyn tlin quan vi nt mng bng nhng quy lutphc tp hn nhng nh lut ca him quy tc.

V d, cc hng smng su phng ca magnesi kim loi l: a = 3,20, c = 5,20, c/a =1,62. Nu cc nguyn tmagnesi phn btheo cc nt ca mng, th theo nhgi thuyt

ca Bravais ta sc ct khai theo mt y. Tuy nhin, magnesi kim loi khng c ct khai.Nguyn tca n xp xp theo cch chng kht cc qucu kiu su phng vi tlrtgn vi t s l tng c/a bng 1,633. iu c ngha l khng c bt k mt dthngno vkhong cch gia cc nguyn ttrong cu trc magnesi kim loi v do khng ckhnng ct khai theo mt y. Trong cu trc ca km v cadmi, tsc/a vt tri tsltng (1,86 v 1,89), v v th, lc lin kt gia cc nguyn ttheo trc chnh yu hn rt

39


39/151

khc nhau. ZnS c ct khai theo mi hai mt thoi {110}, kim cng theo tm mt{111}(hnh 5.18). Trn hnh 5.19 l scc mt mng trong cu trc ZnS theo cc mt

lp phng, mi hai mt thoi v tm mt. Khong cch mt mng dhkl ln nht ng vihnh tm mt (d111= 0,866 so vi d100= 1).

i vi kim cng, theo hng ny sc ct khai. Trong cu trc ZnS, tng ng vikhong cch l hai lp cha cc nguyn tcng loi (Zn hoc S). Lc lin kt ln giachng khin cho sphalerit khng c ct khai theo hng ny. Trong khi , cc mt mnggm nguyn tca chai loi nguyn t bo ho in tch nn lin kt vi nhau yuhn mc d nm gn nhau hn. l trng hp vi mt mi hai mt thoi trong ZnS. Vth, sphalerit xut hin ct khai song song vi mt {110}.

Hnh 5.18.

Ct khai theo mt {111} trong kim cng v mt{111}trong sphalerit

Hnh 5.19.

Lt ct cu trc ca sphalerit (ZnS) vung gcvi mt lp phng, mi hai mt thoi v tmmt

Trong cu trc silicat lp, cc tdin oxy v silic trong lp gn vi nhau bi milin kt ion ng cc rt mnh, cn cc lp chgn vi nhau bng lin kt ion hoc hydroyu qua cc cation ho trthp, iu ny gii thch tnh ct khai rt hon ton theo mt yca cc khong vt silicat lp. Tng t, ct khai theo lng tr cc khong vt nhmpyroxen v amphibol phn nh mi lin kt yu gia cc chui n, chui kp tdin silic(xem hnh 6.12, 6.18).

5.5.6 Cc hsco c, gin nhit

Cc cht c lc lin kt mnh v loi cu trc chng kht theo cc lut xp cu c

co cc tiu c trng. i vi cc kim loi, gi trco theo s liu ca Reis dao ngtrong khong t0,3.106n 4,5.106cm2/kg. Cc oxit kh nng chy cng c gi trcocng bc [(0,5 1).106cm2/kg].

Cc mui v cthng c trng bi cu trc chng kht, tuy nhin nu trong thnhphn ca chng c cc kim loi kim ho tr1 vi lc lin kt ion yu, th chng c co

40


40/151

Bng 5.12.

nh hng ca loi cu trc ti co (cm2/kg) ca cc mui kim loi kim

Hp cht LiCl NaCl KCl RbCl CsCl*A X, 2,57 2,81 3,14 3,27 3,57

Hsco ( .105) 3,50 4,18 5,65 7,40 5,90

xp cht ca ion, % 78,66 65,66 65,01 50,16 68,44

* V loi cu trc, CsCl khc hn vi cc hp cht cn li trong bng (xem thm4.3.2,a).

Cc mui c cu trc loi NaCl c co tng cng vi s tng khong cch gianguyn t.

Cu trc loi CsCl c hsco nhhn rt nhiu so vi don theo kiu din binu n ca cc cht khc trong bng 5.12. Nguyn nhn chnh l cht xt rt thp cutrc chng kht ca cc hp cht vi cation bn knh ln so vi cu trc loi CsCl. iuny th hin rt r qua hin tng gim th tch n 15% ca cc halogenur rubidi khichuyn i cu trc tloi NaCl sang loi CsCl di p sut cao.

Cc hp cht vi cation phn cc mnh c hsco nh, v khng kkhong cch gia

nguyn tl nhnhau th cc anion trong cu trc ny cng co li bt thng do bphncc. C thly v dcc mui halogenur bc (bng 5.13)

Bng 5.13.

Hsco (cm2/kg) ca cc mui halogenur bc v natri

Hp cht AgCl NaCl AgBr NaBr (AgI) NaI

A X, 2,77 2,81 2,88 2,98 2,99 3,23

Hsco ( .106) 2,40 4,18 2,74 5,09 4,14 7,01

Hsgin nhit ca cc nhm cu trc trn thay i tng thsco. Cc kim loikt tinh trong loi cu trc chng kht, cc oxit kh nng chy, cc sulfur c hsgin thtch c0,0001 0,001, cc mui v ccng c hsgin khong (0,0004 0,001).Hsgin th tch ca cc kim loi kim dao ng t0,0018 n 0,0025. Cc hp chthu cphn tc hsgin t gi trcao nht n 0,003. C thquan st sbin i hsgin th tch theo sbin i khong cch nguyn tqua dy mui halogen ca natri(bng 5.14)

Bng 5.14.Mi quan hgia khong cch nguyn tv hsgin

Hp cht NaF NaCl NaBr NaI

A X, 2,31 2,81 2,94 3,18

.104 39 40 43 48

41


41/151

trc tc ng chc bn ngoi li lin quan vi c im i xng ca quo electrontham gia to mi lin kt. V d, trong kim cng, tinh thc xy dng tcc nguyn t

gn vi nhau bi mi lin kt ng cc (quo sp

3

, xem thm 4.2.4) mnh c tnh nhhng cao. Sdch chuyn nguyn thoc sbt ph n ra khi lin kt i hi mt lcrt ln. Chnh v vy m kim cng c cng rt cao.

Trong cu trc tinh th, sxp xp nguyn ttheo cc hng khc nhau thng khng gingnhau; v th, cng cng thay i theo hng (dhng), nhng thng khng nhiu. Tuy nhin

cng c nhng trng hp c bit; v d, khong vt disten Al2SiO5c cng trn mt (100)

thay i t4 n 7 tuthuc vo hng. Cc kim loi v cc mui c cng v nhit nngchy dao ng trong mt gii hn rng. Nhn chung, c thni, cc hp cht ny cng hn v c

nhit nng chy cao hn cc hp cht hu c. Cc hp cht hu cmm v c nhit nngchy thp do chng c mi lin kt van der Waals yu. Di y sxem xt cc yu tnh hngn cng v nhit nng chy ca cc hp cht v c.

Hnh 5.20.

Mi tng quan nghch gia nhit nng chy v khongcch ion trong hp cht ion

Hnh 5.21.

Mi tng quan nghch gia cng v khong cchion trong hp cht ion

Bng 5.15.S thay i cng v nhit nng chy phthuc vo khong cch nguyn tca cc hpcht ion

Hp cht (BeO) MgO CaO SrO BaO

A X, 1,65 2,10 2,40 2,57 2,77

42


42/151

cng ln (hnh 5.21). Khi cu trc cng loi, cc cht vi cc ion cng ho trsc cng v nhit nng chy gim nu khong cch nguyn ttng (bng 5.15).

Tt ccc cht trong bng 5.15 u kt tinh trong cu trc loi NaCl, trBeO c cutrc loi vurtzit. Lin kt ho hc trong cc hp cht gn vi dng ion. Cc hp cht ngcc cng ging cc hp cht ion vc im thay i cng v nhit nng chy khic sthay i khong cch nguyn t(bng 5.16). Tt ccc cht trong bng u kt tinhtrong cu trc loi kim cng sphalerit.

Bng 5.16.

Sthay i cng v nhit nng chy phthuc vo khong cch nguyn tca cccht ng cc

Nguyn t C C C Si Si Si Ge GeA A, 1,54 1,89 2,35 2,43

cng (thang Mohs) 10,0 9,5 7,0 6,0

Nhit nng chy,C 3500 2700 1420 958

Vi cc hp cht c khong cch nguyn txp xc ththy r nh hng ca hotrn cng v nhit nng chy (bng 5.17).

Bng 5.17.

nh hng ca ho trn cng v nhit nng chy

Hp cht NaF MgO ScN TiC

A X, 2,31 2,10 2,23 2,23

cng (thang Mohs) 3,5 6,5 7,5 8,5

Nhit nng chy,C 988 2800 3180

Tuy nhin, trong cc cht trn, c im lin kt ho hc thay i ng kkhi hotrthay i; iu ny cn c xem xt khi nh gi mc nh hng ca ho trn gitrcng v nhit nng chy.

Bng 5.18

nh hng ca lin kt Ion n cng v nhit nng chy

Loi cu trc CaF2 CdCl2* NaCl NaCl NaCl NaCl NaCl

Hp cht SrF2 MgCl2 NaCl AgCl AgBr LiCl AgF

A X, 2,58 2,63 2,81 2,77 2,87 2,57 2,48

Nhit nng chy, C 1280 712 840 455 422 614 435

Loi cu trc NaCl ZnS NaCl ZnS NaCl ZnS NaCl

Hp cht NaF CuCl SrO CdS BaO CdTe PbS

A X, 2,31 2,34 2,57 2,52 2,77 2,80 2,97

Nhit nng chy, C 992 422 2430 1750 1923 1041 1120

43


43/151

trc phi tr v cu trc lp dn n sbin i r rt cc tnh cht vt l. Sthay i ccion c cu trc 8 - in tsang ion 18 - in t(hay ni chung l cc ion khng c cuhnh in tca kh tr) dn n thay i nhvcng nhng thay i kh ln vgi trnhit nng chy (bng 5.18)

5.5.8 nh hng ca dng lin kt hydro n cc tnh cht ho l

Lin kt hydro l dng lin kt yu, nng lng ca n chkhong 5 10 kcal/mol, nu sosnh vi lin kt ion hoc lin kt ng cc th nng lng lin kt hydro chbng phnchc ca cc lin kt trn. iu ny dn n mt nhn thc sai lm l dng lin kt hydro tnh hng n cc tnh cht ho l. Tuy nhin, nu so snh vi lin kt tn dth thy nh

hng ca lin kt hydro li l ng kv nng lng lin kt ca n mnh gp mi ln.Ly cc hp cht phn t lm v d, trong bng 5.19 l mt vi thng sca cc hydrurkhc nhau.

Nhng dthng vnhit nng chy v nhit si ca cc hp cht ca fluor, oxyv nitlin quan vi lin kt hydro tn ti trong cc hp cht trn cthrn, lng v kh.Theo cc sliu trong bng 5.19, bng cch ngoi suy ng cong ni cc nhit nngchy ca H2TeH2SeH2S (hnh 5.22), c th d bo nhit nng chy ca H2O l100C, tuy nhin thc tli l 0C.

C thhiu c schnh lch ln gia cc gi trnhit tan ca bng trong thc tvi gi tr nhn c bng phng php ngoi suy, nu so snh ng nng phn tvinng lng lin kt hydro. ng nng phn tbng phn chc kcal/mol, l qu nh, chthng lc lin kt van der Waals ch hon ton khng th ph v lin kt hydro

44


44/151

HCl 112 84 PH3 134 88

HBr 88 67 AsH3 116 62

HI 51 35 SbH3 88 17

H2O 0 +100 CH4 184 162

H2S 86 60 SiH4 185 112

H2Se 66 41 GeH4 166 88

H2Te 51 2 SnH4 150 22

5.5.9 Hiu ng chn ca ion

Cc phn tvi mi lin kt ion, trung ho vin tch, c th l nhng lng ccmnh. u m ca cc phn t c thht u dng ca phn tthhai, v cc phn tkhc c thtin li gn v c thbgili kh cht. Cc cht vi cu trc nhvy c psut hi nh, dkt tinh v nhit nng chy thp.

Ta hy xt phn tkiu CF4, nguyn tcacbon nm tm, c kch thc nhcbao quanh bi cc nguyn tfluor c kch thc ln hn hn v tnh in m mnh hn.Trong trng hp ny, cc nguyn tF chn nguyn tC trung tm. Carbon b chn,

khng th ht cc u m ca cc phn t khc, bi vy phn t CF4 khng c bt kkhuynh hng lin kt no vi cc phn ttng t. Hp cht loi ny dbay hi v cnhit nng chy thp. Chng thng gi l hp cht ng, ngc vi hp cht mloi NaCl. Nu nguyn t(ion) nm tm c kch thc nh, cc ion chn ca n li ln,th cht sc mi tnh cht ca hp cht ng. Mt cht vi ng dng cng thc trn nh-ng nguyn t(ion) tm c kch thc ln v nhng ion chn khng ln smang cc tnhcht ca mt hp cht m. V d4 ion chlor chn hon ton ion thic v bn knh ca Sn4+= 0,67, ca Cl= 1,81, ra: rx= 0,37. Nhit si ca SnCl4l 114C. Bn ion fluor c

bn knh 1,33 khng thchn hon ton ion thic, hp cht SnF4si 705C.So snh cc hp cht halogenur ca nhm v bo cng c thcho kt lun tng t.

Trong hp cht AlCl3, ion nhm kch thc nhbchn bi 3 ion chlor, bi vy nhit si ca AlCl3 thp(81C). AlF3si nhit cao hn 1000C v nhm khng bchn honton. Ion bo c kch thc nh(B3+= 0,20) nn n bchn hon ton bi 3 ion fluor, vthn tn ti dng kh khi nhit bnh thng, nhit nng chy bng 127C.

Schn khng chxy ra vi phn tm cn vi cc ion phc. Tuy nhin cc hin

tng i km c khc m ttrn, trong c thkn p sut hi, nhit si. Cctnh cht khc c lin quan n s chn ion, ion phc (v dSO42) c thgicht cc

cation trong tinh thbng lc tnh in.

Kch thc ca ion chn squyt nh thnh phn v in tch ion phc. Ta hy xtcc anion phc ca cc oxyacid. Tsbn knh gia cation S6+(0,29), Si4+(0,39) v

5+

45


45/151

Ion [SO6]6v cu hnh [SO6]

6 t c kh nng tn ti. Trong thc t cha gp acidorthosulfuric v cc mui ca n, nhng tn ti cc mui ca acid orthotelluric Te(OH)6

nhAg6TeO6(Te

6+

= 0,56, ra: rx= 0,41) v orthoiodic H5JO6, v dAg5JO6(bn knhJ7+Te6+). Tsbn knh C4+(0,2) trn bn knh oxy bng 0,15 thomn sphi tr 3.T c ththy, ion CO3

2c khnng tn ti, cn ion CO44th khng.

Tcc v dtrn c ththy, xem xt hin tng chn thm ch vi quan im honton tnh in (nhKossel, Goldshmidt, Van-Arkel lm) cng cho php suy lun nhngquy lut c gi trnht nh.

5.5.10ho tan

Trong cc mc trn chng ta xem xt mt stnh cht lin quan n bn vngca vt cht kt tinh nhcng, nhit nng chy ho tan cng l mt tnh chtc trng cho bn vng. Mt mui sho tan trong nc nu nhlc ht ca cc phntnc ln hn nng lng mng. ho tan ca cc mui halogen ca kim loi kimc trnh by trong bng 5.20.

Bng 5.20.

ho tan ca cc halogenur kim loi kim(mi tn chchiu tng ca bn knh ion)

Cation Anion

F Cl Br I

Li

Na

K

Rb

Cs

0,1(18C) 16 11

1,0(15C) 6,1 11 10

16 (18C) 3,7 4,5 7,6

12 (18C) 6,4 5,8 6,5 (7C)

24 (18C) 9,6 6,0 (25C) 1,7

Cation Anion

F Cl Br I

Li

Na

K

Rb

Cs

0,1(18C) 16 11

1,0(15C) 6,1 11 10

16 (18C) 3,7 4,5 7,6

12 (18C) 6,4 5,8 6,5 (7C)

24 (18C) 9,6 6,0 (25C) 1,7

Trong bng trn, ho tan c tnh 0C (nhit khc t trong ngoc). Cc sliu cho thy khng c mi lin htuyn tnh gia ho tan v bn knh ion. R rng lho tan khng nhng ph thuc vo nng lng mng m cn ph thuc vo gi trnhit hydrat ho, m gi trny phthuc vo kch thc ion khc vi nng lng mng.

46


46/151

Nguyn nhn s tng vt ho tan ca LiCl, LiI, NaBr, NaI lin quan vi loi cutrc ca chng. Lc lin kt gia cc ion trong mng yu i do tsbn knh ca chnggn vi t s tinh thhc ca cu trc loi NaCl (0,41). Trong cc cu trc loi ny, lcy gia cc ion tip xc nhau hoc gn tip xc nhau tng ln rt mnh. Stng cao ho tan ca KF, RbF v CsF c gii thch bi cht xt thp (xp) ca cu trc. Tt ccc cht ny nu xt theo tsra: rxphi c cu trc loi CsCl nhng thc tchng li kttinh trong cu trc loi NaCl.

Stng ho trko theo sgim mnh ho tan bi v ng thi vi stng ho tr,nng lng mng tng nhanh hn rt nhiu so vi nng lng hydrat ho. Bi vy, oxit vsulfur ca cc kim loi ho tr2 khc hn halogenur kim loi kim vho tan. Chng

hu nhkhng ho tan trong nc, mc d chng c loi cu trc tng t.Bt u tcc ion ho tr3 c thni n hiu ng chn, nhn mi lin kt gia cc

phn tyu i, dn n ho tan tng ln. nh hng ca ho tr ion v hiu ng chnn ho tan c thy r qua cc sliu trong bng 5.21.

nh hng ca cu hnh in tca ion ti ho tan cng rt th v. Stivel K. Y. chorng cation ng vai tr quyt nh gy nn bin dng ca anion trong mng hoc phn tnc trong dung dch. C thphn bit 4 trng hp khc nhau:

anion dbphn cc hn phn tnc;anion kh bphn cc hn phn tnc;

cation gy phn cc yu do kch thc ln, in tch nh, v 8 - in t;

cation gy phn cc mnh do kch thc nh, in tch ln, vkhng phi loi 8 - int.

Bng 5.21.

Mi lin quan gia ho tan vi ho trcation v hiu ng chn

Hp cht NaF NaCl CaF2 BaF2 AlCl3 PrCl3 ThCl4 SnI4

ho tan 1,0 6,1 0,0002 0,009 6,0 4,2 tt tt

ra+ rx 2,31 2,79 2,37 2,71 2,38 2,81 2,76 2,87

Bn trng hp trn c biu din phn gia sca hnh 5.23. Phn cc dhnnc l cc ion Cl, Br, I, OH; kh hn l Fv cc ion phc kiu (SO4)

2, (ClO4),

(PtCl6)2. Cation gy phn cc yu l Ba, Na; gy phn cc mnh l Mg, Ag.

Khi mt anion bphn cc dhn nc ho hp vi mt cation gy phn cc mnh,nng lng mng s tng nhanh hn nng lng hydrat ho. Bi vy, nhng cht chanhng anion dbphn cc v cation kch thc nh, in tch ln hoc c lp vngoi18 in t, sc ho tan nhhn nhiu so vi cc mui tng tnhng c cation kchthc ln, v8 in t(trng hp AC, hnh 5.24, mi tn chhng tng ho tan).N so snh ho tan ca cc m i A B tc hai hp cht i cng mt cation g

47


47/151

Hnh 5.23.

Sminh honh hng ca cc yu tkhc nhau ti ho tan

Ion natri gy phn cc yu, bi vy nng lng ph trdo phn cc s khng xuthin trong cu trc NaF cng nhtrong nc. Ion bc, ngc li, gy phn cc mnh. Dophn tnc bphn cc mnh hn F, nn Ag+c xu hng chuyn vo dung mi. Ktqu, ho tan ca AgF sln hn ho tan ca NaF (D B).

Hng tng ho tan D C c xc nh bi gi trnng lng mng. Hp chtNaCl c khong cch Na Cl ln hn, nng lng mng tng ng nhhn v nhvy,ho tan ln hn so vi NaF. Nng lng phtrkhng gy nh hng ti qu trnh hotan do mc bphn cc ca anion bi ion natri trong tinh thv ca phn tnc trongdung dch l rt nh.

Bng 5.22 trnh by gi tr ho tan ca mt s mui (mol/l nc) s minh honhng iu ni trn. Do O2v S2bphn cc yu hn nc, cc hp cht ca chng vi

b-kim loi (v dZn, Cd) ho tan yu hn cc oxit v sulfur ca a-kim loi (Mg, Ca).ho tan, nh ni trn, phthuc rt nhiu vo loi cu trc. Cc hp cht c

cu trc phn tv phc tp, ho tan tt hn cc hp cht c cu trc phi tr. Da trn cs, trong phn tch nh tnh c thdng ion chlor (bsung HCl) tch cc cation bho trmt (Ag+)v cation ho trhai vi kch thc ln (Pb2+) ra khi cc cation bho trhai (Zn, Cd) v cc cation ho trln hn. Nhm cc cation thnht to vi chlor cc cutrc phi tr khng ho tan (AgCl, PbCl2), nhm thhai cu trc phn tv lp dhotan (ZnCl2, CdCl2). Cc nguyn t sau cng c th lm kt ta bng S

2 nh b sung

dihydro sulfur (v dZnS).Bng 5.22.

ho tan ca mt smui

Ion F Cl Br I SO42 2OH

Na+ 1 0 6 1 11 3 10 6

48


48/151

Sr2+ 6.104 3,3.102

Ba2+ 6,3.106 2,5.101

5.5.11Ttrng

Ttrng ca cht kt tinh phthuc vo thnh phn ho hc v cu trc tinh th, trong c bit quan trng l trng lng nguyn t, sau l ho trv kch thc ion canguyn tho hc tham gia vo thnh phn. V vn v dtrong thgii khong vt thhin mi quan htrn: cc khong vt to sm mu (khong vt femic) cha nhiu st,magnesi thng c ttrng ln hn cc khong vt sng mu (khong vt salic) giu nhm,silic, kim loi kim. S dao ng thnh phn ho hc ca mt khong vt (sphalerit,wolframit, v.v) hay mt nhm (vi cng chung loi cu trc) khong vt (olivin, granat,v.v..) dn n sbin i ttrng (xem bng 5.23) cng nhhng lot cc tnh cht vt lkhc.

Bng 5.23.

Sphthuc ttrng vo thnh phn ho hc ca cht kt tinh

Nhm khong vt Khong vt Cng thc hohc

Ttrng

Olivin Forsterit Mg2SiO4 3, 22Fayalit Fe2SiO4 4, 40

Granat Pyrop Mg3Al2Si3O12 3, 58

Almandin Fe3Al2Si3O12 4,32

Plagiocla Albit NaAlSi3O8 2,62

Anorthit Ca Al2Si2O8 2,76

Spinel Spinel MgAl2O4 3,55

Magnetit FeFe2O4 5.20

Chromit FeCr2O4 5,09

49


49/151

nhiu v dvsphthuc ca ttrng vo sxp xp nguyn t, ion; tuy nhin, nhng vdin hnh v r nt nht vn l cc bin tha hnh (xem bng 5.2). Trong c ccbin thca carbon nhkim cng v graphit. Cc nguyn tcarbon c cch xp xp khcnhau trong mng tinh thca hai khong vt trn (xem hnh 5.14,b v c). Kim cng ccu trc phi tr cht xt, mi nguyn tcarbon c 4 nguyn tkhc bao quanh, khongcch gia cc nguyn tl nhnhau v u bng 1,54. Trong khi , graphit li c cutrc lp vi cc nguyn tcarbon xp kht nhau trong tng lp, mi nguyn ttip xc vi3 nguyn tkhc, khong cch gia hai nguyn t lin k l 1,42. Tuy nhin, gia cclp li c mt khong rng l 3,40. iu ny dn n schnh lch ln gia ttrng cakim cng (3,52) v graphit (2,23).

Tng t, cc bin tha hnh ca oxit silic cng c ttrng khc nhau do sxp xpcc nguyn toxy v silic khc nhau, c bit, oxit silic v nh hnh c ttrng nhnhtv dao ng nhiu nht do sphn bln xn, khng cht ca cc nguyn toxy v silic.c bit, visphi tr suca silic i vi oxy, stishovit c ttrng ni tri so vi ccbin tha hnh khc u c sphi tr bn: 4,3 so vi 2,20 ca tridymit v cristobalit,2,53 v 2,65 ca thch anh.

Mt v dkhc cng cho kt qutng t, l hai bin thca carbonat calci: calcitv aragonit ln lt thuc cc hba phng v trc thoi (xem mc 6.12 v hnh 4.18). C

thnhn thy rng trong chai cu trc calcit v aragonit mi nhm CO3u c baoquanh bi 6 nguyn tCa, tuy nhin mi quan h phn bgia Ca v O th khc nhau.Trong calcit (hnh 5.24,a), mi nguyn toxy ca nhm CO3 rng buc vi 2 nguyn tCa, v nhm CO3ny nm chnh gia bba nguyn tCa trn v di trong mng csmt thoi.

Trong mng csca aragonit (hnh.5.24,b) mi nguyn toxy nm gia 3 nguyntcalci, hai nhm CO3lin hvi nhau qua tm i xng s ln lt nm gn vi bbanguyn tCa trn v di. Vi sxp xp cc nguyn tnhtrn, cu trc ca aragonit

xp cht hn calcit. mng cssu phng cha 6 n vcng thc CaCO3ca calcitc cc thng s a = 4,9908; c = 17,05951; tng ng, th tch mng c s bng367,87433; 2 mng c s cha 12 n v cng thc CaCO3 tng ng vi th tch735,74863. Trong khi mng c s trc thoi cha 4 vct CaCO3 ca aragonit c ccthng sa = 7,968; b = 5,741; c = 4,959. Tng ng, th tch mng c s bng226,84593; 3 mng cscha 12 phn tCaCO3tng ng vi thtch 680,5378

3.

iu ny dn n kt qutrng lng ring ca aragonit (2,93) ln hn ca calcit(2,71) (xem bng 5.24). Trng lng ring ca cc bin tha hnh CaCO3 c thtnh theo

cng thc: = M/V, vi V l thtch ca mng csv khi lng ca n M = Z(f/L),trong Z l sn vcng thc trong mng, f mol ca CaCO3bng 100,09 g (nguynt lng ca Ca l 40,08, C 12,01, O 16,00), L sAvogadro (sn vcng thccha trong 1 mol).

Bng 5 24

50


50/151

Trong s khong vt silicat, c th thy mt xu hng r rng l cu trc o c ttrng ln hn silicat c cu trc mch, silicat mch li c ttrng ln hn silicat lp, silicatv alumosilicat khung. Ttrng thp nht l ca khong vt zeolit; cu trc khung rng cachng c cc khoang rng ln ni vi nhau bng cc knh di.

Trong cc khong vt alumosilicat, cu trc khung ph bin nht l cc khong vtnhm feldspat, feldspathoid v zeolit. Chng c chung c im cu trc cbn l khungalumosilicat c cu thnh tcc tdin (Si,Al)O4, mi nh oxy chung cho hai tdin.in tch m ca mng c cn bng bi cc cation, chyu l Ca, Na, K, nm trong cckhoang trng ca mng. Cu trc ca feldspat cht nht, trong cc cation (Na, Ca, K)nm trong cc khoang tng i nh, c bao kn bi cc oxy to khung (xem cc hnh

6.29 v 6.30). Cc cation gn cht vi khung n mc chng khng thdi chuyn ddngnu nhcc mi lin kt ca khung khng bgin on. Sthay thNa hoc K bng Cabt buc ko theo sthay i tsSi/Al.

Cu trc ca feldspathoid tng i mhn, cc ion (Na, Ca, K, trong mt strnghp l cc anion xc nh) thng khng chim ht cc khoang trng ln thng nhau. Vth, feldspathoid c cc knh, theo cc ion c thra vo, i khi cc phn tnhc thi qua m khng ph v khu

Documents

HHtinhthe_P2