GERALD M. PETTY Arkansas Co, Inc., Newark, N. J.

An estimation of the amount of silicone in textile ma- terials is required for the control of this process for the durable waterproofing of textile materials. In a method which requires no unusual or specialized equipment, the textile material, treated with silicone, is wet-ashed, using concentrated sulfuric and nitric acids and, eventually, concentrated perchloric acid. The silica is determined by conventional methods. Attempts to extract cured silicones from textile materials by solvents gave unsatisfactory results.

ILICOSE oils, also known as lon- molecular weight polysil- S oxanes, are extensively used in processing textile materials in order to impart a water-repellent finish which is resistant both to washing and to dry cleaning. The silicone oil is dispersed in water with an emulsifying agent or dissolved in a suitable solvent, and is mixed with a catalyst which promotes polymerization. The catalyst is usually an organometallic compound. It is then applied to the textile material in equipment which is found in most textile mills. The silicone oil thus deposited, is then cured (polymerized) by heating the impregnated textile material briefly a t a high temperature. For instance, heating a t 160" C. for 5 to 8 minutes is recommended for silicone oils on cotton

In order to develop a water-repellent finish which has good durability to laundering and t o dry cleaning, it is usually neces- sary to have 0.75 to 1.25% of silicone present in the fabric, de- pending on the type of fiber and the construction of the fabric. Accordingly, the analysis of fabrics treated n-ith silicone assumes considerable importance in connection with this specified silicone content.

The silicone oils which have been most extensively used for

(1) .

this purpose are methyl hydrogen silicone. -Si-0- , and i" ( TIT3 \

dimethylsilicone, -Si-0- , where the siloxane unit is re-

peated several times per molecule (n varies from about 12 to about 70; n = 20 may be considered representative).

McHard, Servais, and Clark ( 2 ) have proposed colorimetric, volumetric, and gravimetric methods for determining the silicon content of organosilicon compounds. I n each case, the organo- silicon compound is converted by peroxide bomb or by wet oxidation with various acids t o sodium silicate or t o silicic acid. After the destruction of the organosilicon molecule, further treat- ment depends on the method selected for the final determination of silicon.

QUALITATIVE TEST FOR SILICONES

When silicone oils, alone or in mixtures, are burned in a crucible, the smoke contains white flakes of silica, and a white collar of silica forms inside the crucible a t the rim. This test holds for silicone oils in textile materials, prior to the heat treatment dur- ing which the silicone oils are polymerized. However, after polymerization this qualitative test usually fails.

Determination of Silicones in Textile Materials

250

SOLVENT EXTRACTION O F SILICONES

Before the silicone has been cured, solvent extraction with petroleum ether (boiling point, 30' t o 60" C,), isopropyl alcohol (about 99.8%), benzene, or solvent naphtha usually recovered 95% or more of the silicone. After curing, prolonged extraction with benzene or solvent naphtha in a Soxhlet apparatus gave non- reproducible recoveries which were generally in the range of 30 to 60%.

QUANTITATIVE DETERMINATION O F SILICONES

Reagents. Fitric acid, 70%, reagent grade. Perchloric acid, 60%) reagent grade. Hydrofluoric acid, 48%, reagent grade. Hydrochloric acid, 3775, reagent grade.

Sulfuric acid, 9570, reagent grade.

Apparatus. Borosilicate glass beakers, watch glasses, and fun- nels, and platinum crucibles were used throughout.

Sampling. Sampling in a textile finishing plant is usually lim- ited to the ends of runs. As samples so taken are less representa- tive of the entire run than samples taken a t regular intervals through the run, larger samples are needed for analysis than in the latter case. As the peroxide bomb procedure is limited to samples generally less than 1 gram, the gravimetric procedure described below is preferred.

For the quantitative determination of silicones in textile fabrics, weigh 5 to 10 grams of the material to 0.01 gram. Place the sample in a 600-ml. borosilicate glass beaker which is covered with a borosilicate watch glass, add 30 ml. of concentrated sulfuric acid, and, in small portions, add about 35 ml. of concentrated nitric acid. Heat moderately ("medium" heat on an electric heater) for 20 minutes to 2 hours. Use a medi- cine dropper to add 1 to 5 ml. of concentrated perchloric acid, and heat the sample vigorously. The earlier addition of per- chloric acid may be hazardous. If the liquid remains opaque, cool it slightly, add 5 to 10 ml. of concentrated nitric acid and, after further moderate heating, add 1 to 5 ml. of concentrated perchloric acid, followed by vigorous heating. Continue this cycle until the liquid is clear. It is usually water-white or only slightly tinted. Heat the sample vigorously until the volume of liquid is reduced to about 20 to 25 ml. Cool to room temperature, dilute cautiously with 100 to 150 ml. of distilled m-ater, and add 1 to 2 ml. of concentrated hydrochloric acid. Boil and filter the solution while hot, on a Whatman No. 40 filter paper or its equivalent. Police the beaker vigorously, as the silica is a verv adherent precipitate. Wash the precipitate several times with hot water, and then ash in a platinum crucible. Weigh the cru- cible and contents to 0.0001 gram. iZdd a few drops of concen- trated sulfuric acid and 2 to 15 ml. hydrofluoric acid, and volatil- ize the acids, together with the silica, a t a temperature low enough so that there is no spattering. Heat the crucible strongly, cool, and weigh again. The difference in the two weights is silica (SiOe). Si02 X 1.00 = methyl hydrogen silicone; SiO, X 1.23 = dimethyl silicone.

Procedure.

'

ANALYTICAL RESULTS

Some strips of acetate-viscose fabric, approximately 9 X 60 inches, which weighed about 65 grams, were treated with methyl hydrogen silicone emulsions of various concentrations on a Butterworth laboratory padder. Two sets of analyses were made, one on samples taken from the middle of each strip, the other on samples taken from the trailing end of the strip. The results were:

Middle Sample End Sample

Number % % % (MeHSiO),,, (MeHSiO)n, Decrease,

B264-9 0.42 B264-10 0.65 B264-11 1.00 B264- 12 1.66

0.34 0.53 0.81 1.34

19 18 19 19

V O L U M E 28, NO, 2, F E B R U A R Y 1 9 5 6

Only insignificant differences have been found in samples taken from mill runs. In small scale laboratory runs, however, in order to obtain significant results, samples for analysis must be taken from the same position on each piece of fabric.

DISCUSSION

Analyses made by this method agreed within 0.02% with those made in another laboratory by a colorimetric method in which the sodium silicate from the peroxide bomb is made t o react with ammonium molybdate, and the intensity of the resulting blue color is measured a t 715 mM. The agreement was very poor with analyses made in still another laboratory by dry oxidation in crucibles, as would be expected from the partial volatility of silicone oils a t high temperatures. The average difference be- tween duplicate samples is 0.007%.

If the textile fabric is not clean, or if silicon-containing compositions such as clay, talc, or colloidal silica have been used in processing, all the silicon present will be reported as silicone when determined by this method. The usual silica content of textile materials finished without the use of silicon-containing baths, and subsequently protected from

Silica is a normal constituent of soil.

25 1

soil, is 0.00 to 0.01%; occasionally amounts up to 0.03% are found. The silicon content of textile materials which have been processed with silicon-containing compositions will be much higher than where silicon compounds are accidentally present. In any case, it is always well to run an analysis for silica on a sample of the fabric before it has been treated with a silicone water- repellent, if such untreated material is available.

ACKNOWLEDGMENT

The author wishes to express his appreciation for the sub- stantial encouragement and advice given by Alton A. Cook, technical director of The Arkansas Co., Inc.

LITERATURE CITED

(1) Cook, A. A, and Shane, N. C., Teztile Research J . 25, 105-10

(2) hIcHard, J. A. , Servais, P. C., and Clark, H. A., ANAL. CHEW (1955).

20, 3 2 5 8 (1948).

RECEIVED for review April 8, 1955. Accepted November 5, 1955. Presented in part before the Analytical Group, North Jersey Section, ACS, Meeting-h- Miniature, January 1955, Newark, N. J.

Titrimetric Determination of Zirconium in Magnesium Alloys PHILIP J. ELVING University of Michigan, Ann Arbor, M ich .

EDWARD C. OLSON The Upjohn Co., Kalamazoo, Mich.

The addition of zirconium to magnesium alloys in- tended for use at high temperatures requires rapid methods for determining zirconium in such alloys. The titrimetric measurement of zirconium by standard cupferron solution, employing amperometric detection of the equivalence point, has been applied to the direct determination of zirconium in commercial magnesium alloys following acid dissolution. The method is rapid, simple, and accurate, and should supplement the colorimetric alizarin S and gravimetric p-halomandelic acid procedures.

HE need for accurate and rapid methods for the determina- T tion of small amounts of zirconium in magnesium and mag- nesium alloys was cited by Wengert ( 5 ) in describing the colori- metric determination of zirconium in magnesium alloys by the alizarin red S method, and Papucci and Iclingenberg (4) in de- scribing a similar gravimetric procedure using p-bromo- or p- chloroniandelic acid. The addition of zirconium t o such alloys improves the operating temperatures and grain structure without adversely affecting the machinability and creep resistance when used for high temperature purposes as in jet engines.

As zirconium can be rapidly and accurately determined gravi- metrically and titrimetrically, employing cupferron as precipitant in 10% (ca. 2M) sulfuric acid solution ( S ) , it seemed that the titrimetric method employing amperometric equivalence-point detection might be advantageous as a supplement to the color- imetric ( 5 ) and gravimetric ( 4 ) methods. The present study de- scribes the application of a titrimetric zirconium procedure to two magnesium alloys which were being used in a cooperative evalu- ation of the colorimetric alizarin red S procedure.

Commercial magnesium alloys containing zirconium fall into two groups; one contains up to 6% of zinc and 0.8% zirconium; the other about 3y0 of rare earths and 0.4% of zirconium. The

zirconium occurs in both acid-soluble and acid-insoluble forms; the amount of the latter is usually small in comparison with the acid-soluble zirconium, and in currently available alloys is usually kept to within 0.02 to 0.05%, since large percentages may be harm- ful. The dissolution procedures used in the present study are based on those proposed by Wengert ( 6 ) , which separate acid- soluble and acid-insoluble zirconium by treating the sample with dilute (1 to 4) hydrochloric acid; the insoluble fraction is changed to a soluble form by fusion with potassium hydrogen sulfate. Essentially the same dissolution procedure was used by Papucci and Klingenberg (4).

EXPERIMENTAL

Reagent grade sulfuric acid (specific gravity 1.84) was diluted 1 to 10 by volume with distilled water. Cupferron was purified and stored as previously described ( 3 ) ; an approximately 0.01 to 0.02X standard solution was prepared daily by dissolving a carefully weighed portion in air-free water. Commercial water- pumped nitrogen was used for deoxygenating without further purification; other chemicals used were of reagent or C.P. grade,

Titration was performed in a 150-ml. beaker fitted with a four- hole rubber stopper to accommodate the electrodes, buret (5- or 10-ml. capacity, graduated to 0.02 or 0.05 ml.) and nitrogen inlet; the beaker lip served as gas outlet. A Sargent ModelXXI polarograph or Fisher Electropode was used in conjunction with a dropping mercury electrode and a reference saturated calomel electrode (S.C.E.).

PROCEDURES

Dissolution (Soluble and Insoluble Zirconium). Weigh 3.0 grams (0.370 Zr) or 2.0 grams (0.6y0 Zr) of sample into a 400-ml. beaker. Cover with a watch-glass, cool in an ice bath, then add cautiously 150 ml. of cold ( I + 1 ) hydrochloric acid. After dis- solution is complete as indicated by the cessation of gas bubbles, filter through KO. 42 Whatman paper into a 250-ml. volumetric flask, wash the beaker and residue with hot water which is trans- ferred to the flask via the filter paper, transfer the residue to the filter paper, and dilute the flask contents to volume; this solution contains the acid-soluble zirconium.