X-ray Fluorescence Spectroscopy Study of Coating Thickness and

NASA/TM—2008–215578

October 2008

National Aeronautics andSpace AdministrationIS20George C. Marshall Space Flight CenterMarshall Space Flight Center, Alabama35812

X-ray Fluorescence Spectroscopy Study of Coating Thickness and Base Metal CompositionT.D. RolinMarshall Space Flight Center, Marshall Space Flight Center, Alabama

Y. LeszczukUniversity of Michigan, Material Science Department, Ann Arbor, Michigan

https://ntrs.nasa.gov/search.jsp?R=20080046987 2018-02-01T06:41:23+00:00Z

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NASA/TM—2008–215578



Nat�onal Aeronaut�cs andSpace Adm�n�strat�on

Marshall Space Fl�ght Center • MSFC, Alabama 35812

October 2008

��

Ava�lable from:

NASA Center for AeroSpace Informat�on7115 Standard Dr�ve

Hanover, MD 21076 –1320443 –757– 5802

Th�s report �s also ava�lable �n electron�c form at<https://www2.st�.nasa.gov>

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TaBle oF ConTenTS

1. INTroDuCTIoN ............................................................................................................. 1

2. BACkgrouND oN EquIpMENT ................................................................................. 2

3. proCEDurE .................................................................................................................... 5

4. DATA AND ANAlySIS .................................................................................................... 7

4.1 Two-layered Samples W�th gold Coat�ngs .................................................................. 7 4.2 Two-layered Samples W�th N�ckel Coat�ngs ................................................................ 8 4.3 Three-layered Samples ................................................................................................. 10

5. CoNCluSIoNS ................................................................................................................ 11

rEFErENCES ....................................................................................................................... 13

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lIST oF FIGUReS

1. F�scherScope X-ray X-dal mach�ne <http://www.helmut-fischer.com> ............................... 2

2. Sample report produced by XrF software .......................................................................... 3

3. Energy spectrum produced by XrF .................................................................................... 3

4. N�, Au, and Cu standards used as samples .......................................................................... 5

5. Descr�pt�on of Au/SS test run ............................................................................................. 8

6. Notes for Au/Cu test run ..................................................................................................... 8

7. Notes for N�/SS test run ...................................................................................................... 9

8. An example of a repeated 60-sec �nterval run ...................................................................... 9

9. Descr�pt�on of �nvest�gat�on regard�ng accurac�es obta�ned us�ng e�ther N� or Al filters for a three-layer sample ...................................................................... 10

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lIST oF aCRonYMS

Al alum�num

ASTM Amer�can Soc�ety for Test�ng and Mater�als

Au gold

Au/Cu Au over Cu

Au/N�/Cu Au over N� over Cu

Au/SS Au over sta�nless steel

Cu copper

EEE electr�cal, electron�c, and electromechan�cal

N� n�ckel

N�/Cu N� over Cu

NIST Nat�onal Inst�tute of Standards and Technology

SrM standard reference mater�als

SS sta�nless steel

μ�n m�cro�nches

XrF X-ray fluorescence

v�

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TECHNICAl MEMorANDuM

X-RaY FlUoReSCenCe SpeCTRoSCopY STUdY oF CoaTInG ThICkneSS and BaSe MeTal CoMpoSITIon

1. InTRodUCTIon

N�ckel (N�) and gold (Au) plated electr�cal, electron�c, and electromechan�cal (EEE) parts are �mportant components on many of NASA’s m�ss�ons. The th�cknesses of these plat�ngs are s�gn�ficant. Even a small d�fference �n measurements on the scale of m�cro�nches (µ�n) can alter the performance of a part. Completed parts must be analyzed to confirm that NASA standards were met �n the�r manufactur�ng. Because of th�s cruc�al need for prec�s�on and econom�cal solut�ons, a method that �s fast, rel�able, and preferably nondestruct�ve has to be employed to ensure proper plat�ng th�ckness.

A mach�ne that �s des�gned for th�s purpose �s the x-ray fluorescence (XrF) spectrometer. Th�s mach�ne �s pract�cal �n many d�fferent appl�cat�ons because �t �s able to measure bulk �tems �n l�qu�d, sol�d, and powdery forms w�th l�ttle or no preparat�on. It employs a nondestruct�ve method that measures layer th�ckness and layer compos�t�on. The mach�ne can also take measurements of substrate mater�als under several coat�ngs.

As w�th any mach�ne that performs measurements, great care must be taken to understand uncerta�nty �n the data. Factors such as detect�on l�m�tat�ons of the mach�ne or �mproper use of the mach�ne can skew data. W�thout rel�able data, parts that do not meet safety standards can be approved for use, �ntroduc�ng potent�al compl�cat�ons. The l�m�tat�ons on the data produced can be understood by compar�ng standards data to real parts data and subsequently apply�ng stat�st�cal methods. By understand�ng the l�m�tat�ons �n the collect�on of the data, accurate compos�t�on and th�ckness measurements can be obta�ned for samples w�th Au and N� coat�ngs.

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2. BaCkGRoUnd on eqUIpMenT

Each XrF spectrometer var�es �n some aspect. Therefore, understand�ng the way a par-t�cular mach�ne works �s �mportant to �nterpret�ng the data found. For th�s report, all data was acqu�red w�th a F�scherScope® X-ray X-dal® mach�ne, as shown �n figure 1. The process starts w�th pr�mary x-rays produced from an x-ray tube. When the pr�mary x-rays str�ke the sample, the atom absorbs them. As the atoms �n the sample absorb the x-rays, all of the energy �s transferred to an electron. Th�s energy removes �t from the atom and leaves the atom �n an unstable state. To return to a stable cond�t�on, electrons from the outer shell fall to the �nner shell and subsequently g�ve off character�st�c x-rays, called XrF. A rad�at�on detector then measures th�s secondary rad�a-t�on. By sort�ng the energ�es of the x-rays rece�ved by the detector, the mach�ne produces a spec-trum of the XrF rad�at�on. The sample’s coat�ng/substrate mater�al comb�nat�on �s obta�ned from th�s spectrum. The �ntens�ty of each character�st�c rad�at�on �s d�rectly related to the amount of each element �n the mater�al.1 Based on propr�etary fundamental parameter methods, the F�scher software can compute the th�ckness and compos�t�on of the coat�ng. F�gures 2 and 3 are examples of XrF outputs.

F�gure 1. F�scherScope X-ray X-dal mach�ne <http://www.helmut-fischer.com>.

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F�gure 2. Sample report produced by XrF software.

F�gure 3. Energy spectrum produced by XrF.

In XrF spectrometry, cons�derat�on should be g�ven to restr�ct�ng the rad�at�on to the area of �nterest by coll�mat�on at the rad�at�on source. Coll�mators are th�n translucent mater�als �n d�f-ferent d�mens�ons and shapes that narrow the beam of pr�mary x-rays. Th�s results �n a reproduc-�ble, controlled, and well-defined pr�mary x-ray beam geometry,1 wh�ch �ncreases the accuracy of measurements. The X-dal system �s equ�pped w�th four coll�mators. The spher�cal coll�mators have d�ameters of 0.1, 0.3, and 0.6 mm. The rectangular coll�mator has d�mens�ons of 0.15 × 0.5 mm. Another useful component of the F�scherScope X-ray X-dal �s a pr�mary filter. The pr�mary filter �s used to �nfluence the compos�t�on of the pr�mary x-ray rad�at�on so undes�rable character�st�cs of the fluorescence spectrum, such as lower energy x-rays and scattered x-rays, can be avo�ded.

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3. pRoCedURe

To understand the l�m�tat�ons of data found, measurements were taken as the parameters were var�ed and compared to true values of standard reference mater�als (SrM). F�gure 4 shows SrM samples. The SrMs used were Nat�onal Inst�tute of Standards and Technology (NIST) trace-able. The�r th�cknesses are cert�fied to be w�th�n 5 percent of the true th�cknesses. For every sample, s�x d�fferent parameters were var�ed to try to reduce measurement error: coat�ng/substrate comb�-nat�on, number of layers, count�ng �nterval, coll�mator s�ze, coat�ng th�ckness, and test area loca-t�on. Each measurement was taken five t�mes �n accordance w�th Amer�can Soc�ety for Test�ng and Mater�als (ASTM) Internat�onal Standards,2 wh�ch calls for the average of the five measurements to d�ffer from the cert�fied th�ckness by less than 10 percent at a 95 percent confidence level. The th�cknesses of the samples used were chosen to fit �n the range of 9.84–295 µ�n, the typ�cal range of coat�ng th�cknesses used by EEE parts manufacturers. Stay�ng �n th�s range of th�cknesses and us�ng filters when appropr�ate ensured l�ttle or no error from poor secondary x-ray s�gnal �ntens�ty. In th�s study, the ma�n focus was on N� and Au plat�ngs and the�r affect on d�fferent substrate com-pos�t�ons. Four d�fferent comb�nat�ons were used as samples: Au over sta�nless steel (Au/SS), Au over copper (Au/Cu), Au over N� over Cu (Au/N�/Cu), and N� over Cu (N�/Cu).

F�gure 4. N�, Au, and Cu standards used as samples.

The standard states, “Measur�ng methods perm�t the s�multaneous measurement of coat�ng systems w�th up to three layers.”2 Such measurements requ�re un�que data process�ng to separate the var�ous character�st�c em�ss�ons �nvolved to allow for any secondary exc�tat�on that may occur between layers and to account for the absorpt�on by �ntermed�ate layers. Two-layer and three-layer samples were used to try and further understand how to handle th�s l�m�tat�on and any error result-�ng from test�ng mult�ple layers. The standard also states that count�ng �ntervals must be chosen �n order to have a net count of at least 10,000 to reduce stat�st�cal error.2 Samples were measured �n d�fferent count�ng �ntervals to test for error �n data due to �nsuffic�ent count t�me.

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Bygatheringdatatakenwithdifferentcollimators,optimalcollimatorshapescanbefoundforspecificsamples.Fourcollimatorsizesweretested.Inadditiontocoatingthickness,thecompositionofthesubstratelayerwasmeasured.Measurementstakenwithasinglecoating,twocoatings,andnocoatingswerecomparedtoevaluatetheimpactthatcoatingthicknesshadonthecompositionmeasurementsofthesubstratelayer.Varyingtheareastestedandcomparingtheirvaluesisthebestmethodtochecktheuniformityofcoatingsonparts.Tosimulatethis,measurementsweretakeninfixedandrandomizedtestareastodeterminedifferencesandsimilaritiesinerror.Alldatawerecollectedusingavoltageof50kVtoproducetheprimaryx-ray.

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4. daTa and analYSIS

4.1 Two-layered Samples With Gold Coatings

The first comb�nat�on of coat�ng/substrate measured was Au/SS. The SS used as a sub-strate was 302 (SS302). Four d�fferent coat�ng th�cknesses were used: 9.36, 46, 76, and 118 µ�n. The pr�mary filter used was a N� filter. The measurements �ncluded th�cknesses of the coat�ngs and the compos�t�on of the substrate layers. Although all the th�cknesses found were all w�th�n 10 percent of the actual value, there were some problems w�th the compos�t�on measurements.

As coat�ng th�cknesses �ncreased, so d�d the �naccuracy of the substrate compos�t�on mea-surements. In general, the percent compos�t�on of N� was h�gher than expected, wh�le the percent compos�t�on of chrom�um was much lower than expected. The compos�t�on of manganese was also �naccurate. In many �nstances, the measurements of substrate compos�t�on had an error of more than 10 percent. As the th�ckness approached 118 µ�n, the error approached 100 percent. Because of th�s large error �n compos�t�on, more var�ables needed to be tested to find a way to reduce error. S�nce the N� compos�t�on was the one w�th the most error overall, the first th�ng tested was chang-�ng the pr�mary filter used.

Tests were run on the 46 µ�n Au/SS sample to determ�ne �f chang�ng the pr�mary filter or �f extend�ng the count�ng �ntervals would y�eld more accurate results. F�gure 5 �s a descr�pt�on of an Au/SS test run. To determ�ne accuracy, the error was found w�th respect to the SS compos�-t�on taken w�th no coat�ng. No pattern �n the percent error was observed as the pr�mary filters were changed or as the count�ng �ntervals were changed. A cal�brat�on set was created and appl�ed because chang�ng these two parameters could not reduce the error.

g�ven that error of the measurements �ncreased w�th Au th�ckness, the 118 µ�n sample was tested w�th a cal�brat�on set to reduce error. The compos�t�on percentages used �n the cal�brat�on set for each element was the mean of all �ts compos�t�on measurements. When a cal�brat�on set was appl�ed, the error �n the th�ckness and compos�t�on measurements s�gn�ficantly dropped. Before a cal�brat�on set was appl�ed, the th�ckness measurements were all under 10 percent; but the error dropped to below 5 percent w�th the cal�brat�on set appl�ed. The compos�t�on measurements st�ll had errors above 10 percent. Errors �n the chrom�um and manganese measurements were often less than half of the�r or�g�nal percentages when a cal�brat�on set was appl�ed. From these tests, �t was concluded that a cal�brat�on set could help reduce error dramat�cally when measur�ng substrate compos�t�on. The th�cker the sample �s, the less l�kely �t w�ll be to find accurate compos�t�ons for certa�n elements.

To see �f the measurement of Au th�ckness would be �nfluenced by the substrate compos�-t�on, tests were performed on Au/Cu for 9.36, 46, 76, and 118 µ�n coat�ngs, us�ng a N� pr�mary filter. Notes for an Au/Cu test run are shown �n figure 6. These tests measured the th�ckness of the Au coat�ng. All the tests y�elded favorable results w�th all measurements hav�ng errors under 10 percent.

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Gold Over Stainless

Good thickness measurement values with error under 10%.

Composition measurements had unacceptable error as thickness

of gold coating increased.

Nickel is the element with the highest error, so an aluminum

primary filter was used rather than a nickel one. Changing the primary

filter used and extending the counting intervals did not reduce

composition error.

Applying a calibration set reduced error dramatically, but some

elements still had error over 10%. The thicker a sample was, the less likely it would be to find accurate

compositions for certain elements.

Gold Over Copper

Good result for thickness measurements with error

under 10%.

F�gure 5. Descr�pt�on of Au/SS test run. F�gure 6. Notes for Au/Cu test run.

Errors were often under 5 percent except �n the case of the th�nnest sample. There was no clear pat-tern �n the d�fference of percent error �n th�ckness measurements between Au/Cu and Au/SS302, so case substrate compos�t�on d�d not affect the measurement of the coat�ng th�ckness �n th�s case.

4.2 Two-layered Samples With nickel Coatings

Measurements were taken of N�/SS us�ng SS302. Notes for the N�/SS test run are shown �n figure 7. The pr�mary filter used was a N� filter. The data collected were the th�ckness of the coat�ng and the compos�t�on of the substrate layer. Both the th�ckness and compos�t�on measurements had unacceptable error. The th�ckness measurements had h�gher than 50-percent error. The results for the compos�t�on were also poor. The N� percentages were �n the negat�ve range and the �ron per-centages were h�gher than expected. Because of such h�gh percentages of error �n the data, �t was concluded that samples w�th N� layers must be tested w�th an alum�num (Al) pr�mary filter.

To test how an Al pr�mary filter would affect the data obta�ned from samples w�th N� layers, measurements of the coat�ng th�cknesses were taken of N�/Cu. The th�cknesses of the samples used were 4.24, 19, 49, 79, and 96 µ�n. The samples tested that had measurements w�th an error of more than 10 percent were the 4.24 and 19 µ�n coat�ngs. The 19 µ�n coat�ng had an error of more than 10 percent w�th the first coll�mator for a 10-sec t�me �nterval w�th var�ed test areas. A test was run

9

Nickel Over Stainless

Error for composition measurements were all above 50%. Measurements taken of samples with nickel layers

were higher in error if a nickel primary filter was used. A good alternative

was an Aluminum filter.

F�gure 7. Notes for N�/SS test run.

aga�n under these cond�t�ons and the error found was 1.05 percent, a large decrease from the or�g�-nal error of 12.1 percent. Therefore, �t was concluded that the large error was due to an operator error.

W�th the 4.24 µ�n sample, almost all the test runs had errors above 10 percent. The first th�ng that was tested to try and el�m�nate th�s error was �ncreas�ng the count�ng �nterval. All of the or�g�nal tests were repeated w�th a 60-sec �nterval run. An example of a repeated 60-sec �nterval run �s shown �n figure 8. The result�ng values of the error �n the measurements were s�gn�ficantly lower than the or�g�nal numbers. These results suggest that a longer count�ng �nterval �s needed when measur�ng th�n samples.

Nickel Over Gold

Good result with error under 10% for thicker samples. Thinnest

samples had error above 10%.

After extending counting intervals to 60 seconds for the

thinnest samples and running all the original test, error was reduced to less than 10%.

F�gure 8. An example of a repeated 60-sec �nterval run.

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4.3 Three-layered Samples

The three-layered sample tested �n th�s study was Au/N�/Cu. The th�cknesses of the Au samples used were 46, 76, and 118 µ�n and the th�cknesses of the N� samples used were 19, 49, 79, and 96 µ�n. To better understand how the accuracy of the measurements changed w�th the d�ffer-ent pr�mary filters, tests were done on the 46-µ�n Au over the 39-µ�n N� over the Cu. Each coll�ma-tor was tested for 20 sec on a fixed test area. Measurements were taken of the Au and N� layers and the�r error was compared. The Al filters generated more accurate results, so the rema�n�ng tests were done w�th an Al filter. F�gure 9 �s a descr�pt�on of an �nvest�gat�on regard�ng accurac�es obta�ned us�ng e�ther N� or Al filters for a three-layer sample.

Gold over Nickel over Copper

Test were done to investigate whether an Aluminum or a Nickel

filter would return the most accurate measurements. The

Aluminum filter returned the more accurate measurements.

Mesurements of Gold coating had error under 10%. Measurements of the

nickel coating had error above 10%.

Calibration set was applied and all error was under 10%.

F�gure 9. Descr�pt�on of �nvest�gat�on regard�ng accurac�es obta�ned us�ng e�ther N� or Al filters for a three-layer sample.

As the Au th�cknesses of the samples were �ncreased, the error of the N� th�ckness measure-ments �ncreased above 10 percent. The error for the N� th�ckness w�th an Au coat�ng was much h�gher than the error of the measurements found for N� samples w�th no coat�ng. In add�t�on, the frequency of the first coll�mator not be�ng able to obta�n measurements of N� th�ckness �ncreased w�th the �ncreas�ng N� th�ckness.

As the th�ckness of the Au coat�ng was �ncreased, the error �n the Au th�ckness measure-ments decreased. In add�t�on, as the th�ckness of the Au �ncreased, the error of the measurements of the Au th�ckness �n the three-layered sample became less than the error of the measurements of the Au/Cu sample. Because of the large error �n measurements, a cal�brat�on set was appl�ed to reduce the error. When a cal�brat�on set was appl�ed, the error was smaller than 10 percent, often less than the error �n the measurements taken for the two-layered samples.

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5. ConClUSIonS

To summar�ze, the XrF spectrometer �s an excellent mach�ne for check�ng that EEE parts meet the standards. obta�n�ng accurate coat�ng th�ckness and substrate compos�t�on measurements �s poss�ble �f cons�derat�on �s taken. When deal�ng w�th th�nner samples, �t �s often benefic�al to use longer count�ng �ntervals to reduce error. As the th�cknesses of the samples were �ncreased, the error also �ncreased. Th�ck coat�ngs become a problem when try�ng to obta�n substrate compos�-t�on. In th�s �nstance, a cal�brat�on set �s useful �n reduc�ng the error. Th�cker coat�ngs resulted �n �naccurate measurements even w�th the use of a cal�brat�on set; th�s error was reduced as th�ckness of the coat�ng was reduced. reduc�ng error �s more d�fficult when analyz�ng three-layered samples. Cal�brat�on sets need to be appl�ed to obta�n measurements w�th acceptable error per the ASTM standard.

When us�ng the smallest coll�mator, 10- and 20-sec t�me �ntervals d�d not produce more than 10,000 counts. The low amount of counts somet�mes resulted �n �ncreased error. Increas�ng the t�me �nterval can reduce the error of the measurements taken by the first coll�mator. A common pattern �n the amount of counts was an �ncrease �n counts per sec w�th an �ncrease of coll�mator s�ze. As the coll�mator s�ze �s decreased, there �s also a decrease �n the �ntens�ty of the s�gnals read by the detector. Th�s can also lead to �ncreased error. S�mply �ncreas�ng the coll�mator s�ze cannot reduce error because other factors affect the accuracy. As the s�ze �ncreases, the detector rece�ves more s�g-nals that often �nclude background no�se, wh�ch can lead to an �ncrease �n error. When deal�ng w�th three-layered samples, the smaller coll�mators can be used to reduce error from �nterfer�ng s�gnals. Because so many factors affect what coll�mator w�ll be the most accurate for each sample, a general relat�onsh�p between coll�mator s�ze and error cannot be found.

These tests also compared the error of measurements taken �n fixed or random�zed test areas. No s�gn�ficant d�fferences were found between the errors �n the fixed and random test area measurements. These measurements often had small standard dev�at�ons, even though they �ncreased when an Al filter was used rather than a N� filter.

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ReFeRenCeS

1. Fischer,H.:Instruments for Coating Thickness Measurement and Materials Testing,Sindelfingen:HelmutFischer,2004.

2. “StandardTestMethodforMeasurementofCoatingThicknessbyX-RaySpectrometry,”ASTMInternational,ASTM Standard B 568,WestConshohocken,PA,1998(2004),<www.astm.org>accessed.

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X-ray Fluorescence Spectroscopy Study of Coat�ng Th�ckness and Base Metal Compos�t�on

T.D. rol�n and y. leszczuk*

george C. Marshall Space Fl�ght CenterMarshall Space Fl�ght Center, Al 35812* un�vers�ty of M�ch�gan, Mater�al Sc�ence Department, Ann Arbor, MI 48109

Nat�onal Aeronaut�cs and Space Adm�n�strat�onWash�ngton, DC 20546–0001

prepared by Space Systems Department

unclass�fied-unl�m�tedSubject Category 38Ava�lab�l�ty: NASA CASI 443–757–5802

For electr�cal, electron�c, and electromechan�cal (EEE) parts to be approved for space use, they must be able to meet safety standards approved by NASA. A fast, rel�able, and prec�se method �s needed to make sure these standards are met. Many EEE parts are coated �n gold (Au) and n�ckel (N�), and the th�ckness coat�ng �s cru-c�al to a part’s performance. A nondestruct�ve method that �s effic�ent �n measur�ng coat�ng th�ckness �s x-ray fluorescence (XrF) spectroscopy. The XrF spectrometer �s a mach�ne des�gned to measure layer th�ckness and compos�t�on of s�ngle or mult�layered samples. By understand�ng the l�m�tat�ons �n the collect�on of the data by th�s method, accurate compos�t�on and th�ckness measurements can be obta�ned for samples w�th Au and N� coat�ngs. To understand the l�m�tat�ons of data found, measurements were taken w�th the XrF spectrometer and compared to true values of standard reference mater�als (SrM) that were Nat�onal Inst�tute of Standards and Technology (NIST) traceable. For every sample, s�x d�fferent parameters were var�ed to understand mea-surement error: coat�ng/substrate comb�nat�on, number of layers, count�ng �nterval, coll�mator s�ze, coat�ng th�ckness, and test area locat�on. Each measurement was taken �n accordance w�th standards set by the Amer�-can Soc�ety for Test�ng and Mater�als (ASTM) Internat�onal Standard B 568.

20

M–1243

Techn�cal Memorandumoctober 2008

NASA/TM—2008–215578

X-ray, fluorescence spectroscopy, measurement, coat�ng th�ckness, elemental compos�t�on

The NASA STI Program…in Profile

Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA Scientific and Technical Information (STI) Program Office plays a key part in helping NASA maintain this important role.

The NASA STI program operates under the auspices of the Agency Chief Information Officer. It collects, organizes, provides for archiving, and disseminates NASA’s STI. The NASA STI program provides access to the NASA Aeronautics and Space Database and its public interface, the NASA Technical Report Server, thus providing one of the largest collections of aeronautical and space science STI in the world. Results are published in both non-NASA channels and by NASA in the NASA STI Report Series, which includes the following report types:

• TECHNICAL PUBLICATION. Reports of completed research or a major significant phase of research that present the results of NASA programs and include extensive data or theoretical analysis. Includes compilations of significant scientific and technical data and information deemed to be of continuing reference value. NASA’s counterpart of peer-reviewed formal professional papers but has less stringent limitations on manuscript length and extent of graphic presentations.

• TECHNICAL MEMORANDUM. Scientific and technical findings that are preliminary or of specialized interest, e.g., quick release reports, working papers, and bibliographies that contain minimal annotation. Does not contain extensive analysis.

• CONTRACTOR REPORT. Scientific and technical findings by NASA-sponsored contractors and grantees.

• CONFERENCE PUBLICATION. Collected papers from scientific and technical conferences, symposia, seminars, or other meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientific, technical, or historical information from NASA programs, projects, and missions, often concerned with subjects having substantial public interest.

• TECHNICAL TRANSLATION. English-language translations of foreign scientific and technical material pertinent to NASA’s mission.

Specialized services also include creating custom thesauri, building customized databases, and organizing and publishing research results.

For more information about the NASA STI program, see the following:

• Access the NASA STI program home page at <http://www.sti.nasa.gov>

• E-mail your question via the Internet to <[email protected]>

• Fax your question to the NASA STI Help Desk at 443 –757–5803

• Phone the NASA STI Help Desk at 443 –757–5802

• Write to: NASA STI Help Desk NASA Center for AeroSpace Information 7115 Standard Drive Hanover, MD 21076–1320

NASA/TM—2008–215578

October 2008

National Aeronautics andSpace AdministrationIS20George C. Marshall Space Flight CenterMarshall Space Flight Center, Alabama35812



Documents

X-ray Fluorescence Spectroscopy Study of Coating Thickness and