Skip to main content

Full text of "NASA Technical Reports Server (NTRS) 19940030754: A Novel Method for Depositing Precious Metal Films on Difficult Surfaces"

See other formats


NASA Technical Memorandum 106607 


5 ? 

A Novel Method for Depositing Precious 
Metal Films on Difficult Surfaces 


L. C. Veitch and W. H. Phillip 
Lewis Research Center 
Cleveland, Ohio 


(NASA-TM- 106607) A NOVEL METHOD 
FOR DEPOSITING PRECIOUS METAL FILMS 
ON DIFFICULT SURFACES (NASA. Lewis 
Research Center) 5 p 


G3/27 0012652 


N9A-35260 
Unc 1 as 


June 1994 



National Aeronautics and 
Space Administration 


A NOVEL METHOD FOR DEPOSITING PRECIOUS METAL FILMS ON DIFFICULT SURFACES 


L.C. Veitch and W.H. Phillip 
National Aeronautics and Space Administration 
Lewis Research Center 
Cleveland, Ohio 44135 


SUMMARY 

A guanidine-based vehicle was developed to deposit precious metal coatings on surfaces known 
to be difficult to coat. To demonstrate this method, a platinum coating was deposited on alumina fibers 
using a guanidine-platinum solution. X-ray diffraction confirmed that the only species present in the 
coating was platinum, and, that all of the carbon species had been removed upon heat treatment. SEM 
results showed that some porosity was present but that the coatings uniformly covered the fiber surface 
and adhered well to the fiber. 


INTRODUCTION 

The preparation of thin metallic films by the decomposition of metallo-organic solutions is a 
technology which has been known for many years; the first publications reporting on this technology ap- 
peared more than one hundred years ago. Although the technique has been known for a long time, its 
primary application has been in the decorative trade. The main emphasis is producing films of precious 
metals on ceramic and glass articles (ref. 1). 

Almost all of the work prior to 1980 used metallo-organic compounds derived from resins or 
other natural products and are commonly called metal resinates. These resinates are suitable for most 
applications in the decorative trade. The variability of the chemistry is a result of the preparation from 
natural products, and is a major impediment to the extensive development of the technical applications of 
the metal-organic decomposition (MOD) processes. In recent years, MOD films have been produced 
from pure, well-characterized compounds and are now used in technical applications (ref. 2). For ex- 
ample, silver films are fabricated by thermally decomposing the MOD silver solutions on silicon for use 
as collector grids for photovoltaic cells. These collector grids required good adhesion, low contact resis- 
tance, low sheet resistance and long-term electrical stability. The fired films are 100 percent solder leach- 
resistant and have good definition and excellent long-term adhesion. This method of metallizing solar 
cells is inexpensive since less precious precursor material is required as compared to source targets 
needed for sputtering silver on silicon (ref. 3). 

The conventional metallo-organic solutions have the advantage of producing film densities near 
the theoretical limit at low temperatures. However, adhesion to some ceramics is poor. Altering the vis- 
cosity of the solutions can alleviate the problems with adhesion. With more organics present in the solu- 
tion, however, there is a greater tendency towards blistering. 

A guanidine vehicle has been developed (ref. 4) that solves the adhesion and the blistering prob- 
lems. This vehicle can be used to deposit precious metal films or metal oxide films on smooth, cylindri- 
cal surfaces and on smooth, flat metal surfaces. Guanidine is a strong base equal in strength to sodium 
hydroxide; thus, guanidine forms stable soaps with organic fatty acids that have high ionicity. This en- 
ables them to wet and to bond to the ceramic substrates. The advantage of these soaps is that they com- 
pletely bum off and leave no residue when fired. The disadvantage of sodium-containing soaps is that 
they leave a sodium oxide ash upon firing. This ash can reduce the high-temperature strength of some 
ceramics. 


1 


For this study, single-crystal A1 2 0 3 fibers were coated with a Pt-guanidine solution. This particu- 
lar coating was chosen because of its ability to act as a sintering barrier for the fibers when placed in an 
oxide matrix. Al 0 O 3 fibers were pulled through a melted guanidine-platinum solution in the guanidine 2- 
ethylhexanoate vehicle, air dried and subjected to a rapid thermal anneal to eliminate the organics and 
produce a porous Pt coating. The coating and firing procedures were repeated several times to increase 
the coating thickness on the fibers. Then, the fibers were annealed at 1000 °C to densify the Pt coating. 
X-ray diffraction and SEM were used to analyze the coatings. 

Debye-Scherrer results indicated that only Pt peaks were present in the coatings. Thermal gravi- 
metric analysis (TGA) of the Pt-guanidine solution confirmed that the organics were completely removed 
at 600 °C and that only some trace metals were evident. These trace metals were also present in the Pt- 
guanidine solution container walls. 

Figures 1(a) and (b) show the surface and cross-section of one of the Pt-coated fibers after the 
anneal. Even though some porosity is still present in the coatings, the adhesion of the Pt coating is good. 
The coating is also fairly uniform over the length of the fiber (fig. 1(a)). Slower heating cycles were tried 
after each coating to reduce the porosity. However, as shown in figure 2, the coating was not as dense as 
those that were fired rapidly after each coating. 

The coating thickness is dependent on the viscosity of the Pt-guanidine solution and on the num- 
ber of applications. The coating and firing procedures for the fibers in this study were repeated four 
times, yielding approximately a 10 pm coating. 

Although no chemical reactions were observed between the Pt and A1 2 0 3 fiber, pitting on the 
surface of the fibers was observed by Jaskowiak (ref. 5) when the fibers were subjected to further heat 
treatments and when placed in an oxide matrix material. This has also been observed when other similar 
sol-gel coatings have been applied to these A1 2 0 3 fibers (ref. 6). The pitting can be correlated back to 
impurities trapped at the surface by the coatings. These impurities, identified as Ca, Ti and other light 
metals, have also been observed using x-ray photoelectron spectroscopy (XPS) on the surface of the fibers 
before and after cleaning and are not necessarily from the Pt-guanidine solution or other chemical pro- 
cesses for coating the fibers. Jaskowiak (ref. 5) also observed that the Pt coating no longer adhered to the 
surface of the fiber above 1300 °C. However, the coating remained intact below 1300 °C. 

It is possible to coat smooth, cylindrical surfaces with noble metals by means of a modified MOD 
process using a guanidine soap solution for the organic vehicle. Application of this process can range 
from thin films used as electric conductors in the microelectronics industry to additional coatings for 
composite materials. The Pt-guanidine solution utilized in this study adhered well to the A1 2 0 3 fibers 
below 1300 °C. The coating was fairly uniform over the entire surface. Some porosity is present in the 
coatings, however, the Pt coating still provided the necessary barrier between the A1 2 0 3 fiber and the 
oxide matrix for high temperature use. 

REFERENCES 

1. Mopper, R.T.: Ceram. Ind., 1963, 80, pp. 74-76. 

2. Langley, R.C.: AFMLTR 65-262, Wright Patterson AFB, OH (1985). 

3. Wachtman, J.B., and Haber, R.A: Ceramic Films and Coatings (Noyes Publications, New Jersey, 

1993), Chapter 9. 

4. DeGuire, M.R., and Phillip, W.H.: J. Mater. Chem., 1993, 3 (6), pp. 571—574. 

5. Jaskowiak, M.H., Phillip, W.H., Eldridge, J.I. , Setlock, J.A., Norkitis, M.E., Helman, J.R.: 5th 

Annual Hi-Temp Rev. Proc., 1992, pp. 59-1-59-14. 

6. Matthieson, M.M., and Jayne, D. T.: to be published in the Journal of the American Ceramic Society. 


2 



(a) Surface view. (b) Cross section. 

Figure 1 .—A platinum-coated single crystal alumina fiber after four coating and firing cycles and final anneal at 1 000 °C. 



Figure 2. — The surface of a platinum-coated alumina fiber 
after 8 coating and slower firing cycles and a final anneal 
at 1 000 °C. 


3 


i'-m 


REPORT DOCUMENTATION PAGE 

Form Approved 
OMB No. 0704-0188 

Public reporting burden for this collection of information is estimated to average 1 hou.r per response, including the time for reviewing instructions, searching existing data sources, 
gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 
collection of information, including suggestions for reducing this burden, to Washington Headquarters Services. Directorate for Information Operations and Reports. 1215 Jefferson 
Davis Highway Suite 1204 Arlington, VA 22202-4302, and to the Office of Management and Budget Paperwork Reduction Project (0704-0188), Washington, DC 20503. 

1. AGENCY USE ONLY ( Leave blank) 

2. REPORT DATE 

June 1994 

3. REPORT TYPE AND DATES COVERED 

Technical Memorandum 

4. TITLE AND SUBTITLE 

A Novel Method for Depositing Precious Metal Films on Difficult Surfaces 

S. FUNDING NUMBERS 




WU-510-01-01 


6. AUTHOR(S) 


L. C. Veitch and W. H. Phillip 


7. 


PERFORMING ORGANIZATION NAME(S) AND ADDRESSES) 


8. PERFORMING ORGANIZATION 
REPORT NUMBER 


National Aeronautics and Space Administration 
Lewis Research Center 
Cleveland, Ohio 44135-3191 


9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESSES) 


E-8886 


SPONSORING/MONITORING 
AGENCY REPORT NUMBER 


11 . 


National Aeronautics and Space Administration 
Washington, D.C. 20546-0001 


NASA TM-1 06607 


SUPPLEMENTARY NOTES 


Responsible person, Lisa C. Veitch, organization code 5160, (216) 433-2456. 


12a. DISTRIBUTION/AVAILABILITY STATEMENT 

12b. DISTRIBUTION CODE 

Unclassified - Unlimited 


Subject Category 50 


13. ABSTRACT (Maximum 200 words) 


A guanidine-based vehicle was developed to deposit precious metal coatings on surfaces known to be difficult to coat. 
To demonstrate this method, a platinum coating was deposited on alumina fibers using a guanidine-platinum solution. 
X-ray diffraction confirmed that the only species present in the coating was platinum, and, that all of the carbon 
species had been removed upon heat treatment. SEM results showed that some porosity was present but that the 
coatings uniformly covered the fiber surface and adhered well to the finer. 


14. SUBJECT TERMS 

Guanidine; Platinum coating 

15. NUMBER OF PAGES 

5 

16. PRICE CODE 

A02 

17. SECURITY CLASSIFICATION 

18. SECURITY CLASSIFICATION 

19. SECURITY CLASSIFICATION 

20. LIMITATION OF ABSTRACT 

OF REPORT 

OF THIS PAGE 

OF ABSTRACT 


Unclassified 

Unclassified 

Unclassified 



NSN 7540-01-280-5500 


Standard Form 298 (Rev. 2-89) 
Prescribed by ANSI Std. Z39-18 
298-1 02