Accession Number : AD0821901

Title :   DEVELOPMENT OF IMPROVED METHODS OF DEPOSITING IRIDIUM COATINGS ON GRAPHITE.

Descriptive Note : Annual summary rept. 31 Jan 66-15 Feb 67,

Corporate Author : GENERAL TECHNOLOGIES CORP SPRINGFIELD VA

Personal Author(s) : Macklin, Buford A. ; Owens, Fred R. ; LaMar, Paul A.

Report Date : AUG 1967

Pagination or Media Count : 78

Abstract : Experimental work was conducted to develop improved methods for depositing reliable oxidation resistant iridium coatings onto graphite. This effort involved the survey and evaluation of vapor deposition, electrodeposition from fused cyanides, aqueous electrodeposition and thermal decomposition or iridium resinate as methods for depositing iridium coatings. Box statistical experimental design methods were used to evaluate and optimize the selected deposition methods. Several grades of isotropic high thermal expansion graphite were evaluated as substrates for the iridium coatings. Irridium coatings were obtained on graphite by electrolysis of fused cyanides, vapor deposition from the halides and by thermal decomposition of iridium resinate. The fused cyanide electrolysis method was the best of the several methods investigated for producing thick (greater than one mil) iridium coatings. However, direct application of the iridium onto the graphite from the cyanide bath resulted in entrapment of electrolyte in the pores of the graphite. Both aqueous electrodeposition and thermal decomposition of iridium resinate yielded flash coatings of iridium. The iridium coating from the resinate method proved to be effective as a barrier coat on graphite which will prevent the absorption of cyanides during electrolysis in fused cyanide electroplating baths. Results on the vapor deposition of iridium from iridium hexafluoride have shown a high processing step. A combination iridium coating on graphite consisting of a thin inner layer deposited from iridium resinate and an outer layer deposited from a fused cyanide electrolyte has provided good oxidation resistance to graphite at 2000 C in air. (Author)

Descriptors :   *IRIDIUM), *CORROSION INHIBITION), (*DEPOSITION, METAL COATINGS), (*METAL COATINGS, (*GRAPHITE, GRAIN SIZE, VACUUM APPARATUS, VAPOR PLATING, ELECTRODEPOSITION, CYANIDES, ORGANIC SOLVENTS, THERMAL EXPANSION, SUBSTRATES, ELECTROLYSIS, THICKNESS, THERMAL PROPERTIES, ABSORPTION, FLUORIDES, HEAT RESISTANT MATERIALS, CHLORIDES, OPTIMIZATION, BROMIDES, TEST METHODS, POROSITY, ADHESION.

Subject Categories : Coatings, Colorants and Finishes
      Fabrication Metallurgy

Distribution Statement : APPROVED FOR PUBLIC RELEASE