Doctoral Dissertations

Abstract

"Molybdenum and tantalum were siliconized in an enclosed system by the hydrogen reduction of silicon tetrachloride with induction heating between 900°C and 1450°C.

The siliconizing process was primarily influenced by the gaseous composition, temperature, time, molar flow ratio (SiCl4/H2), geometrical shape and ionization charges. The rate of siliconizing, measured as the weight gain by the fused quartz helix balance, generally follows a parabolic law, y = k t1/2, where y = weight gain, t = time, and k = rate constant. The activation energy is estimated at 21.6 k cal/mole for siliconizing of molybdenum. Deposition rate is greatly reduced at the later stage of the diffusion controlled process. The growth rate and the temperature of the siliconizing-diffusion treatment may be expressed by log y2/T = a - b/T, where y, t, T, a, and b are the thickness (or weight gain), time, absolute temperature, and constants respectively. Whenever a phase transformation is encountered, a new set of constants may be needed.

Siliconized molybdenum and tantalum were evaluated with metallography, microhardness, X-ray and electron microprobe analysis. Correlation between the coating properties, microstructure, intermetallic phases and phase diagrams were made. Electron microprobe analysis could determine phases and the sharp concentration variation in one micron range between phases of narrow diffusion zones. However, a variation of 1 to 2 per cent in composition is difficult to resolve.

Suggestions for codeposition (such as TaSi2 and TaC), Kirkendall marker determination, diffusion constant and diffusion barrier studies by electron microprobe analyses as well as the deposition under electrically charged field were proposed"--Abstract.

Advisor(s)

Planje, Theodore J., 1919-1980

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering

Publisher

University of Missouri at Rolla

Publication Date

1964

Pagination

xii, 172 pages

Note about bibliography

Includes bibliographical references (pages 145-155).

Rights

© 1964 Gordon Pu Kong Chu, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 1616

Print OCLC #

5959322

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