Reactions of Refractory Silicides with Carbon and Nitrogen

Abstract

The s ilic id e s of T i, Z r, Ce and Nb were Investigated to determine the phases present a t tem peratures around 2000*K* The m o tio n s o f s ilic id e s of T i, Z r, Ce, Nb, Ta, Ho and V with earbon were studied a t these tempera tu re s * Also a U n ited amount of work was dons on the reactions o f some of the s ilic id e s with nitrogen* The data have been used to estab lish tern ary phase diagrams for the systems and to obtain upper and lower lim its fo r the heats o f formation of the silic id e s * The till* on natal m s obtained fra ths J. T. Baker Chesdeal Company 1a the form of lumps. It was ground to finsr than H O math with a steal mortar I and pestle. Spsctroenalyeia showed the main Impurities to bat T1 lass than 1#» Cr 0.1-1# and A1 and fa approximately 0,1#. X-ray analysis showed a ray weak unidentified second phase* The Zr natal was obtained in the font of high parity eposes and of rather impure powder* The main inpurities in the powder tsars dissolved oxygen and nitrogen. X-ray diffraction showed two Zr phases-on# set of lines corre sponding to purs Zr and the other to Zr with dissolved 0 or M. The phase with the emended lattioe (a • 3.26 A, o • 5.19A) corresponds to 22 atomict oxygen assuming that all of ths dissolved gas le oxygen.Î gnition experiments showed that tha Zr contains 214 atomic % (4*54 wt. t) oxygen. The value fra tha ignition experiments is taken to be correct.X-ray analysis of the Ti mstal showed that it also contained dissolved oxygen and nitrogen. Assuming that all of ths d iaaolved gas is oxygen ths lattice constants (a • 2.95 A, c ■ 4*69 A) indicats 4*5 atonic percent oxygen.^ Ths main imparity in ths Ct metal was 5 atomic % carbon.All of ths other ns tala were of 99*91 or greater purity* *• *

Thermodynamic Assessment of the Si-Ta and Si-W Systems

“…However, the stoichiometry of Ta 4.5 Si was not firmly established in their work. Brewer and Krikorian [18] suggested that Ta 4.5 Si was a metastable crystalline phase, which was later confirmed by Deardorff et al [19] A new compound, Ta 3 Si, was further identified by x-ray diffraction (XRD). [19,20] Kocherzhinskii et al [21] carefully measured the phase diagram of the Si-Ta system using metallographic, XRD, and differential thermal analysis (DTA) techniques.…”

“…Most experimental work showed that the solubility of Ta in Si was negligible. [16][17][18][19][20][21] By means of direct-reaction calorimetry, Robins and Jenkins [23] measured the enthalpies of formation of aTa 5 Si 3 (À39.7 kJ/mol) and TaSi 2 (À14.4 kJ/mol) at ambient temperature. Myers and Searcy [24] determined the Gibbs energies of formation (D f G) of four compounds using Knudsen effusion cells.…”

Thermal Stability of W‐xRe/TiC/SiC Systems = 0, 5 and 25 at % Re) at High Temperature

“…Temperature is, however, a limiting factor, because this compound WC reacts with W at 1420 K to form W 2 C, which is not stable in the presence of SiC. [27] As a consequence, this carbide can only be used up to 1420 K. The carbon mobility in these two compounds has to be established. …”

“…Indeed, silicon carbide is a very interesting material for several high-temperature applications; nevertheless, this compound reacts with metals. [1][2][3][4][5][6][7][8][9][10][11][12] In this way, the research of diffusion barriers, limiting diffusion of fast-moving elements such as carbon and silicon, is particularly important. Only a small amount of data about this particular point can be found in the literature; it is also difficult to predict the growth of such a kind of layer.…”

Solid‐State Reactions of SiC/W–25Re Alloy and Thermal Stability of SiC/Ti/W–25Re Alloy under High‐Temperature Annealing

“…[11][12][13][14][15] However, possibilities of solidstate reactions between SiC and refractory materials have substantial interest. For W alloy, thermal reactions between SiC and W have been reported by many researchers; Luo et al, [16] Roger et al, [17] Brewer and Krikorian, [18] and Baud et al [19] Even though SiC was attempted to use as a diffusion barrier in their researches, W and SiC were reacted and formed W-silicides under the high-temperature annealing. Especially according Luo et al, [16] strength degradation of the fiber was reported because of the W/SiC interface reaction at 1 000 C. In order to enhance the thermal stability of W with SiC, the addition of less reactive material can be an effective approach.…”