High-Temperature Phase Studies in the Tantalum-Boron System between Ta and TaB

Abstract

Phase relationships in the tantalum‐boron system between Ta and normalTaB have been studied. A phase diagram of the solid portion of the system has been determined and is shown. Two three‐phase equilibria exist within the system: false(afalse)normalTa‐Ta2B‐Ta3B2 normalat 2040°±30°C , and false(bfalse)Ta2B‐Ta3B2‐normalTaB at 2180°±20°C . The chemical composition of the Ta2B phase is Ta2.4±0.2B . The composition of the Ta3B2 phase is Ta1.00±0.05B . The melting point of normalTaB lies above 2800°C. The extreme slowness of reactions within the system has been investigated qualitatively, and the necessity for seeding at temperatures in the neighborhood of 2000°C has been noted. The results disagree markedly with data previously reported in the literature.

Borides

“…The Cr 23 G 6 family appears much more extensive amongst the borides than the carbides, and of probably the greater general stability; but the exclusion, upon present evidence, of iron analogues (as in Fe 21 Mo 2 C 6 ) amongst the borides is notable.…”

Ta(B, C, N) and (Ta, Mi)(B, C, N) (Mi = Nb, W) ceramics by high‐energy ball milling: processing and solution mechanisms

“…As there is no relevant data on the phase of TaB in FactSage database, the Gibbs free energy change curve of TaB generated by Ta and B reaction cannot be calculated by FactSage. Therefore, CrB is used to judge the difficulty of the reaction between Ta and B, which has the same crystal structure with TaB 31–33 . Therefore, in the initial stage of high‐energy ball milling, solute tantalum tends to dissolve carbon atoms first, followed by nitrogen atoms, and then boron atoms 34 .…”

“…Therefore, CrB is used to judge the difficulty of the reaction between Ta and B, which has the same crystal structure with TaB. [31][32][33] Therefore, in the initial stage of high-energy ball milling, solute tantalum tends to dissolve carbon atoms first, followed by nitrogen atoms, and then boron atoms. 34 When the ball-milling time was less than 8 h, the diffraction peaks of mixed powders shifted to small angle gradually.…”

Thermodynamic Properties of the Tantalum and Tungsten Borides

“…[1] and Ta~B(s) : 2.4 Ta(s) q-B(g) [2] Experimental observations showed that reaction [2] instead of reaction [1] occurred; hence the rate of loss of B(g) must be greater than 2.4 times the rate of loss of Ta(g) from Ta(s). The limiting standard free energy for reaction [2] can be computed by assuming the rate of loss of B(g) equals 2.4 times the rate of loss of Ta(g) from Ta(s). This assumption is equivalent to assuming the pressure of B(g) equals 1/9.82 times the pressure of Ta(g) over Ta(s).…”