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

Abstract

The knowledge of phase diagram and thermodynamic properties of the Si-Ta and Si-W systems is of technical importance for metallic contacts between Ta, W, and SiC in electrical and electronic devices. The phase diagram and thermodynamic properties of the Si-Ta and Si-W systems were assessed using the CALPHAD approach with available experimental data. The intermetallic compounds of the two systems were modeled as stoichiometric ones. A set of self-consistent thermodynamic parameters were obtained and the calculated phase equilibria were found to be in reasonable agreement with most experimental data. The calculated enthalpies of formation of the silicides in the Si-Ta and Si-W systems were compared with the reported values. The enthalpies of mixing of liquid at 2000 K in similar Si-transition metal systems were used for comparison in order to judge the rationality of the calculations. The assessed thermodynamic descriptions of the Si-Ta and Si-W binary systems will serve as part of the thermodynamic database for the Si-C-M (M: Ta and W) alloys.

Temperature and salinity effects on the Raman scattering cross section of the water OH-stretching vibration band in NaCl aqueous solutions from 0 to 300 °C

“…For the experiment at temperatures from 0 to 300°C at 30 MPa, round cross-sectional flexible fused silica capillary tube was used. The sample preparation procedures were similar to those described in our previous studies, [36,40] including the following steps: (1) load an aqueous solution column (15 mm long) into a large capillary tube (665 μm OD and 300 μm ID for pressure less than or equal to 50 MPa) with one end closed; (2) insert a small tube (200 μm OD and 75 μm ID) to a certain length (10 mm) away from the end of the large tube to inject a mercury column (approximately 5 mm in length) into the aqueous solution; (3) the capillary high-pressure optical cell containing a NaCl solution at a specific concentration was connected to a high pressure line ( Fig. 1b) and fixed at the experiment table to ensure that the capillary optical cell does not move during measurements at different temperatures.…”

“…Indeed, the water stretching Raman band is often used as internal standard in the determination of aqueous dissolved species concentration in the molality scale. [24,[31][32][33][34][35][36][37][38][39][40][41][42][43] In our previous works, Ou et al [39,40] found that the Raman peak area ratio (PAR = A CH4 /A H2O ) between the stretching bands of methane and water was affected by temperature and salinity, and the effect of dissolved NaCl on the PAR/mCH 4 (mCH 4 the concentration of CH 4 by mol/kg·H 2 O) became more and more significant with increasing temperature. Nevertheless, the mechanism of the dependence of PAR/mCH 4 on temperature and salinity remains unclear.…”

Diffusion pattern in MSi2and M5Si3silicides in group VB (M = V, Nb, Ta) and VIB (M = Mo, W) refractory metal-silicon systems

“…Interestingly, the marker plane moves inside the NbSi 2 phase -in a clear contrast to the case of the VSi 2 phase, which indicates comparable diffusion rates of Nb and Si in NbSi 2 . The ratio of In the Ta-Si system, as can be seen in Figure 3(a), four phases are present [69]. However, only two phases, TaSi 2 and Ta 5 Si 3 could be detected in the interdiffusion zone, as shown in Figure 3(b) [46].…”

“…This indicates that Si has a much higher diffusion rate compared to Si through this phase. The analysis of the diffusion couples gives the value of Figure 5(a) [69]. In the interdiffusion zone, as shown in Figure 5(b), mainly the WSi 2 phase is visible; however, W 5 Si 3 was found as a very thin layer [48].…”

Study on the Melting Temperature, the Jumps of Volume, Enthalpy and Entropy at Melting Point, and the Debye Temperature for the BCC Defective and Perfect Interstitial Alloy WSi under Pressure

“…Firstly, we find the isothermal compressibility χ T of the BCC interstitial alloy AB according to Equation (35) and the thermal expansion coefficient α T of the alloy according to Equation (40). The specific capacity at a constant volume of the alloy is given by the following relations [2,29,33]:…”