Thermodynamic Calculation of HfB2 Volatility Diagram

Abstract

The thermodynamics of the oxidation of HfB 2 at temperatures of 1000, 1500, 2000, and 2500 K have been studied using volatility diagrams. Both the equilibrium oxygen partial pressure (P O 2 ) for the HfB 2 (s) to HfO 2 (s) plus B 2 O 3 (l) and the partial pressures of B-O vapor species formed due to B 2 O 3 (l) volatilization increase with increasing temperature. Vapor pressures of the predominant gaseous species also increase with P O 2 . At 1000 K, the predominant vapor transition sequence is predicted be BO(g) fi B 2 O 2 (g) fi B 2 O 3 (g) fi BO 2 (g) with increasing P O 2 , and the predominant gas is BO 2 (g) with a pressure of 1.27310 26 Pa under the condition of P O 2 = 20 kPa. At higher temperatures of 1500, 2000, and 2500 K, the system undergoes vapor transitions in the same sequence of B(g) fi BO(g) fi B 2 O 2 (g) fi B 2 O 3 (g) fi BO 2 (g). Under the same condition of P O 2 = 20 kPa, the predominant vapor species is B 2 O 3 (g) with pressures of 2.38, 4.49310 3 , and 3.55310 5 Pa, respectively. Volatilization of B 2 O 3 (l) may produce porous HfO 2 scale, which is consistent with the experimental observations of HfB 2 oxidation in air. The present volatility diagram of HfB 2 shows that HfB 2 exhibits oxidation behavior similar to ZrB 2 , and factors other than volatility of gaseous species affect the oxidation rate.

Electronic structure, phonon spectra and electron–phonon interaction in ScB2

“…Quite a number of theoretical studies of the electronic properties of the diborides are known to date [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Ivanovskii et al [9] performed full potential linear muffin-tin orbital (FP-LMTO) calculations of all hexagonal diborides of 3d (Sc, Ti, ..., Fe), 4d (Y, Zr, ..., Ru), and 5d (La, Hf, ..., Os) metals and analyzed the variations in their chemical stability and some other properties (e.g., melting temperatures, enthalpies of formation).…”

“…21 First-principles calculations of the electronic structure of diborides including HfB 2 have been also presented. 19,20,[22][23][24][25][26][27][28][29] Lawson et al 29 studied the electronic structure and lattice properties of HfB 2 and ZrB 2 in a frame of the density functional theory (DFT). Lattice constants and elastic constants were determined.…”

“…By modeling the real-time data in terms of film thickness and surface roughness, the film nucleation and growth morphology were determined as a function of substrate type, substrate temperature, and precursor pressure. Li et al 28 studied the thermodynamics of the oxidation of HfB 2 at temperatures of 1000, 1500, 2000, and 2500 K using volatility diagrams. They found that HfB 2 exhibits oxidation behavior similar to ZrB 2 .…”

Complex Investigation of the Fermi Surface in HfB$_{2}$

“…By now, the de Haas-van Alphen (dHvA) measurements of the Fermi surface [11], optical ellipsometry measurements [12], magnetic susceptibility [13,14], and NMR measurements [15], as well as firstprinciples calculations of the electronic structure of diborides including HfB 2 have been presented [13,14,[16][17][18][19].…”

“…Li et al [19] studied the thermodynamics of the oxidation of HfB 2 at temperatures of 1000, 1500, 2000, and 2500 K using volatility diagrams. They found that HfB 2 exhibits oxidation behaviour similar to ZrB 2 .…”