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Fe2B is Khatyrkite structured and crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Fe is bonded in a 4-coordinate geometry to four equivalent B atoms. All Fe–B bond lengths are 2.17 Å. B is bonded in a 10-coordinate geometry to eight equivalent Fe and two equivalent B atoms. Both B–B bond lengths are 2.12 Å.
Fe2B crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Fe is bonded in a 4-coordinate geometry to four equivalent B atoms. All Fe–B bond lengths are 2.15 Å. B is bonded in a body-centered cubic geometry to eight equivalent Fe atoms.
Moessbauer absorption spectra have been observed for Fe2B from 290 to 1175 K. A change in the electric quadrupole interaction was observed from 460 to 480 K and interpreted as a result of the rotation of the easy axis of magnetization as a function of temperature. The effective magnetic hyperfine field is defined as a function of temperature. A discontinuity in the isomer shift of 0.018 (plus or minus 0.010) mm/sec was found across the ferromagnetic transition.
NdFe12B6 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Nd is bonded to eighteen Fe and six equivalent B atoms to form distorted edge-sharing NdFe18B6 cuboctahedra. There are six shorter (3.11 Å) and twelve longer (3.28 Å) Nd–Fe bond lengths. All Nd–B bond lengths are 3.04 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a 4-coordinate geometry to two equivalent Nd and four equivalent B atoms. There are two shorter (2.05 Å) and two longer (2.06 Å) Fe–B bond lengths. In the second Fe site, Fe is bonded in a distorted T-shaped geometry to one Nd and three equivalent B atoms. There are one shorter (2.14 Å) and two longer (2.19 Å) Fe–B bond lengths. B is bonded in a 7-coordinate geometry to one Nd and seven Fe atoms.
Scanning electron spectroscopy, X-ray diffractometry, Auger electron spectroscopy, and microhardness measurements, are used to study the surfaces of 4340-steel samples that have been borided in a cold RF plasma which had been initiated in a gas mixture of 2.7 percent diborane in Ar. As a result of the dislocation of the diborane in the plasma, boron is deposited on the surface of the steel substrate and two crystalline phases, tetragonal Fe2B and orthorhombic FeB, are formed. The formation of boride phases then increases the surface microhardness from 2650 MPa to a maximum value of 7740 MPa.
The vaporization of B2O3 in a reducing environment leads to formation of both B2O3(g) and B2O2(g). While formation of B2O3(g) is well understood, many questions about the formation of B2O2(g) remain. Previous studies using B(s) + B2O3(l) have led to inconsistent thermodynamic data. In this study, it was found that after heating, B(s) and B2O3(l) appear to separate and variations in contact area likely led to the inconsistent vapor pressures of B2O2(g). To circumvent this problem, an activity of boron is fixed with a two-phase mixture of FeB and Fe2B. Both second and third law enthalpies of formation were measured for B2O2(g) and B2O3(g). From these the enthalpies of formation at 298.15 K are calculated to be -479.9 +/- 41.5 kJ/mol for B2O2(g) and -833.4 +/- 13.1 kJ/mol for B2O3(g). Ab initio calculations to determine the enthalpies of formation of B2O2(g) and B2O3(g) were conducted using the W1BD composite method and show good agreement with the experimental values.
Current studies at NASA Glenn on oxide thermodynamics are discussed. Previous studies on the vaporization of B2O3 in reducing atmospheres led to inconsistent studies when B was used as a reductant. It is shown that liquid B2O3 does not wet B and a clear phase separation was noted in the Knudsen cell. This problem was solved by using FeB and Fe2B to supply a different and constant activity of B. The thermodynamic data thus derived are compared to quantum chemical composite calculations. A major problem in high temperature mass spectrometry is the determination of accurate ionization cross sections, particularly for molecules. The method of Deutsch and Mark shows promise and some sample calculations are discussed. Finally current studies on the thermodynamics of rare earth silicates are discussed. Here the problems are obtaining a measurable signal from SiO2 vaporization and non-equilibrium vaporization. The use of a Ta reducing agent provides a stronger signal, which is related to silica activity. The Whitman-Motzfeld relation adapted to KEMS measurements is applied to obtain equilibrium pressures.