Boron vapor pressure

The thermal behavior of tetraborides is based on two factors the saturation vapor pressure of the metal, an increase of which increases the dissociation, and the stability of the B—B bonds within the boron sublattice, the strength of the B—B bonds decreasing as the size of the cubic lattice parameter increases. 

The parameters controlling the synthesis are the temperature, the vapor pressure of the alkali metal and the crystalline state of boron. The reactions are unaffected by the atomic ratio, M/B, provided it is much larger than the M/B ratios characteristic of the phases that are to be prepared values of, e.g., ca. 1 /2, 1 or 2, are satisfactory. 

At 1400°C and reduced pressure, ZrB2 and HfB2 codeposit with considerable amounts of -rh boron owing to the low vapor pressure of Zr and Hf tetrachlorides. Excess hydrogen and metal tetrachloride are necessary to minimize the formation of uncombined boron. ... 

E. Example Separation of BF3 and CH2CI2. Boron trifluoride (bp —110.7°C) is readily separated from methylene chloride (bp 40.7°C) as illustrated in Fig. 5.6. Inspection of the vapor pressure data in Appendix V reveals that BF3 exerts 75 torr at — 126°C, whereas extrapolation of the vapor pressure data for CH2CI2 to this temperature (log P vs. 1/T plot) indicates a vapor pressure of less than 10 3 torr for this component. Therefore, the reaction mixture is slowly passed through a trap cooled to — 126°C (methylcyclohexane slush bath, see below), which retains the methylene chloride, and into another trap at — 196°C (liquid nitrogen), which retains the boron trifluoride. The rate of trans-... 

Set the above prepared solution to the bubbling unit as shown in Fig. 14.2. When B203 dissolves in the solution, it reacts with methanol, to form a boron ester. This boron ester has a very high vapor pressure, similar to that of methanol. 

The vapor pressure of /i-[(CH3)2N]B2H5 obeys the relationship log P = 2158.56/T + 1.75 log T - 0.008061T + 7.518831 (101 torr at 0°). The gas-phase infrared spectrum has been reported in detail.5 The compound is a useful intermediate in the synthesis of other boron nitrogen compounds, including those containing NBNB6 and PBNB7 chains, and Na[(CH3)2-N(BH3)2].8 The compound can be stored at 25° for months in sealed, evacuated Pyrex tubes. It is soluble in ethers and aromatic hydrocarbons, but is attacked by protic solvents. 

Borides. Zirconium forms two borides zirconium diboride [12045-64-6] ZrB2, and zirconium dodecabotide [12046-91 -2] ZtB 2- Th diboride is synthesized from the elements, by vapor-phase coreduction of zirconium and boron hahdes, or by the carbothermic reduction of zirconium oxide and boron carbide boric oxide is avoided because of its relatively high vapor pressure at the reaction temperature. 

Since the vapor pressure of B2O3 is low (10 N/m at 1000°C), liquid B2O3 is deposited on the Si surface. If the initial partial pressure of BBrs is kept low enough, formation of a boron skin (SiB. or SiBg) on the Si wafers is avoided, and B-rich borosilicate glass is deposited instead. 

There was 10 mole % excess metal present. The calculated ARTs are presented in Table 1 for the Zr system, as well as the Ti and Hf analogs, which are discussed in the next section. The theoretical total pressures generated in all systems are greater than 1 atm. The composition of the gas phase varies from system to system, though it is composed primarily of metal and boron vapor in all cases suggesting that the ART is controlled by the highly endothermic vaporization of the metal and boron (A//vap = 450 to 650 kJ/mol). 

Boron fluoride-trimethylamine is a white, crystalline solid melting in a closed tube at 138°.3 The vapor pressure of the solid is given by the equation4... 

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