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Vapor pressures of zirconium over zirconium diboride have been measured by the Knudsen technique over the temperature range 2150° to 2475°K. A new type of apparatus was constructed and used successfully in the study. Zirconium diboride was determined to evaporate congruently at a composition of ZrB1.906(+0.025 or —0.010) by heating solid pressed plugs of both zirconium-rich and boron-rich material to constant composition at 2400°C to 2500°C. The over-all reaction is ZrB1.906(s)=Zr(g)+1.906 B(g)Three series of measurements were made using tungsten crucibles and different orifice sizes. Second-law and third-law treatments of the data did not agree. Thermodynamic calculations were made which indicated that water vapor at low background pressures would produce volatile oxides of both zirconium and boron. This reaction was investigated by adding water vapor to the system and the increased transport of zirconium was clearly demonstrated. Accordingly, each pressure measurement was corrected by a factor β, constant for each series, related to the background pressure. From the corrected pressures, values of ΔH0o for the reaction were computed by the third-law treatment. From the three series a vaporization coefficient of 0.025±0.010 was computed, leading to an equilibrium ΔH0o of 458.3±6.5 kcal/mole for reaction 1, or a partial pressure of Zr over ZrB1.906 of 2.38×10—10 atm±20% at 2000°K. The variance between this and an expected value of 477.4 kcal/mole is presumed to be related, at least in part, to discrepancies in the heat of vaporization of zirconium. The results verify the prediction that the Zr–B system exhibits a congruently evaporating phase and suggest that the congruently evaporating composition in many high-temperature systems will occur at nonstoichiometric compositions.

An induction transformer furnace for a neutron diffractometer is described. This furnace has been used for the examination of refractory carbides by neutron diffraction at temperatures up to 2500°C.

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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.

SUMMARYMeasurements of the detonation wave structure at the axis of long cylindrical charges of nitromethane and TNT are described. The measurements show that the structure consists of three zones: (1) a reaction zone, (2) zones, is not predicted by any extrapolation of one-dimensional theory. *In the liquid explosive nitromethane, the pressure at the head of the decay zone is essentially independent of the charge size, but the extent of the zone is very strongly dependent an the charge diameter and length.The decay zone increases in length as the detonation runs. In a 37 mm diameter charge, after a run of 16 diameters, the decay zone is about 0.6 mm long and the pressure falls about 27 kbar in the zone.

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