Abstract
This paper presents experimental measurements of the behavior of diamond and boron nitride at high pressures. The authors show that their melting temperature at extreme conditions are close to the Sun's surface temperature
Highlights
Diamond, the hardest known natural material and a wellknown gemstone, is the main carbon form at high pressure and has attracted attention from physics, geology, materials science, and astrophysics researchers [1,2,3,4,5]
The continuous Debye diffraction rings were treated as evidence of newly crystallized fine grains in the sample when the temperature was above the melting point, while the presence of large diffraction spots signified a large-grained microstructure when the temperature was below the melting point
We chose the value reported by Kimura et al [39] who pointed out that the misjudgment existed in earlier work that underestimated the melting temperature of MgO based on an analysis of the microtexture of quenched samples, which is similar to the means used to judge melting in samples in our experiments, but the error range used in our fitting is ±255 K, not the ±200 K of Kimura’s work, because we considered the discrepancy of melting temperature at 15 GPa between the theoretical data and Kimura’s data
Summary
The hardest known natural material and a wellknown gemstone, is the main carbon form at high pressure and has attracted attention from physics, geology, materials science, and astrophysics researchers [1,2,3,4,5]. The melting points of diamond and cBN at static pressure are still a mystery because diamond and cBN are difficult to melt due to their high atomic density and strong covalent bonds. The high sound velocities collected by Shaner et al [15] associated with the insulating diamond phase determined by Mitchell et al [16] indicated a positive dP/dT slope for the diamond-liquid phase line, which is opposite to the previous negative results by analogy with the melting curves of Si and Ge. Zerr and Boehler [17] measured the melting temperature of cBN at a pressure of 10 GPa, which combined the use of a CO2-laser-heated DAC and in situ visual observation of large increases in temperature near the melting point of cBN, and the melting temperature is 3600 ± 100 K in their results
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