Effects of catalyst height on diamond crystal morphology under high pressure and high temperature

The effect of the catalyst height on the morphology of diamond crystal is investigated by means of temperature gradient growth （TGG） under high pressure and high temperature （HPHT） conditions with using a Ni-based catalyst in this article. The experimental results show that the morphology of diamond changes from an octahedral shape to a cub- octahedral shape as the catalyst height rises. Moreover, the finite element method （FEM） is used to simulate the temperature field of the melted catalyst/solvent. The results show that the temperature at the location of the seed diamond continues to decrease with the increase of catalyst height, which is conducive to changing the morphology of diamond. This work provides a new way to change the diamond crystal morphology.

Synthesis and characterization of NaAlSi2O6 jadeite under 3.5 GPa

The high pressure and high temperature（HPHT） method is successfully used to synthesize jadeite in a temperature range of 1000℃–1400℃ under a pressure of 3.5 GPa. The initial raw materials are Na2SiO3·9H2O and Al2（SiO3）3.Through the HPHT method, the amorphous glass material is entirely converted into crystalline jadeite. We can obtain the good-quality jadeite by optimizing the reaction pressure and temperature. The measurements of x-ray diffraction（XRD）,scanning electron microscopy（SEM）, Fourier-transform infrared（FTIR） and Raman scattering indicate that the properties of synthesized jadeite at 1260℃ under 3.5 GPa are extremely similar to those of the natural jadeite. What is more, the results will be valuable for understanding the formation process of natural jadeite. This work also reveals the mechanism for metamorphism of magma in the earth.

Preparation and Characterization of Fe/Al_2O_3 Nanocomposites

Fe/Al2O3 nanocomposites prepared by using the sol-gel technique were reduced in H： atmosphere at different temperatures, and the corresponding Fe/Al2O3 nanocomposites were obtained after the reduction of Fe/Al2O3 nanocomposites at 1173 K. The structures and properties of the specimens were studied by X-ray diffraction （XRD）, Mossbauer spectroscopy（ MS）, and vibrating sample magnetometry（VSM）. The results show that the reduction temperature has a significant influence on the structure, the grain size, and the magnetic properties of the specimens.

A New Method for Preparation of Nanocrystalline Molybdenum Nitride

Nanocrystalline molybdenum nitride （γ-Mo2N） with the cubic structure is prepared by the direct-current arc discharge method in N2 gas, using metal Mo or W rod as a cathode. The x-ray diffraction （XRD） and transmission electron microscopy （TEM） are used to characterize the product. It is found that the conversion of Mo to γ-Mo2N and affinity of Mo to N2 are determined by the nitrogen pressure. Moreover, we compare the effect of Mo and W rod as a cathode for preparing γ-Mo2N. The average size of γ-Mo2N particles is about 5 nm. The rapid quenching mechanism can be used to explain the formation of nanocrystalline γ-Mo2N.

Thermoelectric performance of Cu_(2)Se bulk materials by hightemperature and high-pressure synthesis

Polycrystalline Cu_(2)Se bulk materials were synthesized by high-pressure and high-temperature(HPHT)technique.The effects of synthetic temperature and pressure on the thermoelectric properties of Cu_(2)Se materials were investigated.The results indicate that both synthetic temperature and pressure determine the microstructure and thermoelectric performance of Cu2Se compounds.The increase of synthetic temperature can effectively enhance the electrical conductivity and decrease the lattice thermal conductivity.A two-fold improvement in the power factor is obtained at synthetic temperature of 1000℃ compared to that obtained at room temperature.All b-Cu2Se samples exhibit low and temperatureindependent lattice thermal conductivity ranging from 0.3 to 0.5 Wm^(-1)K^(-1) due to the intrinsic superionic feature and the abundant lattice defects produced at high pressure.A maximum zT of 1.19 at 723 K was obtained for the sample synthesized at 3 GPa and 1000℃.These findings indicate that HPHT technology is an efficient approach to synthesize Cu_(2)Se-based bulk materials.