Kaiyue Wang

Photoluminescence Studies of Both the Neutral and Negatively Charged Nitrogen-Vacancy Center in Diamond

In this study low temperature micro-photoluminescence technology was employed to investigate effects of the irradiation and nitrogen concentration on nitrogen-vacancy (NV) luminescence, with the photochromic and vibronic properties of the NV defects. Results showed that the NV luminescence was weakened due to recombination of self-interstitials created by electron irradiation in diamond and the vacancies within the structure of NV centers. For very pure diamond, the vacancies migrated the long distance to get trapped by N atoms only after sufficient high temperature annealing. As with the increase in nitrogen content, the migration distance of vacancies got smaller. The nitrogen also favored the formation of negatively charged NV centers with the donating electrons. Under the high-energy ultraviolet laser excitation, the photochromic property of the NV- center was also observed, though it was not stable. Besides, the NV centers showed very strong broad sidebands, and the vibrations involved one phonon with energy of ~42 meV and another with ~67 meV energy.

Annealing and lateral migration of defects in IIa diamond created by near-threshold electron irradiation

The migration of vacancies in diamond is of considerable fundamental interest and has been widely studied previously, while the involvement of self-interstitials in diamond is less common except through centers such as 3H, 515.8 nm, 533.5 nm, and 580 nm. In this paper, the annealing and lateral migration of some interstitial-related centers in type IIa diamond are investigated by low temperature photoluminescence (PL) microscopy, and the distributions of interstitial- and vacancy-related centers are also clearly presented and discussed.

Preparation and characterization of low-cost high-performance mullite-quartz ceramic proppants for coal bed methane wells

Abstract In this study, the mullite-quartz-based proppants were successfully prepared by using the coal gangue as the raw materials. Then, the effects of the additive and the sintering temperature on the composition, microstructure, and properties of the proppants were investigated. Results showed that the proppants sintered at 1250°C with the 10 wt% bauxite additive presented the best performance, which was very close to that of the quartz-proppant, and met the operational requirements of the 52 MPa coal bed methane wells. The viscous flow mechanism of the liquid phase formed during the sintering process also promoted the arrangement of the grains, thus benefiting the densification and the strength of the proppants.

Preparation and characterization of low-density ceramic proppant containing coal gangue additive

Abstract Low-density ceramic proppants were prepared from calcined flint clay and solid waste coal gangue by pelleting, drying, screening and sintering, namely solid state sintering method. The density and breakage ratio of the proppants were systematically investigated as a function of sintering temperature. The morphology and phase composition of the proppants were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the ceramic proppants are composed of acicular mullite and granular cristobalite. Bulk density and apparent density of the proppants rise and thereafter down with increasing the sintering temperature. The proppants sintered at 1400 °C have the best performance with 1.28 g/cm3 of bulk density, 2.84 g/cm3 of apparent density and 7.89% of breakage ratio under 52 MPa closed pressure. The prepared ceramic proppants meet China industrial standard requirements SY/T5108-2014.

Feasible Recycling of Industrial Waste Coal Gangue for Preparation of Mullite Based Ceramic Proppant

Industrial waste coal gangue was successfully utilized to prepare the mullite-based ceramic proppants. The experiments involved the pelletizing technology of proppant through intensive mixer and following the sintering process under different temperatures. The crystalline phase, microstructure, density and breakage ratio of the proppants were investigated. The results showed that with the increasing of sintering temperature, the crystalline phases were transformed to rod-like mullite, which formed the cross-linked structure, improving the densification of proppants. Consequently, the breakage ratio under the closure pressure of 35 MPa exhibited declining trend and reached the minimum value of 6.8% at 1450 °C. Owing to the easy preparation, feasible design, low cost and moderate breakage ratio, the mullite-based ceramic proppant prepared by coal gangue and bauxite is promising candidate for fracturing proppants in future applications.