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Preparation of high emissivity NiCr_2O_4 powders with a spinel structure by spray drying

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International Journal of Minerals,Metallurgy and Materials 2012年第2期19卷 173-178页

作者： Xu-dong Cheng Jie Min Zhen-qi Zhu Wei-ping Ye State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology Wuhan 430070 China School of Materials Science and Technology Wuhan University of Technology Wuhan 430070 China

Spray-drying was used to produce the high emissivity NiCr2O4 powders with a spinel structure. Preliminary investigations focused on fabricating the high emissivity powders for infrared radiation coatings and finding the relationship between microstructure and emissivity. The NiCr2O4 powders were characterized for composition, microstructure, and infrared emissivity by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, infrared radiant instrument, and Fourier transform infrared spectra （FT-IR）. Thermogravimetry and differential thermal analysis show that the appropriate baking temperature for NiCr2O4 powder preparation is about 1200？C. The emissivity measurement and FT-IR spectra show that, because of the special spinel structure, the NiCr2O4 powders have a high emissivity about 0.91. Spray-drying is a suitable method to produce the high emissivity ceramic powders.

关键词： emissivity infrared radiation spray drying powders ceramic materials nickel compounds chromium compounds

Optical and Structural Properties of Cr-Doped GaN Grown by HVPE Method

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Chinese Physics Letters 2010年第12期27卷 184-187页

作者：颜怀跃修向前华雪梅刘战辉周安张荣谢自力韩平施毅郑有炓 Key Laboratory of Advanced Photonic and Electronic Materials Department of Physics Nanjing University Nanjing 210093

Single crystalline Cr-doped GaN fihns are successfully grown by hydride vapor phase epitaxy. The structure analysis indicates that the film is uniform without detectable Cr precipitates or clusters and the Cr atoms are substituted for Ga sites. The impurity modes in the range 510 530cm^-1 are observed by the Raman spectra. The modes are assigned to the host lattice defects caused by substitutional Cr. The donor-aeceptor emission is found to locate at Ec - 0.20 eV by analyzing the photoluminescence spectrum obtained at different temperatures, and the emission is attributed to the structural defects caused by CrGa-VN complex. The superconductor quantum interference device results show that the Cr-doped GaN film without detectable Cr precipitates or clusters exhibits paramagnetic properties.

关键词： chromium compounds GALLIUM nitride SEMICONDUCTORS -- Analysis EPITAXY RAMAN effect TEMPERATURE effect SUPERCONDUCTING quantum interference devices

Study of Sintering Behaviour and Electrical Conductivity of Cr-Zn-Fe-O System

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维普期刊数据库

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Journal of Materials Science & Technology 1999年第1期15卷 79-82页

作者： Hanna, A.A. Khalil, M.Sh. Saleh, H.I. Ali, A.F. Inorganic Chemistry Department National Research Centre Dokki Cairo Egypt

A series of chemical composition based on Cr, Fe and O with Zn as a partially substituting ion has been prepared in the general formula Zn//xCr//1// minus //xFe//2O by coprecipitation method using NH//4OH as the precipitating agent at pH equals 10.3. The prepared samples were identified by both thermal analysis (DTA and TGA) and X-ray diffraction. It was found that no single phase is obtained for any of the studied compositions but a mixture of different phases is observed, depending on the molar percentage of zinc ion substitution as well as on the sintering temperature. The temperature dependence of the electrical conductivity, sigma , of the prepared samples is plotted between 25 and 680 degree C. It was observed that the electrical conductivity increases with temperature for both samples with x equals 0.00 and 0.80 Zn ion content while it is nearly temperature independent for samples with intermediate Zn concentration x equals 0.2 and 0.5 mol fraction. The activation energy, E//a, calculated from the linear relation, lg sigma -1000/T for the final mixtures (sintered at 1300 degree C) was calculated. (Edited author abstract) 16 Refs.

关键词： chromium compounds

Pre-pumped passively Q-switched Nd:YAG/Cr:YAG microchip laser

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Chinese Optics Letters 2004年第9期2卷 536-537页

作者：田信宁闫平柳强巩马理廖云 CenterforPhotonicsandElectronics DepartmentofPrecisionInstrumentsTsinghuaUniversityBeijing100084 UniversityofElectronicScienceandTechnologyofChina Chengdu610054

A pre-pumped passively Q-switched Nd:YAG/Cr: YAG microchip laser is demonstrated with a peak power of 7.5 kW at pulse repetition rate of serveral kilohertzs. The full-width at half-maximum (FWHM) is 734 ps, and the pulse energy is 5.5 μJ with a fundamental spatial mode. In this system, the pre-pumped microchip laser of Nd: YAG/Cr: YAG wafer which is bonded through the thermal-bonding technique has achieved a time jitter value of 12 μs and a Q-switched amplitude instability of 1.26% (1δ) through the pre-pumped modulation technique.

关键词： chromium compounds Optically pumped lasers Q switched lasers Timing jitter Ultrashort pulses