退火对Nd,Cr:GSGG激光晶体吸收光谱的影响

本文应用吸收光谱法,对提拉法生长的Nd,Cr:GSGG晶体在不同气氛下退火后的光谱变化进行了研究.氧化气氛下退火后的吸收光谱中,在1μm处出现了由于晶体中存在Cr4+离子所引起的两个吸收带,被称为1μm吸收损失.还原气氛(CO和H2)下退火后的吸收光谱中,在1μm处的吸收带基本消失,这对于提高激光效率是非常有利的.此外,在642nm处的吸收带强度有一定的减弱.这些数据对于晶体后处理工艺的改进和激光器设计具有重要的参考价值.     

复合金属氧化物脱除SO2的气氛效应及动力学

在模拟烟气气氛中,运用TG法考察了CO2 、H2O对复合金属氧化物脱硫剂脱除SO2 反应的影响.实验表明,CO2 对脱硫反应的速率及转化率影响很小,可视作惰性气体;H2O对脱硫反应的影响有区间性,在H2O%＜7%时,随着水浓度增加脱硫反应速率明显提高,H2O＞7%时,H2O浓度影响很小,可忽略其影响.包括H2O浓度影响的脱硫反应本征动力学方程式为RSO2=(α+4.991 CH2O0.310?6) R'SO2.     

PAN基碳纤维形成过程中热氧稳定化气氛对纤维径向结构演变的关联性研究

采用红外光谱、X射线能谱、激光显微共焦拉曼光谱、X射线衍射光谱和电子自旋共振等多种表征手段,定量探讨了热氧稳定化气氛中氧气浓度与聚丙烯腈纤维的径向结构转变以及与碳纤维结构和性能的关联.结果表明,随着氧气浓度的增大,氧气自皮层逐渐扩散到纤维内部,热氧稳定化纤维的径向结构趋于均质化.当热氧稳定化过程氧体积浓度(Vo)由20.38％增加到21.15％时,热氧稳定化纤维的皮芯结构逐渐减小,环化程度增幅显著,该过程对碳纤维皮部类石墨结构的形成具有促进作用,所得碳纤维的孔隙率减小,拉伸强度增大.当Vo大于21.34％时,热氧稳定化纤维的皮芯结构基本消失,但氧化程度过高且环化程度增幅缓慢,抑制了碳纤维皮部类石墨结构的形成,所得碳纤维的孔隙率增大,拉伸强度降低.控制Vo为21.15％ ～21.34％时,热氧稳定化纤维的环化和径向化学结构的均质化程度均得以提高,所得碳纤维在保持皮部较高石墨程度的同时促进了芯部类石墨结构的形成,此时拉伸强度最高,比在常规空气气氛条件下制备的碳纤维提高了12.22％.     

Effect of high-temperature annealing on AIN thin film grown by metalorganic chemical vapor deposition

The effect of high-temperature annealing on A1N thin film grown by metalorganic chemical vapor deposition was investigated using atomic force microscopy, Raman spectroscopy, and deep ultra-violet photoluminescence （PL） with the excitation wavelength as short as ~ 177 nm. Annealing experiments were carded out in either N2 or vacuum atmosphere with the annealing temperature ranging from 1200 ℃ to 1600 ℃. It is found that surface roughness reduced and compres- sive strain increased with the annealing temperature increasing in both annealing atmospheres. As to optical properties, a band-edge emission peak at 6.036 eV and a very broad emission band peaking at about 4.7 eV were observed in the photoluminescence spectrum of the as-grown sample. After annealing, the intensity of the band-edge emission peak varied with the annealing temperature and atmosphere. It is also found that a much stronger emission band ranging from 2.5 eV to 4.2 eV is superimposed on the original spectra by annealing in either N2 or vacuum atmosphere. We attribute these deep-level emission peaks to the VAL--ON complex in the A1N material.     

Bridgman growth of LiYF_4 single crystal in nonvacuum atmosphere

Using LiF and YF3 as starting materials,we prepare feed material from fluorides according to the molar ratio of LiF:YF3=51.5:48.5.The anhydrous LiYF4 polycrystalline material is synthesized via the fluoridation process with a dried HF flow at elevated temperature.By charging the feed material and adding a small amount of active carbon powder in a sealed platinum crucible,the crystal can be grown via the vertical Bridgman method in a nonvacuum atmosphere.This is possible because the oxidization and volatilization of the melt is avoided.Using optimum conditions,that is,a growth rate of 0.5-0.6 mm/h and a temperature gradient of 25-30℃/cm across the solid-liquid interface under a furnace temperature of 920-930℃,the colorless crystal LiYF 4 with the size of φ25 × 50 (mm) is successfully grown.The optical transmittance of the crystal is as high as 85% above the absorption edge at 190 nm.The induced absorption bands are observed below 700 nm in the transmission spectrum after the crystal is subjected to a high dose of γ-ray irradiation.     

Cd1－xZnxTe晶体的In气氛扩散热处理研究

为了满足辐射探测器件的需要，将生长得到的Cd_1-xZn_xTe晶体在In 气氛下进行退火处理能有效提高晶体的电阻率等性能. 退火处理过程的实质是一个扩散过程 ，因此研究扩散系数与Cd_1-xZn_xTe晶体的性能特别是电阻率变化之 间的关系具有重要的意义. 建立了退火处理过程中Cd_1-xZn_xTe晶体 材料电阻率及导电类型变化与杂质的扩散系数之间关系的模型.结合实验数据，获得了10 关键词： CdZnTe 热处理 In气氛 扩散系数     

GdBaCuO单畴超导块材的制备与性能

在空气中生长同样可以得到具有很高的临界温度(Tc)值和电流密度(Jc)的块材,而且发现少量的钡位替代有助于产生峰值效应.由于GBCO的熔点与用做籽晶的NBCO非常接近,因此在这些工作中多是采用了热籽晶的方法,这给工艺中带来了极大的不便,也不利于批量化的制备.在实验中我们探索了在空气气氛中采用冷籽晶的方法进行单畴GdBaCuO块材熔融织构生长.通过调整Gd123相与Gd211相配比,改变初始的123粉末、211粉末及BaCuO2粉末的烧结温度,控制熔融织构的工艺条件,成功生长出了单畴直径18～25mm的单畴GdBaCuO块材.单畴样品的最大磁浮力密度达到了15 N/cm2,Jc(0T, 77K)达到2.3 × 104 A/cm2.     

Effective Route to Graphitic carbon Nitride from Ball-Milled Amorphous carbon in NH3 Atmosphere Under Annealing

Graphitic carbon nitride (g-C3N4) powders were successfully synthesized from ball-milled amorphous carbon under NH3 atmosphere at high temperature, for the first time to the best of our knowledge. The combined charac-teristic data obtained by x-ray diffraction, high-resolution transmission-electron microscopy, electron energy losss pectroscopy, Raman spectroscopy, energy dispersive spectroscopic analysis, and Fourier transformation infrared spectroscopy provide substantial evidence for the graphite-like sp^2-bonded structure with C3N4 stoichiometry.     

CO气氛下褐煤加压快速热解过程中CH_4的逸出规律

在管式反应器上进行了霍林河褐煤加压快速热解实验,研究了CO气氛下CH4逸出规律。在加压快速热解条件下,由于CO解离态吸附的O(a)吸附在煤上,提供了活性中心,电负性强的O(a)诱发其周围其他原子的电子云向O(a)偏移,减弱了原来化学键的强度,导致芳香环的开裂,侧链、醚键和脂肪链的断裂提供更多的自由基,稳定煤热解生成的碎片,促进了CH4的生成和逸出。因此,CO气氛下CH4产率较N2气氛下的高,在900℃、1.0 MPa时,50%CO气氛下的CH4产率较N2气氛下的提高了12.5%,并且CH4产率随着温度升高、压力的增大而增大。     

CO_2对褐煤热解行为的影响

利用热天平和快速升温固定床进行了CO2气氛下褐煤热解特性的研究,考察了CO2对半焦的产率和气体产物分布的影响。通过对半焦的比表面积、孔结构、官能团和元素含量的分析,确定了CO2对煤热解过程的影响机制。CO2对新生半焦的气化反应破坏了含氢的半焦结构,一方面,促进了羟基、甲基、亚甲基等基团的断裂和苯环的开裂;另一方面,减弱H与其依附本体的结合,增加了氢的流动性,引发了更多的氢自由基生成。这些氢自由基与煤大分子断裂生成的碎片自由基结合生成更多的挥发分,使半焦有较大的比表面积、孔容和开孔率。CO2的引入促进了煤的热解和挥发分的生成,增大了H2、CO、CH4和C2H6等小分子烃类物质逸出,降低了半焦的产率。