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991.
Silicates are one of the most important classes of compounds on this planet, and more than 1000 silicates have been identified in the mineral kingdom. Additionally, several hundreds of artificial silicates have been synthesized. The substitution of oxygen by nitrogen leads to the structurally diverse and manifold class of nitridosilicates. Silicon nitride, one of the most important non-oxidic ceramic materials, is the binary parent compound of nitridosilicates, and it symbolizes the inherent material properties of these refractory compounds. However, prior to the last decades, a broad systematic investigation of nitridosilicates had not been accomplished. In the meantime, these and related compounds have reached a remarkable level of industrial application. This review illustrates recent progress in synthesis and structure-property relationships and also applications of nitridosilicates, oxonitridosilicates, and related SiAlONs. 相似文献
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Dr. Shing‐Jong Huang Chih‐Yi Yang Dr. Anmin Zheng Ningdong Feng Dr. Ningya Yu Pei‐Hao Wu Prof. Dr. Yu‐Chi Chang Prof. Dr. Ying‐Chih Lin Prof. Dr. Feng Deng Prof. Dr. Shang‐Bin Liu 《化学:亚洲杂志》2011,6(1):137-148
The acid and transport properties of the anhydrous Keggin‐type 12‐tungstophosphoric acid (H3PW12O40; HPW) have been studied by solid‐state 31P magic‐angle spinning NMR of absorbed trimethylphosphine oxide (TMPO) in conjunction with DFT calculations. Accordingly, 31P NMR resonances arising from various protonated complexes, such as TMPOH+ and (TMPO)2H+ adducts, could be unambiguously identified. It was found that thermal pretreatment of the sample at elevated temperatures (≥423 K) is a prerequisite for ensuring complete penetration of the TMPO guest probe molecule into HPW particles. Transport of the TMPO absorbate into the matrix of the HPW adsorbent was found to invoke a desorption/absorption process associated with the (TMPO)2H+ adducts. Consequently, three types of protonic acid sites with distinct superacid strengths, which correspond to 31P chemical shifts of 92.1, 89.4, and 87.7 ppm, were observed for HPW samples loaded with less than three molecules of TMPO per Keggin unit. Together with detailed DFT calculations, these results support the scenario that the TMPOH+ complexes are associated with protons located at three different terminal oxygen (Od) sites of the PW12O403− polyanions. Upon increasing the TMPO loading to >3.0 molecules per Keggin unit, abrupt decreases in acid strength and the corresponding structural variations were attributed to the change in secondary structure of the pseudoliquid phase of HPW in the presence of excessive guest absorbate. 相似文献
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水泥砂浆的一个热粘弹性率型损伤本构模型 总被引:1,自引:0,他引:1
利用SHPB实验系统及自行研制的混凝土类材料快速高温加热设备,对水泥砂浆试件进行了不同 温度(20~600℃)和3种冲击速度下的实验,得到了不同温度和冲击速度下水泥砂浆试件的应力应变关系曲 线。基于ZWT粘弹性本构模型,并且考虑高温下水泥砂浆损伤演化规律都服从Weibull分布,提出了一个水 泥砂浆的热粘弹性率型损伤本构模型。通过数据拟合,获得了本构模型的相关参数,结果表明:理论预测和实 验结果吻合良好。 相似文献