微波法快速制备碱式硫酸镁晶须

以七水硫酸镁为原料、氢氧化钠为沉淀剂,采用微波法制备出纤维状的碱式硫酸镁晶须.考察了反应温度、反应时间、物料摩尔比、硫酸镁浓度及晶种添加量等因素对晶须形貌的影响.研究结果表明:在硫酸镁浓度1.6 mol/L、硫酸镁和氢氧化钠摩尔比1∶1、晶种添加量(质量分数)1;、微波反应温度160～ 180℃、反应时间30～ 60 min的条件下,可以制备出纤维状的152型碱式硫酸镁晶须.以微波法制备碱式硫酸镁晶须大大缩短了反应时间.     

Synthesis of Mixed Tail Triphenylene Discotic Liquid Crystals： Molecular Symmetry and Oxygen-Atom Effect on the Stabilization of Columnar Mesophases

Small change in chemical structure of discotic liquid crystals can cause big difference in their mesomorphism. Replacing of the alkoxy peripheral chains of triphenylene by oxygen-atom containing ester chains would result in novel mesomorphism. A series of mixed tail triphenylenes containing propoxyacetyloxy and alkoxy, abbreviated as C18H6（OCnH2n＋1）3（OCOCH2OC3H7）3, n=4-8, and hexa（propyloxyacetyloxy）triphenylene, C18H6（OCOCH2OC3H7）6 were synthesized. Thermal gravimetry analysis （TGA） of three discogens showed that they had good thermal stability till 350 ℃. The mesomorphism was investigated through differential scanning calorimetry （DSC） and polarized optical microscopy （POM）. The preliminary X-ray diffraction （XRD） results of one compound showed that it exhibited ordered hexagonal columnar （Colho） mesophase. These mixed tail triphenylene derivatives possessed much stable Colho mesophase and wider mesophase ranges than their hexaalkoxytriphenylene C18H6（OR）6 and hexaalkanoyloxytriphenylene C18H6（OCOR＇）6 analogues. The asymmetrical compounds 2,6,11-trialkoxy-3,7,10-tri（2-propyloxyacetyloxy）triphenylenes with n=5-8 displayed higher clearing points and wider temperature ranges than their symmetrical isomers 2,6,10-trialkoxy-3,7,11-tri（2-propyloxyacetyloxy）- triphenylenes, while C18H6（OCOCH2OC3H7）6 had the highest clearing point due to the β-oxygen-atom effect.     

Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H2SO4-NaCl-H2O system

Little attention has thus far been paid to the potential effect of solution composition on the hydrothermal crystallization of calcium sulfate whiskers prepared from flue-gas desulfurization(FGD) gypsum.When purified FGD gypsum was used as raw material,the morphology and phase structure of the hydrothermal products grown in pure water,H_2SO_4-H_2O,NaCl-H_2O,and H_2SO_4-NaCl-H_2O solutions as well as the solubility of purified FGD gypsum in these solutions were investigated.The results indicate that calcium sulfate whiskers grow favorably in the H_2SO_4-NaCl-H_2O system.When prepared using 10-70 g NaCl/kg gypsum-0.01 M H_2SO_4-H_2O at 130 ℃ for 60 min,the obtained calcium sulfate whiskers had diameters ranging from 3 to 5 |xm and lengths from 200 to 600 |xm,and their phase structure was calcium sulfate hemihydrate(HH).Opposing effects of sulfuric acid and sodium chloride on the solubility of the purified FGD gypsum were observed.With the co-presence of sulfuric acid and sodium chloride in the reaction solution,the concentrations of Ca~(2+) and SO_4~(2-) can be kept relatively stable,which implies that the crystallization of the hydrothermal products can be controlled by changing the concentrations of sulfuric acid and sodium chloride.     

白云石精制液中不同离子对碳酸钙晶须的影响

以白云石精制液和二氧化碳为实验原料,采用气液接触法制备碳酸钙晶须.研究了杂质离子Mg2+、NH4+和NO3-对碳酸钙晶须长径比和形貌的影响.采用扫描电镜(SEM)和X射线衍射仪(XRD)对样品的形貌和晶体结构进行表征.结果表明:NH4+浓度在0.3 mol/L,Mg2+浓度在0.05 mol/L,NO3-浓度在0.2 ...     

NH4+-NH3缓冲体系制备碱式硫酸镁晶须及生长机理

碱式硫酸镁晶须的分子式为xMgSO4·yMg(OH)2·zH2O,是一种人工合成具有一定长径比的无机功能材料.作为填充剂,可提高材料的抗拉强度等机械性能,也可以起到阻燃的作用.在NH4+-NH3缓冲体系,用常压一步法制备长度为10～30μm,直径为0.05～0.3μm,长径比为30～150的MgSO4·5Mg(OH)2·3H2 O晶须.采用XRD、SEM、TG、TEM对产品进行表征,结合表征结果对反应浓度、反应温度、反应时间和陈化时间等影响因素进行研究.对碱式硫酸镁的生成机理进行第一性原理分析,碱式硫酸镁晶须生长习性符合位错螺旋生长机制.采用缓冲体系稳定溶液酸碱性,降低反应溶液的非理想性,可以使晶体在非受迫情况下定向生长,为进一步工业应用,实现低能耗生产碱式硫酸镁晶须提供了重要参考.     

Growth of threaded AIN whiskers by a physical vapor transport method

Threaded aluminum nitride （A1N） whiskers are grown by a physical vapor transport method in a radio-frequency induction heating furnace. The resultant whiskers are characterized by X-ray diffraction, Raman scattering, scanning electron microscopy, transmission electron microscopy and photoluminescence. The analysis shows that the whiskers are single-crystalline, wurtzite AIN. The threaded A1N whiskers are 0.5 μm~100 μm in diameter and several millimeters in length in the fiber direction, and have lots of tiny sawteeth on the surface. The morphology of this threaded A1N whisker is beneficial for bonding when the whisker is used in composite. The growth of the whiskers is dominated by the vapor-solid （VS） mechanism, and the particular morphology might result from an oscillating condition produced in the radio-frequency induction heating furnace.     

拉伸状态NbSe3在纵向磁场下的负磁阻效应

本文研究了准一维电荷密度波材料ＮｂＳｅ３晶须自然状态（ε＝０）和受到拉伸的状态（ε＞０）下在纵向磁场中的磁阻效应．温度Ｔ≤５０Ｋ时，无论自然状态还是拉伸状态（ε＝１．５％）都没有观察到负磁阻．但是，当温度升高到Ｔ＝７０Ｋ，我们观察到ＮｂＳｅ３晶须受到拉伸至ε＝１．５％时有负磁阻效应；进一步增大ε至１．８％，负磁阻效应更明显；不拉伸（ε＝０）则没有磁阻．文中就这个现象进行了讨论．     

防静电阻燃聚丙烯材料制备方法的研究

进行了以氧化锌晶须为导电性添加剂改善聚丙烯－阻燃物质复合体系防 电性能的试验。发现当氧化锌晶须的含量在10%-12%时，复合材料的表面电阻率和摩擦静电压分别降至最低值10^9Ω和250V左右，表明该添加剂可使聚丙烯获得良好的防静电性能，且与阻烯物质相兼容。认为氧化锌晶须提高复合体系导电性能的微观机理可归结为网络导电、隧道效应和尖端放电等作用。     

热残余应变对金属基复合材料塑性规律的影响

热残余应变是影响晶须增强金属基复合材料的重要因素。本文利用作者改进的等效夹杂理论定量研究了热残余应变对金属基复合材料塑性强化规律的影响，并对２０％ＳｉＣｗ／Ａｌ材料的拉、压断口做了ＳＥＭ观察，通过其拉、压性能实验验证了本文理论的合理性，说明了考虑热残余应变的必要性。     

Influence of disodium hydrogen phosphate dodecahydrate on hydrothermal formation of hemihydrate calcium sulfate whiskers

The influence of Na_2HPO_4·12H_2O on the hydrothermal formation of hemihydrate calcium sulfate(CaSO_4·0.5H_2O) whiskers from dihydrate calcium sulfate(CaSO_4·2H_2O)at 135 ℃ was investigated.Experimental results indicate that the addition of phosphorus accelerates the hydrothermal conversion of CaSO_4·2H_2O to CaSO_4·0.5H_2O via the formation of Ca_3(PO_4)_2 and produces CaSO_4-0.5H_2O whiskers with thinner diameters and shorter lengths.Compared with the blank experiment without Na_2HPO_4·12H_2O,the existence of minor amounts(8.65 ×10~(-4)-4.36 × 10~(-3) mol/L) of Na_2HPO_4·12H_2O led to a decrease in the diameter of CaSO_4·0.5H_2O whiskers from 1.0-10.0 to 0.5-2.0 μm and lengths from 70-300 to50-200 μm.