磷石膏常压酸化法制备无水硫酸钙晶须的实验研究

以磷石膏为原料,一步常压酸化法制备无水硫酸钙晶须.采用单因素实验方法研究了盐酸浓度、反应温度、反应时间和固液比4个因素对制备硫酸钙晶须的影响.采用X射线衍射(XRD)、扫描电子显微镜(SEM)对反应产物样品的物相、微观形貌进行了表征.结果 表明:在盐酸浓度为5 mol/L、反应温度为90℃、反应时间为3h和固液比为0.10g/mL的条件下,一步法制备出了直径为1～4μm、长径比为3～8的无水硫酸钙晶须.分析认为,无水硫酸钙晶须是在二水硫酸钙溶解量达到其过饱和度后从溶液中结晶形成的.     

升温重结晶过程中硫酸钙晶须的形貌控制及其生长机理

利用升温重结晶过程制备硫酸钙晶须,考察了溶液pH值、升温区间、振荡速率等操作条件对晶须生成及形貌的影响,并初步探索了十六烷基三甲基溴化铵(CTAB)、十二烷基硫酸钠(SDS)、聚乙二醇(PEG6000)和乙二胺(EDA)四种表面活性剂对晶须形貌的影响.结果表明:在升温重结晶反应体系中,各操作条件均可对晶须产物的形貌和尺寸产生影响,但pH和升温区间的影响最大;SDS会显著抑制晶核形成,质量浓度为7 g/L时生成的产物形貌为均一棒状,结晶度较高.硫酸钙晶须主要以层状形貌结构生长,少部分晶须呈现类似多晶和外延生长的形貌.     

机械力活化对脱硫石膏制备硫酸钙晶须的影响

对脱硫石膏原料进行机械力活化,然后采用降温重结晶法制备出硫酸钙晶须.借助扫描电镜、图像粒度分析仪和相关软件进行表征,并初步讨论了机械力活化对晶须成核和生长过程的影响.结果表明:经过机械力活化的脱硫石膏可以制备有较大长径比的硫酸钙晶须.在水浴反应温度为75℃,硫酸浓度为2.5 mol/L,机械力活化时间为3.5 h,浆料浓度为2;的条件下,制备的硫酸钙晶须平均长径比为150,平均直径为2.1μm.     

利用脱硫石膏制备高品质二水石膏

利用脱硫石膏在酸性溶液中重结晶的特点,采用重结晶技术对脱硫石膏进行脱色提纯,通过对溶解、结晶过程的控制制备出高纯度、高白度的二水石膏.研究了硫酸浓度、晶种量、料浆浓度、稳定剂、温度、反应时间、陈化时间对二水石膏结晶的影响,并进行了母液循环实验.研究结果表明:常压下,H2SO4用量10.0;,Ca(OH)2用量0.5;,料浆浓度7.4;,聚乙二醇用量0.5;,反应温度120℃,反应时间2.5h,陈化24h后生成的二水硫酸钙结晶形貌良好,白度为94.01;,纯度达99.24;;母液循环3次后生成的二水石膏纯度大于98;.     

电石渣制备硫酸钙晶须及影响因素研究

以电石渣为原料,经酸化处理得到前驱体,再通过水热晶化工艺制备出硫酸钙晶须,探讨了不同水热工艺条件对硫酸钙晶须形貌的影响.水热法制备硫酸钙晶须的最佳工艺条件为:浆料浓度2.5;,水热反应时间8h,水热反应温度130℃,溶液pH值为7.以电石渣为原料制备硫酸钙晶须为电石渣的综合利用开辟了新的思路.     

脱硫石膏制备硫酸钙晶须结晶动力学研究

结晶动力学能够揭示结晶过程本质,通过测定溶液中Ca2浓度来确定硫酸钙晶须的转化率,从而确定硫酸钙晶须结晶动力学参数,得到转化率与时间的关系式:X=1/｛1+e6^[-10.01977t(0.0956-c)+1.1188]｝,(0≤t≤6.0).研究了影响硫酸钙晶须结晶动力学的影响因素降温速率和陈化时间,利用SEM对制备的硫酸钙晶须进行表征.结果表明:自然冷却条件下,陈化时间6h,制备出的硫酸钙晶须结晶发育完整,晶须平均长径比达到150,平均直径为2.1 μm.     

基于响应面法的半水硫酸钙晶须制备工艺优化

本研究以氯化钙、硫酸为主要原料,采用常压酸化法制备半水硫酸钙晶须.以长径比、长度为主要指标,在单因素实验的基础上,运用响应面法中的Box-Behnken design对反应温度、硫酸浓度、反应时间、搅拌速度进行优化,建立半水硫酸钙晶须制备工艺的数学模型,研究制备的最优工艺条件.结果表明,制备半水硫酸钙晶须的最优工艺条件为:反应温度103℃、硫酸浓度7.4;、反应时间60 min、搅拌速度288 r·min-,得到的晶须样品形貌规整、均一,平均长径比为82.2,φ90为53.3,平均长度为562 μm.     

微波外场强化电石渣制备硫酸钙晶须及其机理分析

本文以电石渣为原料,在稀硫酸溶液中制备硫酸钙晶须.在常规水热法最佳制备条件的基础上,不添加表面活性剂,利用微波反应器强化硫酸钙晶须结晶过程.分析了微波反应时间,微波辐射能量对结晶产物的影响.利用X射线衍射仪和扫描电子显微镜对制备的产物进行表征.结果 表明,电石渣与稀硫酸溶液在微波强化的条件下反应10 min,微波辐射能量400 W时,制备的硫酸钙晶须形貌尺寸均一,晶须平均直径为2.2 μm,平均长径比70.在此基础上,进一步分析了微波效应与硫酸钙晶须的生长机理.     

柠檬酸对半水硫酸钙晶须形貌稳定性影响

介绍了柠檬酸对半水硫酸钙晶须的形貌稳定性的影响及其作用机制,重点考察了柠檬酸添加量及稳定化温度对晶须形貌稳定性的影响.采用XRD、SEM和红外光谱表征晶须性质.结果表明,在30～100℃范围内,随着稳定化温度的增加,半水硫酸钙晶须形貌稳定时间增长.其中在100℃,柠檬酸添加量为0.5 wt;,半水硫酸钙形晶须形貌稳定时间可达4.0 h.由于柠檬酸的-COO-与半水硫酸钙晶须表面Ca2+键和成-COO-Ca-结构,柠檬酸以化学吸附方式吸附于晶须表面,使得晶须稳定性提高.     

聚丙烯酰胺/硬脂酸协同改性半水硫酸钙晶须及其形貌稳定性研究

使用聚丙烯酰胺/硬脂酸改性体系对半水硫酸钙晶须进行表面改性,研究聚丙烯酰胺的加入对改性过程中硫酸钙晶须的稳定化影响.通过显微镜观察晶须产品的形貌,利用X射线衍射仪分析其相组成,利用傅里叶红外光谱仪检测晶须产品的表面基团.结果 表明:聚丙烯酰胺/硬脂酸协同改性硫酸钙晶须的晶体形貌及相组成未发生改变,较硬脂酸单一改性后的晶须长径比有所上升,且在水溶液中形貌保持时间延长,改性后晶须的活化指数、接触角较硬脂酸单一改性有明显上升,实现了硫酸钙晶须改性过程中的稳定化处理.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

A SAXS study of kinetics of aggregation of silica sols

SAXS in situ experiments on the evolution of TMOS solutions during hydrolysis and polycondensation lead to power laws with scaling exponents ≈ 2. It is suggested that this could be the result of the polydispersity of the samples and that only an apparent fractal dimension can be obtained in this way. Kinetic studies tend to indicate that agglomeration in the sol is the result of a diffusion-controlled process.     

Study of the possibility of interactive control of the surface profile of X-ray optical elements

We investigate the possibility of controlling the curvature parameters of parabolic mirrors that are modular elements of two types consisting of a base and thin inserts placed at the opposite side of the work surface. In the first type of modular elements, bending is controlled by the difference in the coefficients of the thermal expansion of the base and inserts. In the second type of elements, the profile is changed by the piezoelectric straining of the inserts under an electric field. A correlation is established between the parameters of modular elements and their surface curvature profile.