Preparation and Crystal Transformation Process of Magnesium Carbonate Hydrate Using MgSO4 as Raw Material

以 MgSO4为原料,通过向 MgSO4溶液中滴加（NH4）2CO3得到碳酸镁水合物。借助 X 射线衍射、扫描电子显微镜、差热分析及 Raman 光谱分析了转变过程中晶体组成和形态变化。研究发现,在 25～45 ℃制备的产物均为单斜晶系、空间群为 P21/n（14）的 MgCO3 3H2O 晶体;在 50～60 ℃结晶产物存在由针状的 MgCO3 3H2O 晶体向单斜晶系、空间群为 P21/c（14）的片状 4MgCO3 Mg（OH）2 4H2O 晶体的转变。从 pH 值变化和生长基元的形成对碳酸镁水合物晶体转变过程进行了分析。     

海底甲烷水合物-未来可能的新能源

能源问题是现今我们全人类共同的问题。如何能够尽快找到煤炭和石油的替代能源是解决能源问题的紧迫任务。海底甲烷水合物以其丰富的储量、巨大的能量被科学家视为未来可能的新能源。本文从甲烷水合物的状态和结构、相平衡特征、赋存、勘探方法及深海拟开发技术、开发所面临的困难和可能导致的问题以及目前未能开采的原因几个方面对这一科学问题进行了综述。指出目前海底甲烷水合物尚没有开采,还处于探矿阶段。而且,海底甲烷水合物大规模不当开采可能会导致全球气候变暖、海啸等灾难。但是在未来10~15年将会有成熟的开采技术。海底甲烷作为一种可能的新能源具有乐观的开发前景。     

The System Na2O-CaO-SiO2-H2O

A portion of the quaternary phase diagram for Na₂O-CaO-SiO₂-H₂O has been constructed. Plotting concentrations as their 10th roots allows compounds having solubilities which differ by several orders of magnitude to be represented on a single diagram. The compositional relationships among sodium-substituted calcium silicate hydrate, calcium-substituted sodium silicate hydrate, calcium bydroxide, a quaternary compound of approximate composition 0.25Na₂O · CaO · SiO₂· 3H₂O, sodium hydroxide monohydrate, and miscellaneous sodium silicate hydrates are presented. The quaternary diagram constructed shows the quaternary compound to exist in equilibrium with sodium-substituted calcium silicate hydrate and calcium hydroxide. Conditions in concrete pore solutions which favor the formation of this quaternary compound may also favor the occurrence of the alkali-silica reaction.     

离子对甲烷水合物相平衡的影响

自由水盐度直接影响水合物的生成和分解,为了充分研究自由水盐度对甲烷水合物相平衡的影响,本文利用正交实验设计方法研究了不同离子组成和浓度条件下多孔介质中水合物形成与分解特性。运用正交法研究水合物可减少实验次数、缩短实验周期。甲烷水合物相平衡点通过定容压力搜索法测得。与纯水体系相比,添加离子后相同压力条件下甲烷水合物的平衡温度降低,并且随着离子浓度的增加,平衡温度进一步降低。方差分析证明阳离子中Mg²⁺对水合物平衡影响最显著;极差分析结果表明,阳离子的影响程度从大到小依次为Mg²⁺、Ca²⁺、Na⁺、K⁺。SO^2-₄、CO^2-₃、Cl^-三种阴离子浓度对水合物相平衡点影响均显著。水合物诱导时间变化无明显规律,受离子种类、浓度影响不显著。     

Equilibrium properties and crystal growth of D2O + cyclopentane hydrate for sustainable tritium separation

This study reports thermodynamic properties and crystal growth observations of D₂O + cyclopentane hydrate toward the development of a hydrate-based tritium separation process. We employed D₂O as a host of hydrate with respect to the investigation into the formation of D₂O hydrate substrate, which is a core component of the tritium separation process. The hydrate phase equilibrium temperature in the liquid D₂O + liquid cyclopentane system was 3.2°C higher than the corresponding H₂O hydrate. Experiments on crystal growth were conducted at temperatures ranging from 5.1 to 8.5°C under atmospheric pressure. Under each thermodynamic condition, polygonal hydrate crystals appeared, growing along the D₂O/cyclopentane interface. The geometric shape and size of the crystals varied depending on the temperature. The variation in crystal morphology was comparable to that of the H₂O + cyclopentane hydrate. Implications based on the obtained results for the hydrate-based isotopic water separation process design are discussed.     

Equilibrium conditions for methane hydrate formation in aqueous mixed electrolyte solutions

Equilibrium data on the formation of methane hydrate in six mixtures of NaCl and KCl, six mixtures of NaCl and CaCl₂ and a mixture of eight electrolytes found in sea water were experimentally obtained. The ionic strength (in molality units) of the NaCl and KCl mixtures ranged from 0.97 to 4.72 and that of the NaCl and CaCl₂ mixtures from 1.27 to 3.90. The experimental temperatures ranged from 264 to 284 K and the pressures from 2.5 to 9.7 MPa. Equilibrium pressures predicted using a recently proposed method (Englezos and Bishnoi, 1988) have been compared with the data obtained and it was found that the predictions match the data very well. The standard errors for the mixtures of NaCl and KCl, NaCl and CaCl₂ and the synthetic sea water were 5.54, 3.5 and 1.4%, respectively. The largest prediction error for an experimental data point was 10.1%.     

Impact of the fluid flow conditions on the formation rate of carbon dioxide hydrates in a semi‐batch stirred tank reactor

CO₂ hydrate formation experiments are performed in a 20 L semi‐batch stirred tank reactor using three different impellers (a down‐pumping pitched blade turbine, a Maxblend?, and a Dispersimax?) at various rotational speeds to examine the impact of the flow conditions on the CO₂ hydrate formation rate. An original mathematical model of the CO₂ hydrate formation process that assigns a resistance to each of its constitutive steps is established. For each experimental condition, the formation rate is measured and the rate‐limiting step is determined on the basis of the respective values of the resistances. The efficiencies of the three considered impellers are compared and, for each impeller, the influence of the rotational speed on the rate‐limiting step is discussed. For instance, it is shown that a formation rate limitation due to heat transfer can occur at the relatively small scale used to perform our experiments. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4387–4401, 2015     

赝二元系CaF2-LiAlF4相图

通过差热分析（ＤＴＡ）和Ｘ射线粉末衍射（ＸＲＤ）方法研究了赝二元系ＣａＦ２－ＬｉＡｌＦ４的相平衡关系,该赝二元系在ＣａＦ２：ＬｉＡｌＦ４为１：１处形成一致融熔化合物ＬｉＣａＡｌＦ６,其熔点为８１４℃,并分别在ＬｉＡｌＦ４摩尔分数为８８％主４４１％处出现两个共晶点,其共昌温度分别６９２℃和７８３℃,对照该体系的相图,按摩尔比ＬｉＦ：ＣａＦ２：（ＡｌＦ３＋ＣｒＦ３）＝１：１：１的组成配料,采用密闭条件     

Population balance model for nucleation,growth, aggregation,and breakage of hydrate particles in turbulent flow

This article describes a computational model for the size evolution of hydrate particles in a pipeline‐pump system with turbulent flow. The model is based on the population balance principle, and the simulation results were validated with data from an experimental study of a flow loop containing hydrate particles reported in the literature. It is found that the particle size is significantly influenced by aggregation and breakage, related to shear in the flow, and that these effects are comparable to those of growth and nucleation, related to diffusional processes. Two different approaches for hydrate growth and nucleation, one of continuous nucleation during the process and one of only an initial nucleation‐pulse, were used. This was done to compare the aggregation and breakage parameters which come out when fitting the models output to experiment. These two approaches are found to give rise to similar aggregation/breakage parameters, lending credence to the pbm‐based modeling. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

多孔介质中天然气水合物相平衡条件研究进展

天然气水合物主要赋存于各种沉积物孔隙之中,只有6%左右以块状纯水合物的形式存在。现在对于天然气水合物相平衡条件的研究主要集中在对多孔介质各因素的考察。就目前研究成果来看,理论预测自然条件中水合物稳定条件的准确性仍然较差,其主要原因：水合物稳定存在的天然条件影响因素远比实验室中（大多预测模型基于实验室建立）的影响因素复杂得多;实际中的介质微孔孔径并不恒定,呈分布状态,且分布比较复杂;自然条件下的多孔介质的成分、结构都非常复杂。     

Experimental measurement and thermodynamic modeling of cyclopentane hydrates with NaCl,KCl, CaCl2, or NaCl‐KCl present

Consistent phase equilibrium data for cyclopentane hydrates in presence of salts are vitally important to many industries, with particular interest to the field of hydrate‐based water separation via cyclopentane hydrate crystallization such as desalination. However, there are very little experimental equilibrium data, and no thermodynamic prediction tools. Hence, we set up a method to generate a great deal of much needed equilibrium data for cyclopentane hydrates in diverse saline solutions with a wide range of salt concentrations. Our method does furnish verified, reliable and accurate equilibrium data. Plus, three thermodynamic approaches are developed to predict equilibrium, and provide tools for simulations, by considering the kind of salt and concentrations. All three models are in very good accordance with experimental data. One method, using a new correlation between occupancy factor and water activity, might be the best way to obtain consistent, quick, and accurate dissociation temperatures of cyclopentane hydrate in brine. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2207–2218, 2018     

薄膜蒸发器的分离效率

The recovery of contaminants and useful substances from liquid wastes, the purification of production effluents and the separation of thermally instable mixtures are some of the multivarious applications of thin-film distillors in many processes of the chemical and allied industries and of the food industries. In a study carried out in pilot plants with distillation test systems there was found a good agreement between the experimental separation results and those obtained by computing with a theorectical model; the latter is based on the assumption of phase equilibrium between the vapour formed on an infinitely small element of area in a liquid film of any given concentric periphery of the vertically arranged evaporator. These tests were perfomed under various phase loads.     

籽晶处理工艺对物理气相传输法生长SiC单晶的影响

将块体SiC单晶中切割下的晶片经研磨、抛光和腐蚀不同工艺处理后作为籽晶,用物理气相传输法生长SiC晶体,生长时间为10min。用光学显微镜观察晶片生长前后的形貌,讨论了不同处理工艺籽晶对晶体生长的影响。结果表明,研磨和抛光可以去除晶体切割时产生的凹坑和划痕,但残留的研磨变质层和抛光导致的机械损伤层可诱导晶片在高温晶体生长时产生多晶成核,腐蚀可以去除研磨和抛光时产生的机械损伤层,用腐蚀后的晶片作为籽晶,生长的晶体表面光滑,并且能够很好地复制籽晶的结构。     

A new ternary phase in the system CaO–Al2O3–Cr2O3: Crystal structure and thermal expansion of CaAl2Cr2O7

Polycrystalline material of a novel phase in the system CaO–Al₂O₃–Cr₂O₃ has been obtained by solid-state reactions. Chemical analysis indicated the composition CaAl₂Cr₂O₇. Single-crystal growth of the new compound using borax as a mineralizer was successful. Diffraction experiments at ambient conditions on a crystal with composition CaAl_2.13Cr_1.87O₇ yielded the following basic crystallographic data: space group P 3, a = 7.7690(5) Å, c = 7.6463(5) Å, V = 399.68(6) ų, Z = 3. Structure determination and subsequent least-squares refinements resulted in a residual of R(|F|) = 2.3% for 1440 independent observed reflections and 113 parameters. To the best of our knowledge, the structure of CaAl_2.13Cr_1.87O₇ or CaAl₂Cr₂O₇ represents a new structure type. It belongs to the group of double layer structures where individual double layers contain octahedrally and tetrahedrally coordinated cation positions. Linkage between neighboring sheet packages is provided by additional calcium cations. Furthermore, thermal expansion has been studied in the interval between 29 and 790°C using in situ high-temperature single-crystal diffraction. No indications for a structural phase transition were observed. From the evolution of the lattice parameters the thermal expansion tensor has been obtained. A pronounced anisotropy is evident. The response of structural building units to variable temperature has been discussed.     

Conversion of calcium aluminate cement hydrates at 60°C with and without water

There have been different hypotheses about the transformation mechanisms of calcium aluminate cement hydrates and this work aims to clarify the long‐running debate about the conversion approaches. In this work, CAH₁₀ and C₂AH₈ were produced from the pastes of calcium aluminate cement (CAC) cured for 24 hours at 10 and 20°C separately. And the cured pastes were continually cured at 60°C for 3 days with water and without water, respectively. The hydration of the pastes was halted by freeze‐drying, and the phases and microstructure of hydrates were investigated by XRD and SEM, respectively. The results indicate that CAH₁₀ and C₂AH₈ converted into C₃AH₆ and AH₃ in water presence at 60°C, but did not transform into C₃AH₆ and AH₃ without water. It is confirmed that the conversion of CAH₁₀ and C₂AH₈ to C₃AH₆ and AH₃ happens through preceding solution of CAH₁₀ and C₂AH₈ and subsequent precipitation of C₃AH₆ and AH₃.     

THE USE OF LOCAL THERMODYNAMIC PATH FOR QUALITY PROBLEMS DURING CONVECTIVE DRYING

ABSTRACT

The pharmaceutical drug under investigation in this paper has two hydration states with several polymorphic forms. The two hydration states are tetrahydrate and monohydrate. Two polymorphs of monohydrate are in competition. Process must lead to the metastable therapeutic form (TF) although the non therapeutic form (NTF) is the stable one. The sensitive stage is drying

From desorption isotherms coupled with infrared spectroscopy, an equilibrium diagram of the different forms versus the external conditions (temperature and relative humidity) is performed. A macroscopic study achieved on tangential convective drying shows that the equilibrium diagram does not insure to obtain the metastable form after drying. It is deduced from an experimental analysis of internal temperature and water activity that the final form depends on the local thermodynamic path. Indeed, if NTF favourable conditions occur within the product during the process, this irreversible form remains although the final form predicted by the diagram is TF

It is concluded that NTF is promoted by a slowing down of transfers and an enhanced water vapour removing (greater exchange surface).