半水硫酸钙晶须的水化机理及稳定性调节（英文）

通过探讨半水硫酸钙晶须(HCSW)贮存过程在空气中形貌和晶形的变化,研究了半水硫酸钙晶须的水化机理,分析了不同处理方法对其稳定性的调节。研究发现,HCSW的水化是由晶须表面的-OH基团和Ca~(2+)活性位点以及HCSW存在的内部通道引起的,煅烧和二元醇改性均可提高硫酸钙晶须的耐水性。结果表明,煅烧后,半水硫酸钙晶须转化为无水可溶硫酸钙晶须和无水死烧硫酸钙晶须,易于水化的内部通道消失,耐水性增强;水热合成过程二元醇的加入,可利于醇羟基吸附在HCSW的(200)、(020)和(220)表面,阻止H_2O分子中羟基在晶须表面的吸附,进而提高晶须的耐水性,当添加剂为三乙二醇(TEG)且浓度为18.8 mmol·L~(-1)时,HSCW在空气中耐水稳定性不小于7 d。     

半水硫酸钙晶须稳定化研究

使用多种稳定剂对半水硫酸钙晶须进行稳定化处理,研究了稳定剂用量、稳定化处理温度和时间等对半水硫酸钙晶须稳定性的影响。通过FTIR、SEM、DSC-TG和XRD对稳定化处理后的产物进行了表征,结果表明：在油酸钠用量0.3%,稳定化处理温度100 ℃,稳定化处理时间20 min的条件下,实现了半水硫酸钙晶须的稳定;油酸钠在晶须表面的吸附既有物理吸附又有化学吸附,并通过化学吸附在晶须表面形成了油酸钙。     

微米级硫酸钙晶须的制备

为了制备分布均一、具有较好光滑性和长径比的微米结构二水硫酸钙(CaSO4.2H2O)晶须,在室温条件下,以CaCl2和(NH4)2SO4为主要原料,通过一步超声反应制备出具有比较理想结构的微米级二水硫酸钙晶须。研究发现,在硫酸钙晶须生成过程中无水乙醇的量起着非常重要的作用,过多、过少的无水乙醇都不利于生成目标产物。CTAB的量对于二水硫酸钙晶须的长径比大小具有较大的调控作用。当无水乙醇的量为20mL,CTAB的浓度为0.9mmol/L,超声时间为1h时可以制备较理想的目标产物。120℃热处理2h晶须变碎,结果与热重结果相一致。与一般的晶体制备不同的是陈化时间对硫酸钙晶须的长径比无影响。通过X射线粉末衍射和热重分析分别对产物的结构和热稳定性进行了表征。结合实验简单探讨了二水硫酸钙晶须生成的机理,从中发现了制备较高长径比的二水硫酸钙晶须的一些规律。     

单斜氧化锆表面水合和脱水的动态模拟（英文）

常用的氧化物负载金属催化剂通常在水相中制备,且在使用前常常需要经过煅烧.因此,氧化物载体表面的水合和脱水过程对于负载型金属催化剂的真实建模至关重要.通过第一性原理分子动力学模拟,本文考察了温和温度下无水单斜氧化锆(■)表面在显式溶剂水中的演化.在模拟过程中,所有的双重配位桥位氧位点很快被溶剂水质子化,形成酸性羟基(HO_L),并在锆原子上留下碱性羟基(HO~*).这些碱性羟基(HO~*)可以与表面未解离的吸附水分子(H₂O~*)进行活跃的质子交换,进而在表面自由扩散.在273 K到373 K的温度范围下,第一性原理分子动力学水相模拟可以得到一种较为确定的、有代表性的平衡水合单斜氧化锆(■)表面,其表面锆原子上覆盖度(θ)为0.75.随后,为了模拟低于800 K的温和煅烧温度下的表面脱水过程,本文使用密度泛函理论计算了表面水分子的逐步脱附自由能.通过获得表面的脱水相图,总结了不同煅烧温度下有代表性的、部分水合的单斜氧化锆(■)表面(0.25≤θ<0.75).这些水合单斜氧化锆(■)表面具有重要的理论意义,可以方便快捷地被应用于氧化锆催化剂及...     

从化工废水制备高品质二水合硫酸钙晶须的研究

以含有硫酸根离子的化工废水和钙盐制得的硫酸钙为原料,十六烷基硫酸钠为分散剂,氯化镁为晶型助长剂,用硫酸调节p H,采用水热法制备二水合硫酸钙晶须。研究了反应温度和降温速度对二水合硫酸钙晶须的影响,通过扫描电镜(SEM)测量硫酸钙晶须的长径比,用热重分析仪研究了硫酸钙晶须的热重行为。结果表明,最佳反应温度为125℃、反应降温速度为30℃/30 min,长径比可达80以上。     

PFOS在锐钛型TiO2表面吸附行为的理论研究

采用密度泛函理论(DFT)B3LYP方法对全氟辛烷磺酸(PFOS)在锐钛型TiO2表面的化学吸附和物理吸附行为进行了研究,其中化学吸附包含双齿双核(BB)和单齿单核(MM)在内的4种可能的吸附构型.吸附能(Eads)及反应吉布斯自由能(ΔGads)的计算结果表明,PFOS分子易于与TiO2表面发生氢键作用吸附;化学吸附表现为PFOS分子与TiO2表面的水分子(H2O)和羟基(—OH)反应,且与取代—OH相比,H2O取代相对更容易发生,其中,MM1构型(取代一个表面水分子)为化学吸附中的优势构型.PFOS在锐钛矿表面吸附的热力学稳定性和反应自发性顺序如下:H-Bonded(氢键吸附)>MM1(取代一个表面水分子)>BB1(取代两个表面水分子)>MM2(取代一个表面羟基)>BB2(取代一个表面水分子和一个表面羟基).成键结构分析表明,TiO2表面H2O/—OH官能团与PFOS上的磺酸基之间形成了中等强度的氢键;在化学吸附过程中,电荷从PFOS分子向TiO2表面发生转移,生成Ti—O—S化学键,电荷转移主要来自PFOS分子的O和F原子.     

十八烷基聚氧乙烯表面空间结构和蛋白质吸附行为研究

为探讨聚合物-水界面十八烷基聚氧乙烯链(SPEO)空间结构和白蛋白选择性吸附行为的内在联系,本文采用聚甲基丙烯酸甲酯接枝十八烷基聚氧乙烯(PMMA-g-SPEO),通过不同热处理方式获得了具有“环形链”(A)和“尾形链”(B)结构的两种模型表面.在A表面,水相接触角随水化时间的延长而迅速降低,最终亲水性的界面可同时有效阻抗白蛋白和纤维蛋白原的吸附,但不呈现对白蛋白的选择性吸附;而在B表面,水相接触角随水化时间的延长变化不大,最终疏水性的界面可在有效阻抗纤维蛋白原的吸附同时,有效诱导白蛋白的选择性吸附,具有聚氧乙烯(PEO)阻抗非特异性吸附和十八烷基选择性吸附协同作用的特点.     

聚硅氧烷与纳米SiO_2复合改性光固化水性聚氨酯的制备与性能

以聚碳酸酯二元醇(PCD)和羟基封端的聚二甲基硅氧烷(PDMS)为软段、异佛尔酮二异氰酸酯(IPDI)为硬段,在乳化过程中引入纳米SiO_2,制得光固化水性聚氨酯纳米复合乳液。采用纳米粒度仪、SEM、光学接触角测量仪、电子拉力机等对复合乳液和复合膜的结构与性能进行了表征。研究结果表明:纳米SiO_2相互接触,形成了连续的纳米SiO_2网状结构贯穿于整个聚合物基体中;PDMS与纳米SiO_2的复合引入使复合膜杨氏模量、拉伸强度、断裂伸长率、表面疏水性及耐水性均得到显著提高。     

微米碳化硅晶须在水介质中的分散行为

以去离子水为分散介质,六偏磷酸钠(SHP)和羧甲基纤维素钠(CMC)为分散剂,利用沉降法、ζ电位、傅里叶变换红外光谱(FTIR)、TEM等测试技术研究了微米碳化硅晶须在水介质中的分散稳定机制,探讨了pH值、分散剂种类及含量对SiC微米晶须分散行为的影响机制。结果表明:微米SiC晶须的分散机理为静电稳定机制,pH值、SHP和CMC对微米SiC晶须的分散性和稳定性有较大影响;pH值为11时,微米SiC晶须的分散性和稳定性较好;SHP和CMC含量均为4wt%时,SiC微米晶须悬浮液具有良好的分散性能,分别在沉降时间18.5 h和22 h时相对沉降高度仍达96.89%和98%。六偏磷酸钠的分散机制主要以提高颗粒间的静电斥力为主,而羧甲基纤维素钠则为增大晶须表面的亲水性和提高晶须表面的电位绝对值。     

高性能水性聚氨酯研究进展

综述了近几年水性聚氨酯高性能化研究进展,从多元醇分子设计、硅氧烷改性、纳米复合、可再生资源利用、交联固化等方面进行了综述.电子包装材料利用磺化多元醇提高涂膜断裂伸长率并降低表面电阻为10×1010Ω/cm2,粘合剂应用引入聚二丁烯多元醇提高涂膜耐水性和粘接强度;织物整理引入氟化聚醚多元醇提升棉织物耐水性,表面接触角达到147°;采用特殊二元醇合成新型聚酯多醇改进涂膜耐水性的同时获得高模量和拉伸强度;含羧基聚己内酯二醇可降低水性聚氨酯乳液粒径到20nm以下;采用端羟基聚二甲基硅氧烷降低涂膜吸水率和表面能,使成膜接触角迅速增加;将碳纳米管、蒙脱土、绿坡缕石和多面体倍半硅氧烷等经有机化改性进行纳米原位复合,提升材料力学性能;利用可再生资源进行物理共混提升力学性能同时达到可降解目的;成膜过程引入环氧改性和交联改性,提高涂膜硬度、耐溶剂性和耐水性.     

Surface modification of calcium sulfate whisker using thiol-ene click reaction and its application in reinforced silicone rubber

The hemihydrate calcium sulfate whisker (HCSW) was modified by γ-(methacryloxy)propyl trimethoxy silane (KH570) and trimethylolpropane tris(3-mercaptopropionate) via wet modification and thiol-ene click reaction, and then the unmodified and modified HCSW were added into α, ω-dihydroxy polysiloxane (DPS) matrix to prepare silicon rubber composites. After the dual-surface modification, the surface of HCSW was transformed to hydrophobic, the hydration of whisker was obviously improved, and the whisker dispersed more evenly in the polymer. The mechanical properties, dynamic mechanical properties, and the medium resistance of the silicone rubber composite were compared. The tensile test shows that the silicone rubber shows better mechanical properties after adding the modified whiskers, among which HCSW-KH570-SH has the most significant reinforcement effect. Moreover, DPS/HCSW-KH570-SH shows the best medium resistance in toluene, gasoline, and water. The addition of modified whiskers can improve the storage modulus of silicone rubber significantly, while DMA and DSC show that the addition of modified whiskers can reduce the glass transition temperature of silicone rubber. The bound rubber indicates that the interface interaction between HCSW-KH570-SH and silicone rubber is the best.     

Crystallization and Phase Stability of CaSO<Subscript>4</Subscript> and CaSO<Subscript>4</Subscript> – Based Salts

Summary.  Calcium sulfate occurs in nature in form of three different minerals distinguished by the degree of hydration: gypsum (CaSO₄·2H₂O), hemihydrate (CaSO₄·0.5H₂O) and anhydrite (CaSO₄). On the one hand the conversion of these phases into each other takes place in nature and on the other hand it represents the basis of gypsum-based building materials. The present paper reviews available phase diagram and crystallization kinetics information on the formation of calcium sulfate phases, including CaSO₄-based double salts and solid solutions. Uncertainties in the solubility diagram CaSO₄–H₂O due to slow crystallization kinetics particularly of anhydrite cause uncertainties in the stable branch of crystallization. Despite several attempts to fix the transition temperatures of gypsum–anhydrite and gypsum–hemihydrate by especially designed experiments or thermodynamic data analysis, they still vary within a range from 42–60°C and 80–110°C. Electrolyte solutions decrease the transition temperatures in dependence on water activity. Dry or wet dehydration of gypsum yields hemihydrates (α-, β-) with different thermal and re-hydration behaviour, the reason of which is still unclear. However, crystal morphology has a strong influence. Gypsum forms solid solutions by incorporating the ions HPO₄ ²⁻, HAsO₄ ²⁻, SeO₄ ²⁻, CrO₄ ²⁻, as well as ion combinations Na⁺(H₂PO₄)⁻ and Ln³⁺(PO₄)³⁻. The channel structure of calcium sulfate hemihydrate allows for more flexible ion substitutions. Its ion substituted phases and certain double salts of calcium sulfate seem to play an important role as intermediates in the conversion kinetics of gypsum into anhydrite or other anhydrous double salts in aqueous solutions. The same is true for the opposite process of anhydrite hydration to gypsum. Knowledge about stability ranges (temperature, composition) of double salts with alkaline and alkaline earth sulfates (esp. Na₂SO₄, K₂SO₄, MgSO₄, SrSO₄) under anhydrous and aqueous conditions is still very incomplete, despite some progress made for the systems Na₂SO₄–CaSO₄ and K₂SO₄–CaSO₄–H₂O. Corresponding author. E-mail: daniela.freyer@chemie.tu-freiberg.de Received December 17, 2002; accepted January 10, 2003 Published online April 3, 2003     

Combustion and pyrolysis characteristics of tunçblek lignite

α-Hemihydrate was allowed to hydrate in the presence of tartaric, succinic, malic or citric acids at room temperature at a water/ binder ratio of 0.35. Hydration of hemihydrate leading to the crystallisation of calcium sulphate dihydrate is an exothermic process. The temperature rise during hydration was measured as a function of time using a semi-adiabatic method. The temperature rise–time curves are similar for all investigated systems but with different induction period. The results showed that calcium sulphate dihydrate crystallisation is a nucleation controlled process and different acids are chemisorbed at the surface of forming nuclei to different extent. Processes taking place during nucleation may control the morphology of resultant crystals. Infrared spectral and differential scanning calorimetric studies confirmed the adsorption of carboxylic acids at the surface of dihydrate crystals.     

Synthesis of calcium sulfate hemihydrate whiskers using oyster shells

Herein, the feasibility of preparing long and homogeneous hemihydrate (HH) whiskers using waste oyster shell was investigated. The whiskers formed from the sintered raw material had higher aspect ratios and more uniform morphology than non-sintered. The effect of reaction temperature, reaction time, and concentration were investigated. It was found that the optimum reaction temperature, reaction time, and concentration for stable and well-grown whiskers were 140 °C, 5 h, and 4 wt%, respectively. Direct transition from calcium sulfate dehydrate (DH) to HH was detected by X-ray diffraction (XRD) patterns, and the result showed DH completely transformed to HH after 5 h. The preferred direction of growth along the c-axis was confirmed by XRD pattern, selected area diffraction pattern, and high-resolution transmission electron microscopy (HRTEM).     

Heat of hydration as a method for determining the composition of calcined gypsum

The heat of hydration of a fresh, locally produced sample of some industrial gypsum (plaster of Paris, CaSO₄ · 0.5 H₂O) was determined. An adiabatic calorimeter was used for this purpose. The obtained heat of hydration was ?9 cal g^?1, which is higher than that for the hemihydrate (?5 cal g^?1). The calculated heat of hydration for calcium sulphate hemihydrate from the known heats of formation, and using ordinary thermochemical equations, is ?5 cal g^?1. In the same manner, however, the calculated heat of hydration for the anhydrite (CaSO₄) is ?29 cal g^?1. The higher heat of hydration (?9 cal g^?1) for the tested sample than that for the ordinary hemihydrate (?5 cal g^?1) was attributed to the presence of a certain percent of anhydrite. The composition of the tested sample was proposed by applying conventional chemical and rational analyses. The present work suggests the use of the heat of hydration as a tool for determining the composition of calcined gypsum.     

Effects of the type of calorimeter and the use of plasticizers and hydrophobizers on the measured hydration heat development of FGD gypsum

Thermal phenomena at the hydration of calcium sulphate hemihydrate (CaSO₄·0.5H₂O) are investigated in the paper. Time development of hydration heat of β-calcium sulphate hemihydrate prepared from flue gas desulphurization (FGD) gypsum is determined using two different types of calorimeter, namely the differential calorimeter DIK 04 and the isothermal heat flow calorimeter KC 01, and the differences in measured data analyzed. Then, the effects of plasticizers and hydrophobizers on the hydration process of analyzed gypsum mixtures are studied.     

Calorimetric and thermogravimetric study on the influence of calcium sulfate on the hydration of ye’elimite

Calcium sulfoaluminate (CSA) cements, which represent a CO₂-friendly alternative to conventional Portland cements, are produced by blending CSA clinker with gypsum and/or anhydrite. The hydration kinetics and the hydrated phase assemblages of the main hydraulic phase ye’elimite (calcium sulfoaluminate) with calcium sulfate were studied by isothermal conduction calorimetry, thermogravimetric analysis, X-ray diffraction analysis and thermodynamic modelling. Two calcium sulfates with different reactivities (gypsum and anhydrite) were applied. It was found that the pure phase without any calcium sulfate addition exhibits very slow hydration kinetics during the first 10 h. The hydration can be accelerated by the addition of calcium sulfate or (less effective) by increasing the pH of the aqueous phase. The amount of the calcium sulfate determines the ratio between the hydration products ettringite, monosulfate and amorphous aluminium hydroxide. The reactivity of the added calcium sulfate determines the early hydration kinetics. It was found that the more reactive gypsum was better suited to control the hydration behaviour of ye’elimite.     

The effects of solvents on C–S–H as determined by thermal analysis

Un-hydrated Portland cement consists of several anhydrous and reactive phases, that when mixed with water react to form hydrates. The main hydration product of Portland cement is calcium silicate hydrate (C–S–H). It is the main binding phase in a concrete system, hence is important to construction chemists. The concrete engineer measures the compressive strength of concrete after prescribed hydration periods, typically 1, 3, 7, 28 days. It is often convenient to mimic these intervals by stopping the hydration reaction at the same times. Several techniques can be employed to stop this hydration reaction. One of which is solvent-based and involves mixing a polar solvent such as acetone or isopropyl alcohol, with the hydrated cement. This mixing should be vigorous enough to blend the free water, in the partially hydrated cement system, with the polar solvent without altering the cement system’s matrix. The solvent-water mixture has a much lower boiling point and the mixture quickly evaporates out of the system. This achieves two goals. It stops the hydration reaction at the moment of solvent mixing, and it removes free water to prevent further hydration from occurring. This procedure theoretically leaves behind a dry, chemically unaltered, partially hydrated cement paste. In this way, pastes can be analyzed after the prescribed 1, 3, 7 or 28 days of hydration. This paper uses thermogravimetric analysis (TG) results to investigate the assumption that solvents have no thermodynamic or chemical effect on the hydrated cement paste phases.     

Effects of cellulose whiskers on properties of soy protein thermoplastics

Environmentally-friendly SPI/cellulose whisker composites were successfully prepared using a colloidal suspension of cellulose whiskers, to reinforce soy protein isolate (SPI) plastics. The cellulose whiskers, having an average length of 1.2 microm and diameter of 90 nm, respectively, were prepared from cotton linter pulp by hydrolyzing with sulfuric acid aqueous solution. The effects of the whisker content on the morphology and properties of the glycerol-plasticized SPI composites were investigated by scanning electron microscopy, dynamic mechanical thermal analysis, differential scanning calorimetry, ultraviolet-visible spectroscopy, water-resistivity testing and tensile testing. The results indicated that, with the addition of 0 to 30 wt.-% of cellulose whiskers, strong interactions occurred both between the whiskers and between the filler and the SPI matrix, reinforcing the composites and preserving their biodegradability. Both the tensile strength and Young's modulus of the SPI/cellulose whisker composites increased from 5.8 to 8.1 MPa and from 44.7 to 133.2 MPa, respectively, at a relative humidity of 43%, following an increase of the whisker content from 0 to 30 wt.-%. Furthermore, the incorporation of the cellulose whiskers into the SPI matrix led to an improvement in the water resistance for the SPI-based composites.     

Gas chromatographic analysis of C2−C16 dicarboxylic acids esterified in aqueous solutions as n-propyl esters

Summary C₂−C₁₆ dicarboxylic acids were esterified in aqueous solution in the presence of sulfuric acid. Esterification in water/n-propanol mixtures with mole ratios between 0.03 and 2.21 can be utilized for the quantitative determination of dicarboxylic acids by gas chromatography. The presence of water does not interfere at water/n-propanol mole ratios below 0.45. For mole ratios above 0.45 anhydrous sodium sulfate has been used for binding the water. The mole ratio range tested was 0.12–0.99 for anhydrous sodium sulfate/water, and 0.16–2.55 for sulfuric acid/anhydrous sodium sulfate.