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以高岭土为原料合成沸石分子筛的相变规律 总被引:5,自引:0,他引:5
以天然粘土矿物高岭土为原料, 采用水热晶化法合成了NaX, NaP和SOD三类沸石. 利用XRD、 静态饱和水吸附等测试手段详细考察了晶化温度、 初始反应混合物的碱浓度对沸石结晶的影响. 通过实验研究得到了三类沸石的结晶相区和结晶变化规律, 并优化出最佳合成工艺条件和相转变规律. 相似文献
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以廉价水玻璃为硅源,在晶种替代有机模板剂的条件下采用干胶法合成了ZSM-5分子筛。利用XRD、SEM、TEM、FTIR、N_2吸附-脱附和NH_3-TPD等分析方法对合成样品进行了表征和测试,考察了合成条件对ZSM-5分子筛晶化过程的影响。结果表明,在硅铝比(n/n)为30~70,钠硅比(n/n)为0.12~0.20时都可以得到结晶度良好的ZSM-5分子筛。研究发现,干胶法合成ZSM-5,在不引入外加水的情况下也可以得到ZSM-5样品,外加水的引入能够有效地提高晶化速率;与水热法合成ZSM-5分子筛相比,干胶法可以显著地缩短晶化时间,同时,合成样品的晶体尺寸也有所减小。 相似文献
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以不同分子筛(Nonasil, MCM-22或MCM-49)为晶种, 在水热条件下以六亚甲基亚胺(HMI)为模板剂, 对纯硅沸石Nonasil(HMI)的合成进行了研究. 并且对各种合成参数, 包括晶种类型、硅源、晶化温度和Na+浓度等对Nonasil(HMI)合成的影响进行了探讨. 发现在适量的Na+存在条件下, 晶种的引入大大缩短了晶化时间; 不同类型的晶种对晶化速度有不同程度的提高. 特别是用异类晶种(如MCM-22或MCM-49)能够合成高结晶度的Nonasil(HMI). 相似文献
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复合氟化物Li2BeF4的水热合成、晶化动力学研究及结构表征 总被引:4,自引:1,他引:3
通过中温水热法合成出复合氟化物Li2BeF4,并对合成中反应物的配比、反应温度和反应时间等条件进行了研究.XRD测试结果表明产物物相纯净,SEM显示产物为250μm的六方柱形晶体;IR和XPS测试表明产物中羟基和氧含量低.实验发现了晶化曲线的振荡现象,并做了初步的解释. 相似文献
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高表面积MCM-41的合成与性能 总被引:3,自引:0,他引:3
通过易于控制的手段,合成出了超高表面积的MCM 41分子筛,并采用XRD、N2吸附脱附、热重 差热分析、SEM等测试手段对合成样品进行分析表征,主要考察了晶化时间对分子筛表面积的影响.其XRD结果表明,合成的固体产物具有六方排列的孔道结构,结晶度高.氮吸附脱附实验表明,产物具有单一的孔径分布,其BET表面积可达1300 m2•g-1左右,合成样品的平均孔径约3.2 nm,适宜的晶化时间是50~100 h.热重分析表明,样品热稳定性好,吡啶升温脱附曲线表明合成的样品具有弱酸性. 相似文献
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以廉价水玻璃为硅源,在晶种替代有机模板剂的条件下采用干胶法合成了ZSM-5分子筛。利用XRD、SEM、TEM、FTIR、N2吸附-脱附和NH3-TPD等分析方法对合成样品进行了表征和测试,考察了合成条件对ZSM-5分子筛晶化过程的影响。结果表明,在硅铝比(n/n)为30~70,钠硅比(n/n)为0.12~0.20时都可以得到结晶度良好的ZSM-5分子筛。研究发现,干胶法合成ZSM-5,在不引入外加水的情况下也可以得到ZSM-5样品,外加水的引入能够有效地提高晶化速率;与水热法合成ZSM-5分子筛相比,干胶法可以显著地缩短晶化时间,同时,合成样品的晶体尺寸也有所减小。 相似文献
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考察了硅铝比、碱度、有机胺模板剂、晶化时间及温度等合成条件对ZSM-5、ZSM-57 分子筛和丝光沸石之间相互转晶的影响. 发现较高的碱度、较长的晶化时间有利于合成丝光沸石;较低的碱度、较高的诱导晶化温度、较长的晶化时间有利于合成低硅铝比的ZSM-57 分子筛;合成低硅铝比的ZSM-5分子筛则需要在能合成丝光沸石和ZSM-57 分子筛的碱度区间内精确调节碱度, 缩短晶化时间、降低诱导晶化温度、加入适当晶种, 有利于合成低硅铝比的ZSM-5 分子筛. 合成条件稍微改变, 会导致各种沸石之间发生转晶, 晶化产物出现两种或两种以上的晶型. 相似文献
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V. A. Alvarez P. M. Stefani A. Vázquez 《Journal of Thermal Analysis and Calorimetry》2005,79(1):187-193
Non-isothermal crystallization of polyvinylalcohol-co-ethylene with different ethylene contents was studied. Several models were used to predict the crystallization behavior of these materials under non-isothermal conditions at a constant cooling rate. Kinetic parameters determined from isothermal date were employed. Experimental data were in accordance with model prediction at low cooling rate and relative degree of crystallization lower than 0.8, but it did not fit at high cooling rate. Kinetic parameters obtained by using a non-linear regression method, i.e, Kamals model and Dietzs modification, were able to describe better the non-isothermal crystallization behavior of the studied materials. The full model, that takes into account the induction and growth of the crystal during cooling under non-isothermal conditions was used to obtain a continuous cooling transformation diagrams for polyvinylalcohol -co-ethylene. Finally, non-isothermal models, coupled with the proposed expressions for induction time and kinetic constant, were used to represent the development of crystallinity during the processing of the polymer. 相似文献
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The present work deals with the influence of crystallization temperature, cooling rate and annealing conditions on microhardness, indentation modulus and creep behaviour of ethylene/propylene (E/P) random copolymers with 4, 6 and 8 mol% ethylene as well as α- and β-spherulites in a homopolymer and an E/P random copolymer. The materials are unnucleated, the formation of β-spherulites occurs sporadically. Additionally the indentation creep behaviour of α- and β-nucleated PP is investigated. A nearly linear correlation between hardness as well as indentation modulus and crystallintity of the E/P copolymers can be proved. An increasing cooling rate leads to decreasing hardness and modulus values due to the hindered crystallization. For the investigation of the α- and β-phases different crystallization and annealing temperatures are used. Independent of these conditions, microhardness and modulus determined by indentation testing are lower for the β-phase in both materials. Increasing crystallization temperature and annealing lead to an increasing hardness and modulus in both phases. However, an effective annealing effect takes place only at short times and elevated temperatures above 100 °C. The increasing of microhardness and modulus is correlated with an increasing in lamellae thicknesses. Additionally, indentation creep experiments were carried out on nucleated materials that show the stronger creep tendency of the β-phase PP and the stronger influence of annealing on this phase. 相似文献
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Protein crystallization is important for structural biology. The rate at which a protein crystallizes is often the bottleneck in determining the protein's structure. Here, we give a physical model for the growth rates of protein crystals. Most materials crystallize faster under stronger growth conditions; however, protein crystallization slows down under the strongest conditions. Proteins require a crystallization slot of 'just right' conditions. Our model provides an explanation. Unlike simpler materials, proteins are orientationally asymmetrical. Under strong conditions, protein molecules attempt to crystallize too quickly, in wrong orientations, blocking surface sites for more productive crystal growth. The model explains the observation that increasing the net charge on a protein increases the crystal growth rate. The model predictions are in good agreement with experiments on the growth rates of tetragonal lysozyme crystals as a function of pH, salt concentration, temperature, and protein concentration. 相似文献
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Kang Y Chen S Wang F Zhang J Bu X 《Chemical communications (Cambridge, England)》2011,47(17):4950-4952
Special asymmetric crystallization of porous framework materials from achiral precursors under urothermal conditions is successfully achieved by using an enantiopure liquid as a co-solvent and chirality induction agent, which provides a new strategy for the synthesis of homochiral porous materials containing only achiral building blocks. 相似文献
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In Situ Observation of Successive Crystallizations and Metastable Intermediates in the Formation of Metal–Organic Frameworks 下载免费PDF全文
Dr. Hamish H.‐M. Yeung Dr. Yue Wu Dr. Sebastian Henke Prof. Dr. Anthony K. Cheetham Prof. Dr. Dermot O'Hare Prof. Dr. Richard I. Walton 《Angewandte Chemie (International ed. in English)》2016,55(6):2012-2016
Understanding the driving forces controlling crystallization is essential for the efficient synthesis and design of new materials, particularly metal–organic frameworks (MOFs), where mild solvothermal synthesis often allows access to various phases from the same reagents. Using high‐energy in situ synchrotron X‐ray powder diffraction, we monitor the crystallization of lithium tartrate MOFs, observing the successive crystallization and dissolution of three competing phases in one reaction. By determining rate constants and activation energies, we fully quantify the reaction energy landscape, gaining important predictive power for the choice of reaction conditions. Different reaction rates are explained by the structural relationships between the products and the reactants; larger changes in conformation result in higher activation energies. The methods we demonstrate can easily be applied to other materials, opening the door to a greater understanding of crystallization in general. 相似文献
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Abstract Starch plastic sheets were prepared by extrusion processing of mixtures of granular high-amylopectin and high-amylose starches in the presence of glycerol and water as plasticizers. Amylose content varied between 0 and 70% (w/w). Structural characterization and determination of the mechanical properties of the sheets were performed after aging the materials between 40–65% relative humidity for 2 and 35 weeks and at 90% relative humidity for two weeks. The materials were semicrystalline and viscoelastic. The materials were described as complex heterogeneous multiphase materials. They consisted of amorphous and crystalline phases of amylose and amylopectin as well as granular structures and domains of amylose, amylopectin and amylose-amylopectin helices. Single-helical type crystallinity was formed solely by amylose directly after processing while B-type crystallinity was rapidly formed in amylose-rich materials and slowly during aging of amylopectin-rich materials. The stress-strain and stress-relaxation properties were related to differences in amylose content, degree of crystallization and water content. The amorphous amylopectin rich materials were flexible and soft but showed an increase in stiffness and a decrease in elongation due to crystallization. Amylopectin-rich materials showed unfavorable relaxation, shrinkage and cracking during aging. The materials rich in amylopectin were sensitive to water content while the amylose-rich materials were not sensitive to water in the range of 9–13% (w/w). Stress-strain relaxation behaviors of the materials were dependent on starch structure and on experimental conditions such as strain rate and extension by which the ratio of elastic and viscous response were varied. An increase in relaxation times was found with increasing amylose content and water content for the materials with solely amylose crystallinity. 相似文献
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以低硅铝比焙烧后的硅铝胶固体为初始原料,在含F-近中性与低含水量体系下晶化合成出相对高结晶度的纳米富铝β沸石。实验考察了合成条件、硅铝胶焙烧对晶化产物的影响和晶化过程中Al配位状况变化,并采用XRD、XRF、SEM/TEM2、7AlMAS NMR物化方法对晶化产物进行表征。结果表明,含F-离子、H2O/SiO2摩尔比为2.4~6.0以及高温焙烧硅铝胶有利于合成高结晶度的纳米富铝β沸石;硅铝胶固体焙烧后能产生易于转化为β沸石晶核的Al四配位结构,而部分六配位Al在晶化过程中缓慢溶入β沸石晶核中而最终生成纳米富铝β沸石。 相似文献
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Control of crystallization processes for organic salts is of importance to the pharmaceutical industry as many active pharmaceutical materials are marketed as salts. In this study, a method for estimating the solubility product of a salt of a weak acid and weak base from measured pH-solubility data is described for the first time. This allows calculation of the supersaturation of solutions at known pH. Ethylenediammonium 3,5-dinitrobenzoate is a polymorphic organic salt. A detailed study of the effects of pH, supersaturation, and temperature of crystallization on the physical properties of this salt shows that the desired polymorph may be produced by appropriate selection of the pH and supersaturation of crystallization. Crystal morphology is also controlled by these crystallization conditions. 相似文献