ELECTROCHEMICAL PROPERTIES OF GEL-TYPE ZEOLITE SYNTHESIS MIXTURES

The variation of the potential difference of two electrodes, connected by a voltmeter and immersed into different gel mixtures yielding various zeolites, was observed with respect to synthesis time. The potential difference-time curves obtained for zeolites such as X, A, and HS exhibited characteristic behaviors that might be helpful in their identification. These behaviors could be rationalized by taking into consideration the changes occurring mainly in the dissolved sodium and aluminum concentrations of the liquid phase, before and during the crystallization of zeolites. The relative rates of zeolite crystallization were also reflected on the potential difference-time curves. Reaction mixture compositions with relatively low Si/Al ratios generally led to sharper changes in the potential difference, due to the relatively high crystallization rates obtained in these cases.     

锡硅分子筛：新型杂原子分子筛催化材料

锡硅分子筛能高效催化含氧烃转化，因此其具有重要潜在工业应用价值。本文简述了锡硅分子筛的骨架锡判定、合成方法、多级孔合成研究及应用领域。XRD、NMR和EXAFS等表征方法可以判别锡硅分子筛内锡原子的配位形式及落位。合成锡硅分子筛通常采用水热晶化法、后插入法和干胶转化法。碱性水热合成过程中匹配锡源和硅源的水解速率是使锡原子高效插入分子筛骨架的关键。中性水热合成方法制备的锡硅分子筛结晶度较高，但存在使用剧毒含氟试剂和晶粒较大等问题。干胶转化法可在短时间内制备高结晶度含锡分子筛，但该法存在传质传热差等弊端。采用后插入法可将锡原子插入到不同拓扑结构的分子筛骨架，但锡原子易发生聚集。同时，采用碱处理、硬模板剂法和软模板剂法合成多级孔锡硅分子筛，可提升骨架锡活性中心的可接近性。其中，采用软模板剂法展示出独特的优势，其可制备介孔分布均匀且贯通性良好的多级孔锡硅分子筛。另外，锡硅分子筛的骨架锡原子对含氧官能团具有优异的活化作用，因此其在Meerwein-Ponndorf-Verley-Oppenauer反应、葡萄糖异构化反应、乳酸及乳酸酯制备及Baeyer-Villiger氧化反应中都展示了良好的催化效果。     

Crystallization Behaviors of PbSe Quantum Dots in Silicate Glasses

This study, composed of three parts, aims at studying the crystallization behaviors of PbSe quantum dots (QDs) in silicate host glasses. Firstly, due to the importance of the choice of base glass for the QDs' crystallization, the selection of base glass compositions, the glass fragility, and glass formation ability (GFA) are discussed in details, and the results show that the selected glass compositions have an intermediate fragility and accordingly an intermediate glass transition temperature range among a wide variety of inorganic glass systems together with a good GFA/glass stability (GS). Thus, this base glass is suitable as the host glass in which PbSe QDs crystallize. Secondly, the experimental results on PbSe QDs' crystallizations are presented, and the results show that PbSe QDs can precipitate from silicate glasses favorably with no other chemical compounds precipitation, and the optimized temperature for PbSe QDs crystallization is 600°C. Lastly, the classical nucleation theory is used to analyze the PbSe QD crystallization behaviors in host glasses. The steady‐state nucleation rates and the growth rates of PbSe QDs as well as the time–temperature transformation (TTT) curves are calculated. The results indicate that the free surface energy between the PbSe nuclei and the host glass has great influence on the nucleation rates of PbSe QDs, while it has less effect on the growth rates of PbSe QDs; the crystallization behaviors of PbSe QDs with different volume fractions can be described well by the TTT curves while keeping the dimensionless empirical constant, α, unchanged for one certain curve.     

Strain hardening behaviors and mechanisms of polyurethane under various strain rate loading

The uniaxial tension experiments are performed on thermoplastic polyurethane to investigate its mechanical behaviors and related potential mechanisms, and the loading strain rate is designing to be wide ranging from 0.0001 to 1 s⁻¹. It is found that the polyurethane presents an obvious rate-dependence, and the stress strain curves share distinct strain hardening characteristics under the investigated strain rates. Furthermore, the strain hardening ratios are sharing nearly same trends and appear to be influenced by both strain rate and the induced adiabatic heating. Besides, the ratio is also strain-dependent on previous loading history. Then, a two-dimension unit cell model is built to investigate potential equivalent mechanisms, of which the hard phase as inclusion is equivalent with crystallization zone, crosslinking sites, and so forth. The simulation results facilitate to explain the distinct strain hardening ratios, even for the matrix from the extrapolated curves under super-low strain rate loading. Finally, the analogic mechanisms of equivalent hard inclusions are proposed, which can reasonably explain the strain rate- and strain-dependence characteristics of polyurethane mechanical behaviors.     

Non-isothermal polymer crystallization kinetics and Avrami master curves

The kinetic crystallization model of Avrami is generally accepted as a starting point for the analysis of isothermal polymer crystallization. It is shown in this paper that, in the case of non-isothermal crystallization kinetics with constant heating or cooling rates, an apparent m -order reaction model is approximately equivalent to the nucleation and growth model of Avrami in the vicinity of the inflection points of the corresponding crystallization curves. Since the apparent m -order reaction model is defined for every real, positive apparent reaction-order m , a distinct Avrami index n , which is valid for the characterization of isothermal and non-isothermal crystallization experiments with constant heating or cooling rates, can always be related to any apparent reaction-order m . Therefore, two types of Avrami master curves, which are dependent merely on the Avrami index n and which describe the isothermal polymer crystallization thoroughly, can be obtained by performing non-isothermal experiments with constant heating or cooling rates.     

Seed-induced synthesis of functional MFI zeolite materials: Method development,crystallization mechanisms,and catalytic properties

As an important zeolite material, MFI zeolites, as well as their controllable synthesis, are of great interest in both basic and applied science. Among the developed synthetic approaches, the seed-induced method has gradually evolved into a facile, low-cost, and even green alternative to give zeolites the desirable physicochemical properties. In this review, we briefly summarize the development of seed-induced syntheses of diverse functional MFI zeolites, where the “living” seed crystals not only direct the formation of zeolitic framework but also function as special “templates” or “units” to fine-tune the zeolite materials with diverse sizes, shapes, compositions, morphologies and pore structures. Moreover, on the basis of their structural features and crystallization behaviors in seed-induced synthesis, we reveal the roles of seeds and discuss the related crystallization mechanisms including both classical and non-classical pathways. We also want to guide readers to investigate the structure-performance relationships between these functional MFI zeolite catalysts and suitable catalytic reactions.     

硅藻土为原料原位晶化合成ZSM-5分子筛

以硅藻土为原料,采用原位晶化方法合成ZSM-5分子筛,考察了晶化时间、水硅比、模板剂用量等因素对合成分子筛的影响。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、热重(TG)手段对所合成的样品进行了表征。得出了最适宜的合成条件:晶化温度170℃,晶化时间为72 h,水硅比为n(H_2O):n(SiO_2)=45~96,模板剂用量为n(模板剂):n(Al_2O_3)=12~20。该法合成的ZSM-5分子筛具有较高的相对结晶度,具有较小的粒径且分布均一,粒径为400~500 nm。     

Tailoring the reaction mixture composition for preparing zeolite coatings on aluminum supports in alkaline environments

Various alkaline reaction mixture compositions were tested for determining their suitability to be used in the direct crystallization of zeolites on aluminum supports. No organic materials, such as templates, complexing agents, and corrosion inhibitors were included in the reaction mixtures. It was observed that aluminum supports remained quite stable in alkaline synthesis mixtures when suitable reaction mixture compositions with relatively high silica content were used. These favorable compositions might be recognized from their sodium silicate/(sodium hydroxide?+?sodium aluminate) mass ratios, as depicted in this study. Coatings were prepared on aluminum by using some of these compositions. It was determined that aluminum hydroxide phases commonly forming on the support could be eliminated to a great extent and consequently, crystalline coatings of zeolites P and Y were obtained on aluminum surfaces. The coatings exhibited trivial mass loss in the mechanical stability tests applied.     

以纯天然矿物为硅铝原料水热合成ZSM-5分子筛

以纯化硅藻土和热活化高岭土为硅铝原料,在水热条件下一步合成纯相ZSM-5分子筛。考察分子筛合成参数对产物的影响,得到合成ZSM-5分子筛的适宜条件:硅藻土与高岭土质量比32∶1,晶化温度170℃,晶化时间48 h,合成体系pH=13. 0。采用XRD、SEM及N2吸附-脱附等对样品进行表征。结果表明,最适宜条件下合成的ZSM-5分子筛晶型完整,具有与工业ZSM-5分子筛相似的六棱柱形貌以及相近的总比表面积和总孔容。     

Hierarchically porous zeolites synthesized with carbon materials as templates

Hierarchically porous zeolites are promising candidates in catalytic conversion of relatively bulky molecules, and their syntheses have attracted significant attention. From both industrial and scientific perspectives, different carbon materials have been widely employed as hard templates for the preparation of hierarchically porous zeolites during the past two decades. In this review, the progress in synthetic strategies using carbon materials as templates is comprehensively summarized. Depending on the affinity between the carbon templates and zeolite precursors, the substantial strategies for synthesizing hierarchical zeolites are introduced in direct templates and indirect templates. Direct templates methods, by which the carbon materials are directly mixed with precursors gel as hard templates, are first reviewed. Then, we discuss the indirect templates method (crystallization of carbon-silica composites), by which the carbon is produced by in situ pyrolysis of organic-inorganic precursors. In addition, the technique of encapsulating metal species into zeolites crystals with the assistance of carbon templates is also discussed. In the conclusion part, the factors affecting the synthesis of carbon-templated hierarchically porous zeolites are remarked. This review is expected to attract interest in the synthesis strategies of hierarchically porous zeolites, especially cost-effective and large-scale production methodologies, which are essential to the industrial application of hierarchical zeolites.     

Effect of cryomilling on the thermal behaviors of poly(ethylene terephthalate)

We have studied the effect of cryomilling (high‐energy ball milling under cryogenic temperature) on the thermal behaviors of poly(ethylene terephthalate) (PET) by comparing with original PET and quenched PET. Cryomilling induced the amorphization of crystalline PET, but the thermal behaviors of amorphous PET obtained from cryomilling are significantly different to those of amorphous PET obtained from quenching. Unlike amorphous PET obtained from quenching, the heating curve of amorphous PET obtained from cryomilling shows no cold crystallization peak, but evidences are found that its cold crystallization occurs within a wide temperature range. In addition, the stability of amorphous PET obtained from cryomilling is higher than that of amorphous PET obtained from quenching. The difference is proved to be attributed to the stored energy in cryomilled PET. The hot crystallization behaviors of PET improve a lot after cryomilling, and the heat stability of cryomilled PET is also better than those of original PET during reheating. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

超重力预混+动态水热法制备ZSM-5分子筛——水热过程影响机制

ZSM-5分子筛作为一种重要的催化剂,被广泛应用于石油化工行业,其制备工艺一直是分子筛研究的热点。传统静态水热法制备ZSM-5分子筛存在产物粒度分布不均、晶化时间长等问题,本文提出开展超重力预混+动态水热法制备ZSM-5分子筛,考察了晶化过程中晶化方式、搅拌釜转速、晶化时间和晶化凝胶体积对ZSM-5分子筛粒径的影响规律,获得了较优的操作条件;并针对较优条件下制备的产品进行了系统表征。结果表明,相比于超重力预混+静态水热,动态水热更有利于合成粒径小且分布均匀、酸量大、比表面积大的多级孔ZSM-5分子筛,搅拌釜转速越大、晶化凝胶体积越小所制备的产品平均粒径越小,粒径分布越均匀。本文研究结果表明,水热过程参数对分子筛的粒径、结构和酸性具有重要影响。     

煤系高岭土水热合成干燥用13X型沸石分子筛

研究以内蒙古鄂尔多斯煤系高岭土为原料,水热合成干燥用13X型沸石分子筛。采用单因素条件实验,考察了晶化时间、碱投加量、胶化温度、胶化时间、晶种投加量等制备条件对合成13X型分子筛的影响。通过静态饱和吸水量测定,RD、IR和SEM等表征手段对产品进行表征。发现最佳的反应条件为：合成液中晶种投加量为2%和碱投加量R[n（Na2O）/n（H2O）]控制在5.3,在65℃下胶化3h、然后在100℃下晶化时间24h,此时合成的X型分子筛的静态饱和吸水量为33.47%,合成晶体的外形为八面体晶型,而且形状规则、大小均匀、晶体棱角也比较清晰。     

对二甲苯/间二甲苯在KX和CaX上的吸附平衡和动态吸附性能

通过静态吸附实验,测定了对二甲苯、间二甲苯在分子筛KX和CaX上的吸附速率曲线及吸附等温线;动态吸附穿透实验测定了对二甲苯/间二甲苯混合液在固定床中的连续流出曲线。结果表明,对二甲苯、间二甲苯在CaX上的静态饱和吸附量和动态穿透吸附量均高于KX,但CaX对对二甲苯的吸附选择性不及KX;Langmuir吸附等温线方程可以很好地拟合对二甲苯、间二甲苯在CaX上的等温线;二级吸附速率方程可以较好地描述对二甲苯、间二甲苯的吸附动力学行为。     

Crystallization of polyethylene oxide under shear

A concentric cyclinder dilatometer was designed and built to study the influence of shear on the crystallization kinetics of polymers. This instrument allows crystallization to be followed at both constant temperature and shear rate. Several samples of polyethylene oxide (Carbowax 4000, Carbowax 20-M, and WSR-205) were used. A low molecular weight fraction of the Carbowax 20-M, as well as the unfractionated material, was crystallized under shear. The WSR-205 was studied only in a mixture with Carbowax 4000. It was shown that the kinetics of crystallization of uncrosslinked melts of polyethylene oxide are altered by shear. The induction times for the appearance of crystallinity are shorter in the sheared systems than in the quiescent melts. The Avrami exponents are also higher for crystallization in sheared melts than in quiescent systems and increase with decreasing supercooling. The high values of the Avrami exponent are attributed to the disruption of crystalline aggregates into particles larger than the critical sized nucleus. These particles will persist in the melt and continue to grow spontaneously. A continuous infusion of growing particles into the melt occurs. At constant temperature and shear rate, the induction time of the crystallization curve is influenced by polymer molecular weight. In moderate to high molecular weight samples, the effect of shear becomes saturated at very low shear rates. Decreasing the molecular weight separates the crystallization curves. The curves from the higher shear rates appear at the shorter induction times. However, decreasing the molecular weight below that at the critical entanglement molecular weight allows the nucleation rate, strongly dependent upon the supercooling, to influence the relative positions of the sheared crystallization curves.     

Fe-AlPO4-5分子筛的水热晶化过程研究

采用X射线粉末衍射(XRD)研究了Fe—AlPO4—5分子筛在不同晶化温度下的水热结晶过程。以相对结晶度为指标测定了结晶动力学曲线,用Arrhenius方程计算了Fe—AlPO4-5分子筛的表观成核活化能和表观晶体生长活化能,分别为82．7kJ／mol和28．2kJ／mol。晶化过程中样品单位晶胞体积的测定结果表明大部分骨架位Fe^3 在晶体生长阶段的早期就已经进入了分子筛骨架结构中。晶化温度高于453K时,Fe—AlPO4-5分子筛在结晶度达到最大后还要进行结构调整直至形成热力学上相对稳定的结构。     

低模数水玻璃合成ZSM-5分子筛及工艺条件优化

以低模数（n=1.03）水玻璃为硅源,通过改良水热合成途径,成功制备出无模板剂ZSM-5分子筛。借助X射线衍射仪（XRD）和扫描电镜（SEM）对ZSM-5分子筛结晶度及晶貌进行表征。在n(硅)/n(铝)为50 的情况下,通过考察晶化温度、时间、pH值、水含量、有无搅拌或晶种对ZSM-5分子筛物性的影响,优化合成工艺。结果表明,静置或晶种法得到的ZSM-5分子筛,晶体粒径大且晶貌不规整,不适合用于低模数水玻璃合成ZSM-5体系。ZSM-5沸石最适宜制备工艺为：n(H₂O)/n(SiO₂)=40,pH=10的合成混合物经室温老化24 h,搅拌状态下,170 ℃下水热晶化24 h。与商业级ZSM-5相比,低模数水玻璃合成的ZSM-5分子筛在环己烯水合反应中表现出更高的催化活性和选择性。     

Role of multi-wall carbon nanotube network in composites to crystallization of isotactic polypropylene matrix

The composites (iPP/CNTs) made of isotactic polypropylene (iPP) and multi-wall carbon nanotubes (CNTs) were prepared by solution blending. To improve compatibility between CNTs and iPP and to enhance dispersion of CNTs in iPP matrix, CNTs were chemically modified by grafting alkyl chains. The chemically modified CNTs had about 6 wt% grafted alkyl chains. Rheological measurements indicated that CNTs caused gelation in iPP/CNTs due to CNT network formation and the critical gelation CNT concentration was about 7.4 wt%, which was considered to be high due to the low CNT aspect ratio in this study. Crystallization behaviors of iPP/CNTs were studied by using optical microscopy (OM) and differential scanning calorimetry (DSC). Radial growth rates of spherulites during isothermal crystallization of iPP/CNTs with CNT concentrations less than 2.0 wt% measured by using OM showed decreasing trends with increasing CNT concentration. Avrami analysis of the exothermic heat flow curves during isothermal crystallization of iPP/CNTs measured by DSC indicated that crystallization rates were accelerated when CNT concentrations were lower than the critical gelation concentration, because CNTs mainly functioned as nucleating agents for crystallization, while crystallization rates did not change obviously when CNT concentrations were higher than the critical gelation concentration, because CNT network could form and mainly functioned to provide restriction to mobility and diffusion of iPP chains to crystal growth fronts.     

Effects of spinodal decomposition on mechanical properties of a polyolefin blend from high to low strain rates

The effects of spinodal decomposition, a typical type of liquid-liquid phase separation (LLPS), on the mechanical properties of a pretreated statistical copolymer blend of poly(ethylene-co-hexene) (PEH) and poly(ethylene-co-butene) (PEB) were characterized by tensile testing under different strain rates. An important finding was that the strain rate and the crystallization temperature had to be considered as independent variables in analyzing the effects of spinodal decomposition on the tensile behaviors. At the high strain rate, the stress-strain curves kept irrespective of LLPS time, in which the interfacial relaxation between phase domains could not be detected, except the case crystallizing at 120 °C for 10 min. This was explained in terms of the distribution of the crystals elaborated by differential scanning calorimetry (DSC) results. However, when a relatively low strain rate was employed, a clear deterioration of tensile properties with LLPS proceeding was observed for the cases with low crystallization temperature because of its detection ability for large scale structural information, such as the phase boundary; unexpectedly, the effect of LLPS on the tensile properties was found to disappear in the high crystallization temperature cases which was due to the cooperative functions of the phase boundary and the internal structures of the phase domains. These abundant results provided a novel and indispensable instruction for the processing of polymer blends from the theoretical viewpoint.     

用拟二元方法研究iPP-DBP-DOP三元体系的热致相分离热力学

采用拟二元方法研究等规聚丙烯（iPP）‐邻苯二甲酸二丁酯（DBP）‐邻苯二甲酸二辛酯（DOP）三元聚合物溶液的热致相分离热力学,得出了拟二元相图的数学关联方法.采用光学显微镜法测定浊点温度, 采用差式扫描量热法（DSC）测定熔点、动态结晶温度.利用浊点测定数据回归聚合物-共溶剂的交互作用参数 χ的表达式,χ是共溶剂配比和温度的函数,以此为基础计算的拟二元相图与实验数据吻合较好.发现共溶剂中DBP份数增加,相分离类型由单纯固液分相形式转变为液液分相、固液分相依次发生形式,共溶剂配比能调控拟二元相图结构.研究表明,只需测定一个较低冷却速率下几种共溶剂配比的拟二元溶液的浊点温度、分别测定几个冷却速率下iPP–DOP二元溶液的动态结晶温度即可掌握该三元溶液热致相分离热力学的全部信息.其可用来指导制膜过程,并能准确预测形成的膜结构形貌.