4A沸石分子筛晶体生长过程

用透射电子显微镜研究了４Ａ沸石晶体生长过程．研究表明，随着浆化、晶化、老化条件的变化，４Ａ沸石颗粒的形状及粒度分布也发生变化，以（ＮａＰＯ３）作分散剂，经超声分散，４Ａ沸石晶粒能有效地被分散；４Ａ沸石的结晶度，颗粒组成、颗粒粒度分布，对钙交换量及交换速度有重要影响．     

Hierarchical nanofabrication of microporous crystals with ordered mesoporosity

Shaped zeolite nanocrystals and larger zeolite particles with three-dimensionally ordered mesoporous (3DOm) features hold exciting technological implications for manufacturing thin, oriented molecular sieve films and realizing new selective, molecularly accessible and robust catalysts. A recognized means for controlled synthesis of such nanoparticulate and imprinted materials revolves around templating approaches, yet identification of an appropriately versatile template has remained elusive. Because of their highly interconnected pore space, ordered mesoporous carbon replicas serve as conceptually attractive materials for carrying out confined synthesis of zeolite crystals. Here, we demonstrate how a wide range of crystal morphologies can be realized through such confined growth within 3DOm carbon, synthesized by replication of colloidal crystals composed of size-tunable (about 10-40 nm) silica nanoparticles. Confined crystal growth within these templates leads to size-tunable, uniformly shaped silicalite-1 nanocrystals as well as 3DOm-imprinted single-crystal zeolite particles. In addition, novel crystal morphologies, consisting of faceted crystal outgrowths from primary crystalline particles have been discovered, providing new insight into constricted crystal growth mechanisms underlying confined synthesis.     

Non-classical crystal growth of inorganic and organic materials

Abstract

Investigation of the early stage morphologies of some organic and inorganic systems has established that their crystal growth does not always follow the classical route established 120 years ago. The classical theory assumes that a highly symmetric crystal develops from the nucleation and repeated attachment of atoms, molecules or ions to a single nucleus. In instances where surfactants or polymers are introduced, the crystal growth is often found, however, to follow a ‘reversed crystal growth’ route. This non-classical growth route is initiated by organic molecules adsorbed onto the surface of the nanocrystallites in the early stages of growth. In the reversed route, these nanocrystallites form large disordered aggregates followed by surface crystallisation to create a thin, highly crystalline, dense shell and, finally, an extension of the crystallisation from the surface to the core. Although systems following a non-classical crystal growth route have been known for many years, their formation mechanisms have a much shorter history. Discovery of the reversed crystal growth route in several hollow, core–shell and twin crystal type morphologies not only assists in the designing of materials for industrial applications but also helps to understand the interactions between organic and inorganic components. This review highlights recent research relating to organic and inorganic systems whose growth follows the reversed crystal growth route.     

Surface microscopy of porous materials

Atomic force microscopy (AFM) and high-resolution electron microscopy (HREM) are shown to be powerful tools for the investigation of crystal growth processes in microporous materials. Observations at atomic resolution of zeolite surfaces in the absence and presence of adsorbates reveals both surface structure and the mode of interaction of potential templates for crystallisation. A layer-by-layer growth mechanism is observed for many open-framework materials with organic templates acting by keying into exposed surfaces followed by clathration during growth of the subsequent layer. The role of defects in modifying growth processes can be discerned and predictions made for altering conditions of growth to control the defect type and density. Simulation of AFM micrographs permits the relative rates of fundamental growth processes to be ascertained.     

Predicting the structure of screw dislocations in nanoporous materials

Extended microscale crystal defects, including dislocations and stacking faults, can radically alter the properties of technologically important materials. Determining the atomic structure and the influence of defects on properties remains a major experimental and computational challenge. Using a newly developed simulation technique, the structure of the 1/2a <100> screw dislocation in nanoporous zeolite A has been modelled. The predicted channel structure has a spiral form that resembles a nanoscale corkscrew. Our findings suggest that the dislocation will enhance the transport of molecules from the surface to the interior of the crystal while retarding transport parallel to the surface. Crucially, the dislocation creates an activated, locally chiral environment that may have enantioselective applications. These predictions highlight the influence that microscale defects have on the properties of structurally complex materials, in addition to their pivotal role in crystal growth.     

流动体系中NaA分子筛膜的制备及渗透汽化分离性能研究

以液体硅酸钠、铝酸钠和氢氧化钠为原料,在一种流动体系中制备了工业应用规格的NaA分子筛膜,用XRD和SEM对分子筛膜的晶相结构和表面形貌进行了表征,所制备的NaA分子筛膜具有优良的渗透汽化分离性能.这种流动体系中制备分子筛膜的新方法从根本上避免分子筛合成过程中的浓度梯度问题,有利于制备均匀、连续、致密、分离性能优异的分子筛膜,特别适合于制备工业应用规模的分子筛膜.     

一种测定晶体取向及其分布的简便XRD方法

提出了旋转定向测试法，其原理是使试样的在粉末X射线衍射仪上进行θ扫描的同时绕其端面法线自转，增加了晶面法线通过衍射平面的机会。通过这种方法可直观地区分取向多晶，准单晶或者单晶体，评定研制过程中准单晶和择优取向材料的晶体品质，确定单晶，准单晶及择优取向等材料的晶面相对宏观端面的晶向偏离角和取向分散度，还可对单晶体材料进行三维晶面定向。旋转定向法测试晶体取向具有快速简便，一机多用，精度高等优点，在电子、光学、磁性，机械等材料研究领域具在广泛的应用。     

水热法合成4A沸石的相变/纳米聚合生长过程及其机理研究

用廉价的硅铝系渣料为原料,通过水热法合成了4A沸石,根据不同时间的晶化反 应产物,用XRD、SEM等表征手段对4A沸石的形成机理及晶体长大过程进行了研究,结果 表明:①该反应过程的机理属前驱体固相→硅酸根或铝酸根液相→P型沸石晶相→P型沸石 向A型沸石的相变→A型沸石向P型沸石逆相变;②4A沸石晶体的长大是通过纳米聚合生 长的结果.     

两步晶化制备高性能a&b取向T型沸石膜

采用廉价的大孔α-Al₂O₃作为载体, 通过二次晶种诱导+两步变温水热合成工艺, 成功制备出薄而致密的高性能T型沸石膜。该方法能够充分发挥晶种的诱导成核作用, 通过改变两阶段水热晶化温度和时间来控制晶种外延生长和晶体生长方向, 最终获得了连续、无缺陷的a&b取向T型沸石膜。实验过程中详细考察了第一阶段的晶化温度、晶化时间以及第二阶段的晶化温度对沸石膜表面结构和性能的影响, 并将最优两步晶化条件下制备的膜用于90wt%的异丙醇/水渗透汽化分离, 在75 ℃下膜的通量为3.84 kg·m ^-2·h ^-1, 分离因子大于10000。     

水热法制备A型沸石粉体中的聚合生长

通过水热法制备A型沸石粉体实验和粉体表征,对水热条件下粉体晶粒的生长过程进行较深入的研究,提出了水热体系中A型沸石晶粒同时存在聚集生长和聚合生长。聚集生长是物粒从小尺寸粒子向大尺寸粒子输运的重结晶过程,而聚合生长则是小晶粒之间通过聚合作用形成粒度更大的晶粒的作用过程。两者的热力学驱动力都是由于晶粒平均粒度的增大降低了体系总的表面自由能。水热体系A型沸石晶粒的形成经历了前驱物溶解成核并形成纳米小粒子晶粒的聚合生长晶粒的聚集生长4个阶段,最后得到的晶粒以聚合生长为主,同时伴随着聚集生长的综合结果。     

铁电体陶瓷的晶体结构及介电特性

ＢａＴｉＯ３基铁电体材料的晶体结构和介电特性有密切联系。这类材料有三个铁电相转变。通过离子的置换可以改变材料的介电特性，并可使三个相变温度发生变化。材料的介电损失一般认为由畴界移动和电传导两个机制造成的。材料中异类离子的存在对这些过程有明显的影响。结构中发生正离子的有序化对降低介电损失有重要作用。铅基Ｐｅｒｏｖｓｋｉｔｅ晶体具有无序的八面体堆垛结构和微小的畴区特征，因而这种驰豫型铁电体材料有漫散相变现象和较高的介电率。     

Crystal structure transfer in core/shell nanowires

Structure engineering is an emerging tool to control opto-electronic properties of semiconductors. Recently, control of crystal structure and the formation of a twinning superlattice have been shown for III-V nanowires. This level of control has not been obtained for Si nanowires, the most relevant material for the semiconductor industry. Here, we present an approach, in which a designed twinning superlattice with the zinc blende crystal structure or the wurtzite crystal structure is transferred from a gallium phosphide core wire to an epitaxially grown silicon shell. These materials have a difference in lattice constants of only 0.4%, which allows for structure transfer without introducing extra defects. The twinning superlattices, periodicity, and shell thickness can be tuned with great precision. Arrays of free-standing Si nanotubes are obtained by a selective wet-chemical etch of the core wire.     

Crystal growth as an excitable medium

Crystal growth has been widely studied for many years, and, since the pioneering work of Burton, Cabrera and Frank, spirals and target patterns on the crystal surface have been understood as forms of tangential crystal growth mediated by defects and by two-dimensional nucleation. Similar spirals and target patterns are ubiquitous in physical systems describable as excitable media. Here, we demonstrate that this is not merely a superficial resemblance, that the physics of crystal growth can be set within the framework of an excitable medium, and that appreciating this correspondence may prove useful to both fields. Apart from solid crystals, we discuss how our model applies to the biomaterial nacre, formed by layer growth of a biological liquid crystal.     

Comparison of organic ligand effects on morphology control between disc-like zeolite L crystals and zeolite A and W crystals

Thin disc-like zeolite L crystals were hydrothermally synthesized in the presence of organic ligands, such as catechol and acetylacetone. Thus, zeolite L crystals with many channel entrances on the surface were obtained. Although it was speculated that the complex formation of the organic ligands with aluminate ion in the reaction gels influenced the formation of the disc-like zeolite L crystals, bis-tris which can form a complex with aluminate ion did not show the same effect on zeolite L morphology as catechol and acetylacetone. So, the influence of ligands on crystal morphology was compared between some types of zeolites. Both catechol and bis-tris increased crystal size of zeolite A and zeolite W. Thus, the ligand effect on crystal shapes of disc-like zeolite L was different from that of zeolite A and zeolite W. Moreover, the ligand effect was also examined under agitation. For zeolite L synthesis with the addition of catechol and acetylacetone, the obtained crystalline phase was changed to zeolite T by agitation. Hence, other than the complex formation of aluminate ion with ligands such as catechol, the heterogeneous distribution of reactants probably played an important role in the formation of the disc-like zeolite L crystals.     

膜控晶体生长及纳米微粒的形成

膜控晶体生长不同于一般在溶液中的沉淀与结晶，由膜形成的有机界面具有空间定位和空间约束、定域化学控制及成核过程和晶体生长的立体化学专一的特性，使得晶体的结构、形状和尺寸上得到控制，并具有良好的重现性，由此可获得具有光、电以及磁特性的纳米功能材料。研究膜控晶体生长不仅可以模拟生物体系内的生物矿化作用，而且对于材料科学也有着特别重要的意义和应用前景。     

Effective manipulation of the microstructure of zeolite film by hydrothermal pretreatment

Zeolite films with diverse microstructures were prepared from highly regular seed monolayers by accurate manipulation of various synthetic parameters during secondary growth. The effects of the hydrothermal pretreatment procedure, hydrothermal pretreatment temperature and duration, secondary growth temperature and duration of prepared zeolite films on final microstructures were investigated in detail. Based on these results, a mechanism was proposed to elucidate the effects of hydrothermal pretreatment on the secondary growth dynamics of the zeolite films: hydrothermal pretreatment could induce the separation of secondary nucleation and the subsequent growth process. Consequently, the disordered growth of zeolite films could be effectively avoided.     

水凝胶相中载体预陈化法合成NaX型沸石膜

以相同的组成及晶化温度,首次采用载体预陈化法在α-Al_2O_3载体外表面成功合成NaX型沸石膜.水热处理前,载体在合成母液中经室温陈化,而后在363 K下进行水热处理.通过控制陈化时间,研究陈化对所合成沸石膜的影响.研究发现,陈化把沸石合成分为成核阶段及晶体生长阶段,并能够很好地控制沸石的成核和膜生长.陈化期间,非均相的水凝胶相中形成的沸石晶核沉积在载体表面,形成晶体生长的诱导层.较少的陈化时间会产生杂晶相,如方钠石(SOD)、菱沸石(CHA)、方沸石(ANA),这些杂晶相是沸石FAU的竞争相.随着陈化时间的增加,方解石(FAU)则变成了主要相,而为了获得纯的RAU沸石相,至少陈化一天.分别用XRD和SEM鉴别膜的晶体结构及观察膜的形貌和厚度;通过单气体的渗透测试表征气体传递特性.结果显示,陈化对膜的晶粒大小、晶体互生性以及表面覆盖度有着重要的影响;陈化2天后晶化形成的NaX沸石膜对H_2/N_2的渗透通量及理想选择性最高分别可达37/10 mol/(m~2·Pa·s)和110.     

双模板剂B-EU-1/ZSM-5复合分子筛的快速合成及催化应用

以不同氢氧化物做碱源合成B-EU-1/ZSM-5复合分子筛, 并比较各平衡阳离子的结构导向作用及其形貌特征, 发现钠离子的导向作用最强, 且合成复合分子筛的表面较光滑、无明显晶面界限。对合成样品进行了TG-DTG、N₂吸附-脱附和NH₃-TPD分析。结果表明: 双模板剂一步法合成的复合分子筛模板剂脱除的失重率为5.67%, 小于机械复合分子筛的失重率7.31%, 复合分子筛的比表面积、孔容和微孔平均孔径均有所增大, 同时其酸强度、酸量都增大, 有利于二甲苯优先从复合分子筛的孔道结构中扩散出来。将分子筛应用于甲醇转化制二甲苯催化反应, 结果显示, 双模板剂一步法合成的复合分子筛催化产物油相中芳烃的选择性最高达到66.72%, 芳烃中二甲苯的含量为46.15%, 二甲苯中对二甲苯的含量达到30.75%。这是由于B-EU-1/ZSM-5催化剂的特殊孔道结构具备择形效应, 使得分子动力学直径较小的二甲苯分子优先从其孔道中扩散出来。     

喷流转晶法KDP晶体生长系统的流动与传质模拟

提出了一种通过锥顶喷流改善KDP锥面过饱和度的晶体生长方法。采用有限体积法和滑移网格技术,对传统转晶法及喷流转晶法的KDP晶体生长过程进行了数值模拟。展示了两种生长方式下晶体表面过饱和度时均分布云图及均方差,分析了不同转速、不同喷流速度、不同晶体尺寸对晶面时均过饱和度及均方差的影响。结果表明:相比于传统转晶法,喷流转晶法晶体的锥面过饱和度提高且表面均匀性增加。提高喷流速度可以进一步提高锥面过饱和度,但其均方差却呈现先减小后增大的变化。旋转速度的增加能提高锥面过饱和度并减小其均方差。此外,晶体尺寸也会在一定程度上影响喷流的效果。     

原料空隙率对6H-SiC晶体生长初期的影响

生长准备中不同的装料方式导致原料的空隙率不同.在其它生长工艺参数保持一致的前提下研究了不同空隙率的原料(50%、55%、60%)对SiC晶体生长初期生长速率和结晶质量的影响.实验发现,在晶体生长初期生长速率随原料空隙率的增大而升高,过快的结晶速率导致晶体的结晶质量下降.同时利用有限元方法模拟了不同空隙率的原料(50%、55%、60%)在生长初期内部温度场分布、质量输运以及晶体生长速度.因为在生长温度下原料内的热量传输主要依靠SiC颗粒间的热辐射,所以空隙率增大会导致其等效热导率增大.模拟结果表明:60%空隙率的原料最短时间内达到稳态传热,初期晶体生长速率最大.模拟的结果合理地解释了原料空隙率对SiC晶体生长初期的影响规律.