共查询到18条相似文献,搜索用时 140 毫秒
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(1)通过综合分析广西资源红辉沸石和湖南临澧玻屑凝灰岩的矿物组成、化学成分和部分工艺性能,对这两种矿物原料的资源特性进行了评价.并根据其资源特性,对它们进行了预处理,使之成为水热制备沸石分子筛的合格原料.(2)首次以红辉沸石或玻屑凝灰岩为原料,采用水热反应法制备了沸石分子筛系列产品.并在大量实验研究的基础上,深入探讨了反应混合物组成和反应条件对沸石分子筛水热制备的影响,确定了A型、X型和P型沸石水热制备的最佳工艺技术参数.(3)结合反应过程中固相组分的化学成分及红外光谱变化特征,对沸石分子筛的形成条件、晶核形成及其影响因素、晶体生长及其影响因素作了综合分析,证实了水热体系沸石分子筛的形成机理为液相转化机理.(4)首次运用FKM法对反应初期的反应混合物进行TEM制样,并在透射电镜下对所制样品进行了TEM观察和电子衍射分析.结果表明,在水热反应初期,伴随着前驱物的溶解,沸石分子筛以成核作用为主,形成粒度为几个nm的小粒子,这些小粒子迅速聚合生长生成约50nm的纳米晶粒,从而为纳米晶粒的聚合生长提供了有力的证据.(5)通过对沸石分子筛水热制备的分析表征及其晶体生长过程的深入研究,证实水热反应体系中存在着聚合生长和聚集生长两种晶体生长方式,建立了晶体聚合生长模型.聚合生长是小粒子之间相互作用形成粒度更大的粒子的过程;聚集生长则是物料从小尺寸粒子向大尺寸粒子输运的重结晶过程.两者的热力学驱动力都是粒子平均粒度的增大降低了体系总的表面自由能.水热条件下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→纳米晶粒和微米晶粒的聚合生和→微米晶粒的聚集生长'四个阶段,最后得到的晶粒是以聚合生长为主,同时伴随着聚集生长的综合结果. 相似文献
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本文分别以四氯化钛、硫酸钛和钛酸丁酯为前驱物,研究了水热条件下二氧化钛微晶粉体的结晶晶型、晶粒形貌和晶粒度.采用XRD和TEM等分析手段分别对产物的晶相和晶粒形貌进行表征.实验结果表明:对于200℃水热反应,以四氯化钛为前驱物,通过加入氢氧化钠调节反应介质酸碱度,当溶液pH值小于1时,有利于形成金红石型粉体;当溶液pH值大于3并小于7时,有利于形成锐钛矿型粉体;当溶液ph值大于7时,有利于形成板钛矿型粉体.以硫酸钛为前驱物,通过控制胶体制备工艺及反应温度,制备得到锐钛矿型和板钛矿型粉体.金红石型粉体呈长条柱状,锐钛矿呈菱形或双锥状,板钛矿呈板块状.经过较为系统的实验研究,获得了金红石、锐钛矿、板钛矿三种晶相的粉体,并可通过控制前驱物的种类及酸碱度和水热反应条件随意地制备出以上三种晶相中的单晶相粉体.从结晶学出发,解释了二氧化钛纳米粉体的结晶形貌,并从晶体生长过程及生长机理的角度讨论了二氧化钛同质变体的形成机理. 相似文献
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探讨了合成Pb1.5Nb2O6.5型微波介质陶瓷粉体的焙烧温度、焙烧时间、添加剂等不同工艺因素对Pb1.5-Nb2O6.5粉体物相变化、晶粒生长及形貌的影响,采用X射线衍射(XRD)和扫描电子显微镜(SEM)对制备的粉体进行物相与晶体形貌检测.实验结果表明在其他工艺因素控制得当时,焙烧温度对粉体粒度和物相变化的影响最大,而不同类型的添加剂不仅可以使晶粒生长更为完整,尺寸增大,同时也可以不同程度地改变粉体颗粒的生长趋势与形貌.实验制备出的Pb1.5Nb2O6.5粉体物相单一无杂质、晶粒尺寸较小,适于进一步制备微波介质陶瓷元件. 相似文献
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通过XRD、SEM和动态光散射粒度测定仪(DLS)研究了胶溶及水热晶化过程中纳米TiO2晶粒聚集行为及形貌.实验结果表明,在胶溶无定形沉淀过程中所形成的大小为10-15nm的锐钛矿(A)型胶粒或金红石(R)型胶粒(初级粒子)易定向聚集成更大的、具有(30-50)nm×(80-100)nm的次级晶粒.含有次级晶粒的溶胶前驱液在水热晶化过程中,次级晶粒发生崩裂并生长成结晶度更高的大小约为10-30nm球形(A型)和大小约为20-60nm棒状(R型)纳米TiO2. 相似文献
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通过对产物形貌及晶粒度测试,掌握水热温度、水热时间对水热产物影响的基本规律,运用临界成核理论及颗粒成长理论解释提高水热温度、延长水热时间导致的颗粒形态逆转的原因,结合晶体成长阶段性理论,揭示了提高水热温度或延长水热时间以及增大前躯体过饱和状态条件下诱发的两类聚集生长方式,阐述了第Ⅰ类聚集和第Ⅱ类聚集生长的根本原因,其中第Ⅰ类聚集生长是因为过饱和度的增大使得部分AlOOH颗粒在水热溶液中溶解形成的Al^3+聚集体在另一些颗粒表面的叠合,而发生第Ⅱ类聚集生长的本质是由于pH酸碱环境使得多个AlOOH颗粒通过某些结构相容晶界间的键联而形成的具有特殊生长形态的颗粒。 相似文献
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水热介质pH值对纳米(Ce)ZrO_2晶粒制备的影响 总被引:1,自引:0,他引:1
《中国粉体技术》2000,6(Z1):284-286
用水热法制得纳米 (Ce)ZrO2 粉体 ,其晶粒粒度为 3~ 7nm ,而且为单一分散。用XRD、TEM分析了水热媒介pH值对粒度、m相含量、晶粒形貌的影响关系。结果表明 :水热煤介 pH值增大 ,ZrO2 晶粒也增大 ;pH值减小至酸性时 ,ZrO2 晶粒中出现部分m相 ,且晶粒易团聚 相似文献
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Qibing Chang Jian-er Zhou Yongqing Wang Guangyao Meng 《Advanced Powder Technology》2010,21(4):425-430
Zirconia single crystal nano-particles containing pores were prepared by a sol–gel-hydrothermal method. The unique character of the particles is that some irregular pores are embedded within the single crystals. The results of XRD, TEM and FT-IR show that the gaseous hydrolysates of the superstoichiometric urotropine are the origin of the pores. The gel structure and the hydrothermal treatment are the required conditions resulting in the pores in crystals. The formation mechanism was proposed: zirconia gel was formed after the reaction of ZrOCl2 with urotropine. The superstoichiometric urotropine was dissolved and distributed uniformly in the gel. The small pores were generated because gaseous hydrolysates of urotropine were constrained in the gel during the hydrothermal treatment. During the process of the amorphous gel transferred into the crystals, some of the pores coarsened with the crystals growth. Big pores disappeared due to the break of the crystals. And only the small pores were remained in the interior of crystals, which could hardly be eliminated by the subsequent crystal growth if the calcination temperature is below 550 °C. Thus, the zirconia nano-particles containing pores were generated. 相似文献
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以多晶硅颗粒为硅源, 在泡沫碳化硅载体上原位水热合成silicalite--1型沸石晶体。研究了硅颗粒加入量、NaOH浓度以及合成时间等因素对沸石晶体的负载量、晶体尺寸和沸石晶体/泡沫碳化硅复合材料比表面积的影响。结果表明,
以多晶硅颗粒为硅源控制硅酸根的释放速度, 使沸石晶体在碳化硅载体表面异质界面形核, 从而实现沸石晶体在泡沫碳化硅载体表面的连续生长; 当多晶硅量过少时, 溶液中的硅酸根浓度过低, 不能在载体表面形成连续生长的沸石层;
而当多晶硅量过大时, 溶液中硅的浓度过高, 部分沸石晶体在溶液当中形核, 使沸石晶体在载体表面的负载量下降; 提高溶液中NaOH的浓度, 加快硅的溶解, 使溶液中硅的饱和浓度升高, 沸石晶体的形核率也随之升高, 使沸石晶体的负载量增加。在最优条件下制备的silicalite--1/泡沫碳化硅复合材料其沸石晶体的比表面积为81.28 m2g-1。 相似文献
以多晶硅颗粒为硅源控制硅酸根的释放速度, 使沸石晶体在碳化硅载体表面异质界面形核, 从而实现沸石晶体在泡沫碳化硅载体表面的连续生长; 当多晶硅量过少时, 溶液中的硅酸根浓度过低, 不能在载体表面形成连续生长的沸石层;
而当多晶硅量过大时, 溶液中硅的浓度过高, 部分沸石晶体在溶液当中形核, 使沸石晶体在载体表面的负载量下降; 提高溶液中NaOH的浓度, 加快硅的溶解, 使溶液中硅的饱和浓度升高, 沸石晶体的形核率也随之升高, 使沸石晶体的负载量增加。在最优条件下制备的silicalite--1/泡沫碳化硅复合材料其沸石晶体的比表面积为81.28 m2g-1。 相似文献
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Fan W Snyder MA Kumar S Lee PS Yoo WC McCormick AV Lee Penn R Stein A Tsapatsis M 《Nature materials》2008,7(12):984-991
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. 相似文献
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Andrew P. Lange Amit Samanta Tammy Y. Olson Selim Elhadj 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(29)
Oriented attachment (OA) has become a well‐recognized mechanism for the growth of metal, ceramic, and biomineral crystals. While many computational and experimental studies of OA have shown that particles can attach with some misorientation then rotate to remove adjoining grain boundaries, the underlying atomistic pathways for this “imperfect OA” process remain the subject of debate. In this study, molecular dynamics and in situ transmission electron microscopy (TEM) are used to probe the crystallographic evolution of up to 30 gold nanoparticles during aggregation. It is found that Imperfect OA occurs because 1) grain boundaries become quantized when their size is comparable to the separation between constituent dislocations and 2) kinetic barriers associated with the glide of grain boundary dislocations are small. In support of these findings, TEM experiments show the formation of a single crystal aggregate after annealing nine initially misoriented, agglomerated particles with evidence of dislocation activity and twin formation during particle/grain alignment. These observations motivate future work on assembled nanocrystals with tailored defects and call for a revision of Read–Shockley models for grain boundary energies in nanocrystalline materials. 相似文献
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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. 相似文献
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球形氢氧化镍的微结构形成机制研究 总被引:3,自引:0,他引:3
通过扫描电镜(SEM)和透射电镜(TEM)技术研究了在连续搅拌反应沉淀-结晶过程中生成的球形氢氧化镍的微结构形成机制.研究结果表明,在连续搅拌反应器中,小颗粒的聚集为氢氧化镍微粒生长的主要方式,聚集和重结晶过程进而影响球形氢氧化镍颗粒的表面和内部结构;宏观形貌为球形的每一个氢氧化镍微球由纳米片状氢氧化镍沿径向叠砌而成,纳米片状氢氧化镍晶粒之间相互连接形成三维网络结构;氢氧化镍微球表面结构显示由新生纳米晶氢氧化镍自组装聚集特征,同时微球内存在大量的孔隙.具备这种结构的球形氢氧化镍活性物质在Ni-MH电池的充放电过程中可能具有良好的力学稳定性及质子和电子传导性能. 相似文献
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Hydroxyapatite (HA) is a useful substance because of its biocompatibility and adsorption capability. Tubular HA particles
are highly attractive as novel tissue scaffolds and as drug carriers because of their hollow structures. We previously found
that tubular HA particles were formed when a mixture of α-tricalcium phosphate (α-TCP) and anatase was hydrothermally treated.
However, the formation mechanism is still unclear. In this study, we investigated the effect of anatase on the formation of
tubular HA particles. The formation of tubular HA particles was enhanced when a pellet of a mixture of α-TCP and anatase was
UV-irradiated before hydrothermal treatment. The tubular HA formation was observed only when anatase particles with adequate
size were added in adequate quantities. We found that the surface properties, size, and quantity of the anatase particles
were important for the formation of tubular HA particles. The tubular HA particles were not formed in the early stages of
the reaction, they were formed only after some crystal growth had occurred. The anatase particles controlled the nucleation
and crystal growth of HA. 相似文献
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水凝胶相中载体预陈化法合成NaX型沸石膜 总被引:2,自引:0,他引:2
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. 相似文献