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硫酸盐类晶体中[SO_4]~(2-)四面体的结晶方位与晶体的形貌 总被引:2,自引:0,他引:2
本文从硫酸盐类晶体中负离子配位多面体的结晶方位和相互联结的稳定性出发,探讨了硫酸盐类晶体中[SO4]2-结晶方位与晶体结晶形貌之间的关系;认为[SO4]2-四面体与金属阳离子(Ba2 、Ca2 、Mg2 …)结合时,由于晶体结构和生长条件(如温度、过饱和度等)的不同,在晶体各族晶面上的叠合速率和取向不同;晶体的结晶形貌迥然有别.晶体的结晶形貌与[SO4]2-四面体在晶体中的结晶方位密切相关,四面体的面和棱的法线(L2)所对向的晶面,生长速率慢,顽强显露,均属晶体的板面;四面体的顶角所指向的晶面,生长速率快,显露面积小,经常消失. 相似文献
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钨酸盐晶体中负离子配位多面体的结晶方位与晶体的形貌 总被引:7,自引:0,他引:7
钨酸盐类晶体是重要的闪烁晶体.本文从钨酸盐类晶体中负离子配位多面体的结晶方位和相互联结的稳定性出发,探讨了钨酸盐类晶体中[WO4]2-等负离子配位多面体的结晶方位与晶体结晶形貌之间的关系;认为[WO4]2-四面体与金属阳离子(Ca2+,Pb2+,Zn2+)结合时,由于晶体结构和生长条件(如籽晶取向等)的不同,在晶体各族晶面上的叠合速率和结构取向不同,晶体的结晶形貌迥然有别;四面体的面和梭的法线(L2)所对向的晶面,生长速率慢,顽强显露,均属晶体的板面;四面体的顶角所指向的晶面,生长速率快,显露面积小,经常消失.由此可以合理解释钨酸铅等闪烁晶体的生长特征.最后对ABO4型晶体的结构及习性特征进行了总结归纳. 相似文献
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若干晶体中氧八面体结晶方位与晶体形貌 总被引:1,自引:0,他引:1
本文从结晶化学角度出发,研究了AB和A2B3和ABO3型氧化物晶体中的氧配位八面体的结晶方位与晶体结晶形貌之间的关系,提出晶体的结晶形貌是受晶体中负离子配位多面体结构和结晶方位所制约的。配位多面体顶角所对向的晶面生长速率最快,而面所对向的晶面生长速率最慢,配位体的棱所对向的晶面,生长速率居于两者之间,负离子配位多面体在晶体中的各个面族上连接和稳定性,决定了晶面的显露程度和晶体的结晶形貌。 相似文献
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采用热台偏光显微镜技术观察了聚苯硫醚(PPS)及其玻璃纤维、 炭纤维及芳纶纤维增强复合材料等温结晶过程中球晶结构形态的变化。研究了等温结晶温度对PPS的晶体形态及球晶生长速率的影响。结果表明, 结晶温度对PPS的结晶影响非常明显。在235~265℃, 随着等温结晶温度的升高, 聚苯硫醚球晶形态发生了从细小而具有部分束状结构到大而完善再到细小而不完善的变化过程, 球晶的生长速率随着结晶温度的增大呈非线性下降。而纤维的存在使PPS的结晶形态发生了从球晶结构到横穿晶的变化, 且不同纤维诱导形成横穿晶的程度有所不同。其中玻璃纤维和芳纶纤维可以诱导形成较为明显的横穿晶形态, 而炭纤维则不能诱导形成明显的横穿晶。 相似文献
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结晶性聚合物在熔融态冷却过程中,往往伴随着球晶的生成,球晶的密度和尺寸分布直接影响到制品的热力学、光学及力学性能。文中研究了聚合物冷却过程中球晶的形态学演变;模拟了球晶在生长过程中的形态演化过程;考察了成核诱导时间、成核密度、生长速率和碰撞对球晶形态变化的影响;比较了等温和非等温条件下聚合物的结晶过程。研究结果表明,在等温结晶过程中随着温度的降低,晶粒越来越细化,结晶程度越来越大,球晶碰撞边界为直线;非等温结晶过程中由于温度一直在降低,不断出现新的球晶,晶体大小不一,碰撞后边界为曲线。 相似文献
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本文从结晶化学角度研究了Li2B4O7晶体结构,根据晶体的结构基元为[B4O9]^6-络阴离子,并用计算机绘出了该络阴离子在{001},{100},{110}面上的投影,由[B4O9]^6-络阴离子的结晶方位和分布确定了晶体的开裂是沿着络阴离子之间相连接的桥氧部位所断裂的。 相似文献
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钛合金中TiC晶体的配位多面体生长基元与生长习性 总被引:3,自引:0,他引:3
铸造钛合金中存在八面体、棱面枝晶及光滑树枝晶等不同形态的TiC.本文结合定向凝固试样组织,用配位多面体理论分析了钛合金中TiC的生长基元及生长习性.认为TiC的配位多面体生长基元为六配位的TiC6,TiC6生长基元堆积时, {100}面族和{111}面族上的生长速率不同,容易形成以{111}面为显露面的八面体状TiC晶胚.TiC晶胚在熔体中生长时,在生长速率最快的<100>方向上生长出二次枝晶臂,并在生长过程中始终保持小面界面生长特征,最终形成棱面枝晶状TiC.如TiC晶体生长时生长速率慢的面族上形成大量的螺旋位错等缺陷,则棱面消失,形成树枝晶TiC. 相似文献
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Synthesis of nm-sized barium titanate crystallites using a new LTDS method and their characterization 总被引:2,自引:0,他引:2
A new LTDS method was established to synthesize nm-sized barium titanate crystallites with particle sizes around 10 nm. This LTDS method was the following two features, i.e., (1) a heat of neutralization in a neutralization reaction between strong acid and base can be used as a driving force for a formation of barium titanate, and (2) barium titanate crystallites can be directly synthesized from Ti and Ba ions, not via intermediates. Therefore, using the LTDS method, it can be expected that there is no minimum limit in particle sizes, and also no contamination in barium titanate crystallites. At first, optimum conditions for a formation of barium titanate were screened at various reaction temperatures and Ba/Ti atomic ratios in the starting materials. As a result, the formation of barium titanate was found at higher reaction temperatures than 50°C and higher Ba/Ti atomic ratios than 5. Under a constant temperature, particle sizes decreased with increasing Ba/Ti atomic ratios while under a constant Ba/Ti atomic ratio, particle sizes were independent of reaction temperatures. Finally, barium titanate crystallites with particle sizes below 10 nm were first prepared. These particles were also characterized using various methods. 相似文献
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Surface structure studies on various {1120} (second order prism) faces of synthetic quartz crystals are reported. Horizontal
striations and polygonal growth pyramids are predominant on these faces. Growth layers modified by the presence of guest microcrystals
attached to the host second order prism faces are illustrated and explained. It is shown that microcrystals and impurities
influence growth and development of second order prism faces of synthetic quartz crystals. Mechanism of growth of these faces
is assessed in the light of the observed surface structures. 相似文献
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The morphology and size of hydroxyapatite Ca10(PO4)6(OH)2 (denoted HAP) can be controlled under hydrothermal treatment assisted with different dendrimers, such as carboxylic terminated poly(amidoamine) (PAMAM) and polyhydroxy terminated PAMAM. The structure and morphology were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and transmission electron microscopy (TEM). IR spectra were also used to investigate the complexation of Ca2+ with PAMAM. The results revealed that the inner cores of the PAMAM dendrimers are hydrophilic and potentially open to calcium ions, since interior nitrogen moieties serve as complexation sites, especially in case of the polyhydroxy terminated PAMAM. And the reasonable mechanism of crystallization was proposed that it can be attributed to the localization of nucleation site: external or interior PAMAM. Additionally, the PAMAM dendrimer with carboxylic and polyhydroxy groups has an effective influence on the size and shape of hydroxyapatite (HAP) nanostructures. Different crystal morphology was accomplished by adsorption of different dendrimers onto specific faces of growing crystals, altering the relative growth rates of the different crystallographic faces and leading to different crystal habits. 相似文献
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《晶体工程》2000,3(3):195-200
Ce doped barium strontium titanate single crystals have been grown by high temperature solution growth technique with different concentrations of Cerium. The structure of the crystals has been solved by single crystal X-ray diffraction. The structural properties, filling coefficients and the thermal properties are presented. 相似文献
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Barium titanate powders have been prepared by calcining barium titanyl oxalate precipitated by the Clabaugh and Merker processes,
and their crystallization kinetics, morphology, and phase composition have been assessed. The results demonstrate that the
Clabaugh process allows one to obtain powders with a low content of residual phases and tune the grain size (68–1935 nm) and
crystal structure of barium titanate in wide ranges. The powders prepared through the Merker process have a narrower range
of crystallite sizes (110–740 nm) and higher content of residual phases. 相似文献
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Processing of chemical solution-deposited BaTiO<Subscript>3</Subscript>-based thin films on Ni foils
Tanawadee Dechakupt Song Won Ko Sheng-Guo Lu Clive A. Randall Susan Trolier-McKinstry 《Journal of Materials Science》2011,46(1):136-144
BaTiO3 films on base metal foils are of interest for capacitor applications, but the processing requires reducing atmospheres that
influence the film defect chemistry and density. In this study, powders dried from barium titanate solutions and barium titanate
films were studied by X-ray diffraction, differential scanning calorimetry, thermal gravimetric analysis, infrared spectroscopy,
and spectroscopic ellipsometry at various points in the processing. It was found that atmospheres designed to minimize Ni
oxidation delay decomposition of organics, leading to retained carbonate phases. Thus, crystallization of the barium titanate
occurs via decomposition of a barium carbonate phase. Retained organics that are present during high temperature processing
can cause porosity in the films. On annealing at 1000 °C, there is slightly increase in the refractive index of the film due
to further crystallization and densification. The final refractive index is comparable to that of 95% dense barium titanate
ceramics. Re-oxidation did not change the refractive index of the film over the wavelength range from 350 to 650 nm. 相似文献
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Following the Kinetics of Barium Titanate Nanocrystal Formation in Benzyl Alcohol Under Near‐Ambient Conditions 下载免费PDF全文
Sjoerd A. Veldhuis Tomasz M. Stawski Pablo Gonzalez Rodriguez Huiyu Yuan Rogier Besselink Liane G. Benning Johan E. ten Elshof 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(40)
In complex chemical syntheses (e.g., coprecipitation reactions), nucleation, growth, and coarsening often occur concurrently, obscuring the individual processes. Improved knowledge of these processes will help to better understand and optimize the reaction protocol. Here, a form‐free and model independent approach, based on a combination of time‐resolved small/wide‐angle X‐ray scattering, is employed to elucidate the effect of reaction parameters (such as precursor concentration, reactant stoichiometry, and temperature) on the nucleation, crystallization, and growth phenomena during the formation of nanocrystalline barium titanate. The strength of this approach is that it relies solely on the total scattered intensity (i.e., scattering invariant) of the investigated system, and no prior knowledge is required. As such, it can be widely applied to other synthesis protocols and material's systems. Through the scattering invariant, it is found that the amorphous‐to‐crystalline transformation of barium titanate is predominantly determined by the total amount of water released from the gel‐like barium hydroxide octahydrate precursor, and three rate‐limiting regimes are established. As a result of this improved understanding of the effect of varying reaction conditions, elementary boundary conditions can be set up for a better control of the barium titanate nanocrystal synthesis. 相似文献
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Magnetite crystals with unique morphological characteristics have been grown from hematite under hydrothermal conditions at 150 and 175 °C in the presence of hydrazine and copper (II) oxide. In the absence of CuO, octahedral crystals of magnetite with a distribution of particle sizes were grown in accordance with literature procedures. In the presence of CuO, magnetite crystals with distorted morphology were prepared in which the [111] crystal faces were absent, leaving a framework structure of corners and edges. Examples of crystal intergrowths were observed, as well as the partial collapse of the framework structure of the magnetite. The results are discussed with reference to the possible effect of copper redox couples on the hematite reduction reaction. 相似文献