Nb:KTP晶体的水热法生长研究

文章研究了水热法Nb:KTP晶体的生长习性以及矿化剂体系、籽晶片的取向、矿化剂溶液的填充度对水热法生长Nb:KTP晶体的影响。在上述研究的基础上,采用水热法生长出了尺寸达28.2×24.2×9.8mm3无色透明的Nb:KTP晶体。     

硅酸铋晶体的结晶习性与形貌

从结晶化学角度出发，研究了熔体提拉法生长硅酸铋（ＢＳＯ）晶体的结构与形貌，提出晶体的生长基元为［ＢｉＯ６］ｎ＾９－和［Ｂｉ１２ＳｉＯ３６］ｎ＾３２－负离子配位多面体的论点。研究了晶体中各族晶面的显露程度与［ＳｉＯ４］ｎ＾４－四面体结晶方位的对应关系，晶体中的正极面与硅氧四面体面平等；四面体的顶角正在对负极面。     

水热法生长Mg（OH）_2晶体研究

以MgCl2.6H2O、NH3.H2O为原料,水作为水热介质,乙二醇作为表面活性剂,研究了在不同温度条件及表面活性剂用量对水热法生长Mg（OH）2晶体的影响。利用X-射线衍射仪（XRD）和扫描电子显微镜（SEM）对所制得氢氧化镁颗粒的晶相和形貌进行了表征。实验结果表明,增加乙二醇的用量,有助于获得结晶性和分散性较好的Mg（OH）2晶体。同时,随着生长温度的升高,Mg（OH）2晶体形貌从球状外形的片状晶体向分散的小晶粒过渡。     

水热法制备纳米氧化锆晶体

用水热法制备出了粒径10nm左右且分布均匀的氧化锆晶体,发现矿化剂的添加、反应温度的高低都是水热法制备氧化锆晶体过程中重要的影响因素。同时当反应溶剂为无水乙醇时,我们制备得到了直径6～12nm不等的氧化锆晶体,作者探讨了乙醇的羟基在晶体生长过程中的作用。     

BaAlBO3F2晶体的生长与形貌

以NaF为助熔剂,BaAlBO3F2和NaF摩尔比为11.5,采用熔盐籽晶生长方法,沿[001]方向生长出尺寸为18 mm×18 mm×12 mm的BaAlBO3F2(BABF)晶体.晶体生长参数降温速率为2～4℃/d,晶体旋转速率为15 r/min.研究了BABF晶体的生长形貌,BABF晶体生长过程中,呈现出(001)和(100)晶面.测试了BABF的粉末倍频效应,其倍频系数约为KDP晶体倍频系数的0.8倍.室温下测试了BABF晶体的显微硬度,其(001)面与(100)面显微硬度分别为10.99 GPa和8.137 GPa.     

三聚磷酸钠对二水石膏晶体生长习性与晶体形貌的影响

三聚磷酸钠是建筑石膏高效缓凝剂.用扫描电镜和X射线光电子能谱研究了三聚磷酸钠对建筑石膏凝结硬化、液相离子浓度与过饱和度、二水石膏晶体生长习性与形貌的影响.从晶体生长的角度分析了三聚磷酸钠对二水石膏的作用机理.结果表明:三聚磷酸钠显著改变了二水石膏晶体的生长习性,使其由针状变为短柱状或板状,且晶体尺度增加;三聚磷酸钠通过化学作用选择吸附在二水石膏晶体(111)面,抑制其在c轴方向的生长;改变了晶面在不同轴向的相对生长速率,使二水石膏晶体生长习性和形貌发生了改变;三聚磷酸钠使石膏液相离子浓度和过饱和度降低,晶体成核几率和成核速率降低,导致二水石膏晶体粗化.     

氧化锌晶体的水热法生长及其性能研究

报道了采用水热法生长大尺寸氧化锌单晶体的研究结果.以块状氧化锌陶瓷为培养料,以KOH、LiOH和H2O2的混合水溶液为矿化剂,在温度为350℃～400℃、压力为120MPa的条件下,生长出了尺寸为31.5mm×23.5mm×6.5mm的ZnO晶体.测量了晶体的杂质含量、光吸收率和双晶摇摆曲线.     

水热法反应条件对纳米硼酸盐形貌的影响研究进展

纳米硼酸盐兼具硼酸盐和纳米材料两者性能,在阻燃剂,光学,电池储能等领域具有很大的应用价值,而纳米材料的优越性能很大程度上取决于其形貌,本文综述了利用水热法制备纳米硼酸盐反应温度,反应时间,表面活性剂等反应条件对纳米硼酸盐形貌的影响研究进展,为可控制备特定形貌的纳米硼酸盐提供科学参考。     

KTiOAsO_4晶体的水热法生长

文章报道了水热法生长KTiOAsO4晶体的结果,结果表明,以KH2AsO4和TiO2为培养原料,2mol/L KF为矿化剂,生长出了尺寸可达19×20×12mm3（a×b×c）的KTA晶体,晶体沿（011）方向的生长速度为0.10mm/d,晶体的透过率测试结果表明：晶体在450nm~2500nm波段内透过率60%以上。     

The role of hydrothermal pathways in the evolution of the morphology of ZnO crystals

Understanding growth mechanisms usually leads to the successful preparation of a targeted microstructure. However, the large number of parameters that influence the shape and the size of nanostructures often make it difficult to predict the outcome. We investigated the growth of wurtzite-type ZnO by closely following such a multistage process. We associated the diverse morphology of the precipitated crystals, prepared under the same hydrothermal conditions, to the differences in the transient crystallization processes during the precipitation. By altering the pH of the suspension after the precipitation, we gain control over the resulting morphology of the ZnO and show how to grow identical crystallites with different shapes and crystal sizes. Here we report, for the first time, on how ZnO platelets grow in a certain Zn²⁺/OH⁻ ratio along the basal and one of the prismatic directions to form sphalerites with very high surface area. We also offer an explanation as to how sphere-like hierarchical structures composed of plate- or rod-like ZnO crystals form through self-assembly driven processes.     

Biomolecule and surfactant-assisted hydrothermal synthesis of PbS crystals

PbS crystals were hydrothermally synthesized using Pb(NO₃)₂, l-cysteine, and N-cetyl pyridinium chloride in solutions with different pH values at 140 °C. Flower-like, granular and truncated cubic PbS crystals composing of Pb and S were detected using an X-ray diffractometer (XRD), a scanning electron microscope (SEM), a transmission electron microscope (TEM), a selected area electron diffraction (SAED) technique and an energy dispersive X-ray (EDX) analyzer. In addition, a Raman spectrometer revealed the presence of the first and second overtone modes at 436 and 602 cm⁻¹, respectively. Emission spectra of the products were detected at 412 nm using a photoluminescence (PL) spectrometer.     

Growth,morphology, and reinforcement potential of low molecular weight crystals in amorphous polymeric matrices

The technique of in situ crystallization of low molecular weight organic compounds from amorphous polymers was evaluated as a method of fabricating composite materials. Two workable systems, styrene–acrylonitrile copolymer (SAN)–acetanilide and SAN–anthracene, were found and their phase diagrams determined. In both systems kinetic studies revealed that the maximum crystallization rate takes place at large degrees of supercooling and that below these temperatures the mechanism is diffusion-controlled. The temperature-dependent crystal morphologies were characterized with electron microscopy, which showed three distinctly different morphologies for both systems. From dynamic mechanical measurements, it appears that the elastic moduli of organic crystals are about the same as those of organic polymers in the glassy state, and that relatively little reinforcement took place under the particular crystallization conditions employed.     

Movement of dislocations in polyoxymethylene crystals and related morphology

In crystals of polyoxymethylene grown from bromobenzene the movement of screw dislocations can be traced by the slip-steps resulting on the surface of the crystals. Slip-steps produced by screw dislocation movement were observed in crystals composed of a single spiral, two spirals of opposite sense and two spirals of the same sense. Other processes that form steps resembling a slip-step were also observed.     

Tunable morphology of aluminum oxide whiskers grown by hydrothermal method

Hydrothermal method was used to grow α-Al₂O₃ whiskers by using hydrated aluminum sulfate, urea and poly ethylene glycol as precursors. X-ray diffraction (XRD), selected area electron diffraction (SAED), and high resolution transmission electron microscope (HRTEM) were used to characterize morphology of the whiskers. By increasing the pH of the solution (by adding extra NaOH), by adjusting calcination times and atmospheres it was possible to tune the whiskers morphology and their aspect ratio. Aspect ratio as high as 25 was obtained after hydrothermal treatment of a solution having pH 3 followed by calcination in Ar or N₂ atmosphere at 1200?°C for 6 h.     

Supercritical hydrothermal synthesis of titanium dioxide nanostructures with controlled phase and morphology

A novel template- and organic-free synthesis of TiO₂ nanostructures with controlled phase and morphology was realized through batch supercritical hydrothermal treatment (400 °C) of titanate nanotubes (TNTs) with H₂O₂ in NaOH aqueous solution. Well-defined 3D titanate hierarchical spheres (THSs), 2D multilayered titanate nanosheets (TNSs), and 1D monodisperse anatase nanorods (ANRs) exposing (0 1 0) facets were prepared in 15 min by slightly varying the NaOH solution pH. Specifically, the obtained Na/H-THSs (without/with HCl neutralization) exhibited highly porous structures with large specific surface area (109 m² g⁻¹ and 196 m² g⁻¹, respectively). Temperature-dependent phase and morphology evolutions of products under subcritical condition (200 and 300 °C) were investigated. The formation of the TiO₂ nanostructures from TNTs was proposed mainly following a dissolution–nucleation-growth mechanism, suggesting that both supercritical temperature and NaOH solution pH were determinant factors governing the nucleation and growth process and thus the phase and morphology.     

Growth kinetics of ammonium- and potassium-dihydrogen phosphate crystals

Growth rates of ammonium- and potassium-dihydrogen phosphate crystal faces have been measured in a simple laboratory apparatus under carefully controlled conditions of temperature, supersaturation and solution velocity. The growth process, which was found to be second-order with respect to the supersaturation, is considered to be controlled by surface reaction. Growth rates of the ammonium salt (ADP) are much higher than those of the potassium-salt (KDP) under equivalent conditions. It is suggested that this is due to the occurrence of hydrogen bonding between ADP molecules, which give larger integrating units (thicker growth layers) than occur with KDP.     

Compared structure and morphology of nylon-12 and 10-polyurethane lamellar crystals

A comparative study of the structure and morphology of nylon-12 and 10-polyurethane (10-PUR) lamellar crystals, was carried out. Lamellar crystals were obtained by isothermal crystallization from diluted solution. Electron diffraction of lamellae combined with WAXS data recorded from crystal sediments indicated that nylon-12 crystallized in either α-form or γ-form according to the solvent chosen for crystallization. The α-form was the crystal modification predominant in doubly oriented films of nylon-12 prepared by epitaxial crystallization. On the contrary, 10-PUR invariably crystallized in α-form regardless crystallization conditions. The α-form of nylon-12 and 10-PUR shared the same crystal structure with hydrogen-bonded sheets made of antiparallel chains and stacked with progressive shifting along both b and c directions. Lamellar crystals of nylon-12 in γ-form and 10-PUR in α-form displayed similar morphological features but only the former appeared to be sensitive to temperature. Upon heating the nylon-12 crystals near to melting, the real-time WAXS analysis evidenced the occurrence of a partial γ-to-α crystal transition, and in situ AFM observations revealed the appearing of more or less regular ridges on the crystal surface. None of these changes were observed in 10-PUR crystals when subjected to similar treatment.     

间歇冷却结晶中硫酸铵晶体粒度及形态调控

在间歇冷却结晶器中,采用激光法测定了(NH_4)_2SO_4溶液的介稳区宽度。讨论了冷却速率以及搅拌速率对(NH_4)_2SO_4晶体粒度和形态的影响,给出了优化操作条件。得到平均长度8.0 mm和宽度1.0 mm的针状(NH_4)_2SO_4晶体。此外,研究了添加CaCO_3颗粒对(NH_4)_2SO_4晶体粒度和形态的改变。当CaCO_3添加量(质量分数)为2.0%时,(NH_4)_2SO_4晶体由针状变为均匀颗粒状,平均粒度1.7 mm。研究了CaCO_3对(NH_4)_2SO_4晶体粒度和形态的影响机理。由结果可知:Ca CO3颗粒充当了(NH_4)_2SO_4非均相成核的催化剂,诱导(NH_4)2_SO_4在比均相结晶更低过饱和度下结晶,减少了(NH_4)_2SO_4(001)晶面的生长时间。此外,Ca CO3颗粒表面优先占据了(NH_4)_2SO_4(001)晶面的活性生长点位,抑制了(001)晶面的生长,从而使(NH_4)_2SO_4晶体粒度和形态改变。