水热合成中负离子配位多面体生长基元模型与粉体的晶粒粒度

在负离子配位多面体生长基元模型的基础上深入研究了晶粒的结晶过程,认为成核过程主要包括生长基元的形成和生长基元之间的脱水反应过程,并从成核速度的角度分析了影响晶粒粒度的主要原因,揭示了影响晶粒粒度的主要原因为生长基元的生成能,晶体的晶格能,由此总结出不同结构类型的氧化物粉体晶粒粒度的相对大小,合理地解释了由水热法制得的氧化物粉体的晶粒粒度差别较大的原因以及反应介质,反应温度对晶粒粒度的影响。     

晶粒与颗粒

晶粒与颗粒是两个概念完全不同的名词，在材料科学研究中，它们常用于描述材料的微观形貌和结构特征，经常容易被混淆。本文比较了晶粒和颗粒的定义，并归纳总结了晶粒尺寸及其形貌和颗粒粒度的测试方法．     

Bi4Ge3O12（BGO）微晶粒的水热法制备

以Ｂｉ２Ｏ３和ＧｅＯ２粉为起始物料，经水热反应制得Ｂｉ４Ｇｅ３ｏ１２（ＢＧＯ）微晶粒。晶粒粒度为５－２０μｍ；结晶完好的晶粒呈多面体状。文中对所用前驱物的形式、水热反应的物理－化学条件与产物物相，晶粒形貌关系作了总结。     

甲苯氨化制间甲苯胺

从甲苯制甲苯胺,一般只能得到邻位和对位异构体,而不易制得间位产物。最近美国的柯伐歇克(P.Kovacic)等发现:在Friedel-Craft反应条件下,以N-氯胺为氨化剂,可以制得收率较高的间位产物。不仅间甲苯胺可以用这一方法制备,而且其他的芳香族间位胺基化合物也可以在三氯化铝催化剂存在下高收率地制备出来。     

手性毛细管气相色谱的发展

当两个或两个以上的化合物,其结构的区别仅在于组成原子的空间排列不同时,这些化合物称为立体异构体。若两个异构体对偏振光的偏转方向相反而旋光度相等则称为对映体。对映体互为镜象关系时为手征性化合物。通常,由化学合成方法制得的手征化合物,往往都是外消旋体,而天然化合物则常是构形一定的手征化合物。人们已知,不同构形的旋光异构体,其生理活性(包括药理和营养作用等)、生物活性、毒性、香味、稳定性等可有很大的差别,如青霉素,在八个异构体中     

采用不同模板剂控制合成较大晶粒的ZSM-5分子筛

采用不同模板剂以及模板剂组合比较,研究了合成较大晶粒ZSM-5分子筛的过程。通过XRD表征产物的晶相结构,采用SEM观察了产物分子筛的晶粒大小。在分析不同模板剂的模板效应以及合成较大晶粒分子筛影响因素的基础上,提出了能够控制合成中等粒度ZSM-5分子筛的合成方法。结果表明,采用模板剂的不同组合可以控制合成出晶粒粒径在10 μm左右的均匀的较大晶粒分子筛。     

ZSM-5分子筛在MTP反应中的催化性能

合成了3种不同晶粒尺寸的ZSM-5分子筛,并制得MTP催化剂,对ZSM-5分子筛催化剂在MTP反应中的性能进行系统研究。采用XRD、SEM、N2物理吸附和TGA等对ZSM-5分子筛催化剂进行表征,发现小晶粒的ZSM-5分子筛具有良好的抗积炭性能,在MTP反应中具有较高的稳定性。采用小晶粒分子筛制成的催化剂,考察反应工艺条件对催化剂催化性能的影响,结果表明,丙烯选择性随反应温度和空速提高而增加,降低反应压力和提高水醇质量比也有利于提高丙烯选择性,为调整MTP工艺的产物分布和优化反应工艺条件提供了技术依据。     

碱式碳酸锌晶粒细化的工艺研究

为了使碱式碳酸锌晶粒细化,选用掺杂镁的方法降低碱式碳酸锌的晶粒度.具体方法如下:以碳酸氢铵作沉淀剂,在硫酸锌溶液中掺入一定质量的七水硫酸镁,采用直接沉淀法制得晶粒细化的碱式碳酸锌.考察了影响碱式碳酸锌晶粒度的主要因素,并通过正交试验寻求最佳工艺条件.通过研究,得出以下结论:在碱式碳酸锌中掺杂一定质量分数的镁元素可降低碱式碳酸锌的晶粒度.最佳工艺参数:硫酸锌溶液浓度,2.5 mol/L;碳酸氢铵溶液浓度,3 mol/L;搅拌速度,450 r/min;m(Mg)∶m(Zn)=1.07∶ 22,反应温度,60 ℃;碳酸氢铵滴加速度,12.5 mL/min.在此工艺条件下制得的碱式碳酸锌晶粒度为9.5 nm.     

原料粒度对煤基炭膜孔结构的影响

通过炭膜的孔径分布及ＳＥＭ结果分析，研究探讨了原料煤的颗粒度对煤基炭膜孔结构性能的影响。结果表明，不同原料粒度制得的炭膜具有不同的外观形态和孔隙结构。原料的颗粒度越小、越均一，所制得的炭膜平均孔径越小，孔隙结构越发达。因此，通过调节原料粒度可制得具有不同孔径和分布的炭膜。     

活化温度对LiMnPO_4固相反应制备过程的影响

以氢氧化锂、磷酸二氢铵和醋酸锰为原料,以聚乙二醇PEG-400为表面活性剂,经低热反应合成前驱体NH4MnPO4,再经固相反应制备LiMnPO4纳米晶体.对产物进行了表征,研究了活化温度对LiMnPO4生成过程的影响,探讨其可控制分步合成过程.结果表明,晶体生长动力学指数n=1.1,晶粒生长激活能E=20.98kJ/mol.在LiMnPO4晶粒生长过程中可通过调节温度控制LiMnPO4晶粒粒度.以LiMnPO4为材料制作析氢电极,电极因材料粒度不同在水溶液中催化析氢的程度不同,随电极材料粒度增大,析氢电极反应平衡电势负移.     

Effect of process parameters on the production of nanocrystalline silicon carbide from water glass

Nanocrystalline silicon carbide was synthesized from the precursor prepared by spray drying slurry of water glass and carbon black. The effect of process parameters, such as reaction temperature, reaction time and carbon content, on phase evolution, crystallite size and specific surface of the resulting samples were characterized by XRD, SEM and BET. The results show the powder produced in this process has a very fine crystallite size and high specific area and the reaction can be completed at 1550 °C for 2 h when the C/Si ratio is 5 or larger. In addition, the powder is of high purity, because sodium oxide in the precursor can be eliminated by the escape of sodium at high temperature. It is a simple and cost-efficient method to synthesize nanocrystalline silicon carbide using cheap and abundant water glass as silicon source.     

水热法制备BiVO_4及其光催化性能研究

采用水热反应法并改变反应条件制备不同形貌和晶体结构的BiVO4可见光催化剂,并探讨不同形貌BiVO4的形成机制及其光催化活性的影响因素。借助X-射线衍射（XRD）、扫描电子显微镜（SEM）及固体紫外-可见漫反射光谱（DRS）对产品进行表征,并在可见光（λ〉420 nm）照射下考察其降解亚甲基蓝（MB）的光催化性能。结果表明,高温更有利于单斜型钒酸铋的生成,反应初始pH值对钒酸铋的形貌影响较大。反应过程中,前驱液中的颗粒通过溶解再结晶、定向聚集自组装、熟化过程最终形成不同形貌的钒酸铋颗粒。钒酸铋的光催化降解速率主要受其晶粒粒径和晶体微观应变的影响,晶粒粒径越大,微观应变越小,结晶度越好,降解速率越高。     

Phase development of barium titanate from chemically modified-amorphous titanium (hydrous) oxide precursor

A synthesis procedure for barium titanate involving a chemically modified titanium precursor has been developed. Using a titanium isopropoxide precursor modified with acetylacetone and barium acetate, coprecipitated gels were obtained by addition to a KOH solution. Direct precipitation of cubic BaTiO₃ from such precursor suspensions was obtained under hydrothermal conditions. The pH value was found to be a critical reaction parameter such that production of phase pure BaTiO₃ required high pH (>13.0), a finding consistent with thermodynamic predictions of the Ba–Ti–H₂O stability system and prior hydrothermal syntheses. It was determined that phase-pure barium titanate can be synthesized at temperatures as low as 50 °C and that higher reaction temperatures accelerate the crystallization process. The particle size of the synthesized powder ranged from 50 to 350 nm for the synthesis conditions explored in the current work.. It was demonstrated that particle size can be controlled by proper selection of the hydrothermal synthesis conditions such as reaction concentration, temperature, and time. The chemically modified synthesis produces barium titanate more rapidly at lower reaction temperatures than previously reported for similar syntheses.     

旋转床-水热耦合法制备改性氢氧化铝的研究

利用旋转填充床碳分-水热耦合法制备改性氢氧化铝。考察了碳分过程中的沉淀pH值、温度以及水热处理条件等对产物失重、粒径及收率的影响。结果表明，旋转填充床在不同条件下碳分可得拟薄水铝石、γ-A1OOH和拜尔石等多种氧化铝水合物，均可作为先驱物，在温度130℃以上，改性剂与先驱物摩尔配比高于0．7时，制备出失重温度为360℃，失重率在52％左右，平均粒径在120nm左右超细的改性氢氧化铝，可用作热塑性塑料的阻燃剂。     

体相掺镁球形钴酸锂前驱体的制备及表征

文章通过沉淀法合成了体相掺杂镁元素的球形钴酸锂正极材料前驱体。通过SEM形貌、密度测量、粒度表征等手段研究了共沉淀工艺对合成体相掺杂镁元素钴酸锂前驱体的影响,并通过EDS及ICP测试表征了镁元素掺杂的均匀性。研究结果表明:共结晶的反应时间对颗粒密度、颗粒形貌、粒度大小及分布有较大的影响,随着时间延长密度逐渐增加,颗粒形貌变好,粒度变大且趋于集中;共结晶体相掺杂镁的钴酸锂前驱体,镁元素能达到原子级混合均匀的要求;掺杂镁后,钴酸锂前驱体四氧化三钴物相未发生变化。掺镁钴酸锂前驱体在高压实密度钴酸锂得到了广阔的应用。     

超声波一直接沉淀法制备超细氧化铁

将超声波用于以硫酸亚铁铵、草酸为原料的直接沉淀法制备超细氧化铁。对氧化铁的前驱体——草酸亚铁的合成及焙烧工艺进行了详细研究。讨论了反应温度、物料浓度、超声沉淀反应时间以及焙烧温度、焙烧时间对氧化铁粒度的影响。结果发现，在一定的试验条件下，可获得粒度小于40nm的氧化铁。XRD实验表明，所合成的Fe2O3为α型，TEM的测试结果平均粒径为20nm，且分散性好。     

Non-isothermal decomposition kinetics of nano-scale CaCO3 as a function of particle size variation

We report the synthesis of nanocrystalline calcium carbonate with varying particle sizes by precipitation techniques from an aqueous solution of calcium nitrate and sodium carbonate at controlled pH. The particle size of the carbonate powder was precisely controlled by changing the precursor concentration. The synthesized carbonate powders were characterized by using scanning electron microscopy, X-ray diffraction technique, and transmission electron microscopy. The particle size, along with the crystallite size of as-synthesized carbonate powder, decreases with increasing precursor concentration. The non-isothermal decomposition kinetics of the carbonate powder was also evaluated by using near to the modified Arrhenius equation's exact solution. The experimental results were best fitted at n = 0.5, and the one-dimensional diffusion-controlled transport process mechanism (D₁) and one-dimensional phase boundary movement mechanism (R₁) was found to be very close fit of the corresponding evaluated g(α) value. The apparent activation energy of the nano calcium carbonate decomposition was found in the range of 120–175 kJ/mol, which is also inherently functioning with the average particle size. The apparent activation energy of decomposition of CaCO₃ found to be decreased with decreasing average particle size of nanocrystalline calcium carbonate.     

Synthesis and characterization of nanocrystalline NiO-GDC via sodium alginate-mediated ionic sol-gel method

In this study, nanocrystalline nickel oxide gadolinium-doped ceria (NiO-GDC) powder was synthesized in-situ using Na-Alginate as the template via ionic sol-gel technique. The effects of calcination time and temperature on the particle size and the physiochemical properties of nanocrystalline NiO-GDC are presented in this paper. Using this method, gel beads were formed by contacting sodium alginate solution as the gelling template and metal (gadolinium/cerium/Ni) nitrates as the precursor. The obtained nanocrystallites were characterized using Field Emission Scanning Electron Microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy, thermo gravimetric analysis, nitrogen adsorption/desorption analysis, and Fourier transform infrared spectroscopy. It was observed that the increasing calcination temperature had affected both the particle size and the surface area of the NiO-GDC, whereas the increasing calcination time had only impacted the size of the particles. The smallest mesoporous nanocrystalline NiO-GDC powder (12.1225 ± 0.005 m²/g surface area), composed of cubic GDC (5.18 nm crystallite size) and cubic NiO (7.99 nm crystallite size) were synthesized at a calcination temperature of 500 °C for 2 h. This study hopes to inspire more researches on the ionic-gelation method for synthesizing other metal nanostructures as well as other reaction parameters.     

Low-Temperature Chemical Synthesis of Nanocrystalline MgAl2O4 Spinel Powder

Nanocrystalline MgAl₂O₄ spinel powder was synthesized by pyrolysis of complex compounds of aluminum and magnesium with triethanolamine (TEA). The soluble metal ion–TEA complexes formed the precursor material on complete dehydration of the complexes of aluminum–TEA and magnesium–TEA. Single-phase MgAl₂O₄ spinel powder resulted after heat treatment of the precursor material at 675°C. The precursor and the heat-treated powders were characterized by X-ray diffractometry (XRD), differential thermal and thermogravimetric analysis, and transmission electron microscopy (TEM). The average crystallite size as measured from the X-ray line broadening was around 14 nm and the average particle size from TEM studies was around 20 nm.     

Comparative analysis and antibacterial properties of thermally sintered apatites with varied processing conditions

Hydroxyapatite (HA) and biphasic hydroxyapatite/beta-tricalcium phosphate (biphasic HA/β-TCP) were synthesized using thermal sintering. The parameters- sintering temperature (600°C, 900°C, and 1200°C), biological source used (fish bone, egg shells, and fish scales), and soaking time (2, 6, and 10 hours) were permuted to study their effects on the properties of the resultant apatite. Morphological study revealed that the smallest (60 nm) spherical particle and the largest (470 nm) irregular shaped particle were obtained from the fish bone sample sintered at 600°C and at 1200°C respectively. FTIR and XRD results showed that as the sintering temperature is increased, the phase transformation from HA to β-TCP takes place. Only the final products from fishbone sample at 600°C are pure carbonated HA. The crystallinity of synthesized particles ranged from 79% to 98%. Soaking time has no effect on phase composition of the apatite but has significant effect on crystallite size; increase in soaking time increases crystallite size and particle shape becomes more spherical. Interestingly, the fish bone sample sintered at 900°C has higher crystallinity and crystallite size compared to the fish scale sample sintered at the same temperature. EDX confirmed that non-stoichiometric apatite with Ca/P ratio ranging from 1.47 to 1.91 can be obtained by varying the sintering conditions. The antibacterial test revealed that both calcium apatite obtained from fish bones and fish scales have inhibited bacterial growth; apatite from fish bone works faster than fish scales. The in vitro cytotoxicity test ensured that all the calcium apatite except for eggshell are non-cytotoxic. Thus, apatite with excellent microbial activity can be obtained by using fish wastes, and by tuning the sintering parameters, the apatite with desired types and properties can be synthesized for different biomedical applications.