Hydrothermal synthesis and characterization of LiNbO3 crystal

Lithium niobate crystal was successfully synthesized via hydrothermal synthesis method using LiOH·H₂O or LiNO₃ and Nb₂O₅ as starting materials in water or ammonia solution. X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectra and Scanning electron microscopy (SEM) were used to characterize the as-prepared samples. The synthesis conditions such as crystallization temperature and time as well as ammonia concentration (when using LiNO₃ as Li source) were investigated. The results demonstrate that the crystallization and purity of the as-prepared samples were increased with the increase of time when temperature was at 260 °C. When using LiNO₃ as Li source a basic solution was necessary to synthesize LiNbO₃. In the present work ammonia solution was used instead of water to obtain alkalescence solvent. XRD results revealed that the as-prepared samples had a hexagonal structure. FT-IR results displayed that the LiNbO₃ phase could be completely formed and no secondary phase was found under proper conditions. SEM picture showed that the morphology of the sample was more perfect and bigger with increasing reaction time.     

Calorimetric studies of the adsorption thermodynamic properties of the very large pore molecular sieve VPI-5

Calometric measurements of the heat of adsorption of nonpolar molecules on VPI-5 were performed at 303 K and compared with the results of measurements of the same molecules on the silica faujasite (US-Ex). Both microporous adsorbents show similar adsorption behavior, which is due mainly to the fact that both solids are neutral and comparable in the diameter of the pores or cavities, respectively. The heat curves of ethane, n-butane, n-pentane, and n-hexane on VPI-5 are compared also with the corresponding curves on AIPO₄-5 and AIPO₄-11. From this comparison, it follows that the adsorption heat increases with increasing framework density (or decreasing pore diameter). With decreasing pore diameter, the entropy of the adsorbed molecules also decreases.     

无助剂水热合成CdS微球

利用水热合成法,在不使用任何辅助剂的条件下,制备出形貌均一的CdS微球。利用X射线衍射(XRD)、扫描电镜(SEM)对样品的结构和形貌进行了表征。结果表明水热合成避免了S2-离子的氧化,在适当的保温温度和保温时间下得到了具有明显量子尺寸效应的表面光滑的CdS微球。     

Phase-selective synthesis of a silicoaluminophosphate molecular sieve from dry gels

Silicoaluminophosphate (SAPO) molecular sieves with AFI and CHA structures have been synthesized from a reaction mixture containing triethylamine (TEA) as a template or structure-directing agent. The syntheses were carried out at 180-200 °C for several days both from dry gels (dry gel conversion) and homogeneous gels (conventional electric heating). From similar reaction mixtures, SAPO-5 (AFI structure) and SAPO-34 (CHA structure) molecular sieves are phase-selectively obtained from dry gel conversion and conventional electric heating, respectively. The phase-selectivity may be explained by the slow crystallization of the dry gel conversion due to low water or TEA concentration under the reaction conditions and the difference of the relative stability of SAPOs (AFI < CHA) under hydrothermal conditions. This phase-selective synthesis with dry gel conversion may lead to a new method for the synthesis of relatively unstable molecular sieves (having large pores) such as VFI or VPI-5.     

Growth and study of some gel grown group II single crystals of iodate

Single crystals of calcium iodate and barium iodate were grown by simple gel technique by single diffusion method. The optimum conditions were established by varying various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of the reactants etc. Crystals having different morphologies and habits were obtained. Prismatic, dendritic crystals of barium iodate and prismatic, needle shaped, hopper crystals of calcium iodate were obtained. Some of them were transparent, some transluscent, and few others were opaque. Both the crystals were studied using XRD, FT-IR, and thermal analysis. The crystals were doped by iron impurity. The effect of doping was studied using IR spectroscopy and thermal analysis.     

On the synthesis of the aluminophosphate molecular sieve AIPO4-5

The possibility that formation and stabilization of tetrahedral Al is necessary for the synthesis of a pure AlPO₄-5 phase is examined in relation to the preparation of the reaction mixtures. The Al coordination in the reaction mixtures and products has been characterized by means of solid-state high-resolution ²⁷Al n.m.r. It is concluded that the role of the template (triethylamine) in the formation of AlPO₄-5 is to stabilize the newly created tetrahedral Al and to prevent conversion to octahedral Al by shielding from attack by water.     

资源化利用铁尾矿制备全硅介孔分子筛MCM-41

以鞍山铁尾矿为硅源,CTAB为模板剂,采用水热合成法合成出全硅介孔分子筛MCM-41。采用X射线衍射分析研究了pH值、CTAB与SiO2配比、晶化温度和晶化时间对MCM-41结构的影响,结果表明MCM-41的合成条件为n（CTAB）/n（SiO2）=0.05～0.60,pH值=8～11,晶化时间〉24h,晶化温度60～100℃。TEM可观察到样品具有典型的按六方对称性排列的孔道结构,孔径在2～4nm变化。FT-IR证明了分子筛具有硅氧四面体骨架。     

一种改进的自然纹理合成方法

自然纹理合成方法是一种适合自然景物的基于样图的快速纹理合成方法。但是候选点超越样图边界的问题没有很好得到解决,成为导致合成后图像产生的纹理块间明显变化的主要因素。论文提出了一种改进的自然纹理合成算法,将样图边缘易产生无效候选点的区域用样图内部与之大小和形状相同的像素块来代替,像素块和被替代像素块沿一条不规则的曲线相匹配。合成过程中在接近边缘时像素块的生长会转向纹理内部。该方法减少了因随机产生候选点而形成的块间不连续,有效地改善了视觉效果。     

ZSM-5沸石分子筛的高压吸附储氢特性

研究了ZSM-5沸石分子筛对氢的超临界吸附特性．结果表明,在77K／5MPa、195K／7MPa、293K／7MPa条件下,ZSM-5沸石分子筛的储氢质量分数分别为1．97％、0．65％和0．4％．用Clausius-Clapeyron方程求得的等量吸附热（3．8kJ／mol）与吸附量无关,表明该分子筛是一种表面势场均匀的吸附剂．将表面过剩吸附理论与描述Ⅰ型等温线的诸理论模型结合,分析了超临界吸附等温线,发现基于Toth方程的等温线模型在整个实验范围内与实验数据吻合较好,由该模型计算出的氢吸附相密度在77K达到55．6kg／m^3．根据回归参数讨论了超临界条件下氢在微孔沸石分子筛中的吸附机理,确认了氢在微孔沸石分子筛中的吸附为物理吸附．     

A new approach for synthesis of ZnO nanorod flowerets and subsequent pure free-standing ZnO nanorods

Present work reports the synthesis of ZnO flowerets consisting of nanorod petals of ZnO having a mean aspect ratio ～9, supported on micron sized Ni-enriched particles of size in the range of ～1–4?μm and also free-standing pure ZnO nanorods from mechanically alloyed Ni-Zn powder particles via selective leaching in NaOH solution. Optimization of the composition of the initial alloy powder, the concentration of NaOH and time of exposure in the solution was carried out to get to the ZnO flowerets with an increment in the surface area of the order of 400%. The mechanism and reaction chemistry of ZnO nanorods formation and growth were explained based on the evidence of various characterization techniques including inductive coupled plasma mass spectroscopy (ICP-MS) and electrochemical measurements. Free-standing pure ZnO nanorods were also synthesized by ultrasonically breaking the rod petals of ZnO from the base of the flowerets. Free-standing ZnO nanorods have a mean aspect ratio of 8.5?±?4, where the length and average diameter are ～356?±?64?nm and 42?±?16?nm, respectively, and the specific surface area of 12.5?m²?g^?1 with an increment of ～650% as compared to the mechanically alloyed powder particle.     

An improved sieve point method for the reliability analysis of structures

The efficiency of existing stochastic analysis method depends on the discretization of the random variables domain. The number theoretical method has been proposed to discretize the random variable space and solve the generalized density evolution equation via sampling strategy. This method traditionally involves hyper-ball sieving (HS) algorithm to sample the representative point set. However, the sieving radius of the hyper-ball is determined subjectively, and the efficiency and accuracy of the analysis depend on the selected radius. To avoid this subjective selection, an equal volume hyper-ball sieving method is presented in this paper. By transforming the hypercube spatial volume of random variables into that of an equivalent hyper-ball, the radius of the equal volume hyper-ball is obtained analytically. This radius is further optimized with a minimum star discrepancy in the representative point set. The performance and accuracy of the proposed method are checked in four numerical examples, and the representative point set such obtained is more uniform with smaller NRP leading to more accurate and efficient subsequent stochastic analysis than the HS method.     

A mechanochemical synthesis of nanostructured zinc oxide via acetate route for LPG sensing

This article reports the liquefied petroleum gas (LPG) sensing of nanostructured zinc oxide (ZnO) synthesised via zinc acetate [Zn(CH₃COO)₂·2H₂O] as precursor. The structural and morphological characterisations of the material were analysed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Structural analysis showed that material was highly crystalline having minimum crystallite size 15?nm. Surface morphological studies show nanospheres of ZnO throughout the surface, however not distributed uniformly. Optical characterisation of the sensing material was carried out by UV-Visible spectroscopy and FTIR spectroscopy. By Tauc plot, the estimated value of band gap of film was found 3.45?eV. The LPG-sensing properties of the ZnO pellet were investigated at room temperature for different vol.% of LPG. The variations in electrical resistance of the sensing pellet were measured with the exposure of LPG as a function of time. The maximum values of average sensitivity and sensor response factors were found ～5 and 396, respectively, for 5 vol.% of LPG. The activation energy calculated from Arrhenius plot was found 0.61?eV. The response and recovery time of sensing pellet were found ～90 and 110?s, respectively. These experimental results show that nanostructured ZnO is a promising material as LPG sensor.     

Binary System 4MnO·Nb_2O_5-SiO_2—One of the Binary Sections in the Ternary System MnO-Nb_2O_5-SiO_2

1.IntroductionAs mentioned in our previous paper[1],it is important to study the phase diagram ofthe system Nb_2O_5-MnO-SiO_2.The newcompound 4MnO·Nb_2O_5 has been ascer-tained in the binary system MnO-Nb_2O_5[1].Then,there are three stable compounds     

ZSM-5型沸石膜的合成及应用于乙苯脱氢反应研究进展

重点介绍了国内外关于ZSM－5沸石膜的合成及应用于乙苯脱氢反应应用现状,分析和阐述了当今ZSM－5沸石膜合成的方法和特点及今后面临的挑战。     

Rapid synthesis of hierarchical ZSM-5 zeolites for the reactions involving larger reactant molecules

In this study, the ZSM-5 zeolites with a high hierarchy factor were synthesized rapidly and tested for the furfural hydroxymethylation (FH) to 5-hydroxymethylfurfural (HMF). The effect of seeding techniques (STs) and templates (both soft (Cetrimonium bromide, CTAB) and hard (bio-sourced secondary template, BSST)) on the final zeolite properties were studied. A significant variation in crystallinity and morphology with the ST and type of seed was observed. The CTAB addition increased the hierarchy factor (H factor) by 3 times, and the implicit seeds decreased the hydrothermal time by 2 times. The zeolite yield, crystallinity, and pore geometry were a strong function of [CTA⁺]/[Na⁺] ratio. Slit and ink bottle-shaped pore morphologies were observed with only seed or seed + BSST and with seed + CTAB, respectively, and both exhibited the bimodal pore size distribution. The zeolites with ink bottle-shaped pores outperformed those with slit pores in the FH and showed the highest selectivity to HMF of 65%, at 34% furfural conversion. The zeolites with high H factor showed catalytic and structural stability up to 5 successive recycle runs.     

An improved molecular dynamics potential for the Al-O system

Molecular dynamics (MD) simulations of aluminum oxide material and the aluminum oxidation process require a sufficiently sophisticated and well-calibrated potential, one that takes into account locally varying Al/O ratios and adaptive charge transfer between Al and O atoms. In this work we show that the Charge Transfer Ionic Potential (CTIP) by Zhou et al. [X.W. Zhou, H.N.G. Wadley, J.-S. Filhol, M.N. Neurock, Phys. Rev. B 69 (2004) 035402] in combination with a new, “Reference Free” version of the Modified Embedded Atom Method (RFMEAM) potential performs well for this purpose. This new potential has been parameterized by systematically fitting it to a large database of different Al_xO_y crystal energies, over a range of lattice constants and elastic deformations, using a recent method which separates the electrostatic and non-electrostatic fitting steps. The resulting potential yields more realistic atomic charges, crystal energies and lattice constants than earlier potentials. In particular, we show that the angular forces in the MEAM part are essential for α-Al₂O₃ to be the lowest-energy aluminum oxide. We compare the performance of our potential with the potential of Zhou et al., which lacks angular forces and was parameterized using a less involved fitting procedure, and show the results of a few molecular dynamics simulations. The two-step fitting method is generally applicable and can be adopted for constructing potentials for other metal-oxide systems.     

HZSM-5分子筛负载SrTiO_3光催化降解活性艳红X-3B

采用溶胶-凝胶法制备HZSM-5分子筛负载SrTiO_3,对其进行XRD、FTIR和N2吸附-脱附表征,研究负载对活性艳红X-3B光催化降解过程的影响。通过分析降解液的FTIR谱图、紫外-可见光谱和总有机碳(TOC)数据,对活性艳红X-3B的光催化降解过程进行了探讨。结果表明:催化剂的主要成分为钙钛矿结构SrTiO_3,负载对SrTiO_3晶粒尺寸几乎没有影响。纯SrTiO_3没有明显的孔结构,负载后样品的比表面积和孔隙主要由HZSM-5提供。负载之后催化剂的降解活性显著提高,30%SrTiO_3/HZSM-5对活性艳红X-3B染料溶液的脱色和TOC去除速率最快。     

Microwave-assisted fast vapor-phase transport synthesis of MnAPO-5 molecular sieves

MnAPO-5 was prepared by a microwave-assisted vapor-phase transport method at 180 °C in short times. The products were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectra, UV-vis spectroscopic measurement, NH₃-temperature-programmed desorption and esterification reaction. It was found that dry gels prepared with aluminum isopropoxide, phosphoric acid and manganese acetate could be transferred to MnAPO-5 in the vapors of triethylamine and water by the microwave-assisted vapor-phase transport method at 180 °C for less than 30 min. The crystallization time was greatly reduced by the microwave heating compared with the conventional heating. The resulting MnAPO-5 exhibited much smaller particle sizes, higher surface areas and slightly higher catalytic activity in the esterification of acetic acid and butyl alcohol than those prepared by the conventional vapor-phase transport method and hydrothermal synthesis.     

Microwave-hydrothermal process for the synthesis of rutile

The synthesis of pure rutile titanium dioxide is not an easy achievement, as the crystallization process generally leads to mixtures of two or even three phases; moreover the synthetic processes normally used by industry require harsh reaction conditions. We carried out the synthesis of titanium dioxide from an aqueous titanium tetrachloride solution under microwave irradiation in the reaction time range of 5-120 min. We mostly obtained mixtures of rutile and anatase, but obtained single-phase rutile after a 2-h treatment at 160 °C; transmission electron micrographs revealed well-dispersed spherical nanoparticles. We also investigated the effects of dilution and addition of a dispersant (polyvinylpyrrolidone) on phase crystallization and particle shape.