Precipitation of Stoichiometric Hydroxyapatite by a Continuous Method

In this paper we present the precipitation of hydroxyapatite (HA), Ca₅(OH)(PO₄)₃, from highly concentrated CaCl₂ and K₂HPO₄ solutions, carried out by a continuous method in a MSMPR reactor. The procedure consists of adding the reagents in a ratio Ca to P equal to 1.67, maintaining a temperature of 85 °C, inert N2 atmosphere inside the reactor, and monitoring and adjusting automatically the pH by means of a pH‐stat system (pH = 9.0 ∓ 0.1). Under these conditions HA with a Ca to P ratio equal or close to the stoichiometric composition (Ca/P=1.667), with a high yield (up to 99%) and a high production rate (up to 1.17 g/l.min) is obtained at steady state. The CSD, morphology, crystallinity of the precipitates and impurities present fit the requirement for its biomedical applications.     

Synthesis of ZSM-5 Zeolite with Small Crystallite and its Application in Aromatiration of Propane

Recently.greatinterestswereputonthenano-sizedmaterials.ItwasfoundthatzeoliteZSM-5withsmallornano-sizedcrystallitecouldachieveexcellentcatalyticperformanceincertainreactions'-;.However,mostpublicationsconcerningthesynthesisofZSM-5withsmallcrystallitealwaysusethecostlyTPAOH/Brasorganictemplates.WereportedherefoemethodusingmuchcheaperethylamineastemplateandtheproductswereappliedtoaromatizationofpropaneinwhichthestabilityofcatalystwasimprovedwithoutusingcostlyPt'orPd'asstabilizer.Synthesisof…     

Surfactant-aided hydrothermal preparation of La（2-x）SrxCuO4 single crystallites and their catalytic performance on methane combustion

Perovskite-like oxide La2-xSrxCuO4 (x = 0, 1) single crystallites with microrod-like morphologies and tetragonal crystal structures were prepared hydrothermally at 240°C with poly(ethylene glycol) (PEG) or hexadecyltrimethyl ammonium bromide (CTAB) as a surfactant and after calcination at 850°C. The physicochemical properties of the materials were characterized by means of XRD, BET, SEM, TEM/SAED (selected-area electron diffraction), XPS and H2-TPR techniques. It is found that doping Sr2+ to La2CuO4 lattice enhanced the catalytic activity for methane combustion and the LaSrCuO4 catalyst derived from PEG is the best among the tested ones. It is concluded that factors, such as adsorbed oxygen species concentration, reducibility and surface area, determined the catalytic performance of such single-crystalline materials.     

Growth of GeO2 Crystallite Thin Film on Si Substrate by Langmuir-Blodgett Technique

IntroductionIn recent years,Ge and its oxide haveattracted a considerable interest for their potentialapplication in optical filterdesign[1— 6 ] .To fabricateoptical devices,sometimes it is necessary todevelop a Ge O2 thin film on the surface of othermaterial,e.g.,silica.It is well known that silicasurface is quite inert and it is pretty difficult tosynthesize thin inorganic films on it.Inorganic thinfilms on silica surface are generally prepared byphysical methods,such as ion beam reactive…     

煤快速热解焦的微观结构对其气化活性的影响

在滴管炉内对中国三种不同煤阶的典型煤种在800~1 400 ℃进行快速热解实验,利用XRD和氮气气体吸附法对所得煤焦进行微晶结构和孔隙特征分析,在热重分析仪上进行CO₂气化反应活性的测定,研究不同热解温度煤焦结构特性与气化活性之间的关系。结果表明,随着热解温度的升高,内蒙古褐煤焦和神府烟煤焦的比表面积在1 200 ℃达到极大值,但气化活性却相对较低;遵义无烟煤焦在800~1 200 ℃气化活性逐渐提高,但比表面积在900 ℃达到极大值,表明煤焦比表面积与气化活性不存在严格关联。煤焦碳微晶结构变化所反映出煤焦石墨化进程与煤焦气化活性随热解温度的变化具有一致的变化趋势,表明快速热解煤焦的碳微晶结构变化对煤焦气化活性的影响更大。     

Crystallization of poly(ethylene terephthalate–co–isophthalate)

Melt crystallization behaviors of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate‐co‐isophthalate) (PETI) containing 2 and 12 mol % of noncrystallizable isophthalate components were investigated. Differential scanning calorimetry (DSC) isothermal results revealed that the introduction of 2 mol % isophthalate into PET caused a change of the crystal growth process from a two‐dimensional to a three‐dimensional spherulitic growth. The addition of more isophthalate up to 12 mol % into the PET structure induced a change in the crystal growth from a three‐dimensional to a two‐dimensional crystal growth. DSC heating scans after completion of isothermal crystallization at various T_c's showed three melting endotherms for PET and four melting endotherms for PETI‐2 and PETI‐12. The presence of an additional melting endotherm is attributed to the melting of copolyester crystallite composed of ethylene glycol, tere‐phthalate, and isophthalate (IPA) or the melting of molecular chains near IPA formed by melting the secondary crystallite T_m (I) and then recrystallizing during heating. Analyses of both Avrami and Lauritzen‐Hoffman equations revealed that PETI containing 2 mol % of isophthalate had the highest Avrami exponent n, growth rate constant G_o, and product of lateral and end surface free energies σσ_e. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2515–2524, 2000     

球形片状微晶碱式碳酸镁的制备、表征及其用作纸填料的特性研究

以六水氯化镁和碳酸钠为原料,乙二醇为介质,采用直接沉淀法制备了碱式碳酸镁纳米粉体。分别用热重分析、X射线衍射、扫描电镜和红外对碱式碳酸镁纳米粉体进行了表征,通过分析确定了其组成和结构。用该法制备出的碱式碳酸镁纳米粉体的平均粒径为35.49nm,呈现球形且由片状微晶组成,分子式为4Mg CO3·Mg(OH)2·4H2O。以球形片状微晶碱式碳酸镁为添加剂制得的纸具有良好的吸水性、吸油性和阻燃性能。     

Synthesis of composite TiN/Ni3N/a-Si3N4 thin films using the plasma focus device

Composite films of TiN/Ni₃N/a-Si₃N₄ were synthesized using the Mather-type plasma focus device with varying numbers of focus deposition shots (5, 15, and 25) at 0° and 10° angular positions. The composition and structural analysis of these films were analyzed by using Rutherford backscattering (RBS) and X-ray diffraction (XRD). Scanning electron microscope and atomic force microscope were used to study the surface morphology of films. XRD patterns confirm the formation of composite TiN/Ni₃N/a-Si₃N₄ films. The crystallite size of TiN (200) plane is 11 and 22 nm, respectively, at 0° and 10° angular positions for same 25 focus deposition shots. Impurity levels and thickness were measured using RBS. Scanning electron microscopy results show the formation of net-like structures for multiple focus shots (5, 15, and 25) at angular positions of 0° and 10°. The average surface roughness of the deposited films increases with increasing focus shots. The roughness of the film decreases at higher angle 10° and the films obtained are smoother as compared with the films deposited at 0° angular positions.     

Mechanism for the phase transition of poly(butylene terephthalate)

The α and β forms of poly(butylene terephthalate) transform reversibly by elongation and relaxation. The conformation change occurs in the tetramethylene glycol part, from GGTGG conformation to TSTS?T conformation. In this study, by using a doubly oriented sample, we measured the positions, intensities, and half‐widths of the (100) and (010) reflections of the α and β forms of poly(butylene terephthalate) with a position‐sensitive proportional counter system. During the transformation, the molecules translate only slightly. These slight molecular translations, or distortions, accumulate, and the crystallite of the α form breaks into the small crystallites of the β form as the α–β transformation proceeds, and the crystallite of the α form grows with the relaxation of the distortion accumulated in the crystal and amorphous regions and on the crystallite surface as the β–α transformation proceeds. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 765–771, 2002     

Investigation of the effect of forming gas annealing on front silver electrodes of c‐Si solar cells

Forming gas annealing (FGA) is an effective process to repair low efficiency crystalline silicon (c‐Si) solar cells with overfired screen‐printed paste electrodes. An experimental study was performed to investigate the effect and mechanism of FGA treatment on front silver electrodes of c‐Si cells. To facilitate the FGA mechanistic study, special simulation samples were prepared to magnify the FGA effects on glass frit and overfired electrodes. The micro‐morphology (from cross‐sectional X‐SEM) and elemental composition (from energy‐dispersive X‐ray spectroscopy) data revealed few Ag crystallites in the paste/Si interface because of the thick glass layer from the paste overfiring. The FGA treatment induced phase crystallization (from X‐ray diffraction) in the paste and increased the glass wettability on both Si and Ag substrates, thus resulting in a thinner glass layer, which expedited the precipitation of more pyramidal Ag crystallites at the Ag/Si interface. The wetting angle data of glass samples measured before and after FGA confirmed the mechanism of FGA and concluded that the improvement of glass wettability benefited to reduce the glass layer thickness. As a result, more Ag crystallites diffused toward and precipitated at the Si interface contributing to a lower contact resistance between the paste electrode and the Si matrix and thus improved electrical properties for overfired c‐Si cells. Copyright © 2012 John Wiley & Sons, Ltd.