室温固相反应制备超细碳酸钡粒子的研究

以BaCl2·2H2O和Na2CO3为原料,采用固相法合成了碳酸钡粒子.通过添加合适的晶形控制剂,选择合适的用量,合成了球状和针状碳酸钡粉体,利用扫描电子显微镜(SEM)和x射线衍射仪(XRD)进行了表征,结果表明:在无控制剂和添加控制剂LSX-2时,生成了球状碳酸钡粒子,添加控制剂LSX-3时,生成了针状碳酸钡粒子,且各粒子均为正交晶系碳酸钡.     

系列哑铃形BaCO3晶体的制备

以氯化钡、尿素、氢氧化钠和乙二胺四乙酸二钠(EDTA)为原料,通过络合与均相沉淀法成功合成一系列哑铃形碳酸钡晶体,并采用XRD、SEM、SAED和FT-IR对样品进行了表征.结果表明:添加EDTA对碳酸钡晶形有显著影响,随EDTA浓度变化,可得到一系列哑铃型碳酸钡晶体.反应时间和pH值对晶形也有一定影响.研究表明在EDTA浓度为0.025 mol/L,反应时间为5 min,水浴温度为95 ℃,pH=14条件下,制得的哑铃形碳酸钡粒子为亚微米级多晶,具有纯度高,分散性好,晶形完整均一的特点.     

花生状碳酸钡粒子的制备与表征

本文以BaCl2·2H2O和Na2CO3为原料,采用共沉淀法合成了碳酸钡粒子.通过添加合适的晶形控制剂,选择合适的用量,合成了花生状的碳酸钡粒子,利用扫描电子显微镜(SEM)和X射线衍射仪(XRD)进行了表征,结果表明:当控制剂WHB-1用量在85;以上时,生成的花生状碳酸钡粒子为正交晶系,粒度分布均匀,在500nm左右,且粒子分散性良好,几乎没有团聚现象.并对花生状碳酸钡粒子的形成机理进行了初步的探讨.     

EDTA对超临界二氧化碳法制备碳酸钡粒子形貌影响的研究

以氢氧化钡和二氧化碳气体为原料,采用超临界二氧化碳法,通过添加乙二胺四乙酸(EDTA)并控制其用量,制备出柱状、棒状、椭球状和球状等不同形貌的碳酸钡颗粒.采用TG/SDTA、SEM、XRD和FT-IR等对产品进行分析与表征,结果表明:不同形貌碳酸钡粒子均属于正交晶系.同时对EDTA形貌控制机理进行了初步分析.     

乙二胺四乙酸对碳酸钡粒子形貌影响的研究

以硝酸钡和碳酸铵为原料,采用共沉淀法,通过添加和控制乙二胺四乙酸(EDTA)用量,制备出哑铃状、球状和圆柱状等不同形貌的碳酸钡粒子.采用TG/SDTA、SEM 、FT-IR和XRD等对产品进行分析与表征,结果表明:不同形貌碳酸钡粒子均属正交晶系,粒子分布均匀,粒度较小,形貌完整.同时对形貌控制机理进行了初步分析.     

熔盐条件下反应原料对钛酸钡相形成动力学的影响研究

选择硝酸钡、乙酸钡、碳酸钡、氢氧化钡与二氧化钛作原料,利用熔盐法,在不同温度,不同保温时间下煅烧制备高纯度的钛酸钡纳米晶.采用XRD、SEM对样品进行表征的基础上,通过模拟初步研究了不同反应原料对钛酸钡晶体合成动力学的影响.结果表明:各组反应物均符合JMAK模型和纯界面模型,说明这两个模型是熔盐法制备钛酸钡的生长动力学的通用模型.此外,硝酸钡、乙酸钡两组还符合自由形核、快速生长模型和收缩球面界面模型,而碳酸钡和氢氧化钡两组则不符合,这可能和反应物分解温度有关,不同的分解温度会影响动力学过程.     

碳酸钙掺杂对Ⅰb型金刚石沿不同晶面生长行为的影响

作为天然金刚石生长环境的碳酸盐,研究其掺杂对人造金刚石晶体生长行为的影响具有重要的学术价值。本文运用高温高压下的温度梯度法,将碳酸钙(CaCO₃)按照不同比例掺杂到金刚石合成腔体内的碳源中,用以研究其掺杂对金刚石分别沿(100)或(111)晶面生长行为的影响。利用光学显微成像对掺杂合成金刚石晶体形貌的表征表明:随着碳酸钙掺量的增加,沿(100)面生长的金刚石晶形由塔状变为板状且出现了裂晶、连晶现象,晶体颜色先变浅再变黑,内部出现了包裹体;同样,沿(111)面生长的金刚石晶形由板状逐渐变为塔状且出现了裂晶、孪晶现象,晶体颜色逐渐变黑,内部包裹体增多。用激光拉曼光谱对掺杂金刚石晶体质量的表征表明:随着碳酸钙掺量的增加,沿(100)或(111)面生长的掺杂金刚石的拉曼峰位偏移量均增大,半峰全宽均变大。这说明碳酸钙掺杂使得金刚石晶格畸变增加、内应力变大。本文对碳酸钙掺杂影响沿两不同面生长金刚石的晶形、颜色、内部质量等行为的成因进行了分析,为本课题后续研究奠定了基础。     

Li3N触媒粒度对立方氮化硼单晶合成效果的影响

在压力4.5 ～5.3 GPa,温度1350 ～ 1500℃条件下,分别以不同粒度的Li3N粉末作为触媒,采用高温高压触媒法合成了立方氮化硼(cBN)单晶.研究了Li3N触媒粒度对cBN单晶合成效果的影响,对得到的cBN单晶的产量、转化率、大晶粒含量和抗压强度等待性进行了检测对比.结果表明,当Li3N触媒的粒度为80～ 100 μm时,在高温高压下可以合成出大晶粒含量高、抗压强度高、生长完善且晶形完整度较高的cBN单晶;当Li3N触媒的粒度为60～ 80 μm时,在高温高压下合成出的cBN单晶产量和转化率较高.     

聚乙二醇对合成ZSM-5分子筛形貌影响的研究

为了探索更多具有应用价值的特殊形貌ZSM-5分子筛,本文通过在常规水热合成条件下添加晶形控制剂聚乙二醇(PEG)的方法,制得了不同形貌的ZSM-5沸石分子筛.采用X射线衍射(XRD)、扫描电子显微镜(SEM)和红外光谱(FTIR)等手段对样品进行表征,分析表明:在晶化过程中,PEG对ZSM-5分子筛晶粒起到了晶形控制剂的作用,并且实验中PEG聚合度较小时分子筛的形貌以不规则的椭球形为主,PEG聚合度增大至45时得到的分子筛为较规则的条状结构.相同聚合度的PEG随在体系中加入量的不同对产物的形貌尺寸影响也有较大差异,在PEG量较小时分子筛有较多没有成型的小晶粒,PEG适量时为规则的条状结构.PEG量较大时大量的表面-OH使得离子之间发生空间位阻从而对分子筛晶体形貌控制作用不明显,分子筛主要为短粗的椭球形.     

用FeNiMn55#粉末触媒合成工业金刚石

利用FeNiMn55#粉末触媒在国产六面顶压机上进行工业金刚石单晶的合成,研究高温高压条件下(5.7 Gpa,1400～1600 ℃),C-FeNiMn55#粉末触媒体系中金刚石单晶的生长特性.结果表明,C-FeNiMn55#系能够合成出六-八面体及八面体金刚石,但六面体金刚石生长区间较窄,不易生长.通过光学显微镜观测表明,合成出的金刚石单晶呈黄色,晶形完整,晶体内部有气泡产生.M(o)ssbauer测试结果表明金刚石中包裹体的主要成分为Fe3C和FeNiMn55#合金.     

Size and morphology controlled synthesis of barium sulfate

In this work submicron barium sulfate (BaSO₄) particles were synthesized successfully by chemical precipitation technique. We focused on the effects of pH and additives on the size and morphology of BaSO₄ crystals. Polyacrylic acid, polyvinyl sulfonic acid and ethylenediaminetetraacetic acid were used as crystal growth modifiers. BaSO₄ crystals were characterized using scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared resonance techniques. The results show that the submicron BaSO₄ particles have been synthesized successfully and the particle size of the barium sulfate was effectively controlled under the experimental conditions. Experimental studies revealed that the additive concentration and pH had great effect on the morphology and size of barium sulfate.     

Precipitation of sparingly soluble salts in packed sandbeds in the presence of miscible and immiscible organic substances

Sparingly soluble salts precipitation, e.g. calcium carbonate or calcium sulfate, results in pore clogging in rock formations and in the concomitant reduction of the local permeability of oil wells during the oil extraction processes. On the other hand, in situ controlled salt precipitation is desirable in various applications e.g. waterproofing of concrete constructions suffering from leakages, etc. In the present study, calcium carbonate (CaCO₃) precipitation in sandbeds was investigated, in the presence of organic solvents simulating the conditions prevalent in oil‐well zones. CaCO₃ precipitation was investigated from supersaturated solutions prepared by in‐situ mixing of NaHCO₃ and CaCl₂.2H₂O solutions before the inlet of sandbeds. The solution resulting from the mixing of the two solutions was supersaturated with respect to all calcium carbonate polymorphs. Three types of experiments were performed depending on the supersaturated solutions: a) aqueous solutions b) aqueous supersaturated solutions in contact with sandbeds pre‐saturated with n‐dodecane c) aqueous solutions containing monoethylene glycol (MEG). Results showed that oil–water interfaces enhanced the heterogeneity of the supersaturated solutions and accelerated crystal growth of calcium carbonate at the inlet of the sandbed, resulting in early pore clogging and limitation of local permeability. Maximum sandbed consolidation was obtained with the solutions containing MEG.     

Synthesis from zinc oxalate,growth mechanism and optical properties of ZnO nano/micro structures

We report the synthesis of various morphological micro to nano structured zinc oxide crystals via simple precipitation technique. The growth mechanisms of the zinc oxide nanostructures such as snowflake, rose, platelets, porous pyramid and rectangular shapes were studied in detail under various growth conditions. The precursor powders were prepared using several zinc counter ions such as chloride, nitrate and sulphate along with oxalic acid as a precipitating agent. The precursors were decomposed by heating in air resulting in the formation of different shapes of zinc oxide crystals. Variations in ZnO nanostructural shapes were possibly due to the counter ion effect. Sulphate counter ion led to unusual rose‐shape morphology. Strong ultrasonic treatment on ZnO rose shows that it was formed by irregular arrangement of micro to nano size hexagonal zinc oxide platelets. The X‐ray diffraction studies confirmed the wurzite structure of all zinc oxide samples synthesized using different zinc counter ions. Functional groups of the zinc oxalate precursor and zinc oxide were identified using micro Raman studies. The blue light emission spectra of the various morphologies were recorded using luminescence spectrometer. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

离子交换树脂均匀沉淀法制备MgO纳米粒子

以(Mg(NO3)2·6H2O, (NH4)2CO3 和NH3·H2O为原料,采用两种离子交换树脂均匀沉淀法分别制备MgO纳米粒子.用热分析、X射线粉末衍射(XRD)、透射电子显微镜(TEM)、高分辨电子显微镜(HR TEM)、选区电子衍射(SAED)和BET等对所制备的MgO粒子进行了表征.结果表明:经700 ℃焙烧后制备的MgO纳米晶体属六方晶系,样品分散性较好,平均粒径约为25 nm;MgO纳米晶体清晰、有序的电子衍射点阵,表明晶体的结晶度较好;纳米粒子a和b的比表面积分别为31 m2/g and 32 m2/g.     

片状纳米氧化锌单晶的制备和表征

本文提供了一种应用二步法制备片状纳米氧化锌单晶的实验方法--首先,以尿素为沉淀剂宿主,以氯化锌、碱式碳酸锌为原料,应用均匀沉淀法获得纳米氧化锌的片状纳米级前驱物;然后通过控温热分解前驱物制备出片状纳米氧化锌单晶.用扫描电镜观测了制备的ZnO单晶的形貌,并通过红外光谱对其进行了表征.结果表明:实验制备的氧化锌均为无色透明的片状单晶,结晶形貌为正六边形、五边形、矩形以及其它不规则形状,单晶直径在30～600μm之间,厚30～60nm;影响纳米氧化锌单晶制备的主要因素是反应物料配比、沉淀剂宿主尿素的浓度(1∶6)以及反应温度(70～85℃).此外,乙醇的含量对片状纳米前驱物的形貌影响很大,10;～40;的乙醇含量利于形成片状纳米氧化锌单晶.     

Precipitation kinetics of sodium bicarbonate in an industrial bubble column crystallizer

Sodium bicarbonate is a substance which is produced in the middle stages of the soda ash production process. In this precipitation process, carbon dioxide gas is continuously injected into the bubble column reactor which contains carbonate and bicarbonate solutions. To elucidate the key parameters affecting precipitation kinetics, an experimental study was conducted to understand nucleation and growth in conditions of industrial reactor. The composition of the solution is followed during the crystallization process by titration. Magma density is also monitored and crystal size distribution (CSD) is obtained by sieving. The method of moments was used to determine nucleation and growth rates of crystals. The nucleation and growth rate correlations for sodium bicarbonate precipitation in industrial scale were correlated by empirical power laws as B = 26.685M_T^0.42Δw^1.31 and G = 1.381×10^–4Δw^1.53. The nucleation and growth rate correlations obtained in this study can be used to simulate the crystallization of sodium bicarbonate plants. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of the mechanism of low-temperature DyBa2Cu3O7–x synthesis

The formation of superconducting DyBa₂Cu₃O_7–x was investigated by powder X-ray method. It was found that when oxides and barium carbonate, or precursors were applied the temperature of formation of the ‘123’ phase is the same, only the reaction rates are different.     

Nanosized barium carbonate particles stabilized by cetyltrimethylammonium bromide at the water/hexamethylene interface

Nanoparticles of barium carbonate (BaCO₃) have been synthesized in situ from barium chloride by the slow release of carbon dioxide by alkaline hydrolysis of diethyl carbonate, and stabilized by cetyltrimethylammonium bromide (CTAB) at the water/hexamethylene interface. Transmission electron microscopy, Fourier transform infrared spectroscopy and X‐ray powder diffractometry were used to characterize the products. The results indicate that spherical BaCO₃ nanoparticles are obtained with poor crystallinity and diameters ranging from 30 to 300 nm. The possible formation mechanism of the nanoparticles at the interface is discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of Barium Cerate Crystals from BaCl2 Solution

Barium cerate crystals of 1.5 mm diameter could be grown from melt solutions containing barium chloride, barium oxide (from thermolysis of barium carbonate), and cerium(IV) oxide. The maximum size of the crystals is limited by the low solubility of cerium(IV) oxide in the barium chloride melt (ca. 0.1 Mol%). The flux can be removed by leaching the melt with water. Acid solutions must not be used to avoid decomposition of the barium cerate crystals. Neither congruent melting or incongruent decomposition of the BaCeO₃ crystals could be found up to 1580 degrees centigrade.