A型沸石的水热制备及生长机制研究

通过对A型沸石的水热制备实验和晶体生长过程的检测表征研究，揭示了水热体系A型沸石晶粒的生成经历了前驱物溶解→成核并形成小晶粒→小晶粒的聚合生长(取向连生和配向附生)→晶粒的聚集生长(溶解和结晶)等4个阶段。聚合生长是小晶粒之间通过取向连生与配向附生形成粒度更大的晶粒的过程，而聚集生长则是物料从小尺寸晶粒向大尺寸晶粒输运的重结晶过程，它们的区别在于是否存在小晶粒的溶解和大晶粒的重结晶过程，但热力学驱动力都是由于晶粒平均粒度的增大降低了体系总的表面自由能。聚合生长是A型沸石晶粒长大的主要方式。     

织构化（Na_（1/2）Bi_（1/2））TiO_3-BaTiO_3无铅压电陶瓷晶粒定向生长机制

以熔盐法合成的片状SrTiO3晶粒为模板,利用模板晶粒生长（TGG）技术制备晶粒沿[001]方向为取向的0.94（Na1/2Bi1/2）TiO3-0.06BaTiO3（简写为BNBT6）无铅压电陶瓷,采用X线衍射仪（XRD）、扫描电子显微镜（SEM）对陶瓷试样进行表征,采用透射电子显微镜（TEM）观察SrTiO3与BNBT6基体界面的微观结构.结果表明,BNBT6陶瓷晶粒定向生长过程分为2个阶段：首先是异质外延生长阶段,即在片状模板晶粒的诱导下,BNBT6基体粉体在SrTiO3模板晶粒表面外延生长,形成与模板取向完全一致的单晶生长层的过程;其次是同质外延生长阶段,即单晶生长层生成后吞噬BNBT6基体粉体逐步生长得到各向异性的高取向BNBT6陶瓷的过程.     

油酸辅助水热合成纳米钛酸锶的性能调控与表征

采用油酸辅助一步水热法,以廉价易得的锐钛矿型TiO2为钛源、Sr(OH)2?8H2O为锶源合成SrTiO3纳米颗粒,通过XRD, TEM和SEM研究了SrTiO3纳米颗粒的形貌,考察了反应时间、Sr/Ti摩尔比和油酸浓度对SrTiO3纳米颗粒性能的影响,以所制SrTiO3为催化剂降解亚甲基蓝考察其光催化性能。结果表明,钙钛矿型立方相SrTiO3纳米颗粒具有均匀的尺寸和规则的形貌。实验范围内,随反应时间和Sr/Ti摩尔比增加,SrTiO3纳米粒子的晶粒尺寸呈增加趋势;随油酸浓度增加,SrTiO3颗粒粒度呈下降趋势。添加油酸可调控制备出具有规则形貌的钙钛矿型立方相结构的SrTiO3纳米颗粒;Sr/Ti摩尔比为0.75时,产品纯度高、结晶度好。油酸、反应时间和Sr/Ti摩尔比对SrTiO3纳米粒子微观结构的影响可分别用颗粒间作用力、奥斯特瓦尔德熟化和晶体成核理论解释。     

SrTiO3粉体的水热法合成和光催化性能

应用水热法合成了纳米SrTiO3和TiO2粉体。应用XRD和SEM对粉体进行了分析和表征。XRD分析表明，TiO2和Sr—TiO3粉体分别为纯的锐钛矿相和立方尖晶石晶体，粒子尺寸分别约为12．2nm和25．3nm。两粉体上的甲基橙溶液光催化降解实验表明，起始溶液pH值和H202对光催化性能有显著影响。低的pH-5和H2O2更有利于两种粉体对甲基橙溶液的光降解。尽管SrTiO3比TiO2有较大的粒子尺寸，在pH=5和存在H2O2的情况下SrTiO3比TiO2有更大的降解效率。     

ZnO异质复合对纳米TiO2晶型转变和晶粒生长的影响

以TiCl4,ZnSO4溶液为原料,采用液相沉淀法制备了不同ZnO/TiO2摩尔比的纳米复合粉体.对合成的纳米复合晶的相变、晶粒生长过程以及紫外-可见光吸收性能进行了研究.结果表明:纳米TiO2经ZnO复合后,其晶型转变和晶粒生长均受到抑制.当ZnO为30%(摩尔分数)时,且采用氨水滴入TiCl4和ZnSO4溶液中的沉淀方式制备的ZnO/TiO2纳米复合晶的晶型转变和晶粒生长最缓慢.紫外-可见光吸收测试表明:800℃煅烧的ZnO/TiO2复合粉体的吸收强度比纯TiO2的高;900～1 050℃煅烧的复合粉体,虽然紫外区的吸收强度有所下降,但其光吸收带边比纯TiO2纳米晶的有显著红移.     

多层陶瓷电容器用的SrTiO3纳米粉体制备

采用溶液-溶胶-凝胶法,从Sr(NO3)2-Ti(OC4H9)4-H2O-C2H5OH体系制备多层陶瓷电容器用的纳米SrTiO3粉体.用热重-差示扫描分析研究了由前驱体干凝胶形成纳米SrTiO3粉体的加热过程.用X射线衍射等方法研究了醋酸、水、温度对凝胶化、纳米SrTiO3粉体的粒径和比表面积的影响.用扫描电镜和透射电镜观察了纳米SrTiO3粉体的形貌和颗粒大小.所制备的SrTiO3粉体分散性好,粒径为40～50 nm,比表面积为9～10 m2/g.     

水热合成钛酸锶粉体增强压敏电阻器电性能的研究

以硝酸锶Sr(NO3)2为锶源、酞酸四丁酯Ti(OC4H9)4为钛源,加入矿化剂NaOH/KOH,在130℃下反应24h水热合成了SrTiO3粉体。将水热粉体应用到压敏电阻器中,分别采用XRD、电性能测试、SEM等手段对产物进行表征。电性能测试结果显示,与传统固相法制备的SrTiO3压敏电阻器相比,同配方下此类压敏电阻器电性能获得显著提高,压敏电压V1mA和非线性系数ɑ分别达到120V和8。     

IrO_2-SiO_2涂层钛阳极的失效行为研究

为探讨氧化物涂层阳极的失效原因,采用热分解法在不同焙烧温度下制备了60%IrO2-40%SiO2/Ti氧化物阳极,利用扫描电子显微镜(SEM)、能谱分析(EDX)和循环伏安测试(CV)分析了阳极在硫酸溶液的强化电解过程前后表面形貌、涂层组成和电化学性能的变化。结果表明,IrO2-SiO2涂层钛阳极失效的主要原因是钛基体和涂层之间形成了不导电的TiO2层。在强化电解过程中,低焙烧温度制备的阳极活性组分的电化学溶解和涂层的机械脱落促进TiO2层的生长。高焙烧温度制备的阳极中已生成一定量的TiO2,在电解时加速电极的失效。600℃焙烧温度下制备的电极的强化寿命最高。     

高钛高炉渣酸浸液沸腾水解制备偏钛酸的过程动力学研究

攀枝花钢铁厂高炉冶炼产生的水淬高钛高炉渣经浓硫酸焙烧、稀硫酸浸取后获得富含Ti4+的浸取液,通过沸腾水解法可将浸取液中的可溶性Ti4+转化成H2TiO3沉淀.为探究酸浸液沸腾水解制备H2TiO3的过程动力学行为,研究了底液pH和水解温度在不同反应时间下对Ti4+水解率的影响,并采用Avrami模型和生长动力学模型模拟水...     

过氧改性纳米TiO2溶胶的制备及其光催化性能

以硫酸氧钛为钛源,过氧化氢为络合剂,采用低温水热法制备了过氧改性纳米TiO2溶胶,并对制备过程中的影响因素进行了研究,同时,通过甲醛废水模型体系考察了溶胶的光催化活性。采用X射线衍射、透射电镜、紫外-可见漫反射光谱等测试手段对TiO2进行了表征。结果表明,当水解反应pH值为8.0,硫酸氧钛浓度为0.10 mol/L,陈化时间为24 h,Ti4+/H2O2物质的量比为1∶4,水热反应温度和时间分别为100℃和6～8 h时,可制得直径20nm、长30 nm,结晶良好的锐钛矿过氧改性纳米TiO2和分散均匀的溶胶。经紫外光和太阳光光照180 min后,过氧改性纳米TiO2溶胶对甲醛的降解率分别为95.3%和31.8%,优于相同条件下P25的光催化性能(69.7%和21.1%)。     

预烧温度对LaAlO3和SrTiO3晶相结构及介电性能的影响

以La2O3和Al2O3、SrCO3和TiO2为原材料,用常规的固相法制备了LaAlO3及SrTiO3粉体,研究了预烧温度对LaAlO3及SrTiO3粉体主晶相形成的影响。XRD衍射实验结果表明:La2O3和Al2O3可以在预烧温度1250℃保温时间10h得到单相的LaAlO3晶体;SrCO3和TiO2在预烧温度1150℃保温时间4h可以得到单相的SrTiO3晶体。另外,LaAlO3与SrTiO3组分与性能的关系研究证明,当其摩尔比为0.5∶0.5时,得到了介电常数为38,介质损耗为1.48×10-4,温度系数为-20.5×10-6/℃的介质材料。     

Crystallization of Spherical Ammonium Dinitramide (ADN) Particles

The described process aims to produce spherical ammonium dinitramide (ADN) particles of different sizes with a narrow particle size distribution. The crystallization process presented in this paper consists of two stages. In the first stage, molten ADN is dispersed in a continuous phase in which ADN is insoluble. The droplet size produced can be controlled by varying the amount of mechanical energy supplied to the two‐phase system. In addition to discussing the influence of the different process parameters, such as dispersion rate, dispersion power, emulsification time etc. this paper also reports the influence of emulsifying agents and the rheological behavior of the continuous phase. In the second stage of the process, crystallization of the emulsified ADN droplets to spherical, solid particles is obtained by reducing the temperature of the system. The process described enables production of spherical ammonium dinitramide particles with mean sizes from 10 µm to 600 µm. The product quality of the crystallized ADN, which is also discussed in this paper, was determined using various analysis techniques, including differential scanning calorimetry (DSC), IR spectroscopy, ion chromatography and laser light diffraction spectrometry.     

The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite

The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range of environmentally relevant temperatures (7.5-25 °C) using synchrotron-based in situ time-resolved Energy Dispersive X-ray Diffraction (ED-XRD) in conjunction with high-resolution electron microscopy, ex situ X-ray diffraction and infrared spectroscopy. The crystallization process occurs in two stages; firstly, the particles of ACC rapidly dehydrate and crystallize to form individual particles of vaterite; secondly, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate controlled by the surface area of calcite. The second stage of the reaction is approximately 10 times slower than the first. Activation energies of calcite nucleation and crystallization are 73±10 and 66±2 kJ mol(-1), respectively. A model to calculate the degree of calcite crystallization from ACC at environmentally relevant temperatures (7.5-40 °C) is also presented.     

十氢十硼酸双四乙基铵热分解特性及其动力学参数

为了解十氢十硼酸双四乙基铵(BHN-10)热分解特性及反应动力学,采用同步热分析-红外质谱联用技术(TG-DSC-MS-FTIR)及热裂解原位池-傅里叶变换红外光谱联用技术(FTIR)对BHN-10热分解过程中间产物和最终产物进行分析;使用Kissinger和Ozawa方法计算两个热分解阶段的动力学参数,并利用Coats-Redfern法拟合得到反应动力学方程。结果表明,BHN-10热分解第一阶段和第二阶段的活化能分别为150.9 kJ/mol和161.7 kJ/mol;第一阶段受随机成核和核增长机理控制,第二阶段遵从幂级数法则(Mampel power);两阶段的动力学机理函数分别为G(α)=[-ln(1-α)]1/3(n=3)和G(α)=α1/4;BHN-10热分解反应第一阶段质量损失2.9%,与理论脱氢质量损失相一致,此阶段发生B10H2-10的脱氢产生氢气和非晶态硼的过程,在热分解第一阶段会生成熔融分解型的中间产物四乙基铵阳离子;第二步反应质量损失39.4%,接近第二阶段气体质量损失的计算值43.4%,是四乙基铵阳离子上的质子转移并通过Hoffman消除反应生成乙烯和Et3N,Et3N进一步分解为C 2H 6、NH3、H2和碳单质。     

氧化铝粒子化学气相包覆氧化钛的过程研究

探讨了回转炉化学气相淀积（CVD）包覆新工艺,利用Ti（OC_4H_9）_4水解,在Al_2O_3粒子表面实现了TiO_2包覆,研究了包覆过程特征。结果表明,TiO_2在Al_2O_3粒子表面的包覆是成功的,并具有一定的致密性,包覆量为0.1%～10%;化学气相包覆过程中既存在成膜包覆,又存在成核包覆,通过控制反应物浓度等方法可以强化成膜包覆,提高包覆效果。     

pH值对溶胶-凝胶法制备纳米TiO2的影响

利用溶胶-凝胶法制备了纳米TiO2颗粒,采用透射电镜(TEM)和X射线衍射(XRD)对产物进行了表征,考察了Ti4+-三乙醇胺(Ti-TEOA)络合体系组成随陈化时间的变化及pH对TiO2粒径、结晶习性、产率及Ti-TEOA稳定性的影响. 结果表明,产物为锐钛型TiO2,140℃陈化时,Ti(OH)4凝胶在10 h后全部转化为TiO2颗粒,平均粒径5~22 nm;随pH升高,粒径增大,但TiO2产率在pH>10.6时显著下降,至pH 12时无TiO2颗粒生成;不同pH时TiO2结晶习性变化明显. 25℃下pH>6时Ti-TEOA络合体系稳定.     

Synthesis and Characterization of Ceramic Precursor Aluminum-Containing Polycarbosilane and its Pyrolysis

The aluminum-containing polycarbosilane (Al-PCS) was synthesized by reaction of an aluminum alkoxide with polycarbosilane (PCS). The Al-PCS product was characterized by element analysis, gel permeation chromatography (GPC), as well as Fourier transform (FT-IR) and nuclear magnetic resonance (¹H, ²⁹Si, ¹³C, and ²⁷Al NMR) spectroscopy. The results show that Al-PCS is very similar to PCS in structure. This preceramic precursor is described as a dispersion of Al(AcAc)₃-based particles in the PCS chain matrix. The pyrolysis process of Al-PCS was investigated by thermogravimetry (TG), FT-IR, and X-ray diffraction (XRD). The pyrolysis of Al-PCS includes three sequential stages: First, the condensation and thermal decomposition into the inorganic state; second, the transition toward the third stage involving the thermal decomposition of the side chains into an amorphous state; third, the crystallization of β-SiC.     

Kinetic analysis of crystallization of zeolite beta synthesized by direct heating

To quantitatively investigate the initial crystallization of zeolite beta synthesized by direct heating, the extent of the reaction was precisely evaluated by X-ray diffraction measurements and Rietveld structural refinement, and a kinetic analysis of crystallization was performed using the Avrami-Erofe'ev equation. The activation energy for crystallization was lower than that for hydrothermal synthesis. Reaction and synthesis time curves revealed that the initial zeolite beta crystallization consisted of three stages. The first was an induction period with nucleation by the generation of building units and the formation of an initial coordinated structure. The second stage was crystal growth by a diffusion-controlled reaction, and the third stage involved slowing down of crystallization by the limitation of dehydrocondensation. These stages could be analyzed by calculation of the rate constant and Avrami exponent for each stage.