Hydrothermal synthesis and formation mechanism of tetragonal barium titanate in a highly concentrated alkaline solution

Tetragonal cube-shaped barium titanate (BaTiO₃) was produced by the hydrothermal treatment of a peroxo-hydroxide precursor, a single-source amorphous barium titanate precursor, in a highly concentrated sodium hydroxide solution. Phase pure barium titanate with cube-shaped morphology and particle-sizes in the 0.2–0.5 µm range were formed at temperatures above 80 °C. Also, the cube-shaped morphology of the BaTiO₃ product was preceded by spherical- and plate-like morphologies with, respectively, a Ti-excess and Ba-excess. Coinciding with these morphological observations, changes in the reaction product were also observed. The formation of crystalline BaTiO₃ proceeded alongside secondary BaTi₂O₅ and Ba₂TiO₄ phases. These secondary phases disappeared as the reaction time was increased leaving only BaTiO₃ as the sole reaction product. Kinetic analysis of the formation of hydrothermal BaTiO₃ crystallization by the Johnson-Mehl-Avrami method showed that BaTiO₃ crystallization is a homogeneous dissolution-precipitation reaction. The mechanism is governed by nucleation and growth in the beginning of the reaction and dissolution-precipitation dominating throughout the hydrothermal reaction process.     

Effect of vibro-milling time on phase formation and particle size of barium titanate nanopowders

Barium titanate (BT) nanopowder was synthesized by a solid state reaction via a rapid vibro-milling technique. The effect of milling time on phase formation and particle size of BT powder was investigated. Powder samples were characterized using XRD (X-ray diffraction) and SEM techniques. It was found that the resulting BT powders have a range of particle size depending on milling times. Production of a single-phase BT nanopowder can be successfully achieved by employing a combination of 30 h milling time and calcination conditions of 1200 °C for 2 h.     

空心钛酸钡的制备及其形成机理

以二氧化钛（TiO₂）和八水合氢氧化钡[Ba（OH）₂·8H₂O]为原料,采用水热合成法,成功制备出具有四方相晶型和空心形貌结构的钛酸钡粉体。利用透射式电子显微镜（TEM）和X射线衍射（XRD）对样品的形貌结构和晶型做了表征,通过研究反应过程中钛酸钡粉体的结构和晶型随时间的变化过程,对空心钛酸钡的形成机理做了详细的探讨,并考察了不同反应温度和钡浓度对钛酸钡粉体结晶和生长的影响。研究结果表明：反应温度和钡浓度会影响钛酸钡粉体的晶型和形貌,并以此提出了一种空心钛酸钡的形成机理;当反应温度为180 ℃、钡浓度为3.0 mmol/L时,能获得粒径分布均匀的四方相晶型的空心钛酸钡粉体。     

A facile route for synthesis of mesoporous barium titanate crystallites

Well crystallized BaTiO₃ with meso-structure inside the crystallites was directly synthesized from the solution via a simple sol-precipitation process with cetyltrimethylammonium chloride (C₁₆TMAC) as the cationic surfactant. Mesoporous structure (pore size distribution peaking at 2.2 nm) with single crystalline wall was obtained after removal of the template by calcination. The pores were locally ordered for some regions but wormhole-like on the whole view. The resulting materials were characterized with wide-angle and low-angle X-ray diffraction, SEM, TEM and low temperature nitrogen adsorption–desorption isotherms. A specific surface BET area of 50 m²/g was obtained. Formation mechanisms of the single-crystalline mesoporous structure are discussed. The present method avoids onerous heat treatment procedure for crystallization and provides an efficient way to synthesize mesoporous functional multi-metallic oxides with single-crystalline wall.     

粉体的燃烧合成技术及其在钛酸钡粉体制备中的应用

综述了燃烧法合成陶瓷粉体的原理、方法及其在钛酸钡粉体制备中的应用 ,比较了各种燃烧法合成钛酸钡粉体工艺的优缺点 ,并指出目前经济、有效地制备钛酸钡粉体的方法是以有机燃料和金属硝酸盐为原料的低温燃烧合成法。     

Microwave-hydrothermal synthesis of barium titanate under stirring condition

The role of in situ stirring under microwave-hydrothermal (M-H) conditions on the synthesis of barium titanate was investigated for the first time by powder X-ray diffraction and scanning and transmission electron microscopy. Stirring under M-H conditions in the temperature range of 150–200 °C led to enhanced crystallization of Ba titanate as revealed by yields compared to the static condition. In addition, stirring led to smaller and more uniform crystals under M-H conditions compared to those crystallized without stirring. Powder X-ray diffraction revealed the formation of only cubic polymorph of Ba titanate at or below 200 °C in 4 h with or without in situ stirring under M-H conditions. These results show that stirring is an important parameter during M-H synthesis of nanophase Ba titanate.     

钛酸钡纳米复合材料制备与性能研究

对钛酸钡颗粒进行羟基化和巯基官能化处理,将纳米银粒子成功接枝到钛酸钡颗粒表面制备了x Ag@BT颗粒(x为银质量分数,BT为钛酸钡),并用溶液共混法制备了Ag@BT/PVDF纳米复合材料(PVDF为聚偏氟乙烯)。结果表明,x Ag@BT颗粒为具有草莓结构的纳米颗粒,尺寸为2~16 nm的银粒子成功装饰在钛酸钡颗粒表面;纳米银粒子的引入可以降低复合材料在低频下的介电损耗和电导率,且当纳米银粒子质量分数为1.0%时复合材料的特征击穿强度达到最大值;与传统BT/PVDF纳米复合材料相比,1.0%Ag@BT/PVDF纳米复合材料具有更优良的电性能。     

燃烧合成钛酸钡粉体的研究进展

近年来，高纯超细钛酸钡粉体的制备技术发展十分迅速，它们在钛酸钡电子陶瓷的应用研究中起着日益重要的作用。燃烧法制备陶瓷粉体是一种新型的材料合成工艺技术，有其独特的优点和特点。简要回顾了燃烧法合成的历史，对燃烧法合成无机粉体现有工艺做了新的分类和介绍，最后就燃烧合成钛酸钡粉体的制备技术做了综述。     

Evolved gas analysis during sintering of barium titanate

The gases evolved during the sintering of BaTiO₃ have been examined with a combined dilatometer and mass spectrometer (CDMS) apparatus. The CDMS acquires multiple mass/charge ratios in real time while simultaneously recording dilatometry data. To identify the chemical composition of the numerous recorded mass/charge ratios, cracking patterns, isotopic abundances and decomposition reactions from model compounds (BaCO₃, BaSO₄) were used. Three primary regions of gas evolution were identified. During the heating ramp and into the hold period at 1350°C, CO₂ appears, and below approximately 500°C, this may arise from adsorbed or surface CO₂. Sulphur dioxide was also observed, and its evolution occurred directly after the majority of the CO₂ appeared and immediately preceded the onset of sintering. Above 1200°C, CO₂ is the primary species observed in the gas phase. The implications of the high temperature chemistry on sintering and on microstructural development are discussed.     

Effects on aqueous barium titanate tape properties of passivation of barium ion leaching by using dispersants

To passivate a barium titanate (BaTiO₃) ceramic powder surface from Ba²⁺ ion leaching in water, passivation agent layer (PAL) was formed by drying the slurry after adding a commercial polymeric dispersant. By following the several characteristic steps of actual MLCC production process, slip and green properties were compared for two different polymer-adding modes; one is the PAL and the other is the conventional dispersant mode. Compared to the conventional dispersant adding method, PAL mode was the only effective way in reducing the amount of Ba²⁺ leaching. However, slip viscosity and green body properties were not a function of adding mode but a function of dispersant itself, which means using PAL did not deteriorate any of slip and green properties of BaTiO₃.     

Formation of sodium bismuth titanate—barium titanate during solid‐state synthesis

Phase formation of sodium bismuth titanate (Na_0.5Bi_0.5TiO₃ or NBT) and its solid solution with barium titanate (BaTiO₃ or BT) during the calcination process is studied using in situ high‐temperature diffraction. The reactant powders were mixed and heated to 1000°C, while X‐ray diffraction patterns were recorded continuously. Phase evolutions from starting materials to final perovskite products are observed, and different transient phases are identified. The formation mechanism of NBT and NBT–xBT perovskite structures is discussed, and a reaction sequence is suggested based on the observations. The in situ study leads to a new processing approach, which is the use of nano‐TiO₂, and gives insights to the particle size effect for solid‐state synthesis products. It was found that the use of nano‐TiO₂ as reactant powder accelerates the synthesis process, decreases the formation of transient phases, and helps to obtain phase‐pure products using a lower thermal budget.     

四方相钛酸钡超细粉体的水热合成研究

采用水热法在温和条件下制备出分散性好的四方相钛酸钡超细粉体。通过考察反应物钡（Ba2+）与钛（Ti4+）物质的量比、反应温度、反应时间、反应体系碱度等条件对制备四方相钛酸钡的影响,得出最佳制备条件。在反应物Ba2+与Ti4+物质的量比为2.0∶1、强碱性条件、反应温度为180 ℃、反应时间为72 h条件下,可以制备出粒径在80~140 nm的四方相钛酸钡（BaTiO3）超细粉体。采用化学分析法测得钛酸钡样品Ba与Ti物质的量比为0.995~1.005。在500 L高压釜中进行了工业放大实验,采用工业原料在动态条件下制备出粒径为100~200 nm的四方相钛酸钡超细粉体。     

Accelerated formation of barium titanate by solid-state reaction in water vapour atmosphere

Barium titanate (BaTiO₃) powders were synthesized from commercially available raw materials (BaCO₃ and rutile) without particular mechanochemical processing by solid-state reactions in water vapour atmosphere. The formation rate of BaTiO₃ was accelerated by water vapour and single phase of BaTiO₃ was obtained by calcination at 700 °C for 4 h in water vapour atmosphere, though high temperature (850 °C for 2.5 h) was required by calcinations in air to complete the reaction. The formation kinetics followed the Valensi–Carter equation, which suggested that the reaction proceeded by a diffusion controlled process. The apparent activation energy for the formation of BaTiO₃ in air and water vapour atmosphere was estimated to be 361 ± 20 kJ/mol and 142 ± 17 kJ/mol, respectively. Water vapour is considered to enhance thermal decomposition of BaCO₃ and formation of BaTiO₃ by attacking surface Ti–O–Ti bonds in TiO₂, increasing partial pressure of Ba(OH)₂, and producing vacancies in the BaTiO₃ structure.     

Facile synthesis of nanorods of tetragonal barium titanate using ethylene glycol

Tetragonal barium titanate (BaTiO₃) nanorods were synthesized from hydroxide precursor by a hydrothermal/solvothermal method with 10 vol% ethylene glycol as solvent. The hydroxide precursor slurry was prepared by the addition of 10 M NaOH to a mixed solution of BaCl₂ and TiCl₄. When the above aqueous slurry was heated with water only at 200 °C, cubic BaTiO₃ nanocrystals formed, whereas tetragonal BaTiO₃ nanorods were obtained when heated with 10 vol% ethylene glycol. The crystallization of cubic BaTiO₃ via dissolution–reprecipitation of precursor could be suppressed by the addition of ethylene glycol, resulting in the formation of tetragonal BaTiO₃ under hydrothermal treatment at 200 °C.     

The effect of the hydrothermal synthesis variables on barium titanate powders

In this work, the influence of (a) Ba excess in the starting hydrothermal mixture with TiO₂, (b) hydrothermal reaction temperature, and (c) washing cycles on the hydrothermal synthesis of barium titanate (BaTiO₃) were investigated to assess their relative contributions to the final characteristics of the sintered oxide. BaTiO₃ cake was prepared by hydrothermal synthesis at 150 °C and 180 °C using BaOH₂·8H₂O and TiO₂·xH₂O as starting hydrothermal mixture with an excess of Barium (+1 Ba mol% and +2 Ba mol%). The obtained BaTiO₃ cake was washed several times from 0 to 14 (W_n<15) using simple de-ionized water and then sintered at 1120 °C for 3 h. All considered hydrothermal syntheses variables strongly contribute to the final characteristics of the sintered BaTiO₃ powders in terms of Ba²⁺/Ti⁴⁺ molar ratio, crystalline structure and mean particle size. In particular, it is clear from these experiments that the removal of the unfavorable barium salts from BaTiO₃ cake by long washing cycles before final calcination is a critical step in the hydrothermal synthesis of BaTiO₃.     

Rheological properties of nanosized barium titanate prepared by HGRP for aqueous tape casting

The conditions for the preparation of stable nanosized barium titanate suspensions with high solids content for the production of aqueous tape casting are identified. The rheological behavior of colloidal barium titanate suspension with Ammonium polyacrylate (NH₄-PAA) as a dispersant to aid the powder dispersion has been investigated. Nanosized barium titanate powder was synthesized by a continuous high-gravity reactive preparation (HGRP) technique, and then annealed at 900 °C for 2 h. Measuring the zeta potential, the particle size distributions and ball-milling time, assessed the optimum conditions of the suspension with low viscosity and stability. An isoelectric point (IEP) at pH = 2.8 was found. Particle size distribution tests identified an optimum pH value about 10 and an optimum dispersant addition about 1.2 wt.% (based on the dry powder weight). As the ball-milling time was longer than 8 h, the amount NH₄-PAA adsorbed on the barium titanate reached to saturation. The maximum solid content attained during this work was 45 vol.% at pH of 10, with dispersant addition 1.2 wt.%. High green density value (up to ∼55.4% of the theoretical density) in BaTiO₃ sheet was achieved with a solid content 40 vol.%. After sintering at 1200 °C for 2 h a final density of 95% is reached.     

丙烯酸-马来酸水相共聚合过程中的粒径变化研究

以氧化-还原引发剂Na2 S2O8/Na2S2O5引发丙烯酸-马来酸的水相共聚合,用激光光散射粒径分析仪对共聚合过程中的粒径变化进行了研究.结果表明,体系的平均粒径受聚合物链增长和聚合物链间聚结的影响,随着反应进行而增大.通过分析粒径曲线发现,在加料反应阶段,粒径在100 nm以下的粒子始终保持一定数量,同时周期性地形成粒径在100 nm以上的粒子.     

Reduced sedimentation of barium titanate nanoparticles in poly(vinylidene fluoride) films during solution casting by surface modification

Reduced sedimentation of barium titanate (BaTiO₃, BT) nanoparticles during solution casting to prepare the BT/poly(vinylidene fluoride) (PVDF) films is systematically investigated by surface modification of the BT nanoparticles. The surface of BT nanoparticles is hydroxylated by hydrogen peroxide (H₂O₂) or aminated by γ‐aminopropyl triethoxysilane (γ‐APS). It is found that the compatibility between the fillers and polymer matrix is remarkably improved by such surface treatments. As a result, the agglomeration and sedimentation of BT nanoparticles in the BT/PVDF composite films are significantly reduced, which is supported by morphology observation. Better dielectric properties such as higher dielectric constant, higher breakdown strength, and lower dielectric loss are also obtained for the composite films with surface‐modified fillers than those with raw fillers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42662.     

Influence of feedstock concentration on tetragonality and particle size of hydrothermally synthesized barium titanate powders

Barium titanate (BaTiO₃) powders were synthesized through hydrothermal process with Ba(OH)₂·8H₂O and TiO₂. By increasing the feedstock concentration (FC) from 0.25 to 1.50 M, BaTiO₃ powders maintain a stable average particle size (~180 nm and ~6.4441 m²/g) with an increasing tetragonality (c/a: 1.0065–1.0075). Johnson-Mehl-Avrami and standard reaction rate equations were adopted to analyze the kinetic process of BaTiO₃ formation. The reaction is governed by first-order and phase-boundary-controlled mechanism for 0.25 M and 1.50 M, respectively. Lower extent of reaction is believed to lead to the better tetragonality for BaTiO₃ powders fabricated with higher FC. On the other hand, the relative stable particle size is correlated with the unvaried nucleation frequency and grain growth rate with various FC. This work can provide a guideline to manipulate the properties of BaTiO₃ powders used in electronic industry.