Porous anatase layer formed on titanium substrate through hydrothermal processes

A titanium oxide layer containing crystalline anatase was formed on a titanium substrate under hydrothermal conditions. The titanium substrate was reacted in alkaline solutions, potassium hydroxide and a mixture of potassium hydroxide and calcium chloride, at over 120 °C. Potassium titanate and calcium titanate were formed on the substrate and they showed the typical texture of each titanate, the aggregate of the fibrous and the cubic particles, respectively. The layers of calcium titanate and the potassium titanate changed into a titanium oxide layer in a solution of the hydrochloric acid at 180 °C. Both the potassium and the calcium dissolved from the titanate and then the formed amorphous titanium oxide finally crystallized. The fibrous structure of the potassium titanate did not remain after the acid treatment, although the cubic microstructure of calcium titanate remained. Both samples were mainly composed of fine anatase and the grain size and the crystallite size were almost 40–50 nm and 10 nm, respectively. The photocatalytic degradation of gaseous acetaldehyde by the titanium oxide layer was observed under irradiation of UV light.     

柠檬酸钠辅助水热法制备钛酸钙及其紫外光催化性能

以钛酸四正丁酯((C4H9O)4Ti)水解沉淀的钛羟基氧化物和硝酸钙(Ca(NO3)2.4H2O)为反应物料,加入适宜浓度的矿化剂氢氧化钾和络合剂柠檬酸钠,在温度200℃水热反应12h后得到了CaTiO3粉体。利用SEM、XRD、TEM等对CaTiO3的形貌、尺寸和结构进行表征,通过光催化降解罗丹明B(RhB)对其紫外光催化性能进行了研究。结果表明柠檬酸钠在CaTiO3水热合成过程中起到关键性作用,其形貌和紫外光催化性能随着柠檬酸钠浓度改变而发生巨大变化。     

Effects of milling time and calcination condition on phase formation and particle size of lead titanate nanopowders prepared by vibro-milling

Effect of calcination conditions on phase formation and particle size of lead titanate (PbTiO₃) powders synthesized by a solid-state reaction with different vibro-milling times was investigated. Powder samples were characterized using XRD, SEM, TEM and EDX techniques. A combination of the milling time and calcination conditions was found to have a pronounced effect on the phase formation and particle size of the calcined PbTiO₃ powders. The calcination temperature for the formation of single-phase perovskite lead titanate was lower when longer milling times were applied. More importantly, by employing an appropriate choice of the milling time and calcination conditions, perovskite lead titanate (PbTiO₃) nanopowders have been successfully prepared with a simple solid-state reaction method.     

Preparation of monodispersed spherical barium titanate particles

Spherical barium titanate particles with cubic phase were synthesized by a low-temperature hydrothermal reaction. Firstly, The method of hydrolysis of titanium tetrachloride was used for producing spherical TiO₂ particles (0.45–1.5 μ m) with various concentrations of TiCl₄(0.05–0.2 M) and volume ratios of acetone to water solutions (RH = 0–4). These TiO₂ particles were converted to barium titanate by a hydrothermal conversion in a barium hydroxide solution. The size and morphology of the TiO₂ particles was controlled by the volume ratio of acetone to water (RH ratio) in the mixed solvent. At the RH ratio of 3, the morphology of TiO₂ particles was very uniform and discrete. These TiO₂ particles were in the anatase phase and were converted to the rutile phase when the calcination temperature increased to 700∘C and above. Uniform and spherical barium titanate particles were successfully synthesized from the as-prepared TiO₂ particles by using a hydrothermal reaction in a barium hydroxide solution. The Ba/Ti ratios, reaction temperature, and reaction time did not influence the size and morphology of BaTiO₃ particles, but increased the concentration of unfavorable salts such as Ba(OH)₂ and BaCO₃. The high purity BaTiO₃ particles could be obtained by washing with formic acid to remove the unfavorable salts. The size and morphology of the BaTiO₃ particles remained the same as those of the TiO₂ particles, confirming the in-situ transformation mechanism for the conversion of TiO₂ to BaTiO₃. The as-synthesized particles were cubic phase and transformed to tetragonal phase after calcinations at 1150∘C for 1 h. The mean density of the pellets sintered at 1300∘C for 2 h was 5.86 g/cm³ and accounted for 97.34% of the theoretical density.     

Control of the particle size and morphology of hydrothermally synthesised lead zirconate titanate powders

The particle size and morphology of hydrothermally synthesised lead zirconate titanate (PZT) powders can be controlled by concentrations of the mineraliser such as potassium hydroxide (KOH), and the hydrothermal synthesis temperature and time, which all influence the particle nucleation and growth mechanisms. The mineraliser is crucial in facilitating both the in-situ transformation process during the nucleation stage and the nuclei-coagulation process during the subsequent growth stage. Its concentration must be high enough to ensure the formation of only pure perovskite PZT particles but low enough to prevent excessive PZT particle growth. The minimum necessary mineraliser concentration has, however, strong dependence on both the hydrothermal synthesis temperature and chemical environment in hydrothermal solution. Thus, perovskite PZT powders with ca. 200 nm particle size and narrow particle size distribution can be synthesised hydrothermally at 300°C using KOH as a mineraliser with a minimum concentration of 0.4 M.     

纳米氧化高银的制备及抗菌性能

采用液相氧化沉淀法制备纳米氧化高银颗粒.以硝酸银为原料,氢氧化钠为沉淀剂,过硫酸钾为氧化剂,控制pH值为11,反应温度为80℃,在磁力搅拌器上反应30min,静置3h后,离心洗涤数次,70℃真空干燥3h,得到黑色纳米氧化高银颗粒.通过X射线衍射(XRD)、透射电子显微镜(TEM)对纳米氧化高银颗粒的形貌和结构进行表征;采用异养菌测试瓶法,用制备的氧化高银和粒径为30nm的纳米银对金黄色葡萄球菌进行抗菌性能测试.结果表明:制得的球形纳米颗粒粒径为10～30ntn;纳米氧化高银颗粒比纳米银具有更强的杀菌性能.     

TiO_2-Al_2O_3负载型催化剂的制备及其光催化性能

以钛酸四丁酯和氢氧化钠为反应物,采用两步水热法制备TiO2纳米线,并将其原位负载于Al2O3载体上,研究它们对甲基橙的光催化降解性能。结果表明,锐钛矿相TiO2主要呈纳米线和八面体状负载在Al2O3载体上,当TiO2负载质量分数为30%,焙烧温度为400℃,催化剂用量为1.332 0 g/L时,TiO2-Al2O3负载型催化剂光催化降解甲基橙的性能最佳,光照5 h后,甲基橙在紫外和太阳光下的降解率分别达到58.9%和55.6%。相同实验条件下,TiO2-Al2O3负载型催化剂对甲基橙的降解率比单纯TiO2提高了35.1%。     

Dissolution/recrystallization growth of titanate nanostructures by amorphous precursor

Understanding of growth mechanism is of technical importance for tailoring the size and morphology of titanate nanostructures. However, the growth mechanism of titanate nanostructures in alkali solution systems by using crystalline TiO₂ remains debating currently. In the present work, the amorphous precursor of titanium hydroxide precipitates, a highly disordered raw material, was used as the precursor to prepare the titanate nanostructures under hydrothermal conditions. SEM and TEM results show that the morphology of the titanate nanostructures developed from nanoparticles to nanosheets and then the titanate nanowires with an interlayer spacing of 0.786 nm as the reaction time prolonged. XRD and Raman spectra results display that layered titanate nanostructure were formed. These phenomena are similar to that of the titanate nanostructures prepared by the TiO₂ crystal in alkali solution systems. The findings provide direct evidence to strongly support that titanate nanostructures grow from dissolution/recrystallization process under hydrothermal process, allowing mediating the size and morphology of titanate nanostructures. Moreover, SEM and photocatalytic results implied that the washing process improved the photocatalytic activities, which had no effect on the overall morphology.     

Effects of reaction parameters on solution combustion synthesis of lepidocrocite-like K0.80Ti1.733Li0.267O4: phase formation and morphology evolution

A lepidocrocite-like potassium lithium titanate K_0.80Ti_1.733Li_0.267O₄ (KLTO) with layered structure was synthesized by an auto-igniting solution combustion method using glycine and metal (Ti, K and Li) nitrate as reactants. The crystalline structure and morphology of the as-prepared product were examined using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Effects of reaction parameters such as ignition temperature and oxidizers to fuel ratio on the phase formation and morphology evolution are investigated in this paper. A pure phase of KTLO was obtained at a low temperature (650 °C) within several minutes. Excessive glycine added into the aqueous precursor solution facilitated the synthesis of a pure and well-crystallized product. As-prepared particles exhibited plate-like shape with a length of 5–20 μm and a thickness of about 2 μm. No residual organic compound existed in the product. After the as-prepared product was post solution combustion heat-treated (1100 °C for 2 h), the particles became uniform in size with smooth surface and well-defined crystalline structure. The product exhibited excellent ion-exchange, intercalation, and exfoliation properties. The exfoliated titania nanosheets are characterized by high two-dimensional anisotropy with a thickness of about 20 nm and a lateral size ranging from sub-micrometers to several tens of micrometers.     

Sol-solvothermal synthesis and characterization of fine lead zirconate titanate particles

We present a novel low-temperature sol-solvothermal method to synthesize fine lead zirconate titanate (PZT) particles. This sol-solvothermal method combines the advantages of conventional sol–gel process and the solvothermal method, and isopropyl alcohol (IPA) was used as the solvent. The effects of different parameters including KOH concentration, IPA/(IPA + water) ratio and reaction temperature, on the microstructures of the PZT powder were studied. With increasing KOH concentration and reaction temperature, the crystalline structure of as-synthesized PZT transformed from tetragonal to rhombohedral phase. More IPA added in the solvent can effectively reduce agglomeration of the PZT powder and decrease the crystallization temperature, but impurity phase was also detected at high IPA/(IPA + water) ratio. As a result, the synthesis parameters are optimized, and well-crystallized 700 nm PZT particles were successfully synthesized in 2.0 M KOH and 50 % IPA/(IPA + water) ratio at temperatures as low as 120 °C.     

用水氯镁石制备单分散六角片状氢氧化镁

用水氯镁石为原料,氢氧化钠为沉淀剂,常压下合成氢氧化镁,在不加入任何改性剂的条件下,对反应后的料浆进行水热处理,并用扫描电镜（SEM）、X射线衍射仪（XRD）和激光粒度仪表征所得产品的形貌、结构及粒度分布,主要考察了水热反应时间和水热反应温度对氢氧化镁产品的影响.结果表明：在120℃水热4h条件下的过滤速率是未经水热条...     

AgInSbTe相变薄膜的热刻蚀腐蚀特性

研究了AgInSbTe相变薄膜作为一种新的热刻蚀材料的腐蚀特性。采用射频磁控溅射的方法在室温下制备了非晶态AgInSbTe薄膜, 经真空加热退火晶化. 以氢氧化钠溶液作为腐蚀剂, 研究了退火温度、腐蚀剂浓度、腐蚀时间对晶态、非晶态 AgInSbTe薄膜腐蚀特性的影响. 结果表明: 以非晶态形式存在的沉积态AgInSbTe薄膜在0.001 mol/L氢氧化钠溶液中腐蚀速度小于0.04 nm/min, 退火晶化后, 薄膜的腐蚀速度大幅度提高, 晶态和非晶态薄膜的腐蚀选择比随退火温度的升高而增大. 当腐蚀时间为20 min时, 经300℃真空退火的晶态AgInSbTe薄膜比相应非晶态的腐蚀速度高45倍以上. 腐蚀后薄膜表面质量良好(粗糙度＜1 nm, 10 μm×10 μm区域). 并对AgInSbTe相变薄膜的腐蚀机理进行了讨论.     

Synthesis of nanostructured bismuth titanate microspheres

A hydrothermal method was developed for the synthesis of bismuth titanate nanostructured microspheres. The precursor powder was prepared using a diethylene glycol mediated coprecipitation method. The as-synthesized nanostructured microspheres consisting of granular nanoparticles and nano-platelets were obtained through a hydrothermal treatment of the precursor powder in aqueous sodium hydroxide solution. Tailoring of the morphology was achieved by changing the precursor quantity, sodium hydroxide concentration, and reaction time. The formation mechanism of the nanostructured microspheres probably involves aggregation, followed by dissolution and recrystallization. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the phase purities, morphologies, and composition of the products.     

离子交换树脂法制备高纯超细氢氧化镁

以强碱性阴离子树脂作为沉淀剂,采用离子交换法制备了高纯超细的氢氧化镁粉体,就离子交换反应过程中的反应温度、反应时间、MgCl2浓度等条件对Mg（OH）2粒径的影响进行了探讨,并利用扫描电镜、微机差热天平、X射线衍射仪对产物进行了表征,实验结果表明,在氯化镁溶液浓度为0．1mol／l,反应温度为60℃,反应时间为16h的条件下可制备出形貌规则、分散性较好的六方片状氢氧化镁,平均粒径可达到100nm左右。     

Hydro(Solvo) Thermal Synthesis and Characterization of Bax Sr1-x TiO3 Nanopowders

Nano-sized barium strontium titanate (BaxSr1-x TiO3, BST) powders were synthesized with hydrothermal and solvothermal methods at 120 ℃ for 4 h based on the reaction precursor of barium acetate, strontium acetate, tetrabutyl titanium and (CH3 )4NOH. The crystalline phase, particle size and morphology of the BST powders were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Influences of reaction temperature and reaction time on the morphologies of powders were also discussed.     

Direct precipitation of lead zirconate titanate by the hydrothermal method

Direct precipitation of fine powders of lead zirconate titanate (PZT) in the complete range of solid solution, is investigated under hydrothermal conditions, starting from lead oxide and titania/zirconia mixed gels. The perovskite phase is formed in the temperature range of 165 – 340°C. Sequence of the hydrothermal reactions is studied by identifying the intermediate phases. The initial formation of PbO: TiO₂ solid solution is followed by the reaction of the same with the remaining mixed gels giving rise to X-ray amorphous PZT phase. Further, through crystallite growth, the X-ray crystalline PZT is formed. This method can be extended for the preparation of PLZT powder as well. The resulting powders are sinterable to high density ceramics.     

碳酸铝铵法制备圆饼状α-Al_2O_3粉末

在碳酸铝铵法制备氧化铝工艺的基础上,通过加入晶体生长促进剂及改变热分解工艺等方法,有效控制了α-Al2O3颗粒的大小和形貌。结果表明:促进剂对α-Al2O3的相变过程影响很大,加入促进剂后使其相转变温度降低了200℃,至1000℃时已完全转变为α-Al2O3相;升温方式对α-A2lO3颗粒的形貌影响很大,将含促进剂的样品直接入高温炉煅烧时,倾向于形成六角片状颗粒;而先低温后高温煅烧时则会形成圆饼状颗粒。通过控制升温过程,可以控制得到粒径较小的圆饼状α-Al2O3颗粒,且分散性良好。     

Hydrothermal synthesis of fibrous lead titanate powders

A fibrous lead titanate (PbTiO₃) powder with light-yellow colour has been prepared by hydrothermal synthesis. The influences of Pb/Ti ratio (0.3 to 1.0) in the mixture and reaction time on the formation of fibrous PbTiO₃ under hydrothermal conditions have been investigated. The preferable conditions for preparing fibrous perovskite-type PbTiO₃ from fibrous potassium titanate are that the Pb/Ti ratio is 1.0, reaction temperature 150 °C and time 72 h. The particles of fibrous powder of perovskite type are usually less than 2 m in diameter and more than 50 m in length. The fibrous morphology is essentially unchanged up to about 650 °C, but it disappeared after heating to 1000 °C.     

微波水热法合成钛酸钠盐纳米管

采用微波水热法合成了钛酸钠盐纳米管,考察了原料、反应时间、NaOH浓度等主要影响因素.在微波功率195W、NaOH浓度8—12mol/L、反应时间>70min条件下,得到了形貌均一的钛酸钠盐纳米管,并用TEM、XRD、BET、EDAX和N₂吸附/脱附等对产物进行了表征.研究表明,微波法制得的纳米管合成时间短、热稳定性高,其管壁塌陷温度高于500℃,比普通水热法合成的高100℃左右;所得样品在300℃以上煅烧,可转化为单晶钛酸纳盐纳米管.     

The reactivity of sodium borohydride with various species as characterized by adiabatic calorimetry

The reactivity of sodium borohydride in the presence of other species has been examined by adiabatic calorimetry. In combination with water, sodium borohydride exhibits an exotherm at room temperature accompanied by generation of gas (presumed to be hydrogen). Addition of potassium hydroxide to a sodium borohydride-water mixture is found to stabilize the solution and require a higher temperature for reaction to occur. However, if iron oxide is also included, reaction takes place near room temperature. Very rapid reaction was found when a metal chloride was brought in contact with a solution containing sodium borohydride, water, and potassium hydroxide. When sodium borohydride was added to an oxygenated hydrocarbon, reaction at room temperature also took place, but to a more limited extent. Peak temperatures above 200 degrees C and maximum pressures in excess of 2000 psia were observed in most cases. Kinetics extracted from the calorimetry data are presented for some of the sodium borohydride combinations.