Preparation and photocatalytic kinetics of nano-ZnO powders by precipitation stripping process

Ultra-fine zinc oxalate powders were prepared through a precipitation stripping method with bis(2-ethylhexyl) phosphate (HDEHP) diluted by tetrachloride carbon as the extractant, and oxalic acid ethanol aqueous solution as the re-extractant and precipitator. Zinc oxide powders were obtained by decomposing zinc oxalate powders at 450°C. The prepared zinc oxide powders were characterized by transmission electron microscope (TEM), Scanning electron microscope (SEM), Thermogravimetric analysis (TG), X-ray diffraction (XRD) and Fourier transmission infrared (FT-IR) spectrum. The photocatalytic performance of methylene blue by zinc oxide was studied based on the Langmuir model and Photo-Layer model. The results show that some zinc oxide powders were micro-multipore materials with hexagonal crystal. The particle size was around 32 nm. The photocatalytic process was the control step in the chemical reaction. The photo catalytic process followed pseudo-first order kinetics and •OH concentration inside the photo-layer in different reaction condition were calculated according to the Photo-Layer model.     

蛇纹石/La复合粉体的制备及其摩擦性能

分别采用水溶液沉淀法和乙醇溶液沉淀法制备了蛇纹石/La复合粉体,并分别在120℃（脱除吸附水）和700℃（蛇纹石脱除羟基）对复合粉体进行了干燥和煅烧热处理。利用X射线衍射法、扫描电子显微镜、能谱分析表征了复合粉体的物相组成、微观形貌。利用MM-10W型多功能摩擦磨损试验机对复合粉体的摩擦性能进行了评价。结果表明：蛇纹石/La复合粉体中,La化合物呈纳米颗粒,并包覆在蛇纹石表面;700℃煅烧将导致蛇纹石/La复合粉体物相变化和摩擦性能变差;120℃干燥处理的蛇纹石/La复合粉体具有良好的减摩-抗磨性能,摩擦因数较未添加者降低22.48%以上。     

Synthesis and performance of surfactants based on epoxidized methyl oleate and glycerol

A small series of surfactants based on methyl oleate and glyceroe was synthesized. The synthesis utilizes an epoxidation reaction of methyl oleate followed by a simple esterification. The resultant products have between two and seven glyceride units, and their performance properties, including aqueous surface tensions and dynamic aqueous surface tensions, were studied. The droplet size of soybean oil/water emulsions made with each surfactant was also studied. The surfactants show properties similar to alcohol ethoxylates, such as the reduction of aquous surface tension to ∼34 mN m⁻¹. Additionally, because the synthesis leaves the epoxide functionality in the surfactant, further modification for performance optimization is possible.     

Adhesion of air bubbles to a fluorite surface in the presence of oleate species

Measurements of the detachment force of air bubbles from a surface of fluorite covered with an oleate film immersed in an aqueous sodium oleate solution or water were carried out. The contact angles for the systems fluorite/oleate film-drop of aqueous sodium oleate solution-air, fluorite/oleate film-air bubble-aqueous sodium oleate solution, and fluorite/oleate film-air bubble-water were also measured. The detachment forces were also calculated from the measured contact angles. It was found that the adhesion of air bubbles to the fluorite surface increased considerably in the presence of an oleate film on the fluorite surface, but decreased if the oleate film was at the water-air interface. Good agreement between the theoretically calculated and the measured values of the detachment force for the system fluorite/oleate film-air bubble-sodium oleate aqueous solution when the concentration of this latter solution was in the range 0 to 87.1 mg/dm³ was also found, but for concentrations over 87.1 mg/dm³ the calculated values of the detachment force were higher than the measured values. The calculations and measurements indicate that the most favourable condition for the adhesion of air bubbles to fluorite grains is the presence of a chemisorbed film of oleate without surface precipitation of calcium oleate salt at low concentrations of oleate species in water.     

Oxidation and Degradation of Titanium Nitride Ultrafine Powders Exposed to Air

Titanium nitride ultrafine powders were synthesized by an active plasma-metal reaction method. Gas desorption measurements were conducted to estimate the surface chemistry of the powders after exposure to air and storage at room temperature. H₂O, H₂, CO₂, CO, and NH₃ gases were mainly evolved. These gases were considered to be formed by the surface reaction of adsorbed gases on surface oxide of the powders and decomposition of hydroxide-like or ammonialike compounds, which might be produced during a slow oxidation treatment and storage.     

超细氧化钇粉体的制备

湿化学法制备超细粉体时，反应、分离、干燥以及灼烧都不同程度地影响粉体的粒径及团聚。在传统的草酸沉淀法制备氧化钇基础上对溶液的浓度、pH值以及表面活性剂的选择和用量、颗粒的表面电位进行了考察研究，确定了反应过程中影响粉体粒径的各个因素，得到一次粒径50－100nm，平均粒径0.521μm，晶型良好且具有单分散趋势的超细氧化钇。     

Reaction Sintering of Submicrometer Silicon Powder

Submicrometer silicon powder synthesized by thermally induced, vapor-phase reaction in an aerosol reactor was densified by reaction sintering to form Si₃N₄. The densification behavior of these spherical, nonagglomerated particles in the 0.1 to 0.2 μm size range is described. Competition between densification by silicon sintering and reaction product infilling was observed at typical reaction sintering temperatures. In addition, pore growth during the early stages of silicon presintering adversely affected nitrogen permeability and nitriding rates. The factors influencing the nitridation of ultrafine silicon powders are discussed.     

高分散氧化镁粉体的制备及反常红外特性

以六水氯化镁为原料,氢氧化钠和氨水为沉淀剂,采用直接沉淀法合成出前驱物氢氧化镁粉体;再将氢氧化镁煅烧后得到氧化镁粉体产品。通过X射线衍射(XRD)、扫描电镜(SEM)和红外吸收光谱(FT-IR)等对所得产品进行表征分析。结果表明,在煅烧温度为400℃,煅烧时间为3h的条件下,可以得到高分散性的颗粒状氧化镁;在400℃下煅烧8h得到的氧化镁粉体的红外吸收峰出现了红移和蓝移同时并存现象。     

超临界流体干燥法制备纳米掺锑氧化锡粉体

以SnCl4.5H2O和SbCl3乙醇溶液为原料制备前驱体掺锑氢氧化锡胶体沉淀,采用乙醇超临界流体干燥法干燥前驱体;用TG-DTA、XRD、TEM、BET等方法对粉体的结构、物相、形貌进行表征。结果表明,采用乙醇超临界流体干燥法可得到高比表面积的掺锑氧化锡纳米粉体。     

Combustion synthesis of silicon nanopowders

Silicon nanopowders with high surface area were synthesized by reduction-type combustion reaction between silicon oxide and magnesium. Main advantages of the method are its simplicity and uniqueness of product characteristics. Microstructural analysis of the powders synthesized from different raw materials allowed us to suggest the mechanism of structural transformations taking place in the combustion wave. Based on this mechanism, an effective approach to controlling the microstructure of final product was proposed.     

The correlation between froth flotation response and collector adsorption from aqueous solution. Part I. Titanium dioxide and ferric oxide conditioned in oleate solutions

Samples of pure ferric oxide and titanium dioxide have been conditioned in aqueous oleate solutions over the pH range 2–12. The extent of oleate adsorption was determined from the heat of combustion of the adsorbed film, using DTA. Adsorption isotherms have been constructed at pH values above and below both the pK of oleic acid and the isoelectric points of the oxide surfaces.It appears that at low oleate concentrations, adsorption is due to negatively charged carboxylate ions interacting with positively charged surface sites. When sufficient surface has been covered with hydrophobic hydrocarbon chains, froth flotation becomes possible. With increasing oleate concentration, competition for positive sites forces the adsorbed ions into a vertical orientation, thereby exposing some previously covered surface. Once the positive sites have been “neutralised”, subsequent adsorption must occur at neutral or negative parts of the surface. This is likely to involve mutual attraction between the hydrocarbon groups of vertically adsorbed oleate ions, and those of oleate ions in solution. Newly adsorbed oleate ions would then be expected to be oriented with their negatively charged carboxylote groups away from the surface. Hence, increasing adsorption, as the collector concentration is increased, will lead to the surface becoming progressively less hydrophobic, and froth flotation may cease.     

Preparation and photocatalytic kinetics of nano-ZnO powders by precipitation stripping process

Ultra-fine zinc oxalate powders were prepared through a precipitation stripping method with bis(2-ethylhexyl) phosphate (HDEHP) diluted by tetrachloride carbon as the extractant, and oxalic acid ethanol aqueous solution as the re-extractant and precipitator. Zinc oxide powders were obtained by decomposing zinc oxalate powders at 450uC. The prepared zinc oxide powders were characterized by transmission electron microscope (TEM), Scanning electron microscope (SEM), Thermogravimetric analysis (TG), X-ray diffraction (XRD) and Fourier transmission infrared (FT-IR) spectrum. The photocatalytic performance of methylene blue by zinc oxide was studied based on the Langmuir model and Photo-Layer model. The results show that some zinc oxide powders were micro-multipore materials with hexagonal crystal. The particle size was around 32 nm. The photocatalytic process was the control step in the chemical reaction. The photo catalytic process followed pseudo-first order kinetics and •OH concentration inside the photo-layer in different reaction condition were calculated according to the Photo-Layer model. __________ Translated from Transactions of Beijing Institute of Technology, 2007, 27(7): 641–645 [译自: 北京理工大学学报]     

表面活性剂对纳米氧化锌粉体分散性的影响

以硝酸锌、碳酸氢铵为原料,通过沉淀反应制备ZnO超细粉体。考察了制备过程中不同种类、添加量的表面活性剂(DBS、PEG、Tw-80)对ZnO粉体平均粒径的影响。试验结果表明:在沉淀过程中添加表面活性剂可抑制前驱体碱式碳酸锌的长大和团聚,制备出的ZnO粒径小,粒径分布范围窄,且Tw-80的分散效果优于DBS和PEG。     

高分散氧化镁粉体的晶格畸变研究

以六水氯化镁为原料,氢氧化钠和氨水为沉淀剂,采用直接沉淀法合成出高分散氢氧化镁粉体;再将前驱物氢氧化镁煅烧后得到高分散氧化镁粉体产品。通过X射线衍射(XRD)和扫描电镜(SEM)对所得产品的分析表征结果表明,氧化镁粉体的微结构中存在晶格畸变,表现为晶格膨胀。随煅烧温度的升高,氧化镁粉体的晶格常数减小,晶格畸变量也减小。     

Collector adsorption during froth flotation

The adsorption of oleate on ferric oxide, conditioned in aqueous solution at pH 9.0, has been determined from the heat of combustion of the adsorbed oleate by differential thermal analysis. Measurements were made over a range of oleate concentrations on the conditioned material prior to flotation and on floated ferric oxide. The resulting adsorption isotherms show that the floated material usually carries less, and never more, adsorbed oleate than the conditioned but unfloated material. This is contrary to what would have been expected front the work of Digre and Sandvik; the explanation is probably that sorption equilibrium conditions hare been established in our measurements, but not in those of the workers mentioned above.     

Effect of Sodium on Crystallite Size and Surface Area of Zirconia Powders at Elevated Temperatures

Fine ZrO₂ powders were synthesized by an aqueous precipitation method using zirconyl nitrate. By adding the precursor salt to NaOH, single-phase ZrO₂ powders were formed, and the monoclinic phase did not appear upon heat treatment up to 1000°C. The samples were digested in NaOH for different amounts of time. Different levels of washing of digested samples produced surface area at 900°C for 4 h ranging from 8 to 100 m²/g. It was found that the properties of the powders at elevated temperatures were sensitive to the sodium content. The surface area decreased while the crystallite size and pore size of the samples increased with increased sodium content. Our results indicated that sodium is detrimental to the stabilization of surface area at elevated temperatures.     

Annealing effects for calcination of tin oxide powder prepared via homogeneous precipitation

Tin oxide powders were prepared from a homogeneous precipitation using the aqueous solution of SnCl₄ with urea as a precipitator at 90 °C and followed by a calcination process. The calcination was performed using two different methods; conventional furnace annealing (CFA) and rapid thermal annealing (RTA). The crystallization of the tin oxide finished at 600 °C regardless of the calcination method used. The crystallite size increased with as the calcination temperature increased due to the crystal growth and agglomeration. The tin oxide calcined using RTA has a relative smaller crystallite size than CFA at the same temperature. The tin oxide powders calcined with RTA showed higher specific surface areas than those that used CFA over a wide range of temperatures.     

Sol–gel synthesis and catalytic properties of vanadium phosphates

Vanadium phosphates with variable specific surface areas were synthesized from vanadium alkoxides and phosphoric acid by precipitation in various solvents. The catalytic properties were studied in the reaction of methanol oxidation. Although the specific activities increase with the specific surface areas (BET), the intrinsic activities seem to depend on the particle morphology. The selectivities do not vary within a large range. The same method of precipitation was applied to prepare vanadium phosphates on a silica support. It is shown that the supported phase is highly dispersed, and that these supported catalysts are more stable than silica‐supported vanadium oxide for methanol oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ketones from carboxylic acids over supported magnesium oxide and related catalysts

Silica-supported alkaline earth oxides revealed excellent activity to convert acetic acid selectively into acetone in a vapor-phase fixed-bed flow system. Acetone was obtained through the cyclic formation of alkaline earth acetate followed by decomposition. Magnesium oxide should be supported on the silica surface without formation of magnesium silicate, which was inactive for the present reaction. Attempted syntheses of benzophenone and acetophenone are also described.     

Effect of process parameters on the microstructure and property of hydroxyapatite precursor powders and resultant sintered bodies

Nanocrystalline hydroxyapatite (HA) ceramic could have better potential in biomedical application due to its high bioactivity and mechanical strength. This study aimed at investigating on the relationship between the starting HA powders and resultant HA ceramics. The synthesized HA crystals using chemical precipitation showed different morphology, size, and crystallinity under different reaction temperature and aging time. The spray-dried HA powders from the different HA slurries synthesized at 40, 60, and 80°C had spherical shapes and similar particles size but different specific surface area (SSA). Lower synthesizing temperature resulted in lower crystallinity and need-like shape of the HA crystals, and thus higher SSA of the spray-dried HA powders. After cold isostatic pressing of the HA powders, the HA green compacts were sintered at 1000, 1050, and 1150°C, respectively, and they presented different sinterability, compactness, and mechanical strength, which were tightly dependent on the starting HA powders. As compared to 80°C synthesized powders, 40 and 60°C synthesized powders exhibited better sinterability due to the lower crystallinity and higher SSA, leading to the relatively high compactness and mechanical strength, but small grain size below 100 nm of the resultant HA ceramics even at low sintering temperature of 1050°C.