Effect of pure-solvents without deflocculants for finer SiC particle dispersed MgO based composite

The deagglomeration process and its effects on the microstructure have been investigated for fine MgO, SiC powders and SiC particle added MgO mixed powders which were ball-milled under both polar- and non-polar solvent without deflocculants. During the drying, exothermic reactions are observed at 300–450 °C in MgO and SiC powders ball-milled in alcohol. On the other hand, no chemical reaction could be observed for the powders ball-milled using acetone, and nn-hexane. The observed exothermic reactions, then, are believed to be due to the oxide and/or oxide layer-alcohol reaction product formed during milling. This mechano-chemical reaction directly affects to deagglomerate during the drying process after wet-milling. Among the alcohol media, the well-dispersibility and deagglomeration of SiC powders as well as MgO powders seem to be reached by n-butyl alcohol, considering the balance between the steric effects and the dielectric constant of alcohol. These dispersion characteristics also effect on the microstructure of SiC particle dispersed MgO based composites.     

Synthesis of Micron and Submicron Nickel and Nickel Oxide Particles by a Novel Laser–Liquid Interaction Process

The laser–liquid–solid interaction is a new technique for synthesis of nickel and nickel oxide particles. The process uses a continuous-wave CO₂ laser beam as the source of thermal energy required to induce precipitation reactions in solution. The uniqueness of the process is the synthesis reaction taking place in a localized region, which allows better control of the chemical reaction. Porous nickel and nickel oxide powders have been synthesized by laser-induced reactions between a nickel nitrate hexahydrate [Ni(NO₃)₂·6H₂O] precursor and 2-ethoxyethanol-based mixtures. Nickel powders were produced after irradiating a solution of the precursor salt and a 2-ethoxyethanol and d-sorbitol mixture. Crystalline nickel oxide (NiO) powders were isolated after irradiating a solution containing the precursor salt and a 2-ethoxyethanol and water mixture. Powders containing both nickel and nickel oxide crystalline phases were produced after irradiating a solution of the precursor salt and 2-ethoxyethanol. The mean particle diameter is found to be sensitive to irradiation time, substrate thermal conductivity, irradiation power density, and solution concentration. It is hypothesized that nucleation and growth of crystalline phases occurring in irradiated solutions are thermal driven.     

氧化物晶体的成核机理与晶粒粒度

从微观动力学角度研究了晶粒的成核机理,认为晶粒的成核机理主要包括生长基元的形成,生长基元之间的氧桥合作用和Ｏ桥转变为ＯＨ桥。并从核核速度角度分析了影响晶粒粒度的主要原因,揭示了影响晶粒粒度的内部原因为生长基元的生成能、晶体的晶格能,由此总结出不同结构类型的氧化物粉体的晶粒粒度的相对大小,即具有ＣａＦ２或ＴｉＯ２结构的氧化物粉体的晶粒粒度比具有α－Ａｌ２Ｏ３结构的氧化的晶粒粒度小,具有α－Ａｌ２Ｏ３     

Factors affecting CO oxidation over nanosized Fe2O3

Nanocrystallite iron oxide powders with different crystallite sizes were prepared by co-precipitation route. The prepared powders with crystallite size 75, 100 and 150 nm together with commercial iron oxide (250 nm) were tested for the catalytic oxidation of CO to CO₂. The influence of different factors as crystallite size, catalytic temperature and weight of catalyst on the rate of catalytic reaction was investigated using advanced quadrupole mass gas analyzer system. It can be reported that the rate of conversion of CO to CO₂ increased by increasing catalytic temperature and decreasing crystallite size of the prepared powders. The experimental results show that nanocrystallite iron oxide powders with crystallite size 75 nm can be recommended as a promising catalyst for CO oxidation at 500 °C where 98% of CO is converted to CO₂. The mechanism of the catalytic oxidation reaction was investigated by comparing the CO catalytic oxidation data in the absence and presence of oxygen. The reaction which was found to be first order with respect to CO is probably proceeded by adsorption mechanism where the reactants are adsorbed on the surface of the catalyst with breaking OO bonds, then CO pick up the dissociated O atom forming CO₂.     

等离子喷涂过程中纳米氧化钛的结构变化研究

本文阐述了等离子喷涂过程中氧化钛纳米粉的相变特征和显微结构的变化特征．利用XRD和TEM分析方法分别对氧化钛纳米微粒进行晶体结构和显微结构研究,并对其晶胞参数进行了计算．结果表明,该条件下等离子喷涂的氧化钛微粒属于三斜晶系,其粒径分布大约在10～100um的范围．作为对比,同时进行了氧化钛纳米粉体在烧结过程中相变及微结构变化的研究．     

Detonation synthesis of zinc oxide nanometer powders

Novel zinc oxide nanometer powders have been synthesized via detonation reaction with respect to the presence of an energetic precursor, such as lithium nitrate and zinc nitrate. The detonation products of emulsion explosives were characterized by powder X-ray diffraction. Transmission electron microscopy was used to observe the structures. Zinc oxide with primary particles of diameters from 20 to 50 nm and a distribution with proportional spacing of spherical morphologies were found. The oxides produced by this cheap method affirmed the validity of detonation synthesis of nanosize powders. It is concluded that unconventional emulsion explosives are designed uniquely for synthesis of the nanometer zinc oxide.     

The influence of precursor powders and processing parameters on the properties of SnO2-based gas sensors

Semiconducting tin oxide precursor powders were synthesized via three different chemical processing routes. The influence of powder processing conditions on the physical properties, e.g., particle size, surface area and phase composition of both uncalcined and calcined materials, was investigated. These powders were used to fabricate gas sensors using thick-film screen-printing technology. The effect of precursor powders, sintering conditions, sensor temperature and Pd catalyst on the carbon monoxide, methane, propane and ethanol gas sensing characteristics of the sensors were investigated. Sensors were also fabricated using tin oxide powders obtained from a commercial source and their gas sensing properties were also investigated. The data indicates that the powder processing methodology, sensor fabrication conditions and Pd catalyst can profoundly influence the physical characteristics as well as the gas sensing properties of the sensors.     

燃烧合成ZrB2 / Al2O3 复合粉体及其界面分析

采用燃烧还原合成技术, 以还原体系(B₂O₃ + ZrO2 + Al) 为反应体系制备了ZrB₂ / Al₂O₃ 复合粉体。利用X射线衍射(XRD) 、X 射线光电子能谱(XPS) 和透射电镜( TEM、HRTEM) 对复合粉体的物相组成、化学组成及界面结构进行了表征分析。结果表明, 复合粉体中存在Zr 、B、Al 和O 元素且它们分别以ZrB₂ 和Al₂O₃ 为主要存在形式, ZrB₂ 和Al₂O₃ 为复合粉体的主晶相。复合粉体中有少量ZrO2 的存在, 分析认为是合成反应过程中未参加反应的ZrO2 。ZrB₂ 和Al₂O₃ 颗粒间形成了结合良好的界面, 这主要与ZrB₂ 的结晶过程有关。      

Mechanism and kinetics of treatment of acid orange II by aged Fe-Si-B metallic glass powders

The mechanism and kinetics of acid orange II(AOII) treated by aged gas-atomized Fe-Si-B metallic glass(MG) powders were investigated in this study. The decolorization reaction is shown to obey the pseudofirst-order kinetic model, and the treatment processes could be divided into two stages: a slow step followed by a rapid one. This observation is in accordance with the following results, the azo dye is simply adsorbed onto the Fe-based MG powders in the initial stage, because the oxide layer coated on the powder surface depresses the degradation reaction by covering the activity sites, and then the degradation occurs with the desquamation of the powders. The AOII could be degraded with a rapid reaction rate when the Fe-based MG powders are applied to the treatment process again, because of the consumption of the oxide layer and the unchanged core of the Fe-based MGs. These findings will promote the practical application of MGs in degrading azo dyes.     

Effect of processing on the particle size of tin oxide nano-powders

Nano sized tin oxide powders have been synthesized via two different chemical routes namely solid-state and sol–gel route for the fabrication of tin oxide gas/odors sensor. The synthesized powders have been characterized by simultaneous thermo gravimetric and differential thermal analysis (TG-DTA), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared (FTIR) spectroscopy. The effect of synthesis routes have been investigated on particle size and morphology of tin oxide powders. Powder XRD patterns show that the synthesized powders have tetragonal (rutile) crystal structure. FESEM of formed thick films reveal that powder prepared by solid-state reaction route is less agglomerated as compared to the powder prepared by sol–gel route. XRD and FESEM indicate that there is the formation of tin oxide nanoparticles in the range of 15–50 nm. FTIR spectrums of synthesized powders show Sn-O or Sn-O-Sn stretching modes and its lattice modes at 615 and 494 cm^?1.     

Synthesis and morphological control of rare earth oxide nanoparticles by solvothermal reaction

Eu doped Y₂O₃ and some kinds of other rare earth oxides nanoparticles such as Er₂O₃, Nd₂O₃, Ho₂O₃, Lu₂O₃, and Dy₂O₃ were prepared by a simple co-precipitation-solvothermal treatment-calcination process, where the co-precipitated amorphous hydroxide precursors obtained by adding rare earth nitrate solutions in ammonia solutions were heated in solvents such as water, alcohols and glycols, followed by calcination in air. The morphology of rare earth oxide particles strongly depended on the solvothermal reaction medium but not related to the kind of rare earth oxide. The powders prepared in water and ethanol possessed nanowire structure, where the aspect ratio of powder treated in water was higher than that in ethanol. The powders prepared by co-precipition-solvothermal treatment-calcination process using ethylene glycol consisted of near-spherical nanoparticles whereas that prepared by conventional co-precipitation-calcination method consisted of hardly agglomerated submicron particles. The nanoparticles of Eu³⁺ doped Y₂O₃ prepared by co-precipition-solvothermal treatment-calcination process showed similar intensity of photoluminescence with the submicron particles by co-precipition-calcination process.     

银氧化锡水热体系的共沉积反应协同性研究

研究了水热反应过程中银和二氧化锡共沉积的协同性。分别对水热反应过程中银的还原、二氧化锡的晶化沉积以及银和二氧化锡的共沉积进行了研究,结果表明,水热反应体系中H+或OH-的关联作用使二氧化锡的晶化沉积反应与银的还原反应相适应,并且由于银粉和银氧化锡复合粉体结构形貌上的差异,二者表现出内在的协同性,实现了银和二氧化锡的共沉积。     

Microstructural characteristics and gas content of rapidly solidified powders

The gas content and microstructural characteristics of rapidly solidified powders manufactured by different techniques were studied by Bureau of Mines researchers. Powders were screened and classified into size fractions. Powder characteristics including gas content and porosity were measured and related to powder particle size. Three different atomizing gases, argon, helium, and nitrogen were used in manufacturing the powders. In one series of experiments one gas was used to atomize the melt while a different gas was used in the melting and powder collection chambers. The gas content of the powders was shown to consist of three separate components: (1) solid solution, (2) physical entrapment associated with macroporosity, and (3) surface reaction such as surface oxide. The various components of gas content could be identified by the shape of the curve plotting gas content versus particle size. The identification of the presence of entrained gas as porosity from these curves is important because after consolidation, high-pressure bubbles of inert gas can result. This porosity can cause problems during subsequent heating or joining operations, seriously degrading mechanical properties. Analysis of gas content versus particle size represents a sensitive, technique to detect the presence of porosity.     

ULTRAFINE OXIDE POWDERS PRODUCED BY RAPID THERMAL DECOMPOSITION OF PRECURSORS IN SOLUTION

ABSTRACT

The Rapid Thermal Decomposition of precursors in Solution (RTDS) process is described as an approach to nanoscale particle production. The RTDS method involves a brief (< 2 sec) exposure of an aqueous solution containing dissolved metal oxide precursors to hydrothermal conditions amenable to particle nucleation and growth. Particle growth is terminated by passing the solution through a pressure restrictor and into a cooled collection region. Initial RTDS results involving the production of iron, titanium, and zirconium oxide powders from aqueous solutions are described. Powders generated were characterized using transmission electron microscopy, powder X-ray diffraction, BET surface area analysis, and Mossbauer spectroscopy. Iron oxide (hematite phase) having crystallite sizes ranging from a few nanometers to tens-of-nanometers was produced (rom 0.1 M Fe(NO₃) ₃ and Fe(NH₄)(SO₄) ₂ solutions. Crystallite size in the hematite powders was found to be dependent on the temperature to which the solutions were exposed during RTOS processing. Anatase phase TiO₂ powders having crystallite sizes of 3 to 5 ran were generated from K₂TiO(C₂O₄) ₂solutions, and cubic phase ZrO₂ powders with 3.5 nm crystallites were produced using a solution containing a zirconium (IV) citrate ammonium complex.     

Preparation of ultra-fine copper powder and its lead-free conductive thick film

In this paper, non-agglomerated monodispersed ultra-fine copper metallic powders have been synthesized with chemical reduction method. Fine lead-free glass powders were also prepared by solid synthesis process. Thick film paste prepared by above-mentioned copper metallic powders and lead-free glass powders was applied as conductive paste of MLCC. Mixture of glass and zinc oxide give the thick film a high adhesion strength which is attributed to the rough interface from interfacial reaction between glass and chip, and a good densification. Diffusion of metal between copper thick film and nickel thick film is clear. Ni-Cu solid solution appears under high temperature firing.     

混合导体氧化物SrFeCo0.5Oy粉末的微波合成与表征

采用微波加热方法与常规高温固相法合成了Sr-Fe-Co-O系混合导体陶瓷氧化物粉末.利用XRD,TEM/EDX及SEM等测试方法分析与表征粉体.用微波加热合成的粉体颗粒尺寸分布均匀,一次颗粒尺寸较小,结晶度也好于用常规加热合成的粉体.微波加热合成粉体的结晶相结构是钙钛矿结构Sr(Fe,Co)1.5Oy相,并有少量的正交结构相和尖晶石(Co,Fe)3O4相;高温固相法合成粉末由Sr4(Fe,Co)6O13±δ相及少量的Sr(Fe1-xCox)O3-δ相和CoO相组成.     

Synthesis and study of structural,thermal, optical and magnetic properties of stabilized Mn1−x Ni x O system (0·01 <x < 0·30)

A novel chemical passivation route is established to obtain microcrystalline solid solutions of binary oxidé system Mn_1−x Ni _x O (0·01 <x < 0·30). During the passivation process, controlled thermal decomposition of manganous oxalate is carried out to obtain pure MnO and its subsequent reaction with NiO in oxygen-free nitrogen resulted in microcrystalline powder of these solid solutions. The powder is thoroughly characterized by various physicochemical techniques such as XRD, DTA/TG/DTG, diffused reflectance spectra, magnetic susceptibility, TEM, XPS etc. The observed processing-structure-property correlations confirmed the improved thermal stability of these powders (relative to pure MnO) in air. The important role of dopant paramagnetic Ni²⁺ ions in enhancing the passivation of the bulk Mn²⁺ species is explained on the basis of the formation of mixed oxide complex species on the surface of these microcrystalline powders.     

Internal oxidation of rapidly solidified silver-tin-indium alloy powders

The internal oxidation behaviour of rapidly solidified silver-tin-indium (Ag-Sn-In) alloy powders is described. Internal oxidation of Ag-Sn-ln alloy has gained importance in view of the possible replacement of toxic silver-cadmium oxide (Ag-CdO) material by a better property silver-tin oxide (Ag-SnO₂) electrical contact material. Rapidly solidified Ag-Sn-In alloy powders of composition Ag-6.0Sn-3.0In were prepared by gas atomization. The important characteristics of alloy and powders, from the point of view of internal oxidation, were determined. The powders were internally oxidized and subsequently processed by conventional powder metallurgy techniques. The important physical properties, such as electrical conductivity, hardness, density and microstructure, were determined. The physical properties, especially the microstructure and rate of internal oxidation, were compared with the materials prepared by the conventional internal oxidation route.     

液相聚合物前驱体法制备高熵碳化物纳米粉体

高熵碳化物陶瓷是近年来发展的新型材料,由于具有高硬度、高模量和低热导率等优异性能而备受关注.液相聚合物前驱体法在陶瓷化过程中可以实现多元素的均匀分散,制备高熵陶瓷具有独特的优势,但是相关报道较少.本研究以金属醇盐为原料,通过可控水解缩合反应制备了金属醇盐共聚物溶液,加入碳源烯丙基酚醛(AN)后得到了澄清的粘稠液相高熵碳...     

Effect of temperature on the catalytic oxidation of CO over nano-sized iron oxide

Nanocrystallite iron oxide powders were prepared by co-precipitation method using highly purified FeCl₃ and NH₄OH solution. The prepared powders were tested for the catalytic oxidation of CO to CO₂. The effect of oxidation temperature on the catalytic reaction was isothermally investigated using advanced quadrpole mass gas analyzer system. The mechanism of the catalytic oxidation reaction was estimated from the experimental data. Fe₂O₃ nanocrystallite of 78 nm shows a good response towards catalytic CO oxidation at the temperature range 200–500 °C. The catalytic oxidation efficiency reached 98% at 400–500 °C. The reaction was found to be first order with respect to CO. The average activation energy of the reaction was found to be 26.3 kJ/mol which is smaller than the values reported in the literatures. The mechanism of CO catalytic oxidation was investigated by comparing the CO catalytic oxidation data in the absence and presence of oxygen. It was found that the catalytic oxidation of CO over Fe₂O₃ nanocrystallite proceeded by adsorption mechanism. Based on the experimental results, Fe₂O₃ nanocrystallite powders can be recommended as a promising catalyst for CO oxidation.