Synthesis of SiC nano-powder from organic precursors using RF inductively coupled thermal plasma

Silicon carbide (SiC) has recently drawn an enormous amount of industrial interest owing to useful mechanical properties such as its thermal resistance, abrasion resistance and thermal conductivity at high temperatures. RF inductively thermal plasma (PL-35 Induction Plasma, Tekna Co., Canada) has been utilized for synthesis of fine SiC nano-powder from organic precursors (tetraethylorthosilicate, hexamethyldisilazane and vinyltrimethoxy silane). It was found that powders exposed to thermal plasma consist of SiC with free carbon and amorphous silica (SiO₂), after a thermal treatment and a HF treatment, the impurities are driven off, resulting in fine SiC nano-powder. The synthesized SiC nano-powder lies between 30 and 100 nm, and the characteristics of its microstructure, phase composition and specific surface are determined by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and thermogravimetric (TG) and Brunauer–Emmett–Teller (BET) analyses.     

Synthesis of nanosized zinc ferrites from liquid precursors in RF thermal plasma reactor

Micro- and nanosized zinc ferrite particles were prepared in RF thermal plasma conditions. Ethanol solutions of the mixture of zinc- and iron-nitrates were used as precursors. In the experiments, effects of synthesis conditions on the properties of products were investigated. The products were characterized for chemical and phase composition, morphology and magnetic properties. Zinc ferrite particles having ferrimagnetic properties were produced which refers to formation of zinc ferrites of inverse spinel structure in particular conditions.     

Synthesis of vanadium carbide nanopowders by thermal processing and their characterization

Vanadium carbide (V₈C₇) nanopowders were successfully prepared by thermal processing the precursor which originated from the mixture of ammonium vanadate (NH₄VO₃) and nanometer carbon black. The products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) methods. The single phase V₈C₇ powders can be prepared at ∼ 1100 °C for 1 h with the average crystallite size of 32.6 nm and the powders show good dispersion and are mainly composed of uniformly-sized spherical particles with a mean diameter of ∼ 100 nm.     

Synthesis and characterization of mesoporous anatase TiO2 nanostructures via organic acid precursor process for dye-sensitized solar cells applications

Titania (TiO₂) nanoparticles have been synthesized using organic precursor technique. The titania nanoparticles were characterized. The results indicated that the prepared titanium oxalate and citrate precursors were transformed to anatase TiO₂ phase at temperature 400 °C for 2 h. Dye-sensitized solar cells were assembled using the prepared nanocrystalline TiO₂ with large surface area. The specific surface area S_BET was 80.9 and 78.6 m²/g using oxalic and citric acids, respectively. The power efficiency was 3.5 and 2.4%. A brief discussion on the possible reasons behind the low power conversion efficiency observed for these type of solar cells was reported.     

Selective synthesis of TiO2 nanopowders

Nanosized anatase, rutile, brookite, and mixtures of these materials taken in different ratios are synthesized using the detonation method with variations in the densities and ratios of explosives composed of the TiO₂ precursor, NH₄NO₃, and C₃H₆N₃(NO₂)₃. It is shown that the phase composition, the phase content, and the average particle size of TiO₂ nanopowders depend on the composition of the explosive mixtures and their densities. When the weight ratio between the C₃H₆N₃(NO₂)₃ compound and the TiO₂ precursor lies in the range 0.695–1.270, the average size of rutile particles is larger than that of anatase particles by a factor of approximately two.     

Synthesis and characterization of TiO2 nanoparticles

TiO₂ nanoparticles were synthesized by thermal decomposition of a precipitate obtained from a precursor solution of titanium isopropoxide (IV) and isopropyl alcohol. The as-prepared precipitate was heated at various temperatures and the obtained samples were morphologically, texturally and structurally characterized using TGA–DTA, gas adsorption, SEM, XRD and FTIR. The UV–vis radiation absorption and the photocatalytic activity also were verified. The TiO₂ sample heated at 300 °C shows the best results to be applied as blocker in solar skin protector.     

Synthesis and characterization of Cu-doped ceria nanopowders

Nanopowdered solid solution Ce_1−xCu_xO_2−γ samples (0 ≤ x ≤ 0.15) were synthesized by self-propagating room temperature synthesis (SPRT). Raman spectroscopy and XRD at room temperature were used to study the vibration properties of these materials as well as the Cu solubility in ceria lattice. The solubility limit of Cu²⁺ in CeO₂ lattice was found to be lower than published in the literature. Results show that obtained powders with low dopant concentration are solid solutions with a fluorite-type crystal structure. However, with Cu content higher than 7.5 mass%, the phase separation was observed and two oxide phases, CeO₂ and CuO, coexist. All powders were nanometric in size with high specific surface area.     

苯并咪唑的光催化一步合成及表征

以邻硝基苯胺和甲醛为原料,超细纳米TiO2为催化剂,利用自制的微型光催化反应器一步合成了标题化合物.与传统方法相比,该法反应条件温和,操作简便,耗时短,产率高.利用熔点测定、红外光谱、核磁共振等手段对合成产物进行了表征.利用高效液相色谱和外标法建立了工作曲线.苯并咪唑浓度在10～200mg/L范围内与峰面积线性关系良好.回收率为98.4%～102.9%,相对标准偏差＜1.87%.     

二氧化钛介孔材料的制备

基于溶胶-凝胶过程,以十六烷基溴化铵为模板剂,合成了TiO2以及V/Ce/F-TiO2 介孔材料。利用XRD、Ｎ２吸附、TEM、TG-DTA和UV-Vis DRS等手段表征了材料的晶相组成、晶粒尺寸、介孔结构、热稳定性及吸光性能。通过系统研究表明,延长凝胶时间和优化陈化工艺可以得到TiO2介孔材料。TiO2和V/Ce/F/TiO2的平均孔径为3.1～5.1 nm,最大比表面积可达189 m2/g。焙烧温度大于450 ℃脱除模板剂时可引起孔道的塌陷,而掺杂V/Ce/F后可稳定材料的介孔结构。相对于纯TiO2光催化剂,掺杂V/F的TiO2吸光带边红移至可见光区。     

Benzaldehyde synthesis via styrene oxidation by O2 over TiO2 and TiO2/SiO2

Styrene was oxidized by molecular oxygen over TiO₂ and TiO₂/SiO₂ for the formation of benzaldehyde. In the absence of catalyst at 100 °C and 10 atm O₂, polystyrene is the major product. Over the catalysts, the oxidation of styrene is enhanced with benzaldehyde and formaldehyde being the major whereas phenylacetaldehyde, acetophenone, styrene oxide, benzoic acid, and polymer being the minor products. The polymerization of styrene was initiated by the radicals formed in the oxidation reaction. The addition of radical inhibitor nitrobenzene and/or the employment of a catalyst of high specific surface area can promote the termination of the radicals, and hence improve the selectivity of benzaldehyde.     

Synthesis of TiC-TiB2 composite powders from carbon coated TiO2 precursors

Submicron TiC-TiB₂ composite powders were synthesized by carbo/borothermal reductions from a novel carbon coated TiO₂ precursors method. Reactants were also mechanically mixed for comparison. Precursors and conventionally mixed powders were reacted from 1100 to 1500 °C for 2 h in flowing argon at 1 L/min. Phase evolution, thermodynamic analysis, microstructures, and surface areas were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and Brunauer-Emmett-Teller (BET) surface area analyzer, respectively. Products synthesized from precursors had high purity of TiC-TiB₂ mixture, fine particle size, narrow size distribution, regular shape, loose agglomeration, and high surface area. Powders with different compositions were also prepared by controlling the ratio between reactants. The sintering tests demonstrated that produced powders can be sintered to a 99.6% relative density using 5 wt% nickel additives at 1550 °C for 2 h in flowing argon atmosphere.     

Mg-substituted hydroxyapatite nanopowders: Synthesis,thermal stability and sintering behaviour

This paper reports a systematic investigation on Mg-substituted hydroxyapatite (Ca_10?xMg_x(PO₄)₆(OH)₂) nanopowders produced by precipitation of Ca(NO₃)₂·4H₂O and Mg(NO₃)₂. The Mg content ranged between 0.6 and 2.4 wt%. Semicrystalline Mg-substituted hydroxyapatite powders made up of needle-like nanoparticles were obtained, the specific surface area ranged between 87 and 142 m²/g. Pure hydroxyapatite nanopowder decomposed around 1000 °C. Mg-substituted hydroxyapatites were thermally stable up to 660 °C (x = 1.0), 760 °C (x = 0.5) and 840 °C (x = 0.25) showing a distinct decreased thermal stability with respect to the pure sample.A relevant displacement of the sintering curve at lower temperature as a function of Mg content was observed, comparing to the behaviour of a pure HAp material, synthesized following the same procedure, and ascribed to the β-TCP formation.     

Synthesis,characterization and sinterablity of 10 mol% Sm2O3-doped CeO2 nanopowders via carbonate precipitation

A carbonate coprecipitation method has been used for the facile synthesis of highly reactive 10 mol% Sm₂O₃-doped CeO₂ (20SDC) nanopowders, employing nitrates as the starting salts and ammonium hydrogen carbonate (AHC) as the precipitant. The AHC/RE³⁺ (RE = Ce + Sm) molar ratio (R) and the reaction temperature (T) affect significantly the final yield and precursor properties, including chemical composition and particle morphology. Suitable processing conditions are T = 60 °C and R = 5.0–10, under which precipitation is complete and the resultant precursors show ultrafine particle size, spherical particle shape, and good dispersion. Thus, the processed precursors are rare-earth carbonates with an approximate formula of Ce_0.8Sm_0.2(CO₃)_1.5·1.8H₂O, which directly yield oxide solid-solutions upon thermal decomposition at a low temperature of ∼440 °C. The 20SDC solid solution powders calcined at 700 °C show excellent reactivity and have been densified to ∼99% of the theoretical via pressureless sintering at a very low temperature of 1200 °C for 4 h.     

Synthesis and characterization of Fe doped titanium dioxide nanopowders

Titanium dioxide nanopowders, doped with different amounts of Fe³⁺ ions (0.3-5 mass%), were synthesized by acid-catalyzed sol-gel method in a non-aqueous medium. The obtained powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and determination of izoelectric points as well as particle diameters. Careful investigation of porous structure was provided by application of nitrogen adsorption-desorption method. Structure analysis showed that the obtained nanopowders exhibited the anatase crystal structure, independent of the amount of iron dopants. The presence of Fe³⁺ ions in anatase decreases the value of isoelectric point of undoped TiO₂. Unlike crystal structure, porosity parameters are strongly affected by the amount of iron ions incorporated in TiO₂ lattice. The mesoporosity of TiO₂ can be successfully controlled by changing the amount of iron dopants.     

Synthesis,characterization and sintering of Li2TiO3 nanoparticles via low temperature solid-state reaction

Synthesis of fine Li₂TiO₃ powders via low-temperature solid-state reaction (LTSSR) was studied. Solid Li₂CO₃ and H₂TiO₃ were blended by planetary ball mill with deionized water as medium. Calcination of the milled powder at low temperature of 500 °C resulted in the formation of pure Li₂TiO₃ nanoparticles. Another Li₂TiO₃ powder was also prepared by the conventional solid-state reaction (SSR) and a good comparison between different routes was realized. The results show that the particle size of LTSSR powder is significantly decreased to 19.6 nm while the one obtained by SSR is 146.6 nm. Low temperature calcined powders have less agglomeration and higher sinterability, which can be sintered at lower temperature. Pebbles sintered from the LTSSR powders at 750 °C exhibit small grain size (650 nm), high relative density (85.1%) and satisfactory crush load (42.8 N), whereas the SSR pebbles can only be sintered above 950 °C with the relative density close to 80%. Besides, the LTSSR samples also have a higher conductivity at room temperature, indicating the lower tritium diffusion barrier in ceramics. It is confirmed that H₂TiO₃ rather than TiO₂ is more appropriate for the solid-state reaction to produce Li₂TiO₃ powders with nano-size particles and favorable properties.     

Self-ordered TiO2 quantum dot array prepared via anodic oxidation

The template-based methods belong to low-cost and rapid preparation techniques for various nanostructures like nanowires, nanotubes, and nanodots or even quantum dots [QDs]. The nanostructured surfaces with QDs are very promising in the application as a sensor array, also called ''fluorescence array detector.'' In particular, this new sensing approach is suitable for the detection of various biomolecules (DNA, proteins) in vitro (in clinical diagnostics) as well as for in vivo imaging.The paper deals with the fabrication of TiO₂ planar nanostructures (QDs) by the process of titanium anodic oxidation through an alumina nanoporous template on a silicon substrate. Scanning electron microscopy observation showed that the average diameter of TiO₂ QDs is less than 10 nm. Raman spectroscopic characterization of self-organized titania QDs confirmed the presence of an anatase phase after annealing at 400°C in vacuum. Such heat-treated TiO₂ QDs revealed a broad emission peak in the visible range (characterized by fluorescence spectroscopy).     

TiO_2/ACF复合材料的制备及表征

采用浸渍-提拉法和溶胶-凝胶法制备TiO2/ACF复合光催化材料,用BET、XRD和SEM等进行表征。结果表明,溶胶-凝胶法制备的复合材料由于负载了大量TiO2,其比表面积明显低于浸渍法;浸渍法制备的复合材料随着粘结剂添加量的增加,比表面积呈减小趋势。溶胶-凝胶法制备的复合材料的表面TiO2锐钛晶型较明显,浸渍-提拉法无明显的锐钛晶型。采用浸渍-提拉法制备的TiO2/ACF复合材料,TiO2以粒状负载于ACF表面;溶胶-凝胶法中TiO2在ACF表面形成一层薄膜,由于焙烧,薄膜产生裂隙,暴露出ACF,有利于吸附和催化作用的同时进行。     

聚丙烯酰胺／二氧化钛杂化材料的合成与表征

以丙烯酰胺为有机相,通过钛酸正丁酯的水解引入二氧化钛无机相,采用溶胶-凝胶法制备了聚丙烯酰胺（PAM）／二氧化钛（TiO2）水溶性高聚物杂化材料。讨论了二氧化钛溶胶质量分数、单体质量分数对聚合反应转化率的影响;对合成的杂化材料进行了红外、热性能表征。实验结果表明,二氧化钛包裹在聚丙烯酰胺内部,同时,合成的杂化材料耐热性能有所提高。     

Synthesis,characterization, and thermal stability of PMMA/SiO2/TiO2 tertiary nanocomposites via non‐hydrolytic sol–gel method

In this study, we use PMMA, tetraethoxysilane and titanium ethoxide to prepare tertiary nanocomposites via non‐hydrolytic sol–gel method. Boron trifluoride monoethylamine was used as catalyst. Silica and titanium dioxide are incorporated into nanocomposites to improve the thermal stability. Thermogravimetric analysis was used for rapid evaluation of the thermal stability of different materials. The integral procedural decomposition temperature has been correlated the volatile parts of polymeric materials and used for estimating the inherent thermal stability of polymeric materials. The thermal stability of hybrids increased with the contents of inorganic components. The inorganic components can improve the thermal stability of PMMA copolymer. Two methods have been used to study the degradation of hybrid during thermal analysis. These investigated methods are Kissenger', Ozawa's methods to classify the thermal stability of nanocomposites. The activation energies of hybrids were higher than that of the copolymer. From the results, silica and titania will enhance the thermal stability of PMMA. We use the solubility test to check the network structure of nanocomposites. The results show the residues of composites after extraction increase with the increasing of inorganic contents. We can conclude that the composites possess network structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009