Synthesis of acicular α-Bi2O3 microcrystals by microwave-assisted hydrothermal method

ABSTRACT

Materials based on bismuth(III) oxide are candidate to be used in optical and electronic devices because of their properties such as a variable band gap, photoconductivity, photoluminescence, high refractive index, and dielectric permittivity. These properties are dependent of several factors, e.g., present phases and crystal morphology. The microwave-assisted hydrothermal method (MAH) is a fast and efficient approach of synthesis to obtain semiconductor powders. However, the synthesis of monoclinic bismuth oxide (α-Bi₂O₃) with acicular morphology by MAH was not found in literature. In this paper, microcrystals of acicular α-Bi₂O₃ (monophasic) were successfully obtained by MAH using a synthesis temperature of 80°C for 0.5?h. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron, and transmission electron microscopies showed the formation of a monoclinic structure (space group P21/c) with acicular morphology that grew along the [001] direction. The temperature and time necessary to synthetize acicular microcrystals were significantly lower than those found for acicular microcrystals obtained by conventional hydrothermal method.     

Molten salt synthesis of La2Zr2O7 ultrafine powders

Ultrafine powders of pyrochlore-type La₂Zr₂O₇ were synthesized via a simple molten salt mediated process using zirconium oxide and lanthanum oxide as raw materials, and sodium chloride, potassium chloride and sodium fluoride to form a reaction medium. The effects of reaction temperature, salt/reactant ratio and salt type on the La₂Zr₂O₇ formation were investigated. Among the three attempted salt assemblies (KCl–LiCl, Na₂CO₃–K₂CO₃, and NaCl–KCl–NaF), NaCl–KCl–NaF showed the best accelerating effect on the La₂Zr₂O₇ formation. At a given temperature, the La₂Zr₂O₇ content in the final products increased with the increase in the salt amount. Phase pure submicron sized La₂Zr₂O₇ ultrafine powders were obtained after 3 h firing at 1100 °C with the salt/reactant weight ratio of 5:1 or at 1200 °C with salt/reactant weight ratio of 3:1. The synthesis temperature (1100 °C) was much lower than that required by the conventional solid-state mixing method or a wet chemical method. The “dissolution–precipitation” mechanism had dominated the synthesis process.     

Decarburization Thermodynamics of High-Carbon Ferromanganese Powders During Gas-Solid Fluidization Process

 Thermodynamic conditions of reactions between high-carbon ferromanganese powders and gas decarbonizers like O2, CO2 and water vapor were studied by thermodynamic calculation. In O2, CO2 and water vapor atmosphere, high-carbon ferromanganese powders were decarburized in a fluidized bed. When the temperature is respectively higher than 273, 1226 and 1312 K, the gas-solid decarburization reaction will occur between ferromanganese carbide on the surface of the high-carbon ferromanganese powders and different gas decarbonizers. Since metal manganese is easy to be oxidized by O2, CO2 or water vapor, the decarburization reaction will transfer into a solid-solid phase reaction of ferromanganese carbide and ferromanganese oxide, promoting external diffusion of carbon to achieve a further decarburization of high-carbon ferromanganese powders.     

单组份聚氨酯炮孔填塞剂应用性试验

炮孔填塞是爆破施工过程中的一个关键环节,也是践行精细爆破设计理论的重要措施。传统的炮泥填塞存在着诸多不足,为此,研制了以聚氨酯为基材的TK炮孔填塞剂,通过大量基础性能研究和隧道现场工业性试验,论证了其作为炮孔填塞材料可降低炸药单耗,提高单循环进尺和炮孔利用率,减小空气冲击波、爆破噪声等有害效应的影响,且是安全可靠的。TK炮孔填塞剂优良的填塞效果、方便快捷的施工方法及显著的经济效益,方便于在爆破工程中推广应用。     

Chemical characteristics of spice paprika of different origins

Spice paprika powders from Bulgaria, China, Hungary, Peru, Serbia and Spain were examined to identify the most important differences in their major characteristics and to attempt to find chemical components revealing their origin. Bioactive components, contaminants, aroma and microbiological properties were determined: the amount of carotenoids, tocopherols, ascorbic acid and mycotoxins were determined by HPLC, flavoring properties by GC-MS, lead and cadmium content by atomic absorption spectrophotometry. Carotenoids were found at the highest concentration in samples from Peru and Spain and at the lowest, in Serbian samples. The concentrations of total tocopherol and ascorbic acid were found to be greater in samples from Hungary than from China. Aroma components characteristic to the location were detected in samples from each country of origin. The level of microbiological contamination was acceptable, while contaminants were found in Serbian, Spanish, Peruvian and Chinese samples. The effect of sample origin was also investigated using near infrared spectroscopy.     

Experimental investigation and numerical simulation analysis of sintered micro-fluidic devices

ABSTRACT

This study investigates the use of numerical simulations to describe the solid-state diffusion of a sintering stage during a metal injection moulding process for micro-fluidic components with 316L stainless steel powders. Finite element (FE) analysis based on a thermo-elasto-viscoplastic model was conducted to describe the densification process of a stainless steel porous component during solid-state sintering. The numerical analyses, which were performed on a 3D micro-structured component with various powder volume loadings to take into account the thermal debinding effect to propose a full debinding sintering simulation, demonstrated that the FE simulation results are in agreement with the experimental ones.     

Tribological properties of ethylene–propylene–diene rubber + polypropylene + thermal‐shock‐resistant ceramic composites

This work is part of a program on composites used in thermoelectric devices. Tribological properties of dynamic vulcanizate blends of polypropylene and ethylene‐propylene‐diene rubber filled with 5 wt% of microscale powder have been studied. The microscale thermal‐shock‐resistant ceramic filler contains α‐Al₂O₃, mullite (3Al₂O₃ · 2SiO₂ or 2Al₂O₃SiO₂), β‐spodumene glass‐ceramic and aluminium titanate. We found that our ceramic particles are abrasive; they cause strong abrasion of softer steel ball surfaces during dry sliding friction. To overcome the difficulty of particle dispersion and adhesion, the filler was modified through grafting using three types of organic molecules. Dry sliding friction was measured using four types of counter‐surfaces: tungsten carbide, Si₃N₂, 302 steel and 440 steel. Thermoplastic vulcanizate filled with neat ceramic powder shows the lowest friction compared to composites containing the same but surface‐treated powder. We introduce a ‘bump’ model to explain the tribological responses of our composites. ‘Naked’ or untreated ceramic particles protrude from the polymer surface and cause a decrease of the contact area compared to neat polymer. The ball partner surface has only a small contact area with the bumps. As contact surface area decreases, so does friction and the amount of heat generated during sliding friction testing. Chemical coupling of the ceramic to the matrix smoothens the bumps and increases the contact surface, giving a parallel increase in friction. Copyright © 2012 Society of Chemical Industry     

LPM填充体混凝土空心楼盖施工技术

清华大学综合科研楼采用LPM填充体空心楼盖。介绍该楼盖的构造、施工流程和轻质管抗浮等技术措施。为保证楼盖质量,应重视组合模件的安装铺设和各专业工种的沟通配合。     

A feasibility study of Lactobacillus plantarum in fruit powders after processing and storage

The aim of this study was to develop fruit powders (apple, banana and strawberry) enriched with a probiotic strain (Lactobacillus plantarum 299v). Two methodologies were proposed: (i) drying of the fruit with probiotic culture incorporated (by convection) or (ii) drying of fruit (by convection) and addition of spray‐dried probiotic culture. In the first methodology, processing caused a notable reduction in probiotic viable counts in apple, but this reduction was lower during drying of banana and strawberry. A large reduction in viable cells was also recorded during storage. In the second methodology, the survival of L. plantarum 299v was considerably higher during spray‐drying, and fruit powders with a microbial content suitable for a probiotic food (10⁸–10⁹ cfu g^?1) were obtained. The fruit powders incorporating L. plantarum 299v can be stored at 4 °C or at room temperature, for at least 3 months. This preliminary study demonstrated that fruit powders are good carriers of probiotic cultures, but the techniques used to produce them should be carefully considered.     

Curing enhancement and network effects in multi‐walled carbon nanotube‐filled vulcanized natural rubber: evidence for solvent sensing

Electrically and thermally conductive polymer composites offer great possibilities in various electronic fields because of their low weight and ease of processing. This paper addresses the curing behaviour and network properties of conducting multi‐walled carbon nanotube (MWCNT)‐reinforced natural rubber (NR) nanocomposites, emphasizing the sensing and diffusion performances. NR/MWCNT composites were prepared following a special master batch technique which allows the appropriate distribution of nanotubes within the elastomer. The sensing responses of the composites towards solvents were observed as variations in electrical resistance. Thermal resistance and glass transition behaviour were examined and correlated with the swelling measurements as evidence for solvent sensing. An optimum level of 3 phr of MWCNTs is understood to lead to the best properties for the NR/MWCNT composites. Finally, the structural morphology and interfacial interactions were found to have correlations with cure reactions, glass transition temperatures and sensing responses of all compositions. © 2017 Society of Chemical Industry