α钛富氧层增厚动力学模型

为了实现在工业化生产中对α钛富氧层厚度预测和控制,通过实验研究α钛富氧层在高温空气环境中的形成及增厚过程,讨论热处理温度和时间的影响作用,建立高温(750~850℃)空气环境下关于温度、时间的富氧层增厚动力学模型。结果表明:当恒温热处理温度为750~850℃时,α钛富氧层厚度x与保温时间t0.5呈正比例关系,且升高热处理温度可显著提高富氧层增厚速度。在此温度范围内,氧原子的扩散激活能约为203473 J/mol,计算曲线与实验数据吻合性较好。结合文献中已有的扩散系数方程和实验测得的富氧层厚度数据,推导得到5个富氧层增厚动力学方程,其中3个方程的计算曲线与实验数据吻合性较好,可为实际生产中预估富氧层厚度提供理论支持。     

Accelerated bioactive behavior of Nagelschmidtite bioceramics: Mimicking the nano and microstructural aspects of biological mineralization

The ability of the Nagelschmidtite (Nagel) phase to promote osteogenesis, cementogenesis, and angiogenesis increased the interest in using this calcium silicophosphate bioceramic for tissue regeneration and vascularization applications. Nagel phase is a solid solution with the general formula Ca_7-xNa_x(PO₄)_2+x(SiO₄)_2-x, which allows several substitutions being Ca₇(PO₄)₂(SiO₄)₂ the most reported stoichiometry. Inspired by the well-known 45S5 bioactive glass chemical composition, we developed a synthesis route to obtain a Na-rich Nagel single phase. The effect of this bioceramic chemical and structural properties on apatite formation and crystallization mechanism is reported. The structural aspects at the nano and microscale of the mechanism of apatite growth and crystallization from the Nagel phase were compared to the formation process of Extra-Cellular Matrix (ECM) deposits in biological systems, revealing a biomimetic behavior during the apatite biomineralization process from the bioceramic.     

Electrical and mechanical characterization by instrumented indentation technique of La0.85Sr0.15Ga0.8Mg0.2O3−δ electrolyte for SOFCs

La_0.85Sr_0.15Ga_0.8Mg_0.2O_3?δ pellets obtained by the polymeric organic complex solution method, isostatic pressing and sintering at 1350 °C have been electrical and mechanically studied. Electrical measurements evidenced reasonable ionic conductivities (0.01 S cm^?1 at 800 °C), which were comparable to those reported for the La_1?xSr_xGa_1?yMg_yO_3?δ prepared by other synthesis methods. On the other hand, the mechanical properties (elastic modulus, E and hardness, H) have been determined at micro/nanometric scale using the instrumented indentation technique. While E did not vary significantly with the increasing indentation depth (h), H values strongly decreased with the indentation depth up to 500 nm. For h > 500 nm, both mechanical properties remained almost constant, thus obtaining E = 271 ± 6 GPa and H = 13.2 ± 0.4 GPa. Finally, the residual imprints and fracture mechanisms have been observed by atomic force microscopy (AFM).     

Artificial magnetism in a carbon diamond nanolattice with the spin orientation effect

In this paper, we investigate the spin orientation effects on the magnetic properties of the Carbon diamond nanolattice (CDNL) by using Kaneyoshi approach (KA) within the effective field theory. In our calculations, we use the normalized lattice constant (na = 3.566 = a/1 A⁰) which is obtained from the real lattice constant (a = 3.566 A⁰) of the CDNL. The CDNL has three different magnetic atoms according to nearest-neighbor, and they are defined as corner atoms (m_c), face atoms (m_f) and inner atoms (m_i). For m_c, m_f and m_i, the CDNL has eight spin orientations as +++ (↑↑↑), −++ (↓↑↑), ++− (↑↑↓), −+− (↓↑↓), −−+ (↓↓↑), −−− (↓↓↓), +−− (↑↓↓) and +−+ (↑↓↑), respectively. We find that the CDNL has two kinds of critical temperature behaviors, we call them as high critical temperature behavior (HCTB) for the first four spin orientations and low critical temperature behavior (LCTB) for the second four spin orientations. However, the CDNL exhibits ferromagnetic (FM), antiferromagnetic (AFM), superconductivity (SC), discontinuous diamagnetic (DM) and discontinuous paramagnetic (PM) hysteresis behaviors according to the spin orientation of its atoms. Therefore, we suggest that it is possible to obtain different magnetic behaviors and artificial magnetism from the Carbon and Carbon-based materials with the spin orientations of their atoms.     

Thermodynamic analysis of the carbothermic reduction roasting of a nickeliferous limonitic laterite ore

As the sulfide ore deposits become less economically viable as a source of nickel, increasing attention is being paid to the nickeliferous laterite ores. However, in contrast to the sulfide ores, these oxide ores cannot be as easily concentrated by current technologies. Consequently, considerable research effort is being directed at developing new techniques for beneficiating the nickeliferous laterites. The pyrometallurgical production of a high-grade ferronickel alloy using a low cost carbonaceous reductant at relatively low temperatures is particularly attractive. In the current research, a thermodynamic model has been developed to aid in the understanding of the carbothermic reduction roasting process as a potential upgrading method for the nickeliferous limonitic laterite ores. The effects of process parameters such as temperature and reductant to ore ratio on the grade of the ferronickel alloy produced and the nickel recovery in the alloy have been studied. The thermodynamic predictions are shown to be in general agreement with the experimental results currently available in the literature.     

Fabrication of Different SiC Architecture Via a Simple Method

Silicon carbide architecture with different morphology has been synthesized via catalyst-free carbothermic reduction of silica under normal atmosphere pressure.X-ray powder diffraction(XRD)and Scanning electron microscopy(SEM)were used to characterize the architecture.The results show that the mole ratio of carbon/silica has a great influence on the morphology of silicon carbide architecture.At different carbon/silica mole ratio,platelet-,bamboo-,pagoda-,and bead-like silicon carbide architecture have been synthesized.     

A comparison between state-of-the-art and neural network modelling of solar collectors

The state-of-the-art modelling of solar collectors as described in the European Standard EN 12975-2 is based on equations describing the thermal behaviour of the collectors by characterising the physical phenomena, e.g. transmission of irradiance through transparent covers, absorption of irradiance by the absorber, temperature dependent heat losses and others. This approach leads to so called collector parameters that describe these phenomena, e.g. the zero-loss collector efficiency η₀ or the heat loss coefficients a₁ and a₂.Although the state-of-the-art approach in collector modelling and testing fits most of the collector types very well there are some collector designs (e.g. “Sydney” tubes using heat pipes and “water-in-glass” collectors) which cannot be modelled with the same accuracy than conventional collectors like flat plate or standard evacuated tubular collectors. The artificial neural network (ANN) approach could be an appropriate alternative to overcome this drawback.To compare the different approaches of modelling investigations for a conventional flat plate collector and an evacuated “Sydney” tubular collector have been carried out based on performance measurements according to the European Standard EN 12975-2. The investigations include the parameter identification (training), the comparisons between measured and modelled collector output and the simulated yearly collector yield for a solar domestic hot water system for both models.The obtained results show better agreement between measured and calculated collector output for the artificial neural network approach compared with the state-of-the-art modelling. The investigations also show that for the ANN approach special test sequences have to be designed and that the determination of the ANN that fits the thermal performance of the collector in the best way depends significantly on the expertise of the user.Nevertheless artificial neural networks have the potential to become an interesting alternative to the state-of-the-art collector models used today.     

Optimizing the thermal effectiveness of an insulation wrap with internal folded polypropylene film for the transportation of frozen food

The paper presents an investigation of the thermal performance of an innovative insulation wrap for food freezing, transportation and storage. The wrap is made of two outer polypropylene films and an internal folded polypropylene film welded together to form rectangular internal air cells. A mathematical model of heat transfer is presented and experimentally validated, with discrepancies less than 10% when there is no internal convection effect and generally less than 12% when internal convection is present. A thermal effectiveness of film usage was proposed and analyzed in order to find the best fold geometry. A mathematical model of the effectiveness and its experimental validation showed good agreement (discrepancies less than 13%). By using a criteria map, we recommend the following geometry: wrap thickness more than 5 and less than 10 mm; fold spacing more than 6 and less than 10 mm.     

Austenitic and ferritic stainless steel dissimilar weld metal evaluation for the applications as-coating in the petroleum processing equipment

The current study presents some fundamental observations on the effects of the welding heat input in the chemical composition, microstructure, hardness and petroleum corrosion resistance of the fusion zone, formed by the AWS E309MoL austenitic stainless steel covered electrode and the AISI 410S ferritic stainless steel, being a dissimilar welding procedure. Such welding configurations are widely used as an overlay of equipment in the petroleum and gas industries. The welds were performed with the application of three different levels in heat inputs (6, 9 and 12 kJ/cm). Samples of the weld metals were conventionally prepared for the microstructural characterization by light microscopy and scanning electron microscopy. A corrosion test with samples immersed in heavy oil heated at 300 °C, was carried out for a period of 60 h. The corrosion rate was determined by the weight loss given after the aforesaid test. The fusion zone microstructure has a typical δ-ferrite acicular morphology, from which the level of δ-ferrite was duly altered with the increases of the welding heat input, due to the variations in the composition of the weld metal caused by dilution. It was also concluded that the chemical composition and the weld metal microstructure had a slight influence in the material’s corrosion rate. As a matter of fact, the corrosion rate of the weld metals evaluated herein, was considered satisfactory with few variations between the welding heat inputs duly applied.