Phase Analysis and Thermal Stability of Hot Isostatically Pressed Zirconia–Hydroxyapatite Composites

Composites of zirconia and hydroxyapatite (OHAp) have been processed via hot isostatic pressing (HIP) or sintering in air. When the composites were sintered in air at a temperature of 950°C, decomposition of the OHAp to tricalcium phosphate occurred. Using the HIP technique, composites without any detectable degradation of the OHAp phase were produced at 1200°C. The reactivity between zirconia and OHAp was dependent on both the amount of water lost from OHAp and the geometry of the interaction. The phase composition of the materials prepared was evaluated from their powder X-ray diffraction patterns, and their microstructures were studied via electron microscopy.     

Lipozyme IM‐catalyzed interesterification for the production of margarine fats in a 1 kg scale stirred tank reactor

Lipozyme IM‐catalyzed interesterification of the oil blend between palm stearin and coconut oil (75/25 w/w) was studied for the production of margarine fats in a 1 kg scale batch stirred tank reactor. Parameters such as lipase load, water content, temperature, and reaction time were investigated. The reusability of Lipozyme IM was also studied under optimized conditions. The interesterification products were monitored by analysis of triacylglycerol profiles, the contents of diacylglycerols, free fatty acids (FFA), and solid fat contents. The contents of some triacylglycerol species, which were categorized by equivalent carbon number (ECN), namely ECN34, 36, 48, and 50, decreased by 6.0, 5.9, 5.8, and 13.7%, respectively, after enzymatic interesterification, similar to the reduction of those species after chemical interesterification, 6.6, 6.0, 7.1, and 12.9%, respectively. On the other hand, those of ECN38, 40, 42, 44, and 46 increased by 1.1, 1.6, 6.8, 16.7, and 6.5%, respectively, in comparison with the increase of those species after chemical interesterification, 0.2, 1.5, 6.5, 17.0, and 9.2%, respectively. Lipase load and reaction time had great influence on the degree of interesterification. A Lipozyme IM load of 6% was required for a reaction of 6 h and at 60 °C, to reach a stable degree of interesterification. Temperature variation in the range of 50—75 °C did not affect the reaction degree as well as the contents of diacylglycerols, but the content of FFA slightly increased with higher temperature. Addition of water to the enzyme increased the contents of diacylglycerols and FFA in the products linearly. However, it had no effect on the degree of interesterification for the first batch when the enzyme was reused. Lipozyme IM was stable in the 10‐batch test after adjusting the water content in the system. The relationship between the content of water in the system and that of FFAs in the products was evaluated and discussed.     

Deactivation of V2O5-WO3-TiO2 SCR catalyst at a biomass-fired combined heat and power plant

The deactivation of a commercial type V₂O₅-WO₃-TiO₂ monolith catalyst under biomass combustion was studied at a full-scale grate-fired power plant burning straw/wood using a slip stream pilot scale reactor. The aerosols in the flue gas consisted of a mixture of potassium chloride and sulphate. Three catalyst elements were exposed at 350 °C, and one element was exposed at 250 °C for comparison. The catalyst activity was measured in the reactor at the exposure temperature by addition of NH₃ and extra NO. The activity, in terms of a first-order rate constant, dropped by 52% after about 1140 h indicating a very fast deactivation compared to coal firing. It was also found that the reactor temperature was not of importance for the deactivation rate. SEM-EDX analysis showed that particle deposition and pore blocking contributed to the deactivation by decreasing the diffusion rate of NO and NH₃ into the catalyst. However, potassium also penetrated into the catalyst wall and the resulting average K/V ratio in the catalyst structure was high enough (about 0.3–0.5) for a significant chemical deactivation. Chemisorption studies carried out in situ showed that the amount of chemisorbed NH₃ on the catalyst decreased as a function of exposure time, which reveals that Brøndsted acid sites had reacted with potassium compounds and thereby rendered inactive. When washed by 0.5 M H₂SO₄ the regenerated catalyst regains a higher activity than that of the fresh catalyst at temperatures higher than 300 °C, but even though reactivation is possible, the deactivation rate appears too high for practical use of the SCR process in straw combustion.     

Observation of changing crystal orientations during grain coarsening

Understanding the underlying mechanisms of grain coarsening is important in controlling the properties of metals, which strongly depend on the microstructure that forms during the production process or during use at high temperature. Grain coarsening of austenite at 1273 K in a binary Fe-2 wt.% Mn alloy was studied using synchrotron radiation. Evolution of the volume, average crystallographic orientation and mosaicity of more than 2000 individual austenite grains was tracked during annealing. It was found that an approximately linear relationship exists between grain size and mosaicity, which means that orientation gradients are present in the grains. The orientation gradients remain constant during coarsening and consequently the character of grain boundaries changes during coarsening, affecting the coarsening rate. Furthermore, changes in the average orientation of grains during coarsening were observed. The changes could be understood by taking the observed orientation gradients and anisotropic movement of grain boundaries into account. Five basic modes of grain coarsening were deduced from the measurements, which include: anisotropic (I) and isotropic (II) growth (or shrinkage); movement of grain boundaries resulting in no change in volume but a change in shape (III); movement of grain boundaries resulting in no change in volume and mosaicity, but a change in crystallographic orientation (IV); no movement of grain boundaries (V).     

Mechanisms and Kinetics of Liquid Silicon Oxidation During Industrial Refining

During oxidative ladle refining (OLR) of silicon, the metal surface is partly oxidized, resulting in the formation of a condensed silica fume (SiO₂). This fugitive emission of silica represents a potential health hazard to the workers in the silicon and ferrosilicon industry. In the current work, industrial measurement campaigns aimed at recording the fume generation during OLR were performed at the Elkem Salten plant in Norway. The measured amounts of silica produced were 2.5–5.1?kg/h, depending on the gas flow rate in the refining process. The rate of silica production correlates with the total flow rate and amount of air in the purge gas, and increases as the flow rate increases. The results of this work suggest that fume generation during OLR primarily results from oxidation of the exposed metal surface, with oxygen transport from the surrounding atmosphere to the metal surface being the limiting factor. Other identified mechanisms of SiO₂ formation were splashing of the metal and/or oxidation of SiO gas carried with the refining purge gas.     

Active Oxidation of Liquid Silicon: Experimental Investigation of Kinetics

Small scale laboratory experiments on the oxidation of liquid silicon have reproduced important features of the industrial refining of liquid silicon: active oxidation led to the formation of amorphous silica spheres as a reaction product. The boundary condition for active oxidation in terms of maximum oxygen partial pressure in the bulk gas was found to lie between 2·10^?3 and 5·10^?3?atm at T?=?1,500?°C. The active oxidation of liquid silicon had linear kinetics, and the rate was proportional to bulk oxygen partial pressure and the square root of the linear gas flow rate, consistent with viscous flow mass transfer theory. Classical theory for unconstrained flow over a flat plate led to mass transfer rates for SiO_(g) which were 2–3 times slower than observed. However, computational fluid dynamic modeling to take into account the effects of reactor tube walls on flow patterns yielded satisfactory agreement with measured volatilization rates.     

AlMnFeSi合金退火过程中的微观组织及力学性能的演变

通过2种不同的均匀化热处理及随后的冷轧,使一种3xxx系模型合金获得不同尺寸和分布的弥散析出相,并使铝基体含有不同含量的Mn。系统研究不同均匀化热处理组织和冷轧变形量对退火过程中模型合金的回复与再结晶行为的影响。根据实验结果,绘制出弥散析出相和再结晶过程的相互作用时间-温度-转变曲线（TTT）。TTT曲线显示固溶体中Mn的含量和弥散析出相的颗粒密度对软化行为有强烈的影响。在再结晶退火过程中或再结晶退火之前析出的高密度、细小、弥散析出相显著阻碍软化过程,并形成粗大的再结晶组织。在没有细小、稠密的弥散相影响下的再结晶退火,可以获得均匀、细小的等轴晶。而且,弥散析出相对再结晶过程的阻碍作用取决于再结晶过程的持续时间和弥散析出相的数量。在持续时间长的再结晶过程中,细小、稠密的弥散相对再结晶有着强烈的影响,而在其他情况下影响则有限。不管再结晶过程中是否受到弥散相析出的影响,在再结晶退火之前已经存在于组织中的细小、稠密的弥散相（平均尺寸0.1μm）也会导致再结晶退火之后形成粗大的再结晶组织。     

Effect of the Current Density on Morphology,Porosity, and Tribological Properties of Electrodeposited Nickel on Copper

In the steel industry, nickel coating on copper has increased the lifespan of continuous ingot casting molds. The objective of this work is to estimate the porosity of nanocrystalline nickel electrodeposited onto copper. Characteristics of nickel coating such as hardness, wear resistance, porosity, morphology, and adhesion are very important for maximum performance of molds. The effective porosity in nickel coating was determined by using anodic voltammetry. The porosity of electrodeposited nickel onto copper increased from 0.16% up to 6.22% as the current density increased from 1.5 up to 8.0 A dm⁻². The morphology of the nickel electrodeposited at lower current densities was more compact. Tribological properties were studied using hardness measurements, and calotest. Results of calotest indicated a wear coefficient of 10⁻⁶ for all samples. An extremely low friction coefficient of 0.06-0.08 was obtained for the sample deposited with a current density of 1.5 A dm⁻², and a friction coefficient of 0.15-0.21 was measured for the nickel coating electrodeposited at a current density of 5 A dm⁻². Effects of the current density of the electrodeposition process on the morphology, porosity, and tribological properties were evaluated.