The influence of oxygen ambient annealing conditions on the quality of Al/SiO2/n-type 4H-SiC MOS structure

The effect of reoxidation process in O₂ on the electrical properties of metal-oxide-semiconductor (MOS) capacitors fabricated on n-type 4H-SiC (0 0 0 1) is investigated. All samples were oxidized in wet oxygen at temperature of 1175 °C. Reoxidation process was carried out on four of the five samples. Samples were annealed at temperature of 700 °C and 800 °C for different process times. The reoxidation process in oxygen improves the quality of the dielectric layer and the interface of Al/SiO₂/n-type 4H-SiC MOS structure. The best quality of the SiO₂/SiC interface can be achieved for the MOS structure annealed in O₂ at higher temperature (800 °C) for longer time. However, higher and more uniformly distributed values of breakdown voltage were obtained for MOS structures reoxidized at temperature of 700 °C.     

Effect of mix design inputs,curing and compressive strength on the durability of Na2SO4-activated high volume fly ash concretes

This paper aims to advance research on the use in concrete of a high volume of fly ash, with a high loss on ignition value, aiding in sustainable low carbon footprint construction. To this end, the work explores the benefits that may be achieved in terms of long-term concrete performance from the incorporation of fly ash along with a chemical activator. Durability tests are performed on concrete with an activated hybrid cementitious system: Portland cement (PC) and high volume fly ash with sodium sulfate. The chloride diffusion coefficient significantly decreased over time for the activated system (50% PC - 50% fly ash with added sodium sulfate) compared to the control samples (100% PC and 80% PC - 20% fly ash) at the same water to cementitious material ratio. This behavior is particularly evident in samples cured under controlled laboratory conditions (100% RH and 23 °C). However, outdoor curing increases the permeability for all concretes. Long term carbonation is also investigated under natural exposure conditions, and samples that are cured outdoors exhibit a significant carbonation depth. The compressive strength is correlated with the durability parameters: the durability performance improves as the compressive strength increases, indicating that as is the case for Portland cement (but not always for alkali-activated binders), the microstructural factors which yield high strength are also contributing to durability properties.     

低热固相反应法制备CoFe_2O_4、ZnFe_2O_4和Co_(0.5)Zn_(0.5)Fe_2O_4纳米粉体研究

采用低温固相反应法合成了CoFe2O4、ZnFe2O4和Co0.5Zn0.5Fe2O4纳米粉体。以NH4HCO3和金属盐为原料,生成了前驱体碱式碳酸盐,通过研究不同焙烧温度,并在最佳焙烧温度下得到了CoFe2O4、ZnFe2O4和Co0.5Zn0.5Fe2O4纳米粉体。经X射线衍射(XRD)、热分析(TG-DSC)、透射电子显微镜(TEM)、振动样品磁强计(VSM)等测试手段的分析,结果表明:低温固相反应法能够合成出单相的CoFe2O4、ZnFe2O4和Co0.5Zn0.5Fe2O4纳米粉体。     

Composition and Properties of Crystals Growing in the Ca2+–Mg2+–HPO2- 4–HCO- 3 System in the Presence of Na+, K+, Cl–, and SO2- 4 Ions

Data are presented on crystallization processes in aqueous solutions in the Ca²⁺–Mg²⁺–HPO^2- ₄–HCO^- ₃ system in the presence of Na⁺, K⁺, Cl^–, and SO^2- ₄ ions for molar ratios of the ions similar to those in human blood plasma. The solution concentration is shown to have a significant effect on the chemical composition and physicochemical properties of the forming precipitates.     

氧化物La2-yBayCuO4中Ba对氧原子态密度和氧化物性质的影响

用xa方法计算了氧化物La2-yBayCuO4中O原子的电子态密度及电荷转移。计算结果表明，Ba进入晶格，不仅导致同一原子层内的原子间轨道杂化增强，而且产生了较强的层间轨道杂化效应。这种层间互作用对于氧化物出现绝缘体-金属相变并进而产生超导电性有重要影响。因此尽管氧化物La2-yBayCuO4 4准二维特性，但在研究此类氧化物的微观性质时，不应该简单地将其作为二维系统处理，还必须考虑氧化物中的层间耦合效应。因为强烈的轨道杂化效应，使得Fermi面附近的d电子态密度显著增大，价电子的局城性减弱，而扩展性明显增强。由于Ba掺杂所产生的空穴主要进入O格点，并有少量d空穴进入Cu格点周围。本文认为，d空穴进入Cu格点等效于用三联族元素(Fe、Co、Ni)替代Cu原子，在格点上产生(或诱发)空间净磁矩。因此，空穴进入O格点导致超导电性和d空穴进入Cu格点诱发磁致“对”破坏机制，成为系统中的两个彼此消长、互相竞争的因素。由此可以较好地解释高温超导氧化物材料的超导转变温度随空穴浓度的变化行为。     

Equation of state for liquid helium from 1.4 to 4 K and asymptotic limits at the lamda line

A liquid helium state equation has been constructed for the range 1.4 to 4 K for pressures up to 25×10⁵ Pa consistent with the known asymptotic behavior of state properties at the lamda line. It utilizes a slightly different form of state equation than used in previous studies at the lamba line, resulting in simpler expressions for all thermodynamic variables while retaining good agreement with experimental data. The amplitude ratio, A/A, of the logarithmic term is found to be 1.14±0.03, independent of pressure, in contrast to earlier work which indicated that this ratio was pressure dependent above 15×10⁵ Pa. The state equation can also be used to show that the entropy variation along the lama line is independent of A or A and to predict a finite value of C_v at the lamda line.     

Point-defect formation and temperature coefficient of electrical resistivity of platinum and platinum-(10 wt%) rhodium alloy in the range 1100–1900 K

Measurement of the temperature coefficient of electrical resistivity of platinum and platinum-(10 wt%) rhodium alloy was performed by the modulation method in the temperature range 1100–1900 K. Nonlinear change in the temperature coefficient of resistivity of metals at high temperatures can be explained by the formation of equilibrium point defects. The enthalpy of point-defect formation in platinum md platinum-rhodium alloy has been determined to be 1.6±0.3 and 1.8±0.3 eV, respectively. The modulation frequency was 0.2 Hz; the amplitude of the temperature oscillation was about 10 K. The accuracy of the temperature coefficient of resistivity measurements was about 1%.     

Influence of the electrolysis conditions and composition of electrolytes in the M2WO4-M2W2O7-UO2WO4 system (M = Li, Na, K, Cs) on the oxygen coefficient of uranium oxide

The oxygen coefficient (O/U atomic ratio) of the cathodic product prepared by potentiostatic electrolysis of tungstate melts was studied in relation to the electrolyte composition, deposition potential, temperature of electrolysis, and cation of the solvent salt. With increasing temperature, the oxygen coefficient of the cathodic product increases. With shifting the deposition potential toward more negative potentials, with increasing concentration of W₂O ₇ ^2? anions, and with decreasing concentration of UO₂WO₄ in the tungstate electrolytes, uranium oxides with smaller oxygen coefficients are formed. The oxygen coefficient decreases with increasing radius of the salt cation, other conditions being equal. The abnormal behavior of melts based on Li₂WO₄ is probably due to lower activity of O^2? anions capable to form strong Li₃O⁺ complexes with lithium cations in the melt. The experimental results can be accounted for using the model of the ionic composition of uranyl-containing tungstate melts based on the concepts of complexation and stepwise solvolysis of uranyl ions.     

金属及金属盐改性NaAlH4的放氢反应研究

采用加入金属及金属盐的方法对NaAlH4进行催化放氢作用的研究.实验证明,加入钼粉、氧化钇、氯化铋,NaAlH4脱氢反应性能明显提高,2％(wt,下同)Mo、2％Y2O3和2％BiCl3的加入对NaAlH4的放氢过程产生了较大的影响,改进了其放氢动力学性能,使NaAlH4的放氢量提高1.0％以上.     

Effect of corrosion in 0.1 M Na2SO4 on the structure and properties of a soft-magnetic Fe-P-Si-Mn-V-C alloy in an amorphous and a relaxed state

We have studied a soft-magnetic amorphous alloy with the optimal composition Fe_76.5P_13.6Si_4.8Mn_2.4V_0.2C_2.5, prepared using ferrophosphorus. The results demonstrate that the electrochemical characteristics of the alloy in the amorphous state and after relaxation are comparable to those of a commercially available Fe-Si-B-Nb-Cu (Finemet type) alloy. Corrosion has no effect on the magnetic properties of the alloy.     

Cathodic electrodeposition of cerium based oxides on carbon steel from concentrated cerium nitrate. Part II: Influence of electrodeposition parameters and of the addition of PEG

The mechanisms of formation of cerium based oxides on carbon steel by cathodic electrodeposition from relatively concentrated cerium nitrate solutions were investigated in a previous work (Part I). It was shown that some corrosion products developed on the steel upon and soon after coating, thereby suggesting the films were not protective. This work (Part II) focuses on the influence of various elaboration parameters on the composition and morphology of the deposits likely to improve the corrosion resistance of carbon steel.     

Procedure and Setup for the Investigation of Composite Materials in Torsion at Temperatures up to 3300 K

A procedure and a setup are proposed for the investigation of strength properties of composite materials under torsion at temperatures of up to 3300 K in vacuum and in an oxidizing or inert medium. The setup is fitted with a system for the program heating of specimens to realize conditions that are close to the working conditions of the material. This makes it possible to carry out tests at a heating rate of about 500 deg/s with a uniform temperature field maintained along the specimen length.     

Studies on the Strength and Plasticity of Ti–Nb-Based Laminated Composites in a Temperature Range of 290–1700 K

The test procedure is described, and temperature dependences (290–1700 K) of mechanical characteristics are determined in tension of 9- and 13-layer Ti–Nb-based composites with equal volume contents of components as well as of a VT6S titanium alloy. It is established that composites with a larger number of layers possess higher strength, and among materials with an equal number of layers, the material with a higher degree of compression also exhibits higher strength. The values of ultimate strength obtained agree well with those calculated by the additive equation, except for the range of dynamic strain aging.     

煤制气再燃中NH2与NO反应的物化研究

对煤制气再燃低NOx燃烧过程进行分析,采用量子化学密度泛函理论(DFT)研究NH2自由基与NO的反应机理。全参数优化了各反应物、中间体、过渡态和产物的几何构型,并计算了它们的能量,通过振动频率分析证实中间体和过渡态的真实性。同时用内禀反应坐标(IRC)计算以进一步确定过渡态。为了得到更精确的能量信息,在QCISD(T)水平上计算了单点能。对NH2自由基与NO反应机理进行分析比较,并通过模拟NH2自由基与NO的反应,得出通道NH2+NO→IM1→TS1→IM3→N2+H2O的活化能最低(206.1kJ/mol),为最佳反应通道。揭示其微观机理,对进一步认识再燃脱氮的本质和主要过程提供了重要的理论依据和实践指导。     

Influence of oxygen/argon pressure ratio on the morphology, optical and electrical properties of ITO thin films deposited at room temperature

Transparent conductive oxides (TCOs) such as indium tin oxide (ITO) thin films onto glass substrates are widely used as transparent and conductive electrodes for a variety of technological applications including flat panel displays, solar cells, smart windows, touch screens, etc.ITO films on glass and polycarbonate (PC) substrates were prepared at room temperature (RT) and at different PO₂. The films were characterized in terms of the surface roughness (δ), sheet resistance, the refractive index (n) and extinction coefficient (k). The free carrier density (n_c) and the carrier mobility (μ) of the ITO (In₂O₃:Sn) films were measured and studied. The n_c and μ values vary in different ratio of oxygen partial pressure (PO₂) of ITO deposition. The observed changes in the ITO film resistivity are due to the combined effect of different parameter values for n_c and μ. From AFM analysis and spectra calculations, the surface roughness values of the ITO films were studied and it was observed that the δ values were lower than 15 nm. The energy band gap E_g ranges from 3.26 eV to 3.66 eV as determined from the absorption spectrum. It was observed an increase on the energy band gap as the PO₂ decrease in the range of 20-2% PO₂. The Lorentz oscillator classical model has also been used to fit the ellipsometric spectra in order to obtain both refractive index n and extinction coefficient κ values.     

NaCl-Na_2SO_4-H_2O体系（MVR）与（ME）盐硝联产工艺生产分析

热压制盐（MVR）和多效真空制盐（ME）是两种主要的制盐工艺方法。文章就NaCl-Na2SO4-H2O卤水现有（MVR）与（ME）盐硝联产工艺进行生产分析,指出MVR和ME的各自优点及局限性,供同行参考。     

Studies on the potential risk of liquid metal assisted cracking (LMAC) in normal‐temperature and high‐temperature hot‐dip galvanizing of high strength bolts of dimensions greater M24

Liquid metal assisted cracking (LMAC) mainly occurs due to an unfavorable interaction of three factors: a susceptible material condition, presence of a liquid metal and sufficient tensile stress. Hot‐dip galvanizing of high‐strength bolts induces high thermal loads in bolts made of tempered steel in the presence of a zinc melt and thus, provides the boundary conditions for the above mentioned critical factors to interact. The focus of this study is on investigating thermally‐induced stresses in large diameter bolts and their impact on the formation of liquid metal assisted cracking (LMAC). In order to calculate the thermal loads in hot‐dip galvanizing, simulations were carried out regarding the thermo‐mechanical behavior of bolts during the hot‐dip galvanizing process. The simulations illustrate that cracks are most likely to occur in the first thread turn. This prediction is confirmed by experimental observations.     

Texture development of Ca3Co4O9 thermoelectric oxide by high temperature plastic deformation and its contribution to the improvement in electric conductivity

High temperature uniaxial compression is conducted on Ca₃Co₄O₉ layered cobaltite, in order to achieve a thermoelectric oxide with low resistivity by the development of (0 0 1) texture. It is found that flow stress varies depending on deformation temperature and strain rate. Development of a sharp texture having the maximum (0 0 1) pole density of about 33 times as high as the random level is achieved. It is found that the high temperature compression process is quite effective for the simultaneous achievement of densification and (0 0 1) texture development. It is experimentally confirmed that resistivity decreases drastically by the construction of a sharp (0 0 1) texture.     

富锂锰表面超临界CO2辅助包覆磷酸锰锂及其电化学性能

富锂锰Li[Li0.2Mn0.54Co0.13Ni0.13]O₂(LMCN)是新一代高能量密度锂电池的理想正极材料,但存在首次不可逆容量高、循环寿命短以及电压衰减严重等问题。为此,本研究提出了一种可有效改善富锂锰性能的超临界表面包覆磷酸锰锂(LMP)工艺,探讨了不同包覆量对富锂锰材料结构和电化学储锂性能的影响。结果表明,LMP包覆量为3%(质量分数)的LMP3-LMCN样品,在30 mA·g-1电流密度下,首次库伦效率高达81.1%,经过100次充放电后循环容量保持率为79.2%,并且电压衰减仅为0.47 V,在1 500 mA·g-1电流密度下容量为88.76 mAh·g-1,明显优于纯相富锂锰。