水对食品相变的影响

水是食品材料中最重要的成分。本文介绍了食品中水的性质以及水对食品相变的影响，并从水活性、水的吸附性以及水的增塑性三方面描述了水在食品相变中所起的作用。另外，还着重分析了水对食品冻结温度的影响。     

奥氏体不锈钢凝固相转变规律曲线(SPT曲线)建立

利用自行设计的高温凝固相转变测定实验装置,研究了304奥氏体不锈钢在不同冷却速度下的高温凝固相转变过程,得到了凝固过程中液相（ L）到高温铁素体（δ）到奥氏体（γ）的相变温度。在此基础上分析了304奥氏体不锈钢在不同冷却速度下的高温凝固相转变规律,从而建立了304奥氏体不锈钢的低冷速凝固相转变规律曲线—SPT（Solidification phase transforma?tion）曲线。结果表明：对试样进行液氮酒精淬火有效地保留了试样高温时各相的状态。可以清楚的显示在不同冷速下的不同温度淬火时液相和固相的各相成份比例及在不同淬火温度下各成份体积比例的变化。通过研究体积比例变化,可以得到304奥氏体不锈钢在不同冷速下的液相线、固相线及各种反应开始和结束的转变温度（即SPT曲线）。由SPT曲线也可以看出,随着冷却速度的增大,相转变模式会发生变化,相图会向左移动,各相变反应的温度区间减小。     

Influence of erbium doping on phase transition and optical properties of strontium barium niobate

The optical properties of erbium impurities in strontium barium niobate are investigated measuring optical absorption and emission in the visible and near infrared spectral region. For the main fluorescence band at 1.55 μm, an anomalous dependence of the fluorescence decay time on dopant concentration is found which, however, can be consistently explained by reabsorption effects. A Judd–Ofelt analysis of the absorption spectra together with an appropriate analysis of the reabsorption yields a radiative quantum efficiency of approximately 60%. In addition, erbium dopants are shown to efficiently influence the phase transition temperature of strontium barium niobate.     

Crystallographic phase transition, electrical and magnetic properties of stoichiometric La(Mn,Rh)O3

Temperature-induced phase transitions, electrical conductivity, and some magnetic properties of stoichiometric LaMn_1−xRh_xO₃ (0.1≤x≤0.5) have been studied. The phase transitions of LaMn_0.9Rh_0.1O₃ were investigated by high-temperature X-ray powder diffractometry and orthorhombic-pseudocubic-rhombohedral transitions were observed. The electrical conductivity measurement shows semiconducting property above room temperature. Breaking of slope in the temperature dependence of the conductivity bring the evidence in support of the phase transition for LaMn_0.9Rh_0.1O₃. At low temperature, the compounds show ferromagnetic behavior but the ferromagnetic intensity increases with the increase of the oxygen nonstoichiometry.     

First-principles study of phase transition and elastic properties of XBi (X = Ce, Pr) compounds

The pressure-induced phase transitions of CeBi and PrBi compounds were investigated by using full-potential linearized augmented plane-wave (FP-LAPW) method. The calculations indicate that the transition pressure for CeBi compound from the NaCl-type (B1) structure to the body centered tetragonal (BCT) structure are 11.53 GPa from total energy (E)-volume (V) data and 6.48 GPa from equal Gibbs free energy (G). For PrBi compound, the same phase transition sequence occurred at 10.94 GPa obtained from the slope of the common tangent of E-V curves and 6.04 GPa from the equal G. The detailed structural changes during the phase transition were analyzed. From the elastic constants at zero pressure, we can conclude that B1 phase of XBi (X = Ce, Pr) compounds are mechanical stable, consistent with the experimental observations.     

Thickness dependence of the amorphous-cubic and cubic-hexagonal phase transition temperatures of GeSbTe thin films on silicon nitride

The crystallization temperature of GeSbTe thin films with thicknesses between 11 and 87 nm on silicon nitride was studied through resistance versus temperature measurements. The amorphous-cubic phase transition occurs at ~ 150 °C for all films thicknesses, whereas the cubic-hexagonal phase transition temperature increases with film thickness, from ~ 200 °C for the 20 nm film to ~ 250 °C for the 87 nm film. The cubic-hexagonal transition occurs gradually for the 11 nm film. Implications for phase-change memory devices are discussed.     

Combined effects of high-temperature rolling and ultrafast cooling on the mechanical properties of low-carbon steel

The role of ultrafast cooling (UFC) on the grain refinement of ferrite, the precipitation behavior of cementite particles and the mechanical properties of a mild steel (Q235 grade) was evaluated by applying laminar cooling and UFC and varying the finish cooling temperature ranges during UFC after hot rolling. While UFC refined the ferrite grains, it accumulated the degeneration of pearlite, resulting in complete disappearance of the laminar pearlite at relatively low finish cooling temperatures. The minimum mean size of spheroidized cementite particles reached ~110?nm. Meanwhile, the enhancement of UFC on tensile strengths of mild steels mainly resulted from the grain refinement of ferrite and the precipitation strengthening of cementite particles; however, the contribution varied with the finish cooling temperature of UFC. A modified Ashby–Orowan model was also used for evaluating the yield strength increment of medium plates. This work will provide a theoretical basis for the diversity control of microstructure and for developing stronger and tougher mild steels by introducing UFC technology after high-temperature rolling.     

Determination of the phase transition in Pb0.88Ln0.08Ti0.98Mn0.02O3 (Ln=La, Sm, Eu) piezoceramics based on the Stefan–Boltzmann law

A method for determination of the phase transition in piezoelectric ceramic based on the relationship expressed by the Stefan–Boltzmann law is reported, i.e., by means of the radiation that the piezoelectric ceramic emits when it is subjected to different temperatures. The experiment is performed in piezoelectric ceramic based on PbTiO₃ modified by the partial substitution of rare earths for Pb in the Pb_0.88(Ln)_0.08Ti_0.98Mn_0.02O₃ system (Ln=La, Sm, Eu). From the measured emitted radiation, the value of the emissivity is calculated for each type of piezoelectric ceramic.     

Extending the scope of ‘in silico experiments’: Theoretical approaches for the investigation of reaction mechanisms, nucleation events and phase transitions

The investigation of the atomistic mechanisms of processes in complex systems constitutes a major challenge to both theory and experiment. While experimental studies offer a wide variety of insights at the macroscopic scale, the atomistic level of detail often remains elusive. On the other hand, molecular simulation approaches may easily achieve microscopic resolution and hence appear particularly suited for detailed mechanistic analyses. However, the computational effort is typically quite considerable and in many cases special simulation strategies are needed to make simulations possible. This review is dedicated to special approaches for tackling the time/length-scale problem inherent to molecular dynamics simulations. Employing these techniques opened a series of new perspectives. The latter are illustrated with the example of recent simulation studies of the atomistic mechanisms involved in complex processes like crystal nucleation, phase transitions and reactions in solution. Along this line, we discuss the reaction mechanisms for He insertion into C₆₀ fullerenes, nucleation events and domain morphogenesis in pressure-induced phase transitions in solids and ion aggregation from solution.     

Partial magnetization of siderite via fluidization roasting for efficient recovery of iron: Phase transition,microstructure evolution and kinetics

This study proposes a new process for the partial magnetization of siderite using fluidization roasting, addressing its difficult beneficiation characteristics and lack of large-scale exploitation. Two siderite samples, designated sample S45 and sample S74, with particle sizes of 45–74 μm and 74–150 μm, respectively, were used to optimize the process parameters. The fluidization roasting process rapidly converted siderite to ferromagnetic magnetite, with the magnetite distributed on particle surfaces and internal cracks. CO₂ was used during roasting to facilitate the transformation of siderite to magnetite. The iron recovery reached more than 98 % when the roasting time was only 2 min for sample S45 (or 4 min for sample S74). Partial magnetization of siderite can be achieved in a short time by fluidization roasting with low energy consumption for efficient iron recovery. The isothermal kinetics indicate that the kinetic mechanism of the two siderite samples was the random nucleation and growth model, with the fine-grained sample having a shorter reaction time and lower activation energy.     

Influences of solute content, melt superheat and growth direction on the transient metal/mold interfacial heat transfer coefficient during solidification of Sn–Pb alloys

Several factors such as alloy composition, melt superheat, mold material, roughness of inner mold surface, mold coating layer, etc., can affect the transient metal/mold heat transfer coefficient, h_i. An accurate casting solidification model should be able to unequivocally consider these effects on h_i determination. After this previous knowledge on interfacial heat transfer, such models might be used to control the process based on thermal and operational parameters and to predict microstructure which affects casting final properties. In the present work, three different directional solidification systems were designed in such a way that thermal data could be monitored no matter what configuration was tested with respect to the gravity vector: vertical upward and downward or horizontal. Experiments were carried-out with Sn–Pb hypoeutectic alloys (5 wt.% Pb, 10 wt.% Pb, 15 wt.% Pb and 30 wt.% Pb) for investigating the influence of solute content, growth direction and melt superheat on h_i values. The experimentally obtained temperatures were used by a numerical technique in order to determine time-varying h_i values. It was found that h_i rises with decreasing lead content of the alloy, and that h_i profiles can be affected by the initial melt temperature distribution.     

Quantitative evaluation of effects of shape and size of artificially introduced alumina particles on the fatigue strength of 1.5Ni---Cr---Mo (En24) steel

In order to investigate the effects of non-metallic inclusion on the fatigue strength of high-strength steels, in 1963 W.E. Duckworth and E. Ineson conducted fatigue tests using specimens that contained artificially added spherical and angular alumina particles of various controlled sizes. Although the fatigue tests were carried out under the same nominal stresses in rotating-bending and tension-compression tests the fatigue lives of specimens showed a large scatter. They reported in some detail typical complicated aspects of the effects of non-metallic inclusions on the fatigue strength.

In the present study the authors have reanalysed these complicated fatigue data using the prediction equation that was proposed by Murakami et al for the quantitative evaluation of the effects of small defects on fatigue strength. The geometrical parameter that controls the scatter of the fatigue strength is the square root of the projection area √ area and not the shape of the inclusions, whether they are spherical or angular. It is shown from the data from the failed specimens that the fatigue strength of materials containing inclusions larger than a critical size can be predicted by the Vickers hardness (Hv) of the matrix and √ area of the inclusion regardless of the shape.     

沉积条件对硅基薄膜非晶转微晶相变、沉积速率及其光电性能的影响(英文)

本文采用HWA-MWECR-CVD系统制备了微晶硅薄膜。研究了氢稀释比、反应压强以及微波功率对微晶硅薄膜非晶转微晶相变及其相关性能的影响。实验结果表明:当氢稀释比为94%、反应压强为1.5Pa以及微波功率为500W时,高质量的微晶硅薄膜可以被获得,如2.86*104的高光敏性,1nm左右的沉积速率以及8.9%的光致衰退速率等。     

Effect of oxygen vacancy variation on the photo-assisted degradation and structural phase transition of oxygen defective Ba(Fe,Co)O3−x

The different effect of oxygen vacancy variation on photo-assisted degradation effect and structural phase transition of oxygen defective Ba(Fe,Co)O_3−x in dye degradation were investigated via comparative studies. The samples of perovskite BaFeO_3−x and BaCoO_3−x were synthesized at 700 °C by citrate sol-gel method. Samples synthesized above 700 °C show oxygen deficiency. With oxygen vacancy increasing, the BaFeO_3−x becomes instable, whereas BaCoO_3−x improves the stability. The instability is due to CO₂ adsorption activity of oxygen vacancies, and then this may make negative effects on their photo-assisted degradation effect. So finally, the oxygen vacancies take different effects on photo-assisted degradation effect of Ba(Fe,Co)O_3−x.     

Development of an A356 die casting setup for determining the heat transfer coefficient depending on cooling conditions,gap size,and contact pressure

In this paper, the development of an experimental die casting setup to perform simultaneous in‐situ measurements of temperatures, air‐gap formation and contact pressures is presented. The derivation of the resulting heat transfer coefficients between mold and melt is also included. To take the influence of different cooling rates into account, an active die tempering is applied. For the implementation of this experimental setup, a special mold for a rotationally symmetrical test specimen is developed which incorporates the necessary measuring technique and can be adapted to different cooling conditions by means of exchangeable die inserts. Concluding, first results and the corresponding heat transfer coefficients are presented.     

Filter effects on the wear and corrosion behaviors of arc deposited (Ti,Al)N coatings for application on cold-work tool steel

In this study, (Ti,Al)N coatings were deposited on Japanese Industrial Standard SKD11 modified cold-work tool steel using a cathodic arc deposition system with and without magnetic filter attachment. Coating morphology and properties such as coating structure, adhesion, hardness, abrasion and corrosion behaviors were analyzed to evaluate the effects of magnetic filter on the coatings. The results showed that magnetic filtering slowed down (Ti,Al)N deposition rate, but it improved component homogeneity, roughness and adhesion of the coatings. Although (Ti,Al)N coated specimens produced with or without filter both showed superior abrasion resistance in service, however, filtered (Ti,Al)N coatings yielded better corrosion protection of the steel than unfiltered ones in 3.5 wt.% NaCl aqueous medium.     

Effect of vapour phase hydrogen peroxide,as a decontaminant for civil aviation applications,on microstructure,tensile properties and corrosion resistance of 2024 and 7075 age hardenable aluminium alloys and 304 austenitic stainless steel

Abstract

A response to the chemical or biological contamination of aircraft requires the use of a suitable decontaminant. Among possible chemical decontaminants, vapour phase hydrogen peroxide appears to be a likely candidate in terms of a combination of efficacy, low environmental impact and potential for materials compatibility. The present paper examines the effect of hydrogen peroxide, both in the vapour phase and as a liquid concentrate on two common structural materials used in aviation, namely 2024 and 7075 age hardenable aluminium alloys and on 304 austenitic stainless steel, the latter as employed in galley and lavatory surfaces. The present paper characterises both the effects of hydrogen peroxide on the microstructure of the materials and the impact that decontamination has on the tensile properties and corrosion resistance of these materials. Microstructural effects are both relatively small in magnitude and confined to a region immediately beside the exposed surface. No systematic effect is found on either the tensile properties or the post-exposure corrosion resistance of the three alloys examined. These observations are encouraging in terms of the use of vapour phase hydrogen peroxide for decontamination applications.     

Comparison of creep crack growth rate in heat affected zone of welded joint for 9%Cr ferritic heat resistant steel based on C, dδ/dt, K and Q parameters

Creep crack growth behavior is very sensitive to the materials’ micro-structures such as the heat affected zone of a weld joint. This is a main issue to be clarified for 9%Cr ferritic heat resistant steel for their application in structural components. In this paper, high temperature creep crack growth tests were conducted on CT specimens with cracks in the heat affected zone of weld joints of W added 9%Cr ferritic heat resistant steel, ASME grade P92. The creep crack growth behavior in the heat affected zone of welded joint was investigated using the Q^∗ concept following which the algorithm of predicting the life of creep crack growth has been proposed. Furthermore, three-dimensional elastic-plastic creep FEM analyses were conducted and the effect of stress multiaxiality of welded joint on creep crack growth rate was discussed as compared with that of base metal.