煅烧煤矸石的活性和结构性能研究

对不同温度煅烧的煤矸石进行了系统研究,以寻求煤矸石最大活性的煅烧温度,并对其活化机理进行了初步探讨.采用游离氧化钙法、结合水法、X射线和孔结构等现代测试分析方法研究了煤矸石在煅烧过程中结构和活性的变化规律.结果表明:在一定煅烧温度范围内,煤矸石的矿物组成和微观结构发生了较大的变化,提高了无定型硅、铝氧化物的含量,从而大大提高了水化速率并改善了活性.     

Impression creep of Sn–40Pb–2·5Sb peritectic solder alloy

Abstract

The power law creep behaviour of the Sn–40Pb–2·5Sb peritectic solder alloy was investigated using an impression test apparatus. The tests were carried out under constant stress in the range 17 to 39 MPa and at temperatures in the range 296 to 363 K. Assuming a power law relationship between the impression velocity and stress, power law stress exponents in the range 1–3 were determined. Analysis of the data showed that for all loads and temperatures, the activation energy was stress independent with values in the range 51–56 kJ mol^-1. Based on the stress exponents obtained and activation energy data, it is proposed that grain boundary diffusion is the major mechanism for creep of the Sn–Pb–Sb peritectic alloy under these test conditions.     

挤压态Mg-Gd-Y-Zn-Zr合金热变形行为研究

目的研究挤压态Mg-8.90Gd-5.11Y-3.10Zn-0.47Zr高强镁合金在变形温度300~500℃、应变速率为0.001~1 s-1之间的热变形行为。方法采用Gleeble试验机进行高温单轴压缩试验。结果流变曲线具有典型的动态再结晶特征,应力随应变速率的升高或变形温度的降低而增加。分别采用指数关系、幂指数关系与双曲正弦函数关系对热变形行为进行表征,拟合度最好的是双曲正弦函数关系,平均线性回归系数达到0.974 484。合金的变形激活能随着变形温度的升高呈现下降的趋势。结论热压缩行为可以采用双曲正弦函数关系进行表达,应力指数和平均热激活能分别为:n=3.860 86,Q=234.0476 kJ/mol。     

Thermally activated domain wall motion

A theory of thermally activated domain wall motion is presented in which attention is focused on the functional form of the domain wall energy variation in the direction of motion. It is shown that in general the activation volume is magnetic field dependent, and not necessarily constant, as is often assumed. A simple power law form of the wall energy variation, due to sample inhomogeneities, is found to exhibit a ln (wall veiocity) against field slope which decreases with decreasing temperature as is observed in thin films. The usual assumption of a constant activation volume predicts a slope which increases as the temperature falls.     

Evaluation of low strain rate constitutive equation of 7075 aluminium alloy at high temperature

Abstract

The 7075 aluminium alloy is one of the most important engineering alloys utilised extensively in aircraft and transportation industries due to its high specific strength. In the present research, the flow behaviour of this alloy has been investigated using hot compression test at strain rates of 0·001, 0·01, 0·1 and 1 s^?1 and temperatures of 350, 400 and 450°C. The results reveal that dynamic softening occurred in these temperatures and strain rates. The activation energy, strain rate sensitivity and two constitutive equations (hyperbolic sine law and the power law) are derived from the results. It is shown that the hyperbolic sine law has a better agreement with the experimental results.     

Interface study for stainless steel fibre-reinforced aluminium matrix composite

Regular interface zones with uniform thickness in AISI 304 stainless steel-reinforced aluminium-matrix composite have been obtained using a vacuum high-pressure diffusion-bonding technique. Extensive and intensive experiments were performed to examine the growth of interfacial compounds with the variation of hot-pressing time and temperature. In the initial stage, the overall growth rate of the interface was found to follow a parabolic law. After a certain diffusion time, the interface growth rate fell behind that predicted by the parabolic law. A modified parabolic law has been established to explain the deviation and proved to be a better model to fit the experimental data. An activation energy of 152 kJ mol^-1 was found, which was somewhat lower than that obtained by previous work. The lower value of activation energy is attributed to the pressure (70 MPa) applied during hot pressing. Energy dispersive spectroscopic analysis and microhardness measurement indicated that the interface zone consists of a mixture of intermetallic compounds Fe(Cr, Ni)Al₂, Fe(Cr, Ni)Al₃ and (Fe, Cr, Ni)₂Al₇. This revised version was published online in November 2006 with corrections to the Cover Date.     

From Fracture to Damage Mechanics: A behavior law for microcracked composites using the concept of Crack Opening Mode

Many studies have been carried out in order to build a coherent macroscopic behavior law for a composite containing microcracks. All of them are only partially coherent and none of them is complete. This study proposes a hyperelastic behavior law for a microcracked composite, respecting all the conditions associated with the damage activation/deactivation, stress/strain relation continuity, induced anisotropy and the Clausius–Duhem inequality. This approach is based on the definition of the Crack Opening Mode for Damage Mechanics as it exists in Fracture Mechanics.     

A model based creep equation for 9Cr–1Mo–0·2V (P91 type) steel

Abstract

The isothermal constant stress creep tests data for a 9Cr–1Mo–0·2V (P91 type) steel were submitted for a phenomenological analysis in order to obtain the relevant creep equation for such steel. Namely, the minimum creep strain rate of P91 type steel cannot be described by the simple Arrhenius type power law constitutive model. The incorporation of the threshold stress concept in the analysis of creep data leads to a modified power law, which satisfactorily describes the creep behaviour of the examined P91 steel. However, the threshold stress is not a good material parameter, as it often varies with temperature and/or applied stress. This adds uncertainty to the extrapolation of the creep rates into ranges where experimental data are not available. Besides the fact that the physical foundation for a threshold stress is questionable from a scientific point of view, this is a serious practical limitation of the modified power law creep equation. The second creep equation proposed in the present paper is the improved stress dependent energy barrier model. The improvement of the standard model is based on two assumptions: first, on the hypothesis that the application of a stress also affects the energy barrier to be overcome when a local region transitions from the initial to the final state, and second, by applying a simple power function of stress instead of a hyperbolic sin function in the model based equation. The obtained value of stress exponent, n=5·5, is too high for entirely climb controlled creep. The apparent activation energy of approximately 510 to 545 kJ mol^?1, which is considerably higher than the activation energy for lattice diffusion, is the stress dependent activation energy of the slowest, dominant rate controlling process of the supposed multiple creep mechanisms.     

9Cr低活化马氏体钢在超临界水中的腐蚀行为

利用扫描电子显微镜(SEM)、电子能谱(EDS)以及X射线衍射(XRD)技术研究了9Cr低活化马氏体钢在650℃/25MPa超临界水中的腐蚀行为。结果表明,9Cr低活化马氏体钢腐蚀产物的晶粒随腐蚀时间的延长而长大,晶粒尺寸从200h的5.7μm长大到1000h的10.1μm。表面形成的氧化膜为双层结构,外层为Fe3O4,内层由Fe3O4和FeCr2O4共同组成。由氧化增重结果获得了9Cr低活化马氏体钢在超临界水中腐蚀的氧化动力学表达式,同时其腐蚀机理表现为吸氧腐蚀。     

Comments on “size and temperature dependences of the resistivity of thin alkali metal wires at liquid nitrogen,hydrogen and helium temperatures

The conductivity of PbF₂ thin films was studied as a function of the hydrostatic pressure of a neutral gas at different temperatures. This conductivity varies with pressure according to an exponential law up to a value of about 4 kbar; the measured activation volume is 2.3 cm³ mol^-1. The activation energy of the conductivity at these pressures remains unchanged in comparison with that found at atmospheric pressure, showing that the conduction mechanisms remain unchanged. For pressures above 4 kbar a fast rise in conductivity is attributed to a phase change accompanied by the creation of a large number of defects.     

Strain and stress mapping by mechanochemical activation of spiropyran in poly(methyl methacrylate)

The relationship between fracture‐induced mechanophore activation and the strain and stress ahead of a propagating crack in poly(methyl methacrylate) (PMMA) is studied. The mechanophore spiropyran is used as a secondary cross‐linker in rubber toughened PMMA, and the spiropyran‐linked material is subjected to fracture testing. Mechanophore activation is detected and analysed by fluorescence imaging. Digital image correlation is used to measure the strain field ahead of the crack tip, whereas the corresponding stress field is calculated using the Hutchinson–Rice–Rosengren singularity field equations. Mechanophore activation follows a power law dependence on distance from the crack tip and provides both a qualitative and quantitative measure of the strain and stress fields ahead of the crack.     

Temperature Dependence of the Hall and Longitudinal Resistances in a Quantum Hall Resistance Standard

We present detailed measurements of the temperature dependence of the Hall and longitudinal resistances on a quantum Hall device [(GaAs(7)] which has been used as a resistance standard at NIST. We find a simple power law relationship between the change in Hall resistance and the longitudinal resistance as the temperature is varied between 1.4 K and 36 K. This power law holds over seven orders of magnitude change in the Hall resistance. We fit the temperature dependence above about 4 K to thermal activation, and extract the energy gap and the effective g-factor.     

Practical prediction of time-dependent deformations of concrete

Proposed is a practical model for predicting creep and shrinkage of concrete from the composition of concrete mix, strength, age at loading, conditions of environment, size and shape, etc. The main features are: double power law for basic creep, square-root hyperbolic law for shrinkage, diffusion-type size dependence of humidity effects, additive drying creep term related to shrinkage, and activation energy treatment of thermal effects. Optimization techniques are used to fit numerous test data available in the literature. The work is a continuation of previous investigations and consists of several parts. This first part deals with shrinkage.     

Oxidation of aluminium nitride

The oxidation kinetics of polycrystalline aluminium nitride substrates in air at temperatures in the range 1150 to 1750°C have been studied by measuring the weight increase in the oxidized samples. At the lowest temperature, the oxide layer was not continuous on the AlN surface and the oxidation kinetics followed a linear rate law with an activation energy of 175 kJ mol^–1. At all the higher temperatures, the growth kinetics followed a parabolic rate law with an activation energy of 395 kJ mol^–1. Samples oxidized at these higher temperatures were covered with a dense oxide layer having a fine-grained microstructure.     

Effect of Critical Current Density and Critical Temperature on ac Susceptibility

Based on the flux creep equation, the effect of critical current density and critical temperature on ac susceptibility is investigated numerically in a superconducting slab immersed in an ac magnetic field. The current density dependence of the flux creep activation barrier is employed as the logarithmic law. The fundamental ac susceptibilities of the slab as a function of temperature for the same ac field have been derived in a unified picture. The results show that ac susceptibility in flux creep regime is affected by critical current density and critical temperature.     

Reliability scaling issues for nanoscale devices

We discuss two specific scaling issues that can result in qualitative changes in device reliability prediction for nanoscale devices. The first of these involves a rapid increase in early failures due to a distribution of activation energies of defect precursors. We show that the slopes of the failure functions for hot carrier interface state generation (HCI) and time-dependent dielectric breakdown (TDDB) have simple physical interpretations in terms of a geometrical factor and the activation energy distribution width. The second issue involves a transition from single to multiple electrons causing individual defects. This picture allows simple physical explanations for the larger HCI damage in NMOS versus PMOS, the anomalous isotope effect of activation energies for HCI in the lucky electron model, and the observed power law dependence of the time to breakdown versus voltage for TDDB for ultrathin oxides.     

Fe-38Ni-13Co-4.7Nb合金中的γ'相长大及分布规律研究

研究了Ｆｅ－３８Ｎｉ－１３Ｃｏ－４．７Ｎｂ合金中γ'相长大及分布规律。结果表明,该合金的ｒ１相不稳定,易聚集长大,其平均尺寸增长遵循时间的立方根规律,在７２０℃和６５０℃的长大速率分别为０．１０ｕｍ３／ｓ和４．２６×１０－３ｎｍ３／ｓ。γ'相的大小分布符合ＬＳＥＭ规律。其长大扩散激活能为２４２．１５ｋＪ／ｍｏｌ。Ａｌ元素的缺乏是导致γ'相不稳定的原因。     

Stress dependence on stress relaxation creep rate during tensile holding under creep-fatigue interaction in 1Cr-Mo-V steel

A quantitative analysis of the stress dependence on stress relaxation creep rate during hold time under creep-fatigue interaction conditions has been conducted for 1Cr-Mo-V steel. It was shown that the transient behavior of the Norton power law relation is observed in the early stage of stress relaxation in which the instantaneous stress is relaxed drastically, which occurs due to the initial loading condition. But after the initial transient response in a 5 hour tensile hold time, the relations between strain rate and instantaneous stress represented the same creep behavior, which is independent of the initial strain level. The value of stress exponent after transition was 17 which is the same as that of the typical monotonic creep suggested from several studies for 1Cr-Mo-V steel. Considering the value of the activation energy for the saturated relaxation stage, it is suggested that the creep rate is related to instantaneous stress and temperature by the Arrhenius type power law.     

The correlation between the power-law coefficients in creep: the temperature dependence

In this study we investigated the relationship between the coefficients of the Norton law for low-stress high-temperature deformation results of different materials reported in the literature. These coefficients are interrelated and it is shown that this relation can be theoretically deduced from the assumption of a variation of the activation area with the inverse of the effective stress (i.e. a variation of the activation energy with the logarithm of the stress). As a consequence, all the straight lines ln(strain-rate)–ln (stress) intersected at the same point, named the pivot point. This pivot point is characteristic of each material. Such a correlation can be found in the field of the mechanics of materials when a power-law relation holds. © 1998 Kluwer Academic Publishers     

Lanthanum oxide doping effect on dc electrical conductivity of ferroelectrics sodium vanadate and rubidium vanadate

The temperature dependence of dc electrical conductivity was measured by two-probe technique in the vicinity of phase transition point for ferroelectrics sodium vanadate and rubidium vanadate doped with different concentrations of La₂O₃. These materials show a sharp change in conductivity at their phase transition temperatures. The results were found to obey the conventional exponential law and the activation energies were calculated for ferroelectric and paraelectric states. It was found that activation energy in ferroelectric phase is smaller than in the paraelectric phase. The activation energy increases slowly with increase in doping concentration of La₂O₃ up to 0·1 mol%, however, it decreases with further increase in doping concentration, in both ferro and para states. The dc electrical conductivity below the Curie temperature is of mixed type (ionic-electronic) while it is electronic type above the Curie temperature.