捕收剂混合使用的协同效应与其浮选性能的相关关系研究

本文是关于捕收剂混含使用所产生的协同效应大小的相关因素和相关关系研究。研究结果表明,混用组合的协同效应大小与组合中各药浮选性能差之间存在相关关系,其浮选性能差以收率档次差与品位档次差的算术和表示,并命名为CS值。利用这一相关关系,可以大致预测新的混合用药组合的协同效应,从而为选择和设计新的药剂组合提供了一定的依据。     

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.     

Fracture behaviour of radiolytically oxidised reactor core graphites: a view

Abstract

This paper provides a view on the fracture behaviour of polygranular graphites, used to moderate gas cooled nuclear reactors. Graphite is often cited as a classic example of a brittle material because failure, in tension, is associated with small strains. However, attempts to characterise the fracture behaviour of graphite by linear elastic fracture mechanics methods have been largely unsuccessful. Observations of graphite fracture show that elastic strain energy may be dissipated by the formation of distributed microcracks, and their formation may be responsible for non-linearity in the rising load–displacement curve. Progressive softening behaviour may also be observed in some specimens after the peak load. This type of load–displacement behaviour is a characteristic of quasi-brittle materials. Radiolytic oxidation increases the proportion of porosity within reactor core graphite so that the microstructure becomes increasingly skeletal. Consideration is given to the fracture of radiolytically oxidised graphite to support an argument for quasi-brittle behaviour.     

Pack formation and long term oxidation kinetics of TiAl3 coating on γ-TiAl

Abstract

The aim of this study is to produce microcracking free TiAl₃ coatings on γ-TiAl alloy by the pack cementation process and to determine the long-term oxidation kinetics and thermal stability of the coating at high temperatures. It was shown that microcracking free coatings could be prepared in the AlCl₃ activated packs containing 4 wt-%Al as the depositing source. The conditions required for the formation of a microcracking free coating are discussed in relation to the pack chemistry at high temperatures. The TiAl₃ coatings formed were oxidised in air for more than 6200 h, during which weight gains were measured at regular intervals. The major oxide in the scale was Al₂O₃. It was observed that a TiAl₂ phase zone formed in the subsurface of the scale as a result of preferential oxidation of Al in the TiAl₃ coating. It was found that a linear relationship existed between the weight gain and logarithm of time of oxidation at 800°C: Δm _t = k _lln(αt+ 1). The thermal stability of the coating was assessed by measuring the growth kinetics of the TiAl₂ interlayer at the boundary between the TiAl₃ coating and substrate, which was determined to be d^1·4 = 0·1t (d and t in μm and h respectively) at 800°C using the experimental data measured over a diffusion annealing period of more than 6200 h.     

Process model for strength of age hardenable aluminium alloy welds

Abstract

An existing process model for hardness prediction in age hardenable aluminium alloy welds is presented and analysed. One of the key criticisms of this model is that its derivation assumes softening is due to precipitate dissolution alone. The influence of precipitate coarsening has been determined by developing an equivalent model for softening owing to coarsening. It is shown that the experimentally derived master curves that form the basis of the model are capable of representing softening by a mixture of precipitate coarsening and dissolution. Methods to predict post-weld natural aging are discussed, and a new method is presented based on direct prediction of the Guinier–Preston zone fraction. The model has been applied to friction stir welding. Model predictions agree well with measured hardness profiles, and the sensitivity of the predictions to temperature is discussed.     

Macrostructural changes of polymer replicated open cell cordierite based foams upon sintering

Abstract

The goal of this work was to clarify the macrostructural changes that take place upon sintering of open cell cordierite based foams. A methodology, based on optical image analysis, was developed to assess the structure of open-cell foams, which allowed evaluating the macrostructure of both cordierite based foams obtained by the replication process and their polymeric templates. The parameters used to describe the structures were the size of the cell and the window, the window shape factor, the strut thickness and the volume fraction of the material. The experimental evidence gathered opened the way to understand the physical/chemical transformations involved in the polymer burnout and the ceramic sintering processes, as well as their influence on the ceramic final structure. The observed trends provide guidance for tailoring 'replicated' cordierite based foams, in view of the required application.     

含中草药成分造纸法再造烟叶的制备

介绍了一种造纸法含中草药成分再造烟叶的制备工艺。该工艺应用了类似造纸的原理,将中草药与烟草混合萃取后,取其纤维制成高填充值的纸叶,萃取液经低温真空浓缩处理后浸涂到该纸叶上。该工艺扩大了中草药的用药范围,有效成分可较灵活控制,提高了中草药原料的利用率。制成的含中草药成分再造烟叶充分保留了不溶性有效药用成分,与烟香谐调,安全性好,同时具有较高的填充值,可以明显降低卷烟的制造成本。     

A multi-phase micro-segregation model

Abstract

A multi-component multi-phase micro-segregation model was developed to cope with eutectic transformations of ductile iron, assuming mixed dendritic–globular solidification morphology. Solute partitioning is calculated by an equilibrium assumption at the interfaces using commercial CALPHAD software. Time-sensitive micro-segregation patterns and phase fractions are solved by the micro-segregation model. The development of fraction liquid over temperature with time was compared to Gulliver–Scheil simulations for a model with and without cross-diffusion. The micro-segregation model was coupled to a commercial process simulations tool to deal with interaction effects between material and process scale during solidification of a benchmark test casting made of EN-GJSA-X NiCr 20–2. The precipitation kinetics of phases, especially of graphite, is of particular interest during solidification of ductile iron, due to feeding effects. The coupling procedure as well as important aspects during solidification of ductile iron will be explained.     

The Effect of Trace Elements on the Cooling Curves,Microstructure and Mechanical Properties of Eutectic Aluminium-Silicon Alloy

Abstract

The effect of trace elements, used for modification, on the cooling curves obtained during solidification, microstructure and mechanical properties of eutectic aluminium-silicon alloy was investigated. The results of this study indicate the following: 1 The addition of sodium or sodium plus strontium or antimony modifies the eutectic silicon while the addition of sulphur does not alter the microstructure.

2 Those elements which modify the eutectic-silicon, lower the eutectic solidification temperature, while those elements which do not bring about modification, do not alter the eutectic solidification temperature.

3 The addition of those elements which modify the eutectic aluminium-silicon alloy, viz., sodium or sodium plus strontium or antimony improves the UTS and percentage elongation. The addition of titanium to eutectic aluminium-silicon alloy containing these trace elements improves the UTS and percentage elongation to a further extent. Among the various trace elements added to eutectic aluminium-silicon alloy, the addition of sodium plus titanium improves the UTS and percentage elongation to the maximum extent.

     

Prediction of dilution in GMA and UGMA stainless steel single layer cladding using response surface methodology

Abstract

This paper describes the use of a variant of GMAW process named as UGMAW (universal gas metal arc welding) process for single layer stainless steel cladding, which makes use of a specially designed torch to preheat the filler wire, using an auxiliary welding power source, before its emergence from the torch. The experimental work undertaken was that of single layer cladding of 12 mm thick low carbon steel with the austenitic stainless steel 316L solid filler wire of 1·14 mm diameter. Dependence of dilution was investigated using four factor five level central composite rotatable design to develop relationship for predicting dilution, which enables to quantify the direct and interactive effects of four numerical factors, namely, wire feed rate, open circuit voltage (OCV), welding speed, electrode stickout and one categorical factor, preheat current. External preheating of the filler wire in UGMAW process resulted in greater contribution of arc energy by resistive heating owing to which significant drop in the main welding current and hence low dilution values were observed. Numerical optimisation was carried out and the optimal solutions generated indicate that for same levels of dilution, higher deposition rates are achievable in UGMAW process, thus making it a good choice for low cost surfacing applications.