摘要 :
It is conventionally assumed in the mass production of steels that the processing time must be reasonable and that the material must have uniform properties. The consequence is that short heat treatments cannot be tolerated since ...
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It is conventionally assumed in the mass production of steels that the processing time must be reasonable and that the material must have uniform properties. The consequence is that short heat treatments cannot be tolerated since the scale of engineered products may be so large that uniform temperatures cannot be achieved. Similarly, thermal treatments requiring several days or weeks are not considered practical because of productivity concerns. In this article, I will show that these conservative ideas are a huge disadvantage to the creation of radically different steels whose manufacture could lead to an improvement in the quality of life. Indeed, such steels are capable of wiping out the competition from newcomers in the field of structural materials, such as the infamous carbon nanotubes and metal-matrix composites.
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The control of temperature is the most important tool to avoid postharvest losses during the commercialization of fruits and vegetables. However, one problem usually found during the cold storage of commodities of tropical and sub...
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The control of temperature is the most important tool to avoid postharvest losses during the commercialization of fruits and vegetables. However, one problem usually found during the cold storage of commodities of tropical and subtropical origin is the development of physiological disorders collectively known as chilling injury. Although chilling injury can be prevented by maintaining the commodity at temperatures above the critical threshold, these temperatures cause a significant reduction in the shelf life. Different mechanisms have been proposed to explain both, the physical and biochemical bases of this phenomenon. Over the last years, the theory that oxidative stress may be involved in chilling injury has gained importance. According to this theory, an oxidative unbalance causing an excessive production of reactive oxygen species (ROS) would be the responsible for initiating the damage. Due to consumer concerns about the presence of chemicals in food, the use of physical techniques to avoid the development of chilling injury has been considered in many studies. According to this approach, the exposure of fruit to a stress may be used as a strategy to protect the commodity from the subsequent stress represented by the cold storage. From a biochemical point of view, evidence has been found that links this protective effect with the synthesis of a group of proteins known as heat shock proteins (HSP). The present review discusses the application of different stress treatments and the link between treatment application and HSP production. It is also discussed the role played by these protein in the protection and their potential use as biochemical markers to optimize the application of stress treatments.
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Surface-welds of Hastelloy C4 and some mixed welds of Inconel 600 and Hastelloy C4 were prepared by the plasma-hot-wire-surface-welding method. Intercrystalline corrosion tests were performed in a diluted Streicher-solution. On-li...
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Surface-welds of Hastelloy C4 and some mixed welds of Inconel 600 and Hastelloy C4 were prepared by the plasma-hot-wire-surface-welding method. Intercrystalline corrosion tests were performed in a diluted Streicher-solution. On-line recording of the corrosion potential uses the stability of the redox-pair, Fe(III)/Fe(II) (called the chemical potentiostat). Microscopic observations of specimens after corrosion accompanied the potential recording and gave valuable information about the morphology changes that occur due to intercrystalline corrosion. Potential measurements in a 1/3-diluted Streicher-Test solution showed that 2-layer surface-welds of Hastelloy C4, prepared by the hot-wire-surface-welding method with arc-deflection, were the most resistant to intercrystalline corrosion. A mixed 2-layer surface-weld of Inconel 600 inner-layer and Hastelloy C4 outer-layer was not effective due to the heterogeneous interface formed between both layers.
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To obtain new information about the mechanical and physical properties of dry wood in unstable states, the influence of heating history on viscoelastic properties and dimensional changes of dry wood in the radial, tangential, and ...
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To obtain new information about the mechanical and physical properties of dry wood in unstable states, the influence of heating history on viscoelastic properties and dimensional changes of dry wood in the radial, tangential, and longitudinal directions was studied between 100p and 200pC. Unstable states of dry wood still existed after heating at 105pC for 30 min and were modified by activated molecular motion in the first heating process to temperatures above 105pC. This phenomenon is thought to be caused by the unstable states reappearing after wetting and drying again. Dry wood components did not completely approach the stable state in the temperature range tested, because they did not entirely surpass the glass transition temperatures in most of the temperature range. In constant temperature processes at 135p and 165pC, E' increased and E" decreased with time regardless of the direction. This indicated that the unstable states of dry wood components were gradually modified with time at constant temperatures. On the other hand, anisotropy of dimensional change existed and dimension increased in the longitudinal direction, was unchanged in the radial direction, and decreased in the tangential direction with time at constant temperatures.
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The effects of heat treatment of skim milk (95pC/80 s, 95pC/256 s, 110pC/40 s, 110pC/180 s, 130pC/20 s and 130pC/80 s) and final fermentation pH of yogurt (4.8 and 4.4) on physical characteristics of stirred yogurt were investigat...
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The effects of heat treatment of skim milk (95pC/80 s, 95pC/256 s, 110pC/40 s, 110pC/180 s, 130pC/20 s and 130pC/80 s) and final fermentation pH of yogurt (4.8 and 4.4) on physical characteristics of stirred yogurt were investigated. Physical properties, including graininess and roughness, of stirred yogurt were determined during storage at 4pC for 15 days. Number of grains, perimeter of grains, visual roughness, storage modulus and yield stress decreased, when heating temperature or final fermentation pH increased. For practical applications, processing parameters such as heat treatment and fermentation pH can be optimized to improve quality or modified to create fermented milk products with different physical properties.
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The presentation is devoted to the analysis of the techniques developed at VAZ car plant for stimulation of saturation processes during high-temperature carbonitriding in atmosphere of 20 percent H_2, and low-temperature modes of ...
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The presentation is devoted to the analysis of the techniques developed at VAZ car plant for stimulation of saturation processes during high-temperature carbonitriding in atmosphere of 20 percent H_2, and low-temperature modes of nitride hardening (carbonitriding) in ammonia and exothermic gas.
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Epiphytic fluorescent isolates of the genus Pseudomonas (277), cultured from the fruit and leaf surfaces of citrus, were screened for antagonistic activity against green mould caused by Penicillium digitatum. Three of the Pseudomo...
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Epiphytic fluorescent isolates of the genus Pseudomonas (277), cultured from the fruit and leaf surfaces of citrus, were screened for antagonistic activity against green mould caused by Penicillium digitatum. Three of the Pseudomonas isolates showed greater activity than others against the pathogen in preliminary screening tests and were selected for subsequent experiments. Pseudomonas isolates were evaluated alone and in combination with 24 and 45°C sodium bicarbonate (3%) treatments on artificially inoculated Thomson navel oranges. The Pseudomonas isolates were completely tolerant to sodium bicarbonate up to a concentration of 3%. In addition, their efficacy for controlling green mould was improved when combined with the 3% sodium bicarbonate. A further increase in biocontrol activity was obtained when the bacterial isolates were applied in combination with hot sodium bicarbonate. It was concluded that using the fluorescent Pseudomonas spp. isolates in combination with a treatment of hot sodium bicarbonate could provide a practical alternative or complement to fungicides for postharvest control of green mould on oranges.
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The recrystallization annealing of cold-formed materials is the most important and sometimes the only heat treatment to reduce or eliminate work hardening. This article discusses the mathematical modeling of the structure and prop...
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The recrystallization annealing of cold-formed materials is the most important and sometimes the only heat treatment to reduce or eliminate work hardening. This article discusses the mathematical modeling of the structure and property changes during recrystallization annealing. Experiments and their supporting theories are discussed. This work was limited to various nonferrous alloys such as copper alloys CuSn6 (C51900) and CuZn36 (C35300), and nickel alloys. Wires were drawn to a deformation grade between 0.2 and 2.0, whereupon the mechanical properties were determined in tensile tests. Work hardening is described by two equations. This discussion is followed by treatment of the subject of annealing, or strength reduction. Various annealing temperatures for recrystallization are used and the interactions between that and structure changes are presented. Modeling of these processes must include the type of heat transfer to be expected in any given pull-through oven. The PC program TableCurve 3D was used for the simulation calculations. Tensile strengths and fracture elongation are shown against annealing time in 3D graphs.
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In order to create localized areas of shape memory effect or superelastic effect in a shape memory alloy (SMA) wire, it is necessary to precisely control the temporal and spatial temperature profiles of the treated wire in order t...
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In order to create localized areas of shape memory effect or superelastic effect in a shape memory alloy (SMA) wire, it is necessary to precisely control the temporal and spatial temperature profiles of the treated wire in order to change its composition at specific locations. In this paper, a localized heat treatment system (LHTS) has been developed based on a one-dimensional heat transfer model coupled with a high power fiber laser. This LHTS is capable of achieving various temporal temperature profiles in a point or a section of an SMA wire prescribed by a user. Furthermore, a variable flow inert gas heat treatment chamber has been designed to prevent oxide formation in shape memory alloy heat treatments without causing significant forced convection cooling. Although the method of how to prescribe a suitable temperature profile for a specific SMA property is beyond the scope of this paper, several experiments were carried out to demonstrate the feasibility of localized heat treatment by the proposed LHTS. It has been shown that a region of a superelastic wire can be treated to demonstrate shape memory effects and even show signs of precipitate hardening when over-aged.
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摘要 :AbstractDifferential heat treatment of rails by air on the basis of the rolling heat is considered. The research is conducted at AO EVRAZ ZSMK during the reconstruction of rail production. The influence of the chemical compositi...
展开AbstractDifferential heat treatment of rails by air on the basis of the rolling heat is considered. The research is conducted at AO EVRAZ ZSMK during the reconstruction of rail production. The influence of the chemical composition of the steel and the conditions of plastic deformation and heat treatment on the onset of polymorphic transition is studied. Thermokinetic diagrams are plotted for steels of experimental chemical composition. The cooling rate over the cross section of the rail head is investigated as a function of the heat-treatment parameters. The optimal chemical composition and heat-treatment conditions are determined. The heat treatment of rail samples directly after rolling is experimentally studied. Recommendations for the industrial introduction of differential quenching are developed on the basis of the theoretical and laboratory results. Industrial tests show that the rails produced are of high quality and comply with standard requirements. ]]>
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