China
Africa
Explore chapters and articles related to this topic
High Entropy Alloys
Published in T.S. Srivatsan, Manoj Gupta, High Entropy Alloys, 2020
P. Neelima, S.V.S. Narayana Murthy, P. Chakravarthy, T.S. Srivatsan
The presence of impurities is often undesirable, but unavoidable, in an alloy. The detrimental influence of impurities and gases is many times more influential than the beneficial effects achieved through alloying additions on microstructural development and resultant properties, to include both physical and mechanical, of both metals and their alloy counterparts. The presence of impurities above a certain minimum will exert a serious influence on properties and must therefore be kept to an absolute minimum. The specifications for an alloy containing impurities must often be restricted to a minimum. Care should be exercised to restrict the amount of impurities by using raw materials having a low level of impurity content or by selectively removing the impurities during melting. For the HEAs, the impurities can be contributed by each of the five or more alloying elements chosen. For the purpose of laboratory-related research studies, high purity elements (>99.9+ purity) are often chosen and used. However, for industrial melts, elements having a high level of purity are seldom used, primarily because the cost of a high purity element, at the bulk level, is prohibitively high. As five or more elements are often used in near equal atomic percentages, a higher total impurity content will be present in the alloy than in the individual elements. Furthermore, there is a need to study the influence of the presence and role of impurities on mechanical performance of the engineered HEAs, should they result in the formation and presence of undesirable phases in the microstructure.
Hydrometallurgical Waste Production and Utilization
Published in Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde, Waste Production and Utilization in the Metal Extraction Industry, 2017
Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde
The metal extraction processes discussed in section 7.2 are in most cases followed by solution concentration and purification before final solid metal recovery. There are a number of unit operations that can be used to upgrade the concentration of metal ions and to remove the impurities that would ultimately lower the final purity of the product. Processes such as precipitation, crystallization, SX, ion exchange, adsorption and biosorption have been employed in most hydrometallurgical plants. The choice of the purification and concentration process is largely influenced by the type and quantities of impurities in the process solution and the final purity target level in the resultant product or discharge streams. The next sections discuss some of the processes used to purify and concentrate solutions. These processes can also be used to remove toxic metals and unwanted organic components from waste solutions before discharge into the environment.
Enzyme Catalysis
Published in Harvey W. Blanch, Douglas S. Clark, Biochemical Engineering, 1997
Harvey W. Blanch, Douglas S. Clark
The first task in formulating a purification strategy is to define or acknowledge the required purity of the product. The allowable ranges of impurity concentrations, and the specific impurities which may be tolerated, will be dictated by the end-use of the product. For example, very stringent purity requirements apply to recombinant DNA-derived proteins produced for therapeutic applications. As of 1990, U.S. standards required that the final product, which is usually administered intravenously or subcutaneously, must contain less than 0.1% protein impurities and less than 100 pg nucleic acid per dose. Figure 6.1 illustrates the required purity for different types of products. On the other hand, enzymes can be used as industrial catalysts in relatively crude form. In addition to defining the end-use criteria, it is also important to characterize the starting material (e.g., what contaminants are known to be present?) in as much detail as possible.
Electrically-controlled generation and switching of arbitrary vector vortex beams on multiple hybrid-order Poincaré spheres based on liquid crystal devices
Published in Liquid Crystals, 2023
Xinyi Zhou, Yide Yuan, Zongjie Zhu, Shiyuan Zhang, Xiangsheng Xie, Lishuang Yao, Fan Fan, Shuangchun Wen, Yaqin Zhou
We can see from Figures 4 and 5 that we not only achieve the random generation and switching of arbitrary vector vortex beams on three HyOPS with different topological charges via electrical controlling, but also realise good consistency between the experimental results and theoretical results, we measured the resulting beam conversion efficiency of 75.6% when q1 and q2 and LCVR simultaneously loading half wave voltage. Experimental defects originate mainly from the imperfect preparation of LC devices as well as the insufficient collimation of the light path. To enhance the quality of our fabricated LC sample, experimental operations need to be conducted in a dust-free environment. Care should be taken to ensure proper collimation of the optical path during the orientation process while avoiding the introduction of mechanical vibrations. Additionally, it is advisable to maintain sufficient cleanliness in every step of operation during fabrication process to prevent impurity contamination.
Recycling of spent lithium-iron phosphate batteries: toward closing the loop
Published in Materials and Manufacturing Processes, 2023
Srishti Kumawat, Dalip Singh, Ajay Saini
The performance of active materials is strongly influenced by the synthesis process. The solid-state reaction is the traditional approach for LFP synthesis, which involves two heating stages and produces the desired solid phases while keeping the air inert to avoid iron oxidation.[70] Common carbon-based materials for the solid-state reaction technique include ammonium phosphate (as a source of phosphate), Li2CO3, Fe (II)-oxalate or Fe (II)-acetate (as iron, lithium, and carbon sources). Apart from solid-state methods, solution chemistry methods like sol-gel, hydrothermal, spray pyrolysis, and co-precipitation have recently drawn a lot of attention because of atomic-scale mixing of the raw materials, homogeneous aggregation of fine particles with high purity, adding a carbon source to the synthesis process, and customizing the size and morphology of nanostructures. Additionally, the solution can eliminate some impurities, reducing manufacturing costs and the purity requirement for the precursors.[71] The effect of the precursor solution on electrochemical performance is shown in Table 3.
A review of processing techniques for Fe-Ni soft magnetic materials
Published in Materials and Manufacturing Processes, 2019
Miura et al. studied the effect of mixed elemental and pre-alloyed powders on magnetic properties. The sintered density of 94% was achieved in pre-alloyed Fe-Ni powder compacts while the mixed elemental powder showed higher densification up to 96%. The permeability values of 19500 for mixed and 27,000 for pre-alloyed powders were measured, respectively. The impurity atoms hinder the domain wall motion that results in poor magnetic performance. Thus, impurities should be kept to the lowest level by using high purity materials and optimizing the processing parameters.[70] It was observed that interstitial impurities diminished with increasing dwell time. The densification was enhanced with increasing sintering temperature. The Fe-79Ni-4Mo Perm alloys produced by injection molding show excellent magnetic performance and commonly used in the electrical industry, automotive, electronics, and industrial engineering. Ma et al. reported the temperature effect on processing of Fe-79Ni-4Mo alloy. The injected parts were sintered in the range of 1240°C to 1360°C for 2 h. The sintered density increased from 92.1% to 94.4% with increasing temperature and corresponding magnetic induction from 0.78 to 0.80 Tesla.[71,72] The average grain size measured about 20 microns at 1240°C. The population of porosity decreased, and grain size increased gradually with rise in temperature. The permeability value enhanced to 64,000 while coercivity decreased down to 2.2 A/m. The coercivity and maximum permeability values are degraded by porosity and small grain size.[71,73] The microscopy revealed the large grain size and highly refined pores which results in significantly high magnetic performance. The grain size was increased to 246 µm and grain boundaries became straight after increasing sintering time. Initially, the tensile strength increases with densification but after that, it reduces due to excessive grain growth at high temperatures.[67,71] The influence of different sintering temperatures on microstructures is shown in Fig. 2. The effect of temperature on densification and soft magnetic properties is described in Table 1.