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排序方式: 共有417条查询结果,搜索用时 31 毫秒
251.
Robust single machine scheduling problem with uncertain job due dates for industrial mass production
The single machine scheduling problem which involves uncertain job due dates is one of the most important issues in the real make-to-order environment. To deal with the uncertainty, this paper establishes a robust optimization model by minimizing the maximum tardiness in the worst case scenario over all jobs. Unlike the traditional stochastic programming model which requires exact distributions, our model only needs the information of due date intervals. The worst case scenario for a given seque... 相似文献
252.
Shan-xia Xiong Jian-lei Kuang Qian-fang Zheng Ting Xiao Wen-xiu Liu Qi Wang Peng Jiang Wen-bin Cao 《矿物冶金与材料学报》2021,28(11):1868-1874
Wood-based panels containing urea-formaldehyde resin result in the long-term release of formaldehyde and threaten human health. In this study, inorganic aluminosilicate coatings prepared by combining metakaolin, silica fume, NaOH, and H2O were applied to the surfaces of wood-based panels to obstruct formaldehyde release. The Si/Al, Na/Al, and H2O/Na2O molar ratios of the coatings were regulated to investigate their effects on the structure and formaldehyde-resistant barrier properties of coatings. Results showed that the cracks in the coatings gradually disappeared and the formaldehyde resistance rates of the barrier increased as the Si/Al molar ratio was increased from 1.6 to 2.2. This value also increased as the Na/Al molar ratio was increased from 0.9 to 1.2 because of the improvement of the degree of polymerization. As the H2O/Na2O molar ratio was increased from 12 to 15, the thickness of the dry film decreased gradually and led to the reduction in the formaldehyde resistance rate. When the Si/Al, Na/Al, and H2O/Na2O molar ratios were 2.2, 1.2, and 12, respectively, the inorganic aluminosilicate coating showed good performance as a formaldehyde-resistant barrier and its formaldehyde resistance rate could reach up to 83.2%. 相似文献
253.
Corrosion resistance evaluation of highly dispersed MgO-MgAl2O4-ZrO2 composite and analysis of its corrosion mechanism: A chromium-free refractory for RH refining kilns
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Yi-nan Shen Yi Xing Peng Jiang Yong Li Wen-dong Xue Guo-xiang Yin Xue-qin Hong 《矿物冶金与材料学报》2019,26(8):1038-1046
The corrosion resistance behavior of a highly dispersed MgO-MgAl2O4-ZrO2 composite refractory material is examined by testing with high-basicity and low-basicity RH (Ruhrstahl-Hereaeus) slags. The composite material exhibits greater resistance to the RH slags than the traditional MgO-Cr2O3 composite, MgO-ZrO2 composite, and MgO-MgAl2O4-ZrO2 composite. On the basis of the microstructural analysis and mechanisms calculations, the corrosion resistance behavior of the MgO-MgAl2O4-ZrO2 composite is attributable to its highly dispersed structure, which helps protect the high activity of ZrO2. When in contact with the slag, ZrO2 reacts with CaO to form the stable phase CaZrO3, which protects MgAl2O4 against corrosion, thereby enhancing the corrosion resistance of the composite. 相似文献
254.
The chlorination-volatilization process has been adopted to make full use of gold-bearing and iron-rich pyrite cinder. However, problems of low recovery rate, pulverization of pellets, and ring formation have been encountered during the industrialization of this process. The effects of various parameters on the volatilization rates of valuable metals and on the compressive strength of roasted pellets were investigated in this paper. The parameters include the CaCl2 dosage, heating temperature, and holding time. The results show that heating temperature is the most important parameter for the recovery of target metals. More CaCl2 was needed for the recovery of zinc than for the recovery of gold, silver, and lead. CaCl2 started to react with sulfides/SO2/SiO2 at temperatures below the melting point of CaCl2 to generate Cl2/HCl. Gaseous CaCl2 was formed at higher temperatures and could react with any of the components. The compressive strength of roasted CaCl2-bearing pellets first decreased slowly with increasing temperature at temperatures lower than 873 K, which could result in the pulverization of pellets during heating. Their compressive strength increased dramatically with increasing temperature at temperatures greater than 1273 K. Certain quantities of CaCl2 and Fe(Ⅱ) could improve the compressive strength of the roasted pellets; however, the addition of excessive CaCl2 decreased the compressive strength of pellets. 相似文献
255.
Low-cost solid FeS lubricant as a possible alternative to MoS<Subscript>2</Subscript> for producing Fe-based friction materials
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Three reaction systems of MoS2-Fe, FeS-Fe, and FeS-Fe-Mo were designed to investigate the use of FeS as an alternative to MoS2 for producing Fe-based friction materials. Samples were prepared by powder metallurgy, and their phase compositions, microstructures, mechanical properties, and friction performance were characterized. The results showed that MoS2 reacts with the matrix to produce iron-sulfides and Mo when sintered at 1050℃. Iron-sulfides produced in the MoS2-Fe system were distributed uniformly and continuously in the matrix, leading to optimal mechanical properties and the lowest coefficient of friction among the systems studied. The lubricity observed was hypothesized to originate from the iron-sulfides produced. The FeS-Fe-Mo system showed a phase composition, porosity, and density similar to those of the MoS2-Fe system, but an uneven distribution of iron-sulfides and Mo in this system resulted in less-optimal mechanical properties. Finally, the FeS-Fe system showed the poorest mechanical properties among the systems studied because of the lack of Mo reinforcement. In friction tests, the formation of a sulfide layer contributed to a decrease in coefficient of friction (COF) in all of the samples. 相似文献
256.
Molybdenum disulfide (MoS2) is one of the most commonly used solid lubricants for Cu-Fe-based friction materials. Nevertheless, MoS2 reacts with metal matrices to produce metal sulfides (e.g., FeS) and Mo during sintering, and the lubricity of the composite may be related to the generation of FeS. Herein, the use of FeS as an alternative to MoS2 for producing Cu-Fe-based friction materials was investigated. According to the reaction principle of thermodynamics, two composites-one with MoS2 (Fe-Cu-MoS2 sample) and the other with FeS (FeS-Cu2S-Cu-Fe-Mo sample), were prepared and their friction behaviors and mechanical properties were compared. The results showed that MoS2 reacted with the Cu-Fe matrix to produce FeS, metallic ternary sulfides, and Mo when sintered at 1050℃. The MoS2-Cu-Fe and FeS-Cu2S-Cu-Fe-Mo samples thereby exhibited similar characteristics with respect to phase composition, density, hardness, and tribological behaviors. Micrographs of the worn surfaces revealed that the stable friction regime for both composites stemmed from the iron sulfides friction layers rather than from the molybdenum sulfides layers. 相似文献
257.
Shang-hao Tong Yong Li Ming-wei Yan Peng Jiang Jia-jia Ma Dan-dan Yue 《矿物冶金与材料学报》2017,24(9):1061-1066
The Al-Al2O3-MgO composites with added aluminum contents of approximately 0wt%, 5wt%, and 10wt%, named as M1, M2, and M3, respectively, were prepared at 1700℃ for 5 h under a flowing N2 atmosphere using the reaction sintering method. After sintering, the Al-Al2O3-MgO composites were characterized and analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that specimen M1 was composed of MgO and MgAl2O4. Compared with specimen M1, specimens M2 and M3 possessed MgAlON, and its production increased with increasing aluminum addition. Under an N2 atmosphere, MgO, Al2O3, and Al in the matrix of specimens M2 and M3 reacted to form MgAlON and AlN-polytypoids, which combined the particles and the matrix together and imparted the Al-Al2O3-MgO composites with a dense structure. The mechanism of MgAlON synthesis is described as follows. Under an N2 atmosphere, the partial pressure of oxygen is quite low; thus, when the Al-Al2O3-MgO composites were soaked at 580℃ for an extended period, aluminum metal was transformed into AlN. With increasing temperature, Al2O3 diffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with Al2O3 to form MgAl2O4. When the temperature was greater than (1640 ±10)℃, AlN diffused into Al2O3 and formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and MgAl2O4 at high temperatures because of their similar spinel structures. 相似文献
258.
To enhance the microwave absorption performance of silicon carbide nanowires (SiCNWs), SiO2 nanoshells with a thickness of approximately 2 nm and Fe3O4 nanoparticles were grown on the surface of SiCNWs to form SiC@SiO2@Fe3O4 hybrids. The microwave absorption performance of the SiC@SiO2@Fe3O4 hybrids with different thicknesses was investigated in the frequency range from 2 to 18 GHz using a free-space antenna-based system. The results indicate that SiC@SiO2@Fe3O4 hybrids exhibit improved microwave absorption. In particular, in the case of an SiC@SiO2 to iron(Ⅲ) acetylacetonate mass ratio of 1:3, the microwave absorption with an absorber of 2-mm thickness exhibited a minimum reflection loss of -39.58 dB at 12.24 GHz. With respect to the enhanced microwave absorption mechanism, the Fe3O4 nanoparticles coated on SiC@SiO2 nanowires are proposed to balance the permeability and permittivity of the materials, contributing to the microwave attenuation. 相似文献
259.
To explore the reaction behavior of trace oxygen during the flash combustion process of falling FeSi75 powder in a nitrogen flow, a flash-combustion-synthesized Fe-Si3N4 sample was heat-treated to remove SiO2. The samples before and after the treatment were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, and the formation mechanism of SiO2 was investigated. The results show that SiO2 in the Fe-Si3N4 is mainly located on the surface or around the Si3N4 particles in dense areas, existing in both crystalline and amorphous states; when the FeSi75 particles, which are less than 0.074 mm in size, fell in up-flowing hot N2 stream, trace oxygen in the N2 stream did not significantly hinder the nitridation of FeSi75 particles as it was consumed by the surface oxidation of the generated Si3N4 particles to form SiO2. At the reaction zone, the oxidation of Si3N4 particles decreased the oxygen partial pressure in the N2 stream and greatly reduced the opportunity for FeSi75 particles to be oxidized into SiO2; by virtue of the SiO2 film developed on the surface, the Si3N4 particles adhered to each other and formed dense areas in the material. 相似文献
260.
Peng L Xiao-Tong Wang Sheng-Zhi Yang Yan Li Xiu-Li Hou Qing-Feng Guan 《科学通报(英文版)》2014,59(34):4758-4762
N-type Si (111) wafers have been processed by high-current pulsed electron beam (HCPEB) treatment with an increasing number of irradiation (1, 10 and 20 pulses). The results of this work show that a highly porous nanostructure was formed after irradiation. Moreover, the high-density Si nanocrystals (Si-ncs) about 3 nm were distributed on the surface of Si wafers and exhibited 3.02 eV Photoluminescence (PL) emission in blue band. The PL intensity increases with the increase in the Si-ncs' density in accordance with the quantum confinement model, which can be ascribed to the different pulse time of HCPEB treatment. The possible formation mechanisms of micropores and Si-ncs are discussed. 相似文献