Papers by Author: Jun Yan

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Authors: Jian Jiang Wang, Xin Kang Du, Hong Wei Liu, Jun Yan
Abstract: Based on SHS reactive flame spray technology, Al2O3 multiphase ceramics coatings were produced. Chemical copper-plating technology was used to produce the Al-CuO powders of copper cladding, which became individual SHS reactive units respectively. The phenomena and principles of the SHS reactive flame spray of the Al-CuO powders of copper cladding forming Al2O3 multiphase ceramics coatings were investigated. It was found that copper cladding of Al-CuO powders were necessary for the SHS reaction during the spray process. The better the cladding was, the more sufficient the SHS reaction, and the higher the transformation rate was. The Cu and Al2O3 fine molten drops produced by the SHS reaction bumped the substrate and flatted to form layer-shaped Al2O3-based multiphase ceramics coatings. The binding strength between the coating and substrate was as high as 19.8MPa, and the micro-hardness of the coatings was Hv712. The overall properties of the coatings were better than those of the ceramics coatings sprayed by the traditional flame spray.
Authors: Shi Guo Du, Jun Yan, Bin Wang, Hai Ping Cui
Abstract: Nano-TiO2/micro-Cu composite particles were prepared by peptization method using Ti(OBu)4 and SnCl2•2H2O as the raw materials. The effect of the content of HNO3 on the morphology and composition was investigated. The results showed that when the mole ratio of HNO3 and Ti(OBu)4 was 0.5:1, about 100nm TiO2 of amorphous phase grew on the surface of Cu forming strawberry like particles. When the mole ratio of HNO3 and Ti(OBu)4 was 1:1, Cu powders were coated with TiO2 crystals of several nanometers in size, meanwhile particles of several microns in size was absorbed on the Cu surface, which can be easily removed by water cleaning. The possible mechanism was discussed in the end.
Authors: Hai Ping Cui, Jun Yan, Shi Guo Du, Xin Kang Du
Abstract: Al2O3-Al2Cu3 multiphase coatings were prepared on the surface of steel by reactive flame spray. The binding strength, microhardness and abrasion quality of the coatings were measured and analyzed. The influence of the agglomerate size on the properties of the coatings was emphatically studied to choose suitable size range for Al-CuO reactive system. The results showed that coatings prepared by using –150∼+250 meshes agglomerates exhibited good mechanical properties.
Authors: Xiao Bo Lu, J.Z. Liu, Jin Hua Wen, Bao Hong Han, Jun Yan, Hai Ping Cui
Abstract: Based on the SEM observation on cracks in lined ceramics of the composite pipes, the stress fields in lined ceramics were analyzed. The results indicated that there are the compressive field and heat stress field in lined ceramics, resulting in the existence of radial cracks and net cracks; besides being influenced by wall thickness of ceramic layer, the strength of compressive stress field is also dependent on bonding strength between metal and ceramics, and the strength of heat stress field is dependent on temperature gradient in lined ceramics during cooling of the ceramics.
Authors: Bin Wang, Hai Ping Cui, Jun Yan, Shi Guo Du
Abstract: Nano-TiO2/micro-Cu composite particles were prepared by hydrolysis of Ti(OBu)4 in abundant acidic aqueous solution and subsequent reflux in the presence of micron size Cu powders. The preparation process was optimized using response surface design with the degradation of TiO2/Cu particles to Methyl orange as target. The particle morphology and composition were characterized by FE-SEM, XPS and XRD. The photon absorption properties of composite particles was investigated by the UV-VIS DRS experiments, and the results show the photoabsorption property of composite particles is intermediate between TiO2 particles and Cu powders, showing cooperative effect by the combination of oxide semiconductor particles with metal substrate.
Authors: Jun Yan, Hai Ping Cui, Shi Guo Du, Bin Wang
Abstract: Raspberry-like TiO2/Cu composite particles were prepared under mild conditions (75°C and ambient pressure) by hydrolysis of Ti(OBu)4 in acidic aqueous solution and subsequent reflux in the presence of micron size Cu powders. A 3-level and 4-factor design was employed to evaluate the effect of the main parameters on the coating quality. TiO2 particles of approximate 100nm in size were found coating on the surfaces of Cu powders to form raspberry-like structure. Ti and Cu element mainly existed on the composite particle surface as the chemical state of Ti4+ and Cu2+. TG-DTA analysis showed the TiO2 coating increased the thermal stability of Cu particles. The composite particles began oxidizing at 400°C while pure copper particles oxidized at 200°C.
Authors: Shi Guo Du, Jun Yan, Hai Ping Cui, Xian Jie Liu
Abstract: Amorphous titania coatings on copper particles were prepared by using tetrabutyl titanate to improve the anticorrosion property. The coated particles were characterized by SEM, EPMA and XRD. Experimental results showed that the resistance to oxidation of the coated copper particles depended on the stability and content of the sol. The proper pH value for the sol was about 4, and the ratio of tetrabutyl titanate and water was 1 to 2. The transmissivity of the etching solution of coated copper particles in 5% of H2SO4 was more than 80%, showing that the TiO2 coatings on copper particles exhibit an excellent corrosion resistance.
Authors: Shi Guo Du, Jun Yan, Hai Ping Cui, Bin Wang
Abstract: Molybdate conversion coatings were prepared on the anodized surfaces of aluminum alloy substrates, and the corrosion resistance in 3.5% NaCl solution was also investigated. The effects of the main parameters on the quality of the coatings were discussed. The morphology and chemical composition of the conversion coatings was examined by SEM and EDS. SEM observation showed that the coatings were composed of small sheet grains with tiny cracks between them. EDS analysis showed that the main element of the coatings was molybdenum. The results of polarization curve showed that the coatings effectively inhabited the pitting corrosion of aluminum alloy substrates. In the end the possible conversion mechanism was discussed.
Authors: Jun Yan, Jian Zheng Yi, Hai Ping Cui, Xin Kang Du, Jian Jiang Wang
Abstract: This research focus on the technology of copper chemical plating on Al-CuO agglomerated powders with the size of 150-200µm. Orthogonal design is employed to gain the optimized formula, and the quality of the cladding was analyzed by means of SEM and EPMA. The results show that the cladding is uniform and the Al-CuO powders are primarily coated by copper.
Authors: Shi Guo Du, Jun Yan, Tong Lai Zhang, Hai Ping Cui, J.Z. Liu
Abstract: In this paper the surfaces of Al2O3 fine powders with average size of 500nm were modified by heterogeneous azeotropic distillation process. IR spectrums of the powders show that the distillation can effectively dehydrate hydrous Al2O3 powders, and succeed in substituting the hydrate water with butanol molecular. The dispersion of Al2O3 powders in epoxy resin is improved remarkably, which is observed by means of SEM. Experimental results show that abrasion property of the resin filled with modified Al2O3 powders is improved.
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