Influence of deposition voltage on phase, microstructure and antioxidation property of cristobalite aluminum phosphate coatings

Cristobalite aluminum phosphate (C-AlPO4) coatings were prepared by a hydrothermal electrophoretic deposition process on SiC-coated C/C composites. Phase compositions and microstructures of the as-prepared coatings were characterized by XRD and SEM analyses. The influence of deposition voltage on the phase, microstructure and antioxidation property of the cristobalite aluminum phosphate coatings was investigated. Results show that the as-prepared coatings are composed of cristobalite aluminum phosphate crystallites. The thickness and density of cristobalite aluminum phosphate coatings are improved with the increase of deposition voltage. The deposition amount and bonding strength of the cristobalite aluminum phosphate coatings also increase with the increase of deposition voltage. The deposition mass per unit area of the coatings and the square root of the deposition time at different hydrothermal voltages satisfy linear relationship. The antioxidation property of the coated C/C composites is improved with the increase of deposition voltage. Compared with SiC coatings prepared by pack cementation, the multilayer coatings prepared by pack cementation with a later hydrothermal electrophoretic deposition process exhibit better antioxidation property. The as-prepared multi-coatings can effectively protect C/C composites from oxidation in air at 1 773 K for 37 h with a mass loss rate of 0.53%.     

沉积温度对C-AlPO_4涂层显微结构的影响

采用水热电泳沉积法在C/C-SiC基体表面制备了方石英型磷酸铝(C-AlPO4)外涂层,借助XRD和SEM对涂层的晶相组成和显微结构进行了表征。研究了沉积温度对C-AlPO4涂层显微结构的影响,讨论了涂层的沉积动力学,进行了抗氧化性能测试。结果表明:353~393 K范围内,沉积温度对涂层的显微结构有较大影响;涂层的沉积量随着温度的升高而增加;涂层的沉积规律受C-AlPO4带电颗粒的向阴极表面扩散迁移所控制;涂层的沉积活化能为21.88kJ/mol;在1 773 K空气气氛氧化37 h后,涂层试样失重仅为0.53%。     

水热温度对碳/碳复合材料表面HAp/壳聚糖生物复合涂层的影响

以声化学法合成的纳米羟基磷灰石(HAp)为起始原料,以异丙醇作为分散介质,采用水热电泳沉积法在经壳聚糖(CS)溶液改性后的碳/碳复合材料(C/C)表面沉积HAp/CS生物复合涂层.重点研究水热温度对复合涂层晶相、形貌的影响及涂层的沉积动力学机理.采用X射线衍射仪(XRD)、透射电子显微镜(TEM)、傅立叶变换红外光谱分析仪(FTIR)和扫描电子显微镜(SEM)对所制备的涂层进行表征.结果表明:随着水热温度的升高,涂层表面由微晶疏松结合的多孔结构向紧密结合的多孔结构转变,涂层的内聚力增强;涂层的沉积速率随水热温度的升高而增加,涂层的沉积活化能为43.58 kJ/mol.     

碳/碳复合材料防氧化涂层研究新进展

介绍了最近几年我们制备的几种高性能的碳／碳复合材料的氧化保护涂层的结构和高温氧化行为，表明采用包埋和渗透法制备的Si—MoSi2、SiC—MoSi2、Al2O3-莫来石-SiC—Al4SiC4以及Al2O3-莫来石-SiC涂层不仅具有很好的抗热震性能，而且能够将碳／碳复合材料的高温氧化保护温度提高到1973K;此外还介绍了一些涂层的失效机理。     

温度对C/C复合材料表面HAp涂层的影响

采用水热电沉积法在碳／碳（C／C）复合材料表面制备了羟基磷灰石（HAp）涂层，用XRD、SEM等测试手段对涂层进行表征，重点研究了水热温度对HAp涂层晶相和显微结构的影响以及HAp涂层的沉积动力学机理。结果表明：随着温度的升高，HAp衍射峰有所增强，结晶程度变好，涂层更加致密和均匀；涂层的沉积速率随着温度的升高而增加，涂层的沉积活化能为25．89kJ／mol。     

电泳沉积法在IPMC电极制备中的应用研究

化学镀是制备IPMC（Ionic polymer-metal composites,离子聚合物金属复合材料）电极的常用方法. 传统化学镀银方法制备Ag-IPMC（传统化学镀方法）的周期约为32 h,时间较长. 为此,本文采用电泳沉积法将多壁碳纳米管（MCNT）沉积在Nafion基膜表面作为IPMC电极,以缩短电极制备周期. 由于MCNT与Nafion基膜之间的结合力较小,所以首先进行一次化学镀得到Ag-IPMC（1次化学镀）, 然后再利用电泳沉积法得到MCNT-Ag复合电极IPMC. 同时研究了电泳电压和电泳沉积时间对IPMC电致动性能的影响. 电泳沉积法不仅制备周期为传统化学镀方法的一半,并且制备的IPMC电致动性能也明显优于传统化学镀法. 电泳沉积法是一种非常有应用前景的IPMC电极制备方法.     

不同电源模式对电沉积磷酸钙涂层的影响

采用电化学沉积的方法在钛合金（Ti-6Al-4V）表面制备生物涂层．通过采用恒电流模式和脉冲电源模式考察不同的电源模式对电沉积磷酸钙涂层的影响．试验研究了不同电源模式对涂层的微观形貌及涂层厚度的影响．结果表明：脉冲电流下制备的涂层比恒电流条件下制备的涂层更为均匀致密．在同等的沉积条件下。脉冲电流制备的涂层厚度比恒电流条件制备的涂层厚度增加了16．2μm．XPD分析表明,电源模式的改变并没有影响磷酸钙的生成．     

Microstructure and properties of SiC gradiently coated Cf/C composites prepared by a RCLD method

The SiC gradiently coated carbon fiber/carbon (Cf/C) composites were prepared by a two-step rapid chemical liquid depo-sition (RCLD) method. The microstructure and properties of the composites were investigated using X-ray diffraction, scanning elec-tron microscopy together with energy dispersive X-ray analysis, bending tests, and oxidation tests. The experimental results show that the surface layer of the composites is composed of SiC, pyrocarbon, and carbon fibers. Their inner area consists of pyrocarbon and carbon fibers. The SiC content gradiently decreases with increasing distance from the outer surface to the center of the compos-ites. Furthermore, the thickness of the SiC layer increases with increasing tetraethylorthosilicate content and deposition time. SiC coatings have no significant influence on the bending strength of the composites. However, the oxidation resistance of the compos-ites increases with increasing thickness of the SiC layer.     

水热温度对玻璃纤维增强HAp-CS涂层的影响

为了制备出结合强度较好的生物涂层,采用水热电泳法在碳/碳复合材料表面成功制备了玻璃微纤维增强的羟基磷灰石——壳聚糖(g(f)/HAp-CS)复合涂层,用x-射线衍射仪、透射电子显微镜、扫描电子显微镜、能谱分析仪、红外傅里叶变换分析仪等测试手段对涂层进行了测试和表征,主要研究了水热沉积温度对复合涂层中HAp晶相和涂层显微结构的影响以及HAp涂层的沉积动力学.结果表明:采用玻璃微纤维增强的HAp-CS涂层,致密性和均匀性有了很大提高,显著减少了复合涂层表面的裂纹;随着水热温度的升高,涂层中HAp的衍射峰逐渐增强,表面形貌得到了有效改善,涂层的致密性和均匀性显著提高;涂层的沉积速率随水热温度的升高而加快,其沉积活化能为14.63kJ/mol.     

氧化锌纳米棒阵列涂层的制备及其抗菌性能研究

采用水热法在锌片表面成功制备了三种不同长径比的氧化锌纳米棒阵列涂层,通过X射线粉末衍射,扫描电子显微镜和接触角测量仪对涂层的组成、形貌和润湿性进行了表征,研究了涂层对表面黏附的金黄色葡萄球菌的抗菌性能,并探讨了纳米棒阵列的长径比和表面润湿性对抗菌性能的影响. 结果表明,所制备的氧化锌纳米棒阵列涂层对金黄色葡萄球菌表现出良好的抗菌效果,随着氧化锌纳米棒的长径比增加,涂层表面黏附的死细菌逐渐增多,这可能是由于涂层的亲水性提高而使锌离子在表面扩散速率增加导致的.     

沉积电压对辅助加热PCVD-TiN涂层的影响

研究了不同的沉积电压对辅助加热式PCVD-TiN涂层的影响。实验证明,提高沉积电压可以细化TiN涂层的柱状晶结构,增加TiN涂层的显微硬度和沉积速率。在试验范围内,涂层内残存的氯含量基本不受沉积电压的影响。     

Effect of TiB_2 content on resistance to sodium penetration of TiB_2/C cathode composites for aluminium electrolysis

1　INTRODUCTIONInrecent years ,therehavebeenincreasingeffortstoimprovetheHall Heroult processintheprimaryaluminiumindustry[1 ] .InordertoovercometheshortagesofHall Heroultprocess ,suchashighconsumptionofelectricalpower ,highconsumptionofcarbonanodeandserious pollutionduetocarbonanodemanufactureandconsumptionetc ,anoveltypeofaluminareducedcellsbasedoninertanodeandwettablecathodesystemwasdevelopedtoreplaceconventionalHall Heroultprocess[2 ,3 ] .Titaniumdiboride(TiB2 )appearstobethebestca…     

SiC/Si-W-Mo coating for protection of C/C composites at 1873 K

In order to prevent carbon/carbon composites from oxidation at 1873 K, an efficient oxidation protective SiC/Si-W-Mo coating was prepared by a two-step pack cementation technique. The microstructures and the phase composition of the as-received multi-coating were examined by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. It is seen that the compact multi-coating is composed of α-SiC, Si, and （WxMO1-x）Si2. Oxidation test shows that, after oxidation at 1873 K in air for 102 h and thermal cycling between 1873 K and room temperature for 10 times, the weight loss of the SiC/Si-W-Mo coated C/C composites is only 0.26%. The invalidation of the multi-coating is attributed to the formation of penetrable cracks in the coating. 2008 University of Science and Technology Beijing. All rights reserved.     

Optimizing electrophoretic deposition conditions for enhancement in electrical conductivity of carbon fiber/carbon nanotube/epoxy hybrid composites

The effectiveness of optimizing electrical conductivity of carbon fiber/carbon nanotube (CNT)/epoxy hybrid composites via Taguchi method was demonstrated.CNTs were induced on carbon fabric by electrophoretic deposition (EPD) technique.The essential deposition parameters were identified as 1) the deposition time,2) the deposition voltage,3) the mass fraction of CNTs in suspension,and 4) the distance between the electrodes.An experimental design was then performed to establish the appropriate levels for each factor.An orthogonal array of L9 (34) was designed to conduct the experiments.Electrical conductivity results were collected as the response.The relative influences of design parameters on the response were discussed.Using the model,signal to noise (S/N) ratio and response characteristics for the optimized deposition parameter combination were predicted.The results show clearly that the optimum condition of electrophoretic deposition (EPD) process improves the electrical conductivity of carbon/epoxy hybrid composites.     

Comments on process of duplex coatings on aluminum alloys

Despite the great achievements made in improvement of wear resistance properties of aluminum alloys,their applications in heavy surface load-bearing are limited. Single coating is insufficient to produce the desired combination of surface properties. These problems can be solved through the duplex coatings. The aim of the present study is to overview the research advances on processes of duplex coatings on aluminum alloys combined with micro plasma oxidation process and with other modern processes such as physical vapour deposition and plasma assisted chemical vapour deposition and also to evaluate the performance of micro plasma oxidation coatings in improving the load-bearing, friction and wear resistance properties of aluminum alloys in comparison with other coatings. Wherein, a more detailed presentation of the processes and their performances and disadvantages are given as well.     

Microstructure and growth kinetics of silicide coatings for TiAl alloy

In order to improve the oxidation resistance of Ti Al alloy, silicide coatings were prepared by pack cementation method at 1273, 1323, and 1373 K for 1-3 hours. Scanning electron microscopy(SEM), energy dispersive spectrometry(EDS) and X-ray diffraction(XRD) were employed to investigate the microstructures and phase constitutions of the coatings. The experimental results show that all silicon deposition coatings have multi-layer structure. The microstructure and composition of silicide coatings strongly depend on siliconizing temperatures. In order to investigate the rate controlling step of pack siliconizing on Ti Al alloy, coating growth kinetics was analyzed by measuring the mass gains per unit area of silicided samples as a function of time and temperature. The results showed that the rate controlling step was gas-phase diffusion step and the growth rate constant(k) ranged from 1.53 mg~2/(cm~4·h~2) to 2.3 mg~2/(cm~4·h~2). Activation energy(Q) for the process was calculated as 109 k J/mol, determined by Arrhenius' equation: k = k0 exp[–Q/(RT)].     

增强剂对碳／碳材料沉积速率影响的实验研究

从实验探索了增强剂对碳／碳复合材料沉积速率的影响，提出了提高沉积速率的方法。实验结果表明：采用经过石墨化处理和表面改性处理的碳布作为增强剂，所制得的坯体沉积速率快，样品最终密度高；碳纤维体积含量（为３０％～４５％时）对样品最终密度无明显影响。     

Preparation of bioactive calcium phosphate coating on porous C/C substrate by a novel deposition technique

A novel heat substrate technique, high frequency inductive heat deposition （IHD）, was introduced to coat porous carbon materials, C/C and carbon felt to improve their bioactivity. The morphologies, composition and microstructure of the resulting coatings were examined by scanning electron microscopy （SEM）, energy dispersive spectra （EDS）, X-ray diffractometer （XRD） and Fourier transform infrared spectroscopy （FTIR）. The results show that, the calcium phosphate consisted of non-stoichiometric, CO3-containing and plate- like octacalcium phosphate （Ca8-xH2（PO4）6, OCP） could uniformly cover the entire porous surfaces of carbon materials. Good adhesion of the coating to carbon material substrates was observed.     

Aluminum matrix composites reinforced by molybdenum-coated carbon nanotubes

To extend the application of carbon nanotubes (CNTs) and explore novel aluminum matrix composites,CNTs were coated by molybdenum layers using metal organic chemical vapor deposition,and then Mo-coated CNT (Mo-CNT)/Al composites were prepared by the combination processes of powder mixing and spark plasma sintering.The influences of powder mixing and Mo-CNT content on the mechanical properties and electrical conductivity of the composites were investigated.The results show that magnetic stirring is better tha...     

Improved oxidation resistance of chemical vapor reaction SiC coating modified with silica for carbon/carbon composites

To protect carbon/carbon (C/C) composites from oxidation, a SiC coating modified with SiO2 was prepared by a complex technology. The inner SiC coating with thickness varying from 150 to 300 μm was initially coated by chemical vapor reaction (CVR): a simple and cheap technique to prepare the SiC coating via siliconizing the substrate that was exposed to the mixed vapor (Si and SiO2) at high temperatures (1 923?2 273 K). Then the as-prepared coating was processed by a dipping and drying procedure with tetraet...