Formation of a chromium-carbide conversion coating on silicon carbide

The formation of a chromium-carbide conversion coating on SiC was achieved using the pack-cementation technique. The conversion coating is intended to improve the corrosion resistance of SiC and its derivatives, such as SiC-base continuous fibers and composites, by forming a protective Cr₂O₃ scale upon exposure to high-temperature corrosive environments. Different pack chemistry and processing parameters were evaluated in the laboratory. Results indicated that the coating morphologies and compositions achieved were significantly affected by variation of these processing factors. In this paper, the conversion coating obtained from one of the systems investigated is reported. The coating consists of a multilayered structure with each of the sublayers containing a high-Cr concentration. In addition, the coating surface is relatively dense and pore free compared to the underlying SiC substrate material. A dense and pore-free morphology is highly desirable for coating applications, especially on porous substrates. The multilayered coating structure consists of the following sublayers: Cr₂₃C₆/Cr₇C₃/Cr₇C₃+Cr₃Si/Cr₅Si₃C_x/SiC substrate.     

Corrosion resistance of the electro-galvanized steel treated in a titanium conversion solution

The conversion coating can be obtained by using a solution containing titanium tetrachloride, fluorosilicate acid and nitric acid. The results of X-ray photoelectron spectroscopy (XPS) showed that the titanium conversion coating consisted of ZnO, TiO₂ and Zn₄Si₂O₇(OH)₂. The formation process of the titanium conversion coating was studied. Effects of the immersion time, pH value and solution temperature on the corrosion resistance and the chemical composition of the titanium conversion coating were investigated by the salt spray test (SST) and XPS, respectively. The results of XPS and SST showed that the titanium conversion coating displayed better corrosion resistance with higher contents of Si and Ti. Results of corrosion tests (the salt spray and electrochemical test) indicate that the corrosion resistance of the conversion coating by titanium solution is better than that of the conversion coating using the traditional chromate solution.     

变频开关电源Fuzzy-PID控制器的设计

针对感应式变频开关电源在对金属材料进行热处理过程中，负载的等效参数和谐振频率发生变化，而变频电源的输出频率不能及时调整和跟踪的问题，结合PID和Fuzzy控制技术的优点，设计Fuzzy-PID控制器对变频电源进行控制，在大偏差时用Fuzzy控制，在小偏差时用PID调节。Fuzzy-PID控制器以单片机8098为核心，采用SPWM专用芯片SA4828，实现变频开关电源的电压、电流双闭环控制，使变频电源不仅具有较快的动态响应、更小的超调，并且具有较高的稳态精度和频率跟踪控制特性。     

基于有限差分网格的发动机缸体铸件热应力模拟

对发动机气缸体铸件从浇注完到开箱落砂后的铸造过程应力场进行计算机数值模拟.为了实现形状复杂铸件的热应力分析,应用了有限差分网格向有限元网格的转换方法,得到缸体的有限元模型,并将该模型与经过大量简化后直接剖分得到的有限元模型进行了比较.在此有限元模型的基础上,采用FDM/FEM集成铸件热应力分析系统实现了对发动机缸体铸件热应力分析,模拟结果和实际生产情况相吻合.     

Synthesis and characterization of aromatic polyisoimides derived from PMDA and para-diamines. An approach to in situ generated rigid-rod molecular composites

A new concept for the processing and fabrication of rigid-rod molecular composites aiming at the elimination or minimization of phase separation is proposed. This approach calls for a coil-like aromatic polyisoimide which is soluble and compatible with an amorphous matrix polymer or thermosettable oligomer and can undergo facile transformation to the corresponding rigid-rod polyimide in solid composite state, thus imparting the inherently high strength/high modulus properties to the final form. To this end, various synthetic routes were explored to obtain para-diamines which could afford high molecular weight and aprotic-solvent-soluble polyisoimides upon polymerization with pyromellitic dianhydride (PMDA). Four such polyisoimides were prepared, with their inherent viscosities ranging from 0.25 to 1.89 dl g⁻¹ in dimethylacetamide at 30°C. Facile thermally induced isoimide-imide conversion was demonstrated by solid-state (film) Fourier transform infrared spectroscopy. A preliminary evaluation of the compatibility of the polyisoimide/matrix resin was made. In one instance, a film prepared from the polyisoimide derived from PMDA and 3,3′,5,5′-tetramethylbenzidine (TMB) showed no visually detectable phase separation.     

生物质转化的共性问题研究——生物质科学与工程学的建立与发展

生物质资源的高值转化是研究热点。由于现有的生物质利用技术存在的技术单一,缺乏系统性理论指导等问题,导致原料利用率低,经济效益差,难以实现工业化生产,迫切需要建立新的理论体系。通过深入分析生物质转化过程中的共性问题,在综合多学科知识的基础上,提出了生物质科学与工程学这一理念,从生物质原料工程学,生物质转化过程工程学和生物质产品工程学三方面对生物质利用技术进行了全面、系统的研究,为生物质类可再生资源的高值化利用提供了新的研究思路。     

青岗钾肥厂试车小结

为满足农业生产上对硫酸钾的需求，化工部上海化工研究院复肥所着重开发了硫铵转化法的生产工艺，并在推广过程中，针对操作工艺和设备上所存在的问题，继续探索，取得了新的结果。该技术已用于青岗钾肥厂万吨级硫酸钾生产装置。本文着重介绍了该装置在试车过程中所发生的问题及处理方法。     

黄金峡水利枢纽工程大型水泵机组选型设计及运行调节研究

引汉济渭工程黄金峡水利枢纽是陕西省境内一项重要的大型跨流域调水工程,泵站装机容量和设计流量均为目前国内甚至亚洲在建和已建泵站之最,且调水过程复杂、调水流量分布范围宽广。在分析黄金峡泵站调度原则及运行方式的基础上,综合比较目前国内外大型泵站机组设计制造水平、枢纽建筑物及机电设备投资等因素,详细论证了大型单级单吸离心式水泵机组台数和性能参数的确定方法及其影响因素,并给出了黄金峡泵站机组选型设计的最优方案,同时论证了采用变频调节的必要性及其效果。研究结果可为大型调水泵站机组的选型设计提供参考。     

林业生物质热化学转化利用研究现状

生物质是唯一可转化成常规的固态、液态和气态燃料以及其它化工原料或产品的可再生碳资源.随着化石能源的枯竭和人类对全球性环境问题的关注,生物质资源以其可再生、资源丰富、分布广泛、CO₂零排放等优点日益成为国内外众多学者研究的热点.热化学高效转化利用技术的研究是生物质能源开发利用的最主要途径.作者对近年来国内外生物质热化学转化技术的最近研究进展进行综述,从我国实际情况出发,对生物质能源热化学转化的发展趋势进行预测,提出我国生物质能源研究开发利用的发展前景和建议.     

基于CDT2000 I/O口的A/D转换系统设计

为实现传感器数据快速、高精度地转换,提出了一种采用AD7891芯片的A/D转换系统的设计方法。数据读、写和并行工作时序通过CDT2000 I/O口控制,CDT2000 I/O口的电位变化由PC/104通过总线操作。在AD7891与CDT2000之间添加JK触发器实现对A/D转换完成的识别。试验结果表明,这种方法能够满足数据采集系统的设计要求,并且在硬件上较容易实现。