Adhesion Effects of Intermediate Layers on the Densification of Ceramic Powders

In the ceramic technology the first step to produce sintered bodies is the manufacturing of powders which then are densified. The adhesion mechanisms between the single particles and the agglomerates produced from them determine the densification process. Starting from theoretical considerations adhesion mechanisms, such as solid bridge formation, adhesive bonding and glide-promoting effects, are discussed in principle. Subsequently, the effects of surface-active substances on the densification behaviour of clay-ceramics and oxide-ceramic bodies are discussed. Further, the evaluation of the action of additives to the powder mixtures on the microstructure of the compacts, such as porsity and texture, leads to a compaction equation which describes the transition from the powder pile to a densified green body.     

Composites based on eucalyptus tar pitch/castor oil polyurethane and short sisal fibers

Polymeric materials are being developed with renewable resources to promote industrial progress with environmentally friendly technologies. For this reason, polyurethane samples were prepared with 4,4′‐diphenylmethane diisocyanate (NCO/OH = 1), eucalyptus tar pitch (biopitch), castor oil as a polyol, and dibutyltin dilaurate as a catalyst. These materials were reinforced with different contents of short sisal fibers (0, 2.5, 5.0, 7.5, and 10.0%) and were prepared by resin‐transfer molding. The composites were characterized by IR absorption spectroscopy, thermal analysis (thermogravimetry and differential scanning calorimetry), impact resistance, scanning electron microscopy, and water absorption resistance. These materials showed hydrophobic characteristics, despite the addition of sisal fibers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3797–3802, 2003     

浅谈C语言中循环结构的教学--回答好循环结构的“三个问题”

循环结构是C语言程序设计中的重难点,其掌握情况对于后续章节的学习效果尤为关键。本文以什么是循环、何时需要使用循环以及如何使用循环三个问题为主线,通过精心选择的教学案例和灵活有效的教学方法来进行解答,以激发学生兴趣,培养编程思想。     

Structure and properties of polyimide‐bonded magnets processed from prepolymers based on diacetyl derivatives of aromatic diamines and dianhydrides

We report a novel method of polyimide (PI) synthesis from prepolymers based on dianhydrides and diacetyl derivatives of aromatic diamines that facilitate the preparation of a melt processable mixture at 300 ± 10°C of the prepolymer and magnetic Nd‐Fe‐B alloy to provide PI‐bonded magnets with enhanced properties. It is shown that chemical structure of the prepolymers strongly influences viscosity behavior via crystallization of the oligoimide in the melt, leading to formation of PI with rigid‐rod like structure. This structural ordering of the prepolymers based on diacetyl derivative of diamine used in this study, if not controlled, leads to exponential increase of melt viscosity with time, making it practically impossible to prepare melt processable mixture of the magnetic particles and the PI prepolymers at elevated temperatures. The results obtained demonstrate that appropriate dianhydrides and diacetyl derivatives of diamines that do not lead to crystallization of oligoimides in prepolymer mixture can be used under controlled processing conditions to prepare melt‐processable PI‐bonded magnets containing rigid‐rod like PI structure that significantly increases thermal stability of the magnets. The temperature dependencies of the magnetic properties of the PI‐bonded magnets under conditions that they are likely to encounter during their service life were found to be remarkably similar to that of commercial thermoplastic magnets such as injection‐molded nylon magnets. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 478–485, 2006     

Structure of resorcinol,phenol, and furan resins by MALDI‐TOF mass spectrometry and 13C NMR

The structure of traditional, linear phenol–resorcinol–formaldehyde (PRF) resins, urea‐branched PRF resins, and phenol–resorcinol–furfural (PRFuran) resins has been investigated in depth by both matrix‐assisted laser desorption/ionization time of flight (MALDI‐TOF) mass spectroscopy and ¹³C NMR. The structure of a variety of oligomers has been obtained, and the structures present in each of the three types of resins related to the very different percentages of resorcinol needed for their equal performance as adhesives. The oligomers type and species distribution appeared very different for each case. PRF resins performance is improved by maximizing either the proportion of resorcinol‐containing oligomers or methylol‐groups containing oligomers, even without any resorcinol, or both. It is equally obtained by the minimization of the relative proportion of the low reactivity Phenol (CH₂ Phenol) species in which resorcinol is not present, this being the most important parameter. This can be obtained by more effective use of the resorcinol by just modifying the resin manufacturing procedure. This parameter instead does not appear to be determinant in PRFuran resins. In these, it is the higher molecular weight of furfural in relation to formaldehyde that engenders for the same manufacturing procedure a correspondingly lower proportion of resorcinol in the resin. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2665–2674, 2004     

Pore structure of bulk tungsten carbide powder catalysts

Bulk tungsten carbide catalysts are prepared by direct carburization/reduction of tungsten trioxide in methane-hydrogen mixtures. The catalytic properties of such catalysts have been studied by several authors. The porous structure of these catalysts is studied by adsorption of N₂, Kr, CF₄ and neohexane. Adsorption isotherms and hysteresis loops for the catalysts suggest the presence of a microporous structure made of parallel plates distant approximately by 20 Å. These results are compared to those obtained using such catalysts for hydrogen oxidation and where condensation in the porous structure was observed.     

大型常压锥顶贮罐的设计

以工程实例为依据，论述国内以往较少采用的大型梁柱式支承锥顶贮罐的结构，介绍了国内外相关设计标准，给出了贮罐的典型结构－斜椽，横梁和立柱的计算公式，并用Excel电子表格编制了计算书。     

Damage and deterioration mechanism and curing technique of concrete structure in main coal cleaning plants

Concrete structures in main coal cleaning plants have been rebuilt and reinforced in the coal mines of the Shanghai Da-tun Energy Sources Co. Ltd., the first colliery of the Pingdingshan Coal Co. Ltd. and the Sanhejian mine of the Xuzhou Mining Group Co. Ltd. In these projects, the operating environment and reliability of concrete structures in the main plants of the three companies were investigated and the safety of the structures inspected. Qualitative and quantitative analyses were made on the spe-cial natural, technological and mechanical environments around the structures. On the basis of these analyses, we discuss the long-term, combined actions of the harsh natural (corrosive gases, liquids and solids) and mechanical environments on concrete structures and further investigated the damage and deteriorating mechanisms and curing techniques of concrete structures in the main coal cleaning plants. Our study can provide a theoretical basis for ensuring the reliability of concrete structures in main coal cleaning plants.     

大体积混凝土温升与强度增长的试验研究

针对大体积混凝土结构构件实体强度与普通标准养护试块强度发展规律间的差别等问题,通过研究实际工程尺寸试件温度场的分布和实验室混凝土变温养护试验,以不同养护制度下的试块强度得出了大体积混凝土结构实体强度的发展规律,为工程施工提供了依据,成功地解决了工期与质量的矛盾,取得了较好的技术经济效果.     

合体女裤提臀结构设计的探讨

首先用问卷调查的方式得到人们对合体裤提臀的要求,主要表现在臀突感、臀下以及臀后与人体的贴合度上;其后对6款样裤进行了拓版,得到影响提臀效果的结构设计参数.在此基础上用实验法得出结果:在合体裤制版参数常用取值范围内,总裆宽越小,后上裆倾斜角越大,前后裆宽比越小,裤子的提臀效果越好;通过美观性与舒适性的评价,得出兼顾两者的参数配置.