Friction and wear characteristics of fiber- and whisker-reinforced PTFE composites under oil lubricated conditions

Four kinds of polytetrafluoroethylene (PTFE)-based composites, such as pure PTFE, PTFE + 30(vol.)% carbon fiber, PTFE + 30(vol.)% glass fiber, and PTFE + 30(vol.)% K₂Ti₆O₁₃ whisker composite, were prepared. The friction and wear properties of these fiber- and whisker-reinforced PTFE composites sliding against GCr15-bearing steel (SAE52100 steel) under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester (Timken wear tester). Then the worn surfaces of these PTFE composites and the transfer films formed on the surface of GCr15-bearing steel were investigated by using a Scanning Electron Microscope (SEM) and an Optical Microscope, respectively. Experimental results show that the friction and wear properties of the PTFE composites reinforced with carbon fiber, glass fiber, and a K₂Ti₆O₁₃ whisker can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of these PTFE composites can be decreased by one order of magnitude compared to those under dry friction conditions. Meanwhile, the wear of the fiber- and whisker-reinforced PTFE composites in liquid paraffin lubrication increases with the increase of load, but the friction coefficients of these PTFE composites first decrease with the increase of load, and then increase with the increase of load. The variations of friction coefficients with load for these PTFE composites in liquid paraffin lubrication can be described properly by the Stribeck's curve as given in this article. However, when the load increases to the load limits of the PTFE composites, their friction and wear increase sharply. SEM and optical microscope investigations show that the interactions between liquid paraffin and the PTFE composites, especially the absorption of liquid paraffin into the surface layers of the PTFE composites, create some obvious cracks on the worn surfaces of the PTFE composites. The creation and the development of the cracks reduce the load-carrying capacity of the PTFE composites, and therefore lead to the increase of the friction and wear of the PTFE composites under higher loads. Meanwhile, the transfer of the fiber- and whisker-reinforced PTFE composites onto the counterfaces can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1393–1402, 1998     

谷物中6种除草剂的气相色谱检测方法

介绍一种运用毛细管气相色谱法检测谷物中酰胺类除草剂多残留快速测定方法。采用石油醚作为溶剂提取样品中农药，中性氧化铝的层析柱净化，石油醚／乙酸乙酯（9：1，v／v）洗脱。气相色谱（附ECD检测嚣）检测，用保留时间和外标法定性、定量。对大米样品进行添加回收率实验，分别添加0．50mg／kg、0．20mg／kg、0，10mg／kg、0．05mg／kg、0．02mg／kg。添加回收率在86．5％～109．5％之间，变异系数为3．5％8．1％。     

基于虚拟仪器技术的超临速自磨机振动测试与分析

介绍了开发超临速自磨机的现实意义及超临速球磨机的磨矿特点,并利用虚拟仪器振动测试技术对超临速自磨机在工作状态下进行了振动测量,得出其振动烈度以及振动规律.并测出超临速自磨机的关键部件-导向机构的固有频率.     

From uncertainty to approximate reasoning: part 2: reasoning with algorithmic rules

This is the second part of a three-part paper. In the first part. Civ. Engng Syst. 1 986, 3(3), 143-1 54 different models of uncertainties from the simplest interval representation, to fuzzy sets and random numbers are described. This paper discusses uncertain inference or reasoning based on evidence-hypothesis rules. The rules are expressed in algorithmic, functional form. The process of uncertainty propagation, i.e. from uncertainties in the evidence to the uncertainty in the hypothesis, is discussed with reference to several kinds of uncertainty representations described in part 1. When a hypothesis is supported by several rules with differing uncertainties, ways to aggregate these uncertainties are described. As in part 1, the discussion emphasizes the commonality and differences among the various uncertainty representations and. in particular, theircomputational ramifications on inference within the narrow context of the rule-framework considered.     

Synthesis of π-conjugated polymers possessing 1,3-butadiene-1,4-diyl units by reactions of regioregular organometallic polymer having titanacyclopentadiene moieties in the main chain

The synthesis and properties of π-conjugated polymers possessing phenylene-1,4-diyl and 1,3-butadiene-1,4-diyl alternating units in the main chain by reactions of a regioregular organometallic polymer having titanacyclopentadiene-2,5-diyl unit are described. The polymerization of 1,4-diethynyl-2,5-dioctyloxybenzene with a low-valent titanium complex, generated in situ from titanium(IV) isopropoxide and isopropyl magnesium chloride, was carried out at ?78 °C to ?50 °C for 12 h to give the regioregular organotitanium polymer. The diene-containing π-conjugated polymers were obtained by the reactions of the organotitanium polymer with electrophiles such as hydrochloric acid and iodine. For example, the reaction with hydrochloric acid gave a diene-containing polymer in a 61% yield whose M_n and M_w/M_n were estimated as 5700 and 1.61, respectively (by GPC). The π-conjugated character of the resulting polymer could be supported by its UV–vis spectrum. That is, the absorption maximum (λ_max) of the polymer was observable at 470 nm, which was bathochromically shifted by 115 nm compared to that of a model compound (1,4-bis(2-methoxyphenyl)-1,3-butadiene, λ_max = 355 nm).     

辣根过氧化物酶在巯基丁二酸铜（II）自组装单分子层修饰电极表面的固定及对H2O2传感研究

利用气相沉积技术制备TiO2凝胶膜,将辣根过氧化酶固定在巯基丁二酸铜(II)(CuL-SH)自组装单分子层修饰金电极表面,制得测定H2O2 的电流型生物传感器.金电极表面的CuL-SH同时作为电子媒介体.研究了各种因素如pH、工作电位等对传感器响应电流的影响.传感器对H2O2的还原显示出快速电催化响应(＜10 s),计时电流法测定H2O2的线性范围为2.2 μmol/L -0.6 mmol/L(R = 0.999),检出限为1.0×10-6mol/L.测得酶催化动力学参数米氏常数KMapp＝0.56 mmol/L.传感器的稳定性好,60 d 其响应值仍保持90 %.对其灵敏度和选择性进行了研究,并应用于实际样品测定.     

甲烷浓度对CVD金刚石薄膜晶体学生长过程的影响

采用X射线衍射技术、电子背散射衍射技术和扫描电镜分别观察了不同甲烷浓度条件下沉积的CVD自支撑金刚石薄膜的宏观织构、微区晶界分布和表面形貌.研究了金刚石晶体{100}面和{111}面生长的晶体学过程.研究表明,{100}面通过吸附活性基团CH^2- 2,而{111}面通过交替吸附活性基团CH^-3和CH^-3后脱氢堆积碳原子.低甲烷浓度时,{111}面表面能低于{100}面,使{111}面生长略快于{100}面.甲烷浓度升高,动力学作用增强使{100}面生长明显快于{111}面,使金刚石薄膜产生{100}纤维织构;同时显露的{100}面平行于薄膜表面,竞争生长使位于晶体侧面的{111}面由于相互覆盖而减小,形成了不同于单晶体自由生长的薄膜表面形貌组织.     

安全电子支付系统研究

给出了电子支付系统的安全需求,并深入探讨了各类安全电子支付系统的基本模型、主要特点和相关实例。同时,基于对安全电子支付系统发展现状和未决问题的分析和评述,指出了今后该领域的研究方向。     

无线传感器网络安全研究

随着传感器网络研究的深入和不断走向实用,安全问题引起了人们的极大关注。由于传感器节点的计算速度、电源能量、通信能力和存储空间非常有限,且一般配置在恶劣环境、无人区域或敌方阵地中,这给传感器网络安全方案的设计提出了诸多挑战。本文分析了无线传感器网络(WSN)的安全需求,并从密钥管理、身份认证和攻防技术三个方面归纳了国内外传感器网络安全问题的研究进展情况。最后,基于对传感器网络安全未决问题的分析和评述,指出了今后该领域的研究方向。     

相组成对PMN-PT陶瓷压电性能的影响

研究了ＰＭＮ－ＰＴ陶瓷在准同型相界（ＭＰＢ）区域、不同烧结温度下,化学组成、相组成对陶瓷压电性能的影响．发现对于同一化学组成的陶瓷,随着烧结温度的上升,发生了菱方相→四方相的相转变,同时随着菱方相、四方相相比例的接近,陶瓷的压电性能有显著的提高．而在不同烧结温度下,最佳压电性能所对应的化学组成有微小的变化．据此认为,陶瓷的压电性能不仅与化学组成有关,而且与相组成也密切相关,随着烧结温度的变化,发生了准同型相界的微小移动