直流电弧炉用镁炭砖的导电性能

研究了温度和石墨含量对MgO-C材料导电性的影响，发现石墨含量以10％～12％较为理想。随着热处理温度的升高，MgO－C材料的电阻率降低。经过热处理后，MgO－C材料的电阻率几乎不随温度而变化。     

树脂—石墨系材料性能的研究

用不同含量的酚醛树脂及恒定树脂含量不同比值的环氧/酚醛树脂,分别制成酚醛树脂—石墨组份及环氧酚醛树脂—石墨组份材料。测定材料的电阻率、硬度、体积密度,磨损及摩擦系数。探求上述不同材料与性能的关系及不同热处理温度对材料性能的影响。从而找出材料性能随树脂含量、环氧/酚醛比值及热处理温度的变化规律。     

新型特种连接器—导电橡胶

<正> 像胶添加导电填料后,便成为导电橡胶。随着现代科学技术的发展,特别是集成电路与液晶显示器应用范围的不断扩大,电子对抗中微波吸收材料的性能要求不断提高,电子屏蔽材料的品种不断增加,导电橡胶的应用越来越广。导电橡胶的分类导电橡胶按其填料的不同可分为:石墨、炭墨型,导电金属粉末型(铜粉、银粉及活性氧化铝粉)和高分子聚合物导电型。导电橡胶按其用途和电阻率可分为: 1.防静电导电橡胶:其电阻率为10~3～10~5Ω·cm。用于防静电及一般导电制品,如高速汽车轮胎,输送易燃易爆物品的传送带,危险场所用的三角皮带,输送液体的胶管、以及煤矿、手术室的用具和导电地板     

石墨/聚乙烯导电复合材料PTC效应稳定性的研究

研究了制备方法、硅烷交联、热处理对石墨/聚乙烯复合材料的热循环稳定性的影响,讨论了改善正温度系数(PTC)导电高分子材料稳定性的原因.研究发现,用溶液混合法制备的复合材料具有良好的热循环稳定性;用硅烷偶联剂交联得到的复合材料,负温度系数(NTC)效应得到了有效抑制;热处理也可以有效改善材料的PTC效应的稳定性,经过热处理,材料的室温电阻率、PTC强度变化比较小.     

石墨-陶瓷复合材料电热特性的研究

利用低温快烧工艺制备石墨-陶瓷电热复合材料,首先测定材料的室温电阻率,然后在样品两端施加220 V交流电,测定了材料样品表面不同点的温度变化和电流变化,探讨了材料表面温度随时间的变化规律以及材料的电阻-温度特性.结果表明:试样的升温速率与电阻率有关,电阻率越小,升温速率越快,表面发热温度越高;在通电初期,复合导电材料随温度的升高呈现明显的NTC效应.随着温度的升高,材料的电阻率迅速降低,当温度达到最高时,电阻率最小;随着通电时间的延续,温度略有降低,而电阻率有所回升.当复合材料中石墨含量减少时,NTC效应减弱直至消失.     

基于机械球磨法的茂金属PE/石墨/碳纳米管导电复合材料的制备及性能研究

以茂金属PE为基体,以石墨和碳纳米管为导电填料,采用机械球磨法,制备茂金属PE/石墨/碳纳米管导电复合材料,考察球磨时间、球磨温度、球磨转速和石墨含量等对复合材料导电性的影响。结果表明,在球磨时间60 min,球磨温度50℃,球磨转速150 r/min、导电填料15%石墨、5%碳纳米管的条件下,复合材料的电阻率降到1.36Ω·cm,可作为一种电磁屏蔽材料应用于电子元器件表面。     

基于机械球磨法的茂金属PE/石墨/碳纳米管导电复合材料的制备及性能研究

以茂金属PE为基体,以石墨和碳纳米管为导电填料,采用机械球磨法,制备茂金属PE/石墨/碳纳米管导电复合材料,考察球磨时间、球磨温度、球磨转速和石墨含量等对复合材料导电性的影响。结果表明,在球磨时间60 min,球磨温度50℃,球磨转速150 r/min、导电填料15%石墨、5%碳纳米管的条件下,复合材料的电阻率降到1.36Ω·cm,可作为一种电磁屏蔽材料应用于电子元器件表面。     

低电阻率插溴石墨纤维的制备及其性能

本文对制备低电阻率插溴石墨纤维时,炭源、热处理温度、催化剂的使用以及插溴时间、温度和方式等影响插溴石墨纤维电阻率的因素进行了初步探讨。实验结果表明,将炭纤维进行高温热处理,可使电阻率下降至原来的1/5～1/10;催化高温热处理可以降低热处理温度400℃左右而达到同样的效果;插溴可以使石墨纤维的电阻率下降至原来的1/2～1/5。本文还对炭纤维电阻率下降和力学性能变化的原因进行了讨论。     

固化工艺对银导电胶导电性能的影响

以微米银粉为导电填料、环氧树脂(EP)为基体,制备了银导电胶。研究了固化条件和后固化热处理对银胶导电性能和微观结构的影响。结果表明:当固化温度为150℃时,银胶固化18 min时出现电阻,固化63 min时体积电阻率降至8.33×10-4Ω·cm;当固化温度为180℃时,银胶固化5 min时出现电阻,固化30 min时体积电阻率降至7.51×10-4Ω·cm。低温长时间固化有利于提高银胶的导电性能,高固化温度有利于提高低银粉含量银胶的导电性能,后固化热处理对已固化完全样品的导电性能和微观结构影响不大。     

不饱和聚酯树脂基复合材料的导电性能

以石墨、碳纤维、镍粉和不饱和聚酯树脂为原料通过模压成形固化制备导电复合材料,研究不同比例导电填料及用量、加工工艺对复合材料性能的影响.结果表明:导电填料比例和含量对复合材料的电导率与弯曲性能影响显著,一定含量下的镍粉和碳纤维,可以明显改善体系的强度,同时有助于降低材料的体积电阻率.加入适量丙酮溶剂作为稀释剂,提高了导电填料的分散和浸润,材料的导电性和弯曲性能明显提高.     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.     

Novel polyurethane coating technology through glycidyl carbamate chemistry

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.     

Highly moisture-proof polysilsesquioxane coating prepared via facile sol-gel process

A highly moisture-proof polysilsesquioxane coating was obtained from a new bis-silylated precursor, which was synthesized from 3-aminopropyltriethoxysilane (APTES) and m-xylylene diisocyanate (m-XDI) in tetrahydrofuran (THF) and verified by ¹H MAS NMR. For direct comparison purposes, an SiO₂ coating was also prepared by the Stöber method using tetraethoxysilane (TEOS) as the reactant. Interestingly, the coating obtained from the polysilsesquioxane sol exhibited a much higher moisture resistance capability than its counterpart, which was attributed to its more compact feature between nanoparticles as characterized by N₂ absorption experiment and transmission electron microscopy (TEM). Furthermore, its high transparency of about 92% showed potential for application in the protection of optical crystals.