SiC耐磨材料制备的研究进展

综合评述了国内外SiC耐磨材料诸多制备方法的现状和进展,并指出无压烧结和反应烧结是目前SiC耐磨材料工业化制备最可行的方法。反应烧结法制备SiC耐磨材料工艺比较简单,可以适合多种规格、形状的产品制备,产品的密度比较大,而且由于制备时SiC的取向排列,使SiC材料在使用过程中的自润滑性能好,耐磨性好;无压烧结法通过添加不同的烧结助剂,可以在较低温度(约1850℃)下制备高密度SiC耐磨材料,而且通过今后对复合稀土氧化物烧结助剂的研究,还有望进一步降低SiC耐磨材料的制备温度。     

Nicalon SiC纤维增强SiC复合材料制备工艺研究

本文对SiC纤维增强SiC复合材料的制备工艺进行了研究.将Nicalon SiC短纤维、SiC颗粒、钾长石、高岭土按设计的配方通过干法混合,干压成型后采用常压烧结法制备出SiCf/SiC复合材料;利用DTA分析混合粉体的热物理性能,采用XRD分析烧成前后材料的物相,利用SEM观察样品的显微结构,并测定了样品的致密度和抗弯强度.研究结果表明:常压烧结温度1115 ℃,保温时间2 h可制备出性能良好的SiCf/SiC复合材料.     

固溶体技术用于AlN-SiC微波衰减材料改性

结合AlN SiC二元系相图的理论分析 ,提出了利用固溶体技术实现AlN SiC微波衰减材料性能优化的研究思路 ;采用热压烧结工艺 ,通过合理的烧结温度及保温时间的控制 ,制备了性能优异的AlN SiC微波衰减材料。通过XRD、SEM、网络分析仪等测试手段 ,研究了材料的显微结构 (晶粒尺寸和晶粒形状等 )对材料微波衰减性能的影响 ,结果表明 ,AlN SiC局部固溶体具有广频衰减特性 ,而AlN SiC均质固溶体具有选频衰减特性 ;并初步探讨了AlN SiC固溶体陶瓷的微波衰减机理     

氧化镁-碳化硅复相陶瓷在X波段的衰减性能

以MgO为基体,添加少量SiC,采用热压工艺制备复相微波衰减钮扣材料,通过矢量网络分析仪测试其X波段的微波衰减性能.研究SiC的添加量、烧结温度、保温时间以及介电性能等因素对复相材料衰减性能的影响.结果表明:当SiC质量分数(下同)从1%到10%逐渐增加时,复相材料的损耗谐振衰减频率(f0)随之降低,衰减量也逐渐减小,有效衰减带宽增大;这种现象在SiC含量小于2%时更显著.烧结温度的降低会提高复相材料的f0;保温时间对复相材料衰减性能稳定性的影响较小.从谐振腔及波导的性质入手分析了影响f0而的主要因素,导出了给定钮扣半径下复相材料f0与相对介电常数之间的关系及适用范围,并据此从材料设计的角度对耦合腔行波管"损耗钮扣"的制备进行了探讨.     

凝胶注模成型SiAlON-SiC材料的烧结性能

以SiC、Si、SiO2 和Al为原料 ,采用凝胶注模成型工艺制备了SiAlON -SiC材料。研究了SiC的粒度组成、β SiAlON的设计组成 (z值 )及烧成温度等因素对SiAlON -SiC材料的烧结性能的影响。研究表明 :对于凝胶注模成型的SiAlON -SiC来说 ,当其β SiAlON的设计组成 (z值 )为 2 ,烧成温度为 1 5 70℃时 ,试样具有最佳的烧结性能 ;由两种粒度的SiC配成的试样比由单一粒度的SiC或 3种粒度的SiC配成的试样具有更好的烧结性能 ,所得试样具有最佳的体积密度、抗折强度和显气孔率     

O''''-Sialon-ZrO2-SiC(nm)的制备及力学性能

采用热压烧结工艺合成了O'-SialonZrO2-SiC(nm)复合材料,研究了该复合材料的力学性能及显微结构.结果表明,材料抗折强度随温度的变化属Ⅰ类曲线变化规律,Sialon、SiC多晶以及晶粒粗大、层状结构SiC的存在可能是导致材料强度不高的主要原因.断口的显微结构研究表明,复合材料在室温时的断裂以穿晶断裂为主,中、高温时则为沿晶断裂.     

木粉/TEOS杂化材料制备SiC木材陶瓷的研究

以木粉、正硅酸乙酯(TEOS)为原料,采用溶胶-凝胶方法将TEOS引入到木粉空隙中制备出木粉/TEOS杂化材料,在较低温度下烧结制得SiC木材陶瓷.采用热失重分析(TGA)、X射线衍射分析(XRD)、红外光谱(FT-IR)和扫描电镜(SEM)对其物相变化和显微结构进行了表征,用阿基米德法测定SiC木材陶瓷的显气孔率,研究了烧结温度和杂化材料增重率对SiC木材陶瓷摩擦性能的影响.研究结果表明,木粉/TEOS杂化材料在800 ℃时总的失重率仅为20%,是理想的SiC陶瓷前驱体;杂化材料中的Si-O-C结构可以在1000℃烧结成SiC;SiC木材陶瓷主晶相由β-SiC和SiO2组成,具有类似于木材的多孔拓扑结构;显气孔率随着烧结温度的升高先升后降,而随增重率的增加而增加;耐磨性能随烧结温度和增重率的增加而提高.     

热压烧结制备原位复合（TiB2+TiC）/Ti3SiC2复相陶瓷

采用热压烧结法制备了原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷。采用X射线衍射、扫描电镜和透射电镜对材料的物相组成和显微结构进行了表征,研究了烧结温度对材料物相组成、烧结性能、显微结构与力学性能的影响。结果表明:烧结温度在1 350～1 500℃范围内,随着烧结温度的升高,合成反应进行逐渐完全,材料的密度、抗弯强度和断裂韧性显著提高。1 500℃烧结可得到致密的原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷,材料晶粒发育较完善,层片状Ti3SiC2、柱状TiB2与等轴状TiC晶粒清晰可见,增强相晶粒细小,晶界干净,材料的抗弯强度、断裂韧性和Vickers硬度分别达到741 MPa,10.12 MPa.m1/2和9.65 GPa。烧结温度达到1 550℃时Ti3SiC2开始发生分解,材料的密度和力学性能又显著下降。     

添加TiB_2对SiC基复相陶瓷显微结构和力学性能的影响

以钇铝石榴石(YAG)为助烧剂,利用等离子放电烧结(SPS)制备SiC–TiB_2复相陶瓷。采用X射线衍射、扫描和透射电子显微镜、能量色散X射线能谱对材料物相及微观结构进行了表征。研究了SPS烧结温度及TiB_2的加入对材料微观结构尤其是晶界相形态和力学性能的影响。结果表明:虽然TiB_2的加入对材料致密化起到了一定的阻碍作用,但是促使晶界相从晶态向非晶态转变,提高了晶粒间结合强度,材料的力学性能得到提升。烧结温度为1 750℃制备的SiC–TiB_2陶瓷抗弯强度最高,为753 MPa,烧结温度为1 700℃制备的SiC–TiB_2陶瓷断裂韧性最高,为8.84 MPa·m~(1/2)。     

逆反应烧结制备铝电解槽用氮化硅-碳化硅复合材料

采用常规的反应烧结工艺制作铝电解槽侧壁材料用Si3N4／SiC时存在不足，为此，提出应用逆反应烧结工艺进行生产性试验的设想。在制备Si3N4／SiC复合材料时，常规反应烧结是以Si和SiC为原料经氮化烧结；逆反应烧结是以Si3N4和SiC为原料，首先使Si3N4反向反应生成活性氧化物后进行烧结。结果表明：该工艺特点是新生的Si2N2O或SiO2进行活性烧结；制品具有良好的物理和化学性能。制品结构紧密，新生氧化物或亚氧化物紧密地充填在Si3N4和SiC颗粒间界，新工艺制备的砖的抗冰晶石熔体侵蚀的性能优于常规工艺烧成砖，是铝电解槽侧壁的良好材料。     

Sapindaceae,cyanolipids, and bugs

Scentless plant bugs (Heteroptera: Rhopalidae) are so named because adults of the Serinethinae have vestigial metathoracic scent glands. Serinethines are seed predators of Sapindales, especially Sapindaceae that produce toxic cyanolipids. In two serinethine species whose ranges extend into the southern United States,Jadera haematoloma andJ. sanguinolenta, sequestration of host cyanolipids as glucosides renders these gregarious, aposematic insects unpalatable to a variety of predators. The blood glucoside profile and cyanogenesis ofJadera varies depending on the cyanolipid chemistry of hosts, and adults and larvae fed golden rain tree seeds (Koelreuteria paniculata) excrete the volatile lactone, 4-methyl-2(5H)-furanone, to which they are attracted.Jadera fed balloon vine seeds (Cardiospermum spp.) do not excrete the attractive lactone. Loss of the usual heteropteran defensive glands in serinethines may have coevolved with host specificity on toxic plants, and the orientation ofJadera to a volatile excretory product could be an adaptive response to save time.Mention of a commercial product does not consititute an endorsement by the USDA.     

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.     

2008～2009年世界塑料工业进展

收集了2008年7月～2009年6月世界塑料工业的相关资料,介绍了2008～2009年国外塑料工业的发展情况,提供了世界塑料产量、消费量及全球各类树脂的需求量及产能情况。按通用热塑性树脂(聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂)、工程塑料(尼龙、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚)、特种工程塑料(聚苯硫醚、液晶聚合物、聚醚醚酮)、通用热固性树脂(酚醛、聚氨酯、环氧树脂、不饱和聚酯树脂)不同品种的顺序,对树脂的产量、消费量、供需状况及合成工艺、产品应用开发、树脂品种的延伸及应用的进一步扩展等技术作了详细介绍。     

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.     

Many Drugs of Abuse May Be Acutely Transformed to Dopamine,Norepinephrine and Epinephrine In Vivo

It is well established that a wide range of drugs of abuse acutely boost the signaling of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, where norepinephrine and epinephrine are major output molecules. This stimulatory effect is accompanied by such symptoms as elevated heart rate and blood pressure, more rapid breathing, increased body temperature and sweating, and pupillary dilation, as well as the intoxicating or euphoric subjective properties of the drug. While many drugs of abuse are thought to achieve their intoxicating effects by modulating the monoaminergic neurotransmitter systems (i.e., serotonin, norepinephrine, dopamine) by binding to these receptors or otherwise affecting their synaptic signaling, this paper puts forth the hypothesis that many of these drugs are actually acutely converted to catecholamines (dopamine, norepinephrine, epinephrine) in vivo, in addition to transformation to their known metabolites. In this manner, a range of stimulants, opioids, and psychedelics (as well as alcohol) may partially achieve their intoxicating properties, as well as side effects, due to this putative transformation to catecholamines. If this hypothesis is correct, it would alter our understanding of the basic biosynthetic pathways for generating these important signaling molecules, while also modifying our view of the neural substrates underlying substance abuse and dependence, including psychological stress-induced relapse. Importantly, there is a direct way to test the overarching hypothesis: administer (either centrally or peripherally) stable isotope versions of these drugs to model organisms such as rodents (or even to humans) and then use liquid chromatography-mass spectrometry to determine if the labeled drug is converted to labeled catecholamines in brain, blood plasma, or urine samples.