重结晶碳化硅凝胶注模成型及其性能研究

研究了重结晶碳化硅高温材料的凝胶注模成型，着重讨论了SiC粉体的分散性，悬浮体的流变性、沉降行为以及烧结机理。结果表明，选用适量的分散剂TMAH调整浆料pH=11.9附近可制备出固相体积分数高达70％的SiC浓悬浮体，沉降实验表明，该浓悬浮体中粗细SiC颗粒间能达到均一稳定的分散，服粒子不会明显地沉降，凝胶注膜成型所得坯体在2450℃和氩气氛下烧结可获得重结晶碳化硅高温材料，其体积密度为2．52g.cm^-3，对应的抗弯强度为55．4MPa。     

钛酸镍水基浓悬浮体的制备及流变特性研究

测定了超细NiTiO3粉体的ζ-电位,并研究了分散剂聚甲基丙烯酸铵(NH4PAA)的用量对NiTiO3悬浮体粘度的影响。结果表明:超细NiTiO3粉体在水中的等电点约为5.0;悬浮体的粘度与分散剂的用量有关,并得出最佳用量约为粉体质量的0.4wt%;研究了不同水基浓悬浮体的流变特性,成功地制备出体积分数为60vol%的低粘度(0.75Pa·S,剪切速率为50S-1)悬浮体。     

纳米钛酸钡粉体的分散及水基悬浮体制备

通过测定超重力法制备的纳米钛酸钡悬浮体的Zeta电位和团粒尺寸分布,确定了纳米BaTiO3在水中稳定分散的基本条件,制备了不同体积分数的悬浮体并研究了其流变学特性. 该纳米BaTiO3在水中的等电点约为pH 2.8,加入分散剂PAA-NH4后,颗粒零电点向更低pH值移动;当分散剂用量为干粉量的1.2%(w)时,悬浮体中平均团粒尺寸最小,分散效果最佳. FT-IR分析证明颗粒表面上PAA-NH4的吸附为物理化学吸附. 制备了体积分数高达45%的纳米BaTiO3悬浮体,其流变特性表现为剪切变薄行为,流延成型的BaTiO3陶瓷生坯片具有较高的相对密度(55.4%).     

氧化锆增韧氧化铝陶瓷悬浮体的流变性能

通过ξ电位、流变特性等测试,研究了分散剂添加量、固相体积分数、粉体组成及研磨时间对氧化锆增韧氧化铝(zirconia toughened alumina,ZTA)陶瓷悬浮体流变性能的影响。实验发现：在0～200s^-1的剪切区,不同条件下测得的流变曲线均可用casson模型进行拟合,拟合出的Casson屈服应力τc可较好地反映悬浮体的稳定性。实验结果表明：当pH值在9．0左右,分散剂添加质量分数(下同)为0．90％时,ZTA(20％ZrO2)悬浮体的τc值较低,悬浮体的τc值随固相体积分数和ZrO2含量增加而增加,当ZrO2含量较高时．适当调整分散剂添加量,仍可制备稳定性较好的悬浮体。在所实验条件下,研磨4h的悬浮体的τc值最低。     

亚微米级α-氧化铝水悬浮液稳定性与沉降研究

采用机械化学法制备亚微米级窄粒级分布的α相氧化铝粉体,对比悬浮液pH、固含量、分散剂种类及用量和温度等不同因素的影响,利用Zeta电位、沉降时间、吸光度等考察其分散稳定性,考虑了颗粒在水中的相互作用及小颗粒的布朗运动,通过纳米粒度电位仪、激光粒度分析仪、紫外分光光度计等探索表征不同因素对悬浮稳定性的影响。研究结果表明:选用质量分数为1%的六偏磷酸钠作分散剂,p H在11左右时,得到分散稳定的氧化铝粉体,其亚微米级氧化铝粉体在高温条件下比低温条件下悬浮稳定性更好。     

分散剂对纳米TiO2悬浮液稳定性的影响

选择不同的有机物为分散剂分别对纳米TiO2粒子进行了表面改性。通过采用重力沉降法、Zeta电位法等表征了其分散效果,研究了纳米TiO2悬浮液在不同PH值下的分散行为。结果表明:纤维素能使纳米TiO2悬浮稳定性明显提高。在纳米TiO2悬浮液中,纳米TiO2粉体表面的Zeta电位同水溶液的平衡PH有很大关系。提高颗粒表面电位(Zeta电位)是改善粉体分散体系稳定性的有效途径。     

直接凝胶凝固成型SiC（M,Y）—Al2O3复合陶瓷材料的研究（Ⅰ）稳定的低粘度高固相含量悬浮体的制备

本文研究了复相SiC(M,Y)-Al2O3系稳定的高固相含量的低粘度悬浮体的流变特性，找出了影响流变性的主要因素。在碱性条件下，用实验室合成的PMAA-NH4和CM作为复合分散剂以及引入有机单体制备出固相含量高达62(vol)%，粘度245mPa.s的SiC(M,Y)-Al2O3浓悬浮体。     

直接凝胶凝固成型SiC(M,Y)-Al_2O_3复合陶瓷材料的研究(Ⅰ)稳定的低粘度高固相含量悬浮体的制备

本文研究了复相SiC(M ,Y) -Al2 O3系稳定的高固相含量的低粘度悬浮体的流变特性 ,找出了影响流变性的主要因素。在碱性条件下 ,用实验室合成的PMAA -NH4 和CM作为复合分散剂以及引入有机单体制备出固相含量高达 62 (vol) % ,粘度 2 4 5mPa.s的SiC(M ,Y) -Al2 O3浓悬浮体     

分散剂用量和pH值对纳米氧化锆水基浆料稳定性的影响

在氧化锆陶瓷制作过程中采用凝胶注模成型工艺时,为了获得高分散性、低粘度的浆料,试图使用聚丙烯酸铵(PAA-NH4)作为分散剂,主要研究了氧化锆悬浮体的3个指标:Zeta电位、流变学行为、沉降度,在不同p H值和分散剂用量下的变化规律,并分析其影响机理。试验结果表明:PAA-NH4的加入能够明显提高氧化锆浆料的Zeta电位,用氨水调节悬浮体p H为11的情况下,当添加3.0 wt%的分散剂聚丙烯酸铵PAA-NH4时,Zeta电位为负值,达到最小,粘度和沉降高度也均达到最小值,此时,ZrO2水基浆料的分散性、稳定性和流变学行为达到最佳。     

TiB2泡沫陶瓷浆料的制备

通过沉降实验、Zeta电位的测定及粘度和流变性能测量的方法研究了制备高固相含量TiB2泡沫陶瓷浆料的工艺条件;通过挂挂浆量的测定及烧结体的扫描照片分析研究了浸渍工艺的条件。研究表明：浆料最佳pH值为9,分散剂的引入有效提高了悬浮粒子的Zeta电位,改善浆料的分散性,最佳的分散剂含量为0.3wt%,最佳固相含量为77wt%。     

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.     

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.     

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.