顺丁橡胶/有机蒙脱土纳米复合材料的介电性能研究

采用机械混炼法制备了顺丁橡胶/有机蒙脱土(BR/OMMT)纳米复合材料;采用精密电桥对纳米复合材料的介电性能进行了研究。结果表明,纳米复合材料的相对介电系数(ε)随温度的升高逐渐增加,而介电损耗(tanδ)随温度的升高分别出现β峰和α峰。当晶区完全融化后,ε及tanδ随温度的升高而急剧上升;在频率一定时,纳米复合材料的介电损耗随OMMT含量的增加逐渐增加,并且峰值向高温方向移动;在OMMT含量一定时,在相同温度下,复合材料的ε和tanδ均随着频率的升高而下降;随着频率的升高,介电损耗峰向高温方向移动。     

超高频段轮胎橡胶电性能研究

试验研究炭黑种类和用量等对超高频(UHF)频段轮胎橡胶电性能的影响。结果表明:炭黑种类对橡胶复合材料的电阻率影响较小,但对介电性能影响较大;炭黑用量越高,橡胶复合材料的介电常数(ε)和损耗因子(tanδ)越大。橡胶复合材料介电性能与工作频率关系明显,在UHF频段,随着频率的升高,橡胶复合材料的ε和tanδ下降明显。温度对橡胶复合材料的介电性能有一定的影响,但当频率超过2 GHz时,对tanδ影响较小。     

UHF频段轮胎橡胶电性能研究

试验研究炭黑种类和用量等对超高频（UHF）频段轮胎橡胶电性能的影响。结果表明：炭黑种类对橡胶复合材料的电阻率影响较小,但对介电性能影响较大;炭黑用量越高,橡胶复合材料的介电常数（ε）和损耗因子（tanδ）越大。橡胶复合材料介电性能与工作频率关系明显,在UHF频段,随着频率的升高,橡胶复合材料的ε和tanδ下降明显。温度对橡胶复合材料的介电性能有一定的影响,但当频率超过2 GHz时,对tanδ影响较小。     

BaTiO3／环氧树脂／玻璃纤维复合材料介电性能研究

本文运用热压工艺制备了BaTiO3（BT）／环氧树脂／玻璃纤维和BaTiO3／炭黑／环氧树脂／玻璃纤维复合材料,研究了温度、填料含量和交流频率对复合材料的介电性能的影响。结果表明,复合材料的介电常数（εr）和介电损耗（tanδ）随肌体积分数的增加而升高。当肌体积分数为17％时,复合材料在1MHz下的εr和tanδ分别为7.88和0.027。当炭黑的含量为1.0％时,明含量为17％的复合材料εr和tanδ分别为11.0和0.035。随着频率的升高,复合材料的εr降低,而介电损耗升高。复合材料的εr随温度升高而增加。     

硅烷偶联剂改性SiC晶须/PVDF复合薄膜的制备及其介电性能研究

设计填料为半导体纳米晶须、基体为高分子聚合物是制备具有良好介电性能和力学性能材料的基本要求.首先利用化学改性法将不同硅烷偶联剂修饰在碳化硅晶须(SiCw)表面,再利用溶液流延法制备改性SiCw/聚偏氟乙烯(PVDF)复合薄膜.采用直接观察、FT-IR和热重分析对SiCw的改性效果进行评价,通过SEM观察SiCw在PVDF中的分布情况,并测试了该复合薄膜的介电性能随温度的变化情况.结果表明:利用本文的试验方法可成功将硅烷偶联剂引入到SiCw表面;SEM结果显示,利用化学改性法可有效改善SiCw的团聚问题,使其均匀分布在PVDF基体内;TGA结果表明,添加SiCw作为填料可有效改善复合材料的热稳定性能,且当采用KH792型硅烷偶联剂时修饰率为6.37％.室温介电性能测试结果表明:添加改性SiCw可提高复合材料的介电常数,相对纯PVDF提高了近8倍;在0.1wt％KH792-SiCw/PVDF的介电性能测试中,当f=100 Hz时介电常数εr达到最大值33,介电损耗tanδ达到最小值0.07,且随频率的增加介电常数逐渐减小,介电损耗先减小后又增加;随着温度的增加,介电常数和介电损耗逐渐增加,当f=500 Hz,T=150℃时,εr最大为110,对应tanδ也最大为1.76.     

制备工艺对BNBT陶瓷介电性能的影响

BNT(BaO-Nd2O3-TiO2)系统陶瓷是一种介电性能优良的陶瓷材料.在BNT中添加一定量的Bi2O3,可以得到介电性能更优的BNBT(BaO-Nd2O3-Bi2O3 -TiO2)陶瓷.该文分别研究了球磨时间、烧结温度和保温时间对BNBT陶瓷介电性能的影响.结果表明:当球磨时间为10 h、烧结温度为1160 ℃、保温时间为9 h时,BNBT陶瓷的介电性能为:介电常数ε=99.8281,介电损耗tanδ=2.65×10-4,介电常数温度系数αε≤±30 ppm/℃.     

ZnSO_4溶液包覆Ca_(0.6)La_(0.8/3)TiO_3-Li_(0.5)Nd_(0.5)TiO_3微波介电陶瓷的研究

采用固相合成Ca_(0.6)La_(0.8/3)TiO_3-Li_(0.5)Nd_(0.5)TiO_3(CLT-LNT)微波介质陶瓷基体粉体,以ZnSO_4溶液为先驱体引入ZnO来降低该陶瓷的烧结温度,这种液相引入助烧剂的方法不仅减少了烧结助剂的用量,而且改善了陶瓷材料的介电性能。研究表明:掺入ZnO的CLT-LNT陶瓷在980℃烧结时的介电常数(ε_r)和介电损耗(tanδ)随着ZnSO_4溶液浓度的增大先增大后略有减小。当ZnSO_4溶液的浓度为0.32 mol/L时,CLT-LNT陶瓷在980℃烧结3 h获得较好的介电性能:ε_r=102,tanδ=0.0027,τ_f=-3×10~(-6)/℃。     

湿热老化对石英纤维/聚酰亚胺复合材料力学和介电性能影响研究

本文考察了湿热老化对QW220/902(石英纤维/聚酰亚胺)树脂基复合材料力学和介电性能的影响。研究结果表明:复合材料在80℃下经48 h水煮处理后,由于水分子浸入引起界面脱粘,各项力学性能略有下降,300℃下的层间剪切强度保持率为86.48%,但是其他力学性能保持率仍超过90%;水煮处理后复合材料的介电性能发生明显下降,但是经100℃真空干燥除去水分后,材料的介电性能可以得到基本保持,表明QW220/902复合材料具有良好的抗湿热老化性能,可以作为结构/透波一体化材料,具有很好的应用前景。     

导电炭黑/氯化丁基橡胶力学和电性能的研究

通过共混法制备了导电炭黑/氯化丁基橡胶复合材料,研究了复合材料的拉伸性能与导电、介电性能。研究发现,随着导电炭黑和硫化剂含量的增加,拉伸强度先出现一个极大值随后下降,在炭黑用量为5%,硫化剂用量为3%时,拉伸强度最大,为9.1 MPa;而断裂伸长率一直下降。当导电炭黑超过5%以后,电导率迅速增加,出现渗流现象。介电常数实部ε′和介电损耗因子tanδ随导电炭黑用量的增加而增大,但当导电炭黑用量较高(20%)时,在高频时,ε′和tanδ都下降。     

掺杂氧化铌对钛酸锶钡铁电陶瓷材料显微结构和介电性能的影响

钛酸锶钡(barium strontium titanate,BST)铁电陶瓷材料的介电常数(ε)随外加直流电场的变化呈现非线性特性.纯BST材料由于较高的ε和较大的介电损耗(tanδ)不能满足移相器介质材料的要求.通过在BST中添加氧化铌(Nb2O5)来改善BST铁电陶瓷材料的介电性能.结果表明:在BST体系中微量掺杂Nb2O5,Nb5 以取代Ti4 的方式存在于钙钛矿的晶格中,形成均匀的固溶体Ba0.5Sr0.5Ti1-xNbxO3.随Nb5 添加量的增加,Curie峰逐渐变宽,峰高逐渐降低,相变弥散效应增强.Nb5 的掺杂能显著降低并稳定BST陶瓷的tanδ,改善BST体系的介电性能.     

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.     

ICP-MS法测定地球化学样品中As、Cr、Ge、V等18种微量痕量元素的研究

建立了测定地球化学样品中包括As、Cr、Ge、V等18种微量、痕量元素的ICP-MS方法。地化试样用HF-HNO3混酸分解后,以1 1 HNO3溶解干渣。由于制样不使用盐酸,避免了Cl对As、Cr、Ge、V的质谱干扰。用国家一级地球化学标准物质GBW 07309制备溶液优化仪器工作参数,并用于校准。方法测定限(6s)为:0.007~6.4μg/g,精密度(RSD%,n=12)为:29%~9.4%,经过国家一级地球化学标准物质的分析验证,结果与标准值吻合。方法已应用于国土资源调查的试样分析。     

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.     

基于ATRP法制备的触角状亲水性羟胺树脂的吸硼性能的研究

以大分子引发剂氯乙酰化聚苯乙烯微球(PS-acyl-Cl)经原子转移自由基聚合(ATRP)法引发丙烯酰胺(AM)和甲基丙烯酸缩水甘油酯(GMA)单体的共聚接枝,制得一种触角状亲水性环氧载体(PS-acyl-g-P(AM-co-GMA)),再经二乙醇胺(DEA)的环氧基开环胺化反应,得到一种含多个-NCH2CH2OH螯合配基的多齿-五元螯合环的触角状亲水性羟胺树脂(PS-acyl-g-P(AM-co-GMA)-DEA)。将此树脂用于硼吸附研究,结果表明,PS-acyl-g-P(AM-co-GMA)-DEA树脂对硼的吸附满足Langmuir方程,为单分子层吸附;饱和吸附量约为37.7 mg·g-1,且树脂5 min即可达到吸附平衡,与其它已报道的吸硼树脂相比,该树脂具有更高的吸附量和吸硼速率。吸附动力学研究表明,树脂吸附硼的过程主要由颗粒扩散过程控制。重复使用5次后该树脂的吸附量基本不变,解吸率均在90%以上,重复使用性能良好。