铌酸铅钡晶体及其低温相变

对于铝酸铅钡(PBN)系统中三种不同组份的晶体,研究了300K至10K范围内的介电和热电性能。发现它们在约50-70K发生铁电-铁电相变。相变温度上下晶体点群分别为4mm和m。在4mm相中,自发极化沿[001]方向,在m相中,自发极化在m面内。在降温过程中通过相变时,自发极化从[001]方向发生微小的偏离,但仍保持在一个m面,其方向用四方相的指数表示为[hhl]。     

B位氧化物预合成法制备(1-x)Pb(Fe1/4Sc1/4Nb1/2)O3-xPbTiO3铁电陶瓷及其性能研究

利用传统的陶瓷工艺、通过B位氧化物预合成法制备了高质量、钙钛矿结构的(1-x)Pb(Fe1/4Sc1/4Nb1/2)O3-xPbTiO3(PFSN-PT)铁电陶瓷.结构测定和性能测试表明,1180℃烧结2h制备的PFSN-PT陶瓷呈现相当均匀的显微结构和良好的电学性能,同时具有较高的致密度(约95%),只有PbTiO3(PT)物质的量分数为40%、60%的陶瓷致密度略低(约91%).随着PT含量的增加,PFSN-PT从三方相结构转变为四方相结构,并伴随着晶胞体积的减小(从PFSN的6.6676×10-2 nm3下降到0.2PFSN-0.8PT的6.3555×10-2 nm3)和钙钛矿结构四方性的增大(从0.6PFSN-0.4PT的1.0242增加到0.2PFSN-0.8PT的1.0488).PFSN-PT陶瓷的介电常数最大值(εm)及其峰值温度(Tm)也随着PT含量的增加呈线性增大.介电性能测试和热滞行为研究表明,随着PT含量的增加,PFSN-PT的铁电-顺电相变从弛豫铁电体的弥散型铁电相变向正常铁电体的一级铁电相变转变.     

NBT基无铅压电陶瓷的拉曼光谱研究

利用拉曼散射并结合群论系统研究了(Na0.5Bi0.5)(1-x)TiO3-BaxTiO3(简称NBT-BT)的晶体振动及铁电相到顺电相的结构相变。结果表明,在室温下随着Ba2 含量的增加,521.4cm-1光学声子模劈裂为双峰且高频声子模向高频漂移;随着温度的升高,BT含量为6%的样品在460￣620cm-1范围内,高频峰出现了明显的软化现象。因此,通过拉曼散射的分析,可以表征NBT基陶瓷中相结构的变化趋势。     

开放水热法制备莫来石复相纳米晶体的影响因素

以天然高岭土为原料,经精细化处理煅烧制备莫来石.用常压、开放水热技术制备出莫来石复相纳米晶体材料.实验表明:常压、开放水热条件下制备莫来石复相纳米晶粉体的水热反应中,采用质量比为m(Na2O)/m(SiO2)=2.8,m(H2O)/m(Na2O)=35～30,0～80℃控温升温1 h,在80℃保温2 h,可制备出尺寸为80～100 nm莫来石复相纳米晶体.所制备的莫来石纳米晶体的水热溶液相变驱动力△μ为(3.609～4.672)×10-20 J/mol;水热体系溶解度控制在3.891×10-6 mol/L;熔解热△E为18.846 kJ/mol;晶体生长速率常数选择0.85～0.92,有利于快速成核和晶体生长,并且可以很好地控制晶体尺寸和分散度.     

Ba_2TiSi_2O_8晶体的生长及其电弹常数的测定

采用提拉法生长了尺寸为35mm×35mm×50mm的透明Ba2TiSi2O8晶体。XRD结果表明所得晶体的物相为Ba2TiSi2O8单晶,浮力法测量晶体的密度为4.465g/cm3。利用静电容法测量Ba2TiSi2O8晶体的相对介电常数为ε11/ε0=16.35和ε33/ε0=12.38。干涉法测量的压电常数为d15=17.55 pC/N、d31=-1.49 pC/N,谐振法测量的机电耦合系数为k33=10%,弹性常数sE11=7.5×10-12、sE33=13.3×10-12、sE44=33.6×10-12m2/N和sE66=12.8×10-12m2/N。并测量了Ba2TiSi2O8晶体的电阻率为pa=9.43×1013.cm、pc=5.84×1013 cm。通过测量发现,Ba2TiSi2O8晶体压电常数远大于石英的,且具有大的机电耦合系数和较大的电阻率,是一种优良的压电晶体材料。     

铁电磁体Pb(Fe1/2Nb1/2)O3单晶高温熔液法生长及其结构特征研究

采用高温溶液晶体生长法,选择PbO为助熔剂,以缓慢冷却法获得过饱和度并施以温度振荡,生长出典型尺寸为3 mm×3 mm×3 mm的铁电磁体Pb(Fe1/2Nb1/2)O3单晶.用变温X射线衍射和变温Raman光谱研究了Pb(Fe1/2Nb1/2)O3单晶的结构对称性.结果表明Pb(Fe1/2Nb1/2)O3在实验的最低温度80 K到铁电相变温度383 K之间均为菱面体结构.在反铁磁相变温度Neel点以上,Pb(Fe1/2Nb1/2)O3体对角线逐渐变短,而在该温度以下,其结构没有变化.在测量的温度20～200 K范围内,Raman光谱的峰位不随温度变化,说明其结构在该温度范围内没有明显变化.实验结果将有利于进一步研究铁电磁体的形成机制.     

中温烧结PSBN系统铁电陶瓷结构和性能的研究

本文研究了中温烧结PbO-SrO-BaO-Nb2O5(PSBN)系统铁电陶瓷介电性能.通过XRD分析确定了主晶相为具有钨青铜结构的Pb0.7Ba0.3Nb2O6(PBN)、Ba0.27Sr0.75Nb2O5.78(BSN);分析了添加剂MnCO3、TiO2、Fe2O3、(MgCO3)4.Mg(OH)2.5H2O对PSBN系统铁电陶瓷介电性能的影响.由于这些添加剂的作用使该系统铁电陶瓷介电系数提高,居里区拓宽并向低温方向移动,绝缘电阻提高,损耗降低,制得高介(ε=4300±200)X7R瓷料.     

解构钨青铜氧化物之铁电相变与介电特性演化规律

梳理了钨青铜氧化物铁电相变与介电特性的演化规律,构筑了调制结构对其铁电相变与宏观铁电性能影响的物理图像.A位离子通过对氧八面体倾转的影响使晶体形成不同的调制结构,而调制结构自无公度向公度的转变与铁电相变温度的相互关系、决定了钨青铜氧化物由正常铁电体向弛豫铁电体的演化.低温下调制结构逐渐退出,而调制结构退出过程中与铁电序...     

Growth and Determination of Electro-Elastic Constants of Ba2TiSi2O8 Crystal

采用提拉法生长了尺寸为 35mm×35mm×50mm 的透明 Ba2TiSi2O8晶体。XRD 结果表明所得晶体的物相为 Ba2TiSi2O8单晶,浮力法测量晶体的密度为 4.465g/cm3。利用静电容法测量 Ba2TiSi2O8晶体的相对介电常数为 ε11/ε0= 16.35 和 ε33/ε0= 12.38。干涉法测量的压电常数为 d15= 17.55 pC/N、d31= –1.49 pC/N,谐振法测量的机电耦合系数为 k33= 10%,弹性常数 sE11= 7.5 × 10–12、sE33= 13.3 × 10–12、sE44= 33.6 × 10–12m2/N 和 sE66= 12.8 × 10–12m2/N。并测量了 Ba2TiSi2O8晶体的电阻率为 pa= 9.43 × 1013 ·cm、pc= 5.84 × 1013 cm。通过测量发现,Ba2TiSi2O8晶体压电常数远大于石英的,且具有大的机电耦合系数和较大的电阻率,是一种优良的压电晶体材料。     

解构钨青铜氧化物之铁电相变与介电特性演化规律EI北大核心CSCD

梳理了钨青铜氧化物铁电相变与介电特性的演化规律,构筑了调制结构对其铁电相变与宏观铁电性能影响的物理图像.A位离子通过对氧八面体倾转的影响使晶体形成不同的调制结构,而调制结构自无公度向公度的转变与铁电相变温度的相互关系、决定了钨青铜氧化物由正常铁电体向弛豫铁电体的演化.低温下调制结构逐渐退出,而调制结构退出过程中与铁电序的相互作用应是钨青铜氧化物中普遍存在的低温介电弛豫的结构起源.     

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.     

Methyl 2,4,6-decatrienoates Attract Stink Bugs and Tachinid Parasitoids

Halyomorpha halys (Stål) (Pentatomidae), called the brown marmorated stink bug (BMSB), is a newly invasive species in the eastern USA that is rapidly spreading from the original point of establishment in Allentown, PA. In its native range, the BMSB is reportedly attracted to methyl (E,E,Z)-2,4,6-decatrienoate, the male-produced pheromone of another pentatomid common in eastern Asia, Plautia stali Scott. In North America, Thyanta spp. are the only pentatomids known to produce methyl 2,4,6-decatrienoate [the (E,Z,Z)-isomer] as part of their pheromones. Methyl 2,4,6-decatrienoates were field-tested in Maryland to monitor the spread of the BMSB and to explore the possibility that Thyanta spp. are an alternate host for parasitic tachinid flies that use stink bug pheromones as host-finding kairomones. Here we report the first captures of adult and nymph BMSBs in traps baited with methyl (E,E,Z)-2,4,6-decatrienoate in central Maryland and present data verifying that the tachinid, Euclytia flava (Townsend), exploits methyl (E,Z,Z)-2,4,6-decatrienoate as a kairomone. We also report the unexpected finding that various isomers of methyl 2,4,6-decatrienoate attract Acrosternum hilare (Say), although this bug apparently does not produce methyl decatrienoates. Other stink bugs and tachinids native to North America were also attracted to methyl 2,4,6-decatrienoates. These data indicate there are Heteroptera in North America in addition to Thyanta spp. that probably use methyl 2,4,6-decatrienoates as pheromones. The evidence that some pentatomids exploit the pheromones of other true bugs as kairomones to find food or to congregate as a passive defense against tachinid parasitism is discussed.     

2007～2008年世界塑料工业进展

收集了2007年7月～2008年6月世界塑料工业的相关资料,介绍了2007～2008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、不饱和聚酯树脂、环氧树脂)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.     

2005～2006年国外塑料工业进展

收集了2005年7月～2006年6月国外塑料工业的相关资料,介绍了2005—2006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生产量以及各国塑料制品的进出口情况。作为对比,介绍了中国塑料的生产情况。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（聚酰胺、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚）、通用热固性树脂（酚醛、聚氨酯、不饱和树脂、环氧树脂）、特种工程塑料（聚苯硫醚、液晶聚合物、聚醚醚酮）的品种顺序,对树脂的产量、消费量、供需状况及合成工艺、产品开发、树脂品种的延伸及应用的扩展作了详细的介绍。