无喷霜硫化体系中硫黄用量对三元乙丙橡胶/白炭黑硫化胶性能的影响

采用无喷霜硫黄硫化体系,考察了硫黄用量对三元乙丙橡胶(EPDM)/白炭黑(WCB)混炼胶硫化特性及硫化胶物理机械性能、耐热老化性能、动态力学性能和压缩永久变形的影响。结果表明,在硫黄用量为0.5~1.5份的条件下,随着硫黄用量的增加,EPDM/WCB混炼胶的硫化速率减慢,硫化胶的拉伸强度先升高后下降,当硫黄用量为1.00份时达到最大值(22.4 MPa),同时扯断伸长率和永久变形逐渐下降,邵尔A硬度升高;热空气老化后,硫化胶的拉伸强度、撕裂强度和硬度均提高,但扯断伸长率下降幅度较大;随着硫黄用量的增加,硫化胶的玻璃化转变温度向高温方向移动,损耗因子峰值先升高后下降,储能模量增大,压缩永久变形略有减小。     

EPDM/POE/PP共混制备热塑性弹性体的性能研究

采用动态硫化的方法制备三元乙丙橡胶（EPDM）/聚烯烃弹性体（POE）/聚丙烯（PP）热塑性弹性体,讨论了EPDM、硫化剂、炭黑的用量和填料种类对热塑性弹性体性能的影响。结果表明：随着EPDM用量的增加,EPDM/POE/PP热塑性弹性体的拉伸强度、定伸应力和硬度都呈减小趋势,而拉断永久变形呈上升趋势;随着SP-1055用量的增加,其压缩永久变形显著降低;随着炭黑用量的增加,弹性体的拉伸强度、定伸应力和硬度先下降后增加,而拉断伸长率、拉断永久变形和压缩永久变形先增大后降低;在不同填料种类中用N85作为填料时,弹性体的综合性能最好,压缩永久变形最小。     

EPDM/PP/POE热塑性弹性体性能的研究

研究三元乙丙橡胶(EPDM)/聚丙烯(PP)/聚烯烃弹性体(POE)热塑性弹性体的性能。结果表明:随着溴化辛基酚醛硫化树脂SP-1055用量增大,EPDM/PP/POE的硫化程度增大,硬度呈上升趋势,拉断伸长率、拉断永久变形和压缩永久变形呈减小趋势,定伸应力和拉伸强度先提高后降低;使用POE810,EPDM/PP/POE热塑性弹性体的100%定伸应力、拉伸强度和拉断永久变形较大,压缩永久变形较低,综合物理性能较好。     

硫化体系对EPDM硫化胶力学性能的影响

考察了4,4′-二硫代二吗啉（DTDM）,N,N′-间苯撑双马来酰亚胺（HVA-2）,甲基丙烯酸镁与硫黄和过氧化二异丙苯（DCP）复合硫化体系对三元乙丙橡胶力学性能的影响。结果表明,与纯硫黄硫化胶相比,DTDM/HVA-2/S复合硫化体系的EPDM硫化胶拉断伸长率及压缩永久变形均较小,而拉伸强度、定伸应力和硬度均较大,耐老化性能较好。甲基丙烯酸盐可明显提高硫黄、过氧化物硫化EPDM硫化胶的交联密度、拉伸强度、定伸应力和拉断伸长率。在甲基丙烯酸镁/炭黑/EPDM胶料中添加等量S i69改性白炭黑和石蜡油后,硫化胶各项力学性能都有明显提高,定伸应力和硬度保持较低水平,耐热空气老化性能有所改善。     

防焦剂E对EPDM硫化胶性能的影响

研究了防焦剂N-三氯甲基硫代-N-苯基-苯磺酰胺(简称:防焦剂E)用量对三元乙丙橡胶(EPDM)硫化胶的硫化特性、焦烧性能、填料网络及力学性能的影响。结果表明,随着防焦剂E用量的增大,EPDM硫化胶交联密度和定伸应力均增大,拉断伸长率和压缩永久变形均减小;焦烧时间延长,填料网络化程度增大,拉伸强度和撕裂强度略有下降,无喷霜现象发生。当防焦剂E用量为0.5份时,EPDM硫化胶综合性能较好。     

舰船用高性能密封橡胶研究(Ⅰ)硫化剂对氟橡胶硫化胶物理性能的影响

研究了硫化剂种类、用量对氟橡胶硫化胶的物理性能的影响。结果表明，硫化剂用量增加，硫化胶的硬度增大，扯断伸长率降低，拉伸强度先增大后降低，出现一个极大值，硫化胶的压缩永久变形先减少后增大，存在一极小值。     

聚烯烃弹性体/聚丙烯热塑性弹性体的制备及力学性能

以过氧化物为硫化剂,用动态硫化法制备了聚烯烃弹性体(POE)/聚丙烯(PP)热塑性弹性体,研究了硫化剂用量、填料种类和加工次数对体系力学性能的影响。结果表明,增加硫化剂用量可以提高体系的拉伸强度,降低拉伸永久变形和压缩永久变形。碳酸钙和滑石粉对POE/PP体系无明显增强作用,炭黑的增强作用较此二者明显一些,这三种填料加入后都会使体系的扯断伸长率降低而硬度增大。加入石蜡油会使体系的扯断伸长率和压缩永久变形增大、硬度和拉伸强度降低。加工次数对POE/PP体系的力学性能无明显影响,说明体系具有较好的重复加工性能。     

HMPIB硫化胶及IIR/HMPIB共混胶老化性能的研究

研究了HMPIB硫化胶及IIR/HMPIB硫化胶的力学性能及耐热空气老化、耐臭氧老化、耐酸腐蚀的性能。结果表明:HMPIB硫化胶有较高的拉伸强度、撕裂强度、扯断伸长率,但定伸应力较低,具有良好的耐臭氧老化和耐酸腐蚀性能;IIR中加入HMPIB,随着用量的增加,硫化胶的拉伸强度、撕裂强度、扯断伸长率增加,定伸应力降低。HMPIB能使IIR的耐臭氧、耐酸腐蚀性能得到提升,但不利于IIR的耐热性能。     

氧化铅硫化体系的配合对氯磺化聚乙烯橡胶性能的影响

采用对比试验法和正交试验法,研究了氧化铅硫化体系中配合剂的种类和用量对氯磺化聚乙烯橡胶性能的影响。结果表明,在CSM氧化铅硫化体系配合中,氧化铅和促进剂TRA是影响性能的主要因素;促进剂TRA并用促进剂DM后,可提高CSM硫化胶的拉伸强度、定伸应力;促进剂TRA与TT相比,CSM硫化胶拉伸强度和定伸应力大,永久变形小;氢化松香作为活性剂与松香、SA相比,CSM硫化胶拉断伸长率和撕裂强度高,拉伸强度和定伸应力较大;采用PbO/MgO并用硫化剂,CSM硫化胶硬度、拉伸强度和定伸应力提高,拉断伸长率和撕裂强度下降。     

过氧化物硫化体系中助交联剂对EPDM性能的影响

研究了助交联剂N,N'-间苯撑双马来酰亚胺(PDM)、三烯丙基异氰脲酸酯(TAIC)、硫磺(S)对三元乙丙橡胶(EPDM)过氧化物硫化特性、物理机械性能、耐老化性能及耐压缩变形性能的影响.研究表明,PDM、TAIC与过氧化二异丙苯(DCP)并用,降低了EPDM硫化胶的拉伸强度、撕裂强度和扯断伸长率,提高了定伸应力和硬度,并改善了压缩永久变形性能.而少量S与DCP并用可提高硫化胶物理机械性能,有效降低其压缩永久变形性能,S用量为0.2 phr时效果最佳.     

Compact Swelling in Bi1.4Pb0.6Sr2Ca2Cu3.6Oy During the Formation of High-Tc Superconducting Phase

Compact swelling in Pb-doped Bi-Sr-Ca-Cu-O superconductor has been studied by observing the effects of the size of calcined powders, volatilization of materials, and sintering of high- T _c (2223) powders. The bulk density increases at the early stage of sintering, for about 20 h, and then decreases. Densification occurs when the low- T _c (2212) phase and a liquid phase exist, whereas dedensification occurs with the formation of the 2223 phase regardless of the presence of the liquid. Gas evolution from specimens does not appear to be responsible for compact swelling. Compact swelling is explained by anisotropic growth of thin, platelike 2223 grains in random orientation. When 2223 grains grow in a preferred direction, compact swelling is suppressed.     

Synthetic routes to nanoscale BxCyNz architectures

B_xC_yN_z nanoscale materials, hybrids of h-BN and graphite, have been recently synthesised using various techniques. Here, we present the latest advances in the synthesis and characterisation of B-C-N nanotubes and nanofibres. In particular, we focus on layered BC₂N, BN, BC and CN_x systems, reviewing their production methods as well as their structural and electronic properties. These materials may find important applications in the fabrication of nanotransistors, robust nanocomposites, conducting polymers, storage components and field emission sources.     

Microwave Dielectric Properties of CaTiO3-CaAl1/2Nb1/2O3 Ceramics Doped with Li3NbO4

The microwave dielectric properties of CaTi_{1− x} (Al_1/2Nb_1/2) _x O₃ solid solutions (0.3 ≤ x ≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO₃. The substitution of Ti⁴⁺ by Al³⁺/Nb⁵⁺ improved the quality factor Q of the sintered specimens. A small addition of Li₃NbO₄ (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x = 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛ_r) of 48, a Q × f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τ_f) of −2 ppm/K. Li₃NbO₄ as a sintering additive had no harmful influence on τ_f of ceramics.     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO₄ and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu²⁺ and Ca²⁺, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu²⁺ complex near 240 nm. Dependence of the peak intensity on pH at various q values ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu²⁺ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu²⁺ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu²⁺-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation.     

Structure Evolution from Pb(Mg1/3Nb2/3)O3 to La(Mg2/3Nb1/3)O3

The crystal structure of lanthanum-modified lead magnesium niobates having composition (Pb_{1− x} La _x ) (Mg_{(1+ x )/3}-Nb_{(2− x )/3})O₃ with X = 0 to 1 was investigated by X-ray powder diffraction. It was found that the fundamental reflections from perovskite structure remain in the whole range of composition. The superlattice reflections from the A(B'_1/2-B"_1/2)O₃ ordered structure are also well preserved for La content greater than 50 at.%; however, a series of extra peaks of mixing indices appears, with intensities gradually enhanced with the increase of La content. For the complete substitution of Pb by La, a splitting of some reflections can be observed in the diffraction pattern. The results indicate that the crystal structure evolves continuously with the La content, from disordered cubic perovskite of space group Pm 3 m for X = 0, to ordered cubic perovskite of space group Fm 3 m for X = 0.5, distorted cubic perovskite of space group Pa 3 for 0.5 < X < 0.9, and finally to a rhombohedral perovskite, possibly belonging to the space group R 3 , for X ≥ 0.9. In the evolution of structure, a linear reduction of the lattice constant of the perovskite cell from 4.048 to 3.964 Å was observed.     

Characteristic Spherulitic Microstructure in Partial-Melt-Processed YBa2Cu3Ox/HfO2

The microstructure of partial-melt-processed YBa₂Cu₃O _x /HfO₂ has been studied by transmission electron microscopy. A characteristic spherulitic microstructure is formed in the system. A model for the growth mechanism has been proposed. The critical heterogeneous nucleation of the YBa₂Cu₃O _x phase appears to occur from the melt in an epitaxially controlled manner on CuO particles. Subsequent growth of YBa₂Cu₃O _x platelets from the nucleus region is repeatedly interrupted by the nucleation of hafnium-rich phases in the liquid at the solid/liquid interface in a manner that again appears to be epitaxially controlled and that promotes the splay of the c orientation of the YBaCuO grain.