粘土/炭黑/NR纳米复合材料的性能研究

在乳液插层法制备的粘土／NR纳米复合材料中加入炭黑，制得粘土／炭黑／NR纳米复合材料，并对其微观结构和性能进行研究。结果表明，炭黑的加入并没有影响粘土在NR基体中的分散状态，粘士炭黑和在NR基体中均达到纳米级分散；炭黑的加入削弱了粘土所形成填料网络的强度，从而改善了复合材料的加工性能；与粘土／NR纳米复合材料相比，粘土／炭黑／NR纳米复合材料的综合物理性能较好。     

粘土/橡胶纳米复合材料老化性能研究

研究粘土 /SBR及粘土 /NR纳米复合材料的耐热氧老化和耐臭氧老化性能 ,并考察粘土 /SBR纳米复合材料的热失重和气体阻隔性。结果表明 ,粘土 /SBR纳米复合材料的耐热氧老化和耐臭氧老化性能均优于炭黑 /SBR复合材料 ;粘土 /NR纳米复合材料的耐热氧老化性能略优于炭黑 /NR复合材料 ,耐臭氧老化性能与炭黑 /NR复合材料相差不大 ;均匀分散的纳米粘土可提高橡胶的热稳定性和气体阻隔性 ,减缓氧及臭氧在橡胶中的扩散 ,降低橡胶分子链受攻击的几率 ,有利于提高橡胶耐热氧老化和耐臭氧老化性能     

改性石墨烯/粘土/天然橡胶纳米复合材料的结构与性能

大量研究表明,纳米填料的表面效应、大的比表面积以及纳米粒子本身对基体的强界面效应对橡胶纳米复合材料性能的提升具有极大的帮助。本研究以天然橡胶(NR)为基体材料,采用乳液法制备石墨烯/粘土/NR纳米复合材料。讨论了石墨烯、粘土的用量对复合材料的物理机械性能的影响。结果表明,当粘土用量为3.0 phr时,随着石墨烯添加量的增加,石墨烯/粘土/NR纳米复合材料的力学性能和耐磨性先升高,然后略有下降。当石墨烯添加量为1.0 phr时,复合材料的拉伸强度提高了33.3%,而阿克隆磨耗体积下降了22.7%。     

天然橡胶/顺丁橡胶复合材料抗裂口增长性能影响因素研究

研究炭黑的种类及用量、硫化体系、硫化条件和天然橡胶(NR)/顺丁橡胶(BR)并用比等因素对NR/BR复合材料抗裂口增长性能的影响。结果表明:当炭黑用量在一定范围内时,炭黑的种类和用量影响NR/BR复合材料的抗裂口增长性能;随着促进剂NS用量的增大或硫化时间的延长,NR/BR复合材料抗裂口增长性能变差;适当提高硫化温度或增大硫黄用量,NR/BR复合材料的抗裂口增长性能提高;NR/BR并用比、炭黑分布或硫化体系不同时,NR/BR复合材料的抗裂口增长性能都有差异性。     

环氧化天然橡胶对天然橡胶/炭黑复合材料的改性作用

采用环氧化天然橡胶(ENR)作为界面改性剂,研究其用量对天然橡胶(NR)/炭黑复合材料加工性能、动态力学性能和物理性能的影响。结果表明:少量ENR可以改善NR/炭黑复合材料的加工性能,改善炭黑粒子在橡胶基体中的分散,提高结合胶质量分数,同时改善硫化胶的动态力学性能、物理性能和耐老化性能。当改性剂ENR用量为3~4.5份时,NR/炭黑复合材料的综合性能最佳。橡胶加工分析和动态力学分析结果表明,ENR能够显著提高NR/炭黑复合材料的抗湿滑性能,但滚动阻力略有增大。     

粘土/天然橡胶纳米复合材料在矿用轮胎胎面胶中的应用

采用乳液聚合法制备粘土/天然橡胶(NR)纳米复合材料,并对其结构、性能及在矿用全钢载重子午线轮胎胎面胶中的应用进行研究。结果表明:粘土在NR基体中的分散性较好,粘土/NR纳米复合材料的Payne效应较强;与纯炭黑填充NR胶料相比,粘土/NR纳米复合材料的硬度、定伸应力和拉伸强度增大,耐磨性能下降,压缩生热升高,抗切割和抗屈挠裂纹性能提高;成品轮胎的耐久性能达到国家标准要求,抗崩花掉块性能明显提高。     

紫炭黑/天然橡胶复合材料的制备及性能研究

以黄原胶为辅助剂,采用湿法制备紫炭黑/天然橡胶(NR)复合颗粒胶,研究了紫炭黑用量对紫炭黑/NR复合材料硫化特性、力学性能、加工性能和动态性能的影响。结果表明,紫炭黑/NR颗粒胶粒径大小均一,紫炭黑未渗出或散开,紫炭黑和天然胶乳共凝效果较好;紫炭黑的添加可以改善复合材料的物理性能,当紫炭黑用量为20份时,复合材料综合性能较好;橡胶加工分析(RPA)表明,紫炭黑的加入使复合材料的tanδ增加,弹性模量降低,加工性能得到改善。     

配方因素对天然橡胶胶料动静刚度比的影响

研究含胶率、补强体系和硫化体系对天然橡胶(NR)胶料动静刚度比的影响。结果表明:含胶率越大,胶料的动静刚度比越小;与炭黑N774胶料相比,小粒径、大比表面积炭黑N330胶料的硬度和动静刚度比较大,炭黑用量大的胶料动静刚度比较大;随着硫化时间的延长,普通硫黄硫化体系胶料的动静刚度比增大,半有效硫化体系胶料的动静刚度比基本不变。     

NR/BR复合材料抗裂口增长性能影响因素研究

摘要：研究了填料种类和用量、硫化体系、硫化条件和NR与BR的并用比等因素对NR/BR复合材料抗裂口增长性能的影响。结果表明：对于NR/BR复合材料,炭黑用量在一定范围内时,炭黑用量和种类影响硫化胶的抗裂口增长性能;随着促进剂用量提高或延长硫化时间,抗裂口增长性能变差;而适当提高硫化温度或硫磺用量,NR/BR复合材料的抗裂口增长性能提高;NR/BR并用比、炭黑分布或硫化体系不同时,NR/BR复合材料的耐裂口增长性能都有差异性。     

粘土/NBR纳米复合材料的性能研究*

利用独创的粘土晶层／胶乳纳米互穿技术获得了粘土／ＮＢＲ纳米复合材料。通过Ｘ光衍射、透射电子显微镜证实和分析了其纳米分散相结构。物理性能的研究结果表明,当粘土用量较小时,复合材料的拉伸强度便达到了一个较高的水平,且远高于炭黑Ｎ３３０补强胶料的水平。复合材料的定伸应力随粘土用量的增大而直线上升,耐磨性迅速提高。当粘土用量达到２０份时,复合材料的气密性优于用ＣＩＲ制造的无内胎子午线轮胎气密层胶料。     

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.