聚丙烯/接枝物/蒙脱土纳米复合材料的制备

采用熔融插层法制备聚丙烯／接枝物（PP－g－MAH）／有机蒙脱土（org-mont）纳米复合材料，用X射线衍射法（XRD）检测复合材料层间距的变化，用示差扫描量热法（DSC）研究其非等结晶动力学，并考察了纳米复合材料的力学性能。结果发现，非极性PP大分子链很难直接插入蒙脱土片层，引入适量的接枝物是制备聚丙烯基纳米复合材料的关键。适当用量的蒙脱土和接枝物可使PP的结晶温度和结晶速率提高，分别在10％、20％时出现最大值。随接枝物用量的增加，纳米复合材料拉伸强度先增加后减小，10％时最大，比纯PP增加了14％，“V”缺口冲击强度和纯PP相近。可以得出，org-mont含量为2％，接枝物含量为10％时，纳米复合材料的综合性能最佳。     

高密度聚乙烯／蒙脱土纳米复合材料的制备与性能研究

采用马来酸酐接枝乙烯醋酸乙烯酯（EVA-g-MAH）和马来酸酐接枝低密度聚乙烯（PE-LD-g-MAH）为相容剂，制备了高密度聚乙烯傣脱土（PE-HD／MMT）纳米复合材料。用X射线衍射和扫描电镜对有机蒙脱土和PE-HD／MMT复合材料的结构进行了表征，研究了蒙脱土和相容剂含量对制备的纳米复合材料力学性能及热性能的影响。结果表明，相容剂的加入有利于插层。MMT在复合材料中呈纳米级分散。其层间距可由2．10nm增大至3．85nm。MMT含量为3％（质量分数，下同）、EVA-g-MAH含量为15％时，复合材料的综合力学性能最好，冲击强度和拉伸强度分别较PE-HD提高43．7％和5.8％。     

PVC／OMMT／WF纳米复合材料性能研究

对蒙脱土进行有机改性制得有机蒙脱土（OMMT），并制备了聚氯乙烯侑机蒙脱土／木粉（PVC／OMMT／WF）纳米复合材料。采用硅烷偶联剂对木粉表面进行改性，有效提高了聚氯乙烯／木粉（PVC／WF）复合材料的力学性能，其中加入1．5％（质量含量，下同）硅烷偶联剂可使复合材料的冲击强度和拉伸强度分别提高14．8％和18．5％。研究了OMMT的加入对木粉改性前后的PVC／WF复合材料力学性能、耐热性能及阻燃性能的影响，结果表明，木粉未经改性时，OMMT加入无助于PVC／OMMT／WF复合材料力学性能的提高；木粉用硅烷偶联剂改性后，添加少量的OMMT，可使PVC／OMMT／WF复合材料的冲击强度和拉伸强度明显提高。研究表明，添加OMMT可显著延迟复合材料的点燃时间，燃烧残余率也明显增加，OMMT是PVC／WF复合材料的高效阻燃剂。     

PP／PPMA／Org—MMT复合材料的制备与性能研究

采用熔融插层法制备PP／PPMA／Org-MMT复合材料，考察接枝物含量、不同聚丙烯、不同接枝率接枝物以及不同成型工艺对PP／PPMA／Org-MMT复合材料的制备与力学性能的影响。结果表明，采用PP（F401）、高接枝率接枝物和模压工艺可获得较好的插层效果。接枝物含量为10％时，PP／PPMA／Org-MMT复合材料的拉伸强度达到最大值。     

PP-g-GMA-St／蒙脱土／碳酸钙纳米复合材料的制备和表征

利用钙基蒙脱土的离子交换合成纳米碳酸钙,制得分散均匀的蒙脱土/碳酸钙复合粒子。采用反应挤出对极性很弱的PP进行接枝改性,得到接枝物PP-g-GMA-St,其中甲基丙烯酸缩水甘油酯(GMA)的接枝率为0.7%;然后将其按不同配比与蒙脱土/碳酸钙复合粒子熔融共混,X射线衍射分析显示,蒙脱土的层间距达到4.1nm左右;透射电镜分析也表明碳酸钙和蒙脱土分散得比较均匀。并且,在蒙脱土/碳酸钙复合粒子为3%(质量分数)时,复合材料的拉伸强度和冲击强度分别达到最大值(40.26MPa和30.65J/m),比纯PP有了较大幅度的提高。     

PE-HD／煤粉／OMMT复合阻燃材料制备及性能研究

用有机改性蒙脱土（OMMT）含量为30％（质量分数，下同）的OMMT母料及超细煤粉，通过双螺杆熔融挤出法制得了组成不同的系列PE-HD／煤粉／OMMT复合阻燃材料。用X射线衍射分析、极限氧指数测定等对其插层结构及阻燃性能进行了表征。结果表明，PE-HD／煤粉／OMMT复合材料中OMMT呈现插层型结构，煤粉的加入可以提高复合材料的阻燃性。当煤粉和OMMT含量分别为15％和4．5％时，PE-HD／煤分／OMMT复合材料极限氧指数最高达到21％。热重分析及扫描电子显微镜分析表明，PE-HD／煤粉／OMMT复合阻燃材料阻燃性能的提高归因于大量致密层状炭结构的形成。     

聚丙烯／有机蒙脱土复合材料的制备、结构及性能

以改性聚丙烯作增容剂，用熔融插层法制备了聚丙烯／有机蒙脱土复合材料，研究了有机蒙脱土对复合材料力学性能的影响，并用X射线衍射研究了复合材料的结构。结果表明：增容剂增加了聚丙烯与蒙脱土片层之间的作用力，使蒙脱土片层间距增大，在聚丙烯基体中分散更好，因而使聚丙烯／有机蒙脱土复合材料的缺口冲击强度大幅度提高，当蒙脱土含量达5％时，缺口冲击强度提高120％，并且拉伸性能下降不大，约下降5％，其中有机蒙脱土TJ4的增韧效果最好。     

NBR／PP／蒙脱土纳米复合体系的制备和性能研究

以丙烯酸接枝聚丙烯为增容剂,采用熔融复合方法制备出NBR/PP/蒙脱土纳米复合体系。对丙烯酸熔触接枝PP的增容体系进行了深入得研究,其次还对未处理的MMT和处理过的纳米MMT对共混物结构和性能得影响进行了讨论。研究表明,在使用丙烯酸接枝PP对NBR/PP体系得增容性较好,通过熔融共混得方法制备了NBR/PP/蒙脱土纳米复合材料。对复合材料的介电性能,力学性能和相容性进行了研究,用红外光谱和扫描电镜表征该复合材料的结构。结果表明:丙烯酸接枝聚丙烯能够很好的改善PP和NBR、MMT的相容性,当十六烷基三甲基溴化铵(CTAB)改性的蒙脱土用量为5Wt%、PP-g-AA用量为10Wt%时,NBR/PP/蒙脱土纳米复合材料的断裂伸长率提高20%,拉伸强度提高10%,撕裂强度提高80%。     

聚丙烯/蒙脱土纳米复合材料的制备与性能研究

采用十八烷基三甲基氯化铵（OTAC）和十二烷基二甲基卞基氯化铵（DDBAC）改性蒙脱土,以聚丙烯接枝马来酸酐（PP-g-MAH）作相容剂,通过熔融插层法制备了聚丙烯/蒙脱土纳米复合材料（PP/OMMT）.结果表明,PP-g-MAH能有效地改善PP与OMMT的相容性,当OTAC改性的蒙脱土（OMMT-O）用量为5wt%、PP-g-MAH用量为10wt%时,PP/PP-g-MAH/OMMT-O纳米复合材料的冲击强度为5.4 KJ/m^2,比纯PP提高了80%,极限氧指数（LOI）由PP的18提高到23.X射线衍射（XRD）测试表明,PP已经插层进入到蒙脱土片层中,部分蒙脱土产生了剥离.     

PP／蒙脱土纳米复合材料的性能研究

采用熔融插层法制备出了聚丙烯（PP）／蒙脱土（OMMT）纳米复合材料,研究了蒙脱土的加入量对PP基体力学性能和阻燃性能的影响。结果表明,蒙脱土的加入有助于提高PP基体的力学性能和阻燃性能。     

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.     

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.     

Dielectric-State Analysis in Solid-Solution Pb(Yb1/2Ta1/2)O3–Pb(Lu1/2Nb1/2)O3

The structure and temperature dependence of complex lead perovskite dielectrics were investigated for the system (1 − x )Pb(Yb_1/2Ta_1/2)O₃– x Pb(Lu_1/2Nb_1/2)O₃. Superlattice reflections for the compositions 0.8 < x < 1.0 were observed by X-ray diffractometry, and the temperature-composition dielectric-state diagram was determined. In the present study, the disordered middle composition, with 0.2 < x < 0.8, showed a diffuse paraelectric–ferroelectric phase transition, whereas the ordered end compositions, with 0 ≤ x < 0.2 and 0.8 < x ≤ 1.0, revealed successive sharp paraelectric–antiferroelectric and weak antiferroelectric–ferroelectric phase transitions. The dielectric state was confirmed by examining the variation of polarization ( P ) with electric field ( E ).     

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.     

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.