PA6/蒙脱土熔融插层复合材料结构与性能分析

通过熔融共混法插层复合制备了聚酰胺(PN)6／蒙脱土纳米复合材料，测试了力学性能并对不同蒙脱土含量的PA 6／蒙脱土纳米复合材料进行了对比。实验表明，通过熔融插层可使PN 6基体插层于蒙脱土中，所得到的复合材料的性能较PN 6有很大提高。蒙脱土特殊的层状结构使得利用熔融共混在机械力的作用下插层到纳米级复合材料成为可能。     

PA6/蒙脱土复合材料结构与性能的研究

采用熔融插层法制备了尼龙6(PA6)／蒙脱土插层复合材料,通过X射线衍射仪、透射电镜等表征手段研究了该复合材料的微观结构,采用锥形量热仪、拉伸测试仪等测试了材料的阻燃性能、力学性能以及热变形温度。结果表明,有机蒙脱土片层的间距扩大了,PA6插入了有机蒙脱土片层之间。PA6／蒙脱土插层复合材料具有较低的热释放速率和质量损失,并且当有机蒙脱土质量分数为5％～7％时,该复合材料的综合性能最好。     

有机插层剂对聚酰胺6／MMT纳米复合材料制备的影响研究

以烷基胺、季铵盐和氨基酸作为有机插层剂与蒙脱土片层进行阳离子交换，制备出层间距不同的有机蒙脱土。采用熔融插层法和原位聚合法分别制备聚酰胺（R％）／蒙脱土（MMT）纳米复合材料，并利用XRD、FT-IR、TEM对有机蒙脱土及纳米复合材料进行结构表征。研究结果表明：用烷基胺、季铵盐和氨基酸有机插层剂改性的蒙脱土层间距由原来的1．25nm分别增大到3．21nm、3．99nm和1．82m；季铵盐有机插层剂更适用于熔融插层法制备PA6／MMT纳米复合材料，而氨基酸有机插层剂更适用于原位聚合法制备PA6／MMT纳米复合材料。     

蒙脱土对无卤阻燃PP/PA6复合材料的影响

将PA6、PP、阻燃剂、蒙脱土通过直接熔融共混制备无卤阻燃PP/PA6复合材料。通过水平燃烧、热重分析、氧指数、力学性能测试了蒙脱土在复合材料中的含量对PP/PA6复合材料性能的影响。结果表明,随着蒙脱土在复合材料中含量的增大,其阻燃性能和力学性能都得到了提高,当蒙脱土用量为2phr时,复合材料的综合性能达到最佳。     

阴离子开环聚合制备尼龙6/蒙脱土复合材料及其性能研究

以十六烷基三甲基溴化铵为有机插层剂对无机蒙脱土进行处理制得有机蒙脱土（OMMT），然后采用阴离子开环聚合，制备了尼龙6／蒙脱土复合材料。用FT-IR、TG和XRD对有机蒙脱土的插层情况进行了表征。结果表明，插层剂已插入蒙脱土片层中；当OMMT用量为2％时，复合材料的熔点最高，结晶度最大，力学性能最好。     

三元乙丙橡胶/蒙脱土纳米复合材料的制备与性能研究

采用熔融插层的方法制备了三元乙丙橡胶(EPDM)／蒙脱土纳米复合材料。X-射线衍射和透射电镜的研究结果表明，该材料的结构为插层型纳米分散结构。研究了蒙脱土用量对该复合材料的力学性能、光学性能和热性能的影响。实验结果表明，该纳米复合材料具有优良的力学性能。当蒙脱土的用量为15份时，该材料的拉伸强度和拉断伸长率分别为19．8MPa和540％。由过氧化物硫化剂2，5-二甲基-2，5-二叔丁基过氧己烷制备的EPDM／蒙脱土纳米复合材料是半透明的，蒙脱土用量对材料的透光率影响较小，蒙脱土用量几乎不影响材料的硫化性能。此外，材料的玻璃化转变温度和热分解温度也由于蒙脱土在基体中的纳米分散和基体与填料相互作用的增强而明显升高。     

原位乳液插层法制备丁腈橡胶/蒙脱土纳米复合材料的研究

结合乳液插层蒙脱土的特点，利用原位插层制备了丁腈橡胶（NBR）／改性蒙脱土（HOMMT）纳米复合材料。通过X-射线衍射（XRD）及透射电镜（TEM）证实和分析了蒙脱土的纳米分散相结构。物理性能的研究表明，所制备的复合材料体现了纳米材料的一些特点，填充少量蒙脱土，复合材料的物理机械性能即达到一个较高的水平。     

SMA/MMT纳米复合材料的制备

采用原位插层法制备了苯乙烯-马来酸酐共聚物／蒙脱土（SMA／MMT）纳米复合材料,采用X射线衍射研究了苯乙烯与马来酸酐的配比、蒙脱土用量、引发剂浓度、溶剂类型、聚合温度等因素对插层效果的影响。结果表明,当MMT的用量为3％（质量分数＋下同）时,可制得剥离型的SMA／MMT纳米复合材料;当苯乙烯与马来酸酐的质量比为1：1,MMT用量为15％、引发剂用量为1％、以丁酮为溶剂、聚合温度为90℃时,可制备出部分剥离型的SMA／MMT纳米复合材料。     

新型叶片密炼机对HDPE/OMMT纳米复合材料结构与性能的影响

利用基于体积拉伸流变的新型叶片密炼机制备高密度聚乙烯(HDPE)/有机改性蒙脱土(OMMT)纳米复合材料。研究拉伸流场作用下,蒙脱土含量对复合材料微观相形态、热学、流变和力学性能的影响。结果表明,拉伸流场作用下,蒙脱土含量较大(5 phr)时,其也可以在HDPE基体中理想分散,形成插层或/和剥离的结构;复合材料的熔点(T_m)和耐热性能均有较大提高,结晶温度T_c几乎不变,结晶度呈先增加后降低的趋势;低频区复合材料的储能模量G'、损耗模量G″和复数黏度η*均随蒙脱土含量增加而增大;拉伸强度和断裂伸长率先增加后降低,蒙脱土含量在2~3 phr之间时有最大值,冲击强度整体呈下降趋势。     

母料法制备尼龙6/蒙脱土纳米复合材料及其性能

以高流动性聚丙烯接枝马来酸酐(PP-g-MAH)为载体树脂,制备了接枝聚丙烯/有机蒙脱土插层母料,并以此为增强剂制备了PA6/接枝聚丙烯/有机蒙脱土纳米复合材料,研究了有机蒙脱土(OMMT)含量对复合体系力学性能和耐热性能的影响。通过X射线衍射(XRD)、透射电子显微镜(TEM)研究了复合材料的微观结构。结果表明:在所制备的插层母料中,PP-g-MAH大分子能够部分插入OMMT的晶片层间,其层间距有所增大。母料法制备的PA6/接枝聚丙烯/有机蒙脱土纳米复合材料的力学性能得到了较大提高,当OMMT含量为6%时,拉伸强度和弯曲强度分别比PA6/PP-g-MAH共混体系提高了24%和25.1%。     

Polymorphism of LiGa5O8 and of LiGa5O8-MgGa2O4Solid Solutions

High-temperature X-ray diffraction and differential thermal analyses showed that LiGa₅O₈ exists in two polymorphs related by the first-order transition at 1138°±3°C of the low-temperature simple-cubic form, space group (probably) O⁷, to the high-temperature spinel (fcc) form, space group O _h ⁷. The transition is rapid, and the high-temperature form in pure LiGa₅O₈ could not be quenched to room temperature under the conditions used. However, the high-temperature polymorph can be quenched under equilibrium conditions when 40 mol% or more MgGa₂O₄ is present. The subsolidus equilibrium relations in the system MgGa₂O₄-LiGa₅O₈ are discussed.     

Magnetoresistance of CuxCo1-xFe2O4 Ferrites

Magnetoresistance measurements (Δ/R) were carried out on Cu _x Co_{1- x} Fe₂O₄ samples with x =1, 0.75, 0.50, 0.25 and cobalt ferrite in the range of magnetic intensity (H) from 1.0 to 4.5 kG. Linear plots were obtained between log (Δ/R) and log H for all compositions except that of cobalt ferrite. The values of n at x =0.5 do not agree with the results of some authors. The discrepancy may be attributed to the value of magnetic field intensity at which such measurements were carried out. The similarity of features of n and μ_D with composition leads us to believe that the magnetoresistance may arise from the scattering of conduction electrons by localized electrons involving the s-d exchange interaction.     

Activation and characterization of Fe---Mn---SO4/ZrO2 catalysts

Changes in Fe---Mn---SO₄²⁻/ZrO₂ catalyst formulations during activation have been observed. In air or an inert gas, the added salt, such as iron and/or manganese nitrate, decomposes over a temperature range of about 200–400°C to produce nitric oxide, oxygen and iron and/or manganese oxide. The crystallization of zirconia occurs at 450°C; when the sample contains sulfate the exothermic event occurs at a temperature that is about 200°C higher. Heating in the presence of hydrogen causes the evolution of nitric oxide to occur over a narrow temperature range and at a lower temperature than when the sample is heated in helium or air. It appears that the nitrate ions associated with Fe, Mn and Zr decompose to produce nitric oxide, and presumably water, at different temperatures when the sample is heated in the presence of hydrogen. Heating samples of sulfated zirconia containing iron and/or manganese in hydrogen causes sulfur evolution at a lower temperature, and a significant fraction of it in the form of H₂S.     

The structures of VOx/MOx and alkali-VOx/MOx catalysts and their catalytic performances for soot combustion

Vanadium oxides supported on γ-Al₂O₃, SiO₂, TiO₂, and ZrO₂ were studied on their molecular structures and reactive performances for soot combustion. To investigate the effect of different alkali metals on the structures and reactivities of supported-vanadium oxide catalysts, they were doped into the V₄/TiO₂ catalyst which had the best intrinsic activity for soot combustion in the selected supported vanadium oxide catalysts. The experimental results demonstrated that the catalytic properties of these catalysts depended on the vanadium loading amount, support nature, and the presence or the absence of alkali metals. The spectroscopic analysis (FT-IR and UV–vis) and H₂-TPR results revealed that the higher activity of alkali-promoted vanadium oxide catalysts could be related to the ability of alkali metal promoting the redox cycle of the active vanadyl species. TG results showed that adding alkali to V_m/TiO₂ catalyst was beneficial to lowering their melting points. Low melting points could ensure the good surface atom migration ability, which would improve the contact between the catalyst and soot. Due to the alkali metal components promoting the redox ability and the mobility of the catalysts, alkali-modified vanadium oxide catalysts could remarkably improve their catalytic activities for soot combustion. The catalytic activity order for soot combustion followed Li > Na > K > Rb > Cs in the catalyst system of alkali-V₄/TiO₂, and the reason why it followed this sequence was discussed.     

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.     

Sintering of Si3N4-Y2O3-Al2O3

Sintering kinetics of the system Si₃N4-Y2O₃-Al₂O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si₃N₄ were studied with additions of 4 to 17 wt% Y₂O₃ and 4 wt% A1₂O₃. Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si₃N₄ and glass or β '-Si₃N₄, α '-Si₃N₄, and glass. The compositions and amounts of the residual glassy phases are estimated.     

Oxidation of Ba2YCu3Ox at High Po2

Dense large-grain ceramic samples of Ba₂YCu₂O_x have been oxidized at 400° to 500°C in 10 to 30 MPa of oxygen for 1 to 10 d. The high-pressure treatment has increased the equilibrium content x slightly above 7 but there is no concomitant increase in T_c. At x = 7.03 the superconducting transition, measured by ac susceptibility, has an onset temperature of ∼91 K and ΔT∼4 K and no change in lattice parameter is observed. High oxygen pressure increases the rate of oxidation.     

Effects of Calcium Substitution on the Structural and Microwave Dielectric Characteristics of [(Pb1−xCax)1/2La1/2](Mg1/2Nb1/2)O3 Ceramics

The effects of calcium substitution on the structural and microwave dielectric characteristics of [(Pb_{1− x} Ca _x )_1/2La_1/2](Mg_1/2Nb_1/2)O₃ ceramics (with x = 0.01–0.5) were investigated. All the materials were observed to have an ordered A(B_1/2^'B_1/2^")O₃-type perovskite structure; however, the space group of the structure changed from Fm 3 m to Pa 3 as the calcium content increased to x = 0.1, and then from Pa 3 to R 3¯ at the x = 0.5 composition. During the structural evolution, the lattice parameter of the perovskite cell decreased linearly, and the dielectric constant ( k ) also decreased, from k = 80 to k = 38. However, the product of the quality factor and the resonant frequency ( Q × f ) increased from 50 000 GHz to 90 000 GHz as the calcium content increased. Also, the temperature coefficient of resonant frequency (τ_ƒ) gradually changed from 120 ppm/°C to −40 ppm/°C as the calcium content increased. At the x = 0.3 composition, a combination of properties— k ∼ 50, Q × f ∼ 86 000 GHz, and τ_ƒ∼ 0 ppm/°C—can be obtained.