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。     

OMMT/WF/PVC的耐热性能研究

添加插层蒙脱土(OMMT),制备了有机蒙脱土/木粉/聚氯乙烯(OMMT/WF/PVC)纳米复合材料,对OMMT/WF/PVC的耐热性能进行了测试和分析。空气和氮气两种氛围下的TG测试结果表明,加入OMMT后,一方面使木塑热分解温度降低了约11~25℃,随着OMMT含量提高,样品的热分解温度降低越多,热稳定性下降。同时使木塑复合材料初期降解速度降低,热失重速率变得缓慢;另一方面使总失重百分比增加约7%,而且在高于500℃时,OMMT对WF/PVC降解的促进作用更为明显,失重速率提高近1倍。这说明OMMT中烷基胺易于热降解,并促进了WF/PVC的热氧化降解。当OMMT质量含量少于1.5%时,木塑复合材料的维卡软化温度随OMMT加入而提高,OMMT加量继续增加时,维卡软化温度下降。     

四溴双酚-A阻燃体系在HIPS／OMMT复合材料中的阻燃性研究

采用熔融插层法分别制备高抗冲苯乙烯／有机蒙脱土（HIPS／OMMT）复合材料和四溴双酚-A／三氧化二锑（TBBPA—Sb2O3）体系阻燃的HIPS／OMMT复合材料,透射电镜研究表明,有机蒙脱土均匀地分散于HIPS基体当中,形成了插层复合结构,锥形量热仪和氧指数仪研究表明：与纯的HIPS相比,HIPS／OMMT复合材料的阻燃性和抑烟性有所提高,但阻燃性的提高幅度较有限：与仅添加OMMT时的HIPS／OMMT复合材料相比,添加相同量OMMT时TBBPA—Sb2O3体系阻燃的HIPS／OMMT复合材料的热释放速率（HRR）和热释放速率峰值（PHRR）均有所降低,氧指数有所增加,且随TBBPA—Sb2O3阻燃剂添加量的增加阻燃性能的提高越明显,但TBBPA—Sb2O3的加入会导致聚合物燃烧过程生烟速率和生烟量的显著增加．因此此类阻燃剂的加入量不宜过高。     

SEBS／蒙脱土复合材料结构与阻燃性能的研究

根据蒙脱土（MMT）特殊的片层结构,采用熔融插层法制备热塑性弹性体SEBS／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复合材料的微观结构。使用锥形量热仪评价复合材料的燃烧性能。结果表明,有机蒙脱土（OMMT）片层的间距为1．948nm,SEBS／5％OMMT体系的片层间距为4．307nm,说明聚合物SEBS插入有机蒙脱土片层之间。SEBS／OMMT复合材料具有较低的热释放速率和质量损失速率,且随着OMMT添加量的增加,其热释放速率峰值降低愈明显。通过对复合材料的阻燃性能和微观结构的分析,探讨了其阻燃机理。     

原位聚合法PS／蒙脱土复合材料燃烧性能的研究

采用原位聚合法分别制备了聚苯乙烯／有机蒙脱土（PS／OMMT）复合材料和聚苯乙烯／无机蒙脱土（PS／MMT）复合材料、用锥形量热仪测量测试了复合材料的燃烧性能，结果发现复合材料的热释放速率、质量损失速率、生烟速率等均显著降低，说明复合材料具有阻燃性。通过分析材料的燃烧性能和燃烧残余物，探讨了其可能的阻燃机理。还考察了原位聚合法对聚合转化率的影响。研究表明原位聚合法制备的PS／蒙脱土复合材料是一种阻燃效能高、环境友好且实际可行的阻燃体系。     

纳米有机蒙脱土改性SEBS/PP共混物的研究

通过熔融插层的方法将纳米有机蒙脱土（OMMT）与氢化苯乙烯-丁二烯-苯乙烯嵌段共聚物（SEBS）／聚丙烯（PP）共混制备得到SEBS／PP／OMMT复合材料。X射线衍射实验证明,复合材料SEBS／PP／OMMT5％、SEBS／PP／OMMT10％片层间距分别为4．17nm,3．91nm,说明聚合物插层进入OMMT片层之间,制备得到SEBS／PP／OMMT插层复合材料。采用锥形量热仪测试材料的阻燃性能,燃烧测试结果表明,SEBS／PP／OMMT复合材料具有比较低的热释放速率和质量损失速率,并且随着OMMT添加量增加,复合材料的热释放速率、峰值热释放速率和总热释放先显著降低最后趋于一个稳定值。综合力学测试结果表明,当有机蒙脱土质量分数为5％～10％时,该复合材料的综合性能最好。     

PP/纳米蒙脱土复合材料炭层结构对阻燃性能的影响

采用熔融插层法制备了不同纳米蒙脱土含量的聚丙烯(PP)/有机蒙脱土(OMMT)和PP/无机蒙脱土(MMT)复合材料,且评价了复合材料的阻燃性能:采用数码相机、扫描电子显微镜观察了燃烧残余物结构.加入OMMT可显著提高PP/OM MT的阻燃性能:纯PP的热释放速率(HRR)峰值为1 337.59 kW/m2;w(OMMT...     

HIPS/OMMT复合材料阻燃性能的研究

采用挤出工艺、熔融插层法制备了高抗冲聚苯乙烯／有机蒙脱土（HIPS／OMMT）复合材料。通过X射线衍射仪和扫描电镜研究蒙脱土和复合材料的微观结构，发现OMMT的层间距由改性前的1.52nm增大到2．25nm，复合材料中的OMMT片层被剥离开来，与HIPS基体形成了剥离型的复合材料。用基于耗氧原理的锥形量热仪测试并分析HIPS／OM—MT复合材料的阻燃性能。结果表明，与纯的HIPS相比，HIPS／OMMT复合材料的热释放速率及其峰值、质量损失速率均明显降低，且随OMMT添加量的增加，复合材料的热释放速率峰值降低愈明显；通过对复合材料的阻燃性能和微观结构的分析，探讨了其阻燃机理。     

蒙脱土/SBR纳米复合材料阻燃性能的研究

采用熔融插层法制备蒙脱土／SBR纳米复合材料，并研究其阻燃性能。结果表明，SBR大分子不能有效插入钠基蒙脱土（Na—MMT）片层间，而能有效插入有机蒙脱土（OMMT）片层间，形成插层型纳米复合材料；将OMMT与高抗冲聚苯乙烯（HIPS）制成阻燃母粒能进一步提高SBR的插层效果。OMMT可以明显改善复合材料的阻燃和抑烟性能，随着OMMT用量的增大，复合材料的热释放速率、峰值热释放速率、平均热释放速率、总热释放和总生烟量先明显降低然后趋于稳定；HIPS-OMMT阻燃母粒可以明显改善复合材料阻燃性能，但对抑烟性能的改善效果不如OMMT。     

HIPS/OMMT复合材料炭渣结构对阻燃性能的影响

采用熔融插层法制备了高抗冲聚苯乙烯/有机蒙脱土(HIPS/OMMT)和高抗冲聚苯乙烯/蒙脱土(HIPS/MMT)复合材料,并通过锥形量热仪评价了复合材料的阻燃性能;采用数码相机、扫描电镜(SEM)观察了燃烧残余物结构,对残余物结构进行了热重(TGA)分析。结果表明:OMMT的加入显著提高了复合材料以热释放速率表征的阻燃性能,而HIPS/MMT复合材料的阻燃性能提高不明显;HIPS/OMMT纳米复合材料燃烧热释放速率峰值时形成了皮窝复合炭渣结构,皮层组分主要为硅酸盐及部分难分解的碳质物质,热稳定性较高,窝层起膨胀炭层的作用,二者共同起阻燃作用。     

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.     

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.     

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.     

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.