不同形态的CaCO_3对聚丙烯的泡孔结构和力学性能的影响

通过熔融共混法制备聚丙烯/马来酸酐接枝聚丙烯/碳酸钙(PP/PP-g-MAH/CaCO3)复合材料母粒,利用"二次开模"法注塑成型制得PP/PP-g-MAH/CaCO3复合微孔发泡材料。通过对不同形态的CaCO3粒子对聚丙烯纳米复合材料发泡行为的影响研究,讨论了CaCO3粒子在聚合物微孔发泡中的作用机理,分析了CaCO3粒子对聚丙烯的力学性能及泡孔结构的影响规律。结果表明,不同形态的CaCO3粒子的加入都能够显著降低聚丙烯的泡孔直径和增加泡孔密度;CaCO3粒子使聚丙烯的缺口冲击强度下降;发泡材料的拉伸强度低于未发泡材料的拉伸强度。     

发泡倍率对聚丙烯/纳米二氧化硅复合微孔发泡材料结构与性能的影响

采用双螺杆熔融共混法制备聚丙烯/纳米二氧化硅复合材料。用化学发泡法注塑成型制备聚丙烯/纳米二氧化硅复合微孔发泡材料。研究了发泡倍率对微孔发泡材料结构与性能的影响。结果表明:泡孔平均直径随着发泡倍率的增加先减小后增大,泡孔密度随着发泡倍率的增加先增加后减少;微孔发泡材料的缺口冲击强度随着发泡倍率的增加而增加,拉伸强度随着发泡倍率的增加而线性降低。     

聚丙烯/纳米蒙脱土/高熔体强度聚丙烯复合材料的发泡行为水

利用线性聚丙烯(PP)和有机化处理的纳米蒙脱土(OMMT)在双螺杆挤出机上用熔融插层法制备PP/纳米OMMT 复合材料.通过在PP/纳米OMMT复合材料中加入少量的高熔体强度聚丙烯(HMS-PP),以模压发泡法制备了PP/0MMT和PP/HMs-PP/0MMT复合材料的发泡制品.利用扫描电镜研究了高熔体强度聚丙烯对PP/纳米0MMT复合材料发泡行为的影响.研究结果表明:HMS-PP的加入明显改善了PP的发泡性能,所得的泡孔密度增大,泡孔的合并现象明显改善.     

注射发泡成型聚丙烯/木粉发泡复合材料配方体系的研究

采用化学发泡法,在普通注塑机上制备了聚丙烯（PP）/木粉复合发泡材料,考察了发泡剂偶氮二甲酰胺（AC）、相容剂马来酸酐接枝聚丙烯（PP-g-MAH）和木粉含量对PP/木粉复合发泡材料的力学性能、断面微观结构及表观密度的影响。结果表明,当AC含量为1.2份时,复合材料的发泡效果最好,冲击强度达到最大值20.23 kJ/m2;当PP-g-MAH含量为15份时,显著改善了木粉和PP界面之间的相容性,同时提高了复合材料的力学性能和发泡效果;木粉含量过高时,复合材料的表观密度变大,力学性能下降,发泡效果变差,当木粉含量为30份时,复合材料的各项性能较好。     

微发泡PP/GF复合材料力学性能研究

采用化学发泡注塑成型的方法制备了微发泡聚丙烯/玻璃纤维(PP/GF)复合材料;结合成核理论和玻纤增强机理,研究了发泡质量对微发泡PP/GF复合材料力学性能的影响。结果表明:在PP/GF复合材料中添加5.0%纳米SiO2后,纳米SiO2对PP与GF的相容性并无太大影响,微孔发泡PP/GF复合材料的拉伸强度和冲击强度得到较大提高。     

SiO2对聚丙烯/SiO2复合材料微孔发泡作用

通过熔融共混法把改性过的超细SiO2加入到聚丙烯(PP)中,制备PP/SiO2复合材料母粒,通过化学发泡注塑工艺制备PP/SiO2微发泡复合材料.用扫描电镜观察了发泡样品的泡孔结构,借助电子探针和转矩流变仪研究了超细SiO2粒子在PP复合材料微孔发泡中的作用.结果表明,SiO2粒子之所以能够改善PP微孔发泡材料的微孔结构,一方面是SiO2粒子的成核作用,另一方面是SiO2的加入提高了PP熔体黏度.     

聚丙烯／纳米二氧化硅复合材料性能研究

通过熔融共混法制备了聚丙烯(PP)/纳米二氧化硅(nano-SiO2)复合材料,研究了nano-SiO2用量和第3组分聚丙烯接枝马来酸酐(PP-g-MAH)对材料力学性能的影响.结果表明,nano-SiO2用量为4份时,材料的力学性能最佳.对PP,PP/nano-SiO2,PP/nano-SiO2/PP-g-MAH复合材料进行DSC热分析和SEM照片观察发现,nano-SiO2对PP基体有异相成核作用,PP-g-MAH可以提高nano-SiO2在PP基体中的相容性.     

聚丙烯/蒙脱土熔融插层复合材料性能研究

选用几种不同型号蒙脱土(MMT),分别与聚丙烯(PP)进行熔融插层共混,制得PP/MMT复合材料。讨论了插层共混复合材料的力学性能、耐热性及流动性,同时考察了PP-g-MAH对复合体系相容性的影响。结果表明,MMT可使复合材料的拉伸强度提高7%,弯曲强度提高16%,而冲击强度则有所下降。PP-g-MAH作为MMT与PP的相容剂增容效果较为明显,偏光显微镜照片表明,MMT可使PP球晶尺寸明显减小,晶体结构更为致密。     

PP-g-MAH对PP/纳米SiO_2复合材料性能的影响

采用熔融共混法制备了聚丙烯(PP)/纳米SiO2复合材料,研究了相容剂马来酸酐接枝聚丙烯(PP-g-MAH)对复合材料力学性能、结晶性能及界面作用的影响。结果表明:PP-g-MAH能有效地增强纳米SiO2与PP基体间的界面作用,提高复合材料的力学性能;同时,PP-g-MAH增强了纳米SiO2的成核活性,使PP的结晶温度升高,球晶细化。     

SiO2粒径对PP发泡行为和力学性能的影响

通过把改性过的不同粒径SiO2以不同用量加入到聚丙烯(PP)中,制备PP/SiO2复合材料母粒,在二次开模条件下制备微发泡PP/SiO2复合材料.通过对不同粒径的SiO2粒子对PP纳米复合材料发泡行为的影响研究,讨论了超细SiO2在聚合物微孔发泡中的作用机理,分析了超细SiO2对PP的力学性能及泡孔结构的影响规律.结果表明,不同粒径的SiO2粒子的加入都能够显著降低PP的泡孔直径和增加泡孔密度;SiO2粒子使PP的缺口冲击强度升高,发泡材料的拉伸强度低于未发泡材料的拉伸强度.     

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.     

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.     

Expansive properties of the mixture C4ASH12 − 2CS III. Effects of temperature and restraint

The effects of temperature and restraint upon the hydration and the expansion of $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}\text{? 2}\text{C}\text{S}$ mixture compacts in different contact solutions have been investigated. Temperatures above 20°C do apparently hinder the formation of an impervious felt-like layer of ettringite around the $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}$ particles, thus greatly reducing the retarding effect of the lime. An uniaxial restraint of 1 Kg/cm² is enough to reduce sensibly the expansions which remain however high (about 100%). The results can be satisfactorily interpreted by the reaction and expansion mechanism hypothesized in our previous papers.     

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.     

Raman Study of Glasses of Ba2TiSi2O8 and Ba2TiGe2O8

Raman spectra are reported for fresnoite (Ba₂Ti(Si,Ge)₂O₈ glasses, and comparison is made between the Raman spectra of the corresponding crystalline powders and glasses of Ba₂TiSi₂O₈ and Ba₂TiGe₂O₈. The Ba₂TiGe₂O₈ glass spectra show correspondence with the Ba₂TiGe₂O₈ crystalline Raman spectra; the v _s(Ge–O–Ge) mode occurs at 518 cm⁻¹ in the glass and at 521 cm⁻¹ in the crystalline material. Five-fold coordinated titanium is the majority species present in the Ba₂TiGe₂O₈ glass as revealed by a strong band at 824 cm⁻¹ in the I glass spectrum. The Ba₂TiSi₂O₈ glass spectra are similar to the Ba₂TiSi₂O₈ crystalline spectrum; the strongest band is found at 836 cm⁻¹ in the I glass spectrum. Through comparison with the previous Raman data of other titania silicate glasses, we conclude that the Ba₂TiSi₂O₈ glass has a structure similar to the crystalline phase.     

Effects of metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H₂O₂ titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the $\text{Pd}\text{SiO}{}_2$ catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the $\text{Pd}\text{La}{}_2\text{O}{}_3$ catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

In situ laser raman spectroscopy of the sulfiding of Moγ-Al2O3 catalysts

Raman spectra of sulfided $\text{Mo}\text{γ-}\text{Al}{}_2\text{O}{}_3$ catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% $\text{H}{}_2\text{S}\text{H}{}_2$ at 400 °C, MoS₂ structures were observed. A stepwise sulfiding using 10% $\text{H}{}_2\text{S}\text{H}{}_2$, with spectra recorded at 150, 250, and 350 °C, resulted in observation of molybdenum oxysulfide, reduced molybdate, and surface “MoS₂” phases. Reexposure of these samples to air led to radical modification of the oxysulfide structures as well as transformation of some sulfide phases. A model incorporating terminal and bridging MoS bonding and anion vacancies is proposed. This model is based on the conversion of isolated and aggregated molybdate and MoO₃ species to oxysulfide and reduced molybdenum phases. Conversion of reduced molybdenum phases to sulfides is observed to be slow.     

Wet Milling of Fe/Al/Al2O3 and Fe2O3/Al/Al2O3 Powder Mixtures

Wet milling of Al₂O₃-aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al₂O₃ and Fe₂O₃/Al/Al₂O₃ powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe₂O₃/Al/Al₂O₃ powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al₂O₃ powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8.