高分子复合材料导热性能研究

以Al2O3、MgO和BN三种无机填料作为尼龙6(PA6)的导热填料,研究填料的种类、填充量、粒径大小和粒径配比等对复合材料热导率的影响。结果表明:PA6基复合材料的热导率随导热填料填充量的增加而增大,随导热系数大的填料填充量的增加增大较快;导热系数大的填料的粒径对复合材料的导热系数的影响比较明显;导热系数大的填料,不同粒径的复配可以显著提高复合材料的导热系。     

无压渗透工艺制备MgO/AlN复相材料

采用无压渗透工艺,研究了在高纯氮气氛下Al-Mg-Si合金反应渗透氧化镁预形体制备MgO/AIN复合材料。借助XRD,SEM/EDS,EMPA等测试手段检测了产物的物相组成,观察了材料的微观形貌,并对复合材料微区成分进行了分析。结果表明：在氮气气氛中,用Al-Mg-Si合金渗透氮化原位复合氧化镁形成了MgO/AIN复合材料。在氮化温度范围内,Al-Mg-Si合金中的Mg元素极易蒸发,与气氛中的微量氧发生反应,起到深脱氧作用,而Si元素的存在使合金熔体容易浸渗入MgO预形体中,同时氮化反应生成AIN原位复合氧化镁形成MgO/AIN复合材料。合金熔液向预形体渗透的过程中,同时存在合金熔液的原位氮化自反应。氮化产物中除了AIN,MgO外,还生成了含氮尖晶石。氧化镁颗粒的存在,可能导致合金液在各局部区域中的温度、组成浓度、蒸气压等生长条件存在差异或变化,从而造成AIN生长形态的多样化和生长机制的复杂化。     

环氧树脂/改性AIN导热绝缘复合材料的制备与性能研究

将改性后的高导热的AIN与环氧树脂(EP)进行复合制备了Ep/改性AIN导热绝缘复合材料.研究了改性AIN的含量对EP/改性AIN复合材料的导热性能、电绝缘性能、粘接性能、热稳定性能及微观结构的影响.结果表明,当AlN体积分数为30%时,EP/改性AIN复合材料的热导率达到O.75 W (m·K),约为EP的4倍;线胀系数为6.3×10-5 K-1,仅为EP的50%左右;体积电阻率为1×1013Ω·cm,具有电绝缘性能.EP/改性AIN复合材料具有优于EP的粘接能力.     

PA6/BN/MgO导热复合材料的制备与性能研究

以聚酰胺6（PA6)为基体,以氮化硼（BN）、氧化镁（MgO）为导热填料制备了PA6/BN/MgO导热复合材料。固定填料含量为50%（质量分数,下同）不变,考察MgO/BN配比的变化对复合材料热导率、力学性能和熔体流动性的影响。结果表明,材料的热导率、拉伸强度和弯曲强度随着MgO/BN配比的增大而减小,冲击强度和断裂伸长率随着MgO/BN配比的增大而增大,材料熔体流动性则呈现了随MgO/BN配比的增大先增大后减小的趋势。     

HDPE/BN复合材料的热导率

研究了高密度聚乙烯(HDPE)／氮化硼(BN)复合材料中BN分散状态、含量及粒径对热导率的影响。用粉末混合法制得的复合材料中BN粒子围绕在HDPE粒子周围,形成特殊的网状导热通路,在(?)(BN)为30％时复合材料的热导率达1．20 W／(m·K),是纯HDPE的4倍。随BN粒径减小,复合材料的热导率升高,小粒子在基体中形成导热通路能力优于大粒子。HDPE／BN复合材料具有优良的电绝缘性能和机械性能。     

高导热高绝缘FEP／AIN复合材料的研究

采用聚全氟乙丙烯（FEP）为基体，偶联处理的氮化铝（AIN）为填料，通过共混、模压等方法制备了高导热、高绝缘的FEP／AIN复合材料。结合材料导热计算模型，分析了AIN用量对材料热导率、体积电阻率、力学以及流变性能的影响。结果表明：随AIN填充量的增加，复合材料的热导率呈近线性增加，当AIN的质量分数为30％时，材料的热导率可达2．22W／m·K），体积电阻率可达1．5×10^15Ω·cm，并具有较好的力学性能和流变性能。     

Cu粉粒径对PEEK/Cu导热复合材料性能的影响

以铜(Cu)粉为导热填料,采用模压法制备了聚醚醚酮(PEEK)/Cu导热复合材料,并研究了铜粉粒径对PEEK/Cu导热复合材料导热性能、力学性能及结晶性能的影响。结果表明:随着Cu粉粒径的增大,PEEK/Cu导热复合材料的力学性能逐渐下降;当Cu粉粒用量为30%、粒径为10μm时导热复合材料的导热系数达到最佳值0.396 W/(m·K),相比于纯PEEK提高了67.80%;熔融焓与结晶度随着Cu粉粒径的增大而逐渐减小,因而PEEK/Cu导热复合材料的结晶性能降低。     

玻纤增强PPS/MgO绝缘导热复合材料的研究

通过双螺杆挤出机将聚苯硫醚(PPS)与MgO混合挤出,同时添加玻璃纤维(GF)挤出造粒制备了玻纤增强PPS/MgO绝缘导热复合材料。研究了材料的导热性能与MgO含量的关系。研究发现,材料的热导率随MgO含量的增加而增大;GF替代部分MgO后,导热性能有所降低,但拉伸强度和冲击强度等力学性能得到提高;偶联剂用量在0.5%时可提高PPS/MgO绝缘导热复合材料的热导率。     

聚丙烯/四针状氧化锌晶须/氧化镁导热绝缘复合材料的制备与性能研究

以聚丙烯(PP)为基体,四针状氧化锌晶须(T-ZnOw)和氧化镁(MgO)为导热填料,通过双螺杆挤出机制备了PP/T-ZnOw /MgO导热绝缘复合材料。在T-ZnOw用量为10 %（质量百分含量,下同）,MgO用量在0～60 %的范围内,考察了MgO用量对复合材料的热导率( )、体积电阻率(ρv)、力学性能和加工性能的影响。结果表明,随着MgO用量的增加,PP/T-ZnOw /MgO复合材料的 增大,ρv减小;材料的拉伸强度和弯曲强度以及熔体流动速率均随着MgO用量的增加而下降,而冲击强度则呈先保持稳定,然后减小的趋势。这一变化趋势在MgO用量 30 %时较为显著。当MgO用量为60 %（33 %,体积分数）时,PP/T-ZnOw /MgO复合材料的 最大,达到0.7563 W/(m·K),比未加MgO时的PP/T-ZnOw复合材料和纯PP的热导率分别提高了108.0 %和210.0 %;此时材料的ρv最小,为9.20×1015 Ω·cm,仍可满足绝缘材料的要求。     

导热聚对苯二甲酸丁二醇酯/聚酰胺复合材料的制备与性能

主要研制了导热聚对苯二甲酸丁二醇酯/聚酰胺复合材料(PBT/PA),选用纳米氧化镁(MgO)为导热填料。首先探讨了基体树脂配比PBT/PA对PBT/PA/MgO复合材料导热和力学性能的影响;然后固定基体树脂配比,考察了纳米氧化镁的添加量对PBT/PA/MgO复合体系的导热性能和力学性能的影响。实验结果表明,当PBT/PA配比为1∶1,纳米氧化镁添加量为40wt%时PBT/PA/MgO复合材料在保持一定的力学性能的基础上热导率达到0.787W/(m.K),表明该复合体系具有优良的导热性能和力学性能。此外还研究了不同加工方法对复合材料力学性能和导热性能的影响,采用二步法制备的复合材料的导热性能和力学性能较一步法更为优异。利用二步加工法,同时通过调节PBT/PA配比控制共混物的双连续相形态,从而制备出导热性能较好的PBT/PA/MgO复合材料。     

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.     

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.     

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.     

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.