PVC\弹性体\纳米CaCO3复合体系的加工和组成对力学性能的影响

详细研究了聚氯乙烯(PVC)、氯化聚乙烯(CPE)和纳米碳酸钙(Nano-CaCO₃)的三元复合体系的加工工艺和组成变化与力学性能之间的关系。研究表明:如果先将CPE等弹性体和纳米CaCO₃制成母粒,然后再与PVC进行混合,有利于纳米粒子在基体中的分散,在复合体系中,纳米CaCO₃和CPE达到了协同增韧PVC的作用,同时,纳米CaCO₃具有补强作用,且当母粒的组成为CPE/纳米CaCO₃=1∶2时,对PVC改性效果最佳。      

纳米CaCO_3对CPE/ACR共混增韧PVC力学性能的影响

研究了纳米碳酸钙(CaCO_3)对氯化聚乙烯(CPE)/丙烯酸树脂(ACR)/聚氯乙烯(PVC)共混体系力学性能的影响,并通过动态机械热分析(DMA)和扫描电子显微镜(SEM)对共混体系的力学松弛行为、纳米CaCO_3在CPE/ACR/PVC共混体系中的分散状态及共混体系的断面形貌特征进行了表征。结果表明,纳米CaCO_3能够显著提高CPE/ACR/PVC共混体系的冲击性能,而不降低共混体系的强度。加入纳米CaCO_3后,共混体系的低温损耗(tanδ)峰强度显著增大,并且与冲击强度的变化具有很好的对应性。SEM观察发现,8 phr纳米CaCO_3可在CPE/ACR/PVC基体中形成纳米尺度的均匀分散,加入过多纳米CaCO_3则会出现明显的团聚。     

纳米CaCO3/PVC复合材料的结构形态与性能

研究了纳米CaCO3的用量对PVC复合材料结构形态与性能的影响关系。结果表明，在PVC共混体系中加入纳米CaCO3可明显地提高材料的韧性，而不降低材料的强度。当共混体系中纳米CaCO3的用量为8份(质量)时，复合材料的缺口冲击强度达到81．1kJ／m^2，是不加纳米CaCO3的7．3倍。用透射电子显微镜及扫描电子显微镜观察了纳米CaCO3／PVC复合材料的微观结构及断面形态，发现纳米Ca—CO3在PVC基体中达到了纳米级的分散，复合材料的冲击断裂面产生了大量的网丝状结构。纳米CaCO3的加入使共混体系的加工流动性能变差，加工流动改性荆M的加入可以改善纳米CaCO3／PVC共混体系的流变性能。     

ATRP法在纳米SiO_2表面接枝PBA及其对PVC的改性

采用原子转移自由基聚合法(ATRP)在纳米二氧化硅(SiO2)粒子表面接枝聚丙烯酸丁酯(PBA),并以此对聚氯乙烯(PVC)进行改性。红外光谱(FT-IR)、透射电镜(TEM)、扫描电镜(SEM)及力学性能等测试结果表明,所制备的SiO2-g-PBA纳米复合粒子在PVC中分散均匀,使PVC/SiO2-g-PBA复合材料的缺口冲击强度及拉伸强度均明显高于PVC及PVC/SiO2复合材料。当SiO2-g-PBA纳米复合粒子的质量分数为5%时,PVC/SiO2-g-PBA复合材料的冲击强度达到9.5kJ/m2,较纯PVC提高了280%,同时拉伸强度也有一定的提高,达到了65.3MPa。     

纳米CaCO3复合微粒增韧增强PC/ABS合金

经甲基丙烯酸甲酯和丙烯酸丁酯双单体聚合包覆的纳米碳酸钙形成了核壳结构增韧复合微粒。在双螺杆挤出机中采用二次挤出法制备出PC/ABS/纳米碳酸钙复合材料。研究纳米碳酸钙复合微粒对PC/ABS合金力学性能的影响表明:添加适量纳米CaCO3复合微粒,PC/ABS合金的缺口冲击强度和拉伸强度都得到提高。纳米CaCO3复合微粒具有无机纳米颗粒和弹性体双重协同增韧的作用,其表面的聚合物分子链与基体树脂起到嵌段增容作用。     

丙烯酸酯类共聚物与纳米CaCO3协同改性聚碳酸酯/丙烯腈-丁二烯-苯乙烯三元共聚物合金

研究了聚碳酸酯(PC)/丙烯腈-丁二烯-苯乙烯三元共聚物(ABS)组分配比对合金性能的影响;丙烯酸酯类共聚物(ACR)、纳米CaCO3单独使用与复配对PC/ABS合金性能的影响,并采用电子扫描电镜观察其微观结构。结果发现,随着PC用量的增加,冲击强度与断裂拉伸应变先降后升再降,PC质量分数在50%~60%,出现极大值,拉伸强度先降后升再降再升;随着ACR用量的增加,冲击强度与断裂拉伸应变先升后降,ACR质量分数在5%左右时,出现极大值,拉伸强度呈下降趋势;随着纳米CaCO3用量的增加,冲击强度与拉伸强度先升后降,断裂拉伸应变急剧下降,质量分数在4%左右时,综合性能优异;ACR与纳米CaCO3复配使用时,材料性能明显优于单独使用,当纳米CaCO3质量分数为4%,ACR质量分数为5%时,拉伸强度可达59 MPa,冲击强度可达108 kJ/m2;通过扫描电镜照片发现,ACR改善了纳米CaCO3的界面结合与分散状况。     

纳米CaCO3/ABS/PVC共混体系研究

研究了改性纳米CaCO3对ABS／PVC共混体系力学性能和吸水率的影响。结果表明,在ABS／PVC共混体系中加入纳米CaCO3可以提高体系的冲击强度和表面硬度,提高最大幅度分别为25．2％和10.5％,随着改性纳米CaCO3添加量的增加,冲击强度先增加后下降,表面硬度有所增加,吸水率有所下降。通过SEM和TEM分析表明,纳米CaCO3呈纳米分散,且与塑料基体结合良好。     

纳米CaCO3/PP复合纤维的制备及力学性能研究

通过共混包覆法与母粒法制备出纳米CaCO3/PP复合纤维,研究了2种工艺对复合纤维力学性能和分散性能的影响,分析了其力学性能的不匀率,并讨论了其增强机理.结果表明,在共混包覆法中,高速混合机所提供的高剪切力和聚合物的强黏附性使纳米CaCO3在PP中具有良好的分散性,由FTIP可知在纳米CaCO3与PP之间形成了C-O-Ca键,使纳米粒子与PP基体形成较强的结合力,进而提高了纤维的强度,且加工简易,有效地降低了生产成本,而母粒法效果较差.     

ABS/改性纳米CaCO3复合材料的微观结构和力学性能

制备了改性纳米CaCOa／ABS复合材料,采用SEM和TEM对复合材料的微观结构进行了分析,同时,对复合材料的力学性能进行了考察。结果表明,改性纳米CaCO3可以在ABS塑料中与树脂充分结合,同时改性纳米CaCO3在复合材料中呈纳米分散。复合材料的断面产生了大量的网状结构。分散在丙烯腈一丁二烯一苯乙烯共聚物(ABS)中的改性纳米CaCO3可提高复合材料的裂缝引发能和裂缝增长能。其单缺口冲击强度达到36．77kJ／m^2,与未添加纳米CaCO3的相比提高了44％;邵氏硬度达到34．87N,提高了23．5％。     

微悬浮法CaCO3表面接枝PMMA及其在PVC中的应用

在水介质中,超声作用下用油酸对纳米碳酸钙进行表面修饰,再以微悬浮原位聚合法用PMM A进行接枝包覆,成功制备了PMM A/C aCO3复合粒子。借助透射电镜(TEM)、红外光谱(FT-IR)、热失重(TG)等分析手段对复合粒子的形态结构进行了表征。实验结果表明,油酸可通过羧酸盐的形式吸附于碳酸钙粒子表面,一定量PMM A通过油酸分子的不饱和双键接枝于碳酸钙粒子表面。将所得PMM A/C aCO3复合粒子与PVC共混制得PVC/PMM A/C aCO3复合材料。复合材料的TEM照片表明,C aCO3粒子非常均匀地分散在PVC基体中,两相界面模糊。随着PMM A/C aCO3纳米复合粒子用量的增加,复合材料的强度和韧性同时提高。当复合粒子用量高于12%时,复合材料的冲击强度可提高3倍,而拉伸强度下降很少。     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Magnetic,electrical and thermal studies on the V1−xMox02

The monoclinic-to-tetragonal structure transition of oxides V_1?xMo_x0₂ with $\text{0≤}\text{x}\text{≤0.20}$ has been studied by means of DTA, X-ray diffraction, magnetic susceptibility (powder samples) and electrical conductivity (single crystals) measurements within the temperature region 80 K to 400 K. A linear decrease of the transition temperature of 11 K per atom % Mo was observed. The magnetic susceptibility of the low temperature phase was found to be temperature independent paramagnetic for all preparations. Electrical conductivity measurements on the same phase showed crystals with $\text{x}\text{? 0.04}$ to be semiconducting, while a metallic behavior was observed in the region $\text{0.10 ?}\text{x}\text{? 0.14}$.     

n-PbTep+−Pb1−xSnxTe heterojunctions prepared by a modified hot wall technique

$\text{n-PbTe}\text{p}{}^{\mathrm{+}}\text{?}\text{Pb}{}_{\mathrm{1?x}}\text{Sn}{}_{\mathrm{x}}\text{Te}$ heterojunctions with a long wavelength spectral cutoff (λ_c ≈ 6 μm) were prepared using the double-channel hot wall technique. The electrical and photoelectrical properties of the heterojunctions at 77, 197 and 300 K were investigated. Detectors with R_oA equal to 170 Ω cm² and a quantum efficiency of 25–40% were obtained. Reasons for the shift of the long wavelength spectral cutoff of the heterojunctions towards shorter wavelengths are given.     

Reactive plasma deposited SixCyHz films

Si_xC_yH_z films have been prepared at 200°C by reactive plasma deposition from SiH₄ and CH₄ diluted in helium in a tubular reactor. These films have a ratio s (equal to $\text{Si}\text{(}\text{Si+C}\text{))}$ ranging from 0.2 to 0.8, a refractive index ranging from 1.96 to 2.6 and an optical energy band gap in the range 2.7-2.2 eV. The total quantity of hydrogen in the film is 40% when s=0.5. Infrared analysis shows that these films have large fractions of homonuclear bonds and that this material is best described as a polymer. Mass spectrometric measurements of the gaseous products formed in the SiH₄-CH₄-He plasma have been performed and the results are related to the composition of the deposited layers.     

Core-current-enhanced domain-wall pinning in nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon

We have studied the influence of surface fields H/sub p/ (generated by either direct or alternating core current) on soft magnetic properties of amorphous and nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon. While in an amorphous ribbon the coercive field H/sub c/ decreases with H/sub p/, in the same optimally annealed ribbon (H/sub c/=1.3 A/m, M/sub m//spl ap/M/sub s/) H/sub c/ increases with H/sub p/ for all the explored types of H/sub p/ (static and dynamic with different phases with respect to that of the magnetizing field H). The unexpected increase of H/sub c/ in nanocrystalline ribbon is associated with the influence of H/sub p/ on the surface and main (inner) domain structure. Here, we develop a model that takes into account this influence and explains the experimental results.     

Interfacial microstructure of NiSix/HfO2/SiOx/Si gate stacks

Integration of NiSi_x based fully silicided metal gates with HfO₂ high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi_x film. Ni content varies near the NiSi/HfO_x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi_x/HfO₂ interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi_x/HfO_x was found higher than that of poly-Si/HfO₂, likely due to compositional non-uniformity of NiSi_x. No intermixing between Hf, Ni and Si beyond interfacial roughness was observed.