介孔复合材料声子输运的格子玻尔兹曼模拟

采用格子玻尔兹曼方法对NaCl@Al2O3介孔复合材料内的声子热输运进行了模拟分析.基于德拜物理模型,提出了温度耦合的复合材料界面处理方法,有效实现了复合材料声子输运的格子玻尔兹曼模拟,获得了不同孔径、孔隙率、孔形状、孔排列、界面条件系数下介孔复合材料的热导率,并进行影响因素分析.结果表明:该介孔复合材料热导率,在孔隙率一定时,随着孔径增大而增大,呈现显著的尺度效应;在孔径一定时,热导率随孔隙率增大而减小;孔径和孔隙率一定时,热导率随界面条件系数的增大而减小;孔形状和孔排列均会影响介孔复合材料的热导率,且这种影响会随着界面条件系数的增大而增大.     

电子偶素在OMC/SBA-15,OMC@SBA-15及CuO@SBA-15催化剂中的化学猝灭

以P123为结构导向剂、TEOS为硅源制备了有序介孔二氧化硅SBA-15,并以此为模板制备了有序介孔碳(OMC).小角X射线衍射、高分辨透射电子显微镜和N₂吸附/脱附等测试结果均证实SBA-15与OMC具有高度有序的孔结构、相对较高的比表面积,且孔洞平均尺寸分别约为7.5 nm和3.3 nm.分别采用固相反应法和浸渍填充法制备了OMC/SBA-15复合材料和OMC@SBA-15及CuO@SBA-15复合材料.随着OMC和CuO质量分数的增大,3种复合材料中o-Ps寿命τ₄和其强度I₄均减小.o-Ps湮没率λ₄随OMC和CuO质量分数的变化可用一条或两条直线很好地拟合,OMC/SBA-15,OMC@SBA-15及CuO@SBA-15复合材料中反应速率常数k分别为(2.39±0.44)×10~7 s^-1/(6.65±0.94)×10~6 s^-1,(2.28±0.19)×10~7 s^-1和(8.76±0.47)×10~6 s^-1<...     

NMR研究甲烷水合物在中孔SBA-15内的生成

利用自行研制的高压釜和原位高压核磁共振研究了甲烷水合物在具有孔径均一的中孔SBA-15中的形成过程. 结果发现在静止的状态下,甲烷在中孔SBA-15内与水也能生成甲烷水合物,但其形成所需要的诱导时间比在纯水的条件下要短,SBA-15可促进甲烷水合物的形成;原位高压¹H和¹³C NMR研究表明即使甲烷过量,在一定压力下,SBA-15孔道内的水也不能完全形成甲烷水合物.     

聚乙烯亚胺改性介孔二氧化硅SBA-15微观结构的小角X射线散射及正电子湮没谱学研究

SBA-15由于具有高比表面积、孔容大、孔径可调、热稳定性好和成本相对低廉等优点,在吸附、分离、催化和纳米材料等领域具有广泛的应用前景,而利用有机官能团改性SBA-15已经成为当前材料的热点之一,但有机官能团的引入势必会影响材料的孔结构,进而影响其性能.因此,如何更全面地表征材料的孔结构也成为人们关注的焦点.采用小角X射线散射(SAXS)技术对PEI/SBA-15介孔分子筛的孔结构进行表征,利用相关函数和弦长分布理论得到了聚乙烯亚胺改性介孔二氧化硅(PEI/SBA-15)的孔结构和周期性信息,结合正电子湮没寿命谱(PALS)技术进行比较.结果表明:随着PEI质量分数的增加,PEI/SBA-15介孔分子筛的周期性结构没有发生明显变化,通过弦长分布(CLD)函数得到的孔径尺寸也仅从8.3 nm降至7.6 nm.利用PALS获得了2种长寿命组分τ₃和τ₄,其中τ₃反映了SBA-15基体内部的无规微孔结构,而τ₄反映SBA-15六方孔道的尺寸,与SAXS结果相比,介孔孔径具有相同的变化趋势.通过结合SAXS...     

炭黑/橡胶体系的导热模型及应用研究

针对炭黑/橡胶复合体系分别建立了立方体模型和球形模型,并推导出热导率计算方程.分别估算了N234炭黑和N539炭黑/橡胶复合体的热导率,与实验结果进行比较发现:复合体系的热导率与炭黑用量、结构性及粒径有关;球形模型比立体模型预测炭黑/橡胶复合材料的热导率更加准确;特别是当炭黑体积份数<20%时,用球形模型预测与实验结果取得较好的一致性.为了了解炭黑体积份数超过20%时热导率的变化情况,需提高炭黑填充量作进一步研究.     

多壁碳纳米管/聚丙烯复合材料热导率研究

用Pt细丝代替已有3ω方法中的薄膜热线,并设计了基于Labview程序的虚拟测量系统,准确、方便地测量了聚丙烯复合材料的热导率. 测量结果发现,多壁碳纳米管/丁苯橡胶/聚丙烯三元复合材料的热导率随着多壁碳纳米管/丁苯橡胶粉末含量的增加变化不大;多壁碳纳米管/聚丙烯复合材料的热导率随着多壁碳纳米管含量增加而增大;复合材料热导率远小于简单混合规则预测的结果,而与有效介质理论符合很好. 关键词： ω法')" href="#">3ω法 多壁碳纳米管 聚丙烯复合材料 热导率     

导电PI/纳米炭黑复合材料的制备和测试

以均苯四甲酸二酐、4,4'-二氨基二苯醚、炭黑为主要原材料制成填充型导电PI/纳米炭黑复合材料.经电子显微镜及伏安法等对其性能进行表征,结果发现:掺入纳米炭黑能使PI的导电能力增强,且这种能力随炭黑掺入量增加而提高,但是炭黑含量继续增加却会引起聚合物体系中团聚现象的加剧,导致导电能力下降,当掺入量为6%时复合材料导电性能达最好,电阻为4.02×106 Ω.     

α-Al_2O_3介孔材料导热特性的模拟

本文针对α-Al2O3有序介孔材料的导热特性开展分子动力学模拟分析.提出了一种保证电中性的孔道结构构造方法;采用逆非平衡分子动力学方法(muller-plathe法),选取Matsui势为作用势,模拟计算了Al2O3介孔晶体材料在不同环境温度下沿孔道轴向方向的热导率;并借助全面实验分析法,设计了模拟条件,以考察孔径和孔隙率对热导率的影响.模拟结果显示:介孔Al2O3热导率先随温度的升高呈上升趋势,并在200—400 K之间取得极值;而后在400—1400 K范围内,热导率随温度的升高几乎呈线性下降.孔隙率一定时,随孔径增大,介孔Al2O3材料比表面积降低,界面散射的抑制作用减弱,使材料热导率略有上升;孔径一定时,随孔隙率上升,孔道壁面声子数减少,材料热导率下降明显;相对于孔径因素,材料孔隙率对声子导热影响更大.     

Fe/La/SBA-15对生物质气化影响研究

采用水热法原位法和浸渍法分别制备了La/SBA-15和Fe/La/SBA-15两种SBA-15改性催化剂,两种材料保持了SBA-15材料的高度有序二维六孔结构,并在实验温度范围内具有良好的热稳定性。本文利用松木屑作为生物质原料,讨论了水蒸气流量、实验温度、SBA-15改性催化剂等影响因素对生物质气化过程的影响。一定温度下提高水蒸气流量可促进水蒸气与焦炭反应和焦油的重整反应,降低了焦油和焦炭产量从而提高了产气率;提高温度可以促进焦油的二次裂解;添加La/SBA-15、Fe/La/SBA-15两种催化剂可以促进焦油中难分解物质的裂解以及水与焦炭反应的发生。尤其是Fe/La/SBA-15催化剂,一定温度下提高了产气率的同时提高了燃气的热值。     

介孔二氧化硅双重孔隙的导热特性研究

介孔二氧化硅颗粒的双重孔隙分布特征对材料的导热性能具有显著影响。本文通过微观形态表征分析了介孔二氧化硅的复合孔道，并基于受限空间内的气体分子动力学理论，构建了双重孔隙结构的热导率关联模型。为了验证理论模型的合理性与准确性，采用瞬态热带法测量了介孔二氧化硅材料(MCM-41和SBA-15)在0～30 MPa和20～550℃的环境压力及温度变化下的有效热导率。实验测量结果表明，本文理论模型可以有效预测介孔二氧化硅颗粒热导率的变化规律。进一步根据模型分析可知，材料热导率随着环境温度及压力的升高而增长，表现出明显的正相关性，同时其微观结构的差异也是热导率变化的决定性因素。     

D.C. conductivity and thermal aging of conducting zeolite/polyaniline and zeolite/polypyrrole blends

The d.c. conductivity σ of zeolite/polyaniline (PANI) and zeolite/polypyrrole (PPy) blends of various concentrations in zeolite was measured from 80 to 320 K. Moreover, the thermal degradation of σ was studied by heating the blends at 70 °C under environmental conditions for times between 0 and 600 h approximately. The experimental results indicate a structure of the granular metal type, in which conductive grains are randomly distributed in an insulating matrix and thermal degradation is due to the shrinking of them. As the zeolite content increases in the zeolite/PPy blends, the separation between the conductive grains decreases, the conductivity increases and the thermal stability of the blends improves. On the contrary, the behaviour of the zeolite/PANI samples is almost independent from the zeolite content. An explanation of this difference is proposed based on the crystalline character of the conductive grains in PANI in contrast to the amorphous grains of PPy.     

Thermal conductivity of a kind of mesoporous silica SBA-15

Mesoporous silica SBA-15 consists of uniform hexagonal, unconnected cylindrical channels with diameters that can be tuned within a range of 1.5 nm-30 nm, and is thought to have a special thermal conductivity. The theoretical investigation of the shell thermal conductivity of the mesoporous silica is performed in the relaxation time approximation in this paper and an available one-dimensional heat transfer model is used to predict the effective thermal conductivity （ETC） of the mesoporous silica. The experimental result of the ETC is also presented for comparison. The shell thermal conductivity of the mesoporous silica decreases with mesochannel radius increasing or wall thickness decreasing, but does not strictly decrease with porosity increasing. The thermal radiation possibly plays a primary role in heat transfer at the large porosity scale. The predicted ETC of SBA-15 with only conduction considered is quite low at the large porosity, even lower than the thermal conductivity of the silica aerogels. To realize it, doping carbon or other matters which can strongly absorb infrared light into SBA-15 is a possible way.     

Synthesis,characterization and electrochemical impedance spectroscopy of VOx-NTs/PPy composites

Composites consisting of vanadium oxide nanotubes (VOx-NTs) and polypyrrole (PPy) were synthesized by a two-steps method. VOx-NTs were firstly prepared by a combined sol–gel reaction and hydrothermal treatment procedure, in which V ₂O₅ powder and H₂O₂ were used as raw materials and hexadecylamine as a structure-directing template. Then VOx-NTs/PPy composites were fabricated by a cationic exchange reaction between hexadecylamine and polypyrrole. The structure and morphology of the samples were investigated by SEM, TEM, XRD and FTIR techniques. The results confirmed that the template molecules were successfully substituted by the conducting polymers PPy without destroying the previous tubular structure. Electrochemical impedance spectroscopy (EIS) measurements were performed to evaluate the electrochemical kinetics of the samples. The results indicated that VOx-NTs/PPy composites had a lower charge transfer resistance and a faster lithium-ion diffusion speed than those of VOx-NTs, and the enhanced electrochemical kinetics could be attributed to the excellent electronic conductivity of polypyrrole.     

Preparation of highly conductive CNTs/polyaniline composites through plasma pretreating and in-situ polymerization

In this study, carbon nanotubes (CNTs) were pretreated by plasma, and further in-situ polymerized with aniline to achieve uniform CNTs/polyaniline (PANI) composites with high conductivity. The highest conductivity (2.946 S/cm) of CNTs/PANI composites under optimum plasma treating parameters is much higher than those without CNTs pretreatment or premodified by acid oxidation method. The scanning electronic microscope (SEM) pictures indicate that smooth surfaces of pristine CNTs (diameter: 20-40 nm) changes into rough structures and the size increases to around 90 nm, which is further proved by the X-ray diffraction (XRD), the Fourier transform infrared spectroscopy (FTIR), and the Raman measurements. Thermogravimetric analysis (TGA) results reveal that the thermal stability of CNTs/PANI composite is better than that of pure PANI.     

Synthesis,characterization, conductivity and sensor application study of polypyrrole/silver doped nickel oxide nanocomposites

Conducting polymer composites of polypyrrole (PPy) and silver doped nickel oxide (Ag-NiO) nanocomposites were synthesised by in situ polymerisation of pyrrole with different contents of Ag-NiO nanoparticles. The formation of nanocomposites were studied by Fourier transform infrared (FTIR) and UV–vis spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and AC and DC conductivity measurements. The sensitivity of ammonia gas through the nanocomposite was analysed with respect to different contents of nanoparticles. Spectroscopic studies showed the shift in the absorption bands of polymer nanocomposite than that of pure PPy indicating the strong interaction between the nanoparticles and polymer chain. FESEM revealed the uniform dispersion of nanoparticles with spherically shaped metal oxide particles in PPy matrix. The XRD pattern indicated a decrease in amorphous domain of PPy with increase in loading of nanoparticles. The higher thermal stability and glass transition temperature of polymer nanocomposites than that of pure PPy were revealed from the TGA and DSC respectively. The dielectric properties, DC and AC conductivity of nanocomposites were much higher than PPy and these electrical properties increases with the loading of nanoparticles. The nanocomposites showed an enhancement in sensitivity towards ammonia gas detection than PPy.     

Synthesis,electrical and magnetotransport properties of polypyrrole-MWCNT nanocomposite

The present work describes the preparation of nanocomposites in which the multiwall carbon nanotubes (MWCNT) have been mixed with conducting polypyrrole (PPy) via an in situ chemical oxidative preparation method. To reveal their structural, morphological and thermal properties, the composites have been characterized by X-ray diffraction, field emission scanning electron microscope, Fourier transform infrared, and thermogravimetric analyses respectively. Electrical transport and magnetotransport properties have been investigated in the temperature range 77–300 K in the presence as well as the absence of a magnetic field up to 1 T. The conductivities of the composites are greater than that of pure polypyrrole. All the investigated samples follow Mott’s variable range hopping (VRH) theory whereas the magnetic field dependent conductivity has been explained in terms of two opposite but simultaneously acting hopping effect-wave function shrinkage and forward interference effects.     

有序介孔氧化硅SBA-15/纳米AgI复合材料制备及其物性研究

AgI复合材料因其在电化学器件上的潜在应用而受到越来越多的关注.本文介绍采用浸渍热扩散的方法制备有序介孔氧化硅SBA-15/纳米AgI复合材料,对复合材料进行了XRD、TEM、SEM及交流阻抗谱分析表征.结果发现两相复合后AgI的离子电导率提高了约2个量级、相变温度也有较大改变.我们用界面空间电荷区模型解释了离子电导率...     

Properties of SBA-15 modified by iron nanoparticles as potential hydrogen adsorbents and sensors

SBA-15-Fe was synthesized via the incorporation of Fe⁰ nanoparticles (Fe(0)-Nps) in the mesoporous channels. Electron microscopy and X-ray diffraction showed that dispersion of fine iron NPs occurs mainly inside the channels of SBA-15, producing a slight structure compaction. This was accompanied by a significant improvement of both the affinity towards hydrogen and electrical conductivity, as supported by hydrogen adsorption tests and impedance measurements. CO₂ thermal programmed desorption measurements revealed an attenuation of the acid character of the solid surface. This was explained in terms of strong iron interaction with the lattice oxygen atoms that reduces the SiO–H bond polarity. The close vicinity of fine Fe(0)-Nps combined with the large pore size of SBA-15 appear to contribute to a synergistic improvement of the electrical conductivity. The results reported herein open new prospects for SBA-15 as potential adsorbents for hydrogen storage and carriers for hydrogen sensors. The use of iron in lieu of noble metals for designing such materials is a novelty, because such applications of iron-loaded silica have not been envisaged so far due to the high reactivity of iron towards air and water. The development of such technologies, if any, should address this issue.     

CO2 adsorption on branched polyethyleneimine-impregnated mesoporous silica SBA-15

Adsorption of pure CO₂ on SBA-15 impregnated with branched polyethyleneimine (PEI) has been studied. Materials were prepared by impregnating the pore surface of SBA-15 mesoporous silica with different amounts of branched PEI (10, 30, 50 and 70 wt%). Textural properties, elemental analysis and low angle XRD measurements of the prepared samples showed a progressive pore filling of SBA-15 as PEI loading was increased. Pure CO₂ adsorption isotherms on these modified SBA-15 materials were obtained at 45 °C, showing high adsorption efficiency for CO₂ removal at 1 bar. Chemisorption of CO₂ on amino sites of the modified SBA-15 seems to be the main adsorption mechanism. PEI content of impregnated SBA-15 influences the adsorption capacity of the material, being a relevant variable for CO₂ removal by adsorption. Temperature effect on adsorption was also studied in the range 25-75 °C, showing that temperature strongly influences CO₂ adsorption capacity. Adsorption capacity was also tested after regeneration of the PEI-impregnated SBA-15 materials. Our results show that these branched PEI-impregnated materials are very efficient even at low pressure and after several adsorption-regeneration cycles.     

Crystallization of mesoporous silica SBA-15 in a high pressure hydrothermal environment

Mesoporous silica SBA-15 (with ～6?nm pore size and ～6?nm wall thickness) was exposed to a hydrothermal environment at 2 and 5?GPa. The p,T quenched products were investigated by powder X-ray diffraction and transmission electron microscopy. Infrared spectroscopy and thermogravimetric analysis of a sample subjected to 5?GPa at room temperature suggests functionalization of both inner and outer pore surface by silanol. Partial transformation to nano-sized (20–50?nm) coesite crystals with nonfaceted morphology was observed during short equilibration times of 2?h at 125°C, which is significantly below the melting point of water (～250°C). Untransformed SBA-15 maintained intact pore structure. At 175°C and during 8?h, SBA-15 transformed completely into faceted coesite crystals with dimensions 100–300?nm, suggesting Ostwald ripening and thus significant mass transport in the solid water environment. At 2?GPa the melting point of water is near 70°C. Partial transformation to nano-sized α-quartz was observed at 65°C and during 2?h. Untransformed SBA-15 partially pore collapsed. The reduced pore stability of SBA-15 at 2?GPa is attributed to the presence of liquid water in the pores due to melting point depression of confined water.