氧化锆湿凝胶中乙酰丙酮配体的脱除机理及气凝胶复合材料的制备

利用正硅酸四甲酯、 正硅酸四乙酯、 硼酸三乙酯浸泡聚乙酰丙酮合锆湿凝胶, 通过红外光谱(IR)、 元素分析(EA)、 X射线光电子能谱(XPS)和色谱-质谱联用(GC-MS) 等技术证实了有机硅(硼)烷浸泡湿凝胶可加速乙酰丙酮配体的脱除, 并推断了相关反应机理. 利用正硅酸四甲酯浸泡聚乙酰丙酮合锆湿凝胶显著强化了 凝胶骨架, 通过低成本干燥技术可以获得纳米多孔、 高比表面积的ZrO₂气凝胶. 在石英纤维增强的ZrO₂气凝胶复合材料中, 纤维骨架进一步阻止了干燥收缩, 微波干燥即可获得超轻质石英纤维/二氧化锆气凝胶复合材料(SFZA), 稳态平板测试结果表明, 其在1000 ℃下的导热系数最低可至0.042 W?m^-1?K^-1, 1200 ℃下导热系数最低可至0.063 W?m^-1?K^-1.     

Effect of a novel green modification of alumina nanoparticles on the curing kinetics and electrical insulation properties of epoxy composites

A novel green surface modification was successfully implemented on alumina nanoparticles using chitosan (CS) to prevent nanoparticles' aggregation. To evaluate the surface changes of nanoparticles, FTIR, TGA, TEM, and SEM analyses were used. The cure kinetics of the uncured samples was analyzed by DSC. Different methods such as KAS, Friedman, Starink, and FWO were applied to measure the activation energy. The activation energy of epoxy reinforced with chitosan-functionalized alumina (epoxy/[CS-EPO-alumina]) was less than that of epoxy reinforced with alumina (epoxy/alumina), which was a confirmation of the positive effect of CS on curing reaction kinetics. Using the Malek method, the Sestak-Berggren autocatalytic equation was chosen to investigate the cure kinetics of the epoxy. It was found that the Sestak-Berggren equation is well matched with the experimental data and the model was suitable to predict the epoxy curing reaction reliably. Moreover, the glass transition temperatures of all samples were approximately the same. The effect of surface modification of alumina on the electrical insulating behavior of epoxy was also studied. It was found that CS functionalized alumina (CS-EPO-alumina) increased volume resistivity of epoxy at a temperature range of 30 to 80°C more than that of alumina. Electric stability and breakdown strength of epoxy/alumina and epoxy/(CS-EPO-alumina) also enhanced, where epoxy/(CS-EPO-alumina) experienced a further increase compared to epoxy.     

Characterisation of valves as sound sources: Fluid-borne sound

The sound pressure level in receiving rooms, caused by taps at the ends of pipe systems, is considered. The structure-borne sound power, from the pipes to the supporting wall, was obtained from intensity measurement of the fluid-borne sound power of the tap. The fluid-borne sound power is combined with a ratio of structure-borne sound power to fluid-borne sound power, obtained from laboratory measurements of similar pipe assemblies. Alternatively, a reception plate method is proposed, which avoids the necessity for intensity measurements. The structure-borne power into walls, to which the pipe work is attached, provides input to the standard building propagation model, which yields the predicted sound pressure level in the adjacent room.     

Dynamics of spatial Fourier modes in turbulence

We present the results of an experimental study of the spatial Fourier modes of the vorticity in a turbulent jet flow. By means of an acoustic scattering setup we have recorded the evolution in time of Fourier modes of the vorticity field, characterized by well defined wavevectors k. By computing the auto-correlation of the amplitude of the Fourier modes we evidence that, whatever the length scale (or equivalently k), the dynamic evolution of the vorticity field involves two well separated time scales. We have also performed the simultaneous acquisitions of pairs of Fourier modes with two wavevectors k and k'. Whatever the spectral gap k- k', any pair of Fourier modes exhibits a significant cross-correlation over long time delays, indicating a strong statistical dependence between scales.     

应用时差法测量声速

共振干涉法和相位比较法是大学物理实验中常用的测量声速的方法,但工程应用很广泛的时差法测量声速却很少在大学物理实验内容中涉及。在文中实验用时差法测量声速的实验结果和理论值相符较好,并对实验结果进行讨论和分析。     

驻波法测定超声波声速实验的探究

本文推导了驻波法测超声声速实验中合成声场的位移波动方程、声压波动方程及两者之间的关系。进一步剖析合成声场的性质,从而获得对合成声场更加客观的认识。     

声速测量装置的改进

采用低频数字信号源推动小型扬声器做声源,用静电式驻极体传感器做拾音器,对传统的声速测量装置进行了改进.改进后的装置不仅能测量不同频率的声速,而且又降低了成本.本文详细介绍了电路的组成及测量结果.     

声悬浮现象的研究

分析了声波在垂直谐振腔内使物体悬浮于空中的条件与位置,给出了运用声悬浮现象测量声速的方法并实测了声速.     

Non-resonant sound transmission through double walls using statistical energy analysis

Although SEA is a suitable framework for predicting sound transmission through double walls it has been found that the standard method of computing the non- resonant coupling loss factor from a room to cavity underestimates the coupling. A revised model for computing this coupling loss factor is presented which gives much better agreement with measured data. This allows better predictions to be made of sound transmission through lightweight double walls.     

Indoor Noise Reduction Index with an open window (Part II)

An index to evaluate indoor noise level reduction with an open window Noise Reduction Index (NRI) was proposed [Buratti C. Indoor Noise Reduction Index with open window. Appl Acoust 2002;63(4):431-51]. The reduction was due to the installation of a false ceiling in the room, thus reducing the contribution of the reverberant field. Experimental data related to two different kinds of false ceiling were compared to the results obtained by an original calculation model. Good agreement was found between experiments with two different materials and predictions. The present paper examines six different kinds of false ceiling and arrives at a new validation of the model. Calculations of NRI show good agreement with experimental data: a maximum difference of −1.2 dB(A) was found with a mean difference of 0.5 dB(A) for a wide range of absorption coefficient values. Hence the model represents a reliable instrument for indoor NRI prediction, if the acoustic absorption characteristics of materials are known.