Adhesive Bonding of Oil-Contaminated Steel Substrates

Durability of adhesive bonds formed by curing epoxies against oil-contaminated steel substrates using amidoamine curing agents was determined during exposure to boiling water. The most durable bonds were obtained using amidoamine curing agents with relatively low amine numbers and by blending silane coupling agents such as γ-glycidoxypropyltrimethoxysilane (γ-GPS) and N-(2-aminoethyl)-3-aminopropyltrimethoxy silane (AAMS) into the adhesives. When X-ray photoelectron spectroscopy (XPS) was used to characterize the failure surfaces of the adhesive joints after exposure to boiling water, it was determined that adhesives prepared using amidoamine curing agents with low amine numbers were able to displace the oil from the steel surface but adhesives prepared with amidoamine curing agents with high amine numbers were not. Results obtained from XPS also showed that the amino groups on the substrate fracture surfaces of joints prepared using curing agents with low amine numbers were protonated whereas the amino groups in the bulk adhesive were not, indicating that there was a chemical interaction between the curing agent and the hydrated surface of the substrate. It was also shown using infrared spectroscopy that the amidoamine curing agents formed salts with calcium compounds in the oil.     

Infrared study of salt free and salt treated cellulose pyrolysis under nitrogen atmosphere

The pyrolysis under nitrogen of salt free and salt treated cellulose was studied by infrared spectroscopy. The results confirm the unzipping mechanism suggested by DTA and TGA studies, and show this mechanism to apply to the untreated and salt treated samples. The results also show the unzipping to stop at the stage of char formation. The onset of this stage was found to occur after the volatilization of only 45–50% of the initial sample of the borax treated cellulose, compared with 65–70% of the KCl treated cellulose and 80–85% of the untreated cellulose.     

Vanadia layers supported on TiO2/SiO2 mixed oxides — An ESR and Raman investigation

ESR and Raman spectroscopy have been used to characterize monolayers of vanadia, which had been immobilized on titania and on a 20% TiO₂/80% SiO₂ mixed oxide support from a vanadyl alkoxide precursor. Characteristic vibrations observed in the Raman spectrum, as well as UV-visible reflection data, indicate that the most abundant vanadia species on the surface consists of disordered polymeric arrays: the central vanadium ion is surrounded by the tightly bound vanadyl oxygen, four oxygen ions in the basal plane, and a distant sixth oxygen ligand in bridging position to the support. From the ESR spectra the principal values ofg andA tensors are obtained, and their dependence on the support material and on the vanadia loading is investigated. Comparison with TPR measurements indicates that for structurally and chemically similar catalysts, the ESR-derived deviationg = g – g _e from the free electrong value provides a useful measure of the V=O bond strength.     

Characterization of Polyphasic Silicon Carbide Using Surface-Enhanced Raman and Nuclear Magnetic Resonance Spectroscopy

The present report explores the use of cross-polarization (CP) and single-pulse magic angle spinning nuclear magnetic resonance (MAS-NMR) as well as normal and surfaceenhanced Raman spectroscopy (SERS), in concert, for characterizing highly crystalline polymorphic silicon carbide ceramics. The combined use of these techniques provides a wealth of information regarding bulk, near-surface, and surface speciation. Both Raman and SERS are promising techniques for fracture surface characterization of these systems. The application of CPMAS-NMR and SERS to the study of ceramics is reported for the first time in this investigation.     

Synthesis and Characterization of a SiAION Glass

Homogeneous SiAION glasses containing up to 1 wt% nitrogen were synthesized via a pressureless method with a controlled quench rate and structurally investigated using ²⁷Al and ²⁹Si magic-angle spinning nuclear magnetic resonance (MAS NMR), Raman, and infrared (IR) spectroscopies. Minor changes occur with the incorporation of nitrogen into the aluminosilicate glass structure as evidenced by modifications to spectra of a nitrogen-free aluminosilicate glass. The ²⁷Al MAS NMR spectrum of the SiAION glass shows the existence of aluminum in 4-,5-, and 6-coordination to oxygen. The ²⁹Si MAS NMR spectra show a distribution of silicon sites in 4-coordination to oxygen. Raman and IR spectra of the SiAION glass show additional features due to incorporation of nitrogen in the structure compared with spectra of nitrogen-free aluminosilicate glasses.     

GPOF在FDTD近远场外推中的应用及编程实现*

该文针对FDTD近远场外推中时域解收敛慢和运算量大等问题,改进了FDTD求解方向图的方法.其核心思想是:FDTD近场计算时,只计算前一段时间外推面上的数据,利用GPOF法估算后面时间的数据.在计算过程中,利用奈奎斯特原理,减少了时间和空间上的采样点数,大大节省了运算时间.最后将数值结果与商业软件FEKO与HFSS的结果进行比较,验证了算法的有效性.     

基于相关法的低采样率超声水表时延估计方法

针对当前超声水表中相关法时间分辨率只能达到采样周期的问题,提出了一种基于相关法的低采样率超声水表时延估计方法.首先,研究了超声水表中所能达到的最大时间延迟;其次,讨论了相关法在超声水表当中的具体应用及插值算法对于提高流量测量精度的作用;最后,利用MATLAB软件对算法进行仿真评估了实际噪声条件下算法能达到的时延估计精度...     

考虑死区效应单相逆变器开关频率分析

针对逆变器死区效应引起的输出波形畸变问题,以单相电压型双极性SPWM逆变器为研究对象,提出一种以输出电压THD值最小为指标的选取逆变器开关频率的方法。首先,利用双重傅里叶变换和贝塞尔函数,推导了考虑死区效应情况下输出SPWM的傅里叶级数展开式。通过对输出SPWM电压进行频谱分析,研究了THD值和不同开关频率的关系。经研究发现,存在最优开关频率使得输出电压的THD值最小。其次,采用分段线性拉格朗日插值法,拟合不同死区时间选取最优开关频率的公式。最后,以TMS320F28335为控制芯片,搭建了单相双极性全桥逆变器试验样机,验证了理论分析与所提方法的有效性。实验结果表明,所提出的逆变器开关频率选取方法在减小输出电压THD的同时,减小了开关损耗,提高了直流侧电压利用率。