竹纤维增强制动摩阻材料摩擦学性能研究

采用竹纤维为增强相制备新型无石棉树脂基复合摩擦材料.通过热失重分析、定速摩擦试验及磨损表面形貌观察等手段探讨竹纤维的含量对材料在不同温度下摩擦学性能的影响.试验结果表明:在树脂基摩阻材料中加入适量竹纤维能改善材料摩擦磨损性能,并具有一定的减震降噪的效果,但在超过其热解温度时会造成竹纤维的碳化、挥发,对基体增强失效;竹纤维质量百分数为13%时试样能获得较稳定的摩擦系数及较低的磨损率;竹纤维含量过多会造成摩阻材料制备工艺性变差,且高温下大量竹纤维碳化剥落会破坏摩擦表面膜的连续性,使摩阻性能显著下降.     

竹炭为高效吸附剂的固相萃取分析环境水样中的痕量三氯生

建立了一种由竹炭作为固相萃取高效吸附剂富集环境水样中痕量三氯生的新方法. 研究并优化了几个影响富集效率的参数. 在优化条件下, 三氯生的检测限为0.08 μg/L, 在1～100 μg/L 范围内有良好的线性关系, 相对标准偏差为2.9% (n=7). 方法可应用于实际废水样品的分析.     

基于自编码网络流形学习的毛竹笋不溶性膳食纤维含量红外光谱建模

提出了一种结合自编码网络(AN)流形学习和偏最小二乘(PLS)法的红外光谱建模方法AN-PLS。AN-PLS方法首先用AN算法对红外光谱数据进行非线性降维,再结合PLS建立回归模型。利用该方法建立了毛竹笋中不溶性膳食纤维含量的近红外光谱和中红外光谱回归模型。结果表明,用AN-PLS方法建立的回归模型,比用其他常用光谱数据预处理方法结合PLS及用单独PLS算法建立的模型具有更小的预测均方根误差RMSEP和更高的决定系数R2,因此,AN-PLS具有较优的建模与预测能力,利用近红外光谱和中红外光谱技术结合AN-PLS建模,可实现毛竹笋中不溶性膳食纤维含量的准确测量。     

Palladium charcoal-catalyzed deprotection of O-allylphenols

Allyl aryl ethers can be easily cleaved by the use of 10% Pd/C under mild and basic conditions. The present reaction would involve a SET process rather than a π-allyl-palladium complex. The scope and limitation of this new deprotective methodology is also described.     

Interpretation of water isotherm hysteresis for an activated charcoal using stochastic pore networks

Water vapor adsorption equilibria on activated carbons typically exhibit hysteresis. The size and shape of the hysteresis loop which separates the adsorption and desorption branches is a strong function of the pore size and interconnectivity of the pores. Neither conventional pore filling models nor statistical thermodynamics approaches provide a means for predicting the extent of hysteresis from only adsorption measurements. This work uses the Kelvin Equation in conjunction with the structural concept of a stochastic pore network to describe measured water isotherms on BPL carbon. Using a pore segment distribution function determined from the adsorption branch, it is shown that totally random assemblies underestimate the extent of hysteresis. It is possible, however, to closely fit the measured BPL-water hysteresis loop using a patchy heterogeneity in which a proportion of the larger pores are preferentially located on the exterior, mid-range pores are concentrated in a sub-surface layer and some large pores form shielded voids behind much smaller pores.Nomenclature p vapor phase partial pressure of sorbate - p _sat saturation vapor pressure of sorbate - R gas constant - r pore radius - T absolute temperature - t adsorbed layer thickness - V _L molar volume of adsorbed phase - surface tension - contact angle     

Determination of aminopolycarboxylic acids in river water by solid-phase extraction on activated charcoal cartridges and gas chromatography with mass spectrometric detection. Method performance characteristics and estimation of the uncertainty

A new sample preparation procedure to determine aminopolycarboxylic acids (ethylenediaminetetraacetic acid, EDTA, nitrilotriacetic acid, NTA, diethylenetriaminepentaacetic acid, DTPA, and cyclohexanediaminetetraacetic acid, CDTA) in river water is described. The procedure consists of the solid-phase extraction of the aminopolycaroxyllic acids on activated charcoal cartridges after increasing the ionic strength and acidifying the sample. The extract was eluted with methanol and the analytes were methylated in presence of BF₃/methanol to determine them by GC with mass spectrometric detection. Recoveries were higher than 90% with good repeatabilities and inter-day precision for concentrations close to quantification limits (about 10 μg L⁻¹) and higher. It has been verified that the proposed method is robust according to the Youden and Steiner test and free of matrix effects arisen from the presence of organic matter and iron(III) as deduced from statistical tests. A bottom-up approach was followed to estimate the uncertainty of the measured concentration. At concentrations close to 10 μg L⁻¹ the most relevant step of the method is the calculus of the interpolated concentration which has a high value of relative standard uncertainty.     

Determination of heavy metals in activated charcoals and carbon black for Lyocell fiber production using direct solid sampling high-resolution continuum source graphite furnace atomic absorption and inductively coupled plasma optical emission spectrometry

Reactivity and concentration of additives, especially activated charcoal, employed for the Lyocell process, enhance the complexity of reactions in cellulose/N-methylmorpholine-N-oxide monohydrate solutions. Analytical control of the starting materials is a basic requirement to know the concentration of heavy metals, which are potential initiators of autocatalytic reactions. Seven activated charcoal and two carbon black samples have been analyzed regarding their content of seven elements, Cr, Cu, Fe, Mn, Mo, Ni and V using direct solid sampling high-resolution continuum source graphite furnace AAS (SS-HR-CS GF AAS) and inductively coupled plasma optical emission spectrometry (ICP OES) after microwave-assisted acidic digestion as a reference method. The limits of detection of the former technique are 1-2 orders of magnitude lower than those of ICP OES and comparable to those of more sophisticated techniques. For iron the working range of HR-CS GF AAS has been expanded by simultaneous measurement at two secondary absorption lines (344,099 nm and 344,399 nm). Partial least-squares regression between measured and calculated temperatures for beginning exothermicity (T_on) has been used to investigate the prediction capability of the investigated techniques. Whereas the ICP OES measurements for seven elements resulted in an error of prediction of 3.67%, the results obtained by SS-HR-CS GF AAS exhibited a correlation coefficient of 0.99 and an error of prediction of only 0.68%. Acceptable correlation has been obtained with the latter technique measuring only three to four elements.     

Determination of flavone C-glucosides in antioxidant of bamboo leaves (AOB) fortified foods by reversed-phase high-performance liquid chromatography with ultraviolet diode array detection

A sensitive solid-phase microextraction and gas chromatography-pulsed flame photometric detection technique was developed to quantify volatile sulfur compounds in wine. Eleven sulfur compounds, including hydrogen sulfide, methanethiol, ethanethiol, dimethyl sulfide, diethyl sulfide, methyl thioacetate, dimethyl disulfide, ethyl thioacetate, diethyl disulfide, dimethyl trisulfide and methionol, can be quantified simultaneously by employing three internal standards. Calibration curves were established in a synthetic wine, and linear correlation coefficients (R2) were greater than 0.99 for all target compounds. The quantification limits for most volatile sulfur compounds were 0.5 ppb or lower, except for methionol which had a detection limit of 60 ppb. The recovery was studied in synthetic wine as well as Pinot noir, Cabernet Sauvignon, Pinot Grigio, and Chardonnay wines. Although the sulfur compounds behaved differently depending on the wine matrix, recoveries of greater than 80% were achieved for all sulfur compounds. This technique was applied to analyze volatile sulfur compounds in several commercial wine samples; methionol concentrations were found at the ppm level, while the concentrations for hydrogen sulfide, methanethiol, and methyl thioacetate were at ppb levels. Only trace amounts of disulfides and trisulfides were detected, and ethanethiol was not detected.     

Surface characterization and thermodynamics of adsorption of Sr2+, Ce3+, Sm3+, Gd3+, Th4+, UO 2 2+ on activated charcoal from aqueous solution

Surface parameters of the activated charcoal were measured using precise instrumental techniques for dehydration, carbon content, trace metals impurities, anions, bulk, tap and true densities, surface area, pore volume, porosity and average particle diameter. The adsorption of Sr²⁺, Ce³⁺, Sm³⁺, Gd³⁺, Th⁴⁺ and UO ₂ ²⁺ ions on activated charcoal from aqueous solution was studied as a function of temperature. Thermodynamic parameters such as HH ⁰ and S ⁰ were calculated from the slopes and intercepts of the linear variation of lnK ₁ vs. 1/T, whereK ₃ is obtained from Langmuir equation. The results show endothermic heats of adsorption, but negative free energy values indicate that the adsorption process of metal ions on activated charcoal is favored at high temperature. The value of isosteric heat of adsorption, calculated from the Clausius-Clapeyron equation, shows that the surface of the activated charcoal is heterogeneous with respect to activity. A wavelength dispersive x-ray fluorescence spectrometer was used for measuring the concentration of metal ions.