Rheological and electrical properties of polycarbonate/multi-walled carbon nanotube composites

Rheological and electrical properties of the polycarbonate (PC)/multi-walled carbon nanotube (MWNT) were studied. The MWNT was funtoinalized by treating with the hydrogen peroxide (H₂O₂). The H₂O₂ treated MWNT was dried by thermal and freeze drying methods. From the morphological studies, the degree of entanglement of the MWNT was decreased after treating with the H₂O₂. For the H₂O₂ treated MWNT (thermal drying), the length of the MWNT was shortened compared that of the H₂O₂ treated MWNT (freeze drying). The rheological and electrical properties of the PC/MWNT (H₂O₂ treated) composites increased compared that of the PC/MWNT (untreated) composites. Also, the electrical conductivity showed higher value for the PC/MWNT (H₂O₂ treated, freeze drying) composites compared that of the PC/MWNT (H₂O₂ treated, thermal drying) composites. From the results of the morphological, rheological, and electrical properties of the PC/MWNT composites, it is suggested that the electrical and rheological properties of the PC/MWNT composites are affected by the MWNT-MWNT network structure, which is related with the MWNT morphologies such as the degree of aggregation and aspect ratio of the MWNT.     

Electrical properties of V2O5–WO3/TiO2 EUROCAT catalysts evidence for redox process in selective catalytic reduction (SCR) deNOx reaction

Electrical conductivity measurements on EUROCAT V₂O₅–WO₃/TiO₂ catalyst and on its precursor without vanadia were performed at 300°C under pure oxygen to characterize the samples, under NO and under NH₃ to determine the mode of reactivity of these reactants and under two reaction mixtures ((i) 2000 ppm NO + 2000 ppm NH₃ without O₂, and (ii) 2000 ppm NO + 2000 ppm NH₃ + 500 ppm O₂) to put in evidence redox processes in SCR deNO_x reaction.It was first demonstrated that titania support contains certain amounts of dissolved W⁶⁺ and V⁵⁺ ions, whose dissolution in the lattice of titania creates an n-type doping effect. Electrical conductivity revealed that the so-called reference pure titania monolith was highly doped by heterovalent cations whose valency was higher than +4. Subsequent chemical analyses revealed that so-called pure titania reference catalyst was actually the WO₃/TiO₂ precursor of V₂O₅–WO₃/TiO₂ EUROCAT catalyst. It contained an average amount of 0.37 at.% W⁶⁺dissolved in titania, i.e. 1.07 × 10²⁰ W⁶⁺ cations dissolved/cm³ of titania. For the fresh catalyst, the mean amounts of W⁶⁺ and V⁵⁺ ions dissolved in titania were found to be equal to 1.07 × 10²⁰ and 4.47 × 10²⁰ cm⁻³, respectively. For the used catalyst, the mean amounts of W⁶⁺ and V⁵⁺ ions dissolved were found to be equal to 1.07 × 10²⁰ and 7.42 × 10²⁰ cm⁻³, respectively. Since fresh and used catalysts have similar compositions and similar catalytic behaviours, the only manifestation of ageing was a supplementary progressive dissolution of 2.9 × 10²⁰ additional V⁵⁺ cations in titania.After a prompt removal of oxygen, it appeared that NO alone has an electron acceptor character, linked to its possible ionosorption as NO⁻ and to the filling of anionic vacancies, mostly present on vanadia. Ammonia had a strong reducing behaviour with the formation of singly ionized vacancies. A subsequent introduction of NO indicated a donor character of this molecule, in opposition to its first adsorption. This was ascribed to its reaction with previously adsorbed ammonia strongly bound to acidic sites. Under NO + NH₃ reaction mixture in the absence of oxygen, the increase of electrical conductivity was ascribed to the formation of anionic vacancies, mainly on vanadia, created by dehydroxylation and dehydration of the surface. These anionic vacancies were initially subsequently filled by the oxygen atom of NO. N^o atoms, resulting from the dissociation of NO and from ammonia dehydrogenation, recombined into dinitrogen molecules. The reaction corresponded to

Full-size image

. In the presence of oxygen, NO did not exhibit anymore its electron acceptor character, since the filling of anionic vacancies was performed by oxygen from the gas phase. NO reacted directly with ammonia strongly bound on acidic sites. A tentative redox mechanism was proposed for both cases.     

Degradation of 4-chloro-2-methylphenol in aqueous solution by electro-Fenton and photoelectro-Fenton processes

Degradation of 4-chloro-2-methylphenol (PCOC), a refractory toxic chemical emitted to the environment from the industrial production of phenoxy herbicides was studied in aqueous solution. Electro-Fenton and photoelectro-Fenton processes were used as the degradation methods. H₂O₂, produced by the reduction of oxygen at carbon cathode reacted with dissolved metal ions to form hydroxyl radicals, which in turn reacted with PCOC sequentially to degrade the aromatic ring. The effects of using different [Fe²⁺]/[PCOC]₀ and the effect of replacing Fe²⁺ by Mn²⁺ ion have been examined. It was found that degradation rate was increased with increasing [Fe²⁺]/[PCOC]₀ ratio from 2 to 4. However, the total charge utilized during the treatment was also increased. The efficiency of PCOC degradation was observed to be higher when Mn²⁺ was used as the catalyst. The mineralization of aqueous solutions of PCOC, withdrawn from the reactor at certain time interval, has been followed by total organic carbon (TOC) decay and dechlorination. A fast and complete degradation of the aromatic ring was achieved in photoelectro-Fenton system. 41.7% TOC decay and complete dechlorination were observed by consuming only 141.4 C electrical charge during a 300 min photoelectron-Fenton treatment. In the case of electro-Fenton system, 280.7 C electrical charge was consumed during 450 min of electrolysis to attain a similar degradation of PCOC. 14.9% TOC removal and 89.3% dechlorination have been obtained in this system under the applied conditions.     

PS／炭黑复合材料导电性能的研究

本文通过炭黑（简称ＣＢ）用量、加工工艺、温度对ＰＳ／ＣＢ复合材料导电性能影响的探讨、复合导电材料亚微观结构的观察，研究了ＰＳ／ＣＢ复合材料的导电性能。结果表明，随着ＣＢ含量的增加，材料的电阻率呈非线性下降，当ＣＢ的质量分数在１０％～４０％的范围内时，电阻率下降明显，在此含量范围以后，体积电阻率变化不大；材料的导电性能与加工工艺有关，溶剂法的导电性能比混炼法好；电阻率随温度的升高均有上升的趋势。由复合材料的亚微观结构表明，随着ＣＢ含量的增加，ＣＢ由分散的单个颗粒逐渐连结在一起，最后与ＰＳ形成了一种相互交错式的结构     

旋转变压器信号的标定与解调

针对检波后信号存在直流偏置、幅值不等和相位偏移等问题,采用梯度估计算法,对检波后的包络信号进行离线标定;并设计了基于状态观测器的旋转变压器-数字转换(RDC)算法,对标定后的包络信号进行解调.试验结果表明,梯度估计算法收敛速度快,估计精度高.与反正切法相比,所设计的RDC算法不需通过数值差分即可获得角速度信息,干扰抑制能力强,角位置和角速度估计精度高.     

电子横移伺服LQR最优控制器设计

为了提高系统的稳态精度和动态性能,将LQR最优控制算法应用于高速经编机电子横移伺服控制系统.建立了伺服系统状态空间模型,引入了一类具有指数衰减度的二次型函数作为系统性能指标.仿真结果表明,所提出的电子横移伺服LQR最优控制算法易于工程实现,保证了系统的稳定性,具有良好的频响特性,改善了系统的动态特性,实现了无静差高精度控制.     

Estimating the electrical conductivity of cement paste pore solutions from OH, K and Na concentrations

A proposed method for estimating the electrical conductivity of cement paste pore solution at 25 °C is based on the concentrations of OH⁻, K⁺ and Na⁺. The approach uses an equation that is a function of the solution ionic strength, and requires a single coefficient for each ionic species. To test the method, the conductivity of solutions containing mixtures of potassium hydroxide and sodium hydroxide with molar ratios of 4:1, 2:1 and 1:1, and having ionic strengths varying from 0.15 to 2.00 mol/l were measured in the laboratory and compared to predicted values. The proposed equation predicts the conductivity of the solutions to within 8% over the concentration range investigated. By comparison, the dilute electrolyte assumption that conductivity is linearly proportional to concentration is in error by 36% at 1 mol/l and in error by 55% at 2 mol/l. The significance and utility of the proposed equation is discussed in the context of predicting ionic transport in cement-based systems.     

Aqueous electrochemical intercalation of bromine into graphite fibers

For the first time, graphite fibers have been electrochemically intercalated with Br⁻ that have the same structure and properties as those intercalated from vapor phase Br₂. This was accomplished by intercalating pitch-based Thornel^® K-1100 graphite fibers at low temperature (near 0 °C) and high currents (2 A) for long times (6 h). The mechanism appears to be that Br⁻ is oxidized to aqueous Br₂ which, when sufficient local concentration builds up, intercalates the fiber. This was confirmed by intercalating K-1100 fiber in a saturated aqueous Br₂ solution without passing an electrical current. The applied voltage does apparently lower the activation energy of the reaction as evidenced by the observation that P-120 and P-100 fibers will not intercalate in aqueous Br₂ unless a voltage is applied.     

Effect of H2O adsorption on the electrical transport properties of double-walled carbon nanotubes

Water molecules adsorbed on a double-walled carbon nanotube (DWCNT) serve as charge trapping centers when present in low density and as electron donors when present in high density. There is a discontinuous change between the low- and high-density regions. H₂O molecules are apt to be adsorbed on the outer surface of DWCNTs, and in this case the electrical transport properties are extremely sensitive to environment, which suggests that DWCNTs are hole doped and act as an electric dipole with the inner tube.