Experimental observations on the thermal degradation of a porous bed of tires

In this paper, an experimental study on the forward combustion of a bed of tires and refractory briquettes is presented. Temperature measurements within the reactor were obtained as a function of time as well as the evolution of the fuel bed. The products of combustion were cooled down, and usable liquid fuel was recovered and measured. The reaction was found to become unstable for fuel concentrations lower than 50%. The results show that the airflow and tire concentration define different modes of combustion while the reaction remains oxygen limited. Oil production is maximized when an increase in airflow leads to a transition from a rate-limited reaction to a heat transfer-limited propagation. Variation of the tire concentration shows the importance of the inert in achieving high conversion rates.     

Sonochemical degradation of azo dyes in aqueous solution: a new heterogeneous kinetics model taking into account the local concentration of OH radicals and azo dyes

The sonochemical decolorization and decomposition of azo dyes, such as C. I. Reactive Red 22 and methyl orange, were performed from the viewpoints of wastewater treatment and to determine the reaction kinetics. A low concentration of the azo dye solution was irradiated with a 200 kHz and 1.25 W/cm2 ultrasound in a homogeneous aqueous solution. The azo dye solutions were readily decolorized by the irradiation. The sonochemical decolorization was also depressed by the addition of the t-butyl alcohol radical scavenger. These results indicated that azo dye molecules were mainly decomposed by OH radicals formed from the water sonolysis. In this paper, we propose a new kinetics model taking into account the heterogeneous reaction kinetics similar to a Langmuir-Hinshelwood mechanism or an Eley-Rideal mechanism. The proposed kinetics model is based on the local reaction site at the interface region of the cavitation bubbles, where azo dye molecules are quickly decomposed because an extremely high concentration of OH radicals exists in this region. To confirm the proposed kinetics model, the effects of the initial concentration of azo dyes, irradiated atmosphere and pH on the decomposition rates were investigated. The obtained results were in good agreement with the proposed kinetics model.     

高性能管线钢中镍分析方法研究

用盐酸-硝酸混合酸溶解试样,以酒石酸钠掩蔽铁,氢氧化钠强碱性介质中,过硫酸铵为氧化剂,镍与丁二酮肟生成酒红色络合物,用吸光光度法测定高性能管线钢样品中镍,吸光度与镍含量在0.076%—0.66%范围内呈线性关系。采用不同镍含量的标钢溶液建立校准曲线。并测定了X-100、X-80及X-70钢级管线钢中的镍,结果满意。该方法准确、简便、成本低,具有实用和推广价值。     

A mathematical model of hotspot condensed phase ignition in the presence of a competitive endothermic reaction

We consider the propagation of a combustion front resulting from the gasless combustion of a condensed state fuel. The propagation of the front, essentially a premixed laminar flame, is supported by an exothermic reaction subject to possible heat loss through a competitive endothermic reaction. The dynamics of the endothermic process inducing the heat loss strongly depend on the temperature and the local fuel concentration. Through an analysis based on high activation energy, the steady-state values of the final burnt temperature as well as the burning velocity are obtained, and the control parameters are identified. Using a linear perturbation method, we assess the stability of the propagating front and obtain a condition for oscillatory behaviour. The critical parameter values for the transition from steady to oscillatory burning speeds are identified. The results represent a generalization of those obtained by Matkowsky and Sivashinsky to include the effects of heat loss induced by a competitive endothermic reaction.     

Electron spin polarisation in the photoreduction of xanthone in alcohol: effect of concentration and temperature

Time-resolved EPR studies of the hydrogen abstraction reaction of photoexcited xanthone in 2-propanol were carried out as a function of the concentration of xanthone and the sample temperature. The temperature was varied from 22°C to about ?30°C, and the concentration from about 0.2 to 4.0?mM. At low temperature or concentration, the observed spectra of the xanthone ketyl radical and the propan-2-olyl radical could be simulated as a superposition of a hyperfine-independent component due to the emissive triplet mechanism and a hyperfine-dependent component due to the S–T₀ radical pair mechanism. However, with an increase in the concentration of xanthone, the relative contribution of TM decreases, and, concomitantly, the net absorptive component of only the xanthone ketyl radical increases. As the spin polarisation mechanisms do not predict any concentration dependence, this unusual behaviour is explained by invoking the enhancement of the spin–lattice relaxation rates due to Heisenberg spin exchange occurring at high local concentrations of the radicals. The net absorptive signal is attributed to thermally equilibrated radicals. The observed temperature dependence of the spin polarisation behaviour is similarly explained. The origin of the net absorptive signal in the TREPR spectra of the acetone?2-propanol system is also attributed to thermally equilibrated radicals. The self-quenching mechanism of xanthone is proposed to be an electron-transfer reaction from an excited xanthone molecule to another xanthone in the ground state.     

不同环境氧浓度下聚甲氧基二甲醚（PODE）喷雾燃烧的羟基光谱分布及其反演重构研究

聚甲氧基二甲醚（PODE）是一种有潜力的柴油替代燃料，目前针对PODE的研究更多集中在发动机台架试验，相应的基础喷雾燃烧研究较少，制约了其在动力装置中高效清洁燃烧性能的提升。羟基（OH）性质活泼，大量存在的区域通常认为是高温反应区域。利用羟基光谱可以获得火焰结构、燃烧反应位置以及热释放速率等重要参数。环境氧浓度对火焰结构有很大影响，也是控制燃烧反应速率和污染物排放的重要参数。因此，在一台光学定容燃烧弹上，首先利用羟基的自发光光谱测量，研究了宽环境氧浓度变化（15%～80%）对PODE喷雾火焰浮起长度的影响，进一步利用阿贝尔逆变换方法将羟基自发光光谱强度由积分值反演为点位值，研究了富氧条件下（40%～80%）氧浓度变化对PODE喷雾羟基分布的影响。研究结果表明：环境氧浓度由15%增至40%，PODE火焰浮起长度迅速缩短；氧浓度进一步增加至80%，火焰浮起长度下降趋势逐渐变缓，直至基本不变；相同氧气浓度下PODE火焰浮起长度明显小于柴油。反演后的羟基光谱分布特征表面，富氧条件下PODE羟基光谱的高光强区域主要集中于喷雾边缘扩散火焰薄层中，同时，局部温度的显著提升使得羟基光谱强度在预混反应区下游附近达到最大；羟基光谱高光强区域随氧气浓度增加逐渐向火焰中上游区域迁移，并且其分布表现为轴向上更短，径向上更窄；在火焰达到准稳态时，相较40%氧气浓度条件，60%和80%氧气浓度下的羟基光谱强度在火焰中下游明显减弱，表明高的环境氧浓度下喷雾上游的燃油高浓度区域更快的参与到剧烈的燃烧反应中。     

On the Thermal Explosion Theory of a Heterogeneous Liquid–Liquid System

In this paper, the regularities of a thermal explosion of a heterogeneous system consisting of two immiscible liquids have been studied. Each phase is a solution of A and B reagents. Reagent B is extracted into a solution of reagent A, where the bimolecular exothermic reaction A + B → Products takes place. It has been shown that an exothermic reaction (combustion regime) continues to proceed in the system at high mass-exchange rates between phases after a thermal explosion. As a result, the maximal temperature may significantly exceed the temperature of the thermal explosion. The critical value of the Semenov parameter decreases with an increase in the mass-exchange rate between phases. In the limited range of values of the distribution coefficient of reagent B between phases, the increase of this coefficient is also accompanied by a decrease in the critical value of the Semenov parameter. The concentration of reagent B in the initial phase decreases monotonically due to its extraction into another phase. However, the equilibrium of the extraction of reagent B can shift, due to the temperature dependence of the distribution coefficient during the reaction. Thus, the time dependence of the concentration of reagent B on may be more complex and can pass through a minimum.     

Solution Grafting of Maleic Anhydride on Low-Density Polyethylene: Effect on Crystallization Behavior

Maleic anhydride (MAH) was grafted onto low-density polyethylene (LDPE) by a solution approach with dicumyl peroxide (DCP) as initiator and xylene as solvent. The effects of various experimental conditions on the grafting degree (GD, wt%), such as DCP concentration (A), MAH concentration (B), reaction time (C), reaction temperature (D) and the time for initiator addition (E), were investigated by an orthogonal experiment. The results demonstrated that the DCP concentration had the greatest influence on GD, while the reaction temperature had a minimal influence on GD. A copolymer with high GD (up to 4%) was obtained under the optimum conditions. It was proven that MAH was grafted onto the LDPE successfully by FT-IR. The crystallization behavior of the grafted LDPE was studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD), and the crystallization kinetic parameters of the grafted LDPE were obtained. Compounds of paraffin and grafted LDPE were investigated by XRD. The results demonstrated that a small amount of LDPE-g-MAH could affect the crystallization behavior of paraffin. This suggested that the grafted LDPE has a potential application as a pour point depressant (PPD) for heavy oil.     

基于混合发展的超声速段射流式COIL的数值优化

应用CFD技术,发展三维多组分化学反应流计算程序,对采用超声速段射流方式的氧碘化学激光进行数值模拟,考察分解率与增益等参考变量的详细三维分布.计算结果说明,超声速区域的高速流动以及混合效率降低使COIL无法在有限空间内完成整个运转流程;提高碘含量以加快反应速度的手段导致主流无法提供足够的载能介质,无法形成合理增益.在不改变喷管长度的前提下,提出主流无载气方式的探索,结果证明了超声速段射流方式采用无载气主流配置的可行性与优势,通过减小气流速度保证混合与化学反应在光腔上游完成,在合理的流量配比下光腔位置处可得到1.3%cm^-1的增益峰值.     

Experimental quantification of cavitation yield revisited: focus on high frequency ultrasound reactors

Acoustic cavitation plays an important role in enhancing the reaction rate of chemical processes in sonochemical systems. However, quantification of cavitation intensity in sonochemical systems is generally limited to low frequency systems. In this study, an empirical determination of cavitation yield in high frequency ultrasound systems was performed by measuring the amount of iodine liberated from the oxidation of potassium iodide (KI) solution at 1.7 and 2.4 MHz. Experiments for determining cavitation were carried out at various solute (KI) concentrations under constant temperature, obtained by direct cooling of the solution and variable temperature conditions, in the absence of external cooling. Cavitation yield measurements, reported in this work, extend previously reported results and lend credence to the two step reaction pathway in high frequency systems. Additionally, the concentration of KI and temperature affect the cavitation yield of a system such that the iodine production is proportional to both conditions. It is proposed that direct cooling of sonicated KI solution may be advantageous for optimization of cavitation intensity in high frequency sonochemical reactors.     

Laser-induced spatial structures in a chemically active gas-phase medium illuminated by annular diffracting beams

The laws governing the propagation of diffracting beams in a two-component gaseous mixture are investigated on the basis of a computer simulation. It is discovered that several regions with high concentrations of the reaction product form. It is also found that the beam focus can move both in the direction of beam propagation and in the counter direction, and the change in its position can occur abruptly. It is shown that as time goes on, a high concentration of the reaction product is achieved in the central unilluminated region of the medium near the entrance cross section on account of diffusion (i.e., a diffusional concentration growth occurs). This leads to the formation of a dynamic concentration maximum in this region of the medium. Zh. Tekh. Fiz. 68, 8–14 (March 1998)     

Mole-controlled growth of Y-doped ZnO nanostructures by hydrothermal method

We investigated the mole-controlled growth of Y-doped ZnO (YZO) nanostructures by the hydrothermal synthesis techniques. Through controlling the aqueous solution's mole concentration, we could modify the morphological and structural properties of YZO. The shape of YZO becomes a nanometer-sized rod when using a relatively low mole concentration, whereas the morphology is changed to be flat and mosaic when using a relatively high mole concentration. Since the aqueous solution's mole concentration decides the amount of hydroxide, we ascribe the mole-controlled morphological changes to the alteration of chemical potential during the hydrothermal chemical reaction.     

O2/CO2方式下钙基吸收剂在脱硫过程中微观结构变化的研究

本文研究了O2/CO2方式下钙基吸收剂在脱硫过程中微观结构的变化。研究结果表明,不同浓度的CO2对孔隙结构的影响完全不同;且提高温度有利于改善高浓度CO2气氛下钙基吸收剂煅烧后的孔隙结构,较之空气气氛,高浓度CO2气氛更有利于高温下炉内喷钙脱硫。     

Determination of the effective charge on muonium during its reaction in aqueous solution

The rate of reaction of muonium atoms with solutes of either charge is unaffected by the addition of a high concentration of an inert salt, therefore the effective charge on the muonium at the point of reaction is essentially zero.     

Hydrothermal synthesis of highly nitrogen-doped carbon powder

Nitrogen-doped carbon powder (NCP) with high and controllable dopant concentration was facilely synthesized via hydrothermal treatment of sucrose under ammonia followed by calcination. The dopant concentration of the as-synthesized carbon powder can be easily adjusted in the range of 4.37-17.82 wt.% by careful choice of the reaction conditions. The precursor with high nitrogen content was prepared by aminization reaction between sucrose and ammonia in hydrothermal condition, amine groups are successfully introduced into the precursor molecule, which groups convert finally to pyridinic-like and graphitic-like structure in the followed heat-treatment process. Various techniques, including the elemental analysis, TG-DTA, XPS, XRD, SEM and FTIR, were employed to characterize and assess the compositional and structural properties of the precursor and final nitrogen-doped materials. The present work propose a novel method for synthesis of highly nitrogen-doped carbon materials.     

Dependence of reaction pressure on deposition and properties of boron-doped freestanding diamond films

In this paper, we investigate the reaction pressure-dependent growth and properties of boron-doped freestanding diamond films, synthesized by hot filament chemical vapor deposition (HFCVD) at different boron-doping levels. With the decrease in pressure, the growth feature of the films varies from mixed [1 1 1] and [1 1 0] to dominated [1 1 1] texture. The low reaction pressure, as well as high boron-doping level, results in the increase (decrease) of carrier concentration (resistivity). The high concentration of atomic hydrogen in the ambient and preferable [1 1 1] growth, due to the low reaction pressure, is available for the enhancement of boron doping. The estimated residual stress increases with increase in the introducing boron level.     

NVP在全息聚合物分散液晶光栅中的反应动力学研究

为了提高全息聚合物分散液晶(简称HPDIC)光栅的衍射效率并得到良好的光栅表面形貌,在制备光栅的反应体系中添加了具有吡咯烷酮结构的单官能度小分子NVP,并进一步阐述了NVP对HPDLC光栅在反应动力学方面的影响.分析表明,NVP的添加显著增加了预聚单体的聚合速率,并且能使原本被困在聚合物网络当中的双键继续发生反应,从而大大提高了反应体系的双键转化率;另外,NVP的添加使得光栅的相分离更加彻底,在获得良好的表面形貌的同时也增大了光栅的折射率调制度,从而提高了HPDLC光栅的衍射效率.总之,在添加了NVP之后,体系的聚合速率和预聚单体的反应度都大大提高,从而使得光栅的表面形貌和衍射效率也得到较大的改善和提高,衍射效率提高到96.36%.     

光谱法锌离子检测系统的研究

采取标准锌显色剂与锌发生显色反应，生成不溶于水的絮状络合物。用光谱仪测它的吸光度，研究其特征谱与吸光度的特点，建立其浓度与特征波长吸光度间的数学模型。本文所采用的显色剂主要与锌、铜、镉、镍四种离子发生络合反应。因此分别探索了四种离子高浓度以及低浓度时显色反应的吸光度，最终通过得到锌离子浓度与吸光度的关系式以及锌离子浓度与四波长下四种离子混合溶液显色后的吸光度的关系式，给出了锌离子的吸光度与总吸光度的关系式。显色反应能否满足分光光度法的要求，主要与显色剂的性质有关，同时显色反应的条件也至关重要。因为在显色反应过程中，主要是锌离子与锌显色剂发生络合反应形成络离子，进而形成絮状络合物。络离子一般比较稳定，但在水溶液中也存在着电离平衡，也就是说当显色条件发生变化时，既有可能形成络离子，也有可能发生络离子的分解，从而影响络合反应的程度。显色条件包括显色剂用量、pH值、反应温度、显色时间、待测溶液的盐度以及浊度等。重点研究待测溶液的盐度对锌离子浓度测量值的影响，并通过实验给出影响规律以及校正模型。     

Diffusion of the diboron pair in silicon

We propose a novel mechanism for the diffusion of a diboron pair in Si, based on first principles density functional theory. We find a reaction pathway along which the boron pair diffuses from one lowest energy configuration of [B-B](s)-< 001> to an equivalent structure at an adjacent equivalent site through three local minimum states denoted as [B-B](s)-< 111>, B(s)-B (i), and B(s)-B (s)-Si (i). The activation energy for the diffusion is estimated to be 1.81 eV in the generalized gradient approximation. A kinetic model suggests that the diboron diffusion plays an important role in determining diffusion profiles during ultrashallow junction processing (which requires high boron-dopant concentration as well as high annealing temperature).     

Theory of photoinduced charge separation in solids

We discuss photoinduced ionization and charge separation kinetics in solutions as a way to conserve and utilize light energy. Our interest is in the secret of the high efficiency of reaction centers and the fast and irreversible separation of ions involved in reduction and oxidation reactions in the macromolecule. We present a new theory of reversible charge transfer, which shows high efficiency of charge separation: the charge's recombination has a weak influence on the donor cation-state probability's maximum value but a large effect on its long-time behavior. We give the comparison of new results with recently published ones on charge separation kinetics in condensed media. We use the methods of independent reaction “vessels” and “conditional concentrations”. The influence of back charge transfer is essential for long-time tail of the cation-state probability; its action on the cation-state probability's maximum value grows weak with an increase of forward rate constants and acceptor's concentration.