The propagation and inhibition of an exothermic branched-chain flame with an endothermic reaction and radical scavenging

The effects of the endothermic decomposition of an inhibitory species W to form a radical scavenger on a laminar, pre-mixed flame supported by an exothermic second-order branching reaction are considered. This work extends a previous study, where the effects of the radical scavenger S were ignored. Two cases are identified, dependent on a parameter measuring the relative rate of the decomposition of W. These are described by an high-activation-energy asymptotic analysis and through numerical integration of the propagating-flame equations for representative parameter values. For larger values of the effect of the radical scavenger is to introduce a critical value of the heat-loss parameter for flame propagation. For smaller values of , where there is a critical value of without any S being produced, the effect is to lower this critical value. In both cases the effect of the radical scavenger is to reduce the propagation speed and, if sufficient amounts of S are produced from the decomposition of W, to totally suppress flame propagation, even without any heat loss.     

Treasure of the Past VIII: Molecular Basis of Flame Inhibition

The role played by inorganic chemical additives in fire retardancy and flame inhibition is considered. Particular attention is given to the molecular level aspects of commercially important systems containing compounds of antimony, halogens, and phosphorus. The flame inhibiting function of metal containing additives is also discussed.     

吸热陶瓷涂层的火焰喷涂及其耐磨行为

对在钢材表面采用的氧乙炔火焰喷涂这一新型吸热陶瓷材料的耐磨性能及耐磨机理进行了试验研究结果表明，该涂层具有较低的孔隙率、较高的硬度和抗压强度，以及良好的耐磨性。其磨损机理主要有塑性涂抹、磨粒磨损和疲劳剥落。     

瓦斯爆炸火焰厚度的实验研究

本文对水平管道中瓦爆炸传播火焰的厚度进行了实验研究,对不同浓度的瓦斯／空气爆炸火焰的厚度及传播速度进行了实际的测量,得到了火焰厚度变化的基本规律。在本实验条件下所测得的实际火焰厚度较厚, 而且变化范围较大,其厚度比按传统的静态火焰模型计算出的结果大得多。该实验结果为泊瓦斯爆炸机理的研究、瓦斯爆炸模型的建立以及数值模拟提供了可靠的实验数据。     

Flame Synthesis of Coiled Carbon Nanotubes

A flame synthesis technique of coiled carbon nanotubes using acetylene jet flames and iron catalyst is presented. It was found that acetylene flames generate single wall coiled nanotubes within in a narrow pyrolysis zone above the burner for a limited range of fuel flow rates. The corresponding local convective time scale corresponding to the coiled nanotube formation zone is around 0.04 ms. The yield of the coiled carbon nanotubes was further increased by changing the local convective time scale with the addition of controlled turbulence.     

Effects of Fuel Compositions on the Structure and Yield of Flame Synthesized Carbon Nanotubes

Flame synthesis of carbon nanostructures including nanotubes on galvanized steel was investigated utilizing laminar diffusion flames of different types of fuel. Methane (CH₄), propane (C₃H₈) and acetylene (C₂H₂) were used as fuels. Distinctive carbon nanostructures were produced depending on fuel types and fuel flow rates. The qualitative and quantitative analysis of many transmission electron microscope (TEM) and scanning electron microscope (SEM) images were performed. Methane produced thin multi wall carbon nanotubes as well as nanorods and nanofibers within the fuel flow rate range of 7.18E-07 m³/s to 9.57E-07 m³/s. Propane yielded nanotubes only at the fuel flow rate of 4.20E-07 m³/s. The nanotubes synthesized by acetylene flames were of different types that included helically coiled and twisted nanotubes.     

On hydrodynamic instability of the flame-wedge

The hydrodynamic stability of the premixed wedge-shaped flame involving a burned-gas stagnation zone is considered. It is shown that the Darrieus-Landau instability of the flame interface is reinforced by the Kelvin-Helmholtz instability of the stagnation-zone boundary.     

钛酸锶钡纳米粉体的溶胶-凝胶自蔓延燃烧制备及其介电性能研究

采用溶胶-凝胶和自蔓延燃烧技术,制备了平均晶粒尺寸约20nm的Ba0.5Sr0.5TiO3(BST)纳米粉体.将纳米粉体压制成形后进行烧结,得到BST陶瓷.采用XRD、SEM、TEM和LCR数字电桥研究了BST的结构、形貌和介电性质.结果表明,干凝胶自蔓延燃烧后,可直接形成分散性好、颗粒尺寸均匀、具有钙钛矿结构的BST纳米粉体.BST陶瓷压片经1250℃烧结2h后获得了致密的结构和相对较大的介电常数.粉体的结晶温度和烧结体的烧结温度均低于传统工艺.很明显,溶胶-凝胶自蔓延燃烧法在纳米材料的制备方面具有明显的技术优势.     

Delayed thermal explosion in flammable gas containing fuel droplets: Asymptotic analysis

The problem of thermal explosion in a flammable gas mixture with addition of volatile fuel droplets is studied based on the asymptotic method of integral manifolds. The model for the radiative heating of droplets takes into account the semitransparency of droplets. A simplified model for droplet heat-up is used. The results of the analysis are applied to the modelling of thermal explosion in diesel engines. Two distinct dynamical situations have been considered, depending on the initial droplet concentration. These are far zone (small initial liquid volume fraction and small droplet radii) and near zone (large initial liquid volume fraction and large droplet radii). The conditions of the first zone are typical for the areas in the combustion chamber which are far from the fuel injectors, while the conditions of the second zone are typical for the areas in the combustion chamber which are relatively close to the fuel injectors. It has been pointed out that small droplets heating and evaporation time in the far zone is smaller than the chemical ignition delay of the fuel vapor/air mixture. The total ignition delay decreases with increasing initial gas temperature. In the near zone for large droplets, the process starts with the initial gas cooling and slight heating of droplets. This is followed by a relatively slow heating of gas due to the chemical reaction, and further droplet heating. The total ignition delay in the near zone is larger than in the far zone. It is expected that before thermal explosion in the near zone takes place, the droplets break up and are removed from this zone. In optically thick gas effects of thermal radiation are negligible for small droplets but are noticeable for large droplets.     

Synthesis of nano-sized hydroxyapatite powders through solution combustion route under different reaction conditions

Calcium hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ (HAp) was synthesized by combustion in the aqueous system containing calcium nitrate-diammonium hydrogen orthophosphate with urea and glycine as fuels. These ceramics are important materials for biomedical applications. Thermo-gravimetric and differential thermal analysis were employed to understand the nature of synthesis process during combustion. Effects of different process parameters namely, nature of fuel (urea and glycine), fuel to oxidizer ratio (0.6-4.0) and initial furnace temperature (300-700 °C) on the combustion behavior as well as physical properties of as-formed powders were investigated. A series of combustion reactions were carried out to optimize the reaction parameters for synthesis of nano-sized HAp powders. The combustion temperature (T_f) for the oxidant and fuels were calculated to be 896 °C and 1035 °C for the stoichiometric system of urea and glycine respectively. The stoichiometric glycine-calcium nitrate produced higher flame temperature (both calculated and measured) and powder with lower specific surface area (8.75 m²/g) compared to the stoichiometric urea-calcium nitrate system (10.50 m²/g). Fuel excess combustion in both glycine and urea produced powders with higher surface area. Nanocrystalline HAp powder could be synthesized in situ with a large span of fuel to oxidizer ratio (φ) in case of urea system (0.8 < φ < 4) and (0.6 < φ < 1.5) for the glycine system. Calcium hydroxyapatite particles having diameters ranging between 20 nm and 120 nm could be successfully synthesized through optimized process variable.     

Graphene-oxide-based immunosensing through fluorescence quenching by peroxidase-catalyzed polymerization

A graphene oxide (GO)-based immunosensor is developed for the detection of interleukin-5 (IL-5), a key cytokine associated with asthma pathology and eosinophilia. The immunosensing platform utilizes the innate fluorescence of GO, not demanding biomolecules labeled with fluorescent dyes. The GO-based immunoassay exhibits high specificity for IL-5 among other cytokines and is not affected by nonspecific proteins in human serum.     

TDLAS火焰燃烧温度测量方法改进

基于可调谐二极管激光吸收光谱技术(TDLAS)双线温度测量原理,设计了7153.748-7154.354 cm~(-1)谱线对单激光器TDLAS燃烧温度测量系统,对平面预混火焰燃烧温度进行测量,发现由于吸收较弱、信噪比较低等造成测量结果与热电偶测量结果相对偏差较大。针对这一问题,提出了采用(7185.597-(7444.352+7444.371))cm~(-1)双激光器TDLAS系统,并结合增加光程方法来改进原有的温度测量精度。结果表明:采用双激光器可放宽谱线对的选择范围,选择吸收更强的谱线对可以有效提高信噪比,并且结合增加光程,可实现TDLAS温度测量结果与热电偶测量偏差由10%降低到5%。     

外加电场气相法制备纳米无机氧化物

气相燃烧法纳米无机氧化物粉体特征一方面取决于前驱体的水解反应速度和粒子的成核生长动力学, 另一方面受到燃烧反应器内物料的流动混合、热质传递等多种过程因素的影响。电场控制气相燃烧法制备纳米 无机氧化物是在原有的基础上外加电场,使火焰的轴向高度降低、径向宽度增大,形成厚度相对均匀的火焰层, 火焰温度梯度也随之增大,抑制粒子表面的生长和粒子之间的烧结,获得“粒径分布较窄的粒子和结构相似的 聚集体”。     

火焰法在硬质合金上合成金刚石薄膜

用Ｏ２／Ｃ２Ｈ２燃烧火焰法在各种不同性质的衬底材料上直接合成金刚石薄膜，研究了硬质合金刀头的不同的冷却方式下，对合成金刚石膜的影响。结果表明：ＹＧ６硬质合金由于Ｃｏ的存在影响了金刚石膜的质量；当冷却方法不当时，硬质合金头刃部易过热；采和分段沉积法可改善金刚石膜与硬质合金的附着性。     

A mathematical model for wet-chemical diffusion-controlled mask etching through a circular hole

Asymptotic solutions are presented for diffusion-controlled wet-chemical etching through a round hole in a mask. The three-dimensional diffusion field is assumed to be axisymmetric and fully developed. Two time regimes are considered. The first applies when the etched depth is small in comparison with the width of the mask opening. In the second, the depth of etching is much greater than the width of the mask opening. Explicit solutions are found for the shape of the etched surface as a function of the physical parameters. Among other things it is found that, as long as the etched pits are shallow, etching through small apertures is faster than through larger ones. The opposite is true for deep pits.     

丙烷-氧气预混气体的火焰传播及点火特性

采用有机玻璃管装置,研究了丙烷-氧气预混气体在管道中的火焰传播特性及最小点火能。研究表明:3种惰性气体(CO₂、N₂、Ar)均明显降低了预混气体火焰在管道中的加速进程;其中,CO₂抑制效果最为显著,其次是N₂和Ar。点火敏感电极间距为2 mm。最小点火能（E）随混合气体初始压力的增大而减小,初始压力为100 kPa时,0.16 mJ＜E ＜0.32 mJ;当压力降至30 kPa时,2.00 mJ＜E ＜3.00 mJ。     

甲烷燃烧法合成纳米二氧化钛的试验研究

以甲烷为燃料、空气为氧化剂、TiC14为原料,采用燃烧法合成了纳米二氧化钛,利用扫描电镜和X射线衍射对制备出的纳米TiO2颗粒产品的颗粒尺寸分布和物相组成进行了表征,通过调节甲烷、空气、载气的流量,并通过热电偶测量火焰温度,制备出不同操作工况下的纳米TiO2产品,讨论了工艺参数对颗粒特性的影响。结果表明,获得的纳米TiO2粒径主要分布在50～70nm,产品中大部分为锐钛矿相,含有少量的金红石相。     

Exothermic reaction characteristics of continuously ball-milled Al/Ni powder compacts

Self-propagating reactions in compacted pellets of continuously low-energy ball-milled aluminium (Al) and nickel (Ni) powders at a composition corresponding to AlNi₃ were investigated. The formation of a bi-modal structure with nanoscale lamellae of Al and Ni surrounding thicker Ni layers was observed. The milled powder sizes decreased for milling durations longer than 4 h, but the pellet green densities remained mostly constant for longer than 2 h of milling. The ignited pellets observed using high-speed optical and infrared imaging revealed that the thermal wave velocity, maximum reaction temperature, ignition initiation duration and ignition temperature decreased with increasing milling times due to solid-state diffusion. X-Ray Diffraction (XRD) analysis after ignition tests showed that the AlNi₃ amount increased with milling time. Thermal analysis using interrupted Differential Scanning Calorimetry (DSC) in combination with XRD revealed that the ball-milled pellets have similarities to nanoscale magnetron sputtered multilayer foils in terms of phase formation sequence and exothermic peak shifts.     

A deflagration analysis of porous energetic materials with two-phase flow and a multiphase sequential reaction mechanism

A theoretical analysis for the unconfined deflagration of a porous energetic material is developed for a two-step global reaction mechanism that consists of the condensed-phase combustion of the reactive material to produce gas-phase intermediates, followed by a gas-phase reaction that produces final gas-phase products. An asymptotic approach is employed, leading to explicit formulas for the deflagration velocity in specific parameter regimes. The results clearly indicate the influences of two-phase flow and the multiphase, multi-step chemistry on the burning rate, and serve to further characterize the combustion behavior of a significant class of degraded nitramine-type propellants for which the present analysis is applicable.     

气相燃烧制备无机纳米粉体的心脏-燃烧器的喷嘴

纳米无机氧化物的性质和应用很大程度取决于“聚集体的结构形态和原生粒子的粒径分布”,而这两个特征,一方面受到前驱体的水解反应速度、粒子成核生长动力学等的影响,另一方面受到燃烧反应器内物料的流动混合、热质传递等多种过程因素的控制,同时,前驱体进入燃烧水解区的最初几毫秒就形成原生粒子,说明制备纳米复合粉体的关键设备是燃烧反应器。