Flame Photometric Determination of Submicrogram Quantities of Boron

A procedure for the determination of submicrogram amounts of boron in aqueous solutions is described. The method is based on measuring the chemiluminescence of the molecular species BO_x in either an air/hydrogen or air/acetylene flame. Detection limits obtained with these flames were 0.004 and 0.06 ppm, respectively. Potential interferences may be removed by ion-exchange chromatography. The procedure is applicable to the determination of boron in potable waters.     

Reference natural gas flames at nominally autoignitive engine-relevant conditions

Laminar natural gas flames are investigated at engine-relevant thermochemical conditions where the ignition delay time τ is short due to very high ambient temperatures and pressures. At these conditions, it is not possible to measure or calculate well-defined values for the laminar flame speed s_l, laminar flame thickness δ_l, and laminar flame time scale ${\tau }_l={\delta }_l/s_l$ due to the explosive thermochemical state. Here, the corresponding reference values, s_R, δ_R, and ${\tau }_R={\delta }_R/s_R,$ that account for the effects of autoignition, are numerically estimated to investigate the enhancement of flame propagation, and the competition with autoignition that arises under nominally autoignitive conditions (characterised here by the number τ/τ_R). Large values of τ/τ_R indicate that autoignition is unimportant, values near or below unity indicate that flame propagation is not possible, and intermediate values indicate that a combination of both flame propagation and autoignition may be important, depending upon factors such as device geometry, turbulence, stratification, et cetera. The reference quantities are presented for a wide range of temperatures, equivalence ratios, pressures, and hydrogen concentrations, which includes conditions relevant to stationary gas turbine reheat burners and boosted spark ignition engines. It is demonstrated that the transition from flame propagation to autoignition is only dependent on residence time, when the results are non-dimensionalised by the reference values. The temporal evolution of the reference values are also reported for a modelled boosted SI engine. It is shown that the nominally autoignitive conditions enhance flame propagation, which may be an ameliorating factor for the onset of engine knock. The calculations are performed using a recently-developed, detailed 177 species mechanism for C0–C3 chemistry that is derived from theoretical chemistry and is suitable for a wide range of thermochemical conditions as it is not tuned or optimised for a particular operating condition.     

Synthesis of high refractive‐index melt‐stable aromatic polyphosphonates

The synthesis of aromatic polyphosphonates based on the step polymerization of various bisphenols and dichlorophenyl phosphine oxide was investigated. The effect of catalyst, type, concentration, and polymerization time were systematically varied to obtain high molecular weight polymers. Very high molecular weight tough, ductile materials with a high degree of optical clarity were synthesized. In contrast with the aromatic polycarbonates, the refractive index was increased from 1.58 to 1.60 (for the bisphenol A‐based system) and 1.64 for a biphenol‐based system. The latter was still an amorphous soluble polymer as a result of the non‐coplanar nature of the phenyl phosphine oxide bond, unlike the analogous polycarbonate. Hydrolytically stable melt‐processable cumyl phenol end‐capped polyphosphonates were successfully achieved for the first time. Rheological studies show that these end‐capped systems are melt‐stable at 200 °C, whereas the systems of initially higher molecular weight but without any well‐defined end capping clearly degraded quickly probably as a result of an acid‐catalyzed hydrolysis process. Extensive high char yields were produced upon pyrolysis in either nitrogen or air, suggesting good fire resistance. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2904–2910, 2001     

一种新型含磷-溴-氮阻燃剂的合成

以三氯氧磷、季戊四醇、2 ,3-二溴丙醇及三聚氰胺等为原料合成了一种新型磷 -溴 -氮阻燃剂 0 - (2 ,4,6 -三氧杂 - 1-氧基磷杂双环 [2 .2 .2 ]辛烷 - 4-亚甲基 ) - 0 - 2 ,3- (二溴丙基 )磷酸三聚氰胺盐 (Ⅲ ) .改进了中间体 4-羟甲基 - 2 ,6 ,7-三氧杂 - 1-氧基磷杂双环 [2 .2 .2 ]辛烷 (Ⅰ )的合成条件 ,元素分析、红外光谱等确定了结构     

表面处理剂在氢氧化镁阻燃聚乙烯体系中的应用

探讨了几种常用的表面处理剂对氢气体镁－聚乙烯阻燃体系的力学性能及燃烧性能的影响。实验结果表明,在聚乙烯中添加100phr氢氧化镁后其力学性能已经严重劣化。通过添加适量的表面处理剂可以大大改善体系的新裂伸长率,但是通过会使其拉伸强度有所下降,阻燃性能有所降低。     

Flame‐retardant epoxy resin compounds containing novolac derivatives with aromatic compounds

New flame‐retardant epoxy resin compounds containing novolac derivatives with specific aromatic compounds have been developed. After crosslinking reactions between epoxy resin and hardener, the epoxy resin compounds formed highly flame‐retardant network structures that were obtained by including biphenylene and phenylene moieties in the main chains of novolac‐type epoxy resin and phenol novolac resin hardener. The high flame retardancy is due mainly to the stable foam layers that form during combustion because of the low elasticity at high temperatures and the high pyrolysis resistance of the compounds. Furthermore, the addition of excess phenol derivative hardener not only facilitates the formation of the foam layers by decreasing the crosslink densities but also reduces the amount of flammable substances generated from the epoxy resin compounds during combustion. The use of a multifunctional epoxy resin containing four glycidyloxy groups in the compounds improved characteristics such as heat resistance and strength at high temperatures, while maintaining excellent flame retardancy. Copyright © 2001 John Wiley & Sons, Ltd.     

微重力下环境压力对火焰传播的影响

研究表明,在微重力环境中,当强制对流速度很小时,环境压力的增大会加强氧气的扩散,减弱辐射热损失对火焰的冷却效应,使火焰传播速度增大。但随着强制对流速度的增大,对流成为质量传递的主要途径,化学反应速率受化学反应动力学因素控制,火焰传播速度对压力的变化不敏感。     

载人航天器火灾安全研究进展

理论上和实际上, 载人航天器都有发生火灾的可能, 载人航天器的火灾安全问题是微重力燃烧研究的重要内容. 氧气浓度和气流速度对给定固体材料的可燃性具有显著影响,在固体表面的逆向和同向传播火焰中, 都存在由氧气浓度和气流速度决定的可燃极限, 即气流速度较高时的吹熄和气流速度较低时的冷熄. 极限氧气浓度和极限气流速度两个极限参数, 是衡量材料可燃性的关键指标. 在微重力条件下, 当低速气流存在时, 固体材料发生有焰燃烧和闷烧的可能性都大大增强. 因此, 剔除材料中的潜在燃料是航天器防火的主要措施.但是, 在航天器使用的材料中, 仅有很少一部分是阻燃的, 为了保证火灾安全, 还必须采取火灾检测和灭火措施. 当前美国和俄罗斯采取的火灾安全方案, 既有相似性, 也有各自的特点. 在载人航天器的火灾安全问题中, 尚有很多问题和方案有待研究或检验. 考虑到我国的实际情况, 作者认为, 通过实验对照和数值模拟的方法, 开展材料在微重力条件下的燃烧特性的常重力模拟, 对于我国载人航天器的火灾安全具有现实意义.      

层焰系统奇点结构的研究

在一定的假设条件下,将气体燃烧的物理模型简化为层焰系统．借助于热力学理论和相关的守恒定律建立了层焰系统的数学模型并对其进行了深入地分析．利用常微分方程的定性理论和方法,结合燃烧的实际需要,对应于参数的不同取值,研究了位于瑞利线上奇点的个数和位置,确定了暴燃区和爆炸区内不同奇点的定性结构及其稳定性,给出了在反应速度-滞止焓平面及燃烧速度-滞止焓平面内层焰系统轨线的相图．     

富氧空气-乙炔火焰原子吸收光谱法测定地质样品中痕量铍

研究了用富氧空气-乙炔火焰原子吸收光谱法测定铍的分析方法。当空气流量为6.0 L·min-1,氧气流量为4.2 L·min-1,乙炔流量为7.4 L·min-1时铍有较高的吸光度。在2.5%的8-羟基喹啉介质中,能较好地消除基体干扰且有一定的增感作用。方法的检测限为0.006 μg·mL-1,测定精密度RSD为4.69％,测定地质标准物质中铍的结果与鉴定值吻合。