Diphenylmethane diisocyanate self-polymerization: Thermal hazard evaluation and proof of runaway reaction in gram scale

Thermal analysis by differential scanning calorimetry and thermogravimetric/differential thermal analysis mass spectrometry, adiabatic calorimetry, a gram-scale heating test, and infrared spectroscopy were performed to evaluate the thermal hazards of diphenylmethane diisocyanate (MDI) and prove the occurrence of a runaway reaction. The self-polymerization of MDI was found to occur at about 340 °C under rapid heating conditions. Carbon dioxide was eliminated and heat was generated to allow polymerization. Under adiabatic and closed conditions, the runaway reaction of MDI can begin at least from 220 °C. Besides it is highly probable that the runaway reaction of MDI can begin from a lower temperature in an actual process scale. More heat was generated than in the previous case and the pressure rose rapidly. A closed 2-mm-thick glass vessel exploded because of the runaway reaction of MDI even if the temperature was lower than 300 °C. Therefore, MDI could cause fatal runaway reactions below 300 °C, where MDI had been assumed to self-polymerize by eliminating carbon dioxide previously.     

Calorimetric studies on the thermal stability of methyl ethyl ketone peroxide (MEKP) formulations

The energetic decomposition of methyl ethyl ketone peroxide (MEKP) and its formulations have long been known to present a significant risk. Indeed, MEKP has the highest number of reported decomposition incidents of all organic peroxides, many of which have led to significant numbers of fatalities, injuries and damage. It is noteworthy that incidents have been reported at all stages of the product lifecycle.This paper is derived from incident-investigation work and provides a summary of serious incidents involving MEKP, followed by details of calorimetric experiments performed to investigate thermal stability of representative MEKP formulations containing varying amounts of MEKP monomer. In particular we report the wide degree of variation that exists between commercial MEKP formulations, even between materials that are of the same nominal formulation. Such variations are detectable using differential scanning calorimetry (DSC).Follow-up studies performed on a representative MEKP formulation containing MEKP monomer indicate that a risk of decomposition exists at temperatures well below the reported self-accelerating decomposition temperature (SADT) of the products. As such, the experimental results reported here suggest that lower storage temperatures (commonly recommended by manufacturers to maximise shelf life) should be considered as being essential throughout the product lifecycle to reduce the risk of accidents in storage and transportation.     

隧道下穿桥梁的桥墩稳定性未确知测度评价研究

为指导隧道安全施工,保证路桥的安全运营,对桥梁桥墩稳定性进行评价,运用未确知理论,建立未确知测度评价模型。结合葵坝隧道下穿盐坝高速路桥的工程实际,选取影响桥墩稳定性的10个指标构造评价指标体系,依据每个桥墩的指标分级标准构建单指标未确知测度函数,确定每个对象的单指标测度矩阵;用熵权法计算各对象指标的权重,进而得到了对象的多指标综合测度向量;并依据置信度识别准则得出12个桥墩的隶属等级和稳定性排序。结果表明:12个桥墩中,除有1个桥墩处于不稳定等级外,其余都处于稳定等级。     

城市重大危机事件演化的动力学模型研究

建立了城市重大危机事件的＂事件链＂,并分析了＂事件链＂中各状态的相互关系。基于SEIS传染病模型的思想,提出了一类城市重大危机事件的动力学模型。分别在不考虑外部因素对事件链的影响和考虑外部因素对事件链的影响的情况下,对事件从正常状态到危机状态沿时间的发展趋势和规律进行了分析,并对解进行Lyapunov稳定性分析以及计算机模拟仿真。研究表明：系统自身的修复能力和外部因素对系统的影响是控制危机事件的重要因素。     

浸润线深度对尾矿坝稳定性分析的影响研究

鉴于当前尾矿坝在线监测系统中关于浸润线深度预警指标存在的难定量化问题,基于尾矿库概化模型,假定三种平均坡度,四种浸润线深度,采用FLAC2D软件试用版对尾矿坝的抗滑稳定性程度进行了模拟分析,得到了每种条件下尾矿坝的剪应变云图和相对应的抗滑稳定安全系数,比较了尾矿坝安全系数随着平均坡度以及浸润线深度的变化情况,结果发现：平均坡度对尾矿坝的稳定性影响显著,尾矿坝的整体抗滑稳定系数随平均坡度的减小逐渐增大;此外在平均坡度相同的前提下,浸润线深度自5m增加至10m的区间内,浸润线每增加1m,安全系数提高的程度最大约为5%左右,随后提高的程度逐渐减小,直至稳定在3%左右。此结果为在线安全监测系统的预警提供了技术支持。     

基于AHP与粗糙集理论的采空区稳定性影响因素权重分析

为充分吸收层次分析法和粗糙集理论两类评价方法的优点,同时又能克服各自的缺陷,实现二者的优势互补,通过建立采空区稳定性影响因素综合评价指标体系,以层次分析法确定主观权重、粗糙集理论确定客观权重,然后将主、客观权重进行有机集成得到组合权重,使得采空区稳定性影响因素的评价更具客观性,从而提高采空区稳定性影响因素评价的精度。以老鸦巢矿区为例,构建了13个指标的综合评价指标体系,通过计算组合权重得到影响采空区稳定性的主要因素为高跨比、地质构造、最大暴露面积,这与矿山实际情况基本符合。     

一种纳米气溶胶发生系统的设计及性能测试

气溶胶发生系统是校准大气颗粒物测量仪器、研究纳米颗粒物特性和开展烟雾箱模拟实验的必备仪器之一.针对现有气溶胶发生仪器稳定性差和不利于外场监测等缺点,本研究设计了一款新型纳米气溶胶发生系统(包括气溶胶发生器和扩散干燥管),并通过搭建实验系统对该仪器的工作性能进行了测试.在性能测试中使用氯化钠(NaCl)-水溶液和癸二酸二辛酯(DOS)-异丙醇溶液分别产生固态NaCl和液态DOS气溶胶,利用扫描电迁移率粒径谱仪测试生成气溶胶的粒径分布.测试结果表明,通过调节溶液浓度(0.01～0.50 g·L-1)和载气流量(1.64～3.67 L·min-1),生成不同大小(几何平均粒径:25～51nm)和不同数浓度(106～107个·cm-3)的气溶胶.对仪器稳定性能测试发现,在3 h的测试时间里生成的气溶胶几何平均粒径变化小于6%,数浓度变化小于12%.     

Synthesis and characteristic of polyaniline/Dy2O3 composites: Thermal property and electrochemical performance

A simple route of in situ polymerization by the chemical oxidation method was successfully employed to synthesize polyaniline/dysprosium oxide (PANI/Dy₂O₃) composites. The synthesized materials were characterized by Fourier transform infrared spectra and X-ray diffraction. The thermal stability of the composite was studied by thermogravimetry (TG). The electrochemical performance of the composites was investigated by cyclic voltammetry and alternating current impedance spectroscopy with a three-electrode system. TG results suggested that the thermal stability of PANI/Dy₂O₃ composites showed a tendency to first increase and then decrease with increasing Dy₂O₃ amount. Electrochemical experiments indicated that the composite electrodes showed a lower capacitance than that of pure PANI, which may be attributed to the interaction between PANI and Dy₂O₃ in the composites.     

Synthesis and characteristic of polyaniline/Dy2O3 composites：Thermal property and electrochemical performance

A simple route of in situ polymerization by the chemical oxidation method was successfully employed to synthesize polyaniline/dysprosium oxide (PANI/Dy₂O₃) composites. The synthesized materials were characterized by Fourier transform infrared spectra and X-ray diffraction. The thermal stability of the composite was studied by thermogravimetry (TG). The electrochemical performance of the composites was investigated by cyclic voltammetry and alternating current impedance spectroscopy with a three-electrode system. TG results suggested that the thermal stability of PANI/Dy₂O₃ composites showed a tendency to first increase and then decrease with increasing Dy₂O₃ amount. Electrochemical experiments indicated that the composite electrodes showed a lower capacitance than that of pure PANI, which may be attributed to the interaction between PANI and Dy₂O₃ in the composites.     

VARIATION OF STREAM STABILITY WITH STREAM TYPE AND LWESTOCK BANK DAMAGE IN NORTHERN NEVADA1

ABSTRACT: Many natural and anthropogenic factors contribute to the stability or erodibility of stream channels. Although a stream rating procedure used by more than 60 percent of the U.S. National Forests provides an estimate of overall stability, it does not identify the cause of instability or indicate corrective management. To better sort natural from livestock influences, stream stability rating indicator variables were related to stream types and levels of ungulate bank damage in a large data base for streams in northern Nevada. Stability and the range in stability varied naturally with stream type. Ungulate bank damage had different effects on different stream types and on different parts of their cross-sections. Vegetation is more important for stability on certain stream types than on other types. Streams with noncohesive sand and gravel banks are most sensitive to livestock grazing. Range managers should consider the stream type when setting local standards, writing management objectives, or determining riparian grazing strategies.