Particle evolution during the decomposition of CdCO3

Particle evolution during and following the decomposition of cadmium carbonate was investigated using surface area and crystallite size analyses. Surface area results of decompositions at temperatures ranging from 523 to 775 K showed a maximum corresponding to the total decomposition of the carbonate. The maxima for vacuum and air decomposition occurred at 583 and 613 K, respectively. Crystallite size analyses showed that the sizes of the CdO resulting from the air decomposition of CdCO₃ at low temperatures was significantly larger than the corresponding values obtained for vacuum decomposition. These observations suggest that CdCO₃ sinters favourably in air before decomposition, leading to larger CdO crystallites after decomposition. After complete dissociation, the evolution of CdO particles is the same for vacuum and air decomposition, indicating that the sintering of CdO is essentially the same under these two conditions.     

Product decomposition strategy for optimization of supply chain planning

Optimization of large-scale supply chain planning models requires the application of decomposition strategies to reduce the computational expense. Two major options are to use either spatial or temporal Lagrangean decomposition. In this paper, to further reduce the computational expense a novel decomposition scheme by products is presented. The decomposition is based on a reformulation of knapsack constraints in the problem. The new approach allows for simultaneous decomposition by products and by time periods, enabling the generation of a large number of subproblems, that can be solved by using parallel computing. The case study shows that the proposed product decomposition exhibits similar performance as the temporal decomposition, and that selecting different orders of products and aggregating the linking constraints can improve the efficiency of the algorithm.     

Effects of heating rate, temperature and iron catalysis on the thermal behaviour and decomposition of 2-nitrobenzoyl chloride

Runaway reactions arising from the decomposition of thermally unstable materials are a concern in industry due to the potentially devastating effects that they yield. Studies into the occurrence of thermal runaway incidents have shown the most likely cause to be a result of an inadequate investigation of the process prior to its operation on a large-scale. The chlorination of ortho-nitrated carboxylic acids is an industrially important reaction in the fine and agrochemical industries. The products of these reactions, ortho-nitrated acid chlorides, have been involved in runaway incidents that have resulted in violent explosions; hence, their thermal stability must be studied. Previous studies [S.D. Lever, M. Papadaki, Study of condition-dependent decomposition reactions: the thermal behaviour and decomposition of 2-nitrobenzoyl chloride, Part I, J. Hazard. Mater. 115 (2004) 91-100] showed that the decomposition of the parent molecule, 2-nitrobenzoyl chloride, is highly condition-dependent with the sample heating rate and temperature of decomposition playing a preponderant role in the course of the decomposition. Here, we present the results of studies of the decomposition of 2-nitrobenzoyl chloride, when the sample is subjected to various heating treatments, temperatures and in the presence of iron. As the temperature of decomposition was increased from 150 to 162 degrees C, the heat of decomposition was reduced from -215 to -90 kJ/mol. As the heat up rate applied in bringing the sample to the decomposition temperature increased, the heat of decomposition also increased. An increase in the heat up rate from 2 to 7.5 degrees C/min resulted in an increase in the heat of decomposition from -90 to -215 kJ/mol. The presence of iron and silver was observed to lower the heat of decomposition from -185 to -160 and -110 kJ/mol, respectively. Under most conditions investigated, the temperature at which gas flow was initiated was 147-150 degrees C. The presence of iron reduced this temperature to 140 degrees C. Decomposition was observed to take place over two stages, where the sample was heated directly from 40 degrees C at the required heat up rate. Where the sample was heated in stages and where calibrations had been carried out preceding decomposition, the decomposition took place in one stage alone.     

氧化处理对Ti2分解特性及组织结构的影响

针对制备泡沫铝异型件的熔体路径发泡先驱体二次发泡工艺,对TiH2的氧化处理、变温分解特性、等温分解特性、组织结构进行了研究.研究表明:氧化处理可有效提高发泡剂的开始分解温度,随氧化处理温度的提高,开始分解温度提高;氧化处理后发泡剂的等温分解曲线由低分解平台、快速分解阶段和稳定分解阶段3部分组成,低分解平台随氧化处理温度的提高而延长;400℃/6h+500℃/1h+620℃/30s的处理,可使TiH2的分解量较400℃/6h+500℃/1h处理时有所提高;TiH2氧化处理后在其表面生成了厚约1.1~1.5μm的TixOy致密氧化层,TiH2在300~550℃氧化,其物相依次变化为:TiH1.97—TiH1.97+TiO2—TiH+TiO+TO—TiH+TiO+TO+TiH.     

Magnitude of effect of reaction parameters on 2-chlorophenol decomposition by ultrasonic process.

In the present work, decomposition of o-chlorophenol (2-cp) was carried out using an ultrasonic process. The extent of 2-cp decomposition depends on several parameters such as ultrasound wave energy (ultrasonic amplitude), addition of hydrogen peroxide (H2O2), pH value (H+ concentration), ionic strength, and initial concentration of 2-cp. The experimental results showed that the decomposition of 2-cp was affected by the various reaction conditions. The profiles of 2-cp decomposition fitted well with the first-order kinetic equation. A linear relationship was obtained between the rate constants of 2-cp decomposition and the varying reaction parameters. The magnitude of effect of reaction parameters such as ultrasonic amplitude, H+ concentration, ionic strength, H2O2 and 2-cp initial concentration on 2-cp decomposition were 0.60, 0.48, 0.19, 0.09 and -0.06, respectively.     

PBAMO的热分解反应机理

采用无模型法对聚3,3-双叠氮甲基环氧丁烷(PBAMO)的热分解反应动力学进行了计算,并用热重-红外-质谱(TG-IR-MS)联用技术研究了其热分解反应产物。PBAMO表现出了独特的热分解过程,TG曲线中在210℃~270℃叠氮基团的分解失重之后没有第二个明显的失重台阶;PBAMO第一阶段的热分解活化能为150 kJ/mol,当分解率大于0.4时,活化能降为负值。TG-IR-MS结果表明,在叠氮基团分解时释放的热量加速了剩余氮原子的氧化还原过程,主要产物形式为NO,主链中的氧原子被消耗掉,从而导致了碳链骨架的大量残留。     

The thermal decomposition of dimethoate.

The thermal decomposition of dimethoate, an organophosphorus pesticide, has been studied with the aim at assessing the reaction kinetics, the energy released during the process and the decomposition products. Dimethoate shows a marked tendency to undergo thermal decomposition at temperature higher than 369 K. A moderate pressure increase has been recorded at the end of all runs. Many thiophosphoric compounds have been identified among the decomposition products.     

Domain decomposition of stochastic PDEs: Theoretical formulations

We present a novel theoretical framework for the domain decomposition of uncertain systems defined by stochastic partial differential equations. The methodology involves a domain decomposition method in the geometric space and a functional decomposition in the probabilistic space. The probabilistic decomposition is based on a version of stochastic finite elements based on orthogonal decompositions and projections of stochastic processes. The spatial decomposition is achieved through a Schur‐complement‐based domain decomposition. The methodology aims to exploit the full potential of high‐performance computing platforms by reducing discretization errors with high‐resolution numerical model in conjunction to giving due regards to uncertainty in the system. The mathematical formulation is numerically validated with an example of waves in random media. Copyright © 2008 John Wiley & Sons, Ltd.     

氮杂环类含能材料热分解研究进展

综述了最近儿年国内外氮杂环类含能材料热分解研究的进展.重点介绍了具有代表性的氮杂烷类、呋咱、四唑、嗪类等化合物热分解的实验和理论研究情况,指出了目前研究出现的问题,预测了含能材料热分解的发展前景.     

高岭土在真空下的热分解行为

以含高岭石、一水硬铝石、黄铁矿的高岭土为原料,经过压块烘干后,在真空(15~50 Pa)、不同加热温度下,采用同步热分析仪(DSC-TGA)、X射线衍射(XRD)等分析手段对高岭土在真空下的热分解进行研究。DSC-TGA的结果与高岭石、一水硬铝石、黄铁矿三种矿物常压下的热力学计算出的分解温度相符。实验产物的XRD结果表明:在真空条件(15~50 Pa)下,一水硬铝石AlO(OH)在100~200℃之间脱水,300℃时脱水完全;黄铁矿FeS2在500~600℃分解,分解产物为FeS和S2,在700℃时,黄铁矿FeS2分解完全;高岭石Al2Si2O5(OH)4在实验煅烧过程中,在200~300℃之间脱水,生成非晶态的偏高岭石,比该矿在常压的脱水温度提前200℃左右。继而转变成A-lSi尖晶石,最后形成莫来石与方石英。实验结果与热力学计算符合,充分说明真空条件对高岭土中各种矿物分解产生气体的反应有较大的促进作用。在本实验三种矿物分解产生气体的过程中,先进行的反应对后一反应的发生影响不明显。     

烟酸锌热分解动力学研究

采用流变相反应法合成了烟酸锌配合物,用热分析(TG/DTG)、X射线衍射(XRD)技术研究了固态物质烟酸锌在空气中热分解的过程.热分析结果表明,烟酸锌在空气中是一步分解,其失重率与理论计算失重率相吻合.XRD结果表明,烟酸锌分解的终产物为ZnO.用Friedman法和Flynn-Wall-Ozawa(FWO)法求取了分解过程的活化能E,并用多元线性回归法给出了可能的机理函数,由这些方法得到的动力学数据相互比较吻合.     

初始温度和压力对乙炔分解爆炸参数影响的实验研究

为研究乙炔气体的分解爆炸参数，以电石法制备的乙炔为对象，采用20 L圆柱形爆炸罐，以熔断丝（20 J）作为点火源，通过实验研究了初始温度、初始压力对乙炔分解爆炸相关参数的影响规律。结果表明:初始压力为0.095~0.200 MPa时，乙炔最大分解爆炸压力及最大分解爆炸压力上升速率随初始压力的增大而增大，且初始压力超过0.140 MPa后，增幅变大；初始温度在40~80 ℃范围内，乙炔临界分解爆炸压力、最大分解爆炸压力及最大分解爆炸压力上升速率随初始温度的升高而减小。     

石油醚对乳化炸药基质热分解动力学的影响

采用TG-DSC联用技术对混有石油醚的乳化基质样品的热分解动力学进行了研究,用Ozawa法和Satava-Sestak法对试验数据进行处理,得到各样品的动力学参数和机理函数.讨论了混入石油醚后乳化基质热分解动力学参数变化的原因,认为石油醚的加入会改变乳化基质的热分解动力学行为,具有促进乳化基质热分解的趋势.     

基于改进变分模态分解的滚动轴承故障诊断方法

提出一种改进变分模态分解的轴承故障信号诊断方法。使用改进的奇异值分解降噪方法对信号进行降噪,然后对信号进行变分模态分解;利用分量信号的能量之和占原信号能量的比值,判断变分模态分解的分解效果,从而找出最佳分解层数;根据分量信号间的相关系数,判断中心频率相邻的分量信号是否来自信号中的同一调制部分;最后通过主要分量的包络谱找出故障特征频率,判断故障类型。通过对仿真信号和实际轴承故障信号进行处理,成功提取微弱频率特征信息,验证了该方法的有效性。     

热稳定剂对PVC抑烟作用及其机理研究

利用烟密度箱、TG、GC-MS等分析技术研究了钙锌、铅盐和有机锡热稳定剂对PVC的抑烟作用及对燃烧过程中主体凝聚相和释放的芳烃化合物的影响,并探讨了钙锌稳定剂的抑烟机理。结果表明:这三类热稳定剂对PVC均有一定的抑烟作用,其中钙锌稳定剂的抑烟作用更为明显。钙锌稳定剂通过燃烧过程中生成的ZnCl2改变PVC热降解历程:一方面抑制分子内环化反应,减少有害芳烃化合物的生成;另一方面能促进分子间交联反应,提高残炭量,起到抑烟作用。     

The thermal decomposition of ammonium paratungstate

The thermal decomposition of monoclinic, orthorhombic and freeze-dried ammonium paratungstate (APT) has been studied over the temperature range 100 to 500°C using thermogravimetry, evolved gas analysis. X-ray diffraction and electron optical techniques. The particle morphologies of the original APT have been related to the morphologies of the products of decomposition. A mechanism of decomposition which postulates the formation and subsequent decomposition of amorphous ammonium metatungstate is proposed and substantiated by X-ray diffraction analysis and evolved gas analysis.     

Photocatalytic decomposition of perfluorooctanoic acid (PFOA) by TiO2 in the presence of oxalic acid

Heterogeneous photocatalytic decomposition of perfluoroocatanoic acid (PFOA) by TiO(2) under 254 nm UV light was investigated. Adding oxalic acid as a hole-scavenger significantly accelerated PFOA decomposition under nitrogen atmosphere. Fluoride ion, formic acid and six shorter-chain perfluorinated carboxylic acids (PFCAs) bearing C(2)-C(7) were identified as intermediates. When using perchloric acid (HClO(4)) as a replacement of oxalic acid to maintain the same pH of the reaction solution, PFOA did not decomposition efficiently. Compared with oxalic acid, potassium iodide (KI, another hole-scavenger) also led to a slower PFOA decomposition, while the addition of an electron acceptor (potassium persulfate, K(2)S(2)O(8)) obviously inhibited PFOA decomposition. This suggested that oxalic acid played more than one role in PFOA decomposition rather than simply providing acidity and acting as a hole-scavenger. The electron paramagnetic resonance (EPR) measurements confirmed the existence of carboxyl anion radicals (CO(2)(-)) in the photocatalytic process, which was a result of the reaction between oxalic acid and photogenerated hole. These findings indicated that PFOA decomposition was primarily induced by CO(2)(-) radicals, although photogenerated electron was also conducive to PFOA decomposition. A possible mechanism for PFOA decomposition was proposed.     

尼龙66及其复合材料的热分解动力学

使用热重分析仪测定尼龙66(PA66)和两种不同玻纤增强尼龙66复合材料(GF/PA)的热分解曲线,用Kissinger法和Crane法研究了PA66和GF/PA的热分解动力学。结果表明:PA66、GF/PA-1和GF/PA-2的热分解反应级数分别为0.949、0.912和0.921,表明均为一阶热分解过程;热分解活化能分别为218.65 kJ/mol、121.81 kJ/mol和132.23 kJ/mol,表明玻纤的加入显著降低了PA66的热分解活化能。在加热速率相同的条件下两种GF/PA达到最大热分解速率的温度都比PA66的低,表明玻纤虽然改善了PA66的性能,但是加快了PA66的热分解过程,说明存在着“灯芯效应”。     

一种改进的自适应多元变分模态分解轴承故障信号特征提取方法

针对实际工程中轴承信号的非线性和非平稳性,提出一种自适应多元变分模态分解算法。多元变分模态的分解效果主要与本征模态数k和惩罚参数α相关,为了解决人为经验参数设置对多元信号分解结果的影响,一种自适应的信号分解算法被提出。具体内容如下:首先将混合灰狼算法与多元变分模态分解算法相结合,提出最小模态重叠分量指标,将其作为适应度函数来寻求(k, α)的最优解,按照最优解对多元信号进行分解,提取故障特征。采用仿真信号和实际数据来验证所提方法的有效性和准确性,通过与多元经验模态分解、级联变分模态分解的对比分析,验证该算法在滚动轴承故障特征提取方面的高效性和实用性。     

图像的非均匀B样条小波分解与重构

介绍了一维非均匀B样条小波分解与重构的算法,并将其推广到二维离散图像.给出了对图像进行分解和重构时节点矢量的选取方法、分解和重构的公式,并通过实例介绍了它在图像任意大小缩放中的应用.和传统小波相比,利用非均匀B样条小波对图像进行分解具有更大的灵活性,可以得到小于原图的任意大小的低分辨率图像.