Thermal decomposition of uranium peroxide hydrates

The thermal decomposition of uranium peroxide hydrates, UO₄·4H₂O and UO₄·2H₂O, has been investigated by thermal analyses, X-ray diffraction study and infrared spectroscopy. As a result, it is concluded that the thermal decomposition of uranium peroxide hydrates proceeds in the following sequence:     

40%DCP溶液的热分解模型

准确的热分解动力学模型有助于人们采取各种安全措施预防和控制物料热失控导致的燃烧爆炸事故。以40%过氧化二异丙苯（DCP）的2,2,4-三甲基戊二醇二异丁酯（DIB）溶液为研究对象,运用差示扫描量热仪（DSC）和绝热量热设备（VSP2）进行了量热实验,并采用TSS软件（Thermal Safety Software）对数据进行动力学分析,建立了两种分解模型：“N级+N级”模型（模型1）和“N级+自催化”模型（模型2）,采用Friedman法和非线性拟合方法求算其动力学参数。在运用所建立的两种模型拟合曲线时,发现两种模型对同种量热模式数据拟合的相关系数非常接近,说明单一量热模式在求算动力学上存在局限性。联合采用基于动态扫描模式的DSC数据及基于绝热模式的VSP2数据共同求算动力学,发现相对于模型2,模型1可以更好地反映分解过程,其两步反应的活化能分别为115.5 kJ·mol^-1和135.7 kJ·mol^-1,指前因子的对数分别为28.3和31.6,反应级数分别为0.40和0.84。研究结果表明采用基于不同量热模式的数据求算动力学有助于确定正确的动力学模型,从而获得准确的动力学参数,并克服单一量热模式下动力学求算的局限性。     

2,4-二氯过氧化苯甲酰的热分解及等温动力学模型

引言2,4-二氯过氧化苯甲酰(双-2,4,DCBP)工业上常用作自由基引发剂、高温硅橡胶固化剂和无模硫化剂。因用该物质生产的硅橡胶制品无毒,可用于人工脏器、牙托、奶瓶等,也可用作高功率发电机绝缘用品,尤其适用于导弹、航天器中密封圈及耐热胶管带[1]。有机过氧化物中含有不稳定的"—O—O—"键,导致此类物质易受热分解,并引     

Thermal decomposition of polystyrene

Kinetic studies on the decomposition of polystyrene samples with molecular weights ranging from 900 to 1.8 × 10⁶ have been carried out making use of the differential thermogravimetric and differential scanning calorimetric techniques. Changes in molecular weight distributions with decomposition, at different temperatures or times, have been studied by gel permeation chromatography. This technique was likewise used to carry out component splitting of the undecomposed polymer samples. These components have been shown to break down statistically primarily by a process of random scissions yielding lower molecular weight products. The major portion of the observed weight loss, by the volatilization of small chain segments, is attributed to a rapid and complete depolymerization of chains. These interpretations are based on changes in polydispersity occurring during the decompositions. Similar components, decomposing in a different manner but under identical operating conditions, are suspected of being different stereoregular forms of the polymer. The order of reaction as computed from the method of Freeman and Carroll has been found to be zero for random scissions and one for the process of depolymerization. The activation energy computed by the method of Coats and Redfern was found to increase with molecular weight reaching a maximum value in the 10⁵ molecular weight range.     

Thermal decomposition of tricaproin

Tricaproin was used as model system to study thermal decomposition of simple triglycerides. The tricaproin samples were pyrolyzed under three different conditions: at 250 C for 1 hr, 270 C for 1 hr and 270 C for 15 hr. Hydrocarbons, acrolein, methyl hexanoate, hexanal, hexanoic acid, 6-undecanone, 2-oxoheptyl hexanoate, propanediol dicaproate, propenediol dicaproate, oxopropanediol dicaproate and dicaproin were identified. Mechanisms involving both free radical and nonfree radical reactions were proposed for the formation of these compounds.     

Thermal decomposition of asphaltenes

The thermal decomposition of Athabasca asphaltene at relatively low (< 350 °C) temperatures is believed to proceed by elimination of groups situated on peripheral sites of the asphaltene. More severe degradation of the asphaltene structure does not occur until elevated (> 350 °C) temperatures are attained.     

Thermal storage: Nucleation of melts of inorganic salt hydrates

This paper reviews the heterogeneous nucleation of melts of some inorganic salt hydrates. Five salt hydrates were tested as materials for heat storage.     

Thermal decomposition of sodium dithionite

The thermal decomposition of sodium dithionite (Na₂S₂O₄) in the solid state was investigated by differential scanning calorimetry and the exothermic heat of decomposition was determined. The effect of isothermal pretreatment at various selected temperatures on the subsequently determined decomposition temperature was studied, together with the effect of sample weight on the decomposition temperature and degree of exothermicity.     

Thermal decomposition of 1,4-diphenylbutane

To obtain information relevant to possible reaction pathways in coal liquefaction and gasification reactions, experiments were carried out to elucidate the pathways involved in the thermal decomposition of 1,4-diphenylbutane. The results established unambiguously that the thermal decomposition products arise via free radical pathways and not by a retroene process as has been proposed.     

Thermal decomposition of dimethyllaurylamine oxide

The principal reaction during thermal decom-position of dimethyllaurylamine oxide is deoxy-genation to dimethyllaurylamine; 1-dodecene is also formed. The rates of amine oxide decomposi-tion have been determined in the range of 80-100C. Interpretation of the kinetic data shows that deoxygenation is a primary decomposition process. Comparison of the energy and entropy of activation for olefin formation (36.3 kcal, 12.4 e.u.) and amine formation (20.6 kcal, -30.8 e.u.) shows that these are competing processes with different transition states.     

Thermal decomposition of ammonium nitrate

The thermal decomposition reactions of ammonium nitrate (AN) are reviewed. Both neat AN and AN containing various contaminants are examined, however quantitative kinetics results are not encompassed. Also not included is the performance of AN as the oxidizer in rocket propellants or in explosives such as ANFO. The review is intended to be the most comprehensive review of decomposition reactions of AN since Berthelot's treatise of 1892. Despite hundreds of papers on the topic that have appeared in the intervening years, understanding of decomposition mechanisms remains only modestly more complete than it was in Berthelot's day. However, some additional reaction steps and mechanisms have been identified and these are discussed. Explosions of AN most commonly involve fire as the proximate cause, yet chemical-mechanism research on the topic is nil. A modest number of studies have explored the potentiation of AN decomposition by organic contaminants. These have, thus far, not produced guidance useful for promoting of safety from fire-related causes. Contamination from inorganic sources, notably chlorides is better understood and some mechanisms have been studied. The UN classification of AN as an oxidizer, instead of as an explosive, should not be interpreted literally, since AN has been associated with numerous detonation disasters.     

Thermal decomposition of graphite nitrate

A new technique for gas determination in the thermal decomposition of graphite nitrate II–IV stages has been reported. Its correctness was confirmed by thermogravimetry and infrared spectroscopy. Static and dynamic modes of the decomposition were examined. Firstly, the static mode was carried out in three atmospheres: (1) oxidizing – air; (2) argon – inert; (3) reducing – methane (4 vol%) and argon. A detailed analysis of the evolved gases is presented. The composition of these gases was found to depend on graphite nitrate stage number and the atmosphere in which it was expanded. Following the static mode, the dynamic mode was carried out in the argon atmosphere only. Two-stages of gas evolution with increasing temperature were registered within the dynamic mode. The same two-stage effect was observed on the thermogravimetry curves and infrared spectra. Based on the results obtained from the dynamic mode, chemical reactions occurring in the thermal decomposition have been proposed.     

Thermal decomposition products of cellulose

Untreated and flame-retardant-treated cellulose were thermally decomposed under vacuum and the products were quantitatively analyzed by gas chromatography. An unidentified product at a retention index of 2270 (between 5-methylfurfural and 5-hydroxymethylfurfural), α- and β-D -glucose, and a group of “dimers” that have not been reported previously were found in this study. The identification of this unknown product should assist in studies on the thermal decomposition of cellulose and further the understanding of the mechanism of flame retardancy.     

Thermal decomposition products of polyacrylonitrile

The decomposition products of a polyacrylonitrile yarn thermally decomposed at temperatures of 400°, 600°, and 800°C, under a flow of either air or nitrogen, have been analyzed by GC and GCMS. Hydrogen cyanide and 16 other nitriles were identified and quantified. Decomposition products contained a series of aliphatic nitriles of various chain lengths, and HCN was the predominant toxic product.     

Thermal decomposition of ammonium sulphate

The thermal decomposition and vaporisation of ammonium sulphate, (NH₄)₂SO₄, is shown to take place via two distinct sets of reactions. In the first, ammonium pyrosulphate, (NH₄)₂S₂O₇, is the primary condensed phase product: 2(NH₄)₂SO₄ ← (NH₄)₂S₂O₇+2NH₃+H₂O The second stage concerns the decomposition of the pyrosulphate. Ammonia, sulphur dioxide, nitrogen and water are the major products, the dominant reaction being 3(NH₄)₂S₂O₇ ← 2NH₃+6SO₂+2N₂+9H₂O