Decomposition Chemistry of Tetraethoxysilane

SiO₂ films deposited by the decomposition of tetraethoxysilane (TEOS) at high temperatures have superior insulating properties and excellent step coverage, but are not compatible with aluminum metallization. Earlier work on the deposition of SiO₂ from TEOS concentrated on the properties of the film and on the modeling of thickness uniformity, but no attempt was made to probe the decomposition chemistry. In the present work a three-step model is presented to explain the TEOS deposition chemistry. A useful deposition temperature is determined by the first step where an intermediate is formed in the gas phase. This activated species adsorbs on the surface and later decomposes into SiO₂. Equilibrium constants for the gas-phase intermediate formation and surface adsorption respectively are 1.38 × 10¹⁰ exp[(– 299.24 kJ/mol)/ RT ] and 1.14 × 10⁴ exp[(– 21.80 kJ/mol)/ RT ]. The rate constant for the surface decomposition of the intermediate is 1.29 × 10⁻⁶ exp[(– 12.26 kJ/mol)/ RT ]. This model successfully explains rate dependence on pressure and temperature. Approaches are suggested which would catalyze the formation of the activated species and thus lower the deposition temperature such that this process could be used instead of aluminum metallization.     

Gas Generator Materials Consisting of TAGN and Polymeric Binders

This study introduces a new type of gs generator on the basis of triaminoguanidine nitrate with polymeric binders in the form of polyurethane polymers, cellulose acetate and the azidopolymer GAP with nitroplasticizer. TAGN propellants demonstrate low burning temperatures, high yields of gaseous products adn adjustable medium to high burning velocities. Together with high chemical and thermal stabilities, good mechanical properties to high and low temperatures, no exhaust of corrosive gases and very low sensitivity, the gas-generator propellants exhibit outstanding properties.     

含能材料燃烧过程中热分解化学的研究进展

从模拟燃烧条件、组分相互作用、组分物理状态、分析测试技术等几方面介绍了含能材料燃烧过程中热分解化学研究近几年来的最新进展。着重介绍燃烧热分解中的基元反应对建立推进剂燃烧新型模型的重要性、氧化剂和黏合剂及催化剂之间的相互作用、氧化剂的黏度和相态变化对燃烧和热分解过程的影响。     

Electrochemical Study on TAGN. A differential pulse polarography determination

This work shows an electrochemical study about triaminoguanidine nitrate, estimating the influence of the reaction compounds for the formation of TAGN and secundary compounds and hydrolysis products of this formation reaction. The conditions to determine polarographically the content of TAGN in a propellant without the interference of those compounds are verified. The method used is the differential pulse polarography in aqueous medium, due to the high solubility of TAGN in water. We have used three different media as electrolyte support, verifying the influence of different variables, as pH, drop time etc., to obtain the optimum work conditions.     

Further Understanding of the Chemistry of Manganese‐Induced Peroxide Decomposition

Manganese is the most effective catalyst for the hydrogen peroxide decomposition during peroxide bleaching used in the pulp and paper industry. We studied the chemistry involved in this project. The results showed that Mn²⁺ and Mn³⁺ are present during the course of the reaction. We followed the Mn²⁺ and Mn³⁺ concentrations during the course. It was found that a steady state of Mn³⁺ concentration was attained until the hydrogen peroxide concentration was zero. At this time, the Mn³⁺ concentration was maximum, then it decreased due to the disproportionation to form MnO₂. Removal of O₂ from the system slowed down the rate of decomposition. The detailed reactions involved were discussed.     

Combustion of GAP/HMX and GAP/TAGN Energetic Composite Materials

Energetic composite materials (ECM) have high thermodynamic potential and flexible design capability. Two types of ECM were formulated as mixtures of glycidyl azide polymer (GAP) and crystalline materials. The crystalline materials evaluated were cyclotetramethylene tetranitramine (HMX) and triaminoguanidine nitrate (TAGN). The thermochemical properties of HMX and TAGN were different to each other: HMX is a high energy material but the burning rate is lower than that of TAGN. TAGN produces hydrogen as a combustion product and the thermodynamic potential becomes high even though the flame temperature is low. The results of burning rate measurement tests indicate that the burning rates of both ECM are decreased significantly by the addition of HMX and TAGN even though the burning rates of GAP, HMX, and TAGN are higher than those of the ECM. The temperature sensitivity of burning rate of GAP is reduced significantly by the addition of HMX and remains unchanged by the addition of TAGN. The reduced burning rates of GAP/HMX and GAP/TAGN are caused by the reduced heat flux transferred back from the gas phase to the burning surface. The reduced heat release at the burning surface of GAP/HMX is responsible for the reduced temperature sensitivity.     

An Advanced GAP/AN/TAGN Propellant. Part I: Ballistic Properties

A solid rocket propellant based on glycidyl azide polymer (GAP) binder plasticized with nitrate esters and oxidized with a mixture of ammonium nitrate (AN) and triaminoguanidine nitrate (TAGN) was formulated and characterized. Non‐lead ballistic modifiers were also included in order to obtain a propellant with non‐acidic and non‐toxic exhaust. This propellant was found to exhibit a burning rate approximately twice that of standard GAP/AN propellants. The exponent of the propellant is high compared to commonly used composite propellants but is still in the useable range at pressures below 13.8 MPa. This propellant may present a good compromise for applications requiring intermediate burn rate and impulse combined with low‐smoke and non‐toxic exhaust.     

High Energy Propellants for Advanced Gun Ammunition Based on RDX,GAP and TAGN Compositions

A number of gun propellant compositions based on RDX, GAP, TAGN and combinations thereof were formulated and studied with the aim to select the suitable composition for advanced gun ammunition in respect of processability and ballistic performance. Theoretical thermochemical properties of the compositions were computed using a ‘THERM’ programme and the ballistic performance was evaluated on the basis of closed vessel tests. In addition, sensitivity, thermal characterization, thermal stability and mechanical properties of the compositions were also determined for assessing the suitability for application. A composition containing 28% NC, 45% RDX, 20% TAGN, 6% GAP, 0.7% carbamite and 0.3% resorcinol was found to provide higher level of force constant at relatively lower flame temperature, reasonably good burning rate characteristics and mechanical properties.     

Effect of pH on the Chemistry of the Barium Titanium Citrate Gel and Its Thermal Decomposition Behavior

In this investigation, X-ray diffractometry and ¹³C NMR spectroscopy were used to characterize the effect of pH on the formation of gel and its thermal decomposition by the Pechini process. It was found that the major effect of pH was to destroy the esterification between citric acid (CA) and ethylene glycol, which in turn could influence Ba species and the formation of a mixed-metal CA complex. It was also found that barium carbonate was derived from the Ba species and was not related to the instability of Ba₂Ti₂O₅CO₃, but Ba₂Ti₂O₅CO₃ was formed by the thermal decomposition of a mixed-metal CA complex. Moreover, BaTiO₃ formed via two routes, the reaction of BaCO₃ with Ti species and thermal decomposition of Ba₂Ti₂O₅CO₃.     

An Advanced GAP/AN/TAGN Propellant. Part II: Stability and Storage Life

A solid rocket propellant based on glycidyl azide polymer (GAP) binder plasticized with nitrate esters and oxidized with a mixture of ammonium nitrate (AN) and triaminoguanidine nitrate (TAGN) and including non‐lead ballistic modifiers, was formulated. The propellant was designed so as to produce non‐acidic and non‐toxic exhaust products while still providing reasonably good burning rate and impulse. This propellant was characterized with respect to thermal and chemical stability and storage life by a variety of test methods. The data indicate that the propellant exhibits good stability and is suitably safe for prolonged storage. Characterization data for this propellant with regard to processing parameters, tensile properties, and ballistic performance are presented in a companion paper.     

Decomposition of Mullite

Free surfaces of 2:1 mullite (2Al₂O₃·SiO₂) specimens decomposed with the evolution of SiO and O₂ when they were heated at high temperatures under low partial pressures of O₂; this reaction was analyzed thermodynamically. In addition, bubbles were observed at internal interfaces between mullite and fused-SiO₂ diffusion couples. These bubbles, when formed at 1 atm ambient pressure between 1650° and 1800°C, resulted from reaction of Si particles and residual SiO₂-rich glass in the fused cast mullite.     

有机化学化工中绿色化学的应用

为了全面提升有机化学的生态化发展水平,要积极推进绿色化学研究项目。简要分析了绿色化学的内涵,并集中阐释了有机化学化工中绿色化学的应用路径,旨在提高有机化学的生态化建设水平。     

DL-2-萘普生热分解过程和非等温热分解动力学研究

用热重-差热联用分析(DTA-TGA)技术和差动扫描(DSC)技术研究了DL-2-萘普生在空气中的热分解过程和非等温热分解机理及动力学.DTA-TGA分析表明DL-2-萘普生在((250.722～296.87)±4.88)℃之间发生热分解反应,结合DSC分析表明DL-2-萘普生的熔点为(158.16±0.6)℃,熔融热...     

量子化学在水泥化学领域的研究进展

量子化学能解决许多用传统理论和方法所不能解决的材料科学问题,本文介绍了计算量子化学的基本理论及SCC-DV-Xα方法,综述了近三年来量子化学在水泥化学领域应用的研究进展.     

应化专业化学实验教学体系的构建

化学实验在培养学生＂动手能力和创新精神＂方面具有重要作用。我们化教学内容,我们构建了基础型、综合型与设计型三个层次的实验课程教学模式,并构建了创新性实验教学开放体系、化学实验多媒体教学体系、多元化实验考试评价体系。实践证明,新的实验教学体系更适应创新性人才培养的要求。     

Thermal Decomposition of Brucite: II, Kinetics of Decomposition in Vacuum

Polycrystalline samples, thin single crystals, and—325 mesh powders of brucite decomposed according to a first-order rate equation consistent with a random nucleation process in beds of micron-sized particles formed by disruption during the very early stages of the process and consistent with electron and optical microscope observations. Kinetic data for the decomposition of thick single crystals were more complex but could be fitted to an interface-model equation which predicts that decomposition will be controlled by the movement of an interface reaction along the basal plane. Physical disruption of these crystals was confined initially to the outer edges of the crystals and proceeded along the basal plane in the form of a contracting disk. Since the decomposition occurs in cracked material and not at a strict interface, the fit of the data to the interface model may be fortuitous.     

溴酸钾非等温热分解过程及热分解动力学研究

为了解溴酸钾(KBrO3)的热性能,利用差热分析(DTA)研究了KBrO3的非等温热分解过程.采用Kissinger法和Ozawa法计算了KBrO3的热力学参数,并与硝酸铵(NH4NO3)的热稳定性进行了对比.结果发现:KBrO3在400℃附近开始熔化,随后发生放热分解,其热分解是分两个阶段进行的,在升温速率为5℃?m...     

Decomposition of burning polytetrafluoroethylene

PTFE rods, 0.6–3.8 cm diameter, were burnt from the top downwards in a gently rising atmosphere of oxygen. The burning was only possible in concentrated oxygen, or at elevated temperature or pressure. At its surface temperature of 920 ± 25°K, the polymer evolved monomeric C₂F₄ which oxidized in a surrounding gas flame; 15–35% of all the carbon in the gas was found present as monomer just above the larger rods. Depolymerization of the solid was not its only mode of decomposition, however. The heat radiated and conducted from the flame into the condensed phase was too little to depolymerize it completely, and heterogeneous reactions with species from the gas phase must also have contributed to the decomposition. Overall, the polymer burnt in O₂, but the gaseous reactant which attacked the surface need not have been O₂ or O in all cases, for these rare species just above the larger rods. Elemental fluorine was present in the gas even when elemental oxygen was absent, and calculations indicate that F atoms would be a major flame species at equilibrium. It is possible that heterogeneous attack by flame generated F atoms consumed part of the polymer and also supplied energy to help depolymerize the rest.     

Thermal Decomposition of Sodalites

The decomposition of bromate and hydroxide sodalites was studied by DTA and TG. Bromate sodalite is converted exothermally at 600°C into bromide sodalite. Hydroxide sodalite loses water and is then converted endothermally into a carnegieite phase at 740°C. The conversion of hydroxide sodalite mixed with sodium halide into halide sodalite at temperatures >740°C proceeds via the decomposition of the hydroxide sodalite. After hydroxide sodalite is heated to temperatures between 600°C and the conversion temperature, it exhibits the photoluminescence of O₂⁻.     

Thermal Decomposition of Aminonitrobenzodifuroxan

In this study, the thermal decomposition properties of aminonitrobenzodifuroxan are studied using a differential scanning calorimeter (DSC), a thermogravimeter (TG), an X‐ray diffractometer, a mass spectrometer (MS), and a Fourier transform infrared spectrometer (FTIR). The results demonstrate that aminonitrobenzodifuroxan undergoes thermal decomposition in the solid state. Under elevated temperatures, the decomposition primarily involves two steps: separation of nitro group and ring‐scission of the furoxan circles at 198.1 °C, and decomposition of the relatively stable residues (benzofuroxan circle) at 199.1 °C. Moreover, it is found that among the products, nitrogen dioxide undergoes oxidation and catalysis on the host molecule during the whole decomposition. Based on Kissinger and Ozawa functions, we deduce that the activation energies of these two reactions are 167.68 and 204.55 kJ mol⁻¹, respectively. The released energy (ΔH) of CL‐18 is −1781.8 J g⁻¹.