Theoretical analysis of hydrides in solid and hybrid rocket propulsion

Chemical rocket propulsion can benefit by using hydrides that are able to store high volumes of hydrogen at ambient conditions that can be released during combustion. This paper offers a theoretical investigation concerning the use of hydrides as additives in hybrid fuels and solid propellants. Aluminum hydride is expected to generate interesting performance gains but lack of commercial availability makes industrial application unfeasible. As a consequence, attention is focused on other simple and complex hydrides used in other fields and readily available. A comparative analysis of theoretical performance of gravimetric and volumetric specific impulse, propellant average density, adiabatic flame features, and preliminary estimate of exhaust products is conducted. Eight different hydrides, potentially applicable as replacements for aluminum currently used in solid propellants and hybrid rocket systems are considered.     

Lanthanide(III) halides: Thermodynamic properties and their correlation with crystal structure

Temperatures and enthalpies of phase transitions of 17 lanthanide(III) halides determined experimentally are reported. Correlations were made between temperature of fusion of lanthanide(III) halides, on the one hand, and enthalpy of fusion, on the other, versus atomic number of lanthanide. According to this classification, the lanthanide(III) halides split into groups, as also do the corresponding crystal structures. A correlation between the crystal structure of lanthanide(III) halides and their respective entropy of fusion (or entropy of fusion + entropy of solid–solid phase transition) was inferred from the aforementioned features. Fusion in those halides with hexagonal, UCl₃-type and orthorhombic, PuBr₃-type, structures entails an entropy of fusion change (or entropy of fusion + entropy of solid–solid phase transition change) by 50 ± 4 J mol⁻¹ K⁻¹. The homologous entropy change within the group of halides having the rhomboedric, FeCl₃-type, structure, is smaller and equals 40 ± 4 J mol⁻¹ K⁻¹. Halides with monoclinic, AlCl₃-type, crystal structure constitute a third group associated to an even smaller entropy change upon fusion, only 31 ± 4 J mol⁻¹ K⁻¹. The halides with lower entropies of fusion also have a lower S_1300 K − S_298 K indicating either a higher degree of order in the liquid or a higher entropy in the solid at room temperatures.     

On the occurrence of two-stage combustion in alkali metals

Pool combustion experiments have been conducted for three alkali metals, namely, lithium (Li), sodium (Na) and potassium (K). Lithium and sodium are found to show a two-stage combustion behaviour which has been reported for a number of other metals. Here, the combustion is characterized by a sporadic rise in the flame temperature accompanied by a bright glow. Potassium is found to burn in vapour phase combustion in all cases without sporadic temperature excursions. In the present study, this different burning behaviour is attributed to the formation of thick oxide agglomerates in the case of Li and Na through the pores of which oxygen/metal vapour has to diffuse for combustion to occur. In such cases, a second stage of vapour phase combustion occurs when the oxide agglomerate is heated sufficiently so that the vapour of the liquid metal trapped in the pores breaks through to the surface. In the case of potassium, a self-cleaning mechanism, attributable to the high solubility of the metal oxides in liquid potassium and the relatively low melting point of the potassium oxides, enables a clear liquid surface to be exposed throughout for vapour phase combustion to prevail always. Recorded temperature profiles, SEM analysis of the oxide agglomerates as well as calculations of the metal–oxygen equilibrium thermo-chemistry for the three metals confirm this scenario.     

Synthesis and characterization of lithium-carbon compounds for hydrogen storage

Three carbon materials were prepared for the synthesis of Li-C compounds, such as Li intercalated graphite. The materials were as-received high purity polycrystalline graphite (G), graphite milled under a hydrogen atmosphere (HG), and graphite milled an argon atmosphere (AG). With respect to the difference for them, HG preserved a better crystalline structure than AG. Each material was milled with Li, where the products are denoted as Li-G, Li-HG, and Li-AG. In XRD patterns of Li-G and Li-HG, the peaks corresponding to LiC₆ and LiC₁₂ were revealed, while no peaks were observed in the case of Li-AG. However, the formation of lithium carbide Li₂C₂ was suggested for Li-AG by a thermal analysis under an inert gas. After the hydrogenation, LiH was formed for all the compounds, and graphite was recovered for Li-G and Li-HG. Each hydrogenated compound desorbed H₂ with different profile by heating up to 500 °C. As a reaction product, Li₂C₂ was formed for the hydrogenated Li-HG and Li-AG. In the case of the hydrogenated Li-G with better crystalline structure, Li intercalated graphite were formed after the dehydrogenation. Therefore, it is concluded that the hydrogen absorption and desorption process of Li intercalated graphite was different from those of Li₂C₂.     

氯化镧与丙氨酸配位反应的热化学研究

用新型的具有恒温环境的反应热量计 ,以溶解量热法分别测定了 2 5℃时 (LaCl·7H2 O 3Ala)和Al(Ala) 3 Cl3 ·3H2 O在 2mol·L-1HCl溶剂中的溶解焓。通过设计的热化学循环得到七水氯化镧与丙氨酸配位反应的反应焓ΔrHm=9 738kJ·mol-1,并计算出配合物La(Ala) 3 Cl3 ·3H2 O在 2 98 2K时的标准生成焓ΔfH0m=- 3713 8kJ·mol-1。     

气井热化学解堵技术

中原油田气井地层能量日渐衰弱，致使措施入井液大量漏失，凝析气在孔喉中凝析而产生“液锁”效应等损害地层的因素。针对这种情况，采用了热化学解堵技术，通过室内试验研究了热化学解堵剂配方以及配套施工工艺，应用现场后取得了明显的增产效果。     

Thermal Analysis of Magnesium/Perfluoropolyether Pyrolants

Exothermic reactions between metals and fluorinated polymers are found in a variety of energetic materials, including reactive binder systems and the Magnesium‐Teflon‐Viton incendiary composition. This paper describes the reactions between a high molecular weight perfluoropolyether, Fomblin Y 140/13, and magnesium in a variety of morphologies including μm‐scale powders and nano‐scale layered films. Using Temperature Programmed Desorption and Temperature Programmed Reaction we have found that the magnesium‐perfluoropolyether interaction is characterized by: (1) competition between Fomblin decomposition and desorption, and (2) magnesium passivation by the formation of magnesium fluoride. Differential Scanning Calorimetry measurements establish a lower‐bound estimate of the specific reaction energy of 9.2 kJ g⁻¹. High molecular weight Fomblin (6500 amu) undergoes a competitive reaction/desorption process with desorption occurring at 550 K and decomposition at 610 K. Decomposition becomes more favorable relative to desorption for higher heating rates and thicker films. Perfluoropolyethers produce several characteristic ions in the 70 eV election ionization mass spectra, with the CF₃⁺ ion being the most abundant ion observed during both the molecular desorption and decomposition. Larger fragment ions with masses of 235 and 285 amu are observed in relatively high concentrations during desorption and low concentrations during decomposition. The reaction between magnesium and Fomblin begins at 400 K, producing CF₃⁺, CO⁺, and C₂F₅⁺ in the electron ionization mass spectrum. We propose that these reactions form a passivating layer of magnesium fluoride that protects the remaining metal as it approaches the magnesium melting point. Most of the reaction takes place at 800 K and above when the magnesium fluoride film ruptures.     

Ethyl Oleate and Ethyl Elaidate Ozonides: Thermal Decomposition and Photolysis

Highly pure ethyl oleate and ethyl elaidate were ozonized to their secondary ozonides (respectively EO-SOZ and EE-SOZ). The decomposition enthalpies of EO-SOZ and EE-SOZ were determined by DSC (Differential Scanning Calorimetry) and found, respectively, at --266 kJ/mol and --264 kJ/mol, a value much closer to the theoretically calculated upper limit of --278 kJ/mol than the decomposition enthalpy of --243 kJ/mol measured on EO-SOZ prepared from an ethyl oleate sample conforming to the European Pharmacopoeia. Although a considerable amount of heat was liberated, EO-SOZ and EE-SOZ cannot be defined as explosive based on their DSC traces at a heating rate of 10 °C/min. Pure EO-SOZ and EE-SOZ show a decomposition peak at the DSCs of 137 °C and 139 °C, respectively. The thermal decomposition of EO-SOZ and EE-SOZ was studied also by FT-IR spectroscopy showing that the decomposition involves the loss of the ozonide infrared band at 1110 cm^?1 and the formation of the expected decomposition products (pelargonic acid, pelargonaldehyde, ethyl azelate, etc.). The kinetics of the photochemical decomposition of EO-SOZ and EE-SOZ were studied by FT-IR spectroscopy, and the relative rate constants were determined. EO-SOZ when overozonized forms a spin adduct with nitrosobenzene and the relative nitroxyl radical was clearly detected by the Electron Spin Resonance (ESR). Secondary ozonation products known as trioxides may be responsible for these adducts.     

与数据库相联的平衡表面图绘图软件

平衡表面图是作者近年提出的一种热化学数据图示方法,用于湿法冶金络合物体系矿物浸出或金属离子沉降的条件分析.本文提出一个与微机冶金热化学数据库相联的绘图软件,说明算法与绘图的基本原理及三维数组的生成方法.以铜-氯-水体系为例展示了绘图结果及其意义.