Thermal decomposition kinetics of titanium hydride and Al alloy melt foaming process

Metal foams, now one of research foci, are a newclass of materials with low densities and novel physi-cal, mechanical, thermal, electrical and acoustic prop-erties[1—8]. Demands from high-tech make Al alloyfoam, which has much higher specific strength than ofpure Al foam, the new development focus[9—11]. Melt foaming process is one of the approaches tofabricate Al foam and Al alloy foam and their porestructure (pore diameter and porosity) has close rela-tionship with the thermal decompo…     

Effects of Aluminum on Thermal Decomposition of Hexogen/Ammonium Perchlorate

Thermogravimetry-differential scanning calorimetry-mass spectrometry-Fourier transform infrared spectrometry（TG-DSC-MS-FTIR） simultaneous analysis was used to study the effects of 10.7 μm and 40 nm Al on the thermal decomposition of the Hexogen/ammonium perchlorate（RDX/AP,1/2,mass ratio） mixture.TG-DSC results show that there are two mass loss processes for the thermal decomposition of RDX/AP/Al.The first one is mainly ascribed to the thermal decomposition of RDX.The reaction rate of RDX/AP/10.7 μm Al is so fast that the apparent activation energy,calculated by model-free Friedman method,is negative,which is the same as that of RDX/AP.30％（mass fraction） 40 nm Al added in RDX/AP change the activation energy from negative to positive value.The second mass loss process of the RDX/AP/A1 mixture is ascribed to the thermal decomposition of AP.This process can be divided into three stages for RDX/AP with and without Al.The kinetics model is not changed in the presence of micro-sized Al,while it is changed from CnB/D1/D1 to CnB/D1/D4 after the addition of 40 nm Al to RDX/AP.The reaction rate constant of the first stage and the end temperature of the second stage decrease,while the end temperatures of the third stage increase in the presence of 40 nm Al.The MS-FTIR results show there is a competition between the formation reactions of HNCO,N2O and NO2 during the second mass loss process.     

A study of the oxidation of titanium hydride powder by measurements of its electrical resistance

The oxidation of titanium hydride powder by air oxygen and the influence of oxidation conditions on the degree of oxidation of hydride particles, specific gas content in the powder, and kinetics of its thermal decomposition were studied. The resistometry method was used to determine the effective activation energy of oxidation of titanium hydride by air oxygen. The content of the surface nonconducting phase formed by titanium oxide and oxohydride films under various oxidation conditions was estimated.     

KH添加对Na-Al-H配位氢化物可逆放氢性能的影响

以NaH粉和Al 粉为合成原料, 分别采用2% (摩尔分数, x) CeCl₃和2% CeCl₃/y% KH (y=0.02, 0.04)为催化添加剂, 在室温和3 MPa氢压下, 通过反应球磨(NaH/Al+CeCl₃)和(NaH/Al+CeCl₃/yKH) (y=0.02, 0.04)复合物成功制备出Na-Al-H 配位氢化物. 吸放氢性能测试结果表明, KH的加入能有效改善Na-Al-H 体系中第二步脱氢反应放氢动力学性能. (NaH/Al+CeCl₃/0.02KH)复合物170℃放氢时可在20 min内完成脱氢过程, 且在较低温度(100-140℃)下具有良好的可逆吸放氢性能. Kissenger 方法计算表明, 添加KH可降低Na-Al-H 体系第二步脱氢反应的表观活化能, 降低其放氢峰值温度. 相结构分析表明, KH的添加使Na-Al-H 体系中Na₃AlH₆的晶胞体积发生膨胀, 进而提高体系的第二步放氢动力学性能.     

Al 掺杂对Mg2Ni 合金的电子结构及贮氢性能的影响

采用基于密度泛函理论(DFT)的平面波赝势(PW-PP)方法, 计算Mg_2-xAl_xNiH₄ (x=0, 0.125, 0.25)合金的晶胞体积、电子态密度、键序、电荷布居、生成焓, 分析原子间成键和结构的稳定性, 研究Al 部分替代Mg 对Mg₂Ni 合金及其氢化物的结构和储氢性能的影响. 结果表明: 随着Al 含量的增加, Mg₂Ni 合金晶胞体积减小, 不利于氢原子进入合金中, 导致合金的储氢容量降低. 在Mg_2-xAl_xNiH₄ (x=0, 0.125, 0.25)中, Mg-H和Al-H相互作用远小于Ni-H的相互作用, 随着Al 含量的增加, 氢化物生成焓减少以及Ni-H的相互作用减弱, 氢化物的结构稳定性降低, Al 部分替代Mg能有效改善Mg₂Ni 合金释氢动力学性能.     

Hydrogen storage in LiAlH4: predictions of the crystal structures and reaction mechanisms of intermediate phases from quantum mechanics

We use the density functional theory and x-ray and neutron diffraction to investigate the crystal structures and reaction mechanisms of intermediate phases likely to be involved in decomposition of the potential hydrogen storage material LiAlH(4). First, we explore the decomposition mechanism of monoclinic LiAlH(4) into monoclinic Li(3)AlH(6) plus face-centered cubic (fcc) Al and hydrogen. We find that this reaction proceeds through a five-step mechanism with an overall activation barrier of 36.9 kcal/mol. The simulated x ray and neutron diffraction patterns from LiAlH(4) and Li(3)AlH(6) agree well with experimental data. On the other hand, the alternative decomposition of LiAlH(4) into LiAlH(2) plus H(2) is predicted to be unstable with respect to that through Li(3)AlH(6). Next, we investigate thermal decomposition of Li(3)AlH(6) into fcc LiH plus Al and hydrogen, occurring through a four-step mechanism with an activation barrier of 17.4 kcal/mol for the rate-limiting step. In the first and second steps, two Li atoms accept two H atoms from AlH(6) to form the stable Li-H-Li-H complex. Then, two sequential H(2) desorption steps are followed, which eventually result in fcc LiH plus fcc Al and hydrogen: Li(3)AlH(6)(monoclinic)-->3 LiH(fcc)+Al(fcc)+3/2 H(2) is endothermic by 15.8 kcal/mol. The dissociation energy of 15.8 kcal/mol per formula unit compares to experimental enthalpies in the range of 9.8-23.9 kcal/mol. Finally, we explore thermal decomposition of LiH, LiH(s)+Al(s)-->LiAl(s)+12H(2)(g) is endothermic by 4.6 kcal/mol. The B32 phase, which we predict as the lowest energy structure for LiAl, shows covalent bond characters in the Al-Al direction. Additionally, we determine that transformation of LiH plus Al into LiAlH is unstable with respect to transformation of LiH through LiAl.     

Kinetics and mechanisms of the catalytic reactions of formaldehyde with copper oxides and a copper ion complex in aqueous alkali

The kinetics of the autocatalytic reactions of formaldehyde with copper(II) and copper(I) oxides and with the Cu²⁺ ion of the copper EDTA complex, as well as formaldehyde disproportionation in the presence of copper metal, have been investigated in aqueous solutions of sodium hydroxide. Two likely reaction mechanisms are presented. The difference between these mechanisms does not alter the observed kinetics of the processes, whose rate is determined by their first, slow step, namely, the oxidation of the methylene glycol anion adsorbed on the copper surface into formic acid. In the slow step of the first mechanism, a hydride ion is abstracted from the methylene glycol anion and is transferred to copper. In the slow step of the second mechanism, the methylene glycol anion undergoes anodic oxidation, releasing a hydrogen atom and an electron. In the rapid steps of the first mechanism, the hydride ion undergoes anodic oxidation to hydrogen, the copper compound undergoes cathodic reduction to copper metal, and, simultaneously, the electron and hydrogen are transferred to a nonionized formaldehyde molecule to yield methanol. Mathematical models are suggested for the reactions. The effective rate constants and activation energies of the slow steps of the reactions have been determined. The effective rate constants of the noncatalytic reduction reactions of the copper compounds and the ratios of the rates of the rapid hydrogen and methanol formation reactions have been estimated.     

Synthesis of well-defined soluble polystyrene supports: Impact of polymer chain on grafted organotin reagent activity

The synthesis of well-defined soluble polystyrene supports bearing tin hydride functionalities has been achieved in two steps. First, a precursor was prepared by copolymerization of styrene and acetoxystyrene using atom transfer radical polymerization. Prior any modification, this precursor was fully characterized to check its structure. Then in a second part, tin hydride functions were introduced by a four step process. The chemical modification was monitored by IR and ¹H NMR spectroscopies. The soluble support was also characterized by triple detection size exclusion chromatography at each step. Two families of supports were synthesized by varying the molecular weight and the degree of functionalization. The effectiveness of these tin hydride supports was tested through the reduction of 6-bromohexene and compared with the small counterpart Bu₃SnH. Measurements of rate constant for hydrogen transfer were also reported.     

Evaluation of metal hydride thermograms by a differential-correction technique

A least-squares linear-Taylor differential-correction technique has been used for the rapid evaluation of thermogravimetric curves obtained during the decomposition of magnesium hydride, iron—titanium hydride and lanthanum—nickel hydride. For magnesium hydride and iron—titanium hydride the Avrami—Erofe'ev equation fits the experimental data, thus indicating that nucleation is the rate-determining step under thermogravimetric conditions. For lanthanum—nickel hydride a combination of the Avrami—Erofe'ev equation and the phase boundary movement equation fits the data up to a fractional decomposition of 0.8. For magnesium hydride decomposition the activation energy E and the pre-exponential factor Z are dependent on the hydrogen pressure (E = 101.2 kJ mole^?1 and Z = 8.96 × 10⁷ at 0.30 MPa, while E = 66.3 kJ mole^?1 and Z = 4.77 × 10⁷ at 0.11 MPa). For iron—titanium hydride (E = 28.4 kJ mole^?1) and lanthanum—nickel hydride (E = 13.4 kJ mole^?1) the values are independent of pressure.     

Kinetics of the Thermal Decomposition of Magnesium Salicylate Powder in Air

IntroductionThe chelate complexes of salicylic acid with rareearth and alkali earth ions have attracted considerableattention because of their special antibacterial proper-ties[1—3].The study of the thermal degradation of metalsalicylates is of major int…     

New type of spherical pore Al alloy foam with low porosity and high strength

The Ultra Light Metal Structure with variouskinds of pores (open, close) realizes the lightness andmultifunction of structural material. The functionsinclude lightness (ρ < 1), high specific strength, highenergy absorption, sound insulation, heat insulationand electromagnetism shield. It is one of the hotspotsin material research nowadays[1— . The requirements 6]of high speed movement and high technology make Alalloy foam, which has higher specific st…     

Kinetic and thermodynamic studies of hydrogen storage alloys as negative electrode materials for Ni/MH batteries: a review

This paper reviews the present performances of intermetallic compound families as materials for negative electrodes of rechargeable Ni/MH batteries. The performance of the metal-hydride electrode is determined by both the kinetics of the processes occurring at the metal/solution interface and the rate of hydrogen diffusion within the bulk of the alloy. Thermodynamic and electrochemical properties for each hydride compound family will be reported. The steps of hydrogen absorption/desorption such as charge-transfer and hydrogen diffusion for evaluating the electrochemical properties of hydrogen storage alloys are discussed. Exchange current density (I ₀) and hydrogen diffusion coefficient (D _H) are the two most important parameters for evaluating the electrochemical properties of metal hydride electrode. The values of the two parameters for a number of hydrogen storage alloys are compared. The relationship between alloy composition and electrochemical properties is noted and evaluated.     

ZnSn(OH)6的热分解动力学

用TG/DTG联用技术, 在2.5、5.0、10.0、15.0、20.0 K·min-1不同线性升温条件下, 研究了ZnSn(OH)6的热分解过程. 结果表明, 在氮气气氛下, ZnSn(OH)6在298-873 K范围内发生了一步分解. 其失重率与理论计算值相符. 应用非等温多重扫描速率法对热分解过程进行了动力学分析, ZnSn(OH)6在氮气中分解的活化能E=128.77 kJ·mol-1, 指前因子lg(A/s-1)=10.61, 机理函数为Mample单行法则.     

Kinetics of thermal decomposition of polyfunctional substituted azido-1,2,4-triazoles

The structural and kinetics regularities and the mechanism of the limiting step of thermal decomposition of the polyfunctional substituted 1,2,4-triazoles in the melt and in solutions of inert solvents were established. The activation parameters of the limiting step were determined. Polyfunctional substituents are found to show little effect on the rate of thermal decomposition of azide group in the azole ring.     

Investigation of hydrogen embrittlement of Sn–Al alloy during contact with water vapour

The humid air induced processes of embrittlement of the Sn–Al alloy and hydrogen emission have been investigated. Using the secondary-ion mass spectrometry, X-ray, scanning electron microscopy and energy-dispersive X-ray spectrometry techniques it was found that the brittleness is caused by a failure of phase adhesion due to accumulation of hydrogen and formation of oxidized layers on phase boundaries during contact of the alloy with water vapour. Specific physical and electrochemical properties of the Sn/Al phase boundary satisfy conditions for the formation of atomic hydrogen and its reaction with Sn. Electrochemical corrosion plays an important role at the stage of formation of atomic hydrogen. The penetration of hydrogen and its accumulation in the bulk of the alloy is due to the high energy of the phase boundary and the low energy of formation of unstable tin hydride. Electronic Publication     

Eu2(p-ClC6H4COO)6(C12H8N2)2配合物热分解机理及非等温动力学

The thermal decomposition behaviour of europium p-chlorobenzoate complex with 1, 10-phenanthroline and its kinetics were studied in nitrogen by non-isothermal thermogravimetry.Its thermal decomposition occurs mainly in three steps..The intermediate and residue for each step of decomposition were identified from TGcurve.The kinetic parameters were obtained from analysis of the TG-DTG curves by the Achar method.the Madhusudanan- Krishnan-Niman (MKN) method and Ozawa method respectively.The most probable mechanisms function for the first and second stage were suggested by comparing the kinetic parameters.     

Kinetic coefficient of steps at the Si(111) crystal-melt interface from molecular dynamics simulations

Nonequilibrium molecular dynamics simulations are applied to the investigation of step-flow kinetics at crystal-melt interfaces of silicon, modeled with the Stillinger-Weber potential [Phys. Rev. B 31, 5262 (1985)]. Step kinetic coefficients are calculated from crystallization rates of interfaces that are vicinals of the faceted (111) orientation. These vicinal interfaces contain periodic arrays of bilayer steps, and they are observed to crystallize in a step-flow growth mode at undercoolings lower than 40 K. Kinetic coefficients for both [110] and [121] oriented steps are determined for several values of the average step separation, in the range of 7.7-62.4 A. The values of the step kinetic coefficients are shown to be highly isotropic, and are found to increase with increasing step separation until they saturate at step separations larger than approximately 50 A. The largest step kinetic coefficients are found to be in the range of 0.7-0.8 m(sK), values that are more than five times larger than the kinetic coefficient for the rough (100) crystal-melt interface in the same system. The dependence of step mobility on step separation and the relatively large value of the step kinetic coefficient are discussed in terms of available theoretical models for crystal growth kinetics from the melt.     

Co(II)Schiff碱配合物的合成、氧合反应热力学及热分解动力学的研究

合成了两种新的钴(II)schiff碱配合物水杨醛L-甲硫氨酸-水合钴(II)(1), 邻香兰素L-甲硫氨酸-水合钴(II)(2)。通过元素分析、红外光谱、热分析等测试手段研究了配合物的性质, 并确定了配合物的组成。用气体吸收装置测定配合物在乙腈溶液中不同温度下的饱和吸氧量, 求得氧合反应的平衡常数及热力学参数, 同时探讨了温度和配体结构对配合物氧合性能的影响。用TG-DTG法研究了配合物的热稳定性及非等温热分解动力学, 并采用积分法和微分法相结合的方法,推断了两种配合物的第一步热分解反应机理, 得到了热分解反应动力学参数及其动力学方程。     

Eu_2(p-ClC_6H_4COO)_6(C_(12)H_8N_2)_2配合物热分解机理及非等温动力学

0 IntroductionThe complexes formed by rare earth and aromatic carboxylic acid have many special structuresand interesting luminous properties, thus arouse people's interest to study them. They can be used.in many areas such as extraction and separation, germicide, catalyst, luminous materials andfunctional materials and so on.The crystal structure and luminescence spectra of the europium p-chlorobenzoate complex withl, 10-phenanthroline has been reported"], but the study for its non-isothermal…     

丹酚酸B的热稳定性及其热分解动力学研究

用TG-DTG 方法研究了丹参的有效成分丹酚酸B 的热降解过程. 热重分析结果表明该物质的失重过程分两步进行. 笫一步为脱去吸附水, 其温度范围为305～373 K, 第二步为丹酚酸B 分子骨架大规模降解, 其温度范围在413～864 K. 用Friedman 和Ozawa-Flynn-Wall 两种方法分别计算出该药物降解过程中的三个阶段的活化能, 采用多步线性回归方法, 并参考常用的15 种热解机理函数, 确定了丹酚酸B 热降解过程最佳动力学模型为Fn-F2-F1.