The two steps thermal decomposition of titanium hydride and two steps foaming of Al alloy

1 Introduction Al alloy foam with closed pores prepared by melt foaming, realizing the lightness, high specific strength and multifunction of structure material, is becoming one of the hotspots[1―11]. In order to meet the demand of high-tech, preparing s…     

新型单组份磷-氮膨胀型阻燃剂的热分解动力学

利用热重分析法研究了在不同升温速率下新型单组份磷-氮膨胀型阻燃剂六(4-(9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物)-羟甲基苯氧基)环三磷腈(DOPOMPC)在氮气气氛和空气气氛中的热分解动力学.采用Kissinger和Flynn-Wall-Ozawa(FWO)法分别计算出DOPOMPC在相应气氛下的活化能和指前因子.     

On the thermal stability and thermal decomposition kinetics of some mono- and disubstituted furan-2,3-dions

The thermal behaviour of some compounds derived from 5-phenylfuran-2,3-dione was studied. The thermoanalytical data relating to the decomposition steps and intermediates were completed with mass spectrometric analysis and infrared spectroscopy results. For some of the investigated reactions, the kinetic and structural data correlated satisfactorily.     

Thermal behaviour and non-isothermal decomposition kinetics of some Nd(III) coordination compounds

The authors present the results concerning the thermal behaviour of three polynuclear coordination compounds of Nd(III) and Co(II) or Fe(III) with triptophan. For the dehydration steps the values of the non-isothermal kinetic parameters have been determined.     

Additional force field in cooling process of cellular Al alloy

The foaming process of Al alloy is similar to that of Al, but there is a solid-liquid state zone in the solidification process of cellular Al alloy which does not exist in the case of Al. In the unidirectional solidification of cellular Al alloy, the proportion of the solid phase gradually reduces from the solid front to the liquid front. This will introduce a force and result in a serious quick shrinkage. By the mathematic and physical mode, the solidification of the cellular Al alloy is studied. The data measured by experiment are close to the result calculated by the mode. This kind of shrinkage can be solved by suitable cooling method in appropriate growth stage. The compressive strength of the cellular Al alloy made by this way is 40% higher than that of cellular Al.     

Thermal decomposition kinetics of lanthanum and neodymium bromide complexes with glycine or alanine

Four complexes of rare earth bromides with amino acids, REBr₃·3L·3H₂O (RE=La, Nd;L=glycine or alanine) were prepared and characterized by means of chemical analysis, elemental analysis, molar conductivity, thermogravimetry, IR spectra and X-ray diffraction. Their thermal decomposition kinetics from ambient temperature to 500°C were studied by means of TG-DTG techniques under non-isothermal conditions. The kinetic parameters (activation energyE and pre-exponential constantA) and the most probable mechanisms of thermal decomposition were obtained by using combined differential and integral methods. The thermal decomposition processes of these complexes are distinguished as being of two different types, depending mainly on the nature of the amino acid.     

电感耦合等离子体原子发射光谱法测定钛合金TC4中Fe、Al、V

本文采用电感耦合等离子体原子发射光谱法测定钛合金TC4中Fe、Al、V含量。使用硝酸与氢氟酸溶解试样,大幅缩短了溶样时间;确定了Fe、Al、V分析线分别为238.204nm、309.271nm、292.402nm。精密度实验表明,待测组分的相对标准偏差均低于1.26%（RSD,n=10）,能满足钛合金TC4中Fe、Al、V含量的检测要求。     

Effects of monomer structures on the foaming processes and thermal properties of polyimide foams

Four polyimide (PI) foams were prepared from polyamide acid precursors. The effects of monomer structures on the foaming processes and thermal properties of PI foams were investigated. The foaming processes of PI foams were observed by a self‐made visualization device. The thermal properties of four PI foams were studied by the methods of dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and thermogravimetry/differential thermogravimetry (TG/DTG) analysis. The results indicated that the inflation onset temperatures and maximum inflation degrees of four precursors increased from 123 to 171°C and decreased from 28 to 15 times with the increasing rigidity of the precursor molecule, respectively. The glass transition temperatures, the 5% weight loss temperatures, the decomposed activation energies, and pre‐exponential factors of PI foams increased with increase in the rigidity of monomer. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal stability and decomposition of pharmaceutical compounds

Thermal analysis of fusion and decomposition processes were carried out on recently synthetized pharmaceutical compounds in order to establish thermal stability criteria. This study was carried out using thermogravimetry, TG, and differential scanning calorimetry, DSC. Degradation and fusion temperatures have been produced as thermal data with the aim of to study the thermal stability of the compounds. Relationship is found among stability and a series of effects of structure of the compounds. The compounds which present an amide functional group in the central molecule are more stable because they have a comparatively higher fusion and degradation temperature. In addition, the stability of this type of compounds depends on the position of the electrophilic substitution (in ortho, meta or para). Likewise, the groups linked to the aromatic ring with high electronic density give stability, and therefore are able to delocalize the charge in a greater spacial interval. Therefore, criteria for the selection of substituents have established that improve the stability of compounds     

Reaction pathway and kinetics of the thermal decomposition of synthetic brochantite

The reaction pathway of the thermal decomposition of synthetic brochantite, Cu₄(OH)₆SO₄, to copper(II) oxide was investigated through the detailed kinetic characterization of the thermal dehydration and desulferation processes. The dehydration process was characterized by dividing into two overlapped kinetic processes with a possible formation of an intermediate compound, Cu₄O(OH)₄SO₄. The dehydrated sample, Cu₄O₃SO₄, was found first to be amorphous by means of XRD, followed by the crystallization to a mixture of CuO and CuO-CuSO₄ at around 776 K. The specific surface area and the crystallization behaviour of the amorphous dehydrated compound depend largely on the dehydration conditions. The thermal desulferation process is influenced by the gross diffusion of the gaseous product SO₃, which is governed by the advancement of the overall reaction interface from the top surface of the sample particle assemblage to the bottom.     

过氧化苯甲酸叔丁酯的热分解动力学研究及SADT推算

研究了过氧化苯甲酸叔丁酯的热分解动力学及不同包装规格下的自加速分解温度(SADT),利用C600微量热仪测试了过氧化苯甲酸叔丁酯的热分解特征,得到升温速率分别为0.1 K/min、0.2 K/min、0.5 K/min、1 K/min下热流随时间的变化曲线,并使用Friedman等转化率法对所得的实验数据进行分析处理,得到了过氧化苯甲酸叔丁酯的分解反应活化能、指前因子等热动力学参数,推算了不同包装规格的过氧化苯甲酸叔丁酯的SADT。结果表明TBPB分解活化能及指前因子随转化率变化而变化,活化能范围为42-135.5 kJ/mol,指前因子范围为0.25-33.5,在25L聚乙烯桶包装下的SADT为59℃,50L下为52℃,200L下为46℃。     

柚皮苷的热稳定性及其热分析动力学研究

用TG-DTG/DTA方法研究了柚皮苷的热降解过程及热分析动力学. 热重分析结果表明该物质的失重过程分两步进行. 第一步为结晶水脱出, 其温度范围为343～545 K, 第二步为其分子骨架大规模降解, 其温度范围在545～857 K. 差热分析结果表明, 该物质的熔化温度为439.2 K. 使用Friedman和Ozawa-Flynn-Wall两种方法分别计算出该物质降解过程的活化能. 采用多步线性回归方法, 并参考常用的15种热解机理函数, 确定了柚皮苷热解过程最佳动力学模型为Fn-F2-F1.     

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.     

微孔聚乳酸支架材料的热稳定性与动态热机械特性

采用无溶剂二氧化碳固态发泡技术,在2.5、3.5、4.0和5.0 MPa饱和压力下制备了泡孔孔径为350-20μm的聚乳酸支架材料.利用热重分析技术、动态热机械分析技术和扫描电子显微镜技术,测定了材料的起始分解温度、分解速率、储存/损耗模量和损耗因子等参数,并利用Kissinger、Ozawa-Doyle和Vyazovkin方程进行了热分解动力学计算,推算了氮气环境下材料的降解时间和使用寿命.结果表明,随着发泡压力的减小,支架材料的泡孔孔径增大,材料的柔韧性增强,表观活化能降低,降解时间缩短.     

Effect of mechanical grinding on the reaction pathway and kinetics of the thermal decomposition of hydromagnesite

Effect of mechanical grinding of hydromagnesite on the reaction pathway and kinetic behaviors of the thermal decomposition process was investigated by means of thermoanalytical techniques, together with crystallographic and morphological measurements. A crystalline hydromagnesite, the as-received sample, was decomposed in two distinguished mass loss steps of overlapped dehydration-dehydroxylation and dehydroxylation-decarbonation via an amorphous intermediate of carbonate compound. Thermal decomposition of an amorphous hydromagnesite, obtained by mechanical grinding of the as-received sample, was characterized by three well-separated decomposition processes of dehydration, dehydroxylation and decarbonation. The kinetic behaviors of the respective decomposition steps were estimated separately using a mathematical deconvolution of the partially overlapped reaction steps. From the formal kinetic analyses of the respective reaction processes, it was revealed that the dehydration and dehydroxylation processes indicate the decelerate rate behaviors controlled by diffusion, while the rate behavior of nucleation limited type is predominant for the decarbonation process.     

Thermal decomposition of PTFE in the presence of silicon,calcium silicide,ferrosilicon and iron

Simultaneous TG/DTA has been used to study the thermal decomposition of binary compositions containing polytetrafluoroethene (PTFE) with silicon (Si), calcium silicide (CaSi₂), ferrosilicon (FeSi) or iron (Fe) powders. In nitrogen and under dynamic heating program the thermal decomposition of Si/PTFE and CaSi₂/PTFE is an exothermic process. The other two compositions decompose endothermically. In each case the decomposition reactions show first-order kinetics but only iron does not change considerably the kinetics of PTFE depolymerization. The constants of the decomposition rate at 850 K for silicon containing reducers are about four times higher than those of PTFE and Fe/PTFE. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation,thermal decomposition process and kinetics for terbium<Emphasis Type="Italic">p</Emphasis>-methoxybenzoate ternary complex with 1,10-phenanthroline

The complex of [Tb₂(p-MOBA)₆(PHEN)₂] (p-MOBA=C₈H₇O₃,p-methoxybenzoate; PHEN=C₁₂H₈N₂, 1,10-phenanthroline) was prepared and characterized by elemental analysis and IR spectroscopy. The thermal behavior of Tb₂(p-MOBA)₆(PHEN)₂ in a static air atmosphere was investigated by TG-DTG, DTA, SEM and IR techniques. By the kinetic method of processing thermal analysis data put forward by Malek et al., it is defined that the kinetic model for the first-step thermal decomposition is SB(m,n). The activation energy E for this step reaction is 140.92 kJ mol^-1, the enthalpy of activation H is 136.06 kJ mol^-1, the Gibbs free energy of activation G is 145.16 kJ mol^-1, the entropy of activation S is -15.53 J mol^-1, and the pre-exponential factor lnA is 29.26. The lifetime equation at mass loss of 10% was deduced as ln =-28.72+1.943·10⁴/T by isothermal thermogravimetric analysis.     

Thermal unimolecular decomposition of ethyl 2-furoate and its reactivity toward OH radicals: A theoretical study

Mechanism and kinetics of the thermal pyrolysis of ethyl 2-furoate were studied in a wide range of conditions (ie, 500-1500 K and 1-7600 Torr) using the accurate dual-level theory CCSD(T)&MP2(FC)//B3LYP/aug-cc-pVTZ and state-of-the-art Rice-Ramsperger-Kassel-Marcus based master equation rate model including hindered internal rotation and tunneling treatments. The predicted rate coefficients are found to be in accordance with the experimental data. The mechanism details are revealed as (i) the major decomposition channel occurs via a six-center transition state with the barrier energy of 48.3 kcal/mol at 0 K, leading to the formation of C₂H₄ and 2-furoic acid and (ii) pressure has a slightly positive effect on the rate constant, particularly at the high temperature. Also, the reactivity of ethyl 2-furoate toward OH radicals was discussed in the first place.     

Mechanism and kinetics of thermal decomposition of nickel(II) sulfate(VI) hexahydrate

This work presents results of research on thermal decomposition of nickel(II) sulfate(VI) hexahydrate in air and in helium atmosphere. On the base of TG and XRD results a mechanism of thermal decomposition of NiSO₄ hydrate was established. For calculations of kinetic parameters of the Arrhenius equation, the Coats-Redfern approximation was applied. Choice of g(a) function and thus of a mechanism best describing given stage of decomposition was performed by testing 12 kinetic models. This revised version was published online in July 2006 with corrections to the Cover Date.     

Products and kinetics of non-isothermal decomposition of vanadium(IV) oxide compounds

The kinetics of dehydration and decomposition of VOSO₄·2H₂O, VOSO₄ and VOSeO₃·H₂O was studied under non-isothermal heating on a derivatograph. The stages and products of the thermal decomposition were determined. It was proved that VOSO₄·2H₂O decomposes to V₂O₅ while VOSeO₃·H₂O − to V₂O₄. A number of kinetic models and calculation procedures were used to determine the values of the kinetic parameters characterizing the process. The parameters calculated were compared and analyzed. IR-spectra of the initial substances and the solid residue after decomposition are presented.