Analysis of relative rate of reaction/process

Kinetic or rather thermokinetic analysis of thermal decomposition with releasing gaseous products is a current subject of discussion in many works and still devotes much attention to the property and meaningfulness of the single kinetics triplet determination. Analysis of thermogravimetric data by the relative rate of reaction/process were used to examine the frequently studied process of thermal dissociation of calcium carbonate as a model compound and comparing with published data for chemically defined compounds (azo-peroxyesters) and complex polyolefins?Cliquid paraffin mixtures. Two methods of correlation between parameters of the model were observed: thermodynamic and analytical expression. It was shown that these relations depend on course of the process. For analyzed model substance, enthalpy of reaction can be deduced on the basis of relation between coefficients in three-parameter equation. For large values of coefficients it is not possible, but other type of correlation was proved. Also, the relative rate of CO₂ gasification (Boudouard reaction) of brown and bituminous coals was analyzed and compared to that of its pyrolysis.     

Influence of sample preparation on thermal decomposition of wasted polyolefins-oil mixtures

Significant influence of sample preparation on thermal decomposition of polyolefin-technological oil mixtures was proved during tests. Samples of polymer-oil mixtures were prepared with two methods: reducing size and components mixing and soaking in temperature 170°C. Soaking causes decreasing thermal stability of the charge. This fact manifests itself in decreasing of thermal decomposition temperature in laboratory scale, as well as in change of characteristic decomposition temperatures during thermogravimetric analyses. Data analysis was performed with the use of classic method based on Arrhenius kinetic equation and three-parameter model. The influence of sample composition and preparation method on values of three-parameter equation coefficients was observed.     

Thermal analysis and compatibility studies of prednicarbate with excipients used in semi solid pharmaceutical form

Differential Scanning Calorimetry (DSC), thermogravimetry/derivative thermogravimetry (TG/DTG) and infrared spectroscopy (IR) techniques were used to investigate the compatibility between prednicarbate and several excipients commonly used in semi solid pharmaceutical form. The thermoanalytical studies of 1:1 (m/m) drug/excipient physical mixtures showed that the beginning of the first thermal decomposition stage of the prednicarbate (T _onset value) was decreased in the presence of stearyl alcohol and glyceryl stearate compared to the drug alone. For the binary mixture of drug/sodium pirrolidone carboxilate the first thermal decomposition stage was not changed, however the DTG peak temperature (T _{peak DTG}) decreased. The comparison of the IR spectra of the drug, the physical mixtures and of the thermally treated samples confirmed the thermal decomposition of prednicarbate. By the comparison of the thermal profiles of 1:1 prednicarbate:excipients mixtures (methylparaben, propylparaben, carbomer 940, acrylate crosspolymer, lactic acid, light liquid paraffin, isopropyl palmitate, myristyl lactate and cetyl alcohol) no interaction was observed.     

无柔性间隔基侧链型液晶高分子复合定形相变材料的制备与性能研究

设计合成了一系列具有不同烷氧基尾链长度的单体4′-烷氧基-4-联苯酚甲基丙烯酸酯Mbi Cm(m=1,2,4,6,8,10,12,14,16,18),通过自由基聚合方法合成了相应的具有不同烷氧基尾链长度的无柔性间隔基侧链型液晶高分子PMbi Cm,将所得的侧链型液晶高分子和相变材料石蜡按一定质量比混合,通过"加热-冷却法"成功制备了定形相变材料.通过凝胶测试发现当尾链长度为m=12,14,16,18时,高分子对固体石蜡具有良好的凝胶定形效果,且随着烷氧基尾链的增长,聚合物和石蜡的相容性增加,最低凝胶浓度降低,得到定形相变材料的凝胶解缔温度也相应下降.通过示差扫描量热法(DSC)、热重分析法(TG)、流变(Rheology)等测试考察了定形相变材料的相变储能性能、热稳定性和流变性能,实验结果表明该定形相变材料具有相变焓值高、热稳定性好、凝胶强度高等优点.通过红外光谱(FTIR)、偏光显微镜(POM)和扫描电镜(SEM)等测试发现PMbi Cm通过非共价键作用力自聚集形成三维凝胶网络结构,对石蜡起固定支撑作用.     

涂石蜡大米傅立叶变换红外吸收光谱识别分析

针对11种未涂石蜡大米和18个涂不同量石蜡的大米样品,以石油醚提取的油脂为试样,采用傅立叶变换红外光谱仪,扫描样品的傅立叶变换红外吸收光谱,并对光谱进行预处理,提取红外特征信息,将2855与1746、1462与1163 cm-1处特征峰的面积比值为坐标,采用Origín 6.0软件作识别分类图.结果表明:特征峰的面积比值与所涂石蜡量成线性变化,大米油脂的特征峰面积比值在一定的区域分布,涂以0.05%以上石蜡的大米,其油脂特征峰面积比值与未涂石蜡米油脂的值有一定区别.     

Thermal decomposition mechanism of tenofovir disoproxil fumarate

Tenofovir disoproxil fumarate (TDF) is an antiretroviral medication widely used to prevent and treat HIV/AIDS and to treat chronic hepatitis B. In this paper, thermal decomposition processes of TDF were measured with thermogravimetry, differential scanning calorimetry and thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. The IR spectra, high-performance liquid chromatography and liquid chromatography mass spectrometry of TDF and the residues of its thermal decomposition at various temperatures were determined. The molecular bond orders were calculated using an ab initio method from the GAMESS program of quantum chemistry. The mechanism of thermal decomposition was discussed. The results indicated that the thermal decomposition of TDF is a three-step process, the initial step of thermal decomposition of TDF is the decomposition of carboxylic ester, the first stage mainly is the decomposition of the phosphoric disoproxil section, and the second stage mainly is the decomposition of the tenofovir section and partially goes through adenine stage. The initial decomposition temperature in either nitrogen or air is 138 °C, and the thermal stability of TDF is not very good under routine temperature.

     

Thermospectrometry

Thermospectrometry, a new and unique material testing and analytical method has been developed by combining thermal analysis with atom and molecule spectrometry. The central unit of the method is a stationary furnace that can be heated up to 1700 °C. Nanoparticles of solid, liquid or gaseous samples travel upwards between the two heated walls of the furnace placed 10 mm from each other, where conversion and decomposition processes occur separately in time and space according to the thermal properties of substances. The formation and decomposition of molecules, atoms and ions can be observed directly with narrow light beams of spectral lamps heights of the furnace (maximum of 200 mm). The developed method has been used for studying the atomization of inorganic and organic water soluble mercury salts.     

Thermal behavior of iminodiacetic acid and its disodium salt

The thermal properties of iminodiacetic acid (IDA) and its disodium salt were investigated by DTA, TG and static heating. The gaseous evolved products were analysed by chromatography in order to follow the thermal process. The heating of the samples was stopped at characteristic decomposition steps and the residual substances were investigated by IR spectroscopy. The obtained data suggest the processes of decomposition for these compounds.     

Relation between kinetic parameters for reactions of organic matter degradation in waste environmental matrix

The organic fraction of urban solid residues disposed of in sanitary landfills during the decomposition yields biogas and leachate, which are sources of pollution. Leachate is a resultant liquid from the decomposition of substances contained in solid residues and it contains in its composition organic and inorganic substances. Literature shows an increase in the use of thermoanalytical techniques to study the samples with environmental interest, this way thermogravimetry is used in this research. Thermogravimetric studies (TG curves) carried out on leachate and residues shows similarities in the thermal behavior, although presenting complex composition. Residue samples were collected from landfills, composting plants, sewage treatment stations, leachate, which after treatment, were submitted for thermal analysis. Kinetic parameters were determined using the Flynn–Wall–Ozawa method. In this case they show little divergence between the kinetic parameter that can be attributed to different decomposition reaction and presence of organic compounds in different phases of the decomposition with structures modified during degradation process and also due to experimental conditions of analysis.     

Thermal stability of styrene–(ethylene butylene)–styrene-based elastomer composites modified by liquid crystalline polymer, clay, and carbon nanotube

The thermal decomposition behaviors of styrene?C(ethylene butylene)?Cstyrene (SEBS) thermoplastic elastomer filled with liquid crystalline polymer (LCP), organomontmorillonite (OMMT), and carbon nanotube (CNT) as a heat stabilizing filler, were comparatively investigated using nonisothermal- and isothermal-thermogravimetric analyses in air. The isoconversional method was employed to evaluate the kinetic parameters (E _a, lnA, and n) under dynamic heating. For neat samples, OMMT and CNT exhibited their respective lowest and highest thermal stabilities as revealed from the lowest and the highest T _onset values, respectively. The decomposition rates of the composites containing OMMT at the temperature >250?°C were higher than those containing CNT and LCP, respectively, whereas the elastomer matrix degraded with the highest rate. The obtained TG profiles and calculated kinetic parameters indicated that the incorporation of LCP, OMMT, and CNT into elastomer matrix improved the thermal stability. Especially, the CNT- and OMMT-containing composites significantly improved the thermal stability compared with the neat matrix polymer. Simultaneously recorded DSC thermograms revealed that the degradation processes for the neat polymers and their composites were exothermic in air. From the simultaneously recorded DSC data, the enthalpy of thermal decomposition for each composite system was found to be lower than that of the neat matrix and mostly decreasing with increasing filler loading. The isothermal decomposition stabilities of the neat SEBS and its composites containing the different fillers were in agreement with those of the nonisothermal investigation.     

Thermal degradation of lyocell,modal and viscose fibers under aggressive conditions

Lyocell, modal and viscose fibers were subjected to mercerization or to solar degradation. The ulterior thermal degradation was analyzed by means of differential scanning calorimetry (DSC). Thermal analysis shows wide exothermic processes that began between 250 and 300°C corresponding to the main thermal degradation and are associated to a depolymerization and decomposition of the regenerated cellulose. Thermal degradation was analyzed as a function of concentration and time. Lyocell fiber is the most stable under thermal degradation conditions. Furthermore, mercerized samples are initially more degraded and present a lower thermal stability.     

微乳液中单分散银纳米颗粒的制备及抗磨性能

采用水/液体石蜡/Span 80-Tween 80/正丁醇微乳液体系, 制备了具有良好单分散性的Ag纳米颗粒. 通过X射线粉末衍射仪、透射电子显微镜、傅立叶变换红外光谱仪和热分析仪表征了Ag纳米颗粒的结构、形貌、粒径大小及分布、表面键合性质和热性能. 结果表明, 所制备的Ag纳米颗粒具有立方晶型结构, m(Span 80)∶m(Tween 80)=7∶3时, 粒径分布呈单分散性, 平均粒径约为6 nm. 在四球长时抗磨损试验机上考察了分散于液体石蜡中Ag纳米颗粒的抗磨性能. 实验结果表明, Ag纳米颗粒具有良好的抗磨性, 且能显著提高基础油的承载能力.     

Determination of paraffins in food simulants and packaging materials by liquid chromatography with evaporative mass detection and identification of paraffin type by liquid chromatography/gas chromatography and fourier transform infrared spectroscopy

A liquid chromatographic method with evaporative mass detection (EMD) is described for the determination of paraffins in food contact materials that do not contain polyolefin oligomers, or paraffins migrating from these materials into fatty food simulants or certain simple foods. A normal-phase column operating at maximum column efficiency separates nonparaffinic and paraffinic materials without resolving the latter into individual components, and EMD is used to quantitate the paraffins. An on-line qualitative method that uses liquid chromatography/gas chromatography with flame ionization detection discriminates between paraffin waxes and oils in food contact materials, food simulants, and certain simple foods; a Fourier transform infrared spectrophotometric qualitative method also discriminates between waxes and oils, but is usually restricted to food contact materials that do not contain polyolefins and to migration experiments with organic solvents as fatty food simulants (with some other fatty food simulants, paraffin type must then be identified in the food contact material).     

Thermal Decomposition of Several Layered Zirconium Salts

The thermal decomposition of zirconium molybdate, tungstate and arsenate were investigated. The total mass losses of the investigated materials were 12.5, 11 and 8.5%, respectively. Despite having different crystal dimensions and structure the thermal decomposition of the samples takes place in a similar way. During heating two main endothermic processes with mass loss were observed. At the end of the thermal decomposition, oxides of the original materials were observed. The mentioned mass losses originate partly from the crystal water loss of the materials. The calculated crystal water content in the original molecule was 1.3 and 1 mole/molecule unit, respectively. Furthermore, for zirconium arsenate, a sublimation process was recorded above 960 K.This revised version was published online in November 2005 with corrections to the Cover Date.     

Analysis of the thermal decomposition of azo-peroxyesters by Arrhenius-type and three-parameter equations

Thermogravimetric analysis of azo-peroxyesters revealed two decomposition stages on TG curves. Molecular nitrogen is released in the first stage and carbon dioxide in the second. Fitting the thermogravimetric data by means of the three-parameter model and a classic one based on an Arrhenius-type kinetic equation showed that the former approach satisfactorily describes the process within the wide range of the extent of decomposition. It was found that two coefficients of the three-parameter equation are related to the temperature of maximum reaction rate. One of the coefficients of the three-parameter equation is also related to the activation energy. The compounds investigated can be grouped with respect to their kinetic characteristics, structure and stage of decomposition.     

用于离子迁移率谱仪的快速热解析进样方法

热解析是用于离子迁移率谱仪(IMS)的液体和固体样品进样的重要手段,但在检测高沸点或易分解有机物时,存在易重新凝结或过热分解的问题.本研究建立了一种与IMS半透膜结合的热解析进样方法,设计了可快速加热的微型热解析装置,通过热子通电发热及热电偶测温实现对样品解析区域的升温控制,提高半透膜的进样效率.以低浓度三聚氰胺溶液为...     

Kinetics of fluorine binding from gaseous products of thermal decomposition of M-1 fluorocarbon liquid and a telomeric alcohol by alkaline-earth metal oxides and calcium hydroxide

The reactions of products of thermal decomposition of fluorinated compounds with magnesium and calcium oxides and with calcium hydroxide were studied. The kinetic parameters of the processes were determined. Conditions were found for complete binding of fluorine from M-1 fluorocarbon liquid into environmentally safe products, alkaline-earth metal fluorides.     

硝酸酯的热分解性能

分别在B3LYP/6-31G*和MP2/6-31G*的理论水平下,计算得到硝酸正丙酯、硝酸异丙酯、硝酸异辛酯和二缩三乙二醇二硝酸酯4种硝酸酯的O-NO2键离解能(BDE)。 采用常压DSC和高压DSC实验方法,研究了4种硝酸酯的热分解过程,获得热分解反应动力学参数。 常压下4种物质的热分解反应发生在气相区,当压力增大至2 MPa时,4种物质直接发生液相分解反应。 4种硝酸酯的O-NO2键离解能在很大程度上符合由实验分析得到的活化能,表明4种硝酸酯的热分解反应只是单分子O-NO2键的均裂反应。     

Relations between synthesis and microstructural properties of copper/zinc hydroxycarbonates

Cu/Zn Hydroxycarbonates obtained by co-precipitation of Cu(2+) and Zn(2+) with Na(2)CO(3) have been investigated regarding phase formation and thermal decomposition in two series with varying Cu/Zn ratios prepared according to the decreasing pH and constant pH method. Hydrozincite, aurichalcite and (zincian)-malachite were found to form at differing Cu/Zn ratios for both series. For the constant pH preparation the Cu/Zn ratio in zincian-malachite was close to the nominal values whereas excess values were found for the decreasing pH samples. The degree of crystallinity as well as the thermal decomposition temperatures were lower for the constant pH series. All samples containing aurichalcite revealed an unexpected decomposition step at high temperatures evolving exclusively CO(2). The differences in composition and microstucture were traced back to the different pathways of solid formation for the two preparation methods. Substantial changes were observed during the post-precipitation processes of ageing and washing. The effects were studied in detail on samples with a cation ratio of Cu/Zn 70:30 mol %. Ageing of the precipitates in their own solutions is accompanied by a spontaneous crystallization of the initially amorphous solids. The decreasing pH sample develops from a hydroxy-rich material comprising basic copper nitrate (gerhardtite) as an intermediate. Only small changes in the chemistry of the samples were detected for the constant pH precipitation. The findings are summarised into a scheme of solid formation processes that explains the phenomenon of a "chemical memory" of the precipitates when they are converted into Cu/ZnO model catalysts.     

Thermal characterization of hair using TG-MS combined thermoanalytical technique

Four amino acids and four different hair samples were studied in order to get information about the decomposition of human hair, using combined (TG-MS) and DSC techniques. The thermal stability of the investigated amino acid samples was different. Since they contain identical functional groups (-NH₂, -COOH) some common mass/charge units were identified. However, due to their different chemical composition remarkable differences have also been obtained. The results of the investigation of the amino acids were helpful to study the thermal fragmentation of the hair samples. In our experiments, the effect of the heating rates was also studied. This revised version was published online in July 2006 with corrections to the Cover Date.