Kinetics of Thermal Decomposition of Dolomite

The thermal decomposition reactions of calcitic dolomite were investigated. Simultaneous TG/DTG/DTA were applied under non-isothermal conditions. From the recorded curves, the activation energies, pre-exponential factors and thermodynamic parameters of activation were calculated for the two thermal decomposition steps. This revised version was published online in August 2006 with corrections to the Cover Date.     

超高压微射流均质中花生球蛋白的机械力化学效应研究

以花生球蛋白为原料,研究超高压微射流均质对花生球蛋白作用的机械力化学效应,通过电镜扫描(SEM)、SDS-PAGE、荧光光谱(FLU)和差热式扫描(DSC)对超高压微射流均质后花生球蛋白的微观形貌、亚基组成、表面疏水性和热稳定性进行分析。结果表明：在超高压微射流的机械力作用下,花生球蛋白的亚基和分子量几乎不受影响;花生球蛋白的颗粒和热稳定性随着处理压力的增大而减小,分别在80 MPa和120 MPa时达到最小;表面疏水性随着处理压力的增大而增强,在160 MPa时达到最大。超高压微射流均质过程的机械力化学效应可使花生球蛋白的微观形貌和三维结构改变,热稳定性降低。     

Thermal Decomposition of Dolomite in an Atmosphere of Carbon Dioxide: The effect of procedural variables in thermal analysis

The effects of procedural variables on dolomite decomposition in carbon dioxide were investigated. The partial pressure of carbon dioxide causes dolomite decomposition to split into a two-stage process. It was observed that the first stage of dolomite decomposition is progressively displaced to higher temperatures with an increase in heating rate. However, the second stage is not affected significantly by changes in the heating rate. These studies also indicate that decrepitation analysis on dolomite in CO₂ provides better information as compared to experiments in other atmospheres. The flow rate of the purge gas does not influence the thermal behavior of dolomite.This revised version was published online in November 2005 with corrections to the Cover Date.     

Two Types of Uncertainty in the Values of Activation Energy

The activation energies of the same process are often reported to have different values, which are usually explained by the differences in experimental conditions and sample characteristics. In addition to this type of uncertainty, which is associated with the process (ΔE _process) there is an uncertainty related to the method of computation of the activation energy (ΔE _method). For a method that uses fitting single heating rate data to various reaction models, the value of ΔE _method) method is large enough to explain significant differences in the reported values of the activation energy. This uncertainty is significantly reduced by using multiple heating rate isoconversional methods, which may be recommended for obtaining reference values for the activation energy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization,correlation and kinetics of dolomite samples as outlined by thermal methods

In this study, the decomposition behavior of four dolomite samples of different origin was studied by X-ray diffractometer and simultaneous TG-DTA experiments. Three different decomposition regions were determined known as dehydration of inter-particle water, formation of MgO and calcite and decomposition of calcite. Kinetic analysis of these decomposition regions was analyzed and the related activation energies are determined. It was observed that the activation energies were in the range of 48–137 kJ mol⁻¹.     

Thermal decomposition of mechanically activated arsenopyrite

The changes in specific surface area and structure disorder of mechanically activated arsenopyrite were investigated. The rate of nonoxidative decomposition of mechanically activated arsenopyrite was increased almost 10-times when compared with nonoxidative decomposition of a non-activated sample. An empirical linear relationship was found (r=0.996) between the rate constant of decomposition and the ratio of specific surface to transmission of the absorption band of arsenopyrite at $\bar \nu = 370 cm^{ - 1} $ . This relationship enables us to arrange the reaction 4FeAsS→4FeS+As₄ among structure-sensitive reactions.     

Comments on multiple publications reporting single heating rate kinetics

This note alerts one to multiple Applied Organometallic Chemistry publications that report the single heating rate kinetics for thermal decomposition of organometallic compounds. It is stressed that the single heating rate approach is known to produce erroneous kinetic parameters. Its use is also against the recommendations of the International Confederation for Thermal Analysis and Calorimetry that advises the multiple heating rate approach to be used instead. Examples of the failure are provided and an appeal is made to the community for adopting the multiple heating rate approach.     

X射线衍射法(XRD)分析煅烧白云石的物相组成

采用X射线衍射技术(XRD)对白云石原矿和不同温度煅烧的白云石原矿进行了物相分析,白云石原矿中主相为CaMg(CO3)2,相对含量约为98.6%,杂质相为SiO2,相对含量约为1.4%。白云石原矿经过300和500℃,煅烧2h未见主相CaMg(CO3)2分解,在750℃煅烧2h,主相CaMg(CO3)2部分分解为碳酸钙和氧化镁,在1000℃煅烧2hCaMg(CO3)2全部分解为氧化镁和氧化钙。     

Sublattice Method in Chemical Bond Theory for Dolomite Crystals

The distribution of valence and difference densities in crystalline CaMg(CO₃)₂ was calculated within the framework of the local density functional theory. It is shown that the terminal maxima of difference density located beyond the oxygen atom nuclei have different values due to the polarizing influence of the cations.     

The Effect of Oleic Acid Emulsification using SPE on Fluorite and Dolomite Flotation**

Collector OA, oleic acid, is widely used industrially for fluorite flotation. Low selectivity, dispersibility and collecting capability of the OA collector are always observed. In this study, compared with flotation of dolomite, a collector mixture of OA and SPE (styrylphenol polyoxyethylene ether) demonstrated significantly better performances for the fluorite. An optimal mass ratio 4 : 1 OA : SPE was found, and the recovery of fluorite was increased from over 85 % to more than 94 % compared with pure OA. Furthermore, the dosage of the collector agent was reduced from 50 mg mL⁻¹ to 20 mg mL⁻¹, which did not negatively impact the recovery of dolomite. The results from the contact angle tests indicated that SPE selectively increased the surface hydrophobicity of fluorite but had little effect on dolomite. Besides, zeta potential measurements and IR analyses revealed that the addition of SPE led to strong chemical adsorption on the surface of fluorite, resulting in a significant difference in the flotation performances of the two minerals. Therefore, SPE-emulsified OA is corroborated to prompt more selectivity and collecting capability on flotation of fluorite over dolomite.     

X-射线荧光光谱法测定白云石中主次量组分

采用粉末压片x-射线荧光光谱法测定白云石中氧化镁、氧化钙、二氧化硅、三氧化二铝、三氧化二铁和二氧化钛含量。采用校正曲线和基体校准一体的回归方程进行谱线重叠干扰校正和基体效应校正。将白云石样品进行磨细处理,在压片机上制成样片,直接在X-射线荧光光谱仪上按照选定的分析条件,以标准样品做工作曲线,利用工作曲线测定样品含量。通过与国家标准化学法以及熔片法对照,分析结果与标准值、熔片法结果吻合,主含量元素测定结果相对误差不超过10％,同一样品12次测定结果相对标准偏差不超过10％。该方法简便、快速、准确、重现性好。     

Thermal analysis study of imidazolinium and some benzimid azolium salts by TG

The imidazolinium and benzimidazolium bromide salts with pentafluor substituents on N atom were synthesized. The structures of imidazolinium and benzimidazolium bromide salts obtained were conformed by ¹H and ¹³C NMR, ¹⁹F NMR and elemental analysis. It was found that pyrolytic decomposition occurs with melting in salts. The imidazolinium and benzimidazolium bromide salts were studied by TG-DTG and DTA from ambient temperature to 1000°C in nitrogen atmosphere. The decomposition occurred mainly in one stage and the values of activation energy E, frequency factor A, reaction order n, enthalpy change ΔH ^#, entropy change ΔS ^# and Gibbs free energy ΔG ^#, of the thermal decomposition were calculated by means of Coats-Redfern (CR), MacCallum-Tanner (MC) and van Krevelen (vK) methods. The activation energy value obtained by CR and MC methods were in good agreement with each other while those obtained by vK were found to be 10–12 kJ mol⁻¹ larger.     

Thermal decomposition kinetics of natural fibers: Activation energy with dynamic thermogravimetric analysis

Dynamic TG analysis under nitrogen was used to investigate the thermal decomposition processes of 10 types of natural fibers commonly used in the polymer composite industry. These fibers included wood, bamboo, agricultural residue, and bast fibers. Various degradation models including the Kissinger, Friedman, Flynn-Wall-Ozawa, and modified Coats-Redfern methods were used to determine the apparent activation energy of these fibers. For most natural fibers approximately 60% of the thermal decomposition occurred within a temperature range between 215 and 310 °C. The result also showed that an apparent activation energy of 160-170 kJ/mol was obtained for most of the selected fibers throughout the polymer processing temperature range. These activation energy values allow developing a simplified approach to understand the thermal decomposition behavior of natural fibers as a function of polymer composite processing.     

水合硼酸锶的制备及脱水热分解动力学

以氯化锶和硼酸氢铵为原料,采用液相沉淀法制备了片状水合硼酸锶（SrB6O10•5H2O）粉体,并用XRD、FT-IR及SEM进行了表征。利用热重分析法对片状纳米硼酸锶粉体的脱水热分解动力学进行了研究,分别采用 Coats- Redfern 方程和 Flynn-Wall-Ozawa（FWO）法对热重分析数据进行了处理和拟合,初步确定了水合硼酸锶的四步脱水过程及相应的热分解反应机理,得到各步反应的表观活化能和指前因子。     

Phase Transformations in Mixtures of Calcite and Dolomite with Condensed Phosphates of Calcium during Heating

The thermal interactions of dolomite and calcite with calcium polyphosphates up to 1000°C were studied by thermal (dynamic heating and isobaric conditions) and X-ray diffraction methods. It was found that in mixtures with Ca-polyphosphates less than half of the carbonates reacted before decomposition to oxides with the phosphates. The rates of the reactions of phosphates with MgO were much lower than those with CaO. The scheme of the main crystalline phase transformations was constructed. This revised version was published online in July 2006 with corrections to the Cover Date.     

红外碳硫分析仪测定白云石中硫含量测量不确定度的评定

建立了红外碳硫分析仪测定白云石中硫含量测量结果不确定度数学模型.通过对不确定度分量的计算分析,求得了该检测方法的合成标准不确定度和扩展确定度.结果表明,方法的检测结果可信度较高,适于白云石中硫含量的测定.     

Thermal dehydration and decomposition of M[M(C2O4)2]·xH2O (x=3 forM=Sr(II) andx=6 forM=Hg(II))

Strontium(II) bis (oxalato) strontium(II) trihydrate, Sr[Sr(C₂O₄)₂]·3H₂O and mercury(II) bis (oxalato) mercurate(II) hexahydrate, Hg[Hg(C₂O₄)₂]·6H₂O have been synthesized and characterized by elemental analysis, reflectance and IR spectral studies. Thermal decomposition studies (TG, DTG and DTA) in air showed SrCO₃ was formed at ca. 500°C through the formation of transient intermediate of a mixture of SrCO₃ and SrC₂O₄ around 455°C. Sharp phase transition from γ-SrCO₃ to β-SrCO₃ indicated by a distinct endothermic peak at 900°C in DTA. Mercury(II) bis (oxalato) mercurate(II) hexahydrate showed an inclined slope followed by surprisingly steep slope in TG at 178°C and finally 98.66% of weight loss at 300°C. The activation energies (E ^*) of the dehydration and decomposition steps have been calculated by Freeman and Carroll and Flynn and Wall's method and compared with the values found by DSC in nitrogen. A tentative reaction mechanism for the thermal decomposition of Sr[Sr(C₂O₄)₂]·3H₂O has been proposed.     

Kinetics of thermal decomposition of nickel sulfate hexahydrate

The paper describes the kinetics of all the recorded steps of thermal decomposition of nickel sulfate hexahydrate in air. The thermal decomposition of the salt in air led to NiO at about 1060 K. The kinetic parameters, the activation energyE and the preexponential factorA, and the thermodynamic parameters, the entropy, enthalpy and free energy of activation were evaluated for the dehydration and decomposition reactions. Tentative reaction mechanisms are suggested for each step of the thermal decomposition.     

Thermal Characterization of Dolomites

The decomposition behaviour of dolomite samples has been carried out by simultaneous DTA-TG experiments. Dolomite samples could be classified broadly into two categories as regular and iron-bearing dolomites based on DTA decomposition temperatures. The mass% FeO of all the dolomite samples was identified by DTA and the results are confirmed by atomic absorption spectrophotometer experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

How much is the accuracy of activation energy affected by ignoring thermal inertia?

This work estimates the magnitude of the effect of thermal inertia on the value of the activation energy determined from heat-flux differential scanning calorimetry (DSC) data. The estimates are obtained via analysis of the literature data on crystallization of copper and thermal degradation of isotactic polystyrene (iPS). The copper crystallization data have been obtained for very large masses (200 mg) and fast heating rates up to 80 K min⁻¹. The iPS degradation data have been collected on small masses (3 mg) and at the heating rates up to 20 K min⁻¹. For crystallization of copper, the Kissinger activation energy obtained from the DSC data corrected for thermal inertia is 34% larger than the value estimated from uncorrected data. This difference drops to 8% and becomes statistically insignificant when the fastest heating rate used is decreased to 10 K min⁻¹. For iPS degradation, the difference in the isoconversional activation energies estimated, respectively, from corrected and uncorrected DSC data is less than 3% and is not statistically significant. Overall, the effect of thermal inertia on the activation energy appears negligible provided that DSC measurements are conducted on smaller samples and at slower heating rates, that is, as advised by the International Confederation for Thermal Analysis and Calorimetry (ICTAC) recommendations. It is suggested that the difference in the activation energies should generally be within the typical 5-10% uncertainty as long as the product of the time constant and the maximum heating rate does not exceed 2-3 K.