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Dynamic thermal analysis of solid-state reactions

The ultimate method for data analysis?

Journal of Thermal Analysis and Calorimetry
Authors: Chao-Rui Li and Tong B. Tang

Abstract

There are many reactions of interest in which one or more of the reactants belong to some solid phases. Modern thermoanalytical instruments can conveniently provide reaction kinetic data of high precision and accuracy, from which the underlying activation energyE may be derived in principle. Unfortunately, no ‘best' method yet exists for the derivation when the data have been collected with a programmed linear increase in sample temperature, unlike the case of isothermal measurements, which however suffer from experimental limitations [1]. Here we propose a method for extractingE from non-isothermal data, that promises general validity.

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Abstract  

External-beam PIXE was used for the non-destructive analysis of early glasses unearthed from the tombs of Warring States (475–221BC) and Han Dynasty (BC 206–AD 220) in south China. It was found that these glasses were basically attributed to PbO—BaO—SiO2 system and K2O—SiO2 system. The results from the cluster analysis showed that some glasses had exactly the same recipe. The source of the K2O flux and the correlation between PbO and BaO are discussed. Some archeological information is revealed.

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Summary

A rapid and sensitive method for the identification and quantification of yohimbine in Pausinystalia yohimbe is described. The method used is liquid chromatography-quadrupole ion trap mass spectrometry (LC-QIT/MS). The yohimbine standard solution was directly infused into the ion trap mass spectrometers (IT/MS) for collecting the MSn spectra. The major fragment ions of yohimbine were confirmed by MSn at m/z 355, 224, 212, and 144, in the positive-ion mode. The possible main fragment ion cleavage pathway was studied. Yohimbine provided good signals corresponding to the protonated molecular ion [M + H]+. The method is reliable and reproducible, and the detection limit is 0.1 ng mL-1. The method was validated in the concentration range 0.1–50 μg mL−1; the intra- and interday precision ranged from 1.36% to 2.73% and the accuracy was 96.5–108.2%. The mean recovery of yohimbine was 97.1–101% with a relative standard deviation (RSD) <1.93%. The LC-IT/MS method was successfully applied to determine the yohimbine in P. yohimbe.

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Abstract  

The migration of 99Tc in unsaturated Chinese loess was investigated in-situ with a tracer method. Quartz containing 3H (HTO) and 99Tc (99TcO4 -) was introduced into the bottom of an experimental pit which was then backfilled at the field test site. Then core soil samples were taken and cut vertically into 1 cm long slices. The slice samples were analyzed by liquid scintillation techniques in the laboratory. The results indicate that the migration pattern of 99Tc was quite similar to that of 3H and the vertical diffusion coefficients of 99Tc and 3H were calculated as (4.7±0.4).10-2 cm2/d and (7.8±0.4).10-2 cm2/d, respectively.

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Journal of Thermal Analysis and Calorimetry
Authors: Hanxu Li, Xiang-Zhong Shen, B. Sisk, W. Orndorff, Dong Li, Wei-Ping Pan, and J. Riley

Abstract  

Improved thermoanalytical methods have been developed that are capable of quantitative identification of various components of fly ash from a laboratory-scale fluidized bed combustion system. The thermogravimetric procedure developed can determine quantities of H2O, Ca(OH)2, CaCO3, CaSO4 and carbonaceous matter in fly ash with accuracy comparable to more time-consuming ASTM methods. This procedure is a modification of the Mikhail-Turcotte methods that can accurately analyze bed ash, with higher accuracy regarding the greater amount of carbonaceous matter in fly ash. In addition, in conjunction with FTIR and SEM/EDS analyses, the reduction mechanism of CaSO4 as CaSO4+4H2 ↔ CaS + 4H2O has been confirmed in this study. This mechanism is important in analyzing and evaluating sulfur capture in fluidized-bed combustion systems.

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Abstract  

Positron annihilation lifetime spectra and ionic conductivity have been measured for poly(etherurethane)-LiClO4 as a function of temperature. The effects of Li salt on glas transition free volume and ionic conductivity have been discussed. A correlation between fractional free volume and ionic conductivity was first experimentally confirmed by using the free volume theory.

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Thermodynamic investigation of several natural polyols (II)

Heat capacities and thermodynamic properties of sorbitol

Journal of Thermal Analysis and Calorimetry
Authors: B. Tong, Z. Tan, Q. Shi, Y. Li, and S. Wang

Abstract  

The low-temperature heat capacity C p,m of sorbitol was precisely measured in the temperature range from 80 to 390 K by means of a small sample automated adiabatic calorimeter. A solid-liquid phase transition was found at T=369.157 K from the experimental C p-T curve. The dependence of heat capacity on the temperature was fitted to the following polynomial equations with least square method. In the temperature range of 80 to 355 K, C p,m/J K−1 mol−1=170.17+157.75x+128.03x 2-146.44x 3-335.66x 4+177.71x 5+306.15x 6, x= [(T/K)−217.5]/137.5. In the temperature range of 375 to 390 K, C p,m/J K−1 mol−1=518.13+3.2819x, x=[(T/K)-382.5]/7.5. The molar enthalpy and entropy of this transition were determined to be 30.35±0.15 kJ mol−1 and 82.22±0.41 J K−1 mol−1 respectively. The thermodynamic functions [H T-H 298.15] and [S T-S 298.15], were derived from the heat capacity data in the temperature range of 80 to 390 K with an interval of 5 K. DSC and TG measurements were performed to study the thermostability of the compound. The results were in agreement with those obtained from heat capacity measurements.

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Abstract  

The title compound 3,3-dinitroazetidinium (DNAZ) 3,5-dinitrosalicylate (3,5-DNSA) was prepared and the crystal structure has been determined by a four-circle X-ray diffractometer. The thermal behavior of the title compound was studied under a non-isothermal condition by DSC and TG/DTG techniques. The kinetic parameters were obtained from analysis of the TG curves by Kissinger method, Ozawa method, the differential method and the integral method. The kinetic model function in differential form and the value of E a and A of the decomposition reaction of the title compound are f(α)=4α3/4, 130.83 kJ mol−1 and 1013.80s−1, respectively. The critical temperature of thermal explosion of the title compound is 147.55 °C. The values of ΔS , ΔH and ΔG of this reaction are −1.35 J mol−1 K−1, 122.42 and 122.97 kJ mol−1, respectively. The specific heat capacity of the title compound was determined with a continuous C p mode of mircocalorimeter. Using the relationship between C p and T and the thermal decomposition parameters, the time of the thermal decomposition from initiation to thermal explosion (adiabatic time-to-explosion) was obtained.

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