Dun Chen

A method of assessing solid state reactivity illustrated by thermal decomposition experiments on sodium bicarbonate

Abstract The thermal decomposition of sodium bicarbonate (NaHCO3) was studied under different atmospheres (dry nitrogen, air, and carbon dioxide), with various heating rates in order to characterize the substance. Various non-isothermal methods of kinetic analysis were employed in estimating the Arrhenius kinetic parameters, the activation energy and the frequency factor. All show that the most probable reaction mechanism under dry nitrogen and air is the first-order deceleratory mechanism, whereas under carbon dioxide it is the Avrami-Erofeev equation, with n = 1.5. Thermogravimetric and derivative thermogravimetric analysis (TGA and DTG) were employed for comparing the solid state reactivity of different samples of sodium bicarbonate. The reaction parameters, the extent of the reaction (α) and the reaction temperature were used in comparing the reactivities of various samples of sodium bicarbonate differing in particle size and surface area produced by grinding the substance in a ball mill. A method was utilized, termed here the αsample—αreference (αs—αr) method, by which the solid state reactivity of these samples could be compared with that of a reference. The terms αs, αr refer to the extent of reaction (here the extent of decomposition) at the same temperature for the sample (s) and reference (r).

A generalized form of the Kissinger equation

Abstract An equation is deduced in this paper and an attempt is made to obtain the peak maxima information theoretically from the differential thermogravimetry curves. The calculations are critically assessed. The Kissinger method, which also deals with the peak maxima, is also discussed. A comparison of the equation due to Kissinger and that of the equation deduced in this paper shows that the Kissinger equation is a special case of this equation. The approximation made in the deduction of the Kissinger equation can be restated as “The extent of reaction at the peak maxima under different heating rates is the same”.

The possibility of manufacturing a single-pan differential thermal analyzer unit

Abstract The use of a single-pan differential thermal analyzer (DTA) unit is proposed in this paper based on the experimental results and justified from the theory for DTA units. Such a design would simplify the construction and operation of DTA units. A basic requirement for this kind of design is the accurate measurement of sample temperature. It would also make the design of simultaneous TGA (thermogravimetry analyzer)-DTA units more robust and less likely to mechanical breakage.

The application of non-isothermal methods of kinetic analysis to the decomposition of calcium hydroxide

Abstract In this paper, the kinetic analysis of the thermogravimetric curves for the decomposition process of calcium hydroxide (under dry nitrogen atmosphere) is performed. Various forms of non-isothermal methods of analysis for determining the kinetic parameters are used. The calcium hydroxide samples were a commercial sample and samples prepared by reacting calcium nitrate with sodium hydroxide solutions at concentrations of 1 and 0.1 M. All the methods show that in the heating rate ranges 5–40°Cmin −1 , the most probable reaction mechanism for commercial calcium hydroxide is the Avrami-Erofeev equation (A) with n = 1.5 (i.e. A1.5), for calcium hydroxide prepared from 1 M solutions is A2 and for calcium hydroxide prepared from 0.1 M solutions is A1.5. The data also show that the distribution of particles and the change of the particle size are factors which affect the reaction mechanism.

Identification of solid solutions of coprecipitated Ni-Co oxalates using XRD, TG and SEM techniques

Abstract Homogeneous solid-solution oxalates of Ni 2+ and Co 2+ ions were synthesized by coprecipitation from nitrate solutions using a double-inlet technique. The identification of the solid solutions used X-ray powder diffraction (XRD), thermogravimetry (TG) and scanning electron microscopy (SEM) techniques. The experimental results showed that the coprecipitated powders have characteristics that are different from those of the mechanical mixtures with the same stoichiometry.

Computer Programs for Kinetic Analysis of Non-Isothermal Thermogravimetric Data

Abstract In this paper, computer programs to evaluate kinetic analysis from non-isothermal thermogravimetric data are discussed. The flowcharts for all the programs are shown. These include those based on single-heating-rate and multi-heating-rate procedures. The single-heating-rate methods include the differential and integral calculations while the multi-heating-rate methods include those of Friedman and Ozawa. It is proposed that the multi-heating-rate programs should be used as a reference to distinguish the mechanisms and the single-heating-rate programs should be used to obtain the reaction activation energy, the frequency factor values and the linear regression parameters.

Kinetic analysis of the hydration of 3CaO · 3Al2O3 · CaSO4 and the effect of adding NaNO3

Abstract 3CaO · 3Al 2 O 3 · CaSO 4 is the main component of the sulpho-aluminate early-strength cements. Its hydration properties decide the strength and long-term stability of the hydrated cement paste. In this article, such hydration properties and the effect of hydration temperature, as well as the addition of NaNO 3 , on the hydration process are studied. Using the Calvet conducting C80 microcalorimeter, the rate of production of hydration products was determined quantitatively and the total hydration heats calculated. The kinetic parameters for the hydration process at different hydration temperatures and different hydration periods are also calculated. The change of kinetic parameters between those of pure 3CaO · 3Al 2 O 3 · CaSO 4 and those with added NaNO 3 are discussed, and are used to explain the anti-freezing properties of NaNO 3 on the hydration of cements.

Sinusoidal temperature treatments in thermal analysis

The use of sinusoidal temperature treatments in various thermal analysis techniques is briefly outlined. A generalized approach is described to cover all the techniques in which this approach is utilized. Using a computer simulation, the effect of a sinusoidal temperature variation on the thermogravimetric (TG) trace is investigated. This indicates under what conditions a modulated differential scanning calorimeter (DSC) temperature program can be operated when using a simultaneous DSC-TG unit. Other aspects of the computer simulation are noted.

DSC: the importance of baseline calibration

The issue of the baseline in differential scanning calorimetry (DSC) is outlined. Experimental results demonstrated that incorrectly applied calibration, which is caused by performing experiments under different experimental conditions, can easily result in inaccurate experimental data. A critical factor is the introduction of thermal masses into the system. Therefore, it is imperative that a correct calibration be used for experimental measurements.

The influence of ferric oxide on the properties of 3CaO · 3Al2O3 · CaSO4

Abstract It was determined that at 22.31 wt.%, Fe 2 O 3 reached a maximum solid solution in 3CaO · 3Al 2 O 3 · CaSO 4 by replacing Al 2 O 3 . The physical properties of the compound with and without Fe 2 O 3 were measured and these are combined with the analysis of the hydration process and products by using XRD, DTA and calorimeter equipment to determine the heat of hydration etc. The results show that there was no tricalcium aluminate hexahydrate (3CaO · 3Al 2 O 3 · 6H 2 O) formed in any of the samples. The addition of Fe 2 O 3 into the (3CaO · 3Al 2 O 3 · CaSO 4 caused an initial decrease in the early compressive strength but not much in the final strength. Further, the sample with Fe 2 O 3 has a lower hydration heat.