Effect of microcrystalline and microfibrillated cellulose on the evolution of hydration of cement pastes by thermogravimetry

Journal of Thermal Analysis and Calorimetry - The interest in the use of cellulose fibers of increasingly smaller sizes in cementitious materials has increased in recent years. This paper brings...     

Importance of quantitative thermogravimetry on initial cement mass basis to evaluate the hydration of cement pastes and mortars

Thermogravimetric analysis (TG) curves of cement pastes and mortars are obtained by default on their respective initial sample mass basis. This fact does not allow a direct comparison of TG data of percentual mass losses due to the dehydration of a same hydrated component of differently aged pastes or mortars of same cement because the initial masses of the differently aged sample usually have different initial compositions. To solve this problem, one can transform the original thermal analysis curves from the initial sample mass basis to the initial cement mass basis, to have the same composition basis for any hydration time. This paper presents in detail how this can be done graphically and analytically and applies the method to study the evolution of cement hydration during the first 28 days of pastes and mortars prepared from the same type II cement. It also shows how to compare quantitatively the main cement hydrated phases formed during solidification and setting processes of pastes and mortars with different initial compositions as a function of hydration time.     

Aluminum Nitride Oxidation by Simultaneous TG and DTA

This work is a study, by simultaneous thermogravimetry (TG) and differential thermal analysis (DTA), of the oxidation of a water resistant aluminum nitride powder which has a special protective coating, and an uncoated AlN powder which has become partially hydrated during its use. The activation energy for oxidation is estimated by the Kissinger and isoconversional methods. In the former method, the temperatures of the oxidation peaks were obtained from DTA and DTG curves. The activation energies for oxidation of the water resistant AlN, obtained by the Kissinger method, are 357±10 kJ mol^–1, 392±12 kJ mol^–1 using respectively DTG and DTA data. For the uncoated AlN, the values are 243±7 and 257±8 kJ mol^–1, respectively. By the isoconversional method, the average values obtained for coated and uncoated samples are, respectively, 323±10 and 224±7 kJ mol^–1. Therefore, the special coating, which protects the aluminum nitride from humidity action, also provides a higher resistance to oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Obtaining Modulated Temperature DSC Curves Through a Non-conventional DSC Method

The DSC curve obtained in conventional equipment usually only shows the resultant thermal effect due to simultaneous phenomena, which may occur during isothermal or dynamic analyses. This does not allow one to identify the processes properly and may cause an erroneous interpretation of the resulting curves. Modulated DSC equipment enhances the operating conditions and the analysis capacity of conventional DSC by superimposing a sinusoidal temperature modulation on the linear temperature control. Thus reversing and non-reversing heat flow curves are obtained, which are, respectively, the heat capacity and kinetic components of the DSC curve. Therefore, events that are related to these components can be separately analyzed. A method to obtain curves similar to the MDSC reversing and non-reversing components was developed using conventional DSC equipment in a non-conventional way. It was applied to analyze samples of poly(ethylene terephthalate) (PET) taken from bottles of mineral water. The second PET crystallization step that occurs during its melting was quantified and an apparent initial crystallinity was obtained from the resulting data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preface

Journal of Thermal Analysis and Calorimetry -     

Pozzolanic properties of a residual FCC catalyst during the early stages of cement hydration

The catalyst used in fluidized catalytic cracking (FCC) units of refineries after several recovery cycles in regeneration units, reduces its activity and it is partially substituted by new catalyst in the process. As it has a high silicon and aluminum oxides content, the pozzolanic properties of a Brazilian FCC spent residual catalyst, used in different substitution degrees to cement, were evaluated by three thermal analysis techniques during the early stages of hydration of a type II Portland cement. NCDTA curves show in real time that the residual catalyst, accelerates the stages of cement hydration. TG and DSC curves of respective pastes after 24 h of hydration evidence the pozzolanic activity of the waste, respectively, by the lower water mass loss during the dehydroxylation of the residual calcium hydroxide and by the lower dehydroxylation endothermal effect. Within the analyzed period, the higher is the cement substitution degree, the higher is the pozzolanic activity of the residual catalyst.     

Determination of CO2 capture during accelerated carbonation of engineered cementitious composite pastes by thermogravimetry

Journal of Thermal Analysis and Calorimetry - The present study has evaluated the rheological behavior of an oil-based (5W50) hybrid nanofluid [magnesium oxide (65%)–multi-walled carbon...     

A study of the particle size effect on the pozzolanic activity of an equilibrium catalyst

A self-healing material for coating applications was synthesized using the Diels–Alder (DA) reaction as cross-linking reaction. The built-in reversibility allows local mobility and rearrangements in the polymeric network, which is composed of a furan functionalized epoxy-amine and a bismaleimide. The self-healing material was characterized by physical–chemical means using Fourier Transform Infrared spectroscopy, thermogravimetric analysis (TG) and rapid heat-cool differential scanning calorimetry. It has been shown that the reversibility, as a result of a change in DA/retro-DA equilibrium, occurs in a temperature window ranging from ca. 80 to 150 °C. The repeatability of the non-autonomous healing was checked by TG, showing no evaporation or degradation of the components involved in the temperature window of interest.     

Water content of a Brazilian refinery oil sludge and its influence on pyrolysis enthalpy by thermal analysis

Residual oil sludges represent an environmental problem in the oil industry and need a proper destination in order to allow sustainable industrial processes when exploring natural resources. In the present paper, the influence of the water content on the oil sludge pyrolysis process was studied by thermal analysis. A method using thermogravimetry on calcined mass basis was developed to estimate the water content of oil sludges. The water present in the sludge vaporizes during the first thermal processing stage, interfering in the initial process of the organic components pyrolysis and increasing the total oil sludge pyrolysis enthalpy. By quantitative differential thermal analysis (DTA) it can be seen that the water content of the sludge may significantly affect the thermal balance of its industrial pyrolysis process.