Hydration products in two aged cement pastes

The hydration products in two aged cement pastes (DTA/DTG/TG) were compared with those in fresh ones (static heating, SH) and were also studied by mass spectrometry (MS), IR and thermo XRD-analysis. The products considered here were: the sorbed water, the CSH gel including hydrates, portlandite, calcite, aragonite and vaterite. Except carbonates their content was higher in the stronger paste C-43, than in C-33, but lowered with ageing (only the CSH gel water remained approximately unchanged). The sorbed water content became with time lower and similar in both pastes (it evaporated up to 155-185°C in TG); the escape of the rest moved to higher temperatures (500-700°C). The three DTG peaks at 200-400°C indicated jennite-like phase in the CSH gel; the mass loss (155-460°C) was higher on ageing due to development of organic matter, especially in C-43 (DTA, TG, IR). Portlandite content changed little and carbonate content increased considerably. They decomposed in air at 470 and 720-740°C, in argon at 450 and 680-710°C and in vacuum at 400 and 630°C, respectively (DTG peak, XRD). Between 500 and 700°C the simultaneous evolution of H₂O and CO₂was observed by MS, which is attributed to dehydroxylation of jennite-like phase and/or to decomposition of some carbonate hydrate and/or hydrocarbonate (three peaks on CO₂evolution curve, MS). The d(001) peak of portlandite exceeded the nominal value and will be analyzed separately.     

Phase transformation on heating of an aged cement paste

The standard cement paste (C-43-St) was studied previously by static heating, SH, immediately after 1 month hydration at w/c = 0.4 [J. Therm. Anal. Calorim. 69 (2002) 187]. This paste after 5-year ageing (unprotected from contact with air) was subject to thermal analysis in air and in argon (DTA, DTG and TG), to XRD at various temperatures, T, in a high temperature chamber, to mass spectroscopy (MS) and to IR spectroscopy. The aim of this study was to compare the results of SH (fresh paste) and of TG (the aged one), to verify the assumptions made on SH interpretation and to check the change in hydration products with ageing as measured by phase transformation on heating (ΔM versus the final mass). The sorbed water (EV), escaping at 110 °C from the fresh paste, was bound on ageing with a higher energy and escaped at higher temperatures. The joint water content of hydrates and of C-S-H gel increased on ageing by 1–2% in the dense paste C-43-St and did not change in the less compact one C-43-I. C-S-H gel transformed on heating above 600 °C into C₂S and C₃S. Portlandite content did not change on ageing. In the air atmosphere it became partly carbonated, which was accompanied by an increase in mass between 500 and 600 °C. Carbon dioxide and/or carbonate ions to form carbonates, were sorbed during ageing and were present in the aged paste in some form undetectable by XRD (amorphous or crypto-crystalline). Sensitivity to carbonation ΔM(700–800 °C) increased highly with ageing.     

Thermal and FTIR spectral studies of various proportions of zinc magnesium ammonium sulfate

Mixed crystals of various proportions of zinc magnesium ammonium sulfate were grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterized through thermal (TG–DTA) and FTIR spectral analyses. A fitting decomposition pattern for the compound was formulated on the TG curve which shows two stage mass losses between 133 and 478.75 °C. DTA curve shows exothermic peaks in this temperature range supporting the formulated decomposition pattern. The FTIR spectra show the vibration frequencies due to the formation of zinc magnesium ammonium sulfate mixed crystals. Detailed structural analysis of the compound is under progress.     

Hydration,mechanical properties and durability of high-strength concrete under different curing conditions

The properties of high-strength concrete under standard curing condition (20 °C, 95% RH), high-temperature curing condition (50 °C) and temperature match curing condition were comparatively investigated. The cumulative hydration heat of composite binder containing fly ash and silica fume is lower than that of composite binder containing the same amount of slag. Addition of fly ash and silica fume clearly reduces the adiabatic temperature rise of concrete, but adding slag leads to higher adiabatic temperature rise than Portland cement concrete. High-temperature curing condition and temperature match curing condition lead to the sustainable increase in compressive strength of concrete containing mineral admixture, but they hinder the later-age strength development of Portland cement concrete. For cement–slag paste and cement–fly ash–silica fume paste, the non-evaporable water contents increase significantly and the pore structures are much finer under high-temperature curing condition and temperature match curing condition, which negatively affect the pore structure of Portland cement paste. The differences in properties of concrete among three curing conditions become smaller with time. The properties obtained under standard curing condition can approximately reflect the long-term properties of high-strength concrete in the real structure. The concrete prepared with cement–fly ash–silica fume composite binder has the highest compressive strength, finest pore structure and best resistance to chloride permeability under any curing condition. This composite binder is very suitable to prepare the high-strength concrete with large volume.     

Thermal Studies of Di- and Triphenyltin(IV) Complexes of Salicylhydroxamic Acid

Thermal decomposition of di- and triphenyltin(IV) complexes derived from potassium salicylhydroxamate (KSHA) of compositions Ph2SnCl(SHA), Ph2Sn(SHA)2 and Ph3Sn(SHA) has been studied by TG, DTG and DTA. Based upon thermal mass losses the transitory formation of diphenyltin oxide, Ph2SnO as the possible intermediate from the decomposition pattern of all the three complexes has been proposed. Both DTG and DTA give well-defined peaks in the appropriate regions. These studies reveal the formation of SnO2 as the ultimate product. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth and characterization of 0.1 and 0.25 zinc magnesium ammonium sulphate

Mixed crystals of 0.1 and 0.25 zinc magnesium ammonium sulphate were grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterized by thermal (TG–DTA), FTIR and XRD analyses. A fitting decomposition pattern for the compound was formulated on the TG curve which shows two stage mass losses between 133 and 478.75 °C. In this temperature range, DTA curve shows exothermic peaks supporting the formulated decomposition pattern. The FTIR spectra show the vibration frequencies due to the formation of zinc magnesium ammonium sulphate mixed crystals. Detailed structural analysis of the compound is under progress.     

A Study of the Hydration of Lime-Pozzolan Binders

DTA/TG and TG/DTG thermal studies and XRD investigations were carried out on pastes of lime-pozzolan binders to examine the relative hydration process. The binders were prepared with two natural pozzolans and hydrated lime, mixed together in different proportions. The main hydrated phases formed in the pastes are calcium silicate hydrate (CSH) and mono-carboaluminate. The growth of CSH was greater for the paste of the pozzolan richer in reactive constituents. For pastes with a higher lime/pozzolan ratio, a slowing of the formation of CSH was observed, while the formation of monocarboaluminate was more intense. The calcium hydroxide contents of the pastes obtained by thermogravimetric analysis made it possible to determine the pozzolanic activities of the two pozzolans under examination. The mortars for the various lime-pozzolan binders displayed characteristic hardening. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth and thermal behavior of lead Iodate crystals grown in silica gel

The Pb(IO₃)₂ crystals have been grown in sodium meta silicate gel using the single diffusion method at room temperature. The grown crystals were characterized by thermo analytical techniques (TG, DTA, and DTG), X-ray powder diffraction (XRD), and FTIR spectroscopy. The crystal system is confirmed to be orthorhombic having lattice parameters a = 6.09 Å, b = 16.68 Å, and c = 5.58 Å by powder X-ray diffraction analysis. FTIR study reveals that lead iodate crystal is anhydrous. TG, DTA, and DTG analysis shows a remarkable thermal stability.     

Studies on the dehydration and decomposition of calcium and dicalcium magnesium aconttate hydrates

The thermal decomposition of calcium and dicalcium magnesium aconitate hydrates were studied by TG/DTG, DTA, EGA, SEM and other physico-chemical techniques. The decomposition proceeds in four stages: dehydration; oxidation of the carboxylic acid portion of the salt; complete fragmentation of the hydrocarbon portion; and finally, decarboxylation of the metal carbonate to the oxide. The crystal morphologies of the hydrate and anhydrous salts of each compound are very similar. Tricalcium aconitate consists of well-developed twinned crystals and stellate clusters intergrown with flat platy crystals. On the other hand, dicalcium magnesium aconitate crystals are monoclinic with well-developed pinacoidal faces. The activation energy,E _d (43±2 kJ mol^?1 water), calculated from Borchardt and Daniels' method, for the dehydration process of calcium aconitate trihydrate is of the same order of magnitude as some simple metal salt hydrates. The rate constant, k_d increased from 0.04/min at 238°C to greater than 0.86/min at 295°C. It is concluded that the dehydration process is due to cation bound water.     

Application of chemometrically processed chemical and thermoanalytical data for quality control of soybean oils

The quality assessment of commercial soybean oils was evaluated on the basis of chemical and thermal analyses. The most substantial chemical parameters, viz. the density, refractive index and saponification, iodine and acid numbers were estimated. The thermal parameters were determined on the grounds of the TG and DTG curves. There are temperatures for the onset, end and successive mass losses. To find the relation between the chemical and thermal parameters, regression and principal component analyses were applied. The results of principal component analysis indicate that the TG and DTG techniques are at least in equal degree useful in defining the quality of soybean oils, as compared with the chemical analyses.     

Effect of cerium, holmium and samarium ions on the thermal and structural properties of the HZSM-12 zeolite

The study of the incorporation of rare earth elements as additives in Y zeolites is a very interesting field of research, mainly by its potential application as additives in catalytic cracking process. In this work was studied the thermal and structural properties of cerium, holmium and samarium supported on HZSM-12 zeolite. The obtained materials were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), nitrogen adsorption, thermogravimetry (TG/DTG), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). TG/DSC/DTA analyses showed that the dehydration temperatures of RE/HZSM-12 zeolites (RE=Ce, Ho, Sm) increase in relation to pure HZSM-12. The acid properties were investigated by pyridine thermo desorption via TG. The results showed two events of mass loss attributed to elimination of pyridine adsorbed on the weak+medium acid sites and on the strong acid sites.     

Thermal characterization of hydrotalcite used in the transesterification of soybean oil

Hydrotalcite was synthesised by co-precipitation method, calcined and characterized by XRD, BET, IR and TG/DTA/DTG analyses and tested as solid base catalyst in the transesterification of soybean oil with methanol, achieving a methyl ester content of 99.5%. The thermal decomposition of hydrotalcite calcined occurred in four mass loss steps at 28, 105, 203 and 400 °C. The hydrotalcite was recovered and through a simple evaluation by TG/DTA/DTG techniques it was found that at 500 °C is the temperature, where the organic matter should be eliminated from the catalyst. This study shows the importance of thermal analysis in the evaluation of the recovery temperature of hydrotalcite.     

Thermal, FTIR and Raman spectral analysis of Cu(II)-doped lead iodate crystals

The 0.04 M copper-doped lead iodate crystals grown in silica gel were characterized by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and thermo analytical techniques (TG, DTA, DTG and DSC). Raman and FTIR spectrum clearly indicate that the functional groups of undoped lead iodate were not altered by the addition of the dopant. Thermal analysis suggests that the thermal stability of lead iodate crystals decreases due to copper doping.     

Quantitative analysis of phase transition of heated Portland cement paste

This paper studies Portland cement paste heated up to different temperatures ranging from 105 to 1,000 °C by X-ray diffraction. The heated cement paste samples are kept isothermal in furnace for 6 h and cooled down to 100 °C. Then the samples are picked out and grinded into fine powders. 10 % Corundum is blended with cement paste powders as an internal standard. Quantitative phase analysis of cement paste samples is performed by Rietveld method. With the addition of a crystalline standard, the mass fractions of all crystalline phases as well as amorphous calcium silicate hydrate (C–S–H) are determined. The Rietveld analysis results are compared with independent measurements of the same material by thermal analysis (TG/DSC). The phase transition of Portland cement paste is discussed. An empirical relationship between the dehydration degree of C–S–H and the crystallization degree of C–S–H is derived.     

Growth and thermal behavior of mixed crystals of calcium cadmium tartrate in silica gels

In this study, calcium cadmium tartrate single crystals were grown in silica gel at ambient temperature. Effects of various parameters like gel pH, gel aging, gel density, and concentration of reactants on the growth of these crystals were studied. Crystals having different morphologies and habits were obtained. Transparent, diamond-like pyramidal-shaped crystals of calcium cadmium tartrate were obtained. Some of the crystals obtained were faint yellowish, with some milky white crystals being attched to them due to fast growth rate; faces are well developed and polished. The grown crystals were characterized by thermoanalytic techniques (TG, DTA, and DTG), and powder X-ray diffraction (XRD). The crystal system is confirmed to be orthorhombic having lattice parameters a = 7.9411 Å, b = 7.0396 Å, and c = 6.7271 Å as determined by powder XRD analysis. TG, DTA, and DTG analyses show a remarkable thermal stability. The results of these observations are described and discussed.     

Non-isothermal decomposition of Indian limestone of marine origin

Single crystals of pure and neodymium doped calcium hydrogen phosphate were grown in sodium meta silicate gels, by the single diffusion gel method. Platelet and needle shaped crystals were obtained. The grown crystals were characterized by different techniques. The thermal behaviour of the crystals was studied using the thermo analytical techniques, which included TG, DTA, DTG and DSC. These studies reveal that the decomposition of the material occurs in one or more stages. The enthalpy value is also calculated.     

Thermal analysis of a model bio-membrane

Thermal properties of some shedded snake skins in comparison with human skins are represented by thermogravimetry (TG), derivative thermogravimetry (DTG), and differential thermal analysis (DTA) to predict process condition as dermal pathway for administration of drugs or it be used as model membranes for permeation studies. Thermal behavior by TG/DTG and DTA curves for four kinds of shedded snake skins as Boelens Python (BP), Eastern Indigo Snake (EIS), Emerald Tree Boa (ETB), and Cascavel (CBR) were similar in relation to their decomposition temperatures at 100 °C and 230–400 °C of its constituents, however, their properties were different in the residue content (inorganic or carbonaceous substances). Similar thermal properties were also exhibited by human skins’ samples, however, they presented different residue and constituents’ content.     

Thermal degradation studies on some metal hydrazinic complexes

The paper deals with the characterization of three hydrazinic complexes with Ni, Cu and Cr respectively, by means of non-isothermal thermal methods, TG, DTG and DTA, under nitrogen atmosphere in order to investigate the structure-thermostability-thermal degradation mechanism correlation. The thermal analysis made evident the degradation mechanisms characteristic of every sample in accordance with the chemical structure. The quantitative analysis by TG-DTG afforded the estimation of the metal amount in the complex on the basis of the resulting metallic oxide nature as well as of some aspects of the thermal degradation mechanism supported by mass spectral measurements. The melting points given by DTA and confirmed by the Boetius method and the initial temperatures of thermal degradation from TG-DTG-DTA afforded to ascertain the temperature range proper for using and storing the complexes under study which show potential practical applications as drugs.     

Thermal behavior of five free anthraquinones from rhubarb

The thermal behavior of five free anthraquinones (chrysophanol, emodin, physcion, aloe-emodin, and rhein) from rhubarb had been investigated using TG, DTG and DTA technique. The results show that all the free anthraquinones have the similar TG and DTG curve shapes, however, due to the substituted groups attached on the skeleton of 1,8-dihydroxy anthraquinone are different, every anthraquinone has different mass loss features. Moreover, all the DTA curves of these free anthraquinones have two obviously characteristic peaks, but with special curvilinear types, peak location and peak values. Therefore, thermal analysis (TA) characteristics of anthraquinones above mentioned could be established, and it is possible to easily distinguish these anthraquinones by using TA technique.     

Thermal Studies on Ammonium Uranates

Ammonium uranates are important intermediates in the preparation of nuclear fuel UO₂. These can generally be prepared through two different routes: heterogeneous (conventional) and homogeneous methods of precipitation. In the conventional method, ammonium hydroxide, gaseous ammonia and ammonium carbonate are the precipitating agents. In the homogeneous method, urea hydrolysis is used to generate in situ ammonia needed for precipitation. For the present studies, ammonium hydroxide is used for the conventional and urea for the homogeneous methods of precipitation. The uranates, thusprepared, are characterized by thermogravimetry (TG), differential thermogravimetry (DTG)and differential thermal analysis (DTA). Thermally the numbers of decomposition steps are identical for both uranates but the temperatures of the decomposition and mass losses vary. The intermediate and final oxides are identified by X-ray diffractometry (XRD). This revised version was published online in July 2006 with corrections to the Cover Date.