Thermal characterization of portland cement-magnesia blends

Summary Due to growing environmental concerns and the need to use less energy-intensive building products, alternatives and improvements to Portland cement (PC) are being actively researched worldwide. Use of supplementary materials is now a common practice where PC is the predominant component of inorganic building products. This study aims to investigate the potential of magnesia (MgO), derived from a naturally occurring raw material magnesite, as a supplementary material. Results from mortar samples prepared with 10 and 20% replacements of ordinary Portland cement (OPC) by MgO are presented. DTA-TG was used to study and characterise the hydration behaviour of MgO in OPC environment after 3, 7, 14, 28, 56 and 90 days of moist curing. Microstructural and compressive strength determinations providing additional information on the influence of hydrated phases are also reported.     

The kinetics of dehydrogenated adsorption of ethylene on Ni(111)

The adsorption of ethylene on Ni(111) has been studied with Thermal Desorption and Auger Electron Spectroscopy. With these methods the coexistence of an acetylenic complex and hydrogen for low coverages, and the displacement of the hydrogen by the acetylenic complex for increasing coverage can be quantitatively described.     

DTA-TG Study of the CaO-SiO2-H2O and CaO-Al2O3-SiO2-H2O Systems Under Hydrothermal Conditions

Simultaneous DTA-TG is an excellent technique for evaluating phases formed in hydrothermally treated CaO-SiO₂-H₂O and CaO-Al₂O₃-SiO₂-H₂O systems. Thermal analysis in combination with XRD and SEM, revealed that in the CaO-Al₂O₃-SiO₂-H₂O system the amount of hydrogarnet formed was the largest when gibbsite was used as the Al source, smallest for kaolin and intermediate for metakaolin. The endotherm peak temperature of the hydrogarnet dehydration endotherm was affected by the amount of hydrogarnet and the Si content of hydrogarnet. The thermal stability and structural order of 11 Å tobermorite were reduced with the incorporation of Al and, as a result, 11 Å tobermorite transformed into 9.3 Å tobermorite at lower temperatures while the transformation of the latter into beta-wollastonite required more energy. There exists a direct relationship between the 9.3 Å tobermorite and beta-wollastonite formation temperatures. Solid-state ²⁹Si and ²⁷Al MAS NMR data support these findings.     

Adsorption and desorption of hydrogen and ethene on clean Si (111) faces

Workfunction, surface conductivity, field effect mobility and desorbed species have been measured after adsorption of hydrogen and ethene on heated clean silicon (111) faces. Whereas the hydrogen studies mostly show the same drastic changes as with cleaved faces, ethene does not change the electronic parameters except the electron affinity due to the dipole moment of the adlayer. During that treatment desorption of ethene and hydrogen due to decomposition is observed. The results enable a study of hydrogenation of ethene for simultaneous adsorption.     

Use of DTA-TG in the evaluation of autoclaved cement-based systems: Part I. Cement-brick waste blends

Fired-clay products such as bricks, tiles and pavers, are made in large volumes for use in a variety of construction applications throughout the world. A significant proportion of them ends up being a waste product either during their production process or the demolition of buildings. High pressure steam curing or autoclaving has proven extremely versatile for the manufacture of cement-based building products incorporating waste materials such as fly-ash and blast furnace slag. The nature of hydration products in an autoclaved cement based system incorporating different amounts of finely ground brick waste was investigated by means of thermal analysis and XRD, and is the subject of this paper.This revised version was published online in November 2005 with corrections to the Cover Date.     

Evaluation of phases in a hydrothermally treated CaO-SiO2-H2O system

The evolution of hydration products with reaction time in a hydrothermally cured CaO-SiO₂-H₂O system, when using quartz of different fineness, was investigated by means of thermal, X-ray diffraction and wet chemical techniques. A combination of second derivative differential thermal-, first derivative thermogravimetric- and the equivalent differential thermal- and thermogravimetric curves provided more critical information about the nature of phases formed than X-ray diffraction alone. Phenomena including overlapping dehydration reactions and interactions of phases during the thermal experiment are discussed and illustrated by examples. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal characterisation of autoclaved cement made with alumina-silica rich industrialwaste

The hydration products of hydrothermally cured OPC-quartz blends incorporating clay-brick waste were characterised using simultaneous DTA-TG, XRD and SEM. The exotherm above 800°C on the DTA curve, due to the formation of β-wollastonite (β-CS) was related to the compressive strength. The area and/or height of the exotherm increased with compressive strength and was due primarily to the presence of calcium silicate hydrate phases including 1.1 nm tobermorite. Supporting evidence is provided by XRD and SEM.