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Showing papers on "Calcium aluminates published in 1990"


Journal ArticleDOI
TL;DR: In this paper, the formation of CA2 obeyed the rate law equation 1 - (1 - x)1/3=Kt/r2, and the activation energy for the system (140 kJ·mol−1 (33.4 kcal · mol−1)) was determined by the Arrhenius equation.
Abstract: The kinetics of formation of calcium aluminates was studied by firing the reaction mixes in the temperature range 12000° to 1460°C for reaction times from 15 to 360 min. Phases formed were determined by taking X-ray diffractograms of the samples. It was observed that all stable calcium aluminates were formed and that monocalcium aluminate (CA) grew with calcium dialuminate (CA2) in a 1:2 reaction mix of CaO and Al2O3. CA reacted further with Al2O3 to form CA2. The formation of CA2 obeyed the rate law equation 1 - (1 - x)1/3=Kt/r2. The activation energy for the system (140 kJ·mol−1 (33.4 kcal · mol−1)) was determined by the Arrhenius equation.

77 citations


Journal ArticleDOI
TL;DR: In this paper, it is proposed that the anomalous setting behavior is due to none of the hydrated calcium aluminates can form readily in the range 25-30°C.

52 citations


Journal ArticleDOI
TL;DR: On a prepare des ceramiques de CaAl 12 O 19 par pressage de poudre a 1600°C pendant 2 h sous 39 MPa in atmosphere d'argon.
Abstract: On a prepare des ceramiques de CaAl 12 O 19 par pressage de poudre a 1600°C pendant 2 h sous 39 MPa en atmosphere d'argon. On etudie leur microstructure, leur densite, leur module d'elasticite, leur tenacite, leur resistance a la flexion et leur durete

23 citations


Journal ArticleDOI
01 Aug 1990-Wear
TL;DR: In this article, the wetting ability and reactivity of oxide compounds on cemented carbide inserts at elevated temperatures are studied. But no reactions are observed by scanning electron microscopy and energy-dispersive microanalysis inspection.

11 citations


Journal ArticleDOI
TL;DR: The physical chemistry of "aluminothermic" reduction of calcium oxide in vacuum is analyzed in this article, where various stages of reduction, the end products and the corresponding equilibrium partial pressures of calcium have been established from thermodynamic considerations.
Abstract: The physical chemistry of "aluminothermic" reduction of calcium oxide in vacuum is analyzed. Basic thermodynamic data required for the analysis have been generated by a variety of experiments. These include activity measurements in liquid AI-Ca alloys and determination of the Gibbs energies of formation of calcium aluminates. These data have been correlated with phase relations in the Ca-AI-0 system at 1373 K. The various stages of reduction, the end products and the corresponding equilibrium partial pressures of calcium have been established from thermodynamic considerations. In principle, the recovery of calcium can be improved by reducing the pressure in the reactor. However,, the cost of a high vacuum system and the enhanced time for reduction needed to achieve higher yields makes such a practice uneconomic. Aluminum contamination of calcium also increases at low pressures. The best compromise is to carry the reduction up to the stage where 3CaO-Al,O, is formed as the product. This corresponds to an equilibrium calcium partial pressure of 31.3 Pa at 1373 K and 91.6 Pa at 1460 K. Calcium can be extracted at this pressure using mechanical pumps in approximately 8 to 15 hr, depending on the size and the fill ratio of the retort and porosity of the charge briquettes.

11 citations



Patent
18 Jul 1990
TL;DR: In this paper, a method for separating alkali metal and heavy metal compounds from gases, in particular from combustion gases which have a temperature of 1200 to 1800 DEG C, is described.
Abstract: A method for separating alkali metal and heavy metal compounds, in particular Na, K and Pb compounds, from gases, in particular from combustion gases which have a temperature of 1200 to 1800 DEG C, is described, in which the hot combustion gases are brought into contact with absorbents which consist of SiO2, Al2O3, magnesium aluminates, calcium aluminates, magnesium aluminosilicates and/or calcium aluminosilicates.

9 citations


Book
01 Jan 1990
TL;DR: In this article, the effect of morphology on the hydration characteristics of high alumina cements was investigated, where the authors used nuclear magnetic resonance (NMR) to study the microstructural development in a paste of a calcium aluminate cement, K.L.Scrivener and H.Sawkow.
Abstract: Part 1 Clinker: effect of morphology on the hydration characteristics of high alumina cements, I.N.Chakraborty et al high alumina cements based on calcium aluminate clinker with different phase compositions and sintering degrees, J.Sawkow. Part 2 Hydration: microstructural development in a paste of a calcium aluminate cement, K.L.Scrivener and H.F.W,Taylor on the change of microstructure during the hydration of monocalcium aluminate cement, W.Gessner et al effect of temperature on setting time of calcium aluminate cements, A.Capmas the use of nuclear magnetic resonance (NMR) in the study of high alumina cement hydration, D.J.Greenslade and D.J.Williamson investigations of the composition of phases formed in low cement castables during hydration and after thermal treatment, W.Gessner et al. Part 3 Admixtures: the influence of superplasticizing admixtures on cement fondu mortars, S.M.Gill et al the effect of admixtures on the hydration of refractory calcium aluminate cements, J.H.Sharp et al properties of fresh mortars made with high alumina cement and admixtures for marine environment, N.C.Baker and P.F.G.Banfill. Part 4 Calorimetry: role of foreign cations in solution on the hydration of alumina cement, M.Murat and El.H.Sadok calorimetric studies on high alumina cement in presence of chloride, sulphate and seawater solutions, D.L.Griffiths et al. Part 5 Durability: manufacture and performance of aluminous cements - a new perspective, C.M.George long-term performance of high alumina cement concrete in sulphate-bearing environments, N.J.Crammond behaviour of high alumina cement in chloride solutions, W.Kurdowski et al acidic corrosion of high alumina cement, J.P.Bayoux et al the effect of limestone fillers on sulphate resistance of high alumina cement composites, W.G.Piasta. Part 6 Blended systems: hydration of calcium aluminates in presence of granulated balst furnace slag, A.J.Majumdar et al the effect of curing conditions on the hydration and strength development in fondu slag, J.P.Bayoux et al the microstructure of blast furnace slag/high alumina cement pastes, I.G.Richardson and G.W.Groves effect of microsilica on conversion of high alumina cement, S.Bentsen et al study of hydration properties of aluminous cement and calcium phosphate mixes, J.P.Bayoux et al Ettringite-based cements, S..Brooks and J.H.Sharp. Part 7 Miscellaneous: effect of autoclaving on the strength of hardened calcium aluminate cements, R.Baggott and A.Sarandily effect of temperature rise on properties of high alumina cement grout, S.A.Jefferis and R.J.Mangabhai activation of hydraulic properties of the compound CaO.2Al(2)O(3), T.W.Song et al.

3 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of sintering on the reactivity of solids at high temperature was studied with calcium silicate-aluminate reacting with SO2 between 665 and 800 C.
Abstract: The effect of sintering on the reactivity of solids at high temperature was studied. The nature of the interaction was studied with calcium silicate-aluminate reacting with SO2 between 665 and 800 C. The kinetics of the sintering and sulfation processes were measured independently in terms of the common variables, temperature and specific surface area. Surface reduction parameters were evaluated by the German-Munir sinter model, modified to account for a strong catalytic effect of H2O vapor. Sulfation parameters were determined from a series of conversion vs. time measurements at various temperatures using calcined solids of known surface area. These show product layer diffusion through CaSO4 to be the probable controlling process above 670 C and diffusion through a mixture of CaSO3 and CaSO4 controlling below that temperature. Like sintering, sulfation was enhanced by the presence of H2O in the feed gas. With 7% H2O vapor, the enhancement factor for sulfation was 1.5 at 665 C and estimated to be 5.0 at higher temperatures where only CaSO4 is formed. A combined sinter/sulfation model, based on the parameters evaluated for the independent processes, is compared to sulfation rates measured for the uncalcined solid when sintering is occurring simultaneously.

3 citations


Patent
25 Jan 1990
TL;DR: In this article, a method and composition for accelerating the setting of Portland cement, shortening the stage of migration of the calcium ions into the liquid phase and complexing the reactive lime of the Portland cement is described.
Abstract: Method and composition for accelerating the setting of Portland cement, shortening the stage of migration of the calcium ions into the liquid phase and complexing the reactive lime of the Portland cement. … The invention is characterised in that the said composition is essentially made up of the following constituents: a material based on calcium aluminates and alumina trihydrate.

2 citations



Patent
04 Jul 1990
TL;DR: In this article, a concrete of super dry consistency consisting essentially of 100 pts.wt.cement, 0.1 to 4 pts.c cement, anhydrous gypsum, the water-reducing agent and the aggregate is presented.
Abstract: PURPOSE:To obtain the concrete of super dry consistency which is suitable for application by pressurization and rolling compaction, etc., by disposing calcium aluminate, anhydrous gypsum, water-reducing agent, and aggregate with cement and limiting a unit cement quantity, unit water quantity and VC value. CONSTITUTION:This concrete of super dry consistency consists essentially of 100 pts.wt. cement, 0.1 to 4 pts.wt. calcium aluminate, 1 to 8 pts.wt. anhydrous gypsum, the water-reducing agent and the aggregate and has 50 to 400kg/m unit cement quantity, 60 to 110kg/m unit water quantity and 5 to 100 second VC value. The calcium aluminate to be used is expressed by C3A, C4AF, C12A7, CA, C4A3S, C11A7CaF2, and C3A3CaF2, etc., when CaO is designated as C, Al2O3 as A, F2O3 as F, and SO3 as S, among which the calcium aluminates essentially consisting of the C12A7 and CA are more preferable. The amt. of the calcium aluminate to be used is 0.1 to 4 pts.wt. by 100 pts.wt. cement.