Showing papers on "Calcium aluminates published in 1998"
TL;DR: In this paper, the effect of the preparation method on the catalytic properties and performance of 5.5% Ni on calcium aluminate (molar CaO/Al2O3=1/2) in the reaction of CO2 reforming of CH4 was investigated.
142 citations
TL;DR: In this article, in-situ spinel formation occurs between 1200 and 1400 °C with a net-like morphology interlinked with CaO-MgO-Al2O3-SiO2 phases.
Abstract: Calcium aluminate bonded alumina-spinel castable refractories have been fabricated with in-situ spinel formation Spinel formation occurs between 1200 and 1400 °C with a net-like morphology interlinked with CaO-MgO-Al2O3-SiO2 phases Spinel generated at 1400 °C is nearly stoichiometric but at higher temperatures it progessively enriches in Al2O3 The calcium aluminate phases in the cement bond react to form platey CA6 crystals between 1200 and 1400 °C which coexist with the spinel and penetrate and bond to tabular alumina grains The potential effect of these morphologies on properties is discussed
109 citations
TL;DR: In this paper, preliminary experiments were conducted aimed at developing refractory ceramics of low thermal expansion based on calcium dialuminate CaAl 4 O 7, which was synthesized by a specific cycle of calcination, regrinding and firing (finally at 1450°C), the emerging phases having been identified by X-ray diffraction.
54 citations
Journal Article•
41 citations
TL;DR: In this article, the phase evolution during reaction sintering of stoichiometric mixtures of CaCO 3 /(6 − x )Al 2 O 3 / x Fe 2 O3 was investigated, and the microstructural evolution as a function of iron content and firing temperature was also studied.
Abstract: The phase evolution during reaction sintering of stoichiometric mixtures of CaCO 3 /(6 − x )Al 2 O 3 / x Fe 2 O 3 was investigated. The microstructural evolution as a function of iron content and firing temperature was also studied. It was found that the appearance during sintering of several intermediate phases (CA, CA, and CAF 2 ) as well as the phase evolution during the CaO·6(Al,Fe) 2 O 3 solid solution formation and the final microstructures after sintering, can be explained by means of the CaO-Al 2 O 3 Fe 2 O 3 phase equilibrium diagram.
24 citations
TL;DR: In this article, a novel route to simple processing of an in-situ layered and graded alumina/calcium-hexaluminate (CA 6 ) composite is described.
Abstract: A novel route to simple processing of an in-situ layered and graded alumina/calcium-hexaluminate (CA 6 ) composite is described. The processing involves partial infiltration of a porous alumina preform with hydrolysed calcium acetate to yield a homogeneous layer of alumina and a heterogeneous graded layer of CA 6 /alumina. The homogeneous layer is designed to provide strength, hardness, and wear resistance, while the graded layer is tailored to impart toughness and damage tolerance. The effect of CA 6 on the physical and graded characteristics is discussed.
24 citations
TL;DR: In this paper, a new building material composed of clay and dolomite at the variable mass ratio C D = 1/9−9/1 is developed, which is composed of both the old structure of carbonates and new formations such as calcium silicates, calcium aluminates and MgO in fine crystalline or amorphous state.
Abstract: New building material composed of clay and dolomite at the variable mass ratio C D = 1/9−9/1 is developed. At the firing temperature of 720 °C the interaction between the components takes place resulting in the formation of structure which ensures high mechanical strength of the material obtained. The structure is composed of both the ‘old’ structure of carbonates and new formations such as calcium silicates, calcium aluminates and MgO in fine crystalline or amorphous state permeating through the ‘old’ structure. The mechanical strength of the fired material subjected to hydraulic hardening with following drying increases per 200–300%.
8 citations
TL;DR: In this article, heat-assisted grinding of a mixture of Al(OH) 3 and Ca(OH 2 ) was conducted at different temperatures ranging from room temperature (about 293 K) tp 773 K using a tumbling ball mill.
7 citations
TL;DR: In this article, a planetary ball mill was used to synthesize tricalcium aluminum hydrate (3CaO·Al2O3·6H2O：C3AH6) from mixtures composed of calcium hydroxide (Ca(OH)2) and pseudo-boehmite (γ-AlO(OH)) powders.
Abstract: Tricalcium aluminum hydrate (3CaO·Al2O3·6H2O：C3AH6) is synthesized mechanochemically from mixtures composed of calcium hydroxide (Ca(OH)2) and pseudo-boehmite (γ-AlO(OH)) powders by room temperature grinding using a planetary ball mill. Use of the boehmite sample with inferior crystallinity is more favorable for the mechanochemical synthesis rather than that with well crystalline one. The time required to form C3AH6 from the Ca(OH)2-γ-AlO(OH) mixture is much longer than that from the Ca(OH)2-gibbsite (Al(OH)3) one. Adsorbed water from air during grinding plays a significant role in the formation of C3AH6 from the former mixture. After water addition to Ca(OH)2-γ-AlO(OH) mixtures ground for various times, excess hydrated calcium aluminates such as C2AH8, C3AH8-12 and C2A0.5H6.5 are formed in the starting and the short time ground mixtures, while a few amount of these compounds is formed in these hydrated mixtures after prolonged grinding. Formation of these excess hydrated compounds, which belong to layered structural materials, is enhanced in the presence of free Ca, Al compounds and water.
5 citations
Patent•
29 Jul 1998
TL;DR: In this paper, an accelerator for high mobility shotcrete is proposed, which is capable of being improved in the lowering rate in the compressive strength of sprayed concrete for a long period of time.
Abstract: PROBLEM TO BE SOLVED: To provide an accelerator for high mobility shotcrete capable of being improved in the lowering rate in the compressive strength of sprayed concrete for a long period of time. SOLUTION: This accelerator for high mobility shotcrete comprises 30-90 wt.% calcium aluminates and 10-70 wt.% gypsum and, optionally, 2-30 wt.% alkali aluminate. The slump flow of the accelerator for high mobility shotcrete is 400-750 mm. COPYRIGHT: (C)2000,JPO
3 citations
TL;DR: In this paper, the authors present the development of the multiple quantum magic angle spinning (MQ-MAS) method that provides high resolution isotropic spectra for half integer quadrupolar nuclei such as 27Al or 17O for describing the local structure of crystalline or amorphous materials.
Abstract: The recent development of the multiple quantum magic angle spinning (MQ-MAS) method that provides high resolution isotropic spectra for half integer quadrupolar nuclei such as 27Al or 17O gives increased resolution in describing the local structure of crystalline or amorphous materials. This is especially the case for 27Al in aluminium bearing phases of cement interest. This contribution rapidly describes the different high resolution techniques, their acquisition and processing and shows examples of applications to aluminates, calcium aluminates and strontium aluminates.
TL;DR: In this paper, a new building material composed of clay and dolomite at the variable mass ratio C D = 1/9−9/1 is developed, which is composed of both the old structure of carbonates and new formations such as calcium silicates, calcium aluminates and MgO in fine crystalline or amorphous state.
Abstract: New building material composed of clay and dolomite at the variable mass ratio C D = 1/9−9/1 is developed. At the firing temperature of 720 °C the interaction between the components takes place resulting in the formation of structure which ensures high mechanical strength of the material obtained. The structure is composed of both the ‘old’ structure of carbonates and new formations such as calcium silicates, calcium aluminates and MgO in fine crystalline or amorphous state permeating through the ‘old’ structure. The mechanical strength of the fired material subjected to hydraulic hardening with following drying increases per 200–300%.