Showing papers on "Calcium aluminates published in 1999"

The Synthesis of Calcium or Strontium Hexaluminate added ZTA Composite Ceramics

Abstract: This paper proposes new preparation methods for alumina–tetragonal zirconia–Ca or Sr hexaluminate composites. Two powder preparation routes were explored. In the first, aluminium and calcium or strontium nitrate hydrates were added to alumina zirconia powders and in the second only calcium or strontium nitrate hydrates were used. Powders produced by the second route are to be preferred since reinforcements do not inhibit the composite sintering process.

Tensión superficial, viscosidad y densidad de algunas escorias CaO-Al 2 O 3

Abstract: The metallurgical concepts with regard to the structures and properties of calcium aluminate melts have been based upon analogies within ternary CaO-Al2O3-SiO2 systems. In this work the results of surface tension, density and viscosity of some calcium aluminate slags, in the temperature range of 1500 to 1600°C are presented and the results are discussed based upon recent structural characterisation results of crystalline aluminates. The compositional range investigated was from 45 to 53 weight-% alumina. The results indicate a reduction in density as the molar ratio CaO-Al2O3 decreases. Surface tension falls on increasing either the molar ratio CaO-Al2O3 or temperature. Conversely, viscosity increases with increasing molar ratio CaO-Al2O3 and decreasing temperature. The compositional dependence of both surface tension and viscosity data may be associated with the presence of some aluminium ions in octahedral co-ordination, and a concept of surface behaviour is proposed which involves surface activity of aluminate anions containing aluminium ions in a reduced valence state, such as Al2+.

Moulding material for the production of a fire-resistant lining, fired formed part, lining and method for the production of a formed part

Abstract: The invention relates to a moulding material containing a spinel for the production of a fire-resistant lining by means of firing at a temperature above 1350 °C. The moulding material contains at least 50 % spinel (MgO*Al2O3). Said spinel has less that 95 % wt.% Al2O3 and more than 50 wt.% MgO. The formed part has less than 15 % calcium aluminates (CaO*nAl2O3). Preferably, the formed part has less than 10 % calcium aluminates. The invention also relates to a fire-resistant lining, especially for a combustion chamber in a gas turbine. The invention further relates to a method for the production of a formed part made from said moulding material.

Microstructure of Calcium Aluminates and their Mixes after 3 Days of Hydration

Abstract: Synthetically prepared calcium aluminates such as CA, CA2, C12A7 (C = CaO, A = Al2O3) and their various combinations have been subjected to hydration in water for three days. SEM technique has been applied to study the microstructure of the hydrated phases. Attempts have also been made to investigate the role of crystal morphology of hydrated calcium aluminates towards strength development in refractory concrete. It has been observed that crystal morphology depends on rate of hydration and chemistry of calcium aluminate cement (CAC).

Shigait forming binder mixture

Abstract: The invention relates to a powder binder mixture containing between 50 and 95 % by weight of calcium aluminates or calcium aluminous cement and between 5 and 45 % by weight of manganese sulphates, in relation to the total weight of the binder mixture, wherein alkaline gluconates can be added when appropriate. The invention also relates to the use of said binder mixture in building materials.

Results of X-ray investigations on hydration products of cementitious materials using special specimen holders and preparation techniques

Abstract: Hydration products of calcium silicates and calcium aluminates often are difficult to identify by X-ray methods. In this study the hydration products of the aluminate phase especially under the influence of additional chloride ions were studied. Special X-ray measurement conditions must be applied for accurate identification including 1. In situ control of relative humidity 2. Exclusion of CO2 from air 3. Facilities for easy sample access and exchange 4. Temperature control Proper conditions allows one to distinguish between several chloride containing hydration products of the aluminate phase of cement. For this investigation, a special climate chamber and a high temperature furnace with controlling atmosphere facilities was used.