Calcium aluminates

About: Calcium aluminates is a research topic. Over the lifetime, 490 publications have been published within this topic receiving 9200 citations.

Improved quantum-splitting oxide phosphor, its producing method, and rule for designing the same

Abstract: PROBLEM TO BE SOLVED: To provide an oxide phosphor exhibiting higher quantum efficiency when irradiated by a vacuum ultraviolet ray, its producing method, its designing rule and a light source having higher energy efficiency using the phosphor SOLUTION: Strontium and strontium calcium aluminates and lanthanum and lanthanum magnesium borates activated with Pr and Mn exhibit characteristics of quantum-splitting phosphors Improved quantum efficiency may be obtained by further doping with Gd Refined rules for designing quantum-splitting phosphors include the requirement of incorporation of Gd and Mn in the host lattice for facilitation of energy migration

Development of a model predicting inclusions precipitation in nozzles based on chemical composition and process parameters such as casting rate, liquid temperature, nozzle design and slag composition

Abstract: Objectives The research proposal aimed to achieve the following objectives: 1) increasing casting reliability by optimising calcium treatment in low sulphur and high sulphur steel grades through predicting casting behaviour in calcium treated steels by means of a mathematical model 2) investigating the influence of nozzle design and casting parameters on nozzle clogging and steel cleanliness by means of mathematical and physical models Background The use of calcium additions for improving castability in aluminium killed steels has been studied since the 1970s. Nowadays the calcium treatment is commonly used to control the shape and composition of both oxide and sulphide inclusions in Al killed steels. The calcium reacts with solid Al 2 O 3 inclusions, generating calcium aluminates of lower melting point, thus avoiding nozzle clogging and improving castability. Some of the calcium may also react with dissolved sulphur, resulting in formation of Ca or Ca-Mn sulphide inclusions. Nozzle blockage can also be produced when solid CaS inclusions are present in the steel. CaS formation is influenced by the steel composition (sulphur, calcium, aluminium and total oxygen contents) and temperature, therefore calcium additions must be performed in the right amount to avoid CaS formation. During the process of manufacturing calcium treated steels, high calcium contents may cause refractory erosion, particularly towards aluminous refractories. Therefore calcium treatment, if correctly performed, improves steel castability but worsen steel cleanliness as well: liquid inclusions flow together with steel and can be revealed in final product, unless appropriate devices are settled to decrease the inclusions content. Thus, once that the main castability problems were solved by calcium treatment, major efforts were devoted to improve steel cleanliness, using appropriate covering slags in ladle, tundish and mould to capture inclusions, prevent re-oxidation during casting by protecting metal stream (ladle shroud, submerged nozzle, argon injection) and creating in tundish and mould the favourable conditions for inclusions floatation and removal (dams and argon bubbling in tundish, EMS and EMSbr in mould).

Hydrothermal reaction of fly ash/hydrated lime: characterization of the reaction products

Abstract: Class F coal fly ash was slurried with hydrated lime at 90°C in 1/3, 5/3, 9/3, and 15/3 weight ratios and for 3, 5, 7, and 9 hours of hydration, in a process to prepare sorbents for SO2 removal. The amounts of aluminum, silicon, and calcium in the product of the pozzolanic reaction were determined in order to study the evolution of product composition with the initial raw materials ratio and hydration time and to relate this composition to the desulfurization capability of the material. Al, Si, and Ca were present in the solid product for any raw materials ratio and hydration time, showing that calcium silicates, calcium aluminates, and/or calcium aluminum silicates were obtained simultaneously. The products formed show a nearly constant molar ratio of Al2O3/SiO2 independent of the experimental conditions tested and similar to the Al2O3/SiO2 ratio in the fly ash. The SiO2/CaO molar ratio in the products decreased as the initial fly ash/Ca(OH)2 ratio decreased, being approximately constant for each ratio w...

Preparation of Ca-β-Al2O3 from alumina gel

Abstract: Using aluminium nitrate solution containing calcium and magnesium cations, and saturated ammonium oxalate solution in concentrated ammonium hydroxide as precipitating agent, alumina gel was prepared. The gel was calcined at different heating rates up to 400 °C and then at different temperatures and soaking times. The calcination products successively appeared as aluminium oxides, calcium aluminate and calcium-beta″-alumina. The obtained calciumbeta″-alumina crystallites were plate-shaped and the direction perpendicular to the crystallite surface was parallel to the Z-axis. It was found that the kinetics of calcium-beta″-alumina synthesis depends on the presence of a molten salt during the gel thermal treatment. The mechanism of calcium-beta″-alumina formation is proposed as a reaction between formerly produced calcium aluminate and aluminium oxide of the alpha form. Sintered bodies prepared from the calcium-beta″-alumina powder were characterized by good ionic conductivity.