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Showing papers on "Calcium aluminates published in 2005"


Patent
Ellis Gartner1, Guanshu Li1
19 Jul 2005
TL;DR: In this article, a method for the production and the use of hydraulic binders for hydraulic binding is described, which is based on a belite-sulfo-aluminous clinker.
Abstract: The invention relates to a belite-sulfoaluminous clinker, to a method for the Production and the use thereof for preparing hydraulic binders comprising the following mineralogical composition: 5 to 35 %, preferably 10 to 20 % a calcium aluminoferrite phase whose composition corresponds to a general formula C2AXF(1-X), wherein X ranges from 0.2 to 0.8, 15 to 35 %, preferably 20 to 30 % a calcium sulphoaluminate phase “yee' limite” (C4A3d), 40 to 75 %, preferably 45 to 65 % belite (C2S), 0.1 to 10 % one or several mineral phases selected form calcium sulphates, alkali sulphates, perovskite, calcium aluminates, gehlenite, free lime, periclase and/or a vitreous phase and at least a secondary element selected from sulfur, magnesium, sodium, potassium, boron, phosphorus, zinc, manganese, titanium, fluorine, chlorine, wherein the total content of said secondary elements is equal to or less than 15 %.

84 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the enthalpies of annealed calcium aluminate Ca12Al14O33 with variable amounts of electrons and less than 33 oxygens per formula unit, and showed that the standard enthalpy of oxidation per O2 consumed is −579.4 ± 9.4 kJ/mol.
Abstract: Microporous calcium aluminates with a common formula [Ca12Al14O33-δ]2δ+(2δe-), (0 < δ ≤ 1), represent a new family of electrides with conducting extraframework electrons encaged within the framework. Their enthalpies of oxidation to eliminate these electrons and obtain a stoichiometric Ca12Al14O33 compound, and formation enthalpies relative to the most stable annealed calcium aluminate Ca12Al14O33.46 (which contains excess oxygen probably as O- and O2- species), are studied by transposed temperature drop calorimetry and drop solution calorimetry in molten lead borate at 1080 K. The standard enthalpy of oxidation per O2 consumed is −579.4 ± 9.4 kJ/mol (or −144.8 ± 9.4 kJ per encaged electron). The enthalpies obtained for samples with variable amounts of electrons (and less than 33 oxygens per formula unit) are compared to that for oxidation of a stoichiometric Ca12Al14O33 sample to an oxygen-rich composition. The study supports the idea that the oxidation of the stoichiometric Ca12Al14O33 sample results in...

31 citations


Journal ArticleDOI
TL;DR: In this article, a mixture of calcined alumina and synthetic calcium carbonate was used to synthesize calcium aluminate cement and its kinetics of thermal dehydration was studied under non-isothermal conditions by thermo-gravimetry using the integral approximation model.

30 citations


Patent
22 Jun 2005
TL;DR: A promoted calcium-alumina supported reforming catalyst that is particularly useful for reforming reactions where low H2/CO ratio synthesis gas, such as less than 2.3 is generated directly is disclosed in this paper.
Abstract: A promoted calcium-alumina supported reforming catalyst that is particularly useful for reforming reactions where low H2/CO ratio synthesis gas, such as less than 2.3 is generated directly is disclosed. The catalyst comprises from about 25 wt% to about 98 wt % alumina, from about 0.5 wt% to about 35 wt% calcium oxide, from about 0.01 wt% to about 35 wt% of a promoter, and from about 0.05 wt% to about 30 wt% of an active metal. The promoter is selected from the group consisting of titanium, zirconium, yttrium, niobium, elements of the lanthanum-series, such as, without limitation, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, ytterbium, and combinations thereof. The active metal is selected from the group consisting of nickel, cobalt, rhodium, ruthenium, palladium, platinum, iridium and combinations thereof as active metal, wherein the calcium oxide is combined with the alumina to form aluminum-rich calcium aluminates.

26 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigate the stability between calcium-based materials and aluminum-killed steel and find that both calcium titanate and calcium zirconate react with alumina to form calcium aluminates.
Abstract: Clogging of tundish and submerged entry nozzles (SENs) adversely impacts productivity and quality in the continuous casting of aluminum-killed steels. Clogging results from an accretion layer that develops on the inside surface of the nozzle and restricts steel flow. Current nozzle refractories often react with molten steel to form solid by products that promote clogging. Nozzle materials that are inert with the liquid steel or react with accretions to form liquid reaction products could inhibit or eliminate clogging. Static experiments were conducted to investigate the stability between calcium-based materials and aluminum-killed steel. The results indicate that both calcium titanate and calcium zirconate react with alumina to form calcium aluminates. However, only the reaction between alumina and calcium titanate yielded calcium aluminate chemistries that were molten at steel casting temperatures. Liquid reaction products are preferred since they would be removed from the nozzle by the steel flow, thereby preventing accretion formation and clogging.

20 citations


Journal ArticleDOI
TL;DR: In this article, the initial appearance of carbides and carbide oxides is due to the preferential reaction between carbon and pentahedrally coordinated aluminum atoms, and it is suggested that polymerization of alumina polyhedra rather than particle filler effects is responsible for the viscosity buildup and stream stabilization in the formation of calcium aluminate fibers by inviscid melt spinning.
Abstract: Propane pyrolysis over calcium aluminate melts was carried out to evaluate carbon interactions with calcium, aluminum, and oxygen atoms. Infrared emission and attenuated total reflectance spectroscopies indicate that aluminum carbides and carbide oxides were formed early in the reaction as a result of carbon interactions with the melt. Moreover, time step emission spectra indicate that carbide oxides were formed before carbides, and that the carbon-melt reaction product carbon monoxide accompanied carbide formation. Calcium carbide formation was not observed. It is proposed that the initial appearance of carbides and carbide oxides is due to the preferential reaction between carbon and pentahedrally coordinated aluminum atoms. These results suggest that polymerization of alumina polyhedra rather than particle filler effects is responsible for the viscosity buildup and stream stabilization in the formation of calcium aluminate fibers by inviscid melt spinning.

9 citations


Journal ArticleDOI
TL;DR: In this paper, the reactions between hot-pressed calcium hexaluminate (CaAl12O19, hibonite) and silicon carbide (SiC) at 1100°-1400°C in air and nominal argon atmospheres were investigated.
Abstract: The reactions between hot-pressed calcium hexaluminate (CaAl12O19, hibonite) and silicon carbide (SiC) at 1100°-1400°C in air and nominal argon atmospheres were investigated. In inert atmospheres, there was no evidence of reaction at temperatures up to at least 1400°C. In air, the oxidation of SiC produced a layer of silica or a multicomponent amorphous silicate (depending on impurities) that reacted with CaAl12O19. At temperatures below 1300°C, the reaction resulted in the stratification of two distinct interfacial layers: a partially devitrified CaO-Al2O3-SiO2 glass adjacent to SiC and a CaAl2Si2O8 (anorthite) layer adjacent to hibonite. At 1400°C, a large amount of liquid was formed, the majority of which was squeezed out from between the reaction couple. No distinct layer of anorthite was present; instead, the anorthite was replaced by a layer of alumina between the glass-rich layer and hibonite. An activation energy of 290 kJ/mol was determined for the reaction, which is consistant with oxygen diffusion through a calcium aluminosilicate glass. The reaction between rare-earth hexaluminates and SiO2 was predicted to produce a more-viscous glass than CaAl12O19 and SiO2 and, therefore, have slower reaction kinetics, because of lower mass transport in the glass.

7 citations


Patent
29 Apr 2005
TL;DR: In this article, an ettringite binder comprising calcium sulfate and a mineral compound of calcium aluminates consisting of oxides of calcium (C) and aluminum (A), soluble and combined in one or more crystallised and/or amorphous mineralogical phases in which the effective mol ratio of C/A = 1.2-2.7 and the total weight of the phases (C + A) is at least 30 wt% of that of the mineral compound, polyalkylene oxide(s) with a comb-shaped polymer structure (
Abstract: Dense mortar based on an ettringite binder (calcium sulfate/calcium aluminate) and an organic structuring resin also contains a polyalkylene oxide with a comb-like structure. Dense mortar containing (i) an ettringite binder comprising calcium sulfate and a mineral compound of calcium aluminates consisting of oxides of calcium (C) and aluminum (A), soluble and combined in one or more crystallised and/or amorphous mineralogical phases in which the effective mol ratio of C/A = 1.2-2.7 and the total weight of the phases (C + A) is at least 30 wt% of that of the mineral compound, (ii) polyalkylene oxide(s) with a comb-shaped polymer structure (PCP) and (iii) less than 2 wt% organic structuring resin(s).

4 citations


Journal Article
01 Jan 2005-Europace
TL;DR: The research proposal aimed to achieve the following objectives: 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 and investigating the influence of nozzle design and casting parameters on nozzle clogging and steel cleanliness by Means of mathematical and physical models.
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).

2 citations