Showing papers on "Calcium aluminates published in 1997"

Microstructural analysis of corroded alumina-spinel castable refractories

Abstract: Microstructural analysis indicates that the corrosion of alumina-spinel castables by a liquid steel ladle slag involves initial reaction of CaO in the slag with alumina fines in the refractory bond. The slag becomes saturated in CaO and Al 2 O 3 and CA 2 is precipitated from it along with other calcium aluminates. The spinel fines and grains in the refractory take up the MnO/FeO/Fe 2 O 3 from the slag, which becomes silica-rich as CA 2 is precipitated and highly viscous. The thickness of the remnant slag layer on the corroded samples indicates the viscosity of the liquid slag under the test conditions. Further into the refractory CA 6 is formed, firstly crystallized with a tabular morphology in dense regions and then with a similar morphology in more porous regions. Deeper still in the refractory CA 6 takes a whisker/needle habit suggesting some vapour-phase reaction. MgO-rich spinel-alumina castables undergo less corrosion under these conditions as dissolution of MgO leads to a viscous MgO-rich slag which is less corrosive to the Al 2 O 3 components of the refractory.

Control of microinclusions in calcium treated aluminium killed steels

Abstract: A simple thermodynamic model to predict the formation of microinclusions in calcium treated, aluminium killed steels is presented. Basic data required for the model are the temperature and chemical analysis of the steel. The model can be used to predict the quantity and type of calcium aluminates and sulphides present in the steel, as well as the concentrations of dissolved elements. This model is applied to discussion of different situations occurring in practice, including calcium attack on aluminous ladle and tundish refractories, nozzle clogging by either high alumina calcium aluminates or calcium sulphide, and inclusions in the final product.

Potassium-containing calcium aluminate catalysts for pyrolysis of n-heptane

Abstract: The effectiveness of potassium promoted calcium aluminate to catalyze the steam pyrolysis of n-heptane has been investigated at 1023 K and atmospheric pressure. Various amounts of potassium were incorporated on calcium aluminate (12CaO7Al2O3) by three different methods. Compared to thermal pyrolysis, addition of the calcium aluminate catalyst (either promoted or unpromoted) significantly increased the conversion as well as the yields of CH4, C2H4 and C3H6. The presence of potassium significantly reduced the coke deposited on the catalysts due to the enhanced rate of the coke gasification reaction. A significant amount of potassium was lost from the catalysts during preparation as well as during reaction. The gasification activity was higher for the catalysts in which the K2CO3 was incorporated by incipient wetness method but the potassium loss during reaction was also higher in comparison to catalysts in which the potassium was incorporated by co-sintering.

Crystal morphology of calcium aluminates hydrated for 14 days

Abstract: phase [2–4]. Many researchers [5–7] have investi-gated the development of these hydrated phases byelectron microscopy. The effects of crystal morphol-ogy on the hydration characteristics and setting timehave also been studied by some workers [8–9]. Theaim of the work reported here is to investigateexactly what the crystal habit and morphology are onthe fourteenth day of hydration of calcium alumi-nates, and what their role is in the development ofcompressive strength of the hydrated samples.Calcium aluminates such as CA, CA

Phase composition development of calcium sulphoaluminate belite cement in the SOx atmosphere

Abstract: The usual constituent phases found in calcium sulphoaluminate belite clinker are C 2 S,C 4 A 3 S, C 4 AF, CS and C. C 4 A3S is formed due to reactions of calcium aluminates with the anhydrite (CS) created from gypsum in the raw mix. Anhydrite decomposes slightly at burning conditions so C 4 A3S forms by solid state reaction as well as by gaseous transport. In this work we investigated the influence of gaseous SOx on the formation of clinker phases, especially C 4 A 3 S. Presses powder mixtures calculated to form C 2 S, C 3 A and C 4 AF were calcined at 950°C and then fired in to static SOx atmospheres at 1150, 1200 and 1250°C. Initially C 3 A reacts with SOx to form C 4 A 3 S and C. Then free lime reacts to form CS. The increase in content of sulphate phases has been determined from weight increases and Z-ray records. With increasing SO 3 content the dimensional contraction of clinker pellets was observed. The presence of C 5 S 2 S was not detected at any temperature. Results of phase developments in SOx atmospheres have been compared to those at which CS was included directly into the raw mix.

Quick-hardening material and its production

Abstract: PROBLEM TO BE SOLVED: To obtain a quick-hardening material excellent in applicability as well as in the exhibition of strength by incorporating calcium aluminates, an inorg. sulfate, at least one of a metallic sulfate and a metallic carbonate and a powdery water-reducing agent. SOLUTION: Usually (A) 100 pts.wt. calcium aluminates are mixed with (B) 10-200 pts.wt. inorg. sulfate, (C) 1-30 pts.wt. at least one of a metallic sulfate and a metallic carbonate based on 100 pts.wt., in total, of the components A and B and (D) 1-20 pts.wt. powdery water-reducing agent based on 100 pts.wt., in total, of the components A-C. The starting materials are preferably mixed and comminuted and the fineness of the resultant quick-hardening material is usually regulated to ≥3,000 cm 2 /g Blaine value. The calcium aluminates are preferably based on crystalline minerals. The inorg. sulfate is preferably anhydrous gypsum. The metallic sulfate is preferably alum. The water-reducing agent is preferably a naphthalenesulfonate-formaldehyde condensation product. COPYRIGHT: (C)1999,JPO

Sulphur-containing machinable low alloy or carbon steel

Abstract: A machinable low alloy or carbon steel, which has a carbon content of less than 1.5% and a total alloying content of less than 9% and which contains oxide and sulphide inclusions, has (a) the composition (by wt.) \-0.1% Mn, 0.01-0.05% Al, 0.025-0.3% S, \-0.002% Ca and <= 0.0015% O; (b) a 'KO oxide' index (SEP 1570-71 Standard) of less than 30; (c) all the oxides present as calcium aluminates; and (d) an average calcium content of less than 25% in the type 2, 3, 4 and 5 inclusions. Also claimed are (i) a metallurgical product in the form of a slab, bloom, billet rod or wire produced from the above steel by continuous casting; (ii) production of the above metallurgical product by aluminium deoxidising molten steel, vacuum degassing, injecting pulverulent oxide of melting temperature below 1500 deg C, injecting calcium and casting; and (iii) a core-filled wire consisting of a tubular sheath which melts in molten steel and which encloses an oxide mixture powder of melting temperature le ss than 1400 deg C.