Showing papers on "Calcium aluminates published in 2012"
10 Apr 2012-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the authors studied the transient evolution of spinels in laboratory and industrial heats and found that spinels can be modified readily to liquid inclusions by a calcium treatment, which is a well-established way to modify solid alumina inclusions to liquid or partially liquid calcium aluminates.
Abstract: Calcium treatment is a well-established way to modify solid alumina inclusions to liquid or partially liquid calcium aluminates. Spinels (Al2O3·xMgO) can also form in liquid steel after aluminum deoxidation. Like alumina, the spinels can be modified readily to liquid inclusions by a calcium treatment. The modification of spinels was studied by observing the transient evolution of inclusions, in laboratory and industrial heats. Spinel modification involves the preferential reduction of MgO from the spinel, with Mg dissolving in the steel, and it proceeds through transient calcium sulfide formation, just like in the case of alumina inclusions. Because magnesium dissolves in steel after the calcium treatment of spinels, the reoxidation of the melt will produce new spinels.
121 citations
TL;DR: In this article, a one-dimensional differential equation related to the diffusion reaction behavior of sulfate ions in concrete is presented, and based on chemical reactions between sulfate and calcium aluminates in concrete, the expansive volume strain caused by ettringite growth is analyzed.
76 citations
TL;DR: In this article, changes in the pore space of loess treated with 1% to 8% of lime (CaO) and compacted in the laboratory were studied by the mercury intrusion porosimetry (MIP) over a long term period (1-360 days).
74 citations
TL;DR: Two series of glasses based on high silica (CAS) and low silica calcium aluminates (LSCA) have been investigated for their structural, optical and Tb(3+) luminescence properties, and the compositional modification reduces host phonon energy in LSCA glasses.
39 citations
TL;DR: In this article, Nanocrystalline calcium aluminates with different CaO/Al2O3 ratios were prepared by a facile co-precipitation method using Poly(ethylene glycol)-block-poly(propylene glycol) block-polypoly(ethylenes glycol), (PEG-PPG-PEG, MW: 5800) as a surfactant.
25 citations
TL;DR: In this paper, the formation characteristics of calcium aluminates in the CaO-Al 2 O 3 -SiO 2 system with sodium oxide was investigated by XRD, SEM-EDS and DSC-TG technologies.
25 citations
TL;DR: In this paper, a thermodynamic evaluation of reactions between ZrO2 and aluminum is presented, which indicates that the aluminothermic reduction of zirconium oxides at temperatures above 600°C is only possible when AlxZry intermetallic compounds form in the metallic phase.
Abstract: This paper presents thermodynamic evaluation of reactions between ZrO2 and aluminum, which indicates that the aluminothermic reduction of zirconium oxides at temperatures above 600°C is only possible when AlxZry intermetallic compounds form in the metallic phase. Thermodynamic analysis results are supported by experimental data, which demonstrate that, at ZrO2: Al ratios in the range 0.4–1.4, the aluminothermic reduction of ZrO2 leads predominantly to the formation of the congruently melting compounds Al2Zr and Al3Zr. The phase formation in the slag yields various forms of calcium aluminates and calcium zirconates and leads to a gradual reduction in the oxidation state of the zirconium.
22 citations
Patent•
27 Sep 2012
TL;DR: In this paper, systems, methods, and compositions related to mixtures of calcium aluminate cements with compositions comprising carbonate are described, where carbonates may be formed by sequestering carbon dioxide.
Abstract: Provided herein are systems, methods, and compositions related to mixtures of calcium aluminate cements with compositions comprising carbonate. The compositions comprising carbonates may be formed by sequestering carbon dioxide.
16 citations
TL;DR: In this paper, the effect of TiO2 content on the microstructure, phase composition, and mechanical strength of the Si3N4/TiN composites has been examined.
Abstract: Si3N4/TiN composites have been produced by hot pressing at temperatures from 1600 to 1800°C in a nitrogen atmosphere, using silicon nitride powders prepared by self-propagating high-temperature synthesis and surface-modified with titanium dioxide nanoparticles. We examined the effect of TiO2 content on the microstructure, phase composition, and mechanical strength of the ceramics. It is shown that titanium nitride can be formed by the reaction Si3N4 + TiO2 → TiN + NO + N2O + 3Si. The Si3N4/TiN composites containing 5–20% TiN have a low density, high porosity, and a bending strength of 60 MPa or lower. In Si3N4/TiN ceramics produced using calcium aluminates as sintering aids, the silicon nitride grains are densely packed, which ensures an increase in strength to 650 MPa.
9 citations
TL;DR: In this paper, the influence of SHS aluminum nitride content and particle size on the fabrication conditions (hot pressing in a nitrogen atmosphere) of Si3N4-based ceramics containing CaO-Al2O3-AlN sintering aids.
Abstract: We have studied the influence of SHS aluminum nitride content (5–15%) and particle size on the fabrication conditions (hot pressing in a nitrogen atmosphere) of Si3N4-based ceramics containing CaO-Al2O3-AlN sintering aids. The results demonstrate that the reaction of Si3N4 with a eutectic calcium aluminate mixture during liquid-phase sintering leads to the formation of α-sialon-based intergranular phases: Cam/zSi12 − (m − n)Al(m + n)OnN16 − n. The addition of AlN to starting mixtures contributes to a more complete conversion of the calcium aluminate sintering aid to Ca-α-sialon and influences the relationship between α-Si3N4 and β-Si3N4 in the ceramics. We examine the influence of synthesis conditions and the percentages of added calcium aluminates and aluminum nitride on the density, porosity, and bending strength of the ceramics. Thermogravimetric analysis data demonstrates that the Si3N4 + Ca-α-sialon composites obtained are stable to oxidation in air up to 1300°C.
8 citations
TL;DR: In this paper, the main issues attending the production, composition, and properties of high-alumina cements of the Cembor series are discussed and compared to other Russian-made cements and similar cements made abroad.
Abstract: The Borovichi Refractories Combine developed and continues to make and use high-alumina (calcium- aluminate) cements Cembor-73 and Cembor-70 to produce refractory concretes and concrete products. This article discusses the main issues attending the production, composition, and properties of high-alumina cements of the Cembor series. These cements are compared to other Russian-made cements and similar cements made abroad. Recommendations on the use of cements Cembor-3 and Cembor-70 are made based on data on their composition and properties.
TL;DR: In this paper, the thermal behavior of the three precursors used in the CaAl12O19 synthesis was monitored to underline the thermal effects associated to calcium aluminates formation.
Abstract: CaAl12O19 was synthesised using three different precursors: (a) a polyesteric type precursor resulted from the traditional Pechini method; (b) a polyesteric type precursor resulted from the reaction between citric acid and calcium and aluminum nitrates; and (c) a polymeric type precursor resulted from the reaction between acrylic acid and calcium an aluminum nitrates The thermal behavior of the three precursors used in the CaAl12O19 synthesis was monitored to underline the thermal effects associated to the CaAl12O19 formation Thermal analyses performed on precursors do not reveal clear differences regarding the thermal effects assigned to calcium aluminates formation, at temperatures over 800 °C In contrast, thermal analysis of samples pre-fired at 200 °C, and especially at 600 °C, show clear differences between samples obtained in different ways It is noted that in samples obtained from acrylic acid and nitrates, and citric acid and nitrates, CA6 is practically single phase after calcination at 1,200 °C However, in the sample obtained from citric acid, ethylene glycol, and nitrates, calcined at 1,200 °C, CA6 is present along with CA2 and α-Al2O3
TL;DR: In this article, the processes of synthesizing calcium aluminate in the flow of concentrated solar radiation on large solar furnaces were studied, and the resulting material exhibits high mechanical properties (the modulus of rupture upon bending is 40 MPa).
Abstract: The processes of synthesizing calcium aluminate in the flow of concentrated solar radiation on Large Solar Furnace are studied. It is shown that the synthesis of calcium aluminate takes place through a process of melting of a mixture of aluminum oxides and calcium (Al2O3 + CaO). At values of power of the concentrated flow of 200 W/cm2, thermodynamic conditions for melting of the materials studied were implemented. Full fusion penetration is achieved at a power flow of 400 W/cm2. The resulting material exhibits high mechanical properties (the modulus of rupture upon bending is 40 MPa).
TL;DR: In this paper, a series of model experiments combined with surface analyses were performed to evaluate the mechanisms behind the bioactivity of Ca-aluminate and the formation of possible surface films was studied using SEM, EDX and thin-film XRD.
Abstract: For an implant material, the interface stability to living tissue is of outmost importance since it can control the implant lifetime. Bioactive materials are those proven to form a bond to living tissue. Traditional bioactive materials produced by chemical reactions are known to be weak and as such cannot be used in load bearing applications. Recently, chemically bonded ceramics of the calcium aluminate family have been proven to be bioactive. With water the calcium aluminates form a paste that can be injected into the implant site. The hardened body has a compressive strength considerably higher than that of the traditional bioactive materials. To evaluate possible usage of the material in biological applications several model experiments of its bioactivity were performed. This paper describes the mechanisms behind the bioactivity in detail via a series of model experiments combined with surface analyses. The formation of possible surface films was studied using SEM, EDX and thin-film XRD. It is concluded that the basic nature of Ca-aluminate makes apatite formation possible in body liquid both in a direct reaction and as a transformation reaction of the main hydrate katoite to apatite and gibbsite.
Patent•
26 Jul 2012
TL;DR: In this article, the authors proposed a quick-hardening, highly flowable cement composition for low temperature, which is excellent in flowability and hardly undergoes overexpansion despite having a compressive strength of 10 N/mmor higher at a material age of 3 h, even when the material temperature and the environmental temperature are below 5°C.
Abstract: PROBLEM TO BE SOLVED: To provide a quick-hardening, highly flowable cement composition for low temperature, which is excellent in flowability and hardly undergoes overexpansion despite having a compressive strength of 10 N/mmor higher at a material age of 3 h, even when the material temperature and the environmental temperature are below 5°C.SOLUTION: The quick-hardening cement composition for low temperature comprises particular calcium aluminates, cement, gypsum, alkali metal carbonate and a setting retarder. Preferably, the calcium aluminates have a percentage of glass content within a prescribed range. The cement composition preferably comprises a water-reducing agent and/or an aggregate.
24 Apr 2012
TL;DR: In this paper, the synthesis of high purity barium calcium aluminate in oxidant atmosphere, without the pyrolysis step in hydrogen atmosphere, followed by the high energy ball milling to reduce the average particle size, was investigated to improve the impregnation process of the aluminate by induction heating.
Abstract: The synthesis of high purity barium calcium aluminate in oxidant atmosphere, without the pyrolysis step in hydrogen atmosphere, followed by the high energy ball milling to reduce the average particle size, was investigated to improve the impregnation process of the aluminate in porous tungsten matrices by induction heating.
Patent•
26 Jul 2012
TL;DR: In this article, the authors proposed a quick-hardening cement mixture for low temperature, which is mixed and kneaded into a cement composition to provide excellent pot-life.
Abstract: PROBLEM TO BE SOLVED: To provide a quick-hardening cement admixture for low temperature, which is mixed and kneaded into a cement composition to impart excellent potlife, i.e. 60 min or longer, a compressive strength of 5 N/mmor higher at a material age of 3 hr and a compressive strength of 30 N/mmor higher at a material age of 24 hr, even when the material temperature of the mixed cement composition and the environmental temperature are 5°C, and to provide a quick-hardening cement composition for low temperature, which is excellent in potlife, i.e. 60 min or longer, has a compressive strength of 5 N/mmor higher at a material age of 3 hr and has a compressive strength of 30 N/mmor higher at a material age of 24 hr, even when the material temperature and the environmental temperature are 5°C.SOLUTION: The quick-hardening cement admixture for low temperature comprises calcium aluminates with a prescribed percentage of glass content, gypsum, alkali metal sulfate, alkali metal carbonate and a setting retarder. Preferably, the calcium aluminates comprise crystalline calcium aluminates and amorphous calcium aluminates.
Patent•
08 Mar 2012
TL;DR: In this paper, the problem of providing a cement setting accelerator from which an aluminum ion and a sulfate ion are not eluted, which is friendly to environment, where superior aggregation properties are acquired and which has excellent initial strength development, a spraying material using the same and a spraying method is presented.
Abstract: PROBLEM TO BE SOLVED: To provide a cement setting accelerator from which an aluminum ion and a sulfate ion are not eluted, which is friendly to environment, where superior aggregation properties are acquired and which has excellent initial strength development, a spraying material using the same and a spraying method.SOLUTION: (1) A cement setting accelerator contains a polysilica iron. (2) The cement setting accelerator is (1) having a molar ratio SiO/Fe of the polysilica iron of 0.2-3.0. (3) A spraying material includes cement and the cement setting accelerator of (1) or (2). (4) The spraying material is (3) containing calcium aluminates additionally. (5) A spraying method is characterized by using the spraying material of (3) or (4).
Patent•
24 Oct 2012
TL;DR: In this article, a method for the manufacture of hydraulic lime in a shaft furnace through the combustion of agglomerated raw materials containing primarily calcium carbonate and silicates and aluminates at temperatures above 1100°C was described.
Abstract: The invention relates to a method for the manufacture of hydraulic lime in a shaft furnace through the combustion of agglomerated raw materials containing primarily calcium carbonate and silicates and aluminates at temperatures above 1100°C, the calcined, agglomerated material after passing through the furnace substantially comprising calcium oxide, calcium silicates and calcium aluminates and calcium aluminate ferrite, wherein solid bodies are compressed from fine-particulate raw materials comprising a previously determined mineral and chemical composition as is required for the predetermined properties of the calcined material, said composition having a grain size of 500 µm, together with water for the production of the agglomerated raw material.
Patent•
27 Dec 2012
TL;DR: In this article, a filler of flux cored wire contains the following components, wt %: metal magnesium 30-50, calcium 10-15, alloy of calcium and silicon 30 -50, fluor spar up to 5%, total content of metal barium or mixture of metal boric acid and barium silicide 10-20, and iron is the rest Total calcium content is 20-50% of filler content
Abstract: FIELD: metallurgySUBSTANCE: filler of flux cored wire contains the following components, wt %: metal magnesium 30-50, calcium 10-15, alloy of calcium and silicon 30-50, fluor spar up to 5%, total content of metal barium or mixture of metal barium and barium silicide 10-20, and iron is the rest Total calcium content is 20-50% of filler contentEFFECT: invention allows increasing fixation efficiency of calcium and magnesium and obtaining steel with high level of mechanical properties and increased purity as to content of non-metallic inclusions, and namely calcium aluminates and sulphides1 dwg
Patent•
30 Apr 2012
TL;DR: In this paper, a soil pavement composition is provided to increase initial strength and minimize cracks which are caused by dry shrinkage by using a clinker having particle property of high blain, the clinker is pulverized using 6500-8500cm/g of Blaine and is composed of calcium silicate and calcium aluminates.
Abstract: PURPOSE: A soil pavement composition is provided to increase initial strength and minimize cracks which are caused by dry shrinkage by using a clinker having particle property of high blain. CONSTITUTION: A soil pavement composition includes 100.0 weight % of mixed soil including 85-95 weight% of soil and 5-15 weight% of solidifying material. The soil pavement composition additionally includes 5-15% of liquid composition. The solidifying material comprises 90-99 weight% of clinker and 1-10 weight% of alkaline salt binder. The clinker is pulverized using 6500-8500cm/g of Blaine and is composed of calcium silicate and calcium aluminates. The liquid composition is all of or one selected from water or liquid polymer. The solidifying material additionally includes 0.1-0.3% of reaction accelerator based on 100 weight% of the solidifying material. The reaction accelerator is one selected from calcium formate, sodium carbonate, and potassium carbonate.
TL;DR: In this article, the effect of manganese dioxide on the formation of calcium monoaluminate in the CaO-Al2O3 system during solid-state sintering of five oxide mixtures corresponding to the known calcium aluminates at temperatures from 1100 to 1400°C was studied.
Abstract: We have studied the effect of manganese dioxide (5–20 wt %) on the formation of calcium monoaluminate in the CaO-Al2O3 system during solid-state sintering of five oxide mixtures corresponding to the known calcium aluminates at temperatures from 1100 to 1400°C. X-ray diffraction examination indicated the formation of calcium manganates. The mixture of the calcium manganates melts at 1330°C, promoting the sintering process and the reaction between the calcium oxide and alumina and raising the yield of calcium monoaluminate as the dominant phase. The calcium manganates are shown to be nonreactive with the forming calcium aluminates. The X-ray diffraction results are supported by scanning electron microscopy data for a number of samples.
TL;DR: In this paper, the sintering characteristic and leaching property of calcium aluminates in the CaO-Al2O3-SiO2 system with different FeO additions were investigated.
Abstract: The sintering characteristic and leaching property of calcium aluminates in the CaO-Al2O3-SiO2 system with different FeO additions were investigated. FeO decreases the melting temperature of clinker, and makes the clinker not self-pulverizable. As FeO addition increases from 0 to 4%, the main phases of clinkers sintering at 1350 °C are 12CaO•7Al2O3 and 2CaO•SiO2 as well as some CaO•Al2O3 when the mass ratio of Al2O3 to SiO2 is 5.0 and the molar ratio of CaO to Al2O3 is 1.4. The interplanar spacing of 12CaO•7Al2O3 in the clinker increases with the increase of FeO addition, and the proportion of CaO•Al2O3 in the clinker decreases with the increase of FeO addition. FeO does not affect the Al2O3 leaching rate of clinker obviously, but increases the molar ratio of caustic Na2O to Al2O3 in the leached liquor.