Showing papers on "Calcium aluminates published in 2013"

Raman Spectroscopy of Anhydrous and Hydrated Calcium Aluminates and Sulfoaluminates

Abstract: Recent investigations have revealed the great potential of Raman spectroscopy for the characterization of clinker minerals and commercial Portland cements. The usefulness of this technique for the identification of anhydrous, hydrated, and carbonated phases in cement-based materials has been demonstrated. In the present work, the application of micro-Raman spectroscopy for the characterization of the main clinker phases of calcium aluminate cements and calcium sulfoaluminate cement is explored. The main stable hydrated phases as well as several important carbonated phases are investigated. Raman measurements on the following phases are reported: (i) pure, unhydrated phases: CA, C12A7, CA2, C2AS, cubic-C3A, C4AF, and C4A3S¯; (ii) hydrated phases: ettringite, monosulfoaluminate, and hydrogarnet (C3AH6); (iii) carboaluminate phases: hemicarboaluminate and monocarboaluminate. The present results, which are discussed in terms of the internal vibrational modes of the aluminate, carbonate, and sulfate molecular groups as well as stretching O–H vibrations, show the ability of Raman spectroscopy to identify the main hydrated and unhydrated phases in the aluminate and sulfoaluminate cements. The Raman spectra obtained in this work provide an extended database to the existing data published in the literature.

Thermodynamics for Precipitation of CaS Bearing Inclusion and Their Deformation During Rolling Process for Al-Killed Ca-Treated Steel

Abstract: Thermodynamics for CaS bearing inclusions precipitation and their deformative behaviors during compact strip production (CSP) rolling process for Al-killed calcium treatment steel were researched using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) combined with the results of industrial trials. In addition, thermodynamic software FactSage was applied to calculate component activities of an inclusion and to analyze properties of sulfide-oxide duplex inclusions. It is possible for CaS bearing inclusion precipitation during secondary refining and continuous casting in two manners: the first is that Ca and S react directly after calcium treatment; the other is as the well modified calcium aluminates react with dissolved sulfur and aluminum in liquid steel. Correspondingly, two types of sulfide-oxide duplex inclusion were observed in casting slab. For the first type duplex inclusion, nearly no chemical reactions occur between outer CaS layer and solid inclusion core, thus the outer CaS rich layer is easily separated even taken off from the inner core during rolling process, and a crack may be generated correspondingly. The later one performs a better deformation during rolling process.

Effect of vacuum degassing on non-metallic inclusions in an ASEA-SKF ladle furnace

Abstract: The objective of this research was to study non-metallic inclusions during vacuum degassing in an ASEA-SKF ladle furnace. Five steel and top slag samples were taken before, during and after vacuum degassing for chemical analysis and scanning electron microscopy. It was concluded that the average CaO/Al2O3 ratios in the top slags became close to the phase C3A. The average CaO/Al2O3 ratios in the inclusions of this study were close to the phase CA6, but at the end of degassing, the average CaO/Al2O3 ratios in the calcium aluminates by subtracting the Al amounts of the inclusions that were assumed to form spinel phases with the available Mg amounts in the inclusions were situated between the phases C12A7 and C3A. By decreasing the S and Al contents of molten steel and at [S]3.[Al]2 less than around 10−7 , the ratio of calcium aluminates to spinels increased continously. It was finally concluded that by increasing the Ca amount in inclusions, their equivalent circle diameters grew, and their aspect ra...

Development of oxide inclusions during vacuum degassing process

Abstract: This article sets out to study the development of oxide inclusions during the vacuum degassing process at the ASEA-SKF ladle furnace. During the degassing process, five steel and top slag samples were taken, and their chemical compositions were analysed. All steel samples were further analysed by scanning electron microscopy. It was concluded that the vacuum degassing process was a dynamic process during which spinel and calcium aluminate inclusions were dominant. In addition, it was seen that during this process, the percentage share of calcium aluminates compared with spinels, the Ca weight per cent content of the oxides, the average equivalent circle diameter (ECD) of the oxides and the percentage share of the oxides with bigger ECD were increasing, and the oxides tended to form more round shapes.

Examples of How Fundamental Knowledge can Improve Steelmaking: Desulphurisation Kinetics Calcium and Modification

Abstract: Sulphur control is an essential part of steel production. This paper summarises two aspects of sulphur in secondary metallurgy. First, it is shown that silicon can contribute to ladle desulphurisation if the ladle slag is low in silica; the effect of silicon is primarily on the equilibrium sulphur level, rather than a specific kinetic effect. Second, sulphur is shown to capture calcium (as calcium sulphide) upon calcium injection to modify inclusions. In steels with less than approximately 100 ppm sulphur, the calcium sulphide subsequently back-reacts with alumina inclusions, to modify the oxide inclusions to calcium aluminates.

Blast furnace hearth refractory and coke ash mineral interactions

Abstract: In the blast furnace hearth the calcium aluminate by-products of coke dissolution can react with the hearth refractories. Reactions between these coke ash minerals and the aluminosilicate and alumina-carbon hearth refractories may result in increased refractory wear reducing the blast furnace campaign life. Hence improved understanding of these interactions may have implications for the campaign life of the blast furnace hearth refractory materials. The interactions between the coke ash minerals and aluminosilicate hearth refractory have been assessed by heating samples of calcium aluminates (CA, CA2 and CA6) coupled with aluminosilicate refractory to temperatures representative of the blast furnace hearth (1450 degreesC to 1550 degreesC) in an inert atmosphere over a range of reaction times (4 - 24 hours). It was found that there was significant reaction between the refractory, CA and CA2 but little reaction with the CA6. The reaction layers formed at the interface between the couples were found to consist of CA2, CA6, corundum, plagioclase and melilite. The formation of a layer with these phases is likely to cause refractory wear due to reduced mechanical strength at highest operating temperatures and by spalling induced by volume changes and changes in thermal expansion characteristics. From assessment of the kinetics of the system it was found that the aluminosilicate refractory followed the linear rate law for reactions with CA and CA2. Given the lack of reaction of the refractory with CA6 little comment can be made on the kinetics other than they are slow.

Effect of Nano Calcium Carbonate on Properties of Corundum-spinel Castables

Abstract: Using sintered corundum as aggregate,white fused corundum powder,fused spinel powder,ultra-fineα-Al2O3,nano calcium carbonate and hydrated alumina as matrix,effects of nano calcium carbonate additions(0.4%,0.8%,1.2%,1.6% and 2.0% in mass,the same hereinafter)on modulus of rupture,thermal shock resistance and slag resistance of corundum-spinel castables after treating at different temperatures were studied.The results show that nano calcium carbonate decomposes at high temperatures and in-situ forms calcium aluminates,which can significantly increase the CMOR and HMOR of the castables after treating at 800-1400℃;adding nano calcium carbonate obviously improves the thermal shock resistance of the castables,and has little influence on the high basicity slag resistance,however,significantly decreases the corrosion and penetration resistance to low basicity slag.

High temperature processes of phase formation in the system «cement «Gorkal-70» — microsilica»

Abstract: The use of microsilica in the refractory concrete on calcium aluminates cement contributes to the formation of an effective structure and physico-mechanical properties of concrete in linings of thermal units. The features of high-temperature processes in the system "calcium aluminates cement – microsilica", and the formation of the crystalline and amorphous phases are determined by the ratio of components, their mineralogical and chemical composition. The article presents the results of studies of the physical and chemical processes occurring during the thermal heating of model mixtures of hydrated compositions "cement« Gorkal-70 " – mcrosilica." Using the differential thermal analysis and X-ray diffraction, we have studied the effect of low quality microsilica on the mechanism of phase formation and established the mineralizing effect of impurities on the formation of the crystalline and amorphous phases. The article shows the possibility of directional control of the synthesis of anorthite and gehlenite by varying the proportion of the components of the system "cement« Gorkal-70 "- microsilica," which affects the formation of a given structure and properties of refractory concrete.

Comparison between measured CaO and Al2O3 normalised to CaO–Al2O3 in top slag, calcium aluminate inclusions and results of theoretical calculations

Abstract: This study sets out to compare the wt-% CaOslag and Al2Oslag3 in the binary system of CaO–Al2O3 that were measured in the top slag before teeming, the CaOincl and Al2Oincl3 in calcium aluminates that were analysed by scanning electron microscopy of the steel samples and the CaOcalc and Al2Ocalc3 that were achieved from theoretical calculations using the total measured elements in the top slag and steel before teeming. The CaOincl and Al2Oincl3 in all of the calcium aluminate inclusions of this study did not have the same ratio; in the opposite, they covered a large range. The average CaOincl and Al2Oincl3 in all samples had nearly similar compositions that were close to the border of the phase Ca12Al14O33 in the binary phase diagram of CaO–Al2O3. The CaOslag and Al2Oslag3 in all samples had almost similar compositions that were close to the border of the phase Ca3Al2O6 in the binary phase diagram of CaO–Al2O3. The results of theoretical calculations were close to the CaOslag and Al2Oslag3, but the...

Molten salt synthesis for manufacture of cement precursors

Abstract: A method of manufacturing calcium silicates, calcium aluminates, calcium aluminosilicates and calcium ferrites and the products thereby derived utilizing molten-salt synthesis and/or molten-salt sintering. Molten-salt synthesis enables efficiently manufacture calcium silicate (Ca—SiO 3 ), dicalcium silicate (Ca 2 SiO 4 ), tricalcium disilicate (Ca 3 Si 2 O 7 ) and related compounds such as calcium aluminate (CaAl 2 O 4 ), Gehlenite (Ca 2 Al 2 —SiO 7 ) and tetracalcium aluminoferrite (Ca 4 Al 2 Fe 2 O O 10 ) at temperatures in the range of about 400-750° C. The composition of the synthesized product(s) can be varied by altering the ratio of the precursor compounds and by changing the molten-salt composition, whether used as a sintering flux or molten bath, resulting in the ability to manufacture calcium silicates and related compounds for a wide variety of uses, but most specifically as precursors to the manufacture of hydraulic cements or for use in hydraulic cements such as Portland cements and calcium aluminate and other cements.

Study on Properties of High Performance Marine Concrete under Seawater Attack

Abstract: Through artificial seawater simulation test this paper analyzed erosion mechanism of concrete corroded by the ions in seawater. High performance marine concrete was successful developed because of mineral admixture and corrosion-resistance additive double adding. The paper researched the durability of concrete containing freeze-thaw cycles and chloride ions diffusion. Modern testing technologies were used such as scanning electron microscopy and differential thermal analysis in the experiment. Research founded that the amount of unstable or metastable matter reduced such as calcium hydroxide and high alkaline calcium aluminates in the marine concrete. There were more compact hydration products created which made the structure stabler and denser. Those were the reasons that the marine concrete had excellent performances in terms of erosion-resistance and durability.

Dry CO2 sorbent made of alkali metal promoted calcium aluminates carbonates

Abstract: A dry material is synthesized by alkali metal (Li, Na and K) promoted calcium aluminates carbonates use as CO2 sorbent at higher than 600 DEG C condition. The key composition of sorbents is determined as 52 to 69% of CaO, which is beneficial to capture CO2 at 400 to 800 DEG C. A breakthrough result is achieved by using this sintering-resistant sorbent, which includes the features of 50% initial carbonation capacity and 20 folds CO2 capturing performance maintained after 40 to 60 hour tests. Besides, alkali bearing material provides rapidly kinetic in CO2 capture-and releasing cycles, for example using of Li and K series sorbent, 40 hours is only need for 40 cycles.

The Oxide Composition with a Controlled Expansion of Cement

Abstract: Great scientific interest and practical importance are expanding non-shrink and bend the cement. They are characterized by a uniform, which occurs early in life extension, which compensates for their subsequent shrinkage, which addresses one of the challenges in the field of cement-prevention of negative shrinkage deformation. Expanding most famous cement is due to the formation of calcium hydrosulfoalyuminata. Temperature range expanding cements containing in its composition and gypsum calcium aluminates is within 20-80°C. As an expanding additive may be used oxides of calcium and magnesium for expanding cements. However, their use may be effective if the calcium and magnesium oxides are burned at low temperatures. Such materials react rapidly with water to form hydrates, the volume of which is 2 times more than the amount of starting materials, which, according to the authors and causes the expansion of the cement stone. Getting the emerging and non-shrink cement magnesium oxide and calcium has not received wide acceptance due to the lower scrutiny of the conditions for obtaining MgO and CaO, hydration which, under certain conditions, leads to the expansion of cement. Expanding plugging materials are increasingly used in the construction of wells.

High Temperature CO2 Capture by Regenerable Calcium Aluminates Carbonates Sorbents

Abstract: The calcium aluminates carbonates are prepared as mediumhigh temperature CO2 sorbents The sorbent exhibited excellent performance with 53 wt% capacity and 99% stability in TGA test for 15 h However, using the sorbent in a fixed-bed reactor, it was found that the stability rapidly decreased to about 35% after 10 cycles Hence, development of regeneration methods for reusing this spent sorbents is critical to economic consideration toward CO2 capture technology The calcium aluminates carbonates sorbent makes up layered structure including cations formation (Ca2+, Al3+) and lamella anions (CO32-, OH), which can be re-constructed under aqueous conditions Aqueous hydrolysis provides an efficient route to reactive sorbent The results showed that CO2 capacity could be recovered to around 50 wt% with 98% stability in TGA test for 15 h for spent sorbents The reactive mechanism of sorbent is worthy to further discussing

Hydraulic composition, mortar and concrete

Abstract: PROBLEM TO BE SOLVED: To provide mortar and concrete excellent in a fast curing property or work efficiency of waterproofing work or the like, and having high bending strength, bending toughness or the like even if a steel fiber is not used, and to provide a hydraulic composition used therefor.SOLUTION: This hydraulic composition to be provided includes following components (A)-(F): (A) a fast curing admixture containing at least one kind or more inorganic salts selected from alkali metal carbonates, alkali metal sulfates, alkaline earth metal carbonates and alkaline earth metal sulfates, and also containing calcium aluminates, (B) portland cement, (C) a setting modifier, (D) a water reducing agent, (E) a mixture of an aramid fiber and a vinylon fiber, and (F) water.

Study of CaO·2Al 2 O 3 formation by polymeric precursor method

Abstract: The use of unconventional synthesis methods in the formation of CaO·2Al2O3 (CA2) is justified because it reduces the formation temperature of the compound CA2 is formed by classical method at temperatures above 1,400 °C The polymeric precursor method allows a significant temperature decrease in CA2 synthesis reaching temperatures of 1,000 °C This paper deals with CA2 synthesis by “citrate” method which is often presented as Pechini method, starting from a mixture of citric acid, ethylene glycol and calcium, and aluminum nitrates A method based on the formation of a polymeric precursor was also used, starting from a mixture of acrylic acid and nitrates of calcium and aluminum The results showed a net difference in favor of samples obtained from acrylic acid, which by annealing at 800 °C for 1 h, contain pure CA2 The samples obtained from citric acid, after annealing at 800 °C are amorphous After annealing at 900 °C in all samples CA2 is single phase