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Calcium aluminates
About: Calcium aluminates is a research topic. Over the lifetime, 490 publications have been published within this topic receiving 9200 citations.
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01 Dec 2016
TL;DR: In this article, the influence of impurities such as SiO2 and F2O3 on the hydration behavior of calcium aluminate cement (CAC) was studied.
Abstract: The influence of impurities such as SiO2 and F2O3 on the hydration behavior of calcium aluminate cement (CAC) was studied in this work. The hydration of the cement was characterized by the exothermic profile of cement pastes, and the dissolution-precipitation rate of the cement aqueous suspension was evaluated by electrical conductivity measurement. In order to analyze the resulting hydration products, the cement hydration was terminated via the freeze-vacuum drying method at the designated times. Then the phase development and microstructure evolution during cement hydration were investigated by XRD and SEM, respectively. The results indicate that the hydration rate is faster when the cement contains a higher amount of impurities. It is proposed that the higher hydration rate of the cement is probably related to the lattice imperfection of the main calcium aluminates in CAC.
1 citations
01 Jan 2013
TL;DR: In this article, the authors used oxides of calcium and magnesium oxides for expanding cements to prevent negative shrinkage deformation of the cement. But, their use may not be effective if the oxides are burned at low temperatures.
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.
1 citations
01 Jan 1978
TL;DR: In this paper, a kinetic study has been performed of the apparent solid solid reaction between CaS and CaSO/sub 4/ with a rotary kiln reactor, and the experimental conditions were within the range for regeneration of lime-based sorbents for fluidized-bed combustion.
Abstract: Thermodynamic calculations showed that all the calcium silicates are capable of sorption of SO/sub 2/ from coal combustion gases to meet the standard of 0.2 lb S/10/sup 6/ Btu at below 900/sup 0/C. Temperature limits for the di- and tricalcium silicates are higher than 900/sup 0/C. The silicates are thermodynamically more regenerative from their sulfated states than CaO. Kinetic studies were performed on sulfation and regeneration of various calcium silicate samples. Except for two samples, the silicates showed higher overall rates and, more important, higher capacities for sulfation, compared with CaO on a molar basis. The rates of regeneration of the silicates were much higher than that of CaO; more specifically, the rates of thermal decomposition of the sulfated mono- and dicalcium silicates were about 15 times higher than that of the CaSO/sub 4/, which indicated the relative bond strengths between SO/sub 3/ and the sorbents. X-ray diffraction and infrared analyses of the reaction products are discussed. Rates of sulfation and regeneration were measured for SiO/sub 2/-supported CaO. CaO was precipitated on a high surface area granular SiO/sub 2/ from aqueous solutions of calcium salts followed by a heat treatment. Compared with the Al/sub 2/O/sub 3/-supported CaO, which were actuallymore » calcium aluminates on the surface of Al/sub 2/O/sub 3/, the sulfation rates were about the same, but the regeneration rates were definitely higher for the SiO/sub 2/-supported sample. A kinetic study has been performed of the apparent solid--solid reaction between CaS and CaSO/sub 4/ with a rotary kiln reactor. The experimental conditions were within the range for regeneration of the lime-based sorbents for fluidized-bed combustion. The kinetic parameters of the chemical reaction extracted from the data compared favorably with those obtained directly and independently with a fixed-bed thermogravimetric reactor. Promising results were obtained on the utilization of coal ash as a binder for the fine-sized sorbents.« less
1 citations
Patent•
09 Jan 1991
TL;DR: Water-resistant hydraulic binder based on a mixture of calcium sulphate and of a cement composition containing calcium aluminates was proposed in this article, which is capable, when it sets, of inhibiting the formation of hydrated calcite at the expense of the crystallisation of ettringite in tabular form.
Abstract: Water-resistant hydraulic binder based on a mixture of calcium sulphate and of a cement composition containing calcium aluminates. The said binder contains, in effective quantity, additives capable, when it sets, of inhibiting the formation of hydrated calcium aluminates at the expense of the crystallisation of ettringite in tabular form.
1 citations
TL;DR: In this article, the calcium aluminates carbonates are prepared as medium-high temperature CO2 sorbents, and the results showed that CO2 capacity could be recovered to around 50 wt% with 98% stability in TGA test for 15 h for spent sorbent.
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