Formation Kinetics of Calcium Aluminates

Abstract

The kinetics of formation of calcium aluminates was studied by firing the reaction mixes in the temperature range 1200" to 1460°C for reaction times from 15 to 360 min. Phases formed were determined by taking X-ray diffractograms of the samples. It was observed that all stable calcium aluminates were formed and that monocalcium aluminate (CA) grew with calcium dialuminate (CA,) in a 1:2 reaction mix of CaO and A1203. CA reacted further with AIz03 to form CA,. The formation of CA, obeyed the rate law equation 1 -(1 -x)ln = Kt/rZ. The activation energy for the system (140 kJ-mol-' (33.4 kcal-mol-')) was determined by the Arrhenius equation. [

Electronic band structure and carrier effective mass in calcium aluminates

“…Calcium aluminates (also known as high alumina cements) have a rich phase diagram which includes five lime-alumina compounds -3CA, 12C7A, CA, C2A and C6A [13,14,15,16,17,18,19,20,21,22,23]. Among them, 12C7A has the lowest melting point (1722…”

Synthesis of CaAl4O7 via citric acid precursor

“…MacKenzie et al [23] synthesized CaAl 4 O 7 by the mixed metal citrate method and single phase CaAl 4 O 7 was obtained on prolonged heating at 1400 • C. Therefore, the formation temperature (800 • C) of pure CaAl 4 O 7 via citrate precursor is so far the lowest processing temperature for this compound. By solid-state reaction method, phase pure CaAl 4 O 7 was obtained at 1560 • C [6,7]. The citrate precursor technique can lower the crystallization temperature of CaAl 4 O 7 by 760 • C. The formation of CaAl 4 O 7 at low temperature through the chemical route can be attributed to the homogeneous distribution of cations throughout the liquid phase and, afterward, in the formation of metal oxide clusters imbedded in organic mesoporous carbonaceous material although CaCO 3 and ␥-Al 2 O 3 appear as intermediate phases.…”

“…Conventionally, CaAl 4 O 7 is produced by solid-state reactions between calcia (CaO), or calcium carbonate (CaCO 3 ) and alumina (Al 2 O 3 ) powders at temperatures in excess of 1400 • C [6,7]. When the starting mix of CaCO 3 [6,7].…”

Preparation of refractory calcium aluminate cement using the sonochemical process

“…With an increasing temperature or over time, this phase reacts with the availablecalcium oxide contents are formed initially. As the reaction time progresses or the temperature increases, these phases are converted into the target phase, which in this case is the calcium aluminate, CA 8,9 . Alternative methods of synthesis have become an increasing target of research aimed at preparing calcium aluminates at lower temperatures than those used in conventional processes.…”