The performance and chemical composition of refractory cement are introduced

Refractory cement often refers to the main component of calcium aluminate cement.Refractory cement is the basic binder of amorphous refractories, especially castable refractories.Its chemical composition is mainly Al2O3 and CaO, and some contain quite a lot of Fe2O3 and SiO2.The mineral composition consists of the following five minerals: calcium aluminate CaO·Al2O3 (CA), calcium dialuminate CaO·2Al2O3 (CA2), 12 calcium heptanoaluminate 12CaO·7Al2O3 (C12A7), calcium xanthoclase 2CaO·Al2O3·SiO2 (C2AS) containing inclusions, and calcium ferroaluminate 4CaO·Al2O3·Fe2O3 (C4AF).They are usually divided into three groups according to their chemical mineral composition.

The properties of refractory cement mainly depend on its mineral composition.Calcium aluminate (CA), the main mineral composition of refractory cement, has very high hydraulic activity. Although it does not set very fast, it hardens quickly (the hardening time is not more than one day). It is the main source of the strength of high alumina cement, especially the early strength.Calcium disaluminate (CA2) hydrates and hardens slowly, with lower early strength and higher later strength.Dodecalcium heptanoaluminate (C12A7) has the properties of rapid hydration and rapid coagulation, but the strength is not high.In ordinary high alumina cement containing inclusions (C2AS, C4AF), C4AS plays the role of hardening the cement as soon as possible, while in high alumina cement, C12A7 plays the role of hardening.As for C2AS, they basically don't hydrate, so they don't show strength.

Refractory cement contains 5 calcium aluminate minerals, all of which exhibit intense heating during hydration.Ordinary high alumina cement (53-55% Al2O3) reaches its peak temperature at 5-8h thick, as high as 80-90oc.The high alumina cement with 70%Al2O3 reaches its peak temperature at 10-12h and 80%Al2O3 at 8-10h, respectively at 80 oC and 70 oC.

The heating temperature and the time to reach the maximum temperature of the single castable of different kinds of high alumina cement are determined by the heating characteristics and content of the calcium aluminate.

Fast C12A7 and C4AF have high calorific value.Therefore, the calorific value of high alumina cement will also change with the different aluminate.If too much high alumina cement (C12A7 or C4AF) is added into the casting refractory, the concentrated heat will cause the water in the hardening body of the castable to evaporate fiercely, resulting in cracks and surface peeling.Therefore, it is very important to choose the quantity and quality of cement.

Refractory cement is a kind of binding agent (permanent binding agent) which can be used at room temperature and high temperature.The effect of its fire resistance on amorphous refractories is very important.Generally speaking, the higher the content of Fe2O3 in cement, the lower its fire resistance.The types and contents of calcium aluminate affect the fire resistance of cement.Practice shows that ordinary high alumina cement is used at less than 1300 oC, high alumina cement is used at less than 1500oC, and low calcium high alumina cement (high alumina cement) is used at more than 1600 oC.