What is free calcium oxide?

1. Light burning free calcium oxide

Instability or collapse due to the material quantity, out of the kiln skin, changes in fuel composition or flame or bad shape, so that part of, or even partially calcined raw material temperature is less than in the 1100 ~ 1200 ℃ low temperature of formation of free calcium oxide. Mainly in gluten and raw material powder wrapped sandwich clinker, cement stability harm they is not, but make clinker strength.

2. Once free calcium oxide (CAS NO: 1305-78-8)

They are in the ingredients calcium oxide component is too high, too thick or calcined raw material is poor, not present in the clinker with SiO2, Al2O3, Fe2O3 chemical reaction CaO. These CaO after calcination was "dead-burned state" compact structure, large crystals (10 ~ 20μm), the formation of water is very slow, usually takes three days to react significantly to the hardened cement solid phase took place after volume expansion (97.9% ), formed within the cement local expansion stress, to collapse deformation or cracking.

3. Secondary free calcium oxide

When firing the clinker cooler just slow or reducing atmosphere, C3S decomposition has become calcium oxide and C2S, or clinker alkali replace the C3S, C3A calcium oxide. Because they are freed again, and it is called secondary free calcium oxide, calcium oxide hydration slower kind of cement strength, stability has a certain influence.

4. Low free calcium oxide has the following negative:

In people attach great importance to the harmful effects of free calcium oxide is high, it is necessary to understand the disadvantages of free calcium oxide is too low:

⑴ the free calcium oxide is less than 0.5%, the clinker burning condition was too often, even a dead-burned. At this point the lack of activity of clinker quality, strength is not high.

⑵ the kiln bricks withstand high thermal loads and shorten its life.

⑶ To fully understand not only the free calcium oxide semi-quality indicators, it is an important relationship between the cost of cement production and economic indicators. Abroad, the information reported (ICR, 8/1989, P55): 0.1% lower clinker per free calcium oxide per kg of clinker heat consumption will increase 58.5 kJ (14 kcal); but with such a clinker grinding cement, cement mill system power consumption will increase by 0.5%, especially when the free calcium oxide content is less than 0.5% or less.

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