Calcium oxide, surface energy

Following the original measurements of the surface energy of sodium chloride by heats of solution by Lipsett et al. 18), much more accurate determinations have been carried out recently by Benson and his co-workers 19-22). Other substances which have been investigated include magnesium oxide 23), calcium oxide and hydroxide 24), and silica, unhydrated and hydrated 25). 

Some years ago, Kantro, Weise, and I set out to determine the surface energy of tobermorite. We came to grief, because the practice is usually not as simple as the principle. We decided, therefore, to work on some simpler but closely related substances, and we determined the surface energies of calcium oxide, calcium hydroxide, amorphous silica, and hydrous amorphous silica. Even these determinations did not turn out to be simple. We published these in two papers in the Canadian Journal of Chemistry in 1956 (6, 7). After this work, we felt strong enough to tackle tobermorite, and we published the surface energy of tobermorite in the same journal three years later (8). 

A common problem in boilers is the occurrence of calcium oxide build-up on the heating elements. This is not a corrosion problem in itself, because it is caused by a chemical reaction in the water at high temperatures. However, a scale deposit present on a metal surface may cause corrosion under the deposit. This type of underdeposit corrosion can be aggravated when corrosive species such as sulfides and/or chlorides are present in the water. While scale deposits reduce the thermal conductivity of the steel, and thereby increase energy costs, corrosion of the heating element can lead to a catastrophic tubing failure, which requires costly repairs. 

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