The Chemistry of Cement

Cement, the binder used to hold objects together, most commonly used in concrete and mortar.  The chemistry of cement can be thought of as a deconstruction of a chemical, only to reconstruct the same chemical, but in a different shape. This molecule that we will be looking at is Calcium Carbonate, a component of seashells, and limestone. To start the process of creating cement, the CaCO₃ must be broken down into Calcium oxide through heating it at 825°C, in a process called lime calcination, possessing the equation CaCO₃ → CaO + CO₂. This Calcium oxide exists in a light powdery form, capable of being transported easily to wherever needs to be cemented. Once the cement is ready to be made, the CaO is mixed with water to produce Calcium Hydroxide, Ca(OH)₂, in the equation CaO + H₂O → Ca(OH)₂. This watery paste is ready to be placed into the mould to set. In the setting process, the Calcium Hydroxide returns to it's original state of Calcium Carbonate, through a slow process of combining with the carbon dioxide within the air in the chemical equation Ca(OH)₂ + CO₂ → CaCO₃ + H₂O.

Egyptian Blue: Calcium Copper Silicate

In a recent article by Scientific American, a story is told of Calcium Copper Silicate (Egyptian Blue) being the first artificial pigment made by humans, and soon to be utilized, once again, as a nano ink for biomedical imaging.  I'm not going to go over the details of the article, but I will present some background information of this soft blue colour.

Being the first recorded synthetic pigment, you may ask how it was originally synthesized.  The first procedures, in 3000 B.C., involves the heating of sand, calcium carbonate, copper, and an alkali substance to obtain this blue pigment having a composition of CaCuSi₄O₁₀.  The reaction below is a general understanding of the reaction, where the molecules can be variable in a number of different ways.

Cu₂CO₃(OH)₂ + 8SiO₂ + 2CaCO₃ → 2CaCuSi₄O₁₀ + 3CO₂ + H₂O

The blue colour comes from the absorption of the copper, which can range from the blue, seen above, to a much darker blue, depending on how pure the mixture is. But what wasn't known at that time, was that when irradiated with visible light, the compound emits IR photons, which is the property that will conduct the imaging technologies.

References:
Via: Scientific American
Wikipedia