Silicate Paint
History
Silicate based coating materials can be traced back to 6th millennium BC. Some objects with silicate based coatings belonging to the pharaonic ages were found in excavations. Guesses are that sand and wood ash used to be molten together to obtain silicate. The use of such coatings was also widespread during the medieval era. By the end of the medieval era, the use of silicate based coatings surprisingly came to an end.
The use of silicate based coatings had a restart at the 19th century. The paints produced at those times reached the present days without discoloration. It was observed that churches, municipality buildings, hotels, hospitals, and university buildings that were coated at those years did not have their coatings split off, did have the coatings chemically bonded with the mortar, and the colors did not fade. By the 1970s, the importance of silicate based coatings was on the rise again. In the present days, the production of silicate based coatings constitutes 10 – 15 % of the total production in Europe.
Reactions
The primary raw material used in the production of silicate paints is potassium silicate. It is obtained by melting potassium carbonate and silicon dioxide at 1100°C. It is possible to obtain silicates with varying properties depending on the amounts of the ingredient materials. Such properties are identified by a modulus number.
Modulus: ratio of the amounts of silicon dioxide to potassium oxide.
Potassium silicate is used in the production of silicate paints worldwide. This has two reasons:
· Potassium silicate with a high modulus has a high solubility in water.
· Easily creates polymers with the carbon dioxide in air.
Sodium silicate with a modulus of 3.25 dissolves in vapor under pressure only, and instead of polymerizing, it carbonizes with CO2, and creates a layer of dust on the surface. Thus, it is impossible to create silicate paints with the classical method.
Production
According to my literature studies and to the sources on the
Internet, there is no commercial production of silicate paints in the
world. That’s because entire work is targeted on potassium silicate coatings. I
directed my studies toward sodium silicate because of the high cost of
potassium silicate. I exploited the pozzolanic reaction which occurs with the
reaction of slaked lime, silica, and water, and produces calcium silicate hydrate
(
). This is the reaction of the
Portland cement.
I initially worked on sodium silicate with a modulus of 3.25. I added sodium silicate with a modulus of 3.25 together with SiO2 dispersion and calcite. Calcite becomes calcium bicarbonate which partially dissolves in water by the help of the carbon dioxide in the air, when the paint is applied on a surface. This calcium bicarbonate becomes calcium hydroxide in alkaline environments. Calcium hydroxide reacts with silica dispersion, sodium silicate, and water, and produces calcium silicate hydrate.
The calcium silicate hydrate formed through these reactions is enlarged by polymerization. This reaction completes in 28 days, just like cement mortar.
In my proceeding studies, I employed sodium silicates with modules of 2.8, 2.5, and 2, and I produced silicate paints. I concluded that the modulus number does not have any importance in the production of silicate paints produced by silica dispersion.
While the modulus must be at least 3.25 for classical potassium silicate paints, the modulus number does not have any importance in the production of silicate paints produced by silica dispersion. It is possible to produce silicate paints using silica dispersion with any modulus.
Silicate paint is a single-component, inorganic paint used for coating mural surfaces. Silicate paints do not adhere to metals other than aluminate and zinc. Silicate paints bind chemically with aluminum and zinc, but not with other metals. Silicate paints adhere to the surfaces comprising calcium by creating chemical bonds. Silicate paints bind to the micro-crystals and fuses into the surface, hence no split off.