Calcium carbonate (CaCo3) is the primary constituent of scale in
water systems. Calcium and carbonate ions enter the water as parts of other molecules that
are dissolved in the water. The ions join to form calcium carbonate when they precipitate
out of solution at the surfaces of the equipment.
The calcium and carbonate ions are "hydrated" when they
are dissolved in the water. This means the ions are surrounded by water molecules that are
attracted to the ions by the electrical charge. When ionic compounds such as salt (sodium
chloride) or calcium carbonate enter water, the polar water molecules seek to hydrate the
ions from the molecules, because the electrostatic attraction potential of the water
molecules is very high. The water molecules greatly reduce the attraction of the ions in
the ionic compound molecules, so that the ions only interact weakly with each other and do
not aggregate into crystals.
A substance will dissolve only if the attractions between its ionic
charge centers, and the water molecules are sufficient to overcome the attractions between
its own ionic charge centers. As water dissolves a substance, water molecules will
surround the ions and form electrostatic bonds with the dissolving ions. As these bonds
between water molecules and dissolving ions form, energy is released (known as the heat of
hydration). When this hydration heat becomes larger than the bonding energy between the
ions on the dissolving substance, the ion will dissolve into the water solution.
Heats of hydration are typically much smaller than the bonding
energy between the positive and negative ions of an ionic compound. Therefore, each ion of
a solid unit must be surrounded by many water molecules before it can be solvated. In
other words, large aggregates of water tied up with hydrogen bonds cannot effectively
dissolve solutes, whereas separate water molecules can.
The main culprit in most scale problems is the super-saturated
solution. There is so much scale-causing mineral in the solution that ions are only
partially hydrated. The scale-causing minerals such as calcium and magnesium ions are
unstable and "barely hanging in water" in a super saturated solution. If the
scale-causing minerals are left untreated and conditions such as pH, temperature, and
pressure change in a fluid system, the solubility of scale-causing minerals may decrease.
(In cooling towers, condensers, boilers, and other equipment, changes in temperature are
integral parts of their operation.)
The electrostatic attraction between the dissolved mineral ions and
metal surface area charge makes these minerals stick to the surfaces. This is why the
scales are unavoidable without some active scale prevention measures.
The induced molecular agitation in the Triangular Wave electronic
deposit control system causes the unstable mineral ions to collide with each other and
precipitate. Impurities in the water such as alumina or silica provide initial nucleation
sites for further precipitation of adjacent mineral ions.
A snow ball effect starts, resulting in the growth of many crystals,
each consisting of numerous mineral ions. This enables crystal salts to become large in
size and float with water; thus they do not stick to the metal surfaces, because the
crystals do not have the charges at the surface anymore.
As the byproduct of the above mentioned precipitation and snowball
effect of mineral particles, freed water molecules become available to dissolve existing