What is SACI?
Patented over 30 years ago, thixotropic overbased calcium sulfonate corrosion inhibitors are widely used in industry to protect metal surfaces from corrosion. Stoney Creek Technologies, LLC markets these muli-functional materials under the name SACI®, which stands for
Severe Atmospheric Corrosion Inhibitor.
Since they contain neither lead nor barium, SACI brand products are often used to replace toxic corrosion inhibitors. These multi-functional compounds allow the formulation of materials with exceptional resistance to sag, run-off, and flow even at high film buildup and elevated temperatures. They are useful in coating formulations as antisettling and pigment dispersing agents, and as rheological modifiers to stabilize viscosity and modify sag resistance to meet the requirements of specific applications.
The Chemistry of SACI
The basic structure of SACI is illustrated below. Key elements of this structure are the alkyl group "R" and the aromatic ring with the SO3 group attached. The aromatic ring and SO3 are highly polar and account for the exceptional metal wetting properties of SACI. The alkyl group is a nonpolar and mostly aliphatic chain mixture. It has good compatibility with hydrophobic film forming materials, including waxes and resins, etc.
The Calcium carbonate portion of the SACI structure adds several properties, including reserve alkalinity and thixotropy. The alkaline nature of SACI allows it to react with several formulating ingredients such as oxidized waxes and petrolatums. The carbonate also functions to buffer pH at the coating/ metal interface, thus inhibiting corrosion.
The Calcium carbonate portion of SACI is in the form of small hexagonal platelets which are formed in the product via a carefully controlled chemical process. These platelets perform several functions, including adding mechanical integrity to the film, increasing the path length for corrosives and imparting thixotropy. The illustration below shows how the presence of millions of these platelets increase the distance water and oxygen must travel to reach the substrate, resulting in improved corrosion resistance.
One of the most important functions of SACI's platelet structure is causing thixotropy or non-Newtonian flow characteristics. When most SACI's are subjected to shear from mixing, pumping or spraying, the viscosity drops dramatically. When the shearing stops, the viscosity rapidly returns to its previous level. From a practical point of view, coatings formulated with SACI can be spray applied to very high film thickness with no danger of sagging or dripping.
The illustration below shows how the non-polar portion of the Calcium sulfonate molecule interacts with the platelets to impart thixotropy to SACI products.
Notice that not all sulfonate molecules are associated with platelets. The excess sulfonate migrates to the metal surface, providing a strong wetting action, which actually displaces water. The resulting monomolecular film of sulfonate provides protection to the metal surface even when the film above it is damaged or partially removed.
This effect is illustrated by accelerated and natural weathering tests which demonstrate very little undercutting of films which are scribed to bare metal. Conventional coatings which rely upon barrier properties for protection often fail dramatically when the film is damaged and then subjected to soluble salts from acid rain or road deicing salt. SACI based coatings perform particularly well under these circumstances.
SACI Base Products
Semi formulated SACI Products
Highly formulated SACI Products
Water borne additive SACI Products
Solvent Free SACI Products
Structural Steel Coatings SACI Products
For more information on SACI ® and to request our product table Contact Us.
