Anti-corrosive pigments and method for making the same

#The present invention relates to compositions of anti-corrosive pigments and to a method for making the same. More specifically, the present invention relates to heavy metal free anti-corrosive pigments and to a method for making the same.

#Anti-corrosive pigments are used to protect metal surfaces against oxidation and corrosion. Those pigments usually include heavy metals salts, which hinder the rusting of the metal surface by either cathodic or anodic inhibition mechanisms. Upon dissolving in the aqueous phase, commercial available anti-corrosive pigments partially dissolved to provide hydrated metal cation and hydrated anion solutions, which reacts with the metallic surface. The reaction between the partially solubilized pigments provides the desired inhibition of corrosion.

#Zinc compounds such as zinc phosphate and zinc chromate are currently widely used as anti-corrosive pigments. Zinc is a heavy metal element and is considered to be toxic at certain concentrations.

#The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

#FIG. 1 presents the molar ratio of Mg+2/phosphate as a function of the number of equilibrating steps of a tri-magnesium diphosphate octahydrate product. The small graph presents a fine scale of the above graph.

#FIG. 2 presents the Mg+2/phosphate molar ratio as a function of the number of equilibrating steps of magnesium phosphate salt in access of 50% magnesium oxide.

#In the following description, various aspects of the invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details presented herein. Furthermore, well known features may be omitted or simplified in order not to obscure the present invention.

#Embodiments of the invention relate to a heavy metal free anti-corrosive pigment and a method for producing such anti-corrosive pigment, for inhibiting corrosion of metallic surfaces. Corrosion is defined herein as a process that seeks to reduce the binding energy in metals and to all practical appearances of said process. Metallic or metal is defined herein as any substance able to be subjected to corrosion including, for example, magnesium and calcium. Molar ratio defined herein as the ratio between total metal to anion of the pigment. This ratio is measured by dissolving to equilibrium 10 grams of the dried pigment in 100 ml distilled water at 25° C. and than measuring the quantities of the total metal and anion in the water. Total metal means the total metal in the pigment, i.e., the metal in the salt and in the oxide. The pH of the pigment is measured by suspending 10 gram of pigment in 100 ml distilled water and measures the pH of the suspension.

#In some embodiment of the invention an anti corrosive pigment is produced. The anti corrosive pigment includes a composition of metal having at least one oxygen atom such as metal oxide or metal hydroxide and metal salt where the composition is at least partially soluble in a liquid phase. The metal having at least one oxygen atom includes at least one metal cation and one oxygen or hydroxyl, respectively. The metal salt includes at least one metal cation and at least one anion. The molar ratio of the total metal to the anion is in the range of 1:4 to 1:120.