Abstract:
According to the present invention a saturated aqueous solution comprising at least one alkali metal hydroxide and at least one alkali metal nitrate is provided which can be spray added to a fused anhydrous bath which contains alkali metal materials.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to materials for addition to fused salt baths, and more particularly to materials which are in aqueous solution for addition by spraying to fused, anhydrous salt baths. 
     U.S. Pat. No. 4,113,511 commonly assigned, teaches that aqueous solutions of chemicals can be added to fused non aqueous baths by spraying the aqueous solution of the chemicals over the surface of the bath in droplet size, small enough to allow the water to evaporate before the sprayed composition impinges on the surface. 
     U.S. Pat. No. 4,273,591 teaches an apparatus that is useful in performing such spray addition of chemicals in aqueous solution to a fused anhydrous bath. 
     It has been found, however, that many aqueous solutions of different alkali metal hydroxides and alkali metal nitrates for treating metals, such as for scale conditioning present various types of problems, and hence are less desirable for use in the above process and apparatus. It is therefore highly desirable to provide a balanced, stable aqueous solution of materials which will remain constant, and in solution, and which will spray uniformly and consistently under operating conditions in a commercial environment. This is especially necessary when making aqueous solution additions to fused anhydrous baths containing alkali metal salts. 
     SUMMARY OF THE INVENTION 
     According to the present invention, it has been found that a very good aqueous solution of material for addition to fused anhydrous metal treating baths containing alkali metal nitrate and alkali metal hydroxide is provided by an essentially saturated uniform aqueous solution comprising an alkali metal hydroxide and an alkali metal nitrate, wherein the solution is liquid at 50° C. and has a viscosity sufficiently low to be sprayed through nozzle means to form droplets, and which solution is free of precipitants between 50° C. and 110° C. The bath may contain other materials such as chlorides, permangantes, etc. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It has been found that in practicing the invention as described in the above noted U.S. Pat. No. 4,113,511, for adding alkali metal hydroxide and alkali metal nitrates to fused anhydrous metal treating baths it is extremely desirable to control the addition involved to certain types of aqueous solutions having very definite characteristics. By controlling the characteristics of the additional materials, certain detrimental effects such as unwanted precipitates, nozzle clogging, elimination of detrimental excess water, and composition imbalance can be reduced, or eliminated as well as providing a commercially economical addition system. 
     It has been found that when dealing with the alkali metal hydroxide alkali metal nitrate system, it is most advantageous to utilize a saturated aqueous solution of the alkali metal nitrate and the alkali metal hydroxide. The solution must be of sufficiently low viscosity to be sprayed through a nozzle to form droplets, and be liquid at 50° C. 
     It must also be free of precipitates between 50° C. and 110° C. As used herein the term &#34;essentially saturated solution&#34; means that the least soluble material or materials at the desired level of materials relative to each other be in essentially saturation amounts in the water, the remaining materials being in less than saturation amount. To determine this, the desired anhydrous balance of materials (including water of hydration) is first determined. When this has been determined just enough water is added to provide complete dissolution of the least soluble component, and to insure that the composition is liquid at 50° C., and the material has a low enough viscosity to be sprayed to form droplets, and is free of precipitates between 50° C. and 110° C. 
     Listed below are several examples of aqueous solutions including alkali metal hydroxide and alkali metal nitrates, as well as chlorides and permanganates in some examples. 
    
    
     EXAMPLE I 
     
         ______________________________________55%            WATER15%            SODIUM NITRATE30%            SODIUM HYDROXIDE100%______________________________________ 
    
     EXAMPLE II 
     
         ______________________________________53.6%         WATER30.0%         SODIUM HYDROXIDE15.0%         SODIUM NITRATE 1.4%         POTASSIUM HYDROXIDE*100.0%______________________________________ 
    
     EXAMPLE III 
     
         ______________________________________ 57%          WATER30.0%         SODIUM HYDROXIDE3.6%          POTASSIUM HYDROXIDE*6.4%          SODIUM NITRATE3.0%          SODIUM CHLORIDE100.0%______________________________________ 
    
     EXAMPLE IV 
     
         ______________________________________60.0%       WATER31.4%       POTASSIUM HYDROXIDE* 8.4%       SODIUM NITRATE 0.2%       POTASSIUM PERMANGANATE100.0%______________________________________ 
    
     EXAMPLE V 
     
         ______________________________________55.0%           WATER21.6%           SODIUM HYDROXIDE21.2%           SODIUM NITRATE 2.2%           SODIUM CHLORIDE100.0%______________________________________ 
    
     EXAMPLE VI 
     
         ______________________________________55.0%         WATER27.6%         SODIUM HYDROXIDE13.0%         SODIUM NITRATE 1.4%         POTASSIUM HYDROXIDE* 3.0%         SODIUM CHLORIDE100.0%______________________________________ *Based on commercial grade of KOH at about 85% purity. 
    
     The saturation of the various materials is as follows: 
     EXAMPLE I 
     Sodium Nitrate saturated in the presence of caustic soda. 
     EXAMPLE II 
     Sodium Nitrate saturated in the presence of that much Hydroxide. 
     EXAMPLE III 
     Sodium Nitrate and Sodium Chloride saturated in the presence of that much Sodium and Potassium Hydroxide. 
     EXAMPLE IV 
     Nitrate (NO 3   - ) saturated in the presence of that much Potassium Hydroxide. 
     EXAMPLE V 
     Sodium Chloride and Sodium Nitrate saturated in the presence of Sodium Hydroxide. 
     EXAMPLE VI 
     Nitrate (NO 3   - ) and Chloride (Cl - ) saturated in the presence of that much Sodium and Potassium Hydroxide. 
     It should be noted that in aqueous solution the various materials are ionized and the saturation is determined by the concentration at which these ions form a reaction product which will precipitate. 
     All of the solutions in the above noted examples can be easily sprayed through a nozzle having an equivalent orifice diameter of 0.018&#34; without clogging, at 50° C.