CS251979B1 - A method of inhibiting the blin reaction with an aqueous alkali hydroxide solution - Google Patents

Abstract

The inhibition method is based on the addition of 2-mercaptobenzothiazole to an alkali hydroxide solution at a concentration of 10”3 — 10”* 1 mol. I-1. Inhibition is effective even in the most aggressive alkali hydroxide solution with a concentration of 5.0 mol. 1_1 and at elevated temperatures.

Description

The invention relates to a method of inhibiting the reaction of aluminum with an aqueous solution of an alkaline hydroxide.

The solutions known to date for inhibiting the aluminum reaction in an alkaline medium make it possible to inhibit this reaction more effectively at low concentrations of alkaline hydroxide, as a rule, to a concentration of 0.6 mol. I ^-1 . However, even under these conditions, the inhibitory effect does not exceed a 90% reduction in the reaction rate versus the rate without the use of an inhibitor. Known inhibitors include sulphite liquors, agar-agar, dextrin, gelatin, ethylsilane derivatives, and some others. Podía čs. pat. 131 475 in a strong alkaline environment is an efficient procedure using a three-component inhibitor based on calcium saccharate, sodium sulfate and milk casein. The essence of its action is to form an insoluble calcium aluminate film on the aluminum surface with a suitable adhesion and structure modified with sodium sulfate and milk casein.

The method of inhibiting the reaction of aluminum with an aqueous alkaline hydroxide solution according to the invention consists in adding 2-mercaptobenzothiazole to the alkaline hydroxide solution in a concentration of 10 ^-3 - 10 ^-1 mol. ^-1 . In terms of both economic and technical effects, a concentration of 5.10 ^-3 mol. í ^-1 - 5. . 10 ^-2 mol. I ' ¹ . The effect is increased by adding a soluble calcium or barium salt with a concentration of 1.10 ^-3 - 5.10 ~ ² mol. I ^{-1, for} example, in chloride form.

The main advantage of the process according to the invention is the effective inhibition of the reaction of aluminum with alkaline hydroxides by adding an available single or two-component inhibitor directly to the alkaline hydroxide solution. The inhibitor concentration is low compared to known inhibitors and effective at any concentration of alkaline hydroxide, including the most aggressive 5 mol concentration. I ^-1 . Other advantages include a slight temperature dependence of the inhibitory effect, which allows the process to be used at elevated temperatures up to 80 ° C or higher.

EXAMPLE

The technical aluminum according to ČSN 424 005 on the exposed side was regrinded and polished to a roughness of 0.1 μπι and was exposed to NaOH at a concentration of 5 mol.l ^-1 in the presence of 2-mercaptobenzothiazole at a concentration of 10 ^-2 mol. I ^-1 and BaCl2 at a concentration of 0.8.10 ^-2 mol. I ^-1 . While stirring the hydroxide solution with the inhibitor at 700 rpm. min ^-1 and a temperature of 25 ° C, the reaction rate decreased by 95% over the rate without the use of inhibitor.

Example 2

Industrial aluminum as in Example 1 was exposed to a 1.0 mole NaOH solution. ^-1 I, under conditions as in Example 1. The reaction was quenched substantially in the decrease of 99.9%.

Example 3

Technical aluminum as in Example 1 was exposed to a 1.0 mol NaOH solution. ^-1 I, under conditions as in Example 1 at 55 ° C and the concentration of 2-mercaptobenzothiazole 5.10 ^-2 mol. I ^-1 . The reaction rate decreased by 90%.

Claims (1)

SUBJECT OF A METHOD FOR INHIBITING AN ALUMINUM REACTION WITH Aqueous Alkali Hydroxide Solution, characterized in that 2-mercaptobenzothiazole at a concentration of 10-3 mol is added to the alkali hydroxide solution. I-1 to 10 mol. I "1 is preferably 5.10-3 - 5.10 - 2 mol I-1 and soluble salt of Ba 2+ or Ca 2+ at a concentration of 0 to 10" 1 mol. I '1, preferably at a concentration of 5.10-3.5-10-mol mol-1.