A Silicate-Tungstate Composite Corrosion Inhibitor

There are a large number of processes in industrial production that require water to cool. With the continuous development of social urbanization and industrial production, water resources are becoming more and more tense. In order to save water, the concentration of the industrial circulating water cooling system is continuously increased, reaching more than 4 times.

As the concentration factor increases, the calcium and magnesium ions in the water increase, causing serious scaling in the circulating water cooling system. To solve this problem, demineralized water circulation cooling systems are increasingly being adopted. However, in a circulating cooling system using demineralized water, the calcium and magnesium ions in the water are very low and cannot form scale. Since there is no protection of the scale layer, the dissolved oxygen in the water is directly in contact with the metal, and the corrosion of the pipeline is very serious. Therefore, in the demineralized water circulation cooling system, an effective corrosion inhibitor must be added to ensure that the cooling equipment and piping are not corroded.

Corrosion inhibitors that can be used in demineralized water circulation cooling systems are chromate corrosion inhibitors, molybdate corrosion inhibitors, silicate corrosion inhibitors, and nitrite corrosion inhibitors. The chromate corrosion inhibitor has excellent corrosion inhibition effect but is toxic. Molybdate corrosion inhibitors are less toxic but costly. The silicate corrosion inhibitor has no toxicity, but has high requirements on water quality, and insufficient metering is liable to cause pitting corrosion, which may cause silicon scale. In order to solve these problems, the researchers developed a new type of silicate-tungstate composite corrosion inhibitor, which has low silicate content and avoids the formation of silicon scale. It is suitable for demineralized water circulation cooling system. It effectively prevents corrosion of the demineralized water circulation cooling system. The technical solution adopted is:

The chemical composition of the silicon-tungsten inhibitor used in the demineralized water circulation cooling system is composed of silicate, tungstate, triethanolamine and copper corrosion inhibitor. The weight ratio of each component is: silicate 70-90 %, tungstate 2.5-27%, triethanolamine 2.5-18%, copper corrosion inhibitor 0.5-1.5%. The silicate is sodium silicate, the tungstate is one of sodium tungstate or ammonium tungstate, and the copper corrosion inhibitor is benzotriazole.

After mixing, the three become an oxide film precipitation film mixed type corrosion inhibitor. Oxide film type corrosion inhibitor, also known as passivation film type corrosion inhibitor, can oxidize the metal surface to form a dense corrosion-resistant passivation film to prevent corrosion. Generally, a film of γ-Fe2O3 metal oxide is formed on the surface of the carbon steel by an oxidizing agent in the solution. Due to its presence, the corrosion potential of the metal is changed, and the rate of the corrosion reaction is lowered by the passivation phenomenon.

Test the effect of silicate-tungstate composite corrosion inhibitor: used in cold-rolled open-circuit circulating cooling water system A, which uses demineralized water as system supplement water, after demineralized by biological treatment of municipal sewage treatment plant The medium water is prepared by ultrafiltration plus a reverse osmosis treatment process. The system water supply temperature is 33 ° C, the return water temperature is 38 °C, and the cooling equipment uses a FRP cooling tower.

The rotating coupon corrosion test was carried out. The raw water was de-watered by superfiltration plus first-stage reverse osmosis treatment. The test water temperature was 45 °C, the rotation speed was 145 rpm, the total test time was 163 hours, and the water was replenished about 300 ml every 24 hours. According to the test results, the corrosion rate of carbon steel coupons is 0.0242mm/a, which meets the national standard requirement of less than 0.125mm/a.

The test results show that the newly designed silicate-tungstate composite corrosion inhibitor is suitable for the corrosion inhibition treatment of demineralized water circulation cooling system, and has the characteristics of high efficiency, low dosage, non-toxicity and no pollution.

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