Influencing factors of cloud point of galvanizing surfactant

Since its inception, the chloride galvanizing process has been widely used in the electroplating industry at home and abroad for its unique advantages of high brightness, low pollution and high efficiency. At present, although the variety of brighteners is continuously improved, the composition still contains nonionic surfactants. The cloud point of nonionic surfactants is an important factor affecting the quality of brighteners. To this end, the authors studied the cloud point of nonionic surfactants. Several factors affecting the cloud point of nonionic surfactants are discussed below.

1 test

1.1 Methods and instruments

The visual method is used to measure the cloud point of the plating solution. The process is as follows: (1) taking a certain amount of the solution to which the test agent is added, and heating the electric furnace until the solution is turbid; (2) stopping the heating, slowly cooling under stirring, the solution The temperature at the time of clarification is the cloud point; (3) When it is necessary to observe the influence on the plating layer, the plating performance test is performed using a Hull tank device. Test 3 points for each type of data. If the difference is large, retest.

1.2 Basic liquid formula and process conditions

Potassium chloride (plating grade) 220g/L

Zinc chloride (plating grade) 80g/L

Boric acid (plating grade) 30g/L

Benzylidene acetone 0.4g/L

Flat plus 0-15 4.0g/L

pH 5.0

Temperature 25 ° C

Current density 2.0A/dm2

2 Results analysis

2.1 Influence of main salt concentration

The effect of the concentration of the main salt on the cloud point of the nonionic surfactant depends primarily on the concentration of the salt and the valence of the ions. Generally, the higher the concentration of the salt, the lower the cloud point; the higher the ion valence of the constituent salts, the more the cloud point decreases. Table 1 shows the effect of potassium chloride and zinc chloride on the cloud point.

It can be seen from the test results that as the potassium chloride content increases, the cloud point of the plating solution decreases significantly, which is in accordance with the general rule, but the effect of zinc chloride on the cloud point is abnormal. The test results show that the zinc chloride content has almost no effect on the cloud point, which is far from the general theoretical rule (using distilled water, pipettes, volumetric flasks and other precise weighing means, repeated verification, the results are the same) ). The real cause of this abnormal result needs further study.

2.2 Relationship with the concentration of nonionic surfactants

The effects of nonionic surfactant concentration and cloud point were tested and the results are shown in Table 2.

It can be seen from Table 2 that the concentration of the surfactant increases, the cloud point of the flattened plus O-15 increases slightly, and the increase of OP-20 is more obvious. Considering the normal content of nonionic surfactants in chloride galvanizing, only the concentration ranges in the table were determined, and other concentrations were not measured.

2.3 Relationship with the concentration of benzylideneacetone

Among the chloride galvanizing, benzylideneacetone is still the main brightener. The benzylideneacetone is insoluble in water and mainly relies on the solubilization of the nonionic surfactant to dissolve it. Therefore, the higher the content of the benzylideneacetone, the lower the cloud point of the nonionic surfactant. Table 3 shows the test results.

The test results of the content of benzylideneacetone showed that the content increased and the cloud point decreased, which was in accordance with the general rule.

2.4 Relationship with auxiliary brightener

Auxiliary brighteners are an important component in chloride galvanizing. This test mainly tests the commonly used main auxiliary brighteners (nicotinic acid, cinnamic acid, benzoic acid, diffusing agent). The results are shown in Table 4.

It can be seen from the above that benzoic acid and cinnamic acid have a greater influence on the cloud point, and as the content increases, the cloud point decreases more obviously. The weaker the acidity of the auxiliary brightener (such as cinnamic acid), the more obvious the cloud point reduction. This is because the organic acid in the galvanizing solution is a weak acid, the solubility is greatly affected by the pH value, and the solubility in the weakly acidic chloride galvanizing solution is very low, mainly relying on the dissolution of the nonionic surfactant to dissolve. Therefore, when the temperature is raised, the dissolution of the organic weak acid by the nonionic surfactant is weakened, and the organic acid is first precipitated to cause the solution to cyanate. In fact, the turbidity at this time is not a precipitate of a nonionic surfactant, but a fine solid precipitate of a weak acid.

2.5 Effects of other added components on cloud point

The effects of alkyl ether polyglycol sulfate type, alkyl ether polyethylene glycol sulfonate anionic surfactant and organic solubilizer on cloud point were tested. The results are shown in Table 5.

It can be seen from the results that all three substances have a large effect, but the anionic surfactant foam is too much, and the anionic surfactant of the alkyl ether polyethylene glycol sulfate type is more preferable. In addition, anionic surfactants have an adverse effect on the high current density region, affecting the upper limit of the current density. The organic solubilizer does not produce any foam, and has auxiliary complexation and buffering effect. The content range is also wide. The test range of 100g/L does not have any adverse effect on the solution, and the higher the content, the higher the cloud point. The general rule in the test range is that the content increases by about 4.5 g/L and the cloud point increases by 1 °C. Organic cosolvents have a wide range of sources and low prices, and are of considerable value in chloride galvanizing.

2.6 Relationship with pH of plating solution

The auxiliary additive in the chloride zinc plating solution is a component that must be added, and most of them are weak acids, which have a large influence on the cloud point. Therefore, when the relationship between the cloud point and the pH value was tested, different auxiliary brighteners were added and their contents were changed. The test results of the solution of adding a diffusing agent and benzoic acid are shown in Table 6.

From the results, it was found that in the base liquid containing only the nonionic surfactant and benzalkonium acetone, the pH value had no effect on the cloud point, but when the auxiliary additive was contained, the cloud point was significantly decreased. These indicate that the pH value of the solution to which the auxiliary brightener is added has a large influence on the cloud point. Similarly, weak acid auxiliary additives such as niacin and cinnamic acid have a great influence on the cloud point.

3 Conclusion

The cloud point of the nonionic surfactant decreases with the increase of the content of benzylideneacetone, auxiliary additives (sodium benzoate, diffusing agent, etc.); it increases with the increase of the content of the main salt of the solution, but the content of zinc chloride has no effect; When the weak acid auxiliary additive is used, the cloud point is significantly decreased with the decrease of pH value; it is greatly improved with the addition of alkylbenzene or alkyl alcohol polyethylene glycol salt anionic surfactant and solubilizer; with nonionic surface activity The concentration of the agent is increased slightly.