Film thickness test method - thin chromium coating timing drip method

Use a small drop of the test solution to stay on the partial surface of the coating for a certain period of time, and then replace it with a new drop, and calculate the coating thickness by recording the number of solution drops and the time consumed to dissolve the local coating.

The end point of the dissolution of the coating can be determined by directly observing the change of the characteristic color of the metal.

Due to the low accuracy of thickness measurement by drop method, it is rarely used at present. But for decorative thin chrome deposits, the timed drip method is still a viable method. It is still used as a standard method in CHINA. This method is only suitable for the determination of thin chromium coatings below

1. Test solution

Hydrochloric acid: (11.5±0.2mol), chemically pure.

2. Measurement method

In order to prevent the test solution from spreading, first draw a small circle with an inner diameter of 6mm on the surface of the sample to be tested with melted paraffin or crayon , and then drop the first drop of test solution (0.03~0.05ml) in the small circle, When the bubbles are precipitated, start timing until the middle coating or base metal is exposed. If the bubble precipitation has not stopped when the stopwatch reaches 60s, stop the timing, absorb the first drop of test solution with filter paper or cotton wool, and then add the second drop of test solution, and repeat this until the bare

Until the intermediate coating or base metal is exposed, then record the temperature . Repeat the measurement according to the above operation, and then calculate the coating thickness according to the following formula, and take the average value. If the gas is not generated immediately , a fine nickel wire can be used to touch the inner surface of the small circle to make it react. Thin flake samples should be measured on a thicker metal block to avoid a sharp rise in .

See Table 7-2-5 for the color characteristics of the end point of the chromium coating determination.

3. Coating thickness calculation

The coating thickness is calculated according to the following formula (same as the timing flow method)

h=h _t t (see table 7-2-6 for ht value)