This test is done on tinned copper wire to determine the exposed copper. The tinning process of copper may not be perfect due to which there is possibility of formation of pinholes on the conductors, thereby defeating the purpose of application of tin.
Why Copper Wires are Tinned?
- Tin acts as a barrier between copper and elastomeric insulation otherwise there would be high chance of degradation of insulation due to catalytic effect of copper on elastomers.
- Tin also helps to avoid the formation of oxide on the copper which can reduce its solderability.
Thus, Persulphate Test of conductor ascertains the continuity of tin layer on the surface of conductor. This test is mainly performed on tinned copper wires or conductors.
Methods of Persulphate Test
This test can be done by of the following methods:
In this method the sample is immersed in
In this method, the mass of copper dissolved is expressed as grams of copper per square
Test sample for method A should of such length that there would be sufficient extra length at two ends of the specimen. These extra lengths of the specimen would be projected from the solution surface in which it is immersed during Persulphate Test. Normally as per standard the length of test sample taken is given by L = 300/d + 80 mm, where d is the nominal diameter of conductor in mm.
For method B the length of the sample is chosen as per practicing standard. For example, one such table from the Indian Standard is given as reference (see below). Similar to method A test sample of method B should also be of such length that there would be sufficient extra length at two ends of the specimen in addition to the length specified in
Test Specimen for Tinning Test
The following table is applicable to Method B:
|Diameter and Number of Wires Comprising the Conductor||Length of test specimen(mm) including 40 mm extra length at each end||Number of test specimen|
|Over(mm)||Up to and including(mm)|
|–||0.20||10 or more||580||10|
|0.20||0.30||6 or more||1080||5|
|0.30||0.75||3 or more||750||3|
|0.75||3.20||3 or more||410||3|
Two groups of specimens of continuous length for both method A and method B are taken and marked 40 mm (the extra length) from each end.
In method A after cleaning, immerse the helix in a vessel containing 100 ml persulphate solution with 40 mm end projected above the level of solution. After 10 minutes, the helix is removed and the test solution is compared with an equal volume of reference standard color reagent for the depth of color. If the color of persulphate solution is changed there must be any discontinuation on the tin layer of the wire.
In method B after cleaning, the helix is immersed for 10 min in a vessel containing the persulphate solution in such a manner that the surface of the wire between the marks is exposed to the testing solution and the 40 mm ends project above the level of solution. The mass of copper dissolved from the wire by the persulphate solution is determined colorimetrically by comparison with the standard color reagent. Colorimetric analysis is a method by which one can determine the exact concentration of a specific chemical element or compound in a solution with the aid of a color reagent.
Observation of Method A
|Groups of specimen||Color of the test solution relative to the standard reagent (darker / lighter)|
Observation of Method B
|Groups of specimen||Standard Color Reagent Required to Match the Color, ml|
Method A – No calculation
Mass of copper dissolved per unit area of conductor surface = W/A
W = copper dissolved in grams.
A = surface area of copper which is calculated from diameter of the conductor and the length of the conductor immersed inside the persulphate solution.
|Method A||Method B|
|Specimen no.||Color to reference standard color reagent||Specimen no.||Diameter of wire||Mass of copper dissolved g/m2|
Conclusion Persulphate Test of Conductor
Conclusion – The sample meets/does not meet the requirements of the specification.
Reference taken from : – IS : 10810 ( Part 4) – 1984