Test Items

Tin Coating Weight / Tin Alloy Layer Weight

(1) Coulometric method (coulometry): Electrolytic separation device; separately measure free tin, and tin of the alloy layer. (With Ipen recorder, Pe9801 calculator)

Principle: Dissolve the tin coating of a predetermined area in the electrolyte (10NHCL) under the anode current, and identify and indicate the time required for dissolution of the free tin layer and the alloy layer of the coating through the test piece and by reference to variations of potentials between electrodes. The density of electric currents passing through the test piece remains constant, so the value can be determined by multiplying the amount of electricity consumed for dissolution of a certain layer by the dissolution time of the layer, or the amount of electricity can be directly measured with a coulometer. W = k × i × t

W: Tin dissolution amount; k: electrolytic equilibrium constant; i: constant current; t: electrolysis time

1c / cm2 (10mA / cm2 for 100 sec.); 6.15g / m2 of free tin or 4.06 g / m2 of tin in the alloy is dissolved (the alloy amount is equivalent to the iron-tin alloy amount of 5.06 g / m2).

Accuracy is largely dependent on whether the predetermined area can be maintained.

Some attributes of the tinplate (such as solderability and corrosion resistance) is dependent on the relative amount of the free tin and tin in the alloy layer.

(2) X-ray fluorescence: Rix-1000; quickly measure the total amount of Sn, non-destructive (with a 32-bit computers) Cr24 Sn50 Mg12 P15

Principle: Expose the test sample to the irradiation of the primary X-ray which penetrates the tin coating to cause on the surface of the steel the emission of the secondary fluorescent X-ray, the strength of which is dependent on the thickness of the tin coating that is penetrated. Use an appropriate counter to determine the strength of the X-ray and then convert it to the tin coating weight.

(3) Arbitration test (volumetric method)

Principle: Dissolve the tin coating of a predetermined area in hydrochloric acid, and reduce the tin in the solution to bivalent tin with pure aluminum wire. Then, in the carbon dioxide atmosphere, use the standard titrant KIO3-KI for titration and measure the coating weight. Measuring range: 2.5 ~ 50g / m2; reproducibility: ± 0.1 g / m2

Banshi measurement method (volumetric method) (Na2S2O3 5H2O for back titration of KIO3-KI)

Principle: Use the anode dissolution method to dissolve the tin on the test piece of a predetermined area, which contains excessive standard potassium iodate (potassium iodide solution) of an exact quantity. After tin is dissolved, use the starch solution as the indicator, and use the standard titrant of Na2S2O3 5H2O for back titration of excess KIO3-KI until the blue-black color disappear.

(5) Weight loss method (Clark method) ...... Not applicable for determination of low tin coating weight

Principle: The measured weight loss is the total weight of free tin and the alloy layer (FeSn2) (excluding Fe, about 0.4gFe / m2)

Detinning liquid: HCL-Sb2O3 ---- 100ml of concentrated HCL + 2g Sb2O3

Function of Sb3 +: 1) To accelerate tin dissolution. 2) To retard dissolution of steel base and control detinning: Measure one single side after stopping gas release and holding for around one minute: Coat both sides with cellulosic varnish and then remove the coating mold with acetone.

Oxidation Film Weight (Coulometry)

Electrolytic stripping device; with a recorder and a computer

Electrolyte: 0.001MHB r, with inert atmosphere expressed in mc / cm2

Tin oxidation film is the oxide of bivalent tin or tetravalent tin and its hydrate. Given the fact that its composition is not fixed, its weight is calculated based on the reduction electricity quantity, expressed in mc/cm2. Principle: In an oxygen-free solution that does not react with tin oxide (0.001 MHB r), reduce the tin oxide on the surface of the test piece of tinplate with a certain quantity of miniature potential. Observe the oxide reduction process by measuring the potential. The quantity of tin oxide on the surface is measured by the amount of electricity consumed during the complete reduction of oxide.

New plate: <1 mc / cm2; when> 3 mc / cm2, it will cause downward movement

Chromium Coating Weight

(1) X-ray fluorescence

(2) Spectrophotometric method (Diphenylcarbazide colorimetry): uv-2201 Shimadzu

Principle: Boil and dissolve the test sample with the mixture of NaOH + Na3PO4, and then boil and dissolve it with H2SO4 (25%). Use KMnO4 chromium oxide to Cr + 6, and add hydrochloric acid to reduce the excess KMnO4. Then, determine the chromium coating weight by diphenylcarbazide colorimetry.

(3) Coulometry: Use the anode current to oxidize 1 mc/cm2 to 1mg Cr/m2 of surface chromium amount (also with other reactions)

Oil Film

(Dioctyl sebacate or tributyl O-acetylcitrate) 1.25 ~ 12.5mg / m2

(1) Ellipsograph method: Use Shimadzu AEP-300 to measure the mineral oil (DOS) film, and avoid the difference of front and back polarizing angles to get the thickness of the oil film.

(2) Flatness Method: Transfer and disperse the plate oil to a clean plane to form a monomolecular film (measure cotton oil C.O.S), and measure the area covered by the monomolecular film to get the oil thickness.