The determination of sulphate and chromate in chromic acid plating baths using ion chromatography to reliably and quickly ensure that there is no problem with the component concentrations of the bath
Chrome plating is a procedure whereby a chrome finish is imparted onto a surface through the use of electrolytic depositioning of chromium.
There are two types of chromium plating; decorative and industrial.
Decorative or bright chrome is a thin layer (circa 10um) and imparts a mirror like finish onto for example automotive trim (bumpers, wheel rims etc).
Industrial chrome also known as hard chrome gives a thicker deposit of up to 1000um, typically it is used in industrial equipment (eg, pistons, cylinder shafts) to minimise friction and wear resistance of the components.
It can also be used to restore the surface dimensions of any component that has experienced deterioration.
Two types of industrial chromium plating solutions exist and these can either be hexavalent or trivalent chromium (although to date these are less prevalent due to colour restrictions and film thickness).
A typical hexavalent bath solution will contain chromic acid and sulphuric acid and these can be determined as chrome (VI) and sulphate using the technique of ion chromatography (IC).
Should any inorganic impurities exist in the chromic acid bath solution, these can cause problems and produce rough deposits or dull spot finishes.
In order that the bath retains its optimum characteristics it may be necessary to adjust amount of the electrolyte present.
Decorative baths have a chromic to sulphate ratio of 100-150:1 and industrial baths a ratio of 75-100:1 for chromic and sulphate respectively, these ratios can quickly and reliably be determined using IC.
Another environmental advantage is correction of the bath components so that the amount of heavy metals discharged to waste are reduced especially with regard to chromate as chrome (VI) as this has known toxicological effects.
IC from Metrohm can be used to reliably and quickly ensure that there is no problem with the component concentrations of the bath using only a simple dilution, the whole process can be completely automated using Metrohm Inline Sample Preparation (MISP) and the software facilitates operation even by semi skilled personnel if required.
The effluent discharged to waste can also be determined to ensure compliance with local regulatory bodies making IC a must have analytical technique for any organisation that uses chromic acid plating baths.
A typical instrument configuration would be the Metrohm 861 Advanced Compact IC with 838 Advanced Sample Processor.
The Metrohm IC instruments work using the principal of chemical suppression for a sensitivity enhancement of the analytes of interest.
Metrohm does not use a membrane based suppressor which suffer from precipitation (and ultimately failure) caused by transition metals present in the sample and Metrohm is the only supplier to offer a ten year suppressor warranty for peace of mind and reduced running costs.
Metrohm have sixty years of leading experience in ion analysis and two decades of outstanding research in Ion Chromatography to ensure that the reliability and robustness of the instrument are assured.
