Study On Ti-based Dimensionally Stable Anode For Chromium Plating Application

The project is sponsored from ZhongShan ZhongYue Tinplate Co., Ltd.During production of chrome plating, the lead-tin alloy anode experiences lowdimensional stability and requires maintenance constantly. It not only increasesthe product cost but also causes health issues to employees. It is necessary toseek a chemical and dimensional stable anode to replace tin-lead alloy anode.Among graphite, stainless steels, lead alloys, and dimensional stable anode（DSA）, DSA has low oxygen evolution potential, dimension stability, littleinfluence on the component of bath, low cell voltage, non-pollution etc.Therefore, various methods have been employed to compare the performance ofDSA with PbSn anodes. DSA anodes are titanium-based with the coatings ofIrO₂/Ta₂O₅and IrO₂/Pt.Surface morphology and compositions of the DSA（IrO₂, Ta₂O₅） andDSA（IrO₂, Pt） anodes were characterized by scanning electron microscopy （SEM）and X-ray powder diffraction （XRD）. It was found that both surfaces werecracked dried mud, and cracks of DSA（IrO₂, Ta₂O₅） was finer than DSA（IrO₂, Pt）.Cross-sectional view showed that DSA（IrO₂, Ta₂O₅） has better adhesion.Hull Cell test was adopted to evaluate the plating coating quality withdifferent various density on different anodes. The results showed that the cellwith DSA（IrO₂, Pt） has the widest bright finishings and the most uniformcoating.Oxygen evolution performance was studied as well by cyclic voltammo-grams（CV curves）. The oxygen evolution potential from high to low in turnwere PbSn, DSA（IrO₂, Ta₂O₅）, DSA（IrO₂, Pt） anode. It was found as well thatoxygen evolution performance of DSA（IrO₂, Pt） was better in high currentdensity performance than that of DSA（IrO₂, Ta₂O₅）.Furthermore, to simulate the mass production process of Zhongyue,simulated chromium plating production was conducted in plating bath tocompare the stability of DSA（IrO₂, Ta₂O₅） anode, DSA（IrO₂, Pt） anode and PbSnalloy anode. However, bath with DSA（IrO₂, Ta₂O₅） anode failed after20hcontinuous plating, DSA（IrO₂, Pt） anode bath failed after86h continuous plating,and PbSn alloy anode bath remains stable even after120h plating. DSA（IrO₂,Ta₂O₅） and DSA（IrO₂, Pt） showed erosion naked eyes by SEM. Both EDS andXRD analysis proved that all noble metal catalytic oxides are lost. It is becausethat the presence of F-in plating baths reacted with Ti substrates, then accelerated the substrate dissolution, which loss all the coatings during reacti ons.DSA coatings on other substrate materials （e.g. Nb） instead of Ti arerecommended for further test.