Umicore Electroplating in Germany uses high temperature electrolytic anodes. In this process, platinum is deposited on base materials such as titanium, niobium, tantalum, molybdenum, tungsten, stainless steel and nickel alloys in a molten salt bath at 550°C under argon.
       Figure 2: A high temperature electroplated platinum/titanium anode retains its shape over a long period of time.
        Figure 3: Expanded mesh Pt/Ti anode. Expanded metal mesh provides optimal electrolyte transport. The distance between the anode and cathode components can be reduced and the current density increased. The result: better quality in less time.
        Figure 4: The width of the mesh on the expanded metal mesh anode can be adjusted. The mesh provides increased electrolyte circulation and better gas removal.
        Lead is closely watched all over the world. In the US, health authorities and workplaces are sticking to their warnings. Despite the electroplating companies’ years of experience in dealing with hazardous materials, metal continues to be viewed more and more critically.
        For example, anyone using lead anodes in the United States must register with the EPA’s federal Toxic Chemical Release Register. If an electroplating company processes only about 29 kg of lead per year, registration is still required.
       Therefore, it is necessary to look for an alternative in the USA. Not only does the lead anode hard chromium plating plant seem cheap at first glance, there are also many disadvantages:
       Dimensionally stable anodes are an interesting alternative to hard chromium plating (see Fig. 2) with a platinum surface on titanium or niobium as a substrate.
        Platinum coated anodes offer many advantages over hard chromium plating. These include the following benefits:
        For ideal results, adapt the anode to the design of the part to be coated. This makes it possible to obtain anodes with stable dimensions (plates, cylinders, T-shaped and U-shaped), while lead anodes are mainly standard sheets or rods.
        Pt/Ti and Pt/Nb anodes do not have closed surfaces, but rather expanded metal sheets with variable mesh size. This leads to a good distribution of energy, electric fields can work in and around the network (see Fig. 3).
        Therefore, the smaller the distance between the anode and the cathode, the higher the flux density of the coating. Layers can be applied faster: yield is increased. The use of grids with a large effective surface area can significantly improve separation conditions.
        Dimensional stability can be achieved by combining platinum and titanium. Both metals provide optimal parameters for hard chrome plating. The resistivity of platinum is very low, only 0.107 Ohm×mm2/m. The value of lead is almost twice that of lead (0.208 ohm×mm2/m). Titanium has excellent corrosion resistance, however this ability is reduced in the presence of halides. For example, the breakdown voltage of titanium in chloride-containing electrolytes ranges from 10 to 15 V, depending on pH. This is significantly higher than that of niobium (35 to 50 V) and tantalum (70 to 100 V).
        Titanium has disadvantages in terms of corrosion resistance in strong acids such as sulfuric, nitric, hydrofluoric, oxalic and methanesulfonic acids. However, titanium is still a good choice due to its machinability and price.
        The deposition of a layer of platinum on a titanium substrate is best carried out electrochemically by high temperature electrolysis (HTE) in molten salts. The sophisticated HTE process ensures precise coating: in a 550°C molten bath made from a mixture of potassium and sodium cyanides containing approximately 1% to 3% platinum, the precious metal is electrochemically deposited onto titanium. The substrate is locked in a closed system with argon, and the salt bath is in a double crucible. Currents from 1 to 5 A/dm2 provide an insulation rate of 10 to 50 microns per hour with a coating tension of 0.5 to 2 V.
        Platinized anodes using the HTE process have greatly outperformed anodes coated with aqueous electrolyte. The purity of platinum coatings from molten salt is at least 99.9%, which is significantly higher than that of platinum layers deposited from aqueous solutions. Significantly improved ductility, adhesion and corrosion resistance with minimal internal tension.
        When considering optimizing the anode design, the most important is the optimization of the support structure and the anode power supply. The best solution is to heat and wind the titanium sheet coating onto the copper core. Copper is an ideal conductor with a resistivity of only about 9% of that of Pb/Sn alloys. The CuTi power supply ensures minimal power losses only along the anode, so the layer thickness distribution on the cathode assembly is the same.
        Another positive effect is that less heat is generated. Cooling requirements are reduced and platinum wear on the anode is reduced. Anti-corrosion titanium coating protects the copper core. When recoating expanded metal, clean and prepare only the frame and/or power supply. They can be reused many times.
        By following these design guidelines, you can use the Pt/Ti or Pt/Nb models to create “ideal anodes” for hard chromium plating. Dimensionally stable models cost more at the investment stage than lead anodes. However, when considering the cost in more detail, a platinum-plated titanium model can be an interesting alternative to hard chrome plating.
       This is due to a comprehensive and thorough analysis of the total cost of conventional lead and platinum anodes.
        Eight lead alloy anodes (1700 mm long and 40 mm in diameter) made of PbSn7 were compared with appropriately sized Pt/Ti anodes for chromium plating of cylindrical parts. The production of eight lead anodes costs around 1,400 euros (1,471 US dollars), which at first glance seems cheap. The investment required to develop the required Pt/Ti anodes is much higher. The initial purchase price is around 7,000 euros. Platinum finishes are especially expensive. Only pure precious metals account for 45% of this amount. A 2.5 µm thick platinum coating requires 11.3 g of precious metal for each of the eight anodes. At a price of 35 euros per gram, this corresponds to 3160 euros.
        While lead anodes may seem like the best choice, this can quickly change upon closer inspection. After only three years, the total cost of a lead anode is significantly higher than the Pt/Ti model. In a conservative calculation example, assume a typical application flux density of 40 A/dm2. As a result, the power flow at a given anode surface of 168 dm2 was 6720 amperes at 6700 hours of operation for three years. This corresponds to approximately 220 working days out of 10 working hours per year. As the platinum oxidizes into solution, the thickness of the platinum layer slowly decreases. In the example, this is considered 2 grams per million amp-hours.
        There are many reasons for the cost advantage of Pt/Ti over lead anodes. In addition, reduced electricity consumption (price 0.14 EUR/kWh minus 14,800 kWh/year) costs about 2,000 EUR per year. In addition, there is no longer a need for an annual cost of about 500 euros for the disposal of lead chromate sludge, as well as 1000 euros for maintenance and production downtime – very conservative calculations.
        The total cost of lead anodes over three years was €14,400 ($15,130). The cost of Pt/Ti anodes is 12,020 euros, including recoating. Even without taking into account maintenance costs and production downtime (1000 euros per day per year), the break-even point is reached after three years. From this point on, the gap between them increases even more in favor of the Pt/Ti anode.
        Many industries take advantage of the various benefits of high temperature platinum coated electrolytic anodes. Lighting, semiconductor and circuit board manufacturers, automotive, hydraulics, mining, waterworks and swimming pools rely on these coating technologies. More applications will certainly be developed in the future, as sustainable cost and environmental considerations are long-term concerns. As a result, lead may face increased scrutiny.
        The original article was published in German in Annual Surface Technology (Vol. 71, 2015) edited by Prof. Timo Sörgel from Aalen University of Applied Sciences, Germany. Courtesy of Eugen G. Leuze Verlag, Bad Saulgau/Germany.
        In most metal finishing operations, masking is used, where only certain areas of the surface of the part should be processed. Instead, masking can be used on surfaces where treatment is not required or should be avoided. This article covers many aspects of metal finish masking, including applications, techniques, and the different types of masking used.