Types, characteristics and uses of brush plating anodes
Abstract
This article introduces in detail the basic characteristics and selection principles of different types of anodes for brush plating. This article alaopoints out that each type of anode has its own unique characteristics and shortcomings. Specific problems should be analyzed when selecting anodes. Improper use of anodes may result in deterioration of brush plating quality, increased costs, environmental pollution or safety production issues. In contrast, the use of FJY series self-compensating brush plating technology and the use of metal active anodes have more advantages.
Keywords: FJY brush plating, anodes, brush plating
Preface
Although many materials or brush plating books have introduced the characteristics and usage of brush plating anodes, until now, only a few people can properly choose brush plating anodes. Some people often fail brush plating due to improper use of anodes. In order to further explain the characteristics of different types of anodes and the matters that should be paid attention to during their use, this article again gives specific guidance on the use of brush plating anodes. Using the most suitable anodes can help brush plating workers avoid any economic losses that might encounter due to misuse of improper nodes.
Different Types of Anode
According to the role of anodes in the electrochemical reaction process, they can be divided into two categories, one is insoluble anodes and the other is soluble anodes. Each category of anodes contains many branches with different properties. This article only describes the types, characteristics and methods of use of commonly used brush-plated anodes.
1. Insoluble Anode
During the brush plating process, the anode material itself does not undergo chemical changes (but physical changes may occur, such as pulverization, discoloration, etc.), and the anode only performs a conductive role. The anodic reaction that occurs on the anode is mainly the evolution of oxygen (such as conventional fast nickel), the precipitation of chlorine (such as special nickel), the precipitation of mixed gases (oxygen, chlorine), or the oxidation of low-valent metal ions in the plating solution to high-valent ions ( Such as the oxidation of low-valent iron ions and tin ions in the process of brushing iron and brushing tin). Brush-plating insoluble anodes with this characteristic include graphite, metallic platinum, platinum-iridium alloy, platinum-plated titanium anodes, precious metal materials (gold or gold-plated anodes), DSA anodes (modified materials for surface conductivity of titanium materials), etc. In recent years, some people have begun to use stainless steel anodes. Although it is not strictly an insoluble anode (because stainless steel will undergo electrochemical dissolution to varying degrees when used as an anode), many people use it, as a substitute for the graphite anodes, to brush plate large, special-shaped parts. The types and characteristics of commonly used insoluble anodes are as follows.
1.1. Graphite anode
High purity graphite is the most commonly used insoluble anode. At present, most users use graphite anodes for brush plating. The biggest advantage of graphite anode is that it is cheap and will not cause serious pollution to the plating solution. The biggest disadvantage of graphite is that it is easy to pulverize. The lower the current efficiency of the plating solution (the plating solution with slow deposition speed is usually lower) is, the more severe the pulverization will be. If the powdered layer is not removed in time, it is difficult to brush normally. Graphite has poor mechanical strength, and it is not easy to make light large anodes and small anodes with complex shapes. There are many types of graphite materials, and the graphite used as a brush plating anode should have the characteristics of high purity, high density and high strength. Otherwise, it is not suitable for brush plating anode. The picture below is the actual photo of the graphite anode.
1.2. Metal platinum anode
Metallic platinum (or platinum-iridium alloy) is the best insoluble anode. This is because metallic platinum has the best chemical stability, so it will not contaminate the plating solution. Metallic platinum has better conductivity than graphite, and the overpotential of the anode reaction is small, which is conducive to brush plating of high-quality coatings at lower voltages. But the price of metallic platinum is too expensive (twice as expensive as gold), no one dares to use such expensive brush plating anodes, and we only use it for cyanide-free brush gold plating. The picture below is a sample photo of a metal platinum anode.
1.3. Platinum-plated titanium anode
The best way to replace pure platinum anodes is to use platinum-plated anodes. The currently available platinum-plated anodes are platinum-plated titanium anodes. The platinum-plated titanium anode is to electroplate a layer of pure platinum with a thickness of more than 1 micron on the titanium material, and its electrochemical performance is similar to that of pure platinum. The price of the anode is about 150-250 yuan/square decimeter (the price is related to the thickness of the platinum coating). Many domestic manufacturers produce platinum-plated titanium anodes. In contrast, imported platinum-plated titanium anodes have a longer service life and the price difference is not big. The picture below is the actual photo of the platinum-plated titanium anode.
1.4. DSA anode
Slightly cheaper than platinum-plated titanium anodes, DSA anodes (also called dimensionally stable anodes) are commonly used in the electrolysis industry in recent years. It uses high-temperature firing to form electrochemically active rare and precious metal oxides on the surface of titanium materials, and its function is equivalent to platinum-plated titanium anodes. Compared with platinum-plated titanium anodes, the service life of DSA anodes and the allowable current density are lower. A qualified DSA anode can work continuously for more than 80 hours at a current density of 100A/dm². Many domestic manufacturers produce DSA anodes, the price is about 100 yuan / square decimeter. When using DSA anodes, the appropriate DSA anode should be selected according to different bath characteristics. Oxygen evolution reaction (rapid nickel) on the anode should choose oxygen evolution DSA anode; chlorine evolution reaction (special nickel) on the anode should choose chlorine evolution DSA anode, otherwise it will reduce the anode life. The picture below is the actual photo of the DSA anode.
1.5. Stainless steel anode
Many people begin to like to use stainless steel as anodes. Compared with the several insoluble anodes mentioned above, stainless steel anodes have the characteristics of low price, easy availability, forming and convenient use. In the case of sufficient plating solution supply, the quality of brush plating can also be guaranteed. However, it should be emphasized that low-quality stainless steel (such as 1Cr13, 2Cr13 stainless steel, etc.) cannot be used, and stainless steel of unknown brand cannot be used as anode. Because stainless steel is a kind of alloy material with iron as the main component and added various alloying elements (chromium, nickel, molybdenum, titanium, niobium, etc.), these metal elements will dissolve in the plating solution during the brush plating process, shortening the plating solution The service life of this product reduces the quality of the coating. If you must choose stainless steel as the anode, you must choose ultra-low carbon stainless steel with good chemical stability (such as 316L, 304L, etc.), and at least choose a stainless steel material with better stability than 1Cr18Ni9Ti. Practice has proved that no matter which type of stainless steel is selected, the service life of the plating solution will be reduced. Therefore, the plating solution should be updated frequently and the circulation volume of the plating solution should be increased. Generally speaking, the cost of the plating solution used during brush plating only accounts for 5-10% of the maintenance fee. In order to complete the brush plating task quickly and conveniently, as long as the plating solution can be updated in time, high-quality stainless steel anodes can be used. The picture below is the actual photo of the stainless steel anode.
Soluble anode
The biggest disadvantage of using insoluble anode brush plating is that during the brush plating process, the composition of the plating solution and the performance of the coating are constantly changing, which ultimately leads to the deterioration of the brush plating quality. When the composition of the plating solution changes to a certain level, although the plating solution still contains the metal ions to be plated, the plating solution can no longer be used. Practice has proved that the utilization rate of the plating solution is less than 60%. However, so far, even the internationally renowned companies in the brush plating industry, Selectron, Dalic, and Boeing Aircraft Industries, still use Brush plating technology based on insoluble anodes.
In recent years, more and more people have begun to try soluble anode brush plating technology, and many businesses also claim to have soluble anode brush plating technology. In fact, it is not difficult to use soluble anode brush plating. Generally speaking, as long as you use a strong acid plating solution and add some activators to promote anode dissolution, brush plating at low current density is possible. However, due to the many problems with acidic baths, such as hydrogen embrittlement, corrosion, and loose replacement layers, there are few really good soluble anode brush plating techniques.
There are many soluble anode materials, which should be selected according to the characteristics of the plating solution. For example, iron anodes should be selected in the common acidic brush iron plating technology, and phosphor copper anodes can be selected for acid copper plating. At present, nickel anodes are used in acid nickel plating.
Northwestern Polytechnical University has successfully developed FJY series soluble anode brush plating technology with self-compensation characteristics, which is a kind of near-neutral plating solution, and has been successfully applied in many military and civilian key equipment. For super large and special-shaped parts, it is recommended to use this type of plating solution. The other features of the FJY series self-compensating brush plating technology include a series of advantages such as a 5-10 times reduction in brush plating cost, a 10 times increase in deposition speed, and high coating hardness. The picture below is a physical photo of a self-compensating (nickel) anode.
Conclusions
Through the above introduction on the characteristics and selection principles of different types of brush-plated anodes, it can be seen that each type of anode has its own unique characteristics, and specific problems must be analyzed in detail when selecting. Improper use of anodes may result in deterioration of brush plating quality, increased costs, environmental pollution or safety production issues. In contrast, the use of FJY series self-compensating brush plating technology and the use of metal active anodes have more advantages.