From chromate passivation to chromium-free passivation, what is the advanced way of galvanizing passivation technology

As a metal surface protective layer, additional protective measures are often required to ensure that corrosion resistance requirements are met in certain environments. For example, when zinc is used as a metal surface coating, it needs to have sufficient thickness to protect the substrate metal, mainly relying on the sacrificial anode effect of the zinc layer, as well as the isolation protection effect of the dense basic zinc carbonate film formed on the zinc surface in atmospheric and neutral water environments.

However, in humid and poorly ventilated environments, the zinc layer corrodes quickly, and the white loose products formed cannot protect the zinc layer from further corrosion, resulting in white rust. Common additional anti-corrosion measures include phosphating, chromate passivation, etc. Among them, passivation is an effective protective measure for metals and metal coatings in less harsh environments and has a wide range of applications.

Passivation treatment is a type of chemical conversion film treatment process, the principle of which is to change the metal surface from an activated state to a passivated state, thereby slowing down the dissolution of the metal. The actual passivation treatment process relies on the electrochemical reaction process of the metal surface. This includes an anodic dissolution step, during which the metal surface is oxidized, accompanied by a cathodic process that reduces certain ions in the passivation solution, and the resulting low-valent ions combine with the corrosion products of the metal to form a passivation film on the surface.

Conventional passivation treatment is chromate passivation. The metal mixture passivation layer formed by this chromate treatment mainly consists of trivalent chromium and hexavalent chromium, where trivalent chromium serves as the framework, while hexavalent chromium (chromate ions) can easily leach out of the passivation film as a corrosion inhibitor.

Due to the low cost, simplicity of use, and good improvement of metal corrosion resistance, chromate passivation has been widely used in aviation, electronics, and other industrial sectors. From its initial application on magnesium in 1924, chromate passivation has now been widely used on many metals and their alloys, including aluminum, zinc, tin, cadmium, copper, and silver. The chromate passivation treatment methods include direct immersion and electrochemical treatment, and the solutions used contain chromium in its hexavalent form.

In the past decade, there has been a profound understanding of the toxicity of chromates, which are considered highly toxic and carcinogenic. For example, 1-2g of chromic acid or 6-8g of potassium dichromate can lead to kidney failure, liver damage, blood disorders, and death; long-term exposure to chromates can cause papules, blisters, and ulcers; inhalation of chromates can lead to liver cancer.

Therefore, the level of chromate in the workplace is strictly regulated by the government, and those using chromates must be informed of the health risks that chromates may pose. The U.S. OSHA (Occupational Safety and Health Administration) stipulates that in a workplace with a 40-hour work week and 8-hour workdays, the content of insoluble chromates in the air should be less than 1mg/m3.

With the increasing awareness of environmental protection, the significant harm of chromates to human health has inevitably led the government to strictly limit the use and discharge of chromates. To address this issue, there are basically two methods. One method is to use safer production processes, including the use of protective clothing, gas masks, processes to reduce hexavalent chromium to trivalent chromium, and the use of chromium-free passivation processes. In the future, restrictions on chromates may become stricter, and this method does not ultimately solve the problem of chromate discharge.

The other method is to find low-toxicity or non-toxic alternatives to chromates. In the main research systems for replacing hexavalent chromium passivation both domestically and internationally, silane-based organic-inorganic composite technology is regarded as an advanced technology and a research hotspot internationally.

Qingdao Haiyida New Materials Technology Co., Ltd. is a high-tech enterprise focused on the research and application of new water-based metal surface treatment technologies, with core products including environmentally friendly alternatives in the field of metal surface treatment such as chromium-free, phosphorus-free, fluorine-free, and water-based technologies and materials.

Silane metal surface treatment agent is a newly developed organic silicon composite metal surface treatment agent that forms an intermediary layer connecting organic and inorganic materials through silanization of the metal surface, aiming to replace the hexavalent chromium passivation process. Compared with traditional hexavalent chromium passivation agents, silane metal surface treatment agents do not contain heavy metal ions such as Cr6+ (the product has passed ROHS testing), do not contain chromates, nitrites, phosphates, F-, and other toxic and harmful substances, do not require heating during use, do not require water washing after treatment, have a simpler process flow, theoretically do not require tank changes, and have characteristics of being green, environmentally friendly, and energy-efficient, with comprehensive treatment costs not exceeding existing processes.

In the future, as the process of industrial production becoming more environmentally friendly accelerates, high-performance, green, and environmentally friendly chromium-free passivation technology will become the mainstream trend in the field of galvanized passivation.