Finding Alternatives to Hexavalent Chromium Sacrificial Paint; The Struggle with Hexavalent Chromium in California

Since the International Agency for Research on Cancer (IARC) acknowledged hexavalent chromium as carcinogenic in its 1980 publication, government agencies such as the U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO) have created and continue to increase restrictions on the maximum amount of chromate allowed in industrial and environmental settings. Used around the world in the production of stainless steel, electroplating, leather tanning, textile manufacturing, pigment-making, and wood preservation, ramifications of using the toxic heavy metal hexavalent chromium have played a key role in the development of chemical regulation around the world since the late 1900s.

Hexavalent chromium also has a history as the most powerful corrosion-resistant and self-healing ingredient in protective coatings. Since it was declared cancerous, research attempts to develop alternatives that are as versatile and impervious as hexavalent chromium have only revealed that hexavalent chromium may never meet a match as capable. The goal of the technical project was to find and test alternatives to an aluminum-based hex-chrome sacrificial paint matrix applied to a shaft in a turbine engine. Replacement candidates must have long-term corrosive and thermal resistance properties comparable to hex-chrome, must survive at least 400°C, and must be nontoxic. A promising candidate, a Sherwin Williams sacrificial paint called Zinc Clad II Plus, was applied to 30 AISI 1010 steel substrates. Four different variations of a sol-gel barrier coating called High Temperature Blockade (HTB) were tested on top of this paint. Samples were divided into five groups: one group with only Zinc Clad applied, and one group for each of the four variations of HTB. Samples were subjected to isothermal holds then placed in salt fog chambers to evaluate their corrosion resistance, a laboratory approximation of the high temperatures and salt spray the turbine engine part would experience on a seafaring aircraft carrier.

Between 1952 and 1966, the utility company Pacific Gas & Electric (PG&E) had been using hexavalent chromium to suppress rust in their natural gas compressor station but neglected to safeguard surrounding groundwater, resulting in the deposition of about 370 million gallons (1.4109 liters) of hexavalent chromium into the unlined ponds by small town Hinkley, California, irreversibly impacting the water quality and human health in and around the region. Technological momentum theory and wicked problem framing will assist in an examination of how utility companies, public agencies, and environmentalists have competed to determine the public health response to the hazards of hexavalent chromium in California. Both hexavalent chromium and groundwater pollution present wicked problems, problems that do not have a simple solution. Hexavalent chromium is such a capable material that its use has been limited but not banned. Meanwhile, polluted groundwater requires decades of remediation and monitoring in order to return to a state anywhere near unpolluted, and even then, another chemical plume may return.

Knowing how harmful hexavalent chromium has been to people and the environment and the past inspired an urgency in me when researching these alternative coatings. Dealing with materials that are both widely acknowledged as toxic and still in use requires discussion of ethics and ramifications of their continued use. Since it is so widely coveted, hexavalent chromium cannot be immediately phased out; companies have less infrastructure for non-hexavalent chromium processes and are reluctant to invest extensively into researching alternatives to an effective material. The technical project is meant to be a small contribution to the existing body of research on chromium alternatives. Over two decades of research have not yielded a nontoxic alternative that matches the temperature and corrosion resistance, much less self-healing properties of hexavalent chromium, but we hold out hope that continued research will yield more promising results.

School of Engineering and Applied Science

Bachelor of Science in Materials Science and Engineering

Technical Advisor: James Fitz-Gerald

STS Advisor: Bryn Seabrook

Technical Team Members: Katie Anderson, Marcus Dupart