Applications for authorisation AFA072-01 - Chromium Trioxide

Overview

Public consultation on alternatives

Reference: AFA072-01

Applicant: Rimex Metals (UK) Ltd

Application type: Review report

Substance name: Chromium trioxide

• EC Number: 215-607-8
• CAS Number: 1333-82-0

Proposed use: Use of chromium trioxide as an oxidising and hardening agent in the manufacture of coloured stainless steel.

Broad information on use applied for (conditions of use and function):

The Applicant uses chromium trioxide as an oxidiser and hardening agent in their “INCO process” for the manufacture of coloured stainless steel. Coloured stainless steel is used in several applications such as in architecture (external and interior cladding, columns, doors, signage and street furniture), lifts and escalators, transport (skirting on rail cars, kick plates and doors), refrigeration and food service (refrigeration doors, coldstores, cooker hobs) and other engineering applications.

The INCO method (a two-stage electrochemical process) uses chromic-sulphuric acid baths to create a thin interference film on the stainless-steel surface via immersion. In the first step, chromium trioxide is used as an oxidiser and hardening agent, working with sulfuric acid to form a thin film on the surface of stainless steel, imparting colour through thin film interference. In the second step, the coloured film is subject to a cathodic deposition in an aqueous bath of chromium trioxide to harden it to achieve an aesthetic, decorative surface with high durability when exposed to demanding conditions.

Coatings produced by the INCO process aim to achieve several key properties: enhanced resistance to scratching and marking, a wide range of stable, bright, and uniform colours, as well as good wear and UV resistance. Additionally, the process allows for combining colours and patterns on stainless steel, expanding the variety of products that can be created. According to the Applicant, the INCO process offers versatility, aesthetic appeal, and durability, all at a relatively low production cost.

The technical requirements that have been identified for evaluating suitable alternatives to chromium trioxide in the INCO process are:

• Colour quality (bright, uniform, free of defects)
• Product range (should include all INCO colours, patterns and substrates)
• Durability (resistant to UV radiation and salt-spray testing)
• Process temperature (should be the same or below existing process temperatures)
• Process duration (and whether efficient)
• Use of existing equipment
• Energy consumption (equal or below current levels of energy consumption)

The Applicant’s substitution efforts have included the sponsoring of two PhD projects to investigate new alternatives to chromium trioxide. Although differing levels of alternatives had been identified, these alternatives did not meet all the required performance criteria and thus were deemed not technically feasible.

List of descriptors:

• Environmental release category (ERC): ERC 5: Industrial use resulting in inclusion into or onto a matrix
• Process category (PROC): 4, 8b, 9, 13, 15, 28
• Product category (PC): 14: Metal surface treatment products, including galvanic and electroplating products
• Sector of end use (SU): 15: Manufacture of fabricated metal products, except machinery and equipment
• Article category: not applicable
• Technical Function: Plating agents and metal surface treating agents

Annual tonnage used: 1 - 10 tonnes/year

Review period requested: 25 years

How to submit comments

Provide some basic information on possible alternative(s) in the online survey below but more detailed information should be provided in document(s) prepared using the commenting templates in the related section below. A “public version” should always be completed and will be published after the consultation has closed. If you want to include confidential information in your submission, please additionally complete a “confidential version” and submit both versions as attachments.

The consultation lasts for 8 weeks (unless otherwise specified) and closes at 23:59 London time (BST).