Low-cost coating to save aluminium industry millions

In laboratory tests, a model of an anode coated using the new process (above) lasted significantly longer than an uncoated conventional sample (below).

A simple spray-on ceramic coating that reduces ‘air burn’ of carbon anodes in aluminium cells could potentially save the aluminium industry $530 million annually, reduce carbon dioxide emissions from smelters, and generate significant revenue for CSIRO.

Dr Mahnaz Jahedi of CSIRO Manufacturing and Infrastructure Technology is leading a Light Metals Flagship project to reduce oxidation of the top and sides of the carbon anodes, which help drive the aluminium production process.

High replacement rate
Electrolytic cells in smelters contain a powerful solvent, cryolite (or ‘bath’), in which alumina is dissolved at temperatures above 900°C.

Carbon anodes suspended in the bath are rapidly consumed as they react with liberated oxygen to form carbon dioxide.

But these anodes are not just consumed in the aluminium production process – the exposed faces also react with surrounding air, leading to higher consumption and replacement rates. As a result, carbon anodes have to be replaced frequently.

Past attempts to solve the problem – such as coating the top of the anode with bath – have proved ineffective, as the bath does not adhere to the anode surface.

Spray-on coating
Given the consumption rate of anodes, the Light Metals Flagship saw the need for a coating material that would not only adhere well to the carbon but would also be cost-effective, easy to apply and robust, with minimum contamination of the bath.

Dr Jahedi and her team came up with a ceramic spray-on coating containing alumina and carbon, with a small amount of sodium silicate as a binder.

“The coating is applied in two parts – a thinner undercoat of graphite with a thicker top coat of alumina,” says Dr Jahedi. “The technology has patent protection.

“Laboratory tests showed a carbon loss of about 1% from anode material, compared to the 60-70% losses normally observed in uncoated anodes operating in smelter cells.

“The Light Metals Flagship is discussing the process with two major aluminium companies and my team is currently preparing for on-site smelter trials.”

Benefits for smelters 
Dr Jahedi says that, apart from reduced air burn, smelter operators will benefit through:

• extension of anode life;

• reduced carbon dioxide emissions, less environmental impact;

• use of less costly coke/carbon materials;

• unscheduled changes due to localised air burn of anodes;

• ability to cover anodes with alumina;

• elimination of cleaning of bath contaminant from anode ‘butts’  for recycling; and

• less damage to the anode baking furnace.

Contact:
Dr Mahnaz Jahedi
Ph: 61 3 9545 2064
Mahnaz.Jahedi@csiro.au 

UPDATE Home

Message from the Director 

Heat treatment the road to lighter cars

Low-cost coating to save aluminium industry millions

Model solutions to fit all situations

'Bath' sensor keeps quality in focus

Bauxite to alumina: a cleaner pathway

In brief...

The Light Metals Flagship is a CSIRO initiative and part of the National Research Flagships program that aims to deliver scientific solutions to advance Australia's most important national objectives. One of the largest scientific initiatives ever mounted in Australia, it aligns closely with the Federal Government's National Research Priorities. The initiative brings together our national research resources to deliver breakthroughs in fields ranging from healthcare to light metals and the environment.

If you do not wish to receive this electronic newsletter from the Light Metals Flagship, please reply to this message with the word "unsubscribe" in the subject line. Alternatively, please contact  Mary-Lou.Considine@csiro.au or telephone us on +61 3 9545 8500 to request the removal of your email address.

This E-Newsletter is a publication of CSIRO Communications. It does not purport to be comprehensive or to render professional advice. All material in this publication is subject to copyright. For permission to reproduce any part or all of an article, please contact the editor.