Big reductions - Improvements to the FFC process

Materials World magazine
,
1 Nov 2009

Improvements to the FFC Process are described by Harry Pepper, Chief Financial Officer, and Lee Shaw, Technology Director, from intellectual property company for the speciality metals industry, Metalysis Ltd, UK.

The FFC Process, an electrochemical technology that reduces metal oxides to metals, and a mixture of metal oxides to alloys, without melting is being upscaled. This should result in a cheaper and cleaner route to produce high-value metals and alloys.

The first patent for the FFC Process was filed in 1998 and the invention was announced in September 2000, focusing particularly on titanium applications. For many years the titanium industry had been searching for a replacement for the Kroll process, which is expensive and environmentally damaging.

Metalysis Ltd, UK, acquired outright control of the FFC titanium licence in 2006 and is scaling up the technology to achieve a competitive pricing position. As the technology matures and scale grows, the company is expecting to open up the technology progressively to other markets and applications, including a range of titanium and tantalum products and the aerospace alloy Ti 6-4.

Proven process

A molten salt acts as the electrolyte for the electrochemical reduction of a metal oxide to metal. The oxide is formed and sintered into a suitable shape that becomes the cathode, which is immersed in molten electrolyte (typically calcium chloride) at a temperature of 800-1,000°C. When around three volts are applied between the cathode and carbon anode, the oxygen ions are conducted through the electrolyte and react at the anode to form carbon dioxide and carbon monoxide. Once all the oxygen ions have been removed, the reduced metal is left on the cathode in its solid state. It is taken from the vessel, washed to remove salt, dried and post-processed as needed.

Over the past four years, the technology has been developed to a position where Metalysis now has an fundamental understanding of the process, can prevent and reduce impurities – such as carbon, calcium and chlorine – and can influence the morphology of the powder product. At Metalysis, 12 laboratory FFC reduction cells are used to conduct a mixture of experiments. The equipment has elaborate control, data logging and monitoring systems, including a mass spectrometer for measuring the composition of the process off gases. While these cells reduce only gramme quantities of titanium per run, they are flexible and can be turned around quickly. They can therefore generate large quantities of scientific data in a short space of time.

Two further cells are capable of reducing multi-kilogramme quantities of oxide per cycle. One is dedicated to tantalum and the other to titanium. The cells provide development and scale-up data, as well as samples of FFC product for testing, post-processing and customer evaluation. Like the smaller R&D cells, they operate on a batch process basis and are therefore unsuitable for commercial production quantities.

To address the batch process and other operational and technical limitations of the existing equipment, a novel cell design has been developed. This is the subject of several patent applications. The design has been optimised following laboratory and development cell experiments and a combination of theoretical and physical models. These have helped identify and reduce scale-up risk. Construction of the new semi-continuous cells is underway, with commissioning expected in mid-2010. The design can be scaled-up to larger units for commercial production and is modular so that additional reduction cells can be included as demand increases.

Particle products

The FFC Process generates a powder product directly from the cell. In the case of titanium, the powder is partially sintered as a result of the reduction temperature being close to its melting temperature (Tm = 1,668°C). By way of contrast, tantalum, with its significantly higher melting point (Tm = 3,017°C), does not sinter significantly and remains a powder. A typical reduced product is shown on the previous page, bottom far left and middle left as a scanning electron microscopy (SEM) image. The sintered nature is apparent from the SEM.

While tantalum is used in a powder form in the electronics industry or easily consolidated into a mill product, FFC titanium requires post-processing before it can be marketed. A number of options are available, which are under investigation. The first is to directly consolidate the FFC product into sheet by roll consolidation. Samples of FFC reduced titanium have been consolidated to sheet and successfully tungsten inert gas (TIG) welded.

The other possible consolidation routes are via conventional powder processes. Powders can be produced from FFC titanium directly by grinding, hydriding-grinding-dehydriding, and fusion and gas atomisation.

Although the post-processing work is at a relatively early stage, Metalysis expects to generate significant cost benefits – when compared to the incumbent multi-step production route (Kroll sponge-ingot metallurgy-mill product) – by adopting these processing routes to produce commercial products. Despite the early over promises associated with the technology, which generated sceptism in the marketplace, the FFC Process can now produce commercially pure products suitable for a range of niche powder applications. It is hoped that current scale-up activities will validate both the quality and economics of these products at commercial volumes and provide a platform from which production will expand.

Further information: Metalysis Ltd