abare.gov.au - research report 08.02

2	Recent technology developments

Titanium has a range of physical properties, such as high strength to weight ratio and resistance to corrosion, that provide it with a quality advantage over substitute metals such as steel and aluminium. However, relatively high metal production and processing costs have limited its use to specialised applications such as aerospace, electricity generation and medical. The development of new technologies is likely to reduce production costs in the titanium industry and extend end use applications of titanium metal.

In this chapter, information is presented on the key stages in the titanium supply chain and current R&D projects that aim to develop lower cost production processes to enhance the cost competitiveness of titanium relative to substitute metals.

Titanium supply chain

The titanium supply chain (figure a) includes mining and basic processing, chemical processing and metal processing to obtain titanium metal products that are intermediate inputs in end use applications. More detailed information is provided in, for example, Roskill (2007).

Mineral sands mining and basic processing

Heavy mineral sands deposits are created on beaches over millions of years as waves and wind remove light quartz from the sand and leave behind the heavier minerals. A single mine site will often supply a mix of minerals such as rutile, ilmenite, leucoxene and zircon. The mining process is fairly simple — the sands are either strip mined or dredged and then transported to a mineral separation plant. The plants use physical methods, such as gravity separation spirals and magnets, to separate the different minerals.

The titanium dioxide (TiO₂) content of rutile and ilmenite is around 95 per cent and 60 per cent respectively (Lines 2007). Ilmenite must be upgraded to high TiO₂ content titanium slag or synthetic rutile before it can be chemically processed into titanium tetrachloride (TiCl₄), which is a key input in the titanium metal industry.

In the Russian Federation, the Ukraine and Kazakhstan, ilmenite is upgraded by transforming it into titanium slag. In all other countries, ilmenite is upgraded by transforming it into synthetic rutile. Two methods are used to produce synthetic rutile — the Becher process and the Benilite process. The Becher process is used in Australia, while the Benilite process is used elsewhere in the world. The Becher process involves reduction, aeration and acid leaching. The Benilite process also involves reduction and acid leaching but in the presence of different chemicals. Synthetic rutile is produced in seven locations worldwide. There are three plants located in Western Australia that have a total capacity of 800 000 tonnes a year, accounting for around 86 per cent of global synthetic rutile capacity in 2006 (Roskill 2007).

Chemical processing

Rutile, synthetic rutile and titanium slag must be converted into TiCl₄ before it can be further processed into pure TiO₂ or titanium metal. In 2006, around 97 per cent of TiCl₄ was processed into TiO₂ powder with the remainder used in the titanium metal industry (TZMI 2007). To produce TiO₂ powder, TiCl₄ is superheated in the presence of oxygen. Plants that produce TiO₂ are often vertically integrated from the mine. This is the case for the Tiwest joint venture in Western Australia.

Metal processing

The current method for producing titanium metal uses the Kroll process where titanium sponge is produced as an intermediate product. The Kroll process is costly because it takes a number of days to convert a batch of TiCl₄ into titanium sponge, which needs to be physically removed from the reaction vessel and melted to produce titanium ingot (more detailed information on the Kroll process is provided in appendix A).

The ingot is worked into mill products such as wire, bar, sheet, plate, coil and tube. This stage of production tends to produce 40 per cent scrap, on average, which is remelted into ingot (Roskill 2007). Scrap can also come from recycling end use products, especially from aerospace applications.

Titanium powder is also produced in small amounts as a byproduct of melting the ingot. Ingots can also be intentionally destroyed to produce greater quantities of titanium powder. Titanium powder can be directly melted into an end use form that avoids the need for milling. Titanium powder currently makes up around 5–7 per cent of global titanium metal consumption (CSIRO communication).

The three stages of metal production — sponge, ingot and mill — are often integrated into a single firm. However, there are currently no metal producing firms that are integrated with a mine. In 2006, there were fourteen companies involved in the production of titanium metal (table 1). The largest producer is located in the Russian Federation and accounted for 24 per cent of global capacity. Overall, the top four producers accounted for 70 per cent of global capacity, the next four producers accounted for 23 per cent and six companies accounted for the remaining 7 per cent.

The regional distribution of global capacity in 2006 was 47 per cent in CIS countries (the Russian Federation, Ukraine and Kazakhstan, each with one producer), 29 per cent in Japan (two producers), 14 per cent in China (six producers) and the remaining 9 per cent in the United States (three producers).

End use applications

Around 93 per cent of TiO₂ is used as a white pigment in paint, plastic and paper — its high refractive index makes it ideal in this role (TZMI 2007). It is also used in sunscreens and as a photocatalyst in chemical based solar cells.

Titanium metal is used in specialty applications where its physical properties such as strength, appearance, weight and biocompatibility justify its high cost relative to other metals — information on some key quality attributes of titanium and substitute metals is given in box 1. Historically, aerospace applications have dominated titanium metal consumption — titanium’s high strength to weight ratio makes it an ideal material for use in fuselages, bolts, frames and panels.

In the industrial sector, titanium is used mainly in power generation, chemical processing and marine engineering. In these industries, titanium is used to make condensers, tubing and heat exchangers — titanium’s high corrosion resistance makes it well suited to these applications. Titanium is also used in a large number of other applications such as military armour, architecture, watches, eye glasses, sports equipment and medical implants.

R&D projects on titanium production processes

The first method of producing titanium to be commercialised was the Hunter process, which involved the reduction of TiCl₄ in the presence of sodium rather than magnesium. The Hunter process was made redundant with the exploitation of economies of scale in the Kroll process.

Despite gradual efficiency improvements in the Kroll process, the widespread use of titanium metal is hampered by the high costs of production and the fabrication of end use products. If costs could be reduced, titanium’s unique physical qualities and the abundance of its ores would likely lead to large increases in its use. The potential for widespread titanium use combined with its military applications has encouraged research into new methods of producing titanium.

Twenty organisations are currently conducting research into new methods of producing titanium (table 2). Research into new production methods has focused mostly on either the electrolytic reduction of titanium, a process similar to the smelting of aluminium, or the chemical production of titanium powder. The electrolytic reduction of titanium from titanium tetrachloride or titanium dioxide precursors has, so far, not demonstrated success toward commercialisation. However, chemical processes to produce titanium powder, such as the CSIRO’s TiRO process, are showing promise. The chemical process closest to commercialisation is the Armstrong process marketed by ITP, which also produces titanium powder.

box 1

Quality attributes of titanium and substitute metals

Some key quality attributes of titanium are compared with those of substitute metals including magnesium, steel, aluminium, iron and copper in the table below.

Titanium has the highest strength to weight ratio of any metal up to 500 degrees Celsius (Roskill 2007). The tensile strength of commercially pure titanium is equal to that of steel alloys and twice that of the most commonly used aluminium alloy (6061-T6). Some titanium alloys exhibit tensile strengths over three times greater than commercially pure titanium. For its strength, titanium is also light — titanium is around 45 per cent lighter than most steels and even though it is twice as strong as common aluminium alloys, it is only around 60 per cent heavier.

Titanium is also notable for its corrosion resistance. It is resistant to corrosion from dilute acids, wet chlorine gas and salt solutions. When titanium is exposed to air at high temperature, a protective oxide coating develops that aids in corrosion resistance. At room temperature, titanium resists oxidation in air.

Physical properties of titanium and substitute metals

		tensile	strength to
	density	strength	weight ratio	corrosion rate

	g/cm³	PSI		mm a year

titanium (commercially
pure grade 2)	4.5	40 000	8869	0.0003
magnesium (pure)	1.7	14 000	8046	0.3
steel (316 series)	8	33 000	4110	0.03
aluminium (alloy 1199)	2.7	5000	1852	0.1
iron (pure)	7.9	7250	921	0.1
copper (annealed)	9	4830	539	0.04

Source: www.matweb.com

Titanium’s physical properties do create some drawbacks in commercial use (Roskill 2007). Its affinity for air, although beneficial in end use products, causes problems at the melting and alloying stages of production. This results in most of the stages of the Kroll process being conducted in inert atmospheres or vacuum, which increases the difficulty of extraction and fabrication. Also, despite its high corrosion resistance, titanium still corrodes rapidly in phosphoric, hydrochloric and sulphuric acids, hot caustic soda, dry chlorine, ammonium chloride (above 520°C), ammonia (above 150°C) and hydrogen sulphide (above 150°C).

TiRO/CSIRO process

The TiRO process has been developed recently by the CSIRO as an alternative method for producing titanium metal. It relies on the same chemistry as the Kroll process but allows TiCl₄ to be turned directly into commercially pure titanium powder. It differs from the Kroll process as it produces powder not sponge and does so in a continuous, not a batch, process. The TiRO process also requires less labour than the Kroll process.

In the 2001 assessment of the titanium industry, it was found that Australia did not necessarily have a competitive advantage in producing titanium sponge (DISR 2001a). The TiRO process may be able to provide Australia with a competitive advantage in the production of titanium — this is as a result of TiRO’s continuous process and low use of labour reduce costs. The output of the TiRO process, titanium powder, also means that the expensive and wasteful fabrication of titanium mill products can be avoided. Titanium powder can be formed directly into finished parts using powder metallurgy, a process known as near net shape fabrication.

Alternatively, the powder can always be melted into ingots and machined as normal. More detail on the technical specifics of the TiRO process is provided in appendix A.

Other research projects

The electrolytic reduction of titanium would produce solid or liquid metal. Liquid metal production would make titanium production similar to many other metals. However, the electrolysis must take place at very high temperatures, around 1700 degrees Celsius, and the process involves a number of technical challenges. GTT s.r.l. have pursued this method since around 1980, with little success. BHP Billiton and Rio Tinto have also supported research into electrolytic reduction.

Four groups have received funding from the US Department of Defense — SRI International, MER, FFC Cambridge and ITP. Of these four, the Armstrong process, being marketed by ITP, is the closest to commercial implementation.
In 2006 ITP were producing 16 tonnes a year of commercially pure and alloyed titanium metal using the Armstrong process. The Armstrong process uses the same chemistry as the Hunter process, the reduction of TiCl₄ with sodium. The Armstrong process is, however, nearly continuous. There are currently plans to construct an 1800 tonne a year pilot plant to commence production in 2008. The Illinois Government is offering US$700 000 to support the project.

Importantly, ITP has produced titanium containing less that 0.05 per cent oxygen. This is low enough to have the metal classed as commercially pure grade 1. The current TiRO process operated on the laboratory scale is producing metal with an oxygen content that is above the 0.25 per cent mandated for grade 2 commercially pure titanium, the goal of the project. Promising research addressing this issue is in progress and CSIRO believes that this problem can be fixed in a larger scale pilot plant (CSIRO 2006).

Parts, including racing car brakes, have already been produced from ITP powders and the company is beginning the certification of its powder to industry standards. However, it is not clear whether the ITP process significantly reduces the cost of producing titanium. It uses sodium, a difficult material to work with, and it relies on the same feedstock, TiCl₄, as the Kroll process. Its main advantage is the ability to produce titanium powder, which can allow for near net shape fabrication.