Titanium sponge: properties, grades and applications

Titanium sponge is a primary technical product of industrial titanium production, obtained by magnesium or sodium reduction of titanium tetrachloride according to the Kroll process. It is a porous grey metal mass with uneven porosity, resembling pieces of steel alloy with sharp, bristly edges. Titanium sponge is the starting material for the production of titanium ingots, semi-finished products, powders and alloys, without which modern aerospace, chemical, medical and energy industries would be inconceivable.

Chemical Nature and Physicochemical Properties

Titanium (Ti) is a light refractory silvery-white metal, atomic number 22, atomic mass 47.87 g/mol. The density of titanium is about 4.5 g/cm³, and its melting point is 1668 °C. Titanium possesses exceptionally high specific strength (the ratio of strength to density), surpassing many alloy steels, as well as outstanding corrosion resistance, biocompatibility and the ability to operate over a wide temperature range.

Titanium sponge retains all the key properties of titanium but has a developed porosity, which makes it convenient for subsequent remelting and alloying. The titanium content in commercial sponge ranges from 97.75% to 99.74% depending on the grade. The most important impurities determining the quality and hardness of the sponge are oxygen, nitrogen, iron, silicon, carbon, chlorine and nickel. It is the content of these elements, especially oxygen and nitrogen, that determines the Brinell hardness and the application area of the material. The lower the impurity content, the higher the ductility, fracture toughness and corrosion resistance of the final products.

Classification, Grades and Standards

In Russia and CIS countries, requirements for titanium sponge are regulated by GOST 17746-96 "Sponge titanium. Specifications". The standard applies to sponge titanium obtained by the magnesium-thermal method with vacuum-thermal purification and serving as the starting material for the production of semi-finished products from titanium and its alloys. Depending on the chemical composition and mechanical properties, the following grades are established: TG-90, TG-100, TG-110, TG-120, TG-130, TG-150 and TG-Tv. The letters "TG" stand for "titanium sponge", and the numbers correspond to the maximum Brinell hardness (HB). The higher the number, the greater the permissible impurity content and the lower the product grade. Grade TG-Tv denotes hard titanium with increased iron content, the hardness of which is not standardised.

In international practice, particularly in China, the classification according to GB/T 2524 is widely used, according to which titanium sponge is divided into seven levels: 0A, 0, 1, 2, 3, 4 and 5. Level 0A corresponds to the highest purity (titanium content of at least 99.8%) and minimum hardness, while level 5 corresponds to the lowest purity (about 98.5%). The aerospace and medical industries require the use of sponge of levels 0A, 0 and 1, while the chemical, metallurgical and construction industries can use the more affordable levels 2–5.

Titanium sponge is supplied in the form of pieces of various fractions, usually from 2 to 70 mm (e.g., –70+12 mm, –12+2 mm), as well as in powder form for special applications. Packaging is carried out in hermetic steel drums or containers that protect the material from moisture and oxidation.

Production Technology

Industrial production of titanium sponge is based on the Kroll process, developed in the 1940s and still the main method for producing titanium to this day. The process includes several successive stages.

In the first stage, titanium-containing raw materials (ilmenite or rutile) are beneficiated to produce titanium slag containing 80–90% titanium oxide. The slag is then chlorinated in the presence of carbon (petroleum coke) at a temperature of 900–1250 °C, resulting in the formation of titanium tetrachloride (TiCl₄). The resulting TiCl₄ is purified by rectification from by-product chlorides.

In the second stage, purified titanium tetrachloride is reduced with liquid magnesium in a sealed stainless steel reactor under an argon atmosphere at a temperature of about 850–950 °C. The reaction produces a porous titanium sponge and magnesium chloride (MgCl₂), which is partially drained and partially remains in the pores. After reduction is complete, the sponge is subjected to vacuum distillation or leaching to remove residual magnesium and MgCl₂. The vacuum purification process can take several days depending on the size of the block.

The resulting sponge is removed from the reactor, crushed, screened into fractions and packaged. To produce titanium ingots, the sponge together with alloying elements is pressed into electrode blocks and remelted in vacuum arc or electron beam furnaces.

Applications

Aerospace industry. This is the key and most demanding consumer of high-grade titanium sponge. Titanium alloys are used to manufacture skin, load-bearing structure, landing gear components, turbine blades and aircraft engine casings, as well as components of rocket and space technology. The high specific strength and corrosion resistance of titanium allow the weight of structures to be reduced and their reliability to be increased.

Medicine and biomedical products. Due to their biocompatibility and corrosion inertness, titanium is used for the production of implants (joint endoprostheses, bone plates, screws, heart valves), surgical instruments and dental structures. High-purity sponge with minimal impurity content is used for these purposes.

Chemical and petrochemical industry. Titanium sponge serves as a feedstock for titanium semi-finished products used in chemical engineering for the manufacture of reactors, heat exchangers, pipelines and pumps operating in aggressive environments. Titanium equipment is resistant to chlorine, acids and seawater.

Energy and desalination. Titanium alloys are used in heat exchangers of power plants, desalination plants and cooling systems where high corrosion resistance in seawater is required.

Metallurgy and alloying. Titanium sponge is used as an alloying additive in the production of special steels and alloys, as well as for producing ferrotitanium and other master alloys.

Consumer goods and sports. Titanium is used to manufacture sports equipment (golf clubs, bicycle frames), wristwatches, jewellery and elements of high-quality cookware.

Safety and Storage

Titanium sponge is chemically active and prone to oxidation upon contact with moisture and air. In a finely dispersed state (powder, chips), titanium is fire- and explosion-hazardous. During storage and transportation, the sponge must be protected from moisture and contamination. It is recommended to store it in hermetic containers in dry, well-ventilated areas, away from ignition sources and oxidisers. Long-term storage of titanium sponge can be expensive and hazardous due to possible self-heating and ignition, so the material should be used within the established period.

During mechanical processing (crushing, screening), dust is generated that can irritate the respiratory tract and pose a fire hazard. Personal protective equipment (respirators, safety goggles, gloves) must be used, and effective ventilation of premises must be ensured. Titanium sponge is non-toxic but requires precautions related to its pyrophoricity in a finely dispersed state.

Market and Trends

The global titanium sponge market demonstrates steady growth, driven by the development of the aerospace industry, medicine, chemical industry and energy. The key producers are China, Japan, Russia, Kazakhstan and the USA. China occupies a leading position in output volumes and is actively expanding capacity, including for the production of high-purity grades for aerospace applications.

Key industry trends include tightening requirements for sponge purity for aerospace and medical applications, the development of vacuum purification and impurity control technologies, and growing attention to titanium recycling. Producers with access to quality raw materials and modern refining technologies occupy stable competitive positions.

Conclusion

Titanium sponge remains a fundamental material of modern metallurgy, providing the production of titanium ingots, semi-finished products and alloys for the aerospace, medical, chemical and energy industries. Understanding grade composition, production technologies and quality requirements is necessary for organising stable supplies and effective interaction between producers and consumers. Selecting the sponge grade for specific technological conditions and organising logistics requires an individual approach taking into account impurity content, hardness and fractional composition.