Green bottles on assembly line, coloured with iron chromite

Iron Chromite – Applications and General Uses

Iron chromite is the naturally occurring ore of chromium that is prized for its refractory abilities - making it invaluable in the modern foundry for the most demanding tasks at temperature. Not only this, but chromite finds wide uses even where high temperatures aren’t required. African Pegmatite is the leading supplier and miller of the finest quality iron chromite for any industrial need.

Iron chromite is an inorganic mineral compound that is essential to several industries. It is often called chrome flour, chromite powder,or chromite flour. The chemical composition of is FeCr2O4. This compound is preferred for many industrial applications because of its high heat stability, resistance to thermal shock, and resistance to corrosive gasses and slags. It is a refractory material.

Chromite powder isn’t just used to make industrial materials. Stainless steel dinnerware, wine or beer bottles, ceramic décor, certain bricks, cement and more require chromite powder at some point during their manufacturing processes. It can improve the quality of certain items, change the appearance of others and make production safer for those involved.

Below are some of the most common applications.

Pouring molten material into refractory moulds made with iron chromite

Kilns and Furnaces

Iron Chromite is essential to the production of refractory materials like bricks and cement. Because they are used in high-temperature environments like kilns and furnaces, these materials have to be able to withstand repeated exposure to extreme heat and cooling. The chromite powder used in manufacturing refractory bricks and cement provides the necessary thermal resistance to avoid cracking.

If the refractory materials were to crack or wear down prematurely during the repeated heating and cooling processes, they could cause a loss of heat that would drive production costs through the roof in a best case scenario. A worse case could involve a loss of inventory due to inadequate temperature control. In some cases, damaged refractory materials could cause a dangerous release of heat and pressure from within the furnace.

Various industries rely on the stability of this material in refractory applications. The production, processing, and purification of metals requires a metallurgy furnace. Recycling of steel and iron is done in an electric arc furnace. Cement is created in rotary kilns, and there are a few different furnace types that can be used to make glass. Each of these kilns and furnaces requires refractory materials.

Refractory Bricks And Linings

As mentioned, the high temperature metals production space would not be able to function without refractory materials such as chromite. Starting in the 1960s, foundries began adding oxygen directly into their furnaces, causing higher operating temperatures - these furnaces therefore needed to be able to handle such elevated temperatures. Magnesite-spiked chromite bricks, replacing silicate bricks, started to become used(1) and it was found that the presence of chromite led to fewer shock incidences and less spalling(2). Contemporary refractory bricks containing chromite, alumina and magnesia can be strong and stable at temperatures up to 1,900 °C - far superior to the silica bricks they replaced(3). Casted magnesite chromite is denser than when in brick form due to its lower porosity(4,5). Modern bricks are rarely solely a single material.

Tundish Linings, Ladle Sand And Slide Gate Protection

In continuous casting, various tools and techniques are used to take molten metal from furnace to casting site in a short time and without running the risk of solidification. Production of stainless steel requires hours of extreme heat application.

Tundishes are a vital part of the continuous casting process and are refractory lined vessels used for movement of molten metal around a foundry, for example from smelter or furnace to casting area. The linings in these tundishes are often chromite rich - ensuring that the metal stays molten whilst protecting the structural integrity of the tundish superstructure. Refractory linings for tundishes contain magnesia chrome - made when chromite and manganese oxide have been cured together, with the chromite adding a superior degree of thermal performance and chemical resistance(6).

During the continuous casting process, chromite powder is used as part of a compound that prevents the molten metal from settling in any tap hole and solidifying. Blockage of a tap hole will cost time and other resources to remedy and could cause violent and dangerous expulsions of pressure during release. This material's extreme heat tolerance helps maintain both efficiency and safety during the stainless steel production process.

This deployment of chromite is in the form of sand and is referred to as ‘ladle sand’. It ensures the free flowability of the molten metal out of the ladle used to transfer molten metal. Additionally, it prevents the egress route from getting blocked when the slide gate that controls molten metal flow opens and closes. It is chromite’s resistance to high temperatures that make it useful in this application, in addition to its ability to evenly distribute temperature. These factors work in concert.

Finally in the metal pouring space, chromite is a vital component in refractory plaster. This vital material is manganese heavy and is applied to fill the gaps between refractory bricks in a tundish, ladle or even furnace. The manganese present assists with resistance to slag(7).

Green Sand Castings

Chromite is a popular choice for green sand casting - often being used for the most intricate and high end casting requirements owing to its higher cost than other sands - due to chrome sand’s superior thermal and chemical resistance properties. Chromite can be used as the major component of a sand mold or as a minor additive. Because of the aforementioned superior properties, green sand casting is more tolerant of a wider range of temperatures and metals. Typical deployments can include the manufacture of refractory cores(8), heavy and highly sectioned ferrous castings and for castings with high manganese content steels(9) because of its resistance to chemical attack. It is largely resistant to wetting(10). Anthracite is often used to aid removal.

Use Of Chrome Refractories In Gasifiers

Gasifiers are the reactors in which carbonaceous materials (such as coal, coke and biomass) are converted to synthesis gas, with the most common gasifier type is the entrained flow type gasifier. Gasifiers operate under high temperatures and pressures and can contain harmful chemical residues. Ash production in the process leads to the build up of slag which can cause unwelcome penetration of the refractory lining material of the gasifier, at which undesirable side reactions can occur. A sensible choice for the refractory material is chromite - a material known for robustness and resistance to slag(11). Most modern gasifiers use chrome-alumina as their refractory material of choice(12), despite the heightened costs of acquiring the chrome-alumina refractory(13), especially over magnesia-chrome. Chrome-alumina outperforms magnesia, especially when acidic slag is present(14). Some modern plants elect to use a layered approach to chromite-based refractory linings: high content chrome at the hottest parts of the reactor, with lower amounts at the cooler sections(15). Gasifiers produce synthesis gas which, amongst many other uses, is used in the Fischer Tropsch process.

Architecture and Interior Design

Chrome flour creates beautiful shades in both interior and exterior building materials. The versatile range from dark charcoal to a cloudy, off-white grey provides gorgeous contemporary, natural, and rustic looks

Clay bricks, paving units, and roof tiles can be made in various shades of grey by adding chromite powder to ivory filling clays during production. These hues have become increasingly popular in recent years in architecture and in the construction of both residential and commercial properties.

This range of greys is also applied to ceramics through the use of chromite powder. The desired colour can be created in the ceramic itself or as a glaze. Grey ceramics are in high demand as popular flooring materials. Plain ceramic tiles, as well as ceramic tiles made to resemble natural stone and wood, are made using this material.

Brick wall colour made using chrome flour

Stainless Steel

Stainless steel is used in everything from dinnerware and jewellery to surgical instruments and tools. Stainless steel is not only attractive and nonporous, but is also resistant to rust and corrosion that can affect alternative metals. It’s strong, hygienic, relatively easy to fabricate, and depending on the grade, can be resistant to high and low temperatures. Stainless steel is steel that has been produced with added chromium - chromite can be a source of such chromium.

Various coloured bottles green brown and yellow some made with chrome flour

Knives and Blades

Green compound is a substance applied to pieces of leather or cloth that are used to polish the blades of various cutting tools and optical devices. This compound can also be used in powder form and hones the tools’ edges to a mirror polish. Polishing with this method sharpens better than using a stone or other sharpening device alone.

Pigment

The high stability makes it very useful as a pigment in paints, inks, and coloured glass. Chrome flour provides consistent, uniform colouration throughout the chosen material and is preferred for its rich pigmentation. In paints and inks, it can be used alone or combined with various compounds to create specific shades.
It is used to make both oxidised and reduced green glass containers. Many of these containers also use iron pyrite in order to alter the colour and provide more powerful protection from ultraviolet radiation.
The colours made from iron chromite include:

• Emerald
• Georgia
• Deadleaf (feuille morte)
• Dark Olive
• Champagne
• UV
• Antique

Chromite has an oxidative impact on the batch redox number. To achieve the colours mentioned above, chromite is often combined with iron pyrite. UV protection in glass containers is an essential factor for many industries. Some oils and beverages are sensitive to sunlight and have to be packaged accordingly. Beer, wine, essential oils, and light-sensitive pharmaceuticals are generally stored in glass containers that are either green, amber, or a combination of the two. Some brands also use their container colours to help them stand out and promote brand awareness.

long green bottle necks

Chrome Plating

Chrome plating is a popular process by which a thin layer of chrome is applied to a metal object. Commonly performed on tools, cookware, and car parts, chrome plating provides increased corrosion resistance, increased hardness, more convenient cleaning, and a brilliant metallic shine that is preferred by many over the lustre of the original materials.

The chromium for chrome plating is extracted from chrome flour. It is dissolved in a plating tank and drawn to the desired object by running an electric current through the solution. This process is called electroplating. You might hear chrome-plating referred to simply as “chrome”.

Leather Tanning

Iron chromite as an oxidising agent was adopted by tanners around 1840 as a faster alternative to the widely-used method of vegetable tanning. Tanning alters the protein structure of the hide, improving its durability, reducing the risk of decomposition, and in some cases, applying the desired colourant to the skin. Chrome tanning is preferred for its ability to be done quickly and to produce a stretchable leather. This type of strong, stretchy, and coloured leather is perfect for clothing and accessories like handbags.

Tops of green bottles

Importance of Iron Chromite

Found in large deposits in South Africa, India, and several other countries around the world, it is mined and milled for several industries that produce items used everyday. Its importance - through the applications detailed above and though others - cannot be understated.

Summary

  • Chromite is a naturally occurring ore of chromium and is regarded as a superior refractory and for being ‘almost chemically inert’
  • It has many applications in the refractory space, from furnace linings to tundishes to green sand castings as well as in glassmaking
  • Outside of the foundry, chromite finds wide use in leather tanning and interior design

Ensuring a good quality supply of iron chromite is essential to today’s modern foundry processes including glassmaking and metals production, in addition to a wide range of uses in non-high temperature environments. African Pegmatite is the leading supplier of the finest quality iron chromite, milled to any specification.

Chromite Flour in a pot

References

1          A. Muan and E. F. Osborne, Phase Equilibrium among Oxides in Steelmaking,  Addison Wesley, Reading, United States, 1965
2          W. D. Kingery, H, K. Bowen and D. R. Uhlman, Introduction to Ceramics, 2nd ed., Wiley, New York, 1960
3          E. Ruh and J. S. McDowell, J. Am. Ceram. Soc., 1962,  45, 189
4          W. E. Lee and W. M. Rainforth, Ceramic Microstructures - Property Control by Processing, Chapman and Hall, London, 1994
5          J. H. Chesters, Refractories: Production and Properties,  Institute of Materials, London, 1973
6          R. Cromarty et al., J. S. Afr. Inst. Min. Metall., 2014, 114, 4
7          M. Kalantar et al., J. Mater. Eng. Perf., 2010, 19, 237
8          Fundamentals of Aluminium Metallurgy, R. N. Lumley (ed.), Woodhead Publishing, Melbourne, 2018
9          M. Holtzer et al., Arc. Foundry Eng., 2013, 13, 39
10        J. E. Kogel, N.C. Trivedi, J. M. Barker and S. T. Krukowski (eds.), Industrial Materials and Rocks, 7th ed., 2006, SME Press, Littleton, United States
11        H. B. Kim and M. S. Oh, Ceramics Int., 2008, 34, 2107
12        J. P. Bennett, Refractories Applications and News, 2004, 9, 20
13        W. A. Taber, Refractories Applications and News, 2003, 8, 18

14        J. A. Bonar et al., Am. Ceram. Soc. Bull., 1980, 59, 4
15        Z. Guo, Am. Ceram. Soc. Bull., 2004, 83, 9101