The element zirconium is found in igneous rock such as granite and occurs as the naturally occurring oxide, baddeleyite (ZrO2) and more commonly as a compound with silica: zircon (ZrSiO4).

The weathering of igneous rock has led to the formation of large secondary deposits in beach sands. These deposits are generally associated with other heavy minerals sand such as imenite and rutile. Zircon is often mined as a by-product of these minerals.

Australia and South Africa have the largest commercial deposits of zircon while there are also significant deposits in the USA and India.

While a considerable amount of zircon sand is used in the production of refractories, glass and glazes it is finding increased application as feedstock for the production of added value chemicals and high purity oxides.

Over the last 10 years China has been playing an increasingly important role in the production and refining of these zirconium chemicals and oxides and now accounts for more than 60% of the world's output.

 

The caustic decomposition of zircon sand is a common process route for the production of a high purity zirconium oxychloride. This compound is used as a raw material for applications such as the production of titanium pigments and also as a pre-cursor for the production of a range of zirconium chemicals such as zirconium carbonate and zirconium hydroxide.

Thse basic chemicals are used in a wide range of applications including antiperspirants, paint driers, leather tanning, inks and catalysis. They are also used as the raw materials for the production of high purity chemically precipitated zirconium oxides.

ABSCO Materials supplies a range of high purity zirconium chemicals.

 

There are 2 main types of monoclinic zirconium oxide: one is from a thermal route and the direct fusion of zircon sand; and the other is the chemical precipitiation of zirconium chemicals.

The dissociation of zirconium oxide and silica can be carried out at high temperatures in an electric arc furnace to produce a fused zirconium oxide. The silica is reduced to the volatile silcon monoxide that reoxidises at the furnace mouth and is recovered in dust collectors as silica fume. The zirconia is reduced to the carbide and can be roasted in air to produce the fused zirconium oxide.

Fused zirconium oxide is a lower purity oxide, typically in the range of 98-99% ZrO and is used in refractories, pigments and abrasives. With the reduced availability of baddeleyite, fused zirconium oxide has become the substitute.

For many applications of fused zirconia the particle size distribution is very important. ABSCO Materials supplies a range of mesh sizes and finer particle powders and can supply powders tailored to individual specifications.

Chemical preparation, calcination and milling stages lead to the production of high purity chemical zirconias with specific and very individual physical characteristics. Process control enables very specific particle morphology, particle size and surface area which all greatly efffect the powders' performance.

ABSCO Materials supplies a range of chemcal zirconia powders with different purities, from 99.0 to 99.99% ZrO2, and also physical characteristics including particle size and surface area. ABSCO can also work with customers in the production of tailored powders to meet individual requirements.

ABSCO Materials supplies specialist zirconium oxide powders for use in structural ceramics, electro ceramics, thermal barrier coatings and refractories.

Monoclinic zirconium oxide can be restricted in its applications due to the phase transformations it undergoes during heating. These phase transformations lead to changes in volume resulting in structural cracking and failure. These phase alterations can be controlled by the addition of dopants known as stabilisers. Once stabilised, zirconia can be used in applications running at temperatures in excess of 2200 degrees centigrade.

ABSCO Materials offers a range of stabilised fused and co-precipitated zirconia powders.

Fused zirconium oxide can be stabilised during the fusion process by the addition of stabilisers such as yttria, magnesia and calcia. After fusion the material is crushed and milled to different particle sizes. ABSCO Materials supplies a range of YSZ, MgSZ and CaSZ powders with particle size distributions produced for specific applications or to customer specification.

The chemical co-precipitation of intermediate zirconium and dopant compounds produces a very homegenous product with the doping element well dispersed within the structure. The precipitate is then calcined under controlled conditions to produce very specific particle size, morphology and surface area. All of these physical characteristics are very important in the powder's performance.

ABSCO Materials offers a range of yttria and magnesia stabilised co-precipitated zirconia powders for structural/engineering ceramics and refractories.

Stabilised zirconia powders can be supplied as raw powders or in granular form for spray coating or pressing.

Pure zirconium oxide (unstabilised) is monoclinic at room temperature but its structure changes to a tetragonal form at around 1000 degrees C. With this phase change there is a large volume change that results in structural cracks leading to a very low thermal shock resistence.

Partial stabilisation of zirconia occurs with the addition of a dopant material such as 3-4mol% yttria, 2-3mol% magnesia or 8mol% calcia. This leads to a mixture of structural phases at different temperatures. A mixture of cubic, monoclinic and some tetragonal phase up to 1000 degrees C. and tetragonal at higher than 1000 degrees. Due to the tetragonal phase at higher temperatures partially stabilised zirconia is also known as tetragonal zirconia polycrystal (TZP). It is generally believed that microcracks and induced stress amongst the different phases are reasons for the toughening in partially stabilised zirconia.

Partially stabilised zirconia tends to be used when high temperatures are needed. The low thermal conductivity ensures a low heat loss and the high melting point (2,700 degrees C.) means stabilised zirconia regreactories can be used in temperatures in excess of 2200 degrees C. Partially stabilised zirconia is also finding increased application in specialist structural/engineering ceramics.

Fully stabilised zirconia is generally achieved with dopant levels of 8mol% yttria, 16mol% magnesia or 16mol% calcia. A fully stabilised zirconia has a structure which is a cubic solid solution which has no phase transformation from room temperature up to 2500 degrees C. Fully stabilised zirconia is a very good ion conducting ceramic and is used in applications such as oxygen sensors and solid oxide fuel cells.