Feldspar

Feldspar is the name given to a group of minerals distinguished by the presence of alumina and silica (SiO₂) in their chemistry.  This group includes aluminum silicates of soda, potassium, or lime. It is the single most abundant mineral group on Earth.  They account for an estimated 60% of exposed rocks, as well as soils, clays, and other unconsolidated sediments, and are principal components in rock classification schemes. The minerals included in this group are the orthoclase, microcline and plagioclase feldspars.

The most important properties of feldspar to downstream industries and many other industries are their alumina and alkali content. For this reason, alkali feldspars (potassium feldspars) have a wide range of applications in paint industries, glass, and ceramic making industries. Here are some of the applications of potassium feldspars.

Feldspar is a critical material in the production of glass. It is also a crucial raw material in its production as it tends to act as a fluxing catalyst. As a fluxing catalyst, it reduces the temperature of quartz while simultaneously helping to keep the viscosity of the produced glass at the right correct range. It is the alkali content of the feldspar that helps it function effectively as a flux in glass making.

Fluxes reduce the overall melting point of a given mixture – this has the benefit of reducing the overall energy requirement needed to achieve a particular melt. Fluxes are widely used throughout the glass and ceramic industries for their ability to promote complete liquefaction. Feldspar melts at an early stage in the overall firing process, efficiently and rapidly producing a glassy matrix that is responsible for holding the other materials in the melt together. Additionally, feldspar can give the glass enhanced desirable properties such as increased hardness, durability and resistance to chemical attack. Alumina and calcium ions are responsible for these effects.

It is the alkalis in the feldspar – chiefly potassium and sodium – that lower the melting temperature within the mixture. They promote the melting of and bonding of the other materials going into the glass batch.

One of the advantages to using feldspar as an additive in glassmaking as a flux is that its addition does not change the batch redox number at all. This is beneficial as any change in redox number will require the commensurate addition of another material to negate the change. Feldspar can therefore be thought of as a more environmentally friendly addition – both due to its fluxing capacity meaning less energy is needed, but also the fact that its addition does not force the addition of other materials.

Glassmaking accounts for around two thirds of feldspar used in the United States in any given year, with the majority of the balance being made up of use as fillers and in ceramics. For glassman

king purposes, feldspars are ground to 0.85 mm (20 mesh)

Putting things in perspective, feldspar is considered the other most critical ingredient – besides clay – in the production of ceramics. It doesn’t have a definite melting temperature, as it melts slowly throughout various temperatures. This is one of its advantages as it accelerates the melting of clays and quartz, while simultaneously allowing modulation of this crucial stage in the production process. They are generally used as fluxing catalysts to produce a glassy coating at low temperatures. They are also used as a source of alumina and alkalis in glazes.

Most often than not, feldspars improve the toughness, durability, and strength of the ceramic body. Also, they melt, soften and wet other components of the batch mix. Ceramic grade feldspars are typically ground to no more than 75 μm (200 mesh).

Just like in glassmaking, the basic components of the feldspars (sodium, potassium and calcium) behave as fluxes – they work with soda ash (like in soda glass) to reduce the melting temperature and increase the fusibility of all components. Additionally, feldspar controls the degree of vitrification of the ceramic body during firing.

Feldspars are functionally used as extenders and fillers in paints, rubbers, and plastics. It is an effective filler because of a number of factors. These factors include its stable pH, high chemical inertness, good dispersibility, impressive refractive index, resistance to frosting, high resistance to abrasion and low viscosity at high filler loading. In general, the products used for such purposes are fine-milled grades.

As a filler in plastics, feldspars find little use in thermoplastics due to their relatively high Mohs hardness, however in plastic films feldspars come into their own as leading components for antiblocking. Blocking is where two (or more) materials interact with one another at their surfaces – antiblocking materials aim to prevent this and are therefore commonly referred to as ‘anti-slip’ agents. It is especially useful in low density polyethylene (LDPE), polypropylene and polyvinyl chloride films. Additionally, feldspars can be used to make LDPE films more suitable to heat management, for example in greenhouses and polytunnels.

In paints, coatings and lacquers, ultra-finely milled feldspars are used as fillers. The non-toxic addition of feldspar is appealing as it reduces overall material cost, but does not impact on the colour density owing to its relatively low refractive indices in the region of 1.0 to 1.5.

In enamel glazes, feldspar helps to enhance the aesthetics of the final product by ensuring that there are no errors in the final product. It is useful in the manufacturing of sanitary ware, ceramic tile glazes, tableware, giftware, electrical, and enamel frits. In sanitary wares, feldspars are used to facilitate the optimization process.

Feldspar also has a host of other end-uses which include urethane, mild abrasives, paints, welding of red coating, production of steel and latex foam