Used in the Production of Tiles, Ceramic Bricks and Pavers
Advantages and Features
The oxides of manganese offer those in the ceramic industry a choice of interesting pigments that in some cases add to the mechanical properties of the final material - be that brick, tile or other ceramic. African Pegmatite is the leading supplier of manganese oxides as additives.
Manganese dioxide is a naturally occurring mined resource that can be processed into a ferro-manganese alloy which can either be further refined or used in its originally occurring mined state. MnO2 is used for several purposes and in several industries including oil, glass, health and animal feed industry. Similarly, it is popularly used in the production of bricks, ceramic, tiles and pavers – here; powdered pigments are used to make blue, black, grey and often brown coloured clay products.
Classification and Description
Represented by the chemical formula MnO2, manganese dioxide is an inorganic compound. Usually appearing brown or blackish, it is a solid mineral that exists naturally as an ore of Manganese in the form of ‘pyrolusite’ is an ore which bears multiple oxides of manganese with the chemical formulae MnO, MnO2 and Mn3O4.
When used as a pigment in the production of bricks, it also exists as the synthetic compound of hausmannite, MnO (manganosite) and Mn2O3 (manganese trioxide). MnO2 and Mn3O4 bricks are produced in large volumes globally via the use of the manganese as a brown clay pigment
Derived from the refining of ferromanganese, Mn3O4 is also mined and exists naturally as umbers or braunite and is used in several applications including the production of dense and strong brown bricks, owing to the addition of a brown clay pigment. Likewise, it can also be employed in the production of dark brown bricks with a combination of clay. Clay can be unstable when fired at extremely high temperatures and in some instances requires a stronger variant of manganese to produce a darker shade of brown - or even black.
Manganese dioxides and oxide powder are also used in the production of dark shades of red fired clay and in the production of dark brown facing bricks, ceramic bricks, pavers and roof tiles.
Broadly speaking, therefore, the various oxides of manganese occur in ores together - and are thus mined together. Manganese umber is a mixture of all of these and the iron oxide that is commonly found alongside the manganese in the rock. In some cases, pretreatment of the umber prior to using it as a ceramic pigment is possible via calcination. If this occurs, an even darker pigmentation to the final product is possible.
Manganese umber as supplied by African Pegmatite has the following specification.
|Appearance||Dark brown powder|
|Manganese content (by weight)||43 - 47% |
42% is available on request
|Other notable compounds present||SiO2 4 - 6%; CaO 5 - 7%|
|Particle size||45 μm typical|
|Bulk density (tapped)||1.53 - 1.55 g cm-3|
Bulk stability is good for manganese umber - being shelf stable for lengthy periods of time. Particle size can be tuned to a particular specification, mixability and thorough dispersal is good. When included in a clay mixture for the production of bricks or ceramics, the firing stability is good. Firing temperatures in the standard range (up to ca. 1,300 °C) are well tolerated, although slightly lower temperatures (ca. 1,150 °C) are preferred with the added benefit of requiring less manganese umber to achieve the same colour. With the bulk density value, there is no significant weight penalty to using manganese umber.
As a general rule of thumb, manganese oxide pigments for bricks, tiles and ceramics are preferred as a little pigment goes a long way. In most cases, as little as 1 to 6% by weight of the pigment needs to be used - meaning manganese umber is very cost effective, even on the largest of scales. Naturally, the impact of the identity of the clay itself will play a major role, especially with regard to firing temperature. Manganese umber incorporation into a clay ceramic needs a minimum of 850 °C.
Benefits of Manganese Oxide
Manganese has two major advantages that both help to improve the use and structure of bricks.
- As opposed to regular red bricks, MnO2 bricks and Mn3O4 bricks absorb less water
- The inclusion of the manganese oxides greatly improves the surface structure of bricks, making it a more smooth and homogenous choice.
The combined result is that a smoother, more refined and uniform brick structure is produced that is more visually appealing.
Manganese for Colouring Tiles, Bricks and Pavers
Manganese is one of the most commonly used pigments or colour agents in the production of clay bricks. Some of these range of colours include various shades of brown, ranging from light to dark. As a vital pigment component in clay and ceramic products, manganese may also as a colour agent for:
- Roof tiles
- Facing bricks
- Ceramic tiles
- Paving slabs
The exact colour is often dependent on some factors, including the nature of the clay used for the production process, with high iron content clays often producing darker coloured end products, in general. As mentioned, typical inclusions are on the order of 1 to 8% of manganese umber by mass, with added density not being an issue.
It should be noted that at the higher end of inclusion values, the excess manganese umber will cause crystallisation that will present as a ‘speckled’ appearance on the brick or ceramic. Taking this to the extreme, inclusions in excess of 20% by weight can take on a metallic appearance, which is the result of some of the manganese transitioning to the metal state.
The Role and Application of Manganese Dioxide in The Production of Slabs, Bricks. Tiles and Paving
For the production of bricks, manganese umber is carefully introduced into the production process at a particular stage.
As bricks, slabs and other products can be made from a variety of starting materials (i.e. not always clay in the conventional sense), the starting material is described as ‘aggregate’. The aggregate is formed into the correct size pieces. Water is then introduced and the mixture is uniformly mixed until the mixture assumes a clay-like texture. At this stage, a calculated amount of manganese umber is introduced to the mixture – this is usually added on a per tonne basis, depending on the exact colour required. Other additives are also added at this time. As already mentioned, 1 to 6% by weight is commonplace. The more manganese, the darker the colour. Adding pigments at this stage is crucial to ensure uniform distribution and therefore a uniform final colour.
Once manganese dioxide has been added to form a homogenous mixture, it is then extruded via a long rectangular pipe, where it is then called the slug. Other shaping techniques are available aside from extruding, including hand molding and machine pressing.
The slug then passes through a variety of processes that will determine its size, its weight and then the clay is allowed to dry, typically in specialist dryers. This is a crucial step before firing as firing a wet clay will lead to cracking. All of these steps are done according to the preference of the finished clay product. Firing in a kiln is the final step.
Should a superficial coating be required, manganese umber can be applied to the outer surface of the ceramic before firing, however this will not afford the same level of weather resistance, strength or depth of colour throughout the product. It is therefore recommended to avoid superficial coatings in favour of full incorporation - this has the additional benefit of being less labour intensive.
Braunite is an ore of manganese that falls into a group referred to as ‘compound oxides’. Braunite is represented by the chemical formula Mn2+Mn3+6[O8|SiO4], meaning it interestingly contains manganese in two oxidation states. Braunite will often crystallise and form small crystals of dipyramidal habit when placed in a tetragonal system.
Braunite often spots a pure black, matte black lustre or semi-metallic black colour. Additionally, it can be said to exhibit partial magnetism properties and ranks 4 on the denseness hardness scale.
Braunite is commonly used in the production of pavers, bricks and roof tiles – in these applications braunite is known to produce natural brown hues that shine on the surface of the clay.
Spotlight on K37
K37 is a related product to manganese dioxide, offered exclusively by African Pegmatite. K37 black brick oxide is an in-house developed manganese based pigment for ceramics and bricks. A finely tuned combination of oxides of iron and manganese, the pigment K37 is added in exactly the same way as manganese umber during the manufacture of clay bricks and/or ceramics. K37 typically affords darker colours compared to simple manganese umber. A related product, K37B is also available which is more suited to lower quality clays which require lower firing temperatures.
Because we are pioneers and pacesetters at African Pegmatite, we continuously invest and seek new ways to improve both our production style and methods, in a bid to consistently offer innovative and exciting products to our clients. Recently, we developments include a grey firing oxide, black brick oxide and the exclusive ‘true red’ brick manganese – this isn’t the regular Terracotta or usual orange you are familiar with, but rather a brick with amazing and striking red details. Contact us to learn more about our newest product.
African Pegmatite can also introduce Manganese umber at certain points in the manufacturing process to produce a wide range of textures and finishes.
Besides roof tiles, bricks, pavers and other conventional tile products, Manganese can act as both a decolouriser and colourant in whiteware, glass, pottery and some types of enamels.
Electronics and Battery cathode mixes also use Manganese oxides in certain stages of their manufacturing processes. A future possibility, pending the completion of trials, is the use of Manganese in the production of solid-state Lithium-ion batteries for electric vehicles. Also, the health industry uses Manganese in its pure form to make a variety of dietary supplements.
What We Do
African Pegmatite is a dealer and expert in both the production and distribution of manganese umber – precisely the kind used for colouring pavers, bricks and a host of other clay related products, inclusion additives, pigments and more.
African Pegmatite can also provide similar items such as K37 and chrome flour for tiles, pavers, ceramic black bricks and roof tiles. Similarly, the company also deals in yellow ochre for mortar, concrete mixes and cements. Supply of kaolin for making ceramics and glass powder for the manufacture of ceramic porcelain and a wide range of other uses including as a filler material in concretes.
African Pegmatite stands ready to help customers with any ceramic related discussions or special requirements that they may have. Since a variety of factors such as firing temperatures and the specific kind of clay can affect the outcome, African Pegmatite recommends engaging in an open dialogue so that customers can share their concerns and preferences with us. This will further help us envision your idea and create an intriguing replica.
African Pegmatite actively encourages customers to send a sample of their clay. This would enable us to run real-life tests to offer the customer several options on a choice of colour, texture and style. Additionally, this allows us to tailor the mineral to exactly the right size to ensure optimal incorporation.
African Pegmatite proudly boasts over half a century of experience, combined with the broadest reach and the latest technologies - allowing us to offer a complete service.
- Manganese oxides are able to add a unique colour profile to any brick, ceramic or tile - primarily in the brown colour palette
- The inclusion of manganese not only provides a consistent and persistent pigmentation throughout the finished product, but has advantages in terms of resilience to weathering and chemical attack
- K37 is an in-house designed product for black pigmentation of bricks and ceramics, providing a depth of colour like no other
African Pegmatite is the leading supplier, miller and processor of manganese oxide materials and a whole host of related minerals for the production of high end and coloured ceramics, bricks and tiles. With in-house milling and the widest experience, African Pegmatite is the go-to industrial partner.