Ceramic chemistry is a branch of inorganic chemistry

Inorganic chemistry

Inorganic chemistry is the branch of chemistry concerned with the properties and behavior of inorganic compounds. This field covers all chemical compounds except the myriad organic compounds , which are the subjects of organic chemistry...

 that studies the relationship between the physical properties of fired ceramic glaze

Ceramic glaze

Glaze is a layer or coating of a vitreous substance which has been fired to fuse to a ceramic object to color, decorate, strengthen or waterproof it.-Use:...

s and their chemistry. Although ceramic technicians have long understood many of these relationships, the advent of computer software to automate the conversion from batch to formula and analysis has brought this science within the reach of many more people. Physical properties of glazes in fired products (like thermal expansion

Thermal expansion

Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...

, hardness, index of refraction, color and melting temperature or range) are directly (but not solely) related to the chemistry. Properties of glass melts like viscosity

Viscosity

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 and surface tension

Surface tension

Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...

 are also principally products of chemistry.

Technicians in the ceramic tile

Tile

A tile is a manufactured piece of hard-wearing material such as ceramic, stone, metal, or even glass. Tiles are generally used for covering roofs, floors, walls, showers, or other objects such as tabletops...

, tableware, artware, pottery

Pottery

Pottery is the material from which the potteryware is made, of which major types include earthenware, stoneware and porcelain. The place where such wares are made is also called a pottery . Pottery also refers to the art or craft of the potter or the manufacture of pottery...

, sanitaryware, glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

, fiberglass

Fiberglass

Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...

, bottle glass, optical and related industries all use this science.

In ceramic chemistry, fired glazes are viewed as composed of oxides (examples are SiO₂

Silicon dioxide

The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

, Al₂O₃

Aluminium oxide

Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...

, B₂O₃, Na₂O

Sodium oxide

Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....

, K₂O

Potassium oxide

Potassium oxide is an ionic compound of potassium and oxygen. This pale yellow solid, the simplest oxide of potassium, is a rarely encountered, highly reactive compound...

, CaO

Calcium oxide

Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....

, Li₂O

Lithium oxide

Lithium oxide or lithia is an inorganic chemical compound. Lithium oxide is formed along with small amounts of lithium peroxide when lithium metal is burned in the air and combines with oxygen:Pure can be produced by the thermal decomposition of lithium peroxide, at 450°C-Structure:In the solid...

, MgO

Magnesium oxide

Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...

, ZnO

Zinc oxide

Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

, MnO

Manganese(II) oxide

Manganese oxide is the inorganic compound with formula MnO. MnO is a basic oxide that is insoluble in water but dissolves in acids, forming manganese salts.-Preparation and occurrence:...

, Fe₂O₃

Iron(III) oxide

Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...

, CoO

Cobalt(II) oxide

Cobalt oxide or cobalt monoxide is an inorganic compound that appears as olive-green to red crystals, or as a greyish or black powder...

). Each oxide is known to contribute specific properties to the fired glass. Materials suppliers publish chemical analyses of their products that cite percentages of these oxides as well as volatiles (oxides that burn away during firing like H₂O

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

, CO₂

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, SO₃

Sulfur trioxide

Sulfur trioxide is the chemical compound with the formula SO3. In the gaseous form, this species is a significant pollutant, being the primary agent in acid rain. It is prepared on massive scales as a precursor to sulfuric acid.-Structure and bonding:Gaseous SO3 is a trigonal planar molecule of...

).

For example, in traditional ceramics here are some examples of what the application of ceramic chemistry can accomplish:

• Fix glaze defects
  Glaze Defects
  Glaze defects are any flaws in the surface quality of a ceramic glaze, its physical structure or its interaction with the body.-Body/glaze interaction problems:...
  
   like crazing
  Crazing
  Crazing is a network of fine cracks on the surface of a material, for example in a glaze layer.Crazing is a phenomenon that frequently precedes fracture in some glassy thermoplastic polymers. Crazing occurs in regions of high hydrostatic tension, or in regions of very localized yielding, which...
  
  , blistering, pinholing, settling, clouding, leaching, crawling, marking, scratching, powdering.

• Substitute frit
  Frit
  Frit is a ceramic composition that has been fused in a special fusing oven, quenched to form a glass, and granulated. Frits form an important part of the batches used in compounding enamels and ceramic glazes; the purpose of this pre-fusion is to render any soluble and/or toxic components insoluble...
  
  s or incorporate better, cheaper materials, replace no-longer-available ones.

• Adjust glaze melting temperature, gloss, surface character and color (in ceramic color is a matter of chemistry).

• Identify weaknesses (e.g. proximity to volatile firing zones, use of unreliable materials) in glazes to avoid problems.

• Creating and optimizing base glazes to work with difficult colors or stains and for special effects dependent on opacification, crystallization or variegation.

• Create glazes from scratch and use native materials in the highest possible percentage.

In ceramic bodies the physical properties of the final fired product are more related to the firing curve, the physical properties (e.g. particle size and shape, decomposition history) of the ingredient materials and the mineralogy

Mineralogy

Mineralogy is the study of chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.-History:Early writing...

 and interaction between the different particle types.

Crackle glaze

The chemical make up of the Raku pottery glaze called “crackle” is very unique, and differs from most other glazes. Because it is a Raku pottery glaze, it melts and sticks to the clay piece at a much cooler temperature. The Raku kiln gets to about 1,900˚ Fahrenheit, much cooler than the regular stationary kiln can get up to 3,200˚F but usually stays around 2,200˚F. The Raku glazes melt at around 1800˚F, whereas under glazes, and specialty glazes melt anywhere from 1,200˚F-2000˚F. The specific “crackle” glaze has another variable having to do with the elements in the glaze that other glazes do not. After the firing in the kiln, and the reduction process, most glazes color is already “frozen” and simply needs the “quenching” process (emerging the piece into water) to avoid thermal shock, which can result in cracking of the clay itself. When the crackle glaze is taken out of the reduction barrel the color is not frozen and stuck on the piece entirely, it can have many different visual effects. The time the piece of pottery is in the air before it is “quenched” is a large variable, because the amount of time carbon has to get in the cracks of the glaze is what determines the definition of the black lines in the cracks of the white glaze. The fact that the glaze could still be smeared and altered shows there is room for variations in the look of the glaze. The “quenching” process cools the glazes, and once the glazes are not at their melting point the color and place of the glazes are final.

Reduction Process

One aspect of the Raku

Raku

Raku-yaki is a type of Japanese pottery that is traditionally used in the Japanese tea ceremony, most often in the form of tea bowls...

 firing is the reduction process. The reduction process happens directly after the firing of the pieces in the trash can, one moves the piece to the second trash can filled with a combination of full pieces of newspaper, and small strands of newspaper. One then puts the top of the trashcan back on, blocking off the supply of O2 thus the combustible material uses all of the oxygen, and thus the combustion process begins. During this process the heat from the pot touching the newspaper and the paper immediately ignites . With the lid on, the combustible material uses everything in the can and begins to pull Oxygen out from the glaze . Incomplete combustion leads to the formation of carbon dioxide, which embeds itself in the pot creating a smoky black outer layer.

Factors and Process

Raku ware, the ancient Japanese pottery method . There are many factors that go into the raku process. After an initial firing, step one of this process is to put the piece into the raku kiln . This kiln will heat the piece up to 1800 degrees fahrenheit which melts the glazes . After it is at its maximum temperature the piece is removed with metal tongs and placed in an reduction chamber The piece immediately ignites because of the chemistry. When the chamber is capped, the fire slowly burns out due to the lack of oxygen, creating a combustion reaction. A combustion is a chemical reaction between fuel and oxygen . In the combustion reaction, the lack of oxygen causes a reaction in the glazes, making the glazes crack . The amount of oxygen in the glaze, and the chemical makeup of the glaze depends on what color process it goes through. This process of reduction takes ten to thirty minutes . The last step in the raku process is taking the pieces out of the can, or reduction chamber, and putting them into a bucket of cool water, creating the cooling process.. The factors that go into the results of a raku piece are the temperature you pull at, the temperature outside that day, how fast you go into the can, how fast the paper ignites, how long you hold the piece in the flames before you set it down, and how quickly you get the flames out when you put the lid on the can . The process of raku is what determines the factors, and these factors determine how the piece looks in the end.

Combustible Material

An important part of Raku firing is the combustion reaction that occurs in the trash can as a result of various combustible materials reacting with oxygen once ignited. Every combustion reaction needs fuel and oxygen to occur

In these reactions, fuel is a variable because there are so many different options for fuel. It could be anything that is combustible as long as carbon will be produced . Some examples of these combustible materials are saw dust, newspaper, and dried leaves. The most common combustible material to use in the Raku process is any form of wood, for example sawdust or newspaper. This is because wood is made of 48.5% carbon, an extremely important element in Raku firing.. In Raku, it is important for carbon that is produced in the combustion reaction to absorb in the clay piece. This carbon will also give the piece a black color .

The Kiln

The materials used to make kilns are specially designed to hold heat and quickly rise to high temperatures. The cylinder shaped kilns are often lined with several materials that allow them to concentrate and confine the intense heat.
These materials have hight concentrations of alumina and, or silicon, metalloids which are able to reflect the heat from the pottery so that the Kiln itself dos not melt..
The high specific heat of these materials is what prevents the kiln from melting. Specific types of insulation that are used are refractory bricks, ceramic fiber, and aluminous cement. Gas burners are more commonly used for Raku firing because they allow the kilns to reach the neceassary temperature faster than a firebox using wood. The variations of kilns serve different purposes. An example is the downdraft kiln. It draws hot air into a side chamber where the pottery is located, this allows for a more even temperature throughout the kiln.* These special kilns are the main reason that this process is able to occur so quicly and while reaching such high temperatures at 990-1000°C, or 1652-1832°F