The future of materials: Advanced Ceramics

The future of materials: Advanced Ceramics

In essense he's giving a short history of ceramics and then details all the applications of ceramics he considers fascinating. It becomes boring after a few minutes .. at least for me.

How silicon carbide could help in the development of electri

How silicon carbide could help in the development of electri



How the University of Warwick's Engineering department is developing the use of Silicon Carbide.

Moissanite

Moissanite or silicon carbide (SiC) is a rare mineral that can be found in meteorites and in terrestrial samples. It belongs to the carbon group and because of its similarity to diamonds it is used as a replacement for diamonds in fashion and in science applications.

Ceramic

The word ceramic is derived from the Greek word κεραμικός (keramikos). The term covers inorganic non-metallic materials which are formed by the action of heat. Up until the 1950s or so, the most important of these were the traditional clays, made into pottery, bricks, tiles and the like, along with cements and glass. Clay-based ceramics are described in the article on pottery. A composite material of ceramic and metal is known as cermet. The word ceramic can be an adjective, and can also be used as a noun to refer to a ceramic material, or a product of ceramic manufacture. Ceramics may also be used as a singular noun referring to the art of making things out of ceramic materials. The technology of manufacturing and usage of ceramic materials is part of the field of ceramic engineering.

Many ceramic materials are hard, porous, and brittle. The study and development of ceramics includes methods to mitigate problems associated with these characteristics, and to accentuate the strengths of the materials as well as to investigate novel applications.

Carbon

Carbon (pronounced /kɑɹbən/) is a chemical element with the symbol C and atomic number is 6. It is a group 14, nonmetallic, tetravalent element, that presents several allotropic forms of which the best known are graphite (the thermodynamically stable form under normal conditions), diamond, and amorphous carbon.^[7] There are three naturally occurring isotopes: ¹²C and ¹³C are stable, and ¹⁴C is radioactive, decaying with a half-life of about 5700 years.^[8] Carbon is one of the few elements known to man since antiquity.^[9][10] The name "carbon" comes from Latin language carbo, coal, and in some Romance languages, the word carbon can refer both to the element and to coal.

It is the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is present in all known lifeforms, and in the human body, carbon is the second most abundant element by mass (about 18.5%) after oxygen.^[11] This abundance, together with the unique diversity of organic compounds and their unusual polymer-forming ability at the temperatures commonly encountered on Earth, make this element the chemical basis of all known life.

The physical properties of carbon vary widely with the allotropic form. For example, diamond is highly transparent, while graphite is opaque and black. Diamond is among the hardest materials known, while graphite is soft enough to form a streak on paper. Diamond has a very low electric conductivity, while graphite is a very good conductor. Also, diamond has the highest thermal conductivity of all known materials under normal conditions. All the allotropic forms are solids under normal conditions.

All forms of carbon are highly stable, requiring high temperature to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and other transition metal carbonyl complexes. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil and methane clathrates. Carbon forms more compounds than any other element, with almost ten million pure organic compounds described to date, which in turn are a tiny fraction of such compounds that are theoretically possible under standard conditions

Silicon

Silicon (pronounced /ˈsɪlɪkən/ or /ˈsɪlɪkɒn/, Latin: silicium) is the chemical element that has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon. As the eighth most common element in the universe by mass, silicon occasionally occurs as the pure free element in nature, but is more widely distributed in dusts, planetoids and planets as various forms of silicon dioxide (silica) or silicates. On Earth, silicon is the second most abundant element (after oxygen) in the crust,[1] making up 25.7% of the crust by mass.

Silicon has many industrial uses. Elemental silicon is the principal component of most semiconductor devices, most importantly integrated circuits or microchips. Silicon is widely used in semiconductors because it remains a semiconductor at higher temperatures than the semiconductor germanium and because its native oxide is easily grown in a furnace and forms a better semiconductor/dielectric interface than any other material.

In the form of silica and silicates, silicon forms useful glasses, cements, and ceramics. It is also a constituent of silicones, a class-name for various synthetic plastic substances made of silicon, oxygen, carbon and hydrogen, often confused with silicon itself.

Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals. It is much more important to the metabolism of plants, particularly many grasses, and silicic acid (a type of silica) forms the basis of the striking array of protective shells of the microscopic diatoms.

Chemical compound

A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by mass
Fine-tuning the definition

There are some exceptions to the definition above. Certain crystalline compounds are non-stoichiometric compounds because they vary in composition according to the presence or otherwise of elements trapped within the crystal structure. Some compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which will make the ratio of elements by mass vary slightly. A compound therefore may not be completely homogenous, but for most purposes in chemistry it can be regarded as such.

Not all molecules are compounds. A diatomic molecule of hydrogen, represented by H2, is homonuclear — made of atoms of only one element, so is not regarded as a compound. Compounds are pure substances that contain two or more elements combined in a definite fixed proportion.

Compounds compared to mixtures

Compounds have different physical and chemical properties from their constituent elements. This is the one principal criterion for distinguishing a compound from a mixture of elements or substances: a mixture's properties are generally similar or related to the properties of its constituents. Another criterion is that the constituents of a mixture can usually be separated by simple, mechanical means such as filtering, those of a compound are often very hard to separate. Furthermore, when a compound is formed from its constituents, a chemical change takes place through chemical reactions. Mixtures can be made by mechanical means alone.

An example of a mixture that is often confused to be a compound is an alloy. It is made mechanically, most commonly by heating up all of the constituent(s) and then cooling it quickly so that the constituents are then "caught" in the base metal.

Chemists describe compounds using formula in various formats. For molecules, the formula for the molecular unit is shown. For polymeric materials, such as minerals and many metal oxides, the empirical formula is given, e.g. NaCl for table salt. The order of the elements in molecular and empirical formulas is C, then H and then alphabetical. Trifluoroacetic acid is thus described as C2HF3O2. More descriptive formulas convey structure information, illustrated again with trifluoroacetic acid. CF3CO2H. On the other hand, formulas for inorganic compounds often do not convey structural information, as illustrated by H2SO4 for a molecule that has no H-S bonds. A more descriptive presentation would be O2S(OH)2.

Formula
Elements form compounds to become more stable. They become stable when they have the maximum number of possible electrons in their outermost energy level, which is normally two or eight valence electrons. This is the reason that noble gases do not frequently react: they already possess eight valence electrons (the exception being helium, which requires only two valence electrons to achieve stability).

Silicon carbide

Silicon carbide (SiC) is a compound of silicon and carbon bonded together to form ceramics, but it also occurs in nature as the extremely rare mineral moissanite.

Production

Due to the rarity of natural moissanite, silicon carbide is typically man-made. Most often it is used as an abrasive. More recently as a semiconductor and diamond simulant of gem quality. The simplest manufacturing process is to combine silica sand and carbon in an Acheson graphite electric resistance furnace at a high temperature, between 1600 and 2500 °C.

The material formed in the Acheson furnace varies in purity, according to its distance from the graphite resistor heat source. Colorless, pale yellow and green crystals have the highest purity and are found closest to the resistor. The color changes to blue and black at greater distance from the resistor, and these darker crystals are less pure. Nitrogen and aluminium are common impurities, and they affect the electrical conductivity of SiC.

Purer silicon carbide can be made by the more expensive process of chemical vapor deposition (CVD). Commercial large single crystal silicon carbide is grown using a physical vapor transport method commonly known as modified Lely method.

Purer silicon carbide can also be prepared by the thermal decomposition of a polymer, poly (methylsilyne), under an inert atmosphere at low temperatures. Relative to the CVD process, the pyrolysis method is advantageous because the polymer can be formed into various shapes prior to thermalization into the ceramic.