Nanoceramics are a type of nanoparticle first discovered in the early 1980s composed of ceramics. Industrial or advanced ceramics are made from highly pure, well-chosen materials such as silica carbide and alumina, and are a far cry from the traditional tile pots and tableware made of clay that might spring to mind when ‘ceramics’ are mentioned.
The term nanoceramics refers to materials fabricated from ultrafine particles, less than 100 nm in diameter, and are classified as inorganic, heat resistant, non-metallic solids. The most important ceramic materials are systems of metal oxides, carbides, borides and nitrides, and because of their small size, they have few – if any – flaws.
Nanoceramics were first formed using the sol-gel process – a form of chemical solution deposition – which mixes nanoparticles within a solution and gel to form nanoceramics. In the 2000s production methods began to use heat and pressure in a sintering process. The method of preparation can often be the determining factor in shaping a nanoceramic and its properties: for example, burning magnesium in oxygen results in cubes and hexagonal plates, whereas thermal decomposition of magnesium hydroxide causes irregular shapes, often platelets in hexagonal form.
Over the last 20 years, there has been a huge amount of study into nanoceramics, that has resulted in some positive outcomes not only for academia but industry too. As a result, these advanced materials have a wide range of uses in electronics, medicine and in the nuclear industry for example.
Nanoceramics possess their own chemical, physical, mechanical and magnetic properties that differ from other materials like metals, plastics and conventional bulk ceramic materials. These unique and often improved properties – dielectricity, ferroelectricity, piezoelectricity, pyroelectricity, ferromagnetism, magnetoresistance and superconductivity – depend on the type and amount of materials that the nanoceramic is made of, as well as the raw material’s size. Nanoceramics also possess exceptional processing, mechanical and surface characteristics including superplasticity, machineability, bioactivity, strength and toughness, all of which again depend on the size on the particles used to construct them.
The bulk behavior of materials can be changed dramatically when they are made from nanoscale building blocks – for example, the hardness and strength of a material can be greatly enhanced by consolidating ceramic materials from nanoscale particles – with the size of the building block affecting the properties of the final product.
Nanoceramics are very strong and show substantial resistance against compression and bending. Their strength is similar to that of steel, and most ceramics maintain their strength at high temperatures. However, their brittleness is the biggest technical barrier preventing their practical employment, especially in load-bearing applications.
Traditional brittle materials can be made more ductile by reducing the size of the grain used in making it, so a nanoceramics’ physical and mechanical strength is dependent on the size of the particle used to make them. When constructed from nanoparticles, ceramics can be superplastically deformed at a modest temperature before being heat treated at a higher temperature for high-temperature strengthening.
Nanoceramics are relatively inert, and where reactivity does occur it is where coordinatively unsaturated and defect sites occur. Some ceramics – those that are iron-based, or made with nickel, barium and chromium – have metallic properties and exhibit a high resistance to demagnetization.
The term ceramics incorporates electrically conducting, insulating and semiconducting materials such as chromium oxide, aluminum oxide and silicon carbide. Many electrical properties are particle-size and composition dependent: electrical resistance and dielectric constant for some systems increases as a result of small particle size, for example.
One of the main uses of nanoceramics has been in biomedicine and medical technology, particularly in bone repair. Bioactive ceramics closely match the properties of bone and can act as a nanoscaffold to help support bone regrowth.
It has also been suggested that nanoceramics might find uses in energy supply and storage, communications, transportation systems, aerospace and construction. They have also found use in electronics as insulators, semiconductors, conductors and magnets.
Nanoceramics might also find a use in armor to replace the stiff, tough layers of woven fiber which absorbs impact. A hard body armor is under development that includes ceramic inserts and steel or titanium panels that could offer greater protection against blunt trauma and high velocity ammunition. The inserts could absorb kinetic energy of the projectile and dissipate it in a localized shattering of the ceramic insert.
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