Nanophase ceramics are

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...

s that are nanophase materials (that is, materials that have grain sizes under 100 nanometers). They have the potential for superplastic deformation. Because of the small grain size and added grain boundaries properties such as ductility, hardness, and reactivity see drastic changes from ceramics with larger grains.

Structure

The structure of nanophase ceramics is not too different than that of

s. The main difference is the amount of surface area per mass. Particles of

s have small surface areas, but when those particles are shrunk to within a few nanometers, the surface area of the same amount of a mass of a

greatly increases."What's So Special about the Nanoscale?"
nano.gov. Retrieved December 1, 2014. So in general, nanophase materials have greater surface areas than that of a similar mass material at a larger scale. This is important because if the surface area is very large the particles can be in contact with more of their surroundings, which in turn increases the reactivity of the material. The reactivity of a material changes the material's

mechanical properties A materials property is an intensive property of a material, i.e., a physical property that does not depend on the amount of the material. These quantitative properties may be used as a metric by which the benefits of one material versus another ca ...

and

chemical properties A chemical property is any of a material's properties that becomes evident during, or after, a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity.William L. Masterton, Cecile N. Hurley ...

, among many other things. This is especially true in nanophase ceramics.

Properties

Nanophase ceramics have unique properties than regular

s due to their improved reactivity. Nanophase ceramics exhibit different mechanical properties than their counterpart such as higher

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

, higher

fracture toughness In materials science, fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited. A component's thickness affects the constraint conditions at the tip of a c ...

, and high

ductility Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...

.Szlufarska, Izabela, Nakano, Aiichiro, Vashista, Priya.(August 5, 2005)
"A Crossover in the Mechanical Response of Nanocrystalline Ceramics"
sciencemag.com. Volume 309 pgs. 911-913. Accessed December 1, 2014. These properties are far from

s which behave as brittle, low ductile materials.

Titanium dioxide

Titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolubl ...

(), has been shown to have increased hardness and ductility at the nanoscale. In an experiment, grains of

titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolubl ...

that had an average size of 12 nanometers were compressed at 1.4 GPa and

sintered Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...

at 200 °C. The result was a grain hardness of about 2.2 times greater than that of grains of

with an average size of 1.3 micrometers at the same temperature and pressure. In the same experiment, the

was measured. The

strain rate In materials science, strain rate is the change in strain (deformation) of a material with respect to time. The strain rate at some point within the material measures the rate at which the distances of adjacent parcels of the material change wi ...

sensitivity of a 250 nanometer grain of

was about 0.0175, while a grain with size of about 20 nanometers had a

sensitivity of approximately .037; a significant increase.

Processing

Nanophase ceramics can be processed from atomic, molecular, or bulk precursors. Gas condensation,

chemical precipitation In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...

, aerosol reactions, biological templating,

chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substra ...

, and

physical vapor deposition Physical vapor deposition (PVD), sometimes called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings on substrates including metals, ceramics, glass, and polym ...

are techniques used to synthesis nanophase ceramics from molecular or atomic precursors.Siegel, Richard W.
"SYNTHESIS, PROPERTIES, AND APPLICATIONS OF NANOPHASE MATERIALS"
April 1995. Accessed December 7, 2014. To process nanophase ceramics from bulk precursors, mechanical attrition,

crystallization Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposi ...

from the amorphous state, and phase separation are used to create nanophase ceramics. Synthesizing nanophase ceramics from atomic or molecular precursors are desired more because a greater control over microscopic aspects of the nanophase ceramic can occur.

Gas condensation

Gas condensation is one way nanophase ceramics are produced. First, precursor ceramics are evaporated from sources within a gas-condensation chamber. Then the ceramics are condensed in a gas (dependent on the material being synthesized) and transported via

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

to a liquid-nitrogen filled cold finger. Next, the ceramic powders are scraped off the cold finger and collect in a funnel below the cold finger. The ceramic powders then become consolidated in a low-pressure compaction device and then in a high-pressure compaction device. This all occurs in a vacuum, so no impurities can enter the chamber and affect the results of the nanophase ceramics.

Applications

Nanophase ceramics have unique properties that make them optimal for a variety of applications.

Drug delivery

Materials used in drug delivery in the past ten years have primarily been

polymers A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

. However, nanotechnology has opened the door for the use of

s with benefits not previously seen in

. The large surface area to volume ratio of nanophase materials makes it possible for large amounts of drugs to be released over long periods of time. Nanoparticles to be filled with drugs can be easily manipulated in size and composition to allow for increased

endocytosis Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. E ...

of drugs into targeted cells and increased dispersion through fenestrations in capillaries. While these benefits all relate to nanoparticles in general (including

), ceramics have other, unique abilities. Unlike

polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

s, slow degradation of ceramics allows for longer release of the drug.

Polymers A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

also tend to swell in liquid which can cause an unwanted burst of drugs. The lack of swelling shown by most ceramics allows for increased control. Ceramics can also be created to match the chemistry of biological cells in the body increasing bioactivity and biocompatibility. Nanophase ceramic drug carriers are also able to target specific cells. This can be done by manufacturing a material to bond to the specific cell or by applying an external magnetic field, attracting the carrier to a specific location.

Bone substitution

Nanophase ceramics have great potential for use in

orthopedic medicine Orthopedic surgery or orthopedics ( alternatively spelt orthopaedics), is the branch of surgery concerned with conditions involving the musculoskeletal system. Orthopedic surgeons use both surgical and nonsurgical means to treat musculoskeletal ...

. Bone and

collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...

have structures on the nanoscale. Nanomaterials can be manufactured to simulate these structures which is necessary for grafts and implants to successfully adapt to and handle varying stresses. The surface properties of nanophase ceramics is also very important for bone substitution and regeneration. Nanophase ceramics have much rougher surfaces than larger materials and also have increased surface area. This promotes reactivity and absorption of proteins that assist tissue development. Nano-hydroxyapatite is one nanophase ceramic that is used as a bone substitute. Nano grain size increases the bonding, growth, and differentiation of

osteoblasts Osteoblasts (from the Greek language, Greek combining forms for "bone", ὀστέο-, ''osteo-'' and βλαστάνω, ''blastanō'' "germinate") are cell (biology), cells with a single Cell nucleus, nucleus that synthesize bone. However, in the p ...

onto the ceramic. The surfaces of nanophase ceramics can also be modified to be porous allowing

to create bone within the structure. The degradation of the ceramic is also important because the rate can be changed by changing the crystallinity. This way as bone grows the substitute can diminish at a similar rate.

References

{{Reflist Ceramic materials Ceramic engineering Materials