3D Printing
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The process of creating three dimensional objects from digital data using a materials printer, in a manner similar to printing images on paper. The term is most closely associated with additive manufacturing technology, where an object is created by laying down successive layers of material.
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Adhesive
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A compound that adheres or bonds two items together. Adhesives may come from either natural or synthetic sources. Some modern adhesives are extremely strong, and are becoming increasingly important in modern construction and industry.
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Adsorption
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A process that occurs when a gas or liquid solute accumulates on the surface of a solid or a liquid (adsorbent), forming a film of molecules or atoms (the adsorbate). Most industrial adsorbents fall into one of three classes: 1. Oxygen-containing compounds (e.g.silica gel and zeolites 2. Carbon-based compounds (e.g. activated carbon and graphite) 3. Polymer-based compounds
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Following the adsorption of a material on the surface of an adsorbent.
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Bingham Plastic
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A viscoplastic material that behaves as a rigid body at low stresses but flows as a viscous fluid at high stress. A common example is toothpaste, which will not be extruded until a certain pressure is applied to the tube. It then is pushed out as a solid plug.
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Cathodic Arc Deposition
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Cathodic arc deposition or Arc-PVD is a physical vapour deposition technique in which an electric arc is used to vapourize material from a cathode target. The vapourized material then condenses on a substrate, forming a thin film. The technique is can be used to deposit a metallic, ceramic, and composite films.
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Chemical Beam Epitaxy
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(CBE) An important class of deposition techniques for semiconductor layer systems. This form of epitaxial growth is performed in an ultrahigh vacuum system. The reactants are in the form of molecular beams of reactive gases, typically as the hydride or a metalorganic.
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Chemical Transport Reactions
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A process for purification and crystallisation of non-volatile solids. Entails the reversible conversion of nonvolatile elements and chemical compounds into volatile derivatives. The volatile derivative migrates throughout a sealed reactor, typically a sealed, evacuated glass tube heated in a tube furnace. Elsewhere in the tube where the temperature is held at a different temperature, the volatile derivative reverts to the parent solid and the transport agent is released.
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Chemical Vapour Deposition
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A chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.
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Coffee Ring Effect
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A pattern left by a puddle of particle-laden liquid after it evaporates. Named after the characteristic ring-like deposit along the perimeter of a spill of coffee. The pattern is due to capillary flow induced by the differential evaporation rates across the drop: liquid evaporating from the edge is replenished by liquid from the interior. The resulting edgeward flow can carry nearly all the dispersed material to the edge.
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Colloid
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A type of chemical mixture where one substance is dispersed evenly throughout another. The particles of the dispersed substance are only suspended in the mixture, unlike a solution, where they are completely dissolved within. This occurs because the particles in a colloid are larger than in a solution - small enough to be dispersed evenly and maintain a homogenous appearance, but large enough to scatter light and not dissolve.
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Corona Discharge
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An electrical discharge brought on by the ionization of a fluid surrounding a conductor, which occurs when the potential gradient (the strength of the electric field) exceeds a certain value, but conditions are insufficient to cause complete electrical breakdown or arcing.
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Crystallisation
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The (natural or artificial) process of formation of solid crystals precipitating from a identical solution or melt, or more rarely deposited directly from a gas. Crystallisation is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs.
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Cyanoacrylate
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The generic name for cyanoacrylate based fast-acting adhesives such as methyl 2-cyanoacrylate, ethyl-2-cyanoacrylate (commonly sold under trade names like SuperGlue), and n-butyl cyanoacrylate (used in veterinary and skin glues).
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Deposition (physical)
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A process in which gas transforms into solid (also known as desublimation). The reverse of deposition is sublimation. One example of deposition is the process by which, in sub-freezing air, water vapour changes directly to ice without first becoming a liquid. This is how snow forms in clouds, as well as frost and hoar frost on the ground.
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Electret
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An Electret is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet.
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Solid particles can be attracted by the charge of an electret.
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Electrodeposition
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The process of using electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal. Primarily used for depositing a layer of material to bestow a desired property (e.g., abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.) to a surface that otherwise lacks that property. Another application uses electroplating to build up thickness on undersized parts.
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For example, by electroplating.
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Electrolysis
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A method of separating chemically bonded elements and compounds by passing an electric current through them. Electrolysis involves the passage of an electric current through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at the electrodes.
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Through electrolytic deposition at electrodes.
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Electron Beam
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(also called Cathode Rays or e-beam) are streams of electrons observed in vacuum tubes, i.e. evacuated glass tubes that are equipped with at least two metal electrodes to which a voltage is applied, a cathode or negative electrode and an anode or positive electrode.
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Electron Beam Physical Vapour Deposition is a form of physical vapour deposition in which a target anode is bombarded with an electron beam given off by a charged tungsten filament under high vacuum. The electron beam causes atoms from the target to transform into the gaseous phase. These atoms then precipitate into solid form, coating everything in the vacuum chamber with a thin layer of the anode material.
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Electrophoretic Deposition
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A term for a broad range of industrial processes which includes electrocoating, cathodic electrodeposition, and electrophoretic coating, or electrophoretic painting. A characteristic feature of this process is that colloidal particles suspended in a liquid medium migrate under the influence of an electric field (electrophoresis) and are deposited onto an electrode.
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Electroplating
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The process of using electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal. Primarily used to bestow a desired property (e.g., abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.) to a surface that otherwise lacks that property. Also used to build up thickness on undersized parts.
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Electrostatic Deposition
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Liquid sprayed onto a substrate using electrostatic force. Used to apply a surface coating.
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By depositing the solid in liquid (or possibly powder) form.
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Electrostatics
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The phenomena arising from stationary or slowly moving electric charges
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Epitaxy
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The method of depositing a monocrystalline film on a monocrystalline substrate. Epitaxial films may be grown from gaseous or liquid precursors. Because the substrate acts as a seed crystal, the deposited film takes on a lattice structure and orientation identical to those of the substrate.
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ESAVD
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(Electrostatic Spray Assisted Vapour Deposition) is a technique to deposit both thin and thick layers of a coating onto various substrates. In simple terms chemical precursors are sprayed across an electrostatic field towards a heated substrate, the chemicals undergo a controlled chemical reaction and are deposited on the substrate as the required coating.
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Evaporation
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The change of the physical state of aggregation (or simply state) of matter from liquid phase to gaseous phase.
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For example, evaporation is a common method of thin film deposition. The source material is evaporated in a vacuum. The vacuum allows vapour particles to travel directly to the target object (substrate), where they condense back to a solid state.
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Faraday Wave
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(or Faraday Ripples) Nonlinear standing waves that appear on liquids enclosed by a vibrating receptacle. When the vibration frequency exceeds a critical value, the flat hydrostatic surface becomes unstable. The waves can take the form of stripes, close-packed hexagons, or even squares or quasiperiodic patterns.
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Faraday waves are used as a liquid-based template for directed assembly of microscale materials including soft matter, rigid bodies and biological entities.
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Ferromagnetic Powder
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Ferromagnetic material in a powdered or finely divided form. Ferromagnetic materials (such as iron) form permanent magnets and/or exhibit strong interactions with magnets. Ferromagnetic materials lose their ferromagnetic properties above a characteristic temperature (the Curie Point).
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Ferromagnetic powder will be attracted to the surface of a magnetic substrate.
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Ferromagnetism
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The mechanism by which certain materials (such as iron) form permanent magnets and/or exhibit strong interactions with magnets. Responsible for commonly observed magnetism phenomena, e.g. 'fridge magnets. A material is 'ferromagnetic' only if all its magnetic ions add a positive contribution to the net magnetisation. If some of them subtract from the net magnetisation (i.e. are partially anti-aligned), then the material is 'ferrimagnetic'.
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Filter (physical)
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A device (usually a membrane or layer) that is designed to block certain objects or substances while letting others through. Filters are often used to remove harmful substances from air or water, for example to remove air pollution, to make water drinkable, to prepare coffee. In domestic food and drink preparation where bulk solids are removed from liquids, this is often called a strainer.
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Flocculation
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A process of contact and adhesion whereby the particles of a dispersion form larger-size clusters.
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Fluid Spray
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When a liquid is dispersed as a stream of droplets (atomisation), it is called a spray. Spray nozzles are used to achieve two primary functions: increase liquid surface area to enhance evaporation, or distribute a liquid over an area.
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For example, spraying of a paint layer.
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Fluidisation
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A process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurs when a fluid (liquid or gas) is passed up through the granular material. When fluidized, a bed of solid particles will behave as a fluid, like a liquid or gas.
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Fluidised beds of powdered material are used in surface coating processes.
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Funnel
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A funnel is a pipe with a wide, often conical mouth and a narrow stem. It is used to channel liquid or fine-grained substances into containers with a small opening. Without a funnel, much spillage would occur.
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In the case of, for example, a solid in grannular, powedered or slurry form.
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Gel
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A gel is a solid, jelly-like material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute crosslinked system, which exhibits no flow when in the steady-state. By weight, gels are mostly liquid, yet they behave like solids due to a three-dimensional crosslinked network within the liquid. It is the crosslinks within the fluid that give a gel its structure (hardness) and contribute to stickiness (tack).
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Hydrogel
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(also called aquagel) is a network of polymer chains that are hydrophilic, sometimes found as a colloidal gel in which water is the dispersion medium. Hydrogels are highly absorbent (they can contain over 99.9% water) natural or synthetic polymers. Hydrogels also possess a degree of flexibility very similar to natural tissue, due to their significant water content.
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Some hydrogels have the ability to sense changes of pH, temperature, or the concentration of metabolite and release their load as result of such a change.
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Ion Implantation
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A materials engineering process by which ions of a material can be implanted into another solid, thereby changing the physical properties of the solid. Ion implantation is used in semiconductor device fabrication and in metal finishing, as well as various applications in materials science research.
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Magnetic Field
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A vector field which surrounds magnets and electric currents, and is detected by the force it exerts on moving electric charges and on magnetic materials. When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field. Magnetic fields also have their own energy with an energy density proportional to the square of the field intensity.
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Magnetism
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One of the phenomena by which materials exert attractive or repulsive forces on other materials. Some well-known materials that exhibit easily detectable magnetic properties (called magnets) are nickel, iron, cobalt, and their alloys; however, all materials are influenced to greater or lesser degree by the presence of a magnetic field.
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Molecular Sieve
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A material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids.
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Nucleation
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The extremely localised budding of a distinct thermodynamic phase. Some examples of phases that may form via nucleation in liquids are gaseous bubbles, crystals or glassy regions. Creation of liquid droplets in saturated vapor is also characterized by nucleation. Most nucleation processes are physical, rather than chemical, but a few exceptions do exist (e.g. electrochemical nucleation).
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Oxidation
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A chemical reaction that involves the loss of electrons or an increase in the oxidation state by a molecule, atom or ion.
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Physical Vapour Deposition
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A variety of methods used to deposit thin films by the condensation of a vaporized form of the material onto various surfaces
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Variants include Evaporative Deposition, Electron beam PVD, Sputter Deposition, Cathodic Arc Deposition, Pulsed Laser Deposition
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Physisorption
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(or physical adsorption) A type of adsorption in which the adsorbate adheres to the surface only through Van der Waals (weak intermolecular) interactions, which are also responsible for the non-ideal behaviour of real gases.
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Plasma Enhanced Chemical Vapour Deposition
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(PECVD) A process used to deposit thin films from a gas state (vapour) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creation of a plasma of the reacting gases.
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Plasma Spray
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A method of thermal spraying producing coatings and free-standing parts using a plasma jet. Deposits having thickness from micrometers to several millimeters can be produced from a variety of materials, including metals, ceramics, polymers and composites.
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Precipitation
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The formation of a solid in a solution or inside another solid during a chemical reaction or by diffusion in a solid.
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Pulsed Laser Deposition
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A thin film physical vapour deposition technique where a high power pulsed laser beam is focused inside a vacuum chamber to strike a target of the desired composition. Vaporised target material is deposited as a thin film on a substrate.
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Redox Reactions
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Redox (shorthand for oxidation-reduction) reactions describe all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar(C6H12O6) in the human body through a series of complex electron transfer processes.
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Reduction
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A chemical reaction that involves the gain of electrons or a decrease in the oxidation state by a molecule, atom or ion.
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Sedimentation
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The motion of molecules in solutions or particles in suspensions in response to an external force such as gravity, centrifugal acceleration or electromagnetism. Sedimentation may pertain to objects of various sizes, ranging from suspensions of dust and pollen particles to cellular suspensions to solutions of single molecules such as proteins and peptides.
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Self-Assembly
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A process in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction.
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Settling
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The process by which particulates settle to the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force. For gravity settling, this means that the particles will tend to fall to the bottom of the vessel, forming a slurry at the vessel base.
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Sintering
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A method for making objects from powder, by heating the material below its melting point (solid state sintering) until its particles adhere to each other. Traditionally used for manufacturing ceramic objects. Most, if not all, metals can be sintered - especially pure metals produced in vacuum which suffer no surface contamination. Many nonmetallic substances also sinter, such as glass, alumina, zirconia, silica, magnesia, lime, ice, beryllium oxide, ferric oxide, and various organic polymers.
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Sol
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A colloidal suspension of solid particles (1-500 nanometres in size) in a liquid. Examples include blood, pigmented ink, and paint.
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Sorption
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The action of both absorption and adsorption taking place simultaneously, i.e. the effect of gases or liquids being incorporated into a material of a different state and adhering to the surface of another molecule. Absorption is the incorporation of a substance in one state into another of a different state (e.g., liquids absorbed by solid or gas absorbed by liquid). Adsorption is the physical adherence or bonding of ions and molecules onto the surface of another molecule.
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Sputtering
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A process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic ions. It is commonly used for thin-film deposition, etching and analytical techniques
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Types include: RF Sputtering, Ion-beam Sputtering, Reactive Sputtering, Ion-assisted deposition, High-target-utilisation sputtering, High Power Impulse Magnetron Sputtering
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Sublimation
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The change of the physical state of aggregation (or simply state) of matter directly from solid phase to gaseous phase without passing through an intermediate liquid phase.
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Supercritical Fluid
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Any substance at a temperature and pressure above its critical point. It can diffuse through solids like a gas, and dissolve materials like a liquid. Additionally, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties to be 'tuned'.
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Supercritical fluids can be used to deposit functional nanostructured films and nanometer-size particles of metals onto surfaces. The gas-like surface tension, diffusivities, and viscosities allows access to nano pores much smaller than can be accessed by liquids The liquid-like solubilities allow much higher precursor concentrations than are typical in chemical vapour deposition.
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Thermophoresis
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(also called thermodiffusion or Soret Effect) The effect of temperature gradient on multicomponent (or isotopic) mixtures of particles (i.e. particle movement from hotter to colder regions or vice versa). Regarded as 'positive' when molecules move from hot to cold and 'negative' when the reverse is true. Typically the heavier/larger species in a mixture exhibits positive behavior while the lighter/smaller species exhibit negative.
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Thin Films
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Thin material layers ranging from fractions of a nanometre to several micrometres in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction.
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Vacuum Plasma Spraying
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(VPS) A technology for etching and surface modification to create porous layers with high reproductibility and for cleaning and surface engineering of plastics, rubbers and natural fibres. This surface engineering can improve properties such as frictional behaviour, heat resistance, surface electrical conductivity, lubricity, cohesive strength of films, or dielectric constant, or it can make materials hydrophilic or hydrophobic.
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