Absorption (physical)
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A physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. This is a different from Adsorption, since the molecules are taken up by the volume, not by surface.
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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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For example, by growing larger particles around smaller seed particles.
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Advection
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A transport mechanism of a substance, or a conserved property, by a fluid, due to the fluid's bulk motion in a particular direction. An example of advection is the transport of pollutants or silt in a river.
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Aerosol
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A suspension of fine solid particles or liquid droplets in a gas.
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Centrifugal Force
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An outward force associated with rotation. Centrifugal force is one of several so-called pseudo-forces (or inertial forces), so named because, unlike real forces, they do not originate in interactions with other bodies situated in the environment of the particle upon which they act. Instead, centrifugal force originates in the rotation of the frame of reference within which observations are made.
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Centrifugal Separation
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A process that involves the use of the centrifugal force for the separation of mixtures, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture migrate towards the axis.
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Centrifuge
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A piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to evenly distribute substances (usually present in a solution for small scale applications) of greater and lesser density.
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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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Close Packing
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A dense arrangement of equal spheres in an infinite, regular arrangement (or lattice). There are two simple regular lattices that achieve highest average density: face-centered cubic (also called cubic close packed) and hexagonal close-packed. Both are based upon sheets of spheres arranged at the vertices of a triangular tiling; they differ in how the sheets are stacked upon one another.
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Coatings
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A covering that is applied to an object. The aim of applying coatings is to improve surface properties of a bulk material usually referred to as a substrate. One can improve amongst others appearance, adhesion, wetability, corrosion resistance, wear resistance, scratch resistance, etc.. They may be applied as liquids, gases or solids.
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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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Composite Materials
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(or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure.
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Coprecipitation
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The carrying down by a precipitate of substances normally soluble under the conditions employed.
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Corrugation
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The shaping of an object or surface into parallel ridges and grooves.
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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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Cyclone Separation
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A method of removing particulates from an air, gas or water stream, without the use of filters, through vortex separation. Rotational effects and gravity are used to separate mixtures of solids and fluids.
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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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Electric Field
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The space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field (that can also be equated to electric flux density). This electric field exerts a force on other electrically charged objects.
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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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Electromagnet
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A type of magnet whose magnetic field is produced by the flow of electric current. The magnetic field disappears when the current ceases. Electromagnets are very widely used as components of other electrical devices, such as motors, generators, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment, as well as being employed as industrial lifting electromagnets for picking up and moving heavy iron objects like scrap iron.
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Electropermanent Magnet
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A type of magnet which consists of both an electromagnet and a dual material permanent magnet, in which the magnetic field produced by the electromagnet is used to change the magnetisation of the permanent magnet. Allows creating controllable permanent magnets where the magnetic effect can be maintained without requiring a continuous supply of electrical energy.
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Electrophoresis
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The motion of dispersed particles relative to a fluid under the influence of an electric field.
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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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Electrostatic Induction
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A redistribution of electrical charge in an object, caused by the influence of nearby charges. Electrostatic generators, such as the Wimshurst machine, the Van de Graaff generator and the electrophorus, use this principle. Electrostatic induction should not be confused with electromagnetic induction; both are often referred to as 'induction'.
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Electrostatics
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The phenomena arising from stationary or slowly moving electric charges
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Erosion
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The process of weathering and transport of solids (sediment, soil, rock and other particles) in the natural environment or their source and deposits them elsewhere. It usually occurs due to transport by wind, water, or ice; by down-slope creep of soil and other material under the force of gravity; or by living organisms, such as burrowing animals, in the case of bioerosion.
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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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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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Flow Separation
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For a solid object travelling through a fluid (or alternatively a stationary object exposed to a moving fluid) flow separation occurs when the boundary layer travels far enough against an adverse pressure gradient that the speed of the boundary layer falls almost to zero.The fluid flow becomes detached from the surface of the object, and instead takes the forms of eddies and vortices.
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Forced Convection
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Heat advection by a fluid which is not due to the natural forces of buoyancy induced by heating. In forced heat convection, transfer of heat is due to movement in the fluid which results from many other forces, such as (for example) a fan or pump.
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Free Convection
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Movement of molecules of fluids (or gases) dues to density differences in the fluid (or gas) occurring due to temperature gradients.
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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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Gravitation
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A natural phenomenon by which objects with mass attract one another. In everyday life, gravitation is most commonly thought of as the agency which lends weight to objects with mass.
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Halbach Array
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A special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side. Has many applications ranging from the humble refrigerator magnet through industrial applications such as the brushless AC motor and magnetic coupling, to high-tech applications such as wiggler magnets used in particle accelerators and free electron lasers.
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By attracting particles to the Halbach Array.
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Heating
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The act of increasing temperature.
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Impact Force
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A high force or shock applied over a short time period. Such a force or acceleration can sometimes have a greater effect than a lower force applied over a proportionally longer time period.
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Ion Repulsion/Attraction
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Attraction between ions having opposite charge or repulsion by ions having negative charge.
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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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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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Ostwald Ripening
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An observed phenomenon in solid solutions or liquid sols that describes the change of an inhomogeneous structure over time, i.e., small crystals or sol particles dissolve, and redeposit onto larger crystals or sol particles. Occurs because larger particles are more energetically favored than smaller particles. This stems from the fact that molecules on the surface of a particle are energetically less stable than the ones in the interior. Ostwald ripening is also observed in liquid-liquid systems, causing diffusion of monomers (i.e. individual molecules or atoms) from smaller droplets to larger droplets due to greater solubility of the single monomer molecules in the larger monomer droplets.
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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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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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Roller
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A cylindrical device that rotates around its principle axis, typically to perform useful work, such as the compression of sheet metal between a pair of rollers.
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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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Selective Laser Sintering
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An additive rapid manufacturing technique that uses a high power laser (for example, a carbon dioxide laser) to fuse small particles of plastic, metal, ceramic, or glass powders into a mass representing a desired 3-dimensional object.
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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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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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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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In the case of a divided solid dispersed in a fluid.
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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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Suspension
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A heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase (solid) is dispersed throughout the external phase (fluid - which may be liquid or gas) through mechanical agitation, with the use of certain excipients or suspending agents.
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Tessellation
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A tessellation or tiling of the plane is a collection of plane figures that fills the plane with no overlaps and no gaps.
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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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A thermal precipitator is an instrument that collects aerosol particles using thermophoresis to deposit the particles onto a surface. It employs a heated element, such as a wire, and a collection surface. Aerosol passing between the heated element and the cooler surface will be driven to deposit on the surface.
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Thixotropy
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The property of some non-Newtonian pseudoplastic fluids to show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity. A thixotropic fluid is a fluid which takes a finite amount of time to attain equilibrium viscosity when introduced to a step change in shear rate. Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated.
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Some thixotrophic materials have a divided solid as one of their constituents, e.g. some clays.
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Triboelectric Effect
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A type of contact electrification in which certain materials become electrically charged after they come into contact with another different material and are then separated (such as through rubbing). The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties.
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