Glossary A

Abcess

A local collection of pus within a body cavity having a range of symptoms.   Abscesses are serious and must be treated promptly.

Abrasive

An abrasive is a harder material used to smooth a rough surface, rough a smooth surface, or change the shape or size of a softer material by rubbing or grinding.   The area worn away between the rubbed materials is called an abrasion.   Abrasives are used in 3 ways: (1) Placing the sharpened object against the abrasive, e.g., sharpening a knife or axe against a grinding wheel made of stone.   (2) Coat a substance with an abrasive material.   Examples are sandpaper, emery, natural or synthetic diamond dust, CBN (cubic boron nitride), silicon carbide ("carborundum" = SiC).   For applications against wood, the abrasive is attached to a substrate (e.g., sandpaper) with a glue and rubbed by hand or a motor-driven sander.   For metal applications, it is made into a wheel that is attached to an upright stand and driven by an electric motor.   The stand type is always found in machine shops because of the frequent need to deburr cut metal.   (3) Placing the abrasive in a high-pressure air or water stream and pushing them against the surface to be abraded, e.g., sandblasting or gritblasting.   There are hundreds of abrasive compounds in use.   Cleaning compounds contain abrasives using silica, pumice, or aluminum oxide.   Toothpaste contains powdered chalk as its abrasive.   Abrasives contribute to health by preventing lacerating burrs, called abrasions, and to precise tolerances by removing small amounts of material beyond the capability of a cutting tool (e.g., wood used for furniture).   Before the invention of carborundum (see below), all abrasives were natural minerals.   Examples are sand, garnet, emery, corundum, and pumice.   Sandpaper was patented in the United States on June 14, 1834 by Isaac Fischer, Jr., of Springfield, Vermont.   In 1891, Edward Acheson produced crystals of silicon carbide (SiC), the first synthetic abrasive, which he patented and sold under the trade name, Carborundum.   The SiC crystals can be made at any degree of fineness and can be bonded together into a solid block or coated onto metal discs or belts. ^{How 5}

Absolute Zero

The temperature at which there is no molecular motion and therefore no heat.   It is measured as 0°K = -273.15°C = -459.67°F.

Acceleration

The rate of change of velocity with respect to time.   a = dv / dt, where dv is an increase or decrease in velocity and dt is its corresponding increase in time.   Since the time change is always positive, an increase in velocity results in a positive acceleration, while a decrease in velocity results in a negative acceleration; that is, a deceleration.

Accuracy, Precision & Tolerances

Accuracy is the closeness of a dimension to some accepted standard.   The dimension can be length, area, volume, time, energy, power, etc.   How accurate is the inch measure on a ruler to the international standard?   The area of a built house to its plan?   The volume of a bottle to its intended volume?   The time at noon of a watch to the international time standard at noon?   The amount of power of a motor to its designed power rating?   Accuracy is a relative measure to some standard of acceptability.

Tolerances are the limits of acceptable accuracy.   A ruler inch can be within +/- .00001 inch for a metal shop ruler, +/- .0001 inch for a school ruler.   The area of a specific house can be + 20.0/- 0.0 square feet from plan.   The volume of a specific bottle may + .100/-.005 quarts from its intended volume.   The time at noon of a watch over 1 24-hour period may be +/- .10 second.   The amount of power actually generated by a motor can be +10/-1 hp (horsepower) from its rated power.   Tolerances are determined by the amount of accuracy required for a part to function properly alone or in conjunction with other parts in an assembly.   For examples, if a bullet is too large, then it will not enter the rifle barrel to fire.   If a gear is too small in a transmission, it will not mesh properly with other gears and the transmission will fail.

Precision is the measure of the repeatability or reliability of accuracy.   If 999 of a batch of 1000 metal shop rulers are within the acceptable tolerances, then they are more reliable than another batch that has 997 rulers out of 1000 within the acceptable tolerances.   If 999 triggers out of 1000 in a pistol function properly, then the precision is 99.9%.   For interchangeable parts manufacture, precision must be high enough so that very few parts fail to function properly when assembled into the final product; otherwise, the assembled product is likely to malfunction.   Perfect precision is the ideal that is never quite realized, because its higher cost of achievement must be balanced by the the lower costs of success.

It is possible to have acceptable accuracy and unacceptable precision, acceptable precision with unacceptable accuracy, unacceptable accuracy and precision, and unacceptable accuracy and precision acceptable.   Obviously, the last condition is desirable in making goods and providing services, provided that it can be achieved with an improvement in costs or revenues.     It is absolutely necessary to make interchangeable parts, which are essential to automated, mass production of products.   The history of manufacturing is featured by continued improvements in accuracy and precision of machines, tools and instruments, where they can be justified by overall cost.   Accuracy and precision were neglected by American automobile manufacturers in their quest to keep manufacturing costs low, thus resulting in poor car reliability and greater maintainance costs for American car buyers in the 1960s.   Japanese cars were better quality and more costly to manufacturers, but more reliable and less costly to their buyers, so many Americans bought Japanese cars, which increased the revenues and profits of the Japanese manufacturers and reduced the revenues and profits of the American manufacturers.   The American manufacturers got the message and emphasized quality thereafter, which improved their competitiveness.

Adhesive

An adhesive is a compound that bonds two surfaces together.   Most early adhesives were glues made from rendered animal products such as the horns, hooves and skins of ruminants, or plant gums and resins, or bitumens, which are naturally occurring solid or liquid hydrocarbons, excluding coal.   Modern adhesives are made of synthetic polymers that produce bonds that are stronger than the adhering materials, so they have become less expensive substitutes for traditional fasteners, such as nails, bolts, rivets, and screws.   There are several types of adhesives:

Drying adhesives

These adhesives are a mixture of ingredients (typically polymers) dissolved in a solvent.   Examples are glues and rubber cements.   As the solvent evaporates, the adhesive hardens.   These adhesives are typically weak and used mostly for household applications. ^{Wiki n.p.}

Hot adhesives

These adhesives are applied hot and allowed to harden as they cool.   These adhesives are popular for crafts because of their ease of use and the wide range of common materials to which they can adhere. ^{Wiki n.p.}

Reactive adhesives

Epoxy resins are the most common example of this kind of adhesive.   Reactive adhesives generally come in two separate containers that are mixed immediately before application.  The result is a reaction that solidifies the adhesive.   Reaction adhesives may also react with the surface of the materials to be stuck together by chemical bonding, in contrast to sticking, the action of common glues.   A special kind of reactive adhesive is cyanoacrylate ("super glue") which reacts with moisture in the air and therefore does not need any mixing before application.   Reactive adhesives are very strong and are used for high-stress applications, such as attaching wings to aircraft. Because the strength of a reactive adhesive is a result of chemical bonding with the surface material, reactive adhesives are applied in thin films. Reactive adhesives are less effective when there is a secondary goal of filling gaps between the surfaces. ^{Wiki n.p.}

Temporary adhesives

Temporary adhesives are designed to repeatedly stick and unstick.   They have low adhesion and generally do not support much weight.   They are commonly used on paper, such as, bookmarks, informal notes and office supplies. ^{Wiki n.p.}

Although not usually classified as adhesives, solder and cement also have adhesive qualities.

Aircraft

A generic word for any aerial vehicle.   There are 4 categories of aircraft:   (1) lighter than air aerostats, e.g., airships, balloons (blimps), (2) heavier than air gliders, which are motorless airplanes, (3) airplanes, and (4) rotorcraft, e.g., helicopters and autogiros.   Airships achieve lift by a large gondola filled with a gas that is lighter than air.   Since air pressure varies inversely with height, the pressure against the bottom of the gondola is greater than that at the top of it, so it is pushed upwards.   Engines drive propellers or fans turning inside ducts (cowls).   Gliders provide a cheap way to convey large groups of people (e.g., technicians, aid workers, troops) to remote areas.   They are towed by airplanes and can land without a long airfield.   Gliders operate on the same principle as airplanes except that they do not have a motor that provides them with enough forward thrust to achieve a sufficient pressure difference between the bottom and top of the wing to achieve liftoff.   This thrust is provided by an airplane towing it.   Airplanes have a motor to achieve enough thrust to allow lift by a wing, called an airfoil, designed to maintain a higher pressure on the underside than on the upperside.   Flaps on the wings adjust the lift capacity by increasing or decreasing their areas and inducing the wind to flow faster over and under them.   Ailerons on the wings enable the plane to bank or roll inwards while the rudders turn it.   Tailplanes keep the plane from dipping forward (pitch).   Elevators on the tailplanes achieve up and down motions.   An upright tail fin maintains horizontal left and right (yaw) stability.   It has a rudder to turn the plane left and right.   The propeller, using the same principle as the wing, but applied along the plane axis, pulls the plane at varying speeds.   Jet engines may or may not use propellers or fans to obtain thrust (propulsion).   Rotorcraft move in any direction, including sideways and backwards.   The main rotor provides lift, speed, and motion in any direction by adjusting the blade angle (pitch).   The smaller tail rotor keeps the craft from spinning as a result of by the main rotor torque and assists the main rotor in the desired direction.   The helicopter achieves flight by a motor-driven rotor that acts like a wing or propeller in an airplane.   It can move in any direction, hover, and take off and land vertically, thus needing no airstrip.   The autogyro (Gyrocopter™, gyroplane) uses a rotor that is activated by the wind, like a windmill, not by a motor.   it requires a motor-driven forward propeller and must achieve lift by first moving forward on land; therefore, it cannot lift vertically nor hover like a helicopter. ^{How 49,58,196.}

Alkali Metal

So called because their hydroxides (-OH) and carbonates (-CO₃) for alkalis (bases), they are sodium, potassium, lithium, cesium, rubidium, and francium.   These metals are very soft (they can be cut with a knife), and good conductors of heat and electricity.   Being chemically active, they are never found free in nature.   They react violently with water, so they must be stored in containers under paraffin or in a vacuum.

Alloy

A mixture of two or more elements, at least one of which is a metal.   Brass is an alloy of copper and zinc.   Bronze is an alloy of copper and tin or other metals.   Alloys are made to have more useful properties than either of the alloying metals.   Alloys of metals and mercury are called amalgams.

Anodizing

A process to produce an oxide film (coating) on metals and alloys by electrolysis.   The metal to be treated is made the anode in an electrolytic cell and its surface is electrochemically oxidized.   Anodization can improve certain surface properties, such as corrosion resistance, abrasion resistance, hardness, appearance, etc.   One metal very often anodized is aluminum, on which all the above properties improve.   Furthermore, since the surface film is porous, the aluminum metal can be colored by the application of pigments or dyes in the pores.

The aluminum part to be anodized made the anode (positive electrode) in an electrolytic cell.   This aluminium is immersed in an electrolyte consisting of an acid and water solution.   Sulphuric acid is used for relatively soft, easily dyed coatings and organic acids are used for hard coatings.   The temperature of the solution is controlled to give the desired metallic properties.   For example, at 20°C, a sulphuric acid anodizing solution will give a soft, transparent clear, easily dyed coating, whereas at 5°C a hard, dense, dull grey coating is produced (called hard anodizing).   DC (direct current) electricity is passed between the aluminium that is made the anode, the electrolyte and a cathode, which is often lead.   When the current is applied, the water in the electrolyte breaks down and oxygen is deposited at the anode.   This oxygen combines with the aluminium to form an oxide that builds on the oxide film always present on the aluminum surface.   The acid in the electrolyte tries to dissolve this oxide and produces a porous oxide film on the aluminium surface.   Coating thickness up to 25 microns is recommended for external use.   The oxide grains are hexagonal in shape and each grain contains a hexagonal hole within it.   Once the required thickness of the oxide is obtained, the aluminium is removed from the electrolyte and rinsed thoroughly to remove the acids from the pores in the film.   The oxide produced is porous and will accept or trap any material into its pores, which can be advantageous or disadvantageous, depending on use.   The advantage is the ease of painting or dyeing.   However, if a non-porous finish is desired, then the pores are closed or the coating is "sealed".   This is done by adding water (hydrolyzing) to the oxide, which causes it to swell and close.   The resultant film is then smooth, hard, homogenous and transparent.   The sealing process may be carried out in boiling water, or in chemically enriched water at room temperature.   Anodizing differs from electroplating in that with electroplating, the material to be coated is at the cathode rather than at the anode.   However, they both use the same process. ^{Pennisi, n.p.}

Aqua Regia

Aqua Regia ("royal water", or nitrohydrochloric acid) is a mixture of concentrated nitric acid (HNO₃) and concentrated hydrochloric acid (HCl).   The proportions, respectively, are 1 part to 3 or 4.   It's fame comes from its ability to dissolve gold and platinum (the once royal metals), which each of its constituent acids cannot.   The combination, however, releases water and chlorine (Cl₂), a powerful oxidizing agent, that forms an ion with the metal in the solution.

Aqueduct

An artificial canal for carrying water over some obstacle.   It is used to supply water to a populated area and to convey a boat over a river, ravine, or structures, such as city buildings.

Astringent

A substance that contracts the tissues or canals of the body to diminish discharges, such as blood or mucus.