Metals are electropositive chemical elements

Metals are electropositive chemical elements that are characterised by the following qualities: ductility, malleability, luster, opacity, and conductance of heat and electricity. They can replace the hydrogen of an acid and form bases with hydroxyl radicals. Density is defined as a material's mass divided by its volume. Metals typically have relatively high densities, particularly when compared to polymers. Often, materials with high densities contain atoms with high atomic numbers, such as gold or lead. However, some metals such as aluminum or magnesium have low densities. These metals are useful in applications requiring other metallic properties but in which low weight is also beneficial. Fracture Toughness can be described as a material's ability to avoid fracture, especially when a flaw is introduced. Glass, for example, has low fracture toughness (although it exhibits high strength in the absence of flaws). Metals typically have high fracture toughness. Metals can generally contain nicks and dents without weakening very much. They are also impact resistant. A football player relies on this fact to ensure that his facemask won't shatter. The roll cage on a racecar, for example, is created from steel. This steel should remain intact in a crash, protecting the driver. The ability of a material to bend or deform before breaking is known as plastic deformation. Some materials are designed so that they don't deform under normal conditions. You don't want your car to lean to the east after a strong west wind, for example. However, sometimes we can take advantage of plastic deformation. The crumple zones in a car absorb energy by undergoing plastic deformation before they break. Stress takes place when forces pull (this is known as tension), push (compression) or act in combination on a material. Once the force is applied, the material responds by distorting, counterbalancing the force. With a larger force, there will be a correspondingly greater distortion until the item breaks. Stress is the force applied per unit of cross-sectional area square to the force. This can be expressed mathematically as:: Stress (s) = Force / unit of area The metric system units for stress are Newton per square meter (N/m2) and imperial system units are pounds per square inch (psi). Strain is the amount the material deforms from the unloaded state when the force is applied. Its formula is: Strain (x) = Change in length / original length Since strain is a ratio of length divided by a length, it has no units. By the formula, we can see that it represents a proportional change in size. Deformation occurs when a force is applied to a metal. The metal is therefore strained. The greater the force – the more the deformation (strain). This relationship is recognised in Hooke's Law. Hooke's Law describes an elastic region where stress and strain are proportional (a straight line on a graph). In this region the metal acts like a spring and when the load is removed the deformation (strain) reduces and it returns to its original shape. If instead the load increases, the strain (deformation) rises and the metal undergoes uniform plastic deformation. The stress-strain graph is curved in this region. Eventually, a maximum stress is reached when the metal when the material reaches its limit of necking. Necking is localized thinning that occurs during sheet metal forming prior to fracture. The onset of localized necking is dependent upon the stress state which is affected by geometric factors. Finally, past the maximum stress point, a point is reached where the metal can no longer sustain the load and it yields. The behavior of metals under load is a result of their atomic arrangement. When a material is loaded it deforms minutely in reaction to the load. The atoms in the material move closer together in compression and further apart in tension. The amount an atom moves from its neighbor is its strain. As a force is applied the atoms change a proportionate distance. This model however, does not explain why there is sudden yielding. With most modern metals yielding usually occurs at about 1% of the theoretic strength of the atomic bonds. Many materials yield at about 0.1% of the theoretic strength. Rather, metals exhibit such low strengths because of imperfect atomic structures in the crystal lattices which comprise them. A row of atoms will often stop mid crystal, creating a gap in the atomic structure. These gaps act as dislocations, which are huge stress raising points in the metal. These dislocations move when the metal is stressed. A dislocation is defined as allowing atoms to slip one at a time, making it easier to deform metals. Dislocation interactions within a metal are a primary means by which metals are deformed and strengthened. When metals deform by dislocation motion, the more barriers the dislocations meet, the stronger the metal. The presence of dislocations in metal allows deformation at low levels of stress. However, eventually so many dislocations accumulate that insufficient atoms are left to take the load. This causes the metal to yield. Plastic deformation causes the formation of more dislocations in the metal lattice. This has the potential to create a decrease in the mobility of these dislocations due to their tendency to become tangled or pinned. When plastic deformation occurs at temperatures low enough that atoms cannot rearrange, the metal can be strengthened as a result of this effect. Unfortunately, this also causes the metal to become more brittle. As a metal is used, it tends to form and grow cracks, which eventually cause it to break or fracture. Atoms of melted metal pack together to form a crystal lattice at the freezing point. As this occurs, groups of these atoms form tiny crystals. These crystals have their size increased by progressively adding atoms. The resulting solid, instead of being a single crystal, is actually many smaller crystals, called grains. These grains will then grow until they impose upon neighbouring growing crystals. The interface between the grains is called a grain boundary. Dislocations cannot easily cross grain boundaries. If a metal is heated, the grains can grow larger and the material becomes softer. Heating a metal and cooling it quickly (quenching), followed by gentle heating (tempering), results in a harder material due to the formation of many small Fe3C precipitates which block dislocations. The atomic bonding of metals also affects their properties. Metal atoms are attached to each other by strong, delocalized bonds. These bonds are formed by a cloud of valence electrons that are shared between positive metal ions (cations) in a crystal lattice. These outer valence electrons are also very mobile. This explains why electrons can conduct heat and electricity – the free electrons are easily able to transfer energy through the material. As a result, metals make good cooking pans and electrical wires. In the crystal lattice, metal atoms are packed closely together to maximize the strength of the bonds. It is also impossible to see through metals, since the valence electrons absorb any photons of light hitting the metal. Thus, no photons pass through. Alloys are compounds consisting of more than one metal. Creating alloys of metals can affect the density, strength, fracture toughness, plastic deformation, electrical conductivity and environmental degradation. As an example, adding a small amount of iron to aluminum will make it stronger. Alternatively, adding some chromium to steel will slow the rusting process, but will make it more brittle. Some alloys have a higher resistance to corrosion. Corrosion, by the way, is a major problem with most metals. It occurs due to an oxidation-reduction reaction in which metal atoms form ions causing the metal to weaken. The following technique that has been developed to combat corrosion in structural applications: sacrificial anode made of a metal with a higher oxidation potential is attached to the metal. Using this procedure, the sacrificial anode corrodes, leaving the structural part, the cathode, undamaged. Corrosion can also be resisted by the formation of a protective coating on the outside of a metal. For example, steels that contain chromium metal form a protective coating of chromium oxide. Aluminum is also exhibits corrosion resistant properties because of the formation of a strong oxide coating. The familiar green patina formed by copper is created through a reaction with sulfur and oxygen in the air. In nature, only a few pure metals are found. Most metals in nature exist as ores, which are compounds of the metal with oxygen or sulfur. The separation of the pure metal from the ore typically requires large amounts of energy as heat and/or electricity. Because of this large expenditure of energy, recycling metals is very important. Many metals have high strength, high stiffness, and have good ductility. Some metals, such as iron, cobalt and nickel are magnetic. Finally, at extremely low temperatures, some metals and intermetallic compounds become superconductors. Ceramic: Ceramic materials are inorganic, nonmetallic materials, typically oxides, nitrides, or carbides. Most ceramics are compounds between metallic and nonmetallic elements in which the interatomic bonds are either totally ionic, or predominantly ionic but having some covalent character. While many adopt crystalline structures, some form glasses. The properties of the ceramics are due to their bonding and structure. The term ceramic comes from the Greek word keramikos, which means burnt stuff! This signifies that the desirable properties of these materials are typically achieved through a high-temperature heat treatment process. This process is called firing. Ceramics are often defined to simply be any inorganic nonmetallic material. By this definition, glasses are also ceramic materials. However, some materials scientists state that a true ceramic must also be crystalline, which excludes glasses. The term â€Å"ceramic† once referred only to clay-based materials. However, new generations of ceramic materials have tremendously expanded the scope and number of possible applications, broadening the definition significantly. Many of these new materials have a major impact on our daily lives and on our society. Ceramics and glasses possess the following useful properties: high melting temperature, low density, high strength, stiffness, hardness, wear resistance, and corrosion resistance. Additionally, ceramics are often good electrical and thermal insulators. Since they are good thermal insulators, ceramics can withstand high temperatures and do not expand greatly when heated. This makes them excellent thermal barriers. The applications of this property range from lining industrial furnaces, to covering the space shuttle, shielding it from high reentry temperatures. The aforementioned glasses are transparent, amorphous ceramics which are extensively used in windows and lenses, as well as many other familiar applications. Light can induce an electrical response in some ceramics. This response is called photoconductivity. An example of photoconductivity occurs in fiber optic cable. Fiber optic cable is speedily replacing copper for communications – optical fibers can transmit more information for longer distances, and have less interference and signal loss than traditional copper wires. Ceramics are also typically strong, hard, and durable materials. As a result, they are attractive structural materials. One significant drawback to their use is their brittleness. However, this problem is being addressed by the creation of new materials such as composites. While ceramics are typically good insulators, some ceramics can actually act as superconductors. Thus, they are used in a wide range of applications. Some (the good insulators) are capacitors, others semiconductors in electronic devices. Some ceramics are piezoelectric materials, which convert mechanical pressure into an electrical signal. These are extremely useful for sensors. For superconducting ceramics, there is a strong research effort to discover new high Tc superconductors and to then develop possible applications. Processing of crystalline ceramics is based on the basic steps which have been used for ages to make clay products. The materials are first selected, then prepared, formed into a required shape, and finally sintered at high temperatures. Glasses, on the other hand, are typically processed by pouring while in a molten state. They are then worked into shape while hot, and finally cooled. There are also new methods, such as chemical vapor deposition and sol-gel processing, currently being developed. Ceramics have a wide range of applications. For example, ceramic tiles cover the space shuttle as well as our kitchen floors. Ceramic electronic devices make possible high-tech instruments for everything from medicine to entertainment. There are also some special properties which a few ceramics possess. For example, some ceramics are magnetic materials and, as mentioned above, some have piezoelectric properties. The one major drawback of ceramics and glasses is that they are brittle. As mentioned above, certain types of ceramics possess superconducting properties at extremely low temperatures. For example, there are high-temperature superconducting ceramic materials that have recently been discovered. These materials exhibit virtually no electrical resistance below 100 degrees Kelvin. Also, these materials exhibit what is known as the Meissner effect. This means that they repel magnetic flux lines, allowing a magnet to hang in the space above the superconductor. An example of special group of crystalline ceramics is the group called Perovskites. They have captured the interest of geologists due to the information they can yield about Earth's history. The most intensely studied Perovskites at the present time are those that superconduct at liquid nitrogen temperatures. Ceramics were historically used for creating pottery and artwork, largely because the brittleness and difficulty of manufacturing ceramics restricted them from other uses until recently. However, the market requirement for microelectronics and structural composite components has risen, causing the demand for ceramic materials to likewise increase. Fiber-reinforced composites, an example of a modern ceramic application, are being created from ceramic fibers with extremely high stiffness, such as graphite and aluminum oxide. Polymers: Polymers are substances which contain a large number of structural units joined by the same type of linkage. They are any of many natural and synthetic compounds, usually of high molecular weight. They typically consist of up to millions of repeated linked units, each a relatively light and simple molecule. These substances often form into a chain-like structure. Some polymers have been around since the beginning of time in the natural world. For example, starch, cellulose, and rubber all possess polymeric properties. Man-made polymers, a relatively recent development, have been studied since 1832. However, the polymer industry today has is larger than the aluminum, copper and steel industries combined. Polymers have a huge range of applications that greatly surpasses that of any other class of material available to man. Current applications include adhesives, coatings, foams, packaging materials, textile and industrial fibers, elastomers, and structural plastics. Polymers are also widely used for many composites, electronic devices, biomedical devices, optical devices, and precursors for many newly developed high-tech ceramics (such as the fiber-reinforced composite mentioned at the end of the ceramic section). The word polymer literally has the meaning â€Å"many parts.† A polymeric solid material can be considered to be one containing many chemically bonded parts or units, themselves which are bonded together to form a solid. Polymers are typically good insulators. While a large variety of polymer applications were described above, two of the most industrially important polymeric materials are plastics and elastomers. Plastics are a large and varied group of synthetic materials. They are processed by forming or molding into shape. There are many types of plastics such as polyethylene and nylon. Polymers can be separated into two different groups depending on their behaviour when heated. Polymers with linear molecules are often thermoplastic. Thermoplastic substances soften upon heating and can be remolded and recycled. They can be semi-crystalline or amorphous. The other group of polymers is the thermosets. In contast to thermoplastics, these substances do not soften under heat and pressure and cannot be remolded or recycled. Instead, they must be remachined, used as fillers, or incinerated to remove them from the environment. Thermoplastics are typically carbon-containing polymers which are synthesized by addition or condensation polymerization. This procedure forms strong covalent bonds within the chains and weaker secondary Van der Waals bonds between the chains. Normally, the secondary forces can be easily overcome by thermal energy, which makes thermoplastics moldable at high temperatures. After cooling, thermoplastics will also retain their newly reformed shape. Common applications of thermoplastics include parts for common household appliances, bottles, cable insulators, tape, blender and mixer bowls, medical syringes, mugs, textiles, packaging, and insulation. Thermosets exhibit the same Van der Waals bonds that thermoplastics do. They also have a stronger linkage to other chains. Different chains together in a thermoset material are chemically held together by strong covalent bonds. The chains may be directly bonded to each other, or alternatively may be bonded through other molecules. This â€Å"cross-linking† between the chains is what allows the material to resist softening upon heating. Thus, thermosets must be machined into a new shape if they are to be reused or they can serve as powdered fillers. However, while thermosets are difficult to reform, they have many distinct advantages in engineering design applications. These include high thermal stability and insulating properties, high rigidity and dimensional stability, resistance to creep and deformation under load, and low weight. A few common applications for thermosets include epoxies (glues), automobile body parts, adhesives for plywood and particle board, and as a matrix for composites in boat hulls and tanks. The polymer molecule, a long chain of covalent-bonded atoms, is the basic building block of a plastic. Polymers are typically carbon based and have relatively low melting points. Polymers have a very wide range of properties that enable them to be extensively used in society. Some uses include car parts, food storage, electronic packaging, optical components, and adhesives. Synthetic fabrics are essentially man-made copies of natural fabrics. Synthetic fibers do not occur in nature as themselves. They are usually derivatives of petroleum products. Examples of common synthetic fabrics are polyester, spandex, rayon, and velcro. Recent technological developments have lead to electrically conductive polymers. The behaviour of semiconductors can now be achieved with polymeric systems. For example, there are semiconducting polymers which, when sandwiched between two electrodes, can generate light of any color. This technology has the potential of leading to OLED (organic light-emitting diode) flat panel displays. This display would be light in weight, have low power consumption, and perhaps be flexible. Liquid crystals are another example of polymeric materials. As the name suggests, a liquid crystal is a state of matter intermediate between a standard liquid and a solid. Liquid crystal phases are formed from geometrically anisotropic molecules. This typically means they are cigar shaped, although other shapes are possible. The polymer molecules have a certain degree of order in a liquid crystal phase. Take the simplest case, the Nematic phase, in which the molecules generally point in the same direction but still move around with respect to one another as would be expected in a liquid. However, under the influence of an applied electric field, the alignment of the polymer molecules gives rise to light absorption. Composites: Composites are materials, usually man-made, that are a three-dimensional combination of at least two chemically distinct materials, with a distinct interface separating the components. They are created to obtain properties that cannot be achieved by any of the components acting alone. In composites, one of the materials, called the reinforcing phase, is in the form of fibers, sheets, or particles. This material is embedded in the other materials, called the matrix phase. The reinforcing material and the matrix material can be metal, ceramic, or polymer. Typically, reinforcing materials are strong with low densities while the matrix is usually a ductile, or tough, material. The purpose of the composite, when it is designed and fabricated correctly, is to combine the strength of the reinforcement with the toughness of the matrix to achieve a combination of desirable properties not available in any single conventional material. The downside is that such composites are often more expensive than conventional materials. Some examples of current applications of composites include the diesel piston, brake-shoes and pads, tires and the Beechcraft aircraft in which 100% of the structural components are composites. A structural composite often begins with lay-up of prepreg. At this point, the choice of fiber will influence the basic tensile and compressive strength and stiffness, electrical and thermal conductivity, and thermal expansion of the final pre-preg material. The cost of the composite can also be strongly influenced by the fiber selected. The resin/fiber composite's strength depends primarily on the amount, arrangement and type of fiber (or particle) reinforcement in the resin. Typically, the higher the reinforcement content, the greater the strength. There are also some cases in which glass fibers are combined with other fibers, such as carbon or aramid, to create a hybrid composite that combines the properties of more than one reinforcing material. Additionally, the composite is typically formulated with fillers and additives that change processing or performance parameters. Integrating the ceramic, metallic, plastic and semiconductor materials is a necessary requirement to the fabrication of the micro-electronics package. This is an example of a composite system whose function is to provide interface between the central IC (Integrated Chip) and the other items on, for example, a PCB (printed circuit board). Semiconductors: There is a relatively small group of elements and compounds that has an important electrical property, semi-conduction, which makes them neither good electrical conductors nor good electrical insulators. Instead, their ability to conduct electricity is intermediate. These materials are called semiconductors, and in general, they do not fit into any of the structural materials categories based on atomic bonding. For example, metals are inherently good electrical conductors. Ceramics and polymers (non-metals) are generally poor conductors but good insulators. The semiconducting elements (Si, Ge, and Sn) from column IV of the periodic table serve as a kind of boundary between metallic and nonmetallic elements. Silicon (Si) and germanium (Ge), widely used elemental semiconductors, are outstanding examples of this class of materials. These elemental semiconductors are also known as Mono Semiconductors. Binary semiconductors are formed by a compound of two elements, normally an element from group III combined with an element from group V (such as CdS), or a element from group II combined with an element from group VI (such as GaAs). Tertiary semiconductors are formed by a compound of three elements. These semiconductors are typically compounds of elements from groups I, III and VI (such as AgInS) or elements from groups II, IV and V (such as ZnGeAs). All materials have energy bands in which their electrons can exist. In metals, as stated above, the valence band is partially-filled, and the electrons can move through the material. In semiconductors, on the other hand, there is a band gap that exists, and electrons cannot jump the gap easily at low temperatures. At higher temperatures, more of the semiconductor`s electrons can jump the gap. This causes its conductivity to go up accordingly. Electrical properties can also be changed by doping This too, is one of their great assets. Putting impurities in a semiconductor material can result in two different types of electrical behaviour. These are the so-called n (negative) and p (positive) type materials. Group V elements like arsenic added to a group IV element, such as silicon or germanium, to produce n-type materials. This occurs due to the extra valence electron in group V materials. On the other hand, group III materials like boron produce the p-type because they have only three valence electrons. When n-type material is connected to a p-type material, the device then exhibits diode behaviour. In other words, current can flow in one direction across the interface but not in the other. Diodes can act as rectifiers, but they have also led to the development of the transistor. A bipolar junction transistor (BJT) is a diode with an added third material which creates a second interface. While both npn or pnp types exist, their basic operation is essentially the same as two diodes connected to each other. With proper biasing of the voltages across each diode of the device, large current amplification can be produced. Today, metal oxide semiconductor field effect transistors (MOSFETS) have become widely used and have replaced the BJT in many applications. As a result, millions of transistors can be placed on a single silicon chip or integrated circuit. These IC chips have better reliability and consume less power than the large vacuum tube circuits of the past. The fabrication of electronic devices from the raw materials requires two major steps. The semiconductor is first melted, and a seed crystal is used to draw a large crystal of pure, solid semiconductor from the liquid. Wafers of the semiconductor are sliced and polished. Second, the circuit pattern is etched or deposited using a photolithographic process. The individual chips are finally sectioned from the initial wafer. Semiconductors experience covalent bonding. Their electrons are more tightly bound than the electrons in metals, but much more loosely bound than the electrons in insulators. The atoms in semiconductors are typically arranged in a crystal structure: a diamond-like tetrahedral (in which each atom is bonded to 4 others). Semiconductors are also typically semi-shiny. The intermediate ability of semiconductors to conduct electricity at room temperature makes them very useful for electronic applications. For example, the modern computing industry was made possible by the capability of silicon transistors to act as fast on/off switches. Electronic computing speed has greatly increased with the integrated circuit. For example, the cycle times of today's computers are now measured in nanoseconds. Opto-electronic (laser diode) research is extending the already huge rate at which information can be transmitted. Biomaterials: A biomaterial is any nondrug material that can be used to treat, enhance, or replace any tissue, organ, or function in an organism. The term biomaterial refers to a biologically derived material that is used for its structural rather than its biological properties. It also refers to any material, natural or man-made, that comprises whole or part of a living structure, or biomedical device which performs, augments, or replaces a natural function. A biomaterial can be a metal, ceramic, polymer or composite. They may be distinguished from other materials because they possess a combination of properties, including chemical, mechanical physical and biological properties, which allow them to be suitable for safe, effective and reliable use within a physiological environment. For example, collagen, the protein found in bone and connective tissues, can be used as a cosmetic ingredient. A second example is carbohydrates modified with biotechnological processes that have been used as lubricants for biomedical applications or as bulking agents in food manufacture. The performance of biomaterials depends on material properties, design, biocompatibility, surgical technique, and the health of patient. In particular, biocompatibility relies on the acceptance of the device by the body. Ideally, there should be no irritation, inflammation, or allergic response Both biomaterials and biomechanical expertise are needed to perform in vitro testing of spinal implants. Endo-vascular stents provide structural support vessels following angioplasty and other major medical procedures. After an angioplasty procedure, vessels can experience re-stenosis and eventually return to their original pre-operative diameter. In as many as 10% of the procedures, the vessels may even collapse immediately. To prevent the vessels from shrinking, endo-vascular prosthesis or stents are used. These stents are examples of biomaterials. Stents are tubular structures consisting of a spring, wire mesh or slotted tubes that are deployed inside the vessel. Depending on the design and intended use (coronary/ peripheral), they can range in diameter from several millimeters to many times that size. A biomaterial must be typically have the following properties: it must be inert or specifically interactive, biocompatible, mechanically and chemically stable (or biodegradable), processable (for manufacturability), have good shelf life, be nonthrombogenic (does not cause clot formation) if it is blood-contacting, and be sterilizable. There are examples of biomaterials and compatibility problems which arise from the materials not having the above properties. These include dialysis tubing made of cellulose acetate, a â€Å"commodity plastic†, which is known to activate platelets and blood complement. Additionally, Dacron, a polymer widely used in textiles, has been used in vascular grafts, but only gives occlusion-free service for diameters larger than 6 mm. Finally, commercial grade polyurethanes, initially used in artificial hearts, can be thrombogenic (they cause clot formation). There are many prominent applications of biomaterials used in the medical profession today. Biomaterials are used in orthopedics for joint replacements (hip, knee), bone cements, bone defect fillers, fracture fixation plates, and artificial tendons and ligaments. They are also used for cardiovascular vascular grafts, heart valves, pacemakers, artificial heart and ventricular assist device components, stents, balloons, and blood substitutes. Another application is in ophthalmics, for contact lenses, corneal implants and artificial corneas, and intraocular lenses. They can also have cosmetic applications, such as in augmentation mammoplasty. Finally, other applications include dental implants, cochlear implants, tissue screws and tacks, burn and wound dressings and artificial skin, tissue adhesives and sealants, drug-delivery systems, matrices for cell encapsulation and tissue engineering, and sutures. 2). The following paragraphs will provide an analysis of the modern pop can and the considerations taken by the manufacturer in its design. The overall design of the can has several advantages over another popular beverage container, the glass bottle. The pop can is inherently light weight and cheap due to the aluminum or steel alloys that are used in its creation. The cost of a can accounts for only about 4 cents of the price of a canned beverage. About 10 cents goes for advertising. The 12 ounces of beverage in the container typically costs less than a penny to produce. It is also not easily breakable, unlike glass. The shape of the can is easy to hold in the hand, making it much easier for a customer to use. The aluminum or steel alloys of the can also have the ability to undergo expansion without breaking the container. Thus, if a pop can is frozen, it will not explode, it will simply deform. Glass, on the other hand, would not as easily deform and would likely break in this situation. Pop cans are also allow cheaper packaging methods than bottles to be used. This is because the cans can come into contact with each other without breaking, unlike bottles. This allows many cans to be transported without the need for extensive protective barriers between the individual cans. An additional feature that allows the cans to be more easily transported and organised is the shape of the bottom and top of the can. Both the bottom and top have a lip. This lip protrudes upward from the top and downwards from the bottom. In other words, there is a indentation in both the top and bottom of the can, as shown in the following figure: The radii of the top and bottom lips are matched so that one can is able to be stacked on top of another can. In other words, the top lip of one can fits neatly into the bottom lip of the second can. This is shown in the following diagram. This stacking feature is not possible with bottles, since the bottom base of a bottle does not resemble its top spout. The pop-top soda, with their attached tab, can provide an excellent example of inherently safer design from everyday life. When soda in cans was first introduced, a separate device was required to open these cans, and the first â€Å"pop-tops† represented a major advance in convenience (and environmentalism). The initial pop-tops were scored tear strips in the can top with attached rings or levers to grasp and tear the metal tab from the can. The top was completely removed from the can once the tab was opened, and this top was then discarded. These tabs were therefore environmental hazards when discarded. Alternatively, some people would dispose of the tab by placing it into the can before drinking the soda. This caused the tab to occasionally be swallowed when drinking from the can, so it sometimes had to be surgically removed. The current design of the pop-top soda can, where the tab remains an integral part of the can after opening, represents an inherently safer design. While the tab can be detached by flexing it back and forth until the metal fails, this requires some additional effort to do. It is therefore easier to use the can safely. The procedure involved in creating pop cans will now be outlined. This procedure demonstrates some of the major components of the cans. Modern pop cans are made from either steel or aluminium using advanced engineering and sophisticated technology. There is a special grade of low-carbon steel is used for steel drink cans, which is coated on each side with a very thin layer of tin. This tin allows the surface to be protected against corrosion. It also acts as a lubricant while the can is being formed. In aluminium cans, the aluminium is alloyed with magnese and magnesium, providing greater strength and ductility. Aluminium alloys of different strengths and thickness are used for making the can body and the end. The reason that the alloy used from the end must be stronger than that used for the body will be described shortly. The steps involved in manufacturing cans are illustrated in a simplified way below: The aluminium or steel strip arrives at the can manufacturing plant in huge coils. A thin film of oil is then used to lubricate the strip. The strip is then fed continuously through a cupping press that blanks and draws thousands of shallow cups every minute. Each cup is pressed through a set of tungsten carbide rings. This ironing process redraws and literally thins and raises the walls of the cans into their final can shape. Trimmers are then used to remove the surplus irregular edge and cut each can to a precise, specific height. The excess can material is recycled. These trimmed can bodies are passed through highly efficient washers. They are then dried. As a result, all traces of oil are removed in preparation for coating internally and externally. The clean cans are coated externally with a clear or pigment base coat. This coat provides a good surface for the printing inks. The cans are then passed through a hot air oven to dry the lacquer onto the surface. Next, a highly sophisticated printer/decorator applies the printed design in up to six colours. A varnish is also applied. 9.A coat of varnish is also applied to the base of each can by a rim-coater. 10.The cans pass through a second oven which dries the inks and varnish. 11.The inside of each can is sprayed with lacquer. This special layer is to protect the can itself from corrosion and its contents from any possibility of interaction with the metal. 12.Once again, lacquered internal and external surfaces are dried in an oven. 13.The cans are passed through a necker/flanger. Here the diameter of the wall is reduced or ‘necked-in'. The top of the can is flanged outwards to accept the end once the can has been filled. 14.Every can is tested at each stage of manufacture. At the final stage it passes through a light tester which automatically rejects any cans with pinholes or fractures. 15.The finished can bodies are then transferred to the warehouse to be automatically palletised before dispatch to filling plant. The Can End 1.Can end manufacture begins with a coil of special alloy aluminum sheet. 2.The sheet is fed through a press which stamps out thousands of ends every minute. 3.At the same stage the edges are curled. 4.The newly formed ends are passed through a lining machine which applies a very precise bead of compound sealant around the inside of the curl. 5.A video inspection system checks the ends to ensure they are perfect. TAB.The pull tabs are made from a narrow width coil of aluminum. The strip is first pierced and cut and the tab is formed in two further stages before being joined to the can end. 6.The ends pass through a series of dies which score them and attach the tabs, which are fed in from a separate source. 7.The final product is the retained ring pull end. 8.The finished ends, ready for capping the filled cans, are packaged in paper sleeves and palletised for shipment to the can filler. As mentioned above, a printer/decorator is used in the manufacturing of cans to apply a printed design in up to six colours to the can body. A varnish is then applied. A varnish is a viscid liquid, consisting of a solution of resinous matter in an oil, or a volatile liquid, typically laid on work with a brush. Once it is applied, the varnish soon dries, either by evaporation or chemical action, and the resinous part forms thus a smooth, hard surface, with a beautiful gloss, capable of resisting, to a greater or less degree, the influences of air and moisture. The varnish therefore improves the appearance of the printed design on the can. It also increases the durability of the design by ensuring that it is more resistant to the wearing effects of the elements. This can be readily observed through common experience. Even old, used pop cans retain their printed designs very well, despite being subjected to the elements such as moisture or air. Bottles, on the other hand, typically have paper labels attached with glue. This requires glue and paper. These bottle labels also do not possess the glossy sheen of the pop can design. Finally, they are more easily susceptible to the influences of the elements, particularly air and moisture. For example, placing a glass bottle and its label in water will cause the label to saturate with water. This degrades the legibility and appearance of the label, and greatly increases the chance that it will tear or fall off the bottle. In contrast, placing a pop can in water has no effect on the legibility, appearance, or durability of the printed design. The base-coater gives the can an exterior coat to enable the printing colours to fix properly (the base coat is sometimes The of the pop can is a separate piece to allow filling by the beverage maker prior to the top being installed. It can now be revealed why bottled beer and beer from a tap tastes different from beer in a can. Be forewarned: if you're a six-pack enthusiast, you're not going to like the explanation. When you sip a can of your favorite brew, you are savoring not only fermented grain and hops but just a hint of the same preservative that kept the frog you dissected in 10th-grade biology class lily-pad fresh: formaldehyde. What is formaldehyde doing in beer? The same thing it's doing in pop and other food and drink packaged in steel and aluminum cans: killing bacteria. But not the bacteria in the drink, the bacteria that attacks a lubricant used in the manufacture of the can. Notre Dame's Steven R. Schmid, associate professor of aerospace and mechanical engineering, is an expert in tribology – the study of friction, wear and the lubrication – applied to manufacturing and machine design. The co-author of two textbooks, Fundamentals of Machine Elements and Manufacturing Engineering and Technology (considered the bible of manufacturing engineering), Schmid has conducted extensive research on the manufacturing processes used in the production of beverage and other kinds of cans. Schmid explains that back in the 1940s, when brewers and other beverage makers began putting drinks in steel (and, later, aluminum) cans, the can makers added formaldehyde to a milk-like mixture of 95 percent water and 5 percent oil that's employed in the can manufacturing process. The mixture, called an emulsion, bathes the can material and the can-shaping tooling, cooling and lubricating both. Additives in the oil part are certain bacteria's favorite food. But if the bacteria eat the emulsion, it won't work as a lubricant anymore. So can makers add a biocide to the emulsion to kill the bacteria. Before a can is filled and the top attached, this emulsion is rinsed off, but a small residue of the oil-water mixture is inevitably left behind, including trace amounts of the biocide. The amounts remaining are not enough to be a health hazard, but they are enough to taste, and the first biocide used back in the 1940s was formaldehyde. In the decades since, can makers have devised new formulas for emulsions, always with an eye toward making them more effective, more environmentally friendly and less costly. But because formaldehyde was in the original recipe, people got used to their canned Budweiser or whatever having a hint of the famous preservative's flavor. For this reason, Schmid says, every new emulsion formula since then has had to be made to taste like formaldehyde, â€Å"or else people aren't going to accept it.† Extensive tests are run to make sure the lubricant and additives taste like formaldehyde. â€Å"It's not that it tastes okay. It's just what people are used to tasting,† he says. (Miller Genuine Draft and similar brews, Schmid says, use biocides that have no flavor.) The formaldehyde flavor legacy is one little-known aspect of can-making. Another involves the smooth coating applied to the inside of cans. The rinse cycle that attempts to wash off the emulsion also aims to remove particulate metal debris that forms on the metal's surface during the bending and shaping of a can. Like the emulsion, some of the microscopic debris always remains after rinsing. Unlike the emulsion, it can be dangerous to swallow. To keep powdered metal out of a can's contents, Schmid says, manufacturers spray-coat the inside with a polymer dissolved in a solvent. When the can is heated, the solvent boils away, leaving only the protective polymer coating. The coating not only plasters any microscopic debris to the can wall and away from the food, it keeps the food from interacting with can material, an especially important consideration with steel cans. â€Å"Say you've got tomato soup in this steel can. You don't want that acidic soup corroding your can. It would kill your can, and the can would adulterate your food,† Schmid says. â€Å"It's also why you're advised that when you go camping and you have Spaghettios you don't cook them in the can, because the polymer will degrade and you're going to be eating polymer.† (Industry sources tell Schmid that the typical consequences of such a culinary blunder are headaches and constipation.) Schmid says can manufacturers are forever searching for ways to improve efficiency in their struggle to stay price competitive with plastic and glass bottles. A single can-tooling machine can form 400 cans a minute. In a typical process, all but the top is shaped during a single stroke through a disk of aluminum or steel. The top, seamed on after filling, is made of a more expensive aluminum alloy, rich in magnesium. The added ductile strength of the magnesium is necessary so another machine can mash down a pillar of the metal to form the rivet that attaches the pop top. Today's beverage cans are â€Å"necked† near the top for a reason. The narrower-diameter means less of the expensive lid alloy is needed. It saves a minuscule fraction of a cent per can, but it adds up, Schmid says. â€Å"In this country alone we use about a can per person per day, so you have to make 250 million cans per day. It's an amazing thing to watch these machines kick out these cans.† Rivet is likely a separate part from the tab. It should be strong enough to attach the tab to the can and to ensure that it does not break when the can is opened. Lip on top of can prevents liquid from flowing down the side of the can. Bottom is indented to enable stacking even when the tab has been opened. The indent provides the necessary room for the open tab. For recycling purposes, pop cans can be neatly compacted flat, and are easy to transport using a wide range of containers. Rivet is a separate piece which connects the tab to the can top. Top of the pop can is stamped with words such as â€Å"recyclable† and â€Å"return for refund†. Thus, the alloy of the top must be soft enough to allow this stamping to occur. Aluminum costs more than steel, and the price has been rising. Steel â€Å"minimills† now have continuous casting processes that make sheet steel thin enough to form seamless cans. And there is competition from other materials as well. â€Å"We h ave to find ways to make cans lighter and lighter to keep fending off polymers, steel and glass. Lighter cans means lower prices to the consumer, who's then more likely to buy cans off the grocery shelf instead of two-liter bottles or glass.† ALCOA's answer is lightweighting, designing cans to use the thinnest aluminum possible within the constraints of strength and appearance. In 1993, Americans recycled 59.5 billion aluminum cans, 3 billion more than in 1991, and raised the national aluminum can recycling rate to 2 out of every 3 cans. Aluminum can recycling saves 95% of the energy needed to make aluminum from bauxite ore. Energy savings in 1993 alone were enough to light a city the size of Pittsburgh for 6 years. Special pallets and stacking techniques are used to protect can bodies from crushing stresses and to enable quick and efficient loading into the filling machine line. The first beverage can, filled by a brewer in Newark, New Jersey in 1935, weighed three ounces. Today, an aluminum beverage can weighs one half ounce – 600% less than the original beverage can. Can manufacturers strive to do even better through a process called â€Å"light weighting†-the use of lighter can ends and thinner body walls. Using less material at the beginning of the manufacturing process results in a more effective means of creating safe, reliable, performance-driven packaging. This results in less waste once the packages' contents have been consumed. It also saves manufacturers money – an added incentive. 3). The diameter of the bar is 12.7 mm. Its radius is half the diameter. Therefore, its radius can be calculated to be (12.7 mm)/ 2 = 6.35 mm. By applying the conversion factor that 1000 mm = 1 m, this radius can also be expressed as (6.35 mm) * (1 m / 1000 mm) = 6.35 x 10-3 m. The bar has a cross-sectional area given by the following formula: Cross-sectional area = ?r2 where r is the radius of the steel bar. Using this formula, the cross-sectional area of the bar can be calculated to be: Cross-sectional area = ?(6.35 x 10-3 m)2 Cross-sectional area = 1.266768698 x 10-4 m2 (Cross-sectional area = 1.27 x 10-4 m2 when significant figures are applied). Gravity applies a force to the bar proportional to the bar's mass. This force is given by the formula: Force due to Gravity = (Mass of object) * (Acceleration of Gravity) If we assume that the steel bar is located at the surface of the earth, the acceleration of gravity is approximately 9.8 m/s2 at this elevation. Therefore, the force applied to the bar by gravity can be calculated to be: Force due to Gravity = (7000 kg) * (9.8 m/s2) Force due to Gravity = 68600 kg*m/s2 (Force due to Gravity = 70000 kg*m/s2 when significant figures are applied) The stress placed on the bar is given by the following formula: Stress = (force) / (unit area) Therefore, the stress placed on the bar can be calculated to be: Stress = (68600 kg*m/s2) / (1.266768698 x 10-4 m2) Stress = 541535326.2 kg/(m*s2) (Stress = 500000000 kg/(m*s2) when significant figures are applied) The steel bar has a modulus of elasticity of 205,000 Mpa. 1 Pa is defined to be equal to 1 kg/(m*s2). Using the conversion factor that 1 x 106 Pa = 1 Mpa, 1 Mpa is defined to be equal to 1 x 106 kg/(m*s2). We can therefore express the modulus of elasticity of the steel bar in Pa as (205,000 Mpa) * (1 x 106 Pa / 1 Mpa) = 2.05 x 1012 Pa. The strain experienced by the steel bar is the fractional deformation it undergoes when a stress is applied. This strain can be represented mathematically by the following formula: where l represents the length of bar, and ?l represents the change in length of the bar due to the applied stress. The elastic region of the stress-strain curve refers to the portion of the curve in which an increase in stress will cause a linearly proportional increase in strain. Within this elastic region, removal of the stress will cause the strain to be reduced to zero as well. In other words, the material is not permanently deformed, and removal of the stress causes the material to return to its original dimensions. The strain is therefore reversible, or elastic. In the elastic region, therefore, stress and strain can be related by a proportionality coefficient. This proportionality coefficient relating the reversible strain to stress in the elastic region of the stress-strain curve is known as the modulus of elasticity. This modulus of elasticity can be represented mathematically as: Modulus of Elasticity = (Elastic Stress) / (Unit Strain) This equation can be rearranged to solve for the unit strain. This rearranged equation is expressed as: Unit Strain = (Elastic Stress) / (Modulus of Elasticity) Assuming the stress applied to the bar is small enough to ensure that the bar is still operating in the elastic region of the stress-strain curve, we can use the above equation to determine how much the bar will be strained by the load. Mathematically, this solution takes the following form: Unit Strain = (541535326.2 kg/(m*s2)) / (2.05 x 1012 Pa) Unit Strain = (541535326.2 kg/(m*s2)) / (2.05 x 1012 kg/(m*s2)) Unit Strain = 2.641635738 x 10-4 (Unit Strain = 3 x 10-4 when significant figures are applied) This strain is unitless because it represents the fractional deformation of the bar when the stress is applied.