User:Raleway

Materials Science tests knowledge of the properties and characteristics of metals, ceramics, polymers and composite materials, with a focus on material characterization techniques, intermolecular forces, and surface chemistry.

Rules Review
Each pair of competitors from a team will be allowed 5 front and back pages of cheat sheets. There will a lab section unless listed otherwise, and students must bring safety apparel themselves or be unable to do the lab due to safety concerns. Students will be tested on the field of Materials Science and topics are limited to those listed below, though the scope of each topic is nearly unlimited.

Tips and Tricks
Materials Science covers a vast amount of knowledge, hence the 5 cheat sheets allowed for the event. The extent of each topic is nearly unlimited, such that teams will need to know each topic well without relying on cheat sheets. Graphs are especially important, but only so long as they are useful - too many basic graphs will take up valuable space. Also, cheat sheets can contain large tables of information that would otherwise be impossible to memorize, such as atomic packing for different elements and compounds, melting and boiling points, and more. Many teams have found an optimal layout of 0.5" margins, 3 columns, and Times New Roman font. The font size will depend largely on the amount of information contained, but teams should be cautious to still keep their cheat sheets readable. The best competitors will know their cheat sheets extraordinarily well, such that they can find small bits of information quickly. Less competitive teams will either rely on their cheat sheets for basic information, or rely on the find function during practice and become lost in actual tests. Lastly, screen protectors are incredibly useful for protecting cheat sheets from any damage or spills in the lab section of the event.

General Properties of Material Classes
Although this section can be included on the cheat sheet, only the bare-bones should be on it. Most of it should be meomrized, if not all, for easy and fast recall during the test.

Metals
Mechanical properties: Metals are stiff, strong, ductile, malleable, resistant to fracture, good conductors of electricity and heat, and are lustrous. Many metals, such as iron, cobalt, and nickel, also have good magnetic properties.

Diamagnetism: Diamagnetism is present in all materials. An applied magnetic field induces another magnetic field in the opposite direction, providing a repulsive force. Diamagnetic materials could be considered non-magnetic, as diamagnetism is negligible compared to other, stronger forms of magnetism.

Paramagnetism: Paramagnetism exists due to unpaired electrons in some elements and compounds, which generate a magnetic dipole due to their spin. Paramagnets do not retain magnetization unless they are in the presence of an applied magnetic field.

Ferromagnetism: Ferromagnetism also exists due to unpaired electrons, but works in a different manner. Magnetic moments align themselves parallel to each other and to an applied magnetic field in order to maintain a lowered state. These magnetic moments align even in the absence of an applied magnetic field. Every ferromagnetic material has a Curie temperature, above which it loses any ferromagnetic properties.

Ceramics
Ceramics are relatively stiff and strong, hard, brittle, susceptible to fracture, insulators of heat and electricity, and are very resistant to high temperatures and harsh conditions. Some ceramics (glass ceramics) can be transparent or translucent, while others (clay ceramics) are opaque. Some oxide ceramics also exhibit magnetic behavior.

Polymers
Mechanical properties: Polymers are low density, but not as stiff or strong as metals or ceramics. They are extremely ductile and pliable, chemically inert in a multitude of environments, nonmagnetic (diamagnetic), and usually are not conductive (polymers with a backbone of alternative double and single bonded carbon can conduct electricity through the movements of free electron pairs). Polymers soften or decompose at modest temperatures.

Degree of polymerization: The degree of polymerization, or DP, is defined as the number of monomer units in a macromolecule or polymer molecule. A homopolymer contains only one type of monomer unit, and the number-average degree of polymerization is given by [math]M_n/M_0[/math] where M(n) is the number-average molecular weight and M(0) is the molecular weight of the monomer unit.

Composites
The properties of composites are entirely dependent on their constituent parts and are usually enhanced by fiber lengths. Strength is dependent on fiber length, where smaller fibers are larger. Ductility, meanwhile, can be lowered by using matrices instead of fibers. Ceramic composites are resistant to degradation, but are brittle; metal matrices are useful at high temperatures. Construction also matters. Carbon-carbon composites, which reinforce graphite with fibers, have high tensile strength, resistance to creep, fracture toughness, strength, and thermal conductivity; laminar composites, meanwhile, have high strength in the 2D plane only; sandwich panel cores have low elasticity, light weight, and high shear strength, while their sheets resist tension and compression.

Mining
Metals are often extracted from Earth by means of mining ores that are rich sources of requisite elements, such as bauxite. Ore is located by prospecting techniques, followed by exploration and examination of deposits. Mineral sources are generally divided into surface mines, which are mined by excavation using heavy equipment, and subsurface mines. Once Ore is mined, metals must be extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometallurgy employs aqueous chemistry for the same purpose.methods used depend on metal and their contaminants. When a metal ore is an ionic compound of that metal and a nonmetal, the ore must usually be smelted — heated with a reducing agent — to extract the pure metal. Many common metals, such as iron, are smelted using carbon as a reducing agent. Some metals, such as aluminum and sodium, have no commercially practical reducing agent and are extracted using electrolysis instead. Sulfide ores are not reduced directly to metal but are roasted in air to convert them to oxides.

Native State
Metals are said to be in the native state if they are found in their elementary form. Generally, less active metals are found in the native state.common examples of metals which occur in native state are gold, silver, copper, platinum, etc.

Combined State
Metals are said to occur uncombined state if they are found in nature inform of their compounds. Generally, reactive metals occur inform of their compounds Uncombined state metals are found in the crust of earth as oxides, carbonates, sulfides, silicates, phosphates, etc.naturally occurring chemical substances in earth's crust which can be obtained by mining are known as minerals. Minerals extracted from the crust of the earth are not pure but instead, they are associated with a large number of earthly, rocky and siliceous impurities.impurities associated with minerals are collectively known as gangue or matrix. Every mineral of metal cannot be used for its extraction. In some cases, economic factors while in others availability of mineral may be a hindrance. Minerals from which metals can be economically and conveniently extracted is called ore. For example, earth’s crust contains aluminum inform of two well-known minerals, bauxite (AI2O3.2H2O) and China clay (AI203.2SiO2.2H2O), but extraction of aluminum is cheaper and easy from bauxite. Hence, an ore of aluminum is bauxite. Similarly, minerals of copper are copper glance (Cu2S), cuprite (CU2O), malachite. (CuCO3. Cu(OH)2), copper pyrites (CuFeS2), etc., but more of copper is copper pyrites.Thus, it can be concluded that all ores are minerals but all minerals are not ores.

Hot Working
Hot working is when a metal is deformed at a temperature higher than its temp of recrystallization Forging: Forging is mechanically working or deforming a single piece of a normally hot metal; this may be accomplished by the application of successive blows or by continuous squeezing. Forgings are classified as either closed or open die. For the closed die, a force is brought to bear on two or more die halves having the finished shape such that the metal is deformed in the cavity between them. For open die, two dies having simple geometric shapes (e.g., parallel flat, semicircular) are employed, normally on large workpieces. Forged articles have outstanding grain structures and the best combination of mechanical properties. Wrenches, and automotive crankshafts and piston connecting rods are typical articles formed using this technique.

=Rolling
=

Rolling, the most widely used deformation process, consists of passing a piece of metal between two rolls; a reduction in thickness results from compressive stresses exerted by the rolls. Cold rolling may be used in the production of sheet, strip, and foil with a high-quality surface finish. Circular shapes, as well as I-beams and railroad rails, are fabricated using grooved rolls. Extrusion: For extrusion, a bar of metal is forced through a die orifice by a compressive force that is applied to a ram; the extruded piece that emerges has the desired shape and a reduced cross-sectional area. Extrusion products include rods and tubing that have rather complicated cross-sectional geometries; seamless tubing may also be extruded.

=Drawing
=

Drawing is the pulling of a metal piece through a die having a tapered bore by means of a tensile force that is applied on the exit side. A reduction in cross section results, with a corresponding increase in length. The total drawing operation may consist of a number of dies in a series sequence. Rod, wire, and tubing products are commonly fabricated in this way.

Casting Techniques
Casting is when a heated metal is poured into a mold

=Sand Casting
=

Sand Casting With sand casting, probably the most common method, ordinary sand is used as the mold material. A two-piece mold is formed by packing sand around a pattern that has the shape of the intended casting. Furthermore, a gating system is usually incorporated into the mold to expedite the flow of molten metal into the cavity and to minimize internal casting defects. Sand-cast parts include automotive cylinder blocks, fire hydrants, and large pipe fittings.

=Die Casting
=

In die casting, the liquid metal is forced into a mold under pressure and at a relatively high velocity and allowed to solidify with the pressure maintained. A two piece permanent steel mold or die is employed; when clamped together, the two pieces form the desired shape. When complete solidification has been achieved, the die pieces are opened and the cast piece is ejected. Rapid casting rates are possible, making this an inexpensive method; furthermore, a single set of dies may be used for thousands of castings. However, this technique lends itself only to relatively small pieces and to alloys of zinc, aluminum, and magnesium, which have low melting temperatures.

=Investment Casting
=

For investment (sometimes called lost wax) casting, the pattern is made from a wax or plastic that has a low melting temperature. Around the pattern is poured a fluid slurry, which sets up to form a solid mold or investment; plaster of Paris is usually used. The mold is then heated, such that the pattern melts and is burned out, leaving behind a mold cavity having the desired shape.This technique is employed when high dimensional accuracy, reproduction of fine detail, and an excellent finish are required—for example, in jewelry and dental crowns and inlays. Also, blades for gas turbines and jet engine impellers are investment cast.

=Lost Foam Casting
=

A variation of investment casting is lost foam (or expendable pattern) casting. Here the expendable pattern is a foam that can be formed by compressing polystyrene beads into the desired shape and then bonding them together by heating. Alternatively, pattern shapes can be cut from sheets and assembled with glue. Sand is then packed around the pattern to form the mold. As the molten metal is poured into the mold, it replaces the pattern which vaporizes. The compacted sand remains in place, and, upon solidification, the metal assumes the shape of the mold. With lost foam casting, complex geometries and tight tolerances are possible. Furthermore, in comparison to sand casting, lost foam is a simpler, quicker, and less expensive process, and there are fewer environmental wastes. Metal alloys that most commonly use this technique are cast irons and aluminum alloys; furthermore, applications include automobile engine blocks, cylinder heads, crankshafts, marine engine blocks, and electric motor frames.

=Continuous Casting
=

At the conclusion of extraction processes, many molten metals are solidified by casting into large ingot molds.The ingots are normally subjected to a primary hot-rolling operation, the product of which is a flat sheet or slab; these are more convenient shapes as starting points for subsequent secondary metal-forming operations (i.e., forging, extrusion, drawing). These casting and rolling steps may be combined by a continuous casting (sometimes also termed “strand casting”) process. Using this technique, the refined and molten metal is cast directly into a continuous strand that may have either a rectangular or circular cross section; solidification occurs in a water-cooled die having the desired cross-sectional geometry. The chemical composition and mechanical properties are more uniform throughout the cross sections for continuous castings than for ingot-cast products. Furthermore, continuous casting is highly automated and more efficient.

=Miscellaneous Techniques
=

Power Metallurgy Yet another fabrication technique involves the compaction of powdered metal, followed by a heat treatment to produce a more dense piece. The process is appropriately called powder metallurgy, frequently designated as P/M. Powder metallurgy makes it possible to produce a virtually nonporous piece having properties almost equivalent to the fully dense parent material. Diffusional processes during the heat treatment are central to the development of these properties. This method is especially suitable for metals having low ductilities since only small plastic deformation of the powder particles need occur. Metals having high melting temperatures are difficult to melt and cast, and fabrication is expedited using P/M.

Bond Types
Ionic:

Ionic compounds can be recognized by a combination of positively charged cations and negatively charged anions. They form a three-dimensional ionic lattice.

Ionic compounds often are soluble in water.

In their solid form, ionic compounds do not conduct electricity. However, ionic compounds conduct electricity when dissolved in water or melted as ions are free to move.

Most ionic compounds have a very high melting point and an extremely low volatility.

Metallic:

Metallic compounds are characterized by their "sea" of free electrons. These electrons are free to move and balance out the positively charged cations of the metal atoms.

Metallic compounds are not soluble in water.

Metallic compounds conduct electricity both as solids and as liquids, but not when dissolved in water.

Most metallic compounds have a very high to extremely high melting point and an extremely low volatility due to the strong attractive force between the electrons and cations.

However, the fairly unrestricted motion of electrons allows for properties like ductility and malleability.

Covalent (Network):

Covalent compounds are small molecules composed of covalently bonded atoms, while network compounds have an ordered structure of atoms connected by covalent bonds.

Neither covalent nor covalent network compounds are soluble in water, nor do they conduct electricity.

Covalent compounds (simple covalent bonds) have relatively low melting points and high volatility, while covalent network compounds (giant covalent bonds) have extremely high melting points and extremely low volatility due to intermolecular forces.

Dipole-Dipole/LDF:

These compounds are composed of either covalent nonpolar or barely polar molecules.

They are soluble in both hexane and ethanol due to their lack of charge, but are not soluble or conductive in water.

They have very low melting points and high volatility.

Hydrogen:

Hydrogen bonded compounds are characterized by O-H, N-H, or F-H bonds. These bonds cause regions of positive and negative charge, creating intermolecular attractions.

They are soluble but not conductive in water and ethanol.

They have very low melting points and extremely low volatility.

Crystallinity
Crystalline solids are composed of 1 or more crystals containing completely constant, rigid long range order.

Semi-crystalline solids are also heavily bonded, but lack the rigidity and constant structure of crystalline solids.

Amorphous solids still possess short range order, but have significantly less chain linkage.

Polymers are usually semi-crystalline to some degree, with some crystalline regions with rigid chain linkage and some amorphous regions.

Metals follow a relatively crystalline structure.

Finally, ceramics vary in crystallinity, from highly crystalline, vitrified fired ceramics to amorphous glasses.

Face Centered Cubic
Also known as cubic close packed.

In the FCC cell, atoms are located at each of the 8 corners as well as in the centers of each of the 6 faces.

FCC follows an ABCABC close packing pattern - there are 3 repeating layers, where the atoms of the third layer are located above holes in the first and second layers.

FCC is the most dense of the cubic packing arrangements, with an atomic packing factor of 0.74. Each unit cell contains 4 atoms and has a side length of [math]A = 4R/\sqrt{2}[/math].

Each atom in the FCC matrix has a coordination number of 12.



Body Centered Cubic
In the BCC cell, atoms are located at each of the 8 corners as well as in the center of the cubic cell.

BCC is less dense than FCC, with an atomic packing factor of 0.68. Each unit cell contains 2 atoms and has a side length of [math]A = 4R/\sqrt{3}[/math].

Each atom in the BCC matrix has a coordination number of 8.



Hexagonal Close Packing
HCP is another close packed arrangement.

The HCP cell is composed of two hexagons of 6 atoms each, an additional atom in the center of each hexagon, and a triangle of atoms in between the two hexagons.

HCP differs from FCC in that HCP follows an ABAB packing pattern - there are only 2 repeating layers, where the atoms of the third layer are located above the atoms of the first layer, not above gaps.

HCP also has an atomic packing factor of 0.74, the maximum possible. Each unit cell contains 6 atoms and has two parameters, A (side length) and B (height).

Each atom in the HCP matrix has a coordination number of 12.



Simple Cubic
Simple cubic is a very basic arrangement, only containing atoms at each corner of the unit cell.

SC is the least dense, with an atomic packing factor of 0.52. Each unit cell contains 1 atom and has a side length of [math]A = 2R[/math]

Each atom in the SC matrix has a coordination number of 6.

Atomic Packing Factor (APF)
The atomic packing factor describes the amount of space occupied by atoms.

For example, in the simple cubic packing, each cell has side length 2R and contains 1 atom of radius R.

The volume occupied by the atom is [math](4/3)\pi *R^3[/math], while the total volume is [math](2R)^3 = 8R^2[/math]

The fraction of space occupied by atoms is [math](4/3)\pi *R^3/8R^3[/math] = [pi/6] = 0.524, exactly the amount listed above.

This equation will work for any of the other crystal structures assuming the correct side lengths are used.