Crystal Structures Chapter 7-11 PDF

CHAPTER 7: Basic Concepts of Crystal Structures In the atomic hard-sphere model, all atoms are identical. Lattice is sometimes used in the context CRYSTAL STRUCTURES of crystal structures. Categor...

CHAPTER 7: Basic Concepts of Crystal Structures In the atomic hard-sphere model, all atoms are identical. Lattice is sometimes used in the context CRYSTAL STRUCTURES of crystal structures. Categories of Solids Lattice - three-dimensional array of points Crystalline Amorphous coinciding with atom positions or sphere centers Most common type of Rigid structures, solids - firm, definite & lacking a well-defined UNIT CELLS fixed shape, rigid and shape. Does not have incompressible edges like crystals do Unit cell - basic structural (repeating) unit of a Geometric shape and No geometric shape, crystalline solid flat face non-crystalline Each sphere denotes an atom, ion or molecule and Arrangement of The particles do not it is called a lattice point particles in a crystalline form 3D lattice solid is in a very orderly structures like we see fashion in solids Intermolecular force is Breaks into uneven uniform throughout - pieces with irregular spaces between the edges, no distinct atoms are less due to arrangement or shape this of molecules High melting and Low melting and boiling boiling point point In many crystals, the lattice point does not actually The arrangement of Some naturally contain a particle, instead there may be several atoms is repeated over occurring have atoms, ions or molecules identically arranged in a great distance impurities, so they have each lattice points shorter order arrangement of The possibility of a unit cell that consists of atoms molecules placed only at the corners of a cube does exist and it's called simple cubic (SC) crystal structure. Polonium, a metalloid or a semimetal is the only simple-cubic element that has a relatively low atomic packing factor *atoms or ions (described as crystalline structures) are thought of as solid spheres having well-defined diameters known as the atomic hard-sphere model, in which spheres representing neighbor atoms touch one another SEVEN TYPES OF PRIMITIVE UNIT CELLS Face-Centered Cubic Crystal Structure (FCC) Simple cubic The spheres or ion cores touch one another across a face diagonal; the cube edge length a and the atomic radius R are related through 𝑎 = 2𝑅 2 Example 1. Calculate the volume of an FCC unit Tetragonal cell in terms of atomic radius R. 3 𝑉 = 𝑎 but a = ? then solve for a Orthorhombic Rhombohedral 2 2 2 From the figure, solve a: 𝑎 + 𝑎 = (4𝑅) Therefore, 𝑎 = 2𝑅 2 Monoclinic The FCC unit cell volume 𝑉𝑐 may be computed 3 3 3 from 𝑉𝑐 = 𝑎 = (2𝑅 2) = 16𝑅 2 The face-centered (FCC) is a crystal structure with atoms located at each of the corners and the center Triclinic of all the cube faces. Some familiar metals having this crystal structure are copper, aluminum, silver and gold. Hexagonal The following points are used to calculate the number of atoms in a unit cell. (a) Each corner atom in a cube is shared between eight unit cells. Therefore, a corner atom contributes to ⅛ each unit cell. (b) An atom on the face of a unit cell is shared by the two unit cells. Thus a face atom contributes to ½ to each unit cell (c) An atom inside a cube belongs to that cube only. Hence , that atom contributes fully to that unit cell. 𝑁𝑓 𝑁𝑐 𝑁 = 𝑁𝑖 + 2 + 8 Where Ni = number of interior atoms Example 2. Show that the atomic packing factor for Nf = number of face atoms the FCC crystal structure is 0.74 Nc - number of corner atoms Solution: For the FCC crystal structure, there are eight corner atoms, six face atoms, and no interior 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑡𝑜𝑚𝑠 𝑖𝑛 𝑎 𝑢𝑛𝑖𝑡 𝑐𝑒𝑙𝑙 𝑉𝑠 𝐴𝑃𝐹 = 𝑇𝑜𝑡𝑎𝑙 𝑢𝑛𝑖𝑡 𝑜𝑓 𝑐𝑒𝑙𝑙 𝑉𝑜𝑙𝑢𝑚𝑒 = 𝑉𝑐 atoms. Therefore, from Equation 2: 𝑁𝑓 𝑁𝑐 Volume of a sphere (Vs) in terms of the atomic 𝑁 = 𝑁𝑖 + 2 + 8 radius R is equal to 4 3 π𝑅 , and the number of 3 6 8 atoms per FCC unit cell is four. Therefore, the total 𝑁 = 0 + 2 + 8 = 4 FCC atom or sphere volume is A total of four whole atoms may be assigned to the 4 3 16 3 given unit cell 𝑉𝑠 = (4) 3 π𝑅 = 3 π𝑅 Important characteristics of a Crystal Structure From Example 1, the total unit cell volume is (a) The coordination number (for metals) 3 wherein each atom has the same number of 16𝑅 2 nearest-neighbor or touching atoms (b) Atomic packing factor (APF) which is the Therefore, the atomic packing factor is sum of the sphere volumes of all atoms within a unit cell (assuming the atomic 16 3 𝑉𝑠 3 π𝑅 hard-sphere model) divided by the unit cell volume 𝐴𝑃𝐹 = 𝑉𝑐 = 3 = 0. 74 16𝑅 2 For FCCs, the coordination number is 12. Front face atoms have four nearest neighboring atoms around it, four face atoms that are linked from behind, and four other equivalent face atoms positioned in the next unit cell to the front which is not shown. The Body-Centered Cubic Crystal Structure The Hexagonal Close-Packed Crystal Structure (BCC) The final common metallic crystal structure is the From the Equation 2, the number of atoms per BCC hexagonal close-packed (HCP). The top and is bottom face of the unit cell consists of six atoms 𝑁𝑓 𝑁𝑐 8 that form regular hexagons and surround a single 𝑁 = 𝑁𝑖 + 2 + 8 = 1 + 0 + 8 =2 atom in the center. Between the top and bottom plans, there is another plane that provides three The BCC crystal structure has 8 coordination additional atoms to the unit cell. The atoms in this numbers. The atomic packing factor for BCC 0.68 midplane have as nearest neighbors atoms in both which is lower than for FCC, since BCC has lesser of the adjacent two planes coordination number To compute the number of atoms per unit cell for Edge Length and Atomic Radius Relationships the HCP crystal structure, the formula is Simple Cubic 𝑁𝑓 𝑁𝑐 𝑁 = 𝑁𝑖 + 2 + 6 One-sixth of each corner atom is designated to a unit cell instead of 8 as with the cubic structure. This is because HCP has 6 corner atoms in each of the top and bottom faces for a total of 12 corner atoms, 2 face center atoms (one of each of the top and bottom faces), and 3 midplane interior atoms. Body-centered cubic Using this equation, the value of N for HCP can be found. 2 12 𝑁 = 3+ 2 + 6 =6 (there are 6 atoms assigned to each unit cell) Face-centered cubic Crystal Structure Density Computations 𝑚𝑎𝑠𝑠 A theoretical density (ρ) can be computed with a ρ= 𝑣𝑜𝑙𝑢𝑚𝑒 solve for mass of unit cell knowledge of the crystal structure of a metallic solid through the relationship: 4 𝑎𝑡𝑜𝑚𝑠 1 𝑚𝑜𝑙 197.0 𝑔 𝐴𝑢 𝑚 = 1 𝑢𝑛𝑖𝑡 𝑐𝑒𝑙𝑙 𝑥 23 𝑥 1 𝑚𝑜𝑙 𝐴𝑢 6.022 𝑥 10 𝑎𝑡𝑜𝑚𝑠 𝑛𝐴 ρ = 𝑉𝑐𝑁𝑎 −21 = 1. 31 𝑥 10 𝑔𝑟𝑎𝑚/𝑢𝑛𝑖𝑡 𝑐𝑒𝑙𝑙 Where Solve for volume p = density (g/cm^3) n = number of atoms per unit cell −21 𝑚 1.31𝑥10 𝑔 −23 3 A = atomic weight (g/mol) 𝑉 = = = 6. 79 𝑥 10 𝑐𝑚 𝑝 3 Vc = volume of the unit cell (cm^3/cell) 19.3 𝑔/𝑐𝑚 23 3 Na = Avogadro’s number (6.022 x 10 atoms/mol) Solve for the edge a, we know that 𝑉 = 𝑎 3 Example 3. Copper has an atomic radius of 0.128 Therefore, 𝑎 = 𝑉 nm, an FCC crystal structure, and an atomic weight of 63.5 g/mol. Compute its theoretical density and 3 −23 3 compare the answers with its measured density. = 6. 79 𝑥 10 𝑐𝑚 −8 n (FCC) = 4 per unit cell = 4. 08 𝑥 10 𝑐𝑚 A = 63.5 g/mol −8 R = 0.128 nm or 1. 28𝑥10 𝑐𝑚 From the table of edge and radius relationship, we 3 see the radius of an Au sphere ® is related to the Vc = 16𝑅 2 per unit cell edge length by 𝑛𝐴 𝑛𝐴 ρ = 𝑉𝑐𝑁𝑎 = 3 𝑎 = 2 2r (16𝑅 2)𝑁𝑎 (4 𝑎𝑡𝑜𝑚𝑠)(63.5 𝑔/𝑚𝑜𝑙) Therefore, −8 3 23 8 [16*(1.28𝑥10 𝑐𝑚) * 2] [6.022𝑥10 ] 𝑎 4.08𝑥10 𝑐𝑚 𝑟 = = 2 2 2 2 −2 3 −8 1 𝑥 10 𝑚 1 𝑝𝑚 = 8. 89 𝑔/𝑐𝑚 = 1. 44 𝑥 10 𝑐𝑚 𝑥 1 𝑐𝑚 𝑥 −12 1𝑥10 𝑚 Example 4. Gold (Au) crystallizes in a cubic 𝑟 = 144 𝑝𝑚 close-packed structure (the face-centered cubic 3 unit cell) and has a density of 19.3 𝑔/𝑐𝑚. Calculate the atomic radius of gold in picometers Solution: Density of unit cell → Volume of Unit Cell → Edge Length of Unit Cell → Radius of Au atom Types of Crystals * In determining the structures and properties of crystals, such as melting point, density, and hardness, it is important to consider the kinds of forces that hold the particles together. The classification. The classification of any crystal has four types: ionic, covalent, molecular, or metallic Ionic Crystals There are two important characteristics of ionic crystals and they are as follows: (1) They are composed of charged species (2) Anions and cations are generally quite Ionic crystals different in size CsCl - has the simple cubic lattice because Cs+ is The radii of the ions must be known because it is considerably larger than Na+ helpful in understanding the structure and stability of these compounds. It is hard to measure the radius of an individual ion but sometimes it is impossible to come up with an estimation. For example, the crystal which has a FCC lattice shows that the edge length of the unit cell of NaCl is twice the sum of the ionic radii of Na+ and Cl- Getting the values of ionic radius given in some references: ZnS has the zincblende structure, which is based 2− on FCC lattice. If the 𝑆 ions occupy the lattice Na+ = 95 pm 2+ points, the 𝑍𝑛 ions located one-fourth of the Cl- = 181 pm distance along each body diagonal We can calculate the length of the edge to 2 * (95 + 181) 𝑝𝑚 = 552 𝑝𝑚 𝐶𝑎𝐹2 has the fluorite structure. The 𝐶𝑎 2+ ions Covalent Crystals - Graphite is considered as a good conductor occupy the lattice points, and each F- ion is of electricity in directions along the planes of 2+ tetrahedrally surrounded by four 𝐶𝑎 ions carbon atoms, this is because electrons are free to move around in this extensively delocalized molecular orbital - The hardness of graphite is caused by the covalent bonds that exist in its layers which are held together by weak van der Waals forces. Furthermore, the layers of graphite can slide one another, that’s why it is slippery to the touch and is effective as a lubricant. It is also used in pencils and ribbons made for computer printers and typewriters Molecular crystals Ionic Crystals - The lattice points in molecular crystals are occupied by molecules which has a van der Waals forces and/or hydrogen bonding - The molecules in a molecular crystals (except for ice) are packed together as closely as their size and shape allow. - Since van der Waals and hydrogen bonding are generally quite weak as compared with ionic and covalent bonds, molecular crystals - Most ionic crystals have high melting points are more easily broken apart than ionic and which means strong cohesive forces hold covalent crystals. Additionally, most the ions together molecular crystals melt at temperatures - The higher the lattice energy, the more below 100 C stable the compound - Solid sulfur dioxide (SO2) is an example in - Since the ions are fixed in position, which the predominant attractive force is a therefore these solids do not conduct dipole-dipole interaction. The intermolecular electricity hydrogen bonding is mainly responsible for - The ions are free to move when in the maintaining the three-dimensional lattice of molten state (melted) or dissolved in water, ice. thereby the resulting liquid is conducting electricity Metallic Crystals - Has the simplest structure because ever Covalent Crystals lattice points in the crystal are occupied by - When atoms are held together in an an atom of the same metal extensive three-dimensional network by - Usually body-centered cubic, face-centered covalent bonds. Examples are two cubic or hexagonal close-packed, therefore allotropes of carbon: diamond and graphite. metallic elements are usually very dense. Each carbon atom of diamond is where it is bonded to four other atoms.  - The bonding electrons in a metal are delocalized over the entire crystal which is actually different from other types of crystals. The metal atoms in a crystal can be imagined as an array of positive ions immersed in a sea of delocalized valence electrons and these makes metals a good conductor of heat and electricity Types of Forces Properties Examples Crystal Ionic Electrostat Hard, NaCl, LiF,. ic brittle, MgO, attraction high CaCO3 melting CHEMISTRY OF ENGINEERING MATERIALS: point, poor METALS conductor Metal is an element, compound or alloy that is a Covalent Covalent Hard, high C good conductor of both electricity and heat Bond melting (diamond) point, poor , SiO2 conductor (Quartz) Metal crystal structure and specific metal properties are determined by holding together the atoms of a Molecular Dispersion Soft, low Ar, CO2, metal forces, melting I2, H2O, dipole-dip point, poor C12H22O With the exception of hydrogen, all elements that ole forces, conductor 11( hydrogen sucrose) form positive ions by losing electrons during bonds chemical reactions are called metals Metallic Metallic Soft to All They are characterized by bright luster, hardness, bond hard, low metallic ability to resonate sound and are excellent to high elements conductors of heat and electricity. melting point, good Metals are solids under normal conditions except conductor for Mercury Amorphous solids Physical Properties of Metal - Lack a regular three-dimensional State: Metals are solid at room temperature with arrangement of atoms. the exception of Mercury - Glass commonly refers to an optically Luster: quality of reflecting light from their surface transparent fusion product of inorganic Malleability: ability to withstand hammering and can materials that has cooled to a rigid state be made into thin sheets known as foils. without crystallizing Ductility: Metals can be drawn into wires Hardness: All metals are hard except sodium and potassium Valency: metals typically have 1-3 electrons in the outermost shell of their atoms Conduction - good conductors because they have Production of metal - reduction process to isolate free electrons metal from the combined form Density - have high density and are very heavy Chemical Reduction - reducing agent at Melting and Boiling Points: high melting and boiling high temperature points Electrolytic reduction - suitable for electropositive metals Chemical Properties of Metal Pyrometallurgy, procedures carried out at high temperatures Electropositive Character: Metals tend to have low ○ Chemical reduction ionization energies, and typically lose electrons ○ Electrolytic reduction when they undergo chemical reaction Metallurgy of iron ○ Iron exists in earth’s crust in many Occurence of Metals diff minerals and must be isolated * Most metals come from minerals, a naturally ○ Chemical reduction by carbon in a occurring substance with a range of chemical blast furnace composition ○ Mineral is mixed with carbon and * An ore is a mineral deposit concentrated enough limestone (CaCO3) to allow economical recovery of desired metal ○ Slag removes sand and aluminum oxide impurities Metals exist in various forms ○ Molten iron is removed at the bottom - In the Earth’s surface of the furnace - As ions in seawater - In the ocean floor Steelmaking ○ Steel is an alloy of iron with a small Aluminum, Iron, Calcium, Magnesium, Sodium, carbon content plus various other Potassium, Titanium and Manganese are the most elements abundant metals which exist as minerals in the ○ Oxidation process to remove Earth’s crust unwanted impurities ○ Basic Oxygen process - widely used Seawater is a rich source of some metal ions such due to its simplicity as Na+, Mg2+, and Ca2+ Purification of metals Metallurgy Metals are prepared by reduction usually need further treatment to remove impurities Metallurgy - separating metals from their ores and The extend of purification of course compounding alloys, a solid solution either two or depends on how the metal will be used more metals or of a metal or nonmetal with one or Three common purification procedures are more non metal distillation, electrolysis and zone refining Preparation, production and purification are Band Theory of Electrical Conductivity principal steps involved in the recovery of a metal from its ore - The band structure of a solid describes those ranges of energy, called energy Preparation of the ore - desired mineral is bands, that an electron within the solid may separated from the waste materials or gangue have “allowed bands” and ranges of energy Flotation called band gaps “forbidden bands” Magnetic separation - It models the behavior of electrons in solids Amalgamation by postulating the existence of energy bands Band theory - a model use to study metallic The Alkali and Alkaline Earth Metals bonding, states that delocalized electrons move freely through bands formed by overlapping Alkali metals molecular orbitals - Chemical elements found in Group 1 of the periodic table. They appear silvery This theory can also be applied to certain elements - Lithium, sodium, potassium, rubidium, cesium and that are semiconductors francium - Hydrogen is not technically an alkali metal since it Overlapping molecular orbitals produce rarely exhibits similar behavior. A valence band (lower energy) - Alkali - “al qali” meaning “from ashes” A conduction band (higher energy) Bands are separated by an amount of Common properties of Alkali Metals energy called the band gap - The most electropositive or least electronegative In metals, the band gap is negligible/small elements - Metals are viewed as an array of positive - Common oxidation state +1 charges immersed in a sea of delocalized - Found dissolved in seawater due to the geologic electrons. erosion of minerals - All the discovered alkali metals occur in nature Insulators - ineffective conductors of electricity - These metals have a BCC structure with low - Band gap is large packing efficiency - Electrons cannot move freely - Low melting point Semiconductor are elements that normally are not Lithium - lightest known metal and has great conductors, but will conduct electricity chemical reactivity. Do not occur free in elemental - At elevated temperatures form, are combined with halides, sulfates, - Or when combined with a small amount of carbonates and silicates certain elements - Group 4A elements are semiconductors Alkaline Earth Metals especially Silicon and Germanium - less electropositive and less reactive than Group - Materials that have properties in between 1A those of a normal conductors and - common oxidation state +2 insulators; produced by doping - 2A metals attain stable electron configuration of - Doping can enhance the ability to conduct, the preceding noble gases addition of small amounts of certain - Have much higher melting points than the alkali impurities. metals, harder metals Intrinsic semiconductors - composed of only one Aluminum kind of material; silicon and germanium are two Charles hall - pioneer of development of Aluminum examples. These are also called undoped Production semiconductors or i-type semiconductors. Aluminum Extrinsic semiconductor - intrinsic semiconductors - most abundant metal and the 3rd most plentiful with other substances added to alter their element in the Earth’s crust. properties – that is to say they have been doped - elemental form doesn’t occur in nature with another element - principal ore: Bauxite (Al2O3 * H2O) - considered a precious metal until Hall developed a method of aluminum production Preparation of Aluminum Properties of Transition Metal Anhydrous aluminum oxide (Al2O3 or corundum) is - Good conductors reduced to aluminum by the Hall process. The - Can be hammered or bent into shape easily cathode is also made of carbon and constitutes the - High melting point lining inside the cell. - Hard and tough - High density The key to the Hall process is the use of cryolite, or Na3AlF6 (melting point 1000 *C), as the solvent for Chemical properties aluminum oxide (melting point is 2045 *C) - Less reactive than alkali metals - Form colored ions of different charges The mixture is electrolyzed to produce aluminum - Some are unreactive and oxygen gas. Oxygen gas reacts with the - Many are used as catalysts carbon anodes to form carbon monoxide, which escapes as gas. Transition metals have wide range of uses. Their properties are very similar but not identical. The liquid aluminum metal (melting point is 660.2 *C) sinks to the bottom of the vessel, from which it can be drained from time to time during the procedure. Recycling of Aluminum - Aluminum is one of the most recycled and most recyclable materials on the market today - can be recycled directly back into itself over and over again in a true closed loop - costs 95% less energy compared to producing primary aluminum Transition Metals Transition metals - any of various chemical elements that have valence electrons – that can participate in the formation of chemical bonds – in two shells instead of one Iron - elements that are found in Groups 3-12 (old - Usually too soft to be used as metal alone. groups 2A-3B) Mixed with small amounts of other elements - typically have incompletely filled d subshells, or to make steels, which are harder and readily give rise to ions with incompletely filled d stronger than iron, but easily shaped. Both subshells react slowly with water and air to produce - many transition element compounds are brightly rust. colored due to the inner-level d electron transition Polymer Branched - The packing efficiency is reduced with the Molecular compound that can be distinguished by a formation of side branches, which results in lower high molar mass, ranging into thousands and even polymer density. (also low tensile strength)) millions of mass and they are made up of many repeating units Cross-linked - Adjacent linear chains are joined one to Poly + mer = “many” + “unit” another at various positions by covalent Mono = “one” bonds through synthesis or nonreversible chemical reaction. Natural Polymers have been around since life itself began Network - Occur in nature and can be extracted - Multifunctional monomers forming 3 or more - Water-based active covalent bonds make 3 dimensional networks Synthetic Polymers - A polymer that is highly crosslinked is classified as a network polymer Crude oil is the starting material for many synthetic - These materials have distinctive mechanical polymers in plastics, pharmaceuticals, fabrics and and thermal properties other carbon-based products 6 common types of polymers Homopolymer - a polymer that is made up of only one type of monomer. Polyethylene terephthalate (PETE) - transparent, strong, shatter-resistant. Impervious The molecules in polymers are gigantic and to acids and atmospheric gases.[soft-drink bottles, because of their size they are often referred to as clear food containers, beverage glasses] macromolecules. High-Density Polyethylene (HDPE) The Chemistry of Polymer Molecules - similar to LDPE but more rigid, tougher and slightly more dense [buckets, crates, and fencing] Ethylene (C2H2) is a gas at ambient temperature and pressure. Under appropriate conditions, Polyvinyl chloride (PVC) ethylene gas will react and it will transform to - rigid if not softened with a plasticizer. Clear and polyethylene (PE) which is a solid polymeric shiny but often pigmented. Resistant to most material chemicals, including oils, acids and bases [rigid: plumbing pipe, charge cards, hotel room keys. Molecular Structure of Polymers Softened: waterproof boots, garden hoses, shower curtains] Molecular weight and shape of a polymer is not the only basis of its physical characteristics, the Low-density Polyethylene (LDPE difference in the structure of the molecular chains - translucent if not pigmented. Soft and flexible, must also be considered unreactive to acids and bases. Strong and tough [bags, films, sheets, bubble wrap, wire insulation] Linear - repeat units are joined together end to end in single chains, these long chains are flexible Polypropylene (PP) where each circle represents a unit. - opaque, very tough, good weatherability, has a high melting point and is resistant to oils [bottle caps, yogurt, cream and margarine containers. carpeting and usual furniture] Polystyrene Block - two different units randomly dispersed along - crystal form is transparent, somewhat brittle. the chain Expandable form is lightweight. Both forms are rigid Block - same repeat units are clustered into blocks and degrades in many organic solvents [Crystal: along the chain food wrap, CD cases, transparent cups. Expandable form: Foam cups, insulated containers Graft polymer - side branches of one type may be and food packaging] grafted to homopolymer main chains that are composed of a different repeat unit Polymerization Polymer Crystallinity Number-average molecular weight Mn - In crystalline state, the atomic arrangement in polymer materials are more complex as compared 𝑀𝑛 = ∑ 𝑋𝑖𝑀𝑖 to metals because in polymer, it involved molecules instead of just atoms or ions Mi = mean (middle) molecular weight of size range i Xi = fraction of the total number of chains within the corresponding size range NANOMATERIALS Weight-average molecular weight Mw - can be any one of the four basic types - metals, ceramics, polymers or composites 𝑀𝑤 = ∑ 𝑊𝑖𝑀𝑖 Nanometer - one billionth or 10^-9 of a meter Mi = mean molecular weight Nanotechnology - design, fabrication and utilization Wi = weight fraction of materials and structures and devices less than 100nm Degree of polymerization (DP) Conventional technologies - ”top down” starting 𝑀𝑛 𝐷𝑃 = 𝑚 from large pieces of materials and producing expected structure by mechanical and chemical methods.. Thermoplastics and Thermosets Nanotechnology - “bottom up” atoms or molecules Thermoplastics soften upon heating and later are used as building blocks to produce liquify, then hardens when cooled. This process is nanoparticles, nanotubes, or nanorods, thin films or reversible and can be repeated. layered structures. Thermosets are network polymers, they do not Formation of nanomaterials soften upon heating and they become permanently hard during their formation. Compared to Formation of rods and plates thermoplastics, thermosets are generally harder - influence of surface energy needs to be and stronger and have better dimensional stability. considered. It is possible to grow rods for plates even from isotropic materials. Copolymers Formation of carbon nanotubes Homopolymer - only one type of polymer - graphite and fullerenes as special modification of Alternating polymer - two repeat units alternating carbon is essential in order to understand carbon chain position nanotubes. Graphite crystallizes in a layered hexagonal structure in which carbon atoms is Primitive organisms use energy from the sun to bound covalently to its three neighbors break down carbon dioxide to obtain carbon, and with photosynthesis, the byproduct is oxygen. Properties & Application of Nanomaterials Nitrogen Cycle - conversion of molecular nitrogen fullerenes into nitrogen compound, atmospheric nitrogen gas - C60 molecules known as buckminsterfullerene in is converted into nitrates and other compounds honor of R. Buckminster Fuller who invented the suitable for assimilation by algae and plants geodesic dome, each C60 is simply a molecular replica of such dome Oxygen cycle - atmospheric oxygen is removed through respiration and combustion to produce Carbon nanotubes carbon dioxide. Photosynthesis is when molecular - consists of a single sheet of graphite, that is rolled oxygen is regenerated from carbon dioxide and into a tube. Each nanotube is a single molecule water composed of millions of atoms, and the length of this molecule is much greater than its diameter. Layers of Atmosphere - potential application: More efficient solar cells Troposphere: lowest layer, weather phenomena, Better capacitors to replace batteries clouds, temperature decreases with altitude Heat removal application Stratosphere: contains the ozone layer, Cancer treatment temperature increases with the altitude due to Body armor ozone absorption of sunlight Mesosphere - Karman line, a boundary between Graphene Earth’s atmosphere and outer space. Coldest layer - newest member of the nanocarbons, there is a of the atmosphere, with temperatures dropping as perfect order in its sheets where no atomic defects altitude increases. such as vacancies exist. These sheets are Thermosphere or Ionosphere - Temperatures rise extremely pure and only carbon atoms are present. significantly due to solar radiation absorption. At room temperature, they move much faster than Exosphere - uppermost region of earth’s conducting electrons in ordinary metals and atmosphere, air is extremely thin semiconducting metals - could be labeled as the ultimate material. It is transparent, chemically inert, and has modulus elasticity. Transparent conductors, touch-screens, photo-imaging, artificial muscle, catalysts in fuel cells The earth’s atmospheric cycle Atmosphere - a protective blanket that nurtures life and protects it from outer space. Mainly consists of ammonia, methane and water Ultraviolet (UV) radiation from the sun, probably penetrated the atmosphere rendering the surface of earth sterile