Metals & Metallurgy Metals like bronze (an alloy of Cu and Zn) and Iron have played a big role in civilization - hence the Bronze Age and Iron Age. The abundance of the metals in the Earth's surface varies greatly. Only metals that occur in concentrated deposits - called ores - are economically valuable. About 23,000 kg of materials are extracted from the surface and processed per person in our country each year.

Vanadium Vanadium is a rare element that is a contaminant in crude oil. Oil was produced from the decomposition of once living life forms. Since crude oil is not found near any naturally occurring deposits of vanadium, then how did it find its way into this important resource?

Metals & Metallurgy Most metals are found in solid inorganic compounds known as minerals. Although 75% on the elements are metals, they make up only 25% of the Earth’s crust.

Metals and Metallurgy Distribution of elements in the Earth’s crust.

Principle Mineral Sources Most minerals are oxides, sulfides, or carbonates.

Metallurgy Metallurgy is the science and technology of extracting metals from their ores for usage.

Metallurgy It usually involves up to five steps: Mining of the ore. Concentrating the ore to remove the gangue. Reducing the ore to obtain the free metal. Refining or purifying the metal. Mixing the metal with other elements to modify properties.

Separation by Air In many mining applications, the ore is crushed and then put into an industrial cyclone. A stream of air moves upward through the crushed ore to remove the lighter particles of the gangue.

Separation by Solution In some cases, a detergent solution that attaches to the mineral is added to achieve separation.

Pyrometallurgy This is a process that utilizes high temperatures. Some examples are: Calcination - heating of a carbonate to eliminate carbon dioxide. PbCO3 ® PbO + CO2 Roasting is a thermal treatment that leads to reduction of the free metal. 2 ZnS + 3 O2 ® 2 ZnO + 2 SO2 ZnO + C ® Zn + CO Reduction using H2 or CO often produces the free metal. PbO + CO ® Pb + CO2

Hydrometallurgy Uses an aqueous solution to extract the metal from the ore. Gold was once extracted by dissolving the metal in sodium cyanide. 4Au(s)+8CN-(aq)+O2(g)+2H2O(l) ® 4Au(CN)2-(aq)+4OH-(aq) 2 Au(CN)2-(aq) + Zn(s) ® Zn(CN)4-(aq) + 2Au(s) Streams and rivers were often contaminated by cyanide.

Electrometallurgy This uses the electrolysis discussed in the electrochemistry chapter. Metals high on the activity series (most reactive) can only be produced commercially via molten salt electrolysis. Metals lower on the activity series like Cu can be purified using aqueous electrolysis.

Titanium 4th most abundant metal in Earth’s crust. Mineral sources are rutile (TiO2) and ilmenite (FeTiO3). Ore is first converted to TiCl4 before reduction to pure metal. FeTiO3(s) + 3Cl2(g) + 3C(s) → 3CO(g) + FeCl2(s) + TiCl4(g) TiCl4(g) + 2Mg(s) → 2MgCl2(l) + Ti(s) Titanium metal is used in many parts found on planes due to its lighter weight and superior strength.

Chromium The main ore source is chromite (FeCr2O4) and none is found in the US. Metal is produced by reduction using Al metal. 3FeCr2O4(s) + 8Al(s) → 4Al2O3(s) + 6Cr(s) + 3Fe(s) Chromium metal is an additive used in making different types of steel – mainly known as stainless steel.

Manganese Ore sources include pyrolusite (MnO2) and hausmannite (Mn3O4). Produced by reaction of ore with Al metal like Chromium. Manganese is added to steel alloys to make it deform easier at high temperatures. Steel alloys containing 12% Mn are used for military armor and bulldozer blades.

Cobalt Only ore sources found in Africa. An important additive to make high-strength steel alloys. Cobalt is also found in Vitamin B12, so it is an important trace element in the human body. Cobalt is also added to glass to produce a blue color.

Nickel Most nickel metal comes from meteorite impact in Ontario, Canada Nickel is fairly unreactive and used where resistance to corrosion is critical. Monel alloy contains 72% Ni, 25% Cu, and 3% Fe. Monel is used in marine applications, musical instruments, and by the chemical industry.

Copper High abundance and concentration = useful industrially Easy to recycle Second best electrical conductor – used in electrical wiring and devices High heat conductivity – used in heat exchangers Used in water piping because of its resistance to corrosion

Copper Copper is a high strength metal so it is often used as an alloy with another metal. Bronze = Cu + Sn Brass = Cu + Zn Amounts of each metal can vary to produce different features.

Brass

Zinc Minerals are roasted in air to form oxides, then reduced with carbon Used in alloys with Cu (brass) and Cu and Ni (German brass) Resists corrosion because it forms an adhering oxide coat Galvanizing is plating Zn onto other metals to protect them from corrosion both coating and sacrificial anode Zinc compounds used in paints for metals if scratched, becomes sacrificial anode Zinc phosphate used to coat steel so that it may be painted

Production of Iron One of the most widely produced metals is Fe. Fe is produced from both hematite and magnetite ore deposits. Reduction is achieved via pyrometallurgical techniques in a blast furnace. The main ingredients are the iron ore, coke, and limestone.

Production of Iron Coke is essentially Carbon and serves as BOTH the fuel and the source of the reducing gases CO and H2. 2 C + O2 ® 2 CO C + H2O ® CO + H2 Limestone (CaCO3) produces CaO, which reacts with silicates (sand) to produce the waste product called "slag". CaO + SiO2 ® CaSiO3

Production of Iron In the upper part of the furnace, the iron oxides are reduced by the CO and H2 gases. Fe3O4 + 4 CO ® 3 Fe + 4 CO2 Fe3O4 + 4 H2 ® 3 Fe + 4 H2O Molten iron collects at the base of the furnace with a layer of slag on top. The slag and the molten iron are tapped to drain off. The iron is then transported to convert into steel.

Production of Iron The molten iron contains many impurities like Mn, P, S, and C. This makes it unusable in present form.

Formation of Steel The raw iron is hit with a “blast” of O2 to remove the impurities. Then, the purified raw iron is converted to steel, an alloy of iron.

Formation of Steel There are 1000's of different types of steel that are produced. Each varies in composition to produce the desired properties. Carbon steel contains up to 1.5% C. Alloy steel contains C plus other elements like Cr, Co, Mn, Mo, S, B, and other trace elements.

Production of Iron

Thermite Production of small quantities of iron can be achieved by reacting iron oxide with aluminum powder. This is called the thermite reaction. Fe2O3 + 2 Al  2 Fe + Al2O3

Production of Aluminum Aluminum production involves the use of hydrometallurgy – a process that involves selectively dissolving the metal ion in water – and electrometallurgy – a process that involves using electrical current to reduce the metal ores. In the Bayer process, bauxite is first dissolved in NaOH producing Al(OH)4-. Other metal hydroxides present in bauxite are not soluble. Al2O3 + 2 OH- + 2 H2O  2 Al(OH)4-

Production of Aluminum The Al(OH)4- is then converted to Al2O3 via calcination. H2CO3 + 2 Al(OH)4-  Al2O3 + CO3-2 + 5 H2O The Al2O3 precipitates from the solution, whereas any silicates remain in solution. Melting point of Al2O3 is 2054oC. The Al2O3 is then dissolved in molten cryolite, Na3AlF6, which has a lower melting point , 1012o C.

Production of Al. To the molten salt are inserted graphite electrodes, which serve as the anodes. These are consumed in the electrolytic cell. The voltage applied is about 4.5V and the current used is quite large. This electrolytic cell is called the Hall process. Al+3(l) + 3e-  Al(l)

Rare Earths The rare earth metals are composed of seventeen elements – Sc, Y, and the lanthanides (#57 - #71) Despite their name, they are relatively plentiful in the Earth’s crust. The lanthanides can have larger numbers of unpaired electrons giving them powerful magnetic properties. Used in lasers, electronics, and high- temperature superconductors

Rare Earths Element Uses Sc Light Al-Sc alloy for aerospace parts, additive in Hg vapor lamps Y Y-Ba-Cu-O superconductors Ce Oxidizing agent, yellow color in glass and ceramics Nd Strongest magnets known to man Gd MRI contrast agent Er Alloy with vanadium steel, dental lasers, fiber optic applications Tm Portable x-ray machines

Metallic Bonding Bonding in metals is very unique. The valence electrons in metals are held loosely and are free to move about - this is often referred to as the "sea of electrons". The conductivity of metals is due to this concept of loosely held electrons. This model does not explain all properties of metals - for example, the highest melting points are found for group 6B.

Metallic Bonding Most of the time, the electrons move past the atoms freely. Occasionally, though, the electrons will bump into a nuclei causing friction, which generates heat.

M.O. Model When atomic orbitals on each metal atom overlap, they produce a band of Molecular Orbitals. The energy separations of these M.O.'s are so close that they form a band of M.O.'s.

M.O. Model Because the bands are so close, it is easy to promote electrons to a higher energy level. With M.O.'s, half of the orbitals are bonding and half are antibonding. Thus, with half- filled d subshells, the bonding M.O.'s are filled. After that, the electrons begin to fill antibonding orbitals which weaken the bonding and hence a lower melting point. Silicon and other semi-conductors have an energy gap between the occupied M.O.'s and the unoccupied M.O's.

Conductors, Insulators, and Semiconductors