Lecture Presentation. Chapter 23. Metals and Metallurgy. Sherril Soman Grand Valley State University Pearson Education, Inc.

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1 Lecture Presentation Chapter 23 Metals and Metallurgy Sherril Soman Grand Valley State University

2 Vanadium Petroleum is often contaminated with vanadium. It s believed that some ancient forms of life that decomposed to form oil used vanadium compounds for oxygen transport. Vanadium and many of its compounds are toxic and regulated by the EPA. Vanadium must be removed from petroleum before it is sold. Research is currently ongoing to use metallurgy to economically remove and recover vanadium so it can be sold and used in other ways.

3 What Do We Need Vanadium For? Vanadium is a soft, ductile, silver-gray metal. Vanadium has good resistance to corrosion. Vanadium is unreactive with alkalis, sulfuric acid, and hydrochloric acids. Vanadium is oxidized in air at about 660 C, although an oxide layer forms even at room temperature. Most vanadium is used to alloy with iron to increase the strength of steel. V 2 O 5 is a catalyst used in the production of sulfuric acid, the largest chemical industry.

4 General Properties and Structure of Metals Opaque Good conductors of heat and electricity High malleability and ductility In the electron sea model, each metal atom releases its valence electrons to be shared by all the atoms in the crystal. The valence electrons occupy an energy band called the valence band that is delocalized over the entire solid. However, each metal has its own unique properties to be accounted for.

5 Properties of Some Metals

6 Distribution of Metals in Earth Metals make up about 25% of Earth s crust. Aluminum is the most abundant. Alkali and alkali earth metals make up about 1%. Iron is only the transition metal > 5%. Only Ni, Cu, Ag, Au, Pd, Pt are found in native form. Noble metals Most metals are found in minerals. Minerals are natural, homogeneous crystalline inorganic solids.

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8 Mineral Sources of Common Metals NaCl = halite; KCl = sylvite Both recovered from evaporated sea water Fe 2 O 3 = hematite; TiO 2 = rutile; SnO 2 = cassiterite PbS = galena; HgS = cinnabar; ZnS = sphalerite; MoS = molybdenite; VS 4 = patronite [Pb 5 (VO 4 ) 3 Cl] = vanadinite Found mainly at upper levels of galena mines [K 2 (UO 2 ) 2 (VO 4 ) 2 3 H 2 O] = carnotite Found as crusts or flakes with sandstone Source of V, U, and Ra (because Ra is found with U) [Fe(NbO 3 ) 2 ] = columbite; [Fe(TaO 3 ) 2 ] = tantalite Found in mixed deposits

9 Metallurgy A rock containing a high concentration of a particular mineral is called an ore. The mineral must first be separated from the surrounding ore material by physical means. Extractive metallurgy consists of chemical processes that separate a metal from its mineral. Refining consists of processes that purify the metal for use.

10 Separation The first step is to crush the ore into small particles. The mineral is then separated from the gangue by physical means. The gangue the undesirable material in the ore Using cyclonic winds to separate by density Froth flotation in which the mineral is treated with a wetting agent to make it more attracted to the froth and floated off the mineral Electrostatic separation of polar minerals Magnetic separation of magnetic minerals

11 Separation Methods

12 Pyrometallurgy In pyrometallurgy, heat is used to extract the metal from the mineral. Some minerals can be decomposed on heating into volatile materials that will vaporize easily, leaving the metal behind this is called calcination. Or drive off the water of hydration Pyrometallurgy is an expensive process due to the high cost of the heat energy required.

13 Pyrometallurgy Heating a mineral so that it will react with furnace gases is called roasting. If the roast product is a liquid, it s called smelting.

14 Pyrometallurgy If some byproduct of the roasting doesn t volatilize and escape, a flux can be added to react with the nonvolatile gangue to create a low melting waste product that is easy to separate. A flux is a chemical that reacts with a material to form a lower melting or highly volatile material. The waste liquid is called the slag. The slag separates from the molten metal by density.

15 Hydrometallurgy The use of aqueous solutions to extract the metal from its mineral is called hydrometallurgy. Gold is often extracted by dissolving it in NaCN(aq). 4 Au (s) + 8 CN (aq) + O 2 (g) + 2 H 2 O (l) 4 Au(CN) 2 (aq) + 4 OH (aq) Leaching After the impurities are filtered off, the Au is reduced back to the metallic form. 2 Au(CN) 2 (aq) + Zn (s) Zn(CN) 4 2 (aq) + 2 Au (s) Some minerals dissolve in acidic, basic, or salt solutions.

16 Electrometallurgy Using electrolysis to reduce the metals from the mineral is called electrometallurgy. The Hall process is a method for producing aluminum metal by reducing it from its mineral bauxite (Al 2 O 3 nh 2 O). Bauxite melts at a very high temperature. To reduce the energy cost, bauxite is dissolved in the molten mineral cryolite (Na 3 AlF 3 ). Electrolysis of the solution produces molten Al. Electrolysis is also used to refine metals extracted by other methods. For example, copper

17 Production of Aluminum Bauxite is separated from other minerals by reacting it with a concentrated NaOH(aq) solution at high pressure and C. The Bayer process Hydrometallurgy The solution is filtered to remove the gangue.

18 Production of Aluminum Al(OH) 3 is precipitated out. Al(OH) 3 is converted to Al 2 O 3 by heating. Al 2 O 3 is mixed with the mineral cryolite (Na 3 AlF 6 ) and heated to 1000 C. Al 2 O 3 n H 2 O (s) + 2 NaOH (aq) + 2 H 2 O (l) 2 NaAl(OH) 4(aq) Electrolysis of the molten mixture produces molten aluminum.

19 Hall Process Electrolysis of Al 2 O 3 Dissolved in Molten Cryolite Oxidation: C (s,gr) + 2 O 2 (dissolved) CO 2(g) + 4 e Reduction: Al 3+ (dissolved) + 3 e Al (l)

20 Production of Copper Crushed copper minerals are separated from gangue by froth flotation. Main mineral chalcopyrite, CuFeS 2 This concentrated mixture is then dried and fed into a furnace for roasting. Or fed directly onto a reactor bed for flash smelting 2 CuFeS 2(s) + 3 O 2(g) 2 FeO (s) + 2 CuS (s) + SO 2(g) Limestone and silica are added and the mixture is smelted to remove iron. The iron oxides and sulfides are converted to slag and floated. The remaining copper sulfides are converted to blister copper by blowing hot air through the molten sulfides. The copper blister is refined by electrolysis.

21 Electrolytic Refining of Copper

22 Powder Metallurgy Micron-sized powdered metal particles are compressed into a component. Oxidized powdered mill scraps are reduced. Or, a stream of pure molten metal is atomized by blasting it with a stream of cold water. The component is heated until the metal particles fuse called sintering. The particles never get hot enough to completely melt. This increases the strength and density of the metal. Advantages over milling or casting It produces no scrap. Intricate pieces can be made that would be difficult to cast. It allows for making pieces from high melting metals that would require very high heat to cast.

23 Structures of Metals Metal structures are generally the closest packing of spheres. Most are cubic closest packed, hexagonal closest packed, or body-centered cubic. The exact crystal structure may change with temperature and pressure.

24 Structures of Metals

25 Alloys Alloys are metals that contain more than one type of material. A base metal and alloying materials Alloys show metallic properties. Most common physical properties of alloys are often averages of the component metals. However, engineering properties may be quite different than the components. Like tensile strength and shear strength Most melt over a large temperature range rather than having a fixed melting point.

26 Alloy Composition Some alloys are solid solutions with variable composition. Steel = Fe, C, and other metals Brass = Cu and Zn Bronze = Cu and Sn Some have fixed composition like a compound. Intermetallic compounds solids with different crystal structures than any of their components Alnico used for its magnetic properties NiTi memory metal

27 Types of Alloys In substitutional alloys, one metal atom substitutes for another. Crystal structure may stay the same or change Brass In interstitial alloys, an atom fits between the metal atoms in the crystal. Usually a small nonmetal atom At low concentrations, best described as a solution At high concentrations, better described with a stoichiometric formula

28 Substitutional Alloy: Substituting Nickel into Copper

29 Binary Phase Diagrams These diagrams show the phase an alloy is in at different temperatures and alloy composition. The area above the phase boundary line is the liquid state. The phase boundary line is the melting point curve for the solid solution.

30 Substitutional Alloys: Miscible Solid Solutions The phase-composition diagram for Cu Ni alloys shows a smooth increase in melting point from the lower melting Cu to the higher melting Ni. The alloys all have the face-centered cubic crystal structure as the Cu and Ni are similar sizes.

31 Substitutional Alloys: Miscible Solid Solutions The phase-composition diagram for Cr V alloys do show a smooth increase in melting point. The dip in the curve indicates that some of the alloys melt below either of the pure metals. The composition that gives the lowest melting point is called the eutectic mixture.

32 Substitutional Alloys: Limited Solubility Solid Solutions Because of their different crystal structures, some metals are not miscible. At some intermediate composition, the crystal structure has to change. The result is alloys with two different crystal structures and intermediate area(s) where both exist.

33 Substitutional Alloys: Two Phase Region At point A, the alloy is 50 mole percent Ni and 50 mole percent Cr. There is too much Cr to all fit into the facecentered cubic structure of the Ni. Pure Cr is body centered. The extra Cr form their own body-centered cubic crystals with some substituted Ni.

34 Substitutional Alloys: The Lever Rule The lever rule tells us that in a two-phase region, whichever phase is closest to the composition of the alloy is the more abundant phase. Because point A is closer to the face-centered cubic region than to the bodycentered cubic region, there are more fcc crystals in the solid alloy.

35 Interstitial Alloys H, B, N, C can often fit in the holes in a closest packed structure. Formula of alloy depends on the number and type of holes occupied. Interstitial alloys are often harder and denser than the base metals because more of the space in the crystal is occupied.

36 Octahedral Hole An atom with maximum radius 41.4% of the metal atom s radius can fit in an octahedral hole.

37 Tetrahedral Holes An atom with maximum radius 23% of the metal atom s radius can fit in a tetrahedral hole.

38 Interstitial Alloys

39 Titanium Ninth most abundant element on Earth Fourth most abundant metal Minerals rutile (TiO 2 ) and ilmenite (FeTiO 3 ) Very reactive Oxidizes in the presence of O 2 and N 2 Needs to be arc-welded under inert atmosphere Resists corrosion because of a tightly held oxide coat Stronger than steel, but half the density Denser than aluminum, but twice as strong Used to make jet engine parts Alloyed with 5% Al and trace amounts of Fe, Cr, Mo Most common use is as TiO 2 in paint as white pigment Large rutile TiO 2 crystals resemble diamonds. It is produced from ilmenite.

40 Chromium Forms many compounds with different colors Mineral chromite (FeCr 2 O 4 ) Which is reduced with Al White, hard, lustrous, brittle Cr dissolves in HCl and H 2 SO 4, but not HNO 3 Mainly used as alloy to make stainless steel Compounds used as pigments and wood preservatives Toxic and carcinogenic Oxidation states +1 to +6

41 Chromium

42 Manganese Mineral pyrolusite (MnO 2 ), hausmannite (Mn 3 O 4 ) and rhodochrosite MnCO 3 Which is reduced with Al or Na Heating impure pyrolusite with C produces alloy ferromanganese Mn very reactive, dissolves in acids Used as alloy to make stainless steel Compounds used as glass additives Oxidation states +1 to +7

43 Cobalt Mineral cobaltite (CoAsS) Ferromagnetic Mn very reactive, dissolves in acids Used as alloy to make high-strength steels Carbaloy Used to make magnets Compounds with deep blue colors, used in pigments and inks Covitamin of B 12

44 Copper Found in its native form Minerals are chalcopyrite (CuFeS 2 ), malachite (Cu 2 (OH) 2 CO 3 ) Reddish color Used in ornamentation and jewelry 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 Long exposure to environment produces a green patina mainly malachite and brohchanite (Cu 4 SO 4 (OH) 6 ) Strong metal so used to alloy with metals where strength is needed Bronze = Cu and Sn Brass = Cu and Zn

45 Brass a Mixture

46 Copper

47 Nickel Comes from meteor crater in Ontario Nickel sulfides roasted in air to form oxides, and then reduced with carbon Separated by converting to volatile Ni(CO) 4, which is later heated to decompose back to Ni Ni not very reactive and resistant to corrosion Used as an alloying metal in stainless steel, especially where corrosion resistance is important Monel metal Used in armor plating Ni metal plated onto other metals as protective coat

48 Zinc Minerals sphalerite (ZnS), smithsonite (ZnCO 3 ), and franklinite (Zn, Fe, and Mn oxides) Minerals roasted in air to form oxides, and then reduced with carbon Used in alloys with Cu (brass) and Cu and Ni (German brass) Reactive metal Resists corrosion because it forms an adhering oxide coat Galvinizing 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 Considered safe used to replace Cr and Pb additives Though some evidence it may be an environmental hazard

49 Zinc Phosphate Adhering to Steel Surface