Chapter 23 Metals & Metallurgy

1. Chemistry: A Molecular Approach, 2nd Ed.Nivaldo Tro Chapter 23Metals &Metallurgy Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA

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 Tro, Chemistry: A Molecular Approach, 2/e

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 • V2O5 is a catalyst used in the production of sulfuric acid, the largest chemical industry Tro, Chemistry: A Molecular Approach, 2/e

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 Tro, Chemistry: A Molecular Approach, 2/e

5. Properties of Some Metals Tro, Chemistry: A Molecular Approach, 2/e

6. Distribution of Metals in Earth • Metals make up about 25% of the 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 found in native form • noble metals • Most metals found in minerals • minerals are natural, homogeneous crystalline inorganic solids Tro, Chemistry: A Molecular Approach, 2/e

7. Mineral Sources of Common Metals • NaCl = halite; KCl = sylvite • both recovered from evaporated sea water • Fe2O3 = hematite; TiO2 = rutile; SnO2 = cassiterite • PbS = galena; HgS = cinnabar; ZnS = sphalerite; MoS = molybdenite; VS4 = patronite • [Pb5(VO4)3Cl] = vanadinite • found mainly at upper levels of galena mines • [K2(UO2)2(VO4)23 H2O] = carnotite • found as crusts or flakes with sandstone • source of V, U, and Ra (because Ra is found with U) • [Fe(NbO3)2] = columbite; [Fe(TaO3)2] = tantalite • found in mixed deposits Tro, Chemistry: A Molecular Approach, 2/e

8. 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 metallurgyconsists of chemical processes that separate a metal from its mineral • Refining consists of processes that purify the metal for use Tro, Chemistry: A Molecular Approach, 2/e

9. 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 is 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 Tro, Chemistry: A Molecular Approach, 2/e

10. Separation Methods Tro, Chemistry: A Molecular Approach, 2/e

11. 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 calledcalcination • or drive off the water of hydration • Pyrometallurgy is an expensive process due to the high cost of the heat energy required Tro, Chemistry: A Molecular Approach, 2/e

12. 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 • 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 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 Tro, Chemistry: A Molecular Approach, 2/e

13. 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) + O2 (g) + 2 H2O(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)42−(aq) + 2 Au(s) • Someminerals dissolve in acidic, basic, or salt solutions Tro, Chemistry: A Molecular Approach, 2/e

14. 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 (Al2O3nH2O) • bauxite melts at a very high temperature • to reduce the energy cost, bauxite is dissolved in the molten mineral cryolite (Na3AlF3) • electrolysis of the solution produces molten Al • Electrolysis is also used to refine metals extracted by other methods • e.g. copper Tro, Chemistry: A Molecular Approach, 2/e

15. Production of Aluminum • Bauxite is separated from other minerals by reacting it with a concentrated NaOH(aq) solution at high pressure and 150–200 C • the Bayer process • hydrometallurgy • The solution is filtered to remove the gangue • Al(OH)3 is precipitated out • Al(OH)3 is converted to Al2O3 by heating • Al2O3 is mixed with the mineral cryolite (Na3AlF6) and heated to 1000 C • Electrolysis of the molten mixture produces molten aluminum Al2O3 n H2O(s) + 2 NaOH(aq) + 2 H2O(l) → 2 NaAl(OH)4(aq) Tro, Chemistry: A Molecular Approach, 2/e

16. Hall Process − Electrolysis of Al2O3 Dissolved in Molten Cryolite ox: C(s,gr) + 2 O2−(dissolved) → CO2(g) + 4 e− red: Al3+(dissolved) + 3 e− → Al(l) Tro, Chemistry: A Molecular Approach, 2/e

17. Production of Copper • Crushed copper minerals are separated from gangue by froth flotation • main mineral chalcopyrite, CuFeS2 • This concentrated mixture is then dried and fed into a furnace for roasting • or fed directly onto a reactor bed for flash smelting • Limestone and silica are added and the mixture 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 2 CuFeS2(s) + 3 O2(g) → 2 FeO(s) + 2 CuS(s) + SO2(g) Tro, Chemistry: A Molecular Approach, 2/e

18. Electrolytic Refining of Copper Tro, Chemistry: A Molecular Approach, 2/e

19. 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 • but the particles never get hot enough to completely melt • increases the strength and density of the metal • Advantages over milling or casting • no scrap • intricate pieces can be made that would be difficult to cast • allows making pieces from high melting metals that would require very high heat to cast Tro, Chemistry: A Molecular Approach, 2/e

20. Structures of Metals • Metal structures are generally closest packing of spheres • most are cubic closest packed, hexagonal closest packed, or body-centered cubic • Exact crystal structure may change with temperature and pressure Tro, Chemistry: A Molecular Approach, 2/e

21. 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 • But 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 Tro, Chemistry: A Molecular Approach, 2/e

22. 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 are solids with different crystal structures than any of their components • alnico − used for its magnetic properties • NiTi − memory metal Tro, Chemistry: A Molecular Approach, 2/e

23. Types of Alloys • In substitutional alloysone metal atom substitutes for another • crystal structure may stay the same or change • brass • In interstitial alloysan atom fits in-between the metal atoms in the crystal • usually a small nonmetal atom • at low concentrations it is best described as a solution • at high concentrations it is better described with a stoichiometric formula Tro, Chemistry: A Molecular Approach, 2/e

24. Substitutional Alloy:Substituting Nickel into Copper Tro, Chemistry: A Molecular Approach, 2/e

25. Binary Phase 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 Tro, Chemistry: A Molecular Approach, 2/e

26. 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 • 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 Tro, Chemistry: A Molecular Approach, 2/e

27. Example 23.1: Determine the Composition and Phase of the Cu-Ni Alloy at Point A on the Diagram Below Tro, Chemistry: A Molecular Approach, 2/e

28. 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 Tro, Chemistry: A Molecular Approach, 2/e

29. Substitutional Alloys: Two Phase Region • At Point A the alloy is 50 mole% Ni and 50 mole% Cr • There is too much Cr to all fit into the face-centered cubic structure of the Ni • pure Cr is body-centered • The extra Cr form their own body-centered cubic crystals with some substituted Ni Tro, Chemistry: A Molecular Approach, 2/e

30. 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 body-centered cubic region, there are more fcc crystals in the solid alloy Tro, Chemistry: A Molecular Approach, 2/e

31. Example 23.3: Determine the composition, relative amounts, and phases present at Point B Tro, Chemistry: A Molecular Approach, 2/e

32. 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 Tro, Chemistry: A Molecular Approach, 2/e

33. Octahedral Hole an atom with maximum radius 41.4% of the metal atom’s radius can fit in an octahedral hole Tro, Chemistry: A Molecular Approach, 2/e

34. Tetrahedral Holes an atom with maximum radius 23% of the metal atom’s radius can fit in a tetrahedral hole Tro, Chemistry: A Molecular Approach, 2/e

35. Tro, Chemistry: A Molecular Approach, 2/e

36. Titanium • 9th most abundant element on Earth • 4th most abundant metal • Minerals rutile (TiO2) and ilmenite (FeTiO3) • Very reactive • Oxidizes in the presence of O2 and N2 • 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 TiO2 in paint as white pigment • large rutile TiO2 crystals resemble diamonds • produced from ilmenite Tro, Chemistry: A Molecular Approach, 2/e

37. Chromium • Forms many compounds with different colors • Mineral chromite (FeCr2O4) • which is reduced with Al • White, hard, lustrous, brittle • Cr dissolves in HCl and H2SO4 but not HNO3 • Mainly used as alloy to make stainless steel • Compounds used as pigments and wood preservatives • Toxic and carcinogenic • Oxidation states +1 to +6 Tro, Chemistry: A Molecular Approach, 2/e

38. Tro, Chemistry: A Molecular Approach, 2/e

39. Manganese • Mineral pyrolusite (MnO2), hausmannite (Mn3O4) and rhodochrosite MnCO3 • 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 Tro, Chemistry: A Molecular Approach, 2/e

40. 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 B12 Tro, Chemistry: A Molecular Approach, 2/e

41. Copper • Found in its native form • Minerals are chalcopyrite (CuFeS2), malachite (Cu2(OH)2CO3) • 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 (Cu4SO4(OH)6) • Strong metal – so used to alloy with metals where strength is needed • bronze = Cu and Sn • brass = Cu and Zn Tro, Chemistry: A Molecular Approach, 2/e

42. Brass – a Mixture Tro, Chemistry: A Molecular Approach, 2/e

43. Copper Tro: Chemistry: A Molecular Approach

44. Nickel • Comes from meteor crater in Ontario • Nickel sulfides are roasted in air to form oxides, 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 Tro, Chemistry: A Molecular Approach

45. Zinc • Minerals sphalerite (ZnS), smithsonite (ZnCO3), and franklinite (Zn, Fe, and Mn oxides) • Minerals are roasted in air to form oxides, 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 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 • Considered safe – used to replace Cr and Pb additives • though some evidence it may be an environmental hazard Tro, Chemistry: A Molecular Approach

46. zinc Phosphate Adhering to Steel Surface Tro, Chemistry: A Molecular Approach, 2/e