Metallurgy and the Chemistry of Metals Flashcards

Fundamental Definitions and the Scope of Metallurgy

• Mineral: A naturally occurring substance characterized by a specific range of chemical compositions.

• Ore: A specific type of mineral deposit that is concentrated enough to permit the economical recovery of a desired metal.

• Metallurgy: The scientific and technological field dedicated to the separation of metals from their ores and the compounding of alloys.

• Alloy: A solid solution composed of either two or more metals, or a metal (or metals) combined with one or more nonmetals.

• Primary Steps in Metal Recovery:

  1. Preparation of the ore.

  2. Production of the metal.

  3. Purification of the metal.

Classification and Principal Types of Minerals

• Uncombined Metals: Metals found in their elementary state, including $Ag$, $Au$, $Bi$, $Cu$, $Pd$, and $Pt$.

• Carbonates:

  • Witherite: $BaCO_3$

  • Calcite/Limestone: $CaCO_3$

  • Magnesite: $MgCO_3$

  • Dolomite: $CaCO_3 \cdot MgCO_3$

  • Cerussite: $PbCO_3$

  • Smithsonite: $ZnCO_3$

• Halides:

  • Fluorite: $CaF_2$

  • Halite: $NaCl$

  • Sylvite: $KCl$

  • Cryolite: $Na_3AlF_6$

• Oxides:

  • Bauxite: $Al_2O_3 \cdot 2H_2O$

  • Corundum: $Al_2O_3$

  • Hematite: $Fe_2O_3$

  • Magnetite: $Fe_3O_4$

  • Cuprite: $Cu_2O$

  • Pyrolusite: $MnO_2$

  • Cassiterite: $SnO_2$

  • Rutile: $TiO_2$

  • Zincite: $ZnO$

• Phosphates:

  • Phosphate rock: $Ca_3(PO_4)_2$

  • Hydroxyapatite: $Ca_5(PO_4)_3OH$

• Silicates:

  • Beryl: $Be_3Al_2Si_6O_{18}$

  • Zircon: $ZrSiO_4$

  • Albite: $NaAlSi_3O_8$

  • Talc: $Mg_3(Si_4O_{10})(OH)_2$

• Sulfides:

  • Argentite: $Ag_2S$

  • Greenockite: $CdS$

  • Chalcocite: $Cu_2S$

  • Pyrite: $FeS_2$

  • Cinnabar: $HgS$

  • Galena: $PbS$

  • Sphalerite: $ZnS$

• Sulfates:

  • Barite: $BaSO_4$

  • Anhydrite: $CaSO_4$

  • Anglesite: $PbSO_4$

  • Celestite: $SrSO_4$

  • Epsomite: $MgSO_4 \cdot 7H_2O$

Metal Production and Reduction Processes

• Roasting: A process used to convert carbonates and sulfides into oxides.

  • Carbonate example: $CaCO_3(s) \rightarrow CaO(s) + CO_2(g)$

  • Sulfide (Galena) example: $2PbS(s) + 3O_2(g) \rightarrow 2PbO(s) + 2SO_2(g)$

• Chemical Reduction: The use of reducing agents to obtain pure metal from oxides or halides.

  • Using Magnesium: $TiCl_4(g) + 2Mg(l) \rightarrow Ti(s) + 2MgCl_2(l)$

  • Using Aluminum: $Cr_2O_3(s) + 2Al(s) \rightarrow 2Cr(l) + Al_2O_3(s)$

  • Using Hydrogen: $WO_3(s) + 3H_2(g) \rightarrow W(s) + 3H_2O(g)$

• Electrolytic Reduction: Utilizing electricity to force the reduction of metal ions.

  • Molten oxides: $2MO(l) \rightarrow 2M(\text{at cathode}) + O_2(\text{at anode})$

  • Molten chlorides: $2MCl(l) \rightarrow 2M(\text{at cathode}) + Cl_2(\text{at anode})$

  • Anode reaction example: $2O^{2-} \rightarrow O_2 + 4e^-$

  • Cathode reaction example: $M^{2+} + 2e^- \rightarrow M$

• Reduction Processes by Metal Activity:

  • High Activity Metals (Lithium, Sodium, Magnesium, Calcium): Achieved via electrolytic reduction of the molten chloride.

  • Aluminum: Achieved via electrolytic reduction of anhydrous oxide in molten cryolite.

  • Moderate Activity Metals (Chromium, Manganese, Titanium, Vanadium, Iron, Zinc): Achieved via reduction of the metal oxide with a more electropositive metal, or reduction with coke ($C(s)$) and carbon monoxide ($CO$).

  • Low Activity/Noble Metals (Mercury, Silver, Platinum, Copper, Gold): Often occur in the free uncombined state or are obtained by roasting their sulfides.

Iron and Steel Production

• Blast Furnace for Iron Production:

  • Operates at temperature ranges from $200\,^\circ\text{C}$ to $1200\,^\circ\text{C}$.

  • Key Chemical Reactions within the furnace:

    1. $3Fe_2O_3 + CO \rightarrow 2Fe_3O_4 + CO_2$

    2. $CaCO_3 \rightarrow CaO + CO_2$

    3. $Fe_3O_4 + CO \rightarrow 3FeO + CO_2$

    4. $C + CO_2 \rightarrow 2CO$

    5. $FeO + CO \rightarrow Fe + CO_2$

    6. $2C + O_2 \rightarrow 2CO$

• Steel Manufacturing (Oxygen Process):

  • An oxidation process using oxygen ($O_2$) and fluxing agents like $CaO$ or $SiO_2$ to remove impurities as slag.

  • Transition from horizontal to vertical positions during the melt processing phase.

• Characteristics of Steel Types (Table 20.3):

  • Plain Steel: Contains roughly $1.35\%$ Carbon ($C$), $1.65\%$ Manganese ($Mn$), and small amounts of $P, S, Si$. Includes $Cu (0.2-0.6\%)$. Used for sheet products and tools.

  • High-strength Steel: Contains $0.25\%$ $C$, $1.65\%$ $Mn$, and varying amounts of $Ni (0.4-1.0\%)$ and $Cr (0.3-1.3\%)$. Used for construction and steam turbines.

  • Stainless Steel: Contains low $C (0.03-1.2\%)$ with high amounts of $Mn (1.0-10\%)$, $Si (1-3\%)$, $Ni (1-22\%)$, and $Cr (4.0-27\%)$. Used for kitchen utensils and razor blades.

Purification of Metals

• Distillation (The Mond Process for Nickel):

  • Formation of carbonyl gas: $Ni(s)(\text{impure}) + 4CO(g) \xrightarrow{70\,^\circ\text{C} / 50-80\,^\circ\text{C}} Ni(CO)_4(g)$

  • Decomposition to pure metal: $Ni(CO)_4(g) \xrightarrow{200\,^\circ\text{C} / 200-250\,^\circ\text{C}} Ni(s)(\text{pure}) + 4CO(g)$

  • Historical note: Developed circa 1890.

• Electrolysis (Refining Copper):

  • Anode (Impure): $Cu(s)(\text{impure}) \rightarrow Cu^{2+}(aq) + 2e^-$

  • Cathode (Pure): $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)(\text{pure})$

• Zone Refining: A mechanical purification process where a heating coil moves along a metal rod, concentrating impurities in the molten zone which moves to one end of the rod, leaving the rest of the rod pure.

Band Theory of Conductivity

• Mechanism: Delocalized electrons move freely through "bands" formed by the overlapping of molecular orbitals.

• Example (Magnesium): $Mg$ has the configuration $1s^2 2s^2 2p^6 3s^2$ or $[Ne]3s^2$. In the bulk metal, these orbitals overlap to allow electron flow.

• Band Relationships:

  • Metal: The valence band and conduction band overlap, so there is no energy gap. Electrons flow freely.

  • Semiconductor: A small energy gap exists between the valence band and the conduction band. Electrons can cross the gap if excited.

  • Insulator: A large energy gap exists between the valence and conduction bands, preventing electron flow.

Semiconductors and Doping

• Pure Silicon ($Si$): Configuration is $[Ne]3s^2 3p^2$.

• n-type Semiconductor: Produced by adding donor impurities (elements with more valence electrons, e.g., Phosphorus $P$: $[Ne]3s^2 3p^3$).

• p-type Semiconductor: Produced by adding acceptor impurities (elements with fewer valence electrons, e.g., Boron $B$: $[He]2s^2 2p^1$ or $[Ne]3s^2 3p^1$ type group 13).

Properties and Trends of Alkali Metals (Group 1A)

• General Configuration: $ns^1$ (where $n \ge 2$).

• Chemical Properties:

  • Oxidation: $M \rightarrow M^+ + 1e^-$

  • Reaction with Water: $2M(s) + 2H_2O(l) \rightarrow 2MOH(aq) + H_2(g)$

  • Reaction with Oxygen: $2M(s) + O_2(g) \rightarrow M_2O(s)$

  • Reactivity: Increases as you move down the group from $Li$ to $Cs$.

• Physical Data (Table 20.4):

  • Lithium ($Li$): Density $0.534\,g/cm^3$, MP $179\,^\circ\text{C}$, IE $520\,kJ/mol$, $E^\circ = -3.05\,V$.

  • Sodium ($Na$): Density $0.97\,g/cm^3$, MP $97.6\,^\circ\text{C}$, IE $496\,kJ/mol$, $E^\circ = -2.71\,V$.

  • Potassium ($K$): Density $0.86\,g/cm^3$, MP $63\,^\circ\text{C}$, IE $419\,kJ/mol$, $E^\circ = -2.93\,V$.

  • Rubidium ($Rb$): Density $1.53\,g/cm^3$, MP $39\,^\circ\text{C}$, IE $403\,kJ/mol$, $E^\circ = -2.93\,V$.

  • Cesium ($Cs$): Density $1.87\,g/cm^3$, MP $28\,^\circ\text{C}$, IE $375\,kJ/mol$, $E^\circ = -2.92\,V$.

Properties and Trends of Alkaline Earth Metals (Group 2A)

• General Configuration: $ns^2$ (where $n \ge 2$).

• Chemical Properties:

  • Oxidation: $M \rightarrow M^{2+} + 2e^-$

  • Reaction with Water:

    • Beryllium ($Be$): No reaction with water.

    • Magnesium ($Mg$): Reacts with steam: $Mg(s) + H_2O(g) \rightarrow MgO(s) + H_2(g)$.

    • Calcium, Strontium, Barium ($Ca, Sr, Ba$): Reaction with liquid water: $M(s) + 2H_2O(l) \rightarrow M(OH)_2(aq) + H_2(g)$.

  • Reactivity: Increases as you move down the group.

• Physical Data (Table 20.5):

  • Beryllium ($Be$): MP $1280\,^\circ\text{C}$, IE (1st & 2nd) $899\,kJ/mol$ and $1757\,kJ/mol$, $E^\circ = -1.85\,V$.

  • Magnesium ($Mg$): MP $650\,^\circ\text{C}$, IE (1st & 2nd) $738\,kJ/mol$ and $1450\,kJ/mol$, $E^\circ = -2.37\,V$.

  • Calcium ($Ca$): MP $838\,^\circ\text{C}$, IE (1st & 2nd) $590\,kJ/mol$ and $1145\,kJ/mol$, $E^\circ = -2.87\,V$.

  • Strontium ($Sr$): MP $770\,^\circ\text{C}$, IE (1st & 2nd) $548\,kJ/mol$ and $1058\,kJ/mol$, $E^\circ = -2.89\,V$.

  • Barium ($Ba$): MP $714\,^\circ\text{C}$, IE (1st & 2nd) $502\,kJ/mol$ and $958\,kJ/mol$, $E^\circ = -2.90\,V$.

Aluminum Metallurgy: The Bayer Process and Hall-Heroult Process

• Concentration/Purification (Bayer Process):

  • Bauxite ($Al_2O_3$ impure) reacts with base: $Al_2O_3(s) + 2OH^-(aq) + 3H_2O(l) \rightarrow 2Al(OH)_4^-(aq)$ or $Al_2O_3(\text{impure}) + 2OH^-(aq) \rightarrow 2AlO_2^-(aq) + H_2O(l)$.

  • Precipitation: $AlO_2^-(s) + H_3O^+(aq) \rightarrow Al(OH)_3(s)$.

  • Calcination (Roasting): $2Al(OH)_3(s) \rightarrow Al_2O_3(s) + 3H_2O(g)$.

• Electrolysis (Hall-Heroult):

  • Cathode: $4[Al^{3+} + 3e^- \rightarrow Al(l)]$

  • Anode: $3[2O^{2-} \rightarrow O_2(g) + 4e^-]$

  • Net Reaction: $2Al_2O_3 \rightarrow 4Al(l) + 3O_2(g)$.

• Recycling: Chemistry in Action highlights the significant role of aluminum recycling in modern industry.