GENERAL PRINCIPLES OF METALLURGY GENERAL PRINCIPLES OF METALLURGY

GENERAL PRINCIPLES OF METALLURGY

GENERAL PRINCIPLES OF METALLURGY ELLINGHAM DIAGRAM

GENERAL PRINCIPLES OF METALLURGY Ellingham Diagram Ø The graphical representation of Gibbs energy was given by H. J. T. Ellingham. Ø It provides the choice of taking reducing agent in the reduction of oxides. Ø It also provides the information whether a particular reaction is feasible at particular temperature or not.

GENERAL PRINCIPLES OF METALLURGY ELLINGHAM G Should be Spontaneity Thermodynamics negative Change in Gibbs free energy Change in enthalpy Change in entropy DIAGRAM

GENERAL PRINCIPLES OF METALLURGY M(s) + O 2(g) 2 MO(s) H = –ve Gas S = –ve G = H – T S = – T at HIGH temp Þ G Þ +ve at LOW temp Þ G Þ –ve Solid Thermodynamics principle of Metallurgy

GENERAL PRINCIPLES OF METALLURGY C(s) + O 2(g) 2 CO(g) H = –ve 1 Gas S = +ve G G De crea= ses H with – T S increas = e in – T temp. Higher the temp G Þ decreases 2 Gas Thermodynamics principle of Metallurgy

GENERAL PRINCIPLES OF METALLURGY C(s) + O 2(g) CO 2(g) H = –ve Gas S = (Zero) G = G H – T S is independent of = – T temp. G Independent of temperature Gas Thermodynamics principle of Metallurgy

GENERAL PRINCIPLES OF METALLURGY MO +C M + CO Metal oxide is STABLE Reaction will not happen Carbon monoxide is STABLE Reaction will happen

GENERAL PRINCIPLES OF METALLURGY 1) Ellingham diagram represents a) Change of G with temperature b) Change of H with temperature c) Change of G with pressure d) Change of G - T S with temperature MCQ S

GENERAL PRINCIPLES OF METALLURGY FEATURES & IMPORTANCE OF ELLINGHAM DIGRAM

Temperature /K GENERAL PRINCIPLES OF METALLURGY + 200 G 0 / k. J mol– 1 0 – 200 – 400 – 600 – 800 – 1000 – 1200 O 2 Ag 2 O 2 g. O 4 Ag+ H 2 CO 2 2 2 O g+ O 2 O + H O 2 2 Fe 2 C 2 C+O O 2 2 Fe+ 2 2 C O C+O 2 CO 2 O Zn 2 2 O + 2 Zn 2 Al 2 O 3 3 4 Al+O 2 O 3 Mg 2 O 2 + g 2 M 0 500 1000 1500 2000 Features of ELLINGHAM Ellingham DIAGRAM diagram 3. 1. The Forgraph few for metal the oxides 4. The graph for the formation 2. There is sudden change in ofof 5. The graph for the formation mercury of and metal silver oxides thenegative graph CO isslopes straight line with the for some metal of CO is straight line parallel 2 is at line isoxides, a straight the with upper an part in slope. like to temperature axis. upward Ellingham slope. diagram Mg. O, Zn. O and Hg. O. 2500

Temperature /K GENERAL PRINCIPLES OF METALLURGY G 0 / k. J mol– 1 + 200 O 2 Ag 2 Significance of ELLINGHAM O 2 + O g g 4 A 0 2 H Ellingham DIAGRAM diagram O 2 C 2 2 O stabilities is due to The decrease ing+their 1. The positive slope of 4. Tendency of the metals to 2. The sudden change inmetal the O 2 3. The negative slope of CO + H 0 O O e 2 an increase in G value. F – 200 2 C oxides shows undergo oxidation is inchange the order Graph Shows phase solid to 2 shows that itabecomes more stable 2 C+O 2 O + e 2 F 2 2 C stabilities decrease Mg >with Al Zn >to Fevapor. > temperature Hg > Ag liquid or >liquid increase inwith. O C+O 2 CO 2 increase in temperature. O – 400 Zn 2 2 O + This is due 2 Zton the increase in the – 600 negative of G 0 the 2 formation of oxide Al 2 O 3 in 3 the order goes 2 – 800 4 Al+O Mg. O > Al 2 O Fe. O > Ag 2 O 3 3 > Zn. OM>g. O 2 – 1000 O 2 + g 2 M – 1200 0 500 1000 1500 2000 2500

Temperature /K GENERAL PRINCIPLES OF METALLURGY + 200 G 0 / k. J mol– 1 0 – 200 – 400 – 600 – 800 – 1000 – 1200 O Importance of Ellingham 2 Ag 2 O 2 + O g 4 Ag diagram 2 H At Low temperature 2 O C 2 900 K 2 O Ag Hg. O 4 Fe +agent + 2 O andreducing 3 CO g 2 2 Fe O + 3 C O CO is the better + 2 3 H O O e 2 F 2 C can be 3 +easily decomposed Al 2 O 3 Mg 1500 K 3 Mg. O+at 2 Al 2 2 C+O 2 O + e Zn. O 600 + CK and 700 K Zn + CO 2 F 2 2 C O C+O 2 CO 2 O Zn 2 2 O + 2 Zn 2 Al 2 O 3 3 4 Al+O 2 O 3 Mg 2 O 2 + g 2 M 0 500 1000 1500 2000 2500

GENERAL PRINCIPLES OF METALLURGY ELLINGHAM DIAGRAM

GENERAL PRINCIPLES OF METALLURGY Question Suggest a condition under which magnesium could reduce alumina. Answer: The two equations are: (1) 2 Mg +O 2 → 2 Mg. O (2) Overall reaction

GENERAL 0 PRINCIPLES OF METALLURGY -100 Gv /k. J mol– 1 of O 2 -200 -300 At the point of intersection of the Al 2 O 3 and Mg. O curves the ΔG becomes ZERO for the reaction -400 Temperature below the point of interaction magnesium can reduce alumina -500 -600 -700 -800 O 2 4/3 Al + -900 O 2/3 Al 2 3 O 2 Mg + 2 -1000 -1100 -1200 273 K 673 K 2 Mg. O 1073 K 1473 K Temperature (K) 1873 K 2273 K

GENERAL PRINCIPLES OF METALLURGY Question Although thermodynamically feasible, in practice, magnesium metal is not used for the reduction of alumina in the metallurgy of aluminium, Why? Answer: The temperatures above the point of interaction of Al 2 O 3 and Mg. O curves, magnesium can reduce alumina but the process will be uneconomical.

GENERAL PRINCIPLES OF METALLURGY Question Why is the reduction of a metal oxide easier if the metal formed is in liquid state at the temperature of reduction? Answer: Ø The entropy is higher if the metal is in liquid state than when it is in solid state because randomness increases Ø As ΔS will be high, change in Gibbs energy will be more negative and the reduction becomes easier.

GENERAL PRINCIPLES OF METALLURGY MCQ S 1) G 0 vs T plot in Ellingham diagram slopes downward for the reaction --

GENERAL PRINCIPLES OF METALLURGY THERMODYNAMIC PRINCIPLES OF METALLURGY 1. EXTRACTION OF IRON FROM ITS OXIDES

GENERAL PRINCIPLES OF METALLURGY Thermodynamic Principles of Metallurgy : Applications (a) Extraction of iron from its oxides Ø Oxide ores of iron, after concentration through calcination/roasting are mixed with limestone and coke and fed into a blast furnace. Ø Here, the oxide is reduced to the metal Ø Thermodynamics helps us understand how coke reduces the oxide and selection furnace.

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides One of the main reduction steps in this process is: Fe. O (s) + C (s) → Fe (s/l) + CO (g) Ø It can be seen as a couple of two simpler reactions. Ø In one, the reduction of Fe. O is taking place and in the other, C is being oxidised to CO: [ΔG(Fe. O, Fe)] [ΔG(C, CO)] (1) (2)

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides Ø When both the reactions take place to yield the equation (1) the net Gibbs energy change becomes: ΔG(C, CO) + ΔG(Fe. O, Fe) = Δr. G Ø Naturally, the resultant reaction will take place when the right hand side in equation is negative

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides Ø In ΔG vs T plot representing equation (2) the plot goes upward and that representing the change C→CO (C, CO) goes downward

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides Ø At temperatures above 1073 K (approx. ), the C, CO line comes below the Fe, Fe. O line [ΔG(C, CO) < ΔG(Fe, Fe. O)] Ø So, in this range, coke will be reducing the Fe. O and will itself be oxidized to CO

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides Ø In a similar way the reduction of Fe 3 O 4 and Fe 2 O 3 at relatively lower temperatures by CO can be explained on the basis of lower lying points of intersection of their curves with the CO, CO 2 curve.

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides Ø In the Blast furnace, reduction of iron oxides takes place in different temperature ranges. Ø Hot air is blown from the bottom of the furnace and coke is burnt to give temperature upto about 2200 K in the lower portion itself.

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides Ø The burning of coke, therefore, supplies most of the heat required in the process. Ø The CO and heat move to upper part of the furnace.

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides Ø In upper part, the temperature is lower and the iron oxides (Fe 2 O 3 and Fe 3 O 4) coming from the top are reduced in steps to Fe. O. Ø The CO and heat moves to upper part of the furnace. 1. It is used for the concentration of oxide carbonate and native ores.

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides Ø Thus, the reduction reactions taking place in the lower temperature range and in the higher temperature range, depend on the points of corresponding intersections in the Δr. G vs T plots

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides Ø These reactions can be summarized as follows: Ø At 500 – 800 K (lower temperature range in the blast furnace): 3 Fe 2 O 3 + CO → 2 Fe 3 O 4 + CO 2 Fe 3 O 4 + 4 CO → 3 Fe + 4 CO 2 Fe 2 O 3 + CO → 2 Fe. O + CO 2

GENERAL PRINCIPLES OF METALLURGY Applications (a) Extraction of iron from its oxides Ø These reactions can be summarized as follows: Ø At 900 – 1500 K (higher temperature range in the blast furnace): C + CO 2 → 2 CO Fe. O + CO → Fe + CO 2

GENERAL PRINCIPLES OF METALLURGY (a) Extraction of iron from its oxides Ø Limestone is also decomposed to Ca. O which removes silicate impurity of the ore as slag Ø The slag is in molten state and separates out from iron Ø The iron obtained from Blast furnace contains about 4% carbon and many impurities in smaller amount (e. g. , S, P, Si, Mn) Ø This is known as pig iron and cast iron into variety of shapes.

GENERAL PRINCIPLES OF METALLURGY (a) Extraction of iron from its oxides Ø Cast iron is different from pig iron and is made by melting pig iron with scrap iron and coke using hot air blast. Ø It has slightly lower carbon content (about 3%) and is extremely hard and brittle.

GENERAL PRINCIPLES OF METALLURGY Further Reductions Ø Wrought iron or malleable iron is the purest form of commercial iron and is prepared from cast iron by oxidising impurities in a reverberatory furnace lined with haematite iron is purest form Ø This haematite oxidises. Wrought carbon to carbon monoxide: of iron. It contains Fe 2 O 3 + 3 C → 2 Fe + 3 CO Fe – 99. 5%, C= 0. 1 – 0. 25% Ø Limestone is added as a fluxand and. Mn, sulphur, P, Si. silicon and phosphorus are oxidised and passed into the slag Ø The metal is removed and freed from the slag by passing through rollers.

GENERAL PRINCIPLES OF METALLURGY 1) Iron is extracted from magnetite by reduction with. . a) C b) Mg c) Al d) H 2 MCQ S

GENERAL PRINCIPLES OF METALLURGY 2) The most pure form of iron is… a) wrought iron b) mild steel c) hard steel d) cast iron

GENERAL PRINCIPLES OF METALLURGY THERMODYNAMIC PRINCIPLES OF METALLURGY 1. EXTRACTION OF COPPER FROM ITS SULPHIDE

GENERAL PRINCIPLES OF METALLURGY Applications (b) Extraction of copper from cuprous oxide [copper (I) oxide] Ø In the graph of Δr. G vs T formation of oxides (Fig. 6. 4), the Cu 2 O line is almost at the top Ø So, it is quite easy to reduce oxide ores of copper directly to the metal by heating with coke (both the lines of C, CO and C, CO 2 are at much lower positions in the graph particularly after 500 – 600 K) Ø However, most of the ores are sulphides and some may also contain iron

GENERAL PRINCIPLES OF METALLURGY Applications (b) Extraction of copper from cuprous oxide [copper (I) oxide] Ø The sulphide ores are roasted/melted to give oxides: 2 Cu 2 S + 3 O 2 → 2 Cu 2 O + 2 SO 2 Ø The oxide can then be easily reduced to metallic copper using coke: Cu 2 O + C → 2 Cu + CO

GENERAL PRINCIPLES OF METALLURGY Applications (b) Extraction of copper from cuprous oxide [copper (I) oxide] Ø In actual process, the ore is heated in a reverberatory furnace after mixing with silica Ø In the furnace, iron oxide reacts with silica and form iron silicate (slag) and copper is produced in the form of copper matte Ø This contains Cu 2 S and little Fe. S Fe. O +Si. O 2 Fe. Si. O 3 Slag

GENERAL PRINCIPLES OF METALLURGY Applications (b) Extraction of copper from cuprous oxide [copper (I) oxide] Ø Copper matte is then charged into silica lined convertor. Ø Some silica is also added and hot air blast is blown to convert the remaining Fe. S 2, Fe. O and Cu 2 S/Cu 2 O to the metallic copper.

GENERAL PRINCIPLES OF METALLURGY Applications (b) Extraction of copper from cuprous oxide [copper (I) oxide] Following reactions take place: 2 Fe. S + 3 O 2 → 2 Fe. O + 2 SO 2 Fe. O + Si. O 2 → Fe. Si. O 3 2 Cu 2 S + 3 O 2 → 2 Cu 2 O + 2 SO 2 2 Cu 2 O + Cu 2 S → 6 Cu + SO 2 Ø The solidified copper obtained has blistered appearance due to the evolution of SO 2 and so it is called blister copper.

GENERAL PRINCIPLES OF METALLURGY Applications (b) Extraction of zinc blende [copper (I) oxide] The reduction of zinc oxide is done using coke. Ø The temperature in this case is higher than that in case of copper. Ø For the purpose of heating, the oxide is made into brickette with coke and clay. Ø The metal is distilled off and collected by rapid chilling.

GENERAL PRINCIPLES OF METALLURGY 1) The copper metal is extracted from its a) Carbonate ore b) Sulphide ore c) Sulphate ore d) Chloride ore MCQ S

GENERAL PRINCIPLES OF METALLURGY 2) The impurity present in Blister copper is a) Fe. S b) Cu 2 O c) Cu 2 S d) Fe. O

GENERAL PRINCIPLES OF METALLURGY Thank you…