Preparation of Ceramic Powders. Waldemar Pyda. Scope: Building up processes Breaking down processes. Theory and Practice of Ceramic Processes

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1 Lecture 4 Preparation of Ceramic Powders Waldemar Pyda Scope: Building up processes Breaking down processes 1

2 Requirements for sinterable powders. 2

3 Fine Ceramic Powders for Sintering Mainly Building-up processes 3

4 Fine Ceramic Powders for Sintering Mainly Breaking-down processes Comminution and classification - powders by grinding and milling of row materials that are either natural in origin or a natural mineral after thermal decomposition or materials synthesised in building-up up processes Ceramic Powders for Other Applications Sol-gel processing of colloids nuclear industry, liquid chromatography, abrasives Melt solidification abrasives Ceramic Fibers for Other Applications Blow-spin process Extrusion or draw process Crystallization method Vapour-phase routes (CVD) Chemical transformation ti of precursor fibre Unusual methods ceramic cutting, directional freezing of gels 4

5 I Solid-Phase Synthesis 5

6 I Solid-Phase Synthesis 6

7 SPONTANEOUS REACTION EQUILIBRIUM REACTION THERMODYNAMIC ANALYSIS Gibbs free energy ( G) Calculations from the free energy of formation for each of the species in the balanced reaction equation at given temperature and pressure! G < 0 spontaneous reaction G > 0 nonspontaneous reaction G = 0 reaction in equilibrium 7

8 Oxidation Reactions Oxidation of sulphides Roasting of zinc sulphide Roasting of iron pyrite Oxidation of metals 8

9 Reduction reactions Used for to produce metal powders, e.g. for production of carbide and nitride powders SiO 2 (s) + 2H 2 (g ) Si(s) + 2H 2 O(g) 9

10 Nitridation Reactions 10

11 Liquid-Solid Reactions 11

12 Solid-Solid Reactions Acheson method for SiC production SiO 2( s) + C( s) SiC( s) + CO2 ( g) Distance from the electrode 3 4 SiO 2 ( s ) + 6C ( s ) + 2N 2 ( g ) Si 3N4 ( s ) + 6CO ( g ) Graphite resistant electrode Scheme of reactions during the Acheson process 12

13 II Liquid-Phase Synthesis 13

14 Precipitation Technique 14

15 Morphology of calcined powders 5 mol.% CaO-ZrO 2 powders calcined at indicated temperatures. 15

16 Morphology of calcined powders vs. hydrothermally treated CM/CN 3 mol % Y 2 O 3 -ZrO 2 powder calcined at 950 o C, 3Y-TOSOH commercial calcined zirconia powder, MG - 5 mol.% CaO-ZrO 2 powders calcined at 600 o C, 6N 6 mol % CaO-ZrO 2 powder hydrothermally crystallized at 240 o C. 16

17 Hydrolysis Technique 17

18 Hydrolysis Technique 18

19 Solvent Evaporation Technique 19

20 Citrate Gel Process Elaborated by Marcilly & co-workers (1970) Hydroxy y acid e.g. citric acid, tartaric acid Nitrates solution Organometallic complex Heating e.g. vacuum50-80 C Viscous liquid Amorphous glassy body Burnig of organics Exothermic decomposition Powder Universal method for powders of spinel structures (MgAlO 2 4 ), garnets (Y 3 Al 5 O 12 ), ilmenite, perowskite, LaCrO 3, solid solutions (ThO 2, ZrO 2 ), barium hexaferrite baru (BaFe 12 O 19 ); the powder needs comminution 20

21 Citrate Gel Process Apparatusfor pyrolysis in the citric method Powders of tissue like morphologies are manufactured 21

22 Metoda Pechinniego C 22

23 Hydrothermal crystallization Factors affecting a size and shape of particles : Chemical composition of crystallisation environment mineralizers, ph, temperature, pressure time. 23

24 SEM images of ZrO 2 powders crystallised under hydrothermal conditions (8h, 250 C) from coprecipitated gels; crystallization environments: a) LiOH aqueous solution (2mol/l), b) H 2 O. Relative density of compacts as a function of compacting pressure (P). Powders of 13% mol. CaO - ZrO 2 solid solution 1 hydrothermal crystallisation 2 calcination treatment of the co- precipitated gel. 24

25 III Vapour-Phase Synthesis 25

26 Principle of Powder formation by CVD Technique 26

27 Effect of the equilibrium constant 27

28 Electric Furnace Method (2) Synthesis of nitride and carbide powders 28

29 Plasma method Si 3 N 4 powders: 29

30 Laser Method 30

31 Spray Drying 31

32 Otrzymywanie cienkich warstw ceramicznych z fazy gazowej PVD Physical i l Vapour Deposition FIZYCZNE OSADZANIE Z FAZY GAZOWEJ CVD Chemical Vapour Deposition CHEMICZNA KRYSTALIZACJA Z FAZY GAZOWEJ 32

33 COMMINUTION 33

34 Mechanisms of Grinding 34

35 Main stresses distribution in the spherical grain subjected to a load F 35

36 Elementary processes of comminution 36

37 Comminution Equipment Typical crushers and grinders 37

38 Forces acting in crushers and grinders 38

39 Grinding systems 39

40 Types of Size-Reduction Equipment 40

41 Crushing Equipment 41

42 Grinding Equipment 42

43 Grinding Equipment 43

44 Grinding Equipment 44

45 Energy Required for Size Reduction 45

46 Energy Required for Size Reduction 46

47 Energy distribution during milling 47

48 Theoretical calculations of energy required for grinding 2 σ W = c2( logν ) 2EE Ritenger s model W W = = 10W W ( i 1 c1( 1 d 2 1 d 1 ) 1 1 ) d 2 d 1 Beke 48

49 Grinding Energy from Bond 49

50 Grinding energy vs. product particle size 50

51 Comminution Efficiency K I = σ Πa Stress intensity factor as a function of strength and flaw size Agglomeration processes limit grinding. 51

52 Particle size distribution vs. grinding time A reduction of grain sizes during grinding is accompanied by decreasing of a width of the grain size distribution with grinding time. For ball mills, Beke has proposed: where n is an exponent in the Rossin-Rammler equation, D mill chamber diameter, d - average diameter of grinding media, p ~6. 52

53 Tanaka s Equation 53

54 Effect of environment on grining 54

55 Classification of Ceramic Powders 55

56 Dry Classification Equipment 56

57 Wet Classification Equipment 57

58 Thank you for your kind attention 58

59 Wytrącanie z fazy gazowej metoda PVD Parowanie i kondensacja Sposoby ogrzewania: Piec z łukiem o dużej gęstości prądu (stałego) ok C Odśrodkowy piec z ciekłymi ściankami Proszki złożone z cząstek ą kulistych o rozmiarach nm i powierzchni właściwej m 2 /g Plazmowy piec odśrodkowy z ciekłymi ściankami Proszki: tlenków (np.: SiO 2, Al 2 O 3, Fe 2 O 3, ThO 2, MoO 3, ZrO 2 i inne) oraz węglików ( np.: ThC, TiC, B 4 C, UC, TaC, SiC). 59

60 Samorozwijąjąca się synteza wysokotemperaturowa SHS Morfologia proszku SiC otrzymanego w reakcji węgla drzewnego z krzemem Morfologia proszku SiC otrzymanego w reakcji sadzy z krzemem 60

61 Krystalizacja hydrotermalna Wytwarzanie anie hydrotermalne proszków ceramicznych ch polega na ogrzewaniu substratów w wodzie w podwyższonych temperaturach (do 300ºC) i przy podwyższonym ciśnieniu (do 100MPa). Substratami t mogą być: ć sole metali, tlenki, wodorotlenki lub proszki metali w postaci roztworów lub zawiesin. Zarodkowanie i wzrost w warunkach hydrotermalnych y daje submikronowe lub nanometryczne cząstki tlenków, związków nietlenkowych i metali o kontrolowanym kształcie i rozmiarze. Czynniki wpływające na rozmiar i kształt cząstek proszków: skład środowiska krystalizacji mineralizatory, ph, temperatura, ciśnienie czas. Proces hydrotermalny wykorzystywany jest również w przemyśle ceramicznym do wytwarzania monokryształów kwarcu, do poprawy właściwości kompozycji cementów hydraulicznych i do syntezy skaleni. 61