Timo Kiesi. Materi

Transkriptio

1 Keraamit

2 Timo Kiesi 2 Materi

3 Classification of Ceramics Ceramic Materials Glasses Clay products Refractories Abrasives Cements Advanced ceramics -optical -composite reinforce -containers/ household -whiteware -structural -bricks for high T (furnaces) -sandpaper -cutting -polishing Adapted from Fig and discussion in Section , Callister & Rethwisch 8e. -composites -structural -engine rotors valves bearings -sensors 3

4 Keraamien rakenne Koostuvat kahdesta tai useammasta alkuaineesta Ioni- tai kovalenttinen sidos luja suuntautunut Kationi luovuttaa elektronin Anioni vastaanottaa elektronin 4

5 Kiderakenne Anionien tulee koskettaa kationia 5 5

6 Kiteytyminen riippuu kationin ja anionin kokosuhteesta ja koordinaationumerosta 6 6

7 r cation Coordination # increases with r anion To form a stable structure, how many anions can surround around a cation? r cation r anion < Coord # 2 linear ZnS (zinc blende) Adapted from Fig. 12.4, Callister & Rethwisch 8e triangular tetrahedral NaCl (sodium chloride) Adapted from Fig. 12.2, Callister & Rethwisch 8e Adapted from Table 12.2, Callister & Rethwisch 8e. octahedral cubic CsCl (cesium chloride) Adapted from Fig. 12.3, Callister & Rethwisch 8e. 7

8 Kiderakenne NaCl Kuin kaksi ristikkäistä PKK hilaa 8 8

9 Kiderakenne CsCl 9 9

10 Kiderakenne ZnS Tetra 10 10

11 CaF

12 BaTiO

13 Tiivispakkaukselliset hilat Isot anionit tiivispakkautuvat Kationit välisijoissa 13 13

14 Piioksidit Yleisimmät maankuoren mineraalit 14 14

15 15 15

16 Piilasi Ei-kiteinen rakenne SiO4 -tetraedri on peruselementti Satunnaisesti sijoittuneena 16 16

17 Silikaatit 17 17

18 Kerrostuneet silikaatit Savimaisilla materiaaleilla 18 18

19 Hiilen yhdisteet Timantti Erittäin kova Voidaan valmistaa teollisesti Käytetään pinnoitteena - Työstöterät - laakeripinnoilla 19 19

20 Timanttipinnoite 20 20

21 Hiilen yhdisteet Grafiitti kerroksittain heksagonaalisia kiteitä kerrosten välinen sidos on heikko Erinomainen liukumateriaali 21 21

22 Fullereenit Löydettiin

23 Nanoputket 23 23

24 Hilavirheet 24 24

25 Frenkel -viat Sähköinen neutraalius täytyy säilyttää Viat esiintyvät pareina 25 25

26 Stokiometrisyys 26 26

27 Epäpuhtaudet 27 27

28 Hilavirheitä Keraameissa vastaavia hilavirheitä kuin metalleissa mutta nämä eivät välitä deformaatiota Poikkeustapauksissa deformoitavissa (korkea lämpötila, paine, tms.)

29 Ceramic Phase Diagrams MgO-Al 2 O 3 diagram: Adapted from Fig , Callister & Rethwisch 8e. 29

30 30

31 Mechanical Properties Ceramic materials are more brittle than metals. Why is this so? Consider mechanism of deformation In crystalline, by dislocation motion In highly ionic solids, dislocation motion is difficult - few slip systems - resistance to motion of ions of like charge (e.g., anions) past one another 31

32 Flexural Tests Measurement of Elastic Modulus Room T behavior is usually elastic, with brittle failure. 3-Point Bend Testing often -- tensile tests are difficult for brittle materials. cross section b rect. d R circ. F L/2 L/2 Determine elastic modulus according to: F x slope = F d d linear-elastic behavior E E F d F d L 3 4bd L R 4 Adapted from Fig , Callister & Rethwisch 8e. d = midpoint deflection (rect. cross section) (circ. cross section) 32

33 Flexural Tests Measurement of Flexural Strength 3-point bend test to measure room-t flexural strength. cross section b rect. d R circ. F L/2 L/2 location of max tension Adapted from Fig , Callister & Rethwisch 8e. d = midpoint deflection Flexural strength: s fs s fs 3 2bd F f F f R L 3 L 2 (rect. cross section) (circ. cross section) Material Typical values: s fs (MPa) E(GPa) Si nitride Si carbide Al oxide glass (soda-lime) 69 Data from Table 12.5, Callister & Rethwisch 8e

34 Keraamin murtopinta 34

35 Lujuus edelleen alle teoreettisen

36 Lujuudessa suuri vaihtelu Lujuus paljon alle teoreettisen Syynä alkuviat, jotka ydintävät haurasmurtuman

37 Mekaaniset ominaisuudet Tyypillisesti hauraita (murtuvat ilman plastista deformaatiota) Murtuvat siten, että särö etenee rakeiden läpi Todelliset saavutetut lujuudet ovat paljon alhaisempia kuin teoreettiset Lujuus riippuu vikapopulaatiosta ja materiaalin kyvystä vastustaa murtumaa Puristuslujuudet kymmenkertaisia vetolujuuksiin verrattuna 37 37

38 Puristuslujuutta voidaan käyttää hyväksi saattamalla materiaaliin puristusjäännösjännitys: Teräsbetoni Karkaistu lasi 38 38

39 Lujuudessa suuri hajonta 39 39

40 Lujuus Mitataan taivutuskokeessa (ei vetokokeessa) 40 40

41 Deformaatio Kiteisillä dislokaatioiden liike Ei-kiteisillä viskoosia virtaa 41 41

42 Keraamien käyttö 42 42

43 Lasit 43 43

44 Savet Edullinen ja helposti muovattava materiaali käytetään rakennusaineena ja astioiden jne. valmistukseen Koostuvat lähinnä alumiinin ja piin oksideista Laaja sulamisalue (voidaan polttaa lujaksi) Kerrostunut rakenne Vesi pääsee kerrosten väliin ja mahdollistaa plastisen muovauksen 44 44

45 Mikrorakenne 45 45

46 Korkealämpötilakeraamit 46 46

47 Kulutuspinnat / hionta 47 47

48 48 48

49 Konstruktiokeraamit Laakeripinnoissa Al -Ni Venttiileissä 49 49

50 Ceramics Application: Die Blanks Die blanks: -- Need wear resistant properties! Die surface: -- 4 mm polycrystalline diamond particles that are sintered onto a cemented tungsten carbide substrate. -- polycrystalline diamond gives uniform hardness in all directions to reduce wear. Ao die die Ad tensile force Adapted from Fig. 11.8(d), Callister & Rethwisch 8e. Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission. 50

51 Ceramics Application: Cutting Tools Tools: -- for grinding glass, tungsten, carbide, ceramics -- for cutting Si wafers -- for oil drilling Materials: -- manufactured single crystal or polycrystalline diamonds in a metal or resin matrix. -- polycrystalline diamonds resharpen by microfracturing along cleavage planes. oil drill bits blades Single crystal diamonds polycrystalline diamonds in a resin matrix. Photos courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission. 51

52 Ceramics Application: Sensors Example: ZrO 2 as an oxygen sensor Principle: Increase diffusion rate of oxygen to produce rapid response of sensor signal to change in oxygen concentration Ca 2+ Approach: Add Ca impurity to ZrO2: -- increases O 2- vacancies -- increases O 2- diffusion rate Operation: -- voltage difference produced when O 2- ions diffuse from the external surface through the sensor to the reference gas surface. -- magnitude of voltage difference partial pressure of oxygen at the external surface gas with an unknown, higher oxygen content A substituting Ca 2+ ion removes a Zr 4+ ion and an O 2- ion. + sensor O 2- diffusion voltage difference produced! - reference gas at fixed oxygen content 52

53 Refractories Materials to be used at high temperatures (e.g., in high temperature furnaces). The Silica (SiO 2 ) - Alumina (Al 2 O 3 ) system. Silica refractories - silica rich - small additions of alumina depress melting temperature (phase diagram): Al 2 O 3-2SiO 2 T(ºC) 2000 Liquid (L) mullite alumina + L 1800 crystobalite + L mullite + L mullite + crystobalite alumina + mullite Composition (wt% alumina) Fig , Callister & Rethwisch 8e. (Fig adapted from F.J. Klug and R.H. Doremus, J. Am. Cer. Soc. 70(10), p. 758, 1987.) 53

54 Vuorausmateriaalit teräksen valmistuksessa Timo Kiesi 54

55 Advanced Ceramics: Materials for Automobile Engines Advantages: Operate at high temperatures high efficiencies Low frictional losses Operate without a cooling system Lower weights than current engines Disadvantages: Ceramic materials are brittle Difficult to remove internal voids (that weaken structures) Ceramic parts are difficult to form and machine Potential candidate materials: Si 3 N 4, SiC, & ZrO 2 Possible engine parts: engine block & piston coatings 55

56 Advanced Ceramics: Materials for Ceramic Armor Components: -- Outer facing plates -- Backing sheet Properties/Materials: -- Facing plates -- hard and brittle fracture high-velocity projectile Al 2 O 3, B 4 C, SiC, TiB 2 -- Backing sheets -- soft and ductile deform and absorb remaining energy aluminum, synthetic fiber laminates 56

57 GLASS FORMING Blowing of Glass Bottles: Parison mold Suspended parison Gob PARTICULATE FORMING Pressing operation Compressed air CEMENTATION Pressing: plates, cheap glasses -- glass formed by application of pressure -- mold is steel with graphite lining Fiber drawing: Finishing mold Adapted from Fig. 13.8, Callister & Rethwisch 8e. (Fig is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.) wind up 57

58 Sheet Glass Forming Sheet forming continuous casting sheets are formed by floating the molten glass on a pool of molten tin Adapted from Fig. 13.9, Callister & Rethwisch 8e. 58

59 Glass Properties Specific volume (1/r) vs Temperature (T): Specific volume Supercooled Liquid Liquid (disordered) Crystalline materials: -- crystallize at melting temp, T m -- have abrupt change in spec. vol. at T m Glass (amorphous solid) Crystalline (i.e., ordered) T g T m solid T Glasses: -- do not crystallize -- change in slope in spec. vol. curve at glass transition temperature, T g -- transparent - no grain boundaries to scatter light Adapted from Fig. 13.6, Callister & Rethwisch 8e. 59

60 Glass Properties: Viscosity Viscosity, h: -- relates shear stress ( ) and velocity gradient (dv/dy): glass dy dv dv dy velocity gradient h dv / dy h has units of (Pa-s) 60

61 Viscosity [Pa-s] Log Glass Viscosity vs. Temperature Viscosity decreases with T soda-lime glass: 70% SiO 2 balance Na 2 O (soda) & CaO (lime) borosilicate (Pyrex): 13% B 2 O 3, 3.5% Na 2 O, 2.5% Al 2 O T melt T(ºC) Vycor: 96% SiO 2, 4% B 2 O 3 fused silica: > 99.5 wt% SiO 2 strain point annealing point Working range: glass-forming carried out Soda-lime glass = natronkalkkilasi, soodalasi Fused silica = kvartsilasi Adapted from Fig. 13.7, Callister & Rethwisch 8e. (Fig is from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.) 61

62 Heat Treating Glass Annealing: -- removes internal stresses caused by uneven cooling. Tempering: -- puts surface of glass part into compression -- suppresses growth of cracks from surface scratches. -- sequence: before cooling hot initial cooling cooler hot cooler -- Result: surface crack growth is suppressed. at room temp. compression tension compression 62

63 Ionipinnoitetut ohuet lasit (esim. Gorilla Glass TM) Yleisiä matkapuhelimissa, tableteissa Kestää naarmuja ja kuormitusta normaalia lasia paremmin 63

64 Timo Kiesi 64

65 Timo Kiesi 65

66 Ceramic Fabrication Methods (iia) GLASS FORMING PARTICULATE FORMING CEMENTATION Hydroplastic forming: Mill (grind) and screen constituents: desired particle size Extrude this mass (e.g., into a brick) force Ao container ram billet container die holder extrusion die Ad Adapted from Fig. 12.8(c), Callister & Rethwisch 8e. Dry and fire the formed piece 66

67 GLASS FORMING Slip casting: Mill (grind) and screen constituents: desired particle size Mix with water and other constituents to form slip Slip casting operation pour slip into mold absorb water into mold green ceramic solid component Dry and fire the cast piece PARTICULATE FORMING pour slip into mold drain mold hollow component CEMENTATION green ceramic Adapted from Fig , Callister & Rethwisch 8e. (Fig is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

68 Typical Porcelain Composition (50%) 1. Clay (25%) 2. Filler e.g. quartz (finely ground) (25%) 3. Fluxing agent (Feldspar) -- aluminosilicates plus K +, Na +, Ca + -- upon firing - forms low-melting-temp. glass 68

69 Hydroplasticity of Clay Clay is inexpensive When water is added to clay -- water molecules fit in between layered sheets -- reduces degree of van der Waals bonding -- when external forces applied clay particles free to move past one another becomes hydroplastic Structure of Kaolinite Clay: Adapted from Fig , Callister & Rethwisch 8e. (Fig is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.) charge neutral Shear Shear charge neutral weak van der Waals bonding Si 4+ Al 3+ - OH O 2-69

70 micrograph of porcelain Drying and Firing Drying: as water is removed - interparticle spacings decrease shrinkage. Adapted from Fig , Callister & Rethwisch 8e. (Fig is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.) wet body partially dry completely dry Drying too fast causes sample to warp or crack due to non-uniform shrinkage Firing: -- heat treatment between ºC -- vitrification: liquid glass forms from clay and flux flows between SiO2 particles. (Flux lowers melting temperature). Si0 2 particle (quartz) glass formed around the particle 70mm Vitrification = lasiintuma Flux = juoksute 70

71 Ceramic Fabrication Methods (iib) GLASS FORMING PARTICULATE FORMING CEMENTATION Powder Pressing: used for both clay and non-clay compositions. Powder (plus binder) compacted by pressure in a mold -- Uniaxial compression - compacted in single direction -- Isostatic (hydrostatic) compression - pressure applied by fluid - powder in rubber envelope -- Hot pressing - pressure + heat 71

72 Sintering Sintering occurs during firing of a piece that has been powder pressed -- powder particles coalesce and reduction of pore size Aluminum oxide powder: -- sintered at 1700ºC for 6 minutes. Adapted from Fig , Callister & Rethwisch 8e. Adapted from Fig , Callister & Rethwisch 8e. (Fig is from W.D. Kingery, H.K. Bowen, and D.R. Uhlmann, Introduction to Ceramics, 2nd ed., John Wiley and Sons, Inc., 1976, p. 483.) 15 mm 72

73 Tape Casting Thin sheets of green ceramic cast as flexible tape Used for integrated circuits and capacitors Slip = suspended ceramic particles + organic liquid (contains binders, plasticizers) Fig , Callister & Rethwisch 8e. 73

74 Ceramic Fabrication Methods (iii) GLASS FORMING PARTICULATE FORMING Hardening of a paste paste formed by mixing cement material with water Formation of rigid structures having varied and complex shapes Hardening process hydration (complex chemical reactions involving water and cement particles) Portland cement production of: -- mix clay and lime-bearing minerals -- calcine (heat to 1400ºC) -- grind into fine powder CEMENTATION 74

75 Rakennusteollisuuden keraamiset komposiittirakenteet Betoni: Sementti Hiekka Lisäaineet, täyteaineet (teräs, esijännitys) Muurilaasti: Sammutettu kalkki Hiekka Sammutettu kalkki (Ca(OH)2) reagoi ilman hiilidioksidin kanssa ja kiteytyy kalsiittina (CaCO3), jolloin muodostuu synteettistä hiekkakiveä 75

76 Yhteenveto Useimmat keraamit ovat metallin ja epämetallin yhdisteitä, joiden sidos on kovelenttinen tai ionisidos Keraameja ovat esimerkiksi: tulenkestävät aineet, kehittyneet keraamit, savet, lasit, sementti Keraamien deformaatiokyky on heikko, mutta kovuus korkea Liukusysteemien puute, varaus, sidoksen suuntautuneisuus Mekaaniset ominaisuuksissa esiintyy suurempi hajonta kuin esimerkiksi metalleilla Vikojen vaikutus Koska keraamit ovat jo valmiiksi oksideja, ne kestävät korroosiota ja korkeita lämpötiloja Timo Kiesi 76

77 Metallien väliset yhdisteet

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79 Ylihila

80 Metallien ja keraamien ominaisuuksia Metallisidos Suuntautuneempi Plastinen deformaatio vaikeampaa

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83 Pinnoitteissa

84 Deformaatio laseissa

85 x Network glasses 1.3 STRUCTURE O F MATERIALS 29 Si O Fig Schematic representation of (a) ordered crystalline and (b) randomnetwork glassy form of silica. (a) (b) Example 1.7 Determine t he C C C bonding angle in polyet hylene. The easiest manner to visualize t he bonding angle is to assume that one C atom is in the center of a cube and that it is connected to four other C atoms at the edges of the cube. (See Figure E1.7.) Suppose all angles are equal to α.

86 Glassy Polymers

87 Uudelleenjärjestyminen Pienimmän energian deformaatiotie välittyy usean atomin liikkeen avulla

88 Uudelleenjärjestyminen Pienimmän energian deformaatiotie välittyy usean atomin liikkeen avulla

89 Uudelleenjärjestyminen Pienimmän energian deformaatiotie välittyy usean atomin liikkeen avulla

90 Uudelleenjärjestyminen Pienimmän energian deformaatiotie välittyy usean atomin liikkeen avulla

91 Uudelleenjärjestyminen Pienimmän energian deformaatiotie välittyy usean atomin liikkeen avulla

92 Uudelleenjärjestyminen Pienimmän energian deformaatiotie välittyy usean atomin liikkeen avulla

93 Metallic glasses

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