CERAMICS. (related only to traditional ceramics): Materials made of clays and hardened by fire

Size: px

Start display at page:

Download "CERAMICS. (related only to traditional ceramics): Materials made of clays and hardened by fire"

Rosamund Lynch
6 years ago
Views:

1 CERAMICS Original definition: (related only to traditional ceramics): Materials made of clays and hardened by fire Actual definition: Inorganic non-metallic heterogeneous materials with structure composed of crystals of various composition and usually containing also glassy phase and pores

2 Microstructure of ceramics

3 BASIC TYPES OF CERAMICS CERAMICS TECHNICAL CERAMICS REFRACTORIES BIOCERAMICS BASED ON CLAYS PORCELAIN MgO Al 2 O 3 SiO 2 CERAM. OXIDE BIOINERT (steatite, cordierite, forsterite ceram.) (SiO 2, Al 2 O 3, ZrO 2, MgO, ( Al 2 O 3, ZrO 2 ) EARTHENWARE Cr 2 O 3, CaO oxides and TiO 2 and TITANATES CERAM. their compounds) BIOACTIVE ( Ca phosphates ) STONEWARE FERRITE CERAM. (MeO.Fe 2 O 3 ) NON- OXIDE ( SiC, C, Si 3 N 4.) BUILDING CERAM. MAT. OXIDE CERAMICS (Al 2 O 3, ZrO 2, MgO, ThO 2, PLZT) RAW-MATER. : Kaolin, Quartz, Feldspar NON-OXIDE CERAMICS (carbides, nitrides, borides, graphites) SEMI- and SUPERCONDUCTIVE MICROSRUCTURE: YBa 2 Cu 3 O 7-x Mullite, quartz, cristobalit Glass phase ADVANCED CERAMICS ( TTZ alloys, Si 3 N 4, SiC )

4 Basic scheme of ceramics technology RAW MATERIALS - MILLING - MIXING FORMING FIRING RAW MATERIALS CERAMICS BASED ON CLAYS CERAMICS BASED ON SYNTHETICS Plastics : clays, kaolin (min. 90% kaolinite) Powders of synthetic compounds Non-plastics : quartz, corundum, plasticizers: waxes, PVA ) presintered clays deflocculators : Fluxes: alkali feldspars electrolytes, protective colloids lignosulphates, tannin, synthetic Na-humate, polymers

5 Forming processes FORMING CERAMICS PROCESSES THE AIM: to form and to shape a product and to facilitate formation of microstructure by firing CASTING OF FLUID SUSPENSIONS casting of slips containing water ( %) casting of mixes containing thermoplastic binder (hot pressure casting, injection moulding) PLASTIC FORMING from mixes containing % water or organic plasticizers PRESSING of dry powder mixtures (5 15 % water) of mixtures containing organic binders hot pressing VIBRATION PRESSING SHOCK WAWE FORMING MACHINING of BLANKS Trimming, milling, turning

6 Porcelain examples of raw materials mixtures PORCELAIN KAOLIN QUARTZ FELDSPAR FIRING TEMPERATURE 0 C ( wt. % ) Hard (typical) SiO 2, 26 Al 2 O 3, 5 alkalis (wt.%) Hard Electrotechnical 37,5 37,5 25 Carlsbader (tableware) Soft Dental

7 Phase diagram Al2O3 SiO2

8 Types of rheological behavior a - Newtonian liquid, b pseudoplastic liquid, c plastic ( Bingham) body, d - typical real plastic body, e thixotropic body, f dilatant body

9 Chemical composition of historical porcelains in wt.% (China, France Sévres, Germany Meissen)

10 Phase composition of porcelain (mass %) % mullite 5 25 % quartz 6 10 % cristobalite % silicate glass with a high SiO 2 content

11 Sintering of porcelain full line apparent porosity, dashed line actual porosity Porosity (%) Linear l shrinkage i (%)

12 Chemistry of kaolinite thermal decomposition kaolinite metakaolinite mullite + cristobalite mullite

13 Typical microstructure of porcelain

14 Typical microstructure of porcelain

15 Other types of ceramics based on clays 1. Earthenware Similar composition of raw materials mixture as porcelain but fired on a lower temperature ( C). It is not sintered completely, has a lower strength (~ 30 MPa) and shows higher porosity. Kaolin can be replaced by white-firing clays, the mix composition of raw materials varies, it may contain also CaCO 3. Products: wall tiles, domestic and decorative ware, sanitary ware. Faience earthenware provided with a glaze Majolica twice-fired ceramics painted and glazed

16 Other types of ceramics based on clays 2. Stoneware Dense ceramics coloured yellow to brown. Raw materials mixture: ~ 50 % stoneware clay ~ 40 % quartz ~ 10 % feldspar Sintering temperature C Products: floor tiles,chemical and kitchenware,pipes,electric insulators. The products are usually provided with salt glaze (sodium chloride is introduced into the kiln at the end of firing)

17 Other types of ceramics based on clays 3. Bricks and similar products Raw materials: low-grade, coloured-firing clays sand,slag, fly ash Drying in tunnel dryers, firing in tunnel kilns ( C) Properties: mechanical strength ( ~ 50 MPa in compression), frost resistance, thermal conductivity, thermal expansion. The properties depend on porosity and namely on the type of bricks ( full, cavity types)

18 Refractories CHARACTERISTICS: Materials that withstand at least temperatures of at least C and have following properties: - Resistance to high temperature without chemical or physical changes - Thermophysical properties: strength, deformation under load, resistance to thermal shock and abrasion - Resistance to corrosion by melts and gases and by contact with other refractories or another materials.

19 Main types of refractories I material chem.comp. prevailing phase raw materials Silica SiO 2 tridymite, cistobal. quartzite Fireclay Al 2 O 3, SiO 2 mullite, glass clays Mullite 3 Al 2 O 3. 2 SiO 2 mullite Al 2 O 3, clays Corundum Al 2 O 3 (SiO 2 ) corundum corundum (clay) Magnesite MgO (Fe 2 O 3 ) MgO periclase magnesite Chrome MgO, Cr 2 O 3 periclase, spinel magnesite -magnesite, Al 2 O 3 chrome ore

20 Main types of refractories II material chem.comp. prevailing phase raw materials Dolomite MgO, CaO periclase, CaO dolomite Forsterite MgO, SiO 2 2 MgO.SiO 2 (forsterite) olivine, magn. Chromite Cr 2 O 3,Fe 2 O 3,Al 2 O 3,MgO spinels chromite Zirconium silicate ZrO 2,SiO 2 ZrO 2.SiO 2 (zircon) zircon,sand Fusion cast ZrO 2,SiO 2 ZrO 2 (baddeleyide) zircon, refract. Al 2 O 3 corundum corundum SiC refractories SiC SiC SiC, clay

21 Initial deformation temperatures under load ( 0 C) Silica refractories Fireclays bricks Mullite refractories Alumina refractories ~ Magnesite refractories Fusion cast refractories ~ 1 730

22 Ceramics for electronics I Forsterite ceramics low dielectric losses, joining with metals Steatite ceramics (Enstatite ceramics) high mechanical strength low loss angle Cordierite ceramics low thermal exp.coeff.

23 Examples of composition of ceramics in the system MgO-Al 2 O 3 -SiO 2 Raw material body composition (wt.%) steatites cordierite Talc Clay Feldspar BaCO Magnesite 0 6 -

24 Ceramics for electronics II rutile (TiO 2 ) ceramics mixture of anatase and rutile C rutile grinding, milling mixing ( 5% clay) forming firing sintering at C

Ceramics for electronics III - titanates BaTiO 3 - basic compound for non-linear electronics (ferroelectricum, piezoelectricum, semiconductivity) 1 100 1 300 0 C BaCO 3 + TiO 2 BaTiO 3 milling

25 Ceramics for electronics III - titanates BaTiO 3 - basic compound for non-linear electronics (ferroelectricum, piezoelectricum, semiconductivity) C BaCO 3 + TiO 2 BaTiO 3 milling forming firing ( C) Ba substitution by : Mg, Ca, Pb, Sr, Cd, Ti substitution by: Sn, Zr, Cs, Hf, La, Th, Ce, Transparent ceramics for optoelectronics: PZT (PbO-ZrO 2 -TiO 2 ) and PLZT (PbO-La 2 O 3 -ZrO 2 -TiO 2 ) ceramics

26 Main properties of rutile and titanates ceramics Materials serve as capacitor dielectrics - linear capacitors (permittivity independend of voltage, linear dependence on temperature) - non- linear capacitors (high permittivity depending on temperature and voltage) In general following properties are required: High permittivity (dielectric constant) Low loss angle Defined temperature coefficient of permittivity (close to zero, or variable)

27 Ceramics for electronics IV - ferrites Compounds of MeO. Fe 2 O 3 type exhibiting ferromagnetic properties MeO : MnO, FeO, CoO, NiO, MgO, ZnO, CdO, CuO Trivalent Fe substitution by: trivalent ions Al, Ga, Ce Preparation: Mixing and milling of raw materials (oxides, carbonates) temperature pretreatment in controlled atmoshere (CO : CO 2 ) (reactions giving a mix of ferrites) grinding, forming firing ( C )

28 Oxide ceramics Fine grained ceramics composed completely or predominantly of a single pure oxide (practially one-component ceramics) Composition: Al 2 O 3, ZrO 2, MgO, SnO 2, ThO 2, UO 2, Some basic properties melting point 0 C hardness maximum temp. of use Al 2 O MgO ZrO ThO

29 Sintered alumina corundum ceramics Two basic types: - pure sintered corundum ceramics (no admixtures, impurities content < 1%) - sintered corundum ceramics ( contains admixtures facilitating sintering up to ~ 5-10 %) Preparation: Calcined alumina grinding forming (organic binders) Products: pressing, casting, injection moulding firing ( C) tubes, crucibles, spark plug insulators, cutting tools, substrates for electronics, resistors,..

30 Microstructure of sintered alumina (composed of corundum grains, pores, intergranual interfaces) corundum high temperature stable crystalline modification

31 Zirconia ceramics ZrO 2 phase diagram Monoclin. Tetrag. Cubic Density α ~ 70 - ~ 100 Temp. ( 0 C) stabil.< 1000 max max. 2700

32 Stabilization of zirconia ceramics by Y 2 O 3 addition (partially or full stabilized zirconia)

33 Types of transformation toughened zirconia a PSZ (partially stabilized zirconia), b - TZP (tetragonal zirconium polycrystals), c ZTA (zirconia toughened alumina)

34 Microstructure of TTZ alloy Mg PSZ Y TZP ZTA

35 Transformation toughened ceramics

36 Non-oxide ceramics Carbides: SiC, B 4 C, TiC, UC, WC, TaC Nitrides: Si 3 N 4, BN, TiN Principles of manufacture: SiC - two stages procedure 1. synthesis of SiC - reduction of SiO 2 by C, T = C 2. grinding, forming of powder ( hot pressing, reactive sintering), firing ( ~ C) Si 3 N 4 reaction sintering of powdered silicon compacts with nitrogen at C Si (porous solid compact) + N 2 (g) Si 3 N 4 Sialon variable composition Si 6-x Al x O x N 8-x pressure sintering of a mixture Si 3 N 4 + Al 2 O 3 + AlN, or Si 3 N 4 + SiO 2 + AlN

37 Some properties of structural ceramics I density α thermal conducticity kg. m -3 K -1 W. m -1 K -1 PSZ TZP ZTA Si 3 N SiC FSZ Corundum

Bending strength of structural ceramics bending strength ( M Pa) 20 0 C 500 0 C 1000 0 C 1300 0 C PSZ 600 800 350 200 0 TZP

38 Bending strength of structural ceramics bending strength ( M Pa) 20 0 C C C C PSZ TZP ZTA Si 3 N SiC FSZ Corundum

CERAMIC MATERIALS I. Asst. Prof. Dr. Ayşe KALEMTAŞ

CERAMIC MATERIALS I. Asst. Prof. Dr. Ayşe KALEMTAŞ CERAMIC MATERIALS I akalemtas@mu.edu.tr, akalemtas@gmail.com, Phone: 211 19 17 Metallurgical and Materials Engineering Department Application Base Classification Advanced Ceramics Ceramic Materials Traditional