Ceramics Ceramics inorganic – non-metallic materials china/dishes cement/concrete...

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  • Ceramics

  • Ceramicsinorganic non-metallic materialsstructures depending on a) electrical charge b) atomic radii (rC/rA)stable cations are in contact with surrounded anion

  • Structure of Ceramicse.g.: Al2O3: Al3+: rC=0.053nm, O2-: rA=0.140nm

  • AX Structurese.g. NaCltwo interpenetrating fcc lattices:e.g. MgO, MnS, FeO(coordination number 6)

  • AmXp Structurese.g. CaF2rC/rA=0.8coord. 8center cube positionsonly half-filled

    (CsCl completely-filled)AmBnXp Structures e.g. BaTiO3

  • Close Packing of Anionse.g. ZnSZn anions intetrahedral interstitial positionsspinel structures, e.g. MgAl2O4: O2- fcc lattice, Mg2+ tetrahedral, Al3+ octrahedral

  • Imperfections in Ceramicsdefects:electroneutrality: Schottky pair defect: cation and anion vacancyFrenkel pair defect: cation vacancy+interstitialnon-stoichimetry: e.g. Fe1-xO, 2 Fe3+ ions 1 Fe2+ vacancy, impurities

  • Transparent Conductive Oxides (TCOs)Wide band gap oxide semiconductors (ZnO, SnO2, In2O3 and mixed systems)High doping level (non-stoichiometry, substitution)Electron degeneracy, resulting in High electrical conductivity (n-type) High transmittance in the visible spectral range High infrared reflectivity

  • Properties of undoped and Al-doped ZnO films

  • Applications of TCO thin filmsSolar cells & solar control: - Transparent front contacts for thin film photovoltaics

    Solar cells solar control

  • Displays - LCD (Liquid crystal display) - FPD (Flat panel display) - PDP (Plasma display panel) - Flexible display - PLED (Polymer light emitting device) - OLED (Organic light emitting device)

  • Artists impression of the display of the future. Intrinsic shortcomings of LCDs: Viewing angle dependency, Low contrast and high power consumptionAdvantages of PLED:Excellent viewing angle, contrast and low power consumptionApplications of flexible PLED:Electronic paper, smart cards, wearable devices

    Flexible displays:

  • Organic Light Emitting Device (OLED) technology is emerging as a leading next generation technology for electronic displays and lighting. OLEDs can provide desirable advantages over todays liquid crystal displays (LCDs), as well as benefits to product designers and end users.http://www.universaldisplay.com/tech.htmOLEDs features: Vibrant colors High contrast Excellent grayscale Full-motion video Wide viewing angles from all directions A wide range of pixel sizes Low power consumption Low operating voltages Wide operating temperature range Long operating lifetime A thin and lightweight form factor Cost-effective manufacturability OLEDs

  • As this schematic shows, an OLED is a monolithic, solid-state device that typically consists of a series of organic thin films sandwiched between two thin-film conductive electrodes.The choice of organic materials and the layer structure determine the devices performance features: emitted color, operating lifetime and power efficiency. Structure of OLEDs

  • Silicate CeramicsSi4+O2-basic unit:SiO44- tetrahedroncrystalline: SiO2 (silica, high strength, relatively high Tm: 1710C)

  • Glass general

  • Mechanical Properties of Ceramics/glassesbrittle, no plastic deformationlower fracture strength than theoretical value-flaws (stress raisers)=> statistical approach!!

  • Example: Investigated glass samplesModel-System CaO / Al2O3 / SiO2Glass Sheets:as received (10101 mm3)Cross-section:Crack induced by three-point-bendingAll indents taken within 20min after cracking





    (CaO Al2O3 2SiO2)

  • Time dependent behavior under constant load: Strain Rate SensitivityRelaxation processes under constant loadstrain rate sensitivity (m) describes this behavior:

  • Hardness and Moduli of the samples surfacesBerkovich indenter / 10mN / 10s holdingsignificant influence of composition

  • Hydrated Silicates - ConcretePortland Cement Concrete: sand + gravel (about 60% packing) + cementHydratation (simplified): 2(2CaOSiO2)+4H2O=>3CaO SiO2 3H2O+Ca(OH)2cementsandhydrates

  • Polymorphic Forms of Carbon very strong bond (cubic diamond structure) each C bonds to 4 neighbours (ZnS structure)=> hard, low electric/high thermal conductivitysynthetic diamonds/thin films (tool surfaces)

    graphitediamondlayers of hexagonally arranged Ccovalent bond (3C)between layers weak van der Waals bondgood chemical stability/strengthelectric conductivity (electrodes/contacts)

  • Intrinsic properties of Diamond and its applications

    HardnessAbout100 GPa Wear-protection coatings Chemical resistivityAll chemicalsElectrodes in aggressive chemical environmentThermal conductivity20 W/cmK Insulating heat-sink in the context of laser diodesDisruptive strength Es107 V/cm TransparentUV, VIS, IR Optical windows (UV- to IR-regime) Index of refraction n 2,42 Absorption edge200 nm Band gap Eg5,45 eV High-temperature semiconductors and sensors (up to 600C, compared to 120C for Si) Carrier mobility , Electrons2200 cm2/Vs Holes1600 cm2/Vs

  • CVD-Diamond deposition(3) CH (s) + H = C (s) + H2(4) C (s) + CH3 = C2H3 (s) (2) CH4 + H = CH3 + H2H2 + CH4 (M. Frenklach et al., 1991)Gas inlet

    Thermal or electric activation (HF, Flame, MWP, DC, ...) (1) H2 = 2H Hydrogen-dissociation

    Reactions in the gas-phaseKinetics, transport,surface-reactions, and carbon-incorporationSubstrate

  • Microwave Plasma CVDTS = 500 1100C, CH4/H2 = 0,5 - 2%, Pressure = 10 - 40 mbarP = 300 - 1500 W

  • Hetero-epitaxy of Diamond on SiJiang & Klages, Appl. Phys. Lett. 62, 3438 (1993) SEM

    MaterialLattice-constantsSurface-energyDiamond3,5667 ca. 6,0 J/m2 c-BN3,612 4,8 J/m2 Si5,4388 1,5 J/m2

  • Hetero-epitactic Diamond-films on Si(001)(001)Diamond // (001)Si[110] Diamond // [110] SiX. Jiang et al. J. Appl. Phys. 83, 2511 (1998) {111}-X-ray Pole-figure

  • Coating of cutting-toolsEdge of a cutting-insert coated with (100)-diamondMicro-drill D = 0,15 mm used to machine circuit-boards

  • Adhesion issue limits potential applicationsBackground: thermal stresses : thermal expansion coefficient of substrate and film

    : Youngs modul and Poisson-ratio of film Ts = 800 C

    MaterialDiamondAl2O3Si-SiCTiCSteela (10-6 / K)1,23,34,06,68,312,0f (GPa)0,02,12,75,47,410,7

  • Calculation of thermal stresses by FEM Inherent good adhesion between Diamond-film and compositeGood adhesion of carbide-film on metallic substrate Reduced maximum stressDiamondSteelTiCL. Xiang, PhD thesis TU-Braunschweig, 2002 TiC/Diamond-Gradient layerDiamantSteel1,2 GPa1,94 GPa

  • SEM images of a Diamond/-SiC-composite-layer as well as its SIMS - depth profile

  • Polymorphic Forms of Carbon fullerene C60 (discovered 1985) => carbon nanotube (C sheet + fullerene)hexagons and pentagonsextremely strong (50-200GPa) stiff (1TPa) and ductile (fracture strain 5-20%)=> ultimative fiber for composites, unique electric properties (metal/semiconductor)

  • Carbon nanostructuresSingle-wall-C-Nanotube (CNT)Multi-wall-CNTs:Van der Waals - bonding between individual layers, layer-spacing D=0,34 nm

  • C-C bond-length: d=0.1421nmHelical angels: = 0 30Various single-wall CNTs

  • Production technologiesArc-discharge (high quality, low productivity)Laser-ablation (same as arc-discharge)Chemical Vapor Deposition (CVD)

    Pyrolysis MPCVD HFCVD

    Catalyst-based (Fe, Co, Ni, Pt, etc) growthOrientated CNTs in combination with high productivity

  • Properties and potential applicationsConductivity ranging from metallic to semi-conducting (helical angel, thickness)Low electric field strength for the onset of electron emissionUltra high axial mechanical stability: Youngs Modul = 5 TPa (single-wall-CNTs)

    Low radial mechanical stabilityHandling issues: grabbing, cutting, welding, and othersNano-electronicsScanning probes (AFM)Electronfieldemission-SourcesGas- and energy-storageBiological micro-probesComposite-material (polymers, concrete, and others)Nano-cannula for bio- or medical-applications