Processing, properties and applications of advanced ceramic materials

Processing, properties and applications of advanced Dr. Vaclav Pouchly Advanced Ceramic Materials, Central European Institute of Technology

Outline: 1. Definition of ceramics 2. Ceramic processing 2.1. Powder synthesis and processing 2.2. Shaping 2.3. Sintering 3. New trends in sintering (pressure-assisted sintering, electric field assisted sintering) 4. Example bio- 5. Conclusions

Traditional ceramics Advanced ceramics Raw materials without or with partial treatment Different crystals with glassy phase Synthetic powder Controlled microstructure Better mechanical properties

Metallic Materials classification Non-metallic Organic Inorganic (nonmetallic) C, H (O, N, P, S, )

Bonds in Ionic Covalent Mixed (ionic-covalent) different electronegativity of atoms near electronegativity of atoms portion of ionic bonding increases with increasing difference between electronegativities Bonding in ceramics is responsible for the specific properties of ceramics and diferences between ceramics and metals

Covalent bond Ionic bond Material CaF 2 MgO NaCl Al 2 O 3 SiO 2 Si 3 N 4 ZnS SiC Proportion of ionic bonding 89% 73% 67% 63% 51% 30% 18% 12%

The term ceramics is often limited to inorganic materials of non-metallic nature predominately in crystalline state and prepared from powder material using sintering at high temperatures. We will distinguish: ceramics (according to the limited definition) and glass, (non-metallic single crystals and carbon products)

Technology of non-metallic materials classification into materials groups Polycrystalline ceramics Ceramic single crystals Glass Plastics Composites

Monocrystal Polycrystal Amorphous

Polycrystalline ceramics Advantages: high melting point strength in pressure hardness wear resistance chemical resistance intermediate and lower density Restrictions: brittle behaviour sensitivity to thermal shock difficult preparation and expensive machining

What is dislocation

Movement of dislocation

Cause of brittlness: restricted motion of dislocations Low mobility Low manoeuvrability High Peierls-Nabarro stress in covalent and complex ionic crystals Example: MgO can be partially ductial as a single crystal low P-N stress von Mises criterion is not fulfilled for plastic deformatio of polycrystals (5 independent slip systems) Polycrystalline MgO can be ductile above 1700 C other slip system are initiated

Synthesis methods Mechanochemical synthesis Solid-state reaction Sol-gel synthesis Spray-pyrolysis Hydrothermal (HT) synthesis Sonospray synthesis Ultrasound (US) precipitation synthesis Microwave (MW) precipitation synthesis Ultrasound and microwave precipitation synthesis

agglomerate vs. aggregate

Requirements on shaping 1. Homogeneous structure of ceramic green body 2. Minimum defect size in ceramic green body (bubbles, craks, deformation) 3. Minimum requirements on machining of final sintered body 4. Automatization capability, harmless and enviromentally safe

Shaping methods Dry shaping Wet shaping uniaxial pressing isostatic pressing slip casting (incl. centrifugation, EPD) methods of direct consolidation tape casting Plastic shaping injection moulding extrusion calandering 3D printing Solid free-form fabricatition direct jet printing stereolithography robocasting fused deposition

Uniaxial pressing

One-sided pressing Two-sided pressing

Two-sided pressing with segmented punch

Spray dryer

Electrostatic forces Steric forces Depletion forces

Slip casting

Direct consolidation Principle: Liquid ceramic suspension is transformed to the solid body without removal of a liquid medium Consolidation Physical bonds between ceramic particles DCC Chemical reaction of additives forms a gel Gelcasting

Injection moulding Schematic diagram: Use: Mass production of complex parts Limitations: Defects in thick-wall and fineparticle bodies Injection moulding defects Binder removal defects

Injection moulding

Extrusion

Principle: Computer controlled selective binding of layers of free powder by binder jet printing colloidal SiO 2 polymer solution Layer thickness ~0,1 mm Accuracy of the method: 0.05 mm

Sintering = compaction of particle body at high temperature Driving force of sintering is the decrease of total interface energy by means of replacement of ceramics/ atmosphere interface with higher energy by ceramics/ceramics interface (grain boundary) with lower energy Sintering is realized using a mechanism of vacancy diffusion

Dilatometry

Dilatometry Relative elongation [ ] Temperature

Hot Isostatic Press

Hot Isostatic Press - Advantages External pressure Isostatic distribution of pressure Any shape Disadvantages None?

Hot Isostatic Press - Advantages External pressure Isostatic distribution of pressure Any shape Disadvantages Too expensive Capsulation needed

Our results

Electric Field During Sintering

Spark Plasma Sintering - Advantages external pressure rapid heating rate direct heating pulse heating Disadvantages only easy shapes

Material Advantages Disadvantage Polymers Resiliant Weak Tough Low E Easy to fabricate Not usually bioactive Low density Not resorbable Metals Strong Can corrode in human body Wear resistence High E Tough High density Easy to fabricate Not usually bioactive Not resorbable Ceramics Biocompatible Low tensile strength Wear resistant Difficult to fabricate Can be lightweight Low toughness Not resiliant

Alumina nad zirconia nearly inert No chemical change during long-time use By 2006 >10 6 alumina balls for femoral head

Material Advantages Disadvantage Polymers Resiliant Weak Tough Low E Easy to fabricate Not usually bioactive Low density Not resorbable Metals Strong Can corrode in human body Wear resistence High E Tough High density Easy to fabricate Not usually bioactive Not resorbable Ceramics Biocompatible Low tensile strength Wear resistant Difficult to fabricate Can be lightweight Low toughness Not resiliant

Fracture toughness of t-zro 2 nanoceramics

Fracture toughness of t-zro 2 nanoceramics density 99. 6%t.d grain size 85nm structural ceramics, bioceramics

Hydroxyapatite Generally A 10 (BO 4 ) 6 X 2, A=Ca, B=P,X=OH Dense Particles Porous Augmentation of alveolar ridge Filler in bony defects Filler in bony defects Orthopedic surgery

Bioceramic coatings Protect the substrate against corrosion Make the implant biocompatible Turn a non-bioactive surface into bioactive one Usual combinations Polycrystalline ceramics on ceramics Glass on ceramics Polycrystalline ceramic on metal

Thank you for your attention NF-CZ07-ICP-1-040-2014: Formation of research surrounding for young researchers in the field of advanced materials for catalysis and bioapplications