Ceramic Processingeng.sut.ac.th/ceramic/old/images_news/51.pdf · 7/15/2009 Ceramic Processing/S.Rattanachan 15 Stages of sintering 1st stage (initial) Rearrangement Neck formation

7/15/2009 Ceramic Processing/S.Rattanachan 1

Ceramic ProcessingCeramic Processing

Engineering MaterialsEngineering Materials


Ceramic ProcessingCeramic Processing

Ceramic powders/Raw materials Additives

Mixing

Forming

Drying

FiringDensificationSinteringVitrification

+


Additives of ceramicsAdditives of ceramics

�Binder: �� ก��

�Lubricant: �� !��"#$%&'

�Plasticizer: ��(�ก� )��"$� ��ก �*�� (��

�Deflocculant: +��(#��ก �,��"$�

�Dopants: - $�- (��$"��)../� ��ก��


ShapeShape--Forming ProcessesForming Processes

�Pressing�Uniaxial�Isostatic�Hot pressing�Hot isostatic

pressing

�Slip casting�Drain casting�Solid casting

� Tape casting�Doctor blade�Waterfall

� Plastic forming�Extrusion�Roll forming�Roller head �Injection molding


UniaxialUniaxial PressingPressing

• Free-flowing Powder containing binder, moisture, lubricant• This cycle repeats typically 6 to 100 times per minute.• Presses have a capacity from 1 to 20 tons.

Process steps:• Preparation• Filling• Compression • Ejection • Recycle


Dry pressingDry pressing

• Dry, Semidry or dust pressing •0 – 4 % moisture powder• Products: electrical parts (capacitor, substrate), Bricks


IsostaticIsostatic pressing pressing Cold Cold isostaticisostatic pressing (CIP)pressing (CIP)

Products from CIP

• Pressure from multiple directions • high uniformity • the walls of die deform and transmit the pressure uniformly to the powder.

Process steps:• powder is sealed in a water-tight die• Sealed die is immersed in a liquid contained in a high pressure chamber• seal the chamber• Increase pressure of the liquid by hydraulic pumping• release pressure• remove die


Hot Hot isostaticisostatic pressing (HIP)pressing (HIP)

• near-net shape and high density • Work pieces are heated and an inert gas, generally argon, applies uniform pressure. The temperature, pressure and process time are all controlled to achieve the optimum material properties.


Slip castingSlip casting

• Slip (Ceramic particles suspended in water) is casted into porous plaster molds.• Complex shapes of thin uniform thickness

Process steps: • Slip preparation • Filling mold• Draining• Remove mold• trimming and drying


Tape Tape casting:Doctorcasting:Doctor bladeblade

• Products: substrates and packages for electronics• Thin sheets in large quantity and low cost• Slip contains about 50 vol% organic binder

Process steps:• Slip preparation• de-airing• tape casting• drying • machining and finishing


Plastic forming: ExtrusionPlastic forming: Extrusion

• Mixture of powder and additives are deformable under pressure.• 25 to 50 vol% organic additive.• Products: Dinnerware. Furnace tubes, pipe, bricks, tubular, catalyst support

Process steps:• Powder sizing• Batch formulation• Mixing • Extrusion• Drying • Densification


Injection moldingInjection molding

• Mixture of the ceramic powders with a thermoplastic polymer plus a plasticizer, wetting agentand anti-foam agent.• Products: any complex shapes

Process steps: • mixture preparation• preheat in the barrel• Press the heated materials• injection• Release part from die• Extraction of organics• Densification


� Evaporation from a free water surface: depend on the air temperature, air velocity, water content of air and water temperature

� Drying rates of ceramic body:

Rate of water loss in drying moist clay

Dark to light

DryingDrying


Densification /SinteringDensification /Sintering

� A removal of pores between the starting particles -> shrinkage -> strong bonding


Stages of sinteringStages of sintering

� 1st stage (initial)� Rearrangement� Neck formation

� 2nd stage (intermediate)� Neck growth� Grain growth� High shrinkage� Pore phase continuous

� 3rd stage (final)� Grain growth� Discontinuous pore phase� Grain boundary pores

eliminated


Microstructure after sinteringMicrostructure after sintering

Silicate ceramic: porcelain

Advanced Ceramics

Grain boundary

grain

Closed pores

Intergranular pores


Phase diagramPhase diagram

• Mullite3Al2O3.2SiO2

• Mullite melts inconguently at 1890ºC.

• Refractory ceramic materials


Glass Glass


Glass and crystallineGlass and crystalline

Changes in volume and temperature of a liquid cooling to the glassy or crystalline state.

� Reprinted with permission from Arun K. Varshneya, Fundamentals of Inorganic Glasses. Copyright © 1994 Academic Press, Inc.

Glass: • ไมตกผลึก • ขนาดเปลี่ยนแปลงอยางชาๆขณะเย็นตัว • มี Tg (glass transition temperature)

Crystal:• มีการเปลี่ยนแปลงขนาดอยางรวดเร็วที่ Tm (melting temperature)


Viscosity of silica glasses at varying Viscosity of silica glasses at varying temperaturetemperature

� Viscosity decreases with T

� Impurity lower Tdeform

� T deform : soft enough to deform or work

� Melting point: glass is fluid

� Working point: viscosity is 104 P, glass is easily deformed.

� Softening point: viscosity is 4 x 107 P, glass may be handles without dimensional alterations.

� Annealing point: removed residual stress

� Strain point:Tg will be above the strain point or below the strain point , fracture will occur before the onset of plastic deformation.


Glass formingGlass forming

Optical fiber

Pressing and blowing

Drawing and fiber forming


Float glassFloat glass


Heat treating glassesHeat treating glasses

� Annealing: Thermal stress (the difference in cooling rate and thermal contraction between the surface and interior regions.

� Annealing heat treatment -> heat at annealing point and slowly cooled to room temperature.

Hot Thermal stresscool


Glass temperingGlass tempering

� Tempered glass is manufactured through heat-strengthening process. Strength of Tempered Glass is roughly four times of the regular float glass.

� Manufacturing Process� Float glass is heated to 1150ºC

with tempering oven and then rapidly cooled with high-pressured air at high airflow rate.

� Heat-treated glass hasincreased resistance to impact,mechanical loads and thermalstress breakage as comparedto regular float glass and heat-strengthened glass


Toughened glassToughened glass

� Sheets of glass are heated to about 700º C in a furnace, then chilled rapidly by cold air blown onto both surfaces. Toughened glass is four to five times stronger than float glass and, if broken, disintegrates into small fragments with dull edges which are unlikely to cause serious injury. Glass is now a primary construction material and can form


Laminated glassLaminated glass

� PVB laminated :Two or more sheets of glass arebonded together with one or more layers ofpolyvinyl butyral (PVB), a plastic interlayer in sheetform. Its principle benefit being its performanceunder impact. The glass may fracture but anybroken fragments will remain firmly bonded to theinterlayer.

� Resin laminated glass is manufactured by pouring liquid resin into the cavity between two sheets of glass which are held together until the resin cures. This method is ideal for laminating glass having a heavily textured or patterned surface. Not all resin laminates have safety performance. They are principally used for decorative and accoustic purposes, where safety is normally of secondary importance.

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Ceramic Processingeng.sut.ac.th/ceramic/old/images_news/51.pdf · 7/15/2009 Ceramic Processing/S.Rattanachan 15 Stages of sintering 1st stage (initial) Rearrangement Neck formation