1. 620211 Introduction to Ceramic EngineeringNutthita Chuankrerkkul 28 January 2011

2. RheologyGreek: rheos = stream currentRheology is the science of flow and deformation2 3. www.vscht.cz/sil/sil_cz/seminar/2003/13_Sarraf_Hamid.ppt 3 4. Common flow behaviours NewtonianPseudoplasticDilatant(shear thinning)(shear thickening) Shear stressShear stressShear rateShear rateShear rateViscosityViscosityShear rate Shear rateViscosity Shear rate 4 5. Capillary rheometerA rheometer is an instrumentused to measure rheologicalproperties like shear stress,shear rate, and shearviscosity.Capillary rheometry is atechnique whereby asample undergoes extrusionthrough a die of defineddimensions and the shearpressure drop across the dierecorded at set volumetricflow rates.5 6. Graph from capillary rheometer B AAB 6 7. The powder injection moulding processhttp://www.azom.com/details.asp?ArticleID=1080 7 8. Extrusion- - (conventional) (advance)- 8 9. ExtrusionExtrusion is used to form long shapes with constantcross sectional such as rods, tubes or honeycombs.Feedstock is similar to that used in powder injectionmoulding.The powder-binder mixture is placed in a heatedbarrel.The shaping die is at the exit of the barrel.Usually, the feedstock is evacuated during mixing toavoid bubbles in the extrudate.Once the binder set, it acts as glue to hold particles inplace during handling and is subsequently removedprior to sintering9 10. Examples of compositions used in extrusionCeramic Processing and Sintering 10 11. Four main types of additives are used: 1. Dispersant: decreases the viscosity of themixture & increases the volume concentrationof ceramic particles 2. Binder: ensures the cohesion of the greenparts 3. Plasticizer: is used to modify the intrinsicrheological behaviour of the binder 4. Lubricant: minimizes friction between themixtures and the mixing tools 11 12. ExtruderAn extruder is a machine that forces materialthrough a die by applying pressure.Two basic types include:1. piston type extruders2. screw type extruders12 13. Piston typePiston extrusion is a batch process, typicallyused for small scale forming, i.e. pilot or labtrials.http://www.loomis-gmbh.de13 14. Screw type http://www.designinsite.dkA complex and complicated piece of equipmentWear in the extruder can be serious, reduce life time of parts and barrel , and contaminates the product with metallic particles.14 15. HoneycombHoneycomb ceramics have a uniformlattice structure, low expansion coefficient, goodthermal shock resistance, higher specific surfacearea, low-pressure drop, and low density. Theyremade of either cordierite or mullite ceramicmaterials.Cordierite honeycomb ceramics are mainly used ascatalyst support for the automobile and forpurification waste gas of industrial organicprocessing, and as filters in melting metal. 15 16. VDO Ceramic Extrusion s Productshttp://www.youtube.com/watch?v=rmtFp-SV0tYCatalytic Converter Deconstructedhttp://www.youtube.com/watch?v=eox_vzpDm4kMaking a Three Part Clay Vase 17. ExtrusionPowderBinder MixtureExtrusion DebindingSintering 17 18. Ceramics Bingo.. 18 19. 19 20. Ceramic processing Powder compaction: dry pressing, cold isostaticpressing, hot isostatic pressing Plastic forming: extrusion, injection moulding :-using pressure to shape the green ceramic Casting: slip casting, tape casting:- using amould or using liquid/ slurry containing ceramic20 21. 21 22. 2 1. - solid casting 2. - drain casting 22 23. Slip castingAoki RYOTA Yan-Ze JIANG Japan China Petite Bijoux Assemblage-1Slip casting, porcelainSlip casting, bone chinahttp://blog-bat.blogspot.com/2007_05_01_archive.html23 24. Yan-Ze JIANG Jeongyong LEEChina South Korea Blue VaseSlip casting, porcelain Series of Vases W - Perforations 2006Casting, pierced decoration, porcelain, glazehttp://blog-bat.blogspot.com/2007_05_01_archive.html24 25. Solid casting & Drain castingCallister, Materials Science and Engineering, 200726 26. VDO Slip castinghttp://www.youtube.com/watch?v=W1YCRs6QtEYSlip Casting at the Emma Bridgewaterhttp://www.youtube.com/watch?v=vaUFN-q3_mkHow Toilets are made 27. 1. : ( )2. : 3. : 4. : : .. 28 28. - (Flocculation) (Deflocculation) 29 29. 30 30. (deflocculant) 31 31. Fully deflocculatedhttp://www.worldcyberu.com/samplelessoncp4.htm 32 32. Viscometer 33 33. Slip casting usually carried out at room temperature requires ceramic particles to be suspended in aliquid to form a slurry the slurry is then poured into a porous mould(liquid diffuses out through the mould) a particulate compact is formed in the mould process for traditional ceramics, i.e. table ware,sanitary wares advanced ceramics: alumina crucibles 34 34. Slip casting http://www.keram.se/eng/pdf/slam_eng.pdf35 35. Slip castinghttp://www.britannica.com/36 36. Plaster mould Plaster of Paris A material based on calcium sulfate hemihydrate, nominally CaSO40.5H2O. It is created by heating gypsum to about 150 C.2 CaSO42H2O 2 CaSO40.5H2O + 3 H2O (released as steam)This photo was taken by Rdiger Wlk 37 37. Water-to-plaster ratioConsistency 70Water 70 parts : Plaster 100 partsUsually by weight65 parts of water will give a heavy, dense plaster 75 parts of water to 100 parts of plaster will give a soft, absorbent mould which will wear easily and may break 38 38. Mould making http://www.lenham-pottery-models.co.uk/moldmaking/index_mold.html 39 39. Mould making http://www.lenham-pottery-models.co.uk/moldmaking/index_mold.html 40 40. Mould making http://www.lenham-pottery-models.co.uk/moldmaking/index_mold.html 41 41. Mould making http://www.lenham-pottery-models.co.uk/moldmaking/index_mold.html 42 42. Mould making http://www.lenham-pottery-models.co.uk/moldmaking/index_mold.html 43 43. Mould making http://www.lenham-pottery-models.co.uk/moldmaking/index_mold.html 44 44. Slip casting(1) Pour casting slip (2) When the slip(3) The mold is leftinto the mold,has time to set theinverted to avoidpouring against the required thickness,ripples spoiling thecollar. the surplus away.inside surface.http://potteryhk.com/Slip_casting.htm45 45. Slip casting(4) When the slip has (5) The mold is(6) The seam left bydried sufficiently, the carefully separatedthe mold is gentlyspare inside the collar & the cast removed.fettled or cleanedis trimmed away. when the cast is leather hard.http://potteryhk.com/Slip_casting.htm46 46. Drying and firing: Shrinkage 15-20% of original moist sizeFigure 11.27 Shrinkage of wet clay caused by removal of water during drying. Shrinkage may be asmuch as 20% by volume. Source: F. H. Norton, Elements of Ceramics. Addison-Wesley PublishingCompany, Inc. 1974. 47 47. Figure - Usual steps in traditional ceramics processing: (1) preparation of raw materials, (2) shaping, (3) drying, and (4) firingPart (a) shows the workpart during the sequence, while (b) shows the condition of the powders48 48. Tape casting 49. Tape casting- thin sheets of green ceramic cast as flexible tape- used for integrated circuits and capacitors- cast from liquid slip (ceramic + organic solvent)Callister, Materials Science and Engineering, 200750 50. Tape castinghttp://www.britannica.com/51 51. Tape casting- The process consists of a stationary casting knife,a reservoir for powder suspensions, a movingcarrier and a drying zone. In preparing flat sheetceramic membranes, the powder suspension ispoured into a reservoir behind the casting knife, andthe carrier to be cast upon is set in motion.-The casting knife gap between the knife blade andcarrier determines the thickness of the cast layer.Other variables which are important include reservoirdepth, speed of carrier and viscosity of the powdersuspension.52 52. Tape casting- The wet cast layer passes into a drying chamber,and the solvent is evaporated from surface,leaving a dry membrane precursor on the carriersurface. 53 53. Tape casting- process variables- Particle size and surface area- Formulation (binders, additives)- Cleanliness (dust, etc.)- Tape casting layer thickness- Lamination conditions- Binder burnout cycleshttp://www3.ntu.edu.sg/mae/Research/Programmes/Adv_Materials/tape.htm54 54. Tape castinghttp://www.britannica.com/ http://www.lintec.co.jp 55 55. Gel casting 56. Gel castingSilicon nitride turbine wheelAlumina gearshttp://www.ms.ornl.gov/researchgroups/process/cpg/gelpubs/GelChap.pdf http://www.ornl.gov/info/ornlreview/rev28-4/text/gelcast.htm 57 57. Mix and mill ingredients. Mix ceramic powderwith water (or a nonaqueous solvent), adispersant, and gel-forming organicmonomers (later linked together to form a"binder," or polymer-water gel that binds theceramic particles together).Deair. Place the mixture under a partial vacuumto remove air from it (otherwise bubblescould form, causing flaws in the finalproduct).Add catalyst. Add a "polymerization initiator" thatkicks off the gel-forming chemical reaction.Cast. Pour the ceramic slurry into molds made ofmetal, glass, plastic, or wax to cast it intodesired shapes.Create a gel. Heat the molds in a curing oven.The catalyst will cause the monomers to formlarge cross-linked polymer molecules thattrap water, creating a rubbery polymer-watergel. The gel permanently immobilizes theceramic particles in the desired shapedefined by the molds. It is this setting stepthat gives gelcasting its name.58 58. Unmold. Remove the ceramic from the mold.Dry. Let the cast ceramic dry thoroughly toremove most of the solvent, preferably at ahigh relative humidity (90%) to minimizewarping and cracking.Machine, if desired. The molded and driedmaterial looks and feels like chalk. It has veryhigh strength. At this stage of the process,this "green body ceramic" is stronger than agreen body ceramic made by anyconventional technique before sintering. Butthe gelcast ceramic is soft enough to be"green-machined" by carbide steel tools.Burn out binder and sinter. The last two stepscan be combined into one step. It involvesfiring, or baking, the ceramic at 550C andthen as high as 1800C in a furnace. Thisheating process accomplishes two goals. Atthe lower temperature, it "burns out" thepolymer remaining in the ceramic; thispolymer must be removed carefully or elsethe final product may have defects andcracks. At the higher temperature, thefurnaces intense heat sinters the ceramic,making it hard and dense.59 59. Gel castinghttp://www.ms.ornl.gov/researchgroups/process/cpg/gelpubs/GelChap.pdf60