PorousPorous Problems:Problems: Ceramics - …

1 Orosit y is one of thos e properti es wit h "kill orcure" effectivenes s. In th e right hands, in theright product, it confers exquisit e th e wrong hands or in appropriate applicat ion it canstop the process/p roduct, dead in its tr acks! Porosityshould be well understood, easil y identified,quantifiabl e and cont roll abl e. Why is it th en, th at itcan b e s o e asil y o ver looked o r misunderstood?APorous OverviewPorous properti es impact/confer on a ceramic , bothposit ive and negative. Porosit y is obviously desirablein light-weight products, th ermal insulation, catalystsupports, wickin g and filtr ation uses.

2 Negative aspectsin clu de friability, los s of strength, undesirable fluidabsorption formin g of Ceramics from powders necessarilygenerates porosit y by fixing, in 3-dimensions,posit ions and relationshi ps of in terp art icle pr essur e formin g meth ods generate higherporosit y and higher pr essur es produce les s. Thermaltr eatment, be it simultaneous wit h formin g (HIP) orsubseq uent to it (normal firing) is used to el imin ateso me, most or all porosit y dependin g on end size of th e pores depends on the particle sizedistribution and shape of th e starting powders andvarious addit ives (binders, liquids).

3 Of course, thela creates porosit y in the initial stages of firing dueto their los s or burning out. As sin tering is initiatedsmall pores may co alesce in to larger ones wit h eor no los s of overall pore volume. Loss of porevolume (porosity) must be accompanied byshrinkage o f t he Pore Problems BeginTrouble begi ns by not in place a program ofpore volume and size moni toring at al l stages ofproduction. From consider ation of mass , tr ue densityand geometr ic (envelope) volume one might believeone has all th e in formation just calcul ateporosity.

4 Maybe even det ermine it explicitl y by waterabsorption. But not knowin g th e pore sizedistribution can lead to ser ious misunderstandin ar e probabl y famil iar wit h looking at particle sizedistributions and making cert ain deductions. That'sOK for loose powders, but even th en one cannotdeduce how homogeneous th e blend is from a sizeanalysis. But when the part icles aain a fixed spatialorder by pr essin g, ca sting, extrusion etc. , the resultingpore size distribution plot wil l reveal thehomoge neit y of the blend as it exited the formingprocess.

5 If it 's wort h proceedin g, you wil l now beable to understand the path along which the sin teri ngprocess might take. Small pores wil l be th e mostthermally "reactive", larger pores les s so . Thereforedon' t be surprised if th e final piec e stil l has porosit y -if it started out wit h predominantly large , th e final porosit y is not just a fu nction ofinitial p orosit y but a lso o f p ore s Pore Size Quickly and ReliablyThe best available measur ement method is MercuryIntrusion Porosimetry.

6 Rapid (orders of magnitudefaste r th an gas sorption) very wide dynamic range(orders of magnitude larg er th an gas so rption -unrival ed for pores over microns) and yieldingnetwork str uctu re (more evident than gas sorptionbecause th e fluid penetration is sequential or serial innature). Mercur y intrudes from the outside, in, andwhile there e xists a pressure-pore s ize r elationship, i tis subject to the arrangement and connectivit y of thedifferent pores sizes in the network of in ternal fore , th e resul t not onl y yields pore sizein formation but also str uctu ral or network in forced intrusion of non-we mercur y in to apore network by applying an external force has beenuse d commerciall y for the best part of sixty years.

7 Sowhy is it not more widely used? Perhaps it was thelack of automation, the lack of in terp retation skills ormaybe noise and expense ? But that is not now thecase. Modern mercur y intrusion porosimeters offerhigh th roughput, very wide pore size range, a host ofautomat ed features and near-sil ent operation. Manyanalyses can be co mpl eted in een minutes or less -on t wo s amples a t o ne t , when you need pore size in formation for R&D,process cont rol and qualit y as surance in all fields ofcer amics , consider usin g the mercur y porosimetrymet hod.

8 Mercur y porosimetr y may reveal porositywhere there should be none, identify off-spec greencer amics and allow th em to be removed from theremaining proc ess es, and to opt imize firing condit all, kilns a re n ot i nexpensive t o o perate. For more information about fuel cell s and relatedmeasurement instruments, contact QuantachromeInstruments by phone: (561) 731. 4999, fax: (561) ,email: or MaterialsCeramicsPore size is calculated usin g theWashburn equation:Pore diameter = - ( 4 cos )/ PWhere = sur fac e tension, P = pres sure and = cont act size range is from approximately1mm down to 3.

9 5nmPore volume resolution be than microlit sures required as high as 60 ,000 psi, achieved usin g speciall y designed hydraul ic pres red in a number of standard testmethods includin g ASTM D4284,ASTM D4404, ASTM D2873, UOP578-02 , Problems:Porous Problems:by:Martin A. Thomas , Director of Busin ess DevelopmentQua ntachrome Inst ruments Yourself of Unwanted orUnexplained Porosity In YourFinal GT uses the extremelyeffective rapid mercury intrusion automatic pore size and pore volumedistribution analyzers, you will never haveporosity inconsistency in your products answers to your porosity related questionsand to speak to a Quantachrome consultant,call us at or email us atAdvanced Features:-Automatic air purge-V apor trap-Extremely quietThree Operating Modes.

10 -Pressure Scanning-A utospeed-Step-wisePoreMaster GT 2004-2010 Quantachrome