Strength green bodies

Determine the temperature difference necessary to prevent cracking of a spherical green body when it is cooled down from 90 to 25°C in air if the green body strength is only 500 KPa. 

A ceramic suspension consists of ceramic powder, a solvent, often a dispersant to stabilize the ceramic powder ag2iinst a omeration, a polymeric binder to provide green strength after the green body has been dried, and often a plasticizer to lower the glass transition of the polymeric binder. All these additives must be compatible so the ceramic suspension has the desirable properties needed for green body fabrication. Many of these formulations used in industry are very secretive. 

Determine the temperature required to induce cracking in a mullite green body in the form of a plate with a void fraction of 0.4 that has a strength of only 200 KPa caused by interparticle van der Waals interactions. The following properties of muUite are needed ay = 5 x lO rC, E = 69 GPa [28, pp. 593, 770, 777], v = 0.25. 

Using Griffith analysis [28, pp. 797, 819] for the crack propagation in the green body, the green strength, o-, is given by... 

As the flaw size decreases, the green body becomes stronger. Also note, these Griffith type calculations give higher dry strengths than the van der Waals approach discussed previously. 

Strength of a Dry Green Body with Polymeric Binder... 

Binders are organic substances consisting of long chain molecules. They serve to improve the strength of the green body, to provide plasticity to a powder system during... 

Attempts have been made to relate the extrusion pressure and the strength of the green body to the water content of the plastic mixture. For a wide range of clays, the extrusion pressure p has been observed to depend on the water content w according to the equation ... 

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