TY - THES

T1 - Mould material analysis for highly porous alumina foams and in-situ characterisation of the drying processes

AU - Keidel, Christoph

N1 - embargoed until null

PY - 2013

Y1 - 2013

N2 - In the literature up to the present day the drying and shaping of dense ceramics is well published and researched, however there are hardly any publications for high porous ceramics. The objective of this thesis was to evaluate the drying process of high porous particle stabilised alumina foams as well as investigating the interaction of the foams with mould materials during shaping. To carry out the required research, two methods were devised and backed up to quantify the stated matters. The interaction between the mould material and the foam was characterised with a friction and detachment force-measuring rig that was developed especially for this purpose. With the test rig the influence of different mould materials and material treatments on the detachment force of foams and the friction was examined. The detachment force analysis showed that the force can be influenced strongly by the treatment of the mould material. Untreated and dry moulds made from water adsorbing materials (e.g. gypsum) lead to high detachment forces. These samples also featured large defects after shaping caused by the mould material. It has been observed that actually all samples produced without demoulding agent detached internally during the detachment measurement. The experiments carried out with foams produced on sheet materials as well as moist gypsums and special ceramic mould materials detached within a relatively narrow force level. Obviously the shearing strength of the foams is lower than the detachment force. The characterisation of the friction coefficients did not reveal any large variations for different materials. The friction forces were always observed to be smaller than the detachment forces. Therefore, research can be focused on reducing the latter. The shrinkage during the drying process has been investigated with a photogrammetric method devised to carry out in situ measurements of the drying shrinkage as well as in situ measurement of the weight loss during drying of ceramic foams in a climate chamber. The method devised during this research proved to be a very versatile one to characterise the shrinkage and moisture content of the foam during the drying process. In tests with high porous alumina foams the absolute drying shrinkage was found to be 0.45–07 % and the critical moisture was determined to be 34 ± 2%. In particular it was shown that the temperature influences the drying strongly, reducing the drying time substantially when raised. Implementing the drying characterisation method into R&D allows operators to obtain generate valuable data for the drying process from a single measurement.

AB - In the literature up to the present day the drying and shaping of dense ceramics is well published and researched, however there are hardly any publications for high porous ceramics. The objective of this thesis was to evaluate the drying process of high porous particle stabilised alumina foams as well as investigating the interaction of the foams with mould materials during shaping. To carry out the required research, two methods were devised and backed up to quantify the stated matters. The interaction between the mould material and the foam was characterised with a friction and detachment force-measuring rig that was developed especially for this purpose. With the test rig the influence of different mould materials and material treatments on the detachment force of foams and the friction was examined. The detachment force analysis showed that the force can be influenced strongly by the treatment of the mould material. Untreated and dry moulds made from water adsorbing materials (e.g. gypsum) lead to high detachment forces. These samples also featured large defects after shaping caused by the mould material. It has been observed that actually all samples produced without demoulding agent detached internally during the detachment measurement. The experiments carried out with foams produced on sheet materials as well as moist gypsums and special ceramic mould materials detached within a relatively narrow force level. Obviously the shearing strength of the foams is lower than the detachment force. The characterisation of the friction coefficients did not reveal any large variations for different materials. The friction forces were always observed to be smaller than the detachment forces. Therefore, research can be focused on reducing the latter. The shrinkage during the drying process has been investigated with a photogrammetric method devised to carry out in situ measurements of the drying shrinkage as well as in situ measurement of the weight loss during drying of ceramic foams in a climate chamber. The method devised during this research proved to be a very versatile one to characterise the shrinkage and moisture content of the foam during the drying process. In tests with high porous alumina foams the absolute drying shrinkage was found to be 0.45–07 % and the critical moisture was determined to be 34 ± 2%. In particular it was shown that the temperature influences the drying strongly, reducing the drying time substantially when raised. Implementing the drying characterisation method into R&D allows operators to obtain generate valuable data for the drying process from a single measurement.

KW - hochporöse Aluminiumoxidschäume

KW - Trocknung

KW - Schrumpfung

KW - Formenmaterial

KW - Formenmaterialbehandlung

KW - Trocknungsschrumpfung

KW - Trennmittel

KW - Lösekraft

KW - highly porous alumina foam

KW - Drying

KW - Shrinkage

KW - Drying shrinkage

KW - mould material

KW - mould material treatment

KW - demoulding agents

KW - detachment force

M3 - Diploma Thesis

ER -