Micro-scaled alumina filled preceramic papers are used to produce paper-derived alumina ceramics. The thin (0.6 -0.7mm) and porous ceramics fabricated by this process can be, besides other possible applications, potentially utilized as setter plates on cordierite kiln furniture to avoid contact between the cordierite and powder metal substrate during sintering. The SiO 2 of the cordierite causes objectionable reactions with the powder metal. For this application it is important to investigate the thermal shock behaviour of the paper-derived alumina ceramics especially focusing the residual strength, because fast cooling is a common technique in the metal sintering industry to avoid cost and save production time. Two differently processed types of paper were investigated: calendered (additionally rollpressed) and uncalendered paper. Their remaining strength has been measured by the B3B-test after thermal shocks of a temperature difference DT = 100 K up to DT = 1000 K to evaluate the critical temperature difference DT C and the type of crack growth according to the method of Hasselman. In order to determine the cyclic thermal shock behaviour, at a temperature difference DT of 400 K and 600 K the ceramics have been quenched up to 5 times. The results of these investigations have been compared to the properties of tape casted alumina ceramics, a material already commercially used as setter plates. The initial strength of calendered paper-derived ceramics was 240 MPa. After quenching at a temperature difference DT = 600 -700 K, 50% strength decrease was observed. Temperature differences of more than 800 K caused A90% strength reduction. Uncalendered paper-derived ceramics have 185 MPa strength. Between thermo shocks of temperature differences DT = 700 -800 K, 50% of the strength reduction was measured. With thermo shocks of a temperature difference DT = 800 K only 10% of the initial strength remains. Generally the uncalendered ceramics showed a more stable crack growth than the calendered samples. Cyclic shocking at 400 K causes strength losses for both kinds of paper. But they differ in magnitude. While uncalendered paper only lost 7% strength, calendered paper strength was reduced by 20%, compared to their initial strength. This observation gets even more significant by shocking about 600 K. Calendered ceramics start with a higher initial strength and end up with a lower residual strength than the uncalendered ceramics. Only 30 MPa remain after five cycles of shocking, while the uncalendered paper-derived ceramics have 90 MPa remaining strength. Uncalendered ceramics show a better thermal stress resistance, which can be correlated to their higher porosity and therefore their increased crack deflection in the microstructure. Tape-casted alumina ceramics show a lower initial strength and lesser thermal shock resistance against simple and cyclic shocking. SEM pictures of the tape-casted alumina ceramics show large amounts of small, spherical shape pores, while paper-derived alumina microstructures show long cylindrical...
Paper‐derived ceramics are a new approach to produce thin, lightweight ceramic structures. These ceramics are derived from preceramic papers produced in a paper technological process. The amount of inorganic filler (e. g. stoneware) in the paper is increased up to 85 wt‐%. By firing at high temperatures the cellulose fibres are pyrolized and the inorganic content is sintered. One part of the technological process to produce papers is calendering. A calender consists of two rolls, between which the paper is rolled under pressure. By calendering the paper thickness is reduced and the surface of the paper is improved. Different calender parameters (pressure and temperature) are applied to the preceramic paper and ceramic properties like strength, density and surface roughness are investigated. The strength of paper‐derived stoneware ceramics can be improved by 125% to over 185 MPa by optimizing the calender process. Additionally paper‐derived stoneware ceramics were fired at 1180°C, 1200°C and 1220°C for 1 and for 2 hours at different support distances (10–150 mm) in order to determine the dependence of pyroplastic deformation on support distance. The results show a linear increase between maximum deformation and support distance by 1 hour dwell and a polynomic at 2 hours dwell. Furthermore the Pyroplastic Index (PI) was evaluated according to recent literature. The Pyroplastic Index was correlated to the amorphous content of the differently fired samples. With longer dwell and/or higher temperature the content of amorphous phase increases which lowers the bulk viscosity and supports the pyroplastic deformation. These investigations should give a direction for using paper‐derived stoneware ceramics for special design applications. Paper‐derived ceramics can be systematically deformed in many possible ways to achieve specific shapes.
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