2716 Journal of the American Ceramic Society-Bitterlich and Heinrich Vol. 88. No. 10 ◇cer20-418 cer0-32.5 △cer20-40.6 10 ◇cer40-419 100●Cer40-40.8 100 △cer40-396 cer60-38.5 U 10 Cer 1 (c) shear rate/s-1 shear rate /s Fig 3. Viscosity measurements of laminating pastes with varying contents of pre-ceramic polymer and solven osity increases by a factor of 10 after jumping back to a low When the lamination paste, consisting of the ceramic powder, shear rate. The compositions containing the pre-ceramic poly- the pre-ceramic polymer, and the solvent, is applied onto the mer behave differently: at the jump to a higher shear rate, the green tapes, the liquid components spread into the porosity of viscosity overshoots before it becomes constant. The subsequent the tapes, which is about 30 vol%. In this stage, the tapes jump back to the low shear rate leads to a small decrease held together only by adhesion On heating the laminated tapes scosity because of the shear-thickening behavior(see Fig. 4) to 150.C, the solvent evaporates and cross-linking of the pre- The time necessary to reach a constant value is much shorter ceramic polymer begins. This cross-linked polymer is rigid and than that for the suspension without a polymer, which is because eads to a good green strength of the laminated stack. Further of the weaker inter-particle forces combined with the smaller more, it reduces the chemical sensitivity of the precursor to the change in viscosity. All slurries with a precursor show the same atmosphere (especially water), which is important because the characteristics amples had to be moved from the glove box to the pyre All graphs show a peak during the jump to the low shear rate furnace This effect occurs because the adjustment of the shear rate in the During heating of the laminated stack, the binder burns out viscous paste cannot follow the set value immediately. n the temperature range from roughly 300 to 450C with a of precursor po maximum rate at 393.C(Fig. 5(a)). The pyrolysis of the pre- was varied and the quality of the printed layers was assessed ceramic polymer takes place over a broader temperature range qualIt itatively. A viscosity of 6-10 Pa s at a shear rate of 50 s n two steps(Fig. 5(b)). It begins at approximately 350C and at shown to be best suited. The thickness of the dried screen round 800C, the mass loss is almost completed. during printed layers was around 30 um pyrolysis, the pre-ceramic polymer is converted into an inorcosity increases by a factor of 10 after jumping back to a low shear rate. The compositions containing the pre-ceramic poly￾mer behave differently: at the jump to a higher shear rate, the viscosity overshoots before it becomes constant. The subsequent jump back to the low shear rate leads to a small decrease in viscosity because of the shear-thickening behavior (see Fig. 4). The time necessary to reach a constant value is much shorter than that for the suspension without a polymer, which is because of the weaker inter-particle forces combined with the smaller change in viscosity. All slurries with a precursor show the same characteristics. All graphs show a peak during the jump to the low shear rate. This effect occurs because the adjustment of the shear rate in the viscous paste cannot follow the set value immediately. For different ratios of precursor:powder, the solvent content was varied and the quality of the printed layers was assessed qualitatively. A viscosity of 6–10 Pa s at a shear rate of 50 s
1 was shown to be best suited. The thickness of the dried screen￾printed layers was around 30 mm. When the lamination paste, consisting of the ceramic powder, the pre-ceramic polymer, and the solvent, is applied onto the green tapes, the liquid components spread into the porosity of the tapes, which is about 30 vol%.10 In this stage, the tapes are held together only by adhesion. On heating the laminated tapes to 1501C, the solvent evaporates and cross-linking of the pre￾ceramic polymer begins.15 This cross-linked polymer is rigid and leads to a good green strength of the laminated stack. Further￾more, it reduces the chemical sensitivity of the precursor to the atmosphere (especially water), which is important because the samples had to be moved from the glove box to the pyrolysis furnace. During heating of the laminated stack, the binder burns out in the temperature range from roughly 3001 to 4501C with a maximum rate at 3931C (Fig. 5(a)). The pyrolysis of the pre￾ceramic polymer takes place over a broader temperature range in two steps (Fig. 5(b)). It begins at approximately 3501C and at around 8001C, the mass loss is almost completed. During pyrolysis, the pre-ceramic polymer is converted into an inor￾Fig. 3. Viscosity measurements of laminating pastes with varying contents of pre-ceramic polymer and solvent. 2716 Journal of the American Ceramic Society—Bitterlich and Heinrich Vol. 88, No. 10