This paper offers a review of present achievements in the field of processing of ceramic-based materials with complex geometry using the main additive manufacturing (AM) technologies. In AM, the geometrical design of a desired ceramic-based component is combined with the materials design. In this way, the fabrication times and the product costs of ceramic-based parts with required properties can be substantially reduced. However, dimensional accuracy and surface finish still remain crucial features in today's AM due to the layer-by-layer formation of the parts. In spite of the fact that significant progress has been made in the development of feedstock materials, the most difficult limitations for AM technologies are the restrictions set by material selection for each AM method and aspects considering the inner architectural design of the manufactured parts. Hence, any future progress in the field of AM should be based on the improvement of the existing technologies or, alternatively, the development of new approaches with an emphasis on parts allowing the near-net formation of ceramic structures, while optimizing the design of new materials and of the part architecture.
Since more than a decade ago, the research on highly filled papers, as well as paper-derived inorganic materials, has greatly intensified. As presented in this review, highly filled papers as preforms allow for the design of porous or dense, multilayered, and geometrically complex structures. These paperderived ceramic-or metal-based materials are generated by the heattreatment of highly filled papers. Paper-derived materials are potential materials of choice for applications in transportation, energy-generation, environmental conservation, support structures, medical uses, and electronic components. Due to the adjustability of the filler content and the good machinability of highly filled papers, paper-derived sheets or multilayers may include intricate structures and tailored gradients in phase structure or porosity. Paper-derived multilayers also may contain cast ceramic tapes or other functionalized layers, as presented in some examples. Computer-aided manufacturing processes for paper-derived materials can be supplemented by prediction models for the sintering shrinkage in order to identify optimal post-processing steps, stacking orders and orientations for highly filled paper layers within multilayer green bodies. The accuracy of established component-level sintering models can be significantly increased by microstructure models of the highly filled paper. ParameterName Unit α Mismatch parameter for fiber cross-sections, Equation (5) Dimensionless α p Layer position in viscoelastic paper structure model, Equation (2) Dimensionless A 0 Initial amplitude of perturbation, Equations (15) 10 À6 m A(f) Parameter for evolution of instantaneous carbon conversion rate, Equation (7) Dimensionless A diff Source controlled diffusion parameter, Equations (9) 10 À7 N A match Modeling parameter, Equations (8) Dimensionless a Inter-particle contact-area radius, Equations (19) 10 À8 m a Local average pore area, Equation (4) 10 À6 m 2 b Pore geometry constant, Equation (20) Dimensionless ß evo , m evo Empirical constants for grain evolution in SOVS model, Equation (8) Dimensionless ß r(c)p Proportionality constant for bimodal packing fraction determination, Equation (18) Dimensionless C Modeling constant for debindering pressure calculation, Equation (7) 10 À6 (m 2 Á s)/K C 1 , C 2 , C 3 , C 4 , C 5 Parameters in the Riedel model that are determined by the dihedral angle, Equations (9) Dimensionless c glue Heat capacity of the adhesive layers, Equation (3) 10 À6 s c L , c s Volume fraction of larger-sized/smaller-sized particles in a multimodal mixture of particles, Equation (17)and (18) 10 0 vol% c vol Volume concentration of pulp fibers, Equation (4) 10 0 vol% γ, γ 0 Strain relaxation rate of calendered paper with initial value, Equation (2) Dimensionless γ B Grain boundary energy density, Equation (13) 10 0 J m À2 γ b Specific energy for grain boundary diffusion, Equation (9) 10 3 J mol À1 γ S Material surface energy, Equation (8, 11, and 13) 10 0 J m À2 Δ Half of the inter-particle boundary thickness, Equation (19) 10 À8...
LaCr1−xCoxO3 solid‐solution ceramics (x = 0.0–0.3) were prepared by pressureless sintering of a submicrometer powder. The powder was synthesized by a modified glycine nitrate process at 800°C. The electrical conductivity of the material sintered at 1600°C was measured by AC four‐wire method from room temperature to 1200°C. While undoped (x = 0) LaCrO3 revealed semiconductivity dominated by thermally activated mobility of small polarons over a vast temperature range, substitution of Co for Cr gave rise for a pronounced enhancement of conductivity at temperatures >200°C. XPS analysis showed that the concentration of Cr4+ on the Cr‐site and Co2+ at the Co‐site increased with Co substitution suggesting a thermally activated redox reaction Cr3+ + Co3+→Cr4+ + Co2+ to create additional charge carriers. Thus, Co doping offers a high potential for designing the electrical conductivity making LaCr1−xCoxO3 an interesting resistivity material for high temperature applications.
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