FOOD. Science. Technology. Quality

Food. SCIENCE. Technology. Quality

Food. Science. TECHNOLOGY. Quality

Food. Science. Technology. QUALITY

Authors

C.H. SCHILLING, P. TOMASIK, M. SIKORA, J.C. KIM, V J. GARCÍA, C.P. LI

Title

Molding technical ceramics with polysaccharides

Abstract

Technical ceramics represent a large, international market dominated by electronic applications, such as insulators, substrates, integrated circuit packages, capacitors, and magnets. Typical manufacturing operations involve blending ceramic powder with organic liquids (e.g., polyethylene wax, organic solvents) to form a slurry that is molded into a three-dimensional shape before it is dried and kiln-fired. There are serious problems with the pyrolysis of these organics prior to kiln firing: (i) slow and costly heating (e.g., 200 °C for one week) is required to avoid the formation of cracks and gas bubbles, (ii) toxic fumes are emitted, and (iii) residual carbon contaminates the final microstructure. Aqueous suspending media are needed to eliminate these organic carrier liquids and evaporate safely without causing cracks, shape distortion, and microstructure contamination in sintered parts. Our experiments indicate that various dextrins and maltodextrins are useful to achieve this goal because of their natural tendency to sorb to oxide powders in aqueous suspensions. Small concentrations of these starch hydrolysis products (< 5 wt%) significantly improve molding paste rheology and enable clean pyrolysis with minimal carbon contamination of microstructures. In addition, these polysaccharides form strong, interparticle bonds after water evaporation, which enables processing of strong, crack-free ceramics before they are kiln-fired. In this paper, we begin by discussing background information on surface chemical aspects of controlling the rheology of ceramic molding slurries. Experiments involving sedimentation, filtration, extrusion, rheology, and surface chemical analysis are then presented which illustrate the practical potential of maltodextrins and dextrins as rheological modifiers in ceramic manufacturing.

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