Available online at www.sciencedirect.com Journal of the European Ceramic Society 33 (2013) 1981–1988 Depth and width of cured lines in photopolymerizable ceramic suspensions Susan P. Gentry, John W. Halloran ∗ University of Michigan, Department of Materials Science and Engineering, Ann Arbor, MI 48109, USA Received 14 January 2013; accepted 26 February 2013 Available online 21 March 2013 Abstract When a photopolymerizable ceramic suspension is illuminated, the cured region is characterized by the cure width and cure depth. The cure depth follows a semilogarithmic behavior with increasing energy dose, as expected for Beer–Lambert absorption, and is described by the depth sensitivity (S d ) and depth critical energy dose (E d ). The excess cure width, which is the cured width beyond the incident illumination width, is also found to increase with the logarithm of energy dose. This quasi-Beer–Lambert behavior can be described by a width sensitivity (S w ) and width critical energy dose (E w ). The semilogarithmic dose dependence is demonstrated for ceramic suspensions containing silica, mullite, alumina, and zircon powders. Broadening can be quantified by the broadening depth (D b ), which is the cure depth at which broadening begins to occur. It is shown that the broadening depth decreases with the logarithm of the normalized refractive index contrast between the powder and monomer solution. © 2013 Elsevier Ltd. All rights reserved. Keywords: Processing; Solid freeform fabrication; Gel casting; Photopolymerization 1. Introduction Photopolymerizable ceramic suspensions contain high volume fractions of ceramic powder (50–65 vol%) suspended in a photoactive monomer solution. Selective illumination of the suspension results in localized curing of the monomer by photopolymerization near the surface, allowing fabrication of intricate two-dimensional patterns. Photopolymerizable suspensions are used for the direct digital manufacturing of ceramic parts, which builds parts directly from the computer- aided drawing (CAD) files that were used to design the part. Ceramic stereolithography is one of these methods, using photopolymerizable ceramic suspensions in a commercial stereolithography apparatus. Conventional stereolithography uses an ultraviolet laser to selectively photopolymerize patterns on the surface of a photo-sensitive polymer resin. Scanning a laser beam on the surface creates lines of cured resin, which are combined in a raster pattern to produced cured layers. Many layers are combined to create three-dimensional plastic parts in a layer-by-layer fashion. Ceramic stereolithography replaces the commercial polymer resin with a ceramic suspension ∗ Corresponding author. Tel.: +1 734 763 1051; fax: +1 734 763 4788. E-mail address: peterjon@umich.edu (J.W. Halloran). containing low viscosity monomers, ceramic powder at a high solids loading (50–65 vol%), dispersant, and photoactive species to control the photopolymerization. When this photo- sensitive ceramic suspension is illuminated by the correct intensity and wavelength of light, the monomer polymerizes to form a ceramic green body. 1 The green body can then be fired to remove the organic binder and to sinter the powder, resulting in a three-dimensional ceramic part with a geometry that is given by the CAD file. This process has been demonstrated for a variety of applications, including microfabricated parts, 2 structural components, 3 and complex components 4 such as silica casting molds and millimeter-wave antennas from alumina. This paper addresses the shape of the cured profile, with emphasis on those factors that influence the width of photocured lines. For stereolithography using neat solutions without pow- der, the width of the incident illumination is controlled by the width of the laser beam. The incident energy dose is adjusted to control the depth of polymerization, so that it is matched to the layer thickness of the recoating mechanism. However, different compositions of ceramic suspensions cured with the same incident beam and dose will not necessarily have the same cure depth and cure width. One ceramic suspension may cure much wider than another ceramic suspension, given the same beam width. Stereolithography parameters include the spacing between cured lines and the distance from the nominal edge of 0955-2219/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jeurceramsoc.2013.02.033