Slurry Chemistry Control to Produce Easily Redispersible Ceramic Powder Compacts

Abstract

The slurry-based Three Dimensional Printing (3DP TM ) process requires the production of an easily redispersible powder bed from a well-dispersed slurry. Understanding and control of the interparticle potential in the dispersed state, as well as in the dry consolidated state, are important. The strength of the particle-particle interactions in the dry state determines the redispersion efficiency. One factor that controls the interparticle strength is the chemical stability of the ceramic powders in the dispersed state. For unstable powders, a partial dissolution and/or hydration of the powders can occur and eventually impede the redispersion by forming insoluble salt bridges at the necks of the particles. Redispersion of the powder bed can be improved substantially by weakening the strength of the particle-particle bonds. The formation of strong chemical bonds between particles should be avoided by adjusting the slurry pH to an appropriate range where the powders are chemically stable in the slurry. Replacement of the chemical bonds by soluble physical bonds, using a low-molecular-weight hydrophilic polymer, also reduces the interparticle strength and enhances redispersion.

A review of process development steps for new material systems in three dimensional printing (3DP)

“…If the solution is particle loaded, the viscosity can be reduced by lowering the solids loading [61] or adding dispersant [42,19,71,72]. The viscosity can also be decreased by increasing the mean particle size while maintaining a fixed solid loading, but this option is of potentially limited use given the increased printhead wear and higher risk of nozzle clogging associated with larger particles [70].…”

“…For a polymer-loaded solution, the viscosity can be lowered by shortening the polymer chain [70,59] or lowering the polymer loading [22]. More universal approaches to altering the viscosity that can affect both particle-loaded and unloaded solutions include changing the pH [16,19,41] and diluting the fluid.…”

“…Successful realization of a specific 3DP process involves not only the printing process itself, but also the formulation of a suitable combination of a powder and binder material system along with process details for printing and post-processing, both of which play a major role in determining the mechanical properties of the parts produced. While a significant strength of 3DP is the wide range of potentially suitable materials, including polymers [2][3][4][5][6][7][8][9][10][11][12]; metals [13][14][15]; and ceramics [1,[16][17][18][19][20][21][22][23][24]14,[25][26][27][28][29][30] (or anything else that is available as a depositable powder with particle size in a suitable range), creating a specific instantiation of 3DP with a new material combination requires a number of steps: (1) formulation of a powder, (2) selection of a binding method, (3) formulation of the liquid binder and testing its suitability for printing and interaction with the powder, (4) specification of printing process parameters, and (5) specification of post-processing procedures.…”

Improved surface finish in 3D printing using bimodal powder distribution

“…Surface finish in 3D printed parts can be greatly improved by using very fine powders as they allow the use of thinner layers and also provide improved finish within each layer; Plate 1 shows examples of parts made with 1 mm alumina powders. But these powders have to be processed by the slurry method (Moon et al, 2000) because the fine powders cannot be spread dry. In this process, powders 2 mm or less are deposited as a wet slurry.…”

Ink‐Jet Printing of Binders for Ceramic Components

“…The unprinted powder bed is redispersed in a water bath to retrieve printed three-dimensional ceramic parts. 12 The resulting powder bed in the slurry-based 3DP process is fundamentally different from the powder bed in the dry powders-based 3DP. Spreading dry powder forms loosely compacted powder beds with low-packing density.…”