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Stabilizing Highly Loaded Silicon Nitride Aqueous Suspensions Using Comb Polymer Concrete Superplasticizers
Author(s) -
Rueschhoff Lisa M.,
Youngblood Jeffrey P.,
Trice Rodney W.
Publication year - 2016
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.14432
Subject(s) - dispersant , materials science , polyacrylic acid , chemical engineering , silicon nitride , polymer , shear thinning , aqueous solution , superplasticizer , composite material , acrylate , sodium polyacrylate , polymer chemistry , silicon , copolymer , organic chemistry , rheology , chemistry , metallurgy , compressive strength , raw material , dispersion (optics) , physics , optics , engineering
The stabilization of highly loaded silicon nitride suspensions will afford the processing of complex and near‐net shaped parts using methods such as injection molding or direct write additive manufacturing. In this study, aqueous silicon nitride suspensions up to 45 vol% solids loading were dispersed using commercially available comb‐type copolymer. These copolymers are used as superplasticizers in the concrete industry and are referred to as water‐reducing admixtures ( WRA s). Four different WRA dispersants were examined and chemical analysis determined that each was made up of a sodium salt of polyacrylic acid ( PAA ‐Na) backbone with neutral polyethylene oxide ( PEO ) side chains that afford steric stabilization. The general structures of the WRA s were compared to each other by measuring the relative areas of their prominent FTIR peaks and calculating a PAA ‐Na/ PEO peak ratio. Suspensions were made with as‐received silicon nitride powders with 5 wt% aluminum oxide and 5 wt% yttrium oxide added as sintering aids. Three of the four WRA dispersants studied were able to produce suspensions with 43 vol% solids loading and 5 vol% polymer dispersant, while exhibiting a yield‐pseudoplastic behavior up to 30 s −1 . At higher solids loading (45–47 vol%), a shift to shear‐thickening behavior was observed at a critical shear rate for these WRA s. Those WRA s with a lower PAA ‐Na/ PEO peak ratio displayed better stabilization and diminished shear‐thickening behavior. The vol% of the dispersant was optimized producing yield‐pseudoplastic suspensions containing 45 vol% solids loading with yield stresses less than 75 Pa, no shear‐thickening behavior, and viscosities less than 75 Pa·s for shear rates in the range of 1–30 s −1 .