Influence of powder pre-treatments on dispersion ability of aqueous silicon nitride-based suspensions

Oliveira, M.I.L.L.; Chen, Kexin; Ferreira, J.M.F.

doi:10.1016/s0955-2219(01)00202-3

Cited by 20 publications

(25 citation statements)

References 23 publications

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“…This matches with similar research finding an IEP of silicon nitride from 4 to 7 pH . The IEP of Si 3 N 4 can vary greatly based on the ratio of basic amine to acidic silanol groups present in the surface, the amounts of each varied by pretreatments of starting powders . At pH values above the IEP, the powders exhibited a negative charge in water due to the formation of surface SiO − resulting from the dissociation of surface silanol groups .…”

Section: Resultssupporting

confidence: 90%

“…These GPC results were used only to find the relative molecular weight as this particular method is most reliable for linear polymers, and is less accurate when measuring the molecular weight of branched and more advanced structures, such as the comb polymer copolymer dispersants used here. This magnitude of molecular weight of the polymers shown here is larger than other typical ceramic dispersants used with silicon nitride such as: Darvan 821A (6000 g/mol), Darvan C (13 000 g/mol), and Dolapix PC33 (16 000 g/mol) . This suggests that these larger molecular weight comb polymers could have a greater steric stabilization effect due to their larger size.…”

Section: Resultsmentioning

confidence: 67%

“…The amount of surface dissolution depends on the physical and chemical properties of the starting ceramic powder, as well as its manufacturing and processing history . Other research on producing aqueous silicon nitride suspensions has utilized calcination steps to form a thicker silica layer, and therefore more silanol surface groups, on the surface of the silicon nitride particles . While the increase of these silanol groups increase the particle's negative potential causing repulsion between particles, the increase in silica leads to less desirable high‐temperature mechanical properties of sintered bodies since they contain more intergranular silica glass .…”

Section: Introductionmentioning

confidence: 99%

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Stabilizing Highly Loaded Silicon Nitride Aqueous Suspensions Using Comb Polymer Concrete Superplasticizers

2016

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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 (WRAs). 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 WRAs 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 WRAs. Those WRAs 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.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 67%

Section: Introductionmentioning

confidence: 99%

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Stabilizing Highly Loaded Silicon Nitride Aqueous Suspensions Using Comb Polymer Concrete Superplasticizers

2016

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] This interest is fueled by potential applications such as windows and domes, [16][17][18] transparent armor, 19 light bulb envelopes, 20 scintillators, 21 and solid-state laser materials. [22][23][24][25][26][27][28][29][30][31][32] Advantages of poly-crystalline ceramics over single crystals include that they can be formed into a variety of shapes, can usually be produced in larger sizes more cheaply, and have enhanced mechanical and thermo-mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

Fabrication, optical transmittance, and hardness of IR-transparent ceramics made from nanophase yttria

Eilers

2007

Journal of the European Ceramic Society

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“…Traditionally, the precursors are mixed by dry or wet organic‐based mixing procedures and then consolidated by uniaxial and/or isostatic pressing before sintering. However, dry pressing technologies have limitations in terms of shape capability, the degree of homogeneity achieved in the green bodies, which decreases the yield and the reliability of the parts fabricated by these methods 7–11 . Colloidal shaping techniques enable particle agglomerates to be destroyed and the control of interparticle forces in order to obtain well‐dispersed systems and homogeneous particle packing upon consolidation.…”

Section: Introductionmentioning

confidence: 99%

Effect of Aging Time on the Stability of Aqueous Y‐α‐SiAlON Precursor Powder Suspensions

Pereira

Olhero

Ferreira

2010

Journal of the American Ceramic Society

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A temporarily stable aqueous slip of Y‐α‐SiAlON precursors powders (Si3N4, Al2O3, Y2O3, and AlN powders) was successfully prepared using an AlN powder thermo‐chemically treated against hydrolysis (AlN‐TC). Aqueous suspensions of AlN‐TC and an Si3N4‐based powders' mixture (Si3N4/Y2O3/Al2O3) proved to have long‐term stability under separate deagglomeration by ball milling. However, the kinetic stability decreased when the two suspensions were mixed in the required proportion to obtain a precursor Y‐α‐SiAlON composition. This work aims at understanding better the aging phenomena and evaluating the feasibility of using aqueous processing to fabricate Y‐α‐SiAlON ceramics. The pH and rheological behavior of the suspensions were monitored along the time. The effects of drying conditions (room temperature or humidity‐controlled chamber) of slip‐cast samples on the crystalline phases and oxygen contents before and after sintering were evaluated. Drying under a moisture‐rich atmosphere favored hydrolysis of AlN and the appearance of β‐SiAlON as the main phase after sintering. The results allowed concluding that there is a time frame within which Y‐α‐SiAlON ceramics can be fabricated from aqueous suspensions.

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Influence of powder pre-treatments on dispersion ability of aqueous silicon nitride-based suspensions

Cited by 20 publications

References 23 publications

Stabilizing Highly Loaded Silicon Nitride Aqueous Suspensions Using Comb Polymer Concrete Superplasticizers

Stabilizing Highly Loaded Silicon Nitride Aqueous Suspensions Using Comb Polymer Concrete Superplasticizers

Fabrication, optical transmittance, and hardness of IR-transparent ceramics made from nanophase yttria

Effect of Aging Time on the Stability of Aqueous Y‐α‐SiAlON Precursor Powder Suspensions

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