Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: I, Surface Chemistry of the Powder

Wang, Liwu; Sigmund, Wolfgang M.; Aldinger, Fritz

doi:10.1111/j.1151-2916.2000.tb01260.x

Cited by 20 publications

(10 citation statements)

References 23 publications

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“…Figure A shows the comparison of ζ-potential for three plates in neutral KCl solutions, and it can be found that the sequence of ζ-potential is as follows: SiO 2 < Si 3 N 4 –silica < Si 3 N 4 , even within the whole pH range from 2.0 to 5.5 (Figure S5). Therefore, it can be inferred that compared with the Si 3 N 4 surface, there will be more silanol or hydroxyl groups (Si–OH) connected with the SiO 2 surface in KCl solution, which makes Si 3 N 4 –silica more negatively charged. , Due to the difference in surface hydroxyl groups, it is reasonable to speculate that the Si 3 N 4 –silica surface will be more hydrophilic compared to that of the Si 3 N 4 surface. To prove this conjecture, contact angles were measured for three plates, as shown in Figures C and S5D.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, it can be inferred that compared with the Si 3 N 4 surface, there will be more silanol or hydroxyl groups (Si−OH) connected with the SiO 2 surface in KCl solution, which makes Si 3 N 4 −silica more negatively charged. 10,45 Due to the difference in surface hydroxyl groups, it is reasonable to speculate that the Si 3 N 4 −silica surface will be more hydrophilic compared to that of the Si 3 N 4 surface. To prove this conjecture, contact angles were measured for three plates, as shown in Figures 4C and S5D.…”

Section: ■ Resultsmentioning

confidence: 99%

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Contribution of a Tribo-Induced Silica Layer to Macroscale Superlubricity of Hydrated Ions

et al. 2019

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Hydrated ions (Li + , Na + , and K + ) are capable of achieving macroscale superlubricity under high contact pressures and high normal loads, which mainly originates from the hydration effect and tribochemical reaction related to the in situ formation of an interfacial nanostructured shear layer, namely, a silica-like tribolayer. Nevertheless, the mechanisms governing this macroscale superlubricity especially the growth activities and the specific contribution of such a silica layer formed through the tribochemical reaction to macroscale hydration superlubricity remains unclear. Here, using transmission electron microscopy and the X-ray photoelectron spectroscopy depth profile technique, we resolved the amorphous structure on the atomic scale and determined the thickness of the tribo-induced silica layer. Using atomic force microscope nanoindentation, we reveal the mechanical properties of the 6 nm-thick silica layer generated on a Si 3 N 4 ball, which has a smaller elastic modulus of 75 GPa. Through friction experiments and ζ-potential analyses, we report on two main effects of the silica layer on achieving superlubricity. First, the silica layer can significantly reduce the friction resistance between ceramic surfaces under boundary lubrication at both the macroscale and microscale. Second, the Si 3 N 4 surface exhibits a larger negative potential and better hydrophilicity due to the presence of the silica layer, thereby adsorbing more hydrated cations. The observations show that the superlubricity of hydrated ions can be obtained not only between two mica surfaces but also for ceramic surface pairs with lower surface charge density, higher elastic modulus, and even larger surface roughness. These findings demonstrate that a tribochemical pretreatment of surfaces allows the hydration effect to be effective to the macroscopic regime, thereby promoting the realization of hydration superlubricity.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Resultsmentioning

confidence: 99%

Contribution of a Tribo-Induced Silica Layer to Macroscale Superlubricity of Hydrated Ions

et al. 2019

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“…The surface chemistry of the powder has been described in part I. 18 The powder had a Brunauer-Emmitt-Teller (BET) specific surface area (S BET ) of 12.75 m 2 /g and a broad particle-size distribution, with an average particle size of d 50 ϭ 0.74 m. Much of the powder was oxidized, and the surface mainly consisted of silanol groups.…”

Section: (1) Materialsmentioning

confidence: 99%

“…17 In contrast to aqueous Si 3 N 4 suspensions, the selection of dispersants usually is conducted on an empirical basis for nonaqueous media, and only a few dispersants are known to be effective in organic media with reduced environmental risk. Based on a detailed analysis of the surface chemistry of the Si 3 N 4 powder (given in part I), 18 a novel class of dispersants can be designed that fulfill two primary requirements: the dispersant must have an anchor group that sufficiently adsorbs on the powder surface, and the dispersant must have a steric stabilizing chain that is long enough to overcome the van der Waals attraction and, overall, have good solubility in the dispersing medium that is used. 19 Hydrogen bonding results from the interaction of the anchor group with functional sites on the ceramic powder surface, and Lewis acid-base interactions have been identified as being responsible for the affinity of dispersants onto the ceramic powder in nonaqueous media.…”

Section: Introductionmentioning

confidence: 99%

Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: II, Dispersion of the Powder

Wang

Sigmund

Aldinger

2000

Journal of the American Ceramic Society

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A novel dispersant-O-(2-aminopropyl)-O-(2-methoxyethyl)-polypropylene glycol (AMPG)-was developed to disperse submicrometer-sized Si 3 N 4 powder in nonaqueous media, based on the surface chemistry of the powder. The dispersing phenomena and mechanisms have been studied systematically, both in model systems (using atomic force microscopy and ellipsometry) and in powder systems (using rheological behavior and adsorption isotherms). The results from the model systems correlated well with those from wet powder systems. It is demonstrated that highly concentrated (with a solids volume fraction of >0.50) and colloidally stable nonaqueous Si 3 N 4 suspensions can be realized using AMPG.

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“…Although Si 3 N 4 particles are always covered with an oxide layer, the surfaces of these particles are much more complex than those of oxides . Besides oxygen, commercial Si 3 N 4 powders contain varying amounts of additional impurities and surface groups, which can vary widely between manufacturers and synthesis routines . The interfacial properties of commercial Si 3 N 4 particles can be significantly affected by the presence of surface impurities, the most common of which are metals such as magnesium, calcium, aluminum, and iron …”

Section: Introductionmentioning

confidence: 99%

Surface modification of ultrafine silicon nitride powders by calcination

Yang

et al. 2019

Int J Applied Ceramic Tech

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Calcination was used for surface modification of ultrafine silicon nitride powders, which improved the flowability and dispersion stability of their slurries. Surface characteristics of the powder were investigated by X-ray photoelectron spectroscopy, which showed the generation of an oxide layer and partial elimination of amine groups on the particle surfaces. Ion analysis results suggested a drop in both ion conductivity and supernatant concentration after calcination. For the as-received powder, poor flowability and dispersion stability was caused by high-valence cations, which were detrimental to colloidal processing according to the Schulze-Hardy rule, and surface amine groups were also present; both of these were partly removed by calcination. The oxide layer formed on the particle surfaces hydrolyzes into silanol groups when the powder is dispersed in aqueous solutions, which was favorable for surface charging and formation of higher diffuse layer potential on the particles.These factors contributed to the improved flowability and dispersion stability of the slurries. K E Y W O R D Scalcination, oxide layer, powders, silicon nitride, slurries

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Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: I, Surface Chemistry of the Powder

Cited by 20 publications

References 23 publications

Contribution of a Tribo-Induced Silica Layer to Macroscale Superlubricity of Hydrated Ions

Contribution of a Tribo-Induced Silica Layer to Macroscale Superlubricity of Hydrated Ions

Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: II, Dispersion of the Powder

Surface modification of ultrafine silicon nitride powders by calcination

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