Rheological and surface chemical characterization of alkoxysilane treated, fine aluminum powders showing enhanced flowability and fluidization behavior for delivery applications

Ludwig, Bellamarie; Miller, Timothy F.

doi:10.1016/j.powtec.2015.05.044

Cited by 16 publications

(11 citation statements)

References 21 publications

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“…Previous work in our research group has included the surface analysis of aluminum powders under ambient conditions [29,30]. In this contribution, we report the thermal behavior of metallic aluminum particles using model, high surface area alumina powders as reference materials.…”

Section: Introductionmentioning

confidence: 99%

Infrared Spectroscopy Studies of Aluminum Oxide and Metallic Aluminum Powders, Part I: Thermal Dehydration and Decomposition

Ludwig

Burke

2022

Powders

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In this work, we study three aluminum oxides (alpha, gamma, boehmite) and various oxidized metallic aluminum powders to observe their dehydration and decomposition behavior using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and scanning electron microscopy (SEM). We find that a temperature increase to the aluminum oxides (aluminas) reduces physically adsorbed water molecules to reveal the presence of hydroxyl groups. All three aluminas contained bridged hydroxyls located at 3670 cm−1; we found additional surface hydroxyls, which varied based on the oxidation state of the aluminum atom. Oxidized metallic aluminum powders that were aged resulted in similar behavior; however, the results differed depending on the method of aging. We find that naturally aged aluminum (NA-Al) powders with heavy oxidation in the form of the tri-hydroxide decomposed and did not reveal any detectable surface hydroxyl peaks. When aged using artificial methods (AA-Al), we find both surface hydroxyls, including bridged hydroxyls at 3670, 3700, and 3730 cm−1, and a remaining boehmite-like surface. These results show that metallic aluminum powders can be tailored for specific applications, regardless of age. It also elucidates different ways to pre-process the powders to control the surface oxide layer, corroborated by comparison with the models oxides studied herein.

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Section: Introductionmentioning

confidence: 99%

Infrared Spectroscopy Studies of Aluminum Oxide and Metallic Aluminum Powders, Part I: Thermal Dehydration and Decomposition

Ludwig

Burke

2022

Powders

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“…The hydrogen-bonding tendencies can be mitigated via the application of hydrophobic coatings, and much work has been aimed at developing new coatings and their deposition and stability, even outside the application of powders. − A common approach is to use the hydroxyl groups at the particle surface as reactive groups for the chemisorption of trialkoxysilanes (Figure ). While these coatings successfully improve flowability, there remains a need to understand the fundamentals of the Al-coating process. − …”

Section: Introductionmentioning

confidence: 99%

“…Triethoxysilane was chosen over other common silanes such as chloro- and methoxysilanes because the byproducts are safe in large quantities and ethoxysilanes are known to be more stable than methoxysilanes, allowing greater control of the silane deposition . Additionally, the efficacy of this silane as a hydrophobic coating can be seen through infrared spectroscopic analysis and rheology tests …”

Section: Introductionmentioning

confidence: 99%

“…19 Additionally, the efficacy of this silane as a hydrophobic coating can be seen through infrared spectroscopic analysis and rheology tests. 21 We explore a typical silanization reaction, initiated through acid hydrolysis of the silane to silanol, followed by selfcondensation and the formation of siloxane bonds and thermal grafting. Figure 1 is a schematic representation of a conventional approach to this process and the chemical species that are thought to be present at each stage�though the exact structure at any state may be different from that drawn.…”

Section: ■ Introductionmentioning

confidence: 99%

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²⁷Al Solid-State Magic-Angle Spinning NMR Studies of Aluminum Powder Particle Surfaces Treated with a Methyltriethoxysilane Coupling Agent under Acidic Conditions

2022

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We report on the reaction between methyltriethoxysilane (MTES) and micrometer-sized aluminum particles, facilitated by HCl. This reaction ultimately produces silane-coated aluminum particles. Using 27Al magic-angle spinning solid-state nuclear magnetic resonance, we find that aluminum powder starts with a mixture of tetrahedrally, pentahedrally, and octahedrally coordinated aluminum, with the pentahedral species dominating. In the presence of HCl, however, the aluminum undergoes a restructuring, so that octahedrally coordinated aluminum is the dominant species. Using diffuse reflectance infrared spectroscopy to confirm the deposition of silane, we find that this restructuring of the aluminum in the presence of HCl is both a sufficient and necessary condition for the deposition of the silane.

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“…Hydrophobic alkoxysilane-based coatings produced through bulk solution depositions have been shown to enhance the flow and fluidization properties of metallic aluminum powders (Ludwig & Miller, 2015).…”

Section: Introductionmentioning

confidence: 99%

The effect of gas phase polydimethylsiloxane surface treatment of metallic aluminum particles: Surface characterization and flow behavior

Ludwig

Gray

2017

Particuology

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Aluminum particles were exposed to gaseous polydimethylsiloxane (PDMS) to produce a hydrophobic surface coating for enhanced flow and fluidity. Surface retention of the intact PDMS was confirmed through infrared and X-ray photoelectron spectroscopy. Transmission electron microscopy was used to image cross-sections of the treated particles and energy dispersive spectroscopy element maps demonstrated the presence of a surface layer consisting of silicon and oxygen. Density measurements provided evidence for improvements in the Hausner ratio and Carr index of the PDMS-treated aluminum, indicating a reduction in inter-particulate cohesion through increased bulk density. Stability, compressibility, shear, aeration, and permeability of the particles were assessed by powder rheometer. The compressibility was reduced by approximately 32% following surface treatment, revealing a reduction in void space, while Mohr's circle analysis and shear testing determined that the extrapolated cohesion value was reduced by approximately 53% and the flow factor at 6 kPa was doubled. Aeration testing showed that the air velocity required to obtain a fluidized bed was on the order of 0.35 mm/s for the treated powder, whereas the raw powder could not be uniformly fluidized. PDMS may be a viable option for the large-scale treatment of aluminum powder for flow applications.

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Rheological and surface chemical characterization of alkoxysilane treated, fine aluminum powders showing enhanced flowability and fluidization behavior for delivery applications

Cited by 16 publications

References 21 publications

Infrared Spectroscopy Studies of Aluminum Oxide and Metallic Aluminum Powders, Part I: Thermal Dehydration and Decomposition

Infrared Spectroscopy Studies of Aluminum Oxide and Metallic Aluminum Powders, Part I: Thermal Dehydration and Decomposition

²⁷Al Solid-State Magic-Angle Spinning NMR Studies of Aluminum Powder Particle Surfaces Treated with a Methyltriethoxysilane Coupling Agent under Acidic Conditions

The effect of gas phase polydimethylsiloxane surface treatment of metallic aluminum particles: Surface characterization and flow behavior

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Rheological and surface chemical characterization of alkoxysilane treated, fine aluminum powders showing enhanced flowability and fluidization behavior for delivery applications

Cited by 16 publications

References 21 publications

Infrared Spectroscopy Studies of Aluminum Oxide and Metallic Aluminum Powders, Part I: Thermal Dehydration and Decomposition

Infrared Spectroscopy Studies of Aluminum Oxide and Metallic Aluminum Powders, Part I: Thermal Dehydration and Decomposition

27Al Solid-State Magic-Angle Spinning NMR Studies of Aluminum Powder Particle Surfaces Treated with a Methyltriethoxysilane Coupling Agent under Acidic Conditions

The effect of gas phase polydimethylsiloxane surface treatment of metallic aluminum particles: Surface characterization and flow behavior

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²⁷Al Solid-State Magic-Angle Spinning NMR Studies of Aluminum Powder Particle Surfaces Treated with a Methyltriethoxysilane Coupling Agent under Acidic Conditions