Novel Equipment for the Study of the Compaction of Fine Powders

Chen, Wei; Pechenik, Alexander; Dapkunas, S. J.; Piermarini, G. J.; Malghan, S.G.

doi:10.1111/j.1151-2916.1994.tb07259.x

Cited by 25 publications

(3 citation statements)

References 9 publications

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“…Although the γ-Al 2 O 3 is the only phase present, the sample became brittle and opaque, and it was not possible to measure its density and hardness, showing that the water plays an important role in the process of compaction. According to previous works, , it is very difficult to achieve high density in compacts from nanosize particles, and it was proposed that the use of suitable lubricant can improve their packing properties. This better packing promotes the sintering process through the condensation reaction of OH groups, which is the cold-sintering mechanism already discussed …”

Section: Resultsmentioning

confidence: 99%

Study of Nanocrystalline γ-Al₂O₃ Produced by High-Pressure Compaction

et al. 1999

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Using a high-pressure (HP) technique, samples of γ-Al2O3 were obtained by compaction at 4.5 GPa, in a toroidal-type apparatus, at room temperature (RT) and at higher temperatures. Compaction at RT produced crack-free, translucent, and dense samples. An improvement of these properties was observed for samples compacted at higher temperatures up to 565 °C. The nanocrystalline structure of γ-Al2O3 is retained, and the samples became transparent, showing high hardness (HV = 17 ± 1 GPa) and high density (95% of theoretical density). To understand the mechanisms of consolidation, a comparative analytical study by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) was conducted on the compacted γ-Al2O3 samples and the original powder. An FTIR study was done using the KBr technique and a high-vacuum cell, where the samples were submitted to thermal treatments up to 450 °C. For samples compacted at RT, a reduction in the content of adsorbed water was observed, compared to the original powder. Also, the surface hydroxyl groups became bridged, promoting dehydroxylation reactions, which were confirmed by TGA technique. In the dehydroxylation region, a weight loss was observed, and the water was released only at temperatures above 300 °C. For samples compacted simultaneously with temperature, the FTIR and TGA results did not show water release up to 500 °C. The compaction at temperatures higher than 565 °C yielded the formation of an aluminum hydroxide (diaspore) and the phase transformation from γ- to α-Al2O3. All these results support strongly the idea that the compaction at HP has caused the formation of a strong structure, with closed pores containing trapped water and hydroxylated internal surfaces, which confirms a proposed model for “cold-sintering”. At temperatures higher than 565 °C, this kind of structure is responsible for the formation of diaspore plus α-Al2O3.

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Section: Resultsmentioning

confidence: 99%

Study of Nanocrystalline γ-Al₂O₃ Produced by High-Pressure Compaction

et al. 1999

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“…Recent studies have shown that inhomogeneities in particle packing and the pore size distribution of the green body can be effectively resolved by controlling and manipulating the interparticle forces in the suspension during processing and forming, even when dealing with nanosized powders. 15,16 The distribution of the additives in the matrix become critical when many fine BaTiO 3 particles are associated with a low doping level of coarse-particle additives. Instead of solid-state mixing, chemical mixing techniques such as sol-gel coating, precipitation coating, and solution coating can be effective in enhancing the microhomogeneity (mixedness) of minor constitutents.…”

Section: Introductionmentioning

confidence: 99%

Dielectric Properties of Fine‐Grained Barium Titanate Based X7R Materials

Wang

Dayton

1999

Journal of the American Ceramic Society

119

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The next generations of multilayer ceramic capacitors are expected to have active ceramic layer thicknesses of 3 µm or less. To retain a reliable ceramic device, it is advantageous to engineer a uniform and fine-grained microstructure. In this study, a dense ceramic (>96% of theoretical) with finegrained size (<0.2 µm), and permittivity of 2800, meeting the EIA X7R temperature characteristic has been obtained using hydrothermally synthesized BaTiO 3 powder with precipitation-coated additives. The temperature coefficient of capacitance (TCC) and the dissipation factor (DF) are investigated as a function of active layer thickness and compared with that of a conventional coarse-grained dielectric of similar composition and fired density. The fine-grained ceramic maintained X7R characteristic in active layers as thin as 3 µm under 1 V AC and 1 kHz test conditions. For equivalent active thickness, the DF of the fine-grained version was consistently lower than the coarse-grained material. These results indicate that an improved voltage coefficient is possible for finer-grained materials under otherwise equivalent conditions. The possible causes for this behavior are also discussed.

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“…The development of nanostructured metallic materials has expanded to create more stable structures with various compaction methods using nano powders [1,2]. The important point in the compaction of nano powders is how to achieve full density while maintaining nano-sized microstructure.…”

Section: Introductionmentioning

confidence: 99%

The effect of temperature of magnetic pulsed compaction on the characteristics of nanostructured aluminum compacts

et al. 2003

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Magnetic pulse compaction (MPC) allows one to maintain a nanostructured state in nano powder metallic compacts and to achieve near theoretical density. In this study, nano Al powders of about 80 nm in diameter were prepared with the Pulse Wire Evaporation (PWE) method and passivated with a thin Al 2 O 3 layer on a surface about 2 nm thick to prevent further agglomeration and oxidation. The powders were compacted with the dynamic compaction of magnetic pulsed force. The effects of the compaction temperature and passivated oxide layer of Al powders on mechanical properties were investigated. The prepared compacts were considered as the composite materials of the metal-matrix containing oxides of their own metal. A fine and uniform bulk structure was kept up to 400 o C, which showed neither further agglomeration nor grain growth during compaction and heat treatment due to the formation of Al/Al 2 O 3 composites.

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Novel Equipment for the Study of the Compaction of Fine Powders

Cited by 25 publications

References 9 publications

Study of Nanocrystalline γ-Al₂O₃ Produced by High-Pressure Compaction

Study of Nanocrystalline γ-Al₂O₃ Produced by High-Pressure Compaction

Dielectric Properties of Fine‐Grained Barium Titanate Based X7R Materials

The effect of temperature of magnetic pulsed compaction on the characteristics of nanostructured aluminum compacts

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Novel Equipment for the Study of the Compaction of Fine Powders

Cited by 25 publications

References 9 publications

Study of Nanocrystalline γ-Al2O3 Produced by High-Pressure Compaction

Study of Nanocrystalline γ-Al2O3 Produced by High-Pressure Compaction

Dielectric Properties of Fine‐Grained Barium Titanate Based X7R Materials

The effect of temperature of magnetic pulsed compaction on the characteristics of nanostructured aluminum compacts

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Product

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Study of Nanocrystalline γ-Al₂O₃ Produced by High-Pressure Compaction

Study of Nanocrystalline γ-Al₂O₃ Produced by High-Pressure Compaction