Magnetic Pulsed Compaction Research Articles

Magnetic pulsed compaction of ferromagnetic nano-powders for soft-magnetic core

Densification of nanocrystalline Fe–6.5 wt.% Si powder with 20–40 μm particle size by uniaxial compaction and magnetic pulsed compaction was investigated in the temperature range of 23–400 °C and applied pressure range of 0.3–2.0 GPa. The microstructure of mechanically milled powder for 36 h showed a distribution of α-Fe phase 13–30 nm in size embedded in the matrix. The maximum relative density of Fe–6.5 wt.% Si green compact (core) was achieved more than 82%, by magnetic pulsed compaction (MPC) at room temperature under 2.0 GPa using annealed coarse powder (milled for 4 h), while it was less than 62% by a uniaxial static compaction. Finally, a remarkable effect of the compaction using the MPC process on the final density of Fe–Si alloy was measured in this research. The magnetic permeability of Fe–6.5 wt.% Si and Fe–6 wt.% Al–9 wt.% Si core is increased with the relative density increased.

Conductivity and structure features of Ce 1− xGd xO 2− δ solid electrolytes fabricated by compaction and sintering of weakly agglomerated nanopowders

The conductivity and structure features of Ce 1− x Gd x O 2− δ ceramics prepared using weakly agglomerated nanopowders with the average particle size of about of 15 nm are discussed. The powders were synthesized by the evaporation of coarse-grained target with the use of pulsed CO 2-laser radiation. The magnetic pulsed compaction method was applied to press a dry nanopowder to densities up to 55% of theoretical one. Owing to high activity of the starting powder and uniformity of the compacts, the sintering of ceramics up to near full density was realized in non-conventionally low temperature range of 1100–1300 °C. The structure of sintered ceramics with average grain sizes from the range of 100–300 nm was investigated by X-ray analysis and microscopy methods (AFM, SEM). The structure features are discussed in interrelation with the data on conductivity of ceramics. The significant deviation in lattice parameter of elementary cubic cell for sintered fine-grained ceramics as compared with the known data for conventional coarse-grained material was revealed.

Formation of a thin-layer electrolyte for SOFC by magnetic pulse compaction of tapes cast of nanopowders

From the analysis of the scientific and technical literature it is possible to determine the trend of development of technologies for preparation of thin films of solid electrolytes for SOFC as the most promising one. The use of powder compaction technologies and weakly agglomerated nanosized powders for this purpose has some advantages. The present study deals with physicochemical properties of electrolytes based on zirconia and ceria and electrochemical cells loaded with these electrolytes. Weakly agglomerated nanopowders with particles about 15 nm in size were produced by laser sputtering. Films 15–25 μm thick were obtained from nanopowders of the electrolytes by butyral resin slip casting. Uniaxial and radial magnetic pulse compaction of the cast films was performed at 0.1–1.6 GPa. The apparent density of the compacts accounted for 0.5–0.7 of the theoretical value. Sintering at temperatures of 900–1250 °C provided electrolytes having the relative density of 0.92–0.98. The analysis of the structure and the conductivity of the solid electrolytes, which was performed using samples shaped as flat thin disks 15–30 mm in diameter and 10 μm to 2 mm thick, and the examination of the electrochemical characteristics of the cells made of an ultrafine solid electrolyte in the form of tubes having the diameter of about 10 mm and walls 80–250 μm thick confirmed that the ceramic samples were gas-tight and had not laminations. The conductivity of, e.g. the YSZ electrolyte was 0.08–0.112 S cm −1. The electrochemical cells, which were tested in the regime of a fuel cell with a solid electrolyte synthesized using the proposed technologies, provided the specific power of about 1 W cm −2 at 800–850 °C even without optimization of the electrodes. Thus, the ultrafine solid electrolytes met the requirements imposed on SOFC ceramics.

자기펄스성형법 및 통전가압소결법의 연속공정을 이용한 고밀도 나노 알루미나 세라믹의 제조

In this study the nanostructured <TEX>${\alpha}-Al_{2}O_3$</TEX> ceramics have been fabricated by the combined application of magnetic pulsed compaction (MPC) and subsequent spark plasma sintering (SPS), and their density and hardness properties were investigated. The <TEX>${\alpha}-Al_{2}O_3$</TEX> prepared by the combined processes showed an increase by <TEX>$8.4\%$</TEX> in density, approaching the value close to the true density, and an enhancement by <TEX>$210\~400\;Hv$</TEX> in hardness, compared to those fabricated by MPC or static compaction method followed by sintering treatment.

Influence of the Structure on the Thermal Conductivity of the Al2O3 + Fe Nanocomposite

The structures of the single-phase coarse-grain (∼1000–3000 nm) corundum ceramic material synthesized by the traditional method and the nanocomposite composed of fine-grain (∼300 nm) corundum with iron nanoinclusions and prepared through magnetic pulsed compaction with subsequent sintering are studied using atomic-force microscopy and X-ray powder diffraction. For both ceramic materials, the thermal conductivity is investigated in the temperature range 150–700 K for the purpose of elucidating how the structure affects their thermal and physical properties.

Magnetic Pulsed Compaction of Nanopowders Based on Lithium-Containing Spinels

This paper reports on the results of investigations into the compactibility and structure of powder materials based on lithium-containing spinels that have been considered promising candidates for electrodes of lithium-ion batteries. Dynamic compaction of the powders is accomplished using the uniaxial magnetic pulsed compaction technique, which seems to be an efficient tool for assembling flat and cylindrical lithium-ion batteries. Experiments are performed with sol-gel-derived powders of the electrode materials belonging to the class of lithium-containing spinels (LiMn2O4, Li4Ti5O12), as well as with powder coatings applied in the form of a thin uniform film to an aluminum foil. The influence of the additive type [graphite, poly(vinyl difluoride), carbon black] and temperature on the compactibility of the powder materials under the action of pressure pulses with an amplitude up to 1.6 GPa is analyzed.

Stabilized Zirconia Nanoceramics Prepared by Magnetic Pulsed Compaction of Nanosized Powders

Ceramic materials with a fine structure are synthesized from zirconia-based nanopowders through magnetic pulsed compaction and subsequent sintering under different temperature-time conditions. The kinetics of crystallite growth and polymorphic phase transformations are analyzed. Unstabilized zirconia ceramic materials with a density of 96% and a crystallite size of 50 nm are prepared. It is found that, in the case when the ceramic materials with a cubic or tetragonal yttrium-stabilized zirconia (YSZ) matrix are synthesized with small additives of alumina nanopowders, the temperatures of active shrinkage and the polymorphic transformation γ-Al2O3 → α-Al2O3 are shifted to the high-temperature range, the density and microhardness of the final ceramics slightly decrease, and the size of α -Al2O3 crystallites does not exceed 100 nm. It is also established that the alumina additives have no noticeable effect on the growth of crystallites of the YSZ matrix

Gadolinium-Doped Ceria Ceramics with a Submicron Structure for Electrochemical Applications

The effect of the composition and density of ceramic materials on the electrical conductivity is investigated for solid electrolytes that are sintered from Ce1 − x GdxO2 − δ (x = 0.09–0.31) nanopowders and have a submicron structure (grain size, 0.1–0.3 µm). The powders are prepared through evaporation of a target with a pulsed CO2 laser, followed by magnetic pulsed compaction. The ceramic materials are synthesized at temperatures in the range 1100–1300°C in air. The effect of the composition on the electrical conductivity is studied for the ion-conducting ceramic samples in the density range up to a limiting value (99.8% of the X-ray density).

기계화학적 합금화된 나노 Fe-6.5Si 분말의 자기 펄스압에 의한 동적성형

Nano Fe-6.5wt%Si powders have been synthesized by mechano-chemical process (MCP) for an application of soft magnetic core. Owing to hard and brittle characteristics of Fe-6.5Si nano powders having large surface area, it is very difficult to reach high density more than 70% of theoretical density (~7.4 g/) by cold compaction. To overcome such problem a magnetic pulsed compaction (MPC), which is one of dynamic compaction techniques, was applied. The green density was achieved about 78% (~5.8 g/) by MPC at room temperature.

Fabrication of nanoceramic hin-wall tubes by magnetic pulsed compaction and thermal sintering

Gasproof thin-wall tubes of fine-grained ceramics based on zirconia and gadolinia have been produced by magnetic pulsed compaction and thermal sintering. Data on their structures and electric characteristics are presented. The tubes with a diameter of ~ 15 mm, wall thickness of ~ 0.7 mm, and length up to 80 mm are characterized by an uniform porous-free structure with a mean grain size in the range of 100 - 300 nm. The obtained ceramics possess high electrolytic properties.

Formation of metal matrix composite by magnetic pulsed compaction of partially oxidized Al nanopowder

New nanostructured Al matrix composite Al-Al2O3 with homogeneous distribution of oxide particles was fabricated by magnetic pulsed compaction of partially oxidized Al nanopowders preheated up to 400-500°C in vacuum. The particles of starting powders with the mean sizes of 50-200 nm represent the grains of metal aluminum covered with the shells from hard oxide Al2O3 in amorphous state. Under action of intensive pulsed pressure (1 GPa, 300 microseconds) the mass destruction of oxide shells with the formation of a metal matrix containing the reinforcing oxide nano-sized particles is realized. At pulsed compaction the simultaneous actions of high pulsed pressure, large mechanical pulse of particles and accompanying adiabatic heating are successfully combined. The sintered composite is characterized by fine homogeneous structure, full density and high microhardness (about 2 GPa), which are stable up to 400°C. The tensile strength of a material exceeds 350 GPa at room temperature.

SANS study of microstructural inhomogeneities on Al nano-powder compacts

The nano-crystalline materials have excellent mechanical and electrical properties compared to conventional materials. These advantages mainly come from their nano-sized grain structure. Usually the nano-crystalline materials are fabricated using nano powder. The optimum consolidation process is essential to obtain a fully densified structure. The quantitative characterization of remaining pores is important to study the consolidation process. SANS is the best technique to characterize the nano sized inhomogeneities in bulk samples. Al nano powder was synthesized by pulsed wire evaporation (PWE) method and the nano-powder compacts were fabricated by magnetic pulse compaction (MPC) method. The Aluminum oxide was observed by transmission electron microscopy (TEM) at the surface of Al nano powder. The small angle neutron scattering experiments were performed both at the instrument V4 in HMI and at the SANS facility in Korea Atomic Energy Research Institute (KAERI). The SANS data measured in KAERI were compared with the SANS data measured in HMI. The scattering intensity at high Q region increases with decreasing relative density, while the intensity at low Q region increases with increasing relative density in the Al nano powder compacts. The scattering intensity depends on the content of residual pores and Al oxide particles. The volume fraction of Al oxide particle increases with relative density due to the fragmentation of Al oxide layer. The extra scattering at low Q region results from the presence of Al oxide particles.

Breakage Mechanism of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Layer on Nano Al Powder by Magnetic Pulsed Dynamic Compaction

Magnetic Pulse Compaction (MPC), as a dynamic compaction, can be possible to reach higher relative density of nano metallic compacts owing to sufficiently high pressure and adiabatic heating in very short duration of an order of µsec. The present work is concerned with the magnetic pulsed compaction of the nano-sized aluminum powders, which particle size was a range of 50 ~ 100 nm passivated in air. The compaction pressure was 1.5 GPa for 300 µsec in the temperature range from 20°C to 500°C. The grain size of compacts was maintained less than 50 nm, which was analyzed by X-ray diffraction (XRD) using Scherrer method. From the calculation of adiabatic heat and of pressure induced by thermal expansion, and the observation by transmission electron microscopy (TEM), it was found that Al2O3 could be broken and dispersed with a few nano-meter sizes in the Al matrix and that the ultra fine and uniform bulk structure was maintained up to 400°C of compaction temperature.e

Nanostructures and mechanical properties of copper compacts prepared by magnetic pulsed compaction method

Abstract A main advantage of magnetic pulsed compaction (MPC) is the ability to reach higher relative density of compacts of metallic nano powders owing to sufficiently high pressure in a very short duration of an order of μs. In this study, the compacts of pure and passivated nano Cu powders synthesized by pulsed wire evaporation (PWE) method, have been prepared by the MPC method. The effects of the compaction temperature and passivation of Cu powders on a microstructural change and mechanical property were investigated. The measured green density of the compacts was higher, more than 95% of theoretical density. The optimally processed compacts showed the fine and homogeneous bulk structure without any grain growth. The pure and passivated Cu compacted at 300 °C exhibited maximum hardness of 2.4 and 2.6 GPa, respectively, that is almost two times higher than that of conventional micro-grained pure copper.

The effect of compaction temperature and pressure on the pores in nanostructured metal compacts prepared by magnetic pulsed compaction

The pore behavior of nano Al compacts prepared by magnetic pulsed compaction in a temperature range from 20°C to 300°C and under pressure of 0.7 and 1.6 GPa was studied by small angle neutron scattering (SANS) analysis. The size distribution and volume fraction of pores in the compact were determined by corrected scattering curves using a direct model fitting, under the assumption that the pores were spherical in shape. The densities obtained from the SANS analysis were well matched with those of direct measurement in the range of 76–95% of theoretical density. As the compaction temperature increased from 20°C to 300°C, the size of pores increased from 1.69 to 2.31 nm; however, the number of pores decreased from 169 to 71 (1/cmA2) in the case of 1.6 GPa compaction pressure. As a result, the density increased as the compaction temperature increased.

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

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 Al2O3 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°C, which showed neither further agglomeration nor grain growth during compaction and heat treatment due to the formation of Al/Al2O3 composites.

Nanoionics

Nanostructured materials are distinguished from conventional polycrystalline materials by the size of the structural units that compose them, and they often exhibit properties that are drastically different from the polycrystalline materials. In many instances, this can be related to large fractions of grain boundaries and hence large numbers of surface atoms. Defect thermodynamics in the bulk may then be governed by surfaces. As tailoring of fundamental properties becomes possible in the quantum confinement regime, existing materials may find new applications. In this review, recent studies of the properties of nanostructured electroceramics will be presented. The applications relate to electrochemical devices for energy conversion and storage. A breakthrough in metal hydride technology was achieved by preparing nanostructured hydride forming materials. In addition, several forms of carbon are being studied for hydrogen storage. Alkali-doped carbon nanotubes and nanosized SiC powders are promising as well. Consolidation of nanosized powders by dynamic compaction techniques leads to nanostructured microstructures. Recent examples using Magnetic Pulse Compaction (MPC) will be presented.

Synthesis and Compaction of Al-based Nanopowders by Pulsed Discharge Method

Synthesis and compaction of Al-base nano powders by pulsed discharge method were investigated. The aluminum based powders with 50 to 200 nm of diameter were produced by pulsed wire evaporation method. The powders were covered with very thin oxide layer. The perspective process for the compaction and sintering of nanostructured metal-based materials stable in a wide temperature range can be seen in the densification of nano-sized metal powders with uniformly distributed hard ceramic particles. The promising approach lies in utilization of natural uniform mixtures of metal and ceramic phases, e.g. partially oxidized metal powders as fabricated in our synthesis method. Their particles consist of metal grains coated with oxide films. To construct a metal-matrix material from such powder, it is necessary to destroy the hard oxide coatings of particles during the compaction process. This goal was realized in our experiments with intensive magnetic pulsed compaction of aluminum nanopowders passivated in air.

Influences of dynamic compaction on lithium intercalation into graphite anode

The influences of the dynamic compaction on the structure, morphology, and characteristics of lithium intercalation into compacted graphite powders and foils are presented. Lithium intercalation into the compacted graphite powders is not changed significantly by magnetic pulse compaction (MPC), while it is increased by explosive compaction (EXC) ascribed to the introduction of many boundary defects in the microstructure. A severe kinetic decrease of the intercalation capacity is observed for the compacted graphite foil because of the drastic morphology changes after MPC compaction. The adverse effects of compaction are reduced when the surfaces of graphite particles are modified by copper oxide.

Fabrication of Mg- and Ti-doped submicron-grained alpha-alumina-based ceramics

Nanocrystalline alumina ceramics were prepared by magnetic-pulse compaction followed by pressureless sintering. The relative density of green compacts exceeded 0.7. The medium in which the starting powders were classified (gas, water, or ethanol) was shown to have a significant effect on their sinterability. The effects of Mg and Ti additions on the sintering behavior of Al2O3 were studied under optimized heat-treatment conditions. Mg-doped α-Al2O3 ceramics containing uniformly distributed MgAl2O4 (≃4 wt %) and offering hardness values of up to 24 GPa were prepared. In the course of sintering, the grain size of these ceramics increases from 110 to 300 nm, and their relative density rises from 0.94 to 0.98.