In this paper, the densification mechanism of ultrasonic compaction was analyzed using a force balance model. Ultrasonic compaction is quite a promising way to solve the lower mechanical property problem of green compact in the compaction process, although it has some obstacles to overcome for its various applications. Our model proposes that the resultant density is achieved as the applied and resistance forces reach the equilibrium state. Based on the proposed model, the ultrasonic compaction increases the density of green compact by reducing the internal friction between the powder and compaction die, as well as the internal friction among particles themselves. It was also found that during the powder compaction, the ultrasonic vibration mostly contributes to slipping and the rearrangement of the particles.

Densification Mechanism of Soft Magnetic Composites Using Ultrasonic Compaction for Motors in EV Platforms.

The influence of intense ultrasound applied during pressing on the optical and cathodoluminescent properties of conventionally sintered YSZ ceramics.

AFM was used to study the microstructure of nanoceramics prepared from a plasmochemical nanostructured powder ZrO2-5 wt.% Y2O3 by uniaxial dry compaction under strong ultrasonic (US) impact. It is found that nanoceramics samples have a complicated structural hierarchy consisting of crystallites, subgrains, grains, and agglomerates. The average size of structural elements in the sintered ceramics depends on nanopowder compaction conditions (compaction pressure and ultrasonic power). The XPS data on the chemical composition of nanoceramics fractures indicate correlation between Zr, Y concentrations (at. %) with average grain size. A significant Zr depletion (Y enrichment) of nanoceramics grain surface in comparison with the starting powder is discovered. The US-impact during nanopowder compaction is assumed to intensify intragrain diffusion during ceramics sintering

Microstructure of ZrO2 nanoceramics

Thermal destruction of indium and dysprosium hydroxides coprecipitated from solutions of their nitrate and chloride salts with ammonia was investigated by DTA/TG, XRD and MS methods. The features of these processes were revealed in solutions of different nature. It is shown that the method of thermal decomposition of mixed indium and dysprosium hydroxides coprecipitated from the solution of their chloride salts is environmentally appropriate and economically viable. The size of the coprecipitated hydroxide particles of indium oxide produced through thermal destruction at up to 500 °C (13 nm) allows us to recommend this method for production of nanodispersed mixed oxides of indium and dysprosium.

Thermal destruction of coprecipitated hydroxides of indium and dysprosium

AFM techniques were used to investigate the microstructure, internal grain structure and intergrain interfaces of zirconia nanostructured ceramics sintered from green compacts being compacted by the common uniaxial dry compacting of nanopowders and under powerful ultrasound action. It was confirmed an essential influence of nanopowder compacting conditions on microstructure of sintered ceramics. Introduction Structural or functional nanocrystalline ceramics has improved mechanical and functional properties (fracture toughness, strength, hardness, thermal conductivity, specific electronic or magnetic properties) caused by the reduction of grain size to the nanometer range. However, the microstructure of nanoceramics have an impact on these properties [1]. It has been shown that among various techniques of nanoceramics production the method of the uniaxial dry compacting of initial nanopowders under powerful ultrasound (PU) action is effective to sinter homogeneously dense ceramics having nanostructured grains. Using SEM and XRD analysis we observed the structural-scale hierarchy and phase composition of zirconia nanoceramics (ZrO2 5.4wt%Y2O3) fabricated from the plasma chemically synthesized zirconia nanopowder compacted with PU-action and without it. PU-action at compacting leads to the decrease of grain sizes and grain aggregate sizes in sintered ceramics. Nanoscale grains with mean size of 300 nm in such ceramics are layered packs of subgrains (around 20 nm x 200 nm x 200 nm), with the scaly particles of initial nanostructured powder as their nuclei. The ceramics consist of cubic and tetragonal phases of zirconia [2]. The aim of this work is AFM investigation of microstructure of the zirconia ceramics prepared using the above compacting method at varying PU power (W = 0, 1, 2, 3 kW) and compaction pressure (P = 50, 100, 150, 200 MPa). Experimental Methods and Specimens Nanoceramics were sintered from green compacts of ZrO2 –5%wtY2O3 nanopowder, produced by plasma-chemical synthesis [2]. The powder particles had the shape of polycrystalline plates (scaly morphology) with the average linear size of 150 nm; the mean crystallite size in such a plate was 23 nm. The elemental composition of the powder under study was measured by means of the electronprobe microanalysis using the EPMA-1400 (Shimadzu Inc.) installation. According to the measurements the powder contained 74.13% of Zr, 18.16% of O, 4.28% of Y, and 3.43% of C. The uniaxial dry compacting of green compacts 50 mm in diameter and with an aspect ratio of 0.05 was carried out under PU-action (PU-samples) and without it (O-samples) by the techniques described in [3,4]. Then compacts were sintered in air at Тs =1650°C up to density of 88%. The AFM measurements of the fracture surface of ceramics were performed in semi-contact mode using a scanning probe microscope P47-MDT (NT-MTD, Russia). We used the AFM studies in a mode of phase contrast (PC) images constructed by monitoring the phase shift of cantilever oscillation during the scan. The PC images contain information related to micromechanical properties of the sample materials (elastic modulus, viscoelasticity, or damping) and adhesion generated between the probe tip and the sample surface (surface energy, capillary forces). Recent works conducted by several investigators showed that the phase contrast images were highly effective for estimating structural inhomogeneity of materials [5]. The chemical composition of the fracture surfaces was studied by techniques of XPS-analysis described in [6]. Results and Discussion The microstructure of ceramics sintered from non-sonicated compacts has been determined to be different from that of the sonicated samples. By AFM investigation of the O-ceramics (W = 0 kW), the samples compacted at P=50 MPa had aggregates close to 2 μm involving grains of ~500 nm (Fig. 1a). At Р= 100 and 150 MPa scaly subgrain structure is formed with less subgrain sizes of 100-150 nm (Fig. 1b). The scaly structure becomes less pronounced and grains grow in size with the increase of P up to 200 MPa (Fig. 1c). Apparently, particle deformation at compacting results in the fusion of scales. Fig. 1. AFM image for O-ceramics (a P= 50 MPa, b P= 150 MPa, c P= 200 MPa). In support of above the histograms of grain size Dgr distribution in ceramic samples are shown in Fig. 2. They were calculated and plotted from AFM images using ImageJ 1.28 software. Regarding the PU-ceramics, all samples preserve in grains the scaly structure of initial powder (Fig. 3), because of the sonication of green compacts enables a lower rate of plastic deformation of particles during densification. At the same time the particle structure varies due to a mechanochemical activation under PU vibrations. Subgrains of 25-35 nm detected in the AFM-phase contrast mode for PU-samples are likely to correspond to the regions of stress concentration, that emerge at the secondary recrystallization in sintering process of the samples. The size of the detected structure is similar to the grain size of the initial powder. According to the AFM-data on size distribution of grains, the increase of W together with the increase in P sets a grain size limit, after which a reverse process – coagulation – becomes dominant. In this case grains can be as large as 1500 nm, which is comparable with the agglomerate sizes (Fig. 4a). Fig. 2. Ceramics grain size histograms. a b c

/pdf/investigation-of-structural-hierarchy-of-nanoceramics-31h7nw6pt9.pdf

Investigation of Structural Hierarchy of Nanoceramics Compacted by Dry Pressing under Powerful Ultrasound Action

The structural-scale hierarchy and phase composition of zirconia nanoceramics (ZrO2 — 54wt%Y2O3) fabricated from plasma chemical zirconia nanopowder compacted by ultrasonic (US) action and without it are studied and compared It has been shown, that US-action is rather effective method in technological process of nanoceramics production It involves a reduction of grain sizes and grain aggregate sizes of sintered ceramics; the grain in such ceramics is a layered pack of subgrains, nuclei of which are the scaly particles of initial nanostructured powder (NP) The ceramics consists of cubic and tetragonal phases of zirconia

Effect of Ultrasonic Compaction of Nanopowder on Structure and Fracture Character of Zirconia Nanoceramics

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Effect of Ultrasonic Compaction of Nanopowder on Structure and Fracture Character of Zirconia Nanoceramics