Nanostructured Ceramics Research Articles

Field Assisted Sintering of Nanostructured Zirconia-Alumina Ceramics for Demanding Applications

ABSTRACTFlash and field assisted sintering techniques (FAST) have been demonstrated in many singular ceramic systems. However, little has been done to thoroughly investigate this phenomenon in binary systems. Zirconia-alumina composites are of interest because of their widespread use in demanding situations for health care, petrochemical and energy applications. The prospect of minimizing grain growth associated with FAST whilst achieving maximum densification is vital for the above applications to improve performance. Flash sintering behaviour of several zirconia-alumina formulations was investigated under a range of DC electric fields up to 700V.cm–1. At low alumina contents (<10 wt%) the flash behaviour was controlled by the zirconia phase; intermediate compositions (10-70 wt%) show a composite effect; and at high alumina contents (>75 wt%) the effectiveness of field assisted sintering drops off. These pointers allowed to gain further insight into the mechanisms of flash sintering and will help to develop pathways for the adaptation of the technique to process complex ceramic systems.

High Energy Density Hybrid Pseudocapacitors

Supercapacitors, also called electric double-layer capacitors (EDLC) or ultracapacitors, are of great interest for power applications due to their high power capability (~ 10 kW/kg) and long cycle life (> 10,000 cycles) [1]. However, supercapacitors have much smaller energy densities (< 10 Wh/kg) [2] than their battery counterparts (e.g., ~ 200 Wh/kg for Li-ion batteries) [3]. Historically, research efforts have been focused on incorporating nanostructured transition metal oxides into supercapacitors to increase specific capacitance and energy via Faradaic redox reactions (pseudocapacitance) [4]. Examples of these activities include electrochemically oxidized RuO2 on platelet carbon nanofiber [5], hydrothermal Co3O4 on carbon fiber papers [6], Co3O4/MnO2 nanowires [7], electrodeposition of MnO2 on carbon nanotube (CNT)-textile [8], wet chemistry of MnO2 in CNT [9], hydrothermal Ni(OH)2 on graphene [10], electrochemical anodization of NiO-TiO2 nanotubes [11], and solution synthesis of SnO2-graphenen composites [12]. More recently, atomic layer deposition (ALD) has been used to deposit V2O5 on CNT [13] and amorphous TiO2 on graphene [14]. While these studies have shown improved performance to various degrees, they were invariantly performed in aqueous electrolyte based supercapacitor cells which were limited in their energy density due to low electrochemical window of water (~ 1.23V) [15]. Here we present a novel approach utilizing ALD coated metal oxide on activated carbons (AC) in a non-aqueous electrolyte based, hybrid pseudocapacitor cell configuration analogous to that of lithium ion capacitors [16] where a faradaic intercalation anode (e.g., Li4Ti5O12 or graphite active materials) is paired with a non-faradaic cathode (e.g., AC active material). Our approach utilizes the ALD coated metal oxide on AC as the cathode to store charge and energy both electrostatically (non-faradaic) and electrochemically (faradaic). We will show that this hybrid pseudocapacitor approach leads to a significant improvement in energy density due to pseudocapacitive contributions from the ALD enabled metal oxides on AC cathodes. Figure 1 shows the first discharge voltage vs. specific capacity of an ALD metal oxide on AC based and AC control hybrid pseudocapacitor cells. The first discharge ALD metal oxide-based cells have higher initial voltages, or, fresh cell open circuit voltages (OCV’s) than the AC control cells. It was observed that the increased metal oxide loading (wt%) corresponded to higher OCV. ALD metal oxide-based cells delivered higher first discharge specific capacities than the AC control cells. These observations suggest the intended ALD metal oxide coatings on AC. Figure 2 shows formation discharge voltage vs. specific capacity of an ALD metal oxide on AC based and AC control hybrid pseudocapacitor cells. The ALD metal oxide-based, asymmetric hybrid pseudocapacitor cells showed distinctly different discharge voltage profiles than the AC control cells (without ALD metal oxide coating). The ALD metal oxide-based pseudocapacitor cells delivered higher specific capacity, capacitance and energy. The improved specific energy of the ALD metal oxide-based hybrid pseudocapacitor cells is due to higher specific capacity and higher average discharge voltage. The first round of an ALD metal oxide coating on AC displays an optimal metal oxide loading range (~20 wt%) for maximum specific capacity and energy improvement. The increased specific capacity, capacitance and energy of ALD metal oxide-based pseudocapacitor cells are attributed to pseudocapacitive contributions from the ALD coated metal oxide on AC cathode. A cell level specific energy improvement of ≥ 20% is projected in ALD metal oxide-based asymmetric hybrid pseudocapacitor cells. We will show strategies to achieve high rate capability and long-term cycleability of the ALD oxide-based, high energy density hybrid pseudocapacitor cells. References B.E. Conway, Electrochemical Supercapacitors, Kluwer Academic/Plenum, New York, 1999. A. Burke et al., UC Davis, UCD-ITS-RR-09-07, 2009. M. Alamgir et al., 08CNVG-0036, SAE Intl. Transp. Conf., Detroit, MI., 2008. A. Balakrishnan and K. Subramanian, Nanostructured Ceramic Oxides for Supercapacitor Applications, CRC Press, New York (2014). S. Kim et al., Bull. Korean Chem. Soc., Vol. 31, No. 12, (2010). L. Yang et al., Nano Lett. 12, 321 (2012). J. Liu et al., Adv. Mater. 23, 2076 (2011). L. Hu et al., ACS Nano, 5(11), 8904 (2011). W. Chen et al., Chem. Commun., 46, 3905 (2010). H. Wang et al., J. Am. Chem. Soc., 132 (21), 7472 (2010). J.H. Kim et al., Nano Lett. 10, 4099 (2010). H. Park et al., Bull. Korean Chem. Soc., 34(11), 3269 (2013). S. Boukhalfa et al., Energy Environ. Sci., 5, 6872 (2012). C. Ban et al., Nanotech. 24, 424002 (2013). R. Kotz et al. Electrochim. Acta, 45, 2483, (2002). G. Amatucci et al., J. Electrochem. Soc. 148, A930 (2001). Figure 1

Cold-Sprayed TiO2 Coatings from Nanostructured Ceramic Agglomerated Powders

In this work, synthesis of agglomerated TiO2, which is ready to be used after synthesis via a simple hydrolysis process, is described. The as-synthesized TiO2 powders were characterized by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Field Emission Scanning Electron Microscope (FE-SEM), Transmission Electron Microscope (TEM) and DTA. DTA curve indicated that addition of (NH4)2SO4 into the starting precursor has accelerated the hydrolysis of titanyl sulfate. The XRD patterns showed that single-phase anatase TiO2 was produced using low-temperature hydrolysis at 80°C. SEM confirmed that the as-synthesized powders were in agglomerated form and in micro size. Addition of a structure-directing agent (SDA), (NH4)2SO4, promotes agglomeration, with a denser closed packing of particle arrangement, which reduces the number of existing porosities in the synthesized powder. The TEM image showed that the primary particles were nanoparticles. The preliminary study of coating formation depicted that the powder obtained could be used as the feedstock powder for the cold spray (CS) process to make the coating as it can be deposited onto the ceramic tile substrate.

Characterization of nanostructured MgAl2O4 ceramics fabricated by spark plasma sintering

The aim of this work is to investigate the effect of sintering temperature on the properties of nanostructured spinel (MgAl2O4)fabricated by Spark Plasma Sintering (SPS). The starting material was a pure spinel (MgAl2O4) nanopowder. The sintering was carried out at T=1300°C, 1350°C and 1400°C under a pressure of 73MPa.The samples sintered at 1300°C exhibit a finer microstructure (mean grain size is about ~250nm) than those sintered at 1350°C and 1400°C. The relative density is about 99.93% at 1300°C, 99.63% at 1350°C and 99.58% at 1400°C due to the presence of some porosity in the fabricated samples. Samples sintered at 1300°C have a good transmittance (70% at 550nm and 78% at 1100nm) compared to those sintered at 1350°C and 1400°C.Due to their high density and fine grain size, samples sintered at 1300°C exhibit a Vickers micro-hardness Hv=18GPa, elastic modulus E=228GPa relatively more important than those measured on samples sintered at 1350°C (Hv=15GPa, E=172GPa,) and at 1400°C (Hv=12GPa, E=136GPa). They present the reverse behavior for fracture toughness kIC (1.05MPa √m for samples sintered at 1300°C, 1.43MPa √m for samples sintered at 1350°C and 2.23MPa √m for that sintered at 1400°C). The tribological behavior of the MgAl2O4ceramic was equally studied: the friction coefficient µ is measured and increases with sintering temperature µ=0.06, µ=0.13, µ=0.18, respectively for sintering temperature of 1300°C, 1350°C and 1400°C. The wear behavior is also examined and the mass loss increases with increasing sintering temperature.

Fabrication of Dense Nanostructured Bulk Ceramics by Means of Spark-Plasma-Sintering (SPS) Processing

In order to fabricate fine-grained and dense nanoceramic materials, the effect of spark-plasma-sintering (SPS) conditions was examined in MgAl2O4 spinel as a reference material. The SPS conditions, such as heating rate and loading temperature, strongly affected the microstructures. Although the density can be improved with decreasing the heating rate to less than 10 °C/min, it requires a long processing time. In order to fully utilize the high heating rate that is a primary advantage of the SPS technique, load controlling is very effective to achieve high density with maintaining fine grain size. An increase in the loading temperature during SPS processing can reduce the residual porosity in a spinel even at the widely used high heating rate of 100 °C/min. This suggests that for the SPS processing in ceramics, the load controlling is an important factor as well as the heating rate and sintering temperature.

Near-infrared down-conversion in Er3+–Yb3+ co-doped transparent nanostructured glass ceramics for crystalline silicon solar cells

A two-step energy transfer was achieved in Er3+–Yb3+ co-doped transparent glass ceramics containing CaF2 nanocrystals, which involved down-conversion of an absorbed visible photon to two emitted near-infrared photons.

Ferroelectric Ceramics: Local Distortions in Nanostructured Ferroelectric Ceramics through Strain Tuning (Adv. Electron. Mater. 10/2015)

In article number 1500190 Catherine Elissalde and co-workers successfully obtain nanostructured ferroelectric ceramics (grain size < 20 nm) using the unique combination of fast and low temperature processes including supercritical fluid synthesis and spark plasma sintering in air under high pressure. The stress generated at the nanograin scale can be controlled and used to tune the ferroelectric properties, thus opening new insights towards passive component integration.

Enhanced infrared transmittance properties in ultrafine MgAl2O4 nanoparticles synthesised by a single step combustion method, followed by hybrid microwave sintering

Infrared transparent ceramics found to have potential applications as infrared windows and domes in strategic defence and space missions. Synthesis of ultrafine nanostructured MgAl2O4 ceramics by a modified single step auto-igniting combustion technique, followed by sintering of the sample by resistive and resistive-microwave hybrid heating to high density and their excellent infrared transmission characteristics are presented in this paper. Structural characterisations of MgAl2O4 nanoparticles reveal that the as prepared powder is phase pure, with average crystallite size ∼15nm and possess a cubic structure. Optical band gap calculated using the Kubelka–Munk method is 5.75eV. The thermal stability of the nanopowder at elevated temperatures has been studied using thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). Hybrid heating yield a substantial reduction in sintering temperature and soaking time relative to the conventional resistive heating, and the samples achieved >99% density by microwave-resistive hybrid heating. Scanning electron micrograph (SEM) showed that the pellets are well sintered. The pellet sintered by hybrid heating showed a better transmittance of ∼79% in the UV–Visible region and ∼82% in the mid IR region compared to pellet sintered by resistive heating which has ∼68% in the UV–Visible region and ∼66% in the mid IR region. The results confirm the effective use of nanocrystalline powders from modified combustion synthesis as starting material for the development of high quality IR transparent windows and domes. In addition the microwave hybrid sintering technique employed in the present study also contributes to the results of better transmittance characteristics in highly densified MgAl2O4 ceramic pellets.

Local Distortions in Nanostructured Ferroelectric Ceramics through Strain Tuning

Ferroelectric materials are highly sensitive to grain size reduction because strain and ferroelectric polarization have a direct connection. Using 15 nm (Ba,Sr)TiO3 particles obtained by advanced supercritical synthesis and their densification by high‐pressure spark plasma sintering under air, reproducible and dense nanostructured ceramics are achieved. Taking advantage of the high pressure (up to 600 MPa) applied during the sintering step, the internal stress generated at the grain scale can be monitored to compensate for the particle surface stress due to size effect. Both the local dynamics observed by Raman scattering and the overall dielectric behavior consistently indicate a recovery of the ferroelectric properties as the sintering pressure is increased. This unique behavior shows that low‐temperature and high‐pressure processing enables designing nanostructured functional ceramics exhibiting original properties.

Continuous BaTi1−yZryO3 (0≤y≤1) nanocrystals synthesis in supercritical fluids for nanostructured lead-free ferroelectric ceramics

Abstract This paper addresses for the first time two of the main challenges in the field of electroceramics. The first one is the development of a continuous, fast and reliable synthesis method for producing sub-20 nm barium titanate zirconate (BaTi 1-y Zr y O 3 with 0 ≤ y ≤ 1–BTZ) nanocrystals over the whole solid solution, while keeping a narrow size distribution. The second one concerns the processing of dense and nanostructured lead free electroceramics highlighting the size effect on the crossover from ferroelectric to relaxor, in the case of grains smaller than 100 nm. This was achieved combining the supercritical fluid technology to produce in continuous and at moderate temperature (400 °C) BTZ nanocrystals, with Spark Plasma Sintering (SPS) to prevent grain growth during the sintering.

Atomic Layer Deposition of Metal Oxides on Activated Carbons for High Energy Density and High Performance Supercapacitors

Nanostructured ceramic oxides have shown to increase specific capacitance of supercapacitors via Faradaic redox reactions [1]. Many research and development efforts have focused on transition metal oxides as alternatives to expensive hydrous RuO2. Examples of these activities include hydrothermal Co3O4 on carbon fiber papers [2], Co3O4/MnO2 nanowires [3], electrodeposition of MnO2 on carbon nanotube (CNT)-textile [4], wet chemistry of MnO2 in CNT [5], hydrothermal Ni(OH)2 on graphene [6], electrochemical anodization of NiO-TiO2 nanotubes [7], and solution synthesis of SnO2-graphenen composites [8]. More recently, atomic layer deposition (ALD) has been used to deposit V2O5 on CNT [9] and amorphous TiO2 on graphene [10]. While these studies have shown improved performance to various degrees, they either involve the use of expensive materials, such as CNT or graphene, or processes that are not easy to implement for large scale production. Here we present an alternative and promising method to prepare high energy density and extremely high performance active materials for supercapacitors (or pseudocapacitors) by direct ALD oxide coatings onto high surface area, activated carbons (AC). Figure 1 shows discharge voltage profiles of cells containing ALD oxide coated electrodes, overlaid with a control cell without oxide coating. The cells were built in symmetric configuration with a conventional Li-ion electrolyte. The cells were cycled between 0 to 2.5V under a constant current of 0.15A/g at room temperature. Both NiO and V2O5 coated cells delivered a specific capacitance of 114 F/g (based on single electrode active weight), representing > 50% increase over the control cell (75 F/g). The enhanced specific capacitance of the ALD oxide coated cells is a result of pseudocapacitive contribution from the ALD oxides. Figure 2 shows rate capability test of the symmetric supercapacitor cells. The discharge capacitance is normalized to that of a low current density (0.15A/g). The ALD oxide coated cells showed excellent rate capability, with > 87% and 92% capacitance retention for V2O5 and NiO coated cells, respectively, when discharged at 15 A/g current. Both oxide coated cells showed superior rate capability performance to that of the control cell. The remarkable rate capability demonstrated by the ALD oxide coated cells is attributed to nano-sized oxide coatings afforded by ALD, which results in facile surface redox reactions. Figure 3 shows cycle life test where the symmetric supercapacitor cells were cycled between 0 to 2.5V at a constant current density of 1.5 A/g. The ALD NiO cell showed enhanced specific capacitance while maintaining extremely stable, long cycle performance with > 90% capacitance retention after 30,000 cycles. Such extremely stable cycle life suggests that the nano-structured oxides enabled by ALD are stress/stain free during charge and discharge cycles involving Faradaic charge transfer (redox) reactions. We will show that ALD enabled oxide coatings on AC allow for high operating voltages, leading to increased capacitance and energy density while demonstrating superior electrochemical performance stability to samples without ALD oxide coating. Our results in this study suggest pseudocapacitive oxide coating via ALD on AC is a promising material processing methodology for supercapacitor energy storage devices with significantly enhanced specific capacitance, energy density and electrochemical stability while maintaining exceptionally high rate capability and extremely stable cycle life. Such methodology is scalable economically when high throughput and high volume ALD processes are implemented. References Avinash Balakrishnan and K. R. V. Subramanian, Nanostructured Ceramic Oxides for Supercapacitor Applications, CRC Press, New York (2014). Lei Yang, Shuang Cheng, Yong Ding, Xingbao Zhu, Zhong Lin Wang, and Meilin Liu, Nano Lett. 12, 321 (2012). Jinping Liu, Jian Jiang, Chuanwei Cheng, Hongxing Li, Jixuan Zhang, Hao Gong, and Hong Jin Fan, Adv. Mater. 23, 2076 (2011). Liangbing Hu, Wei Chen, Xing Xie, Nian Liu, Yuan Yang, Hui Wu, Yan Yao, Mauro Pasta, Husam N. Alshareef, and Yi Cui, ACS Nano, 5(11), 8904 (2011). Wei Chen, Zhongli Fan, Lin Gu, Xinhe Bao and Chunlei Wang, Chem. Commun., 46, 3905 (2010). Hailiang Wang, Hernan Sanchez Casalongue, Yongye Liang and Hongjie Dai, J. Am. Chem. Soc., 132 (21), 7472 (2010). Jae-Hun Kim, Kai Zhu, Yanfa Yan, Craig L. Perkins, and Arthur J. Frank, Nano Lett. 10, 4099 (2010). Hun Park and Tae Hee Han, Bull. Korean Chem. Soc., 34(11), 3269 (2013). Sofiane Boukhalfa, Kara Evanoff and Gleb Yushin, Energy Environ. Sci., 5, 6872 (2012). Chunmei Ban, Ming Xie, Xiang Sun, Jonathan J Travis, GongkaiWang, Hongtao Sun, Anne C Dillon, Jie Lian and Steven M George, Nanotechnology 24, 424002 (2013). Figure 1

Multiscale Simulation of Porous Quasi-Brittle Ceramics Fracture

Multiscale computer simulation approach has been applied to research mechanisms of failure in ceramic nanostructured ceramics under dynamic loading. The obtained experimental and theoretical data indicate quasi-brittle fracture of nanostructured ZrB2 ceramics under dynamic compression and tension. Damage nucleation and accumulation in quasi brittle nanostructured ceramics were simulated under impact loadings. Fracture of nanostructured ultra-high temperature ceramics under pulse and shock-wave loadings is provided by fast processes of intercrystalline brittle fracture and relatively slow processes of quasi-brittle failure via growth and coalescence of opened microcracks. For nanostructures ZrB2 ceramics with porosity of 7 %, the compressive strength at strain rate of 1800 s-1 is equal to 2440±50 MPa, the tensile strength at strain rate of 300 s-1 is equal to 155±20 MPa.

Modeling of Mechanical Behavior of Ceramic Nanocomposites

Deformation and damage occurring at the meso-scale level in structured representative volumes (RVE) of modern nanocomposites in wide loading conditions were simulated. The computational models of a structured RVE of ceramic nanocomposites were developed using the data of structure researches on meso-, micro -, and nanoscale levels. The critical fracture stress on meso-scale level depends not only on relative volumes of voids and inclusions, but also on the parameters of inclusion clusters. The critical fracture stress at the meso-scale level depends not only on relative volumes of voids and strengthened phases, but also on sizes of corresponding structure elements. In the studied ceramic composites the critical failure stress is changed non-monotonically with growth of the volume concentration of strengthening phase particles. At identical porosity, concentration of nanovoids in the vicinity of grain boundaries causes the decrease in the shear strength of nanostructured and ultrafine-grained ceramics. It is revealed that the occurrence of bimodal distributions of the local particle velocity at the meso-scale level precedes the nucleation of microcracks. At mesoscale level of ceramic nanocomposites the pressure and particle velocity distribution don’t display a resonance behavior under submicrosecond single shock pulse loading or repeated pulse loadings.

Preparation of phase pure, dense fine grained ceramics by conventional and spark plasma sintering of La-substituted BiFeO3 nanoparticles

High density ceramics of the system Bi1−xLaxFeO3, 0≤x≤0.15, have been prepared starting from nanoparticles obtained by mechanosynthesis. The ceramics have been sintered conventionally at 850°C and by spark plasma sintering (SPS). Sintering conditions have been optimized to obtain single phase ceramics, and the microstructure of the ceramics has been compared. Ceramics prepared conventionally present grain sizes from 5μm to less than 1μm, whereas grain sizes by SPS are in the range from 50 to 100nm, which demonstrates that it is possible to obtain nanostructured ceramics of La-substituted BiFeO3 using mechanosynthesis followed by SPS at low temperature (625–650°C). The as-prepared SPS ceramics show low resistivity, indicating some reduction in the samples. However, after an oxidative anneal in air, ceramics are highly insulating at room temperature and electrically homogeneous. The high quality of the ceramics has also been demonstrated by XRD, EDX, Raman and DSC.

Optical transmission radiation damage and recovery stimulation of DSB: Ce3+ inorganic scintillation material

Recently, a new scintillation material DSB: Ce3+ was announced. It can be produced in a form of glass or nano-structured glass ceramics with application of standard glass production technology with successive thermal annealing. When doped with Ce3+, material can be applied as scintillator. Light yield of scintillation is near 100 phe/MeV. Un-doped material has a wide optical window from 4.5eV and can be applied to detect Cherenkov light. Temperature dependence of the light yield LY(T) is 0.05% which is 40 times less than in case of PWO. It can be used for detectors tolerant to a temperature variation between -20° to +20°C.Several samples with dimensions of 15x15x7 mm3 have been tested for damage effects on the optical transmission under irradiation with γ-quanta. It was found that the induced absorption in the scintillation range depends on the doping concentration and varies in range of 0.5-7 m−1. Spontaneous recovery of induced absorption has fast initial component. Up to 25% of the damaged transmission is recuperated in 6 hours. Afterwards it remains practically constant if the samples are kept in the dark. However, induced absorption is reduced by a factor of 2 by annealing at 50°C and completely removed in a short time when annealing at 100°C. A significant acceleration of the induced absorption recovery is observed by illumination with visible and IR light. This effect is observed for the first time in a Ce-doped scintillation material. It indicates, that radiation induced absorption in DSB: Ce scintillation material can be retained at the acceptable level by stimulation with light in a strong irradiation environment of collider experiments.

Crystal structure transformations induced by surface stresses in BaTiO3 and BaTiO3@SiO2 nanoparticles and ceramics

Lattice structure transformations in nanopowders of ferroelectric BaTiO3 and BaTiO3@SiO2 core-shell nanostructured ceramics were studied by nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) at the temperatures 120–450 K and particle size of 300 and 500 nm. NMR spectra of all studied samples in the paraelectric phase are identical to the spectra in bulk material indicating their perfect perovskite structure without visible influence of particle surface. However, we have found that surface of particles essentially influence the ferroelectric phase transitions detected by both NMR and EPR techniques. The strongest changes as compared to bulk material were observed in BaTiO3@SiO2 core-shell ceramics. Thorough analysis of NMR spectra suggests that the orthorhombic-like symmetry phase coexists here with other polar phases up to the Curie temperature. Depending on temperature, its relative volume varies from 25% to 100%. We assume that the orthorhombic-like symmetry phase is stabilized by anisotropic components of surface stresses which increase also global stability of polar state in nanoceramics to the temperature in bulk material. We summarize our results in a phase diagram.

Preparation of BaTiO&lt;sub&gt;3&lt;/sub&gt; Nano-structured Ceramics by Solvothermal Solidification Method

Preparation of BaTiO&lt;sub&gt;3&lt;/sub&gt; Nano-structured Ceramics by Solvothermal Solidification Method

Nanostructured glass ceramics based on fluorophosphate glass with a high content of rare-earth ions

The possibility of preparing transparent nanostructured glass ceramics based on fluorophosphate glass with a high content of lanthanide fluorides (Er, Ho, Dy, Yb, Tb, Nd, Eu, Pr, Ce, Sm) was demonstrated. The conditions of the formation and the form of nanocrystals containing rare-earth ions, the growth of which can be seen by the results of differential scanning calorimetry, X-ray diffraction analysis, and changes in the absorption and luminescence spectra, were determined.

Observation and Control of Pore Formation in SPS-Synthesized Alumina

Microstructure and control of pore formation in SPS-synthesized alumina were investigated by TEM and SEM observation. In addition, the relationship between the morphology of pores in the alumina and the bending strength of the alumina was examined. SPS consolidation at a high heating rate of 200 °C/min and at a high pressure of 100 MPa is effective for the fabrication of nano-structured and highly-transparent alumina without residual pores. It has been indicated that the interrelation between plastic deformation, neck formation, heating rate, densification and grain growth is important for the synthesis of nano-structured ceramics without residual pores.

Investigation of Nanostructure Formation of Alumina by Magnetic Pulse Compression and Subsequent Spark Plasma Sintering

Comparative analysis of the structure and properties of samples prepared from alumina nanopowder using conventional or magnetic pulse compression (MPC), and the subsequent spark plasma sintering (SPS) was performed. In sintered corundum first identified the presence of areas with bimodal structure and the regularities of their formation. It was concluded that one of the most promising technologies for creating nanostructured ceramics is the application of the MPC and the SPS. Alumina submicron structure was obtained with a grain size of about 200-300nm. The relative density of these samples determined by hydrostatic method was 95-96% of the theoretical.