Search

There still remains a need for new methods of healing large bone defects, i.e., gaps in bone tissue that are too big to naturally heal. Bone regrowth scaffolds can fill the bone gap and enhance the bone regeneration by providing cells with a support to for new tissue formation. Coating of the scaffolds surface with nanocrystalline hydroxyapatite may enhance the osteoinductivity or osteoconductivity of such scaffolds. Here we present the sonocoating method to coat scaffolds with bioactive hydroxyapatite nanoparticles. We show a method, where the material to be coated is immersed in a colloidal suspension of nanoparticles with mean sizes of 10 nm and 43 nm in water, and high-power ultrasound waves are applied to the suspension for 15 min at 30 °C. High power ultrasounds lead to growth of cavitation bubbles in liquid, which implode at a critical size. The implosion energy propels the nanoparticles towards the material surface, causing their attachment to the scaffold. Using this technique, we produced a uniform layer of nanohydroxyapatite particles of thickness in the range 200 to 300 nm on two types of scaffolds: a porous β-TCP ceramic scaffold and a 3D-printed scaffold made of PCL fibers. In vivo tests in rabbits confirmed that the novel coating strongly stimulated new bone tissue formation, with new bone tissue occupying 33% for the nHAP-coated PCL scaffold and 68% for the nHAP-coated β-TCP after a 3-month test. The sonocoating method leads to formation of a bioactive layer on the scaffolds at temperature close to room temperature, very short time and in water. It is a green technological process, promising for bone tissue regeneration applications.

Hydroxyapatite (HAp) nanoparticles of tunable diameter were obtained by the precipitation method at room temperature and by microwave hydrothermal synthesis (MHS). The following parameters of the obtained nanostructured HAp were determined: pycnometric density, specific surface area, phase purity, lattice parameters, particle size, particle size distribution, water content, and structure. HAp nanoparticle morphology and structure were determined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray diffraction measurements confirmed crystalline HAp was synthesized, which was pure in terms of phase. It was shown that by changing the synthesis parameters, the diameter of HAp nanoparticles could be controlled. The average diameter of the HAp nanoparticles was determined by Scherrer’s equation via the Nanopowder XRD Processor Demo web application, which interprets the results of specific surface area and TEM measurements using the dark-field technique. The obtained nanoparticles with average particle diameter ranging from 8–39 nm were characterized by having homogeneous morphology with a needle shape and a narrow particle size distribution. Strong similarities were found when comparing the properties of some types of nanostructured hydroxyapatite with natural occurring apatite found in animal bones and teeth.

Zinc oxide nanoparticles codoped with Co2+ and Mn2+ ions (Zn(1&minus, x&minus, y)MnxCoyO NPs) were obtained for the first time by microwave solvothermal synthesis. The nominal content of Co2+ and Mn2+ in Zn(1&minus, y)MnxCoyO NPs was x = y = 0, 1, 5, 10 and 15 mol % (the amount of both ions was equal). The precursors were obtained by dissolving zinc acetate dihydrate, manganese (II) acetate tetrahydrate and cobalt (II) acetate tetrahydrate in ethylene glycol. The morphology, phase purity, lattice parameters, dopants content, skeleton density, specific surface area, average particle size, average crystallite size, crystallite size distribution and magnetic properties of NPs were determined. The real content of dopants was up to 25.0% for Mn2+ and 80.5% for Co2+ of the nominal content. The colour of the samples changed from white to dark olive green in line with the increasing doping level. Uniform spherical NPs with wurtzite structure were obtained. The average size of NPs decreased from 29 nm to 21 nm in line with the increase in the dopant content. Brillouin type paramagnetism and an antiferromagnetic interaction between the magnetic ions was found for all samples, except for that with 15 mol % doping level, where a small ferromagnetic contribution was found. A review of the preparation methods of Co2+ and Mn2+ codoped ZnO is presented.

This paper reports the possibility of changing the size of zinc oxide nanoparticles (ZnO NPs) aggregates through a change of synthesis parameters. The effect of the changed power of microwave heating on the properties of ZnO NPs obtained by the microwave solvothermal synthesis from zinc acetate dissolved in ethylene glycol was tested for the first time. It was found that the size of ZnO aggregates ranged from 60 to 120 nm depending on the power of microwave radiation used in the synthesis of ZnO NPs. The increase in the microwave radiation power resulted in the reduction of the total synthesis time with simultaneous preservation of the constant size and shape of single ZnO NPs, which were synthesized at a pressure of 4 bar. All the obtained ZnO NPs samples were composed of homogeneous spherical particles that were single crystals with an average size of 27 ± 3 nm with a developed specific surface area of 40 m2/g and the skeleton density of 5.18 ± 0.03 g/cm3. A model of a mechanism explaining the correlation between the size of aggregates and the power of microwaves was proposed. This method of controlling the average size of ZnO NPs aggregates is presented for the first time and similar investigations are not found in the literature.

The aim of the paper is to explain the mechanism of zinc oxide (ZnO) nanoparticle (NP) size control, which enables the size control of ZnO NPs obtained in microwave solvothermal synthesis (MSS) within the size range between circa 20 and 120 nm through the control of water content in the solution of zinc acetate in ethylene glycol. Heavy water was used in the tests. The mechanism of ZnO NPs size control was explained, discussed and experimentally verified. The discovery and investigation of this mechanism was possible by tracking the fate of water molecules during the whole synthesis process. All the synthesis products were identified. It was indicated that the MSS of ZnO NPs proceeded through the formation and conversion of intermediates such as Zn5(OH)8(CH3COO)2 · xH2O. Esters and H2O were the by-products of the MSS reaction of ZnO NPs. We justified that the esterification reaction is the decisive stage that is a prerequisite of the formation of ZnO NPs. The following parameters of the obtained ZnO NPs and of the intermediate were determined: pycnometric density, specific surface area, phase purity, average particles size, particles size distribution and chemical composition. The ZnO NPs morphology and structure were determined using scanning electron microscopy.

The aim of the study was to investigate the impact of pulsed electric field (PEF) treatment on the convective drying kinetics of a carrot and color and microstructure changes of the dried product. Samples were treated by PEF with the specific energy input equal to 5.63, 8 and 80 kJ · kg−1. After PEF treatment, thermal conductivity and electrical conductivity were measured. Drying time of the PEF-treated samples was reduced up to 8.2% (Ws = 8 kJ · kg−1, 5 kV · cm−1; 10 pulses) in comparison to intact tissue. Statistical analysis showed that Midilli et al.’s model was considered to describe the kinetics of the process the most precisely. Pulsed electric field treatment increased the effective water diffusion coefficient up to 16.7%. Moreover, PEF treatment and drying caused the alteration of the sample color. After drying, the lightness and chroma were higher or unchanged in comparison to the intact tissue. The dried PEF-treated samples exhibited significantly higher redness (higher value of a* para...

The aim of this study was to analyze the impact of pulsed electric field treatment on selected bioactive compound content and color of plant tissue. For this purpose apple and carrot tissues were treated by pulsed electric field (PEF) at 0, 1.85, 3, 5 kV/cm and 0, 10, 50 and 100 pulses which corresponded to the specific energy input of 0–80 kJ/kg. The electroporation efficiency was assessed by the means of electrical conductivity (EC) measurement. Immediately and 60 min after the PEF application the optical properties of both materials were measured and compared. Moreover, the total carotenoid content was determined in the case of carrot, whereas in the case of apple the free radical scavenging activity and the total polyphenol content was examined. The highest EC values were observed when 30 and 40 kJ/kg were delivered to the carrot and apple samples, respectively. The total color change (ΔE) of carrot tissue as a result of PEF treatment was smaller (ΔE0min = 1.64–5.51; ΔE60min = 1.33–3.91) than in the case of apple samples (ΔE0 = 0.48–7.20; ΔE60 = 1.25–21.87) which could be linked to the different chemical compositions of these raw materials. The application of PEF at 1.85 kV/cm regardless of the applied pulse number increased the total carotenoid content (TCC) up to 11.34%. In turn, the maximal increase of total polyphenolic content (TPC) and antioxidant activity (EC50) in the case of apple tissue was observed for samples treated by 10 pulses at 1.85 kV/cm. The utilization of 3 kV/cm decreased the TCC up to 25.33% whereas the application of PEF at 5 kV/cm and 100 pulses decreased the TPC and EC50 up to 35.93 and 32.95%, respectively. The research indicated that PEF can be used to enhance the extractability of bioactive compounds from plant tissue and to modify its color. Industrial relevance The paper discusses the impact of PEF treatment on bioactive compound concentration in apple and carrot tissues. Moreover, it deals with the color changes after the PEF treatment. Due to the fact, that pulsed electric field could be applied to the processes which depend on the heat and/or mass transfer such data should be considered of great importance. Firstly, the bioactive compounds (e.g., polyphenols, carotenoids) are very important regarding both their nutritional value and technological functionality (antioxidant properties, coloring agent production, etc.). Moreover, the PEF treatment efficiency depends on many different factors linked to the raw material properties and to the treatment protocol and conditions. This paper demonstrates that it is possible to improve the extractability of the carotenoids or polyphenols by PEF application. However, incorrectly selected PEF treatment parameters can result in the decrease of the bioactive compounds content in the solid material, as described and discussed more deeply in the paper. Color is one of the most important quality parameters. Especially that it is directly perceived by the consumers. As it can be read in the paper pulsed electric field treatment could be used to modify the color of plant tissue before any further processing. Such data is also important considering the minimal process food, which PEF could be involved in (e.g., special minimal process food for elderly people). In the presented experiment the color has been measured directly after the PEF application and after 60 min of it. Such information could be beneficial when considering the proper time interval between particular technological steps (when PEF is applied). i.e. the phenomena that the color change after PEF is accelerating (in the case of apple tissue) should be considered before other processing. The vast majority of publications present this kind of data regarding juices. In our study more complicated matrix is discussed. Thus, the paper, according to the best knowledge of authors, is the first which discusses the impact of PEF treatment on bioactive compound concentration of solid-like, plant material — such often used as a raw material in many different food applications (e.g., yogurt or smoothie ingredient) or further processed (e.g., dried or frizzed).

The correlation between density and specific surface area of ZrO2 nanoparticles (NPs) was studied. The NPs were produced using a hydrothermal process involving microwave heating. The material was annealed at 1100 °C which resulted in an increase in the average grain size of the ZrO2 NPs from 11 to 78 nm and a decrease in the specific surface area from 97 to 15 m2/g. At the same time, the density increased from 5.22 g/m3 to 5.87 g/m3. This effect was interpreted to be the result of the presence of a hydroxide monolayer on the NP surface. A smaller ZrO2 grain size was correlated with a larger contribution of the low density surface layer to the average density. To prove the existence of such a layer, the material was synthesized using 50% heavy water. Fourier transform infrared spectroscopy (FTIR) permitted the identification of the –OD groups created during synthesis. It was found that the –OD groups persisted on the ZrO2 surface even after annealing at 1100 °C. This hydroxide layer is responsible for the decrease in the average density of the NPs as their size decreases. This study of the correlation between particle size and density may be used to assess the quality of the NPs. In most cases, the technological aim is to avoid an amorphous layer and to obtain fully crystalline nanoparticles with the highest density possible. However, due to the effect of the surface layers, there is a maximum density which can be achieved for a given average NP diameter. The effect of the surface layer on the NP density becomes particularly evident for NPs smaller than 50 nm, and thus, the density of nanoparticles is size dependent.

The aim of this study was to analyze the influence of pulsed electric field pretreatment (PEF) on the osmotic dehydration of apple tissue. Osmotic dehydration was carried out in sucrose solution at 40°C and 100 rpm in a water-bath shaker. PEF pretreatment was performed using varying field strength of 5 and 10 kV/cm and 10 and 50 pulses. On the basis of electric conductivity measurement, the cell disintegration index was calculated. The course of osmotic dehydration was described by means of water loss, solid gain, weight reduction, and water content changes. Moreover, the course of the process was described by different mathematical models that are commonly used in the literature. PEF application before osmotic dehydration significantly increased water loss after 60 minutes of the process. In turn, no significant differences were found in the case of solid gain. The highest osmotic dehydration efficiency ratio (WL/SG) was noticed for samples treated by PEF at the electric field strength of 5 kV/cm and 10 ...

The article presents a novel microwave reactor for hydrothermal synthesis of nanopowders. The reactor has a unique design of a process chamber, which, when used in conjunction with a batch control system, allows a highly efficient production of nanopowders. The design of the reactor together with the new principles of operation, structural materials and distribution of electromagnetic field are described. The article also presents a control system for the reactor, which allows for an automatic operation in the stop–flow mode, control of process pressure, continuous monitoring of process parameters and safe operation of the device. The device verification process is shown on the basis of the results of cobalt-doped zinc oxide nanopowder synthesis.

The aim of this work was to study the influence of pulsed electric field (PEF) on the drying kinetics of apple tissue. Therefore, mathematical models that are commonly used in the literature were applied to describe the process. PEF treatment of the samples was carried out at an intensity of E = 5–10 kV/cm and 10–50 pulse numbers. Subsequently, the apples were convectively dried at 70°C and air velocity of 2 m/s. Based on electrical conductivity measurement, the cell disintegration index Z p was computed. Midilli et al.'s(Drying Technology, Vol. 20, pp. 1503–1513, 2001) model was evaluated as the most adequate to describe the moisture transfer in PEF-treated and intact samples. PEF pretreatment induced a reduction in drying time of up to 12% when 10 kV/cm and 50 pulses were applied. For instance, after 60 min of drying, the dimensionless moisture ratio for PEF-treated (10 kV/cm, 50 pulses) samples was 0.18 compared to 0.26 for the untreated apples. The effective moisture diffusivity, calculated on the bas...

Zinc oxide nanoparticles (ZnO NPs) were obtained by the microwave solvothermal synthesis (MSS) method. The precursor of the MSS reaction was a solution of hydrated zinc acetate in ethylene glycol with water addition. It was proved that by controlling the water concentration in the precursor it was possible to control the size of ZnO NPs in a programmed manner. The less the water content in the precursor, the smaller the size of ZnO NPs obtained. The obtained NPs with the average particle size ranging from 25 nm to 50 nm were characterised by homogeneous morphology and a narrow distribution of particle sizes. The following parameters of the obtained ZnO NPs were determined: pycnometric density, specific surface area, phase purity, chemical composition, lattice parameters, average particle size, and particle size distribution. The average size of ZnO NPs was determined using Scherrer’s formula, Nanopowder XRD Processor Demo web application, by converting the results of the specific surface area, and TEM tests using the dark field technique. ZnO morphology and structure were determined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The test performed by the X-ray powder diffraction (XRD) confirmed that crystalline ZnO, pure in terms of phase, had been obtained.

The present investigation aims to develop ultra high strength ferritic steels through consolidation of mechanically alloyed powders of 1.0 wt% nano-Y 2 O 3 dispersed 83.0Fe–13.5Cr–2.0Al–0.5Ti (alloy A), 79.0Fe–17.5Cr–2.0Al–0.5Ti (alloy B) , 75.0Fe–21.5Cr–2.0Al–0.5Ti (alloy C) and 71.0Fe–25.5Cr–2.0Al–0.5Ti (alloy D) alloys (all in wt%) by hot isostatic pressing (HIP) at 600, 800 and 1000 °C using 1.2 GPa pressure for 1 h. Following this mechano-chemical synthesis and consolidation, extensive effort has been undertaken to characterize the microstructural evolution by X-ray diffraction, scanning and transmission electron microscopy and energy dispersive spectroscopy. Mechanical properties including hardness, compressive strength, Young's modulus and fracture toughness were determined using nano-indentation and universal testing machine. The present ferritic alloys record extraordinary levels of compressive strength (2012–3325 MPa), Young's modulus (230–295 GPa), fracture toughness (4.6–21.8 MPa √m) and hardness (15.5–19.7 GPa), and measure up to 2–3 times greater strength with a lower density (∼7.4 Mg/m 3 ) than that of other oxide dispersion strengthened ferritic steels ( 2 O 3 (ex situ) or Y 2 Ti 2 O 7 (in situ) particles in higher volume fraction in high-Cr ferritic matrix.

This article presents the method of size control of cobalt-doped zinc oxide nanoparticles (Zn1−xCoxO NPs) obtained by means of the microwave solvothermal synthesis. Zinc acetate dihydrate and cobalt(II) acetate tetrahydrate dissolved in ethylene glycol were used as the precursor. It has been proved by the example of Zn0.9Co0.1O NPs (x = 10 mol %) that by controlling the water quantity in the precursor it is possible to precisely control the size of the obtained Zn1−xCoxO NPs. The following properties of the obtained Zn0.9Co0.1O NPs were tested: skeleton density (helium pycnometry), specific surface area (BET), dopant content (ICP-OES), morphology (SEM), phase purity (XRD), lattice parameter (Rietveld method), average crystallite size (FW1/5/4/5M method and Scherrer’s formula), crystallite size distribution (FW1/5/4/5M method), and average particle size (from TEM and SSA). An increase in the water content in the precursor between 1.5% and 5% resulted in the increase in Zn0.9Co0.1O NPs size between 28 nm and 53 nm. The X-ray diffraction revealed the presence of only one hexagonal phase of ZnO in all samples. Scanning electron microscope images indicated an impact of the increase in water content in the precursor on the change of size and shape of the obtained Zn0.9Co0.1O NPs. The developed method of NPs size control in the microwave solvothermal synthesis was used for the first time for controlling the size of Zn1−xCoxO NPs.

High strength, amorphous or partly nanocrystalline, multiphase intermetallic alloys with average composition of Al 65 Cu 20 Ti 15 have been processed by mechanical alloying of the elemental powders followed by consolidation using high-pressure (8 GPa) sintering either at room temperature or at 300–450 °C for 1 min. Examination of the microstructural constituents using X-ray diffraction and transmission electron microscopy shows that the alloy pressed at 400 °C is primarily amorphous, while nanocrystalline intermetallic phases, Al 2 Cu, Al 4 Cu 9 and Al 5 CuTi 2 evolve from the amorphous matrix on pressing at 450 °C. The pressing temperature of 400 °C appears most promising, leading to products with negligible porosity, increment in the Young's modulus by about 85% with respect to that of Al alloys, as well as impressive hardness (7.9 GPa) and compressive strengths (1490 MPa). However, absence of ductility and poor fracture toughness (3.8 ± 0.8 MPa√m) appear as the major challenges to be met for widespread application of these alloys.

Mechanically alloyed Al65Cu20Ti15 amorphous alloy powder with 10 wt.% nano-TiO2 dispersion was consolidated by high pressure sintering (HPS) at room temperature and/or 300- 450oC for about 1 min using a uniaxial pressure of 8GPa. The sintered material was examined by XRD and TEM. Excellent hardness and strength were obtained in selected sintered samples of 8.34 GPa and 1600 MPa respectively, although ductility was very low (< 1%).

Luminescence properties of cerium doped Y3Al5O12 (YAG) nanocrystals in form of nanopowders and nanoceramics have been studied. The comparative analysis of luminescence characteristics for nano- and single-crystals has been done. It was detected that an excitonic mechanism of the energy transfer from the host lattice to cerium ions does not work in nanopowders and nanoceramics. It was also shown that antisite-related and self-trapped exciton-related luminescence bands are suppressed strongly in nanopowders, and it can be excited only under certain circumstances. These bands practically disappeared in the nanoceramic samples. It was suggested that nanoparticle's surface, which is an efficient trap for excitons and charge carriers, plays the crucial role in peculiarities of luminescence characteristics in nanocrystals.

The agglomeration of YAG (Yttrium-Aluminum Garnet Y3Al5O12) nanopowders doped with various rare earth ions obtained by the coprecipitation and calcination route is a major problem if it is wished to exploit the nano-size properties such as the transparency of dispersions of the powders or low temperature sintering. Investigations to optimize the preparation process of powders for High Pressure-Low temperature Sintering (HPLS) of semi-translucent pellets was undertaken. The appropriate milling time to decrease the agglomeration was evaluated with the help of ZETA- potential measurement. The dependence of the agglomerate size against the time of hand milling was used to optimize the process.

Cerium doped YAG nanopowders with grain size ∼ 20 nm have been synthesized by co-precipitation method. Time-resolved luminescence characteristics have been studied. The results obtained have been compared with the luminescence characteristics for well-studied YAG single crystals. In contrast to cerium doped YAG crystals, cerium doped nanocrystal does not reveal luminescence bands due to antisite defects under electron beam pulse and X-ray excitations at 80–300 K temperature range. It was detected that decay kinetic of Ce 3 + related emission in the nanocrystal can be approximated by two exponents with time constants ∼ 9 and ∼ 47 ns at 290 K. It is faster than single exponential decay ( ∼ 80 ns ) of cerium ions emission in YAG crystals. The origin of differences in luminescence characteristics for cerium doped nanocrystals and single crystals will be discussed. It is suggested that special Ce 3 + sites which are closely related to surface states have an influence on luminescence properties of cerium doped YAG nanocrystals.

Single-phase YAG nanoparticles have been produced by the rapid hydrolysis and dehydration of Al 3+ and Y 3+ salts in EtOH–H 2 O mixtures using continuous supercritical water hydrothermal synthesis. The effects of the nature of the starting solution, the metal concentration, the EtOH content, the flow rate and the temperature on the particle size were studied. EtOH promotes crystallization and highly crystalline materials are obtained at relatively low temperatures. Furthermore the critical temperature of EtOH–H 2 O mixtures is lower than that of pure H 2 O, reducing the operating temperature. From the variables studied, the most important parameter seems to be the temperature and much smaller particles have been obtained when experiments are conducted under supercritical conditions (average 50 nm), in comparison to near critical or subcritical conditions (average 150 nm). The method is simple and clean and requires neither addition of a base to the system nor the use of very high reaction temperatures and potentially allows the continuous production of large quantities of material.

Zinc oxide nanopowders doped with 1–15 mol % cobalt were produced by the microwave solvothermal synthesis (MSS) technique. The obtained nanoparticles were annealed at 800 °C in nitrogen (99.999%) and in synthetic air. The material nanostructure was investigated by means of the following techniques: X-ray diffraction (XRD), helium pycnometry density, specific surface area (SSA), inductively coupled plasma optical emission spectrometry (ICP-OES), extended X-ray absorption fine structure (EXAFS) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and with magnetometry using superconducting quantum interference device (SQUID). Irrespective of the Co content, nanoparticles in their initial state present a similar morphology. They are composed of loosely agglomerated spherical particles with wurtzite-type crystal structure with crystallites of a mean size of 30 nm. Annealing to temperatures of up to 800 °C induced the growth of crystallites up to a maximum of 2 μm in diameter. For samples annealed in high purity nitrogen, the precipitation of metallic α-Co was detected for a Co content of 5 mol % or more. For samples annealed in synthetic air, no change of phase structure was detected, except for precipitation of Co3O4 for a Co content of 15 mol %. The results of the magentometry investigation indicated that all as-synthesized samples displayed paramagnetic properties with a contribution of anti-ferromagnetic coupling of Co–Co pairs. After annealing in synthetic air, the samples remained paramagnetic and samples annealed under nitrogen flow showed a magnetic response under the influences of a magnetic field, likely related to the precipitation of metallic Co in nanoparticles.

The luminescence properties of ZnO ceramics with grains 100–5000 nm sintered by different techniques from nanopowders were studied. The luminescence decay times were compared with that obtained for ZnO single crystal. The temperature dependence of non-exponential decay of defect luminescence (2.0–2.6 eV) was measured in wide time, intensity and temperature range. The luminescence decay kinetic at T ≤ 20 K shows the decay close to I(t) ∼ t−1 dependence. At temperature region 50–250 K the decay kinetics is more complicate since the TSL was observed in this temperature region. It is shown that the luminescence properties of NP and ceramics strongly depend on defect distribution on grains surface and the volume/surface ratio determine the luminescence decay in ZnO nanostructures and ceramics.

Optical and luminescence properties of transparent nanosized cerium doped Y 3 Al 5 O 12 (YAG:Ce) ceramics have been studied. YAG:Ce nanoceramics were obtained by means of low temperature and high pressure (LTHP) sintering method. Nanoceramic samples were sintered in the 2–8 GPa pressure range, whereas Ce 3+ concentration was varied in the 0.5–5 at. % range. It is shown that, in contrast to the single crystal, a strong rise of absorption coefficient was detected already at wavelength shorter than 400 nm in all nanoceramic samples studied. Furthermore, in nanoceramic samples unusual UV emission band near 3.1 eV was observed, which is not observed in the YAG:Ce single crystal. High pressure applied during nanoceramics sintering leads to significant changes in their optical and luminescence properties.

Fast photoluminescence spectra in the spectral region of 3.1–3.45 eV in ZnO and ZnO:Al ceramics were studied at 14 and 300 K. Ceramics with grains smaller than 100 nm were sintered from nanopowders by high pressure (8 GPa) and low temperature (350 °C). Ceramics with grain sizes 1–5 μm were sintered at 1400 °C. It is shown that excitonic luminescence spectra depend on the ceramics grain size, post preparing annealing and doping. The excitonic luminescence decay time was faster than 2 ns and the afterglow at 30 ns was ∼0.05%.

The Vickers hardness HV of silicon–carbide ceramics (fully dense and with the porosity θ=5%, 16% and 20%) was investigated in the temperature range of 20–900°C. Athermal regions of hardness were detected at low temperatures and the length of these sections increases with the growth of porosity. The results obtained allow the postulation that the formation of the hardness print, in these sections, is conditioned by fracture (but not by plastic deformation as at higher temperatures), and the hardness, in these sections, corresponds to material fracture stress, but not to the yield stress of material. The dependence HV(θ) was described by the Ryshkevitch equation HV=HV c exp (−Bθ) ), where HVc is the hardness of compact material and the value of constant B is determined experimentally for all temperatures in the investigated range. The fracture toughness of ceramics (K1c) decreases monotonically with increasing θ. The diagram of the temperature dependence of hardness for crystals with high level of Peierls–Nabarro stress was proposed. In this diagram, the hardness can be determined by 3 processes: plastic deformation, brittle fracture and phase transformation during the indentation. This diagram may be extended to bcc refractory metals if there is twinning during low-temperature indentation.

Single-phase multiferroic BiFeO3 (BFO) powders were prepared by hydrothermal microwave synthesis and dense BiFeO3 ceramics were fabricated for the first time by the low-temperature high-pressure (LTHP) sintering technique. Effect of sintering temperature ranging from 400 to 800 degrees C (3min and 10min) and pressure of 3-8 GPa on structural, microstructural, electric and magnetic properties were investigated through X-ray diffraction, scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS), density and magnetic measurements. The results highlighted that LTHP sintering method, thanks to the high pressure involved, requires lower temperature and shorter time than other techniques, avoiding BiFeO3 phase degradation. SEM images show that for short experimental time (t = 3min) the average grain size of the sintered samples was approximately the same size of raw powder. Extending the sintering time up to 10min the grain growth phenomena occurred. Moreover the results indicate that the best obtained density value was around 98% of theoretical density. The dielectric behavior of BiFeO3 ceramics was not significantly influenced by the LTHP sintering conditions. Magnetic measurements showed that ceramic BiFeO3 is weakly ferromagnetic at room temperature.

A microwave, solvothermal synthesis of hydroxyapatite (HAp) nanopowder with a programmed material resorption rate was developed. The aqueous reaction solution was heated by a microwave radiation field with high energy density. The measurements included powder X-ray diffraction (PXRD) and the density, specific surface area (SSA), and chemical composition as specified by the inductively coupled plasma optical emission spectrometry technique (ICP-OES). The morphology and structure were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A degradation test in accordance with norm ISO 10993-4 was conducted. The developed method enables control of the average grain size and chemical composition of the obtained HAp nanoparticles by regulating the microwave radiation time. As a consequence, it allows programming of the material degradation rate and makes possible an adjustment of the material activity in a human body to meet individual resorption rate needs. The authors synthesized a pure, fully crystalline hexagonal hydroxyapatite nanopowder with a specific surface area from 60 to almost 240 m2/g, a Ca/P molar ratio in the range of 1.57–1.67, and an average grain size from 6 nm to over 30 nm. A 28-day degradation test indicated that the material solubility ranged from 4 to 20 mg/dm3.

A high-pressure microwave reactor was used to study the hydrothermal synthesis of zirconia powders doped with 1 mol%Pr. The synthesis was performed in the pressure range from 2 to 8 MPa corresponding to a temperature range from 215C∘to 305C∘. This technology permits a synthesis of nanopowders in short time not limited by thermal inertia of the vessel. Microwave heating permits to avoid contact of the reactants with heating elements, and is thus particularly well suited for synthesis of doped nanopowders in high purity conditions. A mixture ofZrO2particles with tetragonal and monoclinic crystalline phases, about 15 nm in size, was obtained. The p/T threshold of about 5-6 MPa/265–280C∘was necessary to obtain good quality of zirconia powder. A new method for quantitative description of grain-size distribution was applied, which is based on analysis of the fine structure of the X-ray diffraction line profiles. It permitted to follow separately the effect of synthesis conditions on the grain-size distribution of the monoclinic and tetragonal phases.

Nanoparticles of ZrO 2:Er 3+, Yb 3+ fabricated by a soft template method combined with microwave heating under high pressures were reported for the first time. Nano ZrO 2:Er 3+, Yb 3+ in concentrations of 0.1–15 mol% have been fabricated in the presence of soft template agent diethylene glycol or polyethylene glycol in a microwave reactor at pressures up to 55 atm. The average size of the as-synthesized nanoparticles was found to be 5–13 nm. The upconversion luminescence of the ZrO 2:Er 3+, Yb 3+ was found in the red region of 630–710 nm and in the green region of 510–570 nm, with excitation by an infrared diode laser at the wavelengths of 830 and 940 nm, respectively. The change in content ratio between monoclinic and tetragonal phases when the annealing temperature increases from 600 to 1200 °C was investigated. The tetragonal phase content decreases and disappears for the samples annealed at 1200 °C. The increase in the content of the monoclinic phase is suggested to be a main reason for the increase in the upconversion luminescent intensity of nano ZrO 2:Er 3+, Yb 3+.

The conditions for obtaining pure yttrium-aluminum garnet (YAG) in a one-step process starting from components soluble in supercritical (SCR) liquids in a flow reactor have been studied. The powders were characterized using XRD, BET, SEM and helium pycnometry. Favorable conditions for YAG production were achieved using acetates (and acetylacetonates) in aqueous-alcoholic solutions as starting materials. Aqueous and alcoholic solutions of nitrates and aqueous solutions of acetates were found not appropriate as precursors for YAG production. The powders obtained had the shape of nano-sized cubes with diameters in the range 80 - 120 nm. After annealing at 600 °C the powders have comparable density as those made via a conventional precipitation-calcination route but differ from the calcinated products form soft agglomerates.