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U okviru ove doktorske disertacije proučene su dve metode dobijanjaAl2O3-Y3Al5O12 kompozita i ispitan je uticaj mikrostrukture na osobine dobijenekompozitne keramike. Ispitivanja su obuhvatila metode sinteze Itrijum (Yttrium)Aluminijum Garneta (YAG) hemijske formule Y3Al5O12 kao i njegove inkorporacije ualumina (Al2O3) matricu u cilju dobijanja kako poroznog tako i gustog kompozita sapoboljšanim osobinama u odnosu na čistu aluminu..., Within this doctoral dissertation, two methods of obtaining Al2O3-Y3Al5O12composite were studied as well as the effects of the microstructure on the properties ofthe obtained composite ceramics. The study included the methods of synthesis ofYttrium Aluminium Garnet (YAG) with chemical formula Y3Al5O12 as well as itsincorporation into alumina (Al2O3) matrix in order to obtain both porous and densecomposites with improved properties relatively to pure alumina...

U okviru ove doktorske disertacije proučene su dve metode dobijanja Al2O3-Y3Al5O12 kompozita i ispitan je uticaj mikrostrukture na osobine dobijene kompozitne keramike. Ispitivanja su obuhvatila metode sinteze Itrijum (Yttrium) Aluminijum Garneta (YAG) hemijske formule Y3Al5O12 kao i njegove inkorporacije u alumina (Al2O3) matricu u cilju dobijanja kako poroznog tako i gustog kompozita sa poboljšanim osobinama u odnosu na čistu aluminu..., Within this doctoral dissertation, two methods of obtaining Al2O3-Y3Al5O12 composite were studied as well as the effects of the microstructure on the properties of the obtained composite ceramics. The study included the methods of synthesis of Yttrium Aluminium Garnet (YAG) with chemical formula Y3Al5O12 as well as its incorporation into alumina (Al2O3) matrix in order to obtain both porous and dense composites with improved properties relatively to pure alumina...

Starting hematite (Fe2O3), zinc oxide (ZnO) and manganese carbonate (MnCO3) powders were homogenized in a planetary ball mill in stainless steel bowls with stainless steel balls for 15 min, calcined in air at 1000 C for 2 h, milled in a planetary ball mill for 30 minutes, followed by 4 h in an aghate mill, sieved through a 325 mesh to form four starting powders: MnFe2O4, ZnFe2O4, Mn0.5Zn0.5Fe2O4 and a two-phase mixture of zinc and manganese ferrite. Structural properties of the obtained powders were analyzed using XRD, SEM and EDS. Electrical properties of disk shaped samples were measured at room temperature on an impedance analyzer in the frequency range 100 to 40 MHz, enabling determination and comparison of dielectric permittivity and complex impedance. Complex relative permeability of toroid shaped samples was measured on an impedance analyzer in the frequency range from 1 MHz to 500 MHz.

Dense CsAlSi5O12 was successfully obtained by hot pressing of Cs-exchanged clinoptilolite at 900 degrees C. Simultaneous application of high temperature and mechanical pressure allowed formation of CsAlSi5O12 at temperature considerably lower than 1150 degrees C which was the lowest reported temperature of CsAlSi5O12 formation in pressureless sintered Cs-exchanged clinoptilolite. CsAlSi5O12 formation was preceded by complete amorphisation of Cs-exchanged clinoptilolite in temperature range between 700 and 900 degrees C. Bearing in mind that clinoptilolite possesses high affinity for Cs cation it is believed that hot pressing of Cs-exchanged clinoptilolite might be an efficient way to immobilize radioactive Cs by its incorporation into crystal lattice of stable CsAlSi5O12. The samples sintered at 950 degrees C had relative density about 84% of theoretical density and open porosity of only 6% which is expected to result in low Cs leaching rate.

Porous acicular mullite (3Al(2)O(3)center dot 2SiO(2)) ceramics containing Cu3Mo2O9 as a soot oxidation catalyst was fabricated by a novel approach using commercial powders of Al2O3 and CuO, and powder obtained by controlled oxidation of ground waste MoSi2. The obtained material consisted of elongated mullite grains which are known to be effective in carbon soot removal from diesel engine exhaust. The presence of in situ created Cu3Mo2O9 was found to catalyze the carbon burnout which is an extremely important feature when it comes to filter regeneration, i.e., the captured soot removal. The carbon burnout temperature in the sample containing 12 wt% CuO was by 90 degrees C lower than that in the sample without CuO. Effect of sintering temperature as well as the effect of amount of CuO additive on mullite properties were studied. It was found that the increase in amount of CuO in samples sintered at 1300 degrees C decreased porosity and increased compressive strength of the porous mullite ceramics. The addition of 12 wt% CuO increased the strength of the porous mullite ceramics up to 70 MPa, whereas the porosity was reduced from 62% in the mullite without CuO to 44% in the mullite ceramics containing 12 wt% CuO. Although affected by the amount of CuO, the microstructure still consisted of elongated mullite grains.

Al2O3-YAG composite was obtained by sintering of porous Al2O3 preforms infiltrated with water solution of aluminium nitrate nonahydrate, Al(NO3)(3)center dot 9H(2)O and yttrium nitrate hexahydrate, Y(NO3)(3)center dot 6H(2)O. Al2O3 preforms with porosity varying from 26 to 50% were obtained after sintering at temperature ranging from 1100 to 1500 degrees C. Sintering of the infiltrated Al2O3 preforms led to formation of YAG particles due to reaction between Y2O3 and Al2O3 at high temperature. It was found that variation of porosity of alumina preforms and sintering temperature is an effective way to fabricate Al2O3-YAG composite with an unusual combination of properties. Open porosity was in the range 15-35%, specific surface was 0.6-6.1 m(2)/g, pore size was 150-900 nm whereas compressive strength was from 50 to 250 MPa. The effect of sintering temperature on YAG formation and phase composition were investigated using X-ray diffractometry whereas microstructure of the composite was analysed by scanning electron microscopy.

Metastabile nanopowder ZnTiO3 pressed into cylindrical compacts at 200 MPa was submitted to conventional heating with isothermal holding at 931oC for 10 minutes, 25 minutes and 40 minutes. Same compacts were heated with two-step sintering schedule with maximal 912oC and isothermal holding at 896oC, for approximately the same holding times as with isothermal. Shrinkage during heating was monitored with dilatometric device, while microstructure was determined with atomic force microscopy. XRD patterns were collected for the most prominent samples. Sintered specimens microstructure showed differences introduced during last sintering stage by two heating schedules.

Starting powders of TiO2 (anatase) and Fe2O3 (hematite) were mixed in the molar ratio 1:1. Pseudobrookite powder was obtained by a combined milling/calcination procedure. Particle size distribution was analyzed on a laser particle size analyzer and correlated with XRD and SEM analysis. The band gap was determined using UV/Vis spectroscopy. Green samples were sintered in a dilatometer and at 1000oC for 2h in air. Thermal diffusivity was determined from photoacoustic measurements. Electrical conductivity measurements were performed. The aim was to obtain pseudobrookite with properties suitable for polymer paste for thick films to be applied as gas sensors.

Metastabile nanopowder ZnTiO3 pressed into cylindrical compacts at 200 MPa was submitted to conventional heating with isothermal holding at 931oC for 10 minutes, 25 minutes and 40 minutes. Same compacts were heated with two-step sintering schedule with maximal 912oC and isothermal holding at 896oC, for approximately the same holding times as with isothermal. Shrinkage during heating was monitored with dilatometric device, while microstructure was determined with atomic force microscopy. XRD patterns were collected for the most prominent samples. Sintered specimens microstructure showed differences introduced during last sintering stage by two heating schedules.

Commercial Mn-Zn ferrite powder was milled in a planetary ball mill for 30-240 minutes. Particle size distribution in the milled powders was analyzed using a laser particle size analyzer and correlated with XRD and SEM analysis of the milled powders. Green disc and torroid samples were sintered in air in the temperature interval 800 -1300oC for 2 hours. SEM/EDS, AFM/MFM analysis of the sintered samples and measurements of their electrical properties such as DC resistance up to 500 MHz enabled establishment of a correlation between the microstructure and properties in the high-frequency range.

Fine tungsten carbide (WC) powder was prepared by solid state reaction between tungsten powder (W) and activated carbon cloth as a new carbon (C) source. The effect of temperature and time of heat treatment as well as the effect of C/W ratio on WC phase formation was studied. The results obtained by X-ray powder diffraction (XRPD) show that obtained powder is single WC. Microstructure and morphology was determinate by means of scanning electron microscopy (SEM). Brunauer-Emmett-Teller (BET) method was used for examining specific surface area and texture of obtained powders. It was found that WC powder was successfully synthesized in excess carbon after eight-hour heat treatment at relatively low temperature (1000 degrees C). (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Analizirano je dobijanje i svojstva biomorfne keramike dobijene od šest vrsta drveta. Izmerene su dimenzione promene i promene mase prilikom pirolize. Na osnovu promene mase prilikom pirolize određen je udeo silicijum-karbida u biomorfnoj keramici. Isprobano je deset mogućih sastava sola koji se koristi u postupku dobijanja biomorfne keramike, pri čemu je praćena brzina formiranja homogenog sola i geliranja. Karbotermalna redukcija je vršena na tri temperature, što je uticalo na sastav dobijenog materijala. Mehanička svojstva biomorfne keramike su analizirana preko određivanja kompresione i čvrstoće na savijanje u tri tačke u dva bitna pravca ovog anizotropnog materijala. Ultrazvučnom metodom je određen modul elastičnosti u aksijalnom, radijalnom i tangencijalnom pravcu. Analizirane su promene koje kod biomorfne keramike izaziva pulsno lasersko zračenje. Difrakcijom X-zraka je određen sastav uzoraka dobijenih pod različitim uslovima. Mikrostruktura pirolizovanog drveta i biomorfne keramike je analizirana pomoću skening elektronskog mikroskopa. Koeficijent termičkog širenja keramike je dobijen pomoću dilatometrijskih merenja, a poroznost metodom živine porozimetrije., Synthesis and properties of biomorphic ceramic obtained from six different species of wood have been analyzed. Changes of dimensions and mass during pyrolysis have been measured. The content of silicon carbide in biomorphic ceramics has been estimated from mass reduction after calcination. The rates of preparation of biomorphic ceramic and gelation have been studied for ten compositions of sol. The influence of carbothermal reduction temperature on the composition of obtained ceramics has been analyzed. The mechanical properties of final material have been analyzed by compression and three point bending tests in two directions. Dynamic Young modulus of elasticity in axial, radial and tangential direction has been measured by ultrasonic pulse velocity testing. Interaction of pulse laser radiation with biomorphic ceramics has been also studied. Crystalline phases were identified by X-ray diffraction. The coefficient of thermal expansion has been measured by horizontal pushrod dilatometer. The pore size distribution has been determined by mercury intrusion porosimeter.

Analizirano je dobijanje i svojstva biomorfne keramike dobijene od šest vrsta drveta. Izmerene su dimenzione promene i promene mase prilikom pirolize. Na osnovu promene mase prilikom pirolize određen je udeo silicijum-karbida u biomorfnoj keramici. Isprobano je deset mogućih sastava sola koji se koristi u postupku dobijanja biomorfne keramike, pri čemu je praćena brzina formiranja homogenog sola i geliranja. Karbotermalna redukcija je vršena na tri temperature, što je uticalo na sastav dobijenog materijala. Mehanička svojstva biomorfne keramike su analizirana preko određivanja kompresione i čvrstoće na savijanje u tri tačke u dva bitna pravca ovog anizotropnog materijala. Ultrazvučnom metodom je određen modul elastičnosti u aksijalnom, radijalnom i tangencijalnom pravcu. Analizirane su promene koje kod biomorfne keramike izaziva pulsno lasersko zračenje. Difrakcijom X-zraka je određen sastav uzoraka dobijenih pod različitim uslovima. Mikrostruktura pirolizovanog drveta i biomorfne keramike je analizirana pomoću skening elektronskog mikroskopa. Koeficijent termičkog širenja keramike je dobijen pomoću dilatometrijskih merenja, a poroznost metodom živine porozimetrije., Synthesis and properties of biomorphic ceramic obtained from six different species of wood have been analyzed. Changes of dimensions and mass during pyrolysis have been measured. The content of silicon carbide in biomorphic ceramics has been estimated from mass reduction after calcination. The rates of preparation of biomorphic ceramic and gelation have been studied for ten compositions of sol. The influence of carbothermal reduction temperature on the composition of obtained ceramics has been analyzed. The mechanical properties of final material have been analyzed by compression and three point bending tests in two directions. Dynamic Young modulus of elasticity in axial, radial and tangential direction has been measured by ultrasonic pulse velocity testing. Interaction of pulse laser radiation with biomorphic ceramics has been also studied. Crystalline phases were identified by X-ray diffraction. The coefficient of thermal expansion has been measured by horizontal pushrod dilatometer. The pore size distribution has been determined by mercury intrusion porosimeter.

The fabrication of SiC-HfC ceramic composite via self-propagating high-temperature synthesis and simultaneous consolidation was investigated. Dense composite consisting of alternating layers of SiC and HfC was obtained by spark plasma sintering of stack of SiC cloths covered by electrophoretically deposited HfO2. The deposited HfO2 was converted into HfC during sintering. The obtained ceramics was characterized in terms of microstructure, cavitation resistance and oxidation resistance. It was shown that spark plasma sintering is effective way to preserve fibre-like mikrostructure of SiC. The obtained material showed good erosion resistance. The surface layer of HfC transformed to HfO2 during oxidation of samples and protected SiC from further oxidation.

Hafnium carbide powder was synthesized by sol-gel polycondensation of hafnium chloride with citric acid. The starting materials were dissolved in water and mixed homogeneously on a hot plate until a precomposite gel was formed. Pyrolysis of the obtained gel resulted in formation of monoclinic hafnia and amorphous carbon, which after subsequent heat treatment transformed into hafnium carbide. Materials were analyzed by means of X-ray diffraction and electron microscopy investigations. The results showed that the obtained carbide powder was composed of nearly equiaxed particles of narrow size distribution. The obtained hafnium carbide powder was densified via spark plasma sintering (SPS) at 1950 degrees C using molybdenun silicide as sintering additive. Microstructure and mechanical properties of the obtained hafnium carbide ceramics were investigated.

Biomorphous beta-SiC ceramics were produced from several species of wood such as ash, wild cherry, black alder, Persian walnut, sessile oak and European hornbeam. The wood was pyrolysed, impregnated with tetraethyl orthosilicate (TEOS) sol in repeated cycles and thermally treated at 1800 degrees C in vacuum. Four specimen groups included charcoal and three groups with 1, 3 and 5 cycles of impregnation were analyzed. Flexural and compressional strength of charcoal and woodlike SiC ceramics were measured using three-point and compression testing in different directions. Experimental results showed that mechanical properties of woodceramics were improved by repeating of impregnation cycles. Porosity measurement, dilatometric analysis, XRD and SEM analysis were used to study the macroscopical and microscopical properties of the resulting biomorphic SiC ceramics. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

A new technology based on bio-templating approach was proposed in this paper. Egg-shell membrane (ESM) has been employed as a natural biotemplate. Fibrous oxide ceramics was prepared by wet impregnation of biological template with water solution of cerium nitrate. The template was derived from membranes of fresh chicken eggs. Repeated impregnation, pyrolysis and final calcination in the range of 600 to 1200 degrees C in air resulted in template burnout and consolidation of the oxide layers. At low temperatures, the obtained products had structure which corresponded to the negative replication of biological templates. Unique bio-morphic CeO2 microstructures with interwoven networks were synthesized and characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD), whereas low-temperature nitrogen adsorption (BET) method was used in order to characterize porous properties.

A new technology for radionuclide trapping which is based on bio-templating approach was proposed in this paper. Porous oxide ceramics was prepared by wet impregnation of biological template with water solution of cerium and strontium nitrates. The template was derived from linden wood (tilia amurensis). Repeated pressure impregnation, heat treatments and final calcination at 1000 °C in air resulted in the template burnout and consolidation of the oxide layers. The obtained products had structure which corresponded to the negative replication of biological templates. X-ray diffraction, scanning electron microscopy, Raman spectroscopy and porosimetry were employed to characterize the composition and structure of biomorphic ceramics. It was found that the wood impregnated with water solution of cerium and strontium nitrates was converted into oxide ceramics (Ce0.9Sr0.1O2−δ), while preserving the microstructural features of the biological preform.

The new porous carbon materials were obtained by templating procedure using mesoporous silica (SBA-15) as template. The ordered mesoporous silica materials were synthesized by using Pluronic P123 (non-ionic triblock copolymer, EO20PO70O20). SBA-15/cryogel carbon composites were obtained by sol gel polycondenzation of resorcinol and formaldehyde in the presence of different amount of SBA-15. The polycondenzation was followed by freeze drying and subsequent pyrolysis. One set of SBA-15/sucrose carbon composites was prepared by using sucrose as carbon source. The silica template was eliminated by dissolving in hydrofluoric acid (HF) to recover the carbon material. The obtained carbon replicas were characterized by nitrogen adsorption-desorption measurements, X-ray diffraction and scanning electron microscopy (SEM). It was revealed that the samples have high specific surface (533-771 m(2) g(-1)), developed meso- and micro-porosity and amorphous structure. Porous structure of carbon replicas was found to be a function of the carbon source, properties of SBA-15 and silica/carbon ratio. Room temperature adsorption of nitrogen and adsorption of phenol from aqueous solutions were investigated. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Ceria ceramics was obtained from multi-doped nanosized ceria powders prepared by both modified glycine nitrate procedure (MGNP) and self-propagating reaction at room temperature (SPRT). Rare earth elements such as Nd, Sm, Gdr, Dy, Y, Yb were used as dopants. The overall mole fraction of dopants was 0.2. One-hour long sintering of powder compacts was performed at 1500 degrees C in oxygen atmosphere. Phase composition, microstructure and ionic conductivity of sintered samples were analysed. Single-phase ceria was detected in all samples. In general, the increase in the number of dopants improved the ionic conductivity. The samples doped simultaneously with five dopants had the highest ionic conductivity, as evidenced by the impedance measurements. At 450 degrees C, the conductivity of sample obtained by MGNP was 3.94 x 10(-3) Omega(-1) cm(-1) whereas the conductivity of sample obtained by SPRT was 2.61 x 10(-3) Omega(-1) cm(-1). The conductivity activation energy for MGNP and SPRT samples was measured to be 0.348 and 0.385 eV, respectively. Finally, the conductivity decreased as the number of dopants increased to six. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The ordered mesoporous silica SBA-15 materials were synthesized using Pluronic P123 (non-ionic triblock copolymer, EO20PO70O20), under acidic conditions. SBA-15/carbon cryogel composites were obtained by sol gel polycondensation of resorcinol and formaldehyde followed by freeze drying, and subsequent pyrolysis, in the presence of different amounts of SBA-15. For comparison purpose, SBA-15/carbon composite was also prepared using sucrose as carbon source. These materials were characterized by room temperature nitrogen adsorption-desorption measurement, X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. It was revealed that the samples have amorphous structure, high specific surface area (350-520 m(2) g(-1)) and developed meso- as well as microporosity. The porosity of structure depends on the carbon source and Si/C ratio which can be easily controlled by varying concentration of starting solution. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Nanometric-sized strontium doped ceria powders were prepared by combustion glycine-nitrate procedure. Cerium nitrate and strontium nitrate were used as starting material whereas glycine is used as a fuel. The tailored composition was: Ce1-xSrxO2-delta with concentration x ranging from 0 to 0.15. The effect of dopant concentration and subsequent calcination on crystal stability and lattice parameter was studied. Results showed that the obtained powders were solid solutions with a fluorite-type crystal structure. The particle size was in the nanometric range ( LT 15 nm). Calcination of as-prepared powders at 850 degrees C caused. the formation of secondary phase (SrCeO3) in samples containing with fraction of Sr2+ ions GT = 9 mol %. The solubility limit of Sr2+ ions in ceria lattice was between 6 and 9 mol % at 850 degrees C. The solid solution of 6 mol % Sr2+ was stable even at temperature as high as 1550 degrees C. (C)2012 The Ceramic Society of Japan. All rights reserved.

Porous CeO2 was obtained by bio-inspired route using egg shell membranes (ESM) as a template. ESM extracted from the fresh chicken eggs were washed with distilled water and immersed in solution of Ce(NO3)(3) x 6 H2O for seven days. Samples were subsequently thermally treated at temperature ranging from 600 to 1200 degrees C in argon and air.To study the crystallization process, samples were heated to temperature ranging from 600 to 1200 degrees C, in air, at different temperatures (600, 800, 1000 and 1200 degrees C). Samples were characterized by nitrogen adsorption measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD of samples revealed that well crystallized CeO2 is obtained even at temperature as low as 600 degrees C. SEM images confirmed that morphology of obtained CeO2 is a replica of the morphology of the original ESM.

Titanium dioxide nanopowders, doped with different amounts of Fe3+ ions (0.3-5 mass%), were synthesized by acid-catalyzed sol-gel method in a non-aqueous medium. The obtained powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and determination of izoelectric points as well as particle diameters. Careful investigation of porous structure was provided by application of nitrogen adsorption-desorption method. Structure analysis showed that the obtained nanopowders exhibited the anatase crystal structure, independent of the amount of iron dopants. The presence of Fe3+ ions in anatase decreases the value of isoelectric point of undoped TiO2. Unlike crystal structure, porosity parameters are strongly affected by the amount of iron ions incorporated in TiO2 lattice. The mesoporosity of TiO2 can be successfully controlled by changing the amount of iron dopants. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Nanometric-sized yttrium doped HfO2 powders were obtained by applying metathesis and combustion reactions. The tailored composition of solid solutions was: Hf1-xYxO2-delta with concentration x ranging from 0 to 0.2. HfCl4 was used as a source of hafnium whereas Y(NO3)(3)center dot 6H(2)O was used as a source of yttrium. The obtained powders were annealed at different temperatures in order to induce crystallization of HfO2. The influence of dopant concentration, annealing temperature and annealing time on powder properties was examined. The XRD analysis revealed that the crystal structure of HfO2 depends on the dopant concentration. The samples doped with 20 mol% of yttrium and annealed at 1500 degrees C had high-temperature, cubic structure even after cooling to room temperature. The presence of relatively large amount of dopant was beneficial in stabilizing highly desirable cubic phase of HfO2. It was found that the crystallite size lies in the nanometric range ( LT 10 nm). (C) 2011 Elsevier Ltd. All rights reserved.

Nanometric beta-SiC powder was prepared by carbothermal reduction of freeze-dried gel. Initially, the gel was obtained by polycondensation of sol consisting of resorcinol and formaldehyde as a source of C and tetraethoxysilane as a source of silicon. The effect of temperature and time of heat treatment (carbothermal reduction) as well as the effect of C/Si ratio on SiC powder properties was studied. It was possible to obtain nanosized (similar to 20 nm) beta-sic powder after one-hour heat treatment at relatively low temperature of 1200 degrees C. The powder was successfully synthesised without the need for excess carbon which is typical for conventional carbotherrnal reduction using some other sources of graphite. The increase in temperature of heat treatment to 1400 degrees C caused considerable growth of SiC particles up to 400 nm. It was found that prolonged heat treatment at 1200 degrees C is an effective way to obtain well crystallized SiC and keep the size of SiC particles below 50 nm at the same time. (C) 2011 Elsevier Ltd. All rights reserved.

SiC-TiB2 particulate composites were fabricated by converting TiO2 to TiB2 through the reaction between TiO2, B4C and C. The presence of initially very fine, in-situ created, TiB2 particles increased driving force for sintering and enabled fabrication of a dense composite utilizing pressureless sintering and the liquid phase created between Al2O3 and Y2O3 additives. The effect of volume fraction of the in-situ formed TiB2 on density, microstructure and flexural strength was discussed. It was found that the presence of TiB2 particles suppressed the growth of SiC grains and enhanced fracture strength. The fracture strength of samples containing 12 vol% TiB2 was more than 30% higher than that of the monolithic SIC. The effect of SIC grain size on fracture strength was also analyzed. (C) 2010 Elsevier B.V. All rights reserved.

Nanopowdered solid solution Ce(1-x)Cu(x)O(2-gamma) samples (0 LT = x LT = 0.15) were synthesized by self-propagating room temperature synthesis (SPRT). Raman spectroscopy and XRD at room temperature were used to study the vibration properties of these materials as well as the Cu solubility in ceria lattice. The solubility limit of Cu(2+) in CeO(2) lattice was found to be lower than published in the literature. Results show that obtained powders with low dopant concentration are solid solutions with a fluorite-type crystal structure. However, with Cu content higher than 7.5 mass%, the phase separation was observed and two oxide phases, CeO(2) and CuO, coexist. All powders were nanometric in size with high specific surface area. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Dense SiC-TiB2 composites with 24 vol% TiB2 were fabricated by pressureless sintering at 1940 degrees C. Al2O3 and Y2O3 were used as sintering additives to create a liquid phase and promote densification. TiB2 was formed by an in situ reaction between TiO2, B4C and C. The sintered samples were subsequently heat-treated at temperatures ranging from 1850 degrees C to 2000 degrees C. The effect of temperature of post-sintering heat treatment on microstructure and mechanical properties of the SiC-TiB2 composite was presented. Heat treatment at 1970 degrees C considerably improved the strength and the fracture toughness of sintered samples while maintaining high density. The elongation of alpha-SiC grains during the heat treatment was found to be responsible for an increase in fracture toughness. The presence of liquid phase assisted the elongation of grains which, in turn, activated crack bridging and crack deflection toughening mechanisms. Maximum strength of 540 MPa was found to be the result of improved fracture toughness. Heat treatment at temperatures above 1970 degrees C led to a deterioration of mechanical properties. (C) 2010 Elsevier B.V. All rights reserved.

The ceria solid solutions doped with rare earth cations were synthesized by two methods and the microstructural and morphological characterization of powders was performed. The results obtained by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) method and Raman spectroscopy were studied and discussed. The results showed that finer powders have not only higher specific surface area, smaller particles and crystallite sizes, but also larger lattice parameters in the case of both single and multidoped solid solutions. (C) 2010 Elsevier B.V. All rights reserved.

SiC-TiB2 composites with up to 50 vol% TiB2 were fabricated by in-situ reaction between TiO2, B4C and C. The densification of the uniaxially pressed samples was done using pressureless sintering in the presence of sintering aids consisting of Al2O3 and Y2O3. The influence of the volume fraction of TiB2 and sintering temperature on density and fracture toughness was examined. It was found that fracture toughness is strongly affected by the volume fraction of TiB2. The presence of TiB2 particles suppresses the grain growth of SiC and facilitates different toughening mechanisms to operate which, in turn, increases fracture toughness of the composite. The highest value for fracture toughness of 5.7 MPa m(1/2) measured in samples with 30 vol% TiB2 sintered at 1940 degrees C. Crown Copyright (C) 2010 Published by Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The alpha-beta phase transformation in Si3N4 was studied for seeded samples using all Y2O3-Al2O3 mixture as a sintering aid. The concentration of beta-seeds varied from 0 to 5 wt.%. The results showed that alpha-beta phase transformation followed the first-order reaction. The calculated activation energy for seeded samples was in the range from 348 to 3 78 KJ/mol, indicating boundary reaction as the rate limiting step.

The aim of this work is the investigation of alpha-tricalcium-phosphate (alpha-TCP) formation from calcium-deficient hydroxyapatite (CDHAP), synthesized by hydrothermal method from CaCl2, EDTA, NaH2PO4 center dot 2H(2)O and urea as precursors at 160 degrees C. Further, the influence of Ca/P ratios in the starting solution on alpha-TCP formation and the settings of obtained cements in simulated body fluid (SBF) were investigated. According to the results of X-ray, FTIR and SEM analyses, it is shown that CDHAP is transformed to beta-TCP at 800 degrees C, and to alpha-TCP at 1200 degrees C. Almost complete transformation of CDHAP into alpha-TCP occur after heating at 1500 degrees C in the case when Ca/P ratio in starting solution was 1,42. Cement powder mixed with the cement liquid (2.5 wt.% solution of Na2HPO4) completely hydrolyzes after 7 days in SBF, forming only CDHAP phase.

Microstructure development and fracture toughness of Si3N4 composites were studied in the presence of seeds and Al2O3 + Y2O3 as sintering aids. The elongated beta-Si3N4 seeds were introduced into two different alpha-Si3N4 matrix powders; one was the ultra fine powder matrix and the other was the coarse powder matrix. The amount of seeds varied from 0 to 6 wt%. The grain growth inhibition and the mechanism of toughening were discussed and correlated with microstructure. The maximum fracture toughness of 9.0 MPa m(1/2) was obtained for ultra fine powder with 5 wt% seeds hot pressed at 1,700 degrees C for 6 h.

The aim of this work is the investigation of alpha-tricalcium-phosphate (alpha-TCP) formation from calcium-deficient hydroxyapatite (CDHAP), synthesized by hydrothermal method from CaCl2, EDTA, NaH2PO4 center dot 2H(2)O and urea as precursors at 160 degrees C. Further, the influence of Ca/P ratios in the starting solution on alpha-TCP formation and the settings of obtained cements in simulated body fluid (SBF) were investigated. According to the results of X-ray, FTIR and SEM analyses, it is shown that CDHAP is transformed to beta-TCP at 800 degrees C, and to alpha-TCP at 1200 degrees C. Almost complete transformation of CDHAP into alpha-TCP occur after heating at 1500 degrees C in the case when Ca/P ratio in starting solution was 1,42. Cement powder mixed with the cement liquid (2.5 wt.% solution of Na2HPO4) completely hydrolyzes after 7 days in SBF, forming only CDHAP phase.

Si3N4-TiN composites, with varying TiN content from 0-50 wt% and beta-Si3N4 seeds up to 5 wt%, were examined in respect of their electrical resistivity and fracture toughness. The composites are produced by liquid phase sintering using 3%Al2O3+7%Y2O3 as additive. beta-seed particles with different particle shape and aspect ratio were used in this investigation. The electrical conductivity of composites exhibits a percolative behaviour, which is characterised by an abrupt decrease in resistivity in composites with 36 wt%TiN. In composites with beta-Si3N4, for the same percolation concentration of TiN, the electrical resistivity is higher than in composites without seed particles. The fracture toughness shows a considerable improvement in Si3N4-36%TiN with 3 and 5 wt% seeds. High fracture toughness of 6.10 MPa m(1/2) could be achieved due to the controlled bimodal microstructure consisting of elongated beta-Si3N4 incorporated into a composite matrix.