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The preparation process and the properties of Al2O3-W nanocomposites obtained by gelcasting are reported. The novelty of the synthesis path is the formation of nano-tungsten particles in an in situ reduction of water-soluble precursor during pressureless sintering. The use of water-soluble salt as a tungsten precursor ensured highly homogenous distribution of reinforcing particles and good adhesion between ceramic and metal phases. The maximum content of tungsten in the composites was approximately 0.5 wt%. The size of the reinforcing particles was less than 100 nm. Presence of metallic tungsten and tungsten carbide (W2C) in the composites lead to the improvement of mechanical parameters: an increase of hardness by about 10 % and of fracture toughness by about 20 %, compared to the reference sample of pure aluminum oxide.

0.83 Pb(Zr1/2Ti1/2)O3-0.11Pb(Zn1/3Nb2/3)O3-0.06Pb(Ni1/3Nb2/3)O3 (PZNNT) samples with plate-like PbTiO3 (PT) template were prepared using tape casting technology. The microstructure evolution and reaction mechanism between the matrix and PT template was investigated systematically. The quench heat treatment experiment was designed and the microstructure was evaluated. The results showed that the plate-like PT template has relatively low thermal stability which would decompose to form Pb-rich liquid phase and Ti-rich region at the sintering temperature of 900 °C–1050 °C. Plate-like PT template reacted with the PZNNT matrix materials during the sintering process, which did not contribute to the grain growth orientation for PZNNT matrix. Finally, the mechanism of grain growth for the PZNNT ceramics with plate-like PT template is clarified. This work demonstrated that the thermal stability of plate-like template is one of the key factors for fabricating textured piezoelectric ceramics.

A sample of 0.83Pb(Zr0.5Ti0.5)O3-0.11Pb(Zn1/3Nb2/3)O3-0.06Pb(Ni1/3Nb2/3)O3 (PZNNT) to which MnO2 was added, with a high mechanical quality factor (Qm) and a good transduction coefficient (d33×g33), were systematically investigated. Based on the SEM analysis there existed two kinds of “secondary phases”, Rich Ti and Rich Zn phases, which arose due to the B-site substation of PZNNT-based ceramics by manganese ions. One phase was due to the Mn3+ replacing the Ti4+ to create oxygen vacancies and induce the hardening effect. Another phase was due to the Mn2+ replacing the Zn-site to stabilize the perovskite phase. When the addition of MnO2 reached the solubility limit of 1.5 mol% in the PZNNT-based ceramics, the sample showed optimal electrical properties (Qm=357, d33×g33=9859 × 10−15 m2/N, kp=0.56), which suggested its potential application for piezoelectric energy harvesting in larger field excitation environments.

Transparent KSr2Nb5O15 (KSN) lead-free ferroelectric ceramics have been synthesized via modified pressureless sintering method. A significant photochromic effect was observed for the transparent KSN ceramics prepared without rare-earth dopant modification. The piezoelectric properties depend on the grain orientations were investigated. The optical transmittance of the KSN ceramics is greater than 40% in the wavelength range of 530–800 nm. After NUV irradiation, the absorbance was enhanced by more than 40% in a broad visible range (more than 79%). The absorbance returned to the initial value after a thermal bleaching process. The results of the cycling tests and response experiments showed the stability and saturation of the photochromic effect. In addition, the possible photochromic mechanism of the KSN ceramics is discussed and the photochromic centers are identified. This transparent KSN ceramics exhibits an obvious photochromic effect and is a potential candidate materials for optical data storage and information recording applications.

Novel plate-like B-site complex Bi4(ZrxTi1-x)3O12 microcrystals consisted with both (Bi2O2)2+ layer and Zr4+substituted [Bi2Ti3O10]2- blocks have been synthesized through molten salt method. With the increase of Zr4+ content, the lattice constant of Bi4(ZrxTi1-x)3O12 increases. From the Raman analysis, the bending vibration was mainly influenced by the Zr4+ content, while both of bending and stretching vibration was influenced at relative high calcination temperature. The reaction conversion process was mainly controlled by the solution-precipitation mechanism and TiO2 provided the basis crystal nucleation in NaCl-KCl molten salt, where the reactant ionic can precipitation, epitaxial growth and finally generated the final bismuth layer-structure products. Finally, fine crystallinity and orientation of plate-like Zr substituted Bi4(Zr0.1Ti0.9)3O12 microcrystals with high aspect ratio can be successful fabricated at 900 °C, which paved a way to design and fabricate the novel plate-like B-site complex perovskite compounds in the future.

Gelcasting is a method which allows for the production of high-quality ceramic-metal composites. In this work, the problem of local polymerisation in gelcasting of alumina-tungsten composite and metal influence on activation energy of glycerol monoacrylate was investigated. The broadband dielectric spectroscopy method was used for the first time to study the kinetics of gelation in ceramic processing. Polymerisation reaction rates constant of pure monomer, and monomer with ceramic and the metal filler, within the temperature range from 313 K to 333 K were determined. The obtained results were compared with rheological measurements. The calculated activation energy of polymerisation for monomer with 0.5 vol% of tungsten is 66 kJ/mol in comparison to a pure monomer which is 290 kJ/mol. This indicates the catalytic influence of metal on the polymerisation. Therefore, in the alumina suspension with tungsten polymerisation begins near the surface of the metal particles resulting in polymer structure inhomogeneity and lower mechanical properties of green bodies.

The paper presents the thermal decomposition of the new, highly efficient organic additives used in colloidal shaping of ceramics, that is lactobionic acid (LAc), galacturonic acid (GAc) and diglyceryl acrylate (DGA). The sugar acids are effective deflocculants, especially for nanopowders, while DGA is the new monomer dedicated to gelcasting process. Most organic additives are indispensable in shaping step but must be then eliminated in order to obtain pure ceramic phase. The DTA/TG measurements coupled with mass spectrometry allowed to determine the thermal decomposition of organic compounds and observe type of gasses released to the atmosphere during heating. Additionally, the influence of the analyzed substances on the properties of selected ceramic suspensions and sintered bodies has been discussed. The new compounds have been examined in the preparation of ZTA (zirconia toughened alumina) composites by gelcasting, slip casting and subsequent sintering. The rheological behaviour of Al2O3-ZrO2 suspensions as well as selected properties (Vickers hardness, fracture toughness and microstructure) of sintered ZTA samples are presented.

The regional distribution of fillers can change the distribution of electric field in the ceramic/polymer composites and further affect the dielectric properties. Here, Ba0.6Sr0.4TiO3/PVDF (BST/PVDF) monolayer and its two kinds of sandwich-structural composites, PVDF-BST/PVDF-PVDF (PBP) and BST/PVDF-PVDF-BST/PVDF (BPB), were fabricated using solution casting method combined hot pressing process. The results showed BPB structural composite possesses the best dielectric performances with a relative permittivity of 17.3, an energy density (Ue) of 10.54 J/cm3 which is 2 times of BST/PVDF monolayer composite with the same BST content, as well as a dielectric tunability of 83.33%. Finite element simulation further proves that sandwich structure, especially BPB structure, can reduce the occurrence of electrical breakdown in the composite, and improve the energy storage characteristics and dielectric tunability. This work gives new thinking for the development of energy storage thin-film composites.

The centrifugal-slip casting method was used for producing the Al2O3-Ni composites with a gradient distribution of the Ni phase. The final products had the shape of hollow cylinders. The casting slurries were water-based and contained alumina and nickel powders with two different particle sizes. The cast samples were then subjected to sintering at a temperature of 1400 °C in an N2/H2 reducing atmosphere with heating and cooling rates of 1 °C/min, and the dwell time - 4 h. The rheological properties of the water-based slurries were examined. It appeared that the presence of the Ni particles strongly affected the slurry properties which was probably associated with the strong interactions between the Ni and α-Al2O3 particles. The Al2O3-Ni composites with a gradient distribution of the Ni particles were examined using the X-ray diffraction method. No new phases such as the nickel aluminate spinel were identified in the sintered composites. The microstructure of the samples was analyzed using Scanning Electron Microscopy (SEM). The observations revealed that the samples were composed of three zones with different distributions of the Ni particles on their cross-section. Finally, the Ni particle distribution in the functionally graded materials was described quantitatively.

This paper reviews recent developments and challenges of (Ba,Sr)TiO3/polymer functional composites. The microstructure of barium-strontium titanate (Ba,Sr)TiO3(BST)/polymer composites with different polymer matrices and the nature of the interface between the BST and polymer matrix is critical in the final dielectric properties. The effects of concentration, particle size and BST filler shape on the dielectric properties of BST/polymer composites are discussed. A theoretical model for the dielectric constants of ceramic/polymer composites and the fabrication of BST/polymer composites are described briefly. The development of a dielectric tunability for the BST/polymer composites is summarized. A dielectric tunability theoretical model is proposed based on our previous research results and the effects of several factors on the dielectric tunability of the composites are discussed, which contributes to a prediction of the dielectric tunability of the composites and provides important theoretical and research significance for future work.

This paper presents a study on the influence of hydroxyl groups and oxygen atoms together with chain length and branching of carrier fluid on the rheological and electrokinetic properties of shear thickening fluid (STF). An STF is non-Newtonian fluid behaviour in which the increase of viscosity increases with the applied shear rate. Ethylene glycol, triethylene glycol, 1,3-propanediol, glycerin, poly(propylene glycol) of different molecular weight and poly(propylene glycol) triol were used as the carrier fluids (dispersants). Silica powder with an average particle size of 100 nm was used as the solid phase. Zeta potential, particle size distribution (by DLS technique), steady-state and dynamic rheological measurements were conducted. Experimental results indicate that a different amount of hydroxyl groups and oxygen atoms together with chain length and branching of carrier fluids have a significant influence on the intermolecular interactions thereby and on the rheological properties of suspensions. Depending on the composition, it is possible to control rheological properties. The use of a suitable carrier fluid allows the required pattern flow to be obtained, from Newtonian through shear thinning to shear thickening, given specific shear conditions.

Results of broadband dielectric spectroscopy and rheological studies of poly(propylene glycol) + SiO 2 nanocomposites are presented. They show that the dynamics in high-concentrated composites is dominated by confinement and adsorption effects. The most notable finding is the impact of nanoparticles on fragility, the fractional translational – orientational decoupling and the shift of dynamics towards the pure Vogel-Fulcher-Tammann pattern, associated with the lack of local symmetry preferences.

Copolymers of N -isopropylacrylamide (PNIPAM) are one of the most promising microgel materials for medical applications, especially as a drug carrier. PNIPAMs present unique properties, such as size variation with changing pH and/or temperature. The results of a study on the uptake and release of a dye (Orange II) by microgels of N -isopropylacrylamide copolymer with 1-vinylimidazole (P(NIPAM-co-Vim) are presented. The dye was used as a model low-molecular substance. Hydrodynamic radius ( R h ) of P(NIPAM-co-Vim) particles was measured by dynamic light scattering as a function of temperature in two pH environments: acidic and basic. The dye particles contraction was monitored as a function of temperature at pH 4. The measurements of the zeta potential indicated a positive charge of P(NIPAM-co-Vim) particles at pH 4 and a negative one at pH 9. The key experiments were the internalization and the release of the dye. The effectiveness of this process was measured by UV-Vis spectroscopy on the supernatant derived from centrifuged P(NIPAM-co-Vim) suspension. At room temperature the efficiency of trapping of the dye by the microgel at pH 4 was 87%. Changing pH of a sample initially saturated with the dye from 4 to 9 led to a complete release of the trapped dye.

Graphene aerogel/PVDF (GA/PVDF) composites with a three-dimensional structure were prepared using a vacuum-assisted impregnation process. The phase structure, morphology and piezoelectric properties have been systematically studied. The results show that GA/PVDF composites have good piezoelectric output characteristics and can provide corresponding feedback according to the magnitude and frequency of the acting force. When the PVDF concentration is 80 mg/mL, the GA/PVDF composite reaches the highest piezoelectric constant (d33 = 16 pC/N). The average peak output current is approximately 0.51 μA and shows good stability under repeated pressing. It is promising to apply to the field of flexible pressure sensors that can be self-powered.

The paper presents the application of 2-carboxyethyl acrylate as a new monomer in gelcasting of alumina. The research showed that the use of 2-carboxyethyl has a positive influence on the properties of green bodies, limiting the negative effect of oxygen inhibition. Oxygen inhibition which hampers polymerization reaction is a well known negative phenomenon in gelcasting but still not fully overcome for samples formed in air atmosphere. As a reference monomer 2-hydroxyethyl acrylate was used in the research. Rheological behavior of alumina suspensions containing both monomers has been studied, as well as the properties of green and sintered bodies obtained by gelcasting have been measured. The differences in the rheological properties and thus ceramic-monomer interactions in the slurries has been analyzed. The high values of densities and mechanical strength, accompanied with the pictures of microstructures of sintered ceramic parts have been presented, as a result of a successfully completed gelcasting process of alumina powder.

The effect of molecular structure of d -galactose, d -mannose, d -glucose, 2-deoxy- d -glucose and 3-O-methyl- d -glucose on the viscosity of aqueous alumina nanoparticle suspensions was investigated by rheological measurements. The viscosity was found to be dependant on the molecular structure of these hexopyranoses. The research reveals that the orientation of primary and quaternary hydroxyl groups in a pyranose ring plays a crucial role in dispersing properties of monosaccharides. Moreover, the most important is the mutual orientation of these hydroxyl groups. Monosaccharides with axial and equatorial orientation of hydroxyl groups at first (C 1 ) and fourth (C 4 ) carbon atom in pyranose ring decrease the viscosity more than monosaccharides with two axial hydroxyl groups in these positions. Due to the differences in molecular structure of saccharides resulting in different shape of molecules and different compatibility to the water structure, the saccharides differ in ability to disturb water layers around alumina particles.

The aim of the current paper is to present the development of the method used for fabricating highly textured α -alumina elements. The experimental procedure described is based on a combination of two techniques: gelcasting is used in tandem with high magnetic field exposure. In the element shaping process, a new, low-toxic and environmentally friendly gelating system was implemented that is based on in situ polymerisation of an acryloyl derivative of galactose. Here, care was taken to achieve a highly textured structure of elements gelcast from the ceramic slurries of high solid contents (45–50 vol%), which have not been processed successfully for magnetic field alignment before. A secondary aim of the study was to investigate the combined effect of magnetic field exposure duration and the idle time of polymerisation on the effectiveness of the alignment. In the course of the experiment, high degrees of crystalline orientation of the gelcast samples were obtained ranging from 0.92 to 0.96, developed after the subsequent sintering at 1600 °C (the parameters were calculated on the basis of XRD pattern of the surface perpendicular to the magnetic field direction). The microstructures of the obtained elements are described in detail at the end of the paper, in a stereological analysis.

Monodisperse Ba0.6Sr0.4TiO3 hollow spheres (HS-BST) with good spherical morphology, uniform size and accurate proportion of Ba/Sr were systhesised using a novel template-assisted method. The particle size and shell thickness of HS-BST particles were adjusted by controlling synthesis conditions, including carbon sphere size, reactant concentrations, reaction time and temperature, as well as the content of hydrolytic inhibitor. The surface morphology of HS-BST could be improved by the addition of appropriate hydrolytic inhibitor (triethanolamine, TEA), as it could reasonably control the diffusion of metal ions and prevent problems such as BST coating uniformity caused by improper hydrolysis rates. The accurate proportion of Ba/Sr was obtained with the presence of hydrolytic inhibitor. The facile synthetic approach would provide a new insight into the design and fabrication of hollow spheres of other perovskite oxides.

Platelet PbBi4Ti4O15 (PBIT) microcrystals were fabricated by molten salt methods using different TiO2 crystal forms (anatase and rutile) as the reactants. The results showed that the pure PBIT phase can be obtained by using rutile as the reactant, while the PBIT and TiO2 phases coexisted when using anatase as the reactant. In comparison to anatase, the co-topping connection of rutile has better stability and accelerates the nucleation growth rate in a molten salt environment. Thus, PBIT microplatelets with the good crystallinity and plate-like morphology (aspect ratio of ~27) can be obtained when rutile is used as the reactant. Specifically, when using rutile as the reactant, a maximum d 33 ∗ of ~153 pm/V can be obtained, which may potentially allow the fabrication of anisotropic perovskite templates for textured ceramics.

Plate-like Ba0.6Sr0.4TiO3/Poly (vinylidene fluoride - trifluoroethylene -chlorotrifluoroethylene) (P-BST)/P(VDF-TrFE-CTFE) functional composite films were prepared via a tape casting method. All samples have textured microstructure, and the orientation degree of the composites is above 50%. Though pure terpolymer has a low dielectric permittivity (20.4) and a high loss (0.52), the introduction of ceramic particles can effectively enhance its permittivity as well as decrease the loss. The composite filled with 40 vol% ceramic fillers showed a high permittivity of 88.3 as well as a low loss of 0.056 accompanying with a high dielectric tunability about 30%. Additionally, the dielectric tunable theoretical model of the composite was investigated. The functional relationship between phenomenological coefficient ratio β1/β2 and the ceramic content was obtained. The final results indicate that the value of β1/β2 is inversely proportional to the ceramic phase content, as opposed to the composites matrix's dielectric constant which cannot be tuned by the electric field.

The controlled development of texture in ceramics allows to improve some electrical, piezoelectric and mechanical properties of advanced ceramics materials by tailoring the microstructure. A highly textured microstructure of undoped dense alumina was attained by applying a novel combination of gelcasting techniques with magnetic alignment followed by sintering. A newly synthesized low-toxic acrylic monomer based on galactose was introduced to the gelcasting procedure. Thermal analysis of the gelcast has been performed to examine decomposition process of the new binder and match appropriate sintering rate. The effectiveness of the proposed procedure has been related to rheological properties of the suspension by clarifying the influence of the powder and the dispersant content. It has been also related to the idle time of polymerization by clarifying the influence of the initiator content. The new method is compared to slip casting in high magnetic field that has been used widely so far.

The article presents the interdisciplinary research among organic synthesis, chemistry of polymers and ceramic technology. It presents the synthesis of monoacryloyl esters of fructose and glucose that is 1-O-acryloyl-D-fructose and 3-O-acryloyl-D-glucose, conditions of their polymerization and application in shaping of advanced ceramic powders by the so called gelcasting method. The paper presents the influence of carbohydrate esters on the viscosity of Al2O3 suspensions and microstructure of final ceramic samples. The results showed that synthesized esters of saccharides can play the role of organic monomers able to polymerize in situ and self-cross-linking compounds in gelcasting. The paper presents the proposed structure of polymeric network which is formed from acryloyl ester of glucose during gelcasting process. The paper describes rheological behaviour of slurries composed of synthesized substances and A2O3 powders, wetting angles of alumina substrate by synthesized compounds, differences in glass transition temperatures of polymers and the microstructure of obtained final ceramic samples.

The aim of the work was to study a use of an acryloyl derivative of glycerol (glycerol monoacrylate), as a low-toxic, water soluble monomer in shaping of ZrO2 by using the in situ polymerization. The derivative was synthesized by the authors in a one-step synthesis. The work presents an interdisciplinary research in polymer chemistry and ceramic technology showing, how the properties of the system monomer/polymer influence the properties of zirconia green bodies. The wetting angle, glass transition temperature and polymeric shrinkage of the synthesized compound were measured at first. Then the zeta potential and rheological properties were measured to characterize the zirconia slurries. Ceramic green bodies were obtained by gelcasting through in situ polymerization of glycerol monoacrylate. The density, porosity and tensile and bending strengths were then measured, and thermal analysis and microstructure observations were performed for zirconia samples. The results have confirmed that glycerol monoacrylate provides a good homogeneity and high mechanical strength of ZrO2 samples both before and after sintering (749 MPa). The density of the sintered samples was around 99% of TD. The polymer is characterized by a very low glass transition temperature (−61 °C). It means that it is elastic at room temperatures, what positively affects the tensile strength of green bodies. The research has shown that the acryloyl derivative of glycerol is a good alternative for commercially available acrylic monomers used in shaping of zirconia by gelcasting.

The paper reports the development of a new system applicable in shaping techniques using in situ polymerization. The system is based on saccharides derivatives and allows to eliminate harmful processing agents from ceramic slurry. Instead of commonly applied 2-hydroxyethyl acrylate or acrylamide (monomers) and N,N,N′,N′-tetramethylethylenediamine (activator) the compounds based on glucose were used. As a monomer 3-O-acryloyl- d -glucose was applied. As a new activator l -ascorbic acid (also known as vitamin C) was used. Research was carried out for YSZ. As initiators ammonium persulfate and hydrogen peroxide were used. The new system was studied in terms of zeta potential, pH and rheological measurements. Ceramic samples were prepared by gelcasting and gel-tape casting methods. The experiments showed that l -ascorbic acid used as the activator has positive influence on rheological properties of suspensions with YSZ and together with ammonium persulfate allows to form defect free ceramic bodies with a homogenous composition.

Water leaching procedure was successfully applied for modification of surface properties and improvement of sinterability of commercial nano-ZrO 2 . It has been shown that the process effectively removes some ionic impurities thus influencing the compositional, electrokinetic and acidic/basic properties of nanozirconia surface. The process purifies the surface and improves the deflocculation susceptibility of nano-ZrO 2 if d -fructose is used as a dispersant. The studies revealed that by using a purified powder, it is feasible to obtain green and sintered samples of satisfactory densification and microstructural features. SEM micrographs of polished sintered bodies have provided some evidences that homogeneous and fully densified microstructure of the samples can be obtained by using water-leached nanozirconia powders.

Aluminum nitride was found to be of great significance in advanced ceramics. A widely applicable semiconductor, AlN is also commonly known for its considerable heat conductivity, as high as 320 W/(m·K). The idea behind the studies was to use AlN dispersions as a heat transferring liquid in closed systems. Such a liquid heat-carrier should give a proper rheological response when under variable shear-temperature conditions. Contrary to other systems reported in literature, i.e. nanofluids [1–20], the systems presented consisted of AlN micropowder and some novel base liquids: poly(propylene glycols) with an average molecular weight of 425 and 2000. The optimal result was to produce dispersions which display Newtonian-like flow at increased temperature and shear rate, as well as a suitable AlN concentration with sustained time-stability. This compilation of research assumptions should result in intensified heat exchange capabilities of liquid transferring media made on the basis of aluminum nitride.

Recently, great effort has been devoted to obtain porous materials with customized pore size distribution, high surface area and submicrometer sized microstructures or nanostructures. In this work, the viability of colloidal processing routes to obtain porous bulk ceramics using alumina nanopowders and d -fructose as a dispersant and a porosity former has been explored. The rheological behaviour of nanosuspensions was studied in order to assure their stability and to analyse the influence of different parameters (solids loading, fructose content, pH, sonication time). Mesoporous green bodies were obtained by slip casting with d -fructose in concentrations ranging from 5 to 50 wt%. The drying and burning-out conditions were determined by DTA-TG measurements and the sintering cycles were selected from the dynamic sintering curve. Sintered alumina materials with high porosity (>60%), open microstructures, submicrometer sized porosity (dp = 140–210 nm) and grain size lower than 500 nm, were obtained for pieces sintered at temperatures of 1300 and 1400 °C. The influence of different processing parameters on the porosity and the microstructure of the sintered materials is discussed.

Synthesis of a new low-toxic monomer obtained from glucose is reported and its application in gelcasting process is presented. The new monomer named 3-O-acrylic- d -glucose is an interesting alternative for the commercially available acrylic monomers. The presence of many hydroxyl groups in the monomer molecule allows to create hydrogen bonds in the polymer network. The resulting network does not need any external cross-linking agent to obtain a rigid ceramic part. The present paper describes the properties of ceramic slurries, green and sintered elements obtained from two alumina powders of different grain size (0.21 μm and 0.70 μm) with the use of the new monomer 3-O-acrylic- d -glucose and commercially available 2-hydroxyethyl acrylate.

A new type of composites, i.e. polymer-in-ceramic (as opposed to the “classical” ceramic-in-polymer approach) was introduced into the field of composite polymeric electrolytes. In this work the preparation of porous ceramic samples based on alumina is designed and their properties are characterised by XRD, porosimetry and SEM. Special setup was developed for the preparation of electrolytes in vacuum/controlled atmosphere conditions and it was used for preparing the composites. The studied systems exhibited excellent mechanical properties, high conductivities and good stability vs. Li metal electrodes under prolonged storage.

An acrylic monomer of low toxicity containing two hydroxyl groups has been synthesized and used for gelcasting in water. The results have been compared to those achieved with the use of a commercially available monomer (2-hydroxyethyl acrylate). Due to the chemical structure of the synthesized monomer, no addition of the crosslinking agent was necessary for gelation and similar results in terms of rheology of suspensions, density and microstructure of the bodies were obtained with respect to those obtained with the commercial monomer. However, higher time for gelation was observed. Two alumina powders with very different particle sizes were used in this study: a commercial submicron-sized powder ( d 50 = 0.35 μm) and a nanometer-sized alumina obtained by freeze-drying from aluminum sulphate solutions. The rheological behavior of concentrated suspensions was studied in order to establish their stability and to analyse the effect of the different monomers used in the process. Once the suspensions were optimized, the influence of the size of the powder on the gelation process was studied. The sintered density of submicrometer-sized alumina was higher (99%) than that measured when the bimodal suspension was used due to the difficulty to obtain highly concentrated suspensions from nanometric powder.

The design of ceramic–metal composites with a gradient concentration of the metal particles fabricated by the slip casting method is presented. The gradient concentration of the metal particles was achieved through their sedimentation under the action of the gravitational force and a magnetic field. The paper describes the method of calculating the distance between the ceramic particles and indicates the correlation between this distance and the size of the metal particles. Preliminary experimental results of fabricated Al2O3–Fe composites confirmed the calculations. The metal particles, whose density is higher than that of ceramic particles, can undergo gravity-induced sedimentation only when the distance between the ceramic particles is greater than the diameter of these metal particles. With a slip casting containing 50 vol.% of solid phase, no concentration gradient of metal particles occurred. The Fe gradient concentration was achieved when the sedimentation was aided by a magnetic field.

The present paper is focused on Al2O3–Al composites obtained via infiltration of porous ceramics by liquid Al. Infiltration of porous ceramics by liquid metal leads to produce microstructure with percolation of metal phase in ceramic matrix. However, the process of Al released caused by pressing is observed. This effect should be taken into consideration in designing of composites (in calculation of the amount of Al which is needed for full infiltration). To improve wettability between Al2O3 and Al the ceramic preforms were coated by the Ni–P. Ni–P deposited in form of a thin, tight film encapsulated ceramic grains and as a consequence, the liquid Al contacts first with Ni and then penetrates inside porous preform. The size of metal phase in this case depends on the size of pores. The size of pores influences also the kinetics and extent of infiltration. This method is useful for fabrication composites with metal phase size in the range of micrometers. During the process of infiltration, the new phases appeared. Among them there are spinel phase and aluminides. These phases are an evidence of diffusion reaction between liquid aluminium and alumina. As a consequence, they can influence the fracture toughness of the composites. Filling up pores by the metal provide a microstructure with interpenetrating network. Such composites are design for their strength and toughness. Moreover, such a microstructure can be an important in applications in which electrical properties of material are relevant.

The present paper describes technology and properties of novel ceramic–polymer construction and functional composites obtained via infiltration of porous SiO2 by polynitrile–urea–urethane elastomer (PNUU). The obtained results show that infiltration method can be used to fabricate composites with percolation of ceramic and polymeric phases. These composites exhibit a high compression strength together with ability to sustain large deformations. During the cycling loading, the elastomer behaves as strengthened by the ceramic. On the other hand, the presence of elastomeric phase prevents the composite from rapid failure. Scanning electron microscopy (SEM) technique was used to describe the composite microstructure and stereological methods for its quantitative description. The elastic modulus and density of composites were measured and discussed in terms of the rule of mixture.

Preliminary results of studies of ceramic–metal composites Al2O3–Fe obtained via infiltration of a porous ceramic matrix are reported. Composites with a thin FeAl2O4 spinel layer, as observed in the present work, on the ceramic/metal interface, will give an opportunity to develop an interpenetrating network with a strong ceramic–metal bonding.

This paper is concerned with the synthesis of composites in the Si 3 N 4 –Al 2 O 3 –TiC–Y 2 O 3 system. The materials obtained have a high density and a good fracture toughness (K IC =9.3 MPa√m). Machining tests show that the service life of the tool blades made of these composites may even be tenfold longer than that of commercial blades made of Si 3 N 4 with an additon of Al 2 O 3 , MgO and Y 2 O 3 .