Recently, a new class of ceramic foams with porosity levels up to 90% has been developed as a result of the association of the gelcasting process and aeration of the ceramic suspension. This paper presents and discusses original results advertising sound absorbing capabilities of such foams. The authors man- ufactured three types of alumina foams in order to investigate three porosity levels, namely: 72, 88, and 90%. The microstructure of foams was examined and typical dimensions and average sizes of cells (pores) and cell-linking windows were found for each porosity case. Then, the acoustic absorption coefficient was measured in a wide frequency range for several samples of various thickness cut out from the foams. The results were discussed and compared with the acoustic absorption of typical polyurethane foams proving that the alumina foams with high porosity of 88-90% have excellent sound absorbing properties competitive with the quality of sound absorbing PU foams of higher porosity.
Magnetic properties of Fe nanowire arrays (NWs) electrodeposited in anodic alumina membranes have been studied. The influence of nanowire geometry (length, pore diameter) and an external magnetic field applied during electrodeposition process on the magnetic properties of nanowire arrays was investigated. With the use of the X-ray diffraction analysis the structure of iron wires was determined. The iron wires have the regular Body Centered Cubic structure. Magnetic measurements show that shape anisotropy aligns the preferential magnetization axis along the wire axis. It was found that the application of an external magnetic field in a parallel direction to the sample surface induces magnetic anisotropy with an easy axis of magnetization following the nanowire axis. The dependence of the height of Fe wires on the electrodeposition time was determined.
In ceramic forming techniques high particles packing can provide better properties of the final ceramic products. The high quality of the material coupled with the shape complexity of the ceramic product is still challenging. The aim of this work was the optimization and preparation of the ceramic samples based on two alumina powders of different particle size (AA05: 0.5 μm and TM-DAR: 0.15 μm). Firstly, ceramic suspensions of 50vol.% solid loading and the volumetric ratio of AA05 to TM-DAR 1:1, 2:1, 3:1, 4:1, respectively have been prepared. The 2-carboxyethyl acrylate was applied as the new monomer limiting the negative effect of oxygen inhibition. Additionally, the cold isostatic pressing (CIP) was used in order to increase relative density of green bodies. The results of presented research have shown that samples with the ratio of AA05 to TM-DAR 2:1 were characterized by the highest green density (62%). Moreover, CIP process proved to be effective and increased the density of green bodies from 62% to 67%. The pore size distribution of the green bodies has been measured. Samples were sintered at different conditions (1400°C, 1450°C and 1500°C for 1h and 1300°C, 1400°C, 1450°C and 1500°C for 5h).
The subject of the study are alumina foams produced by gelcasting method. The results of micro-computed tomography of the foam samples are used to create the numerical model reconstructing the real structure of the foam skeleton as well as the simplified periodic open-cell structure models. The aim of the paper is to present a new idea of the energy-based assessment of failure strength under uniaxial compression of real alumina foams of various porosity with use of the periodic structure model of the same porosity. Considering two kinds of cellular structures: the periodic one, for instance of fcc type, and the random structure of real alumina foam it is possible to justify the hypothesis, computationally and experimentally, that the same elastic energy density cumulated in the both structures of the same porosity allows to determine the close values of fracture strength under compression. Application of finite element computations for the analysis of deformation and failure processes in real ceramic foams is time consuming. Therefore, the use of simplified periodic cell structure models for the assessment of elastic moduli and failure strength appears very attractive from the point of view of practical applications.
The technique of electrospinning was employed to fabricate uniform one-dimensional inorganic-organic composite nanofibers at room temperature from a solution containing equal volumes of aluminum 2, 4-pentanedionate in acetone and polyvinylpyrrolidone in ethanol. Upon firing and sintering under carefully pre-selected time-temperature profiles (heating rate, temperature and soak time), high-purity and crystalline alumina nanofibers retaining the original morphological features present in the as-spun composite (cermer) fibers were obtained. Tools such as laser Raman spectroscopy, scanning and transmission electron microscopy together with energy dispersive spectroscopy and selected area electron diffraction were employed to follow the systematic evolution of the ceramic phase and its morphological features in the as-spun and the fired fibers. X-ray diffraction was used to identify the crystalline fate of the final product.
Bending strength, thermal and electric conductivity and microstructure examinations of Cu based composite materials reinforced with Saffil alumina fibres are presented. Materials were produced by squeeze casting method applying the designed device and specially elaborated production parameters. Applying infiltration pressure of 90MPa and suitable temperature parameters provided manufacturing of copper based composite materials strengthened with Saffil alumina fibres characterized by the low rest porosity and good fibre-matrix interface. Three point bending tests at temperatures of 25, 100 and 300ºC were performed on specimens reinforced with 10, 15 and 20% of Saffil fibres. Introduced reinforcement effected on the relatively high bending strengths at elevated temperatures. In relation to unreinforced Cu casting strength of composite material Cu – 15vol.% Saffil fibres increase by about 25%, whereas at the highest applied test temperature of 300o C the improvement was almost 100%. Fibres by strengthening of the copper matrix and by transferring loads from the matrix reduce its plastic deformation and hinder the micro-crack developed during bending tests. Decreasing of thermal and electrical conductivity of Cu after incorporating fibres in the matrix are relatively small and these properties can be acceptable for electric and thermal applications.
The aim of this work is the development of Cu-Al2O3 composites of copper Cu-ETP matrix composite materials reinforced by 20 and 30 vol.% Al2O3 particles and study of some chosen physical properties. Squeeze casting technique of porous compacts with liquid copper was applied at the pressure of 110 MPa. Introduction of alumina particles into copper matrix affected on the significant increase of hardness and in the case of Cu-30 vol. % of alumina particles to 128 HBW. Electrical resistivity was strongly affected by the ceramic alumina particles and addition of 20 vol. % of particles caused diminishing of electrical conductivity to 20 S/m (34.5% IACS). Thermal conductivity tests were performed applying two methods and it was ascertained that this parameter strongly depends on the ceramic particles content, diminishing it to 100 Wm-1K-1 for the composite material containing 30 vol.% of ceramic particles comparing to 400 Wm-1K-1 for the unreinforced copper. Microstructural analysis was carried out using SEM microscopy and indicates that Al2O3 particles are homogeneously distributed in the copper matrix. EDS analysis shows remains of silicon on the surface of ceramic particles after binding agent used during preparation of ceramic preforms.