Papers by Author: Zbigniew Pędzich

Abstract: In the presented work the effect of graphene platelets (GPLs) grade and mixture homogenization parameters on the microstructure and selected properties of Si₃N₄ – graphene composites have been investigated. Three different commercial grades of the multilayer graphene platelets were used as a filler for ceramic matrix. The mixtures of silicon nitride powder with 2wt% of GPLs were prepared using planetary mill at 200 – 400 rpm for 1 – 16 h. The water, acetone and isopropanol have been tested as a wetting medium. The composites were sintered using Spark Plasma Sintering – SPS at 1650 °C under 35 MPa of uniaxial pressure during the whole cycle. Microstructure, density, Young modulus, hardness and indentation fracture toughness of the sintered samples have been investigated. The microstructure homogeneity of the composites depends mainly on the milling duration. Milling process should last for about 4 – 8 h at 200 rpm for optimum results. Mechanical properties of the composites are slightly varied depending on the mixture preparation parameters. The homogenization time has a little stronger influence on the Young's modulus and hardness in the case of composites containing larger graphene sheets, in connection with the fragmentation of its microstructure. The best properties have composites reinforced by the GPLs characterised both by the smallest thickness and lateral size of nanosheets.

Abstract: The paper concerns composite materials made of silicone rubber matrix and ceramic fillers used as flame resistant coverings for electrical cables. Under fire, such materials must be able to form, relatively quickly, compact and stiff protecting coating, strong enough to maintain integrity of electrical circuit, even up to melting temperature of metal core. The residue of fired silicone rubber or silica filled elastomer exhibit a form of white powder. There is no evidence of solidification of silica particles, even after heating at 1100°C. However, the addition of some ceramic phases results in reaction with silica matrix (starting at about 900°C) producing a liquid phase, what facilitates particle binding. At lower firing temperatures (600°C) the problem of binding between the product of pyrolysis (silica) and filler is also present, what results in formation of fragile surface shield. The problem can be overcome by the addition of certain inorganic materials to the silicone rubber matrix. The paper discusses their influence on ability of silicone rubber composites, additionally containing glassy phase, wollastonite, mica, aluminium hydroxide, montmorillonite or calcined caoline, to ceramization.

Abstract: Paper describes the experiment on manufacturing of composite basing on silicone rubber matrix filled with silica binder and kaolin and also glassy fillers. Such material is oriented on applications connected with potential fire hazard. Investigations performed on three mixes, differentiated in proportion of components, indicate potential simply way of composition of ceramizable composite.

Abstract: The paper presents the analysis of the fracture path in composites with the alumina or zirconia matrix containing inclusions of another oxide or tungsten carbide. The description concerns the fracture of composite systems with 10 vol.% of inclusions (particulate composites), other three-systems with 33 vol.% of inclusions of each phase and the two phase composite with the equal phase content (50 : 50 vol.%). The different phase proportion and diversified content of inclusions cause significant differences in the microstructure of composites. The main difference between particulate composites and composites with continuous phases depends on a possibility of occurrence of toughening mechanisms connected with crack – inclusions interactions. In connection with a different interphase boundary strength, this phenomenon leads to significant differences in the way of composite fracture. The presented results of mechanical properties of composites were analyzed in the aspect of their way of fracture.

Abstract: The paper presents the results of investigation on the wear of alumina-based composites containing submicrometre particles of other phases in different conditions of work. Three types of phases were used as additives: tungsten carbide, yttria stabilized zirconia and metallic tungsten. The above mentioned phases were used separately or simultaneously as mixes. Two types of tests were performed - the Dry Sand Test and the Miller Test in wet pulp. Coarse silicon carbide grains were used as an abrasive medium in both cases. The results indicate that the optimal wear susceptibility in given work environment could be achieved by the addition of different type of additives.

Abstract: The paper presents the results of investigations on the influence of the starting mass grain size distribution on microstructure of sintered magnesia-spinel products. The model investigation was conducted using magnesia clinkers and fused spinel. The grain size distribution of starting mixes were selected according to Dinger and Funk's theoretical curves with different values of n coefficient. The results clearly indicate that the best properties were achieved when n value changed in the range of 0.22 - 0.30 and forming pressure was contained in the range of 160 - 200 MPa.

Abstract: Lead lanthanum zirconate titanate (known as PLZT) ceramic powders have been prepared by the modified sol – gel method, and underwent consolidation by the hot uniaxial pressing method. Application of such technique of preparation permitted to receive fine-grained transparent PLZT x/65/35 ceramics, with x = 8 -10 La at.%. The present publication gives a detailed account of the relationships between technology and physical properties of obtained materials. To analyze all ceramics SEM, EDS and mercury porosimetry were performed, and dielectric properties were studied too. Quite wide light transparency from the visible to nearinfrared range for PLZT ceramics was detected using optical absorption and infrared spectroscopy.

Abstract: Paper presents the results of investigation on wear of alumina and alumina-basing particulate composites by hard abrasive particles in different environments. The results of two tests (The Dry Sand Test and the Miller Test in pulp) were compared. As an abrasive medium coarse silicon carbide grains were used in both cases. The alumina microstructure was modified by different inclusions: zirconia, tungsten carbide, metallic tungsten and their mixtures. The results indicate that the optimal wear susceptibility in given work environment could be achieved by the addition of different type of additives.

Abstract: The paper deals with the results of mechanical properties and microstructure investigations performed in two composite systems: Al2O3/WC and Al2O3/W. The fracture toughness measurements were made for materials characteristics. Microstructure of composites was thoroughly investigated using transmission and scanning electron microscopy. Selected Area Electron Dffractions (SAEDs) as well as Electron Backscatter Diffractions (EBSDs) were applied to establish crystallographic relationships between neighboring grains of different phases both in a local and global scale. Examples of orientation maps and stereographic projections for different crystallographic directions as well as orientation relationships between different phases (alumina and reinforcing inclusions) were shown and described.