Papers by Author: László A. Gömze

Abstract: Yttrium (Y) modified strontium titanate (SrTiO₃) powders with initial concentration of Y in the range of 0 to 15 mol% were produced through sol-gel technique. X-ray diffraction (XRD) studies show that all the prepared compounds have a perovskite cubic structure with the space group (Pm3m). The lattice constant, lattice strain and crystallite size of the as-prepared samples were estimated from the XRD pattern which reveals the incorporation of Y into SrTiO₃ system, moreover to investigate the quality of the prepared SrYT ceramics powder, the scanning electron microscopy (SEM) was used to determined investigate the morphology, grain size and its distribution. The analysis of the thermal conductivity measurements performed on the obtained powders revealed the effect of the combination of temperature and Y content on the thermal conductivity value, Indeed, the minimum thermal conductivity was 4.12 W/(mK) obtained with 15%Y at 464 K.

Abstract: The authors have investigated the influence of sintering time at 1600 °C on microstructure, shrinkage, density, surface hardness and bending strength of Al₂O₃ based ceramic composites. From the ceramic powder mixes, the specimens were compacted by uniaxial pressing and during sintering the heating gradient was 100 °C/h. The experiments have shown that at 1600°C of sintering temperature, the specimen densifications have almost finished within 5 hours, meanwhile the crystal grows processes were continued for up to 9 hours of sintering. The authors have found that the maximum values of hardness and mechanical bending strength of specimens were obtained at 5 hours of sintering and these values have slowly decreased with increasing the sintering times.

Abstract: The present research work deals with the examination and rheological modelling of flow properties of asphalt mastics which are the most important components of asphalt concretes. Asphalt mastics are mixtures of fine grained mineral filler particles (d<0,063 mm) and bitumen, having a stabilizing role in asphalt mixtures and largely determining the cohesion between mineral particles and bitumen. During our examinations two types of mineral fillers – limestone and dolomite – as well as standard bitumen were tested, which are extensively used in Hungarian road construction. Asphalt mastic mixtures were prepared out of these materials and they were tested with dynamic shear rheometer (DSR). According to the test results, rheological models of mastics were determined. It has been established that at different test temperatures and shear rate ranges asphalt mastics behave as Herschel-Bulkley and Bingham-type materials.

Abstract: In the traditional heavy-clay industry, compounds are usually prepared by the addition of organic waste material. These additives originate mainly from the wood, food or paper industries. The purpose of this study is to present the results of the examination of friction contact between the wall of the forming die and the clay compounds containing organic additives. Saw dust and ground sunflower seed shell were mixed to clay in 0 wt%, 3 wt% and 5 wt%. The water content of compounds was also varied. The clay and the additives were described by morphology, XRD, bulk density and equivalent diameter. Friction tests were carried out on a special tribometer up to plastic deformation of the sample. The coefficient of friction decreased when normal stress was increased for all the ten compounds. Average results showed that the tendency of change in the value of the coefficient of friction could be divided into three sections: a decreasing, a quasi constant and a shearing section. It follows from this that the coefficient of friction can be characterized with a number only inside the quasi constant section, i.e. between two definable normal stress values. Averaged coefficient of friction was between 0.17 and 0.21 for saw dust and between 0.19 and 0.21 for the compounds with ground sunflower seed shell.

Abstract: On the basis of several years experiments in investigation of hetero-modulus material structures and using natural biomaterials and high purity quartz powders the authors successfully developed new high porosity low density SiC ceramic cellulars and foams. For the development of new silicon-carbide and carbon-silicon-carbide (C/SiC) cellular ceramic composites and foams the author used high purity SiO₂ powders mined in Fehervarcsurgo (Hungary) and a biomaterial reagents made from renewable vegetable under trade-name IG-R1. These low density high porosity silicon-carbides probably can be successfully applied in development of light weight ceramic reinforced metal alloy composites in the future. The structure and X-ray diffraction (XRD) analysis of used raw materials and the achieved by authors new SiC and C/SiC ceramic composites and foams are described and shown in present work.

Abstract: The aim of the present research work is to examine the influence of mineral composition and grain size distribution on the properties of limestone and dolomite mineral fillers used in Hungarian road construction. Since these properties fundamentally define the features of asphalt pavements, our research goals were assigned accordingly. Different fractions of two mineral fillers (limestone from Alsózsolca and dolomite from Pilisvörösvár) were compared. We have observed deviations in the grain size distribution of some fractions of fillers that were free of contaminations. While limestone consists of a great amount of fines and a relatively small amount of coarse grains, in case of dolomite it is the opposite, that is, small amount of fines and greater amount of coarse grains. The decrease of the grain size of fractions resulted in a slight increase of specific surface area of fillers. We have observed that by the decrease of the grain size of fillers, the hydrophilic coefficient has also decreased. The increasing presence of fines however, resulted in the decrease of the hydrophilic coefficient.

Abstract: To obtain advance hetero-modulus and hetero-viscous complex materials with extreme high dynamic strength, wear and thermal shock resistances a novel approach was applied by the authors. The developed new hetero-modulus and hetero-viscous composites were reinforced with nanoparticles and submicron fibers and whiskers of Si₂ON₂, SiAlON, AlN, Si₃N₄ as well as with special additives, which had turned into amorphous phases during sintering. These types of materials have several Youngs modulus and viscosities simultaneously and have high damage tolerance and ability to absorb and dissipate the elastic energy during crack propagation. Understanding the energy engorgement of high speed collision processes, the material structures and rheological properties of such a complex hetero-modulus and hetero-viscous material the authors could mathematically describe the mechanical shear stresses in these complex materials. Analytical methods applied in this research were scanning electron microscopy (SEM), X-ray diffraction, and energy dispersive spectrometry, digital image analysis was applied to microscopy results, to enhance the results of transformations.

Abstract: In this work the Authors are dealing with the utilization of mineral fillers used in the Hungarian road construction. Six different types of mineral fillers – andesites, basalt, dolomite and limestone – were tested. In the purpose of the applicability of mineral aggregates in road construction XRD, BET specific surface test, as well as SEM tests were made and hydrophilic coefficient of fillers were also determined. The results of the XRD, BET specific surface test, SEM and hydrophilic coefficient tests show that all of the examined fillers are suitable for asphalt-technological applications, particularly limestone filler (Alsózsolca) and dolomite filler (Pilisvörösvár).

Abstract: A novel approach to obtain ceramic matrix composites with extreme high mechanical wear and thermal shock resistance abilities is presented. The developed corundum matrix composites were reinforced with nanoparticles, submicron fibres and whiskers of Si2ON2, SiAlON, AlN and Si3N4. These kinds of materials have several Young’s modulus simultaneously. These new alumina based ceramic matrix composites were obliged to collisions with different metallic bodies having high densities and impact speeds larger than 900 m/s at the moment of the hits. During the experiments in the places of collisions where oxygen was absent new high density „diamond-like” c-Si3N4 cubic crystals have developed with spinel structures, where nitrogen atoms were distributed in the centres of the cubes. These new spinel crystals of c-Si3N4 in the alumina matrix have extreme high dynamic strength, hardness and wear resistance, like diamond. They were fully resistance to oxygen and thermal shock at the tested temperature of 1200 oC.

Abstract: Vegetal materials are generated in high amounts and are applied as additives in clay bricks since ancient times. They have a certain heat contribution to the firing process. As revealed by X-ray Powder Diffraction, main component of vegetal waste materials is cellulose. Thermal and Evolved Gas Analysis revealed the combustion process in its details. Mixtures of clay and vegetal additives prepare for test bodies were analyzed by Thermal Analysis. The thermal effects were quantified by Differential Thermal Analysis and correlated with Thermogravimetry and Derivative Thermogravimetry.