László A. Gömze

Improvement of Insulation Properties of Conventional Brick Products

The use of technologically byproduct agricultural wastes in various segments of the brick and tile industry is increasing continuously. The additives, mixed into the raw clay ignite during the firing process, adding extra thermal energy from inside the mixture decreasing the energy requirements of the manufacturing process. Added to this, through the combustion of the bio-wastes the porosity increases enhancing the thermal insulation properties of the final product. We have investigated some common, agricultural wastes to determine their effect on the thermal properties of bricks. In our experiments industry relevant amounts of additives (sawdust, rice-peel, seed-shell) were added to the basic clay composition. We have prepared mixtures with additive concentrations of 0, 4, 7 percentage by weight. The preparations of the samples were (milling, drying and firing) following industrial standard procedures. Precise thermal conductivity data were gathered from all samples using a RAPID-K type static thermal conductivity measuring instrument. Our measurements show that by increasing the amount of the organic byproducts in the clay mixture it is possible to significantly decrease their thermal conductivity, leading to an improved insulation capability of commercial brick products. On the other hand, there was only a minor reduction in the mechanical strength found during previous works. The investigated agricultural byproducts were also ranked based on their effect on the products thermal properties. It was found that the largest decrease to the thermal conductivity was caused by the sunflower seed-shell additive. Mixing 7 % wt. seed shell to the clay, we can decrease the thermal conductivity of the fired product from 0,27 W/m·K to 0,17 W/m·K (36%). We have found that under the same conditions the sawdust caused the least improvement, only a decrease of 0,27 W/m·K to 0,23 W/m·K (16%) was measured.

Characterization of Mineral Materials as Asphalt Fillers

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).

Hetero-modulus alumina matrix nanoceramics and CMCs with extreme dynamic strength

Applying the well-known alumina powders for matrix, different oxide and non-oxide ceramic submicron and nano-particles as additive materials, and investigating the impact of nitrogen atmosphere on sintering; the authors successfully developed new hetero-modulus alumina matrix ceramic composite materials, reinforced with submicron and nanoparticles of α-Si3N4 β-Si3N4, Si2ON2, SiAlON and AlN. Thanks to the new compacting technology with high speed flying punches in vacuumed N2 atmosphere developed by authors, phase transformation of α-Si3N4 and β-Si3N4 into cubic c-Si3N4 can be observed, creating so-called Si3N4-diamond submicron and nanoparticles in alumina matrix. The α-Si3N4, β-Si3N4, Si2ON2, SiAlON, AlN and c-Si3N4 diamond submicron and nanoparticles reinforced alumina matrix hetero-modulus nanoceramics have excellent mechanical properties and extreme dynamic strength. The dynamic strength was tested through collision with high density metallic flying bodies, with speed higher than 900 m/sec. Analytical methods applied in this research were laser granulometry, scanning electron microscopy, X-ray diffraction and energy dispersive spectrometry. Digital image analysis was applied to microscopy results, to enhance the results of transformation.

The Effect of Temperature and Composition to the Rheological Properties of Asphalt Pavements

Ceramics, concretes and asphalt-mixtures are the most popular building materials in Hungary, because of the highway programme of the government. In spite of their large popularity, some of the mechanical properties of ceramics, concretes and asphalts are not investigated enough till today. Particularly, there is no mechanical model usable to understand and explain the rheological behaviours of these materials with different compositions of mineral raw materials. It is well known, that the viscosity of viscous materials, viscoelastic materials, and viscoplastic materials dynamically decreases, as the temperature increases. The decrease of viscosity by leaps and bounds could be extremely dangerous in case of asphalt pavements in the range of 55 – 75 °C, due to the crossing of cars on the low viscosity pavements which suffer inelastic deformation, as a result. Using a Rheo-tribometer instrument developed by L. A. Gömze and others, the authors have investigated and tested asphalt mixtures with different composition of mineral raw materials, and would like to reveal and review the dependence of the rheological properties of these pavements against the temperature, and the intensity of the dependence.

The influence of porosity on the elasticity and strength of alumina and zirconia ceramics

This work investigates the behavior of porous alumina (with the porosity ranging from 18% to 70%) and zirconia (with the porosity ranging from 10% to 60%) ceramics when subjected to deformation by compression and shearing. The analysis of stress-strain curves showed that there is a transition from a typical brittle state for relatively dense ceramics, to a pseudo-plastic one for ceramics with high porosity. The values of the effective Young’s modulus, effective shear modulus and Poisson’s ratio decrease with the increase of the pore space volume of ceramics, which correlates with the appearance of multiple cracking during the deformation of the high porosity ceramics.

The Transformation of Added Vegetal Waste Materials during Clay Brick Firing

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.

Mechanochemical Phenomena during Fine Comminution of Clay Minerals for Ceramic Bricks and Roof-Tiles

During the fine comminution of clay minerals and layered silicate materials with relative large volume of specific surface area appreciable changes in chemical and minerological compositions can be observed. In this paper is described the mechanochemical investigation of conventional clay minerals from „Lenti” region (Hungary), having natural BET specific surface larger than 35-40 square metres per grams. The laboratory experiments made by author had shown an intensive reduction of specific surface volume at the beginning of grinding, further relatively slow growth and reduction of BET and Langmuir surfaces were observed. The content of mineral Muscovite–2M1 – (K, NH4Na)Al2(SiAl)4O10(OH)2 – has decreased and the contents of Quartz – SiO2 – and Illite-1M (NR) – KO.7Al2(SiAl)4O10(OH)2 – have increased considerable depending on grinding time. Increasing the milling time the amount of Albite – NaAlO.91Si3O8 – and other mineral components were also not stable, but their content have varied not so strong as Muscovite–2M1 or Quartz and Illite–1M. The examined clay minerals had a certain proportion of amorphous particles as well, but in this contribution only the changes in proportions of crystalline particles are described.

Hetero-modulus Nanoparticles Reinforced Corundum Matrix CMC with Extreme Wear and Thermal Shock Resistances

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.

Effect of mechanical treatment on properties of zeolites with chabazite structure

Zeolites are a valuable material having a wide variety of applications. We have examined the effect of mechanical activation on physical-chemical properties of commercial brands zeolite SAPO-34 and SCT-323. It has been shown that the amount of amorphous phase and the specific surface area depends on mechanical treatment. Specific surface area of the zeolites decreases strongly during the grinding process in mills. With the increase of milling time the particles size of zeolites decreased. An increase in amorphisation was observed. Specific surface area of zeolites after mechanical activation in a tumbling ball during 96 hours and annealing up to 800°C with an isothermal holding time of 1 hour does not lead to marked changes and decreases strongly after annealing at 1000°C/h. It has been shown that the milling time of ball milling is a powerful method to obtain the necessary specific surface.

Influence of raw materials composition on firing shrinkage, porosity, heat conductivity and microstructure of ceramic tiles

In this work some new raw material compositions from alumina, conventional brick-clays and sawdust were mixed, compacted and heat treated by the authors. Depending on raw material compositions and firing temperatures the specimens were examined on shrinkage, water absorption, heat conductivity and microstructures. The real raised experiments have shown the important role of firing temperature and raw material composition on color, heat conductivity and microstructure of the final product.