Ákos Lakatos
University of Debrecen
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Featured researches published by Ákos Lakatos.
Building Services Engineering Research and Technology | 2013
Ákos Lakatos; Ferenc Kalmár
This article presents the results of water sorption properties investigation and thermal conductivity measurements of expanded polystyrene thermal insulation materials with different mass densities. The sorption behaviour of the expanded polystyrene materials was achieved in a Climacell 111 type climatic chamber, after drying in a Venticell 111 type desiccator apparatus. The relative humidity varied from 25% to 90% at 293 K for 240 min. The thermal conductivity of each sample was determined using a Holometrix 2000 (HLS) heat flow meter. In this article, the sorption isotherms, sorption kinetics, thermal conductivities and the prediction of changes in function of water content of four pure expanded polystyrene (30, 100, 150, 200 and grey) slabs with different densities (14, 17.5, 23.7 and 27.5 kg/m3) and one expanded polystyrene mixed with graphite are given (grey expanded polystyrene). Practical application: The thermal conductivity as well as the moisture content are key thermal transport properties of building materials. The role of insulating materials in the building energy and moisture balance is more significant when compared with the other materials of the building structures. The laboratory measurements of these values of the insulating materials are very important either for the manufacturers or the contractors. The available bibliographic data for these materials are strongly incomplete and somewhere out of date.
Advanced Materials Research | 2014
Ákos Lakatos
Currently thermal insulating of the buildings is sorely needed from the point of view of energy as well as money savings. It is important to highlight that the most commonly used insulation materials in the building sector are the expanded polystyrene (EPS), the extruded polystyrene (XPS) and the fibrous (mineral, rock) ones. In this communication we confront 6 different insulating materials slabs (EPS 30, 100, 150, 200, a yellow XPS and a mineral wool by their thermal properties. Therefore two types of hypothetic building structures were created and they were insulated with the above presented materials from 0.01 m to 0.3 m thicknesses. For the calculations the thermal conductivity of each sample was determined using a Holometrix 2000 (HLS) heat flow meter. As a result their heat transfer coefficients, delaying abilities, energy storing capabilities and thermal diffusion coefficients were confronted. Besides a material constant had been defined and was paired with the measured thermal conductivity.
Applied Physics Letters | 2010
Ákos Lakatos; G.A. Langer; A. Csik; Cs. Cserháti; Miklos Kis-Varga; Lajos Daróczi; G.L. Katona; Z. Erdélyi; G. Erdélyi; K. Vad; D.L. Beke
We describe a method for measurement of nanoscale shift of interfaces in layered systems by a combination of secondary neutral mass spectrometry and profilometer. We demonstrate it by the example of the investigation of interface shifts during the solid state reaction in Ni/amorphous-Si system. The kinetics of the shrinkage of the initial nanocrystalline Ni film and the amorphous Si layer as well as the average growth kinetics of the product phases were determined at 503 K. The results show that nanoscale resolution can be reached and the method is promising for following solid state reactions in different thin film systems.
Philosophical Magazine | 2013
Dezső L. Beke; G.A. Langer; G. Molnár; G. Erdélyi; G.L. Katona; Ákos Lakatos; K. Vad
Mass transport and solid-state reactions in nanocrystalline thin films are reviewed. It is illustrated that diffusion along different grain boundaries (GBs) can have important effects on the overall intermixing process between two pure films. These processes can be well characterized by a bimodal GB network, with different (fast and slow) diffusivities. First the atoms migrate along fast GBs and accumulate at the film surface. These accumulated atoms form a secondary diffusion source for back diffusion along slow boundaries. Thus the different GBs of the thin films can be gradually filled up with the diffusing atoms and composition depth profiles reflect the result of these processes. Similar processes can be observed in binary systems with intermetallic layers: instead of nucleation and growth of the reaction layer at the initial interface, the reaction takes place in the GBs and the amount of the product phase grows by the motion of its interfaces perpendicular to the GBs. Thus, the entire layer of the pure parent films can be consumed by this GB diffusion-induced solid-state reaction (GBDIREAC), and a fully homogeneous product layer can be obtained.
Vacuum | 2010
Ákos Lakatos; G. Erdélyi; G.A. Langer; Lajos Daróczi; K. Vad; A. Csik; A. Dudás; Dezső L. Beke
Proper understanding of the degradation mechanisms and diffusion kinetics of copper and cobalt interconnections for advanced microelectronics is important from the point of view of fundamental research and technology as well. In this paper Si(substrate)/Ta(10 nm)/Cu(25 nm)/W(10 nm) and Si(substrate)/Co(150 nm)/Ta(10 nm) samples, prepared by DC magnetron sputtering, were in investigated. The samples were annealed at several temperatures ranging from 423 K to 823 K for various times. The composition distributions were detected by means of Secondary Neutral Mass Spectrometry (SNMS). Microstructural characterization of samples was carried out by means of Transmission Electron Microscopy (TEM). It is shown that the changes in the composition profiles were mainly caused by grain boundary, GB, diffusion and the effective GB diffusion coefficients of Ta in Cu were determined both by the ‘‘first appearance’’ and ‘‘centre-gradient’’ methods. The activation energy is 100 kJ/mol. The importance of the Ta penetration into the Cu and its accumulation at the Cu/W interface can lead to an increase of the Ta content in the copper film. This can be an important factor in the change/degradation of the physical parameters (e.g. the electrical resistance) of interconnects. Furthermore a Ta segregation factor in Cu was evaluated. Preliminary results in the Si(substrate)/Co(150 nm)/Ta(10 nm) indicate fast (GB) diffusion of the Si into the Co layer, formation of a cobalt silicide layer at the Co/Si interface and Si accumulation first at the Ta/Co interface and later a retarded accumulation at the free Ta surface. 2010 Elsevier Ltd. All rights reserved.
Building Services Engineering Research and Technology | 2014
Ákos Lakatos; Ferenc Kalmár
Nowadays, the most applied insulation material in the building sector is the expanded polystyrene. Different types of expanded polystyrene are used but more widely used is the graphite added type. Our research focuses on the analysis of heat conductivity and sorption properties of expanded polystyrene as these two are the most important physical properties from energy saving point of view. In this paper, the variation of heat transfer coefficient of an insulated wall is analysed in function of humidity content of insulation material. Brick and concrete walls with 0.4 m thickness were chosen for substrate and 0.1 m expanded polystyrene (30, 100, 150, 200 and the so-called grey expanded polystyrene) materials were applied as insulating layers. The investigations of sorption behaviour of the materials are important from the point of view of fundamental research and building technology as well. Sorption data taken from our previous measurements results were used for predicting the change of the overall heat transfer coefficients of different wall structures constituted this way. Practical application: The present technical note is based on our previous measurement results. Water can cause undesirable changes in the building structures and introduced in this article. During the fixing procedure of the additional insulating of a given building bad weather conditions (high relative humidity and/or low external temperature) can dominate. These phenomena can be imagined for building new houses. By the ‘in-building’ of the moisture into the wall structure, numerous and measurable change can happen in the U-value of the building envelope. The presented changes are estimations only, but can be used and can also help for planning and executing the insulating process.
International Review of Applied Sciences and Engineering | 2011
Ákos Lakatos
Abstract Proper understanding of sorption behaviour of the materials is important from the point of view of fundamental research and technology as well for applied building technology. In this paper a simple method is presented for measuring water sorption capability of solid bodies. Moisture sorption and desorption measurements were carried out on soil samples by using climatic chamber. After drying the samples in a Venticell 111 type drying equipment they were treated with a Climacell 111 type climate chamber, where the relative humidity (RH) was varied from 40 to 83% at 22°C for different times (40, 80, 120 and 240 minutes). The samples reached the equilibrium moisture content after 120 minutes for sorption. The desorption isotherm measurements were carried out at 22°C for 80 minutes of exposure at constant RH. At this point hysteresis phenomenon was observed. Besides the moisture content figures the time evolution of the damping process is also presented in this paper.
Science and Technology for the Built Environment | 2016
Ákos Lakatos
In recent years measurements and calculations of the thermal properties of building physics parameters of materials have become very important for thermal sizing and designing buildings. Moisture is an essential factor to consider when designing and applying building materials. This article investigates the influence of moisture in building physical properties of insulating materials. Thermal insulating of buildings is sorely needed regarding energy as well as saving money. This article presents calculations for the changes in the most important building physics parameters of insulation materials influenced by water after measuring their thermal conductivity, moisture content, and density. Furthermore, this article will also present the positive or negative effects of water. Three different types of polystyrene (expanded, graphite doped expanded, extruded), mineral and glass wool fibers, as well as gypsum boards were tested. The non-equilibrium sorption behavior of the expanded polystyrene materials was achieved in a type Climacell 111 climatic chamber after drying them in a type Venticell 111 desiccating apparatus. The relative humidity varied from 25% to 90% at 293 K for 240 min. The thermal conductivity of each sample was determined by using a Holometrix 2000 heat flow meter after drying the samples to changeless weight in the above mentioned desiccating apparatus.
International Review of Applied Sciences and Engineering | 2013
Ákos Lakatos; S. Szigeti; Ferenc Kalmár
Abstract These days, the investigations of the physical properties of the insulating materials are very important. In this paper we report the measured water uptaking capabilities of a thermal insulating paint. They can be found in liquid phase, but we measured dried solid samples. The thin thermal insulators (insulator coatings) are starting to spread on the market of the building materials. The proper understanding of sorption behavior of the materials is important from the applied building technology point of view. Moisture sorption and desorption measurements were carried out on two samples with different geometry by using climatic chamber method. After drying the samples at 90 °C for one hour in the Venticell 111 type drying equipment they were wetted with a Climacell 111 type climate chamber, where the relative humidity (RH) was varied from 25% to 90% at 293 K for 2 hours. The samples were wetted for 2 and 4 hours as well. Sorption and desorption as well as kinetic curves are presented in this paper.
International Review of Applied Sciences and Engineering | 2017
Ferenc Szodrai; Ákos Lakatos
The laboratory investigations of the heat transfer properties of wall structures are very significant from the point of view of designing the buildings. In this article measurements and calculation...