Miroslava Radeka

Particle size range as a factor influencing compressibility of ceramic powder

The paper reports on an investigation conducted with the aim to determine whether an overall deformation stress of ceramic powder depends on the size of particles present in a system. For this purpose, six fractions (obtained by sieving of raw material, so as to contain particles with defined size range) were compacted and their compaction response diagrams were generated. For each particular fraction the parameters of the Heckel compaction model were calculated and used for estimating the deformation stress of each particular fraction. A correlation between average diameter of particles and the overall deformation stress of powder was found.

Microbial Deterioration Of Clay Roofing Tiles

The study illustrates both the biodeterioration and biomineralization actions of two fungus species (Aspergillus niger and Cladosporium sp.) and two organic acids (oxalic and acetic) and the action of the frost (frost dilatation studies in laboratory conditions) as the main factors of the process of ageing of clay roofing tiles. The nano-crystalline products, formed in this way, contribute to the abundant reactive surface area of the existing and new filled pores (due to the fungus hyphen penetration into the ceramic support) deepening the ageing processes of the clay roofing tiles. A relationship between the textural and microstructural characteristics of the studied systems and the formation of the specific crystal forms, developed after the actions of fungus, and oxalic/acetic acids was set up.

Compaction mechanism as the function of atomized powder particle size

The cold compaction process of spray dried powder for ceramic floor/wall tiles production was followed by compaction response and compaction rate diagrams. Seven fractions of defined size, as well as the industrial powder batch, were compacted at pressures up to 31.5 MPa. The effect of particle size, textural and morphological characteristics on the consolidation mechanism was investigated. Both plastic deformation and brittle fracture were identified, the dominating mechanism in a given pressure range being the direct function of the size and morphology characteristics of the particles.

Microstructural Approach to Frost Resistance of Ceramic Roofing Tiles

Frost resistance of ceramic products is an important factor in the procedure of ceramic roofing tiles durability prediction. This property depends on many factors: raw material characteristics, processing parameters and environmental conditions (temperature fluctuation and moisture content). This paper is focused on the influence of vacuum value of the extruder and the speed of extruded column on the properties of the final products ( plain biber tiles). By alternating the operating parameters of vacuum extruder, the characteristics of the ceramic roofing tiles have been changed and a stable ceramic structure (3rd series, low water permeability, dominant pore diameter range: 0.5 – 1.0 μm) is formed. The frost resistance criterion presented in this work, links the critical pore diameter for water / ice transition, dilatation freezing values and the values of diametrical compression. Introduction A methodology that could be accepted for prediction of the life cycle of roofing tiles, would be a breakthrough in the attempt to obtain a high quality product. Pores and textural inhomogenities, formed during shaping procedure and firing process of ceramic roofing tiles are defects that complicate the response to frost action. The total porosity, pore structure and pore size distribution are important factors which influence the durability of ceramic roofing tiles. These qualities determine the kind of material and moisture interactions, the degree of material saturation and the mechanism of frost action [1]. The pore surface does not affect the formation of ice in macro pores (IUPAC classification) due to the fact that there is enough space for ice expansion. The pores whose surface effects dominate the gravity force are known as mesopores and micropores [2,3]. This is the reason why the optimization of pore size distribution has to be taken into account for avoiding the restricted range of pores in the ceramic system and consequently to improve its frost resistance characteristics. Values of processing parameters play a crucial role in the pore structure design and consequently affect the frost resistance characteristics. This paper is focused on the influence of vacuum value of the extruder and the speed of extruded column on the properties of the final products (plain biber tiles). The defined segments of each series of ceramic roofing tiles, on the basis of the standard testing methods, were selected for further micro investigation: pore size distribution (Hg porosimetry), differential scanning calorimetry and low temperature dilatation. The aim of this investigation was to set up the best operating parameters for the shaping procedure of ceramic roofing tile elements concerning their frost resistance characteristics. Materials and processing parameters The industrial raw material was the mixture of two components: sandy-carbonate clay and illitemontmorillonite clay material. The standard industrial manufacturing line was used for obtaining clay roofing tiles of defined design (plain biber tiles) by application of two different operating parameters: vacuum value (p1= –0.94 bar and p2 = –1.00 bar) and speed of the extruded column (v1 > v2). The worn screw conveyer (12 weeks old, giving the speed v1) was replaced by a new one (speed v2). Four representative samples of the extruded clay roofing tiles (1st to 4th series) were formed on the basis of the mentioned shaping parameters. Each tile sample of the defined series Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 1577-1580 doi:10.4028/www.scientific.net/KEM.264-268.1577

Characteristics of lightweight aggregate concrete interfacial transition zone

The paper presents the characteristics of the interfacial zone between the lightweight aggregate produced on the basis of waste materials and binder matrix with the application of the methods SEM, EDS and the Vickers micro hardness test. On the basis of the SEM and EDS analysis, as well as the criteria for the atomic ratio of elements which compose some products of hydration, we can gain insight into the dominant composition of the interfacial zone. The values of the Vickers micro hardness test for four kinds of tested concrete after seven days of hydration is impossible to correlate with the composition of the interfacial zone in reliable way, whereas after twenty eight days the differences in values are insignificant.