Papers by Author: Dachamir Hotza

Abstract: This work investigates the effect of nanosized Al2O3 addition on the sinterability of YSZ electrolyte. (1−x)YSZ + Al2O3 ceramics with compositions x = 0 to 0.01 were prepared by the conventional mixed oxide route from a commercial powder suspension (particle size <50 nm), and sintered at 1200 to 1500°C for 2 hours in air. Densification, phase evolution, and microstructure were characterized by SEM/EDS and XRD. An improvement in sintered density was observed for the samples with 0.2 to 0.5 mol% Al2O3, though depending on the sintering temperature. Only cubic zirconia was detected as crystalline phase, although XRD features suggested chemical interactions depending upon the amount of Al2O3. The grain size of YSZ was homogeneous and no second phase segregation was detected in the tested range of incorporated nano-Al2O3 and sintering temperatures.

Abstract: This paper presents some of the results of an investigation on the possible applications of use of waste concrete aggregates from mixer trucks concrete productions (WCA) in concrete. The investigation has been carried out using factorial design for experimental design. For the study, the physical and mechanical properties along their durability of concrete produced with WCA were investigated and the results presented. Concrete mixtures were prepared using WCA as the replacement of natural fine aggregate at the level 10%, 20% and 30 wt.% with water/cement ratios of 0.40, 0.50 and 0.60. Properties of fresh and hardened concrete were evaluated: fresh unit weight, consistency, 7-day and 28-day compressive strength were carried out in specimens. The necessary data for establishing a mix proportion design and a quality control method are obtained using a full factorial design 32. The influence of level of WCA on the mineralogical composition has been established, and its suitability for use in a concrete application has been assessed. Empirical contour plots for the physical-mechanical properties of fresh and hardened concrete with WCA were obtained via regression analysis, which predict that as the amount of waste increases, has no or little effect on the compressive strength of concrete mixes. The results form confirmation experiments justify the prediction from the statistical approach.

Abstract: In the present study, the waste scrap agate, obtained as a by-product of rock agate beneficiation as decorating ends and media for wet grinding was used as inert filler in a traditional triaxial red stoneware tiles composition. The effects on the technological properties have been investigated. The study has been carried out using the mixtures experiments method for the experimental design. Characterization results were used to calculate statistically significant and valid regression equations, relating dried and fired body properties with clay, feldspar and scrap agate contents in the unfired mixture. The regression models were then used simultaneously to delimit the combinations of those three raw materials most adequate to produce a ceramic body with specified properties. The use of mathematical optimisation shown that, for the particular raw materials under consideration, there is a rather forgiving composition range of clay (20-68 wt.%), feldspar (17-50 wt.%) and scrap agate (15-45 wt.%) contents within which it is possible to simultaneously specify the technological requirements for triaxial red stoneware tiles bodies, not only of the fired products but also of the intermediate materials at important stages of the processing.

Abstract: The simultaneous effect of raw materials (A, B and C) on physical and technological properties of brick compositions was studied. This investigation was carried out using the statistical design of mixture experiments. Ten mixtures of three raw materials were selected and used in the experiments design. Those mixtures were processed under conditions similar to those found in the ceramics industry. Fired body characterisation results were then used to iteratively calculate statistically significant and valid regression equations (trace plots), relating linear firing shrinkage, open porosity, fired bending strength and water absorption with the proportions of raw materials. The microstructures of some selected samples were studied using scanning electron microscopy. Mixtures with high clay B contents were most adequate to produce, under constant processing conditions, a brick with specified properties. The microstructures are characterized by a low closed porosity and absence of vitreous phase.

Abstract: This work reports some experimental results regarding to a Li2O-ZrO2-SiO2-Al2O3 (LZSA) sintered glass-ceramic material obtained by roll pressing of glass powders (mean particle size ≈ 5 μm) with an added (7 wt.%) inorganic material (bentonite) as binder. The composition was characterized using chemical analysis, laser-scattering particle size analysis, DTA, XRD, thermal expansion, modulus of rupture (MOR) and deep abrasion (DA) measurements as well as density measurements and SEM observations. From the results it was verified that the glass-ceramic materials obtained by sintering and controlled crystallization, in the 850-1030°C temperature range, of glass powders, have properties and characteristics decisively better than those of other traditionally used materials. It is concluded that roll pressing technology is a potential candidate to produce sintered glassceramics for many applications, such as, for example, large sheets panels for electrical and thermal insulation.

Abstract: Mixtures of clays are often used in the manufacture of bricks. In industrial practice, it is desirable to be able to predict, in an expeditious way, what the effects of a change in raw materials or the proportions thereof might be in the various processing steps towards the final product. When the property of interest is basically determined by the combination of raw materials, an optimisation methodology specific to the design of mixture experiments can be successfully used. In the present study, fired bending strength and linear firing shrinkage were selected as the properties to model. Ten formulations of three different clays were selected and used in the experiments design. Those formulations were wet processed, uniaxially pressed, and then fired at 1000 °C for 2 h.. From the experimental results, regression models were calculated, relating each technological property with the proportions of raw materials. The regression models were then used simultaneously to define which combination of those three raw materials was most adequate to produce, under constant processing conditions, a brick with specified properties.

Abstract: The industrial use of wastes in the brick and tile industry has been intensively investigated in the last decade. This work describes a research carried out on the manufacturing of a clay material with granite and marble reject. The reject was obtained direct by from a ceramic industry from rocks which were sawed in blocks or slices. This industrial process produces a very large amount of this reject. The reject is launched in decanting lagoon, landing area or throw in river, resulting environment pollution and degradation. The reject material was investigated in function of chemical and mineralogical compositions using x-ray diffraction and thermal analysis. Granite and marble reject and clay material were mixed and uniaxial pressed. Samples were sintered in an electric furnace at temperature range from 950 to 1150º C. The experimental results (porosity, dilatometric analyses, water absorption, x-ray diffraction) are also presented. The results indicate that it is possible to use granite and marble reject in clay material without to predicate its properties.

Abstract: An optimum amount of deflocculant was determined for three-component suspensions, based on a mixture design approach. Three raw materials were used, characterized as clay, feldspar and quartz. Ten compositions were prepared using the mixture design approach. Deflocculation curves were measured for suspensions with 40 wt.% of solids, adding sodium silicate as dispersant. The optimum deflocculant amount (ODA) was determined for each suspension, corresponding to the lowest value of apparent viscosity considering two nearest experimental points. It was observed that ODA increases linearly with the increase of the clay fraction in the mixture. A response surface and polynomial regression could be used to identify the composition range that satisfies usual conditions in wet ceramics processing.

Abstract: Preliminary results of the use of electroomosis technique for removal of organic contaminants in ceramic filtration porous structure are presented. The method employed provokes the migration of chemical residue and waste retained or adsorbed on the pore surfaces by applying a controlled tension within an electrochemical system. Porous ceramics have been the most common filtration medium employed within a broad range of applications. Conventional cleaning of a ceramic medium is not entirely effective for organic contaminants since they cannot be excluded by size, but retained through chemical affinity to the oxide surface. Under the influence of an electrical current, adsorbed molecules underwent shear stress due to the diffuse moving layer. In their ionic state the specimens are dragged and thus move towards the opposite charged electrode. Phenol was chosen as a standard contaminant and tests carried out using commercial ceramic filtration candles. Relative contaminant concentration was assessed by optical densities (UV-Vis spectroscopy). The results show that removal is proportional for up to 58% of the contaminant in diluted condition.