Albena Yoleva

University of Chemical Technology and Metallurgy | UCTM · Department Technology of Silicates

Hydroxyapatite (HA) is a major non-organic component of bones and is widely used as orthopaedic and dental material. It is widely used in biological materials due to the apatite-like structure of enamel, dentin, and bones. Black Sea Rapana venosa shells may be used as natural raw material for solid-state synthesis of hydroxyapatite. Huge amounts of...

The way to achieve better energy efficiency in buildings is to improve their thermal insulation properties. This can be done by increasing the porosity of the clay bricks by introducing pore-forming additives to the clay or production of perforated bricks. In general, thermal conductivity of the bulk clay bricks is about 1.0 W/mK depending on their...

The aim of the present experimental investigation is to trace the change of some general characteristics (pH, electro conductivity, mineralization and chemical composition) of spring water from Rila mountain in Bulgaria, as well as of electrochemically activated water after different periods in contact with a natural zeolite from Haskovo region, Bu...

The interest towards introduction of agricultural biomass wastes to porous clay bricks is increasing lately. These pore-forming agents start to ignite during the firing process providing extra thermal energy inside the product and decreasing the required external energy required. Besides this effect, their combustion increases the porosity of the f...

Bentonite is hydrophilic in nature due to the cations within its interlayer space. This makes natural bentonites ineffective sorbents of organic compounds. The modification of their surfaces by surfactants is an option to prepare bentonitebased sorbents of organic pollutants and bentonite fillers used for polymer nanocomposites production. The pres...

Some of corundum ceramics properties like high chemical resistance, hardness and mechanical strength make it an extremely suitable material for water tap gaskets and regulators. Solid fragments that normally get into the water, like sand, rust and limestone, cannot damage corundum ceramics. The latter stability allows these products to remain perfe...

The effect of amorphous silicate and zeolite on the thermal conductivity and porosity of ceramic building bricks is studied. The aim of the present work is to produce porous bricks of reduced thermal conductivity and acceptable compressive strength by using a combination of natural raw materials (amorphous silicate and zeolite) as well as sawdust a...

The study of medieval ceramics is important in order to obtain information for development of ceramic production during this period. Various medieval unglazed and glazed ceramic artifacts discovered during archaeological excavations in the monastery of Karaachteke near Varna (Bulgaria) were chemically and structurally characterized by ICPAES, XRD,...

The preparation of ceramic membranes has received a great deal of attention in the last few decades. Ceramic membranes have been used in a number of industries including water purification or filtration, clarification and sterilization of beverages, concentration of proteins in the food and dairy industries. Some advantages of ceramic membranes suc...

During the last few decades, the applications of ceramic membranes have been increased due to their excellent chemical, thermal and mechanical stability, and high separation efficiency. In the near future, the exploitation of natural ceramic materials and simple fabrication techniques could play a significant role for preparation of low cost membra...

The active puzzolanic additives decrease the participation of clinker in the cement composition by decreasing the calcium hydrate products and improving the chemical, acidic and sulphate stability, and mechanical properties. In this paper the properties of cementcontaining naturalpuzzolanic additives trass and zeolite are studied. The experimental...

We studied the application of the sol-gel method for synthesis of powders from the titanate phases Bi4Ti3O12 and Bi12TiO20 on the basis of hydrolysis-condensation reactions in acetic and nitric acid medium. The phase formation was traced during the heat treatment in temperature range from 25 to 600°C. The used precursors for the synthesis were bism...

Ceramic powders in the Al 2TiO 5-BaTiO 3 system, containing 10, 20 and 30 mol. % BaTiO 3, were synthesized via the sol-gel method through hydrolysis and co-condensation reactions of titanium butoxide, barium acetate and aluminum nitrate as starting materials. The gels and the ceramic powders were characterized by the methods of thermal analysis and...

The latest trends in the field of the manufacture of facing tiles are the production of the glazed and unglazed tiles "monocottura" and "monoporosa" single fast fired. The ceramic industry uses mostly natural raw materials for the production of facing tiles. For this reason and in order to reduce the production costs, exploration works are continuo...

Volcanogenic-sedimentogenous rock in the East Rhodopian Paleogene depression is a source of many new natural materials for the ceramic industry. During the period 1997-2005, an economically substantial metasomatic body of white halloysitic clay was discovered at the Kuza deposit near the village of Kralevo, Bulgaria, during the prospection and expl...

The relation between the size of the thermal expansion hysteresis curves area and grain-boundary cracks presence of aluminum titanate ceramic with mullite addition were established. Ceramic samples from Al 2 TiO 5 and mullite were obtained by a two-stage technology. To the sintered by solid state reaction at 1500°C aluminum titanate 5; 7,5; 10; 12,...

Seven glaze compositions for porcelain, in which 0 to 15 wt% of the feldspar in the base glaze composition is replaced by boron-zirconium frit were prepared. The glaze batches were ground in a ball mill until the residue on a 45 μm sieve was 0·5 wt%. The glaze was applied by spraying to unfired 120×120 mm ceramic tiles prepared from sanitary porcel...

The possibility of introducing fired sanitaryware porcelain scrap to the composition of single-fired wall tile bodies was investigated. The aim of the present work was to substitute traditional raw materials with porcelain scrap to obtain an end-product with improved physico-mechanical properties and thus decrease production costs. Compositions, co...

The aim of the present work is to obtain ceramic materials with a hexagonal structure and high density, hardness and mechanical strength at lower synthesis temperature. Ceramic samples with nominal composition La1−xCaxAl11−y−zMgyTizO18 (x=0–1; y=0–3; z=0–3,5) are prepared. The samples are sintered at temperature 1500 °C by one-stage and two-stage c...

Preparation of a cobalt pigment based on the systems CoO-ZnO-SiO2 by a sol-gel method has been studied. Sol-gel preparations were compared with conventional ceramic solid state synthesis. The samples were heat-treated within the temperature range of 200°-1200°C and analysed by X-ray diffraction and infrared spectroscopy. It was established that the...

The phase formation of the TeO2-AIN system is studied by changing the composition and temperature. The TeO2 content is varied in the 0–100 mol.% concentration range and thermal treatment of the batches at 500, 600, 700, 800 and 900 °C is carried out. It is established that as a result of chemical reaction into the TeO2-AIN system a new phase, i.e....

Polycrystalline AIN ceramics have been fabricated with Y2O3, Y2O3 + CaO, CaF2 and CaC2 as additives. Using electron microscopy and microprobe analysis, several microstructural models describing the mechanism of formation of secondary phases have been proposed. The effect of the additives on the thermal conductivity of AIN has been correlated with t...