Journal of Chemical Technology and Metallurgy

PHYSICO-CHEMICAL PROPERTIES OF MALIN-UROTROPIN- COPPER SULFATE SYSTEM

Wed, 06 Nov 2024 00:00:00 +0000

Before seed treatment, the seed must contain several active ingredients. Because the mail significant part of the saved crop depends on the correct seed dressing technology. Seed dressing, or seed treatment with pesticides, is an activity aimed at protecting plants from pests and diseases, using special preparations. In this study, the physicochemical properties of the formalin-urotropine-copper sulfate system were investigated at 25 ^oC. It is established that the isotherms of the system confirmed that the density, viscosity, pH of the solution medium and the crystallization temperature are characterized by inflection points corresponding to concentrations. Analysis of the “composition - properties” diagram of the system shows that the isotherms of the refractive index, density, viscosity and pH of the medium are characterized by two inflection points corresponding to 30 % formalin and 15 % urotropine that equals molar ratio of 1:1:1. Thus, it can be assumed that the interaction of formalin with copper sulfate in aqueous solutions results in the formation of a complex compound of the composition [30 % CH₂O +15 % C₆H₁₂N₄]-CuSO₄·5H₂O. Based on the data obtained, a solubility diagram was constructed, identified by X-ray phase, IR spectroscopic and thermogravimetric. Comparison of the value of the degree of crystallinity of the studied samples shows that the degree of crystallinity increases in the samples.

THE EFFECTIVENESS OF COAGULANTS FOR TURBIDITY AND COLOR REMOVAL FROM NATURAL WATER

Yana Kryzhanovska, Mukola Gomelya, Inna Trus — Wed, 06 Nov 2024 00:00:00 +0000

In this work, the effectiveness of the use of coagulants Al₂(SO₄)₃·18H₂O and RM-1 in reducing the level of turbidity and colour (reduction in colour) of natural water was investigated. The object of the study is natural water, namely water from the Dnipro River. The results showed that the optimal dose of coagulant Al₂(SO ₄)₃‧ 18H₂O was 10.0 mg dm^-3. The optimal dose of coagulant RM-1 was also 10.0 mg dm^-3. Residual turbidity and colour are reduced to 0.0 mg dm^-3, 12.50, 190, when using Al₂(SO₄)₃·18H₂O and RM-1, respectively. Since the residual concentration of aluminium in purified water in all samples after purification with coagulants was less than 0.05 mg dm^-3, it is reasonable to use these coagulants, as they do not have a negative effect on the health of consumers. The efficiency of using the RM-1 coagulant to remove turbidity and reduce the colour of the natural water of the Dnipro is high, so this coagulant has the potential to be chosen as a new coagulant.

ENHANCING SURFACE CHARACTERISTICS OF AA2024-T3 AIRCRAFT ALLOY THROUGH SYNERGISTIC ANODIZATION AND CERIUM CONVERSION COATING. PART I: PERFORMANCE IN MODEL CORROSIVE MEDIUM

Wed, 06 Nov 2024 00:00:00 +0000

The present study is devoted to the monitoring of the performance of AA2024-T3 specimens, after the formation of Anodic Aluminum Oxide (AAO) layer and/or deposition of a Ceruim Conversion Coating (CeCC), obtained at 20°C and 50°C, respectively. Although both methods are well described in the literature, there is no sufficient information regarding the effect of their combination on their behaviour in corrosive media. The performance of the respective specimens was elucidated after 24 h of exposure to 3.5 % NaCl model corrosive medium (MCM) by means of Electrochemical Impedance Spectroscopy (EIS) and acquisition of Potentiodynamic Scanning (PDS) curves. Since the combined AAO/CeCC coating primers revealed superior barrier properties, the respective specimens were
subjected to long-term corrosion tests of up to 672 h of exposure to the MCM to evaluate their durability. The results revealed the synergistic effect of the combination of the surface treatment procedures on effective corrosion mitigation.

A COMPARATIVE STUDY OF THE SURFACE OF FACTORY AND HAND-MADE LOOPS ON TITANIUM-MOLYBDENUM ORTHODONTIC ARCHWIRE

Rozina Yordanova — Wed, 06 Nov 2024 00:00:00 +0000

The most important part of the brackets, used in orthodontic treatment, is the archwire, which, when activated, generate light and long-lasting biomechanical forces that make the teeth move. Different manufacturers offer ready-made expensive solutions for orthodontists - archwire with loops along the length of the wire of different shape, which increases the cost of treatment. However, orthodontic practice is strictly individual, depending on the patient’s orthodontic problems, the stages and methods of treatment.
Orthodontists often have to choose between expensive archwires with pre-made loops or using an archwire that they can manually bend in the right places depending on the patient’s individual characteristics and specific needs. In this case, the orthodontist’s decision depends on preserving the quality of the archwire surface. The surface roughness of the orthodontic archwire plays an important role in the bracket-archwire complex and is an essential factor that determines the effectiveness of the guided movement of the teeth along the arch. Surface roughness not only affects the efficiency of sliding mechanics, due to frictional effects, but also corrosion behaviour and aesthetics. A comparison of the surface characteristics of Ti-Mo archwire - with factory and hand-made loops is made. The surface of the archwire in the bending zones of the loops was investigated by SEM analysis and Surface roughness analysis. The analysis of the results shows that manual bending practically does not change the surface of the archwire, does not introduce additional defects that increase the contact friction, as well as create conditions for faster deterioration of properties and the undesirable breakage of the archwire. Research results give orthodontists confidence that the manual bending process does not degrade the quality of the archwire surface. The hand-bent archwire preserves the possibility of trouble-free movement in the braces when tightening or loosening during the different stages of treatment.

ADEQUATE ASSESSMENT OF COMPETITIVE ADVANTAGES THROUGH PORTER’S DIAMOND. APPLICATION TO BULGARIAN NON-FERROUS METALLURGY

Dimitar Nedelev, Georgi Kondev — Wed, 06 Nov 2024 00:00:00 +0000

The topics of competitive advantages and competitive strategies of the enterprise in the wine sector are becoming more and more relevant these days, given the fact that most enterprises operate under conditions of high competition and minimal amount of resources. Competitive advantages and competitive strategies are precisely one of the main processes that make the enterprise profitable, successful and profitable. The main objective of the present paper is to examine the importance of competitive advantages and competitive strategies for the metallurgical enterprise. An adequate assessment of competitive advantages through Porter’s Diamond Model involves analyzing the four key elements - factor conditions, demand conditions, related and supporting industries, and firm strategy, structure, and rivalry - along with the roles of government and chance. Applying this model to Bulgarian non-ferrous metallurgy, which includes industries producing metals like aluminum, copper, zinc, and lead, can help to assess the competitive position of the sector in the global and European markets. The main research methods used in the development are content analysis, comparison method, intuitive and systematic approach, analysis and synthesis method.

EFFECT OF GRINDING AIDS ON CEMENT PROPERTIES AND GRINDING PROCESS

Aleksandar Popov, Georgi Chernev — Wed, 06 Nov 2024 00:00:00 +0000

The cement industry is one of the most energy-intensive industries, which is why new energy-reducing and reducing
CO2 emissions, additives are being sought. Grinding aid or grinding additives refer to substances that when mixed into the mill contents cause an increase in the rate of size reduction. These terms are very common in cement industries where it increases the throughput of the mill. Grinding aid also affects the cement flowability throughout the circuits. The grinding aid facilitates size reduction so that the mill has to apply less grinding power without hurting any of the properties of the resulting cement. The present research work aimed to investigate the influence of a chemical grinding aid ethylene glycol (EG) on cement properties and mill performance during the grinding of Portland cement beyond 500 ppm reaching up to 1200 ppm. The obtained results show increasing in initial compressive strength and increasing in the productivity of the cement mill.

CHARACTERIZATION OF CLAYS FROM “MINES MARITSA IZTOK” AS RAW MATERIALS FOR CERAMIC INDUSTRY

Ilian Djobov, Emilia Karamanova, Georgi Avdeev, Alexandar Karamanov — Wed, 06 Nov 2024 00:00:00 +0000

The chemical and phase compositions of the clays from coal mining were evaluated by XRF and powder XRD method, respectively. Hot Stage Microscope was used to estimate the thermal behaviour. In addition, the thermal losses of the clays after 1 h thermal treatment at different temperatures were measured. This preliminary analysis elucidates potential prospects for using some of clays as raw materials for ceramic industry. It seems that samples which are montmorillonite type are more plastic, while the others, where higher sand content is observed, and the drying shrinkage is negligible could be characterized as less plastic. The initial results for the thermal behaviour and the structure of a brick sample (obtained by mixing two types of clays) and a foamed geopolymer are also reported. The first sample shows a beginning of the firing shrinkage at about 1000°C, while the second demonstrates intensive bloating after 950°C, leading to specimen with about 56 % closed porosity. Finally, X - ray Computed Tomography and SEM was used to highlight the structure of some test samples.

THE EFFECT OF CEMENT KILN DUST ON THE PROPERTIES OF CEMENT

Aleksandar Popov, Georgi Chernev — Wed, 06 Nov 2024 00:00:00 +0000

Due to the nature of the technological process, the cement industry is a significant source of dust. Managing industrial waste is a global problem worldwide; cement kiln dust is an example of such waste. The dust from the cement kiln is a by-product of the cement production process obtained during the grinding and burning of the raw materials inside the cement kiln. Still, due to its high alkaline content, it cannot be returned to the kiln, but its disposal and landfill can cause many environmental problems. It is necessary to find alternative methods for its utilization. Due to its fineness and composition like that of cement, there is a growing interest in the use of this powder as a partial substitute for ordinary Portland cement. The purpose of this paper is to investigate the influence of dust obtained during the production of cement clinker on the properties of cement (specific surface area, standard consistency, setting time, and compressive strength) and its implications in the conditions of its application.

REDUCING THE CARBON FOOTPRINT IN THE CONSTRUCTION SECTOR BY REPLACING CERAMIC BRICKS WITH ALTERNATIVE MATERIALS

Lubomir Tashkov, Penka Zlateva, Nina Penkova — Wed, 06 Nov 2024 00:00:00 +0000

The use of non-fired materials with additives of vegetable waste instead of traditional building ceramics reduces the energy input and the carbon footprint in the construction sector. This applies to one- and two-story buildings due to the lower load-bearing capacity of non-fired bricks. A possibility for substitution of the fired ceramics with non-fired clay bricks with additives of straw at the building of the walls of a single-family house is analyzed. The subsequent reductions of the embodied energy, carbon dioxide, and thermal losses of the buildings are determined.

SODA LIME SILICATE GLASSES CONTAINING IRON OXIDE - IN VITRO EVALUATION

Wed, 06 Nov 2024 00:00:00 +0000

Three glasses with different iron oxide concentrations (between 5 and 8.1 mol %) were obtained in the CaO - Na₂O - SiO₂ - Fe₂O₃ system by using conventional melting-quenching technique. The amorphous nature of the synthesized materials is confirmed by X-ray diffraction analysis, XRD. The physico-chemical and structural characterization of the glasses was performed by measuring their density, refractive indices, as well as by calculating the molar volume, oxygen packing density and recording the infrared spectra by Fourier Transformed Infrared Spectroscopy, FT-IR, respectively. The glasses were evaluated in vitro by examining bone-like apatite formation on their surfaces in a simulated body fluid, SBF. The structural changes in the glasses during the in-vitro test were traced by means of FT-IR and Scanning Electron Microscopy, SEM. The solutions were examined by Inductively Coupled Plasma Optical Emission Spectroscopy, ICP-OES to determine the ion exchange between the glasses and the starting SBF and the corresponding effect on the pH was also recorded.

NUMERICAL SIMULATION OF DOUBLE SKIN FACADES IN WINTER CLIMATES

Penka Zlateva, Krastin Yordanov, Rositsa Petkova-Slipets, Martin Ivanov — Wed, 06 Nov 2024 00:00:00 +0000

The presented study reveals the analysis of the thermal behaviour of double skin facades (DSF) in winter conditions, using numerical simulation tools. The aim of the study is the development of a 3D simulation model, capable to evaluate the thermal behaviour of the modular elements in the DSF systems. This is essential requirement in the prediction and visualization of the facade’s thermal behaviour in the design stage and in the assessment of the real behaviour of such facade, when the specified modular elements are changed by the customer. The presented numerical simulation model aims to adequately reproduce the resulting set of thermal characteristics of the modular elements, to determine with sufficient accuracy their distribution in the real objects, implemented in
the models in DSF systems. An algorithm is developed in the study and graphical visualization of three models of double facade systems with and without DSF are analysed under winter conditions, using data from a meteorological station located in North-Eastern Bulgaria. A software product was used to represent the processes of heat and mass transfer, in which the corresponding boundary and initial conditions were set, based on which the results and analyses were obtained. The use of such numerical modelling is effective enough to predict the expected thermal behaviour of DSF systems. Thus, when selecting a DSF facade system, awareness of the thermal behaviour is ensured, and the financial efficiency of the project is more easily determined. Such a customized approach not only improves the sustainability and efficiency of buildings, but also satisfies the unique preferences and requirements of the customers.

ABSORPTION REFRIGERATION SYSTEMS FOR WASTE HEAT RECOVERY AT THE SILICATE INDUSTRY

Yordan Stoyanov, Nina Penkova, Kalin Krumov, Ivan Kassabov — Wed, 06 Nov 2024 00:00:00 +0000

The glass, ceramic and cement plants are energy intensive industrial systems, releasing high amounts of greenhouse gases. The dissipation of the waste heat reduces their profitability, energy and ecological efficiency. The absorption refrigeration systems are successful solutions for the recovery of thermal energy at different temperature levels to obtain useful cooling and heating powers for technological needs, and for air conditioning of administrative and industrial buildings. Although the absorption units in a heat pump and refrigeration cycle are currently used in building and industrial systems, they have not yet penetrated widely into the silicate factories. This paper discusses possibilities for the applications of basic types of absorption cycles at heat pump and refrigeration modes to utilize waste energy at different temperature levels in glass, ceramic and cement plants. The examined variants are demonstrated via examples, diagrams and analyses of the possible energy saving.

SPECTROSCOPIC INVESTIGATIONS ON SELF-CLEANING FILMS FOR PHOTOVOLTAIC GLASSES

Wed, 06 Nov 2024 00:00:00 +0000

Titanium dioxide thin coatings are widely used in different fields for the manufacture of various products:
electrochromic displays, photocatalytic systems, photosensitized solar cells and many others. At the same time, the possibilities for obtaining protective coatings based on TiO₂ are of interest. The chemical and physical characteristics of the TiO₂ coatings depend on a large extent of the applied technological method and the temperature values of the heat treatment used. Coatings are prepared by sol gel method applying dip coating technique. The present study characterizes self-cleaning TiO₂ thin films for the photovoltaic application. The studies were carried out at different ratios of the components involved, rate of application of the solution on the glass substrate and different curing and holding temperatures. The coatings are dense and nanocrystal line according to AFM studies and optically transparent according to UV-Vis-NIR spectra.

FT-IR AND RAMAN SPECTROSCOPY OF ZnO AND MgO CONTAINING GLASSES IN THE B2O3/Na2O/CaO/P2O5 SYSTEM

Tina Tasheva, Gabriela Valova — Wed, 06 Nov 2024 00:00:00 +0000

Glasses with compositions 46.1B₂O₃-24.4Na₂O-26.9CaO.2.6P2O5, xZnO/MgO-22.0B₂O₃ -(24.4-x)Na₂O-27CaO-2.5P₂O₅ (x = 2.5, 3 mol%) and 1.5ZnO-1.5MgO-22.0B₂O₃-21.5.Na₂O-27CaO-2.5P₂O₅ were melted by melt quenching technique. The densities of the glasses were measured by the Archimedes principle, using an analytical scale. Glasses possess densities in the 2.538 to 2.623 g cm^-1 range. The short-range order was also discussed from the molar volume Vm, cm3 mol^-1, and oxygen packing density point of view. The molar volume of the glasses varies between 26.566 - 27.420 cm³ mol^-1 and the oxygen packing density is between 73.669 to 76.262 mol cm^-3. The Furie transform infrared spectroscopy and Raman spectroscopy were performed to study the main structural units constituting the structure of the samples. The main structural units were found to be BO₃ and BO₄ probably connected in pentaborate and triborate structural units. The influence of the ZnO and MgO on the structure and chemical bonding of the glasses was discussed.

USING THE ADVANTAGES OF NANOTECHNOLOGY FOR THE PRODUCTION OF COMPOSITE MATERIALS OF THE TYPE NGO/CERAMIC MATRIX

Wed, 06 Nov 2024 00:00:00 +0000

Using the advantages of nanotechnology, composite ceramic materials of the type of graphene oxide nanocolloid/
ceramic matrix were obtained in two stages. First, finely porous corundum (1500ºC) and barium titanate (1300ºC)
ceramic samples containing 2 mass % graphene structures nanoplatelets were synthesized. The next stage of the study involved the preparation of graphene oxide in nanocolloid form (2 mg/ml, dispersion in H₂O) which was impregnated in the solid porous ceramic samples to obtain composite materials. For the characterization of the ceramic samples, mainly infrared spectroscopy, X-ray phase analysis, scanning electron microscopy and light microscopy were used. The results obtained from the studies carried out showed that with the introduction of small amount of graphene nanoplatelets in the initial blends followed by solid state sintering, part of the added graphene is burned out which imparts significant porosity to the ceramics obtained. On the other hand, the addition of graphene initiates the formation of well-shaped fine-grain structure of the ceramic samples, and they had sufficient porosity.

PERFORMANCE CHARACTERISTICS OF A MODIFIED COMPOSITE MATERIAL CONTAINING INORGANIC LIGHTWEIGHT AGGREGATES

Lуubеn Lakov, Bojidar Jivov, Yonka Ivanova, Krasimira Toncheva — Wed, 06 Nov 2024 00:00:00 +0000

A modified thermal and sound insulation composite material, potentially applicable in the field of modern construction, has been developed. Experimental samples based on foam glass aggregate (made from recycled waste glass), perlite (with fraction size up to 3 mm) and hydraulic binders were obtained. The acoustic and mechanical characteristics and the thermal conductivity coefficient of the prepared series of composite samples were studied. Values for Rw in the range from 38 to 46 dB and for λ from 0.04 to 0.15 W m^-1 K^-1 were established. The influence of the different components of the composition on the values of the studied performance indicators and the structure of the composite was analysed.

LOW-TEMPERATURE SYNTHESIS OF FINE-POROUS CORUNDUM BASED ON INCORPORATED GRAPHENE NANOSTRUCTURES

Wed, 06 Nov 2024 00:00:00 +0000

In the present paper, the effect of the addition of graphene nanostructures and 3 mass % TiO₂ on the microstructure and properties of sintered corundum ceramics were studied. Fine-porous corundum ceramics were obtained by the method of solid-phase sintering at relatively low temperatures of 1450^oC, by adding graphene nanostructures in an amount of 2 % or 20 %. To lower the synthesis temperature, 3 mass % TiO₂ was added to the initial ceramic blends.
As a result of the solid solution formed between Al₂O₃ and TiO₂, a well-sintered corundum ceramic is obtained at synthesis temperature lower than that of pure corundum - 1450^oС. For the characterization of the initial blends and the ceramic samples, the methods of X-ray phase analysis, infrared spectroscopy, SEM, TEM EDS and visual microscopy were used. Besides, the basic physicochemical properties of the samples synthesized based on corundum were determined, e.g. water absorption (WA, %), apparent density (AD, %) and apparent (open) porosity (Pa, %).

STRUCTURAL AND LUMIENESCENT STUDY OF EUROPIUM (III) DOPED TUNGSTATES

Aneliya Yordanova, Reni Iordanova, Peter Tzvetkov, Stancho Yordanov — Wed, 06 Nov 2024 00:00:00 +0000

Motivated by the need of new red phosphor for white - light - emitting diodes (WLEDs) application, Eu³⁺ doped Sc_2-xIn_x(WO₄)₃ (x = 0, 1, 2) solid solutions were synthesized by high temperature solid - state reaction. Structural and luminescent properties were obtained by using X - ray diffraction (XRD), infrared and photoluminescence spectroscopic techniques. IR spectrum of the ScIn(WO₄)₃ doped with Eu³⁺ contains the characteristic vibrations of the WO₄ and MeO₆ , (Me = Sc, In) polyhedral, building the Sc₂(WO₄)₃ and In₂(WO₄)₃structures. An effective energy transfer from the tungstate matrix to the active Eu³⁺ ion was observed. Intense red luminescence was obtained in these samples under excitation at 394 nm using the sharp 7F0 → 5L6 transition of Eu³⁺. The calculated asymmetric ratio ( 5D0 → 7F2 / 5D0 → 7F1 ) was about 7.5, suggesting that the obtained materials are characterized with distorted environment around the rare earth ion and with high red emission intensity. The prepared ScIn(WO₄)₃ solid solution demonstrates the highest emission intensity. The obtained chromaticity coordinates of the Eu³⁺ doped Sc_2-xIn_x(WO₄)₃ solid solutions were very close to the red standard recommended by National Television Standards Committee (NTSC).

FUNCTIONAL OPTICAL MATERIALS BASED ON AEROGELS

Dimitar Shandurkov, Nina Danchova, Stoyan Gutzov — Wed, 06 Nov 2024 00:00:00 +0000

Sol-chemistry is an efficient physico-chemical method for the preparation of porous glassy or nanocrystalline materials with tailored electrical, thermal or optical properties. This paper focuses on the dependence preparation–structure-properties of hydrophobic silica aerogel granules, powders and composites with a potential application as optical materials. Using the technique of subcritical preparation of silica aerogel powders, multicolour emitting composites containing Eu(phen)₂(NO₃ )₃ or Tb(phen)₂(NO₃ )₃ nanocrystals are obtained and characterized with luminescence spectroscopy, quantum yield determination and texture measurements. A dependence of the luminescence quantum yield on the degree of hydrophobicity α of the silica aerogel powders is described.

SYNTHESIS AND CHARACTERIZATION OF NANOPARTICLES FROM COAL FLY ASH

Wed, 06 Nov 2024 00:00:00 +0000

In this study, amorphous nanoparticles were extracted from fly ash using a sol-gel method. The obtained nanoparticles were characterized using XRF spectroscopy, XRD, FT-IR and TEM. The XRD curves show the presence of both crystalline and amorphous phases. FT-IR analysis indicated the presence of silanol and siloxane groups. Upon analysis, the primary nanoparticles were found to exhibit a roughly spherical shape with an average size of approximately 65 nm. The findings of this study demonstrate the feasibility of applying the sol-gel method to synthesize nanoparticles derived from coal fly ash (CFA), thereby avoiding other expensive and energy-intensive methods of nanoparticle synthesis.

AUGITE-BASED CERAMICS OBTAINED BY SOLID-STATE SINTERING OF LOESS

Wed, 06 Nov 2024 00:00:00 +0000

Loess from the Danubian Plain (Bulgaria) was used as the raw material for the solid-state synthesis of ceramics.
The mineral phase composition of the loess fraction used was determined by powder X-ray phase analysis, and the chemical composition by X-ray fluorescence analysis. The semi-quantitatively determined mineral phases are quartz, plagioclase, K-feldspar, mica, carbonates (calcite and dolomite), chlorite and amphibole. The major oxides of the chemical composition of loess fraction are (in wt. %): SiO₂ - 53,61; Al₂O₃ - 12.57; Fe₂O₃ - 7.05; P₂O₅ - 0,23; TiO₂ - 1.37; CaO - 19.36; and MgO - 1.48. Experiments were performed with sintering of pure loess without additives, and with addition of MgO and Na₂O in order to obtain a composition corresponding to that of the pyroxene augite - (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)₂O₆. Ceramics were obtained at three temperatures: 1000, 1100 and 1200°C. The phase composition, spectral characteristics and colour coordinates of the obtained ceramics were determined. The results show that when magnesium and sodium are added to the loess raw material, the ceramics obtained after sintering at 1100 and 1200°C have a predominant content of augite and have a yellow-beige colour.

ABOUT THE SINTERING OF HISTORICAL “YELLOW BRICKS” OF SOFIA

Alexander Karamanov, Emilia Karamanova, Vladislav Kostov-Kytin — Wed, 06 Nov 2024 00:00:00 +0000

The historical “yellow cobblestones” of Sofia are a very well sintered ceramic clinker with practically zero water absorption. However, the high amount of crystal phase formed, which explains the extraordinary mechanical properties of this remarkable material, is in formal contradiction with its low final porosity. In fact, in the modern ceramics clinkers the crystallinity is similar or inferior, but the reached degree of sintering is lower; as a result, the mechanical properties are reduced. The aim of this report is to elucidate some peculiarities of the densification process of “yellow ceramics bricks” because such information is essential for the eventual successful production of replica of this emblematic pavement. The chemical and phase compositions of original “yellow paving bricks” together with those of modern clinker from “Vitosha” boulevard in Sofia were evaluated by XRF and XRD analysis, respectively. The structures of both ceramics were investigated with density measurements and SEM.
Their densification behaviour was estimated by re-sintering of milled original samples by Hot Stage Microscopy (HSM) tests. The results elucidate that the sintering temperature of the historical clinker is inferior, and their sintering interval is significantly narrow. This peculiarity is explained by the rapid decreasing of apparent viscosity with temperature rise.
Finally, by secondary holding at the sintering temperatures and subsequent fast quenching of a “yellow brick” sample, it is demonstrated that some phase formation occurred during the industrial cooling step. This result explains both the good degree of densification and the better properties of the “yellow cobblestones”.

OBTAINING OF GARNET CERAMIC MATERIALS BY UTILIZATION OF RICE HUSK ASH AS SILICA SOURCE

Wed, 06 Nov 2024 00:00:00 +0000

The current research aims at the obtaining of new type pigments from the garnet mineral group by utilization
of rice husk ash as silica source (RHA). At the beginning, the mixtures prepared from the starting raw materials are
ground in a ball mill and then subjected to high temperature treatment. Green pigments were synthesized at two
temperatures: 1000°C and 1100°C. Using the tintometer RT 100 Lovibond the colour characteristics were measured
spectrophotometrically. The rice husk ash was investigated using scanning electron microscopy. The conducted hot-
stage microscopic studies show that the pigments remain thermally stable when heated. The highest fire resistance - up
to temperatures of 1380°C - 1400°C show the uvarovite pigments with main phase 3CaO.Cr₂O₃.3SiO₂ or by a general
formula Ca₃Cr₂[SiO₄ ]₃. They are suitable for inserting into ceramic glazes without danger of decomposition or reaction.
Keywords: ceramic pigments, SEM, colour determination, Hot-stage microscopy.