Influence of sintering temperature on thermal stability of low cement high alumina castable

Disertacija je imala cilj da prati ponašanje niskocementnog betona na bazi glinice pri termošoku i kavitaciji. Prvi deo eksperimenata obuhvatio je sintezu betona jednog sastava uz jednake uslove nege svih pripremljenih uzoraka. Nakon toga, uzorci su sinterovani na tri različite temperature, 1100 °C, 1300 °C i 1600 °C u trajanju od tri sata, da bi se pratio uticaj temperature sinterovanja na svojstva betona i nastalu strukturu. Posebna pažnja bila je usmerena na analizu uticaja temperature sinterovanja betona na ponašanje pri ispitivanju termostabilnosti i otpornosti na kavitaciju. Otpornost vatrostalnog betona na nagle promene temperature određena je primenom standardizovane metode kaljenjem uzoraka u vodi. Pri ispitivanju termostabilnosti vatrostalnih materijala praćene su promene uobičajenih parametara, kao što su mehanička i fizička svojstva. Analiza ovih svojstava podrazumevala je primenu destruktivnih metoda. Pored toga, primenjene su i nedestruktivne metode dok su rezultati ovih ispitivanja korišćeni za praćenje ponašanja betona pri termošoku i analizi uticaja temperature sinterovanja na ponašanje uzoraka pri termošoku. Jedna od korišćenih nedestruktivnih metoda bila je analiza slike kojom je praćen stepen oštećenja površine i unutrašnjosti uzoraka sa brojem ciklusa termošoka. Takođe je primenjena metoda ultrazvučnih merenja koja je omogućila praćenje prostiranja brzine ultrazvuka i promena elastičnih osobina sa brojem ciklusa termošoka. Promene pritisne i savojne čvrstoće praćene su klasičnom destruktivnom metodom prema standardizovanoj proceduri. Pored toga, na osnovu promena brzine prostiranja ultrazvuka, stepena oštećenja unutrašnjosti i površine, urađeni su modeli kojima bi bilo moguće predvideti promene pritisne čvrstoće sa brojem ciklusa termošoka. Na osnovu rezultata izračunatih i stvarnih vrednosti promena čvrstoće urađena je validacija dobijenih modela. Takođe je definisan kritičan broj ciklusa termošoka do pucanja sve tri serije uzoraka. Razvijeni su i parametri otpornosti na lom i oštećenja (R parametri) bazirani na termomehaničkim svojstvima vatrostalnog betona kojima je moguće predvideti i definisati ponašanje betona u uslovima naglih promena temperature...The aim of this thesis was to monitor behavior of alumina based low cement castable during the thermal shock and the cavitation. The first part of experiments included synthesis of one castable composition with the same cure conditions for all prepared samples. Then, the samples were sintered at three different temperatures (1100 °C, 1300 °C, and 1600 °C) with dwell time of 3 hours. The goal was to study influence of sintering temperature on castable properties and structure. Particular attention was focused on the influence of sintering temperature on the castable behavior during the investigation of thermal stability testing and cavitation resistance. Resistance of refractory castable to sudden temperature changes was determined by using standardized method of tempering samples to the water. Changes of common parameters such as mechanical and physical properties were monitored during the examination of castable thermal stability. The analysis of these properties included application of destructive methods. Besides, non‐destructive methods were used, too. The results of these tests served for monitoring the castable behavior during the thermal shock and analyzing the influence of sintering temperature. One of applied non‐destructive methods was the image analysis used for determining the damage level on the surface and inside the bulk of the sample depending on the number of thermal shock cycles. Also, the method of ultrasound measurements that allowed the monitoring of the ultrasound speed propagation and elastic properties change during the thermal shock was applied. Changes in compressive and flexural strength were measured by classic destructive method according to the standardized procedure. In addition, models for predicting compressive strength degradation during the thermal shock were made based on the changes in ultrasound velocity and the damage level at the surface and inside the bulk of the samples. Agreement between calculated and experimental strength values proved the validity of the proposed model. Critical numbers of thermal shock cycles until the sample crack for all series of samples were determined. Damage and crack resistance parameters (R parameters) were developed based on the thermomechanical properties of refractory castables. Also, these parameters can be used to predict and define castable behavior in conditions of sudden temperature changes..

Preparation and properties of low cement castable sintered at different temperatures

The low cement high alumina castable (LCC) studied in this paper was synthesised, cured and then treated at different sintering temperatures. Since any inhomogeneity introduced during the castable preparation can remain inside the material degrading its properties and therefore the quality during service life, particular attention was given to the processing procedure in order to produce the material with the optimum characteristics. Composition of the castable regarding particle size distribution was adjusted according to the Andreassen’s packing model. The samples were sintered at 1100, 1300 and 1600°C for three hours. Influence of the different sintering temperatures on the castable properties is discussed. Compressive and flexural strengths were determined by destructive testing method, while the water immersion method was used for determination of the bulk density and the water absorption. Changes of elastic properties and microstructure (porosity) were observed by the non-destructive testing methods, ultrasonic measurements and image analysis. Based on the results, it can be concluded that sintering temperature has strong influence on the properties of the LCC. Exceptionally good properties were obtained for the sample sintered at 1600°C, but it should be highlighted that the samples treated at 1100 and 1300°C were provided with good properties, too. This should not be neglected because of the energy saving importance, in cases where the material sintered at lower temperature satisfies the application requirements

Possibilities of waste sulfur valorization in eco-friendly products

Modifikacija konvencionalnih građevinskih materijala obično se izvodi upotrebom različitih otpadnih materijala. U ovom istraživanju biće prikazana upotreba sekundarnog sumpora kao veziva u betonu. Sumporni beton je termoplastični kompozit koji se sastoji od mineralnog agregata i punila, sa sumporom kao vezivom na temperaturi višoj od tačke očvršćavanja sumpora. Ovaj relativno nov građevinski materijal može da zameni konvencionalni Portland cementni beton u raznim konstrukcijama. U ovom radu biće prikazana svojstva sumpornog betona, kao i rezultati ispitivanja njegove postojanosti u agresivnim sredinama. U cilju ispitivanja svojstava, primenjene su destruktivne i nedestruktivne metode, dok su svojstva korelisana sa strukturom materijala.Predavanje po pozivu (plenarno) - Dr Sanja Martinović / Invited lecture (plenary) - Dr. Sanja Martinovi

Examining erosion resistance of ceramics for electrical engineering applications

In this research, two non-destructive testing (NDT) methods, thermal vision analysis and image analysis, were implemented for monitoring the surface changes- erosion of mullite based ceramic samples in conditions of cavitation exposure. Thermal imaging analysis was focused on determining temperature line profile at the end of the cavitation experiment. Image analysis is a powerful tool for quantification of degradation level caused by different impacts and conditions. Based on the results of image analysis, the degradation level during the testing was determined, as well as number of formed pits with their characteristics (average diameter and area). The results performed by both methods were discussed in order to obtain optimal procedure that should be followed for estimating degradation caused by cavitation erosion

Leaching behavior of sulfur concrete with fly ash used for removal of heavy metals from wastewater

When considering the materials that have become waste in a technological process, one way of their immobilization is for the production of certain new materials. The basic fact is to provide the environmentally acceptable level of the produced material. In this research fly ash from ’’Power Plant Nikola Tesla’’ Obrenovac was used as an sorbent for removal of heavy metals from flotation wastewater originating from artificial lake ’’Cerovo’’. After the sorption, fly ash was used as filler for the production of sulfur concrete. Sulfur concrete samples with standard dimensions were subjected to leaching tests by immersion in distilled water during the period of up to six months. Leaching is the process by which different contaminants are released from the solid phase into the water phase. The process itself is universal, as any material exposed to contact with water will leach components from its surface or its interior depending on the porosity of the material considered. Results of examining leaching degree of heavy metals from the sulfur concrete samples with fly ash as filler showed that the leaching degree of all metals (copper, cadmium, zinc, iron, nickel) except manganese was negligible. It can be concluded that in the sulfur concrete samples with fly ash as filler, immobilization of heavy metals occurred

Non-destructive evaluation of sulfur-polymer composite behavior under induced destruction influence

In order to avoid undesirable effects, caused by interactions between the material and environment, changes in properties of materials during their exploitation periods have to be determined. In this research, the induced destruction methodology was applied for evaluation of material behavior. The methodology is based on the usage of agents in increased concentrations that can lead to destruction of the material (cause changes in physical, chemical and mechanical properties) as fast as possible. Sulfur-polymer composite was exposed to the influence of hydrochloric acid, which was chosen as an induced destruction agent. The analysis of sulfur-polymer composite behavior required methods capable of quantifying the material microstructural characteristics. Since sulfur-polymer composite is inhomogeneous material, evaluation of its properties, as well as the effect of external influence on its microstructure, was investigated using non-destructive methodologies. Image analysis and ultrasonic measurements were applied to quantify the material destruction on the surface and in the bulk. Morphological and structural changes in the inner structure of sulfur-polymer composite were inspected by scanning electron microscopy (SEM). According to the obtained results, used methodologies present a powerful tool for the characterization of phenomena occurring in the specimens during the investigation

Possibility of using diatomaceous earth from Kolubara and Vesje deposits for production of beer filter aids

Diatomaceous earth is a non-metallic mineral raw material composed of skeletal remains of single-cell water plants, known as diatomite. Owing to quite complex structure of skeletal diatomite with numerous fine microscopic pores, cavities and channels and, therefore, large specific surface area and high adsorption capacity, diatomaceous earth can be used as adsorption auxiliary material for filtration. It is suitable for production of filtering compounds used in breweries. Two of several deposits on the Balkan Peninsula, the Kolubara deposit in Serbia and Montenegro, located 60 km south of Belgrade and the Vesje deposit in the Former Yugoslav Republic of Macedonia located near Negotino, were selected for the purpose of investigating their possible application in preparation of beer filter aids. With the aim of predicting the filtration efficiency, chemical, mineralogical and structural properties of diatomite samples were analyzed and parameters of crushing, drying, calcination and classification were defined. The results showed that there are certain differences in processing technology of two investigated deposits but both types of diatomaceous earth can be used for the production of beer filter aids. Beer filtration tests proved diatomites to be satisfactory and not causing any degradation of filtration process or beer quality. Technological flow scheme for obtaining the beer filter aids is proposed in this research

Blast furnace refractories: Past, present, future

Most of the refractories used today are related to iron and steel industry. Grate part of the refractory lining related to blast furnace are combination of different refractory materials selected for different parts of furnace, as well as different process conditions and temperature range. Selection of appropriate refractory combination depends on knowledge and demands for iron making system in combination with the physical, mechanical and chemical properties of the proposed refractories. An improper understanding of the above factors often leads to a refractory failure which, subsequently, becomes a complex problem to solve. Refractory linings whether it is of a blast furnace or any other furnace, usually fail due to any number or combination of such factors. For the convenience of understanding, here we will discuss the types of refractory lining required in a blast furnace area as well as the trend in the refractory lining pattern that has been used during the last decades

Intermediate cervical plexus block for carotid endarterectomy in high risk patients

Background and Purpose: Regional anesthesia is the choice for patients undergoing preventive open carotid surgery. Recently intermediate cervical plexus block has been described as a reliable and safe anesthesia technique in comparison with superficial and deep cervical plexus block. The aim of our study was to assess the complications of intermediate cervical plexus block in high risk patients. Materials and Method: The study was performed in 29 ASA III and ASA IV patients with the intermediate cervical plexus block for carotid endarterectomy from January 2006 till November 2008 in the University Hospital Zagreb. The following data were collected: age, sex, ASA status and preoperative disease. Furthermore, intraoperative and postoperative complications associated with intermediate cervical plexus block and carotid endarterectomy were recorded. Results: Median age was 69 years (range, 46 – 82 years). One patient developed Horner’s syndrome, three patients developed transitory ischemic attack, one developed stroke intraoperatively and died, seven patients developed transitory hemodynamic instability, one was hypotensive in the postoperative period and required vasoactive support. Conclusion: Intermediate cervical plexus block is safe and effective for carotid endarterectomy in high risk patients