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Terzic A.,Serbian Institute for Materials Testing | Andric L.,Serbian Institute of Technical Sciences | Mitic V.,Serbian Institute for Technology of Nuclear and other Raw Mineral Materials
Ceramics International | Year: 2014

A growing demand for refractory castables with advanced properties has given rise to a continuous technological evolution and highlighted the necessity for secondary raw materials reapplication even in refractory industry. For the experiment, refractory shotcretes with the same matrix composition were prepared from 30 wt% of high aluminate cement, 40 wt% of bauxite aggregate and 30 wt% of chamotte filler. The request for obtaining a low-cement castable is fulfilled by application of mechanically activated coal ash as microfiller in one of the bauxite shotcretes. The fly ash was activated by means of vibratory disc mill and ultra-centrifugal mill, and results were compared. The shotcrete samples were dried at 110 °C during 24 h to create specimens for investigation of mechanical and thermal properties. The properties have been studied at temperatures ranging from room temperature to adopted maximal temperature 1400 °C. At maximal 1400 °C, the bauxite shotcretes were mainly composed of anorthite, corundum, mullite and cristobalite. Mechanisms of hydration and sintering were investigated by means of differential thermal analysis (DTA) at three different heating rates. DTA measurements showed different activation energies for ordinary bauxite shotcrete and shotcrete with microfiller. The evolution of the refractory shotcretes properties was investigated and correlated with microstructural changes induced by temperature and microfiller addition. The combination of advantages in investigated refractory shotcretes makes them suitable for use in severe conditions at high temperature applications especially in refractory industries. © 2014 Elsevier Ltd and Techna Group S.r.l. Source

Mitrovic A.A.,Serbian Institute for Materials Testing
AIP Conference Proceedings | Year: 2011

Pozzolans are supplementary materials added to Portland cement in order to increase the mechanical strength and durability of concrete structures. A number of thermal, mechanical and chemical methods have been used to activate the reactive potential of pozzolanic materials. The aim of the study is to obtain pozzolana, from Serbian kaolinite clay by mechanochemical treatment. Kaolinite clay Garaši was subjected to mechanical treatment during different times of milling. The changes were monitored using particle size distribution (PSD) analyses, thermal methods [thermogravimetric analysis (TGA), and differential thermal analysis (DTA)] and X-ray diffraction methods (XRD). The pozzolanic activity was determined using Chapelle method. Milling withing 20 min influences particle size decrease and after that time continuous increase. XDR analysis indicates gradual decrease of cristallinity with prolonged milling time. The higher values for pozzolanic activitie, expressed through consumption of gCa(OH) 2 per gPozzolana are 0.78 and 0.77, and they were obtained for milling times 20 and 40 min, respectively. The values are comparable with commercial pozzolan - metakaolin. The results indicates that milling has caused the disintegration of particles and the consequent formation of new active surfaces in addition to changes in its physico-chemical properties that decrease its crystallinity (through amorphization) and increase it reactivity. © 2011 American Institute of Physics. Source

Terzic A.,Serbian Institute for Materials Testing | Pezo L.,University of Belgrade | Andric L.,Serbian Institute for Technology of Nuclear and other Raw Mineral Materials
Ceramics International | Year: 2015

The differences in the set of the process parameters measured before and after mica mechanical activation and their influence on the grain size distribution related characteristics have been studied. The modification of the behavior for activated samples has been correlated to the particle size distribution effect produced by activation via an ultra centrifugal mill. The mechanical treatments are energetically and economically unsustainable procedures, therefore the mica activation was optimized on basis of assessment of the process variables effect on the final quality of product parameters. Response surface method, standard score analysis and principal component analysis were used as means of the optimization. Developed models showed r2 values in the range of 0.816-0.988 and they were able to accurately predict quality parameters in a wide range of processing parameters. Standard score analysis highlighted that the optimal sample was obtained using sieve mesh of 80 μm set of processing parameters (SS=0.81). Multiple comparison tests revealed that the optimal variation in the processing parameters could reduce the negative effect of mica samples inherent properties on the final score and improve activation procedure energetic and economic sustainability. © 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Source

Mitrovic A.,Serbian Institute for Materials Testing | Zdujic M.,Serbian Academy of Science and Arts
Journal of the Serbian Chemical Society | Year: 2013

Mechanochemical treatment of Serbian kaolin clay was performed in a planetary ball mill using two different milling media, hardened steel or zirconia vials and balls. The samples obtained after various milling times were characterized by particle size laser diffraction (PSLD), X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetry (DTA/TGA) and Fouriertransform infrared (FTIR) analyses. The mechanochemical treatment induced amorphization of the kaolinite phase accompanied by dehydroxylation. It was found that for given milling parameters, amorphization mainly occurred in the milling period up to 15 min, and was completed after about 30 min of milling for both employed milling media. The pozzolanic activities were determined by the Chapelle method. Milling in the hardened steel milling medium had no significant influence on pozzolanic activity, even though there was accumulated iron contamination. For both milling media, a pozzolanic activity of 0.79 was obtained for the samples milled for 15 min and it remained almost unchanged with prolonged milling. The determined pozzolanic activity values were similar to those of commercial metakaolinite or metakaolinite obtained by calcination of the same clay, thereby, indicating that highly reactive pozzolana could be obtained by mechanochemical treatment of Serbian kaoline clay. Copyright (C)2013 SCS. Source

Andric L.,Serbian Institute for Technology of Nuclear and Other Mineral Raw Materials | Terzic A.,Serbian Institute for Materials Testing | Acimovic-Pavlovic Z.,University of Belgrade | Pavlovic L.,Serbian Institute for Technology of Nuclear and Other Mineral Raw Materials | Petrov M.,Serbian Institute for Technology of Nuclear and Other Mineral Raw Materials
Composites Part B: Engineering | Year: 2014

Mica and talc have wide areas of application as a raw material in a number of industrial branches. Mechanically activated mica has specific applications such as: capacitors, insulators, and pearlescent pigments. Talc is widely used as either a basic raw material or as filler. This paper presents a comparative analysis of mechanically activated samples of mica and talc in ultra-centrifugal mechano-activator "Retsch ZM-1". The following mechano-activator parameters were variable: number of rotor revolutions (rpm); sieve mesh size (μm); current intensity (A). In addition, the following parameters were monitored: duration of mechanical activation, t (min); circumferential rotor speed, v (m/s); capacity of mechano-activator, Q (kg/h); and specific energy consumption, We (kW h/t). It was observed that effect of mechanical activation of mica and talc increased with an increase of the load and rotor revolution of ultra-centrifugal mechano-activator. Both mica and talc were successfully treated by mechanical activation procedure. In the processing of mica, mechanical activation is suggested to be applied as a post-treatment, and in the talc processing as a pre-treatment, as the high quality talc is obtained by means of hydrometallurgical concentration method. © 2013 Elsevier Ltd. All rights reserved. Source

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