Effect оf delamination оn physico-chemical properties оf kaolin

To provide the quality required for its use, raw kaolin must be subjected to certain processing procedures like delamination which is applied to the layered structure materials. The aim of this research is to determine the possibility of performing delamination in the extruder and to estimate the effects of this process on the physico-chemical properties of kaolin. The results showed that delamination can be efficiently realized in the extruder by shearing densely packed layers under the influence of friction force and added Na2 CO3 electrolyte. The crystal structure of the system was thus disrupted. This was confirmed by the Hinckley index (HI) decrease and by the dilatometric characteristics changes during heating. The particle size was reduced and, furthermore, new adsorption centers were formed, which led to an increase in the total cation exchange capacity (CEC). The plasticity of kaolin decreased with the increasing delamination degree, as well as the amount of water required for plastic processing, which is favorable in drying ceramic products

Ispitivanje uticaja mehaničke aktivacije smeše MgO-TiO2 na sintezu magnezijum-titanata

In this study, a mixture of magnesium oxide and titanium dioxide was mechanically activated in order to investigate the possibility of mechanochemical synthesis of magnesium titanate. Mechanical activation was performed for 1000 min in a high-energy vibro mill (type MH954/3, KHD Humboldt Wedag AG, Germany). The mill is equipped with housing having a horizontally placed shutter. The cylindrical stainless steel working vessel, with inner dimensions of 40 mm in height and 170 mm in diameter, has working elements consisting of two free concentric stainless steel rings with a total weight of 3 kg. The engine power is 0.8 kW. Respecting the optimal amount of powder to be activated of 50-150 g and the stoichiometric ratio of the reactants in the equation presenting the chemical reaction of magnesium titanate synthesis, the starting amounts were 20.2 g (0.5 mol) of MgO and 39.9 g (0.5 mol) TiO2. During the experiments, X-ray diffraction analysis of the samples taken from the reaction system after 60, 180, 330, and 1000 min of mechanical activation was performed. Atomic absorption spectrophotometry was used for chemical composition analysis of samples taken at different activation times. Based on the X-ray diffraction analysis results, it can be concluded that the greatest changes in the system took place at the very beginning of the mechanical activation due to the disturbance of the crystal structure of the initial components. X-ray diffraction analysis of the sample after 1000 min of activation showed complete amorphization of the mixture, but diffraction maxima characteristic for magnesium titanate were not identified. Therefore, the mechanical activation experiments were stopped. Evidently, the energy input was not sufficient to overcome the energy barrier to form a new chemical compound-magnesium titanate. The failure to synthesize magnesium titanate is explained by the low negative Gibbs energy value of-25.8 kJ/mol (despite the theoretical possibility that the reaction will happen), as well as by the amount of mechanical energy entered into the system during activation which was insufficient to obtain the reaction product. Although the synthesis of MgTiO3 was not achieved, significant results were obtained which identify models for further investigations of the possibility of mechanochemical reactions of alkaline earth metals and titanium dioxide.U ovom radu izvršen je pokušaj mehanohemijske sinteze magnezijum titanata u visokoenergetskom mlinu sa torzionim oprugama i prstenastim radnim elementima. Teorijski, hemijska reakcija je moguća samo ako je Gibsova slobodna energija te reakcije negativna, odnosno ako je energetski sadržaj produkata reakcije na nižem nivou od energetskog sadržaja reaktanata. Na osnovu rezultata dobijenih u ovom istraživanju može se zaključiti da i pored dovedene mehaničke energije u sistem, prisutna slobodna energija nije bila dovoljna da se odigra reakcija između MgO i TiO2 i dobije magnezijum titanat kao produkt. Mehanička energija koja je predata reakcionom sistemu u mehano-hemijskom aktivatoru dovela je do rušenja kristalne strukture i amorfizacije reaktanata, što se vidi na prikazanim diftaktogramima, ali nije bila dovoljna za sintezu magnezijum titanata prema jednačini (1), pa bi u tom cilju bilo neophodno koristiti energetski jači uređaj koji bi polaznim komponentama predao veći sadržaj energije, čime bi se preskočila energetska barijera i omogućilo polaznim oksidima da uđu u hemijsku reakciju tokom mehaničke aktivacije

Optimizacija mlevenja aktivne komponente i hidrofobizacija dobijenog sredstva za gašenje požara]

This work presents a grinding process of monoammonium phosphate (MAP) as an active component in a powder fire extinguisher (PFE). The aim was to determine the grinding time for reaching the optimal particle size of MAP necessary for permanent fire extinguishing. MAP grinding was performed by using a laboratory ceramic ball mill and a vibrating cup mill. The grinding process was controlled by sieving using a 100 µm sieve at precisely defined time intervals. The efficiency of a PFE depends on the share of the -100 µm fraction of the active component, which has to exceed 60 %. The optimal grain size with 64 % of fraction of particle size -100 µm was obtained after 33 min of grinding of ≈3000 µm mm grain size MAP by using a ball mill (single-stage grinding). In two-stage process, by grinding the same initial MAP sample (≈3000 µm) in the vibro mill for 10 min, powder with the upper limit grain size of 300 µm and the mean grain diameter of 120 µm was obtained. This sample with a reduced size was further ground in the ceramic ball mill yielding 67.5 % of the fraction of particle size -100 µm after 19 min. The total time of the two-stage grinding process was 29 min. By analyzing the grinding time of MAP required to get the lowest required share of the fraction of particle size -100 µm that provides the effectiveness of formed PFE it can be concluded that 64 % of this fraction was obtained after 33 min of single-stage grinding, while only after 26 min in the two-stage process. Thus, the grinding time was reduced by 7 min indicating certain energy savings. Stability and hydrophobicity of the obtained PFE were achieved by coating with magnesium stearate (MgSt) at the content of 2 % in a ball mill for 15 min. The coating was confirmed by the standardized procedure for verification of PFE hydrophobic properties in contact with water drops. To obtained PFE had component mass ratios of MAP:AS:CC:QS:MgSt=55:20:18:5:2 (AS-ammonium sulfate; CC-calcium carbonate, QS-quartz sand) and was further characterized by chemical and granulometric analyses. The fire extinguishing efficiency of the PFE was tested in controlled conditions, whereby fires were initiated by burning solid materials and flammable liquids. In both cases, immediate elimination of flames was achieved, thus proving the efficiency of the PFE obtained in this work for practical applications.U radu je prikazan postupak mlevenja monoamonijum fosfata (MAP) kao aktivne komponente u praškastom sredstvu za gašenje požara (SGP). Cilj je bio da se utvrdi vreme mlevenja MAP koje je potrebno za dobijanje optimalne granulacije za potpuno gašenje požara i eliminisanje plamena. MAP je mleven u laboratorijskom keramičkom mlinu sa kuglama i vibro mlinu sa prstenastim radnim elementima. Proces je kontrolisan prosejavanjem na situ 100 μm. Utvrđeno je da se mlevenjem granula MAP veličine ≈3000 μm u laboratorijskom mlinu sa kuglama optimalna krupnoća od 64 % frakcije čestica veličine -100 μm dobija nakon 33 min mlevenja. Za postizanje iste finoće proizvoda u dvostepenom mlevenju vreme je skraćeno na 26 min (10 min u vibro mlinu i 16 min u mlinu sa kuglama). Stabilnost i hidrofobnost SGP je postignuta oblaganjem magnezijum stearatom (MgSt) pri udelu od 2 % u mlinu sa kuglama u trajanju od 15 min. Efikasnost gašenja je testirana na poligonu u realnim uslovima. Na tačno određenom mestu za testiranje, u kontro-lisanim uslovima, izazvan je požar paljenjem čvrstih materijala i zapaljivih tečnosti. U oba slučaja je došlo do trenutne eliminacije plamena. Na taj način je potvrđena efikasnost formiranog SGP i mogućnost njegove upotrebe u praksi

Stochastic method for prediction of subsidence due to the underground coal mining integrated with GIS, a case study in Serbia

The problem of subsidence and damages on buildings above mining works is an inevitable consequence of underground coal mining in large mining basins. Significant development of various methods for prediction of the displacement parameters of the undermined terrain took place in the period from the middle of the last to the beginning of this century. In this paper, a new mathematical model of the stochastic Pataric-Stojanovic method for the predictive subsidence calculation is developed. A case study, as an example for the practical application of the proposed stochastic method, is given for the underground coal mine “Rembas”- Resavica, Serbia. An original MITSOUKO program package, supported by spatial analyses in the Geographic Information System (GIS), was developed for the predictive subsidence calculation based on the stochastic method proposed by the authors Pataric and Stojanovic. The comparative analysis of predicted and measured subsidence values confirms the possibility of using this stochastic method for predictive subsidence calculation in practice, which is a necessity of modern mining

A comparative study on X-ray peak broadening analysis of mechanically alloyed Al2O3 particles dispersion strengthened Al 7017 alloy

AA7017 + x vol. % Al2O3 (x = 5, 10, 20) nanocomposites powders were synthesized by HEBM process with milling time of 0 h and 20 h. The synthesized nanocomposite powders were characterized using XRD (Bruker USA D8 Advance, Davinci) with CuKα (1.5406 Aͦ), 2θ range (30°-90°), and Scan Speed (1°/min) for examining the crystalline nature of the powder samples. The size and shape of the powder particle were identified by HR-SEM (FEI Quanta FEG 200F) with 30 KV voltage, wide magnification range (12x-105 x) and secondary electron mode, and HR-TEM (JEOL Japan, JEM-2100 Plus) with voltage (200 kV), and magnification range (below 50 nm). Powder particles were measured by laser scattering technique using zeta analyzer (Laser Particle size Analyser, M/s Microtrac),and finally, the melting point and peak shift variation of composite powder samples were analyzed using TG-DSC (Netzsch TG-DSC) with temperature range (25–1400 °C), and heating rate (10 °C/min)under argon atmosphere. Furthermore, the particle sizes evaluated from different models of diffraction analysis (Scherrer, Williamson-Hall, and size-strain plot, SSP, methods) were compared with the results from PSA, HR-SEM, and HR-TEM analyses. The obtained mechanical properties explained that 20h milled AA7017 + x vol. % Al2O3 (x = 5, 10, and 20) samples produced higher values; and the properties improvement in all the samples were correlated theoretically by various strengthening mechanisms

Use of image analysis for durability testing of sulfur concrete and Portland cement concrete

Sulfur concrete was prepared by using the following initial components: sand as an aggregate, modified sulfur binder, and alumina as a filler. Portland cement concrete was made of the same aggregate, cement and water. The durability of prepared concrete samples was tested in 10% solution of HCl as a function of immersion time. The changes in mechanical strength and mass of the samples were periodically measured. Sulfur concrete exhibited limited mechanical strength and mass loss, while physico-mechanical properties of Portland cement concrete regressed rapidly. The image analysis used for surface destruction monitoring, performed by Image Pro Plus Program for determination of damaged surface area and original surface area before acid resistance testing, showed the similar results. Based on the image analysis results, model for predicting the mechanical strength degradation during durability testing was presented. The fact that calculated and experimental strength values were not far apart proved the validity of the proposed model

Durability of sulfur concrete in various aggressive environments

Durability of sulfur concrete with different fillers, as well as Portland cement concrete, was tested in the solutions of HCl, H(2)SO(4), and NaCl. Regarding mass changes, in the solutions of HCl and H(2)SO(4) sulfur concrete with talc and fly ash exhibited higher durability, while in NaCl samples with alumina and microsilica were better. The type of filler did not affect durability regarding compressive strength. Strength loss was higher in the solution of HCl comparing to H(2)SO(4), while negligible in NaCl which is in accordance with apparent porosity increase. Portland cement concrete after two months lost 20% of mass

Quantitative evaluation of sulfur-polymer matrix composite quality

In order to predict service life of the sulfur polymer composite, the samples were subjected to the induced destruction using 10% hydrochloric acid solution. Control specimens were prepared using Portland cement binder. Sulfur polymer composite showed limited mechanical strength and mass loss, while physico-mechanical properties of Portland cement composite regressed rapidly. The Image Pro Plus software was used for surface destruction monitoring. The simulations for composites were applied to the previously reported model for predicting the mechanical strength degradation during durability testing, based on the image analysis results. The results proved that the time gradient of structural change was useful for quantification of service life, therefore it can be accepted as a parameter that represents service life

Ispitivanje vatrostalnih uzoraka na bazi talka i domaćeg zeolita na dejstvo kavitacije

Using domestic zeolite from Igroš as row material for ceramic samples for application in condition of cavitation erosion. Samples based on talc with 15 % of zeolite, from Igroš, sintered at 1200oC were used in this investigation. The ultrasonic vibratory cavitation set up with stacionary specimen was used. Mass loss was measured and degradation level of the samples using image analysis and Young modulus of elasticity. Obtained results showed good resistance of the sample to the cavitation erosion, which give the possibility for possible future application of ceramic samples based on talc and yeolite in different conditions where cavitation erosion is expected.U radu su prezentirani rezultati istraživanja korišćenja domaćeg zeolita sa ležišta 'Igroš' za izradu keramičkih uzoraka i primenu u uslovima dejstva kavitacije. Za ispitivanja su korišćeni uzorci talka sa 15% zeolita iz domaćeg ležišta IGROŠ (Brus) sinterovani na 1200oC. Za određivanje otpornosti na dejstvo kavitacije korišćena je ultrazvučna vibraciona metoda sa stacionarnim uzorkom. Gubitak mase i nivo degradacije površine uzoraka praćeni su primenom analize slike i Jungovog modula elastičnosti. Rezultati ispitivanja pokazali su dobru otpornost keramike na dejstvo kavitacije na bazi talka i zeolita što ukazuje na mogućnost primene u različitim oblastima industrije gde se očekuje prisustvo razaranja pod dejstvom kavitacije

The influence of filler type on the corrosion stability of the sulfure concrete

Sulfur concrete was prepared by using the initial components: sand as an aggregate, modified sulfur binder, and talc, alumina, microsilica, and fly ash as fillers. Portland cement concrete was made of the same aggregate and fillers and portland cement. The durability of prepared concrete samples was tested in following aggressive solutions: 10% HCl, 20% H2SO4, and 3% NaCl as a function of time. Changes in mass and strength of the sulfur concrete were monitored periodicallly during the immersion time of 360 days in above solutions. These changes were used as a measure of deterioration level. It should be highlighted that the samples with the ash and especially talc exhibit higher durability in the solutions of HCl and H2SO4 than the samples with alumina and microsilica. In the solutions of NaCl all samples shown excellent durability while the samples with talc were the best. Portland cement concrete samples after two months lost 20 % of mass and shown degradation of mechanical properties. By usage of sulfur for sulfur concrete production, huge environmental problem regarding storage of waste sulfur from oil refining process is solved. On the other hand, sulfur concrete with its low price has an excellent quality for the application in aggressive environments unlike more expensive PCC