Chemical durability of polyphosphate glass in different medium

Proces rastvaranja stakla je veoma kompleksan fenomen, koji zavisi od više faktora: sastava stakla, postupka njegovog dobijanja, površine stakla, temperature, pH rastvarača, brzine protoka rastvarača, vremena dejstva i dr. Ovaj proces se odvija u više faza, te je moguće kontrolisati ukupno vreme procesa, favorizovanjem ili suzbijanjem neke od ovih faza. Iako fosfatna stakla imaju odlične optičke osobine, njihova šira primena je bila ograničena zbog njihove niske hemijske postojanosti. Poslednjih godina, fosfatna stakla su privukla pažnju istraživača zbog toga što poseduju bioaktivnost i biokompatibilnost, što ih svrstava u red materijala pogodnih za primenu u medicini, stomatologiji i poljoprivredi. Upravo zbog toga je veoma značajno da se poznaje ponašanje ovih stakala pri procesu rastvaranja u različitim rastvaračima. Hemijska aktivnost fosfatnih stakala u procesima koji nastaju pri kontaktu sa raznim rastvorima pomaže pri dizajniranju i proizvodnji novih materijala. Dosadašnja istraživanja u oblasti hemijske postojanosti neorganskih stakala su pokazala da i manje postojana stakla mogu da budu od velike koristi u slučaju njihove kontrolisane rastvorljivosti. Glavna prednost stakala je što im se lako može promeniti hemijski sastav. Promenom sastava, odnosno uvođenjem novih komponenti u sastav stakla, moguće je kontrolisati kinetiku i mehanizam rastvaranja. U ovoj doktorskoj disertaciji prikazani su rezultati proučavanja fenomena rastvaranja polifosfatnog stakla sastava: 45 P2O5·3 SiO2·25 K2O·15 CaO·10 MgO·1 ZnO·1 MnO u dejonizovanoj vodi, 2 % rastvoru limunske kiseline i simuliranoj telesnoj tečnosti (SBF) u temperaturnom intervalu 15-50 C za vremena 0,5-720 h. Ispitivanja su izvršena pri stacionarnim uslovima u nezasićenim rastvorima. U ispitivanjima su korišćene dve grupe praškastih uzoraka granulacija: 0,1-0,3 i 0,3-0,65 mm i kompaktni uzorci stakla. Za analizu rezultata eksperimenata korišćene su metode: atomska apsorpciona spektroskopija (AAS), spektrofotometrijska metoda (SF), infracrvena spektroskopija (FTIR), diferencijalno-termijska analiza (DTA), skenirajuća elektronska mikroskopija (SEM), energetska disperziona spektroskopija (EDS), analiza specifične površine staklenog praha i određivanje pH vrednosti sredine...The dissolution of the glass is a complex phenomenon that depends upon numerous parameters, such as glass composition, glass preparation procedure, surface condition, temperature, pH of the solution, leaching solution volume, flow rate, exposing time of the glass to the solution, etc. The process occurs in several steps. It allows the regulation of total dissolution time through the favoring or suppressing some of these steps. Although phosphate glasses have excellent optical properties, their wider application is restricted because of poor chemical durability. In recent years, the remarkable bioactivity and compatibility of phosphate glasses have attracted attention due to their potential application in medicine, dentistry and agriculture. Therefore, detailed knowledge of the dissolution behavior of phosphate glasses in different solutions is very important. Different chemical activity of phosphate glasses, during the contact with different solutions, provides for the opportunity to design and manufacture new materials. Previous studies in the field of chemical durability of inorganic glass show that even less durable glasses can be of great importance if their dissolution process is controlled. The main advantage of glasses is their flexible behavior in response to changes of the chemical composition. This allows the controlling of the kinetics as well as mechanism of dissolution of glass through the introduction of new components in different amount. The subject of this thesis is the dissolution behavior of polyphosphate glass of composition 45 P2O5·3 SiO2·25 K2O·15 CaO·10 MgO·1 ZnO·1 MnO in deionized water, 2 % solution of citric acid and simulated body fluid (SBF) at the temperature interval of 15-50 C for time 0.5-720 h. The dissolution experiments were conducted under static conditions in the unsaturated solution. Two glass powder samples, granulation 0.1-0.3 and 0.3-0.65 mm, and the bulk glass samples, were investigated. The methods employed for investigation were: atomic absorption spectroscopy (AAS), spectrophotometry (SF), infrared spectroscopy (FTIR), differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), analysis of specific surface areas and pH measurements..

Application of analytical, experimental, semiempirical and Monte Carlo methods for efficiency calibration of HPGe detectors in environmental samples gamma spectrometry

Квалитет гама спектрометријских мерења у општем сучају директно зависи од познавања ефикасности детекције за посебне случајеве геометрије мерења и карактеристика мереног узорка. С обзиром на то да узорци који се мере могу бити веома различити по хемијском саставу и геометрији, калибрација није доступна у свакој ситуацији. Поред тога, код мерења у контактној геометрији, што је најчешћи случај приликом мерења узорака из животне средине, феномен коинцидентног сумирања пертурбује спектар и мења површине испод пикова у спектру што резултује нетачним резултатима мерења. Тада се јавља потреба за развијањем различитих метода за калибрацију и специфичних референтних материјала за сваки појединачни случај. Методе калибрације могу подразумевати мерење сертификованих извора или секундарних референтних материјала, одређивање параметара потребних за израчунавање ефикасности или симулирање спектралног одговора инструмента. У овом раду представљено je и примењено неколико различитих приступа калибрацији ефикасности мерног система. То су: - Експериментални метод, који подразумева мерење секундарних референтних материјала који су по геометрији и хемијском саставу најприближнији узорцима који се мере. Овај метод даје најтачније резултате али истовремено захтева дуго време припреме секундарних референтних материјала и дуго време мерења. Све ово може бити извор низа мерних несигурности које су последица управо те припреме. -Аналитички метод, који подразумева успостављање аналитичке зависности између ефикасности и геометријских карактеристика мереног узорка и детектора. Овај метод је апроксимативан с обзиром на то да су интеграли који описују зависност за цилиндричне геометрије врло компликовани и њихово решавање је могуће једино нумеричким путем. Уведене апроксимације доприносе мерној несигурности али у оквирима потреба мерења узорака из животне средине могу бити прихватљиве. -Полуемиемпиријски метод (представљен у овом раду програмом за трансфер ефикасности, EFFTRAN) користи зависност ефикасности детектора од ефективног просторног угла под којим се узорак налази у односу на детектор и на основу тога рачуна трансфер ефикасности од референтне калибрационе криве до криве за реалну мерну геометрију и корекцију на коинцидентна сумирања. -Монте-Карло метод (представљен у овом раду програмским пакетима PHOTON и GEANT4) који се користи за симулацију спектралног одговора детектора на основу познавања процеса који доводе до депоновања енергије у медијуму детектора и случајног избора бројева. Сваки од наведених метода је примењен за калибрацију HPGe детектора који се користе у Лабораторији за заштиту од зрачења и заштиту животне средине Института за нуклеарне науке Винча. Као резултат добијене су ефикасности детектора, са придруженим мерним несигурностима. С обзиром на то да се мерење секундарних референтних материјала сматра најтачнијим методом калибрације, ефикасности добијене другим методама су упоређене са експерименталним резултатима да би се утврдило слагање или неслагање у оквиру мерне несигурности. Поређењем је установљено да се ефикасности добијене аналитичком методом разликују у односу на експериментално добијене ефикасности у опсегу од 1 до 14%, при чему су вредности одређиване за 3 геометрије које су најчешће у употреби у мерењу узорака из животне средине. Резултати добијени трансфером ефикасности, коришћењем калибрације за тачкасти извор као референтне калибрације, одступају од експерименталних од мање од 1% до више од 20%. Највећа одступања су уочена код матрикса веће густине и то на крајевима опсега испитиваних енергија. Остали резултати се налазе у оквиру мерне несигурности. Ефикасности су одређиване и Монте Карло симулацијом помоћу два различита програма. Резултати добијени применом програмског пакета GEANT4 показују одступање од експерименталних вредности која су реда величине неколико процената и та одступања су последица дефинисања геометрије детектора. Симулација програмом PHOTON је дала задовољавајуће резултате са одступањима која се крећу од мање од 1% до приближно 20% у односу на експерименталне резултате, али уз изостављање најнижих енергија, за које су одступања била неприхватљиво велика. Додатни критеријум за поређење различитих метода калибрације била је тачност која је проверена мерењем узорака из животне средине познате активности. Ови узорци су мерени у оквиру различитих међулабораторијских интеркомпарација или су као секундарни референтни материјал набављени од сертификоване лабораторије. Након мерења, активности радионуклида у узорцима добијени су коришћењем ефикасности добијених различитим методама. Поређењем овако добијених активности са референтним вредностима датим за те узорке, извршено је објективно поређење свих метода и установљена њихова еквиваленција по резултатима. Tакође, утврђене су границе применљивости аналитичког модела и програмског пакета PHOTON. Дате су и препоруке у вези са комбиновањем различитих приступа за будуће калибрације. У овој дисертацији први пут је примењено више принципијелно различитих метода на калибрацију детектора за мерење узорака из животне средине у цилиндричној геометрији.The quality of the gamma spectrometry measurements is in general directly dependent on determining of the efficiency for the specific measurement geometry and measured sample characteristics. Due to the fact that measured samples can be very versatile in terms of geometry and chemical composition, the efficiency calibration is not readily available. That is when the need for developing different efficiency calibration methods and specific reference materials becomes obvious. Methods of efficiency calibration may consist of measurement of certified sources and secondary reference materials, determination of the parameters needed for efficiency calculation or simulation of the detector system response. Besides, the measurement in contact geometry, such is the case in measurement of environmental samples, implies the perturbation of the spectrum via coincidence summing effect, which leads to incorrect results of the measurement. Several methods for efficiency calibration of the measurement system are presented and utilized in this thesis. These are: - Experimental method, which implies the measurement of the secondary reference materials that are similar to the realistic samples in terms of geometry and composition. This method produces high accuracy results but at the same time requires long time for production of the secondary reference materials and long measurement time. All this can be the source of large measurement uncertainty. -Analytical method, which implies the existence of analytical dependence between the efficiency and geometrical characteristics of the measured sample and detector. This method is approximate, due to the fact that the integrals describing the efficiency dependence for cylindrical geometry are very complex and their solution is only possible by using a numerical integration. The approximations introduced in the calculation contribute to the uncertainty of the results, but can be acceptable in case of environmental samples. -Semi empirical method (represented in this thesis by EFFTRAN – efficiency transfer software) utilizes the dependence of the efficiency on the solid angle between the sample and detector and calculates the transfer of the efficiency from the reference calibration curve and coincidence summing corrections, accordingly. -Monte Carlo method (represented in this thesis by software package GEANT4 and PHOTON) utilizes Monte Carlo simulation of the detector spectral response based on known processes that lead to photon energy deposition in the medium and random number generation. Each of mentioned methods is applied for efficiency calibration of the HPGe detectors readily used in the Laboratory for Radiation and Environment Protection of the Institute for Nuclear Sciences Vinča. As the result, detector efficiencies and associated uncertainties are obtained. Since the measurement of the secondary reference materials is considered to produce the most accurate results, efficiencies obtained using other methods are compared to the experimental results in order to establish the accordance of the results within the uncertainty limits. The comparison determined that the efficiencies obtained using analytical method differ from the experimental results within the range of 1 to 14%, for the 3 measurement geometries that were analyzed and that are most frequently in use for environmental samples measurement. Results obtained by the efficiency transfer, using point source calibration as the reference, differ from the experimental results that ranges from less than 1% to more than 20%. The largest discrepancies are for high density matrices and at the edges of the investigated energy span. Other results obtained by this method are within the measurement uncertainty limits. Efficiency calibration by Monte Carlo simulation was performed using two different software. Results obtained by using GEANT4 software package show discrepancies from the experimental results that are of order of magnitude of several percent, which is the consequence of detector geometry definition. Simulation performed by PHOTON software produced satisfactory results with the discrepancies that ranged from less than 1% up to 20%, with the remark that the lowest energies were omitted due to unacceptably large discrepancy. Additional criterion for comparison of different efficiency calibration methods was testing of the accuracy by measurement of the realistic environmental samples. These samples were measured within different interlaboratory intercomparisons, or were acquired from certified laboratory as a secondary reference material. After measurement, the radionuclide activities in the samples were calculated using efficiencies obtained by different methods. By comparing the results with the activity target values provided by the intercomparison organizer, an objective accuracy comparison was performed and the equivalence of the results was determined. Also, the limits of the aplicability of anaytical method and PHOTON simulation were established. Recommendations regarding future efficiency calibrations are stated. This thesis applies, for the first time, several principielly different approaches to efficiency calibration of the HPGe detectors for environmental samples measurement in cylindrical geometry

Correlation Between Morphology and Structure of Galvanostatically Electrodeposited Tin Dendrites

Tin dendrites found wide application in various industries.1 They can be obtained by both non-electrochemical and electrochemical methods of synthesis. In this study, they were produced by a galvanostatic regime of electrolysis from alkaline hydroxide solution at a current density of –3 mA cm–2 , 1.5 times larger than the limiting diffusion current density, with an amount of the electricity of 200 and 400 mC. In the dependence of an amount of the passed electricity, Sn dendrites of various morphology and crystal orientation were obtained: the fern-like dendrites predominantly oriented in (220), (440) crystal planes are obtained with 200 mC and the spear-like and the dendrites with prismatic branches showing the strong (200),(400) preferred orientationwere obtained with 400 mC. The strong correlation between morphology and structure of Sn dendrites is established and it can be explained by analysis of chronopotentiometry response obtained at the given current density and by morphological and structural analyses of Sn dendrites obtained by a potentiostatic regime at cathodic potentials corresponding to values attained after the passed amount of the electricity of 200 and 400 mC. The chronopotentiometry response after spent 200 mC was dominantly in the (–1600 – 1740) mV vs. Ag/AgCl range, and the fern-like dendrites with the strong (220), (440) preferred orientation were obtained in this potential range. After spent 400 mC, the chronopotentiometry response was about –1200 mV vs. Ag/AgCl, and the spear-like and the dendrites with prismatic branches with the strong (200),(400) preferred orientationwere obtained at this cathodic potential

Impact of deposition conditions on the electrocatalytic performances of Sn-Pd catalysts in ethanol oxidation reaction

We are reporting the electrochemical behavior of bimetallic Sn-Pd catalysts in ethanol oxidation reaction (EOR). Sn-Pd catalysts were prepared by two step electrodeposition technique whereby by regulating deposition conditions various forms of Sn dendrites and different atomic ratios of Sn:Pd were achieved. The electrocatalytic activity of Sn-Pd catalysts were evaluated for EOR in alkaline solution using cyclic voltammetry (CV) and chronoamperometric (CA) measurements. The highest activity and anti-poisoning ability exhibited Sn0.67-Pd0.33 catalyst due to the better utilization of Pd. At Sn0.67-Pd0.33 catalyst Sn better contribute Pd to oxidize chemisorbed species by providing adsorbed OH- species, thereby enabling well synergy of Sn with PdU ovom radu se bavimo ispitivanjem elektrohemijskog ponašanja Sn-Pd katalizatora u reakciji oksidacije etanola (ROE). Sn-Pd katalizatori su dobijeni dvostepenim elektrohemijskim taloženjem, pri čemu se regulisanjem uslova taloženja dobijaju različite forme Sn dendrita i različiti atomski odnosi Sn:Pd. Elektrohemijska aktivnost Sn-Pd katalizatora je procenjena u ROE u alkalnoj sredini korišćenjem ciklične voltametrije (CV) i hronoamperometrijskim merenjima. Najveću aktivnost i toleranciju prema otrovima je pokazao Sn0.67-Pd0.33 katalizator zbog boljeg iskorišćenja Pd. Primećeno je da kod Sn0.67-Pd0.33 katalizatora Sn bolje doprinosi oksidaciji hemisorbovanih čestica na Pd obezbeđivanjem OH- čestica, omogućujući tako dobru sinergiju Sn sa Pd

Predictability of Lead-210 in Surface Air Based on Multivariate Analysis

Dependence of the lead-210 activity concentration in surface air on meteorological variables and teleconnection indices is investigated using multivariate analysis, which gives the Boosted Decision Trees method as the most suitable for variable analysis. A mapped functional behaviour of the lead-210 activity concentration is further obtained, and used to test predictability of lead-210 in surface air. The results show an agreement between the predicted and measured values. The temporal evolution of the measured activities is satisfactorily matched by the prediction. The largest qualitative differences are obtained for winter months.3rd International Conference on Radiation and Applications in Various Fields of Research (RAD), Jun 08-12, 2015, Budva, Montenegr

Predictability of Lead-210 in Surface Air Based on Multivariate Analysis

Dependence of the lead-210 activity concentration in surface air on meteorological variables and teleconnection indices is investigated using multivariate analysis, which gives the Boosted Decision Trees method as the most suitable for variable analysis. A mapped functional behaviour of the lead-210 activity concentration is further obtained, and used to test predictability of lead-210 in surface air. The results show an agreement between the predicted and measured values. The temporal evolution of the measured activities is satisfactorily matched by the prediction. The largest qualitative differences are obtained for winter months.3rd International Conference on Radiation and Applications in Various Fields of Research (RAD), Jun 08-12, 2015, Budva, Montenegr

Interlaboratory comparison material homogeneity testing

The homogeneity of fertilizer samples for interlaboratory gamma-ray spectrometry comparison was tested by determination of the total. count rate and the count rates for two U-238. lines, one K-40 line and one common U-235 and Ra-226 line. Homogeneity testing was accomplished by determination of the minimum, maximum, mean and standard deviation for each parameter and comparison of their standard deviations with predefined tolerances, by Cochrans test, and by a one-way ANOVA. The standard deviations were all less than these tolerances. All samples passed Cochrans test and the one-way ANOVA test for homogeneity

Seasonal changes of naturally occurring radionuclides and fallout 137-Cs in the samples of leaves of deciduous trees

Specifična aktivnost prirodnih radionuklida 238U, 235U, 226Ra, 210Pb, 232Th i 40K i proizvedenog 137Cs je merena u uzorcima lišća dve vrste listopadnog drveća, kestena (Aesculus hippocastanum) i lipe (Tilia spp) koji potiču iz tri gradska parka na užem području Beograda. Uzorci su sakupljani u vreme prolećne (n=7), letnje (n=2) i jesenje (n=8) sezone u periodu od 2002-2012. godine. Iz svake pojedinačne sezone uzorci lišća su spojeni po vrstama pri čemu je dobijen jedan integralni (sezonski) uzorak za svaki ispitivani park čime je postignuta veća efikasnost detekcije niskog nivoa gama zračenja. Za određivanje aktivnosti primenjen je metod spektrometrije gama emitera. U svim pojedinačnim uzorcima suve materije lišća detekcija radionuklida 210Pb i 40K je bila moguća i njihova specifična aktivnost se nalazila intervalu 15-52 Bq/kg i 310-650 Bq/kg, respektivno. Iako je aktivnost 226Ra bila veoma niska, u intervalu 0,5-5,6 Bq/kg, ovaj radionuklid je bio izmeren u svim uzorcima (osim u dva) i svim sezonama. Aktivnost 210Pb i 226Ra se povećavala tokom godine, pri čemu su njihove najveće vrednosti izmerene u lišću kestena u letnjoj sezoni. Suprotno, aktivnost 40K u lišću lipe i kestena je opadala tokom godine. Za razliku od prethodno navedenih, radionuklidi 238U, 235U i 232Th su retko detektovani samo u letnjem i/ili jesenjem periodu i po četiri uzorka lišća su sadržali 238U (2,7-11,7 Bq/kg) i 235U (0,13-1,0 Bq/kg), a tri 232Th (1,8-3,3 Bq/kg). Proizvedeni radionuklid 137Cs detektovan je u svim uzorcima lišća (osim u dva), a bez jasnog trenda ponašanja po sezonama i nalazio se u intervalu 0,3-1,2 Bq/kg. Cilj rada bio je ispitivanje akumulacije prirodnih radionuklida i njihovog potencijalnog variranja tokom godine u lišću listopadnog drveća.The specific activity of naturally occurring radionuclides 238U, 235U, 226Ra, 210Pb, 232Th, and 40K and fallout 137Cs was measured in the samples of leaves of two deciduous tree species, chestnut (Aesculus hippocastanum) and linden (Tilia spp.) common for the Belgrade urban area. Samples were collected in the spring (n = 7), summer (n = 2) and autumn (n = 8) during the vegetation period from 2002 to 2012. From each season, samples of leaves were combined according to two species and one single integral (seasonal) sample was obtained in order to improve detection efficiency of low gamma radiation level. Specific activities were determined using the gamma-ray spectrometry method. 210Pb and 40K radionuclides were detected in all the samples of leaves and their specific activity was in the range (Bq/kg dry weight): 15 - 52 and 310 - 650, respectively. Although the 226Ra level was very low and in the range from 0.5 - 5.6 Bq/kg, this radionuclide has been measured in all samples (except in the two) and each season. 210Pb and 226Ra activity increased during the vegetation period and their highest values were found in the leaves of chestnut trees in the summer season. In contrast, the activity of 40K in the leaves of linden and chestnut has decreased. Detection 238U, 235U and 232Th radionuclides was scarce and only in the summer and/or autumn. Four samples of leaves contained 238U (2.7 - 11.7 Bq/kg dry wt) and 235U (0,13 - 1.0 Bq/kg dry wt) and three of them 232Th (1.8 - 3.3 Bq/kg dry wt). Man-made radionuclide 137Cs (0.3-1.2 Bq/kg dry wt) was detected in all samples of leaves (except in two) and no clear trend according to seasons was found. The aim was to investigate the accumulation of naturally occurring radionuclides and fallout 137Cs in the leaves of deciduous trees and their potential variations during the vegetation period

Seasonal variations of naturally occurring radionuclides and 137cs in the leaves of deciduous tree species at sites of background radioactivity levels

Activity concentration of natural radionuclides and 137Cs were studied in leaves of the deciduous trees. In the spring and autumn season, leaves were collected in the area of normal background radiation levels represented by city parks in a multi-year period (2002-2012). Measurements by means of gamma-ray spectrometry showed 226Ra and 210Pb seasonal accumulation in leaves, while 238U and 235U could be detected only in autumn. Difference between seasons was not found significant for 40K and 137Cs. The study of radionuclides transfer factors was conducted by analyzing its relationships with basic soil properties at the beginning and the end of the vegetation period. © 2019, Editura Academiei Romane. All rights reserved

Influence of Ni2+/Co2+ ratio in electrolyte on morphology, structure and magnetic properties of electrolytically produced Ni−Co alloy powders

Nickel−cobalt (Ni−Co) alloy powders were produced galvanostatically by using sulphate electrolytes with various ratios of Ni2+/Co2+ (mole ratios). The morphology, phase structure, chemical composition and magnetic properties were examined by scanning electron microscope (SEM), X-ray diffractometer (XRD), atomic emission spectrometer (AES), and SQUID-based magnetometer, respectively. Morphology of the particles changed from cauliflower-like and dendritic to coral-like and spongy-like ones with increasing Ni2+/Co2+ ratio from 0.25 to 4.0. XRD analysis of the Ni−Co powders revealed that the decrease of Ni2+/Co2+ ratios (the increase of Co content) caused a change of structure from face centered cubic (FCC) obtained for the ratios of 4.0, 1.5 and 0.67 to a mixture of FCC and hexagonal closed-packed (HCP) phases for the ratio of 0.25. The increasing content of nickel led to change of mechanism of electrolysis from irregular (up to ~40 wt.% Ni in the electrolytes) to close to equilibrium (between ~40 and 60 wt.% Ni in the electrolytes) and anomalous co-deposition (over 60 wt.% Ni in the electrolytes) type. All of the obtained Ni−Co alloy samples behaved as soft magnetic materials while their magnetic parameters showed immediate composition dependence since both coercivity and saturation magnetization almost linearly increased with increase of the Co content