Preparation of white pigment from hydrated titanium oxide

V diplomski nalogi so predstavljeni procesi, ki potekajo v kalcinatorju oz. rotacijski peči med kalcinacijo na industrijskih vzorcih hidratiziranega titanovega dioksida. Vzorci so bili narejeni po sulfatnem postopku in za termično analizo odvzeti iz podjetja Cinkarna Celje, d. d. Kalcinacija se deli na tri procese: sušenje, desulfurizacijo in rutilizacijo. Diplomsko delo je osredotočeno na prva dva procesa, ki močno vplivata tudi na potek rutilizacije. Kot prej omenjeno, procesi potekajo v kalcinatorju, v katerem se temperatura dviga z dolžino peči in na koncu peči doseže temperature tudi do 1200 °C. Prvi proces je sušenje, s pomočjo katerega poteka eliminacija vode iz vzorcev. Eliminacija poteka v dveh intervalih: v prvem prihaja do izhlapevanja površinske vode, v drugem pa do izhlapevanja porne vode, ki poteka pri višjih temperaturah. Drugi proces je desulfurizacija, s katero se iz vzorca eliminira žveplov dioksid. Tudi ta proces poteka v dveh intervalih. Prvi zajema izhlapevanje prosto vezane žveplove kisline. Tu se eliminirajo še zadnji ostanki vode, hkrati pa zaradi visoke temperature pride do pretvorbe žveplovega trioksida v žveplov dioksid. V drugem intervalu prihaja do razpada sulfatnih mostičkov v sušenem vzorcu, kar sproži potek rutilizacije. S pomočjo podatkov, pridobljenih iz termičnih analiz (te podatke je predhodno pridobil in obdelal Tilen Kopač), sem določil temperaturne intervale za procesa sušenja in desulfurizacije. Na podlagi določitve temperaturnih intervalov sem izračunal pripadajoče aktivacijske energije za oba procesa pri različnih vzorcih. Podatke sem obdelal z neizotermno/izokonverzijsko metodo. Na podlagi primerjave rezultatov različnih vzorcev hidratiziranega titanovega dioksida lahko sklepam, da sem metodo pravilno uporabil in da so dobljeni rezultati natančni. Rezultati diplomskega dela bodo pripomogli k optimizaciji procesov kalcinacije, in sicer k optimalnemu uravnavanju temperatur po dolžini peči za boljši izkoristek in k manjši porabi energije za dosego tako visokih temperatur.The present diploma thesis presents processes, which take place in a rotary kiln during the calcination of industrial samples of hydrated titanium dioxide. These samples were made by the sulphate process and were taken from Cinkarna Celje company for thermal analysis. Calcination is divided into three sub-processes: drying, desulfurization and rutilization. This thesis focuses on the first two processes, which strongly influence the course of rutilization. As mentioned, the calcination process takes place in a rotary kiln, where the temperature rises along the length of the kiln and at the very end can reach temperatures as high as 1200 °C. The first sub-process is drying, which eliminates water from the samples. The elimination of water occurs in two intervals: during the first interval the evaporation of surface water takes place and the second interval is the evaporation of water from the pores of the material. The latter occurs at higher temperatures. The second sub-process is called the desulfurization, where sulphur dioxide is eliminated from the sample and it also occurs in two intervals. The first one involves the evaporation of free sulfuric acid. This eliminates the last residual water and at the same time, due to the high temperature, causes the conversion from sulphur trioxide to sulphur dioxide. During the second interval the sulphate bridges start to decompose which triggers also rutilization. With the help of data obtained from thermal analysis (which was previously done by Tilen Kopač), I determined the temperature intervals for both drying and the desulfurization processes. Based on this determination, I calculated the corresponding activation energies for both processes for various samples. Corresponding calculations were done by data processing using the non-isothermal/isoconversial method. Based on critical review of the obtained results I can conclude that the method was used correctly, and the numbers obtained are accurate. The results from diploma thesis will help optimizing the calcination process, namely the optimization and temperature control along the length of the kiln for better process efficiency and lower energy consumption to achieve such high temperatures

Identifying mathematical literacy of the fifth graders

This master's thesis, titled Identifying Mathematical Literacy of the Fifth Graders consists of two parts. The first, theoretical part discusses literacy from the point of view of definitions and its development. Most attention is devoted to mathematical literacy, which is the focal point of this research. Mathematical literacy is not only analysed in connection with the Maths curriculum, but also in relation to international and national research which study and measure it. The theoretical part precisely analyses results of the latest measurements of the aforementioned studies, relevant for this master's thesis. Solving mathematical problems, one of the main competences when it comes to developing mathematical literacy, as well as the Gagné taxonomy, the basis of most relevant research, are also presented in detail. In the concluding section of the theoretical part are presented individual tasks, included in one Maths test, also part of this research. The tasks are classified in terms of content and taxonomy, and they are also connected with the aims of the mathematics curriculum. The second, empirical part is focused on finding out how developed mathematical literacy is in fifth-graders in Slovenia. For the purposes of this research, our own Maths test was created, testing mathematical literacy with twelve tasks. 246 pupils and 17 class teachers participated in the research. The aim was to find out how well the participants would do in this test, and how the results differ in relation to pupils’ gender and type of school where they come from. We also wanted to know the relation between the levels of the Gagné taxonomy and how proficient the pupils are in different content areas of mathematical literacy. This research has shown that the average result of our test is similar to results of related international and national studies. There are no differences between the two genders, additionally, there are also no differences between schools in urban and rural areas. Further statistical analysis has shown that the result of the test is connected to the pupil’s Maths grade. By this it is meant that pupils who performed better in our test also have a higher grade in Maths. The Maths teacher’s occupational record did not affect test results at all. The fifth graders are most successful when solving tasks that check their conceptual knowledge and when solving tasks involving data processing. This research confirms the assumption that mathematical literacy is a specific part of mathematics, consisting of the use of mathematical knowledge in contexts that are not structured in the same way as usual school contexts. Problem-orientation, the breadth of the knowledge needed and a realistic environment are the fundamental properties of tasks designed for checking mathematical literacy, which course book tasks often lack. At the same time, we need to be conscious that being proficient in basic mathematical skills and having basic knowledge of mathematical concepts are two conditions for mathematical literacy, and therefore these two areas of mathematics are interrelated. The results that were gathered with this study represent a high-quality feedback for teachers and pupils, who participated in this research. They represent an important contribution to the professionals, who deal with mathematical literacy in Slovenia, and the test that was developed for this research allows the fifth-grade teachers to improve their existing practice of developing mathematical literacy

Preparation and characterization of ZnO based thin films by spin-coating method

Transparentni prevodni oksidi (TCO) so električno prevodni materiali, ki v vidnem območju elektromagnetnega spektra absorbirajo majhno količino svetlobe in so posledično prosojni. Uporabljajo se v različnih optoelektronskih napravah, kot so solarne celice, termokromna stekla, prikazovalniki na dotik in senzorji. Večinoma se kot material za električno prevodne komponente v teh napravah uporabljajo tanke plasti na osnovi indijevega oksida z dodatkom kositra (ITO). Za pripravo tankih ITO plasti se uporabljajo fizikalne metode, kot sta lasersko nanašanje in magnetronsko naprševanje, ki zahtevajo nanos v vakuumu in uporabo drage opreme. Poleg tega je In2O3 drag, zato se raziskujejo alternativni materiali, ki so cenejši in dostopnejši od In2O3. Iščejo se tudi enostavne metode priprave tankih plasti, ki ne zahtevajo drage opreme in potekajo pri normalnih pogojih. Eden od obetavnih materialov je cinkov oksid (ZnO), ki ima širok prepovedan pas, dobro mehansko/kemijsko/toplotno stabilnost, v obliki tanke plasti na steklu pa ima tudi visoko prosojnost. Poleg tega lahko na strukturne, električne in optične lastnosti tankih plasti ZnO vplivamo s spreminjanjem kemijske sestave (dopirajem) ter s spreminjanjem pogojev pri procesu njihove priprave. V sklopu magistrskega dela sem pripravil tanke plasti IZO z atomskim razmerjem Zn/(In+Zn) = 0,36 na steklu in siliciju iz raztopin s tehniko vrtenja podlage. Raztopine IZO, koncetracij 0,3 mol/l in 0,147 mol/l, so bile pripravljene z raztapljanjem izhodnih surovin v ustreznih topilih. Cinkov acetat hidrat sem raztopil v etilen glikolu, indijev nitrat hidrat pa v etanolu z dodatkom ocetne kisline. Z mešanjem izhodnih raztopin sem pridobil homogeno in bistro raztopino IZO. S pomočjo termične analize (TG/DTA/EGA) in infrardeče spektroskopije s Fourierjevo transformacijo (FTIR) raztopin in prahov, dobljenih s sušenjem raztopin, sem določil pogoje sušenja posameznih nanosov in žganje plasti. Plasti IZO sem okarakteriziral z vrstično elektronsko mikroskopijo s poljsko emisijo (FE-SEM), mikroskopom na atomsko silo (AFM) in rentgensko praškovno difrakcijo (XRD). Električna upornost pripravljenih tankih plasti IZO je bila izmerjena s štiri-točkovno metodo. Pri sušenju plasti na 350 0C sem na siliciju pridobil tanko plast IZO s plastno mikrostrukturo, z znižanjem temperature sušenja na 200 0C pa sem uspel pridobiti plast s homogeno mikrostrukturo. Primerjal sem tudi vpliv temperature žganja na mikrostrukturo plasti IZO na steklu. Ugotovil sem, da je najbolj primerna temperatura žganja pri 600 0C. Debelina plasti IZO s plastno in homogeno mikrostrukturo je okoli 80 nm z velikostjo zrn do 20 nm. Površina vseh analiziranih plasti IZO je ravna in struktura le-teh nima urejenosti dolgega reda. Najnižjo upornost je imela plast IZO žgana na zraku (pri 6000C) s plastno mikrostrukturo in sicer 0,12 Ω*cm. Z dodatnim popuščanjem plasti IZO v Ar/H2 atmosferi pa se je upornost znižala za približno dva velikostna reda na 4*10-3 Ω*cm. Padec upornosti je posledica tvorbe vrzeli na kisikovih mestih v mikrostrukturi plasti IZO. Ugotovil sem tudi, da plasti IZO v vidnem delu elektromagnetnega spektra prepuščajo med 80 in 92% svetlobe, boljšo prosojnost pa izkazuje plast IZO s plastno mikrostrukturo.Transparent conductive oxides (TCO) are electrically conductive materials that absorb a small amount of light in the visible range of electromagnetic spectrum and are consequently transparent. They are used in various optoelectronic devices such as solar cells, thermochromic glasses, touch displays and sensors. Thin films based on indium oxide with the addition of tin (ITO) are mostly used as material for electrically conductive components in these devices. Physical methods, such as laser deposition and magnetron sputtering, are used for the preparation of ITO thin films, which require deposition in vacuum and use of expensive equipment. In addition, In2O3 is expensive, therefore alternative materials, that are cheaper and more accessible than In2O3, are being researched as well as methods for preparing thin films, that do not require expensive equipment and take place under normal conditions. One of the promising materials is zinc oxide (ZnO) with a wide band gap, good mechanical/chemical/thermal stability, and in the form of a thin film, it is also highly transparent. In addition, the structural, electrical and optical properties of ZnO thin films can be influenced by changing the chemical composition (doping) and changing the conditions during thin film preparation process. As part of my master`s thesis, I prepared thin films IZO with the atomic ratio Zn/(In+Zn) = 0,36 on glass and silicon, using the spin-coating method. IZO solutions, with concentrations 0,3 mol/l and 0,147 mol/l, were prepared by dissolving the starting raw materials in appropriate solvents. Zinc acetate hydrate was dissolved in ethylene glycol, and indium nitrate hydrate in ethanol with the addition of acetic acid. Mixing the starting solutions, I obtained a homogeneous and clear IZO solution. With thermal analysis and infrared spectroscopy with Fourier transformation of solutions and powders, obtained with drying of solutions, I determined the drying conditions of individual coatings and annealing of thin films. IZO thin films were characterized by field-emission scanning electron microscopy, atomic force microscopy and X-ray powder diffraction. The electrical resistivity of the prepared IZO thin films was measured by the four-point probe method. When drying the film at 350 0C, I obtained IZO thin film with a layered microstructure, and by lowering the drying temperature to 200 0C, I managed to obtain a film with a homogeneous microstructure. I also compared the influence of annealing temperature on the microstructure of the IZO thin films on glass. I found that the most suitable annealing temperature is 600 0C. The thickness of the IZO thin films with the layered and homogeneous microstructure is around 80 nm with grain size of up to 20 nm. The surface of all analysed IZO thin films is flat and their structure does not have long-range order. IZO film with a layered microstructure had the lowest resistivity of 0,12 Ω*cm. By additionally annealing IZO thin films in an Ar/H2 atmosphere, the resistivity was reduced by approximately two orders of magnitude to 4*10-3 Ω*cm. This is the result of the formation of oxygen vacancies in the microstructure of IZO thin films. I also found that these thin films transmit between 80% and 92% of light in the visible part of electromagnetic spectrum and the IZO thin film with a layered microstructure shows better transparency

Identifying mathematical literacy of the fifth graders

Magistrsko delo z naslovom Ugotavljanje matematične pismenosti pri učencih v 5. razredu osnovne šole sestoji iz dveh delov. V prvem, teoretičnem delu je predstavljena pismenost z vidika definicij in njenega razvijanja. Največ pozornosti je namenjene matematični pismenosti, ki je središče proučevanja tega dela. Matematična pismenost je proučevana z vidika povezovanja z učnim načrtom za matematiko, analizirana pa je tudi z vidika mednarodnih in nacionalnih raziskav, ki jo proučujejo in merijo. Teoretični del natančno analizira rezultate zadnjih meritev omenjenih raziskav, ki so relevantni za primerjavo z raziskavo, izvedeno v okviru tega magistrskega dela. Podrobneje sta predstavljena reševanje matematičnih problemov, ki predstavlja temeljno kompetenco na področju razvijanja matematične pismenosti, ter Gagnejeva taksonomija, na kateri temelji večina relevantnih raziskav. V zaključku teoretičnega dela so predstavljene posamezne naloge, vključene v preizkus znanja, ki je bil uporabljen v raziskavi. Naloge so vsebinsko in taksonomsko klasificirane ter povezane s cilji iz učnega načrta za matematiko. V drugem, empiričnem delu smo se osredinili na ugotavljanje, kako razvita je matematična pismenost pri petošolcih. Za namen raziskave smo sestavili lasten avtorski preizkus znanja, ki z 12 nalogami preverja matematično pismenost. V raziskavi je sodelovalo 246 učencev ter 17 učiteljev razrednikov. Cilj raziskave je bil ugotoviti, kakšen sploh je dosežek med vsemi sodelujočimi, kako se dosežek na preizkusu znanja razlikuje, glede na spol učenca in tip šole, s katere učenci prihajajo, ter kako je dosežek povezan z učenčevo zaključno oceno pri matematiki ter z delovno dobo učitelja. Zanimalo nas je, kako učenci rešujejo naloge, ki preverjajo različne taksonomske ravni po Gagneju, ter kakšno je znanje učencev na različnih vsebinskih področjih matematične pismenosti. Rezultati raziskave so pokazali, da je povprečen dosežek podoben dosežkom na sorodnih mednarodnih ali nacionalnih raziskavah. Do razlik med spoloma ne prihaja, prav tako ni razlik med mestnim in vaškim tipom šol. Nadaljnja statistična analiza je pokazala, da je dosežek povezan z učenčevim dosežkom pri matematiki, kar pomeni, da imajo učenci, ki so bolje pisali preizkus znanja, tudi boljšo končno oceno pri matematiki, delovna doba učitelja pa na rezultat pri preizkusu znanja ne vpliva. Petošolci so najuspešnejši pri reševanju nalog, ki preverjajo konceptualno znanje, ter pri vsebinah iz obdelave podatkov. Raziskava je potrdila predpostavko, da je matematična pismenost specifičen del matematike in da gre za uporabo matematičnega znanja v kontekstih, ki niso tako strukturirani, kot so običajni šolski konteksti. Problemska naravnanost, širina potrebnega znanja in realistično okolje so temeljne značilnosti nalog iz matematične pismenosti, ki pri učbeniških nalogah pogosto umanjkajo. Hkrati pa je potrebno zavedanje, da je poznavanje osnovnih matematičnih veščin in pojmov pogoj za razvoj matematične pismenosti in da sta torej ti dve področji v matematiki soodvisni. Dobljeni rezultati so tako kvalitetna povratna informacija učiteljem in učencem, sodelujočim v raziskavi. Pomenijo prispevek v razvoju stroke, ki se ukvarja z matematično pismenostjo v slovenskem prostoru, preizkus znanja pa učiteljem petih razredov omogoča, da izboljšajo svojo dosedanjo prakso razvijanja matematične pismenosti.This master\u27s thesis, titled Identifying Mathematical Literacy of the Fifth Graders consists of two parts. The first, theoretical part discusses literacy from the point of view of definitions and its development. Most attention is devoted to mathematical literacy, which is the focal point of this research. Mathematical literacy is not only analysed in connection with the Maths curriculum, but also in relation to international and national research which study and measure it. The theoretical part precisely analyses results of the latest measurements of the aforementioned studies, relevant for this master\u27s thesis. Solving mathematical problems, one of the main competences when it comes to developing mathematical literacy, as well as the Gagné taxonomy, the basis of most relevant research, are also presented in detail. In the concluding section of the theoretical part are presented individual tasks, included in one Maths test, also part of this research. The tasks are classified in terms of content and taxonomy, and they are also connected with the aims of the mathematics curriculum. The second, empirical part is focused on finding out how developed mathematical literacy is in fifth-graders in Slovenia. For the purposes of this research, our own Maths test was created, testing mathematical literacy with twelve tasks. 246 pupils and 17 class teachers participated in the research. The aim was to find out how well the participants would do in this test, and how the results differ in relation to pupils’ gender and type of school where they come from. We also wanted to know the relation between the levels of the Gagné taxonomy and how proficient the pupils are in different content areas of mathematical literacy. This research has shown that the average result of our test is similar to results of related international and national studies. There are no differences between the two genders, additionally, there are also no differences between schools in urban and rural areas. Further statistical analysis has shown that the result of the test is connected to the pupil’s Maths grade. By this it is meant that pupils who performed better in our test also have a higher grade in Maths. The Maths teacher’s occupational record did not affect test results at all. The fifth graders are most successful when solving tasks that check their conceptual knowledge and when solving tasks involving data processing. This research confirms the assumption that mathematical literacy is a specific part of mathematics, consisting of the use of mathematical knowledge in contexts that are not structured in the same way as usual school contexts. Problem-orientation, the breadth of the knowledge needed and a realistic environment are the fundamental properties of tasks designed for checking mathematical literacy, which course book tasks often lack. At the same time, we need to be conscious that being proficient in basic mathematical skills and having basic knowledge of mathematical concepts are two conditions for mathematical literacy, and therefore these two areas of mathematics are interrelated. The results that were gathered with this study represent a high-quality feedback for teachers and pupils, who participated in this research. They represent an important contribution to the professionals, who deal with mathematical literacy in Slovenia, and the test that was developed for this research allows the fifth-grade teachers to improve their existing practice of developing mathematical literacy

Indium-zinc-oxide thin films produced by low-cost chemical solution deposition: Tuning the microstructure, optical and electrical properties with the processing conditions

Indium-zinc-oxide (IZO) films were prepared by spin coating an ethanol-ethylene-glycol precursor solution with a Zn/(In + Zn) ratio of 0.36 on glass. The effects of temperature on the structure, microstructure, electrical, and optical properties of the IZO thin films were investigated by thermal analysis, Fourier-transform infrared spectroscopy, X-ray diffraction, electron and atomic-force microscopy, X-ray photoelectron spectroscopy and variable-angle spectroscopic ellipsometry. The prepared IZO thin films heated at 500, 600, and 700 °C in air were transparent, without long-range ordering, and with an RMS surface roughness of less than 1 nm. The lowest electrical resistivity at room temperature, 0.0069 Ωcm, was observed for the 115-nm-thick IZO thin film heated at 600 °C in air and subsequently post-annealed in Ar/H2. The thin film exhibited a microstructure characterized by grains typically 20 nm in size and had no organic residues. This film exhibits uniaxial optical anisotropy due to its ultra-thin lamellae with a high electron density. The ordinary refractive index was fitted as a Tauc-Lorentz-Urbach function, which is typical of an indirect absorption edge occurring in amorphous semiconductor materials. The principal absorption peak with an onset at about 2.8 eV and a Tauc gap energy of ∼2.6 eV is similar to those observed for In2O3. The described process of chemical solution deposition and subsequent curing is promising for the low-cost fabrication of IZO thin films for transparent electronics, and can be used to tune the structure and microstructure of IZO thin films, as well as their electrical and optical properties