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Influence of potential on passivation of tin : bachelor thesis
No full textU radu je ispitan utjecaj potencijala pasivacije (od 0.0 do 1.6 V) i vremena anodizacije (do 4 sata) na svojstva oksidnih filmova koji se pri potenciostatskim uvjetima formiraju na Sn u 0.1 M otopini natrijevog acetata (pH = 8.3, T = 20 o C). Za vrijeme formiranja oksidnih filmova snimani su struja– vrijeme odgovori, određena je količina naboja koja se utroši u procesu anodizacije te izračunata debljina oksidnog filma. Pasivacija kositra započinje formiranjem Sn(OH) 2 ili SnO (kod ≈ -0.70 V), a stvarno pasivno stanje se postiže formiranjem Sn(OH) 4 filma (kod pozitivnijih potencijala). Pod utjecajem daljnje anodne polarizacije dolazi do transformacije hidratiziranog Sn(OH) 4 filma u termodinamički stabilniji dehidratizirani oblik, SnO 2 · H 2 O. Potencijal pasivacije i vrijeme anodizacije određuju stabilnost oksidnog filma na kositru. Oksidni filmovi s boljim zaštitnim svojstvima (veća debljina, bolja morfologija i veći otpor) dobiveni su u slučaju kada je pasivacija provedena na pozitivnijim potencijalima u pasivnom području, a vrijeme anodizacije duže.The effect of passivation potential (from 0.0 to 1.6 V) and anodization time (up to 4 hours) on the properties of oxide films formed on Sn in 0.1 M sodium acetate solution (pH = 8.3, T = 20 o C) was investigated. During the formation of oxide films, current-time responses were recorded, the amount of charge consumed in the anodizing process was determined, and the thickness of the oxide film was calculated. The passivation of tin starts with the formation of Sn(OH) 2 or SnO (at ≈ -0.70 V), while the actual passive state is achieved by the formation of Sn(OH) 4 film (at more positive potentials). Under the influence of further anodic polarization, the hydrated Sn(OH) 4 film is transformed into a thermodynamically more stable dehydrated form, SnO 2 ·H 2 O. The passivation potential and the anodizing time determine the stability of the oxide film on the tin. Oxide films with better protective properties (greater thickness, better morphology and higher resistance) were obtained in the case when passivation was carried out at more positive potentials in the passive region, and at longer anodizing times
Type 1-2 shell and tube heat exchangers in cooling system of rotary kilns : master thesis
No full textTema ovog diplomskog rada je rješavanje sustava hlađenja rotacijske peći koja služi za proizvodnju Portland cementa na izlaznom bloku peći. Na raspolaganju je bila serija industrijskih višecijevnih (engl. shell and tube) izmjenjivača topline (tip 1-2) s učvršćenim snopom cijevi koje je bilo potrebno ispitati te ustanoviti mogu li se upotrijebiti za hlađenje mineralnog ulja koje podmazuje klizne ležajeve na izlaznom bloku peći. Broj pregrada za svaki od zadanih MITova iznosi 9. Raspored cijevi je u trokutu s korakom od 13 mm. Iz rezultata ispitivanja uočljivo je kako je režim strujanja vode u cijevima u prijelaznom području (2300 < Re < 10 000) pri svim ispitivanim protocima, dok je režim strujanja u plaštu laminaran (Re < Re kr ). Rezultati proračuna također pokazuju kako je za svaki od ispitivanih MITova dobivena vrijednost površine za izmjenu topline bila manja u odnosu na raspoloživu površinu ispitivanih izmjenjivača navedenih karakteristika. Iz toga se zaključuje kako je moguće primjeniti svaki od navedenih tipova izmjenjivača za hlađenje kliznih ležajeva rotacijske peći.The topic of this thesis is the solution of the cooling system of a rotary kiln used for the production of Portland cement on the output block of the kiln. There were available a series of industrial shell and tube heat exchangers (type 1-2) with a fixed bundle of tubes that needed to be tested to determine if they could be used to cool the mineral oil that lubricates the plain bearings on the furnace outlet block. The number of baffles for each of the given MITs is 9. The tube arrangement is in a triangle with a step of 13 mm. From the test results, it is noticeable that the flow regime of water in the tubes is in the transition region (2300 < Re < 10 000) at all tested flows, while the flow regime in the shell is laminar (Re < Re cr ). The calculation results also show that for each of the tested MITs the obtained value of the heat exchange surface was lower in relation to the available area of the tested heat exchangers of the stated characteristics. All of the mentioned information lead to a conclusion that it is possible to use each of the above types of heat exchangers for cooling the plain bearings of a rotary kiln
Volumetric properties of solutions of imidazolium chloride ionic liquids ([mim][Cl], [1.3-dmim][Cl], [emim][Cl], [bmim][Cl] and [hmim][Cl]) in butan-2-olu and butan-2-one : diploma thesis
No full textProvedena su mjerenja gustoća pet imidazolijevih kloridnih ionskih tekućina (mimCl, 1,3-dmimCl, emimCl, bmimCl i hmimCl) u butan-2-olu i butan-2-onu pri određenim temperaturama, / C = 5, 10, 15, 20, 25, 30, 35 i 40, korištenjem automatskog mjerača gustoće Anton Paar DMA 4500M. Dobiveni podaci korišteni su za daljnje računanje volumetrijskih svojstava - prividnih i parcijalnih molarnih volumena. Preko Massonove jednadžbe izračunati su prividni granični molarni volumeni i interakcijski koeficijenti. Također, izračunata je i prividna granična molarna ekspanzibilnost imidazolijevih kloridnih ionskih tekućina u butan-2-olu i butan-2-onu. Eksperimentalni rezultati su raspravljeni i provedena je usporedba sa imidazolijevim kloridnim ionskim tekućinama u vodenom mediju.The density measurements of five imidazolium chloride ionic liquids (mimCl, 1,3-dmimCl, emimCl, bmimCl and hmimCl) in butan-2-ol and butan-2-one at different temperatures, / C = 5, 10, 15, 20, 25, 30, 35 i 40, were performed using Anton Paar DMA 4500M densimeter. The obtained data were used for calculation of volumetric properties – apparent molar volumes and partial molar volumes. The volumetric data have been analyzed using Masson`s equation. The limiting apparent molar volume and the slope of Masson`s equation for imidazolium chloride ionic liquids in butan-2-ol and butan- 2-on at diferent temperatures have been interpreted in terms of ion-ion and ion-solvent interactions. The results were discussed and compared with water medium
Corrosion behavior of CuAlMnZn alloy in Na2SO4 solution : master thesis
No full textU radu je ispitan utjecaj temperature elektrolita, 0.5 mol dm -3 otopine Na 2 SO 4 na korozijsko ponašanje CuAlMnZn legure. Ispitivanja su provedena različitim nedestruktivnim elektrokemijskim metodama kao što su mjerenje potencijala otvorenog strujnog kruga, metoda linearne polarizacije i elektrokemijske impedancijske spektroskopije kao i destruktivnim metodama u širokom području potencijala kao što su potenciodinamička polarizacijska metoda i metoda cikličke polarizacije. Rezultati ispitivanja su pokazali negativan utjecaj temperature elektrolita na korozijsku otpornost legure. Nakon potenciodinamičkih polarizacijskih mjerenja, korodirane površine elektroda ispitane su svjetlosnim mikroskopom. Utjecaj vremena izlaganja elektrolitu na korozijsko ponašanje legure ispitano je određivanjem polarizacijskog otpora mjerenjima metodom linearne polarizacije u vremenskom periodu od 48 h. Ispitivanja su pokazala smanjenje vrijednosti polarizacijskog otpora s vremenom.The effect of electrolyte temperature, 0.5 mol dm -3 Na 2 SO 4 solution on the corrosion behavior of CuAlMnZn alloy was investigated. The measurements were performed by various non-destructive electrochemical methods such as open circuit potential measurement, linear polarization method and electrochemical impedance spectroscopy as well as destructive methods in a wide range of potentials such as potentiodynamic polarization method and cyclic polarization method. The results showed a negative effect of electrolyte temperature on the corrosion resistance of the alloy. After potentiodynamic polarization measurements, the corroded electrode surfaces were examined with a light microscope. The influence of electrolyte exposure time on the corrosion behavior of the alloy was examined by determining the polarization resistance measurements using linear polarization method over a time-period of 48 h. Results have shown a decrease in polarization resistance over time
Kaolin copper sorption equilibrium (T=298 K) : bachelor thesis
No full textIspitana je sorpcija bakrovih iona na kaolinu u ovisnosti o različitim početnim koncentracijama otopina bakrovih iona (2,289 mmol dm-3, 4,789 mmol dm-3, 7,836 mmol dm-3, 10,727 mmol dm-3 te 13,539 mmol dm-3). Eksperiment je proveden pri stalnoj temperaturi od 298 K, brzini miješanja od 200 okr min-1, u trajanju od 48 h. Koncentracije bakrovih iona prije i nakon sorpcije su određene spektrofotometrijski. Na temelju dobivenih rezultata može se zaključiti kako se količina sorbiranih bakrovih iona (qe) ne mijenja s porastom ravnotežne koncentracije bakrovih iona u otopini (ce) te iznosi qe = 0,016 mmol g-1. Tako dobivena vrijednost za količinu sorbiranih bakrovih iona na kaolinu predstavlja maksimalnu količinu bakrovih iona koja se može sorbirati na kaolinu za uvjete pri kojima je eksperiment proveden. Učinkovitost sorpcije bakrovih iona dostiže svoju maksimalnu vrijednost za najnižu odabranu početnu koncentraciju od 2,289 mmol dm-3 te iznosi 3,413 % te nakon toga opada s porastom početne koncentracije bakrovih iona u otopini. Kapacitet izmjene kationa iznosi CEC = 5,3 M+ / 100 g iz čega se može zaključiti kako kaolin nema značajnu sposobnost izmjene iona, dok FTIR spektri, prije i nakon sorpcije, pokazuju kako nije došlo da promjene u strukturi kaolina.The sorption of copper ions on kaolin was studied depending on the different initial concentrations of copper ions solutions (2.289 mmol dm-3, 4.789 mmol dm-3, 7.836 mmol dm-3, 10.727 mmol dm-3, and 13.539 mmol dm-3). The experiment was carried out at a constant temperature of 298 K, stirring speed of 200 rpm for 48 h. Concentrations of copper ions before and after the sorption were determined using spectrophotometer. Based on the results obtained it can be concluded that there is no change in the amount of copper ions sorbed (qe) with the increase of the equilibrium concentration of copper ions in solution (ce) with the value of qe = 0.016 mmol g-1. The obtained value for the amount of copper ions sorbed on kaolin represents the maximum amount of copper ions that can be sorbed on the kaolin for conditions under which the experiment was conducted. The copper ion sorption efficiency reaches its maximum value for the lowest initial concentration of 2.289 mmol dm-3 with the value of 3.413 % and then decreases with the increase of initial concentration of copper ion in solution. The cation exchange capacity is CEC = 5.3 M+ / 100 g from which it can be concluded that kaolin has no significant ability to exchange the ions, whereas the FTIR spectra before and after sorption show that there was no change in the kaolin structure
Effect of PBT impeller speed on the kinetics of ion exchange : diploma thesis
No full textU ovom radu ispitan je utjecaj brzine vrtnje i pozicije PBT miješala na ionsku izmjenu bakra iz vodene otopine bakrovog(II) nitrata na sintetskom zeolitu NaX. Eksperiment se proveo u neprotočnom kotlastom reaktoru uz miješanje pri temperaturi od 27 °C. Ispitivan je utjecaj tri različite pozicije miješala pri čemu je omjer udaljenosti miješala od dna posude (C) i visine stupca kapljevine (H) u različitim eksperimentima iznosio 0,10; 0,33; 0,50. Određen je i iznos zakretnog momenta te izračunat utrošak snage (P). Analizom rezultata je uočeno da povećanjem C/H omjera raste i utrošak snage. Usporedbom eksperimentalnih podataka može se zaključiti da je najpotpunija ionska izmjena provedena pri C/H=0,33. Analizom eksperimentalnih rezultata utvrđeno je kako je proces izmjene iona u početnom periodu brz nakon čega usporava do uspostave ravnoteže. Kinetičkom analizom utvrđeno je da Ritchiev model pokazuje dobro slaganje s eksperimentalnim podatcima za sve tri pozicije miješala, dok s Weber-Morrisovim modelom nema slaganja, što znači da difuzija ne utječe na brzinu reakcije.In this work the influence of the speed and position of the PBT impeller on ion exchange of copper ions from aqueous solutions of copper(II) nitrate on the synthetic zeolite NaX was investigated. The experiment was carried out in a batch reactor with stirring at 27 °C. The influence of three different positions of the impeller was tested, i.e. ratio of the distance of the impeller from the bottom of the vessel (C) to the liquid height (H) were C/H= 0.10; 0.33; 0.50. The amount of torque and mixing power consumption (P) were also determined, and analysed results showed that the increase in C/H ratio follows the increases of the power consumption. It was found that the optimal copper exchange was at C/H= 0.33.The analysed experimental results showed that in the initial period of the experiment the ion exchange process is faster. After, its speed decreases till the equilibrium is reached. The kinetic analysis established that the Ritchie model shows good fit with the experimental data for all three positions of the impeller, while there was no match with the Morris-Weber model which means that the speed of the process is not affected by diffusion
Microwave synthesis of iron oxide particles with different experimental conditions : master thesis
No full textZbog široke primjene nanočestica u biologiji, industriji, pedologiji i istraživanju korozije, znanstvenici su razvili razne metode za njihovu sintezu. Mikrovalna sinteza pokazala se kao najbrža, najjednostavnija i najprihvatljivija metoda sintezu nanočestica te je korištena u ovom radu. Mikrovalna sinteza može se provoditi na visokim temperaturama na siguran, jednostavan i ponovljiv način. Dokazano je da se ovom metodom može povećati i prinos proizvoda. U ovom radu uzorci su sintetizirani na temperaturama od 150, 200 i 250 ° C u vremenu od 20 minuta. Osim utjecaja temperature, cilj je bio pratiti i utjecaj surfaktanta koji je dodan u količinama od 0,1, 0,2 i 0,4 i 1 g. Surfaktant koji se koristio za sintezu bio je polietilen glikol (PEG). Svi uzorci su na kraju snimljeni IR-spektrometrom s Fourirerovom transformacijom (FTIR). Odabrani uzorci prikazani su u tablici i grafovima.Scientists have developed various methods for nanoparticles synthesis because of their wide application in biology, industry, paedology and in corrosion research. The microwave synthesis proved to be the fastest, simplest and the most acceptable method. It can be performed at high temperatures in a safe, simple and repeatable manner. It has been proven that this method can also increase quantity of product. Samples were synthesized at temperatures of 150, 200 and 250° C over a period of 20 minutes in this thesis. The aim was to observe the effect of temperature and surfactants which were added in amounts of 0,1 , 0,2, 0,4 and 1 g. Polyethylene glycol (PEG) was used as surfactant. All samples were eventually recorded by IR spectrometer with Fourier transformation (FTIR). Selected samples are shown in tables and graphs
Evolution and critical approach towards pearson concept of acids and bases - HSAB theory : bachelor thesis
No full textRalph G. Pearson (1963.) je predstavio koncept koji objašnjava kemijsku reaktivnost, selektivnost, te stabilnost kemijskih vrsta. Kemijske vrste koje uključuju atome, molekule, ione i slobodne radikale, je kategorizirao na „tvrde“ i „meke“ Lewisove kiseline i baze. „Tvrde“ vrste su općenito malenog radijusa, velikog naboja, te niske polarizabilnosti, dok „meke“ vrste imaju suprotna svojstva. S vremenom su se mnogi dijelovi kemije objasnili korištenjem HSAB koncepta. Poput koordinacijskih spojeva, kompleksa prijenosa naboja, vezanja vodika, kompleks slobodnih radikala, interakcije otapala i otopljene tvari, čvrstih spojeva, itd. Uistinu, većina anorganskih i organskih spojeva se mogu smatrati kiselo-baznim kompleksima. Pearson je naglasio kako jedan od nedostataka HSAB teorije je korištenje samih izraza „tvrdo“ i „meko“ jer one ne znače isto što i jako i slabo. Što stvara problem prilikom kvantifikacije jakosti tvrdih i mekih kiselina i baza. Nemogućnost formiranja univerzalne skale Lewisove bazičnosti (kiselosti) uzrokuju postojanje mnogih skala kiselosti (bazičnosti). Iako, ove skale općenito nemaju međusobnu korelaciju, postoje korelacije unutar određenih skupina spojeva koje omogućavaju formiranje skala, u jednom općenitom obliku, za baze određene skupine spojeva, npr. skupina kisikovih baza. Te je stoga i dalje upitna kvantitativna primjena Lewisovog koncepta kiselina i baza.Ralph G. Pearson (1963) brought forth a concept by which chemical reactivities, selectivities, and stabilities of chemical compounds may be readily rationalized. Chemical species, including atoms, molecules, ions,and free radicals are categorized as “hard” and “soft" Lewis acids or bases. The “hard” species in general have small radius, high nuclear charge, and low polarizability, whereas “soft” ones possess the opposite characteristics. Over time, many parts of chemistry have been identified that can be rationalized by using the HSAB principle. Including coordination compounds, charge-transfer complexes, hydrogen bonding, free-radical complexes, solvent-solute interactions, solid-state compounds,. Indeed, most inorganic and organic molecules can be thought of as acid-base complexes, Pearson notes one of the pitfalls of the HSAB theory is that the adjectives “hard” and “soft“ don't mean the same as strong and weak. Which makes it difficult in general to quantify the strength of hard and soft acids and bases.The impossibility of establishing a universal scale of Lewis basicity (acidity) is the reason for the existence of many scales of acitidy (basicity). Moreover, although these scales are generally not interrelated, there exist family-dependent relationships that permit ranking, in a rather general order, of bases belonging to a given chemical family, for example, the family of oxygen bases. Therefore, the skepticism about the quantitative usefulness of the Lewis concept of acids and bases still exists
Trends in use of plant extract in food : bachelor thesis
No full textDanas se sve više pazi na kvalitetu hrane koju konzumiramo i postalo je važno da dodatci prehrani budu prirodnog podrijetla. Biljni ekstrakti, kao dodatci prehrani, imaju konzervirajuću ulogu kod određenih namirnica kao što su meso, riba i mliječni proizvodi. Zbog svog kemijskog sastava, a najviše zahvaljujući polifenolima, biljni ekstrakti imaju snažno biološko djelovanje. Među njima ističu se antimikrobna aktivnost prema različitim patogenim bakterijama i bakterijama koje uzrokuju kvarenje hrane, visoka antioksidacijska aktivnost koja uspješno sprječava pojavu lipidne oksidacije i učinkovito antifugalno djelovanje. Pregledom dostupne literature i dosadašnjih istraživanja biološkog potencijala različitih biljnih ekstrakata možemo potvrditi opravdanost njihove primjene u prehrambenoj industriji.Today, more and more attention is paid to the quality of the food we consume and it has become important to add dietary supplements to be of natural origin. Herbal extracts, as dietary supplements, play a preservative role in certain foods such as meat, fish and dairy products. Due to their chemical composition, mostly thanks to polyphenols, plant extracts have a strong biological effect. Among them are antimicrobial activity against various pathogenic bacteria and bacteria that cause food spoilage, high antioxidant activity that successfully prevents the occurrence of lipid oxidations and effective antifungal action. By reviewing the available literature and previous research on the biological potential of various plant extracts, it can be confirmed justification of their application in the food industry
Review of selected methods for determination of clozapine in pharmacological preparations and biological samples : bachelor thesis
No full textKlozapin je lijek koji spada u skupinu atipičnih antipsihotika. Koristi se kao terapija za shizofreniju rezistentnu na liječenje. Kako bi se poboljšao klinički ishod liječenja i smanjila mogućnost nuspojava, u novije vrijeme se primjenjuje terapijsko praćenje koncentracije lijeka u krvi. Iz navedenih razloga, razvoj preciznih i osjetljivih analitičkih metoda za određivanje klozapina u različitim uzorcima popularna je tema brojnih istraživačkih radova. Rad opisuje odabrane kromatografske i voltametrijske metode analize uzoraka te njihovu praktičnu primjenu za određivanje klozapina u farmaceutskim oblicima i različitim biološkim uzorcima. Na temelju pregleda različitih znanstvenih radova, ovaj rad uspoređuje rezultate metoda određivanja klozapina i prikazuje prednosti i nedostatke opisanih metoda.Clozapine is a drug that belongs to the group of atypical antipsychotics. It is used as a therapy for treatment-resistant schizophrenia. In order to improve the clinical outcome of treatment and reduce the possibility of side effects, therapeutic monitoring of drug concentration in the blood has recently been applied. For these reasons, the development of precise and sensitive analytical methods for the determination of clozapine in various samples is a popular topic of numerous research papers. This paper describes selected chromatographic and voltammetric methods of sample analysis and their practical application for the determination of clozapine in pharmaceutical forms and different biological samples. Based on a review of various scientific papers, this paper compares the results of clozapine determination methods and presents the advantages and disadvantages of the described methods