Elektrokemijska oksidacija aluminija

Sve većim napretkom industrije dolazi do sve većih zahtjeva za materijale, aluminij kao drugi najzastupljeniji materijal mora odgovarati tim zahtjevima. Potreba za sve boljim mehaničkim i fizikalnim svojstvima aluminija rezultira sve većim brojem legura istoga. Važno svojstvo aluminija je njegovo stvaranje oksidne prevlake koja ga štiti od korozije, ta prevlaka može biti stvorena i umjetnim putem odnosno elektrokemijskom oksidacijom. Prevlaka nastala elektrokemijskom oksidacijom je mnogostruko djelotvornija u zaštiti aluminija od korozije od one nastale prirodnim putem. Kako bi korozijska postojanost te prevlake bila što veća aluminij se podvrgava brojnim istraživanjima, u kojima se različitim tehnikama i dodacima pokušava dobiti što bolja zaštitna svojstva oksidne prevlake. Rad se sastoji od dva dijela teorijskog i eksperimentalnog. Teorijski dio rada objašnjava podjelu legura aluminija kao i njihova svojstva, korozijsku postojanost i primjenu. Navedene su metode zaštite aluminija te je detaljno objašnjena zaštita aluminija oksidnim prevlakama odnosno elektrokemijskom oksidacijom. Eksperimentalni dio je obuhvatio pripremu uzoraka od aluminija podijeljenu na dva djela. Jedan dio uzoraka je elektrokemijski oksidiran u elektrolitima s različitim koncentracijama cerija dok drugi dio uzoraka je uronjen u otopinu s različitom koncentracijom cerija u cilju ispitivanja inhibitorskog djelovanja. Na uzorcima su zatim provedena metalografska i elektrokemijska ispitivanja

Structural characterization and analytical application of aromatic hydrazones derived from nicotinic acid hydrazide

Proučavano je dvanaest aromatskih hidrazona izvedenih iz nikotinohidrazida i različito supstituiranih benzaldehida, odnosno fenil-metil-ketona. Identifikacija i karakterizacija spojeva provedena je spektrometrijom masa i spektroskopskim metodama (NMR, UV-Vis i spektrofluorimetrija). Spektrometrijom masa razlikovani su metoksi derivati uslijed različitog pomaka keto-enolne tautomerne ravnoteže u plinskoj fazi. Dihidroksi- i klor- derivati razlikovani su na temelju "ortho efekta". Hidrazoni se u otopini nalaze u najstabilnijem enoliminskom obliku, osim nitro derivata koji u dimetilsulfoksidu podliježe deprotonaciji, E/Z izomeriji i keto-enolnoj tautomeriji. Za klor- i nitro- derivate uočena je fluorescencija u lužnatom. Spektrofotometrijskim titracijama određene su konstante protoniranja svih spojeva u sustavu metanol/voda 1/1. Vrijednosti pKa smanjuju se povećanjem elektron-odvlačećeg djelovanja supstituenta na salicilidenskom prstenu. U istom sustavu otapala praćena je hidroliza svih spojeva. U kiselim otopinama hidrolizu ubrzavaju elektron-donirajući supstituenti u para, a u lužnatom elektron-odvlačeći supstituenti u meta položaju u odnosu na dvostruku vezu C=N. Metoksi-derivati primijenjeni su kao ekstrakcijski reagensi za željezo(III). Razrađena je spektrofotometrijska metoda određivanja željeza spojem N'-(2-hidroksi-3-metoksifenilmetiliden)-3-piridinkarbohidrazidom.Twelve aromatic hydrazones, derived from nicotinic acid hydrazide and differently substituted benzaldehydes or phenyl-methyl-ketone were studied. Identification and characterization of compounds were performed by mass spectrometry and spectroscopic methods (NMR, UV-Vis, and spectrofluorescence). Methoxy derivatives were distinguished by mass spectrometry duo to keto-enol tautomeric interconversion in gas phase. Dihydroxy and chloro derivatives were distinguished by "ortho effect". In solution, hydrazones were present in most stable enolimino form, apart from nitro derivative, which was subjected to deprotonation, E/Z isomerization and keto-enol tautomeric interconversion. Fluorescence was observed for chloro and nitro derivatives in basic media. Protonation constants for all compounds were determined in methanol/water 1/1 system by spectrophotometric titrations. The pKa values were lowered by electron-withdrawing substituent on the salicylidene ring. The hydrolisys of all compounds was studied in the same system. In acidic solutions the hydrolysis was faster due to electron-donor substituent in para, and in basic media by electron-withdrawing groups in meta position to the C=N double bond. Methoxy derivatives were used as extracting agents for iron(III). The spectrophotometric method for iron(III) determination by N'-(2-hydroxy-3-methoxyphenylmethylidene)-3-pyridinecarbohydrazide was developed

Utjecaj temperature medija na iniciranje rupičaste korozije Cr-Ni čelika

U ovom radu je ispitan utjecaj temperature medija na pojavu rupičaste korozije kod nehrđajućih čelika. Teorijski dio rada objašnjava podjelu nehrđajućih čelika kao i njihova svojstva, te utjecaje i podložnosti pojedinim vrstama korozije od kojih je detaljnije objašnjena rupičasta korozija. Eksperimentalni dio je obuhvatio pripremu uzoraka od nehrđajućeg čelika te postupak njihovog ispitivanja za određivanje kritične temperature pitinga. Analizom rezultata su doneseni zaključci o temperaturi medija potrebnoj za nastanak rupičaste korozije na ispitivanim nehrđajućim čelicima

Structural characterization and analytical application of aromatic hydrazones derived from nicotinic acid hydrazide

Proučavano je dvanaest aromatskih hidrazona izvedenih iz nikotinohidrazida i različito supstituiranih benzaldehida, odnosno fenil-metil-ketona. Identifikacija i karakterizacija spojeva provedena je spektrometrijom masa i spektroskopskim metodama (NMR, UV-Vis i spektrofluorimetrija). Spektrometrijom masa razlikovani su metoksi derivati uslijed različitog pomaka keto-enolne tautomerne ravnoteže u plinskoj fazi. Dihidroksi- i klor- derivati razlikovani su na temelju "ortho efekta". Hidrazoni se u otopini nalaze u najstabilnijem enoliminskom obliku, osim nitro derivata koji u dimetilsulfoksidu podliježe deprotonaciji, E/Z izomeriji i keto-enolnoj tautomeriji. Za klor- i nitro- derivate uočena je fluorescencija u lužnatom. Spektrofotometrijskim titracijama određene su konstante protoniranja svih spojeva u sustavu metanol/voda 1/1. Vrijednosti pKa smanjuju se povećanjem elektron-odvlačećeg djelovanja supstituenta na salicilidenskom prstenu. U istom sustavu otapala praćena je hidroliza svih spojeva. U kiselim otopinama hidrolizu ubrzavaju elektron-donirajući supstituenti u para, a u lužnatom elektron-odvlačeći supstituenti u meta položaju u odnosu na dvostruku vezu C=N. Metoksi-derivati primijenjeni su kao ekstrakcijski reagensi za željezo(III). Razrađena je spektrofotometrijska metoda određivanja željeza spojem N'-(2-hidroksi-3-metoksifenilmetiliden)-3-piridinkarbohidrazidom.Twelve aromatic hydrazones, derived from nicotinic acid hydrazide and differently substituted benzaldehydes or phenyl-methyl-ketone were studied. Identification and characterization of compounds were performed by mass spectrometry and spectroscopic methods (NMR, UV-Vis, and spectrofluorescence). Methoxy derivatives were distinguished by mass spectrometry duo to keto-enol tautomeric interconversion in gas phase. Dihydroxy and chloro derivatives were distinguished by "ortho effect". In solution, hydrazones were present in most stable enolimino form, apart from nitro derivative, which was subjected to deprotonation, E/Z isomerization and keto-enol tautomeric interconversion. Fluorescence was observed for chloro and nitro derivatives in basic media. Protonation constants for all compounds were determined in methanol/water 1/1 system by spectrophotometric titrations. The pKa values were lowered by electron-withdrawing substituent on the salicylidene ring. The hydrolisys of all compounds was studied in the same system. In acidic solutions the hydrolysis was faster due to electron-donor substituent in para, and in basic media by electron-withdrawing groups in meta position to the C=N double bond. Methoxy derivatives were used as extracting agents for iron(III). The spectrophotometric method for iron(III) determination by N'-(2-hydroxy-3-methoxyphenylmethylidene)-3-pyridinecarbohydrazide was developed

ESI MS/MS Study of Calix[4]arene Derivatives and their Metal Complexes

The peptidocalixarenes 1-3 bearing tryptophan, phenylglycine and leucil units at the lower rim and their complexes with alkali-metal (Li+, Na+, K+, Rb+, Cs+) and selected lanthanide cations (La3+, Ce3+, EU3+, Yb3+) were analyzed by ESI MS. The influences of the solvent (acetonitrile, methanol, addition of formic acid or sodium acetate) and the calixarene:cation molar ratio on signal intensities were investigated. Comprehensive MS/MS analyses were performed of all singly and doubly charged ions of 1-3 and their complexes, and fragmentation pathways were proposed. An inductive cleavage was observed during dissociation of protonated ions, while the presence of alkali-metal or lanthanide cations caused homolytic cleavage and formation of radical cations. The results of MS analysis were in accordance with those obtained by other techniques (spectrophotometric, potentiometric, and conductometric titrations). The MS/MS experiments could be used as fast and sensitive method for prediction of relative stabilities of calixarene complexes with metal ions

Ružička days : International conference 16th Ružička Days “Today Science – Tomorrow Industry” : Proceedings

Proceedings contains articles presented at Conference divided into sections: open lecture (1), chemical analysis and synthesis (3), chemical and biochemical engineering (8), food technology and biotechnology (8), medical chemistry and pharmacy (3), environmental protection (11) and meeting of young chemists (2)

Electrochemical oxidation of aluminium

Sve većim napretkom industrije dolazi do sve većih zahtjeva za materijale, aluminij kao drugi najzastupljeniji materijal mora odgovarati tim zahtjevima. Potreba za sve boljim mehaničkim i fizikalnim svojstvima aluminija rezultira sve većim brojem legura istoga. Važno svojstvo aluminija je njegovo stvaranje oksidne prevlake koja ga štiti od korozije, ta prevlaka može biti stvorena i umjetnim putem odnosno elektrokemijskom oksidacijom. Prevlaka nastala elektrokemijskom oksidacijom je mnogostruko djelotvornija u zaštiti aluminija od korozije od one nastale prirodnim putem. Kako bi korozijska postojanost te prevlake bila što veća aluminij se podvrgava brojnim istraživanjima, u kojima se različitim tehnikama i dodacima pokušava dobiti što bolja zaštitna svojstva oksidne prevlake. Rad se sastoji od dva dijela teorijskog i eksperimentalnog. Teorijski dio rada objašnjava podjelu legura aluminija kao i njihova svojstva, korozijsku postojanost i primjenu. Navedene su metode zaštite aluminija te je detaljno objašnjena zaštita aluminija oksidnim prevlakama odnosno elektrokemijskom oksidacijom. Eksperimentalni dio je obuhvatio pripremu uzoraka od aluminija podijeljenu na dva djela. Jedan dio uzoraka je elektrokemijski oksidiran u elektrolitima s različitim koncentracijama cerija dok drugi dio uzoraka je uronjen u otopinu s različitom koncentracijom cerija u cilju ispitivanja inhibitorskog djelovanja. Na uzorcima su zatim provedena metalografska i elektrokemijska ispitivanja.With industry growing, demands for better material properties are increasing, aluminum as the second most representative material must meet these requirements. The need for the better mechanical and physical properties of aluminum results in an increasing number of aluminium alloys. An important feature of aluminum is its formation of an oxide coating that protects it against corrosion, this coating can be created by artificial means or by electrochemical oxidation. The coating made by electrochemical oxidation is more effective in protecting aluminum from corrosion than the natural made one. Aluminum is subjected to numerous studies in order to increase corrosion resistance of this coating, in witch various techniques and additives are tried to obtain the best protective properties of the oxide coating. This research contains two parts, the theoretical and experimental. The theoretical part of the paper explains the division of aluminum alloys as well as their properties, corrosion resistance and application. Aluminum protection methods are outlined and aluminum protection with oxide coatings or electrochemical oxidation is explained in detail. The experimental part included the preparation of aluminum samples divided into two pieces. One part of the samples was electrochemically oxidized in electrolytes with different cell concentrations while the second part of the sample was immersed in a solution with a different concentration of the cerium in order to investigate the inhibitory activity. The samples were then subjected to metallographic and electrochemical tests

Influence of solution temperature on initiation of stainless steel pitting corrosion

U ovom radu je ispitan utjecaj temperature medija na pojavu rupičaste korozije kod nehrđajućih čelika. Teorijski dio rada objašnjava podjelu nehrđajućih čelika kao i njihova svojstva, te utjecaje i podložnosti pojedinim vrstama korozije od kojih je detaljnije objašnjena rupičasta korozija. Eksperimentalni dio je obuhvatio pripremu uzoraka od nehrđajućeg čelika te postupak njihovog ispitivanja za određivanje kritične temperature pitinga. Analizom rezultata su doneseni zaključci o temperaturi medija potrebnoj za nastanak rupičaste korozije na ispitivanim nehrđajućim čelicima.This paper deals with the effect that medium temperature has on the occurence of pitting corrosion in stainless steels. Theoretical part of this paper contains division of stainsless steel types as well as their properties, and deals with the susceptibility of each type to certain types of corrosion, whereas pitting corrosion is explained in detail. Experimental part of the paper encompasses preparation of the stainless steel types' samples and the procedure of testing the critical pitting temperature. Analysis of the results helped to form conclusions about medium temperature essential to occurence of pitting corrosion in tested stainless steel types

CAPITAL BUDGETING SPECIFICS OF INVESTMENT PROJECTS OF NON-INTEGRATED PHOTOVOLTAIC POWER PLANTS IN THE REPUBLIC OF CROATIA

Donošenje odluka o prihvaćanju ili odbijanju investicijskog projekta važan je zadatak menadžmenta poduzeća. Kako bi se mogla donijeti kvalitetna investicijska odluka potrebno je pripremiti adekvatne podloge u vidu proračunatih kriterija financijskog odlučivanja. Tradicionalni pristup postupka budžetiranja kapitala koji je korišten u ovom radu temelji se na sadašnjoj vrijednosti budućih novčanih tokova investicijskog projekta i koriste se sljedeće metode financijskog odlučivanja: čista sadašnja vrijednost, interna stopa profitabilnosti, indeks profitabilnosti i modificirana interna stopa profitabilnosti. Dodatno je izrađena i analiza osjetljivosti kojom se analizira utjecaj postotnih promjena ključnih varijabli koje utječu na novčane tokove investicijskog projekta na iznose temeljnih metoda financijskog odlučivanja čiste sadašnje vrijednosti i interne stope profitabilnosti. Za analizirani investicijski projekt odabrana je izgradnja neintegrirane fotonaponske elektrane na području Republike Hrvatske. Napredak u tehnologiji proizvodnje fotonaponskih sustava doveo je do znatnog smanjenja cijena opreme te tako proizvodnju električne energije izravno iz Sunčevog zračenja učinio interesantnom i isplativom, čak i bez korištenja prijašnjih sustava poticaja. Korištenjem tradicionalnog postupka budžetiranja kapitala, analizirano je ulaganje u investicijski projekt izgradnje fotonaponske elektrane na lokaciji u Dalmatinskoj zagori, na području Splitsko-dalmatinske županije, a koji isporučuje električnu energiju u javnu distribucijsku mrežu. Sve metode financijskog odlučivanja pokazale su kako je predmetni investicijski projekt isplativ.Making decisions on accepting or rejecting an investment project is an important task of company management. In order to be able to make a quality investment decision, it is necessary to prepare adequate bases in the form of calculated financial decision-making criteria. The traditional approach to the capital budgeting process used in this paper is based on the present value of the future cash flows of the investment project and uses the following financial decision making methods: net present value, internal rate of return, profitability index and modified internal rate of return. In addition, a sensitivity analysis was prepared to analyze the impact of percentage changes in key variables that affect the cash flows of the investment project on the amounts of basic financial decision-making methods of net present value and internal rate of return. The construction of a non-integrated photovoltaic power plant on the territory of the Republic of Croatia was selected for the analyzed investment project. Advances in the technology of photovoltaic systems production have led to a significant reduction in equipment prices, thus making the production of electricity directly from solar radiation interesting and cost-effective, even without the use of previous incentive systems. Using the traditional capital budgeting procedure, the investment in the investment project for the construction of a photovoltaic power plant at a location in the Dalmatian hinterland, in the Split-Dalmatia County, which supplies electricity to the public distribution network, was analyzed. All methods of financial decision-making have shown that the investment project in question is profitable

Influence of solution temperature on initiation of stainless steel pitting corrosion

U ovom radu je ispitan utjecaj temperature medija na pojavu rupičaste korozije kod nehrđajućih čelika. Teorijski dio rada objašnjava podjelu nehrđajućih čelika kao i njihova svojstva, te utjecaje i podložnosti pojedinim vrstama korozije od kojih je detaljnije objašnjena rupičasta korozija. Eksperimentalni dio je obuhvatio pripremu uzoraka od nehrđajućeg čelika te postupak njihovog ispitivanja za određivanje kritične temperature pitinga. Analizom rezultata su doneseni zaključci o temperaturi medija potrebnoj za nastanak rupičaste korozije na ispitivanim nehrđajućim čelicima.This paper deals with the effect that medium temperature has on the occurence of pitting corrosion in stainless steels. Theoretical part of this paper contains division of stainsless steel types as well as their properties, and deals with the susceptibility of each type to certain types of corrosion, whereas pitting corrosion is explained in detail. Experimental part of the paper encompasses preparation of the stainless steel types' samples and the procedure of testing the critical pitting temperature. Analysis of the results helped to form conclusions about medium temperature essential to occurence of pitting corrosion in tested stainless steel types