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The 8-mm diameter bars of Cu-Al-Mn shape memory alloys were produced by continuous casting technique. The samples were characterised using optical microscopy and scanning electron microscopy along with EDX analysis. The continuous cast alloy revealed some martensitic phase, which, after quenching, led to the microstructure that is completely martensite. Quenching of samples had an effect on several mechanical properties and change in morphology of fracture. After ageing at 200 °C and 300 °C, the tensile strength increased and elongation drastically decreased. Morphology of fracture surface changed from primary ductile to a mixture of intergranular and ductile. This work is licensed under a Creative Commons Attribution 4.0 International License. Šipke promjera 8 mm proizvedene su iz legure Cu-Al-Mn s prisjetljivosti oblika tehnikom kontinuiranog lijevanja. Uzorci su karakterizirani pomoću optičke mikroskopije i pretražne elektronske mikroskopije uz analizu EDX. Kontinuirano lijevana legura je pokazala mjestimičnu prisutnost martenzitne faze, dok je nakon kaljenja nastala potpuno martenzitna mikrostruktura. Kaljenje uzoraka utjecalo je na mehanička svojstva i na promjenu morfologije prijeloma. Nakon starenja pri 200 °C i 300 °C porasla je vlačna čvrstoća a izduženje se drastično smanjilo. Morfologija prijelomne površine se mijenjala od duktilne do mješavine interkristalne i duktilne. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.

Rad se bavi razvojem pojma elementa od antičkih vremena (Empedoklo, Aristotel) preko razdoblja alkemije i rane kemije (Paracelsus, Petar Bono, Boyle) te početaka moderne kemije (Lavoisier, Mendeljejev) do suvremenih shvaćanja utemeljenih na atomskoj teoriji. Pokazuje se da pojam elementa ima dva značenja, elementarne (jednostavne) tvari i elementa u užem smislu; dok se prvi pojam razvijao prateći napredak metoda kemijske analize, za razumijevanje drugog pojma, pojma elementa, bilo je nužno steći dublji uvid u narav kemijskih promjena.

Bone tissue engineering (BTE) is a fast growing field focused on the development of bioactive 3D porous scaffolds as temporary extracellular matrixes that support cell attachment, proliferation and differentiation, and stimulate bone tissue formation in vivo. Over more than ten years, our group has been devoted to developing new biomaterials and methods to prepare 3D porous scaffolds for BTE applications. The potential of natural porous structures such as marine skeletons, composite materials, and hydrogels based on biodegradable polymers and bioresorbable hydroxyapatite ceramics have been studied. In this paper, an overview of our research and main achievements, published in international scientific publications, is provided. This work is licensed under a Creative Commons Attribution 4.0 International License. Inženjerstvo koštanog tkiva brzorastuće je polje istraživanja usmjereno na razvoj bioaktivnih 3D poroznih nosača, kao privremenih izvanstaničnih matrica, koji podržavaju prianjanje, umnažanje i diferencijaciju stanica te potiču stvaranje koštanog tkiva in vivo. Više od deset godina istraživanja naše grupe posvećena su razvoju novih materijala i postupaka za pripravu 3D poroznih nosača za inženjerstvo koštanog tkiva. Kao mogući nosači istraživani su porozni skeleti morskih organizama te kompozitni materijali i hidrogelovi na temelju biorazgradljivih polimera i bioresorbirajuće hidroksiapatitne keramike. U ovom radu dan je prikaz naših istraživanja i glavnih postignuća, objavljenih u međunarodnim znanstvenim publikacijama. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.

It is of great challenge and significance to recycle activated carbon (AC), yet still with various problems in operation. Here, we have performed a simulation on the regeneration of AC by using an indirect heating method with an unsteady cylindrical heat transfer model. The result has shown that the optimal parameters for a regeneration tube of outer diameter Φ = 108 with wall thickness 4 mm were: heating in the tube for 30 min at a surrounding temperature of 550 °C. In these conditions, a temperature of 417.5 °C could be obtained at the centre of the cylindrical tube, reaching the temperature required for AC regeneration. The experimental values obtained in our laboratory were consistent with the simulation, providing significant references for scaling up pilot plant of AC regeneration.

Physicochemical and microbiological characteristics of a local traditional olive mill wastewater, at Ennakhla-Chlef in northern Algeria, were evaluated. The olive mill wastewater samples had slight acidity of 0.65 % with a pH = 4.88, and electrical conductivity of 34 mS cm–1. The chemical oxygen demand (COD) and the biological oxygen demand (BOD5) reached up to 183 g l–1 and 7 g l–1, respectively. In addition, the samples showed 1.72 g l–1 of total phenolic compounds. Preliminary microbiological analysis of the wastewater showed the presence of various microorganisms represented especially by lactic acid bacteria and Enterococcus sp. to the aim of this work was to investigate the possibility of using yeast strains isolated from olive mill wastewater in the fermentation of the latter. The results shown that fermentation with yeast can produce ethanol at an extent of 1.4 % (v/v). This can constitute a strategy for treating mentioned wastewater and transforming it into valuable biomolecules. This work is licensed under a Creative Commons Attribution 4.0 International License. U ovom radu analizirane su fizikalno-kemijske i mikrobiološke karakteristike otpadnih voda tradicionalnih postrojenja za preradu maslinova ulja u Ennakhla-Chlefu u sjevernom Alžiru. Uzorci otpadne vode imali su slabu kiselost od 0.65 % uz pH = 4,88 i električnu provodnost od 34 mS cm–1. Vrijednosti kemijske i biološke (BPK5) potrošnje kisika kretale su se do 183 odnosno 7 g l–1. Nadalje, uzorci su sadržavali 1,72 g l–1 ukupnih fenola. Preliminarna mikrobiološka analiza ukazala je na prisutnost raznih mikroorganizama, osobito bakterija mliječne kiseline i Enterococcus sp. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.

The influence of portland cement class on the corrosion rate of steel reinforcement in cement mortar caused by penetrating chloride or sulfate from the environment in already hardened cement mortar is investigated in this paper. Three classes of portland cement have been used for the tests, PC 35, PC 45 and PC 55. Cylindrical samples of cement mortar with steel reinfor- cement in the middle were treated 6 months at room temperature in the following solutions: w(SO42-) = 2.1 % and w(Cl-) = 5 %. Two techniques have been used for testing corrosion rate of steel reinforcement in cement mortar: Tafel extrapolation technique and potentiodynamic polarization technique. Investigations were conducted by potentiostat/galvanostat Princeton Applied Research 263A-2 with the software PowerCORR®. The results of both techniques indi-cate the most active corrosion of steel reinforcement in the samples prepared from cement PC 35 in both treated solutions, while the lowest corrosion of the steel reinforcement was observed in cement samples prepared from cement PC 55. This conclusion was drawn by analyzing the results shown in Figs. 1–4. Comparing corrosion current density of samples, working electrodes, Figs. 1 and 2, Table 2, the results show the most stable corrosion of steel reinforcement in samples prepared from cement PC 55, and the most active corrosion in samples prepared from ce- ment PC 35. The most active corrosion in samples prepared from cement PC 35 is evident from the positions of the open circuit potentials whose values are less for samples prepared from cement PC 35 in both the treated solution, Figs. 1 and 2, Table 2. Comparison of the anodic polarization curves of the working electrodes in both the treated solutions, Figs. 3 and 4, also shows that the intensity of corrosion is the largest for the working electrodes prepared from cement PC 35 and the smallest for the working electrodes prepared from cement PC 55. Investigation results should be considered as preliminary. To make the recommendations for the construction of reinforced concrete structures in the maritime environment the impact of sulphates on concrete and steel bars should be investigated. U ovom je radu ispitivan utjecaj klase portland-cementa na brzinu korozije čelične armature u cementnom mortu, uzrokovane prodiranjem klorida ili sulfata iz okoliša u već očvrsli cementni mort. Za ispitivanja su upotrijebljene tri klase portland-cementa, PC 35, PC 45 i PC 55. Radi navedenih ispitivanja cilindrični uzorci od cementnog morta s čeličnom armaturom u sredini tretirani su šest mjeseci na sobnoj temperaturi u sljedećim otopinama: w(SO42-) = 2,1 % i w(Cl-) = 5 %. Za ispitivanje brzine korozije čelične armature u cementnom mortu primijenjene su elektrokemijske tehnike potenciostatske polarizacije, i to tehnika ekstrapolacije Tafelovih krivulja i tehnika potenciodinamičke polarizacije. Ispitivanje je provedeno na potenciostatu/ galvanostatu Princeton Applied Research 263A-2, programskim paketom PowerCORR®. Rezultati obje primijenjene tehnike pokazuju da su korozijski najaktivnije čelične armature u uzorcima pripremanim od cementa klase PC 35 u obje tretirane otopine, dok su korozijski najstabilnije čelične armature u uzorcima pripremanim od cementa klase PC 55. Rezultate provedenih istra?ivanja treba smatrati preliminarnima. Radi davanja preporuka za gradnju armiranobetonskih konstrukcija u morskom okolišu, potrebno je provesti ispitivanja utjecaja sulfata na beton i armaturu, na betonskim i armiranobetonskim uzorcima.

The necessity to remove organic pollutants from the industrial wastewater streams has forced the development of new technologies that can produce better results in terms of pollutant removal and process efficiency in combination with low investment and operating costs. One of the new emerging processes with a potential to fulfil these demands is catalytic wet peroxide oxidation, commonly known as the CWPO process. The oxidative effect of the hydrogen peroxide is intensified by the addition of a heterogeneous catalyst that can reduce the operating conditions to atmospheric pressure and temperatures below 383 K. Zeolites, among others, are especially appealing as catalysts for selective oxidation processes due to their unique characteristics such as shape selectivity, thermal and chemical stability, and benign effect on nature and the living world. In this work, catalytic activity, selectivity and stability of Cu/Y-5 zeolite in phenol oxidation with hydrogen peroxide was examined. Catalyst samples were prepared by ion exchange method of the protonic form of commercial zeolite. The catalysts were characterized with powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and AAS elemental analysis, while the adsorption techniques were used for the measurement of the specific surface area. The catalytic tests were carried out in a stainless steel Parr reactor in batch operation mode at the atmospheric pressure and in the temperature range from 323 to 353 K. The catalyst was prepared in powdered form and the mass fraction of the active metal component on the zeolite was 3.46 %. The initial concentration of phenol solution was equal to 0.01 mol dm−3 and the concentration of hydrogen peroxide ranged from 0.01 to 0.10 mol dm−3. The obtained experimental data was tested to a proposed kinetic model for phenol oxidation r = k1 cF cVP and hydrogen peroxide decomposition rHP = k2 cHP. The kinetic parameters were estimated using the Nelder-Mead method of nonlinear regression. On the basis of the obtained results of characterization process and conducted catalytic tests, the following can be observed. Zeolite structure of the prepared catalyst was confirmed through powder X-ray diffraction, scanning electron microscopy and adsorption techniques. Their catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversions, hydrogen peroxide decomposition, by-product distribution and degree of copper leached into the aqueous solution. The obtained experimental results indicate that in the space of 180 minutes, the use of these catalysts allows almost total elimination of phenol and significant removal of total organic carbon content with the use of small amounts of catalyst (0.1 g dm–3) and substoichiometric level (71.4 %) of oxidant required for complete oxidation of organic pollutant. The main product among aromatics was catechol, followed by hydroquinone and benzoquinone, which exhibited the typical pattern for a series reaction scheme. The distribution of carboxylic acids was as follows: maleic, fumaric, acetic and oxalic acids. These low-molecular carboxylic acids and aromatic compounds were responsible for the TOC that remained after almost complete removal of phenol. Moreover, one of the most interesting options was to use CWPO as a pre-treatment prior to biological treatment, for simple organic acids that are highly biodegradable. During the reactions, destabilization of the catalyst was observed in terms of leaching of copper from zeolite into the reaction mixture, but the previous investigations of similar catalytic systems showed that the activity of the solid catalyst was not due to the homogeneous contribution of the copper leached from the catalyst, but was more likely due to the activity of the heterogeneous catalyst. Further investigations on the mechanism of catalyst destabilization and methods of stabilization are the subject of the following article in the series. The proposed kinetic model adequately fits the experimental data. The rate of phenol oxidation and hydrogen peroxide decomposition increases with the increase in reaction temperature and decrease in initial concentration of hydrogen peroxide. The rate of phenol oxidation is first order toward the concentration of phenol and first order toward the concentration of H2O2. The rate of H2O2 decomposition is first order toward the concentration of H2O2. Activation energy in phenol oxidation was 86.0 kJ mol−1 for phenol oxidation, and 107.6 kJ mol−1 for hydrogen peroxide decomposition, which is in accordance with previously published results. Potreba za uklanjanjem organskih nečistoća iz industrijskih otpadnih voda uvjetovala je razvoj novih, djelotvornih tehnologija s posebnim naglaskom na uštedu sirovina i energije te ekonomičnost procesa. Katalitička oksidacija organskih zagađenja vodikovim peroksidom u vodenom mediju, poznata kao metoda CWPO (eng. Catalytic Wet Peroxide Oxidation), jedan je od postupaka koji ispunjava navedene zahtjeve. Upotrebom vodikova peroksida, kao oksidacijskog sredstva, i pogodnog heterogenog katalizatora moguće je proces provoditi pri atmosferskom tlaku i temperaturi ispod 383 K. Zeoliti su zbog svojih specifičnih značajki (selektivnost prema veličini i obliku molekula, termička i kemijska stabilnost, neškodljivost živom svijetu) izrazito pogodni katalizatori za uporabu u selektivnim oksidacijskim procesima. Stoga su u ovom radu proučavani aktivnost, selektivnost i stabilnost katalizatora Cu/Y-5 u reakciji oksidacije fenola vodikovim peroksidom. Katalizator je pripravljen ionskom izmjenom protoniranog oblika komercijalnog zeolita. Karakterizacija katalizatora obuhvaćala je rendgensku difrakciju (XRD), pretražnu elektronsku mikroskopiju (SEM) i elementnu analizu atomskim apsorpcijskim spektrometrom (AAS), te određivanje specifične površine i obujma pora (standardna BET-metoda). Reakcija je provođena u šaržnom Parrovu reaktoru pri atmosferskom tlaku i temperaturama od 323 do 353 K. Katalizator je pripravljen u praškastom obliku, a maseni udjel bakra u zeolitu iznosio je 3,46 %. Početna koncentracija fenola u reakcijskoj otopini bila je 0,01 mol dm−3, a vodikova peroksida od 0,01 do 0,10 mol dm−3. Dobiveni eksperimentalni podaci testirani su sljedećim kinetičkim modelima za oksidaciju fenola rPh = k1 cPh cHP i raspad vodikova peroksida rHP = k2 cHP, a kinetički parametri procijenjeni su Nelder-Meadovom metodom nelinearnog optimiranja. Rezultati provedenih istraživanja pokazali su da je pri ispitivanim reakcijskim uvjetima primjenom postupka CWPO uz katalizator Cu/Y-5 moguće iz početne reakcijske smjese u potpunosti ukloniti fenol uz istodobno 54,5 %-tno smanjenje sadržaja ukupnog organskog ugljika.

U radu je dan sažet pregled dosadašnjih istraživanja termodinamike protonacije linearnih homopolikiselina, posebice onih visoke gustoće naboja. Pored prikaza eksperimentalnih rezultata koji se mogu naći u literaturi, u radu su opisani i teorijski modeli za obradu ovisnosti protonacijskih konstanti ravnoteže o stupnju disocijacije monomera, odnosno o ionskoj jakosti (cilindrični model temeljen na Poisson-Boltzmannovoj jednadžbi, Sternov cilindrični model, Isingov model, Högfeldtov model, Mandelov model i model Katchalskoga). Primjenjivost navedenih modela za opis protonacijske ravnoteže linearnih homopolikiselina razmatrana je s obzirom na gustoću naboja poliiona, koncentraciju dodanog elektrolita i vrstu protuiona koji kompenziraju naboj makroiona. Ukratko su prikazani i rezultati Monte Carlo simulacija protonacijske ravnoteže. Dodatno, dan je osvrt na česte pogreške vezane uz baždarenje elektrokemijskih članaka prilikom određivanja specijacije polikiselina u otopinama. The paper presents a short summary of investigations dealing with protonation equilibrium of linear homopolyacids, in particularly those of high charge density. Apart from the review of experimental results which can be found in the literature, a brief description of theoretical models used in processing the dependence of protonation constants on monomer dissociation degree and ionic strength is given (cylindrical model based on Poisson-Boltzmann equation, cylindrical Stern model, the models according to Ising, Högfeldt, Mandel and Katchalsky). The applicability of these models regarding the polyion charge density, electrolyte concentration and counterion type is discussed. The results of Monte Carlo simulations of protonation equilibrium are also briefly mentioned. In addition, frequently encountered errors connected with calibration of of glass electrode and the related unreliability of determined protonation constants are pointed out.

Hydrogels are materials displaying the ability to absorb large amounts of water. Cellulose is a widespread, biocompatible, and biodegradable polysaccharide with hydrophilic OH groups in a structure that allows various modifications. By introducing new functional groups to the repeating units of the polysaccharide chain, it is possible to modify properties of the material in order to prepare hydrogels of desired properties such as antibacterial properties or response to external stimuli. In this work, 2-dimethylaminoethyl methacrylate (DMAEMA) grafting on cellulose was performed. The polymerization of DMAEMA on cellulose was carried out in solvent N,N-dimethyl acetamide / LiCl with a peroxide initiator at 90 °C and N,N-methylene-bis-acrylamide (MBA) as a crosslinker. Nanoparticles of silver, well known for their antibacterial properties, were also introduced into the prepared hydrogels. The relative proportion of PDMAEMA in hydrogels was determined by infrared spectroscopy. The morphology of the dried samples and the presence of silver were determined by scanning electron microscopy, which showed that the addition of PDMAEMA and drying of the hydrogels by freeze-extraction resulted with a very porous structure. In this way, the binding of silver nanoparticles to hydrogels was also facilitated. Samples of copolymers prepared by drying in a dryer showed a higher degree of swelling in water (~ 109 %) than pure cellulose (80 %). The same materials prepared by freeze-drying formed into porous hydrogels showed much higher swelling rates (256 % and 505 %) compared to pure cellulose (80 %). This work is licensed under a Creative Commons Attribution 4.0 International License. Hidrogelovi su materijali koji se odlikuju mogućnošću upijanja velike količine vode. Celuloza je vrlo rasprostranjen biokompatibilan i biorazgradljiv polisaharid s hidrofilnim OH skupinama u strukturi koje omogućuju raznovrsne modifikacije. Uvođenjem novih funkcijskih skupina na osnovni polisaharidni lanac moguće je mijenjati svojstva hidrogela kako bi se pripremili hidrogelovi željenih svojstava: antibakterijska svojstva, osjetljivost na vanjske podražaje i slično. U ovom radu provedeno je graftiranje dimetilaminoetil-metakrilata (DMAEMA) na celulozu. Polimerizacija DMAEMA na celulozu provedena je u otapalu N,N-dimetil acetamid/LiCl uz peroksidni inicijator pri temperaturi od 90 °C te N,N-metilen-bis-akrilamid (MBA) kao umreživačem. U pripravljene hidrogelove unesene su i nanočestice srebra, dobro poznate po antibakterijskim svojstvima. Relativni udio PDMAEMA u hidrogelovima određen je pomoću infracrvene spektroskopije. Morfologija osušenih uzorka i prisutnost srebra određene su pretražnom elektronskom mikroskopijom koja je pokazala da je dodatkom PDMAEMA i sušenjem hidrogelova ekstrakcijom zamrzavanjem dobivena vrlo porozna struktura. Na taj način pospješeno je i vezanje nanočestica srebra na hidrogelove. Uzorci kopolimera priređeni sušenjem u sušioniku pokazuju veći stupanj bubrenja u deioniziranoj vodi (~ 109 %) u odnosu na čistu celulozu (80 %). Isti materijali sušeni ekstrakcijom zamrzavanjem i tako oblikovani u porozne hidrogelove pokazuju znatno veće vrijednosti stupnja bubrenja (256 % i 505 %) naspram čiste celuloze (80 %). Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.

The region of Médéa (Algeria) located in an agricultural site requires a large amount of drinking water. For this purpose, the water analyses in question are imperative. To examine the evolution of the drinking water quality in this region, firstly, an experimental protocol was done in order to obtain a dataset by taking into account several physicochemical parameters. Secondly, the obtained data set was divided into two parts to form the artificial neural network, where 70 % of the data set was used for training, and the remaining 30 % was also divided into two equal parts: one for testing and the other for validation of the model. The intelligent model obtained was evaluated as a function of the correlation coefficient nearest to 1 and lowest mean square error (RMSE). A set of 84 data points were used in this study. Eighteen parameters in the input layer, five neurons in the hidden layer, and one parameter in the output layer were used for the ANN modelling. Levenberg Marquardt learning (LM) algorithm, logarithmic sigmoid, and linear transfer function were used, respectively, for the hidden and the output layers. The results obtained during the present study showed a correlation coefficient of R = 0.99276 with root mean square error RMSE = 11.52613 mg dm–3. These results show that obtained ANN model gave far better and more significant results. It is obviously more accurate since its relative error is small with a correlation coefficient close to unity. Finally, it can be concluded that obtained model can effectively predict the rate of soluble bicarbonate in drinking water in the Médéa region. This work is licensed under a Creative Commons Attribution 4.0 International License. Regija Médéa (Alžir) smještena na poljoprivrednom zemljištu zahtijeva veliku količinu pitke vode te je stoga analiza vode od iznimne važnosti. Da bi se ispitao razvoj kvalitete pitke vode u toj regiji, najprije je napravljen eksperimentalni protokol za dobivanje skupa podataka uzimajući u obzir nekoliko fizikalno-kemijskih parametara. Zatim je dobiveni skup podataka podijeljen na dva dijela za stvaranje umjetne neuronske mreže, gdje je 70 % skupova podataka upotrijebljeno za trening, a preostalih 30 % dodatno je podijeljeno na dva jednaka dijela: jedan za testiranje, a drugi za validaciju modela. Dobiveni inteligentni model procijenjen je kao funkcija koeficijenta korelacije najbližeg 1 i najnižeg korijena srednje kvadratne pogreške (RMSE). U ovom istraživanju upotrijebljen je skup od 84 podatkovnih točaka. Za modeliranje ANN-a upotrijebljeno je osamnaest parametara u ulaznom sloju, pet neurona u skrivenom sloju i jedan parametar u izlaznom sloju. Za skriveni i izlazni sloj upotrijebljeni su algoritam učenja Levenberg Marquardt (LM), logaritamski sigmoid i funkcija linearnog prijenosa. Rezultati dobiveni tijekom ovog istraživanja pokazali su koeficijent korelacije R = 0,99276 s korijenom srednje kvadratne pogreške RMSE = 11,52613 mg dm–3. Ti rezultati pokazuju da je dobiveni model neuronske mreže dao daleko bolje rezultate, jer je točniji a njegova relativna pogreška je mala s koeficijentom korelacije blizu 1. Konačno, zaključeno je da taj model može učinkovito predvidjeti brzinu topljivosti bikarbonata u vodi za piće u regiji Médéa. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.