STUDIA CHEMIA - Issue no.3 / 2020 - Table of contents
Professor Liana Maria Mureşan on his 65th Anniversary
Prof. emerit dr. Ionel Catalin POPESCU, Prof. emerit dr. eng. Petru ILEA, Prof. habil. dr. eng. Graziella Liana TURDEAN
Professor Liana Maria Mureşan was born on May 3rd, 1954. In 1977 she graduated from University “Babes-Bolyai” of Cluj-Napoca as a chemist. In 1992 she received her PhD degree in Chemistry, under the supervision of the distinguished Professor Liviu Oniciu. In 1977 she started to work as chemist at “Intreprinderea de Cazane Mici şi Arzatoare” Cluj-Napoca. Starting in 1981, as researcher at “Institutul de Energetica Chimica şi Biochimica” (Cluj-Napoca branch), Liana Maria Mureşan was interested by fuel cells and metals electrodeposition / electrorefining research fields. In 1986, she begins a successful academic career at University Babeş- Bolyai, Cluj-Napoca. As Teaching Assistant (1986), Assistant Professor (1990), Associate Professor (1997) and Professor (2002) at the Faculty of Chemistry and Chemical Engineering Cluj-Napoca, Liana Maria Mureşan was teaching “Electrochemistry” for undergraduate and graduate programs. Her research interest was constantly focused on metals electrodeposition, corrosion, and chemically modified electrodes. From 2016, Professor Liana Maria Mureşan is heading the “Center for Electrochemical Research and Nonconventional Materials” at the Department of Chemical Engineering, Faculty of Chemistry and Chemical Engineering. In addition to over 120 scientific papers and 4 invention patents, Professor Liana Maria Mureşan co-authored 4 books, 5 book-chapters, and managed numerous grants and research projects. She counts more than 130 participations to scientific conferences with lectures, posters and oral communications. The results obtained during the research grants she coordinated, have substantially contributed to better understanding of metal nanocomposites electrodeposition and their application anticorrosive coatings. The quality of research performed by Professor Liana Maria Mureşan (Hirsch Index 20) allowed her to develop a broad network of scientific collaborations, being invited as researcher or visiting professor at many European universities such as: University “Pierre et Marie Curie”, Paris, France (1990-1991, 1996, 1999 and 2005); University “Eotvos Lorand”, Budapest, Hungary (1993); University “Joseph Fourier”, ENSEE Grenoble, France (1996); Free University, Brussels, Belgium (1999); Cagliari University, Italy (2017); Pisa University, Italy (2018). Professor Liana Maria Mureşan was one of the founders of the Graduate School at the Department of Physical Chemistry. At the same time, she was an active member of the academic community serving as the head of the Department of Physical Chemistry (2008-2012). This issue of Studia Universitas Babeş-Bolyai Chemia is dedicated to Professor Liana Maria Mureşan in recognition of her achievements within the academic community. The intention of the editors was to bring together contributions from the circle of her coworkers, scientists that developed common scientific interests during more than 30 years. Now, at this anniversary moment, we – the colleagues of the Electrochemistry group, as well as all the colleagues and researchers of the Faculty of Chemistry and Chemical Engineering of the Babeş-Bolyai University, express Professor Liana Maria Mureşan their appreciation for her entire activity, along with the best wishes for a long life of successful future achievements!
Determination of Biogenic Amines by Using Amperometric Biosensors Based on Grass PEA Amine Oxidase and OAT Polyamine Oxidase
LAURA AQUILANTE, MIHAELA NISTOR, STEFANIA TAORMINA, MAREK ŠEBELA, IVO FRÉBORT, IONEL CĂTĂLIN POPESCU
Grass pea amine oxidase (GPAO) and oat polyamine oxidase (OPAO) were immobilized along with horseradish peroxidase (HRP) and an Os-redox polymer (Os-RP) onto the surface of a graphite electrode by crosslinking with poly(ethylenglycol) diglycidyl ether. The resulted reagentless amperometric biosensors were inserted in a flow injection setup and used as electrochemical detectors for the biogenic amines (BA) detection. Both biosensors were operated at low applied potential (-50 mV vs. Ag/AgCl, KCl0.1M) where electrochemical interferences are minimal. The quantification of ten BA (tyramine, putrescine, cadaverine, histamine, cystamine, phenylethylamine, agmatine, tryptamine, spermine, and spermidine) either individual or in mixture (after a preliminary separation by using cation exchange chromatography) was reported. G/(Os-RP)-HRP-GPAO biosensor detected all ten BA, while G/(Os-RP)-HRP-OPAO biosensor detected only spermine and spermidine. Finally, a simple and low-cost method for free and acetylated polyamines determination in human urine samples, by using the highly selective G/(Os-RP)-HRP-OPAO biosensor, was proposed.
Keywords: Amine oxidase, polyamine oxidase, amperometric reagentless biosensors, biogenic amines, human urine
Improving the Corrosion Resistance of Mild Steel by Zinc-Graphene Oxide Coatings
NICOLETA COTOLAN, GRAZIELLA LIANA TURDEAN, JULIETA DANIELA CHELARU
The main purpose of this work is to improve the corrosion resistance of steel substrates using the characterization of new composite zinc electrodeposits containing graphene oxides and reduced graphene oxide. The zinc-graphene based composite deposits were obtained by electrodeposition of an acidic electrolyte (pH = 5) at a current density of 20 mA/cm2. Anionic surfactant (i.e., sodium dodecyl sulfate) was used to obtain uniform and compact coating morphology. Also, the investigated deposits had in their structure the graphene oxides produced by graphite exfoliation and the results concerning corrosion behavior of the zinc electrodeposits (Zn/S235 and Zngraphene/ S235) were compared using the same experimental conditions. Microstructural characterization was carried out by SEM‐EDS, whereas corrosion resistance was evaluated by EIS and polarization curves.
Keywords: Graphene Oxide, Electrochemical Impedance Spectroscopy, Polarization Curves, Corrosion Resistance, Steel Corrosion
Selective Electroextraction of Base Metals from Leaching Solutions Obtained During the Recycling of Waste Printed Circuit Boards. I. Intensive Galvanostatic Electrodeposition of Copper
MARIAN-IOSIF FRÎNCU, ENIKO COVACI, SORIN-AUREL DORNEANU, PETRU ILEA
This article presents our results concerning the feasibility of selective electroextraction of copper from leaching solutions obtained during base metals recycling from waste printed circuit boards. The researches were focused on the intensive copper electrodeposition as a potential parallel paired process for the electrochemical regeneration of the leaching solutions. Preliminary tests, performed by cyclic voltammetry on 316 stainless steel disc electrode in synthetic solutions of CuBr2, SnBr2 and PbBr2, indicate the possibility of selective electroextraction of Cu if the electrodeposition potentials of Sn and Pb are not exceeded. Therefore, selective and intensive Cu electrodeposition tests were accomplished in galvanostatic mode, in a real sample of leaching solution, using also 316 stainless steel sheets cathodes. The experimental results demonstrate that the selective electrodeposition of Cu is possible in a wide range of current densities, between 200 and 600 A/m2, if the concentration of Cu in solution of at least 12 g/L is maintained. Under these conditions, the purity of the obtained Cu deposits can attain 99.6%.
Keywords: waste printed circuit boards, selective electroextraction, copper recovery, electrochemical parallel paired processes
Computational Image Analysis as an Alternative Tool for the Evaluation of Corrosion in Salt Spray Test
VITOR BONAMIGO MOREIRA, ALEX KRUMMENAUER, JANE ZOPPAS FERREIRA, HUGO MARCELO VEIT, ELAINE ARMELIN, ALVARO MENEGUZZI
The current standards for evaluating corrosion during salt spray tests rely on the visual analysis of the specimens, and this may be a limitation when higher resolution quantitative outputs are desired. In this work, computational image analysis was used to measure the area affected by corrosion during salt spray tests with aluminum alloy, copper, carbon steel and galvanized steel plates. The software ImageJ was used to select and measure the corroded areas differentiating the corrosion products from the metals uncorroded surfaces according to their different colors. With ten measurements for each selected exposure time, a 95 % confidence interval was calculated for each material and time of exposure, giving an indication of the precision of the estimated corroded area. These data were compared with a visual inspection carried out by an experienced technician. The results indicate that computational image analysis may be a powerful tool to obtain higher resolution in the results interpretation in comparison with the standard visual analysis.
Keywords: salt spray test, computational image analysis, corrosion assessment
Chemically Modified Chitosan Coatings: Wetting and Electrochemical Studies
PÉTER MÁRTON, EMŐKE ALBERT, NORBERT NAGY, BORBÁLA TEGZE, GABRIELLA STEFÁNIA SZABÓ, ZOLTÁN HÓRVÖLGYI
Native chitosan coatings were prepared on glass and zinc substrates by dip-coating method. The native coatings were chemically modified: crosslinked with glutaraldehyde and sodium-tripolyphosphate and then silylated with dichlorodimethylsilane. The native layers prepared on zinc substrate were acylated with acetic anhydride and impregnated with indigo carmine (IC). Native coatings on different substrates showed different morphology and physical structure, which were explored by AFM studies. Examining the wetting properties of the coatings, it was found that the chemical modification can form a stable, hydrophobic (advancing contact angle of ca. 97°) and water repellent (HΘ = 2°) layer on the glass substrate, while the same modifications reduce the hydrophobic nature and stability of the coating on zinc (contact angle decreases from ca. 100° to ca. 60°). Electrochemical studies of the coatings have shown that IC increases the corrosion protection (>90% inhibition efficiency) and reduces the permeability of the coating through ionic crosslinking, while acylation has the opposite effect and the acylated coating protection is worse than the native chitosan. The results can be used in the development of hydrophobic, water-repellent and temporary anti-corrosion coatings.
Keywords: chitosan coating, contact angles, electrochemical measurements
Estimation of the Usefulness of Glassy Carbon Electrode in Non-Aqueous Solvents Polarized to Higher Anodic Potentials
LÁSZLÓ KISS, SÁNDOR KUNSÁGI-MÁTÉ
In this paper suitability of glassy carbon electrode in numerous non-aqueous solvents used widely in electrochemistry (methanol, acetone, dichloromethane, nitrobenzene, nitromethane, 1-butanol, dimethyl sulfoxide, dimethyl formamide, tetrahydrofuran) was studied by changing the potential of preanodisation. The potential range studied in viewpoint of preanodisation effect was between 1 and 3 V. At higher potentials, glassy carbon electrode deactivated in many solvents which was clearly demonstrated using the aqueous solution of a redox probe 1,4-dihydroxybenzene. Due to the low permittivity some solvents (ethyl acetate, chloroform) were investigated using a preanodisation at 3 V because of the significant ohmic drop and the surface state also changed. Results highlight the importance of this limitation caused by polarizing above 2 V and it must be considered when glassy carbon electrode is selected for the investigations carried out in these conditions.
Keywords: Glassy carbon; Preanodisation; Permittivity; Deactivation; Nonaqueous solvents
Na+ - NH4+ Cation Exchange Study on Treated Zeolitic Volcanic Tuff in Fixed Bed Column
S. ANDRADA MĂICĂNEANU, HOREA BEDELEAN
In this work Na+ - NH4+ cation exchange process was studied on various samples of treated zeolitic volcanic tuff (ZVT). Irrespective of the treatment applied (washing, NaCl, acid, thermal), the Na+ concentration evolution closely mirrors the NH4+ concentration evolution indicating that Na+ - NH4+ is the main ion exchange process that takes place. Cation exchange capacities (CEC) between 5.42 and 33.8 mg NH4+/g were obtained suggesting that not all treatments improved the ZVT’s abilities to remove ammonium from wastewater. Changes in flow rate, Na+ concentration, NH4+ concentration, ZVT amount, and ZVT grain size have all influenced the CEC in the considered system.
Keywords: zeolitic volcanic tuff, clinoptilolite, ammonium, ion exchange, column, wastewater
Comprehensive Assessment of Antioxidant And Chelating Capacity of Some Biogenic Amines and Related Drugs
ALEXANDRINA GUIDEA, AUGUSTIN C. MOŢ, COSTEL SÂRBU
The radical scavenging, reducing power and metal-chelating capacity of some biogenic amines and related sympathomimetic drugs were clarified using various in vitro antioxidant assays as DPPH (1, 1-diphenyl-2- picryl-hydrazyl), ABTS (2,2’-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid), SORS (superoxide anion (O2-) radical-scavenging), nitric oxide (NO) radical scavenging, FRAP (ferric reducing antioxidant power), CUPRAC (cupric reducing antioxidant capacity) and CHROMAC (chromium reducing antioxidant capacity), including also FIC (ferrous ion-chelating capacity). The highest radical scavenging values in the case of DPPH test, for example, were obtained for methyldopa (93.14%), isoprenaline (92.92%) adrenalone (90.76%) and dopamine (90.51%). The highest reduction power, according to FRAP test, presented the same compounds: adrenalone (96.02%) methyldopa (95.97%), dopamine (94.67%) and isoprenaline (93.72%), except metaraminol (5.79%). Concerning the chelating capacity, adrenalone (66.35%), metaraminol (55.31%), metaproterenol (49.58%) and terbutaline (45.64%) showed the higher chelating capacity. The lowest value, in this case, was obtained for methyldopa (0.28%). According to the results obtained in the present study, the investigated drugs showed an effective in vitro antioxidant and radical scavenging ability and metal-chelating capacity. In addition, applying hierarchical cluster analysis (HCA), principal component analysis (PCA) and the sum of ranking differences (SRD) similarities and differences of investigated compounds and considered assays were clearly proved.
Keywords: Antioxidant and chelating capacity, biogenic amines, sympathomimetic drugs, chemometrics
Investigation, Simulation and Comparison of Various Routes for Bioethanol Production
LETITIA PETRESCU, ANA-MARIA POSA
Bioethanol has proven its value as an alternative fuel to gasoline, in fact, more as an adding than a competitor. Bioethanol has attracted a lot of interest due to its biodegradable nature, low cost, low toxicity and safety. The present work is focused on process modelling and simulation of bioethanol production using biomass and / or CO2 and H2 as raw-materials. The first scenario investigated considers the biomass fermentation, the second scenario considers the thermo-catalytic hydrogenation of CO2 while the combination of the previously methods was assumed in the third scenario. The main advantages of these routes are the reduction of greenhouse gas emissions and the production of one valuable chemical, bioethanol. A productivity of 30,000 tones/year of bioethanol is set for all three cases. Purities, higher than 90% for the main product, are obtained. The technical comparison of the three scenarios leads to the conclusion that the best option to obtain bioethanol is from cellulosic biomass. In this first case, the energy consumption is 0.08 kW / kg bioethanol and the carbon dioxide emissions are 0.96 kg CO2 / kg bioethanol being much lower than in the other two considered cases.
Keywords: Bioethanol production, process modelling and simulation, technical comparison
The Influence of Geographic Location and Enzyme- Assisted Extraction on Essential Oils Composition of Thymus Serpyllum Growing Wild in Transylvania
IOANA GOJA, ADELINA ULICI, MONICA CULEA, VASILE MUNTEANU, PAULA PODEA
A comparative study concerning the influence of geographic location and also the influence of enzyme-assisted extraction on the essential oils isolated from Transylvanian wild Thymus serpyllum was achieved. The collected Thymus serpyllum plants, from three different regions from Transilvania, were hydrodistilled to yield essential oils. The influence of enzymatic assisted extraction on the essential oils isolated from Thymus serpyllum was evaluated. All analyzed plants proved to belong to carvacrol chemotype class. The major constituents of wild Thymus serpyllum from these three regions were carvacrol (26.58%-47.62%), p-cymene (8.61%-18.97%), methylcarvacrol (8.81%-13.35%), thymol (1.6%-11.07%), gamma-terpinene (2.09%-7.55%), beta-bysabolene (3.42%-5.18%), caryophyllene (3.17%- 4.83%). Using the enzymatic treatment, the percentage in composition of some components was modified and proved to have an improvement on antioxidant and antimicrobial properties. All studied essential oils exhibited considerable antioxidant and antimicrobial activity.
Keywords: Thymus serpyllum essential oils, enzyme assisted extraction, antioxidant activity, antimicrobial activity, GC/MS.
Radiocarbon Dating of the Historic Livingstone Tree at Chiramba, Mozambique
ADRIAN PATRUT, ROXANA T. PATRUT, MICHAEL J. SLATER, LASZLO RAKOSY, DANIEL A. LÖWY, KARL F. VON REDEN
The article reports the AMS (accelerator mass spectrometry) radiocarbon dating results of the Livingstone Tree, a large African baobab on the right bank of the Zambezi, near Chiramba, Mozambique. In 1858, David Livingstone, who discovered the baobab, carved his monogram on the walls of its inner cavity. In 1996, the historic baobab was uprooted when a cyclone struck the area. Several wood fragments were extracted from the remains of the toppled tree. Five samples which originate from these fragments were subsequently dated by radiocarbon. The oldest sample had a radiocarbon date of 1598 ± 17 BP, that corresponded in 1996 to a calibrated age of 1490 ± 35 calendar years. According to this value, the Livingstone Tree at Chiramba becomes one of the oldest known African baobabs, with an age of over 1500 years. The Livingstone Tree had a closed ring-shaped structure, that consisted of 4 fused stems around a false cavity and also 2 additional stems outside the ring.
Keywords: AMS radiocarbon dating, Adansonia digitata, tropical trees, age determination, closed ring-shaped structure, false cavity
Synthesis and Characterization of Nano Biotricalcium Silicate, as a Component of an Endodontic Sealer
LUCIA TIMIŞ, ALEXANDRA AVRAM, MARIA GOREA, LILIANA BIZO, SANDA CÎMPEAN, RADU SEPTIMIU CÂMPIAN
Endodontic sealers are designed to be used in conjunction with semi-rigid materials during endodontic treatment, in order to obtain a three dimensional obturation of the root canal. During the last years, tricalcium silicate (C3S), due to its increased biocompatibility, and superior physicochemical properties, has been investigated as an important component of endodontic filling materials. For most materials available on the market the source of C3S alongside C2S is MTA (mineral trioxide aggregate), but obtaining C3S through synthesis is considered to be a much better alternative due to its superior purity and controlled size of the particles. In this study C3S was synthetized in nanosized particles, by sol-gel method, from TEOS and calcium nitrate tetrahydrate without or with mineralizer NaF. A study was conducted in order to analyze the obtained powder and the hydrated samples which were prepared by mixing the powder with water in a ratio of 0.4, and cured for 28 days. The dried gels were thermally treated at 1450 ºC respectively at 1350 ºC. XRPD and TEM revealed the main presence of nanosized tricalcium silicate besides dicalcium silicate and small quantities of calcium hydroxides at both of synthesis temperatures. The hydration compounds evidenced by XRPD were calcium silicate hydrate alongside calcium hydroxide and calcium carbonate. FTIR analysis evidenced the specific vibration bands for O-H and Si-O bounds in hydrated calcium silicates.
Keywords: endodontic sealer, calcium silicate
A Straightforward Synthesis of Novel 1,3,5-Triazine-Based Macrocyclic Scaffolds
COSMIN V. CRIŞAN, NICULINA D. HĂDADE, ION GROSU, ANDREEA P. CRIŞAN, ANAMARIA TEREC
The synthesis and structural investigation of a series of three macrocycles bearing 2,4,6-tris(p-phenylene)-1,3,5-triazine central units and oligoethyleneoxide bridges are reported. The approach implied the synthesis of non-symmetrical 1,3,5-triazines obtained via a cross-cyclotrimerization reaction, followed by a direct macrocyclization with the corresponding ditosylated oligoethyleneglycols. The obtained non-symmetrically C-substituted 1,3,5-triazines macrocycles were characterized by NMR spectroscopy and High-Resolution Mass Spectrometry (HRMS).
Keywords: macrocycles, 1,3,5-triazine, cross-cyclotrimerization, oligoethylene bridges
The Correlation Between Reactive Oxygen Species and Antioxidants
ALINA OANA RUSU (MOLDOVAN), MARIA IULIANA GRUIA, VIORICA LAZAR LORDEAN, DAN MIHU
Oxidative stress represents as an important factor in carcinogenesis and may play a role in initiation and progression of tumors. Oxidative stress is responsible for DNA damage, and includes a multitude of lesions, many of which are mutagenic and have multiple roles in cancer and aging. The aim of the study is to demonstrate that an antioxidant treatment administration before surgery can influence the breast cancer patients’ immune response.Whole blood samples from 113 patients with breast cancer, admitted in the Surgery Department III of the Oncology Institute of Bucharest were collected and the blood serum was isolated, and then made determinations of malondialdehyde, ceruloplasmin, albumin thiols, and total antioxidants. What was shown in this study is that ROS can increase cell proliferation and genomic instability, which stimulates disease progression, and the tumor is an oxidative stress inducer that can influence the redox balance. The key of an effective compensatory body response to this imbalance, cannot be done without exogenous antioxidant support.
Keywords: ROS, breast cancer, oxidative stress mechanisms, antioxidants.
Determination of the Composition and Contamination with Heavy Metals of Soils from the Srebarna Lake Reserve
METODI MLADENOV, SPASKA YANEVA
The wetlands in direct contact with large rivers, such as the connection between Srebarna Lake and the Danube River, are particularly vulnerable to heavy metals. These metals can be a serious problem due to their toxicity, long persistence and bioaccumulation in the food chain, at the top of which in the wetlands are the waterfowl. For this reason, they are extremely susceptible to the accumulation and influence of heavy metals in their bodies and it is possible to come on to accumulation of significant concentrations, leading to negative effects for them. In this regard, subjects of study in this article are soils from the reserve area. Eight soil samples were tested for pH, electrical conductivity, nutrient content and heavy metals presence. The presented results show that the soils in the area have a relatively good stock in terms of carbon (humus), Ca, Mg, K and P, and although some heavy metals and metalloids have been found, their concentrations are below the permissible normatively established values.
Keywords: soil composition, bioaccumulations, nutrients, heavy metals, contamination, toxicity
Determination of Optimal Extraction Parameters of Polyphenols from Forsythia Europaea Degen & Bald. Bloom Using Response Surface Methodology
DANIJELA KOSTIC, BILJANA ARSIC, MILAN MITIC, SNEŽANA MITIC, MARIJA MARKOVIC, GORDANA, STOJANOVIC
The study was designed to examine the influence of ethanol and acetone solvent concentration, extraction time (45-135 min) and extraction technique: maceration and ultrasound extraction on the extraction of total phenolics and flavonoids from petals of Forsythia europaea Degen & Bald. The highest content of total phenolics in the extracts was obtained using the pure ethanol and acetone in both the extraction processes. The differences in the content of total phenols in different compositions of the mixture for the extraction are the results of different polarities of the applied solvent systems. When ethanol solutions were used for the extraction, the optimum conditions for the extraction of phenols and flavonoids from dried petals by maceration and ultrasound extraction from F. europaea were 135 min and 100% ethanol. In the case of acetone solvent system, the optimum conditions for the extraction by maceration were 135 min and 98.07% acetone and for the ultrasound extraction 135 min and 88.76% acetone. The optimum conditions for the extraction of flavonoids when the acetone solvent system was used, by maceration and ultrasound extraction were 135 min and 77.95 % acetone. Obviously, ultrasonic extraction was less time consuming, and it requires for all performed extractions solvent with less percentage of acetone.
Keywords: phenolics; flavonoids; maceration; ultrasonic extraction; response surface methodology
Doxepin as Corrosion Inhibitor for Copper in 3.5 Wt. % NaCl Solution
SIMONA VARVARA, ROXANA BOSTAN, MARIA POPA, LUIZA GAINA, FLORIN POPA
The effect of 3-(dibenzo[b,e]oxepin-11(6H)-ylidene)-N,Ndimethylpropane- 1-amine (doxepin) on the corrosion behaviour of copper in 3.5 wt.% NaCl solution was investigated by electrochemical techniques, SEM-EDX and quantum chemical calculations. Polarization curves indicate that doxepin acts as a mixed-type inhibitor. Impedance data also prove the anticorrosive proprieties of doxepin, due to its adsorption on the copper surface. The inhibition efficiency of doxepin increases with increasing its concentration, reaching a maximum value of 88.8% at 5 mM. SEM-EDX analysis revealed that doxepin is able to prevent the formation of the oxides on the copper surface. Quantum chemical calculations are in agreement with the results obtained by electrochemical measurements.
Keywords: corrosion, copper, doxepin, electrochemical impedance spectroscopy, polarization curve, SEM-EDX, quantum chemical calculations
CORROSION RESISTANCE OF CERIUM-CONVERSION COATINGS FORMED FROM CERIUM(III) SALTS ON ALUMINIUM ALLOY 7075-T6
PETER RODIČ and INGRID MILOŠEV
Cerium conversion coatings were explored as an alternative to chromium conversion coatings for corrosion protection of aluminium alloy 7075- T6. Conversion coatings were formed in a conversion bath of 0.05 M cerium salt and 0.25 M hydrogen peroxide at room temperature. Various cerium salts were used: Ce(III) acetate, Ce(III) nitrate and Ce(III) chloride. The conversion process from Ce3+ to Ce4+ was followed by UV-vis spectroscopy. The conversion of cerium coatings on alloy surface was monitored by measuring open circuit potential. To investigate the corrosion properties of uncoated and coated samples, the linear polarization and electrochemical potentiodynamic curves were recorded in 0.1 M NaCl. Additionally, salt spray chamber testing was carried out. Samples were characterized by scanning electron microscopy. Results revealed that the cerium conversion and corrosion resistance were dependent on the type of cerium salt and conversion time in the conversion bath. The most compact and uniform cerium conversion coating were produced from solution of cerium(III) acetate, but better protection was obtained in nitrate and, especially, chloride solutions due to thicker coatings.
Keywords: aluminium alloy 7075-T6, corrosion, cerium conversion coatings, cerium salts
MORPHOLOGICAL AND STRUCTURAL INVESTIGATION OF THE POLY(VINYL CHLORIDE) / GRAPHENE OXIDE COMPOSITES
LUIZA STINGESCU, CALIN CADAR, LIVIU COSMIN COTET, LUCIAN BAIA, KATA SASZET, KLARA MAGYARI, ALIN GRIG MIHIS, CARMEN IOANA FORT, MALVINA STROE, ELENA MATEI, ANDREEA NILA, ION ANGHEL, MONICA BAIA, MIHAELA BAIBARAC, VIRGINIA DANCIU
The morphological and structural properties of the poly(vinyl chloride)/graphene oxide (PVC/GO) composites are reported. By the mixture of the two constituents, the PVC/GO composite membranes with a concentration of the GO sheets varying from 0 wt.% to 0.5, 1, 2, 3, 4 and 5 wt.% were prepared. Using scanning electron microscopy (SEM) and the analysis of the atomic force microscopy (AFM) images we observed that as increasing the GO concentration in the PVC mass from 0 wt.% to 5 wt.%, the average surface roughness decreases from 235 μm to 227 μm. Using Raman scattering, we report that as increasing the GO concentration in the PVC mass, the ratio between the relative intensities of the Raman glines situated in the spectral ranges 600- 650 and 2850-3000 cm-1 (I600-650/I2850-3000) increases as a consequence of the change of GO carbon atoms hybridization from sp2 to sp3. An increase in the number of C-C bonds, simultaneous with the appearance of O-C=O bonds and the decrease of the chlorine concentration, when the GO concentration increases in the PVC weight is reported by X-ray photoelectron spectroscopy (XPS). The down-shift of the main diffraction signal from 24º to 26º when the GO concentration increases in the PVC/GO composite mass from 0 wt.% to 5 wt.%, confirms the incorporation of GO in the polymeric matrix and the modification of the original PVC sample structure. Using transmission electron microscopy (TEM), no agglomerations of the GO structures within the PVC/GO matrix contrast limit were observed.
Keywords: poly(vinyl chloride), graphene oxide, membranes