Zaštita Materijala 1. 2023

Characterization of zirconium oxidecoating stabilized with cerium and yttrium oxide deposited on the bonding coating nickel chromium aluminum cobalt yttrium oxide

Abstract

Zirconium dioxide ZrO₂ is used as a basic material for thermal barriers and as a biomaterial for manufacturing parts for hip implants in orthopedic surgery and in dentistry for making crowns. Use of ZrO₂ ceramics as an insulating material and biomaterial is due to its good chemical and dimensional stability, mechanical strength, toughness and elastic modulus. The aim of this study was to analyze the characteristics of zirconium oxide coating of stabilized cerium and yttrium oxide deposited by atmospheric plasma spraying (APS) process on the bond coating of nickel chromium cobalt yttrium oxide. Coatings were deposited on cold substrates and on substrates preheated to 180°C. Composite powder nickel chromium/aluminum/cobalt/yttrium oxide was used for the production of bond layers and for the ceramic layers zirconium oxide stabilized with cerium and yttrium oxide powder. Testing the quality of coatings was done by measuring microhardness of layers using the HV method and for bond tensile strength of the coating system tensile testing was applied. Metallographic evaluation of the share of pores in the bond and ceramic layers was performed with image analysis – processing of images from a light microscope. Powder particle morphology and EDS analysis were performed on the SEM. The obtained results confirm that the preheating temperature of the substrate has a significant impact on structural mechanical properties of the tested coatings system.

Keywords:Atmospheric plasma spraying (APS), microstructure, interface, microhardness, bond strengthZrO₂8%Y₂O₃, Ni22Cr10Al1Y, microstructure, interface, microhardness, bond strength.

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Karakterizacija prevlake cirkonijum oksida stabilizovanog cerijum i itrijum oksidom deponovane na veznoj prevlaci nikl hrom aluminijum kobalt itrijum oksid

Izvod

Cirkonijum dioksid ZrO₂ se koristi kao osnovni materijal za izradu termalnih barijera i kao biomaterijal za izradu delova implanata kuka u ortopedskoj hirurgiji i u stomatologiji za izradu kruna. Korišćenje ZrO₂ keramičke kao izolacionog i biomaterijala je njena dobra hemijska i dimenzionalna stabilnost, mehanička čvrstoća, žilavost i modul elastičnosti. Cilj rada bio je da se analiziraju karakteristike prevlake cirkonijum oksida stabilizovanog cerijum i itrijum oksidom deponovane plazma sprej (APS) postupkom na veznoj prevlaci nikl hrom aluminijum kobalt itrijum oksid. Prevlake su deponovane na hladnim substratima i na predgrejanim substratima na temperaturi 180 °C. Za izradu veznih slojeva primenjen je kompozitni prah nikl hrom/aluminijum/kobalt/itrijum oksid, a za izradu keramičkih slojeva prah cirkonijum oksida stabilizovanog cerijum i itrijum oksidom. Ispitivanje kvaliteta prevlaka je urađena merenjem mikrotvrdoće slojeva metodom HVi zatezne čvrstoće spoja sistema prevlaka ispitivanjem na zatezanje. Metalografska procena udela pora u veznim i keramičkim slojevima je urađena image analizom – obradom slika sa svetlosnog mikroskopa. Morfologije čestica prahova i EDS analiza je urađena na SEM-u. Dobijeni rezultati potvrđuju da temperatura predgrevanja substrata ima bitan uticaj na strukturno mehanička svojstva testiranih sistema prevlaka.

Ključne reči: Atmosferski plazma spreing (APS), mikrostrukture, interfejs, mikrotvrdoće, čvrstoća spoja.

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The capacities of Hedera helix from the Bor region for PAH accumulation in the root and implications for phytostabilization

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are considered as the pollutants of highest priority, and their remediation is of a global concern. The purpose of this study was to investigate the phytoremediation potential of Hedera helix (Hh) determining the content of 16 priority PAHs in its soil and root samples collected from the rural and industrial zones of the Bor’s municipality (Serbia). The content of Ʃ16 PAHs in the soils was: 326.49 μg/kg at the site Borsko jezero to maximal 1937.64 μg/kg at the site Slatinsko naselje. The level of soil pollution (depending on the concentration of Σ16 PAHs), was high at many tested sites and it was under the significant influence of anthropogenic activities. The concentration for Σ16 PAHs in the samples of roots ranged from 480.71 μg/kg at the site Krivelj to 1748.32 μg/kg at the site Naselje Sunce. Interestingly, the extremely toxic benzo(a)pyrene, was not detected in the roots of Hh. Bio-concentration factors (BCFs) were applied to determine the capacity of Hh for PAH accumulation in the root, and consequently, for determination of its phytostabilization potential. In most cases, BCF values were higher at the locations from UI zone. The calculated BCFs were higher for LMW PAHs than for HMW PAHs. At the majority of the investigated locations, the tested plant species was especially successful in the root accumulation of the compounds such as acenaphthene, fluorene, anthracene, dibenzo(a,h)anthracene, and the sum of benzo(k)fluoranthene and ben­zo(b)fluoranthene. These findings showed that Hh can be successfully used in phytostabilization of many PAHs.

Keywords: Soil pollution, PAHs, Hedera helix, phytostabilization

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Kapaciteti  Hedera  helix iz borskog regiona za akumulaciju PAH u korenu i implikacije za fitostabilizaciju

Izvod

Policiklični aromatični ugljovodonici (PAU) smatraju se zagađujućim materijama najvišeg prioriteta, a remedijacija PAU iz životne sredine predstavlja problem na globalnom nivou. Cilj ovog istraživanja bio je da se ispita fitoremedijacioni potencijal Hedera helix i da se utvrdi sadržaj 16 prioritetnih PAU u uzorcima zemljišta i korena koji su prikupljeni iz ruralnih i industrijskih zona opštine Bor (Srbija). Sadržaj Ʃ16 PAH u zemljištu je bio od 326,49 μg/kg na lokalitetu Borsko jezero do 1937,64 μg/kg na lokalitetu Slatinsko naselje. Stepen zagađenosti zemljišta (u zavisnosti od koncentracije Ʃ16 PAU) bio je visok na većem broju ispitivanih lokacija i pod značajnim uticajem antropogenih aktivnosti. Koncentracije Ʃ16 PAU u uzorcima korena kretala su se od 480,71 μg/kg na lokaciji Krivelj do 1748,32 μg/kg na lokaciji Naselje Sunce. Zanimljivo je da ekstremno toksičan benzo(a)piren nije detektovan u korenu ispitivane biljke ni na jednoj ispitivanoj lokaciji. Bio-koncentracioni faktori (BCF) bili su primenjeni za određivanje kapaciteta Hedera helix za akumulaciju PAU u korenu, a samim tim i za određivanje njenog fitostabilizacionog potencijala. U većini slučajeva, BCF vrednosti su bile veće na lokacijama UI zone. Takođe, izračunati BCF su bili veći za nisko molekularne u poređenju sa visoko molekularnim PAU. Na većem broju lokacija ispitivana biljna vrsta pokazala se veoma uspešno u akumulaciji jedinjenja u korenu, kao što su acenaften, fluoren, antracen, dibenzo(a,h)antracen i zbira benzo(k)fluorantena i benzo(b)fluorantena. Dobijeni rezultati su pokazali da se Hh može uspešno koristiti u fitostabilizaciji mnogih PAU jedinjenja.

Ključne reči: Zagađenje zemljišta, PAU, Hedera helix, fitostabilizacija

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Synthesis of nanoparticles in dual biodiesel and enchancement in performances and emission characteristics

Abstract

Biodiesel is being advertised as a realistic alternative fuel. Since it has a lower environmental effect than standard fuel properties, biodiesel has risen in popularity recently, and there has been a lot of study done on it all around the world. Biodiesel is prone to oxidation due to the presence of unsaturated fatty acids in the ester, which has been one of the biggest downsides. When biodiesel comes into contact with oxygen during storage or even with metal impurities, it oxidises. Antioxidants are really helpful in resolving problems with oxidation stability. In this paper, mainly discussed about dual biodiesel (40:60), mixed with TiO₂ Nanoparticles at various 25 ppm levels for the blend DBNP20, DBNP40 and DBNP60 respectively. The results implies good performances and emission characteristics with lower SFC and reasonable values are tabulated in the with neat diesel values.

Keywords: Oxidation stability, CFPP, NO_x, CO, HC, Smoke opacity.

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Sinteza nanočestica u dualnom biodizelu i poboljšanje performansi i karakteristika emisije

Izvod

Biodizel se reklamira kao realno alternativno gorivo. Pošto ima manji uticaj na životnu sredinu od standardnih svojstava goriva, biodizel je postao popularan, a o njemu je rađeno mnogo studija širom sveta. Biodizel je sklon oksidaciji zbog prisustva nezasićenih masnih kiselina u estru, što je jedan od najvećih nedostataka. Kada biodizel dođe u kontakt sa kiseonikom tokom skladištenja ili čak sa metalnim nečistoćama, on oksidira. Antioksidansi su zaista od pomoći u rešavanju problema sa oksidacionom stabilnošću. U ovom radu se uglavnom govori o dvostrukom biodizelu (40:60), pomešanom sa TiO₂ nanočesticama na različitim nivoima od 25 ppm za mešavinu DBNP20, DBNP40 i DBNP60. Rezultati impliciraju dobre performanse i karakteristike emisije sa nižim SFC i dobijene vrednosti su tabelarno prikazane u urednim vrednostima dizela.

Ključne reči: oksidaciona stabilnost, CFPP, NOk, CO, HC, neprozirnost dima.

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The inhibitive effect of magnetic fields on mild steel corrosion in acidic media

Abstract

The inhibitive effect of applied magnetic fields on the corrosion of mild steel in 1.0M HCl and 0.5M H₂SO₄ acid solutions has been investigated at room temperature by using the gravimetric technique. A locally made electromagnet with variable outputs and powered by a direct current source voltage provided the magnetic fields. In a typical experiment, the applied magnetic field was applied perpendicularly onto the surface of a mild steel coupon immersed completely in a chosen acid solution for an exposure time of two hours. It was observed that the corrosion rates of mild steel determined for each case of 1.0M HCl and 0.5M H₂SO₄ test solutions decrease as the applied magnetic field increases. This indicates that the presence of the applied magnetic field inhibits the corrosion of the mild steel in the test solutions. Results also show that the protection efficiency of the magnetic field increases as the applied magnetic field increases. More specifically, as the magnetic field was increased from 118.2 – 764.3mG [or 0.01182 – 0.07643 mT], the protection efficiency increased from 36.34 – 62.67% for mild steel in 1.0M HCl acid solution, while for mild steel in 0.5M H₂SO₄ acid solution, the protection efficiency increased from 12.68 – 46.88%. It was demonstrated that the observed inhibitive effect of the magnetic fields can be attributed partly to the phenomenon of transverse magnetoresistance and partly to the effect of the magnetic fields on the mass transport properties of the constituent ions in the electrochemical system.

Keywords: Mild steel, magnetic field, gravimetric technique, corrosion rate, protection efficiency, magnetoresistance.

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Inhibitivni efekat magnetnog polja na koroziju mekog čelika u kiselom mediju

Izvod

Inhibitivni efekat primenjenih magnetnih polja na koroziju mekog čelika u 1.0 M HCl i 0.5 M H₂SO₄ kiselinskim rastvorima ispitan je na sobnoj temperaturi gravimetrijskom tehnikom. Lokalno napravljen elektromagnet sa promenljivim izlazima i napajan iz izvora jednosmerne struje obezbeđivao je magnetna polja. U tipičnom eksperimentu, korišćeno magnetno polje je primenjeno okomito na površinu kupona od mekog čelika koji je u potpunosti uronjen u izabrani rastvor kiseline tokom vremena izlaganja od dva sata. Uočeno je da se brzine korozije mekog čelika određene za svaki slučaj testnih rastvora od 1.0 M HCl i 0.5 M H₂SO₄ smanjuju kako se primenjeno magnetno polje povećava. Ovo ukazuje da prisustvo primenjenog magnetnog polja inhibira koroziju mekog čelika u ispitivanim rastvorima. Rezultati, takođe, pokazuju da se efikasnost zaštite magnetnog polja povećava kako se primenjeno magnetno polje povećava. Tačnije, kako je magnetno polje povećano sa 118,2 – 764,3 mG [ili 0,01182 – 0,07643 mT], efikasnost zaštite je porasla sa 36,34 – 62,67% za meki čelik u 1.0 M rastvoru HCl kiseline, dok je za meki čelik u kiselini 0.5M H₂SO₄ efikasnost zaštite povećana sa 12,68 – 46,88%. Pokazano je da se uočeni inhibicijski efekat magnetnih polja može delom pripisati fenomenu poprečne magnetootpornosti, a delom uticaju magnetnih polja na svojstva transporta mase konstitutivnih jona u elektrohemijskom sistemu.

Ključne reči: meki čelik, magnetno polje, gravimetrijska tehnika, brzina korozije, efikasnost zaštite, magnetootpornost.

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Electrochemical studies on the corrosion resistance of gold 18K and thermo active alloy in artificial sweat in presence of sodium chloride

Abstract

Corrosion resistance of Thermo active alloy and Gold 18K alloy immersed in artificial sweat in the absence and presence of 100 ppm of NaCl has been investigated by polarization study and AC impedance spectra. It is observed that corrosion resistance of thermo active alloy and also Gold 18K alloy immersed in artificial sweat in the presence of 100 ppm of NaCl increases. Hence it is concluded that people wearing ornaments made of these two alloys need not worry about the excess of sodium chloride in their sweat. When thermo active alloy is immersed in artificial sweat in the presence of 100 ppm of NaCl, linear polarization resistance  value increases from 1760283 Ohm cm² to  9506106 Ohm cm²; corrosion current decreases from 1.845×10^-8 to 4.008×10^-9 A/cm²; charge transfer resistance value increases from  4884 Ohmcm² to 12210 Ohm cm²; impedance value increases from 4.367 to 4.8; double layer capacitance decreases from  1.0442 x10^-9  to  4.1769×10^-10  F/cm² , and phase angle increases from 48.1  to  66.34°. When Gold 18K alloy is immersed in artificial sweat in the presence of 100 ppm of NaCl, linear polarization resistance  value increases from 1079199 Ohmcm² to  2385141  Ohm cm²; corrosion current decreases from 4.036×10^-8 to 0.1966 x 10 ^-8A/cm² ; charge transfer resistance  increases from  4291 Ohm cm²  to   48880 Ohm cm²; impedance value increases from 4.652 to 5.114; double layer capacitance decreases from 1.189 x10^-9 to  1.0434 x10^-10 F/cm², and phase angle increases from 61 to  88.

Keywords: Corrosion resistance, Thermo active alloy, Gold 18K alloy, Artificial sweat, NaCl, polarization study, AC impedance spectra

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Elektrohemijske studije otpornosti na koroziju zlata 18K i termoaktivne legure u veštačkom znoju u prisustvu natrijum hlorida

Izvod

Otpornost na koroziju termoaktivne legure i legure zlata 18K uronjene u veštački znoj u odsustvu i prisustvu 100ppm NaCl je ispitana polarizacionom studijom i spektrom impedanse naizmenične struje. Primećeno je da se povećava otpornost na koroziju termo aktivne legure, kao i legure zlata 18K uronjene u veštački znoj u prisustvu 100ppm NaCl. Otuda se zaključuje da ljudi koji nose ukrase od ove dve legure ne moraju da brinu o višku natrijum hlorida u svom znoju. Kada se termo aktivna legura potopi u veštački znoj u prisustvu 100ppm NaCl, vrednost otpora linearne polarizacije raste sa 1760283 Ohmcm² na 9506106 Ohmcm²; struja korozije se smanjuje sa 1,845×10^-8 na 4,008×10^-9 A/cm²; vrednost otpora prenosa naelektrisanja raste sa 4884 Ohmcm² na 12210 Ohmcm²; vrednost impedanse se povećava sa 4,367 na 4,8; kapacitivnost dvostrukog sloja se smanjuje sa 1,0442 x10^-9 na 4,1769×10^-10 F/cm², a fazni ugao se povećava sa 48,1° na 66,34°. Kada se legura zlata 18K potopi u veštački znoj u prisustvu 100ppm NaCl, vrednost otpora linearne polarizacije se povećava sa 1079199 Ohmcm² na 2385141 Ohmcm²; struja korozije se smanjuje sa 4,036×10^-8 na 0,1966 x 10A/cm²; otpor prenosa naelektrisanja raste sa 4291 Ohmcm² na 48880 Ohmcm²; vrednost impedanse se povećava sa 4,652 na 5,114; kapacitivnost dvostrukog sloja se smanjuje sa 1,189 x10^-9 na 1,0434 x10^-10 F/cm², a fazni ugao raste sa 61° na 88°.

Ključne reči: otpornost na koroziju, termoaktivna legura, legura zlata 18K, veštački znoj, NaCl, studija polarizacije, spektri AC impedanse.

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Ceramic rolls for rolling of steel foils

Abstract

High hardening of the steel, which is caused by martensitic transformation through cold forming, leads to significant local elastic roll deformation (flattening). The rolling of strain-hardened steel requires higher rolling forces and higher torques, which result in high rolling force. Roll flattening can be reduced by using rolls made of a material with a significantly higher modulus of elasticity. The suitability of ceramic materials for the rolls of modern cold and hot rolling mills was examined. The rolling tests with silicon nitride rolls were carried out with a two-high rolling stand with coilers. The industrial applications of silicon nitride rolls in the rolling of thin steel foils in a 20-high Sendzimir mill consistently showed excellent applicability of this material. A review of conducted research has shown that the use of silicon nitride work rolls minimizes roll flattening and leads to a significant reduction in rolling force.

Keywords: work rolls, flattening, strain-hardened steel, silicon nitride, Sendzimir mill

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Keramički valjci za valjanje čeličnih folija

Izvod

Visoko očvršćavanje čelika, koje je uzrokovano martenzitnom transformacijom kroz hladno oblikovanje, dovodi do značajne lokalne elastične deformacije valjaka (spljoštenja). Valjanje čelika očvrščenog deformacijom zahteva veće sile valjanja i veće obrtne momente, što rezultira visoko opterećenje valjačke pruge. Spljoštenost valjaka može se smanjiti upotrebom valjaka od materijala sa znatno većim modulom elastičnosti. Ispitivana je pogodnost keramičkih materijala za valjke savremenih hladnih i toplih valjaonica. Laboratorijska ispitivanja valjanja sa valjcima od silicijumnitrida vršena su na valjačkoj pruzi sa dva valjaka. Industrijska primena valjaka od  silicijumnitrida u valjanju tankih čeličnih folija u Sendzimirovoj valjačkoj pruzi konstantno pokazivala odličnu primenljivost ovog materijala. Pregled sprovedenih istraživanja je pokazao da upotreba radnih valjaka od silicijumnitrida minimizira spljoštenje valjaka i dovodi do značajnog smanjenja sile valjanja.

Ključne reči: radni valjci, spljoštenje, očvrščenje deformacijom, silicijumnitrid, Sendzimirova pruga

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Influence of a candy on the corrosion resistance of orthodontic wire made of Gold 18K in the presence of artificial saliva

Abstract

Corrosion resistance of an orthodontic wire made of Gold 18K alloy immersed in artificial saliva in the absence and presence of 500 ppm of Éclairschocolate candy has been investigated by potentiodynamic polarization study and electrochemical impedance spectra (EIS). It is observed that corrosion resistance of Gold 18K alloy immersed in artificial saliva in the presence of 500 ppm of Éclairs chocolate candy increases. Hence it is concluded that people clipped with orthodontic wire made of Gold 18K alloy need not worry about taking Éclairs chocolate candy orally. When Gold 18K alloy is immersed in artificial saliva in the presence of 500 ppm of Éclairs chocolate candy, Linear Polarisation Resistance (LPR) value increases from 4844947 Ohmcm² to 35700904 Ohmcm²; corrosion current decreases from 7.726×10^-9A/cm² to 1.350×10⁹A/cm²; charge transfer resistance value(R_t) increases from 172100 Ohmcm² to 398800 Ohmcm²; impedance value increases from 5.445 to 5.975; double layer capacitance decreases from 2.963×10^-11F/cm² to 1.1279×10^-11F/cm², and phase angle increases from 44.68° to 48.23°.

Keywords: Corrosion resistance, Gold 18K alloy, Artificial saliva, Éclairschocolate candy, potentiodynamic polarization study, electrochemical impedance spectra (EIS), pediatric dentistry.

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Uticaj bombona na otpornost na koroziju ortodontske žice od zlata 18k u prisustvu veštačke pljuvačke

Izvod

Otpornost na koroziju ortodontske žice napravljene od legure zlata 18K uronjene u veštačku pljuvačku u odsustvu i prisustvu 500 ppm čokoladnih bombona ispitana je potenciodinamičkom polarizacionom studijom i spektrom elektrohemijske impedanse (EIS). Primećeno je da se poveća­va otpornost na koroziju legure zlata 18K uronjene u veštačku pljuvačku u prisustvu 500 ppm čokoladnih bombona. Otuda se zaključuje da ljudi koji imaju ošišani ortodontsku žicu od legure zlata 18K u ustima ne moraju da brinu o uzimanju čokoladnih bombona. Kada se legura zlata 18K uroni u veštačku pljuvačku u prisustvu 500 ppm čokoladnih bombona, vrednost linearne polari­zacione otpornosti (LPR) se povećava sa 4844947 Ohmcm² na 35700904 Ohmcm²; struja korozije se smanjuje sa 7,726×10^-9A/cm² na 1,350×10^-9A/cm²; vrednost otpora prenosa naelektrisanja (Rt) raste sa 172100 Ohmcm² na 398800 Ohmcm²; vrednost impedanse se povećava sa 5,445 na 5,975; kapacitivnost dvostrukog sloja se smanjuje sa 2,963 x10^-11F/cm² na 1,1279 x10^-11F/cm², a fazni ugao se povećava sa 44,68° na 48,23°.

Ključne reči: otpornost na koroziju, legura zlata 18K, veštačka pljuvačka, čokoladna bombona, potenciodinamička studija polarizacije, spektri elektrohemijske impedanse (EIS), pedijatrijska stomatologija.

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Removal of bemacid red dye by adsorption on sawdust and carbonized sawdust

Abstract

Today, huge amounts of coloured wastewater, released into ecosystems are a big problem, because they have harmful effects on humans, the environment, as well as the aquatic environment. One of the common treatments for removing dyes from wastewater is the adsorption process, with an emphasis on the use of cheap adsorbents. Therefore, the subject of this paper is the possibility of removing the anionic dye bemacid red (BR) on wood biomass sawdust and carbonized sawdust. The experiments examined the equilibrium contact time, the effect of initial pH, the effect of adsorbent dose, as well as the effect of the initial adsorbate concentration on the process of adsorption. By applying linear kinetic models, it was found that the adsorption process follows a pseudo-second-order kinetic model. It was found that pH does not have a significant effect on adsorption onto carbonized sawdust. By examining the effect of the initial adsorbent dose, it was found that optimal adsorption requires twice the mass of sawdust compared to carbonized sawdust. The use of linear adsorption isotherms shows better agreement with the Freundlich model for both adsorbents. The maximum adsorption capacity for sawdust is 30.18 mg/kg, while for carbonized sawdust it is 74.60 mg/kg. Use of sawdust and carbonized sawdust can be an effective adsorbent for removing the dye bemacid red from wastewater, which is confirmed by the experiment on a real sample of wastewater. The obtained efficiency of dye removal from real wastewater for sawdust is 42.9 %, and for carbonized sawdust 95.1 %.

Keywords: Bemacid red, adsorption, wood sawdust, carbonized sawdust

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Uklanjanje boje bemacid red adsorpcijom na piljevini i karbonizovanoj piljevini

Ogromne količine obojene otpadne vode, ispuštene u ekosisteme danas predstavljaju veliki problem, jer imaju štetne efekte na čoveka, životnu i vodenu sredinu. Jedan od postupaka uklanjanja boja iz otpadnih voda jeste proces adsorpcije, sa naglaskom na upotrebu jeftinih adsorbenata. Zbog toga je i tematika ovog rada mogućnost uklanjanja anjonske boje bemacid red (BR) na piljevini drvne biomase i karbonizovanoj piljevini. Provedenim eksperimentima ispitano je ravnotežno vrijeme kontakta, uticaj pH vrijednosti, zavisnost adsorpcije od mase adsorbenta, kao i zavisnost adsorpcije od početne koncentracije adsorbata. Primjenom linearnih kinetičkih modela ustanovljeno je da proces adsorpcije prati kinetički model pseudo drugog reda. Adsorpcija na karbonizovanoj piljevini ne pokazuje značajniju zavisnost od pH vrijednosti. Ispitivanjem zavisnosti adsorpcije od početne mase adsorbenta ustanovljeno je da je za optimalnu adsorpciju potrebna duplo veća masa piljevine u odnosu na karbonizovanu piljevinu. Primjena linearnih adsorpcionih izotermi pokazuje bolje slaganje sa Freundlichovim modelom za oba adsorbensa. Maksimalni kapacitet adsorpcije za piljevinu iznosi 30.18 mg/kg, dok je za karbonizovanu piljevinu 74.60 mg/kg. Dobijeni rezultati pokazuju da primjena piljevine i karbonizovane piljevine može biti efikasan adsorbens za uklanjanje boje bemacid red iz otpadnih voda,što je i potvrđeno na realnom uzorku otpadne vode. Dobijena efikasnost uklanjanja boje iz realnih otpadnih voda, dobijene nakon bojenja poliamidne tkanine bojom bemacid red, za piljevinu iznosi 42.9 %, a za karbonizovanu piljevinu 95.1 %.

Ključne riječi: bemacid red, adsorpcija, drvna piljevina, karbonizovana piljevina

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Inhibition of corrosion of L 80 alloy in sodium hydroxide solution (pH=12) by succinic acid

Abstract

Inhibition of corrosion of L80 alloy in sodium hydroxide solution (pH=12) by succinic acid has been evaluated by electrochemical studies such as polarization and AC impedance spectra. The study reveals that succinic acid is able to control corrosion of L80 alloy in NaOH solution (pH = 12). When L 80 alloy is immersed in NaOH solution , the linear polarisation resistance (LPR) increases and the corrosion current (I_corr) decreases as revealed by potentiodynamic polarization study. Succinic acid at pH=12 functions as anodic type of inhibitor. When L80 alloy is immersed in NaOH solution , the charge transfer resistance (R_t) increases, impedance increases, phase angle increases and double layer capacitance (C_dl) value decreases . These results suggest that a protective film is formed on the metal surface and probably the protective film consists of Fe ²⁺ -inhibitor complex (Iron succinate).

Keywords: corrosion inhibition, L80 alloy, sodium hydroxide solution, electrochemical studies, succinic acid

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Inhibicija korozije legure L 80 u rastvoru natrijum hidroksida (ph=12) ćilibarnom kiselinom

Izvod

Inhibicija korozije legure L80 u rastvoru natrijum hidroksida (pH=12) ćilibarnom kiselinom je procenjena elektrohemijskim studijama kao što su spektri polarizacije i AC impedanse. Studija otkriva da je ćilibarna kiselina u stanju da kontroliše koroziju legure L80 u rastvoru NaOH (pH = 12). Kada se legura L80 potopi u rastvor NaOH, otpor linearne polarizacije (LPR) se povećava, a struja korozije (Icorr) opada, što je otkriveno istraživanjem potenciodinamičke polarizacije. Ćilibarna kiselina pri pH=12 funkcioniše kao anodni tip inhibitora. Kada se legura L 80 potopi u rastvor NaOH, otpor prenosa naelektrisanja (Rt) se povećava, impedansa raste, fazni ugao se povećava i vrednos11t kapacitivnosti dvoslojnog sloja (Cdl) opada. Ovi rezultati sugerišu da se na površini metala formira zaštitni film i verovatno se zaštitni film sastoji od Fe 2+ -inhibitornog kompleksa.

Ključne reči: inhibicija korozije, legura L80, rastvor natrijum hidroksida, elektrohemijska ispitivanja, ćilibarna kiselina.

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Effect of hybrid SiC/TiO₂ nanoparticles on tribological and mechanical performance of polymethylmethacrylate dental base material

Abstract

Many researches dealt with PMMA dental base material and the development of its properties to reach a longer life span for implants and fillings. The current work pay attention to examine the loading amount of hybrid nanoparticles, SiC and TiO₂, and find out how it affects the mechanical and tribological properties. Hybrid NPs were dispersed on PMMA resin with filler amount of 0.4%, 0.8%, 1.2%, 1.6%, and 2.0 wt.%, 50/50 between SiC and TiO₂ NPs. The mechanical properties were evaluated by determining the hardness, Shore D, compressive strength, and modulus of elasticity. While the tribological performance was assessed via examining the COF, wear rate and scanning the worn surfaces using optical and SEM images. The results can be indicated that the PMMA resin exhibits a good reaction bonding with low loading amount of the hybrid NPs. Moreover, the high loading content had a negative effect on the mechanical and tribological properties. Subsequently, the loading content of 0.8 wt.% of SiC/TiO₂ NPs indicates that it has the best performance comparing with the pure PMMA.

Keywords: PMMA, Friction, Wear rate, Mechanical properties, SiC Nano Particles, TiO₂ Nano Particles.

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Uticaj hibridnih sic/tio₂ nanočestica na tribološke i mehaničke performanse polimetilmetakrilatnog stomatološkog osnovnog materijala

Izvod

Mnoga istraživanja su se bavila PMMA dentalnim osnovnim materijalom i razvojem njegovih svojstava za postizanje dužeg životnog veka implantata i plombi. Sadašnji rad posvećuje pažnju ispitivanju količine opterećenja hibridnih nanočestica, SiC i TiO₂, i saznanju kako to utiče na mehanička i tribološka svojstva. Hibridni NP dispergovani su na PMMA smoli sa količinom punila od 0,4%, 0,8%, 1,2%, 1,6% i 2,0 tež.%, 50/50 između SiC i TiO₂ NPs. Mehanička svojstva su procenjena određivanjem tvrdoće, šor D, čvrstoća na pritisak i modul elastičnosti. Dok su tribološke performanse procenjene ispitivanjem COF-a, stope habanja i skeniranjem istrošenih površina korišćenjem optičkih i SEM slika. Rezultati mogu ukazati na to da PMMA smola pokazuje dobro reakciono vezivanje sa malom količinom hibridnih NPs. Štaviše, visok sadržaj imao je negativan uticaj na mehanička i tribološka svojstva. Nakon toga, sadržaj punjenja od 0,8 tež.% SiC/TiO₂ NPs pokazuje da ima najbolje performanse u poređenju sa čistim PMMA.

Ključne reči: PMMA, trenje, stopa habanja, mehanička svojstva, SiC nano čestice, TiO₂ nano čestice.

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Investigation of stress-corrosion cracking of welded joint of Х70 steel under cathodic polarization in near neutral environment

Abstract

Study of stress-corrosion cracking of welded joints made of X70 steel at cathodic polarization in near neutral solution NS4 was carried out. It was established that the tendency of base metal of X70 steel to stress-corrosion cracking, estimated by K_S coefficient, increases from 1.07 to 1.13 whereas polarization potential changing from the corrosion potential to maximum protective potential -1.05 V. Such regularity correlates with increasing of hydrogen penetration through X70 steel, which at maximum protective potential -1.05 V is equal to 0.000518 mol/m³. Susceptibility of welded joint is lower than the base metal, K_S coefficient change not much near the value 1.0. With increasing of polarization potential from -0,75V to -1.05V fracture surface of X70 steel characterized by decreasing in the size of holes and the appearance of flat areas, through that the rupture occurred. A similar nature of the rupture was observed for the welded joint, but visually larger proportion of flat areas can be noted. It was established that the rupture of the welded joint occurs on the base metal, which allows to propose stress-corrosion cracking susceptibility factor K_S to be legitimately used for estimation to stress-corrosion cracking of welded joint, provided the weld is performed in a high-quality manner. Stress-corrosion cracking results of welded joint of X70 steel correlate satisfactorily with the experience of stress-corrosion cracking on main gas pipelines, where stress-corrosion cracks form and develop along the base metal of gas pipelines.

Keywords: pipe steel X70, welded joint, near-neutral environment, cathodic polarization, stress-corrosion cracking, slow strain rate test, voltammetry, fractography

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Istraživanje naponsko-korozijskog prskanja zavarenog spoja čelika X70 pri katodnoj polarizaciji u blisko neutralnoj sredini

Izvod

Izvršeno je istraživanje naponsko-korozionog pucanja zavarenih spojeva od čelika X70 pri katodnoj polarizaciji u skoro neutralnom rastvoru NS4. Utvrđeno je da se sklonost osnovnog metala čelika X70 ka naponsko-korozionom pucanju, procenjena koeficijentom K_s, povećava sa 1,07 na 1,13, dok se polarizacioni potencijal menja od potencijala korozije do maksimalnog zaštitnog potencijala -1,05V. Ovakva pravilnost je u korelaciji sa povećanjem prodora vodonika kroz čelik X70, koji je pri maksimalnom zaštitnom potencijalu -1,05V jednak 0,000518 mol/m3. Podložnost zavarenog spoja je manja od osnovnog metala, promena K_s koeficijenta nije mnogo blizu vrednosti 1,0. Sa povećanjem potencijala polarizacije sa -0,75 V na -1,05 V površina loma čelika X70 karakteriše smanjenje veličine rupa i pojava ravnih površina, kroz koje je došlo do loma. Slična priroda rupture je primećena i za zavareni spoj, ali se može primetiti vizuelno veći udeo ravnih površina. Utvrđeno je da do pucanja zavarenog spoja dolazi na osnovnom metalu, što omogućava da se predloži faktor osetljivosti na naponsku koroziju K_s koji bi se legitimno koristio za procenu pucanja zavarenog spoja od naponske korozije, pod uslovom da je zavar izveden na visoko kvalitetan način. Rezultati prslina od naponske korozije zavarenog spoja čelika X70 zadovoljavajuće koreliraju sa iskustvom prslina od naponske korozije na magistralnim gasovodima, gde se prsline od naponske korozije formiraju i razvijaju duž osnovnog metala gasovoda.

Ključne reči: čelik za cevi X70, zavareni spoj, skoro neutralna sredina, katodna polarizacija, naponsko-koroziono pucanje, deformacija, voltametrija, fraktografija

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