Electrochemical tuning of capacitive response of graphene oxide

Increasing energy demands of modern society requires deep understanding of the properties of energy storage materials as well as their performance tuning. We show that the capacitance of graphene oxide (GO) can be precisely tuned using a simple electrochemical reduction route. In situ resistance measurements, combined with cyclic voltammetry measurement and Raman spectroscopy, have shown that upon the reduction GO is irreversibly deoxygenated which is further accompanied with structural ordering and increasing of electrical conductivity. The capacitance is maximized when the concentration of oxygen functional groups is properly balanced with the conductivity. Any further reduction and de-oxygenation leads to the gradual loss of the capacitance. The observed trend is independent on the preparation route and on the exact chemical and structural properties of GO. It is proposed that an improvement of capacitive properties of any GO can be achieved by optimization of its reduction conditions.Comment: 23 pages, 7 figures, 59 reference

Corrosion Characteristics of Raw and Anodised Aluminium

Korozijsku postojanost aluminija i njegovih legura u mnogim medijima moguće je povećati različitim postupcima, među kojima se ističu metode anodizacije ili anodne oksidacije, koja se obično naziva eloksiranjem. Korozivna postojanost aluminija nije apsolutna. Aluminij ima slabu otpornost na koroziju u okolišu sa slabom cirkulacijom kisika ili bez nje, obnavljanje pasivnog filma je onemogućeno, materijal više nije korozivno postojan i u tom slučaju odvijaju se korozivni procesi, što se očituje na različite načine. Kao korozivni mediji uzeti su: otopina NaCl (w = 3 %), otopina HCl (w = 3 %), otopina H2SO4 (w = 10 %), otopina NaCl + NaOH (pH = 10,09), otopina NaOH (pH = 10,17), morska voda iz Ploča. Eloksiranjem se postiže da su u svim korozijskim sredinama potencijali veći, što znači da se stvara zaštitni film oksida. Oksidni sloj najstabilniji je u otopini sumporne kiseline, a najmanju zaštitnu ulogu pokazuje u 3 %-tnoj otopini HCl, 3 %-tnoj otopini NaCl i morskoj vodi. Povećanjem debljine oksidnog sloja s 10 na 20 mikrometara ne postiže se poboljšanje zaštite od korozije izuzev u otopini NaOH. Eloksiranjem se smanjuju polarizacijski otpori prema sličnoj ovisnosti o korozijskoj sredini. Sličan i veći zaštitni učinak pokazuje eloksirani aluminij s debljinom sloja 20 mikrometara. Eloksiranjem se brzina korozije smanjuje za nekoliko desetaka puta, što potvrđuje da se eloksiranjem aluminij štiti od korozije. Vrijednosti su od 3,57 do 2699,00 mma-1.Corrosion resistance of aluminium and its alloys in different media can be improved by many procedures. One of the most used methods is anodisation or anodic oxidation, which is commonly known as anodising. Solutions of: NaCl, w = 3 %, HCl, w = 3 %, H2 SO4 , w = 10 %, NaCl + NaOH (pH = 10.09), NaOH (pH = 10.17), and seawater taken from Ploče were used as corrosive media. Anodisation enables higher potentials in all corrosive environments, indicating that a protective oxide film has been formed. This oxide layer is the most stable in a solution of sulphuric acid, and has the lowest protective role in 3 % HCl solution, 3 % NaCl solution and seawater. By increasing the thickness of anodising from 10 to 20 micrometres, no improvement of the corrosion protection was achieved, except in the NaOH solution. Anodising also reduces the polarization resistance by a similar dependence of the corrosive environment. An even greater and similar protective effect is exhibited by anodised aluminium with a thickness of 20 micrometres. Anodising decreases the corrosion rate by several orders of magnitude, which confirms that aluminium anodising protects against corrosion. Values are from 3.57 to 2699.00 mm a-

Corrosion Characteristics of Raw and Anodised Aluminium

Korozijsku postojanost aluminija i njegovih legura u mnogim medijima moguće je povećati različitim postupcima, među kojima se ističu metode anodizacije ili anodne oksidacije, koja se obično naziva eloksiranjem. Korozivna postojanost aluminija nije apsolutna. Aluminij ima slabu otpornost na koroziju u okolišu sa slabom cirkulacijom kisika ili bez nje, obnavljanje pasivnog filma je onemogućeno, materijal više nije korozivno postojan i u tom slučaju odvijaju se korozivni procesi, što se očituje na različite načine. Kao korozivni mediji uzeti su: otopina NaCl (w = 3 %), otopina HCl (w = 3 %), otopina H2SO4 (w = 10 %), otopina NaCl + NaOH (pH = 10,09), otopina NaOH (pH = 10,17), morska voda iz Ploča. Eloksiranjem se postiže da su u svim korozijskim sredinama potencijali veći, što znači da se stvara zaštitni film oksida. Oksidni sloj najstabilniji je u otopini sumporne kiseline, a najmanju zaštitnu ulogu pokazuje u 3 %-tnoj otopini HCl, 3 %-tnoj otopini NaCl i morskoj vodi. Povećanjem debljine oksidnog sloja s 10 na 20 mikrometara ne postiže se poboljšanje zaštite od korozije izuzev u otopini NaOH. Eloksiranjem se smanjuju polarizacijski otpori prema sličnoj ovisnosti o korozijskoj sredini. Sličan i veći zaštitni učinak pokazuje eloksirani aluminij s debljinom sloja 20 mikrometara. Eloksiranjem se brzina korozije smanjuje za nekoliko desetaka puta, što potvrđuje da se eloksiranjem aluminij štiti od korozije. Vrijednosti su od 3,57 do 2699,00 mma-1.Corrosion resistance of aluminium and its alloys in different media can be improved by many procedures. One of the most used methods is anodisation or anodic oxidation, which is commonly known as anodising. Solutions of: NaCl, w = 3 %, HCl, w = 3 %, H2 SO4 , w = 10 %, NaCl + NaOH (pH = 10.09), NaOH (pH = 10.17), and seawater taken from Ploče were used as corrosive media. Anodisation enables higher potentials in all corrosive environments, indicating that a protective oxide film has been formed. This oxide layer is the most stable in a solution of sulphuric acid, and has the lowest protective role in 3 % HCl solution, 3 % NaCl solution and seawater. By increasing the thickness of anodising from 10 to 20 micrometres, no improvement of the corrosion protection was achieved, except in the NaOH solution. Anodising also reduces the polarization resistance by a similar dependence of the corrosive environment. An even greater and similar protective effect is exhibited by anodised aluminium with a thickness of 20 micrometres. Anodising decreases the corrosion rate by several orders of magnitude, which confirms that aluminium anodising protects against corrosion. Values are from 3.57 to 2699.00 mm a-

Experimental design of the Cu-As-Sn ternary colour diagram

The aesthetic appearance of metals has long been recognised in archaeometric studies as an important factor driving inventions and innovations in the evolution of metal production. Nevertheless, while the studies of ancient gold metallurgy are well supported by the modern research in colour characteristics of gold alloys, the colour properties of major prehistoric copper alloys, like arsenical copper and tin bronzes, remain either largely understudied or not easily accessible to the western scholarship. A few published studies have already indicated that alloying and heat treatment change the colours of copper alloys, although they are mainly based on the examples of prehistoric tin bronze objects and experimental casts. Here we present the procedure for building the Cu-As-Sn ternary colour diagram, starting with experimental casting of 64 binary and ternary alloys in this system. We used two types of information to produce two different ternary colour diagrams: one, based on photographs of the samples, and the other, established on the colorimetric measurements. Furthermore, we developed the procedure for creating a graphic representation of colours in the Cu-As-Sn ternary diagram using QGIS. As an initial case study, we plotted the composition of the world’s earliest tin bronze artefacts; the graphic representation further supports claims about the importance of golden hue for their invention and demand, c. 6,500 years ago. We argue that the presented colour diagrams will find wide use in future investigations of aesthetics of prehistoric copper alloys.AH/J001406/1 DM McDonald Awar

Experimental design of the Cu-As-Sn ternary colour diagram

The aesthetic appearance of metals has long been recognised in archaeometric studies as an important factor driving inventions and innovations in the evolution of metal production. Nevertheless, while studies of ancient gold metallurgy are well supported by modern research in colour characteristics of gold alloys, the colour properties of major prehistoric copper alloys, such as arsenical copper and tin bronzes, remain either largely understudied or not easily accessible to the western scholarship. A few published studies have already indicated that alloying and heat treatment change the colours of copper alloys, although they are mainly based on examples of prehistoric tin bronze objects and experimental casts. Here we present a procedure for building the Cu-As-Sn ternary colour diagram, starting with experimental casting of 64 binary and ternary alloys in this system. We used two types of information to produce two different ternary colour diagrams: one based on photographs of the samples, and the other based on the colorimetric measurements. Furthermore, we developed a procedure for creating a graphic representation of colours in the Cu-As-Sn ternary diagram using QGIS. As an initial case study, we plotted the composition of the world's earliest tin bronze artefacts; the graphic representation further supports claims about the importance of a golden hue for their invention and demand, c. 6500 years ago. We argue that the presented colour diagrams will find wide use in future investigations of aesthetics of prehistoric copper alloys

Electrochemical tuning of capacitive response of graphene oxide

The increasing energy demands of modern society require a deep understanding of the properties of energy storage materials, as well as the tuning of their performance. We show that the capacitance of graphene oxide (GO) can be precisely tuned using a simple electrochemical reduction route. In situ resistance measurements, in combination with cyclic voltammetry measurements and Raman spectroscopy, have shown that upon reduction GO is irreversibly deoxygenated, which is further accompanied by structural ordering and an increase in electrical conductivity. The capacitance is maximized when the concentration of oxygen functional groups is properly balanced with the conductivity. Any further reduction and deoxygenation leads to a gradual loss of capacitance. The observed trend is independent of the preparation route and the exact chemical and structural properties of GO. It is proposed that an improvement in the capacitive properties of any GO can be achieved by optimization of its reduction conditions.This is the peer-reviewed version of the following article: Gutić, Sanjin J., Dževad Kozlica, Fehim Korać, Danica Bajuk-Bogdanović, Miodrag Mitrić, Vladimir M. Mirsky, Slavko V. Mentus, and Igor A. Pašti. "Electrochemical tuning of capacitive response of graphene oxide." (2018). [https://doi.org/10.1039/C8CP03631D]Published version available at: [http://vinar.vin.bg.ac.rs/handle/123456789/7877

Gratitude and hospitality: Tamil refugee employment in London and the conditional nature of integration

Healy, R. L. 2014. The definitive, peer-reviewed and edited version of this article is published in Environment and Planning A, 2014, 46(3), pp. 614-628, http:dx/doi.org/10.1068/a4655The policy of integration attempts to address different elements of exclusion, yet relatively little research has considered what integration means to the refugees themselves. This paper explores one key area for supporting integration: employment.ESRC PTA-030-2005-0082