Keywords : Oxidation

Synthesis and Characterization of Platinum and Platinum based Alloy Nanoparticles Anchored on Various Carbon Materials for Methanol Oxidation in a DMFC – A Short Review

Richa Baronia; Jyoti Goel; Sunil K. Singhal

Advanced Materials Letters, 2021, Volume 12, Issue 4, Pages 1-22
DOI: 10.5185/amlett.2021.041617

In the fabrication of direct methanol fuel cells (DMFCs) having high performance the essential conditions are (i) the design and construction of a suitable anode electrocatalyst comprising of Pt or a Pt based alloy nanoparticles methanol oxidation reaction (MOR) efficiently and effectively (ii) nature of support materials onto which these nanoparticles are anchored. In MOR one of the major problems is the adsorption of poisoneous carbonmoxide and other similar intermediates near the active surface of Pt active leading to its deactivation and also the crossover of methanol solution towards the cathodic side. All these factors, therefore, lower the overall electrochemical performance of the electro-catalysts. In the present review paper we report some of our important results of the synthesis of different Pt and Pt based anode electro-catalysts (Pt, PtCo alloys, PtCu alloys) anchored on different support materials such as reduced graphene oxide (rGO), Nitrogen doped rGO and a hybrid of rGO/CNTs for MOR and compared with few of those already reported recently. A detailed characterization of raw materials and the electro-catalysts synthesized in this work is also discussed using XRD, FT-IR, SEM, TEM etc. The electrochemical measurements were made using cyclic voltammetry in acidic medium at room temperature.

The Catalytic Efficiency of Au3+ metal ions and Au NPs on the Oxidation of Carbonyl Compounds by in situ Generated Na2FeO4 under Microwave Irradiation for Industrial Point of View

Anamika Srivastava; Anjali Yadav; Manish Srivastava

Advanced Materials Letters, 2020, Volume 11, Issue 8, Pages 1-5
DOI: 10.5185/amlett.2020.081549

The catalytic activity of the Au NPs and Au 3+ metal ions used in the oxidation of carbonyl compounds by in situ generated Na2FeO4 from an industrial point of view. In the subsequent study used the chemical reduction and green method in favor of the fabrication of 30 to70nm in the size of Au NPs. Carbonyl compounds converted to aromatic and aliphatic acids by the oxidation process. Au NPs give better yield as compared to Au 3+ ion since in case of bulk metal the size is enlarged and surface area reduce but converted to nanoparticles the surface area increased so catalytic activity augmented.

Phase selective growth of Ge nanocrystalline films by ionized cluster beam deposition technique and photo-oxidation study                           

S. Mukherjee; A. Pradhan; T. Maitra; A. Nayak; S. Bhunia

Advanced Materials Letters, 2017, Volume 8, Issue 9, Pages 891-896
DOI: 10.5185/amlett.2017.1462

In this paper, we report the possibility of phase-selective growth of Ge nanocrystals by changing the kinetic energy of the clusters in an ionised cluster beam deposition system. Typically, the films are of mixed phase of normal cubic and high energy tetragonal structures, the relative proportion of which could be controlled by controlling the ionisation and applied accelerating potential as has been confirmed from Raman spectroscopic study. The films deposited using neutral clusters showed higher yield of the tetragonal phase with nanocrystallites of diameter ~7 nm as evidenced from HRTEM data. The optical bandgap of the nanocrystals were observed to be blue shifted upto 1.75 eV compared to the bulk Ge attributing to the presence of Ge tetragonal ST-12 phase and the resulted quantum confinement effect inside the nanocrystals. The tetragonal-rich films were further studied by controlled photo-oxidation to tune their optical band gap. A visible photoluminescence due to excitonic transitions have been observed from the as-grown Ge film enriched in tetragonal phase with average crystallite size ~7 nm. The photoluminescence peak was further blue shifted after the course of photo-oxidation due to reduced nanocrystallite size. 

New polycrystalline MC-reinforced nickel-based superalloys for use at elevated temperatures (T > 1100°C)

Patrice Berthod

Advanced Materials Letters, 2017, Volume 8, Issue 8, Pages 866-872
DOI: 10.5185/amlett.2017.1683

In some high temperature applications, there is a constant need of refractory alloys able to resist oxidation by hot gases, hot corrosion by various melts and creep deformation. The best superalloys are currently the g/g’ nickel-based single crystals but they cannot be exposed to 1200°C and more without losing their mechanical resistance. New principles of conventionally cast polycrystalline nickel alloys, combining good resistance against both hot gas oxidation and melts corrosion are explored in this work. Among them, the most promising system involves a reinforcement by HfC carbides. The studied alloy has kept its chromia-forming behaviour which allows good resistance against both oxidation resistance and corrosion by melts. Interesting for a nickel-based alloy containing no g’ precipitates, its creep resistance at 1200°C still remains to be improved to allow using it at so high temperature.

Tunneling Effect Of Photon-assisted AZO/SiOx/n-Si Heterojunction Device At Reverse Bias

H. W. Du; J. Yang; F. Xu; L. Zhao; Z. Q. Ma

Advanced Materials Letters, 2016, Volume 7, Issue 5, Pages 349-352
DOI: 10.5185/amlett.2016.6169

Physical asymmetrical Metal / AZO / SiOx / n-Si / Metal devices in semiconductor-insulator-semiconductor (A-SIS) framework were investigated for their anormaly current-voltage characteristics under light irradiation. The devices showed a normal rectifying character in dark but manifested a peculiar current-voltage feature at reverse bias under illumination. Considering the change of energy band structure at the reverse electric field, it was found that the transport of electrons was mainly dominated by the thermionic emission and quantum tunneling at low voltage. With the increase of the reverse bias, the electrons were able to tunnel through the reduced barrier of ultra-thin SiOx layer (<1nm) and an effective triangle-like barrier of silicon. An appropriate simulation of the J-V relationship demonstrated that the photons acting as the assisted part magnified the reverse current density, and the thickness of SiOx layer managed the amount of the reverse saturation current. 

Cerium(IV) Oxidations Of Sulfated Polysaccharides In Aqueous Perchlorate Solutions: A Kinetic And Mechanistic Approach

Ahmed Fawzy; Refat M. Hassan; Ismail Althagafi; Moataz Morad

Advanced Materials Letters, 2016, Volume 7, Issue 5, Pages 376-382
DOI: 10.5185/amlett.2016.6327

The kinetics of oxidation of iota- and lambda-carrageenans as sulfated polysaccharides by cerium(IV) was studied spectrophotometrically in aqueous perchlorate solutions at a fixed ionic strength of 2.0 mol dm -3 and a temperature of 25 o C. The reactions showed a first order dependence on [Ce IV ], whereas the orders with respect to each carrageenan concentration were less than unity. The reactions exhibited fractional-first order kinetics with respect to [H + ]. Increasing ionic strength increased the oxidation rates. The oxidation products of carrageenans were characterized by elemental analysis and IR spectra as their diketo-acid derivatives. The oxidation products were found to have high tendencies to form coordination polymer complexes with some metal cations such as Ba II , Cd II , Pb II and Ag I . Kinetic evidences for the formation of 1:1 complexes were revealed. Plausible mechanistic scheme for cerium(IV) oxidations of carrageenans were proposed. The activation parameters with respect to the slow step of the reactions were evaluated and discussed. The rate laws have been derived and the reaction constants involved in the different steps of the mechanisms were calculated. The activation parameters associated with the rate-determining step of the mechanism along with thermodynamic quantities of the equilibrium constants were computed and discussed. 

Cyclic Oxidation Behavior Of Bare And Cr3C2-25 (NiCr) Coated Super Alloy At Elevated Temperature

Sanjeet Kumar; Deepa Mudgal; Surendra Singh; Satya Prakash

Advanced Materials Letters, 2013, Volume 4, Issue 10, Pages 754-761
DOI: 10.5185/amlett.2013.2428

High temperature oxidation is the main cause for the degradation of materials used at elevated temperature which is responsible for the major shut down of turbines, boilers and incinerators used in large units. An attempt has been made to use Cr3C2-25%NiCr coating deposited by D-gun technique on Superni 600 alloy. These coatings are generally used for wear applications. This coating has been studied for oxidation at 900C under cyclic conditions. Sound and adherent coatings of 150-250 μm can be obtained by D-gun process. The bare and coated alloys were subjected to cyclic oxidation in air for 100 cycles. Weight change/area has been plotted against number of cycles and to monitor the oxidation kinetics. The scale formed after oxidation both on the bare and coated alloys has been examined using FESEM/EDX, XRD, and Cross-sectional/Mapping analysis. The weight gain by coated Superni 600 was found to be about 80% less than that of bare Superni 600. D-gun sprayed Cr3C2-NiCr coating has contributed to increase in the oxidation resistance of coated superalloy. These types of coatings can be developed for high temperature applications for both corrosion and erosion resistance.