Corrosion behaviour of crystalline and amorphous forms of the glass forming alloy Fe43Cr16Mo16C15B10

The corrosion behaviour of both crystalline and largely amorphous forms of the Fe-based glass forming alloy, Fe43Cr16Mo16C15B10 alloy was investigated. Two different methods were used to induce transformation to the amorphous form of the alloy: laser melting and HVOF spraying. Both methods produced largely amorphous material, however the high brittleness of the alloy makes it susceptible to cracking during laser treatment, hence this technique is not suitable for largescale application. Potentiodynamic scanning showed that in 0.5M H2SO4 and 3.5% NaCl electrolytes both amorphous forms of the alloy had better corrosion resistance (lower current densities for -200 to +1000mV SCE) compared to the crystalline material. The laser treated material and HVOF coating performed similarly in 3.5% NaCl. In 0.5M H2SO4 the HVOF coating had a lower current density than the laser melted material for almost all of the potential range -300 to +1000mV SCE. The improved corrosion behaviour of the largely amorphous material is attributed to its homogeneity, and particularly to the elimination of the Mo-rich phase that underwent preferential corrosion in the crystalline form of the material

X-ray photoelectron spectroscopy study of the passive films formed on thermally sprayed and wrought Inconel 625

There is a well known performance gap in corrosion resistance between thermally sprayed corrosion resistant coatings and the equivalent bulk materials. Interconnected porosity has an important and well known effect, however there are additional relevant microstructural effects. Previous work has shown that a compositional difference exists between the regions of resolidified and non-melted material that exist in the as-sprayed coatings. The resolidified regions are depleted in oxide forming elements due to formation of oxides during coating deposition. Formation of galvanic cells between these different regions is believed to decrease the corrosion resistance of the coating. In order to increase understanding of the details of this effect, this work uses X-ray photoelectron spectroscopy (XPS) to study the passive films formed on thermally sprayed coatings (HVOF) and bulk Inconel 625, a commercially available corrosion resistant Ni-Cr-Mo-Nb alloy. Passive films produced by potentiodynamic scanning to 400mV in 0.5M sulphuric acid were compared with air formed films. The poorer corrosion performance of the thermally sprayed coatings was attributed to Ni(OH)2, which forms a loose, non-adherent and therefore non-protective film. The good corrosion resistance of wrought Inconel 625 is due to formation of Cr, Mo and Nb oxides. Keywords

Screening of fungi isolates from soil, pulp waste water and rotten wood for cellulase producing potentials

Pulp waste water, soil from agricultural waste dump site and rotten wood were investigated for the presence of fungi with cellulolysic ability. Fungi Isolates obtained from the samples were identified based on cultural and morphological characteristics. Seven species of fungi namely, Aspergillus niger, Rhizopus oryzea and Fusarium from soil, Penicillium notatum, Mucor resmosus and Aureobasidium sp from rotten wood, Trichoderma citrinoviride, Fusarium salani, A niger and P notatum from pulp waste water were isolated. Among the seven fungi species , A. niger, F. salani, and P. notatum recorded the highest frequency of occurrence, (2), while T. citrinoviride, R. oryzea, Aureobassidium sp recorded frequency occurrence of one (1)each and the cellulytic activity was determined by the ratio of zone of clearing and colony diameter. The difference in zone of clearing produced by the fungi isolates (A. niger, T. citrinoviride, F. salani), on CMC containing plate were not significantly different at (p˂ 0.05). Highest cellulase activity ratio was exhibited by T. citrinoviride (1.39), followed by A. niger from soil (1.30).This result highlights the potential of T citrinoviride as strain for industrial production of cellulolysic enzyme.Keywords: Cellulase, Enzymes, Aspergillus sp., A. nige

Visualisation of the local electrochemical activity of thermally-sprayed anti-corrosion coatings using scanning electrochemical microscopy

Scanning electrochemical microscopy was used to probe the local electrochemical activity of anti-corrosion coatings formed from Inconel 625, a Ni-Cr-Mo alloy commonly used in engineering applications. The coatings were formed using a high velocity oxygen fuel thermal spraying technique. Upon spraying onto mild steel substrates, clear splat boundaries were formed at the interface between droplets of the alloy as they cooled on the substrate surface. Scanning electrochemical microscopy in the feedback mode, employing ferrocenemethanol as redox mediator, was used to determine the local electrochemical activity of samples of the wrought alloy, the sintered alloy and the thermally-sprayed coating. Significantly, the wrought and sintered materials generally showed responses typical of those expected for a purely insulating material. However, feedback approach curve data showed that the electrochemical activity of the entire thermally-sprayed coating was higher than that of the bulk alloy. Local variations in the coating’s activity were then visualised using scanning electrochemical microscopy. These observations indicate that the spraying process increases the conductivity of Inconel 625 and that localised regions of increased electrochemical activity are generated throughout the material, which appear to be related to the splat boundaries formed during spraying

Ethanol production from lignocellulosic materials by fermentation process using yeast

Rapid industrialization and growing population result to high demand for energy. Depletion and rise in price of petroleum as well as environmental pollution necessitates the need for alternative source of fuel, hence bioethanol production. Rice bran (Oryza sativa), Corn bran (Zea mays) and Sorghum bran (Sorghum guinense) and saw dusts of Khaya senegalensis (Red wood), Terminalia superba (Black wood), Gmelina arborea (White wood), were used for the study. The yeasts used for the study were isolated from fermented beverages (Sorghum beer, Millet beverage and Palm wine). The results of the lignocellulosic biomass of white saw dust, red saw dust, black saw dust, rice bran, corn bran and sorghum bran revealed cellulose components as 77.78%, 75.55%, 68.59%, 64.83%, 54.82% and 55.14% respectively. A total of 25 yeasts were isolates and identified using API 20C AUX strip. The yeast isolates, K2, B5, B7 and P1 had the highest ethanol tolerance value of 14%. The results showed that the ethanol-producing ability of the yeast isolates ranged from 4.1% to 10.3%. Fourier Transform Infrared Spectrophotometer (FTIR) and Gas Chromatography and Mass Spectrometry (GC-MS) analyses showed that ethanol is the main compound produced by yeasts from the lignocellulosic materials. This study revealed that Saccharomyces cerevisiae isolated from palm wine (P1) is best in ethanol production and tolerance, and this high prolific strain can be exploited or engineered for ethanol production. Therefore, Lignocellulosic biomasses are recommended as raw materials for producing ethanol, which is a promising alternative energy source as against the depleting petroleum.Keywords: Ethanol, Lignocellulose, Yeasts, Beverages and Saccharomyces cerevisiae

The effects of microstructural features on the performance gap in corrosion resistance between bulk and HVOF sprayed Inconel 625

It is commonly observed that there is a performance gap between the corrosion resistance of thermally sprayed coatings and the equivalent bulk material. This is attributed to the significantly modified microstructure of the sprayed coatings. However, currently there is no detailed understanding of which aspects of microstructural modification are primarily responsible for this performance gap. In this work several deliberately microstructurally modified versions of the Ni-based superalloy Inconel 625 were produced. These were subjected to potentiodynamic electrochemical testing in 0.5M H2SO4 to investigate the links between specific microstructural features and electrochemical behaviour. Samples were prepared by high velocity oxy-fuel (HVOF) thermal spraying, laser surface remelting using a high power diode laser and conventional powder sintering. Microstructural features were examined by optical and scanning electron microscopy and X-ray diffraction. Potentiodynamic testing was carried out on the following forms of Inconel 625: wrought sheet; HVOF sprayed coatings; sintered powder compacts; laser melted wrought sheet and HVOF sprayed coatings. Using the corrosion behaviour, i.e. passive current density, of the wrought sheet as a baseline, the performance of different forms of Inconel 625 were compared. It is found that a fine dendritic structure (with associated microsegregation) produced by laser remelting wrought sheet has no significant effect on corrosion performance. Up to 12% porosity in sintered powder samples increases the passive current density by a factor of only around 2. As observed previously, the passive current density of HVOF sprayed coatings is 20 - 40 times greater. However, HVOF coatings subjected to laser surface remelting are found to have a passive current density close to that of wrought material. It is concluded that, whilst porosity in coatings produces some decrease in corrosion resistance, the main contributing factor is the galvanic corrosion of localised Cr-depleted regions which are associated with oxide inclusions within HVOF sprayed samples