Graphene films with large domain size by a two-step chemical vapor deposition process

The fundamental properties of graphene are making it an attractive material for a wide variety of applications. Various techniques have been developed to produce graphene and recently we discovered the synthesis of large area graphene by chemical vapor deposition (CVD) of methane on Cu foils. We also showed that graphene growth on Cu is a surface-mediated process and the films were polycrystalline with domains having an area of tens of square micrometers. In this paper, we report on the effect of growth parameters such as temperature, and methane flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene as determined by Raman spectroscopy, and transmission and scanning electron microscopy. On the basis of the results, we developed a two-step CVD process to synthesize graphene films with domains having an area of hundreds of square micrometers. Scanning electron microscopy and Raman spectroscopy clearly show an increase in domain size by changing the growth parameters. Transmission electron microscopy further shows that the domains are crystallographically rotated with respect to each other with a range of angles from about 13 to nearly 30°. Electrical transport measurements performed on back-gated FETs show that overall films with larger domains tend to have higher carrier mobility up to about 16,000 cm(2) V(-1) s(-1) at room temperature.     

Initial Stage Oxidation and Surface Morphology of Modified 9Cr–1Mo Steel at High Temperatures in Air

Modified 9Cr–1Mo steel was oxidized in air at 550 and 750 °C for 25, 100, 250 and 500 h and the oxide scales formed were analysed. The surface morphology and the chemical state of the oxide scales were evaluated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The different exposure temperatures and time showed significant variations on the surface morphologies, the nature of oxide scale, and oxide constituents. The energy dispersive X-ray spectroscopic (EDS) analysis revealed the segregation of Mn at 750 °C even for short exposure time. Grazing incidence X-ray diffraction (GIXRD) patterns revealed the scales to be enriched with haematite and less intense magnetite peaks. Detailed XPS characterization indicated the presence of mixed oxides of iron (Fe), chromium (Cr) and manganese (Mn) in the oxide scales. The Fe–Cr spinel in the oxide scale offered resistance to oxidation of the steel, whereas Mn–Cr spinel was deleterious in nature as it promoted cracking and formation of blisters.     

Comparison of Microwave and Conventional Frying on Quality Attributes and Fat Content of Potatoes

A comparative analysis of quality attributes (moisture, fat, color, and relaxation modulus) of French fries was performed between conventional and microwave frying. Experiments were performed in triplicate for both frying operations at temperatures of 177, 185, and 193 °C for frying times of 60, 90, and 120 s. The real‐time pressure and temperature profiles at above conditions indicated that during microwave frying, gage pressure had greater magnitudes that lasted longer, and the temperature increased to boiling point of water faster in comparison to conventional frying. Lower magnitude of negative pressure during microwave frying is expected to have caused lower fat content in fries obtained using this method (0.08 g/g solids less at 185 °C and 0.07 g/g solids less at 193 °C) than conventional frying. The lightness parameter (L^*) decreased to a lesser extent in microwave frying than in conventional frying. The stress relaxation function of the French fries were significantly different between the 2 frying operations. Consumer test confirmed that reduced fat uptake during microwave frying did not compromise with desirable quality attributes of French fries. X‐ray micro‐computed tomography scanning provided complementary understanding about differences in microstructural properties of fries made using microwave and conventional frying.     

Production and structural characterisation of dextran from an indigenous strain of Leuconostoc mesenteroides BA08 in Whey

In this work, the production of dextran was carried out in whey‐supplemented media using Leuconostoc mesenteroides BA08. Different growth and nutritional parameters were optimised to maximise the dextran production. Batch production in whey‐based media under optimised nutritional and growth conditions yielded a dextran concentration of 17.25 g/L. Structural analysis of the purified polymer by FT‐IR, 1D ¹H and ¹³C nuclear magnetic resonance methodology revealed that polymer was a linear dextran having 93% α‐(1→6) linkage in the main chain. The morphology of the dried dextran and dextran‐producing cells was also studied by scanning electron microscope which showed a granular and porous or weblike structure, respectively. The results obtained showed that the industrial whey supplemented with nutrients such as sucrose, yeast extract and K₂HPO₄ can serve as an ideal growth medium for dextran production. The optimised fermentation and nutritional parameters can be further scaled up to establish the potential for the commercial production of food‐grade dextran from whey as part of a novel cost‐effective and environment‐friendly approach.     

Mechanical properties and morphology of PBT/FE blends

The mechanical properties such as tensile properties and Izod impact strength of melt compounded poly (butylene terephthlate)(PBT)/Fluorocarbon terpolymer elastomer (FE) blends at FE concentration from 0 to 0.26 volume fraction were studied. With increase in the FE concentrations the tensile properties decreased while the impact strength increased. Good dispersion and adhesion of FE with major phase PBT was shown by the morphological studies. Crystallinity of PBT and interphase adhesion influenced the tensile properties. Use of simple models relating normalized relative tensile parameters where the data were divided by the crystallinity of PBT in the blends and in the matrix, respectively, supported the interphase adhesion. The concentration and the interparticle distance of the dispersed phase FE influenced the impact toughening.     

Distribution of technetium in PUREX process streams

Extraction of technetium has been carried out from the aqueous medium containing nitric acid under different experimental conditions to investigate its extraction behaviour in 30% tri-n-butyl phosphate in n-dodecane. In order to study the distribution behaviour of technetium in different streams of PUREX process, experiments were carried out under process conditions. The distribution of technetium was also studied using anion-exchange resin. Based on these results, the path of technetium in the PUREX process streams has been established which will be useful in the development of an advanced PUREX flow-sheet for containment and isolation of technetium in an environmental friendly fuel cycle.     

Streptococcus thermophilus strains of plant origin as dairy starters: Isolation and characterisation

Streptococcus thermophilus strains have been isolated mainly from dairy environments. To prospect for new strains of S. thermophilus, isolation was made from different plant sources. In this study, 74 plant isolates were characterised as S. thermophilus by a polyphasic approach and by 16S rRNA sequencing. The isolates were further evaluated for their physiological and biochemical properties. Plant isolates exhibited good acid production and varying proteolytic activity. All the isolates showed acetaldehyde and capsular exopolysaccharide (EPS) production and few revealed diacetyl production. In contrast to industrial strains, six isolates were able to ferment galactose and 25 were found to have no urease activity. Both the plant isolates and reference dairy cultures were found to possess similar physiological and biochemical properties and can be considered for developing new starters.