Anti-bacterial biofilm activity of magnesium ferrite thin film

ABSTRACT

Thin films of magnesium ferrite (MgFe₂O₄) are synthesized on the glass substrate by using thermal evaporation technique and studied their anti-bacterial biofilm activity against the gram-negative and gram-positive bacterium. The MgFe₂O₄ thin films (100 nm) were prepared at a deposition rate of 10 ± 2 Å/S, followed by annealing at 600°C. The morphological and structural study using scanning electron microscope, X-ray diffraction, and transmission electron microscope reveals crystalline structure of the magnesium ferrite. The model organisms for anti-bacterial biofilm activity were tested with E. coli (gram negative) and S. aureus (gram positive). The E. coli and S. aureus biofilms grown on the glass slides and MgFe₂O₄ coated glass slide were imaged using fluorescent microscope. It is observed that the MgFe₂O₄ coated glass slides exhibit minimum bacterial growth (both negative and positive bacteria) compared to the uncoated glass slide.     

Stepwise Oxidation Mechanism of HVOF Sprayed NiCrAlY Coatings in Air

High velocity oxide fuel sprayed NiCrAlY coatings on the Superni 76 superalloy have been oxidized cyclically at 900 °C up to 200 cycles. Weight change measurements were taken after each cycle to obtain kinetics of the oxidation process. The surface and cross-section of oxidized samples have been examined by XRD, FESEM/EDS to characterize the corrosion products. The formation of Al₂O₃ at the surface as well as at the coating/scale interface as a sub-layer was observed. Other oxides such as Ni (Al, Cr)₂O₄ and Cr₂O₃ were also present above this Al₂O₃ sub-layer. An oxidation mechanism has been proposed for the oxidation of the coating for 200 cycles by correlating the results after different cycles of oxidation.     

Alginate-Coated Alginate-Polyethyleneimine Beads for Prolonged Release of Furosemide in Simulated Intestinal Fluid

Furosemide-loaded calcium alginate (ALG), calcium alginate-polyethyleneimine (ALG-PEI) and alginate-coated ALG-PEI (ALG-PEI-ALG) beads were prepared by ionotropic/polyelectrolyte complexation method to achieve controlled release of the drug. Effects of several formulation factors on the characteristics of the beads were investigated. Although variation in formulation factors did not influence the drug-loading efficiency (DLE) of ALG beads, rapid release of the drug in simulated intestinal fluid (SIF) could not be prevented. PEI treatment of ALG beads, however, prolonged the drug release considerably. Ionic interaction, as appeared from FTIR studies, between alginate and PEI led to the formation of polyelectrolyte complex membrane, the thickness of which was dependent on the conditions of PEI treatment as demonstrated by scanning electron microscopy (SEM). The membrane acted as a physical barrier to drug release from ALG-PEI beads. Alginate coating of ALG-PEI beads further prolonged the release of the drug by increasing membrane thickness and reducing swelling of the beads possibly by blocking the surface pores. Differential scanning calorimetry (DSC) study indicated that drug was not degraded by PEI treatment. The release data from ALG-PEI beads showed a good fit in power law expression, whereas the release data from ALG-PEI-ALG beads were found to fit in modified power law expression, and the mechanism of drug release changed from super case II transport to nearly Fickian transport, depending on the degree of gelation and formation of polyelectrolyte complex membrane.     

Rapidly solidified low-silver brazing filler alloy foils

A rapidly solidified (RS) low-silver brazing alloy with 50% saving in silver has been developed as a potential substitute for the conventional Ag 72% — Cu 28% eutectic alloy. Major applications are envisioned in the electronics and vacuum tube industries. The RS alloy possesses brazing characteristics better than its conventionally cast counterpart, and superior to the traditional silver-copper eutectic alloy.     

High-Temperature Exposure Studies of HVOF-Sprayed Cr<Subscript>3</Subscript>C<Subscript>2</Subscript>-25(NiCr)/(WC-Co) Coating

In this research, development of Cr₃C₂-25(NiCr) + 25%(WC-Co) composite coating was done and investigated. Cr₃C₂-25(NiCr) + 25%(WC-Co) composite powder [designated as HP2 powder] was prepared by mechanical mixing of [75Cr₃C₂-25(NiCr)] and [88WC-12Co] powders in the ratio of 75:25 by weight. The blended powders were used as feedstock to deposit composite coating on ASTM SA213-T22 substrate using High Velocity Oxy-Fuel (HVOF) spray process. High-temperature oxidation/corrosion behavior of the bare and coated boiler steels was investigated at 700 °C for 50 cycles in air, as well as, in Na₂SO₄-82%Fe₂(SO₄)₃ molten salt environment in the laboratory. Erosion-corrosion behavior was investigated in the actual boiler environment at 700 ± 10 °C under cyclic conditions for 1500 h. The weight-change technique was used to establish the kinetics of oxidation/corrosion/erosion-corrosion. X-ray diffraction, field emission-scanning electron microscopy/energy-dispersive spectroscopy (FE-SEM/EDS), and EDS elemental mapping techniques were used to analyze the exposed samples. The uncoated boiler steel suffered from a catastrophic degradation in the form of intense spalling of the scale in all the environments. The oxidation/corrosion/erosion-corrosion resistance of the HVOF-sprayed HP2 coating was found to be better in comparison with standalone Cr₃C₂-25(NiCr) coating. A simultaneous formation of protective phases might have contributed the best properties to the coating.     

Oxidation Studies on Base Metal,Weld Metal and HAZ Regions of TIG Weldment in 2.25 Cr–1Mo (T22) Boiler Tube Steel Under Cyclic Conditions

A weldment was made using the TIG welding process to weld together 2.25Cr–1Mo (T22) boiler tube steel. Oxidation studies were then conducted on different regions of the TIG weldment, i.e. base metal, weld metal and heat-affected zone (HAZ) specimens, by exposure to air at 900 °C under cyclic conditions. The thermogravimetric technique was used to study the kinetics of oxidation. Scanning electron microscopy/energy dispersive of X-ray (SEM/EDX) analysis and X-ray diffraction (XRD) techniques were used to analyse the oxidation products. The HAZ showed more weight gain than that of base metal and weld metal due to the formation of a scale that was low in Cr-rich oxide (as confirmed by EDX), with cracks and spallation.     

Hybrid analogs for the production of porous calcium phosphate scaffolds

A polymer–inorganic sol mixture has been used to develop interconnected and highly porous calcium phosphate networks. The inorganic sol was developed by reacting triethyl phosphite and calcium nitrate. The sol was directly added to an aqueous solution of PVA with molecular weights between 40,500 and 155,000 g/mol. This mixture was electrospun at a voltage of 20 kV to produce fibers, whose diameter was less than 1 μm. This electrospun structure was calcined at 600 °C obtain to a highly interconnected sub-micron fibrous network (fiber size ∼ 200 nm) of calcium phosphate. The crystal size is on the order of 30 nm. Micropores could be introduced in each of the fibers by controlling the polymer molecular weight and the sol volume fraction. Such structures can have many potential uses in the repair and treatment of bone defects and in drug delivery.     

Surface engineering analysis of detonation-gun sprayed Cr3C2–NiCr coating under high-temperature oxidation and oxidation–erosion environments

Detonation-gun (D-gun) spray technology is a novel coating deposition process which is capable of achieving very high gas and particle velocities approaching 4–5 times the speed of sound. This process provides the possibility of producing high hardness coatings with strong adherence. In the present study, this technique has been used to deposit Cr₃C₂–NiCr coating on T22 boiler steel. Investigations on the behaviour of this coating subjected to high-temperature oxidation in air and oxidation–erosion in actual boiler environment at 700 ± 10 °C under cyclic conditions have been carried out. The weight change technique was used to establish the kinetics of oxidation. X-ray diffraction (XRD), field emission-scanning electron microscopy/energy-dispersive spectroscopy (FE-SEM/EDS) and EDS elemental mapping techniques were used to analyse the oxidation/oxidation–erosion products. The uncoated boiler steel suffered from a catastrophic degradation in the form of intense spalling of the scale in both the environments. The Cr₃C₂–NiCr coating showed good adherence to the boiler steel during the exposures with no tendency for spallation of its oxide scale.