M. Noor-A-Alam

Correlation between microstructure, electrical and optical properties of nanocrystalline NiFe1.925Dy0.075O4 thin films

Dysprosium-doped nickel-ferrite (NiFe1.925Dy0.075O4) thin films were fabricated using sputter-deposition using a stoichiometric bulk target prepared by the solid state chemical reaction. The structural, electrical and optical properties of NiFe1.925Dy0.075O4 thin films were studied in detail. The grain-size (L) and lattice-expansion effects are significant on the electrical and optical properties of NiFe1.925Dy0.075O4 films. Air annealing (Ta) at 450–1000 °C results in the formation of nanocrystalline NiFe1.925Dy0.075O4 films, which crystallize in the inverse spinel structure, with L = 5–40 nm. The lattice constant of NiFe1.925Dy0.075O4 increases compared NiFe2O4 due to Dy-doping. Electrical conductivity of NiFe1.925Dy0.075O4 films (at 300 K) decreases from 1.07 Ω−1 m−1 to 3.9 × 10−3 Ω−1 m−1 with increasing Ta (450 to 1000 °C). Conductivity was found to decrease exponentially with decreasing the temperature from 300 K to 120 K indicating the characteristic semiconducting nature of all the films. Band gap increases from 3.17 to 4.08 eV for NiFe1.925Dy0.075O4 films with increasing Ta from 450 to 1000 °C. A correlation between grain-size, electrical conductivity and optical band gap in nanocrystalline NiFe1.925Dy0.075O4 films is established.

Growth, Structure, and Thermal Conductivity of Yttria-Stabilized Hafnia Thin Films

Yttria-stabilized hafnia (YSH) films of 90 nm thickness have been produced using sputter-deposition by varying the growth temperature (T(s)) from room-temperature (RT) to 400 °C. The effect of T(s) on the structure, morphology, and thermal conductivity of YSH films has been investigated. Structural studies indicate that YSH films crystallize in the cubic phase. The lattice constant decreases from 5.15 to 5.10 Å with increasing T(s). The average grain size (L) increases with increasing T(s); L-T(s) relationship indicates the thermally activated process of the crystallization of YSH films. The analyses indicate a critical temperature to promote nanocrystalline, cubic YSH films is 300 °C, which is higher compare to that of pure monoclinic HfO(2) films. Compared to pure nanocrystalline hafnia, the addition of yttria lowers the effective thermal conductivity. The effect of grain size on thermal conductivity is also explored.

Studies on the Mechanical Properties of Gelatin and Its Blends with Vinyltrimethoxysilane: Effect of Gamma Radiation

Gelatin films were prepared by casting. Tensile strength (TS), elongation at break (Eb) and tensile modulus (TM) of the gelatin films were found to be 56 MPa, 6.1% and 1.14 GPa, respectively. Effect of gamma radiation (Co-60) on the mechanical properties of the gelatin films was studied. Vinyltrimethoxysilane (VTMS) was added to the gelatin during casting varying 1–7% by weight and found to increase the TS and TM significantly. Then the films were irradiated and found further increase of TS and TM. Water uptake of the gelatin films and 5% VTMS containing gelatin films were also evaluated.

Studies of the Physico-Mechanical, Interfacial, and Degradation Properties of Jute Fabrics/Melamine Composites

Jute fabrics/melamine composites (20% fiber) were prepared by compression molding. Mechanical properties of the composites were evaluated. Mechanical properties of starch-treated jute/melamine composites, including tensile strength (31%), bending strength (29%), tensile modulus (23%), bending modulus (25%), impact strength (113%), and hardness (4%), inproved significantly over the untreated composite. Fracture surfaces of untreated and treated composites were studied by scanning electron microscopy (SEM) and supported poorer fiber matrix adhesion for the untreated composite than that of the treated composite. Water uptake and soil degradation tests of untreated and treated composites were also performed.

Enhanced stability of hafnia based coatings in a hot gas environment

Yttria stabilized hafnia (YSH) coatings have been fabricated by magnetron sputtering, a physical vapor deposition (PVD) method. Coatings of a mixed composition of hafnia (HfO2) and zirconia (ZrO2) (YSHZ) stabilized by yttria (Y2O3) were also fabricated in order to compare and contrast the resulting properties. The composition of the material was varied by varying the ratio of HfO2 and ZrO2 (4:1, 2:1, 1:1, 1:2 and 1:4) while keeping the Y2O3 stabilizer content constant at 7.5 mol%. Thermal and chemical stability along with the durability of the YSH and YSHZ coatings were evaluated by exposing the coatings to hot gases in a combustor rig. A nanoindentation technique was used to evaluate the mechanical properties. A diamond tipped, sharp nanoindenter with known geometry and mechanical properties was forced into the sample while both the force and indentation depth were recorded. Hardness (H) and Youngs modulus were estimated for the YSH and YSHZ coatings. Atomic force microscopy was utilized to provide imagery of the indentation area on the sample surface. Residual stress analysis was performed using X-ray diffraction (XRD). The results from nano-indentation indicate that the YSH sample possesses values of hardness and Youngs modulus as high as 18 GPa and 220 GPa, respectively. The residual stress estimated using XRD indicates very high compressive stress within the coatings. The stability and durability tests demonstrate the enhanced stability of YSH coatings in a hot gas environment created by burning natural gas with oxygen.