Satish C. Gupta

Water repellent porous silica films by sol-gel dip coating method

The wetting of solid surfaces by water droplets is ubiquitous in our daily lives as well as in industrial processes. In the present research work, water repellent porous silica films are prepared on glass substrate at room temperature by sol-gel process. The coating sol was prepared by keeping the molar ratio of methyltriethoxysilane (MTES), methanol (MeOH), water (H(2)O) constant at 1:12.90:4.74, respectively, with 2M NH(4)OH throughout the experiments and the molar ratio (M) of MTES/Ph-TMS was varied from 0 to 0.22. A simple dip coating technique is adopted to coat silica films on the glass substrates. The static water contact angle as high as 164° and water sliding angle as low as 4° was obtained for silica film prepared from M=0.22. The surface morphological studies of the prepared silica film showed the porous structure with pore sizes typically ranging from 200nm to 1.3μm. The superhydrophobic silica films prepared from M=0.22 retained their superhydrophobicity up to a temperature of 285°C and above this temperature the films became superhydrophilic. The porous and water repellent silica films are prepared by proper alteration of the Ph-TMS in the coating solution. The prepared silica films were characterized by surface profilometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform Infrared (FT-IR) spectroscopy, humidity tests, chemical aging tests, static and dynamic water contact angle measurements.

Effect of concentration of trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) silylating agents on surface free energy of silica aerogels

The surface free energy of a solid determines its surface and interfacial behavior in processes like wetting and adhesion which is crucial for silica aerogels in case of organic liquid absorption and transportation of chemicals at nano-scale for biotechnological applications. Here, we have demonstrated that the surface free energy of aerogels can be tuned in wide range from 5.5892 to 0.3073 mJ/m(2) by modifying their surface using TMCS and HMDZ silylating reagents. The alcogels were prepared by two step acid-base catalyzed process where the molar ratio of precursors Tetraethoxysilane (TEOS):Methanol (MeOH):Oxalic acid:NH(4)OH:NH(4)F was kept at optimal value of 1:2.7:0.18×10(-4):0.02:0.22×10(-3), respectively. To modify gel surfaces, TMCS and HMDZ concentration have been varied from 3% to 12% and such alcogels were dried at ambient pressure. It is observed from FTIR for aerogels that increase in concentration of silylating reagent resulted increase in hydrophobicity. This leads to increase in contact angle for water from 123° to 155° but leads to decrease in surface free energy from 5.5892 to 0.3073 mJ/m(2). As there is not direct method, we have used Neumanns equation of state to estimate surface energy of aerogels.

Shock-induced vaporization of anhydrite and global cooling from the K/T impact

Discovery of abundant anhydrite (CaSO_4) and gypsum (CaSO_4•2H_2O) in the otherwise carbonate sediment comprising the upper 3 km thick layer of the target rock at the K/T impact site has prompted research on these minerals. Evaluation of the severity of the proposed extinction mechanism involving injection of impact-generated SO_2 and SO_3 into the stratosphere entails determination of criteria for shock-induced vaporization of these minerals. In the present work we present new data on the vaporization criteria of anhydrite. These are based on the reanalysis of the shock wave experiments of Yang and Ahrens [Earth Planet. Sci. Lett. 156 (1998) 125–140], conducted on material with 30% porosity, in which the shock- (fully or partially) vaporized sample interacts with an overlying LiF window. The velocity histories, monitored using a velocity interferometer, are compared with numerical simulations employing an improved equation of state for porous anhydrite and its vaporization products. We also employ the ‘entropy criterion’ for vaporization of material under shock compression. The values of the entropies of incipient and complete vaporization for anhydrite are determined to be 1.65±0.12 and 3.17±0.12 kJ (kg K)^(−1), respectively, and the corresponding pressures for incipient and the complete vaporization along the Hugoniot for the solid material are 32.5±2.5 and 122±13 GPa, respectively as compared with 81±7 and 155±13 GPa previously reported by Yang and Ahrens. Along with these criteria, the use of the recent estimate of diameter (100 km) for the Chicxulub transient crater [O’Keefe and Ahrens, J. Geophys. Res. 104 (E11) (1999) 27091–27104; Morgan et al., Nature 390 (1997) 472–476] that is smaller than previously assumed, along with Ivanov et al.’s [Geol. Soc. Am. Spec. Pap. 307 (1996) 125–142] 2-D hydrodynamic simulation to determine the shock attenuation and Pope et al.’s [J. Geophys. Res., 102 (E9) (1997) 21645–21664] radiative transfer model, yields the maximum decrease in the average global surface temperature of 12–19 K for 9.0–9.5 years at the K/T boundary. Thus, the global cooling is inferred to have been less severe than that indicated by the upper limit of the range of 5–31 K decrease lasting for ∼12 years calculated by Pope et al. Because ambient global surface temperatures at K/T time were ∼18–20°C warmer than present values, this cooling event produced cold, but not freezing conditions at the Earth’s surface.

Battery powered tabletop pulsed neutron source based on a sealed miniature plasma focus device

The development of a novel and portable tabletop pulsed neutron source is presented. It is a battery powered neutron tube based on a miniature plasma focus (PF) device having all metal-sealed components. The tube, fuelled with deuterium gas, generates neutrons because of D–D fusion reactions. The inner diameter and the length of the tube are 3.4 cm and 8 cm, respectively. A single capacitor (200 J, 4.0 µF, 10 nH) of compact size (17 cm × 15 cm × 13 cm, 6.5 kg) is used as the energy driver. A power supply system charges the capacitor to 10 kV in 10 s and also provides a 30 kV trigger pulse to the spark gap. An input of 24 V dc (7.5 A) to the power supply system is provided by two rechargeable batteries (each 12 V, 7.5 A, 20 h). The device has produced neutrons for 150 shots within a period of 120 days in a very reliable manner without purging the deuterium gas between the shots. For the first 50 shots, the average yield is (1.6 ± 0.3) × 106 neutrons/shot in 4π sr with a pulse width of 23.4 ± 3.3 ns. The estimated neutron energy is 2.47 ± 0.22 MeV. The neutron production reduces slowly and reaches the detection threshold value of 3 × 105 neutrons/shot towards the last shots. The device produces neutrons in a similar manner on evacuation and refilling. The height of the mounted PF tube with the capacitor and the spark gap is 35 cm. The complete setup comprising the capacitor with spark gap, the PF tube, the power supply system with two batteries and the control panel weighs only 23 kg.

Durability and restoring of superhydrophobic properties in silica-based coatings

The durability and restorable properties of superhydrophobicity are a most important issue essential for utilization of superhydrophobic materials in industrial and domestic fields. In this work, we have focused on the sol-gel dip coating synthesis, durability, and restoring properties of a superhydrophobic surface composed of spherical silica particles with low energy free surface successfully achieved on the surface of glass substrates. The water contact angle (WCA) of the as-prepared superhydrophobic coatings reached as high as 170±1° (WCA=170±1°) and the sliding angle was 3±1° (WSA=3±1°). The behavior of wettability on superhydrophobic coating surface under various external disturbances including outdoor environments, heat, and mild acidic condition is investigated. It is shown in particular that degradation and repairing of surface methyl groups between two such surfaces leads to a fully restorable coating surface by the surface modification with trimethylchlorosilane (TMCS) at room temperature. The coating also holds good thermal stability; it holds superhydrophobicity up to 550 °C and gets degrade into superhydrophilicity above 600 °C without deforming surface morphology. The results confirm the durability of the silica coating under different external disturbances and sol-gel dip coating method and restoring property provide the best solution to fabricate superhydrophobic silica coating surface with extended durability at low cost.

The equation of state and structural stability of titanium obtained using the linear muffin-tin orbital band-structure method

Room-temperature isotherms of titanium in HCP and omega -phases are calculated by the first-principles linear muffin-tin orbital energy band method. Comparison with experimental data shows excellent agreement. Structural phase stability analysis by the Andersen force theorem shows that the omega -phase is the lowest-energy phase at 0 K and normal volume. The possibility that the s to d electronic transition is the cause of shock discontinuity at 17.5 GPa.

Shock temperature in calcite (CaCO3) at 95–160 GPa

The temperatures induced in crystalline calcite (CaCO3) upon planar shock compression (95^160 GPa) are reported from two-stage light gas gun experiments. Temperatures of 3300^5400 K are obtained byfitting six-channel optical pyrometer radiances in the 450^900 nm range to the Planck gray-body radiation law. Thermodynamic calculations demonstrate that these temperatures are some 400^1350 K lower than expected for vibronic excitations of the lattice with a 3R/mole-atom specific heat (R is gas constant). The temperature deficit along the Hugoniot is larger than that expected from onlymelting. In addition to melting, it appears likelythat shock-induced decomposition of calcite occurs behind the shock front. We modeled disproportionation of calcite into CaO (solid) plus CO2 (gas). For temperature calculations, specific heat at constant volume for 1 mole of CO2 is taken to be 6.7R as compared to 9R in the solid state; whereas a mole of calcite and a mole of CaO have their solid state values 15R and 6R, respectively. Calculations suggest that the calcite decomposes to CaO and CO2 at V110 8 10 GPa along the Hugoniot. Recent reanalysis of earlier VISAR measurements of particle velocity profiles [1] indicates that calcite shocked to 18 GPa undergoes disproportionation at much lower pressures upon isentropic expansion. = 2002 Elsevier Science B.V. All rights reserved.

Structural stability of hafnium under pressure

A theoretical analysis on the structural stability of HF under pressure, using the linear muffin-tin orbital method in conjunction with the Andersen force theorem, predicts a new phase transition to a BCC phase at high pressures, in agreement with recent diamond cell experiments.

Shock‐induced amorphization of q‐GeO2

Polycrystalline samples of the α‐quartz phase of GeO2 (q‐GeO2), recovered from peak shock compressions of 5, 6.8, and 10 GPa, have been examined by x‐ray diffraction, thermoluminescence, and Raman techniques. The measurements show that q‐GeO2 irreversibly amorphizes above 6.8 GPa. The estimates of the shear band temperature suggest that the mechanism of shock‐induced amorphization in q‐GeO2 is a solid‐solid one, in contrast to that in SiO2 quartz which has both solid‐solid and fusion‐quenched components.

HIGH pressure structural investigations of zirconium using LMTO method

Abstract The structural energy differences have been calculated for zirconium as a function of pressure at zero temperature using the Andersen force theorem and the linear muffin tin orbital method. The structures included are the following: α (hcp), the room temperature room pressure phase, ω- a three atom simple hexagonal, bcc and fcc. Our calculations show that the bcc structure would become energetically most favourable above 11 GPa. This results is in agreement with well known correlation between the crystal structure and the d-electron population in transition metals at normal volume. The diamond anvil cell based high pressure x-ray diffraction experiments are in progress to verify this result.