Effect of preparation pH on pore structure of silica gels

Surface characterization of silica gels prepared at different gelation pH from water glass and sulphuric acid were made by argon adsorption at 77 K using continuous volumetric method. While microporous silica gels prepared in the pH range of 1–3 had BET surface areas of 504–571 m² g^–1, total pore volumes of 0.26–0.31 cm³ g^–1 and micropore volumes of 0.16–0.23 cm³ g^–1, mesoporous silica gels prepared in the pH range of 3.36–0.65 had BET surface areas of 374–530 m² g^–1 and pore volumes of 0.61–0.79 cm³ g^–1.     

Methods of humidity determination Part II: Determination of material humidity

Part II covers the most common methods of measuring the humidity of solid material. State of water near solid surfaces, gravimetric measurement of material humidity, measurement of water sorption isotherms, chemical methods for determination of water content, measurement of material humidity via the gas phase, standardisation, cosmonautical observations are reviewed.     

The mechanical response of core-shell structures for nanoporous metallic materials

Nanoporous gold (NP-Au) exhibits microscale plasticity, but macroscopically fails in a relatively brittle manner. This current study suggests that a core-shell structure can increase both ductility and strength of NP-Au. A core Au foam structure was created using conventional dealloying methods with average ligament size of 60?nm. Nickel was then electroplated on to the NP-Au with layer thicknesses ranging from 2.5?nm to 25?nm. Nanoindentation demonstrated a significant increase in the hardness of the coated Np-Au, to about five times of that of the pure Np-Au, and a decrease in creep by increasing the thickness of the coated Ni layer. Molecular dynamics simulations of Au–Ni ligaments show the same trend of strengthening behavior with increasing Ni thickness suggesting that the strengthening mechanisms of the Np-Au are comparable to those for fcc nano ligaments. The simulations demonstrate two different strengthening mechanisms with the increased activity of the twins in plated Au–Ni ligaments, which leads to more ductile behavior, as opposing to the monolithic Au ligaments where nucleation of dislocations govern the plasticity during loading.     

Interface states and impurities in MOS structures with very thin tunneling barriers

Electron tunneling spectroscopy was used to investigate MOS junctions with very thin silicon oxide or silicon oxynitride layers (2–5 nm) as tunneling barriers. For the tunneling measurements at 4.2 K highly degenerate P-doped (3×10²⁰ cm^-3) Si substrates, oxidized in dry oxygen at 600°C were used. Silicon oxynitride layers were prepared by plasma nitridation in an NH₃ discharge. As gate electrodes evaporated films of Al, Au or Pb were utilized. Changes in the tunneling conductivity were attributed to changes in the density of interface states, caused by hydrogen annealing or by high field stress. The results indicate a correlation between the generation of interface states and the removal of Si-H configurations. Vibrational modes of phonons, dopants and impurities were detected by inelastic electron tunneling spectroscopy.     

Sorption and diffusion of water vapour on edible films

Two types of films consisting of sodium salt of carboxymethyl cellulose (NaCMC) and hydroxypropyl cellulose (HPC) as film forming materials and glycerin as plasticizer were prepared, characterized and their water vapour sorption properties were determined. The water sorption isotherms of the films were measured using a magnetic suspension balance. Results show that diffusion of water vapour in NaCMC based film is faster than that in HPC based films, due to the heterogeneous structure and larger pore dimensions of the NaCMC films.     

Local thermal conductivity of polycrystalline AlN ceramics measured by scanning thermal microscopy and complementary scanning electron microscopy techniques

The local thermal conductivity of polycrystalline aluminum nitride (AlN) ceramics is measured and imaged by using a scanning thermal microscope (SThM) and complementary scanning electron microscope (SEM) based techniques at room temperature. The quantitative thermal conductivity for the AlN sample is gained by using a SThM with a spatial resolution of sub-micrometer scale through using the 3ω method. A thermal conductivity of 308 W/m·K within grains corresponding to that of high-purity single crystal AlN is obtained. The slight differences in thermal conduction between the adjacent grains are found to result from crystallographic misorientations, as demonstrated in the electron backscattered diffraction. A much lower thermal conductivity at the grain boundary is due to impurities and defects enriched in these sites, as indicated by energy dispersive X-ray spectroscopy.     

Scanning near field thermal microscopy on a micromachined thin membrane

A resistive probe based scanning thermal microscope (SThM) has been used to perform complementary near field thermal measurements on the surface of a thin semiconductor membrane. This thin structure is part of a micromachined thermal rf power sensor and includes an integrated resistive heater used as an absorbing element for the input power. The resulting 2D surface temperature distribution and the 2D thermal wave propagation characteristic were determined. Considering the thermal wave behaviour at near field conditions, the local thermal conductivity of the thin membrane and the surrounding bulk material was investigated by usage of the 3ω-method.     

Inelastic electron tunneling spectroscopy on MOS structures with very thin oxide films

Inelastic electron tunneling spectroscopy at 4.2 K was used to investigate the defect structure of MOS capacitors with very thin SiO₂ films. Samples were degeneratelyP-andB-doped Si substrates, oxidized in O₂ at 600°C and provided with evaporated Pb, Au, In, Al or Mg electrodes. The observed peaks in the second derivative of theI-U characteristic were assigned to the excitation of phonons and of vibrational modes of the dopants and impurities. The results were found to correlate with infrared data. In addition, a distinct effect of Si/SiO₂ interface states on the characteristic was found.     

The effect of zinc stearate on thermal degradation of paraffin wax

In this research, the effects of zinc stearate addition on paraffin wax degradation were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The apparent activation energies of wax decomposition in nitrogen and air atmospheres were determined as 76 and 37 kJ mol⁻¹, respectively applying Kissinger method to TG data. The degradation rate constants of paraffin containing zinc stearate (0.1–0.5%) were found to be almost two times greater than that of paraffin only in air atmosphere. However, zinc stearate did not affect the rate constants in nitrogen significantly.