No abstract

Lithium mixed sodium tntltanates with 0.3, 0.5 and 1.0 M percentage of Li z C0 3 (general formula Naz-xLixTi 3 0 7 ) have prepared by a high temperature solid-state reaction route. EPR analysis, high temperature range (473-773 K) and variable frequency range (100 Hz-1 MHz) ac conductivity measurements were carried out on prepared sample. The lithium ions are accommodated with the sodium ions in the interlayer space. The EPR specta of lithium mixed sodium Trititanates confirm the partial reduction of Ti 4 + ions to Ti 3 +. Four distinct regions have identified in the LnaT versus 1,0001T plots. Various conduction mechanisms which dependence on concentration, frequency and temperature are reported in this paper for lithium mixed layered sodium Trititanates. The dilation of interlayer space has further been proposed to occur due to inclusion of lithium ions in the interlayer space. The conductivity increases as the concentration of lithium increases. The increase of ionic conductivity in these compounds is due to accommodation of lithium ions with sodium ions in interlayer space.

The manganese doped layered ceramic samples (Na 1·9 Li 0·1 )Ti 3 O 7 : XMn(0·01≤X≤0·1) have been prepared using high temperature solid state reaction. The room temperature electron paramagnetic resonance (EPR) investigations exhibit that at lower percentage of doping the substitution of manganese ions occur as Mn 3+ at Ti 4+ sites, whereas for higher percentage of doping Mn 2+ ions occupy the two different interlayer sodium/lithium sites. In both cases, the charge compensation mechanism should operate to maintain the overall charge neutrality of the lattice. The manganese doped derivatives of layered Na 1·9 Li 0·1 Ti 3 O 7 (SLT) ceramics have been investigated through frequency dependence dielectric spectroscopy in this work. The results indicate that the dielectric losses in these ceramics are the collective contribution of electric conduction, dipole orientation and space charge polarization. Smeared peaks in temperature dependence of permittivity plots suggest diffuse nature of high temperature ferroelectric phase transition. The light manganese doping in SLT enhances the dielectric constant. However, manganese doping decreases dielectric loss due to inhibition of domain wall motion, enhances electronhopping conduction, and impedes the interlayer ionic conduction as well. Manganese doping also gives rise to contraction of interlayer space.

Concrete forms a major component of the national infrastructure. Corrosion of reinforced steels embedded in concrete has recently received wide attention in R&D programmes. Different cases have been reported showing failures of concrete structures which means huge loss. An attempt has been made to identify the different factors affecting the corrosion of embedded steel. Comparative evaluation of different protective schemes use of additives in concrete admixtures and the application of the cathodic protection technique has been discussed.

Solar selective coatings are designed and formulated for effective collection and retention of solar energy. Several types of coatings can be utilized for economical collection of solar energy, the most common and simplest will be ordinary non-glass, heat resistant black paint. The coatings may be moderately selective or non-selective absorbers, consisting of organic or inorganic matt black paints. These are easiest to apply and the least expensive of all collector coatings. In this category other types are ceramic and organic enamels and chemical or electrochemical metal conversion coatings. An impending energy crisis has already aroused interest and scientific pursuit in the field. An analysis of the state-of-the-art in solar selective coatings was felt necessary at this time.