Influences of High Calcination Temperature on Densification and Magnetic Properties of Low-Temperature-Fired NiCuZn Ferrites
Traditional low-temperature-fired NiCuZn ferrites (900 °C sintered) were generally prepared at relatively low calcination temperatures to increase the activity of the calcined powders and promote sintering. However, in this study, we changed the calcination temperature from 700 °C to 1000 °C to investigate the influences of high calcination temperature on the densification characteristic and magnetic properties of the low-temperature-fired NiCuZn ferrites. It was found that although a high calcination temperature decreased the activity of the calcined powder, the NiCuZn ferrite could attain a higher sintered density with an adequate sintering aid. Furthermore, a uniform microstructure with small average grain size was obtained for the sample calcined at 1000 °C with 1 wt% Bi2O3 sintering aid. It also displayed high performances on Q-factor and permeability. Hence, choosing a high calcination temperature and adding more sintering aid was also an option for obtaining high performance and low-temperature-fired NiCuZn ferrites.
Effects of Bi2O3 addition on the microstructure and electromagnetic properties of NiCuZn ferrites
Effects of Bi2O3 addition on the microstructural development and magnetic properties of NiCuZn ferrites were studied. For low temperature sintering (<900 °C), 0.1–1.0 wt % of Bi2O3 was added to the NiCuZn ferrites. The grain size and bulk density gradually increased with the increase in the Bi2O3 content. Above 0.5 wt % Bi2O3, abnormal grain growth was observed. The specimen with 0.25 wt % Bi2O3 showed the highest initial permeability with good quality factors and a uniform microstructure. However, the specimen with greater than 0.5 wt % Bi2O3 demonstrated abnormal grain growth with lower initial permeabilities and poor quality factors.
Inhibition of Mild Steel Corrosion Using L-tryptophan and Synergistic Surfactant Additives
The corrosion inhibition characteristics of nitrogen containing amino acid L-tryptophan on mild steel in 0.1 M HCl solution, in the temperature range of 30-50 o C, was studied by weight loss and potentiodynamic polarization measurements. L-tryptophan significantly reduces the corrosion rates of mild steel; the maximum inhibition efficiency being 83% at 50 o C in presence of inhibitor concentration of 500 ppm. The effect of the addition of very small concentrations of anionic surfactant, sodium dodecyl sulfate (SDS), and of cationic surfactant, cetyl trimethyl ammonium bromide (CTAB), on the corrosion inhibition behavior of L-tryptophan was also studied. The inhibition efficiency (IE) of L-tryptophan significantly improved in presence of both surfactants. The effect of SDS and CTAB on the corrosion inhibition behavior of L-tryptophan appears to be synergistic in nature, the values of synergism parameter being greater than unity. The adsorption of inhibitors on mild steel surface obeyed Langmuir’s adsorption isotherm. The calculated thermodynamic parameters for adsorption reveal a strong interaction between the inhibitors and the mild steel surface. The results obtained by electrochemical studies are consistent with the results of the weight loss measurements. L-tryptophan acts more anodic than cathodic inhibitor.