G.A.EL-Mahdy (Chemistry Dept.
,
Faculty of Science
,
Helwan University
,
Helwan
,
Cairo
,
EgyptS-S.MahmoudChemistry Dept.
,
University College for Women
,
Ain-Shams University
,
Helopolis
,
Cairo
,
Egypt)
材料科学技术（英文）
The effect of fluoride ions on the formation and dissolution behaviour of anodic oxide films on Ti has been investigated in acidic fluoride media (pH=1) using impedance and galvanostatic techniques. A5 the fluoride ion concentration and temperature increase the rate of oxide film formation decreases while the dissolution process increases. oxide film formed at high tem-perature and formation voltage was found to contain more defect sites in the film than that formed at a lower one. Activation energies are calculated during the oxide film formation and dissolution and found to be 20.76 and 28.72 kJ/mol, respectively. Formation rate and reciprocal capacitance data are reported as a function of polarizing current density. Values are recorded for the electrolytic parameters A and B. Potentiostatic curves are derived from the galvanostatic results.
关键词:
I.M.El-Anwar and I.Z.Selim(Physical Chemistry Dept.
,
National Research Center
,
Dokki
,
Cairo
,
Egypt)( To whom correspondence should be addressed)(To whom correspondence should be addressed)A.A.Foad(Faculty of Science
,
Helwan University
,
Helwan
,
Cairo
,
Egyp
材料科学技术（英文）
The dielectric constant e' and dielectric loss e" of several mixtures of propionaldehyde-polyethylene glycol (system 1) and benzaldehyde-polyethylene glycol (system II) have been measured within the frequency band 105-107 Hz and the temperature range 20-50℃. The dielectric behaviour is discussed. on the other hand, the dielectric relaxation time T. activation energy △He, and entorpy change △Se for the dielectric relaxation as well as activation energy of viscous flow △Hv are calculated for the same temperature range. It is suggested that the observed increase in T values with increas.ng glycol content is due to an increase in the hydrogen bonding in the aggregates or clusters which would be formed between the carbonyl group of the aldehyde and the hydrogen atoms from the glycot molecules. In addition, the higher values of T, △He, and △Se in case of system (II) than that in case of system (I) may be due to the greater volume of the aggregates and the stronger dipole-dipole forces in system (II) compared with those in system (I).
关键词:
