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:
S.A.El-Henawii(Faculty of Science
,
Helwan University
,
Cairo
,
Egypt)
材料科学技术（英文）
The variation of the dielectric constant e' and the dielectric loss e" of polyesteramide, alkyd polyesteramide and alkyd varnish dry films were measured within the frequency range from 105 to 107 Hz and the temperature range from 20 to 50℃. The varnish films were subjected to accelerated ageing by heating at 110℃ for diferent durations. The efect of the accelerated ageing on e' and e" were measured. The activation energy and the entropy change of dielectric relaxation for the dry films before and after ageing were also calculated. All the results obtained were recorded and discussed in correlation with the molecular structure of the investigated varnishes.
关键词:
S.A.El-Henawii(Faculty of Science
,
Helwan University
,
Cairo
,
Egypt)
材料科学技术（英文）
The dielectric constant, the dielectric loss and the power factor of three types of resins namely polyesteramide, alkyd polyesteramide and alkyd resins were measured with in the frequency range of 105 to 107 Hz and the temperature range of 20 to 50℃. The activation energy of dielectric relaxation and the entropy changes were also calculated using the usual rate equation. The results obtained are recorded and discussed.
关键词:
