S.M.Morsy (Metallurgy Dept. Nuclear Research Center
,
Atomic Energy Authority
,
Cairo
,
Egypt) I.Z.Selim (Physical Chemistry Dept.
,
National Research Center
,
Dokki
,
Cairo
,
Egypt)S. H. Tantawi (Building Research Institute
,
Dokki
,
Cairo
,
Egypt)
材料科学技术（英文）
Electrochemical techniques of the corrosion measurements of reinforcing steeI in concrete have been evaluated. These techniques include half-cell potential measurements, impressed voltage method, impressed current method and potentiostatic polarization technique. The results of corrosion behaviour of the steel in both 5%NaCl and 5%MgSO4 show that each electrochemical technique provides some information about the condition of the steel bar or the corrosivity of the environment being evaluated, yet none provides a complete data regarding the corrosion resistance of reinforcing steel in aggressive media
关键词:
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:
S.H. Tantawi (Building Research Institute
,
Dokki
,
Cairo
,
Egypt)I.Z.Selim (Physical Chemistry Dept.
,
National Research Center
,
Dokki
,
Cairo
,
Egypt (To whom correspondence should be addressed)
材料科学技术（英文）
The use of a natural white juice, taken from magrabe banana stem, as concrete admixture to improve mechanical and physicrvchemical properties of concrete has been studied. The compressive strength, bulk density the free lime liberated during hydration and the combined water content were determined. The results indicate that the admixture acts as a retarder in most cases and as accelerator in some ones. Also, the admixture effect on the corrosion resistance of the reinforcing steel against surrounding aggressive media has been investigated using galvanostatic polarization technique. The addition of 0.2% admixture leads to the more inhibition of the steel
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:
A .A.Khedr
,
I.Z.Selim
,
K.M.El-Sobki and O.S.Shehata(Physical Chemistry Dept.
,
National Research Centre
,
Dokki
,
Cairo
,
Egypt)
材料科学技术（英文）
Electrochemical behaviour of stainless steel type 430 in acidic solutions of methanol, ethanol and in their binary mixtures with water (from 0 to 100% alcohol) at 25℃ has been studied. using potentiostatic poIarization technique and weight loss method. It was found that the corrosion rate of the metal was affected by the physico-chemical properties of the media such as, viscosity, state of solvation, molar volume contraction, proton availability and dielectric constant, it was demonstrated from the potentiostatic study that the active passive transition strongly depended on the concentration of the acid, and on the water content of the media.
关键词:
A.F.Waheed and H.M.Soliman(Dept. of Metallurgy
,
Nuclear Research Center
,
Atomic Energy Authority
,
Cairo
,
Egypt)
材料科学技术（英文）
The beginning of failure of a (ZrO2-7%Y2O3)/(Ni-22%Co-17%Cr-12.5%Al-0.6%Y) duplex andgraded coating systems on lnconel 617 and IN738LC in burner rig tests has been characterized.The test conditions are 40 s heating up to 75O℃ substrate temperature followed by 80 s aircooling. Failure is considered at the appearance of the first bright spot during heating period.Stresses due to thermal expansion mismatch strains on cooling are the probable cause of life-limiting in this conditions of testing.
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:
I.M.EI-Anwar (National Research Center
,
Dokki
,
Cairo
,
Egypt)S.A.El-Henawii (Faculty of Science
,
Helwan University Egypt)
材料科学技术（英文）
Fatty acid esters have been prepared by reacting the acid C18 with polyethylene glycols having varying numbers of Oxythylene units (4~88 units) by the direct eSterification reaction method.Surface and interfacial tensions are studied at various experimental conditions, including, concentration, temperature, and chemical constitution of the surfactants. Critical micelle concentrations (CMC), surface excess Г and residual area occupied by each surface active agent molecule A have been calculated using Gibb's equation. CMC values range from 10 to 55x10-5 mole/L for all studied agents, while the residual area occupied by each molecule varies from 0.6 to 1.5 nm2. Variation of CMC of some of these agents with temperature have been also examined and data obtained are used to calculate the heat of micellization △Hm and the entropy change during micellization △Sm. Values of △Hm varies from 14.63 kJ/mole to 2.717 kJ/mole depending on the chemical constitution of the agent under consideration. The apparent dipole moments μ of three surfactants were measured following the Headstrand's method. Values of μ are 3.24, 3.14 and 3.02 D for stearates. oleates. and linoleates adducts with polyethylene glycol (1000).
关键词:
H.M.Soliman
,
K.E.Mohamed
,
M.E.Abd El-Azim and F.H.Hammad(Metallurgy Dept.
,
Atomic Energy Authority
,
Cairo
,
Egypt)
材料科学技术（英文）
Low and medium carbon steels were aluminized by the pack aluminizing technique using halideactivated pure-Al and Fe-Al packs. The effect of mixture composition, aluminizing temperatureand time and C content of the steel substrate on the structure and thickness of the aluminidelayer, and on the oxidation resistance was investigated. The optimum oxidation resistance canbe achieved with a low carbon steel substrate when the intermetallic phases Fe3Al and FeAlform the surface of the aluminide layer. In this case, the Al concentration at the surface of thealuminide coating is at least ≥15 wt pct. Formation of high Al concentration phases (FeAl3 andFe2Al5) during aluminizing should be avoided as they tend to embrittle the aluminide layer andreduce its oxidation resistance.
关键词:
Z.M.Hanafi
,
F.M.Ismai and M.Sb.Khalil (Inorganic Chemistry Dept.
,
National Research Centre
,
Dokki
,
Cairo
,
Egypt)
材料科学技术（英文）
Infrared absorption spectra of orange, black and transferred Sb2S3 samples have been Studied in the spectral range 200~4000cm-1. The pronounced difference between the different samples is the appearance of excess sulphur present in the orange and transferred samples except those of transferred at 543 K and the black Sb2S3. The change of sharpness of some IR peaks reveals the amorphous/crystalline change. The effect of the degree of crystallinity and stoichiometry on the energy gap values was investigated using optical method. The obtained dielectric parameters ε'and ε" of the different samples are thoroughly afFected by the degree of cryStallinity and smoothly affected by either the frequency or the temperature or both, except at lower frequencies.
关键词:
