The recent intense development of modern powder metallurgy has provoked a sudden interest in amorphous powders, particularly metallic ones. These materials represent a relatively new state of matter with an interesting combination of physical and physical-chemical properties that make them very attractive from the technical point of view. It is due to their great possibilities to be applied in the manufacturing of precise components for various types of equipment by hot and cold sintering.
The amorphous state of matter is, however, structurally and thermodynamically unstable and very susceptible to partial or complete crystallization during thermal treatment or nonisothermal compacting. The latter imposes the need to know its stability in a broad region of temperature.
The Fe-W powders of different compositions were obtained by electrolyzing aqueous solutions containing Na2WO4, C2H2O4, glycine and FeSO4 at a current density of 8 A/dm2 by changing the ratio of iron to tungsten but maintaining their total molar concentration of 0.26 M in the solution.
The electrolysis was performed using a Cu cathode and a Pt anode in a stream of purified nitrogen, whose continuous flow was used for stirring the electrolytes in the electrolyzer at 80 °C.
Microscopic analysis showed that 97% of the particles have dimensions 0.5/4.5m
The compositions of the electrolytes and obtained alloys
X-ray diffractograms on as-prepared samples of:
X-ray diffractograms on as prepared samples of:
The crystallinity and the enthalpy of the absorption of hydrogen
Fe91.2W8.8 for heating
and cooling cycles in
argon flow, heating
rate of 20K/min
The DSC thermograms of the alloys
in the temperature range from 20
°C to 500 °C show complex
exotherms. They can be ascribed to
the reduction of the oxide film
formed on the surface of the alloy
particles during drying after the
synthesis and partially to a process
of poor absorption of hydrogen
between 120 °C and 300 °C
DSC thermograms in hydrogen flow of:
The M thermograms of the alloys össbauer spectra of the as prepared Fe91.2W8.8 at room temperature and at 20 K
The M and LA2 and doublets DA1 and DA2. The singlets were ascribed to the össbauer spectra after thermomagnetic curve measurement of Fe91.2W8.8
The M and LA2 and doublets DA1 and DA2. The singlets were ascribed to the össbauer spectra of the Fe91.2W8.8 after heating at 1073 K
Thermomagnetic curve of Fe intensity of the magnetic part at the expense of the paramagnetic one was observed.91.2W8.8 measured at 3.98 kA/m (50 Oe) with the heating and cooling rate of 4 K/min.