5 Metallic Technetium, Corrosion, Technetium Alloys …
115
electrodeposition yield was high, above 99% and the deposits of up to 18 mg cm
−2
were obtained.
A similar to Box (1968) composition of electrodeposition bath was described by
Wotteen (1977). The bath contained 0.7 M ammonium oxalate and 1.4 M sulfuric
acid and its pH was equal to 1. Tc was deposited as a protective coating of stainless
steel using a current density of 1.3 A cm
−2 .
Electrodeposition from bath with high pH leads to the formation of the technetium
oxide instead of pure metal (Boyd 1959).
Zakharov et al. (1991) deposited technetium on Ni electrodes from a bath with
pH of 1 using currents of 7 or 12 A dm
−2 . He determined on the basis of crystallographic studies that such obtained deposit was a mixture of crystalline and amorphous
phases. He established that technetium hydride with maximum hydrogen content
corresponding to TcH x<0.27 and with lattice constants a = b = 2.793 ± 0.002 Å and
c = 4.444 ± 0.002 Å can be formed during this process.
Mausolf et al. (2011), in turn, deposited metallic technetium from 1 M H 2 SO 4
containing 2 or 10 mM TcO
−
4 and applying 1.0 A×cm
−2 and various deposition
times from 100 to 2000s. They observed that the deposition of the metal is hindered
by generation of Tc(IV) species characterized spectroscopically by the band near
500 nm. The efficiency was below 10% for 2000s of the Tc electroplating.
Deposition of technetium from 1 M H 2 SO 4 solutions was discussed also by Engelmann et al. (2008). The electrolysis was carried out in a two-electrode system with
a platinum disk acting as a cathode. The technetium was deposited from 0.25 ml
solutions containing 25 ng of Tc at the voltage of 5 V (~20 mA). The deposition
efficiency varied from 69 to 84% for 6 and 18.6 h of the electrolysis, respectively.
The electrolysis with the current of 0.1 ÷ 0.5 A carried out for 1.5–4 h led to the
formation of the Tc coatings with the yields from 20 to 48%.
Boyd et al. (1960) investigated codeposition of technetium and rhenium from
slightly acidic solutions. He concluded that the electroplating can be effectively
carried out at pH of 5.5 and in the presence of 2 mM F
− . The electrolysis of 15 ml of
the solution at 100 mA cm
−2 for 2 h with a copper cathode yielded the Tc deposition
at a level of 89%. The deposit obtained under such experimental conditions was most
likely composed with a hydrated TcO 2 .
Metallic technetium can be obtained also in concentrated potassium acetate or
mixed potassium and ammonium acetate solutions at potentials lower than −1.4 V
or −1.15 V (vs. saturated Ag, AgCl reference electrodes) respectively (Kuznetsov
2020). This process is multistep and occurs via generation of Tc(IV) and Tc(III)
forms. An earlier work of Maslennikov et al. (1998) has shown that metallic
technetium can be electrodeposited with relatively high efficiency (92–95%) from
aqueous formate solutions (pH = 6.0–7.5) by applying potential lower than −1.4 V
versus SCE.
A summary of the described baths used for the technetium deposition from
aqueous solutions is provided in Table 5.2.
A procedure to fabricate smooth coatings of transition metals (Cr, Zr, Hf, W,
Mo, Mn, Tc, Re or lanthanides) with a 10-point average roughness below μm using
electrodeposition from molten salt baths was patented by Inazawa et al. (2016). The
115
electrodeposition yield was high, above 99% and the deposits of up to 18 mg cm
−2
were obtained.
A similar to Box (1968) composition of electrodeposition bath was described by
Wotteen (1977). The bath contained 0.7 M ammonium oxalate and 1.4 M sulfuric
acid and its pH was equal to 1. Tc was deposited as a protective coating of stainless
steel using a current density of 1.3 A cm
−2 .
Electrodeposition from bath with high pH leads to the formation of the technetium
oxide instead of pure metal (Boyd 1959).
Zakharov et al. (1991) deposited technetium on Ni electrodes from a bath with
pH of 1 using currents of 7 or 12 A dm
−2 . He determined on the basis of crystallographic studies that such obtained deposit was a mixture of crystalline and amorphous
phases. He established that technetium hydride with maximum hydrogen content
corresponding to TcH x<0.27 and with lattice constants a = b = 2.793 ± 0.002 Å and
c = 4.444 ± 0.002 Å can be formed during this process.
Mausolf et al. (2011), in turn, deposited metallic technetium from 1 M H 2 SO 4
containing 2 or 10 mM TcO
−
4 and applying 1.0 A×cm
−2 and various deposition
times from 100 to 2000s. They observed that the deposition of the metal is hindered
by generation of Tc(IV) species characterized spectroscopically by the band near
500 nm. The efficiency was below 10% for 2000s of the Tc electroplating.
Deposition of technetium from 1 M H 2 SO 4 solutions was discussed also by Engelmann et al. (2008). The electrolysis was carried out in a two-electrode system with
a platinum disk acting as a cathode. The technetium was deposited from 0.25 ml
solutions containing 25 ng of Tc at the voltage of 5 V (~20 mA). The deposition
efficiency varied from 69 to 84% for 6 and 18.6 h of the electrolysis, respectively.
The electrolysis with the current of 0.1 ÷ 0.5 A carried out for 1.5–4 h led to the
formation of the Tc coatings with the yields from 20 to 48%.
Boyd et al. (1960) investigated codeposition of technetium and rhenium from
slightly acidic solutions. He concluded that the electroplating can be effectively
carried out at pH of 5.5 and in the presence of 2 mM F
− . The electrolysis of 15 ml of
the solution at 100 mA cm
−2 for 2 h with a copper cathode yielded the Tc deposition
at a level of 89%. The deposit obtained under such experimental conditions was most
likely composed with a hydrated TcO 2 .
Metallic technetium can be obtained also in concentrated potassium acetate or
mixed potassium and ammonium acetate solutions at potentials lower than −1.4 V
or −1.15 V (vs. saturated Ag, AgCl reference electrodes) respectively (Kuznetsov
2020). This process is multistep and occurs via generation of Tc(IV) and Tc(III)
forms. An earlier work of Maslennikov et al. (1998) has shown that metallic
technetium can be electrodeposited with relatively high efficiency (92–95%) from
aqueous formate solutions (pH = 6.0–7.5) by applying potential lower than −1.4 V
versus SCE.
A summary of the described baths used for the technetium deposition from
aqueous solutions is provided in Table 5.2.
A procedure to fabricate smooth coatings of transition metals (Cr, Zr, Hf, W,
Mo, Mn, Tc, Re or lanthanides) with a 10-point average roughness below μm using
electrodeposition from molten salt baths was patented by Inazawa et al. (2016). The