Q2. What is the reason for the large open spacing among the metallic particles?
a large open spacing among the metallic particles should be maintained even after the heat treatments, because the sintered pellet is used as the anode in the capacitor after adding the liquid electrolyte into the spaces among the particles.
Q3. Why is the oxygen level not crucial in this work?
Because Nb can absorb oxygen as a solid solution (the maximum solubility is 0.31 mass%oxygen at 1153 K [30]), the oxygen level is not crucial in this work.
Q4. What is the reason why the oxygen level of Type II was higher than those of the others?
A thin oxidized layer on the particle surface may form during handling after the reduction, and may constitute one of the reasons why the oxygen level of Type II was higher than those of the others.
Q5. What is the mechanism of the sol-gel treatment?
During the sol-gel treatment in basic solution with Ca(OH)2, a strong bond between Ca and Nb atoms may be formed in the amorphous structures, and this bonding is maintained even after water removal.
Q6. What was the standard method for tantalum capacitors?
The capacitance (CV), leak current (LC), and dielectric energy loss of the capacitor (tangent of loss angle; tan δ), were measured by the standard wet method for tantalum capacitors [26], because an international standard method for niobium capacitors was not yet regulated.
Q7. How was the dehydration of the raw material monitored in air?
The dehydration of raw material Type The authorwas monitored in air by differential thermal analysis and simultaneous thermal gravimetric measurements (TG/DTA) at the heating rate of 1/12 K/s.
Q8. Why did the reduction rate of the metal particles differ from the morphology of the starting material?
(5)The less reducibility and slower reduction rate presented a concern because of reductant loss byconsumption due to the reduction of NaOH and because of the lower activity of Ca by alloying.
Q9. What are some modifications that were used to anodize the type II pellets?
Some modifications include an anodizing voltage of 50 V, current increase to 60 mA per 1.0 g Nb sample, and continuous current for 7.2 ks.
Q10. How was the reaction temperature of the raw material set?
Those samples were reacted at 1153 K for 7.2 ks in an Ar gas atmosphere, and the molar ratio of the raw material : Ca reductant : CaCl2 solvent was set as 1 : 30 : 60.
Q11. What is the morphology of the raw material Type II reduced particles?
At present, the authors conclude that the strange morphology of the raw material Type II reduced particles is closely related to the adhesion of CaO, which formed a thin layer but was tightly to the hydroxide particles.
Q12. What is the morphology of the reduced metallic particles?
In the calciothermic reduction of Ta oxide, the morphology of oxide particles is reflected in that of the reduced metallic particles [13-16].
Q13. What is the effect of reducedpowders on capacitors?
This work shows that reducedpowders are favorable for capacitors resistant to higher voltages, if the residual oxygen concentration can be suppressed.
Q14. What was the cross-section of the type II sample?
The bar-like particles were homogeneously sintered even at the central part of the pellet, and the cross-section was macroscopically smooth.
Q15. Why was the morphology of Type IV not studied?
Because the morphology of Type IV was similar to that of Type I, its character was not studied, partially because the amount of Type IV obtained was too small.
Q16. How many open pores remained in the sample?
Many open pores remained in the sample, and a sufficient anodization treatment could be performed even at the central part of pellet.