While doing Electro Chemical discharge machining, we have heated the electrolyte to predetermined temperature. But we are not sure how chemical etching process is affected, though process seems to be faster with precipitation and vaporization of electrolyte.
In my present works, I am using NaOH as electrolyte, silicon wafer of 500 micrometer thickness as workpiece and graphite plate as anode with Stainless steel wire of 300 microns diameter as cathode.Its a bit complicated process as I use spark erosion and chemical etching for material removal.I am keeping temperature of electrolyte at around 60 degree centigrade
It depends on nature of solution system and solid surface to be etched, and enthalpy of solution.
If dissolving the solid in the solution has negative enthalpy change (exothermic), then heating the solution will lower solubility and consequently will make etching less favorable.
If enthalpy change of solution is positive (endothermic) then heating will make solution and etching more favorable.
Therefore, it depends.
Actually, preheating is used to control the etching time period so that it will be more convenient for researchers to conduct the etching process with sufficient time.
Hello Prasad
Higher temperature increases rate of annealing (thus shortens time) if a process takes place (kinetic issue here).
On the other hand, temperature effect of spontaneity of the etching process (thermodynamic issue) depends on whether it is exothermic or endothermic.
This is a very delicate matter to consider.
Usually this things behave according to Arrhenius type of equation and with increased temperature you get increased chemical activity. But, then is also depends on surface energy and with rough surfaces you have increased area for reaction with same amount of solution. Another thing you need to bear in mind is if you want repeatable results you need to do everything at same temperature, which if you heat up electrolyte might be difficult.
The term "enhance" has no meaning within the context of chemistry. Would the process by "faster?" Probably yes, but possibly too fast. Would it be more even? Probably not. Would the etching be deeper? Probably if you left it for the same amount of time. But these are all speculations based on the fundamental properties of chemical systems, an individual system can behave differently. All one can do is try it and see what happens
Bonder is correct. Enhance has meaning of better result, which in this context should mean higher smoothnes.
But again, higher temperature increases rate (kinetic issue, Arrhenious equation)
In thermodynamics, higher temperature will shift equilibrium forward (more etching) if dissolution is endothermic; and will shift equilibrium backward (less etching) is dissolution is exothermic.
Typically NaOH attacks silicon. Using 60 degree heating would surely speed up etching process.
Etching preheated surfaces is very tricky. In overal reaction, the chemical activity of etchant increases with increased temperature. But once you pour etchant over your sample is impossible to control cooling gradient and you might get bands where etchant causes deeper groves. Aslo you should note, that at least for steels, some need to be etched directly after polishing as oxide that develops on surface desreases efficiency of etchant.
Bombac is correct. However, Paul's question is concerned with silicon etching with NaOH
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