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I use Sodium Persulfate as an enchant at a maximum temperature of 50 C.

My experience with glass heaters is that they break if they are not fully submerged or if they are removed while it is warm which makes me feel that glass is fragile and has tendency to break easily.

I see that ceramic heaters are cheaper compared to titanium ones. I wonder if the enchant corrodes the ceramic material? Does a ceramic heater break if it is not fully submerged or removed while it is warm? and are they resistant to mechanical shock from a drop or hit?

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  • \$\begingroup\$ I read that ceramics are chemically very resistant. It would be good to have confirmation for that part of the question \$\endgroup\$ – Angs Aug 1 '14 at 9:18
  • \$\begingroup\$ can you provide some link of the heater(s) you want to use? Ceramic should resist to pretty much any chemical attack, while it might suffer drops 'n hits... You just need to pay attention though. \$\endgroup\$ – Vladimir Cravero Aug 1 '14 at 9:47
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    \$\begingroup\$ Thank you Vladimir. I could not find any suitable product yet. I can only see options for an aquarium heater. But, sellers don't specify the used materials if it includes different materials (like steel etc.) on the outer body. If you know any ceramic heater that is good to use on an etching tank, I would be happy to know it. \$\endgroup\$ – Angs Aug 1 '14 at 9:57
  • \$\begingroup\$ I am sorry, I can't help you on that, I'm sure somebody around here can help you though. What etchant are you using? \$\endgroup\$ – Vladimir Cravero Aug 1 '14 at 10:03
  • \$\begingroup\$ Sodium Persulfate \$\endgroup\$ – Angs Aug 1 '14 at 10:08
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About glass heaters:

  • You are absolutely right about the common glass envelope heaters, like the ones used as aquarium heaters. They are usually made of soda-lime glass, which has a high coefficient of thermal expansion, making it very sensitive (fragile) to sudden changes in temperature. I have also experienced myself how a glass envelope literally "explodes" if taken out abruptly out of the water, while still hot.
  • As an alternative to common glass envelope heaters, you may purchase a heater with borosilicate glass, less subject to thermal stress.

Other alledgelly known as "unbreakable" heaters:

  • If the glass breaks, either because of thermal stress or by accident, why not simply substitye the envelope material?
  • Metal (titanium) envelope heaters do exist, resisting several degrees of corrosion. For instance, check here.
  • Plastic envelope heaters also do a good job by being "harder" to break than glass and also resistant to some types of corrosion. For instance, check here. The only drawback is that the thermal resistance of the plastic makes the system reach much more slowly to the target temperature, which I don't think is an issue for an etching application (the bath can be pre-heated to the target temperature before actually starting the etching process).

Now, delving specifically into your etchant (Sodium Persulfate),

  • According to the Chemical Resistance Guide of Burkert, Sodium persulfate in aqueous solution is compatible with the following plastics, among others: PVC and PP.

I will not dare to use directly a ceramic heater without a proper enclosure. Except if you are willing to make it in a DIY fashion. For a professional (even for a hobbyst) application, I will use an appropriate plastic heater. As last resort, if you cannot find a commercial PVC enclosed heater, maybe you can create your own PCV enclosure, for an standard ceramic heater, then adding an external temperature PID controller with the appropriate configuration (trial and error).

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