# Ultrasonic bath operation time

I use an ultrasonic bath in my lab for some chemical treatment of samples. It usually takes several hours with short breaks or even without it. I have a timer at the bath with a limit 90 min. So I have to run it every time again after it ends. My colleague told me that if I'm not giving a rest to the bath after every 90 min run, then the ultrasonic generator will be broken very soon. So, in general, how much time should be between the runs? Can external chilling enhance the safe treatment duration? It is a 3 liter, 100 W, 40 kHz Finnsonic bath with a heater.

• Read the user manual. If the manufacturer is concerned about overheating the element or the driving circuit, it will say. Or call their service rep or applications engineer. – Jon Custer Jun 26 '17 at 14:02
• You'd be amazed how often outdated, incorrect advice gets passed down as fact in just about any field. Ask your colleague if they have a source for their statement aside from "XX told me." – chipbuster Jun 26 '17 at 15:07
• Keep an eye on the temperature of the water in the bath. I have found significant temperature rises over hours of operation. – Waylander Jun 26 '17 at 15:19
• That advice from your colleague might be nonsense (see @chipbuster 's comment), but do YOU have aquired any evidence that five hours of ultrasonication is actually helpful for your problem? (Sorry if you have, but you wouldn't be the first who wasted many hours on a similar, useless procedure. It's called Cargo Cult Science. ) – Karl Jun 26 '17 at 21:04
• Yes, I do. It's not for cleaning of some parts. It is for chemical etching of glass. According to some article, it can take up to several days depending on the etching volume. – Dmitrii Kliukin Jun 27 '17 at 6:41

Beside Jon Custer's comment, to be taken with a grain of salt (as the op mentions a heating unit implemented in the ultrasonic bath), if the manual allows, it depends.

You will recognise that by simple use (even if nothing but water is in the trough), that the temperature of the water will increase simply bu use. Hence, to keep the results reproducible from one batch, to the next, you power on the bath until this temperature stabilises. (It is better to briefly switch off the sonification to record the temperature with a thermometer.)

In terms of duration of sonification: while one aims to keep the reaction time under sonification short(er) than by conventional heating (alone), like

there are examples, where the sonification reportely has to last much longer than $\pu{90 min}$, for example

(source)

I've seen colleagues run reactions from morning till noon, for the sake of selectivity of the reaction intentionally cooling the bath by intermittent addition of water ice into the trough.

To attenuate the cavatational noise the bath may generate, esp. if your flat bottom vessel hovers with some distance just above the resonators (the hot spots), either consider a different room (or at least, keep the sash closed), or have a "noise-proof shoe box" like

(source)

that you may design by yourself, too, covering your bath durin the operation. Instead of the foam-lining, a wooden box lined with polysterene is even cheaper, but offers less "relief". It is even better to place the bath (if weight permits) at the same time on a sheet of expanded polysterene that you get "for a smile" at at your departemental chemical shop, or appliance shop.

But do not forget the ultrasound bath underneath the box / in the other room, especially if your heating unit is used.

(source)

Beside this, you may interested in periodicals like Ultrasonics and Ultrasonics Sonochemistry, or Luche and Capelo-Martínez as secondary references, too.

• Just to add to my comment to the OP - if the heating unit was part of the OEM equipment, their manual should give the appropriate limits. If you added it yourself, well, you really should call their application engineer. Looking at one manufacturer (not the one mentioned by the OP), they note their heated baths allow for continuous operation, just like their normal ones. – Jon Custer Jun 26 '17 at 17:30
• This is an important aspect I agree with if there were the aim to install post factum a heat unit not foreseen by the manufacturer should be done only in agreement with the corporation. In addition, for safety / insurance and OSHA (and perhaps I forgot one point, too), my university would allow such a modification only if both announced in advance and agreed, and eventually performed by a trained & authorized personnel (including a new safety-check sticker on the back + entry in the log). – Buttonwood Jun 26 '17 at 20:12
• In "Eco-efficient ultrasonic responsive synthesis of pyrimidines/pyridines" by Ramakanth Pagadala, Suresh Maddila, Sreekantha B. Jonnalagadda (Ultrasonics Sonochemistry 21 (2014) 472–477, doi 10.1016/j.ultsonch.2013.08.024), several sonifications last 2 (two), some even 4 (four) hours. – Buttonwood Jul 28 '17 at 11:57