How to choose a cleaning solution

in today's video I'd like to talk about cleaning things so there's a huge selection of solvents available but how do you actually choose one so today I'd like to give away some tips and tricks and also explain some of the science behind these cleaners first of all don't forget that water itself is actually a really great cleaning solvent and for some types of dirt it's actually the best possible solvent and so to show this I've got a microscope slide with some salt that I've dried on it just plain old sodium chloride and I'm going to start off by drizzling some anhydrous alcohol on this so if you buy this from an electronics store you can see it's 99% anhydrous alcohol meaning that there's very little water in this it's almost entirely pure isopropyl alcohol and so I've got some in a wash bottle here and we're just gonna spray this over the salt and see what happens as you can see not very much and the reason is that the alcohol is not particularly polar and it doesn't dissolve the salt particularly well so let's try this again with just plain old distilled water this time the water was very effective in dissolving the salt and as the water was sprayed across the slide it carries away the dissolved salt and effectively cleans the surface and so this holds true for other substances as well this slide has some dried on sugar which doesn't crystallize quite like the salt does but we'll try the same thing by putting isopropyl alcohol and their anhydrous it kind of makes the the sugar harder to see but trust me it's still there unaffected let's try the same thing with just distilled water so the first rule for choosing a cleaning solvent is like dissolves like and so the thing that you want to dissolve is polar like salt or sugar then you want to use a polar solvent like water to dissolve them and using something that's not correct like isopropyl alcohol actually won't have much effect at all it won't help your cleaning job in the slightest and it's partially for this reason that most of the alcohol sold at supermarkets and drug stores is actually 70% the additional 30 percent of water in there is actually what allows you to clean away a lot of the dirt so if you're gonna clean like dried on blood or grass stain or something like that the 70% isopropanol is actually more effective because it has the water already in there the reason that you might want anhydrous alcohol is if your the thing you're cleaning is sensitive to water like an electronic circuit then you'll want this just to avoid using the water altogether so how do you know if the thing you want to clean is polar or not well as it turns out most of the dirt that we actually have trouble cleaning in the world turns out to be nonpolar if it were polar then we could just use plain old water and be done with it but the entire cleaning industry is pretty much dedicated to cleaning difficult nonpolar substances so for example I have this permanent pen mark on the microscope slide and if we just try to clean it with plain old water of course it's if nothing happens and it's permanent pens not supposed to come off in water so we'll sort of turn our efforts up a little bit here and we'll go to the isopropanol and see how this does it's starting to dissolve it as you can see it's removed some of the pens so some of the chemical compounds in the permanent pen mark have dissolved in the alcohol but it hasn't really cleaned the slide it hasn't gotten everything so if we up our efforts again and switch over to acetone acetone is a partially non-polar and partially polar solvent now let's see how well this does the acetone has no trouble at all just completely removing the permanent pen mark so let's talk a little bit more about how to choose the solvents and the differences between them there are a few numerical scales that have been developed to describe how effective a solvent is at doing its job and so I'll put links in the description one of them is the khari butanol and another one is the Hildebrand and they aren't used all that commonly because each cleaning job is so unique it's kind of hard to use a single number to describe how good a solvent is so for example if you're cleaning wax off of a circuit board you might choose one solvent that has a lower you know KB number than another one but it's really well suited to that task for a number of other reasons so I'm not going to go into detail about the exact you know ratings for each of these but just keep in mind that some solvents are quite a bit more effective at than others for a specific job so as we saw with the marker isopropanol only sort of half removed the marker whereas acetone you know had no trouble with it at all and going up from acetone the solvents get quite a bit more effective until we're into chlorinated hydrocarbons like this that you typically can't buy at the hardware store because they're just a little too good keep in mind that no matter how good the solvent is we still have to remove the dirt so here's a microscope slide with a little bit of grease on it and if we put a drop of solvent on there imagine that this is you know the best solvent in the world and it instantly dissolves all the grease if we don't do anything and we just let the droplets sit there what's happening is we now have a mix of all the dirt plus the solvent and if we wait long enough all the solvent is going to evaporate away and 100% of the dirt that we started with it's still going to be there so an important part of cleaning with a solvent is having a flow or using some mechanical means to remove the dirt so let's take a look at that in the simplest case we could just use a paper towel I mean a rag or a paper cloth is fine and what happens is the solvent will allow the grease to be dissolved and then it comes off in the cloth and the space between the fibers in the cloth or what catch the dirt and allow it to be removed however there's a slight problem with this even if your cloth is really absorbent and is able to pull as much of the grease as you can see off of the surface there's still a vanishingly thin layer of grease left on there so let me show you a test that will allow you to see if there's a thin layer of grease left here's the slide that looks clean but if we just take a regular old jet of distilled water and spray it on the apparently clean section we can see the water actually pulls away from the glass let me switch over to a piece of stainless steel so it's easier to see it looks very clean but if we try the the water test on it we can see that the water just beads up and what should be happening if the surface was really really clean was that the water would form a nice sheet across it the water would sheet off having a surface that passes the water break test in other words allows the water to sheet off and not beat up is important if you want to paint or put an adhesive on this surface if your last project that involved paint didn't work out so well it's possible because that the surface wasn't prepped properly and it's a very sensitive test so if you use one of the methods that I'm going to show you in this video to clean the surface such that it passes the water break test and then you just leave this sitting around in the air for a day or two just the random amount of oil and dirt floating around in the air will actually cause it to fail the test after just sitting around for a day or two so it is a very dirty world and it takes a lot of effort to clean things and keep them clean so I mentioned that the main problem with using a paper towel to clean something off is that it just pushes the solvent and the dirt around and there isn't really any removal of the dirt even if you use pure solvent and you change paper towels off and you're still going to be a very thin film of grease on the surface and this is partially because the solvents that you buy at the hardware store aren't pure anyway and if you want to have a really good painting job or a really good adhesive job that last layer of grease has to go so one of the sneaky ways that we can get around this problem is to boil the solvent in a container and then let the vapor drift up and I'm going to just dip the slide into the vapor that's in this beaker and what will happen is the solvent vapor will condense onto the slide and then the grease will dissolve or the dirt in this case the permanent marker will dissolve and drip off down into the bottom of the beaker so let's see how that works it's extremely effective and what's cool about it is that the boiling vapor of the boiling solvent just condenses on the slide and the dirt stays down in the liquid there because it doesn't boil it's much less volatile and if with the right selection of solvents and everything the slide even dries itself so the thing is really really effective and what I'm showing here is actually trichloroethylene which is how they clean circuit boards and lots of other things in the 80s before we found out that chlorinated hydrocarbons weren't so good but you just saw how amazingly effective this is let's try this on a more demanding application here's a slide with some authentic rode grease from the bottom of my car smeared on there so we'll put this into the vapor stream and see what happens very effective and so most of the of the grease has just dripped off and you can see there's a few spots where it's still a little stuck that was probably nonpolar dirt like literal dirt from the earth you know earth smeared on there that's just holding on by a very weak sort of physical connection you can also see that the effectiveness of the vapor cleaning goes down the longer that the slide is in there and the reason is that when the slide is cold it condenses a lot of vapor onto those onto the slide and that's what causes the washing action whereas after it's been in the bath for a while it's warmed up so we'll take it out and just kind of let it cool to air temperature and give it another pass and see how that goes what's interesting is the dirt that's left on the slide is completely dry there's not a trace of the grease left in there because the solvent cleaning is so effective and so if we just use one of these air dusters it actually just blows away the remaining dirt entirely and there's like a trace of something left so if you were designing an industrial cleaning process for this maybe a trip through the vapor cleaning and then an air blast and then a trip through there again would be a sufficient as you can see all the dirt is left in the bottom of the beaker and if you can if you watch carefully you might be able to see the vapor coming out as I mentioned the trick with this is that as it's boiling it's only the vapor that comes up in the dirt stays down there but the problem is that I just released a whole bunch of volatile organic compounds into the atmosphere chlorinated volatile organic compounds on top of all that and you know that this process isn't really used industrially so much because the escaping solvents are bad and then even if you capture the solvents you have to do something with the dirty like the really sludge at the bottom that's you know saturated with the solvents so let's look at another alternative for getting that last film of oil off of something if you need to critically clean something that doesn't involve solvent cleaning okay so here we are with the piece of metal that looks clean but is failing the water test and just to show that this is not going to work with the solvent approach we're going to take fresh legs of propanol right out of the bottle fresh kimwipe right out of the box and try to clean it and so you'd think well we're doing a really good job cleaning it now it was a completely new kimwipe and new solvent and we'll try the water break test you can see the alcohol is evaporating away it's better it looks a slightly better than it was that you can still see the water is beating up so if we wanted to paint this I'd be concerned that the paint would flake off in short order because it's just not going to get a good bond there because of that last remaining film of oil and we also determined we can't use the solvent cleaning option because it's environmentally you know a problem luckily there is another alternative and that's to use a substance that chemically converts the dirt that's on the surface so instead of using a solvent that just sort of pushes the dirt away or dissolves it and then washes it away if we use something like this that contains bleach the bleach will actually oxidize those hydrocarbons that film of oil that's on the surface and converted into a different substance so instead of just pushing the dirt away we're actually actively changing it so let's try a little bit of this stuff and we're just going to use plain old water and I'll try to do half of it so that we can see the water break test is different on the other side and then we should be able to just rinse with plain old water and as you can see it's already significantly different so if I turn it this way so that this was the half we treated and the other half is untreated you can see that side is just beating up just like it was when we started this side is now passing the water break test quite well and this is what you want to see before painting something because then you'll know that you've got that last bit of film off so the takeaway point is that just because a solvent is you know extremely aggressive and potentially banned for being a health problem and all that doesn't actually necessarily make it more suited to your cleaning task if you're prepping a surface for a pain definite and your surface can tolerate being wet using a cleaner like this is actually really good it's mildly abrasive it includes an oxidizer and basically a soap to get the PERT the part as clean as possible I learned this trick from Dan Gelbart and I'll put a link in the description who has a whole bunch of really great videos that are worth watching but let's say your part can't tolerate being wet and you can't use solvents like this because they're falling out of favor and you still want to clean your hydrocarbon gunk off the surface there are more alternatives and one of them that's pretty hot these days is using liquid or supercritical co2 I have a number of videos about supercritical co2 and this is the chamber that I've shown in previous videos even though co2 is a gas and you're probably not thinking of it as a cleaning solvent if you compress co2 and make it into a liquid and then heat it up to make it into a supercritical substance it's actually a really good solvent it's so good that dry cleaners use it again because it's not wet and so you can't get the garment wet but if you put the shirt into a chamber with liquid co2 and make it go super Critic you can actually clean oil stains out with that and everyone likes co2 because it's a totally inert solvent you can just release it to the atmosphere and it's it's totally fine it's such a good solvent that my chamber which is built out of acrylic is actually slowly dissolved by the supercritical co2 that it's containing and so I would not use this chamber to hold the the substance for a very long time I've only you know let it sit in there for a couple days at most and it'll take a long time for the supercritical co2 to penetrate through this thickness of plastic but what's interesting is that you can see it's sort of got the case of the bends here let me show you what it looks like here's what one of the acrylic windows looks like after it's been at pressure for a while and then decompresses as you can see it's got a one heck of a case of a bends and so what's happened is the liquid co2 is penetrated into the plastic and then over the course of an hour or two the co2 decompressed and this was a very soft material because the solvent was working on it but there's actually another cool invention that lets you use the cleaning power of co2 outside of a chamber there's at least one company that makes a co2 cleaning gun and it basically works by having a large tank of liquid co2 and a nozzle and the idea is that when you open the valve you get a stream of co2 liquid that's coming off the pipe and when it hits the atmospheric pressure air it freezes into co2 dry ice and then the dry ice snow basically hits the surface that you want to clean and as it strikes the surface it converts momentarily back to a liquid and solvent cleans the surface and then continues off into a gas and blows away so the idea is that you're able to sort of blow the dirt off of surface in one fell swoop using the cleaning power of liquid co2 so I've tried to get this to work let's zoom in on this slide where I've got a little bit of grease on it and I'm gonna use this nozzle here and just see if we can clean it this way as you can see I'm not really having much luck with it well I'll put a link in the description and I've seen their product actually worked quite well so don't don't take my word that it's that it's no good but the concept is really cool and it actually is used for cleaning glass and optics because it actually is very gentle on the surface and leaves no trace since the co2 just completely evaporates right away this is actually water vapor just because it's so cold I think their guns the chips of co2 in a room-temperature Airstream to try to prevent the condensation problem I thought we done with a less common but really interesting cleaning problem this is a bowl from my kitchen and you might have some in your house that look like this - do you see the sort of the scratches at the bottom those are actually not scratches in the porcelain it's actually a metal deposit left from metal utensils scratching it so you can see that we scratched the bowl what's happening is the porcelain of the bowl is much harder than the metal of the fork and it's leaving some of the metal on the surface of the bowl and depending what kind of metal your utensils are made of this might be not so hard to clean off or it might be almost impossible so you can get in there with you know comet is a good choice because it's slightly abrasive and you might be able to with enough rubbing get that off however there are some metals that will leave a mark and you will not be able to get them off with any household cleaner and cleaners so I've got this titanium bar here and we'll leave a nice big scrape with the titanium and believe me there's no amount of scrubbing with comet that's going to get that off and the reason is that the titanium deposits a little bit of metal on here because again because the porcelain is harder than the titanium even and then after a few minutes the titanium forms a very tough oxide skin on this metal which is why this is so corrosion resistant it forms a protective oxide layer and the titanium oxide is just as hard as the porcelain so if we were to go in here with an abrasive we would be rubbing the bowl 'we just as effectively as we were rubbing this oxide protected band of titanium so it's really an effective way to mark glass and porcelain permanently and in fact they even sell titanium pens for artists that work with glass and they can sign their name with the titanium pen and it's practically indelible however let me show you a secret chemical blend that will get this off very effectively okay so the magic cleaning solution that will instantly take off that mark I'm going to mix up in this little bottle and it is ten parts by volume just plain water and the exact quantities are actually not so critical for this for this recipe one part hydrogen peroxide and you cannot use bog-standard like two or three percent hydrogen peroxide you have to use something like eighteen percent is commonly available on eBay and then the really secret ingredient fairly concentrated hydrofluoric acid this is about 50 percent or forty eight percent I think is the theoretical maximum and it'll be one part by volume of that and I know the safety guys are already jumping out of their seats yeah it's pretty bad stuff just don't let it get on your skin unlike chemicals that are pyrophoric or explosive or react with everything I actually don't think this is so bad but definitely don't let this get on your skin using it is pretty straightforward you just want to get a little bit onto a a rag let me zoom in so you can see this takes it off lickety-split the name given to this substance is called piranha and it works by a very clever technique it relies on both the hydrogen peroxide and the hydrofluoric acid since I mentioned the titanium forms this protective oxide layer what happens is the hydrofluoric acid etch is away that titanium dioxide and exposes fresh metal and then the hydrogen peroxide oxidizes that exposed titanium surface and creates more oxide and then the hydrofluoric h's that away so it's kind of this combination symbiotic reaction that kind of that is able to clean it off so effectively so it does etch glass very slowly but the dilution is low enough where if you just rub it on there for a while you notice there's really no surface problem it's not like there's a trench or anything edged into it okay hope you found that interesting I'll probably do some more videos on specific cleaning things so let me know if you have any questions see you next time bye

Channel: Applied Science

Views: 241,530

Keywords: solvent, cleaning, critical cleaning, vapor cleaning, polar, nonpolar, hydrocarbon, chlorinated, oil, grease, bleach

Id: HiL6uPNlqRw

Length: 21min 40sec (1300 seconds)

Published: Mon Oct 05 2015