What does the zinc do in an engine oil?

g'day everyone and welcome to lubrication explained today i'm going to be talking about zinc additives in engine oils so if we were to look at any internal combustion engine there are literally thousands of moving parts most of them we are relying on the engine oil to protect now if we were to look at the cams specifically what we'd find is that they are generally the most heavily loaded engine component as a result they can be a significant pain point particularly in older engines now there are a wide variety of cam designs cam and follower designs one of the overarching themes is that there's been a move from flat tappet to roller tap it for example but fundamentally they all operate in roughly the same way so let's take a look at the cam in detail at the surface what we really want as with most other components is for the lubricant to be able to carry the load between them and sufficiently separate the two metal surfaces so that they don't come into contact with each other the challenge that we have with cams is that the loads can be so high that a lubricant would have to have a really really high viscosity to be able to separate the two out if we were to have an oil with sufficient viscosity that it could separate the cams from the tappets what we would actually find is that we would end up with an engine oil that is way too thick for the rest of the engine we would run into all kinds of problems when it came to cold temperature start for example or getting sufficient lubricant around the engine on a start so instead what we want is another solution we want some kind of sacrificial surface protector and what we ideally need is for it to bond with the metal surfaces in the engine it needs to form a hard sacrificial barrier and it has to have no or positive impact on oil oxidation enter zinc diet zinc dialycal diet yeah stuff this let's just call it as it's topically known zddp this is roughly what the molecule looks like now in actual fact if you looked at it in three dimensions the the first two sulfurs from the left as well as the alkyl groups are kind of in a different plane so i'll try and represent that here this molecule as you'll notice has a few things it's got sulfur in it phosphorus zinc and oxygen so to just call it zinc as it's commonly known is a bit of a misnomer the r you so there's four of those and you can see them attached to the ends that's called an alkyl group so that's a polymer chain of lots of carbon and hydrogens and the thing is r can take an infinite array of forms so in actual fact zddps are a family of different zinc containing additives not all zincs are the same now one thing that we know is that sulfur and to a lesser degree phosphorus are known catalyst poisoners so over the last 20 years a lot of the regulation has been focused on reducing zddp content in engine oils and that's predominantly for emissions purposes this is why we can sometimes run into problems with older engines using newer style lubricants because a lot of these older engines were designed at a time where there was less emissions regulations and the zinc content of engine oils tended to be a fair bit higher okay so we've got this zddp molecule so what's the active ingredient in it well in actual fact from an anti-web perspective it's the last bit of that molecule the thiophosphate thiophosphoric acid is actually a very potent anti-wear additive now unfortunately because it's an additive if you were to pour it into an engine oil it would damage all the seals in your engines and so that's why we don't use it during the manufacturing process what we actually do is we take thiophosphoric acid and we have to neutralize it with a base so some kind of metal oxide zinc oxide is the most common one and that's how we end up with this zinc thiophosphate so it's actually the phosphorus which is performing the anti-wear function there are a lot of engine oils out there that are advertised on their zinc content 1000 parts per million zinc 1300 parts per million zinc in actual fact the zinc is inert it's the phosphorus that is doing all the hard work so in actual fact we should be rather than pronouncing this as zinc diocledithiophosphate we should be saying zinc dialectical diphthia phosphate the p is the important thing all right so let's go back to the surface of our cam tappet in this case what does that sacrificial layer look like well it actually is a layer that's really thin so somewhere between the order of 50 and 150 nanometers so that's all that's protecting the cam surfaces now what does that layer look like we don't actually really know our analytical techniques that we have in the lab are not sophisticated enough to really understand the complex structure of this zinc layer so this is our kind of best guess at what we think it looks like there's some kind of iron or zinc sulfide above that is a sort of a glass structure and when i say glass i mean in the scientific term which is a solid that is kind of amorphous not not crystalline and at the top we have a zinc polyphosphate so that's zinc as an anti-wear but the good thing about zddp is it actually has it's a multi-functional additive it does a few things in your engine the second of which is it acts as sulfated ash so what is sulfated ash and why is it needed well one thing is that in any engine the intake and the exhaust valves are constantly slamming into the valve seat if we were to do this without any kind of lubrication what you would eventually get is valve recession and that can be a really big problem in some engines now sulfated ash is actually the residue that's left over when a lubricant is burnt and zddp is one of the major contributors to the ash level of an engine oil that ash will then sit just above the valves and it will help cushion the impact with the valve seat the last function that zinc performs is as an antioxidant so it helps prevent oxidation which is effectively the aging of the oil or the cooking of the oil in use now the most common antioxidants are probably the aminic and the phenolic antioxidants and what they do is they neutralize free radicals in the oil zddp doesn't really work like that it's actually a hyper peroxide inhibitor so what does that mean well for anyone who is interested in the chemistry which you don't really need to know this effectively what happens is that you have radicals that are created in the oil that radical then bonds with more oxygen and creates a hydroperoxide and that zinc then helps inhibit the chain reaction by neutralizing that hydroperoxide and so that's how zinc can help slow down the aging process in an engine oil all right so zinc what does it do remember it's a family of anti-wear additives not all zincs are the same and it performs three main functions the first is anti-wear that's the main one the second is it provides sulfated ash to help cushion the valve seats and the third is it acts as an antioxidant by neutraling neutralizing hyperoxides thanks for listening this has been lubrication explained

Channel: Lubrication Explained

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Id: 3PeqJqss0Ao

Length: 9min 31sec (571 seconds)

Published: Mon Nov 23 2020