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Where does that silicon keep coming from? Is it all bad and can it be helpful in my oil? Bonus feature – how do anti-foams works

5ab4440e 1d75 45ae b683 ff5d6de69a74l0001 img 8128.jpg 1024x683 Where does that silicon keep coming from? Is it all bad and can it be helpful in my oil? Bonus feature   how do anti foams works
Silicon has many sources and it’s not all sand

I was asked the question the other day how high would silicon have to be in an oil before you would change it based on that parameter alone. The system in question was an injection moulding machine which have exceptionally strict cleanliness levels. The samples were not tested by our lab, but the lab they were using was a reputable one and the results for silicon were between 40 and 70ppm with nothing else highlighted. To answer this question, it very much depends on the source of Silicon as some are actually useful and some are very damaging to the system. Annoyingly they all have the same primary chemical element of Silicon so it takes a little experience to spot which one it might be.

So what are the sources of Silicon and how do I fix them if they need fixing?

Silicon is the second most abundant element on earth after Oxygen, so it can be found in lots of places. Silicon has a few sources namely:

What is foam and how does anti-foam work?

To answer this we must first define what foam is. Foam is the gas dispersed in a liquid that when the gas bubbles reach the surface the bubbles do not burst faster than they are created. In a pure liquid it is thermodynamically unstable for this to happen. Hence there needs to be something else in the liquid to stabilise this foam production and this can be explained by the Marangoni effect. If you are into your wines you may already be aware of this term as the cause of the “tears of wine” effect. This nice YouTube video below gives a really good demonstration of this effect in a wine glass if you have never seen it.



You can also see these swirls that give the pretty colours to a soap bubble (see picture above).

The effect works because all the liquid molecules are slightly attracted to each other by very weak molecular forces. These combine to give surface tension.

How do these molecules produce surface tension?

If you imagine you are a molecule in the middle of a glass of water you are attracted equally to all the other molecules and so you stay in place. However if you were one near the top of the glass the overall direction of pull is down as there is no liquid above you to pull you up, which gives the effect we call surface tension.

If you imagine you are now an air bubble, trying to form a foam bubble, it’s a little like when you try blow a balloon at the start. If you recall, the very early part is the most difficult because the rubber film has too much tension before it is stretched.

In a pure compound the surface tension between the liquid and the air is very high much like that early stage of a balloon blowing making it difficult to separate the liquid molecules to form a bubble. The addition of surfactants lower the surface tension so the surface is much easier to overcome and so much easier to form a bubble.

How does a surfactant work and how is foam formed?

The surfactant molecules work as they are equally attracted to both of the surface tension phases ie the liquid and gas, and by the Marangoni effect they concentrate at areas of high surface tension, dragging more liquid with them and thickening the liquid film. You may think this would create more tension as you are thickening the film, but instead it stabilises that area making it stronger and resistant to bursting where the bubble might otherwise be at risk of collapsing. Think of it like adding a reinforced lintel to a doorway to stop it collapsing under the weight of the house above. So this extra material goes and reinforces the areas of the bubble that might otherwise collapse under the ‘weight’ of surface tension.

How does antifoam work?

Antifoam works by disrupting the effects of surfactants and other products that are reducing surface tension, making the bubbles less elastic and more stiff/rigid – hence easier to break. To do this they firstly need to be very low viscosity to allow easy movement. Secondly they need to not be soluble in the main fluid. They also often need to be denser to penetrate the foam and the main liquid. Silicone oils density is higher than that of most mineral lubricating oils which also helps with its antifoam properties.

Anti-foams replace the surface active molecules that are stabilising the foam. They do this by bridging the gap across the foam bubble liquid film and cause a weak spot between bubbles. This causes foam bubbles to rupture forming bigger and bigger bubbles (as 2 bubbles become 1 big bubble) that eventually burst altogether. The diagram below helps explain this bridging effect.

What to do about high silicon?

Your individual report will advice you on some practical next steps if any are needed, but as a general rule if silicon is the only flag then just continue monitoring. It’s only if it’s causing other parameters to be abnormal or increased wear you would start to address the problem.

If you would like more help on how to handle a silicon issue in your system then get in touch to discuss with us by clicking the contact us button on the bottom right.

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