How Vci Work

How VpCIs Work nHitek

Electronic Materials Limited

This is a brief introduction to the technology involved in Cortec’s Corrosion Inhibiting products for more information please contact Hitek.

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Vapor-Phase Corrosion Inhibitors Definition

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Vapor-phase corrosion inhibitors condition an enclosed atmosphere with a protective vapor that condenses on all metal surfaces (recessed areas, cavities)

The delivery of the protective vapour/ or molecule is one of Cortec's strengths. These delivery systems include films sprays, foams and coatings to name but a few. The vapour needs to be in a enclosure to make sure that there is sufficient of it to be effective, more of this later.

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Vapor-Phase Corrosion Inhibitors History

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US Navy (boilers, piping systems) Late 1940s

It may be a surprise to those of you who haven’t heard of this technology but it isn’t new. Its been around since just after WWII, However at that time it had very specialised applications, mainly in the military and the chemicals used were generally very toxic. Thanks to time and Cortec this has changed dramatically.

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Factors Vapor pressure n Diffusion n Temperature n Air change

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These are the factors that affect the effectiveness of the Vapour Phase Corrosion inhibitor. The first is the partial Vapour pressure of the vapour in the atmosphere, a more complete definition of this will be given in the next slide. The second is diffusion the rate at which molecules in a high concentration area move to a lower concentration area until equilibrium is achieved (Ficks Law) The next item is temperature the higher the temperature the more rapid the movement of the molecules and finally the rate at which the air is changed. If the air is always changing there can be no build up of molecules on the surface of the metal so there is no protection. In these cased coatings or covers need to be employed

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Vapor Pressure n

Vapor pressure: – The pressure exerted when a solid or liquid is in equilibrium with its own vapor. The vapor pressure is a function of the substance and of the temperature

Here is the text book definition of vapour pressure note that vapour pressure is a function of temperature. It should be noted that the vapour pressure exerted from a solid at a given temperature tends to be extremely low. Most of Cortec emitters are in solid form. It was one of the challenges in the development of Cortec's patented technology that the required vapour pressure be low so that the resulting life of the delivery system would be long enough to make it economic.

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Vapor Pressure

VCI A

VCI B

This is just a slide illustrating vapour pressure not that the pressure exerted by VCI A is lower than that of VCI B Under the same conditions.

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Vapor Pressure Atmospheric pressure: 760 mm Hg n Water: 18 mm Hg at 68ºF (20ºC) n Typical VCI: 10-4 mm Hg at 68ºF (20ºC) n Sodium nitrite: ~ nil n

This is a table showing the various pressures exerted at atmospheric pressure by various vapours at around room temperature. Note that the Sodium nitrite does not exert a vapour pressure at this temperature. Sodium Nitrite corrosion inhibitors for steel need to come into contact with the surface at this temperature in order to be effective. They have been around for about 30years and should really be classed as contact corrosion inhibitors, unless being used at considerably higher temperatures. Sodium nitrite is only good for ferrous metals, unlike the Cortec materials which are multimetal compatible. There have been some serious issue with staining and embrittlement of platings and metals when using sodium nitrite based coatings and films.

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Diffusion n

Diffusion governed by Fick’s Law – VCI molecules diffuse from a high VCI concentration region to a low VCI concentration region until equilibrium is reached

Here's the text book definition of diffusion

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Diffusion High Concentration VCI Source

Low Concentration

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Temperature n

The higher the temperature, the higher the vapor pressure

The higher the temperature the higher the rate of depletion of the delivery system. For most Cortec products at around 20C the life is approx 2years. If a higher ambient temperature is expected the souces need to be reinforced with additional foams and coatings to extend the life.

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Air Change Accelerates the depletion of VCIs n Judicious placement of the VCI source can reduce the effect of air changes

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As mentioned before if you change the air you reduce the effectiveness of the solution

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So here is the graphic representing what we have discussed. The VCI souce at the top, exerts a vapour pressure in the enclosure. The molecules are drawn to the metal surface and protect it with a monomolecular layer of the vapour that are very fond of bonding to the metal. The bond however is not strong and is always being replenished by the vapour in the enclosure. It is a dynamic equilibrium.

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How to Weather Bad Conditions?

Metal

Think of each molecule as a little umbrella that protects against the adverse weather conditions

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Contaminants

Oxygen

Water

Metal

Lots of these line up to protect against the elements that attack the metal

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Metal

And they continue to work whatever the weather, making you happy

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Vapor-Phase Corrosion Inhibitors Benefits

Cost effectiveness (VCI/barrier bags+dess.) n Ease of use (recessed areas) n Cleanliness (thin layer) n Safety/Environment (LD50)

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The really good thing about Cortec Corrosion inhibitors is that they are cost effective, they are easy to use and Are very clean, the monomolecular layer is un-noticeable. The molecule itself is derived from vegetable matter making it relatively safe when compared with sodium nitrite

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Cortec’s VCIs Multi-metal protection (VCI-126) n Multi-functional (VCI-125, VCI-377) n Very low toxicity (VCI-309) n Environmental friendly (ISO 14001) n Superior quality system (ISO 9001) n

So here are some of the main features and benefits of using Cortec Corrosion inhibitors

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Test Methods n

Vapor Inhibiting Ability (Fed. Std. 101C)

These are the test methods used by Cortec to test their products

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Important Parameters Surface cleanliness n Surface finish n Conditioning n Contaminants n Source exhaustion n Others

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Here are some of the factors you need to be aware of before you start, if you do not address them then the VpCI will not work, for example if the surface is encrusted with dirt the molecule will not be able to reach the surface.

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Defining Performance n

Protection – Long/short term – Distance from source

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Conditions – Humidity – Temperature – Corrosive agents, contaminants

You need to define what you want to do and what conditions it will be in Cortec as different solutions based on the same technology depending on your needs

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Conclusions Corrosion n Corrosion prevention n Corrosion inhibitors n Vapor-phase corrosion inhibitors n Cortec’s VCIs n Benefits n Applications

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If you want a cost effective solution to your corrosion problems consider Cortec and Hitek

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