About the Cleaning Fluids, In Detail

• Solvent Azeotropes
• The Wetting Index
• Kb Values
• Materials Compatibility
• Recycling Cleaning Fluids
• Shipping and Disposal

Solvent Azeotropes and Their Importance in Vapor Degreasing

All of the MicroCare precision cleaners, all of the Bromothane^™ blends, and most of the Vertrel^® products are azeotropes. This is important because it lowers cleaning costs, boosts cleaning effectiveness and enhances worker safety. Here’s how…

First, an azeotrope is described as a constant boiling blend. To be an azeotrope, the material has to be a mixture or a blend of at least two different elements or compounds.

Let's consider the boiling point of HFC 43-10. The boiling point of HFC 43-10 is about 40°C. But mix in a small but precise amount of alcohol and the boiling temperature suddenly changes. The two chemicals are still separate and distinct in the mixture; there has been no chemical reaction in which they actually change their chemical state. But the two chemicals work together to change their behavior. Importantly, the two ingredients boil off at the same rate.

Let's suppose the mixture under test is 97% nPB and 3% alcohol. If an instrument measures the vapors coming off the boiling liquid, the mixture of vapors remains the same 97:3 mixture. When those vapors are condensed back into liquid, it again will have the same 97:3 mixture. In fact, no matter what thermal chances the mixture endures, it always stays at the 97:3 proportions. This means the blend is an azeotrope.

There is a bit of magic to making azeotropes. Not all mixtures form azeotropes because the density, boiling point and surface tension all has to be exactly right. But the effect is very useful. Azeotropic behavior allows clever engineers to deliver the benefits of a mixture with the convenient handling and storage of a single compound.

For example, azeotropes are very easy to distill and recover, which is part of the genius of vapor degreasing.

Another important benefit of an azeotrope is the unexpected ability to mix flammable and nonflammable ingredients to produce a stable nonflammable mixture.

Lastly, azeotropes permit the "tweaking" of a blend to obtain unique physical properties which makes the blends useful across a broad range of applications. For example, HFC 43-10 is a very mild cleaner. But add some other ingredients in azeotropic proportions, and MicroCare can make a blend that is almost as strong as the Bromothane^™ products. The possibilities are almost limitless.

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The "Wetting Index" and Cleaning Efficiency

The MicroCare cleaners are the best choice for precision cleaning of difficult shapes and awkward pieces. The reason for this success is the very low surface tension, high density and low viscosity of the chemicals:

• A low surface tension means the solvent can get into tight spaces more easily than solvents with high surface tensions (like aqueous systems).
   
• A dense, heavy solvent literally can float away contamination that other types of cleaning agents cannot move.
   
• And a solvent with low viscosity flows in and around objects more effectively than solvents with high viscosity (think molasses, or maple syrup).

A clever way to understand all these different measurements is to combine them into a single index. DuPont recommends combining the density of the solvent, the viscosity of the solvent and the surface tension into an index called the wetting index. With the wetting index, the higher the score the better the cleaning.

The formula for computing the wetting index is:

                                         ( Density x 1000 )

Wetting Index       =      ------------------------------

                                        ( Surface Tension x Viscosity )

In particular, the wetting index is a superior predictor when comparing particulate cleaners. It's a better gauge to use when selecting a solvent for applications in which the object is not to dissolve the contamination but to float it away.

The chart below displays this index for a number of popular cleaners. The results confirm popular experience: a heavy, dense solvent with a low surface tension and low viscosity will clean better than anything else on the market today. Here's how the numbers rack up:

The Wetting Index of Popular Solvents

So here's the short answer: when it comes to tough cleaning problems, MicroCare^® specialty fluids are the ideal choice. They are great replacements for ozone-depleting solvents such as CFC-113, 1,1,1-trichloroethane, HCFC-141b, nHFE solvents and HCFC-225, as well as high-global-warming solvents such as perfluorocarbons (PFCs).

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K_b Value and Cleaning Efficiency

The MicroCare and DuPont Vertrel precision cleaners have K_b values ranging from 20 to 70. The Bromothane^™ solvents have K_b values near 125. See each product specification for details.

Technically, the cleaning power of a solvent usually is measured by an industry benchmark called the Kari-Butanol test. In this lab test, a standardized test material – a thick, rubbery, eraser-like gum – is immersed in the solvent for a certain period of time and under certain prescribed conditions (e.g., temperatures, pressures, etc.). The lab technician then measures the remaining gum to determine the quantity of material that was dissolved by the solvent. The result of the test is an index called the Kari-Butanol value. This is usually reported on product spec sheets as a K_b value. Higher is better and means the fluid is a stronger, more aggressive cleaner. Mild cleaners have low scores in the tens and twenties; powerful cleaners like the old chlorinated solvents have ratings in the low hundreds.

But a word of warning: K_b values don't tell the whole story because modern fluxes and oils are very different from kari-butanol gum. In the place of raw Kari-Butanol scores most engineers are substituting systematic testing procedures, rigorously testing solvents on their components, their contamination and their cleaning processes. This makes sense because it's a test of real-world conditions.

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MicroCare Cleaners and Materials Compatibility

The MicroCare cleaners and the Vertrel^® products have excellent materials compatibility across almost all of the common materials of construction, including metals (zinc, stainless steel, carbon steel, aluminum and copper, for example), FR-4 substrates, fiber glass, resins, plastics, ceramics, glass and most elastomers. Some of the stronger blends have minor compatibility concerns with soft plastics, such as acrylics, ABS, and polycarbonate. Gaskets and elastomers will demonstrate some swelling and will, in most cases, revert to within a few percent of original size after air drying. Thorough testing prior to deployment is particularly important. EPDM, butyl rubber, Buna-S, and neoprene are recommended for elastomeric parts.

The Bromothane^™ solvents have good materials compatibility, including fiber glass, resins, plastics, ceramics, glass and metals. Bromothane^™ products are compatible with zinc, stainless steel, carbon steel, aluminum and copper. Under certain circumstances they may react with white metals. Bromothane^™ products have compatibility issues with soft plastics such as polycarbonates and certain component, such as capacitors. Contact with highly basic process materials, pH 10 or above, is not recommended. Thorough testing prior to deployment is particularly important.

If there are specific questions about plastics or elastomers, check the individual product spec sheets, or contact MicroCare. Regardless of the documentation, however, please take this important advice: test the solvent before deploying it. A few simple tests will eliminate a great deal of uncertainty about products, components and processes.

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Recycling MicroCare Cleaning Fluids

Yes, companies can and should recycle the MicroCare Cleaners. Every vapor degreaser is a still in addition to being a vapor cleaning system. That means that every vapor degreaser automatically recycles and reclaims the solvent while it is operating.

Under normal conditions, after months of use and prior to cleaning and dumping of contaminated solvent, the degreaser is used to concentrate the contamination into the boil sump. (This is called "boil down.") In this way, users reclaim most of the solvent for re-use, which minimizes waste disposal.

In addition, there are companies with a thriving business in reclaiming solvents. They will pick up the exhausted solvent, distill it and purify it, and then re-sell it at a reduced cost. This was an excellent program because it allowed companies to re-use perfectly good solvent that otherwise would have been disposed.

For the name of a company that offers a solvent reclamation service, contact MicroCare.

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Acid Acceptance Testing in Modern Vapor Degreasing

No customers will have an acidity problem with the MicroCare cleaners and the Vertrel^® products. It's simply not a problem with that class of chemical technology. Since these products do not contain “free” chlorine, they cannot turn acid. This means that the MicroCare cleaners and the Vertrel^® products are much safer and easier to handle than the old chlorinated solvents.

However, the old chlorinated solvents (as well as the Bromothane^™ products and any cleaner based on nPB) can turn acid if the condition of the fluid is not monitored. This acidity is caused by water mixing with the solvent, say, after a plating operation. Chlorinated and brominated solvents require a "stabilizer" to prevent the hydrolysizing of the water with the solvent. If there is too much water it will “exhaust” the stabilizer, which permits the solvent to deteriorate into an acid and could potentially damage the parts being cleaned and even the cleaning machine itself.

So Bromothane^™ solvents can turn acid. This is prevented by adding additional stabilizer from time to time. MicroCare sells BromoBooster^™, a concentrated stabilizer.

BromoBooster^™ is added to the solvent when the results from an acid acceptance test indicate the need to add the concentrate. The acid acceptance test is available from MicroCare as the BromoTest^™ kit. The BromoTest^™ kit contains everything needed to conduct the simple test. It takes about ten minutes once a week, and is as simple as being able to count drops falling from an eyedropper. A strong background in chemistry is not required.

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Shipping and Disposal of the MicroCare Cleaners

Because the MicroCare cleaners are nonflammable and non-corrosive, they are not regulated as hazardous materials by the Department of Transportation. Even though some cleaning agents are mixtures that include other solvents such as alcohol, none of the mixtures are classified as flammable, poisonous or corrosive by the friendly folks at the D.O.T. They all are shipped under the classification of "Non-Regulated/Non-Hazardous."

(However, the BromoBooster^™ stabilizer concentrate and the Vertrel^® XSi are flammable and are regarded as a hazardous for transportation purposes. From a practical point of view, this is only critical if when shipping the material by air. For ground transportation, it's mostly a paperwork issue.)

As for disposal, the same rules would apply unless the user has introduced a RCRA hazardous material during use. Users should test the exhausted product to ensure proper RCRA classification for waste disposal and should check local, state, and federal requirements in determining disposition of spent product. Most spent solvent is incinerated in cement kilns; typically that service costs $150 per drum. Contact a hazmat disposal service for details; normally they will require a chemical analysis of the material to determine the exact chipping classification.

Some locations now are offering a recycling service, which takes back spent solvent and returns "reclaimed" solvent, similar to the service which was widely offered for CFC-113, HCFC-141b and other major solvents. MicroCare has a list of names of companies offering this service; contact MicroCare to see if there is a company in your area.

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