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Sand Man: We See it Everywhere, But What Does Silica Do?

May 14, 2009
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Silica is sand and sand is silica. Sound simple? It is anything but. The good news is that we will probably never run out of silica anywhere in the world.

The bad news is that a tire made of silica filler, as opposed to carbon black filler, will not deliver as much tread life – at least not yet – according to the experts. But tire compounders are working overtime to change that.

Aside from this downside, a silica compound delivers decidedly better wet and snow traction, dramatically improved rolling resistance and enhanced wet handling.

Important to know is this: a tire can be manufactured using 100% silica as a filler, 100% carbon black as a filler or a blended compound using both. These are highly secretive formulas, to be sure.

In the process of manufacturing silica for use in tires, the raw material is melted, baked, dried and a host of other things before it makes its way to opening new doors in the world of tire technology. Some of the big names in silica production include Evonik-Degussa, Rhodia and Dow Corning.

As one of those companies points out, the addition of silica is an expenditure that pays off. According to one spokesman, the buyer of a tire that uses silica as filler can recover the cost of their purchase in just one year thanks to a 3% to 8% drop they will attain in the cost of fuel. On the flip side, they will lose 10% to 15% in tread life. As we’ve said for decades, tire performance is a series of compromises, it just depends on how and where they are used.

Those customers who are shopping for dry handling at higher speeds will be happier with tread compounds using higher levels of carbon black. Those seeking greater snow, wet traction and lower rolling resistance will want silica as a filler. Of course, those in the middle will probably be satisfied with a blended compound that’s part silica, part carbon black.

A trip around the world reveals that 70% of tread compounds produced in Asia and Europe are silica-based, with just 30% of tires using a carbon black filler. In the U.S., simply transpose those numbers. Further, the 30% of tires using a silica compound in the U.S. find a home on ultra-high-performance cars equipped with H or higher speed rated tires. The owners of these vehicles like the wet handling silica delivers, and will pay to get it.

Another note before moving on. It is precisely the rolling resistance of a car tire that is playing a huge role in today’s economy, since it cuts fuel consumption. In addition, lower fuel consumption in a silica-based filler emits fewer CO2 emissions – and that is a benefit to the environment, say the scientists with whom we talked.

Rhodia Group, based in France, says that up to this point, the best silicas have made it possible to reduce rolling resistance by approximately 25%, bringing about a reduction in fuel consumption. No doubt you’ll be hearing more about eco-points as we move through time.

Touting its innovative ways, Rhodia refers to a study of tires in use for 40,000 kilometers, in which a tire containing silica filler in its tread delivered a gain of 5 eco-points – or 11% – in comparison with a tire that contained only carbon black filler. This gain, according to Rhodia, is equivalent to the total environmental impact of the tire’s production and the raw materials from which it is made. In other words, says Rhodia, “the energy savings made possible by the use of silica tire technology far outweigh the impact of its manufacture.”

The French company even goes so far to say that since 2001, the use of silica in tires, in terms of energy use, has contributed to the savings of 20 billion litres of fuel and the reduction of 50 million tons of CO2 emissions.

Silicone Surroundings
Did you know that silicone, a relative of silica, is all around you, improving your driving experience in diverse and unexpected ways? Silicone joint sealants and waterproofing chemicals extend the life of roads and bridges, while silicones in automotive care products help you polish and protect your investments.

Moreover, silicones offer unique properties that enable them to thrive in a harsh engine compartment, as well as under various vehicle, weather and driving conditions. Silicone is stable over a wide range of temperatures from -58⊄šF to 392⊄šF, and is resistant to thermal shock. This enables flexible joint movement with excellent sealability and excellent sound and vibration dampening capabilities.

Tire compounds normally contain about 30% reinforcing fillers – including silica, but not silicone – that are essential for providing the rubber compounds with the required features they are called upon to deliver, including grip, as well as abrasion and cut resistance.

Newest on the scene is a silica compound with a structure so complex it allows polymer molecules and filler particles in the tread of the tire to couple more effectively.

Creating Silica
Here’s a brief description of how silica used in tires is made. First, a mixture of alkali silicate is prepared by melting sand and mixing it with a caustic solution. As far as the difference between sand and silica, they both have the same base chemistry – silicon and oxygen – but they just have different forms. Sand is the crystalline form while silica is amorphous (without definite form) and is shapeless, much like soot or charcoal granules. Carbon can be a diamond, coal or soot.

At this point, the precipitated product consists of 86% to 88% SiO2 and 10% to 12% water, the latter being present both in the molecular structure and physically bound on the surface.

Next, the liquid silica suspension obtained from precipitation is transported to filter presses in which the salt resulting from the precipitation is washed out and as much water as possible is removed. The filter cake still contains considerable quantities of water, so a drying state is necessary to evaporate up to six times the amount, by weight, of water.

For this reason, drying accounts for a considerable proportion of the production costs. The particular drying method used depends on the desired target properties of the end product.

Are you lost? Don’t be. Just like cotton, rayon, nylon, polyester, butyl, fiberglass, steel, Kevlar and other materials, this is simply a learning process and we’re only studying the first chapter. While it’s true that the properties just mentioned are tire cord materials, not fillers, it is now becoming more and more important to understand everything that goes into the manufacture of a tire.

The more you know about the properties of a tire, the more you will sell and the more comfortable your customers will be. This is a world based on price and performance, and your knowledge of how a tire performs and what makes it such an integral part of a vehicle is key.

If you have questions, don’t hesitate to call the makers of silica or carbon black or tires. They have the answers you need.

Submit a Comment   Legacy Comments
avatar   William Surgeon   star   10/21/2009   6:16 PM

Where does the silica used in U.S. tires come from?