A Staff Report from the Straight Dope Science Advisory Board

What's up with silicon and silicone?

September 9, 1999

Dear Straight Dope:

While perusing today's paper I saw an article that said silicone implants can't be directly linked to health problems in women. That started me thinking--what's the deal with silicon (the element) and silicone? Are they related? Silicon seems to be just 'bout everywhere and in everything, from computer chips to implants to weather sealants to God know what else. I'm old enough to remember the days when silicon/silicone wasn't an everyday presence in our lives and now it seems that, without it, modern life would just about fall apart. What is it 'bout silicon (scientifically) that makes it so flexible for so many uses? My guess (after some thinking) is that it may have something to do with its being metallic (?), plentiful (i.e., sand) and right below carbon on the periodic element table (talk about useless knowledge--I still remember some H.S. chemistry). Beyond that, I seek your resources and enlightenment.

Wow. First glass, now silicon. Some days I think it actually paid to get that degree in ceramic engineering!

OK, from the top. Yes, it is true that a number of large and prestigious scientific studies have shown that silicone breast implants are not linked to the systemic diseases that many claimed they caused. Unfortunately, this knowledge comes a bit late for many of the lawsuits that manufacturers have already lost or settled. It seems that many of the plaintiffs (and juries) were unaware that correlation is not the same as causation. They went by the false logic of: "I got implants; I got a disease; they must be related." Studies have shown, however, that the occurrence of such diseases is no higher in women with breast implants than in women without. Thus, silicone implants don't cause the diseases. It's simply coincidence and while I feel bad for the women who have gotten these diseases, that doesn't mean silicone is to blame.

The worst effect this may have had, other than on the stockholders of the manufacturers, is that companies are now potentially less likely to use silicone in their medical devices. Scientifically, we know that it is safe, but just try to convince the public of that. Cecil tries his best to fight ignorance, but ignorance has a huge head start. Even with our help here at the Mailbag, it's hard to fight sensationalized and unscientific media accounts.

OK, off my soapbox and back to your question. What's the deal with silicon and silicone? To start, silicon is the second-most abundant element in the Earth's crust, making up about 26% of the elements found there (oxygen is the first, with about 50%, aluminum is third, with about 8%). Therefore, as noted in Introduction to Ceramics, second edition, by Kingery, Bowen, and Uhlmann (known as the ceramic engineering bible, in case you were wondering), "It is not surprising that the dominant minerals are silicates and aluminum silicates." Silicon, like carbon and boron, forms a wide variety of binary compounds with metals, which means it sees a lot of use. Also, since these materials are so widely available, they are fairly inexpensive.

You may think you're old enough to remember when silicon wasn't all over the place, but it's more likely you just didn't know it. You can find silica (SiO2) in such low-tech uses as glass, glazes, enamels, refractories, bricks, abrasives, and whiteware.

As for the more high-tech aspects, silicon is very useful because it and germanium (and some forms of tin as well) behave as semiconductors. Careful control of the chemical purity of these allows precise control of their electronic properties. While germanium was used first in this capacity because it was easier to purify, silicon is superior. Since the late '60s, it's been almost all silicon.

Finally, yes, silicone and silicon are related. The polymer silicone contains the element silicon as part of its backbone structure. Silicone is chemically inert, flexible, stable, and resistant to weathering and temperature. What's more, the textbook Inorganic Chemistry by Shriver, Atkins, and Langford notes, silicone's "low toxicity leads to [its] use in medical and cosmetic implants." So it's excellent for use in medical devices, presuming people stop falsely blaming it for their diseases. Lest anybody think, "Oh, sure, easy for him to say he doesn't have to worry about using silicone," I'd like to point out that I specifically sought out silicone pacifiers for my son because I felt they were safer than the other polymer choices.

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Staff Reports are written by the Straight Dope Science Advisory Board, Cecil's online auxiliary. Though the SDSAB does its best, these columns are edited by Ed Zotti, not Cecil, so accuracywise you'd better keep your fingers crossed.

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