Bending phone fires.
I guess this is why..
Apple has patented a fireproof material that could finally banish the misery of mobile phone trouser explosions. All too often, mobes can go pop in a person's pocket, causing hideous burns and ruining a perfectly good pair of trousers to boot. Now Apple has decided to step in and make sure that fanbois' nether regions are …
In tune with the puerile nature of schoolboy humour in the 70's, we scoured the dictionary for 'rude' words to have a giggle at - it was a Kent boys grammar, so we had little else to amuse us.
Most I've forgotten, but "fart" I vividly remember as "a slight explosion between the legs".
A lardy arse deforms more than a toned or boney arse - it would spread aroudn the phone to make contact with the seat - so less of a chubby user's weight would be bourne by their phone than would the phone of a skinny person. The chubby person's phone would also be subject to a more uniform load.
Scaling Laws 101 - Mass is proportional to the cube of the linear size, while surface area is proportional to the square of the linear size.
So if you assume that the mass is constant, then the increased area provides less pressure per unit area. Butt that's a false assumption. The mass has probably increased by a higher ratio than the area, so even the pressure (per unit area) will have increased.
This article is simply not up to the standards I expect of El Reg. I mean, honestly, you write:
Apple's invention has "excellent flame retardancy, electric insulation properties, and crack resistance, and produces only negligible amounts of toxic substances during incineration, if any at all".
However, it seems that even sitting on a mobe can cause a fire. Basic physics would suggest a larger bottom might make this more likely, as a bigger behind exerts more pressure on anything carried in the back pocket.
Why the hell has the phrase "crack resistance" not been worked into the latter paragraph?
Here are a few points to keep in mind, courtesy of your friendly neighborhood materials boffin:
* The title of the piece is unfortunate in that it implies that Apple has just recently come up with a way to protect you that did not exist before. This is misleading because I can absolutely guarantee that the plastics used in these devices were flame-retarded prior to the development of this IP. The point is not that there is anything new as far as the fire properties of the plastic are concerned; rather, the point is that they have come up with a different means of getting to the same or similar properties (i.e. without using persistent brominated flame retardants, which is probably what they were using before).
* Given that the application was submitted in 2009 and published in 2011, this is not exactly a recent development; what is recent is that the patent application was converted to a patent, which was then published. I seriously doubt they would've waited until that time to apply the technology, however, so in reality, assuming they had any intention of using the technology at all (not a guaranteed thing - just because it's patented doesn't mean it gets used in practice), this has probably been in use for a couple of years at least ("patent pending", etc.).
* Making most common plastics truly fireproof is quite difficult, and regardless of how fire resistant this renders the outer casing, it will not have any impact on whether the battery of a mobile device can explode or not. Explosions can still happen, and if the case cracks open, the hot, nasty, NSFW innards of the battery can still cause burns, even if the plastic doesn't catch fire. This will always be true simply because we demand greater and greater power densities of our portable power sources. Their physicochemical basis is almost irrelevant, the point is that there is a lot of energy in a small volume - energy that is designed to be readily released. That's fine so long as it doesn't come out all at once; it's when it does that you move from iPhone to iPhlame. Makes me wonder how much more development it'll take before the TSA decides that power sources above a certain energy density could be too easily repurposed as incendiary and / or explosive devices and outlaws them on passenger aircraft (they already regulate batteries and such).
* Another consequence of taking this approach is the amount of flame retardant additive necessary to make this work. The claims of the patent in question (i.e. where you want to go if you want to find out what they really care about) call out compositions that contain 50-70 wt% or so of flame retardant additive (see claim 9, do some math). Since these additives have densities much greater than the plastics themselves, this is not as much as it sounds like, but it's still a lot, and the consequences of putting this much of a dense, brittle inorganic compound into the plastic are typically that it becomes, well, more dense and brittle. In other words, there is a definite trade-off as far as the physical and mechanical properties are concerned. This may turn out to be a real problem depending on how much bending the case needs to withstand.
As a final point, I am a bit surprised that El Reg insists on linking to the USPTO, given the archaic and incredibly crappy looking user interface that website presents. I would strongly recommend using the European Patent Office as the source for all patents from now on. Here is the link to this same IP via the EPO, for comparison purposes (note that I have stripped down the URL to remove some additional lookup terms not necessary to retrieve the patent - your URL will be longer if you search for this):
All of the bibliographic data is there and hotlinked, and you can download the full document in PDF format via a reasonably modern / usable interface - as opposed to the USPTO site, where a URL a half-mile long links to a site that makes the Windows 3.x UI look flashy and modern that forces the user (because links are for losers!) to perform separate searches for every prior publication. At least they no longer force one to install a TIFF reader plug-in and download individual pages in uncompressed TIFF format - that's how it used to be some years back. Given the great leap forward to PDF technology, I guess they must've finally sprung for that math co-processor...
Might be applicable to EV packs.
That said, lithium imide is supposed to be flameout proof, in fact the papers I have seen suggest that by the time the imide decomposes the cell would only be on fire because the plastic casing was.
Hawker Energy was working on this, not sure how far they got but the problem was internal resistance AFAICT.
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