Prev: Quantum Gravity 299.1: Russia Moves Toward Reals Rather Than Complex Numbers in Physics
Next: The fate of the Earth?
From: Andrew Usher on 20 Dec 2008 21:11
On Dec 20, 12:38 pm, Uncle Al <Uncle...(a)hate.spam.net> wrote:
> Andrew Usher wrote:
>
> > It came to me one day when observing paraffin wax freeze, that the wax
> > could not be a perfect crystal since it is not a pure substance.
> > Rather, it consists of countless isomers;
>
> Linear hydrocarbons and they all pack alike in two groups, even or odd
> number of carbons.

Petroleum-based wax is not going to consists solely of linear
paraffins.
Further, your statement about them all packing in two groups applies
only to pure isomers, not a random mixture.

> > yet, it seems to be
> > crystalline from its opacity and apparent sharp melting and freezing.
> > Natural fats and waxes must be the same as paraffin in this regard, as
> > their physical properties are exactly analogous.
>
> No, stupid. Glycerol triesters are all over the map. Biological
> waxes are linear and behave.

Again, natural waxes are far from pure substances.

Andrew Usher
From: Andrew Usher on 20 Dec 2008 21:13
On Dec 20, 6:58 pm, Mark Thorson <nos...(a)sonic.net> wrote:
> Salmon Egg wrote:
>
> > This is certainly not my field of expertise. My question is: What is the
> > x-ray diffraction pattern of solidified wax? Is there any evidence of
> > microcrystals?
>
> If you break a piece of wax (or paraffin masquerading as wax),
> you'll see a fine polycrystalline fracture surface. More pronounced
> with paraffin (US usage, not UK) than with natural waxes (beeswax).

I know that wax is not amorphous, but how can it be entirely
crystalline? That was my question.

> Some additives such as stearic acid are often used as hardeners
> for paraffin wax. Pure stearic acid solidifies into a large-grain
> polycrystalline solid.

So it wouldn't be so without additives?

Andrew Usher
From: RLW on 20 Dec 2008 23:56
On Sat, 20 Dec 2008 17:12:09 -0800, Uncle Al wrote:

> ... phosphatase assay... Avoided walking through that hall thereafter.

Yeah.

The "Danger Building" at the local U. had a floor on which every single
door bore a hazard emblem of some sort.

Some doors you knew not to approach without even seeing the emblem.
From: RLW on 21 Dec 2008 00:45
On Sat, 20 Dec 2008 00:32:53 -0800, Andrew Usher wrote:

> It came to me one day when observing paraffin wax freeze, that the wax
> could not be a perfect crystal since it is not a pure substance. Rather,
> it consists of countless isomers; yet, it seems to be crystalline from
> its opacity and apparent sharp melting and freezing. Natural fats and
> waxes must be the same as paraffin in this regard, as their physical
> properties are exactly analogous.
>
> I drew, therefore, an immediate parallel with crystalline plastics,
> which seem very similar (though having a much higher tensile strength).
> Am I correct in doing so? I have never read anything about the solid
> structure of fats and waxes but I do not think I can be wrong here.
>
> So we have a group of materials that can not form perfect crystals (or
> segregate into solids that do), which are all organic, but there can be
> made inorganic polymers that surely behave the same way. They are, of
> course, thermodynamically unstable, as all organics are.
>
> So can I set down a general rule, that the thermodynamically most stable
> state of any aggregation of elements, will form one or more crystalline
> phases, which form the whole bulk, at sufficiently low temperatures?
>
> Andrew Usher

Probably not. Piles of sufficiently long, variegated, chain-shaped
molecules will freeze into amorphous solids. Glass is an example.

As for "wax", the word covers a lot of ground.

Yours sounds like the stuff we used to make candles when I was a kid. It
contained a fairly narrow range of molecular weights, would soften
slightly with increasing temperature but would then melt quite suddenly.
Fracturing it would reveal a granular surface, which explains its
translucence as a solid: lots of internal refraction.

Other "waxy" substances, containing a much broader range of sizes of
molecules, would behave more "glassily" inasmuch as they would soften
gradually with increasing temperature. (In some cases you can see the
short-chain stuff bead up on the surface before the bulk of the material
melts.) Some, when frozen slowly, are pretty transparent.

As for things being "partially crystalline", you do get that sort of
structure when you quench metal during forming. A Web search for "anneal
quench crystal" will provide lots of interesting reading material.

Mind you, I'm not an expert in physical chemistry or materials science
(or for that matter, any chemistry or any science). I did think I should
give you my best shot at an answer, better at least than my earlier post
giving Uncle Al his daily ration of grief.
From: jmfbahciv on 21 Dec 2008 08:52
Uncle Al wrote:
> RLW wrote:
>> On Sat, 20 Dec 2008 10:38:49 -0800, Uncle Al wrote:
>>> No, stupid. Glycerol triesters. . . .
>> Gee Al, the IUC is not going to penalize you if you just call them
>> "triglycerides", like everyone else does.
>
> Uncle Al endured a 5-credit term of biochemistry at 0800 hrs during
> winter term in Michigan.

<GRIN> I'm enduring one of those mornings right now.

> Two direct results,
>
> 1) don't take biochemistry; and
> 2) Solved a lab's phosphatase assay problem - "don't use phosphate
> buffer." Avoided walking through that hall thereafter.
>
> Buncha maroons.

But they fix horses.

/BAH

First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4 5
Prev: Quantum Gravity 299.1: Russia Moves Toward Reals Rather Than Complex Numbers in Physics
Next: The fate of the Earth?