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Author Topic: growing crystals - gravity?  (Read 5150 times)

Offline anders

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growing crystals - gravity?
« on: 24/02/2005 20:44:11 »
Hi, I am growing a crystal KAl(SO4)2 * 12H2O, and I'm very fascinated by the beauty of the crystals I'm getting. I'm using a seed crystal in a solution, and I was wondering why I seem to only get crystals (3 so far) perfectly oriented with the pointy end of the octaheder pointing straight down, and the other end pointing straight up. It's like they're perfectly aligned with the force of gravity.

I was wondering if gravity affects how the crystal grows, or are my (3) results just a coincidence?

(I'm only a first year student in chemistry. I'm sorry if it seems like a stupid question)

anders


 

Offline anthony

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Re: growing crystals - gravity?
« Reply #1 on: 21/05/2005 14:15:02 »
I'm assuming these crystals are free floating somehow, if they can be growing up and down simultaneously. You're answer is yes, they are aligning with gravity, but their growth is not determined by gravity. Given good conditions most crystals will form with a variety of shapes and symetries determined by their crystaline "unit cell". Growth on some faces of the crystal is faster than others, hence the long shape of the crystal. Which face has fastest growth is determined by the atomic structure on the surface. Some scientists, growing nanoparticle crystals, use detergents to make crystalisation faster on some faces than others and select the shape of crystal they want to form.
 

Offline bigtim

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Re: growing crystals - gravity?
« Reply #2 on: 22/09/2006 21:34:09 »
quote:
Originally posted by anders

... aligned with the force of gravity...


This is a common missconception. Gravity is not a force. The force is the product of mass and the strength of the gravitational filed, ie, the quotient of the ratio force/mass.

Big Tim
 

Offline Mr Andrew

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Re: growing crystals - gravity?
« Reply #3 on: 29/09/2006 21:29:56 »
bigtim,

You obviously haven't had physics because the force of gravity is almost universally understood to mean the force due to gravity by even people that aren't especially scientifically minded.  You're explanation was correct of what the force due to gravity is mathematically but when we name things with words, there are many synonymous ways to name the same thing and the use of one different word does not nessecarily suggest an misunderstanding of a concept.  Take for example the force of friction.  Friction is not a force but the electromagnetic interaction of the surface atoms of the two materials rubbing past each other.  Even so it is referred to as the force of friction because it enacts a reactive force.

Technically, the statement "aligned with the force of gravity" is correct because force is a vector and thus something can be aligned with it.  I can see where some confusion might arise in someone's mind who is not a scientist but I think it is safe to assume that anders is some sort of scientist (in fact he said he was a student in chemistry) as he used the chemical formula for potassium aluminum sulfate dodecahydrate.  Thusly he is most likely familiar with gravity (both the field and the resulting force) and only used the word "of" as a matter of convinience.

"His mind is the ultimate weapon!"-MacGyver television series
 

Offline Mr Andrew

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Re: growing crystals - gravity?
« Reply #4 on: 29/09/2006 21:34:23 »
Ok, now back to crystals:

I myself am only 16 (though I know my stuff when it comes to chemistry).  Consequentially, I have not had much expirience with growing crystals.  I would like to know more about how one would grow crystals (in general, not anything specific) and even though I am familiar with unit-cells, I am interested in how they affect shape of crystals and how adding detergents would allow one face to grow faster.

"His mind is the ultimate weapon!"-MacGyver television series
 

ROBERT

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Re: growing crystals - gravity?
« Reply #5 on: 05/10/2006 17:20:22 »
Here are some camphor crystals on a glass slide (in polarised light):-



These tiny crystals formed in less than a minute (above image is 10x actual size),
other larger crystals can take weeks or months to grow:-

http://www.waynesthisandthat.com/crystals.htm#single%20crystals

« Last Edit: 05/10/2006 17:29:17 by ROBERT »
 

The Naked Scientists Forum

Re: growing crystals - gravity?
« Reply #5 on: 05/10/2006 17:20:22 »

 

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