Jump to content

Why Do The Fluxing Molecules Only Have One Oxygen Atom


mrcasey

Recommended Posts

The other week, I was explaining to an art center member about glaze bases being comprised of

glass formers, stabilizers, and fluxes.  I also gave some examples of the 3 different kinds of

oxides from those RO/R2O, R2O3, and RO2 groups.  She asked me why the fluxes have only

one oxygen atom.  I couldn't answer her question but am curious myself. 

 

                  

Link to comment
Share on other sites

It has to do with the kind of bonds the fluxes, glassformers, etc. form.  Look at a periodic table, on the one side you've got the alkali metals, alkaline earths, etc.  On the other, you've got the halogens, chalcogens, etc.  Sodium chloride is a prime example of an ionic bond--the metal is the cation, the anion a halogen.  You can dissociated the sodium ion from the chlorine ion by introducing something like water which has a polarity to it (a positive and a negative side).

 

On the other side of things, you have covalent bonds, which are considerably stronger and much harder to break.  Silicon dioxide is a covalent bond that forms giant covalent structures.

 

It's important to note that most bonds are a hybrid and covalent and ionic bonds form a spectrum rather than hard and fast differentiation. Polar bonds are exactly in the middle (like water).

 

So, the fluxes have one oxygen atom because of the charge they have.  Sodium, potassium (and all the alkali metals) ions have a charge of +1, Calcium ions (and all the alkaline earth ions), +2.  Oxygen has a -2 charge. Therefore, all the common fluxes, which have weaker ionic bonds, must, by virtue of their charge, have only one oxygen atom.

 

Borates, of course, are the wild card.  Actually, there are a lot of wild cards, but they function on similar principles, just in more complicated ways.  ;)

 

Make sense?

Link to comment
Share on other sites

Guest JBaymore

Tyler got it. Also look up the chemistry concept of "valence".  Also relates to the number of electrons a given "orbit" can hold on a given atom..... and how many are already there.  And how they "play nicely with others". ;)

 

best,

 

...................john

Link to comment
Share on other sites

Although I learned a lot from your post, I think I've
asked the wrong question.  Here's the question that I more meant
to ask:  What is it about an alkali metal or alkaline earth
metal bonded to a single oxygen atom that brings down the
melting temperature of silicon dioxide.  That is, do the number
of oxygen atoms in the molecule have anything to do with whether or not the
alkali/alkaline earth atoms work as fluxes?

 

 

Link to comment
Share on other sites

mrcasey, 

 

I think I see what you're getting at.  The number of oxygen atoms itself does not cause the flux to be a flux, it is coincident with the cause, but is not a cause itself.  Alkali metals and alkaline earths are just going to form salts (ionic bonds), it's what they do.  They give up their electrons too easily not to do so.

 

As I said above, the ionic bond that allows the dissociation of ions in table salt (NaCl) in water for example, is the mechanism at work in a flux.  It's common knowledge that salt lowers the melting point of ice.  The ions interlace with the polarized water molecules and change the way they form their lattice.

 

Ceramic fluxes work the exact same way.  Alkali metals, and alkaline earths with their single oxygen atom are one configuration of this, but so are borates (B2O3), and phosphates (P2O5), and a number of others.  The way they work as fluxes is the same, however they're treated like single units by themselves.  That is, like the Na+ or Cl- in table salt, not as "NaCl."  They're a covalent unit that forms an ionic bond-sortof.  Of course, borates and phosphates can also be glass-formers--wild cards.

 

I hope that answers your question.

 

Edit:  I feel the need to add that while I'm speaking of "charge" a lot, what I'm actually talking about are "oxidation states."  They're not an actual charge, but a hypothetical one that an atom might form when they come in contact with an atom of a different oxidation states.  With the exception of the alkaline earths and halogens, most elements have multiple oxidation states, some (like silicon), can have both positive and negative oxidation states.  

Link to comment
Share on other sites

@Tyler Miller explains this better than I've seen in a while...and that appreciation is coming from someone who would still be an undergraduate if he had to take one more chemistry class. Thanks Tyler!

 

On a less serious note, when I first read the topic question I was reminded of an old joke:

 

Two hydrogen atoms walk into a bar...

One says, "I've lost my electron".
The other responds, "Are you sure?"

The first replies, "Yes. I'm positive!"

 

-Paul

Link to comment
Share on other sites

I am still confused.

 

I understand how a salt could dissolve into water and interact with the water molecules but in a glaze how does this happen. Does the increase in energy in the silicon dioxide allow the fluxes to interact with the solid in a more liquid way? How are the ions in my CaO dissociating into a crystal of SiO2...  :unsure:

 

I didn't attend many of my chemistry lessons after the age of 16 because of the terrible teachers I ended up having. Any links that you know of which might explain this more would be a great help.

 

Should have gone to digital fire "Fluxes interact with the surface molecular structure of other materials and pull them away (dissolve them) molecule-by-molecule." 

It all seems very complicated. A flux can be very refractory by itself but with the right conditions and ratios it can dissolve SiO2.

Link to comment
Share on other sites

You've basically got it.  

 

The fluxing action of Na2O or CaO on SiO2 is essentially the same as NaCl or CaCl2 on ice, just at higher energies.  Note that CaCl2 works to melt ice at a much lower temperature than NaCl, and Na2O works at a lower temperature than CaO on SiO2.

 

Google "molecular model of ice" and "molecular model of silicon dioxide" and you'll see they're very similar.  Not the same, but similar.  

 

One last edit:  SiO2 is, as I noted, really a giant lattice of covalent bonds, whereas water/ice is just individual molecules oriented in a particular way due to their charge.  This is why it takes tremendously more energy to melt silicon dioxide (or even lower its melting temp)--you're overcoming a much stronger bond.

Link to comment
Share on other sites

Guest JBaymore

A flux can be very refractory by itself but with the right conditions and ratios it can dissolve SiO2.

 

Bingo... key concept.  Ratios of molecules.  THAT is what the study of eutectics is about....and a lot of what glaze chemistry is also.

 

best,

 

.................john

Link to comment
Share on other sites

@Tyler Miller explains this better than I've seen in a while...and that appreciation is coming from someone who would still be an undergraduate if he had to take one more chemistry class. Thanks Tyler!

 

On a less serious note, when I first read the topic question I was reminded of an old joke:

 

Two hydrogen atoms walk into a bar...

One says, "I've lost my electron".

The other responds, "Are you sure?"

The first replies, "Yes. I'm positive!"

 

-Paul

When two elements love each other very much, they come together to form a compound.

 

Sorry, I'm not helping.

Link to comment
Share on other sites

It's important to note that most bonds are a hybrid and covalent and ionic bonds form a spectrum rather than hard and fast differentiation. Polar bonds are exactly in the middle (like water).

 

Still trying to get my head around this, so a covalent and ionic bond are the same thing or different?

 

I was doing some youtubing and found this table

 

post-23281-0-80920300-1421605439_thumb.png

 

I can see the Silicon with a charge of 4 and the Oxygen with a charge of two so I get that equals SiO2 but yet it is a massive covalently bonded structure. 

 

I am finding it hard to understand the difference between charged ions bonding because of a charge from electrons or protons and atoms sharing electrons covalently. Are they not all sharing electrons as the charge is from the difference in electrons or is it the charge bonding and not the electrons.

 

Is it only really covalent if the protons are equal to the electrons?

 

I am confused   :(

post-23281-0-80920300-1421605439_thumb.png

Link to comment
Share on other sites

This is where the concepts of electron configuration, atomic radius, ionization energy, and valence come into play.

 

Ionic bonds and covalent bonds are different in nature.

 

Look at a periodic table.  You'll notice that the elements are organized into blocks.  S-block, P-block, D-block, and F-block.  

 

These blocks correspond to the number and arrangement of electrons into "shells."  The tendency of atoms is to try and fill out their shells if nearly complete, or to get rid of electrons back to where it is most complete.  This is the principle behind both covalent bonds and ionic bonds.  Ionic bonds are where the electron is actually pulled off one shell onto another and the atoms stay together because of their electrostatic charge, covalent bonds are where the atom share the electrons.

 

The term for the energy required to remove an electron is "ionization energy."  Ionization energy increases as you move from left to right across the table, and from bottom to top.  The Alkali metals and alkaline earths have relatively low ionization energies, and the halogens, chalcogens, and noble gases have very high ionization energies.  Elements with larger atomic radii have lower ionization energies than those with smaller ones--electrons closer to the proton are less eager to leave.

 

So, if we had some caesium, and some fluorine, and we combined them, we'd get a vigorous reaction where the caesium atoms would each very readily get rid of their extra electron, and the fluorine would very powerfully pull the electrons off.  Highly dangerous, scary powerful reaction.  

 

If we took some gaseous hydrogen (H2), we'll see a pretty pure example of a covalent bond.  Two atoms of equal ionization energy that just want to fill out their two electron shells.  If we raise their energy in the presence of oxygen, that bond breaks, and it forms H2O.  Oxygen has a higher ionization energy, but not so much to actually pull the electrons off the Hydrogen (like Fluorine or chlorine would), so it forms a covalent bond with a polarity to it.  This polarity is what allows water to dissolve lots of salts, and why it's so useful for us to live.

 

Ions are pretty common in nature.  PH (acidity) is a measure of the number of hydrogen ions present in a solution.  In biology hydrogen ions are sometimes just called protons (since that's what they are), and if you ever have stomach troubles, like an ulcer, a doctor might prescribe you a proton pump inhibitor.

 

Now, covalent bonds aren't always that strong, and the Carbon column is a good example of that.  It's sort of in the middle of the ionization energy spectrum, and so those elements readily form and break bonds.  CO2 is a good example of this.  A kiln atmosphere is readily altered from oxidizing to neutral to reducing with very little effort.  And loose charcoal is easily changed from C to CO to CO2 and back.  This aspect of Carbon's nature, along with the natures of Oxygen, Nitrogen, Phosphorus, Sulphur and hydrogen, form the backbone of the chemistry of life.  CO2 also needs some pretty low temperatures to get it to be solid.  Carbon can, however, become very strong if it's coaxed into making a certain kind of lattice of covalent bonds with itself (diamond lattice).  Diamonds aren't actually all that chemically stable--graphite is far more chemically durable, but the lattice is physically very strong.

 

Silicon has similar properties.  There's no such thing as SiO2, really.  It doesn't exist.  What does exist is a lattice of Silicon and oxygen atoms with one silicon atom(+4) at the centre of four oxygens (-2), which each connect up to more silicon atoms ad infinitum.  So really, SiO2, which is just a convenient way of writing one complete unit, is SiO4SiO4SiO4SiO4 and so on forever.

 

Does this help?

Link to comment
Share on other sites

Guest JBaymore

We can keep going into this deeper....... BUT... I want to point out here before we do for those OTHERS maybe reading this ..........

What is being discussed here is important and is actual core scientific concepts..... and that is certainly "good stuff"...... but this level of understanding is NOT a necessary component of understanding glaze chemistry effectively enough to work on it as a potter and also to utilize glaze chemistry software like Insight to help you in your studio work.

I don't want to "scare off" some people from potentially looking a little more into the world of "glaze chemistry" when they look at this kind of discussion.

This is "Glaze Chemistry III" stuff. ;)

 

best,

 

.......................john

Link to comment
Share on other sites

Thank you Tyler, going to have to re-read that a few times and let it sink in. I have vague memories of all these terms you are using but it has been a long time since these brain pathways were exercised.

 

Exactly John, you don't need to know bubble dynamics, surface tension and thermal dynamics to whisk up egg whites with sugar and bake a meringue. I think this has gone a little past glaze chemistry and into material science or at least my questions came from watching this video.

 

Who knew the word ceramics came from the greek word Keramicos that means burnt stuff.

 

 

Link to comment
Share on other sites

Guest JBaymore

I know the elementary level of this stuff Tyler, did college chem and calculus myself...... but I currently teach this stuff to potters at the college level.  And these days most of their eyes glaze over when you start talking about "complex chemistry stuff"... like writing CaO  on the board ;) .

 

I'll chime in now and again on the thread in case I think you missed something iomportant (which s CLEARLY unlikely... you have this stuff down)..... just wanted to make the point that this is not all that necessary to use a basic glaze chem understanding to solve basic studio issues.

 

Personally I find the science and engineering base of ceramics very interesting and fun.  Many in the arts don't.

 

best,

 

........................john

Link to comment
Share on other sites

The problem about posts like this is that they make my brain "itchy" and I have to go and drag books off shelves etc to stop or quell the itch a lttle. 

I go along with the the immersion theory of learning...   if you stay immersed for some time,bit by bit some of it  begins to feel normal ie sinks in a bit. Like learning a language.

Like High Bridge, so grateful for the explanations and advice given here on this forum.

Tyler, did you learn chemistry to do Ceramics, or what?? Just interested on how you landed , what with your classical languages study?

Wierd bunch ,we what ever we call ourselves..

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.