Calcium Borate

[High Bridge Pottery]

So it is a silica that come out the ground already 'ground up' but stuck together?

[glazenerd]

Morphology is one of those fancy chemistry terms that means: how it was formed. Men grind it.

 

I do agree with their claim- "it is the ultimate silica"...98.8% pure a=phase quartz

[bciskepottery]

We mods have been following the thread and want to remind everyone to keep to the high ground during discussions. Each of us brings to the forum a wide range of expertise, knowledge, and experience -- formal and informal -- that we respectfully share with the community. Anyone is welcome to post a comment -- or not post a comment or to stop participating in a thread. Just remember that we are dealing through an impersonal medium that does not provide the same context to words that one would have in a personal discussion.

[glazenerd]

My father was the batch mixer from the 50's up until the mid 80's. Back in those days they got 60-80 grit silica because modern machinery was not available to grind ssilica down. So they would process it, to turn it into silica flour before melting.

[Tim T]

Glazenerd,

I think if you reread your last but one post, you'll agree that you are conflating melting point and chemical reactions.

The melting point is a physical property of the material, and is unaffected by the surface area. The only difference that particle size or surface area can make is in making it easier to transfer heat into the material, which may mean that it melts sooner, but it will still melt at the same temperature.

Particle size affects reactivity in two ways. First, if we are looking at the initial reactions before solids are immersed in a molten flux, i.e. basically at a sintering stage, smaller particles will have a higher number of contacts points, and so the reaction will occur more rapidly when viewed at a macroscopic scale. Secondly, smaller particles have a smaller radius of curvature and are generally rougher than larger particles, so there are more exposed edges with discontinuities in the atomic structure. These are generally weaknesses that allow chemical reactions to occur more readily than if there is a more regular atomic stucture.

[Pieter Mostert]

+1 for what Bruce said.

Just to put things in perspective, the silica you need to be worried about is that less than 10 micrometers in diameter (see http://digitalfire.com/4sight/hazards/ceramic_hazard_quartz_crystalline_silica_toxicity_251.html). From the spec sheet for Sil-Co-Sil 45 that Tyler linked to, that's about 50% for a 325-mesh silica. I couldn't find any particle size distributions for Imsil A-25, but given that its median particle size is 5 micrometers, compared about 10 micrometers for Sil-Co-Sil 45, I would guess that the percent of Imsil A-25 less than 10 micrometers is equal to the percent of Sil-Co-Sil 45 less than 20 micrometers, i.e. 80%.

Of course, this doesn't tell the whole story, since the smaller the diameter of the silica particles, the more hazardous they are, so you'd need to compare the tails of the particle size distributions if you really wanted to quantify how much more dangerous Imsil A-25 is than Sil-Co-Sil 45.

[High Bridge Pottery]

Does that mean then all silica would melt at 2900F but it would just take far too long? Is there actually a certain melting temperature as heatwork seems to be important in ceramics, maybe it is different for pure silica.

 

I had a quick look at some crystal glaze recipes as I have never really looked at one. All seems to have a good ~20% zinc and ~20% pure silica and still the silica unity values are so low. When you used a standard pottery blend silica what difference did you find? Was there a big difference in the melt? It does look like you are really trying hard to get everything to melt before you stop and it falls back out into these crystals. A glass that it what, 6:1 silica zinc maybe 8:1 sounds interesting to melt.

[glazenerd]

Finally, a conversation. Believe I stated in my first posts in this forum that I have been doing ceramic glazes for 5 years. Also said I have been reading and studying everything I can get my hands on- IE_ self taught. Have gotten several things wrong along the way, will get more things wrong as I go. Reason I came here, realized I was not putting certain pieces together right. . Came here to learn- finally found some teachers.

 

Glaze Nerd

[Mark C.]

Imsil is air floated if I recall so thats why the smaller size. I have some air floated materials and the particle sizes are smaller.

[Tim T]

Joel,
If they are of the same structure then yes, the melting points will be the same. But there are multiple forms or structures of silica, and these have different MPs (e.g. 1670C for beta tridymite, 1713C for beta cristobalite) but with quartz generally with heating they will transform from one to another rather than melt (see http://www.quartzpage.de/gen_mod.htmlfor more info).

 

But melting point isn't everything in  glaze, as the phase diagrams show. One thing that may be happening is that when two solids are in contact (as in sintering) a chemical reaction occurs at the point of contact, the result of which may be solid or liquid. Also, once some liquid has started to form, whether from melting or through a chemical reaction, other components may dissolve into the liquid. Where we are using minerals (rather than just mixtures of particles of pure chemicals), I think that they will melt at the appropriate temperature from their phase diagram. Phase diagrams are generally based on steady state conditions, i.e. the temperature is held long enough for an equilibrium state to form, which is seldom the case when firing a kiln unless you have an unusually long soak time.

 

It is interesting that analysis of mos Chinese copper red glazes show an element of lead. Almost all of this would have evaporated off during the firing, but I wonder if they used it as a flux in the earlier stages of the firing to get the glaze chemistry started off for that glaze.

 

Heatwork is actually measuring multiple things - it is portrayed as a combination of temperature and time, but that is too simplistic. As an example, you could heat any cone to 100C and no matter how long you hold it there, it won't bend over. Conversely, with a powerful enough kiln you could ramp up the temperature much more quickly than the cone can react. So really it is some type of integral of temperature and time above a given threshold temperature, within a range of temperature rates of change. Here in the UK we tend to specify top temperature and soak time, whereas in the States cones are used more, but it would be more accurate to use both, or even give the full firing curve.

[Guest JBaymore]

.......... i.e. the temperature is held long enough for an equilibrium state to form, which is seldom the case when firing a kiln unless you have an unusually long soak time. .........

 

This is a key issue that many folks miss when looking at results and how they often do not match "theoretical" expectations.

 

 

Also..... great comments on heatwork there above you gave, Tim.  There was a great presentation that was at NCECA a few years ago... by engineers and manufacturers that were working on changing the models that computerized controllers use to model "heatwork".  It was fascinating.  A lot of stuff I knew....... but "packaged" in a different way.  Chris Campbell and I sat together for that one.  

 

I was kind of amazed at how FEW people were in the room listening.  It is a core aspect of executing our craft.

 

best,

 

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

[Mark C.]

Send me the roasted beans please .I will grind them myself as I like a fresh FINE grind like 2500 mesh.

[Min]

Okay, just in case I made a mistake I emailed the manufacturer and got the info straight from the source. 

 

my email:

 

Hi,

 

Quick question if I may, I am trying to determine the mesh size of your Imsil 1-25 silica.I see that it is 5 micron, does that correlate to 2500 mesh size?

 

Thanks in advance for clearing this up for me, 

Madeleine

 

response: 

 

Hi Madaleine,

 

At 5 microns, mesh size is too small to exist as actual screen size but for reference, yes, it would be 2500 mesh.

 

Many thanks,

Angela Le

Sales Representative

The Cary Company

C 630-215-9781 | O 630-629-6600

TheCaryCompany.com 

[High Bridge Pottery]

I am glad you brought up the silica because I would be interested to try some compared to what I have already in stock after finding out most of my bubbles in glaze are through silica melting so a smaller mesh should in my theory melt faster so have less bubbles at the end.

 

It makes more sense in your journey for pure ingredients after seeing what sodium can do for crystal growth although I do quite like the black spiders webs across the pot You lost me on the thermal conductivity and how that relates to sodium competing in the crystals but being different shapes makes sense that crystals that you don't want would be seeded from those impurities.

 

All the talk about silica melting reminds me when I watched a little clip about refractory bricks and their claim it goes from crystalline solid to amorphous solid without melting. Ceramics are tricky little buggers.

[Tim T]

I'm not totally clear on why you equate thermal conductivity (i.e. the ability for a material to conduct heat (and so energy) within itself, and the ability of a material to act as a flux.

As a counter example, diamond, although not commonly used in ceramics(!), has exceptionally high thermal conductivity, but is a much less powerful flux than, say, lead or cryolite, to name two active fluxes.

Perhaps you could explain your thinking or cite your sources here?

[Pieter Mostert]

Min, the figure of 5 microns given here is for the median particle size (half the particles are smaller than this). Mesh size relates to the maximum particle size. If the maximum particle size of Imsil A-25 were 5 microns, then yes, it would be 2500 mesh, but I suspect the rep you emailed just assumed the figure you gave was the max size without checking. I don't know what the actual maximum size is, but unless the particle size distribution is very narrow, the mesh size is likely to be significantly smaller than 2500. I haven't seen anything shows it to be 325 mesh, and even if it were, it would still pose more of a risk than Sil-Co-Sil 45, where the median particle size is about 10 microns.

On the other hand, if you look at the graph for Sil-Co-Sil 45, you'll see it has slightly less than 30% of its particles smaller than 5 microns, so the difference isn't massive. Maybe it's not worth the increased risk to use a silica where 50% of the particles are less than 5 microns, maybe it is.

 

Okay, just in case I made a mistake I emailed the manufacturer and got the info straight from the source. 

 

my email:

 

Hi,

 

Quick question if I may, I am trying to determine the mesh size of your Imsil 1-25 silica.I see that it is 5 micron, does that correlate to 2500 mesh size?

 

Thanks in advance for clearing this up for me, 

Madeleine

 

response: 

 

Hi Madaleine,

 

At 5 microns, mesh size is too small to exist as actual screen size but for reference, yes, it would be 2500 mesh.

 

Many thanks,

Angela Le

Sales Representative

The Cary Company

C 630-215-9781 | O 630-629-6600

TheCaryCompany.com 

 

[bciskepottery]

http://www.thecarycompany.com/adobe/unimin/imsil-techdata.pdf

 

Link to technical data sheet.

[Guest JBaymore]

Glaze Nerd,

 

To augment your own research... you might want to also look here to fill in some of the gaps.

 

http://art.alfred.edu/academics/glaze-formulation.cfm

 

And if you want to get to the folks that really know what they are doing in the science side.... develop a relationship with the folks in the engineering school there.

 

best,

 

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

[glazenerd]

Ty kindly John.. right up my alley.

 

I do have an ace in the hole: remodeled a house for a physics professor at the State University a couple of years back. His wife does terra-cotta Pueblo and Navajo reproductions. When I get to the place where I have some idea of what I am doing, going to corner him with it.

 

 

Nerd

[curt]

Wondering where eutectics fit into this discussion?

[glazenerd]

Curt:

 

More than happy to add that to the conversation. Here is an excerpt from Wiki about eutectics: "in this atomic/molecular ratio that the eutectic system melts as a whole,"  A question I asked in another thread: does eutectics apply to crystalline glaze? Should make for an interesting debate.

 

A homogeneous mixture is a mixture with completely uniform composition, and a heterogeneous mixture contains unevenly mixed components. Is the basic crystalline formula homogeneous or heterogeneous? The basis for eutectics is a homogeneous mixture with glaze uniformity.

 

Nerd

[curt]

Not sure homogeneity is necessary for eutectics to apply. Would also say crystalline glazes are not homogenous by construction, otherwise all the crystals would be identical and evenly distributed around the surface? (All else equal)

 

However, before worrying too much about splitting silica to the nth (2500th?) degree, or where molecular heat is coming from or where it is going, I would have thought eutectics would need to be assessed for the materials involved in order to have some idea about whether or not the brew is designed to melt optimally for the purpose - in your case growing crystals.

 

Or maybe your entire analytical approach subsumes the whole eutectics discussion and renders it irrelevant? Just wondering, honestly not sure based on what has been said so far.

[Tim T]

Surely eutectics are independent of the type of chemical bond?

They are just the apices of boundaries in a phase diagram, describing the behaviour of a mix of materials at a macroscopic scale, and not at the atomic/molecular scale.

I'm afraid to say that I do think you have confused a number of concepts in your thirst for understanding.

If you want to increase your understanding of phase diagrams and eutectics, a good starting point is "The Effect of Heat on Ceramics" by W.F.Ford. There are more recent books, but these tend to assume a greater depth of kmowledge of chemistry theory.

[glazenerd]

Tim:

 

Went back and read through some of the definitions, applications, and variables of eutectics. Came across a section that I need to revisit:

 

"Compositions of eutectic systems that are not at the eutectic composition can be classified as hypoeutectic or hypereutectic."

 

Guess I will nose around studying these two variables; see what applies. Just so happens the downtown St. Louis library has a copy of that book.. 1967 hey? Yes, I suppose a phase diagram could be used to find an eutectic point. That still leaves me void of how to formulate precisely for the crystal itself.

Nerd

[Babs]

Just an onlooker/reader but what are you actually searching for ? Optimal blend of glaze ingredients to produce best crystals ever all the time? As I think you'd need a pretty good chem set up to find that info from the home pottery studio, just interested, are you being side tracked into searching for the "holy Grail"' of absolutes which don't exist in my world of ceramics...The phrase "it depends"  tolls forever in my ears

Enjoying the distraction of reading these posts,  from bookwork.

Good luck with your obsessions!