# Mesh size



## Digitaria (Jun 1, 2015)

Hi 

I wondered could anyone enlighten me - with regard to mesh size. Salt lake metals detail that the typical mesh size of gold mud is: Particle size 400 microns (0.016 inch) - With regard to blackened gold fall out, precipitated by a copper bus bar, I was wondering if anyone could tell me what mesh size this would be in comparison to standard gold mud? 

I am wondering because I wanted to experiment with precious metal clay, and apparently the finer divided gold makes better finished pieces because the gold particles are finely divided, being close together, so my thinking was that this black fall out, might make a better precious metal clay?

Lisa


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## goldsilverpro (Jun 1, 2015)

https://www.gvc.net/docs/Screen%20Mesh%20Chart.pdf


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## Digitaria (Jun 2, 2015)

Thank you - for the pdf

I've come to the conclusion - that I could ball mill the powder to reduce its mesh size.


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## nickvc (Jun 2, 2015)

Doubt that will work as you will turn the powder back into metal and probably lose some to the mill and balls, but perhaps redissolving the powder increasing the volume to say 20-30+ times and adding dissolved precipitant may work to reduce the powder size, whenever I have dropped gold from low yielding large solutions in volume the precipitant seems very fine. Perhaps butcher or one of our other clever chemists can comment.


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## Palladium (Jun 2, 2015)

Gold powder is a metal. lol

Pure gold is so soft you can't ball mill it. All you would wind up with is smeared gold probably pulverized into thin sheets.


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## Digitaria (Jun 2, 2015)

ok then - so no ball mill. I know you could in theory take your relatively pure gold powder, and then redissolve and perhaps cement out with a copper bus bar, by observations this seemed to be finer? What else would make the mesh finer?


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## Geo (Jun 2, 2015)

Precipitated gold powder is most likely as fine as you can get. The gold goes from a liquid phase to a solid phase by the atom and sticks together loosely. If the gold is pure, it clumps together but it is still a loose conglomerate of gold molecules. Perhaps a sonicator will break the powder up finer. I've seen gold precipitate out in particles so small, you need a loupe to see it.


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## Digitaria (Jun 5, 2015)

View attachment G504,505.pdf
I found this about atomized gold - thoughts anyone?


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## g_axelsson (Jun 5, 2015)

It's not atomized, it is in spherical particles.

Göran


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## Westerngs (Jun 5, 2015)

Goran is right, definitely not atomized.

To make gold powder near this mesh size I would try precipitating out of a gold solution using oxalic acid. It would take some experimenting with different gold and oxalic concentrations at different temperatures. 

I would guess that the more dilute solutions at colder temperatures would make smaller particles, but I haven't actually verified that.

I would definitely NOT use cemented gold, way too many impurities. 

One thing to keep an eye on is that gold agglomerates very well, you will have a hard time keeping the powder at the mesh size you are looking at.


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## Geo (Jun 6, 2015)

Notice that all of the items have "chemically precipitated powder". I would recommend dissolving some gold of known purity and dilute the solution greatly, as much as 5 to 10 times with water and precipitate using SMB. The gold is sure to precipitate out in fine particles. Use a stirrer to keep the particles suspended until fully precipitated. Drain and rinse well and refill the container with clean water and turn the stirrer back on. You may keep the stirrer going until you are ready to use the gold. The company you are looking at most likely just classifies the powder through different mesh sizes anyway.


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## Palladium (Jun 6, 2015)

The warmer the solution the better.


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## g_axelsson (Jun 6, 2015)

Those particles are huge actually. We produce a lot smaller particles without thinking of it when testing for gold with stannous chloride.

For a lot of how to make small particles (still not atomic) look at...
https://scholar.google.com/scholar?q=preparation+of+nanogold+particles
https://www.google.com/search?q=synthesis%20of%20gold%20nanoparticles

And here is a good article on how to make different nano gold particles...
http://www.researchgate.net/publictopics.PublicPostFileLoader.html?id=5369883bd4c11850538b5259&key=60b7d5369883b8f807

This is still far from monoatomic, the purple stannous colloidal gold is about 100 nm in size and with gold atoms roughly at 135 pm they are still made up of close to 200 million atoms each.

Göran


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## Digitaria (Jun 6, 2015)

Thank you - I quite like the idea of diluting the already pure precipitated gold further, so it becomes finely divided when precipitated again and this also was mentioned earlier in the thread, which detailed dirty solutions. This at least - I could see working because the precipitated gold powder, is at least an accepted method of making gold metal clay.

I know the nano gold can be made by employing the citrate method of converting the gold powder to gold metal, changing the gold chloride particles from rod to round particles using the turkevich method, however when using the citrate it turns the gold powder into metalic gold, and I don't know how this would affect the clay, if say a concentrate of gold charged colloid was used with a binder to make the clay, other than that, I would presume that a concentrate of colloidal gold would be made first, then poured onto cloth to dry before incineration, and then put the gold ash and gold back into solution before dropping again? Whether this would revert the gold back to its former state, pre-atomised or produce a finely divided fall out, I have no idea?


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## g_axelsson (Jun 6, 2015)

I don't think colloidal gold is used to make clay from, the particles are probably too small, but that's just a guess.

I don't understand why you are talking about dissolving colloidal gold and then drop it again, there is no memory in the atoms so when dissolved it could be from a solid piece or colloidal gold, it's all the same.
By the way, all colloidal gold is still metallic gold, it's just so small particles that they don't settle.

Göran


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## Digitaria (Jun 6, 2015)

I don't think colloidal gold is used to make gold metal clay, however you mentioned colloidal gold with regard to its size at an atomic level previously, so I was just furthering my observations. I know that its actually metal in colloidal gold, which can be consumed because of the gold powder has been converted into metal whereas gold chloride cannot be consumed, not even if dissolved, if it has not been converted into metal, although it is still gold.

I was wondering whether fine atomized gold from colloidal gold could be put in hcl and redropped as a finer gold powder, not that it has memory but that already being fine, it may continue to be so, in the same logic of dropping gold from a dilute solution, in an effort to make it finely divided.


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## Geo (Jun 6, 2015)

I am a little confused with your reference of gold powder turning metal. I'm assuming that you mean metal as in shiny metal. The gold powder is still metal but in pieces so fine that the light being reflected from it is diffused in all directions. If you look at the gold powder under a microscope, it will look like shiny gold particles that you are more accustomed to when melted into larger pieces. I believe the spheres are made by agitating precipitated gold to round off the particles, much like a nugget rolling on a stream bed, and then classified. Oxalic acid will precipitate gold in much larger particles that resemble shiny metallic gold hence the recommendation to use SMB.


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## g_axelsson (Jun 6, 2015)

Yes, you can dissolve colloidal gold and drop it again, just as with solid pieces of gold. The resulting size of the gold dropped has nothing to do with where it came from, only the conditions when it is dropped.

But you need more than HCl to dissolve gold or you can't drop it at all. Colloidal gold is already precipitated metal, just so fine that it won't settle.

Göran


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## Digitaria (Jun 7, 2015)

Thank you - I was previously talking about gold chloride the sticky stuff which can be used to make colloidal gold, in that you cannot consume it, like you can after it has undergone changes in the chemical method of making colloidal gold, as opposed to plasma.

The ions are converted with the water and citrate into particles with citrate encapsulating the gold ions to form colloidal particles of gold, first rod then sphere without the citrate the mix would clump in large rods, then fall out quite quickly. However the fall out, is shown as a purple colour, I wonder why not brown, or maybe it would be brown again, after the citrate was burned off?


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## goldsilverpro (Jun 7, 2015)

On one PM clay patent I found, the ideal particle size of the metal used ranged from 5-30 microns, which seems more reasonable to me. As far as I can tell, the particle size of 400 microns (huge - about 1/64") on the Salt Lake site has nothing to do with PM clays. It's just what they happen to be selling.


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## Digitaria (Jun 8, 2015)

Thank you for the helpful comments.


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## Lou (Jun 8, 2015)

Several ways to do this, but some helpful hints:


1. More dilute the solution, the finer the gold precipitate as there are less gold atoms per unit volume.
2. The faster the reduction, the finer the gold precipitate as there is less time to agglomerate into larger clusters
3. The lower the ionic strength, the finer the gold precipitate, as there is more repulsion.
4. A lowered temperature, less kinetic energy, less collisions, less agglomeration.


I would try dilute solution and reduce with sulfite. If powder XRD still says too big, then I'd try borohydride at pH 1.

Alternatively, 

Make gold (III) hydroxide. It's typically quite fine a precipitate. Quoting Brauer, p1060:


_Gold (III) Hydroxide Au(OH)3
2KAuCl4 + 3Na2CO3 + 3 H2O (7i H2O)
773.9 318.0 54.0
= 2Au(OH)3 + 6NaCl + 2KC1 + 3CO2 496.0 350.7 149.1 132.0
A solution of KAuCl4 is heated for several hours on a water bath with an excess of Na2CO3. The resultant precipitate is filtered, thoroughly washed, digested with warm, dilute sulfuric acid, and carefully washed in a glass filter crucible until the filtrate is free of H2SO4. The product is dried at room temperature over H2SO4.
Alternate methods: a) Precipitation of AuCl3 solution with MgCO3 [G. KrUss, Liebigs Ann. 237, 290 (1887)].
b) Hydrolysis of gold sulfate or nitrate [P. Schottla'nder, Liebigs Ann. 217, 312 (1883)].
c) Fusion of gold with Na2O2 and decomposition of the re- sultant sodium aurate with dilute sulfuric acid [F. Meyer, Compt. Rend. Hebd. Seances Acad. Sci. 145, 805 (1907)].
d) Anodic oxidation of gold in IN sulfuric acid [F. Jirsa and O. Buryanek, Z. Elektrochem. 29, 126 (1923); W. G. Mixter, J. Amer. Chem. Soc. 33, 688 (191)].
SYNONYM:
Auric hydroxide. PROPERTIES:
Formula weight 248.02. Brown powder. Insoluble In H2O, soluble in cone, acids and hot KOH. When dried over P2O5 in vacuum, the compound is converted to AuO(OH) (slowly at room temperature, rapidly at 100°C), whereby the color changes, the final one ranging from yellowish red to ocher-brown. Converts to Au3O3 at 140-150°C.
_

This material, when heated, turns into gold powder.


EDIT:

Or just tell me what micron size and I can recommend where to go.

Lou


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## Digitaria (Jun 9, 2015)

hi - this description details how to drop gold from solution with potassium sulfite, for round particles whilst stirring constantly, at set temperature and excess reducing agent. Seems to be what I was looking for, what do you professionals think?

http://www.google.co.uk/patents/US3771996

a. preparing an aqueous gold chloride solution;
b. precipitating the gold from solution by rapidly adding an excess amount of a reducing agent selected from the group consisting of potassium sulfite, sodium sulfite and mixtures thereof, while agitating the solution and maintaining the temperature within the range of 0C. 30C.;
c. separating the precipitated gold powder from the solution; and
d. washing the precipitated gold powder until the sulfite and sulfate ions have been removed from the powders.
One of the most important aspects of this invention resides in the use of a reducing agent selected from the group consisting of potassium sulfite, sodium sulfite and mixtures thereof. While many other reducing agents are well known and could be used to precipitate a gold powder, it has been found that under specified conditions, this class of reducing agents precipitates the gold powder of this invention having a specified size, shape and density. The amount of reducing agent utilized is not critical; but to obtain maximum precipitation, an excess is generally used.
Another important feature of this invention involves maintaining the temperature of the solution within the range of 0C. -30C. Of course, below 0C. the solution has a tendency to freeze. Above 30C., the particles of gold become exceedingly fine and the bulk density becomes too low for purposes of producing good electrical properties. The preferred temperature is within the range of l0-20C.
The precipitation (reduction) is performed by adding reducing agent(s) to the aqueous gold chloride solution. The addition of the reducing agent to the gold chloride solution should be carried out as rapidly as possible to provide maximum efficiency of the overall process. It is pointed out that the reducing agent is added to the aqueous gold chloride (not visa versa) to provide gold particles having the proper particle size and shape. For example, the particles become too small when an aqueous gold chloride solution is added to a solution of the reducing agent. Also, although not necessary, it is preferred to agitate the solution while the precipitation reaction takes place. This provides a greater contact between the reducing agent and the gold chloride, and results in a complete precipitation in a shorter period of time.
The process of this invention is not particularly sensitive to the concentration of the reactants. Therefore, concentrated solutions or dilute solutions of the gold chloride and reducing agent may be used. However, somewhat larger particles are obtained when higher concentrations of gold chloride and reducing agent are utilized. Typical and preferred concentrations of gold chloride and reducing agent in their respective solutions are within the ranges of 40-70 gms/liter and l00-200 gms/liter.

The separating step and the washing step are procedures which can be carried out according to .wellknown techniques. For example, filtration or centrifuging may be used. The washing operation may be carried out by using tap water or distilled water to remove the sulfate and/or sulfite ions from the precipitated gold. A methanol wash may bealso used to remove the water from the gold powder.
As stated above, the process of this invention produces a gold powder having spherical particles with a particle diameter within the range of 1-10 microns. The gold powder has a bulk density within the range of 5-9 gms/cc. In a preferred embodiment of this invention the particle size is within the range of 2-6 microns.
'The invention is illustrated by the following examples. In the examples and elsewhere in the specification, all parts, ratios and percentages of materials or components are by weight.
EXAMPLE 1 A gold chloride solution was prepared by dissolving 300 grams of metallic gold in aqua regia. By successive boil downs of this solution and with several additions of HCl, the oxides of nitrogen were removed; five liters of water were added to the dissolved gold. In a separate container, 700 grams of potassium sulfite crystals were dissolved in five liters of cold water. Then the gold chloride solution was slowly agitated while the potassium sulfite solution was poured into the gold chloride solution as rapidly as possible. The reaction proceeded very rapidly with no bubbling or frothing. The temperature of the solution was maintained at approximately 20C.
The reaction was complete in less than one minute. The entire batch was filtered on a sintered glass filter plate and washed with water until the precipitated gold was free of the sulfite and sulfate ions. The gold powder was then washed in methanol to remove the water; the powder was then dried at room temperature.
The gold powder was weighed and found to contain 296 grams of spherical particles; the bulk density was approximately 8.0 gm/cc and the micron size ranged from 2-3 microns.
EXAMPLE 2 A metalizing composition was prepared from the gold powder of Example 1. The composition contained 90.3 percent gold powder, 4.3 percent of a finely divided glass frit, 5.4 percent Bi O The glass frit consisted of 65% Pb(), 34% SiO and 1% A1 The total solids were dispersed in a vehicle consisting of percent ethyl cellulose and 90 percent beta-terpineol. The solidszvehicle ratio was 9:1. The gold composition was printed onto an alumina substrate (One inch square and 25 mils thick) in the form of electrodes which were five mils wide, spaced five mils apart and 0.8 mil thick. The printed substrates were fired at 875C. for three minutes. The electrodes of the resulting printed circuits were tight opaque lines having good conductivity, :1 resistivity less than 3 milliohrns/square, and were diebondable and wirebondable.
EXAMPLE 3 The gold composition of Example 2 was utilized except that the vehicle consisted of 10 percent hydrogenated rosin, 10 percent ethyl hydroxyethyl cellulose, 19 percent kerosense, 37 percent beta-terpineol, 19 percent of an aliphatic hydrocarbon mixture and 5 percent hydrogenated castor oil. The electrodes, which were printed with an etched metal mask, were 2 mils wide, 2 mils apart and l mil thick. The electrodes of this printed circuit were also tight opaque lines having good conductivity, 3 resistivity less than 3 milliohms/square, and were diebondable and wirebondable.
2. A process in accordance with claim 1 wherein the reducing agent is potassium sulfite.
3. A process in accordance with claim 1 wherein the precipitated gold powder is washed first with water and secondly, with methanol.
4. A process in accordance with claim 1 wherein the temperature in the precipitating step is within the range of l020C.
5. A process in accordance with claim 1 wherein the particle size of the gold powder is within the range of 2-6 microns.
6. A process in accordance with claim 1 wherein, prior to the precipitating step, the aqueous gold chloride solution contains 40-70 gms/liter of gold and the reducing agent is in a solution containing -200 gms/liter of said agent.


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## goldsilverpro (Jun 9, 2015)

Sounds OK. If it works, it works. If it doesn't, it doesn't.


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## Digitaria (Jun 20, 2015)

I've been looking into the binders for pmc alot more, as I am getting closer to making some experiments with my own precious metal clay. I think flaxseed gel aka flax mucilage will be suitable. It is a jellylike (cellulose) binder albeit naturally occurring unlike its chemical cousin. As its made fresh it will be fully hydrated and not suffer the problems of re-hydrating its powdered chemical cousin, in that it swells on the outside but does not fully penetrate the core causing excess kneading of the metal powder and the binder. Although gelatinous substances can be generally described for use in the patents they are not recommended as the use of gums, have issue with malleability and starch derivatives have issue with cloudiness in the finished pieces. Methyl cellulose compared to flaxseed gel has been proved inferior with flaxseed gel having advantages, due to it being natural with regard to artificial tears and saliva, it also has a trillion other uses, including being a source of soluble dietary fibre. It also does something pretty fantastic after being frozen for a short time, which could well be an advance in the production of metal clay.

Extract from patent
The moldable mixture is produced by preparing a precious metal powder, preparing a jellylike cellulose binder by blending a cellulose with water and leaving for a prescribed period of time, and blending the precious metal powder and the jellylike cellulose binder together. The most preferable moldable mixture contains 50 to 90% by weight of precious metal powder, 0.8 to 8% by weight of water-soluble cellulose binder, 0.08 to 3% by weight of a surface-active agent. 0.1 to 3% by weight of oil, balance water and unavoidable impurities. The precious metal powder preferably contains gold powder and powder of an alloy containing silver or copper, and the gold powder is obtained by submerged-reduction method.


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