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Granulation basics


#1

Was: Argentium or sterling?

Lenoid,

... granulation is based on soldering and not fusing. I know that
it is not obvious, but if technique of granulation understood
completely, the soldering becomes self-evident.

What??? Lets not confuse them.There are three main techniques that
can be called granulation: hard soldering, fusing/diffusion bonding,
and colloidal soldering.

The technique I am known for is NOT a soldering technique. The only
soldering I do is in the final fabrication stages. Nothing can be
fused after soldering has taken place. Fusing takes place at a
higher temperature than soldering. Once I am done fusing or
granulating, I then solder. Here I am referring to hard soldering.
And the ?fusing I am referring to is diffusion bond/fusing not a
eutectic or colloidal soldering.

For further clarification, go to my blog: What is Granulation? I
have electron microscope analysis of my work to back up what I say.

And, in my experience, 24k granulation is much harder than 22k. The
reason I think the 22k is easier than the 24k is that 24k is pure
fusing/diffusion bonding, where as22k, being an alloy, has a wider
melting range. A pure metal goes from solid to liquid andhave a
single melting point. That makes them hard to fuse. 22k granulation
may be done by either fusing or colloidal soldering. I personally do
not add copper (there is copper in the alloys). And granulating with
Argentium is almost idiot proof it is so easy. Especially compared
with Fine Silver Granulation. And here I am referring to
fusing/diffusion bonding, not hard soldering or colloidal soldering.

Ronda Coryell


#2
For further clarification, go to my blog: What is Granulation? I
have electron microscope analysis of my work to back up what I
say. 

I followed your advice and read your blog. I understand the
distinction that you are making between fusion, granulation (eutectic
bonding), and hard soldering. Let’s put hard solder aside. You
described process of eutectic bonding correctly. But you are missing
is that during argentium fusion, the same is taking place, only
instead of copper you have germanium.

I can offer simple experiment to prove my point. Anybody can try it
with very little preparation: prepare regular silver or gold sheet and
granules. anneal sheet, DO NOT USE ANY PROTECTIVE SOLUTIONS. use
excess of oxygen in the flame. The sheet and granules should be
black. Brush sheet with flux and arrange granules. Now use soft
reducing flame on your arrangement. Once you notice shimmer on the
surface, the granules will be soldered to the sheet.

What is taking place is first we create copper oxide on the surface
and than we restore copper oxide to pure copper, which in contact
with gold or silver creates solder in place.

Germanium in argentium acts the same way. In reducing flame
germanium oxide converts to germanium metal, which create solder in
place and bonds the granules.

Leonid Surpin
www.studioarete.com


Orchid Granulation Contest - With prizes sponsored by Scientific Alloys
#3

Hi Leonid,

As Rhonda mentioned, there are more ways than one to granulate.

I don’t mess with Argentium much, so I’m not sure what’s going on
with As granulation. It may be the Germanium, it may not be. It may
simply be that the Ge doesn’t oxidize like the copper in standard
sterling. Copper oxide will definitely cause diffusion to fail. No
Cupric Oxide, no problems. (possibly)

What I can tell you is that it’s entirely possible to do pure fusion
granulation with fine silver on fine silver. No copper or other
alloying elements anywhere.

It’s not fun, but it’s possible. I tend to use elmer’s glue cut
60/40 with spit to stick the granules in place first, but I’m
reasonably sure that the copper content of my spit is minimal. (I
believe the fine silver/fine silver technique is what Jean Stark
was/ is teaching, at least occasionally. I learned it from someone
who claimed to have learned it from her, about 20 years back.)

The fun part of it is that your torch control must be immaculate.
You have maybe 5-10 degrees of leeway between “not hot enough” and
a puddle.

(This is the version where you fire it on a beehive kiln, if you’re
familiar with that style.) Also a really handy technique for welding
fine silver bezels together with no solder joints to worry about in
later assembly. That’s probably the reason I do it 90% of the time.

All things being equal, I’d rather do the colloidal version, with
copper carbonate. Much more forgiving. On the other hand, doing it
the hard way is definitely good for teaching you how to control your
torch.

Regards,
Brian.


#4

Leonid, in Rhonda’s defense, read her blog again, please. She
specifically states that she IS protecting the sheet with flux. She
is not oxidiing the surface or otherwise enriching the surface with
copper or germanium. She is simply heating a clean metal, to clean
metal, contact to just barely below melting or the eutectic temp
between the two metals if bonding two dissimilar metals. It’s not
soldering, or eutectic soldering or colloidal soldering. It’s just
plain diffusion bonding blending it to barely actually fusing,
without causing parts to actually melt. It depends on there being a
very slight “slushy” temperature range between liquidus and solidus
temps of the metal, so the surface can start to melt without parts
losing shape… It’s perhaps the hardest way to do granulation if you
want really good results, since a slight mis step, a moment too long
or not long enough, and it fails. And the method is not well suited
to all metals, as she notes that granulating with 24K us much harder
than 22K. If she was using 24K, perhaps with added copper, as in
plating or added salts, then 24K is no harder than 22K Maybe easier
even… Her method requires very good torch and temperature control
to master, but she is just that: A master at granulation…

Peter Rowe


#5
Leonid, in Rhonda's defense, read her blog again, please. 

I did and she is wrong about fusion. Fusion takes time. Much longer
than one sit and wave the torch. I think I explained it once. Heat
bring germanium to the surface; it alloys with silver and creates
solder in place.

Leonid Surpin


#6

If you do not know what the word eutectic means please stop using
it. There is so much misuse of metallurgical terms and concepts in
this thread it makes the mind reel.

ALL granulation is one form or another of liquid phase diffusion
bonding even if you use solder !!!

First and foremost Eutectic:

" relating to or denoting a mixture of substances (in fixed
proportions) that melts and solidifies at a single temperature that
is lower than the melting points of the separate constituents or of
any other mixture of them."

If you heat an alloy that is eutectic to he point where it just
begins to melt the whole damn thing will melt. You cannot apply this
concept to granulation unless you are using a eutectic solder to
bond the granules to the base material. In order for there to be a
eutectic alloy present there must be a very precise ratio of metals
if you do not have this you don’t have a eutectic alloy. If you want
to get fancy about it you will either have a hypoeutectic or
hypereutectic alloy present if the system will produce a eutectic
but you are not at the correct ratio of component metals.

Second colloidal:

"a homogeneous, noncrystalline substance consisting of large
molecules or ultramicroscopic particles of one substance dispersed
through a second substance. "

This has nothing to do with the processes of granulation unless
possibly you have a flux that is a colloidal suspension rather than
a solution.

Rhonda, you should not use these terms to describe granulation with
the aid of a copper bearing material or copper plating of granules
to lower the melting temperature. If you want to try to
differentiate this kind of diffusion bonding from what you are doing
with Argentium then call it Transient Liquid Phase Diffusion
Bonding. By adding copper salts or plating the granules with copper
on either gold or silver alloys and then heating you temporarily
depress the local melting point of the granules surface. Once the
temperature rises high enough for this localized melting to occur
the bond is made between the granule and the surface. The copper
supplied by this process will rapidly diffuse away from the joint
and the melting point will climb back up the that of the bulk metal
hence the name Transient Liquid Phase.

Leonid, this is also what you are describing but using copper oxides
that are then reduced by the flux to elemental copper to provide
localized reduction in melting point.

In what Rhonda and Peter are referring to as diffusion or fusing
what is happening is the Argentium or other non eutectic alloy is
heated to a temperature somewhere above the solidus burt below the
liquidus of the alloy and there are now both solid and liquid metal
present. Assuming everything is clean and oxide free the liquid will
flow by gravity and capillary attraction into the space between the
granules and the base metal. Once the heat is removed the alloy
solidifies and the granules are bonded to the surface. This is
Liquid Phase Diffusion Bonding.There is no magic of Argentium that
makes this happen, you can do exactly the same thing with many gold
and silver alloys. Where Argentium makes this easier is it has a
lower solidus temperature and a little wider range between solidus
and liquidus so it requires less skill on the part of the person
doing the granulation or fusing to get a successful outcome.

And finally if you were to use powdered solder in your flux/glue
solution like the Indonesian craftsman you are still creating a
diffusion bonded assembly because solder bonds by diffusion between
the metals/alloys being bonded. There is just less skill required
because you have lots of low melting alloy present. But this excess
alloy shows up easily on inspection and makes for a less
aesthetically pleasing result than the other two methods.

James Binnion
James Binnion Metal Arts


#7

Following some of the recent discussion about granulation,
specifically that regarding Argentium silver I thought that I should
post some technical to inform the debate.

Before I go further I should make it clear that I am employed by
Argentium International and have worked on the development of the
Argentium silver alloys for a number of years.

Argentium silver alloys are essentially an alloy of silver, copper
and germanium. They form a two phase structure; the primary phase is
silver-rich and the secondary phase is copper-germanium-rich. In this
respect they are similar to traditional sterling silver in their two
phase structure; in traditional sterling silver the primary phase is
also silver-rich and the secondary phase is copper-rich.

In Argentium 935 Original the silver-rich primary phase has an
approximate composition of 95.5% silver, 3.5% copper and 1%
germanium; the secondary copper-germanium-rich phase has a
composition of approximately 2.5% silver, 79% copper and 18.5%
germanium. It is important to note two things, the first is that the
germanium is distributed in both phases and that it is bonded to the
silver and copper, the second is that the exact compositions of the
primary and secondary phase in Argentium silver alloys depend on the
cooling rates of the pieces (for castings) and the working and
annealing cycles for wrought materials. In comparison in traditional
sterling silver there is a very limited solubility of copper in the
primary silver-rich phase and similarly a limited solubility of
silver in the secondary copper-rich phase.

This difference in composition in the primary and secondary phases
between Argentium silver alloys when compared to traditional sterling
silver gives some clues to the reported difference in the ease of
granulation between Argentium silver and traditional sterling silver.
In my opinion it all comes down to the different melting ranges that
the two different types of silver alloys have.

With traditional sterling silver you have a relatively narrow
melting range for the alloy and as a consequence you need to have
very good temperature control with your flame to achieve the bonding
but avoid the complete melting of the piece. In contrast the
Argentium silver alloys have an extended melting range and by
carefully working at a point when just the lowest melting point
phases are molten it is possible to get the fusing results with
Argentium silver alloys that others have reported in this thread.

Finally the Scanning Electron Microscope work that Ronda Coryell has
linked to in her Blog clearly show that there is no ‘germanium
solder’ created at the interface between the two fused components.
Indeed if this was the case I would expect a very weak bond when
Argentium silver alloys are fused and this is definitely not the case

Charles Allenden
Quality Assurance Manager
Argentium International Limited


#8
With traditional sterling silver you have a relatively narrow
melting range for the alloy and as a consequence you need to have
very good temperature control with your flame to achieve the
bonding but avoid the complete melting of the piece. 

What are the solidus and liquidus temperatures for Argentium 935?

I thought it was 1410F solidus and 1610F liquidus which is a 200F
melting range while standard sterling is 1475F to 1650F or 175F
melting range. I would not call 175 F a relatively narrow melting
range in comparison to the 200F range of Argentium. I was wondering
if it might be that there is more liquid phase present at a lower
temperatures with the Argentium?

James Binnion
James Binnion Metal Arts


#9

Hello Charles,

Thank you for your contributions regarding Argentium (AS). After
reading your comments, I have two questions.

You refer to AS Original 935 - Does this mean that the original AS I
bought years ago is not.925 silver, but is actually .935 silver? Not
that this would be a problem, but I want to know.

I do not understand what you mean by the “two phase structure.” Is
this a description of how the alloy acts when heated for fusing? Can
you speak some more about this.

Thank you,
Judy in Kansas, who has been using AS since it was introduced.


#10

Hi Charles,

Thanks for the explanation.

Can you please explain what is meant by the “two phases”? When and
where and why is the second phase?

Thanks!
Cynthia Eid
http://www.cynthiaeid.com


#11
Can you please explain what is meant by the "two phases"? When and
where and why is the second phase? 

I look forward to seeing what Charles has to say but I know I have
posted this link before http://www.ganoksin.com/gnkurl/1tm and
discussed phases of silver copper alloys.

That website is absolutely the best quick tutorial on phases of
alloys, phase diagrams, eutectic, hypereutectic and hypoeutectic
alloys. Check it out it is easily accessible and no math required
:-).

James Binnion
James Binnion Metal Arts


#12

Hello James,

As always you raise an excellent technical point about the solidus
and liquidus values. To define the terms we are discussing; the
solidus is the temperature below which an alloy is completely solid,
the liquidus is the temperature above which an alloy is completely
liquid. The temperature range between these two points is the melting
range of the alloy where there exists a mixture of solid and liquid
phases; this is sometimes termed the ‘mushy zone’.

What we need to consider when thinking about the different 'fusing’
characteristics of traditional sterling silver and Argentium silver
is what I would call the ‘effective’ melting range of an alloy. If we
step back from silver alloys and consider the difference between the
effective working temperatures of silver-copper-phosphorus brazing
alloys and silver-copper-zinc-tin brazing alloys (here I am using the
AWS definition of brazing alloys which is “a joining process that
produces coalescence of materials by heating them to the brazing
temperature in the presence of a filler metal having a liquidus above
450 C (840 F) and below the solidus of the base metal. The filler
metal is distributed between the closely fitted faying surfaces of
the joint by capillary action”) then my use of the term 'effective’
melting range may become clearer.

In EN 1044:1999 alloy CP105 (2% silver, 91.7% copper, 6.0%
phosphorus) has a defined solidus of 645C and a liquidus of 825C.
However for all the CP range of brazing alloys this standard also
gives a working temperature, for this alloy 740C, which is
significantly below the liquidus, i.e. this brazing alloy works
producing effective joints at temperatures well below the point where
it is fully molten.

In comparison the EN 1044:1999 alloy AG 103 (55% silver, 21% copper,
22% zinc 2% tin) has a defined solidus of 630C and a liquidus of
660C. However there is no working temperature specified and any
general guidance on best brazing practice would be that an effective
working temperature would be at or just above the liquidus at 660C.

The reason for the CP alloy family having a working temperature
specified in the standard is that it was recognised that the majority
of the alloy was completely molten at a temperature well below the
liquidus of the alloy and in effect there was no need to overheat the
alloy by using joining temperatures above 825C. In comparison the AG
alloy family are not sufficiently molten or fluid at temperatures
below the liquidus of the alloy and require heating to slightly above
the liquidus temperature to form an effective joint.

So, what I have tried to do in this round about way is to illustrate
the point that James has made that although the solidus and liquidus
give you a melting range, at different points within this melting
range, dependent on the composition of the alloy, there may be a
significant difference in the total amount of liquid phase compared
to solid phase.

I have spent may years looking at different cross-sections of
traditional sterling silver alloys to assess their metallurgical
soundness (freedom from phosphides, oxides etc) and I can say that
commercial sheet and wire products generally have very little
copper-rich second phase present. In comparison Argentium silver
alloys do have a greater proportion of their overall structure
constituted from the copper-germanium-rich second phase. I cannot
definitively prove this final statement, but in my opinion the
Argentium silver alloys have a sufficient amount of molten material
present at just above the solidus temperature to facilitate the
’fusing’ operation and by contrast traditional sterling silver alloys
need to be heated to just below the liquidus to obtain the same
reaction. So this would be why I would term Argentium silvers as
having a wider ‘effective’ melting range than the traditional
sterling silver alloys and I can say that we are continually working
towards a better understanding of this phenomenon.

So having gone through all of the above I could have simple said, I
agree! More liquid phase present at the lower temperatures of the
melting range!

A couple of other comments; first I have not put all the temperature
conversions in above so for those that are not bilingual;
645C=1193F; 825C=1517F; 740C=1364F; 630C=1166F; 660C=1220F. Secondly
where I have used the term ‘fusing’ above I have used quotation
marks, this is to prevent me being told off for not calling this
process Transient Liquid Phase Diffusion Bonding!

Charles Allenden
Argentium International


#13

In reply to those who have asked for a further explanation of what I
meant by the term ‘second phase’ when I posted previously about
granulation, I have copied a drawing of the silver-copper phase
diagram taken from a book called the Properties of Engineering
Materials by R.A. Higgins (ISBN 0340179090).

If we only consider the left hand side of the diagram (the
silver-rich side) and consider how the structures shown in the
drawings on the left hand side of this diagram are formed for a
simple silver-copper alloy.

The line PQ1RV on the left hand side of the diagram is for an alloy
of composition 95% silver and 5% copper. The drawings down the left
hand side show the structure of the metal as it is very slowly cooled
from its melting point until it is solid.

The first drawing (top left) shows the liquid metal at the start of
solidification. The solidification starts in the form of structures
called dendrites in the liquid metal. When the cooling metal passes
through the point Q1, at the temperature S1 it becomes fully solid.
In this region of the phase diagram it only consists of one phase
(alpha) which is silver-rich and contains all the copper in the metal
held in solution in the silver. This is shown in the second drawing
which shows a simple single phase grain structure.

As the metal cools further it passes through the point R. This is a
critical temperature as at this point the silver is completely
saturated with copper and as the temperature drops further some
copper is precipitated from the solid solution. It is not pure copper
that is precipitated though; it is copper with a very small amount of
silver present in it. This is the start of the formation of the
second phase (beta). The third drawing shows how the secondary (beta)
phase is precipitated initially at the grain boundaries of the
primary (alpha) phase. The formation of the second phase starts at
the grain boundaries because of the slight ‘mismatch’ in the atoms
where the grains meet.

By the time the temperature of the metal has fallen to about 300C
the primary (alpha) phase contains about 0.5% copper and the
secondary (beta) phase contains about 0.2% silver. The last drawing
shows the final structure that you would end up with when the metal
has finished cooling. Here the secondary (beta) phase has grown at
the grain boundaries and can also be seen as precipitates in the
larger grains of primary (alpha) phase.

However it is important to remember that these changes only occur if
the cooling rate is very slow. In real life we either quench our
castings or work and anneal our sheet. This means that we very rarely
get all our copper into solid solution in the silver (the second
drawing) unless we carry out a very specific solution heat treatment.
This more rapid cooling that we carry out in real-life conditions
means that the structure in silver-copper alloys is nearly always a
mixture of the two phases, the silver-rich primary (alpha) phase and
the copper-rich secondary (beta) phase.

I do not intend to elaborate much on the Argentium silver structure,
suffice to say that as Argentium silver alloys essentially consist of
three constituents, silver, copper and germanium the phase diagram
becomes a lot more complicated. However the basics are still the
same, there is a primary silver-rich phase and now a secondary copper
and germanium rich phase present in the alloy.

Charles Allenden
Argentium International

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#14
So, what I have tried to do in this round about way is to
illustrate the point that James has made that although the solidus
and liquidus give you a melting range, at different points within
this melting range, dependent on the composition of the alloy,
there may be a significant difference in the total amount of liquid
phase compared to solid phase. 

This agrees with my experiments in diffusion bonding standard
sterling at temperatures above the solidus. I had to get much closer
to the liquidus than I would have believed before I did these
experiments to see much in the way of liquid phase presence. I have
not done any of these type of experiments with Argentium. Maybe at
some point I will have time to try this.

A couple of other comments; first I have not put all the
temperature conversions in above so for those that are not
bilingual; 645C1193F; 825C1517F; 740C1364F; 630C1166F; 660C1220F.
Secondly where I have used the term 'fusing' above I have used
quotation marks, this is to prevent me being told off for not
calling this process Transient Liquid Phase Diffusion Bonding! 

Ok Im going to have to make a comment here, I just can’t help my self
:slight_smile: For it to be Transient Liquid Phase bonding one would need to add
something to the faying surface to locally lower the MP like copper
in the case of standard sterling granulation with the aid of a copper
salt or plating copper on the granules which would then diffuse away
from the joint returning the MP back to that of the bulk metal.
Fusing, would have been just fine :slight_smile:

Thank you for your detailed post.

Regards,
Jim

James Binnion
James Binnion Metal Arts


#15

Hello Jim,

I am glad that you found the post useful. If you do want to look into
the fusing of Argentium silver at anytime please feel free to contact
me for any technical you need. I know the definitions was
a little bit of fun :slight_smile: but you always make a very correct and
serious point when scientific and/or metallurgical terms get used for
applications where there is no real correlation to what the process
really is. Please keep up your vigilance!

Charles Allenden
Argentium International