Field of the Invention
The invention refers to compositions which allow the removal of the
oxides, which are formed either superficially or inside the crystal lattice, from
alloys of precious metals or similar with the advantage of stabilising the alloys
themselves; the invention refers also to the process of stabilisation comprising
the use of such composition.
State of the art
It is known that during the melting processes of ingots of alloys
of precious metals or similar for the moulding of different objects, both for aesthetic
or industrial purposes, oxides are formed both on the surface and inside the crystal
lattice of the metals constituting the alloy. These oxides can be detrimental to
the subsequent use of the objects for example by altering their external appearance
or causing more serious problems. For example in the case of parts in precious
alloys commonly used in dental application (capsules, bridges, pins, inlays, etc.),
when these are implanted in the mouth of a patient the oxides can, under the saliva
action, be attacked and thereafter absorbed by the patient, similarly the properties
of the parts of precious alloys used in electronics can be adversely affected by
the formation of oxides.
It is therefore evident how important it is to make available a product
which allows the removal of the oxides from precious metals alloys.
Detailed description of the invention
The present invention allows one to overcome the above said problems
through the use of compositions of gelatine containing sodium borate.
Such compositions once spread on the objects to be treated and thereafter
heated, allow the total removal of superficial and internal oxides possibly formed
during the previous working phases of the metal alloy and allow the preparation
of products which do not present any of the drawbacks caused by the presence of
According to the invention a precious metal or similar alloy is an
alloy consisting of metals of the groups VIII and Ib of the Periodic Table of Elements,
in particular alloys consisting of gold, silver, palladium, iridium, platinum,
in all their different possible combinations.
The gelatinous product in the composition according to the invention
as defined by claim 1 is a gelatinous material capable of burning completely when
heated, without leaving any residue.
Homogeneous materials, i.e. lump-free materials, are preferred since
they allow a better spreading of the composition.
For the invention purposes, the gelatinous product is chosen from
agar-agar, carrageenin or pure cellulose.
The two products forming the composition, i.e. the gelatinous product
and sodium borate, can be present each in a quantity comprised between 20 - 70%
(by weight) of the total; particularly preferred is a composition consisting of
50% sodium borate and 50% gelatine (by weight).
The invention further relates to the use of the compositions according
to claim 1 or of a composition consisting of sodium borate and gelatine in a treatment
for removing oxides from alloys of precious metals.
The compositions according to the invention can also obviously be
used to remove the oxides in the case of objects wherein the precious metal alloy
is combined with resins or ceramics making it possible to obtain products having
The preparation of a composition according to the invention is very
simple and is performed by mixing the desired quantities of both components in
a mixer, preferably equipped with microniser, under vacuum and in a nitrogen current.
Very simple is also the use of the compositions according to the invention.
The piece to be treated, obtained by moulding the melted ingots in
the appropriated mould, is cooled, polished and cleaned with vapour jet streams.
The composition according to the invention is spread with a brush
on the surface of the object and dried, normally at 500°C; after drying a white
chalk-like patina forms.
The alloy is thereafter submitted to thermal annealing or homogenised
in oven, normally at 950°C, as indicated by the producer of the alloy.
The object is cleaned by ultrasounds and immersion in pickling liquid
or hydrofluoric acid 40%, thereafter neutralised in water with bicarbonate and
washed with water.
If alloy-ceramic products are desired the alloy is ceramised according
to the usual techniques.
If alloy-resin objects are desired the above said thermal treatment
can be performed in an oven or over the flame.
The composition according to the invention is particularly useful
to remove the oxides on metal parts which must be grinded.
In the case of products requiring ceramisation, after elimination
of the glasure excess the composition is applied to the metallic part and is heated
at a temperature largely inferior to the one requested for the ceramic burning,
thereafter the same procedure described above is applied (treatment with ultrasounds,
pickling, neutralisation and washing).
By operating as described it is possible, for example, to completely
remove the oxides in the internal part of the ceramised dental cups making the
surface particularly bright.
30 g of carrageenin are placed in a mixer under vacuum and in nitrogen
current and 30 g of sodium borate are added. The products are mixed up to the formation
of an homogenous paste which is collected and stoked in fridge up its use.