U.S. patent application number 10/469146 was filed with the patent office on 2004-04-08 for bath for the galvanic deposition of gold and gold alloys, and uses thereof.
Invention is credited to Ruebel, Susanne, Stuemke, Manfred.
Application Number | 20040065225 10/469146 |
Document ID | / |
Family ID | 26008695 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040065225 |
Kind Code |
A1 |
Ruebel, Susanne ; et
al. |
April 8, 2004 |
Bath for the galvanic deposition of gold and gold alloys, and uses
thereof
Abstract
The invention relates to a bath for the electrodeposition of
gold and gold alloys and to its use for producing dental moldings.
In this bath, the gold is in the form of a gold sulfite complex.
The bath according to the invention and/or the use according to the
invention is distinguished by the fact that in addition to the
optional presence of further metals and standard additives for gold
sulfite baths of this type, there is at least one bismuth compound.
This bismuth compound is preferably a complex compound, in
particular with the complex-forming agents NTA, HEDTA, TEPA, DTPA,
EDNTA or EDTA. The invention has a whole range of advantages
associated with it. One advantage which should be particularly
emphasized is that the addition of bismuth can be added to the bath
as early as during its preparation. This means that the user is
provided with a bath which is able to function for a prolonged
period of time and to which it is not imperative to add further
additives prior to the electrodeposition.
Inventors: |
Ruebel, Susanne; (Auerbach,
DE) ; Stuemke, Manfred; (Pforzheim, DE) |
Correspondence
Address: |
Nath & Associates
Sixth Floor
1030 15th Street N W
Washington
DC
20005
US
|
Family ID: |
26008695 |
Appl. No.: |
10/469146 |
Filed: |
August 27, 2003 |
PCT Filed: |
February 28, 2002 |
PCT NO: |
PCT/EP02/02128 |
Current U.S.
Class: |
106/1.18 ;
205/266 |
Current CPC
Class: |
C25D 3/62 20130101; C25D
3/48 20130101 |
Class at
Publication: |
106/001.18 ;
205/266 |
International
Class: |
C25D 003/48 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2001 |
EP |
10110743.9 |
Apr 4, 2001 |
EP |
01108448.0 |
Claims
1. Bath, preferably aqueous bath for the electrodeposition of gold
and gold alloys, in which the gold is in the form of a gold sulfite
complex, characterized in that the bath contains at least one
bismuth compound, preferably at least one water-soluble bismuth
compound, and if appropriate at least one compound of at least one
further metal and standard additives for gold sulfite baths of this
type.
2. Bath according to claim 1, characterized in that the gold
sulfite complex is an ammonium-gold sulfite complex.
3. Bath according to claim 1 or claim 2, characterized in that it
has a pH of >7, preferably from 7 to 9.
4. Bath according to one of the preceding claims, characterized in
that it contains copper as a further metal.
5. Bath according to one of the preceding claims, characterized in
that it contains iron as a further metal.
6. Bath according to one of the preceding claims, characterized in
that it contains at least one precious metal, preferably at least
one precious metal from the platinum group, as a further metal.
7. Bath according to one of claims 4 to 6, characterized in that it
contains at least one water-soluble bismuth compound and at least
one water-soluble copper compound.
8. Bath according to claim 5 or claim 6, characterized in that it
contains at least one water-soluble bismuth compound and at least
one water-soluble iron compound.
9. Bath according to one of claims 4 to 8, characterized in that it
contains at least one water-soluble bismuth compound, at least one
water-soluble copper compound and at least one water-soluble iron
compound.
10. Bath according to one of the preceding claims, characterized in
that the bismuth compounds and preferably also the compounds of the
further metals are complex compounds, preferably chelate
compounds.
11. Bath according to claim 10, characterized in that the complex
compounds contain organic complex-forming agents, preferably
organic chelate-forming agents.
12. Bath according to claim 11, characterized in that the
complex-forming agents or chelate-forming agents are NTA, HEDTA,
TEPA, DTPA, EDNTA or in particular EDTA.
13. Bath according to one of the preceding claims, characterized in
that the bismuth compounds are present in the bath in a
concentration of between 0.05 mg/l and their saturation
concentration.
14. Bath according to claim 13, characterized in that the bismuth
compounds are present in the bath in a concentration of between
0.05 mg/l and 1 g/l in particular between 0.1 mg/l and 10 mg/l.
15. Bath according to one of the preceding claims, in particular
according to one of claims 1 to 14, characterized in that the
compounds of the further metals are present in the bath in a
concentration of between 0.1 mg/l and 200 g/l, preferably between
0.1 mg/l and 500 mg/l.
16. Bath according to claim 15, characterized in that the compounds
of the further metals are present in the bath in a concentration of
between 1 mg/l and 20 mg/l, preferably between 2 mg/l and 10
mg/l.
17. Bath according to one of the preceding claims, characterized in
that it is substantially free of physiologically harmful additives,
preferably is free of arsenic, antimony and thallium compounds.
18. Bath according to one of the preceding claims, characterized in
that the gold is present in the bath in a concentration of between
5 and 150 g/l.
19. Bath according to claim 18, characterized in that the gold is
present in the bath in a concentration of between 10 and 100 g/l,
preferably between 10 and 50 g/l, in particular between 30 and 48
g/l.
20. Use of a bath according to one of the preceding claims for the
production of prosthetic moldings for the dental sector by means of
electrodeposition, in particular for the production of dental
frames, such as crowns, bridges, superstructures and the like.
21. Use of at least one bismuth compound, preferably of at least
one water-soluble bismuth compound, for the production of
prosthetic moldings for the dental sector by means of
electrodeposition, in particular as a constituent of a bath
according to one of claims 1 to 19.
22. Use according to claim 21, characterized in that the bismuth
compound is a complex compound, in particular chelate compound,
which preferably contains an organic complex-forming agent or
chelate-forming agent.
23. Use according to claim 22, characterized in that the
complex-forming agent or chelate-forming agent is NTA, HEDTA, TEPA,
DTPA, EDNTA or in particular EDTA.
24. Use according to one of claims 21 to 23, characterized in that
the bismuth compound is added directly during preparation of the
bath.
25. Use according to one of claims 21 to 23, characterized in that
the bismuth compound is added to the bath immediately before or
during the electrodeposition.
26. Use according to one of claims 21 to 25, characterized in that
the bismuth compound is added to the bath after an
electrodeposition step for top-up purposes.
27. Use according to one of claims 20 to 26, characterized in that
the prosthetic molding is deposited in a layer thickness of more
than 10 .mu.m, preferably in a layer thickness of between 100 and
300 .mu.m, in particular in a layer thickness of approx. 200
.mu.m.
28. Process for producing prosthetic moldings for the dental sector
from gold and gold alloys by electrodeposition, in particular for
the production of dental frames, such as crowns, bridges,
superstructures and the like, characterized in that a gold or gold
alloy layer is deposited from a bath according to one of claims 1
to 19 on a suitable substrate, e.g. on a cast which has been molded
from a tooth stump, and is then separated from the substrate.
29. Process according to claim 28, characterized in that the
substrate is composed of an electrically nonconductive material, in
particular plaster or plastic, the surface of which has been made
conductive, in particular with the aid of conductive silver.
30. Process according to claim 28, characterized in that the
substrate is composed of at least one metal.
31. Use or process according to one of claims 20 to 30,
characterized in that the deposition takes place at high current
densities, preferably at current densities of up to 10
A/dm.sup.2.
32. Use or process according to one of claims 20 to 31,
characterized in that the deposition takes place using what is
known as the pulse-plating process.
33. Use or process according to one of claims 20 to 32,
characterized in that the prosthetic molding is veneered with
ceramic and/or plastic.
34. Use or process according to claim 33, characterized in that a
molding veneered with ceramic is fired.
35. Use or process according to claim 33, characterized in that a
molding veneered with plastic is cured using light, in particular
using visible light.
Description
[0001] The invention relates primarily to a bath for
electrodeposition of gold and gold alloys and to its use. In this
bath, the gold is in the form of a gold sulfite complex.
[0002] It has already been known for a very long time to
electrodeposit gold or gold alloys from preferably aqueous
solutions which contain the gold and/or the corresponding alloy
metals. After predominantly cyanide-based gold baths were initially
used, in recent times baths based on gold sulfite complexes have
been becoming increasingly important. This trend was attributable
primarily to the fact that the gold sulfite baths are non-toxic
compared to the cyanide-based gold baths in which hydrogen cyanide
is known to be released. This non-toxicity and the good quality of
the layers deposited has led to the gold sulfite baths being used
to an ever increasing extent, in particular in the field of dental
technology, despite their higher production costs and despite the
problems with the stability of the baths. Furthermore, baths based
on gold sulfite complexes are relatively easy to handle, which is
an important factor for users without high levels of specialist
chemical engineering knowledge, such as dental technicians,
dentists and their staff.
[0003] Particularly in the field of dental technology, particular
demands are imposed on deposits formed by electroplating. In
addition, these demands also vary according to the type of dental
frame or prosthetic molding produced. For example, a homogenous
layer build-up, i.e. a homogenous microstructure, a layer thickness
which is as uniform as possible and a reproducible composition of
the deposited layer are preconditions if it is subsequently to be
possible for a ceramic or plastic veneer to be applied to the
molding. This applies in particular to ceramic veneers, for which
the molding has to be fired at relatively high temperatures after
the ceramic material has been applied. In these cases, the metallic
basic framework also has to have the required firing stability.
Minimum demands also have to be satisfied with regard to further
properties, such as wear resistance, porosity, corrosion
resistance, inter alia. Moreover, the layers deposited, in
particular in the dental sector, have to comply with particular
aesthetic requirements, for example relating to the color, the
shine or the surface condition. Finally, certain further demands
may be imposed on the composition of the deposited layers, for
example with regard to biocompatibility. Biocompatibility of the
materials may be particularly important especially in the dental
sector, since gold or gold alloy layers with the maximum possible
purity are required for example for patients suffering from
allergies.
[0004] Irrespective of their field of use and irrespective of the
form in which the gold is present in the bath, gold and gold alloy
baths contain certain additives in order to at least partially
comply with the requirements imposed on the electroplated deposits.
Additives of this type are also known as fine-grain additives or
shine additives. These may be organic additives, such as
polyamines, polyimines and mixtures thereof or semimetal compounds,
for example of arsenic, antimony or thallium. All the additives
mentioned may be incorporated to a greater or lesser extent in the
deposited gold layer. In the case of the organic additives, this
causes problems in the dental sector, since the layer properties
(e.g. ductility and firing stability) may be adversely affected by
this incorporation. The incorporation of the semimetals causes
problems in the dental sector in particular in the case of arsenic
and thallium, since the required biocompatibility is then no longer
ensured on account of the use of these toxic substances. The result
of this is that, as far as the Applicant is aware, currently only
antimony has gained any significance as an additive in the dental
sector. However, in physiological terms it is by no means
undesirable for the antimony compounds used to be replaced.
However, when prosthetic moldings are being lined with dental
ceramic, no metal compounds other than antimony compounds have
proven suitable for reasons of firing stability.
[0005] A further problem involved with the use of previously known
additives for gold and gold alloy baths, in particular for baths
based on gold sulfite complexes, is that these additives generally
have to be metered in immediately before the baths in question are
used. This is because the compounds which are present in these
additives are not stable in the baths in question, but rather
decompose over the course of time, losing their effectiveness. This
may be caused, for example, by the pH of the baths in question or
by the fact that the additives react with other constituents
contained in the bath.
[0006] In the case of the addition of antimony compounds to baths
based on gold sulfite complexes, the antimony is generally used as
Sb(III), for example as potassium antimony tartrate. The latter
reacts in the bath to form jelly-like antimony oxide hydrate gel,
which is likely to destroy the action of this additive. For its
part, the antimony oxide hydrate gel is not stable under the
standard bath conditions and reacts to form crystalline antimony
oxide, which no longer reveals the desired effect. This is the
reason why the additive can only be added to the bath just before
use and why the additive loses its effect after a certain time.
[0007] Consequently, it is not possible to produce a gold or gold
alloy bath comprising all the required components which is able to
function over a prolonged period of time.
[0008] A further problem is that the additives not only have to be
metered in at a later stage, but also that the correct metering,
i.e. the required quantity of additive, is dependent on the other
bath and process parameters. Factors of influence in this context
are, for example, the proportions of the other constituents in the
bath, the concentration of the electroactive ions, the geometry of
the deposition vessel (cell geometry) the temperature and the
current density. In most cases, the user attempts to solve these
problems by, on account of his lack of specialist chemical
engineering knowledge, working according to what is known as a
metering table provided by the manufacturer of the bath and
measuring the quantity of additive as a function of the number of
objects to be electroplated. Since the size and shape of the
objects which are to be electroplated and the desired layer
thickness of the deposit vary considerably, and accordingly so does
the quantity of metal to be deposited, metering per object in this
way is subject to a relatively high error level. This can lead to
very varying qualities of the electroplated deposits, and
consequently even objects which have been coated at the same time
in a single operation may differ in terms of the composition of the
deposit. This can make deposition difficult for the user to
manage.
[0009] EP-B1 0 126 921 has described an aqueous bath for the
electrodeposition of gold-copper-bismuth alloys that contains the
gold in the form of a gold cyanide complex. This involves the
deposition of ternary alloys with high bismuth contents. The bath
described in that document is particularly suitable for the
deposition of pink-to violet-colored coatings on decorative
objects, such as for example jewelry, watches and spectacles. The
technical significance is supposed to lie in the fact that the
bismuth can be incorporated in the alloys in extremely high levels
of up to 30% by weight and above. This is intended to open up new
application areas, such as for example the treatment of electronic
components, such as plug connections, since the corresponding
deposits are particularly hard and have a good electrical
conductivity and resistance to abrasion. The baths described in
EP-B1 0 126 921 are unsuitable for the dental sector, inter alia
both on account of their high toxicity and on account of the fact
that high levels of the bismuth are to be incorporated in the
alloy.
[0010] DE-C2 2 723 910 (corresponds to FR-A 2353656) claims a
multiplicity of additive mixtures for baths for the electrolytic
deposition of gold or gold alloys. These additional mixtures are
intended to improve the properties of the deposits formed.
Compulsory constituents of these additive mixtures are at least one
organic water-soluble nitro compound of a certain general formula
and at least one water-soluble metal compound of an element
selected from the group consisting of arsenic, antimony, bismuth,
thallium and selenium. Additive mixtures which, in addition to the
nitro compound, also contain a water-soluble bismuth compound are
in this case too restricted to use in cyanide-based baths. In the
case of baths based on a gold sulfite complex, this document
proposes the use of an additive comprising nitro acid and
antimony-potassium double tartrate. The use of the additive
mixtures mentioned in DE-C2 2 723 910 and of the gold baths
produced therefrom is restricted to the technical application of
plating electronic components for semiconductor technology.
[0011] Furthermore, U.S. Pat. No. 5,277,790 has disclosed an
additive for a bath based on a gold sulfite complex which likewise
has to contain both an organic polyamine or a mixture of polyamines
and an aromatic organic nitro compound. DE-A1 3 400 670 describes a
bath based on gold sulfite complex which contains an additive
comprising water-soluble thallium salt and a carboxylic acid which
is free of hydroxyl and amino groups.
[0012] The invention is based on the object of providing a bath for
the electrodeposition of gold and gold alloys which at least
partially avoids the drawbacks outlined above. In particular, it is
intended to make the production of prosthetic dental moldings by
electrodeposition even more reliable and safer and to further
simplify handling of the baths used for this purpose. Furthermore,
it is intended to create the option of providing the user with a
bath which has already been provided with all the required
constituents and additives and is therefore able to function.
Finally, the intention is for it to be possible for the baths in
question to be operated substantially with biocompatible, i.e.
physiologically harmless compounds without the quality of the
layers deposited being adversely affected.
[0013] This object is achieved by the bath having the features of
claim 1 and by the uses having the features of claims 20 and 21.
Preferred embodiments of these subjects of the invention are
explained in the dependent claims 2 to 19 and 22 to 27. The wording
of all the claims is hereby incorporated by reference in the
content of the present description.
[0014] The bath according to the invention for the
electrodeposition of gold and gold alloys based on a gold sulfite
complex is distinguished by the fact that in addition to any
further metal compounds which may be present and other standard
additives for such gold sulfite baths, it contains at least one
bismuth compound. This bismuth compound is preferably a
water-soluble bismuth compound, which results in the bath itself
also preferably being an aqueous bath.
[0015] In principle, the bismuth compound used may be any suitable
inorganic or organic bismuth compound. The bismuth compound is
preferably a complex compound, preferably what is known as a
chelate compound. Compounds of this type are known to be cyclic
compounds in which a ligand (complex-forming agent) occupies a
plurality of coordination sites of a central atom (metal), and
consequently are generally particularly stable complex compounds.
It is also preferable according to the invention if the bismuth
compound contains an organic complex-forming agent, preferably an
organic chelate-forming agent. Examples of complex-forming agents
or chelate-forming agents in this context are in particular NTA
(nitrilotriacetic acid), HEDTA
(N-(2-hydroxyethyl)ethylenediaminetriaceti- c acid), TEPA
(tetraethylene pentamine), DTPA (diethylenetriaminepentaacet- ic
acid), EDNTA (ethylenedinitrilotetraacetic acid) and the preferred
complex-forming agent/chelate-forming agent EDTA
(ethylenediaminetetraace- tic acid).
[0016] Other examples of bismuth compounds which can be used in
accordance with the invention are water-soluble bismuth salts (e.g.
sulfates, nitrates, sulfamates, phosphates, pyrophosphates,
acetates, citrates, phosphonates, carbonates, oxides, hydroxides,
inter alia). In addition to the preferred complex-forming agents
which have already been mentioned above, such as NTA and the like,
other examples of organic complex-forming agents which can be
mentioned include: organic phosphonic acids, carboxylic acids,
dicarboxylic acids, polyoxycarboxylic acids, hydroxycarboxylic
acids, diketones, diphenols, salicylaldehydes, polyamines,
polyaminocarboxylates, diols, polyols, dipolyamines, aminoalcohols,
aminocarboxylic acids, aminophenols.
[0017] It is also preferable in the context of the invention if the
bismuth compound (or if appropriate a plurality of such compounds)
is(are) present in the bath in a concentration of between 0.05 mg/l
and the saturation concentration of this(these) bismuth compound(s)
in the bath. In particular, concentrations of between 0.05 mg/l and
1 g/l in the bath are preferred. Low concentrations are generally
preferred, with concentrations between 0.1 mg/l and 10 mg/l being
particularly useful within the latter range.
[0018] In a particularly preferred embodiment, the bath according
to the invention is substantially free of additives which are
physiologically harmful (harmful to health), the bath preferably
being free of arsenic, antimony and thallium compounds. This
ensures that there are no compounds, in particular metals, which
are harmful to health and could restrict the usability of the
layers or of the resulting prosthetic moldings in dental
technology, incorporated in the deposited layers. Amazingly, it has
also been found that the inventive addition of bismuth compounds is
also in a position to reduce or even prevent physiologically
harmful additives from being incorporated in the prosthetic
molding. As has already been mentioned in the introduction,
conventional gold sulfite baths contain at least one antimony
compound as an additive. Accordingly, the antimony is incorporated
in the prosthetic molding in a concentration of normally 0.2 part
per thousand. If an antimony compound, such as potassium antimony
tartrate, and a bismuth compound, such as bismuth EDTA, are used
simultaneously, however, it has surprisingly emerged that both
antimony and bismuth are present in quantities of less than 30 ppm
or 40 ppm (these are the detection limits with the analysis method
used for these elements) in the deposited molding. This shows on
the one hand that the bismuth itself is not incorporated in the
molding and on the other hand that the bismuth is able to
considerably reduce the extent to which the antimony is
incorporated.
[0019] The concentration of gold in the bath according to the
invention is not fundamentally critical. It is preferable for the
gold to be present in the bath in a concentration of between 5 and
150 g/l. In particular, gold concentrations of between 10 and 100
g/l, preferably between 10 and 50 g/l, in the bath are selected. A
particular advantage of the invention is that it is possible to
select gold concentrations in the bath of between 30 and 48 g/l.
These relatively high concentrations make the bath according to the
invention particularly suitable for the rapid deposition of thick
layers, as is fundamentally desirable in the field of production of
prosthetic moldings in dental technology. Particularly in the case
of baths with high gold concentrations, it is possible to obtain
prosthetic moldings with layer thicknesses of approximately 200
.mu.m in less than 14 hours, preferably in less than 12 hours. It
is even possible, given a suitable procedure, to deposit moldings
with layer thicknesses of this type in less than 6 hours. The
particular advantages of the invention also manifest themselves in
particular in the case of deposition operations which are carried
out in less than 2 hours, preferably within one to two hours. In
this context, reference is also made to the examples.
[0020] In preferred embodiments of the invention, the bath contains
at least one further metal. This metal can be incorporated in the
deposited layer and is in these cases referred to as an alloying
metal. However, in other cases it may also be used only for
(improved) deposition of the gold or gold alloy layer. This metal
may in particular be copper and/iron and/or at least one precious
metal. If precious metals are added, precious metals from what is
known as the platinum group are preferred, in particular palladium
or platinum. Precious metals, in particular those belonging to the
platinum group, are particularly suitable in the field of
prosthetic dental moldings on account of their high
biocompatibility.
[0021] By way of example, the concentration of the further metal in
the bath can also be varied within wide limits as a function of the
alloy which it is desired to deposit. In principle, the metals can
be added in the form of their preferably water-soluble compounds,
in particular salts, or in the form of preferably water-soluble
complex compounds. In this context, it is once again possible to
employ in particular the complex-forming agents and chelate-forming
agents which have already been mentioned above in connection with
bismuth. The concentrations of the metal compounds may preferably
be selected to be between 0.1 mg/l and 200 g/l. Within this range,
the concentration may be between 0.1 and 500 mg/l and in particular
between 1 and 20 mg/l. In this case too, low concentrations are
preferred. Concentrations of between 2 mg/l and 10 mg/l are further
preferred within the latter range.
[0022] The gold sulfite complex in the bath according to the
invention may in principle be any complex which is known from the
prior art. It is preferably what is known as ammonium-gold sulfite
complex, in which, therefore, the gold ion has been complexed by
the sulfite ions and at least one ammonium ion is present at
"counterion".
[0023] The baths according to the invention preferably have a pH of
at least 7, i.e. they are either neutral or alkaline. In
particular, the baths are (weakly alkaline, with pHs of from 7 to 9
being preferred.
[0024] The preferred ammonium-gold sulfite complex has a range of
advantages over other gold sulfite complexes. For example, compared
to sodium/potassium-gold sulfite complexes, a significantly
increased stability of the complex in the gold bath is responsible
for a range of advantageous properties. These are, for example, a
longer shelf life, reduced sensitivity to impurities and a lower
light sensitivity. Moreover, baths comprising ammonium-gold sulfite
complexes can be operated at a significantly lower pH of
approximately 7-9. This makes baths of this type easier and safer
for users with a lack of specialist chemical knowledge to handle
compared to the Na/Ka-gold sulfite complex baths with pHs of
approximately 10.
[0025] Surprisingly, a particularly advantageous relationship
between chemical composition of the gold bath and chemical
composition of the deposit formed by electrodeposition has resulted
in the bath according to the invention which is based on the
preferred ammonium-gold sulfite complex and contains at least one
bismuth compound. This relationship is improved still further by
the presence of the further metals in the gold bath, in particular
of copper and/or at least one precious metal and/or iron. In
addition, it has been possible to determine a widened range of
applications, since in addition to plaster it is also possible to
use a wide range of dental modeling and framework materials in the
gold bath.
[0026] For example, the use of the bismuth compound has made it
possible in an amazingly simple way to accurately control and
predictably set the composition of the electroplated gold layer and
its functional properties. This has hitherto been impossible or
almost impossible with the known gold baths which are used in
dental technology, and consequently with those baths the
composition of the deposit is generally determined by technical
factors, such as electrode geometry and the other apparatus
technology factors.
[0027] As has already been mentioned a number of times, the demands
imposed on a gold bath and the layers formed by electrodeposition
are of a particular nature in the field of dental technology, and
consequently in this sector, in addition to the requirements
mentioned in the introduction, the need for biocompatibility and
for the desired gold or gold alloy layers to be as pure as possible
should be emphasized once again. For this reason, it is
particularly important for the composition of the deposits formed
by electrodeposition to be controlled in a targeted manner and set
reproducibly.
[0028] Furthermore, in the case of the preferred further metal
copper, it has emerged that in these preferred baths according to
the invention a specific quantitative ratio between bismuth and
copper is advantageous for the composition of the gold layer. A
surprise in this context was that the standard parameters of
influence in electrodeposition which are known to the person
skilled in the art, such as for example electrode geometry,
electrodeposition time, current density, temperature, form of
current, etc., have only a minor effect on the deposition.
Consequently, the copper content in the gold layer can be set
accurately and reproducibly by setting the bismuth-copper ratio in
the bath. The high level of purity which is advantageous for dental
technology can therefore deliberately be achieved by targeted
control of a low copper content in the layers without this
adversely affecting the functionality of the layers. The targeted
incorporation of low copper contents in the gold layer, while at
the same time avoiding incorporation of bismuth, in addition to the
high level of purity also enables the functional properties of the
gold layer to be accurately controlled, such as for example the
hardness, shine, surface properties, color, etc.
[0029] If gold layers which are as pure as possible are to be
deposited with copper and bismuth present in the bath, the
bismuth:copper ratio (based on the metals) is <1, in particular
between 0.3 and 0.5. If alloys are to be deposited by the
incorporation of copper, this ratio is >1.
[0030] In the case if iron as a further metal in the gold bath,
surprisingly still further advantages have resulted in the bath
according to the invention. Iron does not cause any problems in use
and is even required by the body as an essential trace element. In
addition, on the one hand by selection of the quantitative
iron-bismuth ratio in the gold bath and on the other hand by
selection of the type of iron compound/iron complex compound, it
allows the composition and properties of the gold layer deposited
to be controlled even more accurately.
[0031] By way of example, particularly advantageous gold layers
resulted using the iron complexes Fe-DTPA, Fe-EDTA, Fe-EDNTA with
quantitative bismuth-iron ratios from approximately 1.5 to
approximately 2. By contrast, if iron citrate is used, an
advantageous quantitative bismuth:iron ratio is approximately 0.18
to approximately 0.3.
[0032] In this context, the surprising observation that, despite
the advantageous effect of the iron compounds during the
deposition, no iron (<10 ppm) is incorporated in the gold layer,
was of particular significance. This now even makes it possible, by
way of example, to deposit gold layers with a purity of up to
99.99% and with excellent technical properties, such as for example
absolutely reproducible firing stability, by electroplating. This
was not hitherto the case with standard gold electrolytes which are
able to deposit such pure layers.
[0033] A further surprise was that despite the different positions
of copper and iron in the electrochemical series, it is also
possible for the two metals to be used together, in a wide range of
quantitative ratios with respect to bismuth, in the bath according
to the invention. Therefore, the large number of possible
combinations for the bismuth-copper-iron ratios opens up a wide
range of options for new possible ways of controlling the
properties, composition and function of gold and gold alloy layers
formed from baths in accordance with the invention. In situations
in which bismuth, copper and iron are simultaneously present in the
bath, the quantitative bismuth:copper ratio is preferably >0.4
and the quantitative bismuth: iron ratio is preferably >0.3.
[0034] Furthermore, it has amazingly been found that in the bath
according to the invention (including the bismuth compound and the
interaction between the above-described additions of compounds of
further metals in the gold bath), the reduction or prevention of
the incorporation of physiologically harmful additives in the layer
formed by electroplating, as described in the introduction, is
nevertheless retained. Therefore, even when various metals, such as
for example copper and/or iron, are present, the bath according to
the invention is also able to selectively prevent the incorporation
of, for example, antimony.
[0035] As mentioned above, the bath according to the invention may
contain further standard additives which are customarily present in
baths of this type based on a gold sulfite complex. Additives of
this type are known to the person skilled in the art and can be
varied in the standard ranges within the scope of his specialist
knowledge. For example, conductive electrolytes with their
conductive salts, buffer systems/buffer mixtures, what are known as
stabilizers and wetting agents are present. If appropriate,
brighteners and/or fine-grain additives which are known from the
prior art may also be present in the bath according to the
invention.
[0036] The invention also comprises the use of the bath according
to the invention as described above for the production of
prosthetic moldings for the dental sector by means of
electrodeposition. A use of this type is intended in particular for
the production of what are known as dental frames, such as crowns,
bridges, superstructures and the like. The prosthetic moldings are
in this case electrodeposited on a substrate. In this context, one
also refers to the process known as galvanoforming. The
self-supporting, stable molding is separated from the substrate and
processed further. The substrate may, for example, be a cast molded
from a tooth stump or an implant build-up part (prefabricated or
individually prepared).
[0037] In a corresponding way, the invention also encompasses the
use of at least one bismuth compound, preferably of at least one
water-soluble bismuth compound, for the production of prosthetic
moldings for the dental sector by means of electrodeposition. In
particular, the bismuth compound is used as a constituent of a bath
according to the invention as described above. Bismuth compounds
which can preferably be used have already been explained
extensively above, and consequently reference can be made to the
corresponding parts of the description.
[0038] A particularly important feature of the invention which
should be emphasized is that the bismuth compound which is used in
accordance with the invention and if appropriate also the compounds
of further metals can be added to the bath directly during its
production. This means that the user is provided with a bath which
is fully functional in terms of having all its constituents and
additives. Unlike with the known baths from the prior art, the user
does not have to meter in any additive before carrying out the
electrodeposition process, which would entail the drawbacks which
have already been explained above.
[0039] However, it is pointed out that the bismuth compound which
is used in accordance with the invention may also be metered into
the bath before or during the electrodeposition if desired. A
variant of this type may also be provided, for example, when an
aqueous bath to which a completely or partially water-insoluble
bismuth compound, e.g. bismuth oxide, has been added during
production is used. This water-insoluble compound can then be
converted into a water-soluble bismuth compound immediately before
or even during the electrodeposition by addition of a suitable
complex-forming agent, and this water-soluble bismuth compound then
reveals the desired action in the bath.
[0040] The situation in which the bismuth compound is added to the
bath after an electrodeposition operation for top-up purposes
should be mentioned as a further referred variant of the invention.
This relates to the situations in which the concentration of gold
and/or further metal in the bath is sufficient for a plurality, in
particular a multiplicity, of deposition operations. In this case,
the bismuth compound (and if appropriate also the compounds of the
further metals) can be topped up appropriately for subsequent
deposition cycles.
[0041] As has already been mentioned briefly, the use in accordance
with the invention is intended for the production of prosthetic
moldings which have sufficient stability in the galvanoforming
process. Accordingly, it is customary to provide molding layer
thicknesses of more than 10 .mu.m. The layer thicknesses of the
molding are preferably between 100 and 300 .mu.m, with in
particular layer thicknesses of approx. 200 .mu.m being deposited.
The provision of layer thicknesses of this type means that the
invention is suitable not just for the production of crowns but
also of bridges and other superstructures.
[0042] Finally, the invention also comprises a process for
producing prosthetic moldings for the dental sector from gold and
gold alloys by electrodeposition. This process is intended in
particular for the production of dental frames, such as crowns,
bridges, superstructures and the like. In this process, according
to the invention, a gold or gold alloy layer is deposited on a
suitable substrate from a bath in accordance with the invention,
and the layer obtained is separated (demolded) from the substrate.
As mentioned above, the substrate may, for example, be a cast which
has been molded from a tooth stump or an industrially prefabricated
or individually treated implant build-up part.
[0043] The substrate is preferably composed of an electrically
nonconductive material, in particular plaster or plastic. This
normally relates to situations in which a cast has been molded from
the tooth stump. The surface of the nonconductive substrate is then
made conductive prior to the electrodeposition, in particular with
the aid of conductive silver.
[0044] In other preferred cases, the substrate is composed of at
least one metal which is itself already conductive. In this case,
examples of suitable substrates which may be mentioned are inner
telescopes (usually made from a cast and milled dental alloy) or
implant build-up parts, such as implant build-up posts. Parts of
this type usually consist of titanium or titanium alloys.
[0045] The process according to the invention and also the uses
according to the invention are preferably characterized in that the
deposition takes place at high current densities, which usually
results in short electrodeposition times. It is preferable to
select current densities of up to 10 A/dm.sup.2, in particular
current densities of up to 8 A/dm.sup.2. The bath according to the
invention can still be used very successfully at such high current
densities.
[0046] The use according to the invention or the process according
to the invention can preferably be carried out in such a way that
the deposition takes place using what is known as the pulse-plating
process. This type of electrodeposition of metal likewise uses
direct current. However, this direct current is applied as a pulsed
current, i.e. in the form of current pulses which are interrupted
by pauses. With regard to the prior art, reference can be made at
this point, by way of example, to the "Pulse-Plating" volume from
the series of papers entitled Galvanotechnik und
Oberflchenbehandlung [Electroplating and Surface Treatment],
Leuze-Verlag, Saulgau, 1990. The use of the pulse-plating process
in dental technology is shown in DE-A1 198 45 506 in the name of
the present Applicant, the content of which is in this respect
incorporated by reference in the content of the present
description. The use of the pulse-plating process in the present
invention has the advantage that the deposits can be formed in the
desired thickness, for example of approx. 200 .mu.m, within
relatively short times.
[0047] Furthermore, the use according to the invention and the
process according to the invention are preferably characterized in
that the prosthetic molding deposited is veneered with ceramic
and/or plastic during its further processing. The desired tooth
replacement is produced in this way. A molding which has been
veneered with ceramic is fired in the usual way after the ceramic
has been applied, for example at temperatures of up to
approximately 950.degree. C. A molding which has been veneered with
plastic, after the plastic has been applied, is irradiated with
light, in particular with visible light, in order for it to be
cured, after the surface of the molding has previously been
conditioned using suitable processes which are known to the person
skilled in the art.
[0048] As has already been mentioned to some extent and as is also
shown by the examples listed below, a wide range of advantages are
associated with the invention.
[0049] For example, the bath according to the invention is
eminently suitable for the production of prosthetic moldings
(dental prostheses). The properties of the deposits are at least as
good as those achieved with deposits formed from gold sulfite baths
which operate, for example, with antimony compounds being metered
in. The quality of the deposits in the bath according to the
invention tends to match the specific requirements of dental
technology even more successfully.
[0050] The pure gold layers obtained with the bath according to the
invention are a golden yellow color and are extremely shiny, and
therefore satisfy particularly high aesthetic demands. Of course,
it is optionally also possible to produce matt and/or rough
surfaces. The firing stability of these layers, which is imperative
if they are to be veneered with ceramic, is provided with a
reproducible reliability despite the fact that it is possible to
dispense with an antimony compound in the gold bath. As far as the
Applicant is aware, this has not hitherto been the case in any bath
which is able to operate without an antimony compound.
[0051] A further advantage of the bath according to the invention
is that it is clearly insensitive to plastics which have been
introduced into the bath and are provided, for example, as tooth
stump materials or to cover metallic parts which are not to be
coated by electrodeposition. In the baths of the prior art,
plastics of this type (cast molding plastics) or enamels (covering
enamels) during deposition in the gold bath release constituents
which have an adverse effect on the action of the fine-grain or
shine additives of the gold bath. This adverse effect becomes more
noticeable the higher the current density is selected to be during
deposition. In the invention, this results in the advantage that,
since the bath is insensitive to such disruptive influences, it is
possible to operate at relative high current densities (cf. above,
up to 8 A/dm.sup.2 or 10 A/dm.sup.2).
[0052] It must also be mentioned that the efficiency of the bath
according to the invention, for the same profile of demands imposed
on the electrodeposited layers, is entirely comparable with
conventional baths based on gold sulfite complexes which operate,
for example, with antimony or arsenic additives. It is even
possible to increase the efficiency compared to known baths if the
bismuth additive is selected appropriately.
[0053] The possibility of dispensing with compounds which may be
harmful to health, for example of arsenic, thallium and if
appropriate also of antimony, in the bath according to the
invention by using the bismuth additives has already been explained
above.
[0054] Surprisingly, a further advantage of the bath according to
the invention is found to be that a bath of this type with bismuth
additive functions without problems, and in particular with
above-average results, in various devices (including from a number
of different manufacturers) which are in commercial use in the
dental sector for electrodeposition. Hitherto, it has normally been
necessary either for the composition of the gold or gold alloy bath
to be precisely matched to the device used or for a device of this
type to be precisely matched to a specific bath, in particular with
regard to its process parameters. The result of this has been that
each manufacturer has normally offered a specific gold bath for a
very specific device whose process parameters have been matched to
this gold bath.
[0055] With the bath according to the invention, it is now
possible, for example, to operate various devices using this gold
bath without these devices having to be adjusted to this bath in a
complicated way. For example, an AGC micro-appliance produced by
the present Applicant, which achieves a layer thickness of 200
.mu.m usually in 12 hours, can be operated with the bath according
to the invention equally successfully as an AGC MicroPlus appliance
which achieves the same layer thickness in just 5 hours. The bath
according to the invention is also suitable for use in devices
which operate using the pulse-plating process, for example the AGC
Speed appliance produced by the present Applicant. In devices of
this type, layer thicknesses of 200 .mu.m are achieved, depending
on the size of the part which is to be electroplated, within 1 to 2
hours. Therefore, the bath according to the invention can
advantageously be matched to existing electroplating deices owned
by the user. The range of applications from "slows " devices
through to the "fastest" devices, which may also be operated
completely automatically, illustrates how useful the invention is
to the user.
[0056] Finally, it should be mentioned once again that the additive
comprising a bismuth compound which is present in the baths
according to the invention can be added as early as during
preparation of the bath. The result of this is that the user is
provided with a fully functional bath without being forced to add
further additives prior to the electrodeposition process.
Furthermore, it has emerged that the baths according to the
invention with the bismuth additive are stable over prolonged
periods of time. This means that the bath remains able to function
even after it has been stored for prolonged periods and the
additive does not lose its effectiveness. All this makes the bath
easier to operate and more reliable when carrying out the
electrodeposition process both for the manufacturer of the bath and
for the user, since all the sources of faults which can occur with
retrospective metering in excluded of additives are ruled out from
the outset.
[0057] The features described and further features of the invention
will emerge from the following description of preferred embodiments
in conjunction with the subclaims. In this context, the individual
features may in each case be realized on their own or in
combination with one another.
EXAMPLES
[0058] Standard electrolysis cells which are known from the prior
art and are commercially available can be used for the
electrodeposition of prosthetic moldings made from gold or gold
alloys which is carried out in accordance with the present
examples. These electrolysis cells may, for example, be the
AGC.RTM. devices produced by the present Applicant under the names
"Micro", "Micro 5h", "Micro Plus" or "Speed", depending on the
desired procedure.
[0059] An electrolysis cell which can be used in accordance with
the examples comprises a vessel for holding the bath. This vessel
is usually provided with a cover. Furthermore, there is an anode,
which may comprise a plurality of parts, and at least one cathode.
The gold or gold alloy is electrodeposited on this cathode, which
is formed, for example, by the substrate, such as a plaster stump
or build-up post. The anode consists, for example, of
platinum-coated titanium. A suitable current/voltage source is
provided for the deposition itself. Furthermore, there is usually a
magnetic stirrer with heating, which simultaneously ensures a
constant (normally elevated) deposition temperature in the bath and
is responsible for driving a magnetic stirrer rod which is present
in the electrolysis cell. Accordingly, a temperature sensor is also
introduced into the electrolysis cell.
[0060] It is expressly pointed out that the invention does not
require any particular configuration of the electrolysis cell or of
the apparatus which includes this electrolysis cell. The
corresponding apparatus for deposition from gold sulfite baths are
well known to the person skilled in the art.
[0061] As has already been explained in the description, in
accordance with the examples (purely as a selection)
[0062] plaster stumps/plaster casts which have been made conductive
using conductive silver,
[0063] cast and milled inner telescopes in which parts which are
not to be electroplated are filled with a suitable plastic and the
surface which is to be electroplated is covered with conductive
silver,
[0064] build-up posts for the production of cap-like moldings which
can be cemented to implant build-up posts, and
[0065] plaster casts which have a block for connecting two adjacent
teeth and have likewise been coated with conductive silver, are
electroplated.
[0066] Bath composition, deposition parameters, substrate and
deposition result of the examples carried out can be found in Table
1. In all cases, the particularly advantageous bath based on an
ammonium-gold sulfite complex was used.
[0067] In addition to the constituents listed, the baths used also
contain standard additives for gold sulfite baths. These additives
are known to the person skilled in the art. For example, they are
conductive salts (sulfites, sulfates and phosphates), wetting
agents or stabilizers, such as for example nitro acids. The bath
according to the invention differs from the known baths in
particular through the addition of the bismuth compound, and on
account of this addition it is if appropriate possible (although
not necessary) to dispense with additives which are present in
conventional baths, such as for example antimony compounds or nitro
compounds.
[0068] Where the deposition result in the following table refers to
a "defect-free" functionality, this is intended to mean that the
layer obtained during the deposition does not have any cracks,
pores or holes.
1TABLE 1 Example 1 2 3 4 5 Bath Au 16.5 g/l 15.7 g/l 15.7 g/l 16.5
g/l 15.7 g/l composition Bi compound Bi-EDTA: Bi-EDTA: Bi-EDTA:
Bi-EDTAL Bi-NTA: 1.2 mg/l 3.2 mg/l 2.5 mg/l 640 mg/l 2.5 mg/l Other
Cu-EDTA: Cu-EDTA: Cu-EDTA: Cu-EDTA: Cu-TEPA: 5 mg/l 10 mg/l 10 mg/l
5 mg/l 10 mg/l Bi: metal Bi/Cu: Bi/Cu: Bi/Cu: Bi/Cu: Bi/Cu: ratio
0.24 0.32 0.25 128 0.25 Deposition Time 12 h 5 h 6.9 h 5 h 6.9 h
parameters Mean current 0.5 A/dm.sup.2 1.5 A/dm.sup.2 1.5
A/dm.sup.2 1.5 A/dm.sup.2 1.5 A/dm.sup.2 density Form of Direct
current Direct current Direct current Direct current Direct current
current Temp. 65.degree. C. 65.degree. C. 65.degree. C. 65.degree.
C. 65.degree. C. Substrate Type/quantity Plaster Inner Build-up
post Plaster Plaster cast stumps; telescope made made from stumps;
of a block; conductive from a dental gold-titanium conductive
conductive silver gold casting alloy; silver silver alloy filled
conductive with Pattern silver Resin (from GC); conductive silver
Deposition Thickness 200 .mu.m 200 .mu.m 300 .mu.m 200 .mu.m 300
.mu.m result Gold content >99.9% >99.9% >99.9% >99.99%
>99.9% Bi content Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm
Bi < 40 ppm Bi: <40 ppm Alloy content -- -- -- -- --
Efficiency of 82% 86% 86% 82% 86% the bath Appearance gold color,
gold color, gold color, gold color, gold color, shiny; smooth
shiny; smooth shiny; smooth matt; shiny; smooth uniformly covered
with extremely fine buds Functionality defect-free; defect-free;
defect-free; defect-free; defect-free; stable during stable during
stable during the desired stable during the subsequent the
subsequent firing in the roughness firing of the ceramic or
processing and case of the deliberately subsequent plastic fully
ceramic increases the ceramic veneer veneering functional as
veneering and boundary a secondary suitable for surface area part
cementing to with respect the implant to the veneer build-up post
ceramic Example 6 7 8 9 10 Bath Au 48 g/l 40 g/l 100 g/l 15 g/l 8
g/l composition Bi compound Bi-HEDTA: Bi-EDTA: Bi-NTA: Bi-DTPA:
Bi-EDTA: 5.9 mg/l 3.5 mg/l 6 mg/l 50 mg/l 5 g/l Other Cu-EDTA: --
Cu-EDTA: Cu-EDTA: Cu-TEPA: 20 mg/l 15 mg/l 200 mg/l 20 g/; Bi:
metal Bi/Cu: -- Bi/Cu: Bi/Cu: Bi-Cu: ratio 0.295 0.40 0.25 0.25
Deposition Time 105 min 3 h 1 h 6.91 h 12 h parameters Mean current
3.6 A/dm.sup.2 2.0 A/dm.sup.2 10 A/dm.sup.2 0.5 A/dm.sup.2 0.5
A/dm.sup.2 density Form of pulsed direct pulsed direct Pulsed
direct Direct current Direct current current current; current;
current; relative on relative on relative on time 86% time 86% time
88% Temp. 65.degree. C. 65.degree. C. 65.degree. C. 65.degree. C.
65.degree. C. Substrate Type/quantity Plaster Plaster Plaster Inner
Plaster stumps; stumps; stumps; telescope made stumps; conductive
conductive conductive from a dental conductive silver silver silver
gold casting silver alloy filled with Pattern Resin (from GC)
conductive silver Deposition Thickness 200 .mu.m 200 .mu.m 200
.mu.m 200 .mu.m 200 .mu.m result Gold content >99.9% >99.99%
>99.9% >99.78% >95% Bi content Bi < 40 ppm Bi < 40
ppm Bi < 40 ppm Bi < 40 ppm Bi: 60 ppm Alloy content -- -- --
Cu: 0.22% Cu: 5.0% Efficiency of 48% 50% 10% 86% 50% the bath
Appearance gold colored, gold colored, gold colored, Gold colored,
gold colored, shiny; smooth matt, smooth shiny; smooth extremely
extremely shiny; smooth shiny Functionality defect-free;
defect-free; defect-free; Defect-free; defect-free; during the
stable during stable during stable during stable during subsequent
the plastic the plastic the subsequent the subsequent ceramic
veneering veneering processing and plastic veneering fully
veneering functional as a secondary part Example 11 12 13 14 Bath
Au 16.0 g/l 15.7 g/l 16.6 g/l 16.6 g/l composition Bi compound
Bi-EDTA: Bi-EDTA: Bi-NTA: Bi-EDTA: 2.4 mg/l 5.39 mg/l 2.33 mg/l 4.5
mg/l Other Cu-EDTA: Cu-EDTA: Fe-EDNTA: Fe-citrate 10 mg/l 10 mg/l
1.53 mg/l 17.72 mg/l Antimony Fe-DTPA: tartrate: 1.26 mg/l 54 mg/l
Bi: metal Bi/Cu/Sb: Bi/Cu/Fe: Bi/Fe: Bi/Fe: ratio 1/0.24/0.044
1/0.54/4.3 1/1.52 0.26 Deposition Time 5 h 5 h 5 h 5 h parameters
Mean current 1.5 A/dm.sup.2 1.5 A/dm.sup.2 1.5 A/dm.sup.2 1.5
A/dm.sup.2 density Form of direct current direct current direct
current Direct current current Temp. 65.degree. C. 65.degree. C.
65.degree. C. 65.degree. C. Substrate Type/quantity Plaster Plaster
Plaster Plaster stumps; stumps; stumps; stumps; conductive
conductive conductive conductive silver silver silver silver
Deposition Thickness 200 .mu.m 200 .mu.m 200 .mu.m 200 .mu.m result
Gold content >99.9% >99.9% >99.9% >99.9% Bi content Bi
< 40 ppm Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm Alloy
content Sb: <30 ppm Fe < 10 ppm Fe < 10 ppm Fe < 15 ppm
Efficiency of 82% 86% 86% 86% the bath Appearance gold colored,
gold colored, gold colored, Gold colored, shiny; smooth shiny;
smooth shiny; smooth satin finish; smooth Functionality
defect-free; defect-free; defect-free; Defect-free; stable during
stable during stable during stable during the subsequent the
subsequent the subsequent the subsequent ceramic or ceramic or
ceramic or ceramic or plastic plastic plastic plastic veneering
veneering veneering veneering Example 15 16 17 18 Bath Au 15.7 g/l
16.3 g/l 15.7 g/l 15.7 g/l composition Bi compound Bi-EDTA:
Bi-EDTA: Bi-EDTA: Bi-EDTA: 2.33 mg/l 3.3 mg/l 1.61 mg/l 3.24 mg/l
Other Fe-citrate: Cu-EDTA: Cu-EDTA: Cu-EDTA: 8.86 mg/l 5 mg/l 5
mg/l 7.5 mg/l Fe-citrate Fe-citrate: Fe-citrate: 8.86 mg/l 2.215
mg/l 4.43 mg/l Bi: metal Bi/Fe: Bi/Cu/Fe: Bi/Cu/Fe: Bi/Cu/Fe: ratio
0.26 1/0.66/0.37 1/0.322/0.72 1/0.432/0.731 Deposition Time 6.9 h 5
h 5 h 5 h parameters Mean current 1.5 A/dm.sup.2 1.5 A/dm.sup.2 1.5
A/dm.sup.2 1.5 A/dm.sup.2 density Form of Direct current Direct
current Direct current Direct current current Temp. 65.degree. C.
65.degree. C. 65.degree. C. 65.degree. C. Substrate Type/quantity
Built-up post Plaster Plaster Inner made from stumps; stumps;
telescope made gold-titanium conductive conductive from a dental
alloy; silver silver gold casting conductive alloy filled silver
with Pattern Resin (from GC); conductive silver Deposition
Thickness 300 .mu.m 200 .mu.m 200 .mu.m 200 .mu.m result Gold
content >99.9% >99.9% >99.9% >99.9% Bi content Bi <
40 ppm Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm Alloy content
Fe < 10 ppm Fe < 10 ppm Fe < 10 ppm Fe < 10 ppm
Efficiency of 86% 86% 86% 86% the bath Appearance gold colored,
gold colored, gold colored, gold colored, silk finish; shiny;
smooth shiny; smooth shiny; smooth smooth Functionality
defect-free; defect-free; defect-free; defect-free; stable during
stable during stable during stable during firing of the the
subsequent the subsequent the ceramic ceramic or ceramic or
subsequent veneer and plastic plastic processing suitable for
veneering veneering and fully cementing to functional as the
implant a secondary build-up post part
* * * * *