U.S. patent application number 12/384574 was filed with the patent office on 2009-09-10 for sealing of ceramic substances by means of electromagnetic centimetre waves, and receptacle for carrying out the inventive method.
This patent application is currently assigned to Vita Zahnfabrik H. Rauter GmbH & Co. KG. Invention is credited to Marc Stephan, Norbert Thiel, Markus Vollmann.
Application Number | 20090223950 12/384574 |
Document ID | / |
Family ID | 30771720 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090223950 |
Kind Code |
A1 |
Stephan; Marc ; et
al. |
September 10, 2009 |
Sealing of ceramic substances by means of electromagnetic
centimetre waves, and receptacle for carrying out the inventive
method
Abstract
A method for manufacturing ceramic parts with a certain porosity
by sintering using microwaves, the materials to be sintered being
arranged in a vessel, wherein the microwaves introduce sintering
energy into the materials to be sintered via electromagnetic waves
in the range of vacuum wavelengths between 5 cm-20 cm in multimode
having an electromagnetic power of up to one kilowatt, and besides
being built from primary materials for the structure of the vessel,
the vessel is built from a secondary material which comprises, in
particular, a mixture of or mixed crystals of non-metallic, para-,
ferro- or antiferromagnetic materials.
Inventors: |
Stephan; Marc; (Lorrach,
DE) ; Vollmann; Markus; (Bad Sackingen, DE) ;
Thiel; Norbert; (Bad Sackingen, DE) |
Correspondence
Address: |
PAUL D. GREELEY;OHLANDT, GREELEY RUGGIERO & PERLE, L.L.P.
10th FLOOR, ONE LANDMARK SQUARE
STAMFORD
CT
06901-2682
US
|
Assignee: |
Vita Zahnfabrik H. Rauter GmbH
& Co. KG
|
Family ID: |
30771720 |
Appl. No.: |
12/384574 |
Filed: |
April 7, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10520722 |
Dec 1, 2005 |
|
|
|
12384574 |
|
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|
Current U.S.
Class: |
219/679 ;
219/762 |
Current CPC
Class: |
C04B 2235/80 20130101;
C04B 41/009 20130101; C04B 41/86 20130101; C04B 41/5022 20130101;
C04B 35/64 20130101; C04B 2111/00836 20130101; C04B 2235/3243
20130101; C04B 2235/3284 20130101; C04B 35/42 20130101; A61C 13/203
20130101; C04B 2235/667 20130101; C04B 41/009 20130101; C04B 35/00
20130101; C04B 41/009 20130101; C04B 35/48 20130101; C04B 41/009
20130101; C04B 38/00 20130101 |
Class at
Publication: |
219/679 ;
219/762 |
International
Class: |
H05B 6/80 20060101
H05B006/80 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2002 |
DE |
DE10232818.8 |
Nov 20, 2002 |
EP |
EP02025674.9 |
Jul 5, 2003 |
EP |
PCT/EP2003/007212 |
Claims
1. Vessel for manufacturing ceramic parts with a certain porosity
by sintering using microwaves, said vessel comprising a primary and
a secondary material, wherein said secondary material comprises at
least one material selected from the group consisting of: a
non-metallic material, a para-magnetic material, a ferro-magnetic
material and an antiferromagnetic material.
2. Vessel of claim 1, wherein said secondary material is
zincochromite (ZnCr2O4) with 0-99 percent by weight of zincite
(zinc oxide ZnO).
3. Vessel of claim 1, wherein, to increase the dense sintering
temperature, the secondary material further comprises a refractory
non-metallic material having a high transparency for super high
frequency waves in a wide temperature range.
4. Vessel of claim 3, wherein said refractory non-metallic
secondary material having a high transparency for super high
frequency waves is zinc oxide (ZnO).
5. Vessel of claim 1, further comprising a receiving portion for
receiving said primary and secondary material to be sintered, said
secondary material being provided at least partly around the
receiving portion.
6. Vessel of claim 5, wherein said receiving portion is surrounded
by at least one, secondary material element.
7. Vessel of claim 1, wherein said secondary material is surrounded
by said primary material.
8. Vessel of claim 5, wherein said secondary material extends over
the entire height of said receiving portion.
9. Vessel of claim 6, wherein said secondary material element is
rod-shaped.
10. Vessel of claim 6, wherein said secondary material element is
divided regularly around the receiving portion.
11. Vessel of claim 6, wherein said secondary material element is
encapsulated with said primary material.
Description
CROSS-RELATED APPLICATION
[0001] This application is a Divisional Application of U.S. patent
application Ser. No. 10/520722, filed on December 1, 2005, which is
incorporated herein in its entirely.
BACKGROUND
[0002] 1. Field of the Disclosure Densification of ceramic
materials using electromagnetic super high frequency waves, as well
as vessel for performing the method
[0003] The preset disclosure refers to the thermal densification of
porous ceramic parts, in particular with a small material volume of
up to 10 cm.sup.3. The thermal densification is effected by
electromagnetic radiation in the wavelength range of 5 to 20 cm
using dissipative electric or magnetic polarization effects of the
material. Further, the disclosure refers to a vessel or a device
for performing the method.
[0004] 2. Discussion of the Background Art
[0005] Presently, such methods are used in drying, removing binding
agents and sintering very large ceramic components in an industrial
production scale. The advantages of this method lie with the
clearly lower energy consumption, the more homogeneous heating
(lower temperature gradient) and reduced densification times. This
results in an economic production process.
[0006] These methods are still critical for oxide ceramics such as
Al.sub.2O.sub.3 and ZrO.sub.2 in that no effective electromagnetic
dissipation occurs at ambient temperature. Until today, this
obstacle was obviated using a conventional heating, since the
effectiveness of the dissipative coupling of the super high
frequency waves increases drastically from a certain temperature.
However, this increases the time and energy input so that the above
mentioned advantages of this technology are greatly relativized.
Avoiding the conventional heating can be achieved by adding
suitable materials that show significant polarization losses
already at ambient temperature, or by suitable sintering additives.
This method has disadvantages in the reduced mechanical properties
of the cooling ceramics as compared to the pure material. They are
especially unsuitable for use in prosthetic medical products for
aesthetic and biocompatibility reasons.
[0007] Moreover, the question of insulating material for thermal
insulation of the baking chamber from the environment is still
unanswered for large scale industry purposes. The difficulty lies
with the low thermal conductivity and the simultaneous high
transparency to super high frequency waves The technical problem
the disclosure is based on was to provide a method, and a vessel
for performing this method, which would allow to use microwave
treatment also other fields than in large scale industry,
especially in the field of dental ceramics.
SUMMARY
[0008] The technical problem is solved with a method for
manufacturing ceramic parts with a certain porosity by sintering
using microwaves, the materials to be sintered being arranged in a
vessel, wherein [0009] the microwaves introduce sintering energy
into the materials to be sintered via electromagnetic waves in the
range of vacuum wavelengths between 5 cm-20 cm in multimode having
an electromagnetic power of up to one kilowatt, and [0010] besides
being built from primary materials for the structure of the vessel,
the vessel is built from a secondary material which comprises
non-metallic, para-, ferro- or antiferromagnetic materials.
[0011] The present disclosure solves the above mentioned problems
by using non-metallic para-, ferro- or antiferromagnetic materials
that are suitable as a crucible material that is characterized by
dissipative partial absorption of the electromagnetic super high
frequency waves at ambient temperature, a high melting point and a
partial transparency to super high frequency waves even at high
temperatures (up to 1,800.degree. C., in particular up to about
2,000.degree. C.).
[0012] Using this so-called secondary material in a vessel has the
advantage of a contamination-free densification of the primary
material the vessel is otherwise made of. The primary material is
supported in the vessel, such as a crucible, for example by high
temperature resistant anorganic fiber materials with low absorption
of super high frequency waves and low thermal conductivity. These
are known per se in the field of the construction of high
temperature kilns. The fact that this fiber material only serves as
a support, the above mentioned disadvantages are eliminated.
Preferred vessel materials are, above all, non-metallic para-,
ferro- or antiferromagnetic materials, such as the oxides of
chromium, iron, nickel and manganese and the Spinell or Perowskit
structures to be derived therefrom (formed with metalloxide without
significant absorption of super high frequency waves, e.g. ZnO) or
ferro- or antiferromagnetic Spinell materials, such as
zincochromite, or ferroelectric Perowskit materials such as barium
strontium titanates. It is advantageous that the melting
temperature of these materials be as high as possible. If this is
not the case, a refractory non-metallic material with a high
transparency to super high frequency waves, such as zinc oxide,
should be admixed. The advantage of this design of the super high
frequency wave kiln is that even at powers of 1 kilowatt at 2.45
GHz in multi-mode, a high temperature of 1,800.degree. C. is
achieved. Thus, this kiln becomes very low-priced and smaller than
conventional kilns for this temperature range.
[0013] In the present method, the material used advantageously is a
para-, ferro- or antiferromagnetic material such as zincochromite
or a ferroelectric material such as barium strontium titanate.
[0014] The advantages of certain antiferromagnetic Spinell
structures lie with the high melting temperature and the power
dissipation of microwave radiation at the typical frequency in the
range from 2-3 GHz, preferably 2.3-2.6 GHz, and most preferred 2.45
GHz, the dissipation being high already at ambient temperature.
[0015] In one embodiment of the present method, the wavelength
range of the electromagnetic waves is from 11 to 13 cm.
[0016] This is the frequency range most common in consumer
electronics so that significant cost savings are realized.
[0017] The ceramic parts obtained according to the disclosure have
a porosity of 0-50 percent by volume, preferably 10-30 percent by
volume. The porosity can be controlled through the sintering
temperature. Densely sintered ceramic materials (porosity of nearly
0%) have the advantage of high strength in combination with a high
translucence.
[0018] According to the disclosure, a glass could be infiltrated
into the ceramic parts to obtain the final strength of the products
manufactured.
[0019] The porous parts can later be finished easily and be
solidified by suitable infiltration methods on the basis of
anorganic glasses (e.g. lanthanum silicate glasses) or organic
materials (e.g. UDMA, bis-GMA).
[0020] The present method allows for a sintering of the ceramic
parts to a defined final density. Until today, achieving high final
densities for ceramic materials, such as aluminium oxides or
zirconium oxides, has been possible only with very high time input
and expensive conventional heating methods.
[0021] The present method is particularly useful in the manufacture
of dental restorations.
[0022] To comply with aesthetic requirements, dental ceramic frame
parts could be veneered with suitable glass materials, such as
feldspar glass, lithium disilicate glass or fluoroapatite
glass.
[0023] In one embodiment of the present disclosure, the materials
used to manufacture dental ceramic restorations consist of
Al.sub.2O.sub.3, Spinell, Ce- or Y-stabilized ZrO.sub.2 (e.g. TZP,
PSZ) or mixtures of these materials.
[0024] These ceramic materials show the highest values of strength
and fracture toughness of ceramic materials.
[0025] According to the disclosure, full ceramic dental
restorations can be made from dental ceramic masses, such as
feldspar glass, lithium disilicate glass or fluoroapatite glass,
the present method being adapted for use as pressing oven or a
preheating oven in glazing full ceramic dental parts or, e.g., for
pressed ceramics for dental purposes.
[0026] In this case, the advantages are the clearly reduced process
time and simultaneously reduced energy input and, thus, costs.
[0027] To increase the dense sintering temperature, the disclosure
provides that the material of the vessel may be a mixture of that
material with a refractory non-metallic material with a high
transparency to super high frequency waves in a wide temperature
range.
[0028] If the secondary material is only one substance that has a
high microwave absorption at ambient temperature, the microwave
amplitude can be decreased to an extent that the material to be
sintered will no longer be heated sufficiently.
[0029] In particular, the refractory non-metallic material with
high transparency to super high frequency waves is zinc oxide.
[0030] Zinc oxide has a high melting temperature of about
2,000.degree. C.
[0031] The disclosure further refers to a vessel that is
particularly suitable for carrying out the above method. According
to the disclosure, the vessel has a primary and a secondary
material, the secondary material including a non-metallic para-,
ferromagnetic or antiferromagnetic material. Because such a
secondary material is provided in the vessel, it is possible to
achieve a high temperature in the vessel at ambient temperature and
within short time, in particular within a few seconds. Temperatures
of about 2,000.degree. C. can be achieved. Thus, it is also
possible to sinter oxide ceramics without providing a conventional
auxiliary heating. This is possible with conventional microwave
means operating in a range of about 700 Watt and being operated
according to the multi-mode method.
[0032] It is particularly preferred to make the vessel from
materials that have been described above in the context of the
method. Preferably, the secondary material is a mixture of para-,
ferro- or antiferromagnetic materials, such as zincochromite
(ZnCr.sub.2O.sub.4) with 0-99 percent by weight of zincite
(ZnO).
[0033] Preferably, the present vessel has a receiving portion into
which the material to be sintered is placed. In this particularly
preferred embodiment, the receiving portion is at least partly
surrounded by secondary material. For example, the receiving
portion is cylindrical and is surrounded by a circular ring of
secondary material. Preferably, a plurality of secondary material
elements are provided surrounding the receiving portion. Thus, a
plurality of elements is provided that do not form a closed ring or
the like. For example, the secondary material elements are a
plurality of ring segments. However, the secondary material
elements ma have any other shape, such as a rod shape, or they may
have a polygonal, in particular a rectangular cross-sectional
shape.
[0034] It is preferably preferred to have the secondary material be
surrounded by the primary material. Hereby, the secondary material
serving to generate the temperature is arranged close to the
receiving portion, yet a direct contact between the secondary
material and the material to be sintered is avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The following is a detailed description of the disclosure
using preferred embodiments and making reference to the
accompanying drawings. In the figures:
[0036] FIG. 1 illustrates a schematic exploded sectional view of a
first preferred embodiment of the vessel according to the present
disclosure,
[0037] FIG. 2 is a schematic side elevational view of a first
preferred embodiment of the vessel,
[0038] FIG. 3 is a schematic sectional view taken along the line
III-III in FIG. 2,
[0039] FIG. 4 is a schematic exploded sectional view of a second
preferred embodiment of the vessel according to the present
disclosure,
[0040] FIG. 5 is a schematic sectional view of the second
embodiment of the vessel according to the preferred vessel, and
[0041] FIG. 6 is a schematic sectional view along line VI-VI in
FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0042] The first embodiment (FIGS. 1-3) of the present vessel for
carrying out the present method for manufacturing ceramic parts
comprises a bottom element 10, a cover element 12 and an
intermediate element 14. The elements 10, 12, 14 are preferably
made from primary material. The bottom element 10 and the cover
element 12 are cylindrical in shape and each have a cylindrical
projection 20 or 22 located on the inner surface 16 or 18,
respectively. The intermediate element 14 is annular in shape and
has a cylindrical opening 24 which, in the assembled condition
(FIG. 2), defines the receiving portion 26. The diameter of the
cylindrical opening 24 corresponds to the diameters of the
cylindrical projections 20 and 22. In the assembled condition, this
results in a cylindrical closed receiving portion 26.
[0043] The intermediate element 14 has an annular recess 28 for
receiving secondary material. The recess 28 surrounds the receiving
portion 26, where the recess does not necessarily have to be a
circular ring. In the preferred embodiment illustrated in FIGS. 1
to 3, the recess 28 is of circular ring shape and completely
surrounds the receiving portion 26. A wall 30 is formed between the
receiving portion 26 and the circularly annular recess 28, the wall
being made from primary material as is the entire intermediate
element 14. Thus, the secondary material is surrounded by primary
material. Either a secondary material element 32 of secondary
material is placed into the circularly annular recess 28, or the
secondary material 32 is filled into the annular shape. The recess
28 is then closed with a closure element 34, preferably also made
from primary material. The closure element 34 also is an annular
element with an annular projection 36 extending into the recess 28
(FIG. 2).
[0044] The secondary material element 32 and, thus, the secondary
material, preferably extends over a large part, especially more
than two thirds, of the height of the receiving portion 26. It is
particularly preferred to have the secondary material extend over
the entire height of the receiving portion.
[0045] It is further possible, in FIG. 2, to provide elements of
secondary material below and/or above the receiving portion 26.
[0046] In the second preferred embodiment (FIGS. 4-6), elements
similar or identical to those in the first embodiments (FIGS. 1-3)
bear the same reference numerals.
[0047] The bottom element 10, as well as the cover element 12 are
substantially identical. An intermediate part 40 also has a
circular cross section. A substantially cylindrical receiving
portion 26 is formed through the intermediate part 40. However, the
inner wall 42 (FIG. 6) of the receiving portion 26 is not smooth.
Rather, cylindrical chambers 44 are provided starting from the
inner wall 42. Individual rod-shaped secondary material elements 46
are inserted into the cylindrical chambers 44. In the embodiment
illustrated, the secondary material elements 46 are encapsulated.
The secondary material elements 46 are thus entirely enclosed by a
shell layer 48. The shell layer 48 preferably consists of primary
material.
[0048] In the following, the present disclosure will be explained
in more detail with reference to two examples:
[0049] A vessel of high-temperature resistant aluminium oxide
material (resistant to up to 1,800.degree. C.) was made with the
vessel shape illustrated in FIGS. 1-3. This was filled with a
secondary material 32 in the annular indentation or recess 28. The
secondary material was a mixture or comprised mixed crystals of 50
percent by weight of zincochromite (ZnCr.sub.2O.sub.3) and 50
percent by weight of zincite (ZnO).
EXAMPLE 1
[0050] The material to be sintered was a dental crown material of
yttrium-stabilized zirconium oxide. This crown cap was placed into
receiving portion 26 in the vessel on aluminium oxide baking wool
and put into a conventional microwave (900 W, multi-mode, 2.45 GHz)
together with the vessel. The same is operated for 15 minutes at a
power of 700 W. The final density of the zirconium oxide material
is 6.06 g/cm.sup.3 and thus corresponds to the theoretical density
of the material.
EXAMPLE 2
[0051] The material to be sintered is a three-part dental bridge
with an overall length of 35 mm prior to dense sintering. This
three-part bridge is placed into the vessel on an aluminium oxide
baking substrate and put into conventional microwave (see above)
together with the vessel. The same is operated for half an hour at
a power of 700 W. The final density of the zirconium oxide material
is 6.0 g/cm.sup.3 and thus corresponds to the theoretical density
of the material.
* * * * *