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.

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 cm3. 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 me...

AI Technical Summary

Benefits of technology

[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° C. is achieved. Thus, this kiln becomes very low-priced and smaller than conventional kilns for this temperature range.

[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.

[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).

[0026]In this case, the advantages are the clearly reduced process time and simultaneously reduced energy input and, thus, costs.

[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° 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.

Problems solved by technology

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.

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.

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.

Thus, this kiln becomes very low-priced and smaller than conventional kilns for this temperature range.

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.

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