US20050211414A1

US20050211414A1 - Method for the production of a muffle for precision or model casting, method for the production of a metallic, ceramic or glass ceramic casting or blank and kit for the production of such a casting or blank

Info

Publication number: US20050211414A1
Application number: US11/086,285
Authority: US
Inventors: Thomas Wiest; Stephan Dierkes; Martin Schluter
Original assignee: Bego Bremer Goldschlagerei Wilh Herbst GmbH and Co KG
Current assignee: Bego Bremer Goldschlagerei Wilh Herbst GmbH and Co KG
Priority date: 2004-03-25
Filing date: 2005-03-23
Publication date: 2005-09-29
Also published as: EP1579934A1; ATE416051T1; EP1579934B1; DE502005006110D1; DE102004014573A1

Abstract

Methods are described for the production of a muffle for precision or model casting having the following steps: preparation of a pattern preparation of an investment, comprising a mixture of: a) a dispersing agent, b) a ceramic powder containing (i) a fraction having a diameter of less than 500 nm (nanoceramic powder fraction) in a proportion of 2-74% (V/V), based on the volume of the total mixture, and (ii) a fraction having a diameter of more than 500 nm (microceramic powder fraction) in a proportion of 2-74% (V/V), based on the volume of the total mixture c) optionally a metal powder consisting of metals and/or alloys and/or intermetallic compounds, d) optionally one or more further additives and e) optionally inorganic or organic binder investing or covering the pattern with the investment solidification of the investment investing or covering the pattern by a) freezing, b) gelling, in particular on the basis of a change in pH value and/or c) dehydrating, during and/or after the solidification, drying the investment investing or covering the pattern by removing the dispersing agent and optionally other volatile constituents removal of the pattern from the dry investment and heating the dried investment so that a muffle for the precision or model casting results.

Description

The invention relates to a method for the production of a muffle for precision or model casting, a method for the production of a metal, ceramic or glass ceramic casting or blank and a kit for the production of such a casting or blank.
Methods are known for the production of a muffle in dental engineering for casting dental restorations, for example inlays or onlays, crowns, bridges and model castings. In order to produce such dental restorations, the dentist takes an impression of the situation in a patient's mouth. A carving material (for example plaster or plastic) is poured into this impression. The planned dental restoration is then carved in casting wax or plastic on this model and removed from the model. A wax wire is placed on this casting wax or plastic pattern and joined to it, so that a pattern for the subsequent casting is obtained. The wax wire serves to form a sprue in a latter process step. In terms of its dimensions, the casting that is obtained at the end of the process should correspond as precisely as possible to this pattern.
The pattern thus obtained is fixed to the bottom of a muffle base using the wax wire. A muffle former is then fitted which encloses the pattern at the sides. The muffle former is now completely filled with dental investment. After the dental investment has set, this is removed from the muffle former. In the case of a metal muffle former, this remains on the muffle.
Alternatively, an investment duplicate of the model is produced. The pattern is made on the duplicate, provided there with sprues of wax or plastic and invested after fitting a muffle former. In a further process modification the pattern of photo-curable material made on the investment duplicate is cured using light of a specific wavelength, lifted from the duplicate and invested as described above.
The muffle obtained is optionally removed from the muffle former and heated continuously from room temperature up to approximately 600° C.-1100° C. (depending on the indication). As an alternative, the muffle consisting of suitable dental investment can also be placed directly in the furnace pre-heated to higher temperatures. In particular, it is also possible to place it in the furnace at 1000° C. to 1100° C. In the furnace the pattern consisting of casting wax or plastic melts or combusts virtually without residue. Thereafter a cavity and a sprue, which have been formed from wax wire by the combustion of the casting wax, are then present in the interior of the muffle.
The muffle obtained in this way is filled in the hot or cold state with liquid melt or flowable ceramic or glass ceramic composition and cooled slowly. After destruction of the casting mould, which for this reason is also termed a lost mould, the casting can be removed and finally worked to the finished product. Casting in the lost casting mould is a method that has been known and mastered for a long time in dental engineering in order to produce dental restorations from metal, ceramic or glass ceramic and it is regularly used in the dental laboratory.
In order to ensure a good fit of the casting produced in this way as dental restoration, it is necessary to maintain narrow tolerances. Because of the large difference in temperature between the solidification temperature of the melt and room temperature, the expansion and shrinkage, respectively, of the casting and of the casting mould play a decisive role here.
Therefore, special investments have been developed in order to be able to set the expansion of the casting mould as a function of the temperature in a manner that is as controlled as possible. Dental investments according to the state of the art contain proportions of quartz and crystobalite or tridimite, which on heating contribute to the thermal expansion of the casting mould as a result of a change into the high temperature modification which is of clearly increased volume. In the case of the compositions according to the state of the art the thermal expansion of the investment is based, as well as on the thermal expansion of the entire composition, in particular on the thermally activated re-orientation of the SiO₂lattice modification. In the case of these investments the thermal expansion is dependent on the temperature in a non-linear manner and is largely reversible. In addition to the thermal expansion, the conventional investments also undergo an expansion that develops during setting. As a rule this setting expansion can be controlled by variation of the concentration of a mixing liquid to be used. In this way it is possible to respond to the various requirements in dental engineering practice (mixing parameters, alloys, shape and mass of the objects to be produced, etc.).
In order to achieve a homogeneous expansion of the casting mould, according to the state of the art the components used for the investment must usually be in the form of a microcrystalline powder. The problem here is that these quartz and crystobalite or tridimite particles used in the investments can be so small that they can pass into the lungs. Therefore it is feared that such particles could be carcinogenic, similar to asbestos. This circumstance necessitates extensive safety precautions when processing investments. It is therefore desirable to be able to dispense with substances known to be potentially carcinogenic (or to design the processing processes and the materials in such a way that liberation of the constituents that can pass into the lungs can be effectively and completely prevented).
The documents DE 196 07 380 C2 and DE 196 49 306 C2 relate to ceramic investments for the production of casting moulds.
The aim of the present invention is to propose (a) methods for the production of a muffle for precision or model casting, (b) a method for the production of a metallic, ceramic or glass ceramic casting or blank and (c) a kit for the production of such a casting or blank, which overcome the abovementioned disadvantages.
According to the invention the aim is achieved for a method for the production of a muffle for precision or model casting by a method having the following steps:

- preparation of a pattern
- preparation of an investment, comprising a mixture of:
  - a) a dispersing agent,
  - b) a ceramic powder containing
    - (i) a fraction having a diameter of less than 500 nm (nanoceramic powder fraction) in a proportion of 2-74% (V/V), based on the volume of the total mixture,
    - and
    - (ii) a fraction having a diameter of more than 500 nm (microceramic powder fraction) in a proportion of 2-74% (V/V), based on the volume of the total mixture
  - c) optionally a metal powder consisting of metals and/or alloys and/or intermetallic compounds,
  - d) optionally one or more further additives and
  - e) optionally inorganic or organic binder
- investing or covering the pattern with the investment
- solidification of the investment investing or covering the pattern by
  - a) freezing,
  - b) gelling, in particular on the basis of a change in pH value and/or
  - c) dehydrating,
- during and/or after the solidification, drying the investment investing or covering the pattern by removing the dispersing agent and optionally other volatile constituents
- removal of the pattern from the dry investment and heating the dried investment so that a muffle for the precision or model casting results.

In this context the reference to “metals” in characteristic c) above is also to be understood to be a reference to “metalloids”; this applies correspondingly for the following text. The use of metals (in the narrower sense) is, however, preferred.
It has been found, advantageously, that with the present invention it is possible to shift the ratio of thermal expansion to setting expansion decisively in the direction of thermal expansion. This is advantageous since setting expansion is susceptible to external influences, in contrast to which thermal expansion is readily adjustable and reproducible.
In particular, bodies that do not irreversibly deform under the pressure that exists when investing or covering with the investment are suitable as patterns. In addition, preferred patterns can be removed from the dried investment substantially free from residue, for example by burnout or by chemical reaction with ambient gases to give a gas. Dissolution of the pattern with a suitable solvent or other methods for removing from the mould before heating the dried investment are also conceivable. Patterns of dental restorations consisting of casting wax or plastics, such as are used in dentistry, are particularly advantageous, as are also completely removable materials that are used in conventional casting practice or for rapid prototyping methods.
The indicated diameters of the particles are those that are determined in accordance with ISO 13320-1, for example using the LS 13320 instrument from Beckman Coulter GmbH.
In the course of the method according to the invention an investment is produced that contains a dispersing agent, a nanoceramic powder fraction and a microceramic powder fraction, optionally a metal powder, optionally one or more further additives and optionally inorganic or organic binders.
The proportion of nanoceramic powder fraction and microceramic powder fraction based on the volume of the total mixture is determined by relating the volume of the separated nanoceramic fraction and macroceramic fraction, respectively, to the initial volume of the entire mixture. The volume determinations are in each case carried out under standard conditions (25° C., 1013·hPa).
Nanoceramic powder fraction and microceramic powder fraction in the mixture can be obtained in that the mixture is prepared by using a first ceramic powder, which essentially consists of particles that are less than 500 nm in size, and a second ceramic powder which essentially consists of particles that are more than 500 nm in size. Another possibility is the use of a polymodal ceramic powder that has two or more maxima in the density function of the particle size distribution function, for example one below 500 nm and one above 500 nm.
Preferred further additives are: bactericides, bacteriostatic agents, wetters, wetting agents, pore forming agents, flow agents, anti-foams, latex, etc.
Binders are chemical substances that intensify the cohesion of the particles to one another and thus lead to a mechanically stable investment after solidifying or after heating. The following have proved particularly advantageous as inorganic and organic binders: magnesium oxide/monoammonium phosphate, magnesium oxide/magnesium chloride mixture, cement, plaster, starch, hydroxymethylcellulose, polyvinyl alcohol/polyvinyl acetate copolymer, a magnesium acetate/magnesium oxide mixture, low-loss binders etc.
One advantage of the method according to the invention is that the dried investment is capable of plastic working before heating and an adequate processing time remains between the process steps. The dried investment is, moreover, easy to remove from a muffle former that is frequently used when investing or covering the patterns with the investment; moreover, it has a high strength. The muffle resulting from the dried investment has a strength that is sufficient to withstand the pressure produced in operation when duplicate casting of the muffle or when injecting, for example, a ceramic composition. Moreover, it is resistant to high temperature corrosion in contact with melts and, in the case of muffles produced according to the invention, there is hardly any contraction during the casting delay time. Furthermore, muffles that have been produced in accordance with the method according to the invention have a high resistance to thermal shocks.
Furthermore, such a muffle is usually fine-grained, which enables an accurate impression even of fine details of the pattern and is nevertheless sufficiently porous to allow gases to escape during casting. Furthermore, the high porosity leads to a high insulating effect of the muffle and facilitates the removal of the casting from the muffle in subsequent operation (in this context see below). Since removal can be a time-consuming process step, a distinct cost advantage results from this. Moreover, the components of the investment used have good storage stability, which permits larger, and thus less expensive packs.
An important advantage is that in the method according to the invention the preparation of the investment can be carried out without the use of quartz particles that can be inhaled and pass into the lungs, which increases safety for the user. Moreover, it is possible to adopt a procedure such that no setting expansion, or a setting expansion that is only very weakly pronounced, of the investment produced in the method according to the invention is obtained, which improves processing reliability.
The expansion of the investment that is necessary to ensure high dimensional stability of the casting can be accurately controlled during heating of the dried investment. An increase in volume can be achieved, in particular, by oxidation of a metal powder that in this case is used in the production of the investment. Reactions that contribute to an increase in the volume are, for example, the oxidation of (a) aluminium (to aluminium oxide) or (b) niobium (to niobium pentoxide), which are advantageously contained in the metal powder. An increase in the volume of the investment is also achieved by reactions of constituents of the metal powder to give reaction-bonded systems (RBS) or spinels. The metal powder content can be so chosen that, after cooling, the muffle produced in accordance with the method according to the invention has a cavity that has precisely the dimensions of the original pattern. However, alternatively, by means of an increased proportion of metal powder it is possible to achieve a cavity that has larger dimensions than the original pattern. This is advantageous especially if, after using the muffle in the casting operation, finishing by a machining operation on the casting is to be carried out.
A further advantage is that the muffle obtained consists of a material that has only a low affinity for melts of commercially available dental alloys, which facilitates removal and reduces chemical reactions between muffle surface and melt.
Therefore, the result of the advantageously high dimensional stability is also that there is no pronounced shrinkage during solidification of the investment investing or covering the pattern. During drying, which follows the solidification, dispersing agents, water, binders and other volatile constituents can be removed without any alteration in the macroscopic structure of the green body. The reason for this is that microscopically small pores form during drying but the skeleton consisting of the non-volatile constituents remains (at least essentially) intact.
The purpose of the solidification is to fix the non-volatile constituents spatially, so that in the subsequent process steps they form a green body that displays only very slight shrinkage. In order to suppress thermal expansion, the solidification is preferably carried out at or below room temperature (25° C.). Therefore, in the method according to the invention solidification takes place by (a) freezing, (b) gelling, especially on the basis of a change in pH value, and/or (c) dehydration. These processes can each be supported by the addition of binders.
If solidification is carried out by freezing, this is referred to as freeze casting. During freezing phase separation takes place within the sol that is formed from nanoceramic powder and dispersing agent. In this context a nanoceramic powder is understood to be a ceramic powder in which the primary nanoceramic powder fraction makes up more than 95% (m/m) of the ceramic powder. During freezing ice and solvent crystals form, which can be removed from the structure in the drying step. The solid particles, on the other hand, are compacted. The space previously filled by the ice crystals then forms a pore. There is therefore no change or only a slight change in the volume of the green body. The pore structure can, moreover, be influenced in a targeted manner by control of the thermal transport processes during freezing. In this way the resistance of the muffle to thermal shocks can be improved. The pore structure can be influenced in respect of its pore size and also its pore distribution by the ratio of solid to dispersing agent and by the cooling rate. In addition to the physical properties of the slip constituents (thermal conductivity, solidification temperature of the dispersing agent, etc.), the cooling rate is mainly determined by the temperature of the coolant and thus the temperature gradient; smaller ice crystals form at a high cooling rate.
So that the properties of the investment are as homogeneous as possible, it is advantageous to mix the starting substances well. In the case of a nanoceramic powder the problem can arise here that whirling up takes place and nanoceramic powder particles pass into the air for respiration. In order to suppress such whirling up and in order to achieve a homogeneous mixture, a method is preferred in which, for production of the investment, a sol of the nanoceramic powder in the dispersing agent is prepared and this sol is then mixed with the microceramic powder fraction, optionally the metal powder and optionally the further additive or additives.
The purpose of the dispersing agent is, in particular, to prevent clumping of the constituents in the investment. Preferably, wetting agents are added to the dispersing agent in order to achieve good wetting of the particles and (as a secondary effect) of the pattern and to suppress agglomeration of the particles of the ceramic powder. In addition to this stabilisation, the viscosity can also be lowered by the addition of corresponding additives. In principle, the processability of the slip and the ability to take an impression are distinctly improved by a low viscosity. In order to make the investment or mixtures of the precursor substances thereof storable for longer, it is advantageous to add stabilisers. These can, for example, suppress oxidation or other chemical reactions of the metal powder.
In order to suppress infestation with microorganisms, it is advantageous to add antimicrobial active substances, for example bactericides and/or fungicides. A method according to the invention is preferred in which the dispersing agent is water, an alcohol or an aqueous or alcoholic mixture of liquids and optionally contains one or more wetting agents and/or stabilisers and/or antimicrobial active substances.
As already explained above, for high precision casting it is necessary to counterbalance the shrinkage of the green body at high temperatures and the different coefficients of expansion of the material forming the muffle and of the casting material in a suitable manner. In a preferred embodiment of the method according to the invention provision is therefore made that the mixture contains a metal powder and/or one or more further additives which (a) can be reacted with one another and/or with gaseous reactants to give an increase in volume or (b) by means of thermal activation can be induced to a change in the crystal lattice (phase change) and thus to an increase in volume, and the investment being so treated after solidification, optionally with the addition of one or more gaseous reactants and/or gas-forming reactants, that the metal powder and/or the ceramic powder and/or one or more of the further additives react chemically giving rise to an increase in size. The metal powder used is preferably Al/AlMg5 and/or niobium and/or titanium, that is to say substances that react with an increase in volume.

Reaction Increase in volume [%] Reaction product

2Al + 3/2 O₂−> Al₂O₃ 28 aluminium oxide

2Nb + 5/2 O₂−> Nb₂O₅ 174 niobium oxide

Ti + O₂−> TiO₂ 76 titanium dioxide
The increase in volume of the investment can be precisely controlled by targeted metering in of the reactants. In this way the irreversible increase in volume can be precisely matched to the particular melt to be used later, so that a maximum degree of precision and dimensional stability of the casting is achieved.
A method according to the invention in which the treatment leading to the increase in volume takes place during heating of the investment is particularly preferred. Physical reactions, such as, for example, vaporisation of volatile constituents or incipient sintering of the investment can be produced on heating. The resulting loss in volume can be compensated for by targeted metered addition of the reactants.
A method according to the invention in which the investment (of appropriate composition) is treated with the addition of a gaseous reactant that has been selected from the group that consists of: oxygen, nitrogen, carbon monoxide, carbon dioxide and mixtures thereof, has proved advantageous.
A method according to the invention is preferred in which the metal powder used is

- a powder of a metal and/or
- a mixture of powders of metals and/or
- a powder of an alloy or compound of two or more metals that has/have been selected from the group that consists of: aluminium, magnesium, zirconium, niobium, yttrium, hafnium, vanadium, calcium, potassium, tantalum, titanium, iron, silicon, germanium, molybdenum, manganese, zinc, tin, bismuth, nickel and cobalt. (Note: as mentioned, to this extent “metals” also denotes “metalloids”).

A method in which the microceramic powder fraction consists of oxides, mixed oxides, nitrides, silicides and/or carbides of one or more elements that have been selected from the following group: lithium, beryllium, boron, sodium, magnesium, aluminium, silicon, potassium, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, hafnium, tin, cadmium, lead, strontium, barium and antimony, has also proved advantageous.
The size of the particles of which the substances forming the investment consist, and the proportion of particles with a size of more than 500 nm, have a decisive influence on the properties of the investment. In order to obtain sufficiently large pores within the muffle to be produced, a method in which the microceramic powder fraction has a proportion of 30-60% (V/V), based on the volume of the total mixture, is preferred.
A method in which the nanoceramic powder fraction used consists of one, two or more ceramic compounds that have been chosen from the group that consists of: SiO₂; Al₂O₃, in particular boehmite; mullite; ZrO₂; zirconium nitrate; TiO₂, yttrium oxide and yttrium salts, has proved particularly suitable.
Advantageous characteristics of the muffle are obtained in particular if, in the method according to the invention, the nanoceramic powder fraction has a proportion of 2-30% (V/V), based on the volume of the total mixture. In this case an investment can be obtained that can be solidified by freezing and, at the same time, does not display any cracking or shrinkages during drying or sintering. Furthermore, in a corresponding method when thawing, no liquefaction of the slip occurs; consequently, no sublimation of the muffle is required for drying.
Good results have been obtained with metal powders that clearly differ in respect of their particle sizes. However, it has been found that metal powders with a particle size in the range of 100 nm to 500 μm,, in particular 0.5 μm, to 100 μm,, are particularly advantageous.
Organic solvents are subject to a multiplicity of regulations with respect to heath and safety at work. Thus, their use frequently requires extensive safety precautions. Moreover, health risks cannot always be excluded. Organic solvents are frequently needed when organic binders are used for production of an investment. Therefore, a method in which the investment does not contain any organic binder is preferred.
In some cases it has proved advantageous to design the method according to the invention such that the investment contains 20-70% (V/V) solids before the investment or covering of the pattern. The proportion of solids is obtained by subtracting the volume of the liquid constituents from the volume of the investment under standard conditions.
According to a further aspect of the invention, the set aim is achieved by a method for the production of a metallic, ceramic or glass ceramic casting or blank, which comprises the following steps:

- production of a muffle in accordance with the method according to the invention for the production of a muffle,
- (a) duplicate casting of the muffle with a metal or a metallic alloy or (b) injecting a flowable (i) ceramic or (ii) glass ceramic composition.

The remarks with regard to preferred embodiments of the method according to the invention for the production of a muffle of course also apply to this extent.
As already mentioned above, for a precise impression of the pattern and thus high dimensional stability of the casting it is necessary to compensate for the different expansion and shrinkage processes as completely as possible. Therefore, a method according to the invention for the production of a metallic, ceramic or glass ceramic casting or blank is particularly preferred in which

- the conditions for the production of the muffle, including the selection of the constituents of the mixture for the production of the investment, and
- the conditions (a) when duplicate casting, including the selection of the metal or of the metallic alloy, or (b) when injecting the ceramic or glass ceramic composition,
  are so matched to one another that during the production of the muffle an increase in volume is produced that at least partially compensates for the contraction in the volume of the metal or of the metallic alloy or of the ceramic or glass ceramic composition on solidification after duplicate casting or injection in the muffle.

According to a further aspect of the invention, the aim is achieved by a kit for the production of a metallic, ceramic or glass ceramic restoration, which comprises:

- (a) one or more components, in total comprising the following constituents:
  - a sol of a ceramic powder with particles of a diameter of less than 500 nm (nanoceramic powder fraction) in a dispersing agent,
  - a ceramic powder with particles of a diameter of more than 500 nm (microceramic powder fraction),
  - a metal powder and
  - optionally one or more further additives,
  - wherein the constituents are so matched to one another that a muffle for precision or model casting can be produced therefrom and
- (b) (i) a metal or a metallic alloy,
- wherein the constituents and the metal or the metallic alloy are so matched to one another that during the production of a muffle from the constituents an increase in volume can arise that at least partially compensates for the contraction in volume of the metal or of the metallic alloy on solidification after duplicate casting in the muffle
- and/or
  - (ii) a ceramic or glass ceramic,
- wherein the constituents and the ceramic or the glass ceramic are so matched to one another that during production of a muffle from the constituents an increase in volume can arise that at least partially compensates for the contraction in volume of the ceramic or the glass ceramic on solidification after filling the muffle.

For the production of muffles it is advantageous if all necessary components are combined in a kit such that no risks to health are to be feared when processing. The kit according to the invention contains the nanoceramic powder fraction as a sol, so that the investment can be produced with little effort. Moreover, the good storability makes it possible to offer the kit in larger packages, compared with the state of the art. Alternatively, a slip containing all components, or other combinations of the administration form can also be chosen, such as, for example, slip/liquid, first slip/second slip, etc. The first and second slips may have the same or different compositions.
Therefore, it is preferred that it contains a first slip comprising at least two components. In particular, it is preferred that it comprises the dispersing agent or a second slip in addition to the first slip.
The method according to the invention for the production of a muffle for precision or model casting is described below on the basis of an illustrative embodiment:

EXAMPLE

Production of a Muffle

1. First of all a pattern of a dental restoration, which is surrounded by a wax wire, is produced from dental casting wax from BEGO Bremer Goldschlägerei Wilh. Herbst GmbH & Co. KG, Wilhelm-Herbst-StraBe 1, 28359 Bremen. Germany.
2. The investment is then produced. For this purpose 50 g of an already stabilised sol that is marketed by Akzo Nobel under the name BINDZIL NH3/30 is used. This sol consists of 15 g silicon dioxide as nanoceramic powder, which is contained in 35 g water stabilised with ammonia. 50 g aluminium oxide CT3000SG from Alcoa and 100 g mullite SYMULOX M72 from Nabaltec are admixed, as microceramic powder fraction, with this sol, with stirring.
15 g of a AlMg5 alloy from Eckart is then added as metal powder. The alloy powder is atomised by means of compressed air. Classification was carried out using a 25 μm, sieve; only the fine fraction is used. A binder is not added.
3. The pattern is fixed on the bottom of a muffle base with the wax wire facing downwards and a muffle former for a triple muffle is slipped over it. The investment is poured into the muffle form thus produced, in which the pattern placed on the base is present, so that the pattern is completely embedded.
4. The muffle form is placed in an ice compartment at —18° C., frozen and the investment is thus solidified. The investment is removed from the mould in this state. The solidified investment is then dried overnight in an oven at 60° C. The dried investment is then heated to 1000° C. at a heating rate of 7 K/min. The casting wax largely melts away during heating; residues remaining in the muffle produced from the investment combust virtually without residues.
During heating the AlMg5 powder reacts with atmospheric oxygen to form aluminium oxide, magnesium oxide and spinel, with an increase in volume. In this context the proportion of AlMg5 powder in the investment is so chosen that the increase in volume compensates for the thermal contraction of the metal to be cast.

Claims

1. Method for the production of a muffle for precision or model casting having the following steps:

preparation of a pattern;

preparation of an investment, comprising a mixture of:

a) a dispersing agent,

b) a ceramic powder containing

(i) a fraction having a diameter of less than 500 nm (nanoceramic powder fraction) in a proportion of 2-74% (V/V), based on the volume of the total mixture,

and

(ii) a fraction having a diameter of more than 500 nm (microceramic powder fraction) in a proportion of 2-74% (V/V), based on the volume of the total mixture

c) optionally a metal powder consisting of metals and/or alloys and/or intermetallic compounds,

d) optionally one or more further additives and

e) optionally inorganic or organic binder;

investing or covering the pattern with the investment;

solidification of the investment investing or covering the pattern by

a) freezing,

b) gelling, in particular on the basis of a change in pH value and/or

c) dehydrating;

during and/or after the solidification, drying the investment investing or covering the pattern by removing the dispersing agent and optionally other volatile constituents; and

removal of the pattern from the dry investment and heating the dried investment so that a muffle for the precision or model casting results.

2. Method according to claim 1, wherein, for production of the investment,

a sol of the nanoceramic powder fraction in the dispersing agent is prepared; and

this sol is mixed with the microceramic powder fraction, optionally the metal powder and optionally the further additive or additives.

3. Method according to claim 1, wherein the dispersing agent is water, an alcohol or an aqueous or alcoholic mixture of liquids and optionally contains one or more wetting agents and/or stabilisers and/or antimicrobial active substances.

4. Method according to claim 1, wherein the mixture contains

a metal powder and/or

a microceramic powder fraction and/or

one or more further additives which (a) can be reacted with one another and/or with gaseous reactants to give an increase in volume or (b) by means of thermal activation can be induced to a change in the crystal lattice (phase change) and thus to an increase in volume, and

wherein the investment is so treated after solidification, optionally with the addition of one or more gaseous reactants and/or gas-forming reactants, that the metal powder and/or the ceramic powder and/or one or more of the further additives (a) react chemically or (b) perform a phase change giving rise to an increase in size.

5. Method according to claim 4, wherein the treatment leading to the increase in volume takes place during heating of the investment.

6. Method according to claim 4, wherein the investment is treated with the addition of a gaseous reactant that has been selected from the group consisting of oxygen, nitrogen, carbon monoxide, carbon dioxide and mixtures thereof.

7. Method according to claim 1, wherein said metal powder comprises

a powder of a metal and/or

a mixture of powders of metals, and/or

a powder of an alloy or compound of two or more metals selected from the group that consists of: aluminium, magnesium, zirconium, niobium, yttrium, hafnium, vanadium, calcium, potassium, tantalum, titanium, iron, silicon, germanium, molybdenum, manganese, zinc, tin, bismuth, nickel and cobalt.

8. Method according to claim 1, wherein the microceramic powder fraction consists of oxides, mixed oxides, silicides, nitrides and/or carbides of one or more elements that have been selected from the group consisting of: lithium, beryllium, boron, sodium, magnesium, aluminium, silicon, potassium, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, hafnium, tin, cadmium, lead, strontium, barium and antimony.

9. Method according to claim 1, wherein the microceramic powder fraction has a proportion of 30-60% (V/V), based on the volume of the total mixture.

10. Method according to claim 1, wherein the nanoceramic powder fraction comprises one, two or more ceramic compounds that have been chosen from the group that consists of: SiO₂; Al₂O₃, in particular boehmite; ZrO₂; yttrium oxide; yttrium salts; zirconium nitrate; and TiO₂.

11. Method according to claim 1, wherein the nanoceramic powder fraction has a proportion of 2-30% (V/V), based on the volume of the total mixture.

12. Method according to claim 1, wherein the metal powder consists essentially of particles with a particle size in the range of 100 nm to 500 μm.

13. Method according to claim 1, wherein the metal powder consists essentially of particles with a particle size in the range of 0.5 μm, to 100 μm.

14. Method according to claim 1, wherein the investment does not contain an organic binder.

15. Method according to claim 1, wherein the investment for investing or covering the pattern contains 20-70% (V/V) solids, based on the total volume.

16. Method for the production of a metallic, ceramic or glass ceramic casting or blank, comprising the following steps:

production of a muffle in accordance with a method according to claim 1, and

either (a) duplicate casting of the muffle with a metal or a metallic alloy or (b) injecting a flowable (i) ceramic or (ii) glass ceramic composition.

17. Method according to claim 16, wherein

the conditions for the production of the muffle, including the selection of the constituents of the mixture for the production of the investment, and

the conditions (a) when duplicate casting, including the selection of the metal or of the metallic alloy, or (b) when injecting the ceramic or glass ceramic composition,

are so matched to one another that during the production of the muffle an increase in volume is produced that at least partially compensates for the contraction in the volume of the metal or of the metallic alloy or of the ceramic or glass ceramic composition on solidification after duplicate casting or injection in the muffle.

18. Kit for the production of a metallic and/or ceramic and/or glass ceramic casting or blank, comprising:

(a) one or more components, in total comprising the following constituents:

a sol of a ceramic powder with particles of a diameter of less than 500 nm (nanoceramic powder fraction) in a dispersing agent,

a ceramic powder with particles of a diameter of more than 500 nm (microceramic powder fraction),

a metal powder and

optionally one or more further additives,

wherein the constituents are so matched to one another that a muffle for precision or model casting can be produced therefrom, and

(b) (i) a metal or a metallic alloy,

wherein the constituents and the metal or the metallic alloy are so matched to one another that during the production of a muffle from the constituents an increase in volume can arise that at least partially compensates for the contraction in volume of the metal or of the metallic alloy on solidification after duplicate casting in the muffle

and/or

(ii) a ceramic or glass ceramic,

wherein the constituents and the ceramic or the glass ceramic are so matched to one another that during production of a muffle from the constituents an increase in volume can arise that at least partially compensates for the contraction in volume of the ceramic or the glass ceramic on solidification after filling the muffle.

19. Kit according to claim 18, characterized in that said kit contains a first slip comprising at least two components.

20. Kit according to claim 19, characterized in that said kit comprises the dispersing agent or a second slip in addition to said first slip.