WO2000037391A1 - Werkstoff auf basis von siliciumnitrid, dessen herstellung und verwendung in mikrowellenprozessen - Google Patents
Werkstoff auf basis von siliciumnitrid, dessen herstellung und verwendung in mikrowellenprozessen Download PDFInfo
- Publication number
- WO2000037391A1 WO2000037391A1 PCT/EP1999/009916 EP9909916W WO0037391A1 WO 2000037391 A1 WO2000037391 A1 WO 2000037391A1 EP 9909916 W EP9909916 W EP 9909916W WO 0037391 A1 WO0037391 A1 WO 0037391A1
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- Prior art keywords
- microwave
- sic
- crystalline
- silicon nitride
- component
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Classifications
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
- C04B38/007—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof characterised by the pore distribution, e.g. inhomogeneous distribution of pores
- C04B38/0074—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof characterised by the pore distribution, e.g. inhomogeneous distribution of pores expressed as porosity percentage
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
- C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
- C04B35/591—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride obtained by reaction sintering
Definitions
- the present invention relates to a material and components based on
- Silicon nitride process for producing such a material / component and microwave processes using firing aids.
- Microwaves in which a gas is first heated and ionized by means of microwave absorption, so that a plasma is formed at the location of the goods to be heated and this plasma heats the goods (Nature 217 (1968) 1287f).
- Susceptor substances have often been added directly to the material to be heated, so that after e.g. sintering, melting or recrystallization are part of the material (US 4606748, 1986).
- the disadvantage is that the susceptors used as an additive to the material often change the technologically relevant properties of the materials.
- the material to be heated is surrounded with a powder bed which, in addition to other substances, also contains susceptor substances (WO 91/05747).
- a powder bed which, in addition to other substances, also contains susceptor substances (WO 91/05747).
- susceptor substances WO 91/05747
- Another variant of susceptors is to store the material, which can be heated very efficiently with microwaves, spatially separated from the material which is actually to be heated.
- Different variants are possible here: in addition to carbon, which is housed in an inert gas chamber and thus remains reusable even during heat treatment in an oxygen-containing atmosphere, but only indirectly
- SiC rods have been used which directly surround the material to be heated (so-called “picket fence arrangement") or silicate ceramic plates on which the material to be heated rests. Clark discloses another, reusable, heater heater called “Microwave Hybrid Hearing”. This consists of SiC which, as a lining, surrounds the material to be treated in such a way that no SiC layer is present only at the top and / or at the bottom.
- Microwaves which are directly absorbed by the material to be heated, result from the respective ratio of the losses (i.e. the absorbed microwave radiation converted into heat by dielectric relaxation processes and AC conductivity) between the susceptor and the product, which can also be variable with increasing temperature. In extreme cases, the entire available microwave power is absorbed by the susceptor.
- a disadvantage of permanent susceptors is that the intensity and spatial distribution of the microwave radiation is influenced, which also determines the microwave heating of the goods.
- a permanent SiC susceptor creates a different microstructure in the side of a component facing the susceptor than in the center of the component. This prevents technical use for the production of homogeneous materials and components.
- Another possibility of using an external susceptor is to remove the susceptor (for example carbon) at a specific point in time during the heat treatment, for example by a chemical reaction with a briefly changed atmosphere (for example air or oxygen) (DE 4 224 974.0). The disadvantages associated with this are obvious.
- porous materials based on carbon which can be used as all-round heat insulation in the conventional inert gas furnace, absorb the microwave radiation very well, as a result of which direct microwave heating of the less absorbent sintered material located therein is no longer possible.
- Porous materials based on Al 2 O 3 and / or Si0 2 also have very good heating properties with respect to microwave radiation at such high temperatures, so that the same problems exist with regard to microwave absorption in the sintered material as with C materials.
- the free silicon content should be very low in order to prevent the sintered parts from caking due to melting Si. As can be seen from the following description of the invention, this disclosure is not a solution to the problem according to the invention.
- the object of the present invention is to provide a new material based on silicon nitride (Si 3 N 4 ), which is particularly suitable as a starting material for fuel for microwave processes and meets the requirements mentioned above. Furthermore, processes for the production of such substances and a corresponding microwave process are to be developed.
- This object is achieved by a material based on silicon nitride (Si 3 N 4 ), which has a free silicon content of 0.1 to 40% by weight, preferably 1 to 20% by weight.
- Si 3 N 4 silicon nitride
- the material preferably has a porosity of up to 50% by volume, particularly preferably from 5 to 50% by volume. Furthermore, the oxygen content in particular less than 3% by weight, the carbon content less than 3% by weight and / or the content of other impurities less than 3% by weight.
- the material additionally contains crystalline phases, which preferably consist of SiC, TiN, TiCN, TiC, ZrN and / or ZrC in concentrations of up to 40 vol.% And with average grain sizes of up to 10 ⁇ m .
- crystalline phases which preferably consist of SiC, TiN, TiCN, TiC, ZrN and / or ZrC in concentrations of up to 40 vol.% And with average grain sizes of up to 10 ⁇ m .
- Various components that contain silicon nitride can be produced from the material according to the invention.
- these can be temperature-resistant firing aids in microwave processes.
- These are preferably in the form of integral containers or are constructed from plates, supports, rods and / or pipes.
- the residual Si increases the microwave absorption behavior compared to Si-free Si 3 N 4 materials in a certain temperature range (cf. FIG. 1)
- the distribution of the microwave field is not significantly influenced by the container, as was shown for large batches on the basis of measured densities of sintered bodies
- the microwave absorption behavior of the container changes with the temperature and with the number of microwave sintering cycles by nitriding the residual Si (see FIG. 2),
- the container emits more heat to the applicator walls at T> 1000 ° C than the material to be sintered, this results in the substance-specific microwave absorption behavior of the porous Si 3 N 4 container serving as a firing aid at high temperatures, a higher microwave absorption of the sintered material (see FIG. 3 for the sintering of additive-containing Si 3 N 4 parts).
- the container acts as a temperature up to approx. 1000 ° C
- the container remains colder than the material to be sintered, since heat is given off to the applicator (hot Mo wall or cold furnace wall) and the microwave absorption behavior of the sintering ceramic improves compared to the container.
- the prerequisite for this is that the amount of firing aid used is not too great in relation to the sintered material, so that, despite poorer microwave absorption, more microwave powers are not absorbed than by the sintered material.
- boron nitride materials are thermally stable over the entire temperature range of interest and have sufficient microwave transparency for the microwave sintering of, for example, Si 3 N 4 moldings, they are very expensive and in the large format required as plates, supports, rectangular or round container etc. not commercially available.
- Graphite has a very high microwave absorption, especially at temperatures ⁇ 1000 ° C and thus prevents the coupling or heating of the sintered material from room temperature using a microwave.
- SiC behaves similarly to graphite, but in addition the high microwave absorption is maintained up to very high temperatures.
- Dense, sintered Si 3 N 4 has a microwave absorption behavior that is comparable over the entire temperature range, such as additive-containing Si 3 N 4 to be sintered.
- the invention also includes a method for the regeneration of a material according to the invention. After a certain number of sintering cycles (> 10), the residual Si content of the porous Si 3 N 4 firing aids drops to less than 1%, as a result of which the susceptor effect of the arrangement during microwave sintering is greatly reduced. Attempts to regenerate the otherwise undamaged kiln furniture moldings surprisingly led to the result that a
- the invention thus provides a reversible active firing aid made of porous Si 3 N 4 for the microwave sintering of ceramic materials and components.
- the susceptor effect of the kiln furniture produced from the porous Si 3 N 4 according to the invention can be regenerated by coating them with an Si-Si 3 N 4 slip on the outer wall.
- porous Si 3 N 4 - Synthesized materials that contained ß + ⁇ -Si 3 N 4 other crystalline phases.
- the absorption behavior and thus the heating behavior of the kiln furniture can be influenced in a targeted manner by temperature-resistant metal carbides, carbonitrides and nitrides such as SiC, TiN, TiCN, TiC, ZrN, ZrC etc., the increase in absorption being almost shows linear relationship with the concentration of the crystalline secondary phases, without loss of thermal stability of the base material.
- the materials based on porous Si 3 N 4 with one or more of the crystalline secondary phases mentioned contain the latter preferably in concentrations of up to 40% by volume in order to specifically influence the microwave absorption behavior of the firing aids formed therefrom.
- Temperature-resistant firing aids for microwave processes are preferably produced as components, particularly preferably integral containers for this or a construction made of plates, supports, rods and / or tubes.
- the wall thickness of the parts must be selected so that at T> 1000 ° C. and the particular microwave wave frequency used there is sufficient transparency of the container wall for the microwaves.
- the task is to provide materials in the form of suitable parts, such as plates, rectangular and cylindrical containers, etc., for their use in microwave sintering.
- suitable parts such as plates, rectangular and cylindrical containers, etc.
- Reaction sintems the basic powder silicon with an average grain size of ⁇ 50 ⁇ m and less than 50% by weight silicon nitride powder (grain size ⁇ 25 ⁇ m), organic additives such as celluloses, stearates, paraffins, glycols, silicones, oleic acid etc. in Concentrations of 5 to 40 wt .-% are mixed, a humidity between 5 and 30% is set simultaneously and after an intensive mixing and
- Cycles must be coordinated with the desired residual silicon content in the material.
- the result is a material with ⁇ 50% by volume porosity in addition to ⁇ + ⁇ - Si 3 N 4 , ⁇ 20% free Si, ⁇ 3% oxygen, ⁇ 3% carbon and ⁇ 3% other impurities.
- the shaping can also be carried out by customary dry-press shaping of the powder or powder mixtures mentioned, preferably in the form of granules, if appropriate after adding conventional organic binders and / or plasticizers.
- Another option is slip casting, preferably on an aqueous basis, or gel casting. Suitable slip for the slip pour have a solids content of ⁇ 70% by weight and a pH of ⁇ 7 in order to avoid excessive Si hydrolysis with H 2 release.
- the material variants containing nitride phases can also be introduced into the base silicon by adding metallic powders with average grain sizes ⁇ 10 ⁇ m, via precursors or via metal alkoxides. If the latter two classes of substances are used, pyrolysis with decomposition of the volatile organic constituents must take place under inert gas or vacuum before the reaction sintering. This is preferably carried out simultaneously with the heating of other organic additives which are added as aids for semi-plastic shaping, under protective gas or vacuum. The pure metals or metal compounds added or produced by pyrolysis react under the conditions of the reaction sintem simultaneously with the conversion of the Si to the Si 3 N 4 to the desired metal nitrides.
- the resulting material has the phases ⁇ + ⁇ -Si 3 N 4 , ⁇ 20% free Si, ⁇ 3% oxygen, ⁇ 3% carbon, the specifically synthesized Me nitrides and ⁇ 3 % other impurities.
- Another process variant of synthesizing a porous Si 3 N 4 material is based on Si 3 N 4 powder, preferably with an average grain size of ⁇ 5 ⁇ m. This is carried out as for Si + Si 3 N 4 , the specified organic additives are added and the moisture required for the semi-plastic shaping is adjusted. After shaping and drying, the organic ones turn
- this material variant In order to adjust the microwave absorption behavior according to the invention, this material variant must be subjected to a thermal aftertreatment, as was described for the regeneration of the material variant produced by reaction sintering. With this method, the free Si content is then set to ⁇ 20%.
- the residual Si content of these porous Si 3 N 4 firing aids drops to ⁇ 1%>, whereby the susceptor effect of the arrangement during microwave sintering is greatly reduced.
- the desired Si content can be set again by a regeneration treatment as described.
- This method variant can also be produced with additional crystalline phases such as SiC, TiC, TiCN, TiN, ZrC, ZrN etc. in order to set a stable microwave absorption behavior.
- the preferred embodiment consists in adding the desired crystalline secondary phases as powder with average grain sizes ⁇ 10 ⁇ m to the base Si 3 N 4 powder with an average grain size ⁇ 5 ⁇ m in the desired concentration.
- suitable precursors or alkoxides can also be used. If such precursors or solutions are used, the moldings must be pyrolyzed under inert gas or vacuum before the thermal solidification treatment. This is preferably done simultaneously with the heating of other organic compounds.
- Additives as aids for shaping which must be done in an inert atmosphere or in a vacuum in the process route last carried out.
- the raw parts pretreated in this way, as described for this route, are thermally treated at ⁇ 1750 ° C under 1 bar N 2 or at T ⁇ 2200 ° C lower 100 bar N 2 for solidification without causing significant shrinkage ( ⁇ 2% linear) comes.
- the resulting material has the phases ⁇ + ⁇ -Si 3 N 4 , ⁇ 5% free Si, ⁇ 3% oxygen, ⁇ 40% by volume of the specifically added or synthesized crystalline secondary phases, ⁇ 3% free C and ⁇ 3% other impurities.
- a further embodiment of the porous Si 3 N 4 material which is very interesting from a cost point of view, is the use of recycled powder obtained, for example, from the processing of defective or worn parts.
- this material (sorted by type) is processed to ⁇ 20 ⁇ m and added to the starting silicon in the case of using the reaction sintering process or the starting silicon nitride in the case of using the route via the thermal solidification treatment in concentrations of ⁇ 50% by weight of the Si 3 N 4 component.
- Figure 1 shows the absorbed MW power.
- FIG. 2 shows the change in the Si concentration in the sintering container (casket) with repeated sintering.
- FIG. 3 shows the temperature profile between the sintered container (casket) and the sintered material.
- FIG. 1 shows the MW power absorbed as a function of temperature for different Si contents in Si 3 N 4 .
- the influence of the Si concentration on the MW heating behavior is clearly visible.
- the absorption behavior deteriorates significantly (RBSN-old).
- FIG. 2 shows the change in the Si concentration (ordinate) in the RBSN sintered container (casket) during MW sintering, the temperature passed through being plotted on the abscissa. Due to the manufacturing process, the RBSN box typically has a residual silicon content. During the MW heating, the silicon is partially nitrided by the nitrogen atmosphere, so that the Si content drops until the decomposition reaction starts at very high temperatures and Si is released again.
- FIG. 3 shows a comparison of the temperature profile between sintered container (casket) and sintered material (temperature on the ordinate over time on the
- the sintered material is primarily Casket heated and only at high temperatures is the batch hotter than the sintered material, provided the surrounding furnace space is colder than the sintering arrangement.
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- Engineering & Computer Science (AREA)
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Abstract
Description
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Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP99964571A EP1144336A1 (de) | 1998-12-22 | 1999-12-14 | Werkstoff auf basis von siliciumnitrid, dessen herstellung und verwendung in mikrowellenprozessen |
AU30387/00A AU3038700A (en) | 1998-12-22 | 1999-12-14 | Silicon nitride-based material, the production and utilization thereof in microwave processes |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE19859292.2 | 1998-12-22 | ||
DE1998159292 DE19859292A1 (de) | 1998-12-22 | 1998-12-22 | Werkstoff auf Basis von Siliciumnitrid, dessen Herstellung und Verwendung in Mikrowellenprozessen |
Publications (1)
Publication Number | Publication Date |
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WO2000037391A1 true WO2000037391A1 (de) | 2000-06-29 |
Family
ID=7892136
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/EP1999/009916 WO2000037391A1 (de) | 1998-12-22 | 1999-12-14 | Werkstoff auf basis von siliciumnitrid, dessen herstellung und verwendung in mikrowellenprozessen |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP1144336A1 (de) |
AU (1) | AU3038700A (de) |
DE (1) | DE19859292A1 (de) |
WO (1) | WO2000037391A1 (de) |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
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DE102005018323A1 (de) * | 2005-04-20 | 2006-10-26 | Siemens Ag | Keramik-Grünkörper und Keramik-Bauteil, sowie Mikrowellen-Sinterverfahren für Piezostack-Grünkörper |
DE102013013401A1 (de) | 2013-08-02 | 2015-02-05 | Harald Benoit | Nutzung von Siliciumcarbid (Dielektrikum)als ggf. Verbrauchsmaterial zur Erwärmung dünner Materialschichten mittels Mikrowellenstrahlung |
EP4235073B1 (de) * | 2022-02-23 | 2024-03-20 | Erlus Aktiengesellschaft | Gebrannter keramischer formkörper und verfahren zur herstellung eines gebrannten keramischen formkörpers unter verwendung von elektromagnetischer strahlung mit einer frequenz von maximal 300 ghz |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS60260197A (ja) * | 1984-06-07 | 1985-12-23 | 島田理化工業株式会社 | マイクロ波吸収体 |
JPH03159970A (ja) * | 1989-11-16 | 1991-07-09 | Japan Metals & Chem Co Ltd | 耐熱性多孔質非酸化物系セラミックス焼結体とその製造方法 |
EP0534797A1 (de) * | 1991-09-27 | 1993-03-31 | General Mills, Inc. | Gesinterter keramischer Suszeptor zum Heizen mit Mikrowellen |
WO1995008519A2 (en) * | 1993-09-17 | 1995-03-30 | Saint Gobain/Norton Industrial Ceramics Corporation | Coarse reaction bonded silicon nitride |
-
1998
- 1998-12-22 DE DE1998159292 patent/DE19859292A1/de not_active Ceased
-
1999
- 1999-12-14 WO PCT/EP1999/009916 patent/WO2000037391A1/de not_active Application Discontinuation
- 1999-12-14 AU AU30387/00A patent/AU3038700A/en not_active Abandoned
- 1999-12-14 EP EP99964571A patent/EP1144336A1/de not_active Withdrawn
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS60260197A (ja) * | 1984-06-07 | 1985-12-23 | 島田理化工業株式会社 | マイクロ波吸収体 |
JPH03159970A (ja) * | 1989-11-16 | 1991-07-09 | Japan Metals & Chem Co Ltd | 耐熱性多孔質非酸化物系セラミックス焼結体とその製造方法 |
EP0534797A1 (de) * | 1991-09-27 | 1993-03-31 | General Mills, Inc. | Gesinterter keramischer Suszeptor zum Heizen mit Mikrowellen |
WO1995008519A2 (en) * | 1993-09-17 | 1995-03-30 | Saint Gobain/Norton Industrial Ceramics Corporation | Coarse reaction bonded silicon nitride |
Non-Patent Citations (2)
Title |
---|
CHEMICAL ABSTRACTS, vol. 104, no. 18, 5 May 1986, Columbus, Ohio, US; abstract no. 154475, T. SETOGUCHI ET AL.: "Microwave absorbing ceramics" XP002135133 * |
DATABASE WPI Week 199133, Derwent World Patents Index; AN 1991-243568, XP002135134 * |
Also Published As
Publication number | Publication date |
---|---|
AU3038700A (en) | 2000-07-12 |
DE19859292A1 (de) | 2000-06-29 |
EP1144336A1 (de) | 2001-10-17 |
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