DE10297835B4 - Process for producing a silicon / silicon carbide ceramic using a bio-preform, silicon / silicon carbide ceramic thereby obtained - Google Patents

Abstract

method for producing a silicon / silicon carbide ceramic using a biopräform, by preheating a piece a trunk of a monocot caudex plant at a temperature in a range of 50 to 90 ° C with a warm-up rate from 1 to 10 ° C per minute, keeping the preheated stem piece at a peak temperature, followed by heating the preheated stem piece in one closed container, which is provided with an outlet, at a temperature in one Range from 350 to 1000 ° C with a warm-up rate from 1 to 15 ° C per minute, holding the trunk piece at the peak temperature under a self-generated ambient atmosphere, followed of furnace cooling and further followed by the joint heating of the obtained Biopräform and Silicon in a crucible under vacuum at a temperature in one Range of 1450 ° C up to 1600 ° C, Keep the peak temperature above a period in a range of 2 to 4 minutes, followed by Furnace cooling.

Description

Field of the invention

The The present invention relates to a process for the preparation of a Silicon / silicon carbide ceramic using a Biopräform, the is derived from a monocot Caudexpflanzenstamm. The present Invention also provides a silicon / silicon carbide ceramic those using a biopräform is derived from a monocot caudex plant stem.

Background of the invention

The Silicon (Si) / silicon carbide (SiC) duplex ceramic, hereinafter referred to as Si / SiC indicates excellent physicochemical properties such as high oxidation, corrosion and thermal shock resistance, superior High temperature strength and strength along with other properties in relation to this, for example Young's modulus, hardness, and is therefore of a special technological Importance. These properties can be found in the uses of Take advantage of materials in the field of furnace equipment, in particular in the heating of sanitary ware, in firing capsules and crucibles for the calcination of fluorescent Powders in fluorescent lamp industries, high speed and high performance durable burner for households and industry, rocket nozzles, Recovery plants for using excess heat in industrial furnaces, heat exchangers in indirectly fired open / combined cycle gas turbine for Generation of electrical energy, ceramic seals for pumps for handling corrosive liquids, abrasion resistant inserts etc.

SiC ceramics are made of synthetic powders by means of hot pressing / isostatic hot pressing, pressureless sintering, polymer pyrolysis, chemical vapor deposition, liquid Silicon Infiltration Processing (LSIP) or Reaction Binding / Reaction Sintering produced. Reference is made to the thesis ("reaction sintering of Silicon carbide "from O. P. Chakrabarti, University of Calcutta, 1998) and also to an article ("Reactive infiltration of Si-Mo alloyed melt into carbonaceous preform of SiC ", published by O. P. Chakrabarti and P. K. Das in J. Am. Ceram. Soc., 83 [6], 1548-1550 (2000)), in which the authors a complete one review to the different processing paths for SiC ceramics with particular emphasis on the production of Si / SiC ceramics by the melt infiltration of Si or alloyed Si.

The Disadvantages of the above-mentioned reviews Refereed works are the requirement of expensive synthetic Raw powder, complex preform production and difficult processing of the obtained product, etc. The synthesis of ceramic materials of course However, growing plant structures has lately received special interest. Plants often have natural composite structures and show high mechanical strength, low density, high stiffness, elasticity and damage tolerance. These advantages are due to their hierarchical anatomy, the developed in a long-term genetic evolutionary process and optimized. There is the possibility of new ceramic materials with a unique microstructure that is pseudomorphic to that, of course grown plant structures. The derived from biostructure ceramic materials adjustable properties for a variety of possible Applications. The synthesis of a SiC ceramic from naturally grown Plant structures has recently Time arose an interest among scientists.

Reference is made to (i) US-A-3,754,076 (entitled "Production of silicon carbide from rice husk" by I. Cutler, August 21, 1970, and also to an article ("Formation of silicon carbide from rice hulls" of JG Lee and IB Cutler, published in Am. Ceram, Soc., Bull., 54 [2] 195-98 (1975)), in which the authors report the production of SiC whiskers by thermal decomposition of rice hulls, a by-product ( ii) an article ("Formation and structure of silicon carbide whiskers from rice hulls" by NK Sharma, WS Williams and A. Zangvil, published in J. Am. Ceram. Soc., 67 [11] 715-720 (1984)) in which the authors report an investigation relating to the distribution of silicon (Si) in the shells of ordinary brown Indian rice, which was carried out to understand the formation of SiC whiskers and also ultrafine β-SiC particles by thermal decomposition, (iii) an article ("Growth of β-SiC whis kers by LVS process "by JV Milewski, FD Gac, JJ Petrovic and SR Skaggs, published in J. Mater. Sci., 20, 1160-1166 (1985)), in which the authors describe a vapor-liquid-solid process for forming SiC whiskers by the catalyzed thermal decomposition of rice hulls, (iv) on IN-B-172941 (U.S. the title "A process for the production of silicon carbide fibers (β-form) from rice husk" by M. Patel, CB Raju, AK Ray and A. Karera, 8 January 1994) and also to an article ("Effect of Thermal and chemical treatments in rice husk "by M. Patel, A. Karera and P. Prasanne, published in J. Mater. Sci., 22, 2457-2464 (1987)), in which the authors discuss the formation of SiC whiskers Carbonization of coked rice hull pretreated with hydroxides of metal catalysts, (v) to an article ("SiC whisker from rice husks: role of catalysts" by M. Patel and A. Karera, published in J. Mater. Sci. Letts., 8, 955-956 (1989)), in which the authors describe the formation of SiC whiskers by carbonization of rice hulls without added catalyst, (vi) to an article ("Direct Pyrolyisis of raw rice husks for maximization of SiC whisker formation "by RV Krishnarao and MM Godkhindi, M. Chakraborty and PG Mukunda, published in J. Am. Ceram Soc., 74, 2869-2875 (1991)), in which the authors describe the formation of SiC whiskers by pyrolysis of crude Describe rice hulls without any catalyst or pre-coking, (vii) to an article ("Conversation of raw rice husks to SiC by pyrolysis in nitrogen atmosphere" by RV Krishnarao, YR Mahajan and TJ Kumar, published in J. Euro Ceram Soc. 18, 147-152 (1998)), in which the authors describe the formation of SiC whiskers by pyrolysis of crude rice hulls without precocoking, (viii) to an article ("Synthesis and characterization of SiC whiskers from coconut shells") of A Selvam, NG Nairand, P. Singh in J. Mater. Sci. Lett., 17, 57-60 (1998)), in which the authors describe a process for producing SiC whiskers by pyrolysis of crude coconut shells soaked in 10% iron chloride solution and then dried. The disadvantages of the mentioned works are the high pyrolysis temperatures, the low yield, the uneconomical conversion, because a very large pyrolysis reactor is required to control the voluminous arrangement of rice hulls and unshaped whisker / powder, which still needs to be processed, around the molds with controlled microstructure to be able to handle.

Reference is made to an article ("Biomimetic process for producing SiC wood" by T. Ota, M. Takahashi, T. Hibi, M. Ozawa, S. Suzuki and Y. Hikichi, published in J. Am. Ceram. Soc. 78 [12] 3409-11 (1995)) in which the authors disclose a method of producing wood-like SiC by infiltrating tetraethyl orthosilicate (TEOS) into a piece of oak charcoal followed by hydrolysis by treatment with ammoniacal solution and by heat treatment of the coal, contains the SiO ₂ gel described. The disadvantages of this work mentioned are the requirement for multiple TEOS infiltration, followed by subsequent firing, the porous end product with unconverted carbon in the structure, and incomplete conversion of C to SiC.

reference is also taken to a two-part article ("Biomorphic cellular silicon carbide ceramics from wood: I. Processing and Microstructure "by P. Greil, T. Lifka and A. Kaindl, published in J. Euro. Ceram. Soc., 18, 1961-1973 (1998) and "Biomorphic cellular silicon carbide ceramics from wood: II. Mechanical Properties "by P. Greil, T. Lifka and A. Kaindl, released in in J. Euro. Ceram. Soc., 18, 1975-1983 (1998)), in which the authors a process for the preparation of cellular SiC ceramics with anisotropic Pore structure by infiltrating liquid silicon at 1600 ° C for 4 hours without pressure in carbonated woody (beech, oak, maple, pine, Balsa and ebony) describe samples. The long infiltration cycles, low product density and in coincidentally without any correlation with the starting wood varying microstructure of the final product represent the main ones Disadvantages of mentioned Work.

reference is taken to an article ("Silicon / silicon carbide composites fabricated by infiltration of a silicon melt into charcoal "by D.W. Shin, S.S. Park, Y.H. Choa and K. Nihara, published in J. Am. Ceram. Soc., 82 [11] 3251-53 (1999)), in which the authors describe a method for producing dense Si / SiC composite by infiltration of liquid Si (obtained by melting powdered Si) at 1700 ° C under vacuum in a porous commercially available Oak carbon sample. The disadvantages of this work are in the high infiltration temperature and difficulty in the infiltration process which is most likely a result of the use of powdered silicon below Vacuum conditions is.

reference is also on US-A-6,124,028 (entitled "Carbonized wood and materials formed therefrom "by Denis C. Nagle and Christopher E. Byrne, September 26, 2000), in which Authors describe a method for the production of SiC ceramic by implementing a stoichiometric or greater than stoichiometric Amount of silicon at 1500 ° C for 10 minutes up to 2 hours in an argon stream with carbonized wood samples (red oak, Balsa, linden, maple, weymouth pine, redwood).

The Disadvantages of this work are the incomplete infiltration, the difficulty during the removal of the final product because of the problems with the stickiness and the lack of correlation between the microstructure and the Structure of the wood used.

Reference is made to an article ("Environment conscious ceramics (Ecoceramics)" by M. Singh, published in Ceram. Closely. Sci. Proc., 21 [4] 39-44 (2000)), in which the authors describe a method of making SiC-based ceramics by reactive infiltration of molten silicon at 1450 ° C for 30 minutes into pyrolyzed wood samples (Brazilian Rosewood, African Zebra wood , ceylonese lemon wood, African bubinga, "pau lope", "Australian jarrah" and Indian mango wood). The disadvantages of this work are the long infiltration cycles required to make the ceramic and the variations in product microstructures of the wood structures used, but this is not correlated.

It be a big one Number of plants for the production of various varieties of SiC ceramics used. The plant husks enable the production of SiC whiskers or fibers but the manufacturing process are not yet economically feasible. Biological preforms (preforms) from different course growing plant trunks including softwoods and hardwoods are used to produce SiC mass ceramics. Because the dimensions, Compositions and morphologies of naturally grown plant structures can also vary the shape and composition of the produced. Si considerably vary.

It However, no studies could be identified that were based on the suitability of plant structures in terms of anatomical and structural features that after their transformation into carbonaceous preforms to a faster infiltration and reaction of the liquid through the porous Contour for contribute to the transformation into SiC. No investigation was conducted on the overcoming difficulty in removing the infiltrated sample the contact liquid after complete Infiltration and reaction relates. There is no investigation at costly treatment after infiltration for removal the adhering melt from the product surface is avoided. The present The invention was made in view of the above-mentioned and other difficulties developed in the prior art.

Objectives of the invention

The The main object of the invention is an improved method for the production of a silicon / silicon carbide ceramic, where a biopräform is used, which is derived from a monocot Caudexpflanze such as coconut (Cocos nucifera), Palmyra palm (Borassus flabellifer), date palm (Phoenics dactylifera), which are the above overcomes specified disadvantages.

One Another object of the invention is the use of a Biopräform made from the Caudex strain of a monocotyledonous plant whose carbonaceous Skeletal structure is particularly advantageous for the infiltration of liquid Si in the production of silicon / silicon carbide ceramic with significantly reduced process cycles.

One Another object of the invention is to provide a method for the production of Si / SiC ceramic from a Biopräform followed of a liquid silicon infiltration process using the Way of contacting the silicon with the Biopräform simplified.

Yet Another object of the invention is to provide a method for the production of Si / SiC ceramic from a Biopräform with an infiltration technique with liquid silicon, which is the costly Instrumentation and the expensive and expensive equipment that for making contact between the Si-infiltrant and the carbonaceous preform after the usual Procedures are required avoids.

Yet Another object of the invention is to provide a A method of making Si / SiC ceramic, wherein the silicon reactant Completely is consumed so that no solid silicon remains, thereby causing sticking of the final product to remaining solidified silicon melt overcome is so that no silicon adheres to the outer surfaces of the final product, making the costly process for removing silicon from the surfaces does not apply such as etching, High-temperature evacuation, treatment with chemicals

Summary of the invention

The The present invention provides an improved method of manufacture of (bulk) Si / SiC ceramic composite, followed by a fast one Infiltration of the liquid Siliciums in biopräformen, distinguished from tribes monocotyledonous caudex plants such as coconut (Cocos nucifera), Palmyra Palm (Borassus flabellifer), Date Palm (Phoenics dactylifera).

The Novelty of the present invention is that the Si / SiC ceramic duplex composite produced while maintaining the cellular characteristics of biopräformen and thus corresponds to that of the precursor plant and therefore it is a completely new ceramic composite material with unique macro- and microstructural properties that to those of the precursor plant is almost isomorphic.

There she a big one Number of tracheal pore channels of smaller diameter, which are statistically distributed and vertical extended are, along with micropores, made of woven microfibrils surrender and above In addition, a variety of cavities have, arising from the leaves trace bundles in in the same direction, these bioprä forms a larger contour for the Infiltration and reaction of the liquid Siliciums ready, what possible does that eventually obtained Si / SiC composite in a significantly shorter time to obtain.

The tracheal porosity, the micropores and leaf trace samples eventually complete the rest Filled in silicon, which is a lot of reinforcements (Stiffeners) random distributed and aligned in the growth direction yields, where increased the anisotropic mechanical properties of the final material become.

Accordingly the present invention provides a method for producing a Silicon / silicon carbide ceramic using a Biopräform, the derived from monocotyledonous caudex plant strains, ready to by preheating a piece a trunk of a monocot caudex plant at a temperature in a range of 50 to 90 ° C with a warm-up rate from 1 to 10 ° C per minute, keeping the preheated stem piece at a peak temperature, followed by heating the preheated stem in a closed container, which is provided with an outlet, at a temperature in one Range from 350 to 1000 ° C with a warm-up rate from 1 to 15 ° C per minute, holding the trunk piece at the peak temperature under a self-generated ambient atmosphere, followed of furnace cooling and further followed by the joint heating of the obtained Biopräform and Silicon in a crucible under vacuum at a temperature in one Range of 1450 ° C up to 1600 ° C, Keep the peak temperature above a period in a range of 2 to 4 minutes, followed by furnace cooling is obtained.

To an embodiment The invention derives from the biopreform of Cocos nucifera, Borassus flabellifer and Phoenics dactylifera.

To another embodiment the invention is the amount of silicon absorbed in the range from 5.7 to 13.0 g for a biopräform with a weight in the range of 1.1 to 3.6 g.

To another embodiment According to the invention, the vacuum is in a range of 1.0 mm to 0.05 mm Hg held.

The The present invention is also directed to a silicon / silicon carbide ceramic, which is obtainable by a method as described above.

Detailed description the invention

In the method according to the invention the synthesis of the non-oxide duplex ceramic is carried out under Use of infiltration of molten silicon into structured Pores of a carbonaceous Biopräform, resulting in a reaction of silicon (Si) with carbon (C) to form silicon carbide (SiC) leads and wherein the unreacted silicon (Si) in the remaining porosity is present. The novelty of the present invention is that unlike other methods of making SiC-based Ceramics made of biostructures derived from preforms, the final material produced in a cheap process in the present case, because it is a precursor which is transformed from a plant locally as a cheap natural or agricultural product is available and the one from Caudex stem of a monocot tree is produced, which eventually becomes leads to faster process cycles. In the method according to the invention For the production of silicon / silicon carbide ceramic is a strain of a monocot Caudex plant, such as coconut (Cocos nucifera), Palmyra Palm (Borassus flabellifer), Date Palm (Phoenix dactylifera), for the production of biopräform used.

• (i) Verwendung einer verarbeiteten Biopräform einer beliebigen Größe und Gestalt, abgeleitet vom Stamm einer monokotylen Caudexpflanze was es ermöglicht, neue Verfahrensparameter zum Einsatz zu bringen wie beispielsweise Einsatz eines Tiegels einer einfachen zylindrischen Gestalt, die eine zu verbrauchende Menge an Si zusammen mit der Biopräform zur Infiltration und Reaktion bei einer Temperatur im Bereich von 1450 bis 1600°C unter einem Vakuum in einem Bereich von 1,0 mm bis 0,05 mm Hg, Halten über einen Zeitraum von 2 bis 4 Minuten bei der Spitzentemperatur, was eine einfache und sofortige Entnahme des Endproduktes ermöglicht.

According to the invention, the production of such a novel Si / SiC ceramic from said biopreform is made possible by the use of the following inventive steps:

• (i) Use of a processed biopreform of any size and shape derived from the stem of a monocotyledonous caudex plant which makes it possible to use new process parameters such as using a crucible of simple cylindrical shape containing an amount of Si to be consumed together with the biopreform for infiltration and reaction at a temperature in the range of 1450 to 1600 ° C under a vacuum in a range of 1.0 mm to 0.05 mm Hg, holding for a period of 2 to 4 minutes at the peak temperature, which is a simple and immediate removal of the final product allows.

worin r der Porenradius ist und I die Porenlänge, Δp ist das Druckdifferenzial zwischen den Enden der Porenkanäle, n die Anzahl an Poren und η die Viskosität der Si-Schmelze. Man kann annehmen, dass der negative Effekt des kleineren Porenradius für die volumetrische Fließgeschwindigkeit durch das höhere Druckdifferenzial ausgeglichen wird, das durch Anbringen eines Vakuums und eine höhere Anzahl von Poren/Kanälen erhalten wird. Als Nettoeffekt wird dann eine höhere Rate der Infiltration und der Reaktion des flüssigen Si bei solchen neuen Biopräformen möglich, was schließlich zu einer deutlichen Verminderung der Prozesszeit für das erhaltene Si/SiC-Keramikkomposit führt. Die Verwendung der neuen Biopräform, abgeleitet vom Stamm einer monokotylen Caudexpflanze, zur Infiltration von flüssigem Si mit signifikant verminderten Prozesszyklen für eine (Bulk) Si/SiC-Keramik mit makro- und mikrostrukturellen Merkmalen, die zu der Zellstruktur der Ausgangspflanze isomorph sind, ist ein vollständig neues und einzigartiges Verfahren im Vergleich zum Stand der Technik.When a porous carbonaceous preform is contacted with the molten Si, the liquid wets the preform and penetrates into its pores. The infiltration of the liquid Si is accompanied by a simultaneous chemical reaction between Si and C, which in turn is influenced by the volume diffusion of Si through the solid reaction product. The reaction rate between C and Si is greater than the infiltration rate [See "Fiber-reinforced silicon carbide" by E. Fitzer and R. Gadow, published in Am. Ceram. Soc. Bull., 65 [2], 326-35, 1986]. Thus, a commonly very short estimated infiltration time may not be achieved in practice. The channels can become clogged and the conversion of C to SiC can be incomplete. In particular, this problem is overcome by the use of a new Biopräform derived from a monocot Caudexpflanzenstamm. This biopreform has been described because of its genesis and the uniqueness of the process for its preparation, as a co-pending patent application (entitled "A process of making biopreform from the mono Kotyledonous caudex plant is suitable for liquid infiltration and gaseous transportation processing of materials "by OP Chakrabarti, HS Maiti and R. Majumdar [WO 2004/055133]), a porosity through a multitude of tracheal channels, which statistically benefits and is aligned along the stem axis , Micropores resulting from microfibrils, and hollow tubular portions originating from the leaf track bundles aligned in the same direction, giving rise to an increased volumetric flow rate for liquid Si, according to the equation [see "Liquid phase reaction bonding of silicon carbide using alloyed silicon molybdenum melt "by RP Messner and YM Chiang, published in J. Am. Ceram. Soc., 73 [5], 1193-1200, 1990]:

where r is the pore radius and I is the pore length, Δp is the pressure differential between the ends of the pore channels, n is the number of pores and η is the viscosity of the Si melt. It can be assumed that the negative effect of the smaller pore radius for the volumetric flow rate is counterbalanced by the higher pressure differential obtained by applying a vacuum and a higher number of pores / channels. As a net effect, a higher rate of infiltration and reaction of the liquid Si in such new biopreforms becomes possible, eventually leading to a significant reduction in process time for the resulting Si / SiC ceramic composite. The use of the novel biopreform, derived from the stem of a monocot caudex plant, to infiltrate liquid Si with significantly reduced process cycles for a (bulk) Si / SiC ceramic having macro and microstructural features isomorphic to the cell structure of the parent plant is a completely new and unique process compared to the state of the art.

The The present invention provides a process for producing a Silicon / silicon carbide ceramic prepared using a biopreform, which itself derived from a monocot Caudexpflanze that the disadvantages of the prior art avoids. The carbonaceous skeletal structure the biopräform is very advantageous for the infiltration of the liquid Si in the production of silicon / silicon carbide ceramic with significantly decreased process cycles because of the large number of smaller tracheal ones Pore channels, which are statistically distributed and vertically elongated, along with micropores that arising from the interwoven microfibrils and a large number at cavities, resulting from the leaf origins bundles in the same direction, giving a rapid infiltration and ensuring reaction of the molten silicon therethrough. The inventive method simplifies the production of Si / SiC ceramic from the above Biopräform under Use of an infiltration technique with liquid silicon, wherein the Silicon the biopreform contacted, because of the possibility to introduce the reacting silicon together with the biopreform to be infiltrated resulting in costly instrumentation and expensive and elaborate equipment for contacting between the Si-infiltrant and the carbonaceous Preform at the usual Procedure are necessary to be avoided. The reacting Silicon is used in a completely consumable amount, so that no solid silicon remains behind, so the opportunity bonding the final product to the remaining consolidated silicon melt is eliminated. There is no silicon adhering to the outer surface of the final product, so that costly methods of removing silicon from the surfaces such as etching, high temperature evacuation, treatment with chemicals, be avoided.

The inventive method includes the common heating preferably 1.1 to 3.6 g of a piece of biopreform derived from Strain of a monocotyledonous caudex plant and preferably 5.7 to 13.0 g silicon in a crucible under a vacuum of 1 mm to 0.05 mm Hg at a temperature in a range of 1450 to 1600 ° C with a Hold at the peak temperature over a period of time in one Range of 2 to 4 minutes, followed by cooling the oven.

The Production of the biopräform is filed in co-pending application no. WO 2004/055133, described. This method will be briefly described here.

The Process for the preparation of the biopreform, wherein the microstructural, structural and anatomical properties of the typical plant precursor preserved be, includes the preheating a 4 to 13.4 g piece a trunk of a monocot caudex plant at a temperature in a range of 50 to 90 ° C, preferably with a warm-up rate from 1 to 10 ° C per minute, hold over a period of 24 to 48 hours at the peak temperature, followed by warming up the preheated Sample in a closed container, the provided with an outlet, at a temperature in a range from 350 to 1000 ° C, preferably using a warm-up rate of 1 to 15 ° C per minute, Hold over a period of 5 minutes at the peak temperature below one self-generated ambient atmosphere, followed by cooling of the oven.

• (i) Auswahl von Stämmen von monokotylen Caudexbäumen, gekennzeichnet durch: (a) große Zahl von kleineren Trachealkanälen, die statistisch verteilt und vertikal entlang der Stammachse ausgerichtet sind (b) extrem hohe Geradheit der Körner und im wesentlichen longitudinale Ausrichtung der Trachealkanäle parallel zu der Stammachse ohne sekundäres Wachstum wegen der Abwesenheit von Cambium (c) verwobene und geordnete Mikrofibrillen, die die leitenden Kanäle umgeben und definieren (d) minimierte Querwände senkrecht zur Stammachse wegen der Abwesenheit vom Cambium (e) viele Blattspurenbündel, die einzeln in den Stamm hineinragen (f) Vorhandensein von typischen mineralischen Elementen (wie beispielsweise Silicium)
• (ii) Trocknen oder Vorerwärmen des monokotylen Caudexbaumes bei geringer Temperatur unter Verwendung einer langsamen Aufwärmgeschwindigkeit
• (iii) pyrolytische Transformierungsbehandlung bei 350 bis 1000°C unter selbsterzeugter Umgebungsatmosphäre bei nahezu normalen Drucken unter Verwendung einer langsamen Aufwärmrate.

The preparation of a Biopräform, which is substantially isomorphic to the monocot Caudex is a precursor and is suitable for liquid infiltration and processing of the composite materials by gas transport, is made possible by:

• (i) selecting strains of monocotyledonous caudex trees, characterized by: (a) large numbers of smaller tracheal channels that are statistically distributed and aligned vertically along the stem axis (b) extremely high straightness of the grains and substantially longitudinal orientation of the tracheal channels parallel to the stem Stem axis without secondary growth due to the absence of cambium (c) interwoven and ordered microfibrils surrounding and defining the conducting channels (d) minimized transverse walls perpendicular to the stem axis due to the absence of the cambium (e) many leaf track bundles individually projecting into the stem ( f) presence of typical mineral elements (such as silicon)
• (ii) drying or preheating the monocot Caudex tree at low temperature using a slow warm-up rate
• (iii) Pyrolytic transformation treatment at 350 to 1000 ° C under self-generated ambient atmosphere at near normal pressures using a slow warm-up rate.

• (i) es ist übliche Praxis, geschmolzenes Paraffin (schmilzt bei 60 bis 65°C) in histologischen Untersuchungen einzusetzen (siehe "Histochemistry: Theoratical and Applied", von G. Everson Pearse, Vol. I & II, 4. Auflage, 1985, Churchil Livingstone)
• (ii) Pflanzenzellenkernmaterialien sind bis zu 65 zu 70°C stabil (siehe "Plant Biochemistry", herausgegeben von James Bonner und J.E. Verner, Academic Press, 1965, Seiten 49-50).

The main purpose of drying or preheating is to remove moisture from the pores and micropores of the woody stem. The preheating of the tracheal channel is preferably performed at a relatively lower temperature with a gentle and non-aggressive warming rate of 1 to 2 ° C per minute to obtain the original cell structure of the starting plant material in the dried wood. The selection of 65 ° C as preheating temperature is based essentially on two facts:

• (i) It is common practice to use molten paraffin (melts at 60 to 65 ° C) in histological studies (see "Histochemistry: Theoratical and Applied", by G. Everson Pearse, Vol. I & II, 4th Edition, 1985 , Churchill Livingstone)
• (ii) Plant cell nuclear materials are stable up to 65 to 70 ° C (see "Plant Biochemistry", edited by James Bonner and JE Verner, Academic Press, 1965, pages 49-50).

In both cases Maintaining the cellular structure is achieved with high precision. The preheating will over a period of 24 to 48 hours until completion continued to add a constant weight of the preheated product receive.

• (i) die Pyrolyse vollständig ist
• (ii) kein Kollabieren oder Verzerren der Zellstruktur stattfindet
• (iii) keine Graphitisierung stattfindet
• (iv) mineralische Reststoffe nicht in stabile Verbindungen umgewandelt werden,

so dass sichergestellt ist, dass die biologischen Strukturmerkmale der Elternpflanze in der erhaltenen Gestalt des porösen kohlenstoffhaltigen Rückstandes – der Biopräform – erhalten werden.Thermogravimetry of dry or preheated monocotyledonous caudex powdery woody samples shows that pyrolytic weight loss is practically completed at 600 ° C. The slow heating at a rate of up to 5 ° C per minute, up to 750 to 800 ° C, of the prewarmed monocot Caudex strain sample is carried out under self-generated ambient atmosphere at near normal pressure without vacuum or purging with inert gases (nitrogen or argon) , so that

• (i) the pyrolysis is complete
• (ii) there is no collapse or distortion of the cell structure
• (iii) no graphitization takes place
• (iv) mineral residues are not converted into stable compounds,

so that it is ensured that the biological structural features of the parent plant in the obtained shape of the porous carbonaceous residue - the Biopräform - are obtained.

A warming at lower temperatures to an incomplete Pyrolysis. warming at higher Temperatures cause partial oxidation of the biopreform and can help to turn the residual minerals into stable products. Higher warm-up speeds and higher warm temperatures denature the cell structure and destroy the almost isomorphic structural features of the precursor plant in the biopräformen. The Synthesis of Biopräformen from trunks of monocot caudex trees at low temperatures and near normal pressures and below self-generated ambient atmosphere with properties that this for a quick liquid infiltration or gaseous Making the transport processes of materials suitable is a new one and unique procedure.

The biopreform obtained from monocotyledonous caudex plant stem suitable for liquid infiltration and processing of materials by gas transport overcomes the disadvantages of the prior art. The pyrolytic process, as compared to conventional methods of preparing preforms from naturally grown plant structures, simplifies the preparation of a macro and microstructure of a bioprecipitate with high precision that is isomorphic to the parent plant structure because of ambient heating, lower processing temperatures, and shorter hold times. The anatomical structure of the biopreform made from the caudex strain of a monocotyledonous plant is particularly advantageous for fluid infiltration because of the presence of many vascular bundles that are randomly distributed in the basal tissue and whose shape is obtained with high precision in pyrolytic transformation and the increasing contours give what a faster infiltration and Re ensures the action of the liquids or transport of the gases with suitable compositions.

One Another outstanding advantage is that the biopräform by Pyrolytic transformation of the stem of a monocot caudex plant obtained in tropical countries such as India (which is the third largest manufacturer of coconuts in the world is; The inhabitants of India traditionally use their own Fruit, leaves and various parts to make food, drinks and a big number of essential items for the daily life derive. Indeed are the trees an indispensable part of their social and cultural life) abound available.

• (i) Es wird ein 1,1 bis 3,6 g Stück einer Biopräform genommen, die sich vom Stamm einer monokotylen Caudexpflanze ableitet
• (ii) 5,7 bis 13,0 g Silicium wird zusammen mit der Biopräform in einen Tiegel gegeben
• (iii) dieser wird dann unter einem Vakuum von 1 mm bis 0,05 mm Hg bei einer Temperatur in einem Bereich von 1450°C bis 1600°C mit einem Halten bei der Spitzentemperatur über einen Zeitraum im Bereich von 2 bis 4 Minuten erwärmt, um das Endprodukt zu erhalten
• (iv) das Endprodukt wird im Ofen abgekühlt.

The steps of the present invention are:

• (i) A 1.1 to 3.6 g piece of biopreform is taken, which is derived from the stem of a monocot caudex plant
• (ii) 5.7 to 13.0 g of silicon is placed in a crucible together with the biopreform
• (iii) it is then heated under a vacuum of 1 mm to 0.05 mm Hg at a temperature in the range of 1450 ° C to 1600 ° C with a holding at the peak temperature for a period in the range of 2 to 4 minutes, to get the final product
• (iv) the final product is cooled in the oven.

EXAMPLE 1

It was a 1.1 g piece a fracture-free biopreform derived from coconut wood and manufactured according to ours simultaneously filed application no. WO 2004/055133 and as further summarized above together with 5.7 g of elemental silicon in a boron nitride coated cylindrical graphite crucible from a Size of about Given 50 mm in diameter, 5 mm in thickness and 115 mm in length. The bottom of the Tiegel was filled with elemental silicon, onto which the biopreform was applied has been. The graphite crucible containing the biopreform and the silicon was then in a commercial Oven with a water jacket at a temperature of 1450 ° C under one Vacuum of 1 mm Hg over heated for a period of 4 minutes. The temperature control was by means of an infrared radiation pyrometer guaranteed. The exact temperature of the crucible was separated with an optical Type of disappearing pyrometer through a quartz window measured. The oven was then cooled to obtain the ceramic.

The product was analyzed for linear dimensions, bulk density and porosity using a boiling water method. Percent change in linear dimension was noted at 1.32% (shrinkage), 2.56% (expansion), and 1.45% (shrinkage), respectively along the length, width, and thickness, indicating nearly net shape retention of the product. The bulk density and the porosity were found to be 2.61 g / cm ³ and 5.92%. The product was further analyzed by XRD analysis (X-ray) and found to contain both Si and SiC phases.

EXAMPLE 2

It was a 3.6 g piece a fracture-free biopreform derived from coconut wood and manufactured according to ours simultaneously filed application no. WO 2004/055133 and as further summarized above together with 12.4 g of elemental silicon in a boron nitride coated cylindrical graphite crucible from a Size of about Given 50 mm in diameter, 5 mm in thickness and 115 mm in length. The bottom of the Tiegel was filled with elemental silicon, onto which the biopreform was applied has been. The graphite crucible containing the biopreform and the silicon was then in a commercial Oven with a water jacket at a temperature of 1500 ° C under a Vacuum of 0.95 mm Hg over heated for a period of 2 minutes. The further procedure was carried out as in Example 1.

The product was analyzed for linear dimensions, bulk density and porosity using a boiling water method. Percent change in linear dimension was reported as 1.40% (shrinkage), 2.44% (expansion), and 1.47% (shrinkage), respectively along the length, width, and thickness, indicating nearly net shape retention of the product. The bulk density and the porosity were found to be 2.68 g / cm ³ and 8.41%. The product was further analyzed by XRD analysis (X-ray) and found to contain both Si and SiC phases.

EXAMPLE 3

A 2.3 g piece of fracture-free biopreform derived from coconut wood and prepared according to our copending application no. 2004/055133 and as summarized above together with 13.0 g of elemental silicon in a boron nitride coated cylindrical graphite crucible of size given about 50 mm in diameter, 5 mm in thickness and 115 mm in length. The bottom of the crucible was filled with elemental silicon to which the biopreform was applied. The graphite crucible containing the biopreform and the silicon was then placed in a commercial oven with a water jacket at a temperature of 1500 ° C under a vacuum of 0.20 mm Hg over a period of 2 minutes warms. The further procedure was carried out as in Example 1.

The product was analyzed for linear dimensions, bulk density and porosity using a boiling water method. Percent change in linear dimension was reported as 1.24% (shrinkage), 2.04% (expansion), and 1.07% (shrinkage), respectively along the length, width, and thickness, indicating nearly net shape retention of the product. The bulk density and the porosity were found to be 2.67 g / cm ³ and 2.87%. The product was further tested by XRD analysis and found to contain both Si and SiC phases.

EXAMPLE 4

It was a 2.3 g piece a fracture-free biopreform derived from coconut wood and manufactured according to ours simultaneously filed application no. WO 2004/055133 and as further summarized above together with 13.0 g of elemental silicon in a boron nitride coated cylindrical graphite crucible from a Size of about 50 mm diameter, 5 mm thickness and 115 mm length. The bottom of the Tiegel was filled with elemental silicon, onto which the biopreform was applied has been. The graphite crucible containing the biopreform and the silicon was then in a commercial Oven with a water jacket at a temperature of 1500 ° C under a Vacuum of 0.95 mm Hg over heated for a period of 2 minutes. The further procedure was carried out as in Example 1.

The product was analyzed for linear dimensions, bulk density and porosity using a boiling water method. Percent change in linear dimension was reported as 1.22% (shrinkage), 2.06% (expansion), and 1.01% (shrinkage), respectively along the length, width, and thickness, indicating nearly net shape retention of the product. The bulk density and the porosity were found to be 2.63 g / cm ³ and 4.61%. The product was further tested by XRD analysis and found to contain both Si and SiC phases.

EXAMPLE-5

It was a 2.2 g piece a fracture-free biopreform derived from coconut wood and manufactured according to ours simultaneously filed application no. WO 2004/055133 and as further summarized above together with 12.2 g of elemental silicon in a boron nitride coated cylindrical graphite crucible from a Size of about 50 mm diameter, 5 mm thickness and 115 mm length. The bottom of the Tiegel was filled with elemental silicon, onto which the biopreform was applied has been. The graphite crucible containing the biopreform and the silicon was then in a commercial Oven with a water jacket at a temperature of 1600 ° C under a Vacuum of 0.20 mm Hg over heated for a period of 3 minutes. The further procedure was carried out as in Example 1.

The product was analyzed for linear dimensions, bulk density and porosity using a boiling water method. Percent change in linear dimension was reported as 1.22% (shrinkage), 2.08% (expansion), and 1.11% (shrinkage), respectively along the length, width, and thickness, indicating nearly net shape retention of the product. The bulk density and the porosity were found to be 2.72 g / cm ³ and 0.65%. The product was further tested by XRD analysis and found to contain both Si and SiC phases. Further optical studies with the microscope showed that the cellular ring structure of the bioprecipitate was obtained with a solidified amount of silicon in the cavities and converted SiC in the cell wall. Microscopic examination of the polished section, which was cut along a length of the infiltrated sample, also showed that the longitudinal tube channels of the vascular bundles contained solidified silicon with converted SiC in the tube wall. The fact that the cellular ring structure of the Biopräform was obtained with high precision in the infiltrated sample was further confirmed by detailed SEM examination. The presence of Si and SiC phases could be confirmed by EDXA during the SEM examination.

EXAMPLE 6

It was a 2.2 g piece a fracture-free biopreform derived from coconut wood and manufactured according to ours simultaneously filed application no. WO 2004/055133 and as further summarized above together with 12.1 g of elemental silicon in a boron nitride coated cylindrical graphite crucible from a Size of about 50 mm diameter, 5 mm thickness and 115 mm length. The bottom of the Tiegel was filled with elemental silicon, onto which the biopreform was applied has been. The graphite crucible containing the biopreform and the silicon was then in a commercial Oven with a water jacket at a temperature of 1600 ° C under a Vacuum of 0.07 mm Hg over heated for a period of 2 minutes. The further procedure was carried out as in Example 1.

The product was analyzed for linear dimensions, bulk density and porosity with a cooking water process. Percent change in linear dimension was reported as 1.25% (shrinkage), 2.06% (expansion), and 1.13% (shrinkage), respectively along the length, width, and thickness, indicating nearly net shape retention of the product. The bulk density and the porosity were found to be 2.70 g / cm ³ and 2.26%. The product was further tested by XRD analysis and found to contain both Si and SiC phases. Further optical studies with the microscope showed that the cellular ring structure of the bioprecipitate was obtained with a solidified amount of silicon in the cavities and converted SiC in the cell wall. Microscopic examination of the polished section, which was cut along a length of the infiltrated sample, also showed that the longitudinal tube channels of the vascular bundles contained solidified silicon with converted SiC in the tube wall. The fact that the cellular ring structure of the Biopräform was obtained with high precision in the infiltrated sample was further confirmed by detailed SEM examination. The presence of Si and SiC phases could be confirmed by EDXA during the SEM examination.

EXAMPLE-7

It was a 2.2 g piece a fracture-free biopreform derived from coconut wood and manufactured according to ours simultaneously filed application no. WO 2004/055133 and as further summarized above together with 11.9 g of elemental silicon in a boron nitride coated cylindrical graphite crucible from a Size of about 50 mm diameter, 5 mm thickness and 115 mm length. The bottom of the Tiegel was filled with elemental silicon, onto which the biopreform was applied has been. The graphite crucible containing the biopreform and the silicon was then in a commercial Oven with a water jacket at a temperature of 1600 ° C under a Vacuum of 1.00 mm Hg over heated for a period of 4 minutes. The further procedure was carried out as in Example 1.

The product was analyzed for linear dimensions, bulk density and porosity using a boiling water method. The percent change in linear dimension was reported as 1.26% (shrinkage), 2.04% (expansion), and 1.09% (shrinkage), respectively along the length, width, and thickness, indicating nearly net shape retention of the product. The bulk density and the porosity were found to be 2.68 g / cm ³ and 3.06%. The product was further tested by XRD analysis and found to contain both Si and SiC phases.

• (a) billige und leicht verfügbare Rohstoffe von lokaler, ursprünglicher Herkunft und aus erneuerbarem und nicht die Umwelt verschmutzenden Quellen
• (b) relative Leichtigkeit bei der Herstellung wegen der vollständigen Vermeidung von komplexer Pulverherstellung und schwierigem Gestaltformung
• (c) gesteigerte Gestaltfähigkeit wegen der Verwendung von leicht herstellbaren/verarbeitbaren Biopräformen
• (d) Fähigkeit, nahezu die Nettogestalt zu erhalten
• (e) einfache und schnellere Herstellungsverfahren verbunden mit leichten und sofortigen Mitteln zur Entnahme ohne Erfordernis der teuren Instrumentierung und aufwendigen Ausrüstung
• (g) kostengünstiges umweltfreundliches Verfahren

The main advantages of the present invention are:

• (a) cheap and readily available raw materials of local origin and of renewable and non-polluting sources
• (b) relative ease of manufacture because of the complete avoidance of complex powder production and difficult shape shaping
• (c) Increased design ability due to the use of easy-to-produce / processable biopreforms
• (d) Ability to get close to net shape
• (e) simple and faster manufacturing processes associated with easy and immediate removal means without the need for expensive instrumentation and equipment
• (g) low cost environmentally friendly process

Claims (5)

Process for producing a silicon / silicon carbide ceramic using a biopräform, by preheating a piece a trunk of a monocot caudex plant at a temperature in a range of 50 to 90 ° C with a warm-up rate from 1 to 10 ° C per minute, keeping the preheated stem piece at a peak temperature, followed by heating the preheated stem in a closed container, which is provided with an outlet, at a temperature in one Range from 350 to 1000 ° C with a warm-up rate from 1 to 15 ° C per minute, holding the trunk piece at the peak temperature under a self-generated ambient atmosphere, followed of furnace cooling and further followed by the joint heating of the obtained Biopräform and Silicon in a crucible under vacuum at a temperature in one Range of 1450 ° C up to 1600 ° C, Keep the peak temperature above a period in a range of 2 to 4 minutes, followed by Furnace cooling. The method of claim 1, wherein the biopreform is of Cocos nucifera, Borassus flabellifer and Phoenix dactylifera derives. The method of claim 1, wherein the used Amount of silicon in a range of 5.7 to 13.0 g for Biopräform with a weight in a range of 1.1 to 3.6 g. The method of claim 1, wherein the vacuum is in a Range is maintained from 1.0 mm to 0.05 mm Hg. Silicon / silicon carbide ceramic obtainable by a method according to any one of the vorste existing claims.