Method for the manufacture of a ceramic component
The invention relates to a method for the manufacture of a ceramic component or carbon component
of desired final geometry using at least a cellulose-containing semi-finished moulded part, which is
pyrolised in non-oxidising gas atmosphere
A corresponding method for the manufacture of plate-shaped component exhibiting an even geometry
can be seen in EP-B-1 453,773 A high-density fibre board with homogeneous distribution of the
density over the diagonal board is used as semi-finished moulded part, which is then pyrolysed in
such a manner that a desired density is achieved. Subsequently, a siliconisation takes place A
homogeneous wide ceramic component can be manufactured as mass-produced part by these
measures
The DE-A-198 23 507 refers to a method for the manufacture of moulded bodies on the basis of
carbon, carbides and/or carbonitndes. Thereby, biogenous materials are used, which are converted
into a mainly carbon-containing product by carbonisation, in order to subsequently to process to high-
carbon-containing moulded bodies Fibre composites in the form of non-woven web, mats or woven
fabrics, that is long-fibre composite, as well as wide thin-walled planar formations are suggested as
biogenous raw materials Appropriate technical planar formations are subject to a crucial limitation in
their use as carbon materials with mechanical function, since the carbon densities attainable for most
applications are too small, so that the strength does not fulfil the requirements of mechanically high-
stressable components Such a product is used only with restrictions as carbon model for a reaction
siliconising, since a high portion of free silicon in the final product causes definite limitations in the
corrosion and high temperature behaviour
The use of wood-like products as raw materials for economical SiC-ceramics, which are formed by
means of a so-called "biocarbon preforms" through liquid phase siliconising, is known from "Krenkel
Biomorph SIC-ceramics from technical woods", Symposium "Composite materials and material
composites", published by K Schulte, K Kainer, Wiley Publishing House Chemie Weinheim 1999 as
well as "Low cost ceramics from wooden products", Material Week, Munich 23-28 9 2000
Experimentally, thereby, above all carbon bodies of pyrolysed veneered plywood is sihconised and
converted into a C/SiC/Si-material
A Method for the manufacture of a component of SiC-ceramic is given in DE-A-199 47 731 Thereby,
a ceramic component is manufactured from cellulose-containing initial body by pyrolysis and
subsequent infiltration with silicon The initial body consists of a technical semi-finished material,
which is formed from cellulose-containing material in the form of splinters and/or individual layers of
laminar wood parts Thereby, the structure of the semi-finished material is controlled by different ratios
of cellulose-containing material and binding agent, whereby the binding agent content is more than

5% A semi-finished material with a high portion of translaminar pore channels is produced by the
layer formation and selection of the cellulose-containing material, which facilitates an infiltration with
liquid silicon. This method is supported in case of a layer-wise developed semi-finished material still
by crack formation during pyrolysis A carbon perform is produced from this inhomogeneous, strongly
porous structure, which can be utilized only for very restricted SiSiC-special applications The
resulting high portion of free Si in the final product restricts decisively both the mechanical
characteristics and the corrosion- and high temperature behaviour
It is known from the Japanese Patent JP-A-2001 -048648, to manufacture a component on the basis
of carbon using a lignocellulose-containing semi-finished moulding, which is pyrolysed under oxygen
exclusion The carbon mouldings exhibit less mechanical strength
The WO-A-01/64602 refers to a ceramic component, which has been manufactured on the basis of a
lignocellulose-containing semi-finished moulding. A less material density as well as inhomogeneities
of structure and density result from the material composition and processing technology
The German patent DE-C-39 22 539 discloses a method for the manufacture of high-precision heating
elements of CFC, which suggests a pressed carbon textile fabric or wove carbon mono filament fibres
as initial body Thereby, there is the possibility of siliconismg the pyrohsed body
JP-A-2026817 A refers to the manufacture of carbonisat boards on the basis of wood fibre
The GB-A-1 346 735 refers to carbon components of post-impregnated cellulose-containing thin semi-
finished products Here, neither a siliconisation is addressed, nor a reference is made to a
homogeneous density distribution or isotropic characteristics
A ceramic component on the basis of a lignolcellulose-containing semi-finished moulding is indicated
in the citation Greil, P "Biomorphous ceramics from lignocellulosics", Journal of the European
Ceramic Society, Elsevier Science Publishers, Barking, Essex, GB, Bd 21, No 2, February 2001
(2001-02), Pages 105-118 Starting point are thereby monolithic natural woods and hgnin-free
cellulose precursors Less material densities with high porosity allow only less mechanical
characteristics
Due to outstanding strength even at high temperatures, less density, high hardness and wear as well
as excellent modulus of elasticity and corrosion resistance, a wide area of application opens up for
ceramic materials in machine building and plant construction The small coefficient of thermal
expansion predestines ceramic structural components lightweight support functions under extreme
climatic conditions and precision requirements

Various applications in the area of optics, aeronautic engineering and space technology and in the
special equipment manufacture are possible only by means of these structural ceramic inherent
characteristics
A still broader application is often limited by the costs of such complex structural components The
limited manufacturing possibilities stand in the way of high demand for such products. The typical
powder-technology manufacturing processes in a chain over powder preparation, moulding and high
temperature thermal treatments for debindmg and sintering up to thermal and mechanical finish
processes Technically and economically, thereby very fast limits are reached, particularly if it
concerns large and complex components like unique parts or small lot
Generative manufacturing processes like the selective laser-internal or laminated object moulding are
extremely complex and the products usually restricted in the mechanical output potential
The manufacture of complex Sl-SiC-components proved to be good by means of joint sihconising of
individual modular components, which must be finish processed earlier narrow tolerances This
method is however very cost-intensive and practical only with restrictions
The initially mentioned biogenous ceramic materials on the basis of regenerating plant raw materials
proved to be an alternative to ceramics manufactured according to the methods described earlier
Thereby, the use of the board-type semi-finished material on wood fibre basis is found to be
particularly favourable.
However, the ceramic structural components with three-dimensional dimensions greater than 10~1 m
can neither be manufactured economically by multiple layering of such fibre boards nor by injecting
prepared natural fibre or their pyrolysis products
An important obstacle of a defective-free carbonisation of wood raw forms, apart from structural
inhomogeneities, is the necessity for stable exit paths for the pyrolysis waste products in particular in
the form of gases. Cracks, delaminations and profile distortions appear already in case of component
dimensions in the decimetre area in case of non-compliance
The present invention is the based on the task to further develop a method of initially specified type in
such a way that the process-technical limitations during the pyrolysis of plant fibre-containing raw
forms can be avoided At the same time however, the cost advantages are to be maintained, which
can be achieved in the utilization of known raw material semi-finished products like fibre board semi-
finished products
In particular, bulk components are to be manufactured, without the cracks, delaminations or profile
distortions occurring due to waste products like gas during the pyrolysis

In order to resolve this task, the invention essentially provides that at least two semi-finished moulded
parts are joined tightly either in semi-finished form or after at least partial carbonisation and that the
joined moulded parts are processed for achieving the desired geometry or additionally an oversize of
corresponding geometry and are available as carbon portion after carbonisation in non-oxidizing gas
atmosphere and converted if necessary by a subsequent metal infiltration process during
simultaneous reactive joining of at least two moulded parts into the ceramic component, thus a CMC
(ceramic matrix composite) - composite material
Based on the theories according to the invention, complex components can be manufactured by
modular assembly of moulded parts, in order to make a desired complex composite component
available Thereby, the individual semi-finished moulded parts exhibit dimensions, which ensure that
the waste products occurring during pyrolysis do not lead to crack formation, delaminations or profile
distortions Thereby, it in particular provided that the wall thickness D of the semi-finished moulded
part amounts to D ≤160 mm, in particular D ≤ 120 mm, preferably D ≤ 50 mm
It is particularly provided that the semi-finished moulded parts in the semi-finished state are firmly
joined by means of an organic adhesive resin such as wood glue Organic adhesive resins can be
used expediently for joining, whose carbon yield during pyrolysis can be adapted by mixing of or
several carbon carriers such as graphite, soot, pitch and/or pyrolysed fibres to the requirements of the
following reactive ceramisation
The firm joining of preferably at least partly carbonised, thus either not yet completely carbonised or
completely carbonised moulded parts, is effected by means of adhesives and/or by impregnation In
particular, firm joining of moulded parts, which are assembled in modular form, takes place with resin-
based carbon-containing adhesives, which can also be optimized by supplementing additives as for
example graphite, soot, pitch and/or pyrolysed fibres with regard to their carbon level for the
subsequent reactive ceramisation
Further, it is provided that a matching of the pore structure takes place by means of joining agent like
adhesive or impregnating medium facilitating the firm joining in the individual moulded parts In
particular, this happens due to the concerted carbon doping in the joining agents used
The semi-finished material moulded parts can be impregnated with resins and/or other ceramic
precursors, so that structures and final product characteristics of the ceramic component can be
controlled as per the requirements Thereby, the precursors are materials, which are converted by
thermal treatment into ceramic material.
In a further development of the invention, it is suggested that such products are used as semi-finished
product in their raw form, which exhibit an outline, which is roughly matched to the desired final
geometry considering the contraction arising during the manufacture of the ceramic component

In particular, it is intended that the assembled moulded parts after carbonisation are processed in final
form geometry and/or almost final form geometry, whereby due to the soft carbon state of the
assembled moulded parts, complicated geometrical outlines, undercuts, recesses, steps or threads or
complex assembled forms can be produced
Further, it is intended that the processing takes place in the carbon state to an extent that a final
processing of the ceramic component is limited grinding to the most necessary functional surfaces
such as sealing surfaces
In particular, it is intended that MDF boards (medium density fibre boards) with apparent densities
between 600 kg/m3 and 800 kg/m3 and/or HDF boards (high-density fibre boards) with apparent
densities > 800 kg/m3 are used as semi-finished moulded parts Appropriate boards can be joined and
subjected then to the process steps described earlier, in order to make a ceramic composite
component available It is in particular intended that in the semi-finished state, i e in the organic
compacting condition, a rough outline increased by the later oscillation dimension is thus worked out
An embodiment of the invention provides that the fibre boards are reduced in thickness, if necessary
to avoid the density gradient unfavourable to a ceramisation, i e the denser surface areas are
removed by machining
Further, it is intended according to the invention that inorganic active components for carbide
formation and/or development of later specific characteristics are introduced in the organic semi-
finished moulded part by metallic and/or metal-organic additives to the pressable packing The
additives can be silicon, titanium, chromium, siloxane or Silazane, to name only exempianly metallic
and/or metal-organic additives, which are in the pressable packing as additive The pressable packing
is thereby the raw material, i e plant and wood fibres plus bonding agents
According to the invention, there is the possibility to work out a rough outline increased by the later
shrinking dimension already in the organic compacting state is already or to join suitable segments by
sticking
Complex structural components can be joined both in the wood- and unfinished state by wood
adhesives and in the carbonised state (after possibly necessary intermediate processing) by carbon
adhesives of individual system elements. Adding by sticking in the carbon state can be supported with
measures of positive joining, in order to support the structure homogenization at the seam and avoid
any delaminations
The pyrolysis of the performs takes place under exclusion of air at temperatures > 250 °C A complete
carbonisation of the joined structural components requires temperatures > 900 °C likewise again
under exclusion of air, in order to be able to exclude unacceptable changes of geometry of the

components machined to final dimension in the later siliconising If necessary, a pre-carbonising can
take place After this, all content materials are not carbonised Then, the joining takes place firmly and
additionally if necessary positively Subsequently, the appropriate module consisting of the joined
moulded parts is completely carbonised
Alternatively, joining can also be done after complete carbonisation of the moulded parts
Subsequently, a heat treatment is carried out again, in order to carbonise the joining agent
Preferably, mechanical machining methods are used for final processing of the carbon forms
However, special methods like for example water jet cutting or laser machining are also suitable
There is no change in volume or shape in case of subsequent reactive metal fusion infiltration or
gaseous phase infiltrating into the finish machined carbon components
Siliconisation methods are preferably named for the formation of Si-SiC-C-composite materials In
case of capillary method, Si-melt will infiltrate into the pore areas and reacts immediately with the
carbon stand to silicon carbide. The siliconisation by means of Si-containing steam is to a large extent
diffusion-controlled and requires correspondingly longer process times
Surprising realization of the method according to invention is that despite serious differences in the
structure of resin-based joining zone and vegetable fibre-based to joining partners, mechanically very
stable and to a large extent structurally homogeneous ceramic components can be manufactured A
sufficient basis for a good quality of siliconising joint can be ensured by matching the pore structure in
the individual components, partly also with measures of specific carbon doping in the adhesives used
The decisive advantages of the manufacturing process according to the invention for complex ceramic
compound systems are the use of economical wood-technological moulding method, suitable joining
techniques by means of joining methods, the compound structures and above all a very effective
working out of final geometry favouring the metal fusion infiltration process by the fibre morphology in
the soft carbon state Finish processing in the ceramic final state is limited to necessary functional
surfaces
The pyrolysis preceding the carbonisation should be carried out at a temperature between 250 °C and
800 °C The carbonisation takes place at a temperature of at least 1000 °C, in particular from at least
1100°C
During pyrolysis and/or carbonisation of the joined semi-finished moulded parts, heating takes place
in rates between 1K/h to 1K/min , in particular less 0 1 K/mm
In particular, the invention marks a method for the manufacture of a ceramic composite material and a
composite components based on it, in which preformed semi-finished products of resin-bound plant

fibres are used as raw material, from which manufactured raw forms with wood adhesives joined or
not joined are carbonised at temperatures > 800 °C, brought to the final geometry by possible
additional sticking/joining processes or impregnation processes in the carbon state and after a
complete carbonisation at temperatures > 1000 °C by machining in the carbon state considering
necessary grinding tolerances for the ceramic finish process and then made available as carbon
products or are transformed by a subsequent metal infiltration process under exclusion of air into a
CMC-composite material with simultaneous reactive joining of the modular developed ceramic
component
Further details, advantages and characteristics of the invention are evident not only from the claims,
which are to be inferred from these characteristics - for itself and/or in combination -, but also from the
following description of the drawing with preferred embodiments
Fig 1 A composite component in the form of a spherical reflector and
Fig 2 A heat exchanger module
As example 1, below the theories according to the invention are described in detail with a adjusting
segment for exposure optics
Adjusting segments for exposure optics have to meet extreme requirements with regard to high
structural rigidity and low thermal coefficients of expansion, which cannot be fulfilled any more by the
metallic materials
Here, ceramic materials present a solution to the problem In case of larger components, however
substantial costs arise, which can be distinctly reduced with the methods according to the invention
Additionally, new positioning- and adjusting possibilities are obtained, since for example thread,
joining supports and offset bores can be machined already in the carbon state according to the
invention
In the present example 1, a positioning unit of the dimensions 150 mm x 150 mm x 20 mm on the
basis of medium-density wood fibre boards MDF was manufactured In addition, two boards MDF 210
mm x 210 mm x 22 mm are joined with each other by an organic wood adhesive, enriched with 10 wt -
% graphitic powder Earlier, a circular disk diameter of 110 mm was cut out from the individual
boards, which form later a cylindrical central opening of diameter 90 mm as circular objective
attachment The pasted composite material was carbonised after air hardening under nitrogen at 1150
°C Each fibre board and thus the entire component in the board plane shrink by 23%, in height by
42% The carbon component is obtained by milling to final geometry. Functionally necessary through-
holes and threads are bored The carbon density of 0.62 g/cm3 attained is suitable for a siliconisation
This is carried out as capillary infiltration with liquid silicon at 1600 °C under argon atmosphere

At the silicomsed component, only still functionally crucial sealing surfaces are to be reground with
diamond tools A static modulus of elasticity of 320 GPa is achieved in case of a 4-point-flexural
strength of 280 MPa The thermal linear coefficient of expansion with 2.9 x 10"6 K"1 likewise meets
the requirements
The method according to the invention is explained in detail by means of the complex composite
components in form of a spherical reflector 10 (Fig 1) represented in the figures and a heat
exchanger module 12 (Fig. 2). Thereby, the process steps are considered, which have been
described in the example described earlier.
Example 2 (spherical reflector 10)
As study for a ceramic radiation reflector, a Si-SiC-light-weight concept was implemented on the basis
of MDF-boards With consideration of the pyrolysis contractions specified in Example 1, annular and
circular board elements MDF 22 mm were stuck according to the concept of Fig 1 in 7 board planes
with wood adhesive and carbonised up to 1700 °C The geometry 0 320 mm x 90 mm so obtained
from seven even board elements 1 - 7 is milled to final dimension in the carbon state Only the later
spherical reflector surface got as grinding tolerance a radius less by 0 5 mm Holes for fastening
elements and structurally important steps were supplemented
The ceramisation took place as Si-fusion infiltration at 1650 °C in argon atmosphere Material
densities of 2 ,90 g/cm3 are reached without provable open porosity
The grinding took place after the ceramisation, in order to remove the excess material on the reflector
surface
Example 3 (ceramic heat exchanger 12)
Ceramic heat exchangers are for many years an object of development. The composite material
SiSiC is particularly promising due to its heat conductivity. Problem of many manufacturing
attachments are the necessary component dimensions, gas-tight joints and lastly the substantial
production costs
The solution according to the invention provides a modular type structure as per Fig 2 For prototypes
MDF-boards 150 mm x 150 mm x 16 mm were carbonised at 1150 °C under nitrogen atmosphere,
whereby densities of 0.64 g/cm3 are achieved From this, the individual planes of the heat exchanger
as per Fig 2 are milled with retaining support frames and rotated alternately by 90° and joined to a
total block of each 2x6 channel levels by means of carbon adhesive

After pyrolysis of the adhesive at 900 °C under nitrogen atmosphere, the overall system is ceramised
by silicon melt at 1650 °C under argon and thereby firmly bonded Due to high Si-portion in the
structure, only densities 2 70 to 2 80 g/cm3 is realised in case of a remainder porosity of 4 to 6%
The hot exhaust air flow in such a heat exchanger cube of 106 mm x 106 mm x 106 mm heats up the
fresh air flow, shifted by 90°, entering into the respective intermediate levels The strict separation of
both gas flows is ensured by laterally gas-tight incident flow hoods

We claim

1 Method for the manufacture of a ceramic component or a carbon component of desired final
geometry using at least a cellulose-containing semi-finished moulded part, which is pyrolysed
in non-oxidizing gas atmosphere, characterized by the fact that
at least two semi-finished moulded parts are firmly bonded either in rough form or after at
least partial carbonisation that the joined moulded parts help achieving the desired final
geometry or an appropriate geometry machined to the final geometry plus machining
allowance and available as carbon component after carbonisation in non-oxidizing gas
atmosphere or are converted by a following metal infiltration process with simultaneous
reactive joining of at least two moulded parts into a CMC-composite material
2 Method according to claim 1, wherein firm joining of the semi-finished moulded parts is
accomplished in the rough state by means of an organic adhesive resin such as wood glue
3 Method according to claim 2, wherein carbon carrier such as graphite, soot, pitch and/or
pyrolysed fibres is added to the adhesive resin.
4 Method according to claim 2 or 3, wherein an adhesive resin with carbon carriers added if
necessary is used for joining, whose carbon yield with pyrolysis and/or carbonisation is
matched to the requirements of the reactive ceramisation
5 Method according to claim 1, wherein at least partly carbonised moulded parts are joined by
sticking and/or impregnating using carbon-containing bonding agents
6 Method according to claim 1, wherein a resin-based carbon-containing adhesive is used for
firm joining of at least two moulded parts after at least partial carbonisation
7 Method according to claim 6, wherein the adhesive used for joining of preferably at least partly
carbonised moulded parts is set by supplementing additives such as graphite, soot, pitch
and/or pyrolysed fibres with regard to carbon yield for the reactive ceramisation
8 Method according to claim 1, wherein silicon is used for the metal infiltration process and/or
that metallic carbide forming agents separately or in mixture are introduced for the metal
infiltration process and/or that the metal infiltration process is carried out by means of
capillary-controlled liquid infiltration and/or metal vapour-containing gas atmosphere
9 Method according to claim 1, wherein such products are used as semi-finished product in
their rough form, which exhibit an outline, which is roughly matched to desired final geometry
considering the shrinkage occurring during the manufacture of the ceramic component
10 Method according to claim 1, wherein the pyrolysis preceding the carbonisation is carried out
at a temperature TB with 250 °C ≤ TB < 800 °C and/or that the carbonisation is carried out at a
temperature Tv with Tv > 1000 °C, in particular Tv > 1100 °C.
11 Method according to claim 1 or 10, wherein the joined semi-finished moulded parts are
heated up in steps from 1k/h to 1K/min, in particular by less than 0 1 K/min during pyrolysis
and/or carbonisation and/or that during the metal infiltration heating of the moulded parts is
carried out in steps of 3 K/min to 7 K/min, in particular by in approximately 5 K/min, whereby

in particular in the metal infiltration after attaining the final temperature, this is retained over
period of t with 20 min ≤ 20 mm ≤ t≤ 40 min, in particular t in approximately 30 mm
12 Method according to claim 1, wherein the preferably modular joined semi-finished moulded
parts exhibit maximum wall thickness D with D ≤ 160 mm, in particular D ≤ 120 mm,
preferably D ≤ 50 mm
13 Method according to claim 1, wherein the cellulose-containing semi-finished moulded part
consists of at least a resin-containing bonding agent and at least a raw material of plant-
and/or wood fibres
14 Method according to claim 1, wherein as semi-finished moulded part a medium-density wood
fibre board (MDF) with apparent densities between 600 kg/m3 and 800 kg/m3 and/or a high-
density (HDF) fibre board with apparent densities ≥ 800 kg/m3 are used, whereby in particular
material is removed from the surface areas of the of the wood fibre boards, whose density is
greater than the mean density of the wood fibre board
15 Method according to claim 1, wherein the semi-finished material moulded parts are controlled
with resins and/or other ceramic precursors structure and final product characteristics by
impregnation as per the requirements, and/or the component geometry and material structure
are specifically controlled by joining processes and/or impregnating processes of at least
partly, in particular completely carbonised moulded parts
16 Method according to claim 1, wherein after at least partial carbonisation, in particular after
complete carbonisation of the joined moulded parts, the desired geometry, rear-cutting,
recesses, steps and/or threads as per the end form or almost as per the end form are worked
out
17 Method according to claim 1, wherein a final machining of the ceramic component is limited
by grinding to necessary functional surfaces such as sealing surfaces
18 Method according to claim 1, wherein inorganic effect components for carbide formation
and/or development of later specific characteristics of the ceramic component are introduced
into the semi-finished moulded part through metallic or metal-organic additives to the
pressable packing
19 Methods for the manufacture of a ceramic composite material and composite components
based on it, in which prefabricated semi-finished products of resin-bound plant fibres are used
as raw material, the unfinished forms manufactured from it joined with wood adhesives or
released at temperatures > 800°C are carbonised, by possible additional stickmg-/joinmg
processes or impregnating processes in the carbon state and after a full carbonisation at
temperatures > 1000 °C by machining in the carbon condition considering necessary grinding
tolerances for the ceramic finish process to final geometry and then are available as carbon
products or are converted into a CMC-composite material by a subsequent metal infiltration
process under air exclusion with simultaneous reactive joining of the modular structured
ceramic component

The invention relates to a method for the manufacture of a ceramic component of desired final
geometry using at least a cellulose-containing semi-finished moulded part, which is pyrolysed in non-
oxidizing gas atmosphere. In order to manufacture complex components, it is suggested that at least
two semi-finished moulded parts are firmly joined either in raw form or after at least partial
carbonisation The joined moulded parts are subsequently machined to achieve the desired final
geometry or a geometry corresponding to the desired final geometry plus the machining allowance
Then, the carbon parts are available after carbonisation of the moulded parts in non-oxidizing
atmosphere Alternatively, these can be converted into a CMC composite material in a non-oxidizing
gas atmosphere by a metal infiltration process with simultaneous reactive joining of at least two
moulded parts.