Volume 6 Preprint 70
Development of new corrosion resistant coatings based on chemical nanotechnology
W. Fuerbeth, H.-Q. Nguyen, M. Schuetze
Keywords: coating, nanotechnology, sol-gel, corrosion protection
Because you are not logged-in to the journal, it is now our policy to display a 'text-only' version of the preprint. This version is obtained by extracting the text from the PDF or HTML file, and it is not guaranteed that the text will be a true image of the text of the paper. The text-only version is intended to act as a reference for search engines when they index the site, and it is not designed to be read by humans!
If you wish to view the human-readable version of the preprint, then please Register (if you have not already done so) and Login. Registration is completely free.
Volume 6 Paper H014
Development of new corrosion resistant coatings
based on chemical nanotechnology
W. Fuerbeth, H.-Q. Nguyen, M. Schuetze
Karl-Winnacker-Institut der DECHEMA e. V., Theodor-Heuss-Allee 25, D60486 Frankfurt am Main, Germany, firstname.lastname@example.org
Nanoparticles and nanostructured films have gained an increasing interest for
industrial application in the last years. Based on chemical nanotechnology
glass-like protective coatings thermally processed at comparatively lower
temperatures around 500 °C were developed for metal substrates by two different ways. Starting from polymeric sols (suspension consisting of branched
macromolecules) containing multicomponent oxide of the SiO2-B2O3-P2O5Na2O system produced by hydrolysis and polycondensation of an alkoxide
mixture under acidic condition, thin, hard, transparent, crack-free and corrosion resistant coatings could be applied to aluminium and steel. Coatings from
particulate sols (suspension consisting of solid particles) containing multicomponent oxide synthesized under basic condition by electrophoretic deposition
(EPD) proved to be a promising method when very thick coatings are required.
Both routes offer the potential of a new type of purely inorganic coatings for
corrosion and abrasion protection.
Keywords: coating, nanotechnology, sol-gel, corrosion protection
Nanostructured silicon dioxide based ceramic coatings could offer high
corrosion resistance as well as high abrasion resistance. However, a defectfree, transparent, inorganic glass-like protective coating for metals is not easy
to achieve due to its poor fracture-mechanical properties and its high melting
temperature, which may exceed the thermal stability of the metals. The last
aspect is a particular issue for the light metals with a low melting point, e. g.
-2aluminium alloys. Nanostructured ceramics have been establishing themselves
as a modern generation of high performance materials in many areas. Their
applicability ranges from optic, electronic, chemical and automotive
engineering etc. to bioengineering owing to a vast array of unique properties.
Among the properties of ceramic nano-powders the extremely high sintering
activity and the significant improvement of ductility of bodies or coatings
sintered from these powders are of great interest, so that based on the
application of nano-scaled ceramic particles, there is a potential for a new
class of protective coatings for metals.
The tiny size of the nanoparticles produces an extraordinary high surface
energy, an increased number of surface atoms and hence a short diffusion
path way for atoms during thermal treatment. As a result the sinterability of
nano-particles is kinetically enhanced compared to common micro-particles.
Liu has found a logarithmic dependence between the particle size and the
minimum sintering temperature by investigating different sizes from
submicron- to nano-sized powder particles [#ref1]. This property of
nanoparticles allows coating procedures using thermal processing of
nanoparticles in a lower temperature range, which is tolerable also for metal
substrates of comparatively low melting temperature to be coated.
Furthermore, based on new phenomena including effects on the deformation
behaviour (grain boundary sliding and grain rotation) [#ref2], a tendency has
been observed that compared to conventional coarse-grained relatives,
materials in the nanocrystalline state show better mechanical and fracture
mechanical characteristics, e. g. hardness, strength, plasticity and ductility
[#ref3–16]. Several previous studies have also shown that the formation of a
nanostructured surface layer significantly enhances corrosion resistance
By using silicon dioxide based hybrid organic-inorganic coatings, named
ORMOCER (organically modified ceramic) or ORMOSIL (organically modified
silicate), already good corrosion resistance can be achieved. Such surface
layers still have a certain organic character, however, the organic part of the
matrix limits the thermal and mechanical stability in comparison to inorganic
systems. Moreover, better barrier properties can be obtained by dense, purely
inorganic layers. Starting from nanoparticles on the basis of silicon dioxide
-3doped with additives such as sodium oxide, boron oxide and phosphorus
pentoxide the work presented here will show a new way to produce a
protective coating for light metals and steels with high corrosion resistance
and high thermal stability, as well as durably scratch resistant, transparent,
decorative surface. The new coatings should be of great value for such
industrial sectors as automotive industry, building industry etc., where the
surface treatment will have to fulfil a protective as well as a decorative
The effect of a low sintering temperature, caused by employing nano-sized
particles, is reinforced by the addition of additives to obtain a low value for the
softening temperature. Adding phosphorous atoms into the –O-Si-O-network
leads to an increased chemical resistance [#ref30]. The presence of sodium
ions induces a change in the coordination number [BO3] → [BO4], which results
an improved strength of the coating. The sodium oxide component in the silica matrix also increases concurrently the thermal expansion coefficient of the
glass layer. An adaptation of the thermal expansion of the layer to the one of
the substrate, in order to relieve stresses in the layer/substrate-interface, in
addition to the formation of strong Si-O-Me-bonds should provide good coating adhesion.
To accomplish the aim of a corrosion and abrasion resistant, dense and fully
inorganic SiO2-based protective coating, two different methods have been
developed. On the one hand a polymeric suspension consisting of
multicomponent branched macromolecules on silica basis (polymeric sol) is
used for the coating, on the other hand a colloidal suspension containing
spherical solid oxide particles (particulate sol) is applied as a coating material.
These precursor coatings are compacted and converted into a fully inorganic
coating by a thermal treatment. Due to its inorganic character this kind of
layer can be called a nano-enamel.
2. Coatings from polymeric sols
The first way we followed was the formation of coatings from polymeric sols
obtained via sol-gel technology. This well known technology is based on the
hydrolysis and polycondensation of alkoxides. It starts with a solution of the
alkoxide in ethanole, which is prehydrolysed by the addition of a stoichiomet-
-4ric amount of water with an acid as a catalyst. In our investigations different
silicon alkoxides (tetraethoxysilane TEOS, triethoxysilane TES, methyltriethoxysilane MTES and phenyl-triethoxysilane PTES) have been used separately or in combination. The molar ratio between water and alkoxide used was
1.5:1. The acidic catalyst used was hydrochloric acid, so that a pH of 2 could
be adjusted. After some minutes of prehydrolysation of the silanes the additives (triethylborate TEB, sodium ethoxide SE and triethyl phosphate TEP as
precursors for boron oxide, sodium oxide and phosphorus pentoxide, respectively), were added to the solution so that further hydrolysis and polycondensation took place. The resulting sol, which is a suspension of polymeric
nanoparticles with a size below 10 nm, can be applied to the substrate surface
by dipping, spraying or spin-coating. This step has to be carried out in an
inert atmosphere (nitrogen) as boric acid may be formed by hydrolysis in humid air leading to some cloudiness of the coating. The resulting „green layer“
is dried at 100°C for 8 hours forming a gel layer and can afterwards be condensed to a coating by a heat treatment at 200 to 600°C for several hours. By
varying the temperature of the final heat treatment the character of the resulting coating may be adjusted between a hybrid organic-inorganic coating (at
lower temperatures) or a purely inorganic coating (after treatment at higher
Transparent, inorganic multicomponent sol-gel coatings on dif-
ferent substrates after heat treatment at 400 °C for 4 h
Coatings were prepared from mixtures of tetraethoxysilane and additives. The
resulting coatings are very transparent as shown in Fig. 1 which are coatings
-5made from TEOS + additives (10 mol-% boron oxide) on aluminum alloy (AlMg
5), carbon steel (QSt 36-3) and glass substrate, respectively. Due to the low
viscosity of the sols coatings can be obtained with a thickness in the submicron range. The dried sol layers obviously have very low porosity as no oxidation of a steel substrate can be observed during the heat treatment at 400°C
for 4 hours.
The coatings are free of microcracks if they are kept below a certain critical
thickness, which depends on the substrate. As the thermal expansion of
aluminum is twice as high as that of steel, the critical coating thickness for
aluminum is much lower than that for steel. Moreover it depends on the
modification of the silane that is used as a precursor. If only TEOS, TEB, SE and
TEP are used for the sol-gel procedure the resulting coating will be formed by
a purely inorganic network with oxygen-bridges. Therefore the flexibility of
such network is rather low, leading to a high crack sensitivity. The
consequence is that the critical thickness that can be adjusted without
cracking is only about 1 µm. In order to improve the critical thickness some
modified trifunctional silanes, like triethoxysilane, methyltriethoxysilane or
phenyl-triethoxysilane, have been used in mixture with the tetrafunctional
silane. The non-hydrolisable groups in these molecules become part of the gel
network and should therefore make it strain tolerant. By this modification of
the process the critical coating thickness was improved. By using
methyltriethoxysilane instead of tetraethoxysilane, for example, the critical
film thickness for aluminum increases from 0.4 to 2 µm. It could be shown
that the non-hydrolisable groups are stable up to a temperature of about
400°C. However, at higher temperatures during the heat treatment the carbon
based ligands may decompose leading to some coking of the layer. This may
be avoided by using hydrogen atoms as non-hydrolisable groups.
Microhardness measurements were carried out with free-standing plates of
the coating materials of 1 mm thickness produced from the sols as described
above. Figure 2 exhibits the microhardness as a function of temperature of the
heat-treatment for two different coatings, one based on tetraethoxysilane, the
other one based on a triethoxysilane/tetraethoxysilane mixture. The hardness
increases with increasing densification temperature. While the maximum hardness is higher for the tetrafunctional silane, densification is starting earlier for
-6the modified coating. At 500°C the hardness of the coating based on the mixture is much higher than the one of the steel substrate itself.
Micro-hardness of the free-standing coating material as a func-
tion of sintering temperature and type of precursor (4 h heat-treatment)
a. Pure Tetraethoxysilane (TEOS)
b. 90 vol.% TEOS + 10 vol.% Triethoxysilane (TES )
Corrosion stability of the coatings has been tested by delamination
experiments starting from an artificial defect with 0.5 M sodium chloride as an
electrolyte. Corrosion potentials have been measured by using a Scanning
Kelvinprobe. The delamination front can be observed as a very sharp potential
gradient (Fig. 3). Delamination kinetics of a sol-gel coating have been
compared with a commercial organic primer typically used for rubber lining
systems as shown in Fig. 4. Delamination of the new sol-gel coatings occurs
more slowly than the commercial primer. Obviously the adhesion to the
substrate is quite good and corrosion protection is achieved. Evaluation of
electrochemical impedance spectroscopy of the intact sol-gel-coating leads to
a dielectric constant of 5.6, which is similar to technical glasses.
U / mV(SHE)
x / mm
U / mV(SHE)
x / mm
x / mm
U / mV(SHE)
Delamination experiments of sol-gel coating by using a Scanning
Kelvinprobe: sharp potential gradients reflect the delamination front of 0.5 M
Comparison of delamination kinetics of a sol-gel coating and a
commercial organic primer on steel (Scanning Kelvinprobe measurements
starting from an artificial defect in 0,5 M NaCl)
3. Coatings from particulate sols
In the first method which was described above the protective layer is obtained
by cross-linking of branched oxide macromolecules forming a threedimensional network of a solid oxide phase and nanopores containing fluid
phase. The resulting high capillarity induced by the solvent removal in the
densification stage limits the maximum crack-free thickness of inorganic
coatings. In contrast to polymeric sols the particulate sols consist of dense
oxide particles, which may be alternatively employed to produce thicker coatings.
First of all, to verify the feasibility of the coating process, several series of
commercially available nanosilica products with the brandnames Aerosil,
Carbosil, Insusil, Ludox, Levasil provided by different suppliers were
-9investigated. These products are nearly pure silicon dioxide with different
particle sizes. However, only a wet-chemical shaping method can supply a
homogeneous distribution of additives if they are separately doped to the pure
silica particles. In this case, solutions of dissolvable compounds of boron,
sodium and phosphorus (boric acid, sodium tetraborate, sodium
metaphosphate) were used as additives to a nanosilica suspension. Afterwards,
the obtained suspension was electrostatically stabilized and then stirred with a
high speed dispergator (U-Turrax T50, IKA). After a further homogenizing
process in an ultrasonic disintegrator (Sonorex RK 103 H, Bandelin) airbubbles can be eliminated via an evacuation box (Epovac, Struers). The final
dispersion is ready for coating onto the substrate by dipping or spinning, or
also for the formation of shaped bodies, which were used to examine the
sintering kinetics by a dilatometer (L75/1550, Linseis). Specimens for
dilatometric measurements were fabricated following the gelcasting process,
in which a soluble monomer (acrylamide) is added to the nano-silica
a. Pure Aerosil of different particle sizes
- 10 -
b. Sodium oxide doped Aerosil 300 ( 7 nm)
Sintering behaviour of Aerosil SiO2 nanopowders
Representatively, the sintering behavior of the Aerosil particle series sized
from 20 nm down to 12 nm is documented in figure 5. With decreasing
particle size, the softening point moves to lower temperatures. Accordingly,
from Aerosil 90 to Aerosil 200 the sintering curves move to the left in Fig. 5a.
Further reduction of the sintering temperature can be achieved already by
dosing small quantities of a sintering additive, e.g. sodium oxide (Fig. 5b).
Sintering starts at about 1000 °C if pure Aerosil 300 sized 7 nm is applied, at
about 850 °C if only 0,8 wt% sodium oxide is added, and a content of 10 wt%
leads to an even earlier beginning of sintering at about 550 °C. Coating
thickness produced by dipping is controlled by the withdrawal rate of the
specimen from the solution. A hydraulic apparatus built at our institute allows
exact adjustment of the withdrawal speed up to 1 cm/min. Considering also
the suspension viscosity, the total coating thickness can be adjusted between
5 and 25 microns. The nanostructure of the surface layer can be maintained
after thermal processing, as the surface profile recorded via AFM (atomic force
microscopy) shows (Fig. 6). Mechanical coating methods like spin- or dip-
coating need highly concentrated suspensions, which should at the same time
have a low viscosity. This condition is required to guarantee a high density of
the “green” layers, which are the layers before densification. Affinity to
agglomerate or to gelate because of strong interactions (Van der Waals forces,
hydrogen bridging) between particles is a great problem for colloidal
processing. The solid particle content in the suspension is limited due to its
- 11 increasing viscosity. Therefore, obtaining dense coatings after heat-treatment
(without cracks and interagglomerate pores) is difficult.
Surface structure of a sintered layer of Aerosil + additives (10
mol% B2O3 + 5 mol% Na2O) after densification at 550 °C for 4 h in air
In order to bypass the required high content of solid phase in the suspension,
spherical multicomponent oxide particles produced by the sol-gel technique
were electrophoretically deposited onto the metal substrates. Depending on
the pH of the suspension the particles carry surface charges (formation of
double layer), characterized by their Zeta potential. Under the influence of an
electric field the charged particles migrate through the stable colloid
suspension towards the substrate (oppositely charged electrode) and
coagulate on the substrate surface forming a dense layer (Fig. 7). The
concentration of particles in the suspension here may be as low as 1- 5 wt%
still obtaining a dense coating.
- 12 -
Principle of electrophoretic deposition (EPD) of nano-scaled silica
The multicomponent oxide particles applied by electrophoretic deposition
(EPD) were synthesized from alkoxides similarly to the formation of polymeric
sols described above. Tetraethoxysilane TEOS, triethyl borate TEB, sodium
ethoxide SE and triethyl phosphate TEP were used as precursors for silicon
dioxide, boron oxide, sodium oxide and phosphorus pentoxide, respectively.
Instead of an acidic catalysis used for the synthesis of polymeric sols the
formation of particulate sols took place under basic conditions. Additives
were directly doped to the silica matrix by hydrolysis and polycondensation
reactions. A mixture of about 17 vol.-% alkoxides and 83 vol.-% ethanol was
homogenized by 15 minutes of ultrasonic treatment and filled afterwards into
a dropping funnel as illustrated in figure 8, which is connected to a four-necks
flask containing ethanol, water and 25% ammonium hydroxide solution in a
volume ratio of 100 : 20 : 5.
- 13 -
Schematic of the set-up for the synthesis of nanoparticles
The flow-control valve controls the dosing rate of the precursor mixture into
the ethanol/water/ammonia solution which is continuously stirred during the
whole course of the synthesis. The reactions proceed under ambient nitrogen
atmosphere to avoid inhomogeneous deposition of a boric acid phase. The
resulting sol has an oxide content of about 22 g/l and can be separated from
the fluid phase and repeatedly washed with distilled water by high speed
centrifugation. After drying the contamination free powder is stored at 40 °C
for later investigations and EPD application. The monomodal, spherical
particles shown in figure 9 are monodispersed and have a very low tendency to
- 14 -
a. about 12 nm
c. about 145 nm
b. about 50 nm
d. commercialized silica
(Aerosil OX 50)
Morphology of multicomponent oxide particles produced by sol-
Defined particle sizes can be controlled by variation of the precursor dosing
rate. Up to a limit of 15 sec./drop the dosing rate/particle size dependence
becomes less. In the progress of this research a digital dosing system which
allows automatic regulation of the precursor adding rate in defined unit
(ml/sec.) will be used in place of the dropping funnel. Cooling of the
ethanol/water/ammonia mixture also leads to a smaller particle size. The
FTIR-spectra of the dried powder (ternary Si/B/P-oxide system) in the
- 15 examined wavemumbers range between 400 – 2000 cm-1 by the KBr-disk
standard method are reported in Fig. 10. Assignments of the main absorption
band characteristics are compared to results of earlier investigations [#ref32 –
35]. The most intensive band observed around 1100 cm-1 belongs to a
stretching vibration combination of the P-O-P and P-O-Si bridging units, the
band at 1325 cm-1 is caused by a stretching vibration of P=O groups [#ref32],
the shoulder situated around 1200 cm-1 exhibits the asymmetric stretching of
Si-O bonds [#ref35], deformation vibration of O-Si-O bonds appears at 460
cm-1, a less intensive band observed at 670 cm-1 is assigned to the Si-O-B
deformation vibration, a clearly noticeable band at 1400 cm-1 exhibits the BO stretching, the peak at 950 cm-1 is related to the Si-OH stretching and a
band at 1630 cm-1 corresponding to the H-O-H deformation vibration
indicates the presence of water still remaining in the KBr-sample. It is
interesting to find a peak at 780 cm-1 which does not occur in the case of
binary systems (e.g. SiO2-P2O5 or SiO2-B2O3 only). This band may be caused by
the B-O-P bond. However, it has been shown that the particles from the
ternary system tested above consist of a mixed matrix, the network of which is
built by [SiO4]-, [PO4]-tetrahedrons and [BO3]-trihedrons. The [PO4]tetrahedron is characterized by three single oxygen bridging bonds and a
double bond to the phosphorous atom. With the further addition of sodium
ions into the network (planned for experiments in the near future) the
appearance of [BO4]-tetrahedrons is to be expected.
- 16 -
Wavenumber [cm ]
Figure 10: FTIR-spectra of multicomponent oxide synthesized by sol-gel
In contrast to the tests with the commercially available nano oxides, all
specimens for dilatometric experiments of the multicomponent oxide particles
were shaped by EPD to guarantee the reproducibility of measuring results,
which actually should reflect the sintering behaviour of the coatings (also the
coatings were produced by EPD). Therefore a double cell was constructed for
EPD on a membrane similar to what has been described in [#ref36 – 38]. The
cell used for the formation of a free standing, planar green body is built of two
separate sections connected by a dialysis membrane, which is a cellulose
based sheet and has selective porosity. The very small pore size of 30 – 35
Angstrom prevents particle movement from the suspension compartment to
the electrolyte compartment, but it does not block the ion migration.
Therefore due to the application of a dc voltage solid particles move towards
the membrane and are deposited on it, provided, the electrode in the
electrolyte section is reversely poled against the particle charge. Preparation of
an aqueous suspension of multicomponent oxide particles is carefully
performed in the same manner as described already for commercially available
nano silica. Ammonia solution is added to the suspension to provide a final
pH of 10 – 11. At this pH the suspension is stable, its solid content is about 10
- 17 wt% and the nanoparticles are negatively charged. Equal pH is applied for the
electrolyte. CrNi-steel sheets of 40 × 40 mm have been used as electrodes.
The distance between the electrode in the suspension section and the
membrane was 40 mm, the electrode in the electrolyte section was placed 10
mm away from the membrane. The shaping process started under a constant
voltage of 40 V. After a deposition time of 10 min and removement of the fluid
phase in the cell, the deposited compact can be memoved from the
membrane, then dried at 150 °C and used for the dilatometry experiment. By
this way the softening point of the nanoparticles could be measured as being
at a temperature of 700 °C (Fig. 11) and the samples were sintered to
Figure 11: Sintering behaviour of spherical multicomponent nanoparticles
For direct deposition onto metal substrates instead of the “double” cell a “single” cell is positioned. Considering this situation, an aqueous medium is not
suitable for direct EPD, as decomposition of water by hydrolysis and the involving gas formation in front of the electrode surface disturb the continuous
deposition process and lead to some inhomogeneity in the layer. As a consequence an ethanol/water mixture (10 ml water in 100 ml sol) is needed as a
dispersing agent. Then in combination with EPD under lower voltage the formation of gas bubbles can be avoided. A suspension of 2 wt% of oxide parti-
- 18 cles with a pH of 10, corresponding to a Zeta potential of – 30 mV, is prepared
for anodic deposition (also cathodic deposition will be performed in the progress of this project). A little amount of polydiethoxysiloxane (PDES) is added
to improve the interparticulate adhesion in order to decrease cracking sensi-
bility. 15 × 20 mm steel substrates (X5CrNi18 9) act as an anode, a platinum
net (30 × 30 mm) is connected as a counter-electrode. A coating thickness up
to 40 µm can easily be adjusted by varying the applied voltage (4 – 20 V) or
deposition time (1 – 10 min.). When the dc voltage is kept constant a reciprocally logarithmic current density/time relation is observed which describes the
deposition kinetics of the oxide particles. This phenomenon may be explained
by a potential drop at the substrate surface/electrolyte interface due to the
deposited layer. On the one hand, the potential drop indicates that the deposition rate slows down steadily with time, on the other hand, it reveals a high
density of the deposited layer. In any case, AFM-scans show, that the particles
are located side by side in a dense packing after EPD (Fig. 12).
Figure 12: Dense particle packing after drying at 150 °C of a 30 µm thick
coating of multicomponent nanparticles applied by EPD on CrNi-steel
Crack-free coatings up to a critical thickness of 30 µm after heat treatment up
to 400 °C can be obtained by particle surface modification with polydiethoxysilane PDES (Fig. 13). The effect obtained by adding PDES has been
investigated by TEM (transmission electron microscopy). A thin cloud with a
- 19 polymeric structure surrounds the particle surface. This polymeric cloud may
consist of a branched silica network formed by splitting-off of the ethoxy
groups from PDES in the presence of water. However, fully sintered coatings
(700 °C, 4 h) still have some micro-cracks as a result of shrinkage and substrate expansion. Further optimization as mentioned already above (sodium
doping, particle surface modification etc.) will be performed to suppress crack
formation totally. In spite of the cracking an excellent wear resistance in abrasion tests by grinding with 14 µm silicon carbide grain paper was observed.
a. without PDES
b. with PDES
Figure 13: Effect of surface modification with polydiethoxysiloxane (PDES):
the modified coating with a thickness of 30 µm is crack free after heat
treatment at 400 °C for 4 h
Summary and outlook
Novel coatings based on submicron-scaled multicomponent oxides were developed and tested on different substrates. Purely inorganic, transparent protective coatings may be obtained in a thermal densification process at rather
lower temperatures using polymeric sols as well as particulate sols. In any case
a good adherence is observed.
Flexibility of the oxide network and hardness of the coatings produced by
mechanical dipping from polymeric sols have to be controlled by using
- 20 adequate precursors in order to avoid cracking of the coating during heattreatment. Addition of triethoxysilane to the tetraethoxysilane/ethanol mixture
increases the critical coating thickness without leading to a carbon residue
after treatment at higher temperatures. This is an improvement to the silica
based hybrid organic-inorganic sol-gel coatings used so far. The resulting
coatings are quite hard, transparent, crack-free and have a good resistance
Coating formation from particulate sols by electrophoretic deposition is a
promising method if rather thick coatings are required. Coating properties can
well be adjusted by the synthesis and modification of nanoparticles. Moreover
commercially available silicon dioxide nanoparticles could be covered with a
thin hull of multicomponent oxides. Further development and optimization
should provide a significantly lower softening point of spherical particles
around 500 °C and suppress crack formation totally.
The financial support of this study by the Bundesministerium für Wirtschaft
und Technologie (BMWi) via the Arbeitsgemeinschaft industrieller
Forschungsvereinigungen e.V. (AiF) under contract no. 5 ZN ZUTECH is
gratefully acknowledged by the authors. Thanks are also due to Degussa AG
and FEW Chemicals GmbH for their technical support of these investigations.
The authors would like to thank Bayer AG, Vinings Industries, CABOT GmbH,
Nyacol Nano Technologies, Inc., Grace Davison and FUSO Chemical Co.,Ltd. for
providing their nano-products.
#ref1 D. M. Liu: J. Mater. Sci. Letters , 17 (1998), 467.
#ref2 R. W. Siegel: Mater. Sci. Forum 235-238 (1997), 851.
#ref3 J. R. Weertman, D. Farkas: MRS Bulletin 24 (1999), 44.
#ref4 H. Kung, T. Foecke: MRS Bulletin 24 (1999), 14.
#ref5 C. C. Koch, D. G. Morris, K. Lu and A. Inoue: MRS Bulletin 24 (1999), 54.
#ref6 A. J. A. Winnubst, M. M. R. Boutz: Ceram. Inter. 23 (1997), 215.
#ref7 P. M. Anderson, T. Foecke and P. M. Hazzledine: MRS Bulletin 24(1999),
- 21 #ref8 B. M. Clemens, H. Kung, S. A. Barnett : MRS Bulletin 24 (1999), 20.
#ref9 R. C. Cammarata, J. C. Bilello, A. L. Greer, K. Sieradzki and S. M. Yalisove:
MRS Bulletin 24 (1999), 34.
#ref10 D. Josell and F. Spaepen: MRS Bulletin 24 (1999), 39.
#ref11 Z. Zhang and H. Liming: Brit. Ceram. Trans., 95 (1996), 205.
#ref12 H. Mavoori, S. Sin: J. Elec. Mat. 27 (1998), 1216.
#ref13 H. Hahn, J. C. Logas, H. J. Höfler, R. S. Averback: MRS Symp. Proc. 206
#ref14 M. Jain, T. Christman: Acta Metall. Mater. 42 (1994), 1901.
#ref15 K. Niihara: J. Ceram. Japan 99 (1991), 974.
#ref16 J. Karch, R. Birringer, H. Gleiter: Nature 330 (1987), 556.
#ref17 El Kedim O, Gaffet E, EFC Publications No. 20, The Institute of Materials,
London (1997), p.267
#ref18 C. A. C. Sousa, C. S. Kiminami: J. Non-Cryst. Solids, 219 (1997), 155.
#ref19 O. C. Brandt, S. Sigmann and H.-P. Isch: In: Thermal spray: A united
forum for scientific and technological advances (Eds C. C. Berndt), ASM Intern.,
Materials Park, Ohio, USA, 1997.
#ref20 H. Dent, A. J. Horlock, S. J. Harris, D. G. McCartney: Proceedings of the
15th Intern. Thermal Spray Conference, 25-29.05.98, Nice, France.
#ref21 M. Schneider, W. Zeiger, D. Scharnweber and H. Worch: Mater. Sci.
Forum 225-227 (1996), 819.
#ref22 F. F. Marzo, A. R. Pierna, A. Lorenzo, A. Altube: Mater. Sci. Forum 289292 (1998), 1047.
#ref23 L. Roue, M. Blouin and D. Guay: J. Electrochem. Soc., 145 (1998), 1624.
#ref24 F. S. Shieu, M. J. Deng and S. H. Lin: Corr. Sci. 40 (1998), 1267.
#ref25 H. Leth-Olsen, N. J. Halvor and K. Nisancioglu: Electrochem. Soc. Proc.
97-26 (1998), 584.
#ref26 M. Schneider, W. Zeiger, U. Birth, K. Pischang, O. El Kedim and E. Gaffet:
Mater. Sci. Forum 235-238 (1997), 931.
#ref27 J. Bhattarai, E. Akiyama, H. Habazaki, A. Kawashima: Corr. Sci. 40
#ref28 D. Clark, D. Wood and U. Erb: Nanostr. Mater. 9 (1997), 755.
#ref29 R. B. Inturi, Z. Szklarska-Smialowska: Corrosion 48 (1992), 398.
#ref30 T. K. Pavlushkina, O. A. Gladushko: Glass and Ceramics 57 (2000), 310
- 22 #ref31 A. C. Young, O. O. Omatete, M. A. Janney, P. A. Menchhofer: J. Am.
Ceram. Soc. 74 (1991), 612.
#ref32 M. D´ Apuzzo, A. Aronne, S. Esposito, P. Pernice: J. Sol-Gel Sci. Tech.
17 (2000), 247.
#ref33 J. D. Soraru, F. Babonneau, C. Gervais, N. Dallabona : J. Sol-Gel Sci.
Tech. 18 (2000), 11.
#ref34 M. Prassas a. L. L. Hench: In ultrastructure processing of ceramics,
glasses & composites (Eds. L. L. Hench, D. R. Ulrich), Wiley, New York, 1984.
#ref35 M. A. Villegas, J. M. Fernandes Navarro: J. Mater. Sci., 23 (1988), 2464.
#ref36 R. Clasen, S. Janes, C. Oswald, D. Ranker: In: Ceram. Trans., vol. 51,
Ceram. Proc. Sci. Tech. (Eds. H. Hausner, G. L. Messing, S. Hirano), Am. Ceram.
Soc., Westerville, 1995, 481.
#ref37 R. Clasen: In: Ceram. Trans., vol. 54, Sci., Tech. and App. of Colloid.
Sus. (Eds. J. H. Adair, J. A. Casey, C. A. Randall, S. Venigalla), Am. Ceram. Soc.,
Westerville, 1995, 169.
#ref38 K. Moritz, R. Thauer, E. Müller: Cfi/Ber. DKG 77 (2000), E8.