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Oxidation kinetics of silicon carbide in steam at temperature rangeof 1400 to 1800℃ studied by laser heating
Pham V. H., Nagae Yuji, Kurata Masaki, Bottomley D., Furumoto
Kenichiro
Journal of Nuclear Materials,529,p.151939_1-151939_8
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https://jopss.jaea.go.jp/search/servlet/search?5066266

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https://doi.org/10.1016/j.jnucmat.2019.151939© 2020. This manuscript version is made available under the
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Japan Atomic Energy Agency

Oxidation Kinetics of Silicon Carbide in Steam at Temperature Rangeof 1400 to 1800ºC Studied by Laser Heating
Hai Vu Pham*,1, Yuji Nagae1, Masaki Kurata1, David Bottomley1 andKenichiro Furumoto2
1

Collaborative Laboratories for Advanced Decommissioning Science, Japan Atomic

Energy Agency, Fukushima, Japan2

Mitsubishi Nuclear Fuel Co. Ltd, Ibaraki, Japan*corresponding author:
Phone: +81-240-21-3524
Fax: +81-240-22-0100
E-mail: pham.hai@jaea.go.jp
Postal address: 790-1 Aza-Outsuka, Tomioka-machi, Futaba-gun, Fukushima 979-1151,
Japan

Oxidation Kinetics of Silicon Carbide in Steam at Temperature Rangeof 1400 to 1800ºC Studied by Laser Heating
As expected for accident tolerant fuels, the investigation of steam oxidation forsilicon carbide under beyond design basis accident scenarios is needed. Many
studies focused on steam oxidation of SiC at temperatures up 1600ºC have beenreported in the literature. However, behavior of SiC in steam at temperatures above
1600ºC still remains unclear. To complete this task, we have designed andmanufactured a laser heating facility for steam oxidation at extreme temperatures.
With the facility, we report the first results on the steam oxidation behavior of SiC
in the temperature range of 1400-1800ºC for short term exposure of 1-7 h underatmospheric pressure. Based on the mass change of SiC samples, parabolicoxidation rate and linear volatilization rate were calculated to be 𝑘p =exp(1.44 ± 1.8 +−96±30 [kJmol−1 ]−95±10 [kJmol−1 ]

𝑅𝑇[K]

𝑅𝑇[K]

) , and 𝑘l = exp(4.7 ± 0.6 +).

The oxidation layer appears to be maintained at 1800°C in steam, but the bubble
formation phenomenon suggests other volatilization reactions may limit its life.
Keywords: SiC; steam oxidation; accident tolerant fuels, laser heating

1. Introduction
Since the nuclear disaster in March 2011 at the Fukushima Daiichi Nuclear Power
Plant, development of new materials for accident tolerant fuels for light water reactors
has become a heavily discussed issue. During severe accidents as at Three Mile Islandor Fukushima Daiichi, the peak temperature of fuel rods could reach very high level,
beyond melting temperature of current fuel claddings such as Zircaloy-4. In addition,
severe degradation of Zircaloys in light water reactors already occurs below its melting
temperature by exothermic oxidation in water vapor resulting in brittle and bursting of
claddings (loss of barrier effect) as well as hydrogen and heat release. To provide larger
safety margins and potentially avoid severe core degradation under beyond-design
conditions, one strategy is to develop fuel systems that tolerate severe accident conditions

better than the current Zircaloy claddings. Various alternative materials [1] for fuelcladding have been proposed for this application: ceramics such as silicon carbide (SiC)[2], advanced steels, for example Fe-Cr-Al alloys [3] or advanced Zircaloys such as Crcoating Zircaloy.
SiC has attracted much attention as a high-temperature structural material overthe past decades particularly in a composite form (such as SiC fibers in a SiC matrix).
The applications of SiC can range from gas turbines blades to heat exchanger tubes forindustrial furnaces due to its advantages such as high strength, high thermal shock
resistance and excellent oxidation resistance [4]. As it has been proposed for hightemperature applications, oxidation of SiC have been extensively studied [4-16].
Oxidation of SiC at high temperatures induces formation of both a condensed phaseoxide, SiO2, and a volatile sub-oxide SiO or hydroxide Si(OH)4, depending on the oxygen
potential, oxidizing species and temperature. The condensed phase oxide, SiO2, forms aprotective, surface layer which is termed “passive oxidation”. This is a compact layerthat limits oxygen ingress by diffusion across a SiO2 layer that is thickening with time
and therefore gradually slowing the diffusion processes and SiC oxidation, and yielding
a parabolic kinetics. Whereas the formation of volatile products, such as SiO which
occurs in environment with very low oxygen potentials such as high-CO content CO/CO2
mixtures, and H2/H2O, is termed “active oxidation”. Here the oxidation product SiO
volatilizes increasingly with temperatures beyond 1200°C exposing a fresh SiC surface,
and typically yields high linear kinetics at constant temperature, until the SiC is
exhausted.
Recently, SiC is also being developed as a replacement for Zircaloy cladding inlight-water reactors. SiC is known as a high-temperature structural material, and with aconsiderable improvement in the fabrication technology of SiC components, both

monolithic SiC and SiC composites (eg. SiC fibers in SiC matrix). It is also reported tohave many features suitable for nuclear industry such as high radiation damage tolerance,high thermal conductivity and high neutron economy [17]. As an alternative for theaccident tolerant fuel, the performance of SiC in steam at extreme temperatures up to1800°C and beyond, for severe accident scenarios, must then be investigated. However,the study of oxidation behavior in steam at temperatures above 1600ºC presents achallenge. Most of the conventional test facilities for steam oxidation require heating theentire test chamber where refractory lining materials such as alumina and/or zirconia may
not survive the test. To complete this task, we have designed and developed a new test
facility using a laser heating technique where the heat will be localized and focused on
the test sample only.
In this study, steam oxidation of monolithic SiC was investigated at temperaturesin the range 1400-1800ºC for 1-7h using laser heating facility (LAHF). The oxidation
behavior of SiC was then discussed, based on the mass evolution with time.

2. Experimental details
Test facility
Fig. 1 shows the Laser Heating Facility (LAHF) which was specificallymanufactured for this study.

Main features of LAHF are: a controlled oxidizing

environment, in situ observation ports, off-gas analysis, extremely fast heating/coolingrate and operational temperature above 2000ºC. The main unit consists of a laser head,
two radiation pyrometers, video camera, airtight test vessel, vacuum pump, gas line
heaters and flow rate controllers. The test vessel is made of stainless steel. The sample
holders inside the test vessel are made of zirconia. Five quartz windows are positioned
in the vessel wall for the purposes of laser light transmission, pyrometer temperaturemeasurement and in situ observation. The temperature of the test vessel and gas flow canbe controlled in the range of room temperature to 200ºC. The flow rates of steam, Ar
carrier gas and hydrogen can be controlled in the range of 0.1~3.0 g/min, 0.1~5.0 l/min
and 0.06~3.14 g/min, respectively. The laser module has a maximum power of 2500W
which allows the sample to be heated at the rate of 1000K/s. The test program, including
gas flow rates, temperatures of gas and vessel can be remotely setup, monitored andlogged in the control system. A gas chromatograph is attached to the off-gas system tosample and measure the generation of hydrogen and carbon monoxide. The gas analysis
of LAHF can also be implemented with a mass spectrometer if needed.

Experimental procedure
The SiC samples (10x10x1 mm, approx. 0.32 g) used in this study were made ofmonolithic β-SiC (above 99% theoretical density). After placing the SiC sample into thetest vessel (see Fig. 2), the ambient air inside the vessel was evacuated and then purged
with Ar gas. After heating the vessel to 150oC, a pre-heated (150ºC) gas mixture of steam
and Ar-carrier was then introduced into the vessel. The entire gas pipe system, andviewing ports were also heated up to 150ºC to keep dry steam conditions (i.e. nocondensation). After setting the gas flows and test conditions as described in Table 1, thelaser beam was switched on and the beam (approx. 6.5 mm diameter) was focused on thesample surface. Two radiation pyrometers (FTK9S, Japan Sensor Corporation) were used
to measure the sample temperature (spot size: 1.5 mm, effective wavelength: 1.95-2.5µm). The value of the pyrometer reading at the sample center was used to give feedback
to the temperature control system. A second pyrometer (with the same specifications),
focusing on the sample periphery, was used for reference. The difference between thevalues from the first and second pyrometer remained 100ºC under the test conditions.
During the tests, physical appearance of the sample was observed and recorded by a video

camera located on top of the test vessel. The gases (H2 and CO) generated during the test
were analyzed via a gas chromatograph (SGHA-P2, Nissha FIS, Inc.). The sample mass
was measured before and after the tests using an analytical balance (XSE205, Mettler
Toledo (0-80g scale; reproducibility ≤ 0,02mg). The microstructure of the sample after
testing was observed using field-emission scanning electron microscope (JSM-7800,
JEOL Ltd.) with energy dispersive x-ray spectroscopy (EDS). Phase identification ofsample was carried out using x-ray diffraction (XRD) technique with the CuKα1 line at
an operating voltage of 40 kV, and a current of 30 mA. The step size was 0.02º for 2θ
ranging from 3 to 80 º at a speed of 2 deg/min.

3. Results
Figure 3 shows a typical temperature profile of the oxidation test conducted formonolithic SiC using the laser heating facility. The SiC sample was heated up from room
temperature to 1000ºC within 10 s in the first step. From 1000 to 1800ºC, the heating rate
was set as 0.5ºC/s to simulate a prototypic loss-of-coolant accident. After reaching thetarget temperature, the steam oxidation of SiC sample was continued for a fixed interval
to investigate the time variation of the interaction. After the dwelling time, the coolingrate was 100ºC/min.
Figure 4 shows photographs of SiC samples before and after steam oxidation tests
performed at 1400, 1600, 1700 and 1800ºC for 7 h of dwelling time. Due to the heat loss
at the contact points between sample holders and test sample, the oxidation rate at the
sample periphery seems to be lower than the rate in the center. Steam oxidation ofmonolithic SiC at 1400ºC for 7 h appears to be insignificant as its physical appearance
did not change much. At 1600ºC, a brightly-contrasting and amorphous-like phase wasobserved on the sample surface. At 1800ºC, a bubbling phenomenon was observed at thecenter of the sample during steam oxidation tests. Figure 5 shows an oxide noduleobserved from cross sectional view of the SiC sample after steam oxidation at 1800ºC for
7 h and with EDS maps of O, Si and C of the cross-section. The oxide nodule is attributed
to the formation of gaseous products such as H2 and CO at temperatures above 1700ºC
where the SiO2 scale started to melt.
Figure 6 shows the oxide layer formed on the surface of SiC samples after steam
oxidation at various temperatures. The formation of an oxide layer on SiC sample after
steam oxidation at 1400ºC for 7 h (Fig. 6a) was barely noticeable. For 1600ºC and 1700ºC
exposures (Fig. 6b and c), a thin, dense oxide layer approximately 3 µm formed on the
SiC substrate. As for steam oxidation at 1800ºC, Fig. 6d shows a dense, thicker oxide
layer, approximately 10 µm between nodules. At this temperature, the oxide layer did
not form homogeneously on the SiC substrate. According to the XRD patterns as shownin Figure 7, SiO2 in Cristobalite form was detected on the surface of the SiC samples after
exposure high temperature steam.
Figure 8 plots the mass change of monolithic SiC samples as a function of
dwelling time after steam oxidation at temperatures of 1400-1800ºC. It appears that the
SiC samples underwent a mass loss that steadily increased with temperature. The mass
evolution at each temperature seemed to obey near-linear or paralinear laws. At hightemperatures, SiC reacts with water vapor to form SiO2 on the sample surface via thefollowing reaction:
SiC + 3H2O(g) → SiO2 + 3H2(g) + CO(g)(1)

The formation of the SiO2 layer is controlled by diffusion of oxidizing species throughthe protective oxide layer which obeys parabolic laws [5-10] . The mass gain (Δw1) due
to the formation of oxide layer is then expressed by:
Δw1 = 𝑚SiO2formed − 𝑚𝑆𝑖𝐶 reacted = (kp.t)1/2(2)

where kp is the parabolic rate constant and t is time. In the presence of water vapor athigh temperatures, the oxide layer reacts with steam and undergoes volatilization process
via the following reaction:
SiO2 + 2H2O(g) → Si(OH)4(g)(3)

The mass loss (Δw2) caused by the volatilization of oxide layer in steam is given by thefollowing equation:
Δw2 = - kl.t

(4)

Where kl is the linear weight loss rate of SiO2 (equivalent to the volatilization rate of
Si(OH)4) and t is time. The total mass evolution of SiC samples when exposed to water
vapor at high temperatures is the sum of mass gain due to oxide layer formation (Δw1)
and the mass loss due to oxide layer volatilization (Δw2). The total mass evolution is thenexpressed as following:
ΔW = (kp.t)1/2 - kl.t

(5)

Based on the Eq. (5) and the mass change of SiC samples in Fig. 8, the parabolic oxidation
rate, kp, and the linear volatilization rate, kl, were calculated and are shown in Table 2.

4. Discussion
4.1 Oxidation kinetics of SiC
Figure 9 shows the parabolic oxidation rate constant as function of temperaturefor steam oxidation of SiC in comparison with previous reports. The apparent activationenergy of the parabolic oxidation rate constant based on this data was calculated to be
96±30 kJmol-1.

Depending on the permeation behavior and diffusing species, theactivation energy can range from 28 to 527 kJ/mol and has been discussed
comprehensively elsewhere [6,7]. For example, Opila [6] reported the activation energyof 28-156 kJmol-1 for steam oxidation of SiC under various H2O/O2 conditions at

temperatures up to 1400ºC. In another work, Terrani [5] reported the activation energyof 238 kJmol-1 in a study of pure steam oxidation for SiC at temperatures up to 1600ºC.
No activation energy value for kp of SiC in steam-inert gas mixtures at temperatures up
to 1800ºC has been found in the literature. In comparison to the previous reports, theactivation energy derived from this study was slightly higher than that of Opila foroxidation of SiC in 90%H2O/O2 but lower than that of Terrani conducted under 100%
steam environment. Based on the data-fitting in Fig. 9, the Arrhenius relationship is asfollows:

𝑘p = exp(1.44 ± 1.8 +−96±30 [kJmol−1 ]
𝑅𝑇[K]

)

(6)

Figure 10 shows the linear volatilization rates calculated from mass change dataat their corresponding temperatures. The activation energy for the linear volatilization
rate constant in this study was 95±10 kJmol-1. The Arrhenius relationship for the linear
volatilization rate is as follows:𝑘l = exp(4.7 ± 0.6 +−95±10 [kJmol−1 ]
𝑅𝑇[K]

)

(7)

Terrani [5] discussed that the activation energy for kl should be comparable to theenthalpy of formation of the volatile species at the gas-solid interface under the relevant
test temperatures. The activation energy for linear volatilization rate constant calculated
in this study appears to be higher than the enthalpy of formation of Si(OH)4(g) which isapproximately 57 kJmol-1 at 1500ºC [5].
In consideration of the paralinear behavior of SiC in steam at high temperatures,the formation rate of SiO2, vf [mg/cm2/h], according to the parabolic oxidation rate, is asfollows:vf =d(m𝑆𝑖𝑂2 formed)d𝑡=d( 3√𝑘p 𝑡)

d(3Δ𝑤1)
=

d𝑡

=

d𝑡

3/2 √𝑘p /𝑡(8)

In the meantime, the volatilization rate of SiO2, vv [mg/cm2/h], was the linear
volatilization rate constant:vv =d(m𝑆𝑖𝑂2 volatilized)
d𝑡

=

dΔ𝑤2
d𝑡

=

d(𝑘l 𝑡)
d𝑡

= kl

(9)

In a steady state, the formation rate of SiO2 is equivalent to its volatilization rate as shownin Fig. 11. From Eq. 8 and Eq. 9, the time to reach the steady state, ts, is then given by:

ts =

9𝑘p
4𝑘l2

(10)

Based on the Eq. (10), the time to achieve a steady state of SiC in steam under theinvestigated conditions was calculated and is presented in Table.3. After the achieving a
steady state, the loss of SiC is directly proportional to the volatilization rate of SiO2.

4.2 Formation of bubbles on SiC samples
Bubble formation was only observed on SiC sample surface from in-situ video
camera during steam oxidation tests at 1800℃. Figure 5 shows small gas bubbles
attached to the SiO2 droplet-SiC interface at 1800°C; while video shots (Fig. 12)
demonstrate the rapid bubbling of the plastic SiO2 film. During the steam oxidation tests
at lower temperatures (1400-1700℃), bubble formation was not observed (although themacroscopy of the 1700°C sample (Fig. 4d) shows a roughened surface). It implies thatthe temperature range of 1700-1800℃ was a critical region for the bubble formation of
SiC in the steam environment. As depicted in Fig. 13, oxidation of SiC can be explainedby chemical reactions at the top surface and the interface between SiC substrate and SiO2
scale. On the top surface, silicon dioxide reacts with water vapor to form volatile Si(OH)4.
In the meantime, at the interface, SiC reacts to form SiO2, with H2O or oxidizing OH• or

H• radicals. The radicals can diffuse through the oxide scale generating gaseous products(CO & H2) at the interface and creating a certain level of pressure. When the temperatureof the oxide layer reaches its melting point or becomes viscous, bubbles of SiO2 emerge,
which grow and burst. The gas chromatograph was able to detect the oxidation productsof SiC (ie. CO & H2) at the higher temperatures, unfortunately the limits of detection werereached and these results were purely qualitative. The chromatographic equipment isbeing updated and a publication concentrating on these aspects for kinetic measurementsof the SiC oxidation is intended in the near future.
Similar phenomena of SiO2 bubbles formation on SiC samples in various
environments have been reported elsewhere [5,11,18,19]. Depending on the fabrication
method and impurities, formation of SiO2 bubbles during oxidation of SiC occurred at1300-1800℃ with different bubble sizes going up to several millimeters [18]. In general,the melting point of pure silica is higher than that of silicates. Thus the lower the
impurities of SiC, the higher the temperature of bubble formation. As for chemical vapordeposited SiC, formation of SiO2 bubbles mostly occurred at 1700-1800℃ which is thesame temperature range observed for bubble formation as in this study. The melting
temperature of SiO2 is given as 1726°C and a softening range of 1675-1800°C [20].
Although bubble formation was observed at 1800℃ in this study, no significant
influence on the overall mass evolution of samples was found. When SiO2 bubbles formon SiC surface, the oxide layer is no longer protective which leads to significant
degradation of SiC. It implies that the parabolic oxidation rate of SiC may become linear
at longer durations. However, data on the mass change of samples oxidized at 1800℃
and the thicker scale 10µm as opposed to 3µm at lower temperatures did not reflect abreakaway phenomenon.

This investigation of monolithic SiC is only a first step on the way to qualify SiCbased as materials since cladding tubes will be SiCfiber-SiC ceramic-matrix compositesof different designs. Further investigations will be conducted in the near future with an
upgraded gas chromatograph to confirm the kinetics of SiC oxidation and clarify for what
durations the protective behavior (or passive oxide layer) can be maintained at 1700°C
and 1800°C. Moreover, SiC (monolithic) should be tested at higher temperatures (e.g.
1900°C) to see how much the surface liquid SiO2 persists and what is its effect onoxidation resistance. A further option is to examine protective coatings if the passiveoxidation of SiC is limited to 1800°C in steam.

5. Conclusions
Investigation of steam oxidation for monolithic SiC was conducted at atemperature range of 1400-1800ºC for 1-7 h in a mixture of steam and argon gas
containing 97% of water vapor under atmospheric pressure. Although a dense oxide layer
was observed on sample surface, SiC samples experience an oxidation to SiO2 and a massloss under the investigated conditions (due to SiO volatilization). The oxidation kineticsof SiC followed paralinear laws. Based on the mass change of SiC samples, parabolicoxidation rate and linear volatilization rate at corresponding temperatures were calculatedtobeexp(4.7 ± 0.6 +𝑘p = exp(1.44 ± 1.8 +−95±10 [kJmol−1 ]𝑅𝑇[K]−96±30 [kJmol−1 ]
𝑅𝑇[K]

)

,

and

𝑘l =

). These equations appear to be closer to the values ofOpila [6] than Terrani [5], although they only go to a maximum temperature 1600°C in
one case [5]. Bubbling phenomenon of SiC at 1800ºC was clearly observed with large
bubbles forming in a near molten SiO2 layer; small bubbles were observed to initiate at
the interface. Although the microscopy indicated a thicker SiO2 film formation at 1800°C,
the mass change data did not reflex any change of the oxidation mechanism. Moreextensive investigation is needed to clarify this behavior in the temperature range of 17001800°C.

Acknowledgements
This study is the result of “Development of Technical Basis for Introducing Advanced
Fuels Contributing to Safety Improvement of Current Light Water Reactors” carried out
under the Project on Development of Technical Basis for Improving Nuclear Safety by
Ministry of Economy, Trade and Industry (METI) of Japan.

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Table 1. Test conditions for steam oxidation of SiC samples.
Temp.

Duration

Heating rate

Steam

Carrier gas (Ar)

ºC
1400
1600
1700
1800

h

ºC/s

g/min

L/min

Steam partialpressure
atm

1~7

0.5

3

0.2

0.97

Table 2. Calculated parabolic oxidation rate and linear volatilization rate constant fromthe mass change data based on Eq. 3.
Temperature,
T/ºC
Parabolic rate
constant

1400

1600

1700

1800

0.004±0.002

0.009±0.003

0.012±0.002

0.015±0.003

0.12±0.01

0.255±0.005

0.335±0.005

0.45±0.005

kp/mg-2cm-4h-1
Linear rate
constant-2 -1

kl/mgcm h

Table 3. The time to achieve steady state determined by kp and kl.
Temperature,
T/ºC
Time to achieve
steady state
9𝑘p

ts = 4𝑘 2 [h]
l

1400

1600

1700

1800

0.63±0.2

0.3±0.07

0.24±0.03

0.17±0.03

Figure 1. Illustration of the Laser Heating Facility (LAHF).

Control system
Main unit
In situobservation

Gas analysis

Figure 2. Schematic diagram of the laser heating facility (LAHF).

Figure 3. Temperature profile of steam oxidation of monolithic SiC conducted at
1800ºC for 1 h using the laser heating facility.

Time, t/min
0 10 20 30 40 50 60 70 80 90 100 110 120

Temperature, T/°C

1800
Dwelling

100°C/minCooling

1500
1200
900

0.5 °C/s
Heating

600
300
0

1

2

3

4

5

Time, t/ks

6

7
3

[10 ]

Figure 4. Photographs of SiC samples (a) before and after being exposed to steam at (b)1400, (c) 1600, (d) 1700 and (e) 1800ºC for 7 h.

(a)

Before(b)

1400ºC

2 mm

2 mm
(d)

2 mm

1700ºC(c)

1600ºC

2 mm
(e)

2 mm

1800ºCFigure 5. SEM images from a cross-sectional view of monolithic SiC samples after steam
oxidation at 1800ºC for 7 h showing bubble formation (see arrows) that are nucleating at
the SiC/SiO2 interface and EDS maps of O, Si and C, of the same area.

O

Resin
bubble

50 µm

Si

C
O
Si

Figure 6. SEM images from a cross-sectional view of monolithic SiC samples showing
the oxide layer formed after steam oxidation at (a) 1400, (b) 1600, (c) 1700 and (d)1800ºC for 7 h.
(a)

(b)

(c)
3 µm

(d)

3 µm
10 µm

1400ºC, 7h

1600ºC, 7h

1700ºC, 7h

1800ºC, 7h

2 µm

2 µm

2 µm

10 µm

Figure 7. XRD patterns of monolithic SiC samples before and after steam oxidation at
1400-1800ºC for 7 h.

-SiC
Cristobalite

Steam oxidation of Monolithic SiC
Dwelling time: 7 hIntensity, I/a.u.

1800°C

1700°C
1600°C
1400°C
As-received

0

15

30

45

60

75

90

Diffraction angle, 2 /deg

Figure 8. Mass change of monolithic SiC samples as a function of exposure time insteam in the temperature range of 1400-1800ºC. The error bars on the points below are

Mass change, W/mg.cm-2

smaller than the dots used in the graph

Monolithic SiC

01400°C-1

1600°C-2

1/2

W=(kpt) -k1t

1700°C

Paralinear

-3
0

1

2

1800°C

3

4
5
Time, t/ h

6

7

8

Figure 9. Temperature dependence of parabolic rate constants for steam oxidation of
SiC in comparison with previous reports.
Temperature, T/°C
1800 1700 1600 1500 1400

Parabolic Rate
Constant,
2-4 -1
log(kp/mg cm h )

-1

1300

1200

1100

Atmosphericpressure-2

52 kJmol-1
Opila [6]90% H2O

96 kJmol-1
This study
97% H2O

238 kJmol-1
Terrani [5]100%H2O

-3
5

6

7
4

-1

Temperature, (1/ T)10 /K

Figure 10. Linear volatilization rate constant derived from this study in comparison withthe data reported by Terrani [5] in a study using thermogravimetry and high-temperature
furnace tests conducted at lower temperatures.

Linear Volatilization Rate Constant,-2 -1
log(kl/mg.cm h )Temperature, T/°C

01800 1700 1600 1500 1400

1300

Atmosphericpressure

-0.5
-1
-1.5

1200

95 kJmol-1
This study
97% H2O-2
123 kJmol-1
Terrani [5]100%H2O

-2.5
-3
5

6

4

-1

Temperature, (1/ T)10 /K

7

Formation/Volatilization
rate of SiO2
-2 -1
v/ mg cm h

Figure 11. Formation rate and volatilization rate of SiO2 as a function of time at 1800ºC.

1

vf = 3/2(kp/t)1/2
Formation rate
Volatilization rate

0.8
0.6
0.4

vv = kl

0.2 Steady
Steadystage
state
0

0.2

0.4

0.6

0.8

1

Time, t/h.

Figure 12. In-situ observation of bubble formation on a SiC sample during a preliminary
test at 1800℃ in steam atmospheres.

Figure 13. Depiction of bubble formation during steam oxidation of SiC at temperatures
below and above SiO2 melting/softening points between 1700°C and 1800°C.