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Title On the Atmospheric Oxidation of Pure and Siliconized Ta Metal Sheets at 1000℃
Author(s) Nishida, Keizo; Hachinohe, Mitsuo
Citation 北海道大學工學部研究報告 = Bulletin of the Faculty of Engineering, Hokkaido University, 79: 139-147
Issue Date 1976-03-19
Doc URL http://hdl.handle.net/2115/41343
Type bulletin (article)
Additional Information There are other files related to this item in HUSCAP. Check the above URL.
File Information 79_139-148.pdf
Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP
;iヒ幸毎・道プく学コニ学音i‘石序5豊酒粕テ
㌶ッ79.場・ (1昭孝1…5!脅の
Bulletin of the Faculty of Engineerins;,
Hokkaido University, No. 79 (1976)
On the Atmespheric Oxidation ef Pure and Silicenized
Ta Metal Sheets at 10000C
Keizo NISHIDA and Mitsuo HACHINOHE (Received September 20, 1975)
Abstract
With a pure silicon vapor technique Ta sheets were siliconized in an evacuated quartz
ampoule up to 49 hr at 10000C, and then these siliconized sheets as well as untreated
ones were oxidized at 10eOOC for 15 min in an atmospheric air in order to determine the
resistance of siliconized Ta metal against oxidatioR. Severe oxidation of pure Ta sheets
almost prevented by using this method under the above-metioned conditions. Next, the
mechic nism of this protection process of siliconizing was discussed.
1. lntroduction
Investigati,on and development of new metallic materials aganist the high-
temperature oxidation attack are in stroRgly demand, since the environment in
which metallic materials ai-e used has recently become increasingly detrimental.
There are yarious methods to improve the anti-corrosioR property of refractory
rnetals. The practice of surface coating with vapored metals has dyawn special
attention as an effective method. For example lnconel alloys now widely used
for turbine blades are at times coated with the anti-corrosion metal by a vapor-
diffusion ’method, resulting in a satisfactory modification of the oxidation re-
slstance.
From thl,s point of view, the present investigatin was carried out to examine
in what manner a siliconized Ta sheet shows better resistance against the oxidation
attack than that of an untreated Ta sheet, because pure Ta metal fails easily in
atmospheric environrnent above 10000C in spite of its excellent mechanical proper-
ties at elevated temperatures aRd furthermore, the vapor pressure of Si is relatively
high and easily produced.
So far the oxidation of pure Ta metal has been investigated by Peterson etal.i), Gulbransen and Andrew2}, Bakish3), M[ichael‘〉, and Albrecht et al“”}. Recently,
there is a detailed report by Dooley et al.6’7) on the oxidized structure of single
and polycrystalline Ta metals. General}y, the oxidation of polycrystalline Ta is
found to obey a logayithmic corrosion rate law below 5000C and a parabolic rate
law in a range of 500 to 10000C, and it is oxidized linearly above 10000C.
The effect of alloying elements for Ta metal against oxidation was investigated
comprehensiveiy by Kloop et al.S), who showed good improvment of anti-oxida-
tion properties in the order of Ni, Mo, Cr, and Si in atmospheric oxidation for
lhr at 12000C. From those results, if Si could penetrate into Ta metal through
its surface, the treated metal would show good resistance in air-oxidation at elevated
temperatures. Consequently, siliconizing of Ta sheets in Si vapor will be probably
Metals Research lnstitute, Faculty of Engineering.
140 Keizo NlsMDA and Mitsuo HACHINOHE 2
accompiished relatively easily and an excellent resistance of the metal aginst the
oxidation attack may wel! be obtained.
2. Experirnetal proeedures
Test pieces for the preseRt experiment were prepared from sheets (O.3 mm
thick) made by Van steel Co., U. S. A. These were cut down to a size of about
10×10mm and annealed at正000QC for l hr iなaquartz ampoule evacuated of air
up to 4×10-6 mmHg and then their surfaces were polished up to #1000 emery
paper fol}owed by washing and degreasing.
Such test pieces were capsuled once more in a quartz tube at an order of
10-6mmHg with pure Si powder (T200 mesh) prepared by The Shin-etsu Chemical
lndustry Co. Ltd. and diffusion-annealed in an electric furnace as shown in Fig. 1
for various lengths of time at 10000C.
Tabie 1 shows the details of this siliconizing experiment, listing the purities
and vapor pressures of both metals. The siliconized metal sheets were thenoxidized in the apparatus shown in Fig. 2, iR which a test piece was hung in a
vertical quartz tube through which air was allowed to fiow up at a rate of
leO cc/min. This fiow rate of air was determined after comparing its effect on
the oxidation rate of pure Ta sheets. Moreover, the variation of oxidation rate
was checked with or without desiccating the fiowing air and the effect of such
treatmeRt oR the corrosion was found to be much less.
These oxidized test pieces were observed microscopically and diffractometrically
and also the sectioned parts were checked by means of an elecron probe microa-
nalyzer (EPMA).
「孫、。,.i (一200mesh)
1 ....g.一9.pmsu/ rl一一IO’6mmHg
Fig. 1
「一一葡’.,,・..黒6ムt&【ロ「パ)sh包et o o
1 eoxioxo.3mm)L一
Table 1
Schematic presentation of siliconlzing
ampoule and its furnace
Test piece and si}iconizing condition
Time(hour)
1000。C … 4 9 16 25 36 49
SILICON
X9.999%Si
TANTALUMX9.9%Ta min,n,03%Femαx.n.03%Cmqx.
VAPQR PRESSURE TOOO。C ,
10-5mmHg 10-21mm”9,
MEしTING TEMPERATURE
1410 。C 2996 。C
I
E
t
1,
1
一Air outlat
Sjljconjt
gt
SPecimen
一 Air inlet
Ftow meter
Air pur叩
o
Fig. 2 Schematic presentation of
oxidation apparatus
3 On the Atmospheric Oxidation of Pure and Siliconized Ta Metal Sheets at 1000eC 141
3. Results
3.1 Oxidation of pure Ta sheet
On account of the shape of a test piece oxidation over a long period failed
owing to its descent. Hence the oxidation test was carried out within 15min at
10000C. The results obtained for the change in weight with the square root of
corrosion time was shown in Fig. 3 (a) in which the oxidation seems to obey a
parabolic rate law in general, showing only a slight deviation from that law.
This behavior is more clearly indicated by a log-log expression .shown in Fig. 3
(b),which shows that the relation of weight gain(」アのwith time(の;AW=ktn
holds with the value of n==O.64, because it is mainly due to the abnormal
oxidation at the corners of the test piece as will be stated later. From the
experimental results the metal shows a weight increase of about 23.5 mg/cm2 in
15皿in at lOOO。C and the rate constant k in this case is abut 4.0(mg/cm’2 mini?2).
The surface of oxidized sheet was pale grey and was firmly adhered to the
substrate, but the oxide scales showed some cracks from which white oxide was
30
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毛,。
要
It T,
g,,
.tug
ls
o oCG)
一
@,I 一
■
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旨
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Fig. 4
ra)
’わノ
?a
Fig. 5
50
ρ「.0
52。
も E vlO ≡… ’07 団5
三 .93 ゆ ≧2
T2.
@ 3 4 S 1 2 3 5710 Time(mln) (b) 丁imeCmin)
Fig.3Weight gain vs. time
/に’、 -
ずF
/’o.
n=0、5
ま
./ 5づ
1
O署idqtiqn o野Tq 5hoet αt IOOOoC for15 min@ F.【【5cα1。;3・1♂ζpn
Pur噂.Tα
T(亀05
Crロ¢k
20ド
一 一
20 30
Distapce(V)
EPMA profile from oxidized Ta sheet
30 40 50 60 70’ eO 90 ILIO 11.) 12J 130
20 rdeg.) iv・ith CrKot
X-ray diffraction patterns from oxidized
Ta (Ta20s)
(a); Surface, (b): White oxide powder
竃2爵1:…爵…由自営癬. 衛}.群嚇…灘麟;幽幽;幽幽…幽幽囎.
ζ…嚇i.鷺…農…嬢.響;.㈱《轟…{趨1;
職欝繋騨犠1Ch6毛6丁1 E一.ternww.1’tihd”S66ti6fitt’1”
views of oxidized Tasheet
Photo. 2 Sectional view of oxide
with markers on its sur-
face.
left : Ta, right : plated Ni
142 Keizo NISH工DA and Mitsuo HAcHINOHE 4
seen extruding. The stripes seen on the oxidized surface may be scratches from
the polishing abrasion. At tlte corners of the test piece abnormal behayior was
seen. Namely, the above-stated white oxide crystals extruded and appeared curled
up as seen in Photo. 1. Detailed inspections showed that the corners had noscales as pointed out previ,ously by Dooly et a17).
The microstructure of the sectioned part of oxidized meta1s was shown in
Photo. 2. The oxide appears dark grey, and the metal/oxide interface was not
fiat, showing an irregular oxidation. This fact would be attributabl,e to the
preferential oxidation at the grain boundary of the metal substrate. An EPMAresult showed the distribution of Ta in the section as seen i.n Fig. 4 for example,
from which the scales seemed to be Ta,O, (identified later) equaliy thyoughout
the oxide scale. Such scales are very hard and are adhered to the substrate as
stated above, so that the removal of it from the metal substrate was very difficult.
The removal was not done to check the oxide crystal by rneans of an x-ray
diffractometer.
The x-ray diffraction of the oxidized surface made for various oxidation times
all indicate the same crystal patterns, and that from th.e white oxide crystal
powder shows also the same crystal, although it contained some other diffyaction
patterns which were probably due to the dfference between the orientations ofthe same crystal (see Fig. 5 (a) and (b)). ln order to investigate the oxidation
mechanism of Ta metal, alumina particles (O.5 pt¢) were placed on the surface of
the test piece as markers. After the oxidation the almina maker was still found
on the oxide scale・ of Ta sheet, as seen in Photo. 2. Consequently, the oxidation
of Ta metal at 10000C was concluded to be performed by only an inward diffusion
of oxygen atoms through the oxide (Ta,O,,). According to Kubaschewski et al.9)
Ta20s was classified into a metal-excess type (n-type semiconductor), but as a result
of consideration of these atomic sizes and observation of the marker i fi this
experiment this oxide may be rather regarded as an anion-deficit n-type at 10000C,
so that movable species seems to be oxyen atoms alone rather than Ta atoms.
3.2 Siliconizing of pure Ta sheet
The surface appearance of siliconized Ta sheets is dark grey with a disap-
pearance of the metallic luster observed before the treatma.ent, but theye was no
difference among the test pieces for various treating intei”vals.
The results from the x-ray diffraction analysis for each test piece are shown
in Fig. 6, in which x-ray patterns on its surface for a short time (4hr) are almest
the same (TaSi,) as those for a long time (49hr) except the former shows other
peaks. These peaks were clearly identified as Ta,Si,, so that the compound formed
for a short time may be regarded to be i.n a transient phase. Therefore, the
surface seems to consist mainly of the same compound in spite of the various
treating intervals.
The behavior on w’hich pure Ta metal was siliconized was shown in Fig. 7.
This figure shows that the weight gain (mg/cm2) of Ta sheets obeys a parabolic
rate law, with a two-step siliconizing.
Next, Photo. 3 shows representative sectional features of these test pieces.
The formation of alloy正ayers was very slow and£he structure of them was not
clear for a short time (4 and 9 hr), but after 16 hr the layer was th,ickeRed and
a metal/alloy interface was fiat and also the adhesion between metals and alloys
seemed to be good. For comparison the hardness of the surface was examiRed
and the metal subtsrate was about Hv=115, while alloy iayer showed Hv=一1032
5 On the AtmQspheric Oxidation of Pure and Siliconized Ta Metal Sheets at 10000C 143
Fig・. 6
鮮5「吊’.嘩.ve ・:. ・ ㌦双. di=・1 筆 ・・. ;‘夢; ・± .蹴.ニ ご と ド
欝灘鍛 紬醜ゴ(a) 4hr
.髪.
t
4こ, .5㌧1 6J 70 30 9J PO ノノ1フ 1?0
2θrde.9/ w~舗 」一r’κ感
X-ray diffraction patterns from
siliconized Ta(a): 4hr, ((b): 49hr. x: TasSi3,
0thers: TaSi2
’t ” t/”
(b) 9hr
重; 1・;
130
(c) 16hr
一100
c51-e
も1’4
1’a3
0for2’i
0 1234S67 Timethr)
Fig. 7 Siliconizing of Ta sheet at 10000C
25
(d)25hr. (e)36hr 3’
Photo.3 Sectional views of siliconized Ta sheets 缶20 at 10000C;upper part Ni plated, lower 台 part:Ta;intermediate layer:silicide 一 ド あ 暑 15
ぢ
↑ 鴇 th- 210 ℃ 着 に ロ エニ
£ ト
も
き ε ε ・ミ 0 1 ? 3 → E
Weight Gαin(m9’⊂111乞)
Fig.9Weight gain vs. thickness of
D’stance‘ノs, alloy layer of siliconized Ta
Fig.8EPMA patterns from siliconized Ta sheet
±50.From the above results the alloy layer was found to be very hard. so that
this coating may be very useful for the other fields.such as antiabrasive parts.
The distribution of Si as well as Ta in the treated section was examined by
an EPMA me.thod with results as shown in Fig.8. In this figure another compound
in case of the low concehtration of Si for short-time treatments was present(4 and
ghr). This wes identi且ed as Ta5Si3. After a g hr.treatment, higher silicide w.as
clearly seen in the figure, and the compound was determined to be TaSi2 corre-
sponding to the x-ray diffraction results. Moreover, from the detailed examlnatlon
of this pro丘le the inside of the alloy layer seemed to have a sl.ight solubility of
Si in Ta metal(in this figure it could not be indicated clearly). For example,
the 16hr-treatment showed a penetration depth of about lOμ. Of course, the
phase diagram of a Ta-Si system1。)indicates that Ta has a solubility of about
O,Q2 wt%of S.i, so that the above stated obs.ervation is highly probable. Further-
mqre, the TaSi, compound has no solubility in the present phase diagraln, but in
a diffusion treatment such as the present investigation a calculation from the
且gure of the results for 36 hr-treatment showed to have a solubility range of
about 1.4 wt%Si.
As the thickness of an alloy layer for different treating intervals also indicated
the same relation against the square root of time as Fig.7, the thickness of an
4伽r@I
9hr ’ hr 25拘r@I
1
R6hr
9 F勧ro丁b
一凸 一 「 一
9 - 一
一一 層 一 ●.
Tα
puqrtz c隊stαis“しdr一「αy
e.U,。・1・、3,1げ・p暁
ri
jAP cry5tαl
rtK的一r剛euUs・d・・1♂cρη
而 而 掬 知 而
跨’0
s’
@曜 .
s’晒.s「.’
、4
3’’
s’, .
◎
一 ” ., 一 7 一
144 Keizo NISHIDA and Mitsuo HACHINOHE 6
alloy layer was found to have a linear relation with silicollized amount(mg/cm2)
as shown in Fig.9. But there is a certain veriety of Iayer depths at different
positiohs even in the same test piece.
3.3 0xida1:io皿of siliconized Ta sheets
In order to compare the anti-oxidation property of siliconized Ta sheets with
that of pure Ta ones, Ta sheets siliconized for vafious intervals were oxidized
for 15 min at lOOO。C under the same condition as that of the latter. Fig.10
shows the results obtained. This indicates that test pieces treated for a short
time were severely oxidized, but an amount of oxidation was markedly decreased
in those siliconized for g hr. For example, the 4 hr-treated test piece was almost
covered with the white powdered oxide covering the surface, but those treated for
along time showed orlly a slight oxidation and a grain boundary attack wasnoted. These oxidized surfaces were also checked by means of all x-ray dif-
fractometer as seen in Fig.11, in which it was revealed that the test piece treated
fQr 4 hr had the same patterns of.simple Ta2050xide and some of those of the
original TaSi2 alloy. The surface of a 49 hr-treated sheet is considered almost
the same as the original one.
Here it is noteworthy that the existence of Si oxide was not recognized and
it is considered that there is no Si oxide on the test piece. However, the Si
oxide might be not detectable by means of an x-ray diffractometer because of its
amorphous structure even if it was contained in the. oxide scale. For the purpose
7
4ゐ「.s
6
s hrs ロ 筆5
芝 49んr∫ ロ s4
.E O 2θ(deg、ノ wノ’わCrKOt
ロ 看3 Fig.11 X.,ay.diff,ac・i。n p。tt。m・f・。m
塁2 0xidation of siliconized Ta
o:Oxide(Ta205), x=TaSi2
1
o
oπ’ゴσ”α70∫5〃σσπ‘2団階
@ 副000・Clbr 15層.’丹
1
1
1 2 3 4 5 6 7
Siliconizing time(hr)
Fig. 10 Oxidation of siliconized Ta at
10000C
(q)4hr 切16hr (⊂)25hr (dl 36 hr (e)4.9hr
. 一 . . 一 . 一 - 一 ■ . { . 一 . PureTq
1Tq205 1 工⊆s2
一 . 一 .
一
Oxide[qye.「芦lllci働
「 l@ x由e ’
Sill,ide 、
I l垂сニ.Si贋
唖・ 15陛聖
ll IC kI 「
P1C「q⊂k1 Fu115c.α【e:
R.葺。5cpm
@106叩mfo「丁αL匡r
?C窒ri K.凶 1・、1 ピ「 ρ●
「
@「@’j
20H
黶@ . 一 ・ 曹 一 一 ・
.]v」l l,_製 」_.
1.s
@ トー
@且.⊥.
,
o o o o D D o 諾
o 0 o x x o.o x x
∫ o x o 罵 o x耳 篤 x 裏κ x x x
2G 30 4050 60 70 δ0 90 100 1ア0 120 β0
8壬
器
ゴ
s
5診2
sE
騨…雛繍議灘町民
.穣
勢.f
n「獣t.:
…瞬1灘裁!撮魏蕪鎌上騰…
ご
Distance(H)
Fig. 12 EPMA patterns from oxidized Ta sheet after
siliconizing for various times
騰識撫灘灘藻轍繍書懸蕪繋犠.
:轟醐
..i蝋瞬.:騰§晒達.1醸級.蜜.....嚢醗麟..... .
Photo. 4 Sectional views of oxidized Ta
sheets aiter siliconizing for
varlous t1エneS
7 On the Atmospheric Oxldation of Pure and Silieonized Ta Metal Sheets at 10000C 145
alloy layer
oxidation. This is probably attributable to the migration
of Si toward the alloy layer during the oxidation process.
3.4 Kinetics of the oxidation of siliconized Ta
sheets
In order to investigate the oxidation behavior of
siliconized Ta sheets, 49 hr-treated test pieces were used
at 10000C up to 70 min. The results obtained are
shown in Fig. 13. From the observation it is suggested
that siliconized Ta sheets were oxidized obeying a
parabolic rate law with a much lesser corrosion rate(rate constant k==O.181) than that of the pure Ta sheet
(k =一 4.e).
of the detection of the existence of such an oxide, the newly prepared pure Si
powder was oxidized for more than 1 hr under the same condition as before, but
still such oxide could not be detected. Hence it is probable that some oxide filrn
may exsist in spite of the lack of a reliable detecti.on method. This shall also
be discussed later in the paragraph where checking with an EPiMA method will
be described.
Photos. 4 (a) to (e) indicate some of the sectioned microstructures of oxidized
samples. According to Photo. 4 (a) the test piece after 4 hr-treatment has the
same metal/oxide interface as pure Ta sheets corresponding to the EPtMA result
(Fig. 12) and the alloy layer is already destroyed (refer Fig, 12 (a)), ln this case
it is clear tha.t the oxide layer reaches the Ta substrate.
Moreover, there is a characteristic distribution of constituents, i. e., Si seems
to enrich the oxide, Accordingly, it may be surmized that there may be some Si
oxide in the scales, in spite of the fact that the compound is unknoun. Another
special feature which is notable is that there is an even more enriched zene ofSi in the alloy layer than the concentration before t2r一一一一一….一一一一一一…,一一一……一一,一一一.,.....
一. IQI
芝ao,sE
E’6 a6
a芸an(届’a
O,2
r”
了es.
SIIIc
atlO
k=0.翠8
1t..一..rrttt. Gttt-ttTt
l
l
一一…一…
G一一一一
l
I
......k...
∈ ノ
。
一
Fig. 13
」2 4 6 e lo Time(min)
Oxidation ef sili-
conized Ta sheet at loooc
4. Consideration of results
From the above stated results it is suggested that the oxidation behavior is
closely related to the siliconizing (mg/cm2) as seen in Fig. 14. lt is quite clear
shat the siliconizing amount of about 1 mg/cm2 shows a strong suppressing effect
against oxidation. Moreover, another semi-log expression of the above relation
is shown in Fig. 15. There are two stages in the behavior, namely the first
stage of the reaction corresponds to the oxidation in which the weight gain
decreases largely with the increase in an amount of siliconizing. The latterstage of the curve involves further the oxidation of remaining Ta silicide (TaSi,)
in the substrate and the weight gain by oxidation decreases in proportion to an
amount of siliconizing in this representation, so that these two stages must be
discussed separately.
Of course, the former stage of oxidation corresponds to that of Ta一一rich silicide
(Ta,Si,) as stated before. Thus, the oxidation of this alloy layer will be relatively
rapid and under the present experimental conditions the alloy layer is oxidized
up to the thickness formed after 9 hr-treatment. Nevertheless, the thin oxide
layer formed strongly retarded further oxidation.
Here, considering the latter stage of the oxidation, it would be, at first,
necessary to clarify the relation between the oxidation of this alloy layer and the
146 Keizo NlsHIDA and Mitsuo HACHINOHE 8
25
藍
g這
蕊
ヨ。1
.二
塁
6 s1
黶D
[.…マ.. 一
@ 口
Silicenizlng(mgicm’)
Fig. 14 Siliconizing vs. oxidation
Toe
70
50
3e
20
10:s
蓉
s.萎
琶
.9
6 1.O
O.7
0.s
o,]
o.i U
Fig. 15
1 2 3 4 5 6 Siticaml:ing Cmg!cma)
Oxidation vs siliconizingcurvefor Ta sheet at 10000C
diffusion behavior of Si atoms in this layer. The observation that in the latter
stage the oxidation is not too extensively retarded even with a relatively thick
alloy layer will be expiained by another mechanism. lt is generally assumed that
Si atoms migrate into Ta metal and then the released Ta atoms at the interface
will combine with oxygen atoms because oxygen atoms readily migrate throughthe oxide. lf Si atoms oniy migrate towards Ta in the alloy layer and Ta atoms
only combine with oxygen, then Si atoms will be forced to migrate into the Ta
metal leaving oniy Ta oxide behind, so that the TaSi, layer will not change its
thickness even after oxidation for a long time.
we then examined whether the above stated assumption of the oxid. ation of
alloy layers was valid by using 49 hr-treated test pieces. However, th’e change
in the thickness of alloy layer could not be clearly recognized before and after
the oxidation for about l hr because of the small variation of each alloy layer
formed under the same conditions and the irregularity of the alloy thickness at
various positions of the same test piece. Accordingly, it is suggested that the
flux of Si atoms will decrease with the thicker alloy layer on account of the
decrease・in the concentration gradient, so that Ta atoms remaining on the surfaces
per unit time will be increasingly decreased by thicker layers, resulting in the
decrease of the oxidation of the alloy.
Since it is recognized from the EPMA penetration curve in the sectioned ailoy
layer that there are some amount of Si even in the oxide layer and that Si is
much enriched in the alloy near the alloy/oxide interface, the above assumption
will be partly valid.
5. Conclusion
Ta sheets were siliconized in the pure Si vapor in an evacuated quartz ampoule
up to 49 hr at 10000C, and then oxidized in flowing air in order to compare with
the results of oxidation of pure Ta sheets for 15 min at IOOOOC. The results
obtained were as follows:
(1) Siliconizing of Ta sheets obeys a parabolic rate law and shows a two-stage
behavior, the first is formation of a lower silicide layer (Ta,Si,) with a slower
9 On the Atm◎spheric Oxidation o正Pure and Siliconized Ta M、etal Sheets at 1000。C 147
rate, and next after about 9 hr the second stage corresponding to the formation
of a higher silicide layer (TaSi,) with a higher growth rate occurs.
(2) Oxidation of pure Ta sheets showed an anomalous behavior in which the
corners of a test piece were strongly oxidized and curled back in spite of the
fact that the center of the sheets were of a compact type. However,both oxides
show the same compound (Ta,O..) with different growth orientations at each po-
sitions. By using alumina markers this chemical process was determined to
proceed with the inward diffusion of oxygen atoms through Ta oxide.
(3) Oxidation of siliconized Ta sheet showed a greater resistance with the
increase in the amount of siliconizing and the behavior of oxidation was divided
into two stages corresponding to the formation of two kinds of silicides. The
former stage showed a large decrease of corrosion because of the protection of
oxide against further oxidation and the latter one did not show too large a
resistance and could be controlled with the inward diffusion of Si atoms through
the silicide layer after the formation of an initial oxide layer. ln the present
experiment the oxidation of Ta sheets showed a retardaition down to about one
hundredth on account of the siliconized layer formed in 49 hr at 10000C.
Acknowledgement
The authors wish to express their hearty thanks to the Shinetsu Chemical
Industry Co. Ltd. for supplying high purity Si metal used in the experiment.
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
References
Peterson R. X. W. H. Fassell, Jr. and M. E. Wadsworth: Trans. AIME, 20日目(1954), 1038.
Gulbransen E. A. and K. F. Andrew:Trans. AIME, 188 (1950), 586.
Bakish R.: J. Electrochem. Soc. 105 (1958), 71.
Michael A. B. : “The Oxidation of Co-base and Ta-base Alloys”, Reactiye Metals, Vol. 2,
Metallurgy Soc. Conf.,工959, Interscience Publisher Inc., New York.
Arbrecht W. A. W. D. Klopp, B. G. Koeland, and R. 1. Jaffee: “Reaction of Pure Ta
with Air, N2 and 02” AIME Symposium on Preparation, Purification and Properties
of Refractory Metals, Chicago, Nov. (1959).
Dooly R. B. and J. Stringer: Corrosion Science, 10 (1970), 265.
Dooly R. B. and J. Stringer: X Less-Common Metals, 24 (1971), 139.
Klopp W. D. D. J. Maykuth, and R. 1. Jaffee: Trans. ASM,1 53 (1961), 137.
Kubaschewski O. and B. E. Hopkins: “Oxidation of Metals and Alloys”, Butterworths,
London (1962), 2nd ed., 24.
H’ansen M. and K. Anderko: “Constitution of Binary Alloys” McGrow-Hill, New York (1958), 1194.
Kubaschewski O. and E. LL. Evans : “ Metallurgical Thermochemistry ”, An lnternational
Series of Monographs edited by G. V. Raynor, Pergamon Press, LoBdon (1956), 2nd
ed., 272; 274.
Powers R. W. and M. V. Doyle: L Appl. Phys. 30 (1959), 514, and Trans. AIME, 209
(1957), 1285.