Low-temperature glass bonding for development of silicon carbide/zirconium tungsten oxide porous ceramics with near zero thermal expansion coefficient

Article abstract of DOI:10.1111/j.1551-2916.2011.04520.x

Near zero thermal expanding porous ceramics are useful in many applications in advanced manufacturing techniques, especially electronics engineering. Zirconium tungsten oxide (ZrW₂O₈) has been expected to be an excellent negative thermal expansion material for reducing thermal expansivity of composites. However, at 777°C ZrW₂O₈ decomposes to ZrO₂ and WO₃, which have positive thermal expansion coefficient and limit applications of ZrW₂O₈. Therefore, a low temperature sintering technique is required to use ZrW ₂O₈ in zero thermal expanding composite. This work develops a low temperature glassy bonding agent to fabricate near zero thermal expanding SiC/ZrW₂O₈ porous ceramics. The results show ZrW₂O₈ reacts with alkali and alkaline earth oxides at lower temperatures than the decomposition temperature of ZrW₂O ₈. Nevertheless, ZrW₂O₈ is inert with Al ₂O₃, B₂O₃, and SiO₂. By using borosilicate glass (B₂O₃-SiO₂) as a bonding agent, SiC/ZrW₂O₈ porous ceramics are sintered at temperatures lower than the decomposition temperature of ZrW₂O ₈ and have near zero thermal expansion coefficient (-0.2×10^-6 K^-1). No reaction is found between the glassy bonding agent and ZrW₂O₈ or SiC.

Full text of DOI:10.1111/j.1551-2916.2011.04520.x

J. Am. Ceram. Soc., 94 [5] 1354–1356 (2011)
DOI: 10.1111/j.1551-2916.2011.04520.x
r 2011 The American Ceramic Society
ournal
J
Low-Temperature Glass Bonding for Development of Silicon Carbide/
Zirconium Tungsten Oxide Porous Ceramics with Near Zero Thermal
Expansion Coefficient
Anurat Poowancum,w Koji Matsumaru, and Kozo Ishizaki
Department of Materials Science and Engineering, School of Mechanical Engineering, Nagaoka University of
Technology, Nagaoka, Niigata 940-2188, Japan
Near zero thermal expanding porous ceramics are useful in
many applications in advanced manufacturing techniques, espe-
cially electronics engineering. Zirconium tungsten oxide
(ZrW2O8) has been expected to be an excellent negative ther-
mal expansion material for reducing thermal expansivity of
composites. However, at 7771C ZrW2O8 decomposes to ZrO2
and WO3, which have positive thermal expansion coefficient and
limit applications of ZrW2O8. Therefore, a low temperature
sintering technique is required to use ZrW2O8 in zero thermal
expanding composite. This work develops a low temperature
glassy bonding agent to fabricate near zero thermal expanding
SiC/ZrW2O8 porous ceramics. The results show ZrW2O8 re-
acts with alkali and alkaline earth oxides at lower temperatures
than the decomposition temperature of ZrW2O8. Nevertheless,
ZrW2O8 is inert with Al2O3, B2O3, and SiO2. By using boro-
silicate glass (B2O3–SiO2) as a bonding agent, SiC/ZrW2O8
porous ceramics are sintered at temperatures lower than the de-
composition temperature of ZrW2O8 and have near zero ther-
In previous studies, the porous ceramics are sintered at 8501C by
using SiC as a positive thermal expansion material and LiAlSiO4
or ZrW2O8 as a negative thermal expansion material bonded by
a commercial glassy material.13,14 The results show LiAlSiO4
and ZrW2O8 reacts with the glassy bonding agent and forms
new phases, consequently, thermal expansivity of the composites
is inconsistent with the estimated values.13,14
The aim of this work is to develop a low temperature glassy
bonding material for fabrication of near zero thermal expanding
SiC/ZrW2O8 porous ceramics. The reaction between ZrW2O8
and the new glassy bonding agent, as well as, thermal exp-
ansivity of SiC/ZrW2O8 porous ceramics are examined.
II. Experimental Procedures
Solid-state reaction was used to synthesize ZrW2O8. A mixture
of ZrO2 (Sigma Aldrich, St. Louis, MO) and WO3 (Sigma Ald-
rich) in a stoichiometric ratio was milled in a 100 mL polyeth-
ylene pot containing 150 g of zirconia balls (4 mm diameter)
with rotating speed of 500 rpm for 24 h. The powder mixture
was heated to 12001C for 9 h in a covered platinum crucible,
then water-quenched to room temperature. The synthesized
ZrW2O8 was milled by alumina mortar and sieved into sizes
smaller than 25 mm.
Starting materials used to prepare thermal treatment were
Li2CO3 (Nacalai Tesque, Kyoto, Japan), Na2CO3 (Sigma Ald-
rich), CaCO3 (Sigma Aldrich), ZnO (Kojundo Chemical Lab.,
Saitama, Japan), Al2O3 (Strem Chemicals, Newburyport, MA),
H3BO3 (Sigma Aldrich) and SiO2 (Nacalai Tesque). Each pow-
der was mixed with ZrW2O8 by alumina mortar in stoichio
metric ratio as the following possible reactions:
mal expansion coefficient (ꢀ0.2 ꢁ 10ꢀ6 ꢀ1). No reaction is
K
found between the glassy bonding agent and ZrW2O8 or SiC.
I. Introduction
EAR zero thermal expanding porous ceramics are required
N
for many applications, especially in precision technologies
to avoid dimension change due to temperature variation.1 Com-
bination of positive and negative thermal expansion materials
have been proposed to fabricate near zero thermal expanding
materials.2–7
Silicon carbide (SiC) porous ceramics are the topic of intense
study because they have low thermal expansion coefficient and
excellent mechanical properties.8 Zirconium tungsten oxide
(ZrW2O8) is expected to be a useful negative thermal expansion
material, because it shows isotropic negative thermal expansion
for a wide temperature range.9–11 The disadvantage of ZrW2O8
is that, it is stable in the limited temperature range between
11051 and 12571C,11 can be quenched to room temperature, is
metastable to around 7771C after quenching,11 and decomposes
above this temperature into ZrO2 and WO3.11 Hence, quenching
method is used to preserve ZrW2O8 phase.2–7 However, serious
problem of quenching process is fracture due to crack formation
by rapid cooling.12 Therefore, a low temperature sintering tech-
nique is required for using ZrW2O8.
2Li2O þ 3ZrW2O8 ! 2Li2ZrW3O12 þ ZrO2
2Na2O þ 3ZrW2O8 ! 2Na2ZrW3O12 þ ZrO2
2CaO þ ZrW2O8 ! 2CaWO4 þ ZrO2
2ZnO þ ZrW2O8 ! 2ZnWO4 þ ZrO2
4Al2O3 þ 5ZrW2O8 ! 2Al4W5O21 þ 5ZrO2
4B2O3 þ 5ZrW2O8 ! 2B4W5O21 þ 5ZrO2
SiO2 þ ZrW2O8 ! ZrSiO4 þ 2WO3
(1)
(2)
(3)
(4)
(5)
(6)
(7)
Our research group has developed a low temperature sinte-
ring technique by using a glassy material as a bonding agent.13,14
The mixed powders were pressed uniaxially under 10 MPa to
form cylindrical shape with 10 mm diameter, then heated up to
7001C for 1 h.
T. Ota—contributing editor
Borosilicate glass (B2O3–SiO2) was prepared by mixing
H3BO3 and SiO2 in mass fraction 0.76 and 0.24, respectively,
the glass in this fraction melts at 7001C.15 The powders of
H3BO3 and SiO2 were mixed in a 100 mL polyethylene pot
Manuscript No. 29239. Received January 23, 2011; approved February 19, 2011.
wAuthor to whom correspondence should be addressed. e-mail: anurat4@yahoo.com
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and 150 g of zirconia balls (4 mm diameter) with rotating speed
of 150 rpm for 2 h. The mixed powder was melted at 12001C for
3 h then quenched to room temperature by dipping alumina
crucible into water. Borosilicate glass was crushed by alumina
mortar after that milled by planetary ball mill, using a 25 mL
zirconia jar and five zirconia balls (12 mm diameter) with
rotating speed of 2800 rpm for 15 min. The borosilicate glass
powder was sieved into sizes smaller than 45 mm.
The powders, SiC (Showa Denko K.K., Tokyo, Japan) with
particle mesh size #90, ZrW2O8 and borosilicate glass were
mixed in volume fraction 0.12, 0.44, and 0.44, respectively, by
alumina mortar for 20 min. The powder mixture was pressed by
uniaxial dry press into a parallelepiped shape under 30 MPa for
1 min, and cold isostatically pressed under 300 MPa for 1 min.
The green body was sintered at 7001C, heating rate 5 K/min,
and soaking time 1 h. The porosity was measured by
Archimedes method. The sintered sample was cut into a size
of 3.5 mmꢁ 3.5 mm ꢁ 50 mm for thermal expansivity measure-
ment. Sintered porous ceramics were expected to have zero
thermal expansion coefficient by Eq. (8):14
ac ¼ aSiCvSiC þ agvg þ aZrvZr
(8)
where ac, aSiC, ag, and aZr are thermal expansion coefficient of
sintered porous ceramics, SiC (4.0ꢁ 10ꢀ6 Kꢀ1 at RT-8001C16),
borosilicate glass (7.8ꢁ 10ꢀ6 Kꢀ1 at ꢀ151–1901C) and ZrW2O8
(ꢀ8.8 ꢁ 10ꢀ6 Kꢀ1 at ꢀ2531–1501C17,18), respectively, vSiC, vg,
and vZr are the volume fraction of each raw material. The real
value of aSiC in the temperature range of our interest is lower
than this value, because the value is normally positively increas-
ing function with respect to temperature. Therefore, the value
used is safe estimation for our work.
X-ray diffraction (XRD, SHIMADZU XRD-6000t, Chukyo,
Kyoto, Japan) with CuKa radiation was used for analyzing
reactions between glass composition and ZrW2O8. The micro-
structure of the sintered sample was observed by scanning electron
microscopy (SEM, KEYENCE VE 7800t, Higashiyodogawa,
Osaka, Japan). Thermal expansivity of the sintered sample was
evaluated by a dilatometer (ULVAC DLY 9200t, Yokohama,
Kanagawa, Japan) from ꢀ151 to 1901C by using a quartz support
and a quartz rod under helium atmosphere.
Fig. 1. X-ray diffraction (XRD) spectra of thermal treatment samples;
(a–g) The powder mixtures of ZrW2O8 with Li2O, Na2O, CaO, ZnO,
Al2O3, B2O3, and SiO2, respectively. The XRD peaks of the reacted
phases can be detected in (a–d). There are not any peaks detected for
reacted phases in (e–g).
bump, which consists of two dents at around 1001C and at
around 1601C.
III. Results
The X-ray diffractograms of heat-treated samples are seen in
Figs. 1(a) – (g), and are for the powder mixtures of ZrW2O8 with
Li2O, Na2O, CaO, ZnO, Al2O3, B2O3, and SiO2, respectively.
Figures 1(a) and (b) show the XRD peaks of the reacted phases
between alkali oxides (Li2O and Na2O) and ZrW2O8. Figure
1(a) shows the XRD peaks of Li2ZrW3O12 and very small peaks
of Li2WO4. Figure 1(b) shows Na2ZrW3O12 peaks and very mi-
nor peaks of Na2W2O7. Figures 1(c) and (d) show the XRD
peaks of the reacted phases between alkaline earth oxides (CaO
and ZnO) and ZrW2O8. The XRD peaks of CaWO4 and
ZnWO4 are detected in Figs. 1(c) and (d), respectively. No
evidence of reaction can be found in Figs. 1(e–g).
IV. Discussion
Thermal expansion coefficient of sintered SiC/ZrW2O8 porous
ceramics is ꢀ0.2 ꢁ 10ꢀ6 Kꢀ1 (ꢀ151 to 501C), as calculated from
Figure 2 shows the XRD pattern of SiC/ZrW2O8 porous ce-
ramics after sintered at 7001C, by using borosilicate glass as a
bonding agent. Only XRD peaks of ZrW2O8, SiC, and WO3 are
detected. There is no evidence of reaction between SiC, ZrW2O8,
and the glassy bonding agent.
Figure 3 shows SEM micrograph of sintered SiC/ZrW2O8
porous ceramics. The SEM micrograph shows borosilicate glass
is melted and has good wettability with particles of SiC and
ZrW2O8, these particles are bonded well by the glassy bonding
agent.
The results of thermal expansivity measurement are seen in
Fig. 4, solid and dashed lines show the empirical relative expan-
sion and the calculated value, respectively. Relative expansion of
sintered porous ceramics with 23 vol% porosity agrees well with
the expected value. Thermal expansion curve in Fig. 4 has a
Fig. 2. XRD pattern of SiC/ZrW2O8 porous ceramics after sintered at
7001C, by using borosilicate glass as a bonding agent. There are not any
reacted phases between SiC, ZrW2O8 and the glassy bonding agent.

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thermal expansion materials. These are the reasons why SiC/
ZrW2O8 porous ceramics have near zero thermal expansivity,
which agrees well with the expected value as illustrated in Fig. 4.
A bump in Fig. 4 has two dents at around 1001C and at around
1601C. The dent at around 1601C corresponds to a ZrW2O8
phase transformation from a-ZrW2O8 to b-ZrW2O8.11 How-
ever, the cause of another dent at around 1001C is not clear.
Kanamori et al.12 fabricated ZrW2O8/SiO2 composites. They
got a similar behavior. Unfortunately, they could not explain the
reason why the composites had a dent at this temperature.
V. Conclusions
In this study, a low temperature glassy bonding agent for near
zero thermal expanding porous ceramics is developed. Near zero
thermal expanding SiC/ZrW2O8 porous ceramics were sintered
by using borosilicate (B2O3–SiO2) glass as a bonding agent with
SiC and ZrW2O8 as positive and negative thermal expansion
materials, respectively. The porous ceramics are sintered at
temperatures lower than the decomposition temperature of
ZrW2O8, and have near zero thermal expansion coefficient.
Borosilicate glass does not react and shows good wettability
with ZrW2O8 and SiC. Alkali and alkaline earth oxides have
reactions with ZrW2O8 at lower temperatures than the decom-
position temperature of ZrW2O8. No reaction was observed
between ZrW2O8 and Al2O3, B2O3, or SiO2 at the sintering
temperatures.
The development of the low temperature glassy bonding
agent in this work opens new applications of ZrW2O8.
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