J. Am. Ceram. Soc., 1–4 (2012)
DOI: 10.1111/j.1551-2916.2012.05224.x
©
2012 The American Ceramic Society
ournal
J
Synthesis of Lithium Metasilicate Powders at Low Temperature
via Mechanical Milling
‡
‡
‡,†
Aixia Yang, Huijun Wang, Wei Li, and Jianlin Shi
‡,§
‡
School of Materials Science and Engineering, East China University of Science and Technology,
30 Mei long Road, Shanghai 200237, China
1
§
Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Ding Xi Road, Shanghai 200050, China
The Li
low temperature via mechanical milling process. By using
LiOH·H O and tetraethyl orthosilicate (TEOS) as raw materi-
als, Li SiO powder with grain size of about 100 nm could be
2
SiO
3
powder has been successfully synthesized at
powder is not very good and it would completely transform
to Li Si at higher temperature (900°C).
Recently, Zhang et al. synthesized pure Li
with high thermal stability at a very low temperature of 40°C
via sol-gel route by using C ·OLi and tetraethyl orthosili-
cate (TEOS) as raw materials. This result suggests that by
choosing suitable raw materials, Li SiO powder might be
2
2 5
O
1
1
2
2 3
SiO powder
2
3
obtained at room temperature (~20°C) after mechanical milling
for 120 h. This nano Li SiO powder shows excellent thermal
2 5
H
2
3
stability that no decomposing reaction or phase change would
happen even after calcined at 900°C for 4 h. Experiments show
that high concentration of the raw materials is helpful to the
2
3
obtained at lower temperatures. The reaction process of
LiOH and TEOS could be described as follows:
forming of Li
materials is too low, no Li SiO phase could be obtained. The
2 3
SiO phase. When the concentration of the raw
2
3
investigation also shows that small content of B
accelerate the densifying speed of Li SiO ceramics and
decrease the thermal stability of Li SiO phase.
2
O
3
could
5SiOðOC2H5Þ þ 12H2O ¼ 5SiO2 þ 12C2H5OH
ð1Þ
ð2Þ
4
2
3
2
3
2
LiOH þ SiO2 ¼ Li2SiO3 þ H2O:
I. Introduction
SiO has attracted significant attention
due to its special performance in several fields. For exam-
ple, Li SiO is strongly considered as a kind of breeder mate-
which could be applied in the fusion reactor because
of its good tritium solubility, thermo-physical, physical and
As we know, the first step (reaction 1) could be finished
under room temperature very easily, so the whole reaction
was controlled by the second step (reaction 2). According to
the law of thermodynamics, for any reaction:
N recent years, Li
2
3
I
2
–3
3
1
rial
DGh ¼ DHh
ꢀ TDSR;T:
ð3Þ
R;T
R;298K
4–7
chemical stability at high temperature.
tial fast-ion conductor material since [SiO
ture is found in lithium metasilicate. Furthermore, it can
It is also a poten-
] tetrahedral struc-
GhR,T: standard Gibbs free energy of formation; H R: stan-
dard enthalpy; DSR,T: entropy change. H, T, and S are state
functions.
h
4
8
,9
be used for CO captures due to its fine sorption effect for
2
10,11
CO
2
.
According to a specified formula (3) and thermodynamical
data (Table I), the Gibbs free energy of the reaction (2) were
Up to now, many different processes, such as solid-state
reaction, precipitation, modified combustion and sol-gel,
5
2,4
10
h
calculated: DG
R,25°C
= ꢀ54.96<0. This result indicates that
–13
have been successfully applied to synthesize Li SiO .
2
the reaction can occur spontaneously at room temperature.
On the basis of the calculation result, the objective of the
present work is to synthesis pure Li SiO powders at a very
3
Solid-state reaction process is the simplest way to prepare
Li SiO powder by calcining the mechanical mixture of silica
2
3
2
3
and a lithium compound. However, this simplest process has
some serious shortcomings including high calcination temper-
atures (700°C–1000°C), low purity, and serious aggregation
of the product. To overcome these drawbacks, wet chemical
processes, especially the combustion and sol-gel processes,
low temperature (~20°C) via mechanical milling using LiOH
and TEOS as precursor. The factors which would influence
the reaction process such as temperature and milling time on
the powder have also been investigated.
2
have been widely investigated in recent years. Cruz et al.
II. Experimental Procedure
studied the effects of temperature on Li
fied combustion method using LiOH and H
sor. They synthesized Li SiO phase with a few impurities
2
SiO
3
phase by modi-
2
SiO as precur-
3
(1) Material Preparation
Lithium hydroxide (LiOH·H O) and tetraethyl orthosilicate
2
3
2
(
et al.
Li
2
Si
2
O
5
, SiO
2
) at 450°C and pure Li
2
SiO
3
at 650°C. Zhang
(TEOS, Si-(OC H ) ) were selected as starting materials.
2
5 4
1
0
obtained Li SiO powder at 450°C via sol-gel pro-
2
3
Stoichiometric proportions of the above raw materials with
different concentrations were mixed in distilled water medium
using zirconia balls as milling media at room temperature
2 3
cess. Unfortunately, the thermal stability of this Li SiO
(
~20°C) for 12, 24, 72, and 120 h. The rpm of the devices we
are using can reach 50 rpm/min. The concentrations are
listed in the following table (Table II). After milling, the wet
mixture was dried in air. The obtained powders were divided
into three parts. One part was characterized directly. Another
part was calcined at different temperatures to investigate the
thermal stability. The third part that was milled for 120 h
A. Borrell—contributing editor
Manuscript No. 30850. Received December 31, 2011; approved March 21, 2012.
†
1