Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Content or effect of a constituent of a liquid mixture
Reexamination Certificate
1999-03-19
2002-03-12
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Content or effect of a constituent of a liquid mixture
C073S061750, C310S321000, C310S324000
Reexamination Certificate
active
06354144
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a ZrO
2
porcelain and a waterproof ZrO
2
member which are to be used as members of a fluid sensor or the like
A ZrO
2
porcelain is widely used as a material comprising an vibrating sheet which is used for disposing a piezoelectric/electrostrictive element in a fluid sensor. The fluid sensor usually comprises a sensor unit which consists of a plate like member
2
having a piezoelectric/electrostrictive element
10
mounted thereon and a cylindrical member
1
which supports the sensor unit, for example, as shown in FIG.
5
. The fluid sensor is configured to allow a sample fluid to be introduced into the cylindrical member
1
and used to measure, for example, a degree of deterioration of a battery by detecting a viscosity, density of the electrolyte or a specific compound in the electrolyte. Both the plate like member
2
and the cylindrical member
1
are made of ZrO
2
. Ordinarily used as such, a ZrO
2
is a partially stabilized ZrO
2
which contains 3 to 4 mol % of yttria.
However, the ZrO
2
which contains 3 to 4 mol % of yttria poses a problem that it is low in long-term durability and reliability, though it is sufficient in its strength. Speaking concretely, it poses problems described below when it is kept in contact with a liquid or a gas which contains a liquid vapor for a long term, for example, in a condition used as a member of a fluid sensor.
When the fluid sensor is used to evaluate deterioration of a battery, for example, it evaluates a degree of deterioration by utilizing a definite relationship of a viscosity, density of a deteriorated electrolyte of the battery versus a concentration of sulfuric acid and a fact that a concentration of sulfuric acid changes in an electrolyte as the battery is deteriorated. In this case, an acid solution used as the electrolyte is kept in direct contact with the vibrating sheet and the cylindrical member. The vibrating sheet and the cylindrical member may be eroded when they are kept in contact with the acid solution continuously for a very long term, for example, several to some tens of years though no problem is posed in use for a relatively short term. The inventor et al. conducted accelerated tests by keeping vibrating sheet of ZrO
2
porcelains in continuous contact with 40% sulfuric acid at 80° C. and found a problem that a porcelain containing yttria at 3 mol allowed the sulfuric acid to leak to an opposite surface of the surface where sulfuric acid contact in Five to thirty days and a porcelain containing yttria at 4 mol allowed the sulfuric acid to leak to a side opposite to an vibrating sheet in ten to Forty days.
It is considered that the leakage is traced to gradual transformation of a tetragonal phase, out of the ZrO
2
crystalline structures, into a monoclinic phase which is caused when ZrO
2
is left standing in a liquid or a gas containing a liquid vapor.
Though it can be considered to change the crystalline structure of ZrO
2
into a cubic crystal which is stable in a liquid or a gas containing a liquid vapor in order to avoid such inconvenience, the cubic crystal has low toughness and is fragile, thereby posing a problem that cracks
11
are formed as shown in
FIG. 6
at portions of an integral structure consisting of an vibrating sheet and a cylindrical member on which stresses are concentrated.
Furthermore, there is available a method which makes a ZrO
2
porcelain stable in a liquid or a gas containing a liquid vapor by reducing a particle size of a raw material powder or using an additive, such as magnesia or alumina. However, this method poses a problem that it makes stability of the ZrO
2
porcelain insufficient and requires high temperature to sinter a piezoelectric/electrostrictive element which is disposed on a vibrating sheet, thereby enlarging the particle size and lowering the stability.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the circumstances described above and has an object to provide a ZrO
2
porcelain which is not only stable but also tough, can hardly be eroded and has sufficient strength in a liquid or a gas containing liquid vapor.
That is, the present invention provides a ZrO
2
porcelain comprising a ZrO
2
porcelain flexible member having at least a part which is brought into contact with a liquid or a gas containing a liquid vapor,.wherein the contact part has a relative density (bulk density/theoretical density) not lower than 95% and contains a cubic crystal at a ratio not lower than 75%.
In the ZrO
2
porcelain, it is preferable that the ZrO
2
flexible member consists of a contact part and a substrate adjacent to the contact part, and that the substrate is composed of a tetragonal crystal or a mixture phase consisting of a cubic crystal and a tetragonal crystal or a cubic crystal, a tetragonal crystal, and a monoclinic crystal. Furthermore, it is preferable that the contact part covers at least one surface of the substrate and that a thickness of the contact part is 0.2 to 2 times of that of a thinnest portion of the substrate.
The ZrO
2
porcelain may consist of a cylindrical member made of a ZrO
2
porcelain and a ZrO
2
porcelain flexible member which is composed by disposing a contact part at least on one surface of a plate like member consisting of the substrate, and having an integral structure obtained by integrating the ZrO
2
porcelain flexible member with the cylindrical member which is a supporting member for the flexible member so that an end surface of the cylindrical member is brought into contact with the contact part disposed on the plate like member and the contact part closes an opening of the cylindrical member.
Furthermore, the ZrO
2
porcelain may consist of a cylindrical member made of a ZrO
2
porcelain and a ZrO
2
porcelain flexible member which is composed by disposing a contact part at least on one surface of a plate like member consisting of the substrate, comprise a connecting layer which is formed on at least one end surface of the cylindrical member and has a configuration which is the same as that of the contact part, and having an integral structure which is obtained by integrating the ZrO
2
porcelain flexible member with the cylindrical member which is a supporting member for the flexible member so that the connecting layer is brought into contact with the contact part disposed on the plate like member and the contact part closes an opening of the cylindrical member.
Furthermore, the ZrO
2
porcelain may consist of a cylindrical member made of a ZrO
2
porcelain and a ZrO
2
porcelain flexible member which is a plate like member consisting of the contact part, and have an integral structure obtained by integrating the ZrO
2
porcelain flexible member with the cylindrical member which is a supporting member for the flexible member so that an end surface of the cylindrical member is brought into contact with the plate like member and the contact part closes an opening of the cylindrical member.
Furthermore, the ZrO
2
porcelain may consist of a cylindrical member made of a ZrO
2
porcelain and a ZrO
2
porcelain flexible member which is a plate like member consisting of the contact part, comprise a connecting layer which is formed on at least one end surface of the cylindrical member and has the same configuration as that of the contact part, and have an integral structure obtained by integrating the ZrO
2
porcelain flexible member with the cylindrical member which is a supporting member for the flexible member so that the connecting layer is brought into contact with the plate like member and the contact part closes an opening of the cylindrical member.
For the ZrO
2
porcelain according to the present invention, it is preferable to dispose a contact part which has a relative density (bulk density/theoretical density) not lower than 95% and contains a cubic crystal at a ratio not lower than 75%, on inside walls of a space formed by the ZrO
2
porcelain flexible member and the cylindrical member which is a supporting memb
Hirota Toshikazu
Nakao Shigeki
Shibata Kazuyoshi
Takeuchi Yukihisa
Burr & Brown
Larkin Daniel S.
NGK Insulators Ltd.
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