JPH10241702A - Fuel electrode of solid electrolyte type electrochemical cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel electrode of a solid electrolyte type electrochemical cell which can enhance electrode reaction property and suppress shrinking property, while maintaining matching property of thermal expansion with solid electrolyte and high conductivity. SOLUTION: By a constitution, wherein a fuel cell 2 is composed of a metal parts 2a comprising Ni, Co, or its alloy, a stabilized zirconia part 2d such as YSN (stabilized zirconia with Y2 , O3 dissovled), an oxidized compound part 2b with a smaller coefficient of thermal expansion than that of solid electrolyte 3, comprising a stabilized zirconia such as YSZ, and a cement with a hole 2c, the fuel cell is made so that shrinkage when deoxidizing is suppressed by the firmly stabilized zirconia part 2d, while a surface area of a three-phase boundary surface S3 to produce an electrochemical reaction is substantially increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel electrode for a solid oxide electrochemical cell used for a solid oxide fuel cell, a solid oxide steam electrolyzer, and the like.

[0002]

2. Description of the Related Art In an electrochemical cell of a solid oxide fuel cell, a solid electrolyte is sandwiched between a porous fuel electrode and an air electrode, and the above-mentioned fuel electrode is formed on a porous plate-like or tubular base. It has a structure in which a plurality are arranged to be in contact with each other.

In such an electrochemical cell, an oxidizing gas such as air or oxygen flows through the outside of the base, and a fuel gas such as hydrogen or methane flows through the inside of the base, while the temperature is raised to about 1000 ° C. Then, the fuel gas permeates the base and the fuel electrode, and the oxidizing gas permeates the air electrode, and these gases electrochemically react with the solid electrolyte to obtain electric power.

[0004] By the way, Ni and YSZ are mixed in the material of the fuel electrode in order to match the coefficient of thermal expansion with YSZ (stabilized zirconia in which Y ₂ O ₃ is dissolved) as the material of the solid electrolyte. Cermet is mainly used. Since this cermet generally has a Ni content in the range of 30 to 50%, it is difficult to obtain high conductivity.
For this reason, for example, Ni-3Al ₂ O ₃ .2SiO ₂ -based cermets (Japanese Patent Application No. 3-41855) and Ni-T
As in the case of a ₂ O ₅ cermet or Ni—ZrSiO ₄ cermet (Japanese Patent Application No. 7-308773), Y
By using a cermet in which the Ni content is increased by using an oxide compound (ceramic) having a lower coefficient of thermal expansion than that of SZ for the fuel electrode, it is possible to achieve both compatibility of thermal expansion with the solid electrolyte and high conductivity. Proposed.

[0005]

For example, in a flat-type electrochemical cell for a solid oxide fuel cell expected to have a high energy density, it is difficult to manufacture the electrochemical cell with a scale-up (large area). In order to reduce as much as possible the thermal stress that has been applied to the interface between the anode and the solid electrolyte during operation, rigorous matching of the coefficient of thermal expansion between the anode and the solid electrolyte has been studied, and the internal resistance has been studied. In order to suppress the increase in the fuel electrode as much as possible, various studies have been made on increasing the conductivity of the fuel electrode. As a result, Ni-3Al ₂ O _3.
2SiO ₂ cermet or the like (Japanese Patent Application No. 3-41855, etc.), Ni-Ta ₂ O ₅ based cermet and Ni-ZrSi
It has been proposed to use a cermet such as an O ₄ cermet (Japanese Patent Application No. 7-308773) for the fuel electrode.

However, due to the internal resistance of the electrochemical cell,
Is the ohmic resistance and electrode resistance depending on the conductivity of the electrode.
3Al_TwoO_Three ・ 2S
iO _Two, Ta_TwoO_Five, ZrSiO_FourOxidation such as
Compounds do not have the effect of accelerating the electrode reaction.
At the anode made of cermet using oxidized compound,
It has been difficult to further improve the performance of the electrochemical cell.

[0007] In an electrochemical cell using a cermet as a fuel electrode as described above, the fuel electrode sometimes contracts when the fuel electrode is reduced with fuel gas during operation. For example, Ni-40 vol.% MgAl ₂ O ₄ (thermal expansion coefficient: about 10 × 10 ⁻⁶ / ° C., conductivity: about 2000 S / c)
In the cermet of m), as shown in FIG. 11, the cermet shrinks immediately after the start of the reduction. When such a cermet is used for the fuel electrode, the vicinity of the fuel electrode is deformed during operation, which may not only cause a decrease in power generation performance, but also may cause cell damage in the worst case. .

The cause of such shrinkage is considered to be that when NiO is reduced to Ni during cell operation, the volume shrinks (about 40%) while drawing in the oxidizing compound as the aggregate. For this reason, if the skeleton of the oxidizing compound serving as the aggregate is strong, the amount of contraction when NiO is reduced to Ni remains as a gap as it is, resulting in a porous body having gas permeability, but as an aggregate. Since the volume shrinks while the oxidizing compound is being drawn in, the shrinkage during the reduction from NiO to Ni does not remain much as a gap, and there is also a problem that the gas permeability decreases.

The above-mentioned problem is not limited to the fuel electrode of the electrochemical cell of the solid oxide fuel cell, but is also the fuel electrode of the solid electrolyte electrochemical cell such as the fuel electrode of the electrochemical cell of the solid electrolyte steam electrolyzer. If so, it can happen in the same way as described above.

From the above, it can be seen that the present invention maintains the thermal expansion consistency and high conductivity with the solid electrolyte,
An object of the present invention is to provide a fuel electrode of a solid electrolyte type electrochemical cell capable of improving electrode reactivity and suppressing shrinkage during reduction.

[0011]

In order to solve the above-mentioned problems, the fuel electrode of the solid electrolyte type electrochemical cell according to the present invention comprises Ni, Co or an alloy thereof, stabilized zirconia, and the stabilized zirconia. And a cermet with an oxide compound having a smaller coefficient of thermal expansion.

[0012] In the fuel electrode of the solid electrolyte type electrochemical cell described above, the oxide compound is a silicate compound of a metal oxide and silicon oxide.

[Operation] At the interface between the fuel electrode and the solid electrolyte, the following reaction occurs.

[Formula 1] ^{_{H 2 + 1/2 O 2- → H}} 2 O + e -

That is, the hydrogen in the fuel gas that has passed through the pores of the fuel electrode reacts with the oxygen ions in the oxidizing gas that has passed through the pores of the air electrode and flowed through the solid electrolyte (stabilized zirconia). As a result, water vapor and electrons are generated, and the water vapor passes through the pores of the fuel electrode together with the fuel gas and is emitted to the outside, while the electrons flow through the metal part of the fuel electrode to obtain electric power. . Therefore, the above reaction occurs at the three-phase interface between the vacancy of the fuel electrode through which hydrogen and water vapor flow, the stabilized zirconia portion through which oxygen ions flow, and the metal portion of the fuel electrode through which electrons flow. As shown in FIG. 2B, the fuel electrode 2
At the three-phase interface S ₃ between the pores 2 c, the solid electrolyte (YSZ) 3, and the metal (Ni) portion 2 a of the fuel electrode 2. In FIG. 2B, reference numeral 2b denotes an oxide compound part having a smaller coefficient of thermal expansion than the solid electrolyte 3.

Therefore, as shown in FIG.
If to use the fuel electrode 2, further comprising a stabilized zirconia portion 2d, such as, the surface area of the three-phase interface S ₃ described above is increased greatly, it is possible to greatly improve the electrode reactivity.

Further, in the fuel electrode 2 having the stabilized zirconia portion 2d, even when NiO is reduced to Ni during operation, the stabilized zirconia portion 2d is strong, so that it does not significantly shrink. Therefore, the contractility at the time of reduction can be significantly suppressed.

For this reason, in the above-mentioned fuel electrode 2,
Since the volume of contraction during the reduction from NiO to Ni remains as it is and the pores 2c are reliably formed, the permeability of the fuel gas and the like is increased, and the electrode reactivity is further improved. Can be.

Incidentally, as a material of the above-mentioned metal part 2a,
In addition to Ni, Co and alloys of Ni and Co are listed.
I can do it. Further, as the stabilized zirconia portion 2d, Y
Not only SZ but also fully or partially stabilized to cubic
Zirconia may be used. In addition, the oxidized compound part 2b
Is a silicate compound of metal oxide and silicon oxide
And especially HfSiO_Four, Y_TwoSiO_Five, Zn
_TwoSiO_Four, SrAl (SiO_Four)_TwoLike metal
Silicate compound of oxide and silicon oxide, Yb _TwoSi
O_Five, Er_TwoSiO_Five, Dy_TwoSiO_Five, Gd_TwoSiO
_FiveLanthanoid metal oxides and silicon oxides
More preferably, it is a silicate compound with the above.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a fuel electrode of a solid oxide electrochemical cell according to the present invention is applied to a fuel electrode of an electrochemical cell of a solid oxide fuel cell will be described with reference to FIG. FIG. 1 is a schematic structural view of the main part.

In FIG. 1, 1 is a substrate, 2 is a fuel electrode, 3
Is a solid electrolyte, 4 is an air electrode, and 5 is an intermediate connector (interconnector).

The substrate 1 is porous and has a plate shape or a tubular shape. The fuel electrode 2 is porous and, as shown in FIG.
Alternatively, a metal part 2a made of these alloys and YSZ (Y
A stabilized zirconia portion 2d made of stabilized zirconia, such as stabilized zirconia in which ₂ O ₃ is dissolved;
It is composed of an oxidized compound part 2b made of an oxidized compound having a smaller coefficient of thermal expansion than the stabilized zirconia part 2c and a cermet having pores 2c, and a plurality of cermets are provided on the base 1 at predetermined intervals. The solid electrolyte 3 is made of stabilized zirconia such as YSZ, and is provided on the fuel electrode 2. The air electrode 4 is made of a perovskite-type composite oxide which is porous and exhibits stable high conductivity even in a high-temperature oxidizing atmosphere, and is provided on the solid electrolyte 3. The intermediate connector 5 is made of a La—Cr-based perovskite-type composite oxide or the like, and is connected between the single elements including the fuel electrode 2, the solid electrolyte 3, and the air electrode 4 so as to electrically connect the single elements. Is provided.

In such an electrochemical cell, an oxidizing gas 12 such as air or oxygen flows through the outside of the base 1, ie, the air electrode 4 side, and hydrogen or methane flows inside the base 1, ie, the fuel electrode 2 side. While circulating the fuel gas 11 such as
When the temperature is raised to about 1000 ° C., the fuel gas 11 penetrates the base 1 and the fuel electrode 2 and the oxidizing gas 12
Pass through the air electrode 4 and these gases 11 and 12 react electrochemically with the solid electrolyte 3 to obtain electric power.

At the time of this electrochemical reaction, since the fuel electrode 2 has the stabilized zirconia portion 2d, the pores 2c of the fuel electrode 2 and the fuel electrode 2 Stabilized zirconia part 2d or solid electrolyte 3 and fuel electrode 2
Since the surface area of the three-phase interface S ₃ in contact with the three-phase metal portion 2a of is increased, the electrode reactivity is very high.

Further, since the stabilized zirconia portion 2d is strong, as described above, even if it is reduced during operation, it does not significantly shrink, so that the shrinkage during reduction is very low. Become smaller.

Therefore, since the pores 2c are surely formed with the contracted volume during reduction remaining as a gap as it is, the permeability of the fuel gas 11 and the like is increased, and the electrode reactivity is further increased.

Therefore, according to the fuel electrode 2, it is possible to improve the reactivity of the electrode and to suppress the shrinkage during reduction while maintaining the consistency of the thermal expansion with the solid electrolyte 3 and the high conductivity. Can be planned.

In this embodiment, the case where the present invention is applied to a fuel electrode of an electrochemical cell of a solid oxide fuel cell has been described. The fuel electrode of the electrochemical cell can be applied in the same manner as in the present embodiment, and the same effect as in the present embodiment can be obtained.

[0028]

EXAMPLE The following experiment was conducted to determine the optimum composition ratio of the fuel electrode of the solid oxide electrochemical cell according to the present invention.

[Experimental Example 1: NiO-Y ₂ SiO ₅ -YS]
Z-based material] <Preparation of test piece> NiO, Y ₂ SiO ₅ , and YSZ raw material powders were mixed in various amounts, dried, classified to 150 μm or less, uniaxially press-formed, and heated at 1400 ° C. After sintering by heat treatment for a time, this was cut into a size of 3 × 4 × 14 mm to obtain a test piece.

<Experimental Method> Method of measuring thermal expansion coefficient The thermal expansion coefficient was calculated from the elongation at 1000 ° C. at a reference temperature of 25 ° C. in the air.

Method for Measuring Conductivity The conductivity was measured by a DC four-terminal method in a hydrogen reducing atmosphere at 1000 ° C., and the value at the time when the measured value no longer fluctuated (after several hours) was determined.

Method for Measuring Electrode Reaction Resistance The solid electrolyte formed by the doctor blade method was bonded to the fuel electrode and then sintered at 1400 ° C., and the result was measured by the AC impedance method, and the measurement results were plotted by the Cole plot method. Thus, the size of the arc appearing at that time was regarded as the value of the electrode reaction resistance.

Method of Measuring the Rate of Change in Length The test piece used in the measurement of the coefficient of thermal expansion was reduced at 1000 ° C. for 5 hours, and the rate of change in length before and after the reduction was determined.

<Experimental Results> Measurement Results of Thermal Expansion Coefficient FIG. 3 shows the measurement results of the thermal expansion coefficient. As can be seen from FIG. 3, as the amount of Y ₂ SiO ₅ increases, the coefficient of thermal expansion gradually decreases, and in particular, the amount of Y ₂ SiO ₅ increases by 30 vo.
l.%, the coefficient of thermal expansion of YSZ (about 10 × 10 ⁻⁶ /
° C).

Measurement Results of Conductivity FIG. 4 shows the measurement results of the conductivity and the coefficient of thermal expansion at that time. As can be seen from FIG. 4, NiO-30 vol.% Y ₂ S
When 10 vol.% of YSZ is blended in the iO ₅ system, the conductivity becomes smaller (about 2000 S / cm) as compared with the case where YSZ is not blended, but it has a sufficient size and the thermal expansion coefficient is hardly changed. It has been found.

FIG. 5 shows the measurement results of the electrode reaction resistance. As can be seen from FIG. 5, when 10 vol.% Of YSZ is blended in the NiO-30 vol.% Y ₂ SiO ₅ system, the electrode reaction resistance is reduced by half compared to the case where YSZ is not blended (about 3 Ω · cm ² ). 1.5 Ω · cm ² ).

FIG. 6 shows the measurement results of the length change rate. As can be seen from FIG. 6, YSZ is 1 in NiO-30 vol.% Y ₂ SiO ₅ system.
When 0 vol.% Was blended, it was found that the rate of change in length was very small (0.1% or less) and no reduction shrinkage occurred.

From the above results, it can be seen that depending on the size and shape of the cell,
However, the solid electrolyte is YS
In the case of Z, the amount of NiO is about 60 vol._TwoS
iO _FiveAbout 30vol.%, And the amount of YSZ
Approximately 10 vol.%, Consistency of thermal expansion with solid electrolyte
Electrode reactivity while maintaining high electrical conductivity
That can most efficiently suppress shrinkage during reduction and reduction
It is determined that a pole is obtained.

[Experimental Example 2: NiO-HfSiO ₄ -YS]
Z-based Material] <Preparation of Test Piece> NiO, HfSiO ₄ , and YSZ raw material powders were mixed at various compounding amounts, and a test piece was obtained in the same manner as in Experimental Example 1 described above.

<Test Method> Method of Measuring Coefficient of Thermal Expansion The coefficient of thermal expansion was determined in the same manner as in Experimental Example 1 described above.

Method of Measuring Conductivity Conductivity was determined in the same manner as in Experimental Example 1 described above.

Method for Measuring Electrode Reaction Resistance The electrode reaction resistance was determined in the same manner as in Experimental Example 1 described above.

Method of Measuring Length Change Rate The length change rate was determined in the same manner as in Experimental Example 1 described above.

<Experimental Results> Measurement Results of Thermal Expansion Coefficient FIG. 7 shows measurement results of the thermal expansion coefficient. As can be seen from Figure 7, the amount of the HfSiO ₄ increases, the thermal expansion coefficient becomes progressively smaller, in particular, the amount of HfSiO ₄ is 30vo
l.%, the coefficient of thermal expansion of YSZ (about 10 × 10 ⁻⁶ /
° C).

Measurement Results of Conductivity FIG. 8 shows the measurement results of the conductivity and the coefficient of thermal expansion at that time. As can be seen from FIG. 8, NiO-30 vol.% HfS
When 10 vol.% of YSZ is blended in the iO ₄ system, the electrical conductivity becomes smaller (about 2600 S / cm) as compared with the case where YSZ is not blended, but it has a sufficient size and the thermal expansion coefficient hardly changes. It has been found.

FIG. 9 shows the measurement results of the electrode reaction resistance. As it can be seen from Figure 9, the NiO-30 vol.% HfSiO the YSZ at ₄ system 10 vol.% Formulated, the electrode reaction resistance is reduced by half as compared with the case of not blending the YSZ (about 3Ω · cm ²⁾ (about 1. 5 Ω · cm ² ).

Measurement Results of Length Change Rate FIG. 10 shows measurement results of the length change rate. As can be seen from FIG. 10, YSZ in NiO-30vol.% HfSiO ₄ system
Was found to be very small (approximately 0.1%) and did not cause reduction shrinkage.

From the above results, it can be seen that depending on the size and shape of the cell,
However, the solid electrolyte is YS
In the case of Z, the compounding amount of NiO is about 60 vol.
iO _FourAbout 30vol.%, And the amount of YSZ
Approximately 10 vol.%, Consistency of thermal expansion with solid electrolyte
Electrode reactivity while maintaining high electrical conductivity
That can most efficiently suppress shrinkage during reduction and reduction
It is determined that a pole is obtained.

[0049]

The fuel electrode of the solid oxide electrochemical cell according to the present invention uses a cermet of Ni, Co or an alloy thereof, stabilized zirconia, and an oxidized compound having a smaller coefficient of thermal expansion than the stabilized zirconia. From becoming
Since the surface area of the three-phase interface where the electrochemical reaction occurs increases, the electrode reactivity can be improved.

Further, since the stabilized zirconia is strong, it does not shrink even under a reducing atmosphere, so that the shrinkability under a reducing atmosphere can be extremely reduced.

For this reason, since the contracted volume at the time of reduction remains as a gap as it is, voids can be reliably generated, so that the permeability of fuel gas and the like can be increased, and the electrode reactivity can be further increased. be able to.

Therefore, it is possible to improve the reactivity of the electrode and to suppress the shrinkage at the time of reduction while maintaining the consistency of the thermal expansion with the solid electrolyte and the high conductivity.

When the oxidized compound is a silicate compound of a metal oxide and silicon oxide, the above-described effects can be exhibited more efficiently.

[Brief description of the drawings]

FIG. 1 is a schematic structural diagram of a main part of an embodiment in which a fuel electrode of a solid oxide electrochemical cell according to the present invention is applied to a fuel electrode of an electrochemical cell of a solid oxide fuel cell.

FIG. 2 is an explanatory diagram of an operation of a fuel electrode of FIG. 1;

FIG. 3 shows Y ₂ S of NiO—Y ₂ SiO ₅ —YSZ-based material
₅ is a graph showing the relationship between the amount of iO ₅ and the coefficient of thermal expansion.

FIG. 4 shows Y ₂ S of NiO—Y ₂ SiO ₅ —YSZ-based material
₅ is a graph showing the relationship between the YSZ content and the coefficient of thermal expansion and electrical conductivity when the content of iO ₅ is 30 vol.%.

FIG. 5: Y ₂ S of NiO—Y ₂ SiO ₅ —YSZ-based material
iO ₅ amount of a graph showing the relationship between the 30 vol.% and YSZ amount in the case where the electrode reaction resistance.

FIG. 6: Y ₂ S of NiO—Y ₂ SiO ₅ —YSZ-based material
iO ₅ amount of a graph showing the relationship between the 30 vol.% and YSZ amount in the case where the length variation rate.

FIG. 7: HfS of NiO—HfSiO ₄ —YSZ-based material
₄ is a graph showing the relationship between the amount of iO ₄ and the coefficient of thermal expansion.

FIG. 8: HfS of NiO—HfSiO ₄ —YSZ-based material
It is a graph showing the relationship between the amount of YSZ, the coefficient of thermal expansion, and the electrical conductivity when the amount of iO ₄ is 30 vol.%.

FIG. 9 shows HfS of NiO—HfSiO ₄ —YSZ-based material.
It is a graph showing the relationship between the amount of YSZ and the electrode reaction resistance when the amount of iO ₄ is 30 vol.%.

FIG. 10 shows the Hf of NiO—HfSiO ₄ —YSZ-based material
₅ is a graph showing the relationship between the YSZ content and the rate of change in length when the content of SiO ₄ is 30 vol.%.

FIG. 11 is a graph showing a relationship between a reduction time and an expansion rate of a Ni-40 vol.% MgAl ₂ O ₄ material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base 2 Fuel electrode 2a Metal part 2b Oxide compound part 2c Stabilized zirconia part 2d Void 3 Solid electrolyte 4 Air electrode 5 Intermediate connector 11 Fuel gas 12 Oxidizing gas

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[Procedure amendment]

[Submission date] April 4, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007] In an electrochemical cell using a cermet as a fuel electrode as described above, the fuel electrode sometimes contracts when the fuel electrode is reduced with fuel gas during operation. For example, Ni-40 vol.% MgAl ₂ O ₄ (thermal expansion coefficient: about 10 × 10 ⁻⁶ / ° C., conductivity: about 2000 S / c)
In the cermet of m), as shown in FIG. 11, the cermet shrinks immediately after the start of the reduction. The use of such cermet fuel electrode, the vicinity of the fuel electrode will be deformed during operation, not only there is a fear that causes a decrease in power generation performance, resulting in damage to the cell in the worst case a risk There is.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

In the fuel electrode 2 having the stabilized zirconia portion 2d, even when NiO is reduced to Ni during operation, the stabilized zirconia portion 2d maintains the structure of the aggregate.
Since it has the function of reducing, it does not significantly shrink, so that the shrinkage during reduction can be greatly suppressed.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a fuel electrode of a solid oxide electrochemical cell according to the present invention is applied to a fuel electrode of an electrochemical cell of a solid oxide fuel cell will be described with reference to FIG. FIG. 1 is an example of a schematic structural diagram of the main part.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction contents]

The stabilized zirconia portion 2d is formed of an aggregate.
Since it has the function of maintaining the structure, as described above, even if it is reduced during operation, it does not significantly shrink, so that the shrinkage during reduction is very small.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0050

[Correction method] Change

[Correction contents]

Further, stabilized zirconia maintains the structure of the aggregate.
Since it has the function of maintaining, it does not shrink even under a reducing atmosphere, so that the shrinkability under a reducing atmosphere can be extremely reduced.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG. 1 is an example of a schematic structural diagram of a main part of an embodiment in which a fuel electrode of a solid oxide electrochemical cell according to the present invention is applied to a fuel electrode of an electrochemical cell of a solid oxide fuel cell.

Claims (2)

[Claims] 1. A fuel for a solid electrolyte type electrochemical cell comprising a cermet of Ni, Co or an alloy thereof, stabilized zirconia, and an oxide compound having a smaller coefficient of thermal expansion than the stabilized zirconia. very. 2. The fuel electrode according to claim 1, wherein the oxide compound is a silicate compound of a metal oxide and silicon oxide.