JP2019019038A - Silver oxide and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new silver oxide. SOLUTION: 707.5 g (1.2 mol times of reaction equivalent) of a 0.4 mass% sodium hydroxide aqueous solution is mixed with 200 g of a 5.0 mass% silver nitrate aqueous solution over about 5 minutes for 15 minutes. The mixture is left to stand, neutralized by decantation washing, treated at 100 ° C. for 5 hours to obtain silver oxide powder (average particle size of about 4 μm), and the silver oxide powder is uniaxially pressurized. After tentative molding, cold isotropic pressure was applied (pressure 150 MPa, 4 minutes) to form pellets (diameter about 16 mm, thickness about 3 mm), and a sample table was provided so that the pellets did not come into contact with the solution. It was placed in a Teflon-lined autoclave, heat-treated at 150 to 200 ° C, and after the heat treatment, it was washed with dilute nitrate (concentration: 3.0% by mass) for 30 seconds to obtain pelletized silver oxide, and the obtained oxidation was obtained. A method for producing silver oxide, which has pores of about 4 to 5 μm on (the surface of) silver and has an open pore ratio of 17% or more, preferably 18 to 25%. [Selection diagram] Fig. 2

Description

  The present invention relates to novel silver oxide and the like.

  Silver oxide is a material that can be used in various industrial fields.

For example, Patent Document 1 includes single particles having an average particle diameter of 5 to 30 μm, a bulk density of 1.4 g / cm ³ or more, and a specific surface area (BET value) of 0.04 to 0.5 m ² / g, It is described that silver oxide having a pulverization amount of 15% or less is suitable for a battery, and that the upper limit of the bulk density is about 2.5 g / cm ³ .

Japanese Patent No. 3269427 (claims, paragraphs [0001] [014], Examples)

  An object of the present invention is to provide a novel silver oxide.

  Another object of the present invention is to provide a novel method for producing silver oxide.

  As a result of intensive studies, the present inventors have found that a novel silver oxide (for example, silver oxide having a relatively high open porosity and bulk density) can be obtained by adopting a specific method, etc. The present invention has been completed.

In Patent Document 1, an object is to obtain silver oxide particles by subjecting silver oxide particles to heat and pressure treatment in an alkaline solution to grow silver oxide particles in an alkaline solution.
Such a method involves grain growth of silver oxide grains, and the resulting grains are dense. Actually, in Patent Document 1, it is not assumed at all to form open pores, and to increase the open porosity.

That is, the silver oxide of the present invention may be, for example, silver oxide having an open porosity of 17% or more.
The silver oxide of the present invention may also be a silver oxide having a bulk density of 3 g / cm ³ or more.

The silver oxide of the present invention is a silver oxide having an intensity ratio I ₄₄ / I ₃₃ between a peak intensity I ₃₃ near a diffraction angle of 33 ° and a peak intensity I ₄₄ near a diffraction angle of 44 ° of 0.1 or less. Also good.

Representative silver oxides of the present invention include
The open porosity is 18-25%,
The bulk density is 4-7 g / cm ³ ,
Silver oxide, etc., in which the intensity ratio I ₄₄ / I ₃₃ between the peak intensity I ₃₃ near the diffraction angle 33 ° and the peak intensity I ₄₄ near the diffraction angle 44 ° is 0.05 or less are included.

  The silver oxide of the present invention may be a molded product, for example, a powder molded product (powder molded product).

  The silver oxide of the present invention may be silver oxide for use in at least one application selected from a coolant, an electrode material, and a catalyst.

  The present invention includes a method for producing silver oxide by heat-treating silver oxide (raw material silver oxide) in the presence of water vapor (or in water vapor). The silver oxide produced by such a method may be the above-described silver oxide (for example, silver oxide having an open porosity of 17% or more).

  In such a method, a silver oxide compact [particularly, a silver oxide powder compact (for example, a silver oxide powder ship (cold isostatic pressing) compact) etc.]] may be heat-treated.

  Specifically, the method of the present invention includes a forming step of forming raw material silver oxide [for example, powder forming of silver oxide (ship forming)], and a heat treatment step of heat-treating the formed raw material silver oxide compact. It may be configured.

  In the method of the present invention, heat treatment may be performed at 120 ° C. or higher under pressure or saturated water vapor pressure.

  The present invention includes a material containing the silver oxide (for example, silver oxide having an open porosity of 17% or more) [or a reduced product thereof (that is, silver)]. Such a material may be a material for use in at least one application selected from a coolant, an electrode material, and a catalyst material.

In the present invention, novel silver oxide (silver oxide (I), Ag ₂ O) can be provided.
Moreover, in this invention, the novel manufacturing method of silver oxide can be provided.

In an Example, it is a SEM photograph of the silver oxide before heat processing. 2 is a SEM photograph of silver oxide obtained in Example 1. 2 is a SEM photograph of silver oxide obtained in Example 2. 3 is a SEM photograph of silver oxide obtained in Example 3. 4 is a SEM photograph of silver oxide obtained in Example 4. 4 is a SEM photograph of silver oxide obtained in Example 5. 2 is a SEM photograph of silver oxide obtained in Reference Example 1.

[Silver oxide]
The silver oxide of the present invention satisfies specific physical properties (characteristics). There may be at least one physical property that the silver oxide of the present invention satisfies, and two or more physical properties may be satisfied. In addition, the silver oxide satisfying such physical properties can be produced by, for example, a method described later.

  Silver oxide may have pores (or pores, particularly open pores). Note that all or part of the pores may be through holes. The open porosity of silver oxide having open pores may be selected from the range of, for example, 10% or more (for example, 12% or more), 15% or more (for example, 16% or more, 16.5% or more), It may be 17% or more (for example, 17.5% or more), more preferably 18% or more (for example, 19% or more, 20% or more, etc.).

  Although the upper limit of the open porosity of silver oxide is not particularly limited, it may be, for example, 50%, 45%, 40%, 35%, 30%, 25%, 23%, 22%, or the like. Note that the range may be set by appropriately combining the upper limit value and the lower limit value of the range (for example, 18 to 30%, etc. The same applies hereinafter).

  By setting such an open porosity (relatively porous), the specific surface area can be relatively increased. Such a large specific surface area can increase the contact point with the outside. Moreover, it becomes easy to diffuse and permeate | transmit a medium (gas etc.) to the inside of silver oxide (molded object). Therefore, it can be a material that can be suitably used in applications such as coolants, catalysts, and electrode materials.

The method for measuring the open porosity is not particularly limited. For example, the amount of open pores (P) is the dry weight (W ₁ ) of silver oxide (molded product), and the weight in water (W ₂ ). From the weight (W ₃ ) at the time of heating, the following formula may be used.
P (%) = 100 × (W ₃ −W ₁ ) / (W ₃ −W ₂ )

  In addition, the magnitude | size of an open pore is not specifically limited, For example, about 1-10 micrometers may be sufficient by a hole diameter (pore diameter).

The bulk density of silver oxide may be selected from the range of 2 g / cm ³ or more, for example, 2.5 g / cm ³ or more (for example, 2.7 g / cm ³ or more), preferably 3 g / cm ³ or more ( For example, it may be 3.5 g / cm ³ or more, more preferably 4 g / cm ³ or more (for example, 4.5 g / cm ³ or more), or 5 g / cm ³ or more (for example, 5.2 g / cm ^3). The above may be 5.3 g / cm ³ or more, 5.4 g / cm ³ or more.

The upper limit value of the bulk density of silver oxide is not particularly limited, and is, for example, 7 g / cm ³ , 6.5 g / cm ³ , 6 g / cm ³ , 5.8 g / cm ³ , 5.7 g / cm ^3, etc. May be.

  By setting it as a comparatively large bulk density, it becomes easy to raise heat conductivity, and can become a material which can be used conveniently in a cool storage material use etc.

  In addition, although the measuring method of bulk density is not specifically limited, For example, you may measure by Archimedes method.

  The theoretical density ratio of silver oxide may be selected from a range of 0.45 or more, for example, 0.5 or more (for example, 0.55 or more), preferably 0.6 or more (for example, 0.65 or more). More preferably, it may be 0.7 or more (for example, 0.73 or more, 0.75 or more, 0.76 or more, 0.77 or more, etc.).

  The upper limit of the theoretical density ratio of silver oxide is, for example, 0.9, 0.88, 0.85, 0.84, 0.83, 0.82, 0.81, 0.8, 0.79, etc. There may be.

The theoretical density ratio is the ratio (d1 / d) of the bulk density (actual density) d1 to the theoretical density (theoretical maximum density) d (about 7.2 g / cm ³ ) of silver oxide. That is, the theoretical density ratio can be calculated by dividing the bulk density by the theoretical density.

  Silver oxide may contain silver (silver as an impurity). As described above, in the silver oxide containing silver, the proportion of silver can be appropriately selected depending on the use of silver oxide and the like, but the present invention can efficiently provide silver oxide having a relatively low proportion of silver.

Such a ratio of silver can be estimated as an intensity ratio of peaks corresponding to silver oxide and silver by X-ray diffraction (XRD). For example, in the X-ray diffraction pattern of silver oxide, the intensity ratio I ₄₄ / I between the peak intensity I ₃₃ near the diffraction angle 33 ° corresponding to silver oxide and the peak intensity I ₄₄ near the diffraction angle 44 ° corresponding to silver. ₃₃ may be 0.3 or less, preferably 0.2 or less, more preferably about 0.1 or less, 0.08 or less, 0.05 or less, 0.03 or less, 0.02 or less, 0 .01 or less.

The lower limit value of I ₄₄ / I ₃₃ is not particularly limited, and is 0, 0.00001, 0.0001, 0.0003, 0.0005, 0.0007, 0.001, 0.0015, etc. Also good.

  As will be described later, the silver oxide of the present invention includes silver oxide in the form of a molded body, and thus in a form having a relatively large size. Generally, such a large size silver oxide is a silver oxide. Silver is likely to be contained in the molding process due to the thermal stability of the steel. However, in the present invention, surprisingly, even a molded body or a large-sized silver oxide has a high purity (moreover, both high purity and the above-mentioned high porosity and high bulk density can be achieved). Silver oxide can be provided.

  As will be described later, the silver oxide of the present invention can be used after being converted (reduced) into silver. In such a case, the silver oxide is not necessarily required to have a high purity as described above.

  The form of silver oxide is not particularly limited, but may be usually a form containing a plurality of particles (secondary particles, aggregates, aggregated particles).

  In particular, the silver oxide of the present invention may be in the form of a molded body (silver oxide molded body). For example, the silver oxide may be in the form of a powder molded body (powder molded product). Such a molded body is obtained, for example, by molding silver oxide powder (or powder) under pressure.

  Moreover, in the silver oxide of the form containing a some particle | grain or the form of a molded object, each particle | grain may be melt | fused or sintered.

  The shape of such a molded body is not particularly limited, and can be appropriately selected depending on the application. For example, it may be granular (particulate), pelletized, or the like.

  The size of the molded body can be appropriately selected according to the application and molding method, and is not particularly limited. For example, the diameter may be 30 μm or more, 40 μm or more, 50 μm or more. In a more specific aspect, the diameter of a granular molded body (for example, a granular molded body for use as a coolant) may be about 50 μm to 2 mm. Also, the diameter (diameter, maximum diameter) of the pellet-shaped molded body may be 100 μm or more (for example, 500 μm or more, 1 mm or more, 1.5 mm or more, 2 mm or more, etc.).

[Method for producing silver oxide]
The method for producing silver oxide is also included in the present invention. Silver oxide obtained by such a production method may or may not satisfy the above physical properties. In particular, the production method of the present invention is suitable as a method for efficiently producing the above silver oxide.

  The production method of the present invention includes at least a step of heat-treating silver oxide with water vapor (or in the presence of water vapor) (heat treatment step).

  It does not specifically limit as a silver oxide (raw material silver oxide) with which it heat-processes, What was synthesize | combined may be used and a commercial item may be used.

  For example, the raw material silver oxide may be obtained by reacting metal silver and / or a silver salt (such as silver nitrate) with an alkali component (such as an alkali metal hydroxide such as sodium hydroxide).

The ratio of alkaline component is not particularly limited, in order to form a reliable silver oxide (Ag 2 _O), or equivalent amount of silver constituting the metallic silver and / or silver salts [e.g., 1 molar equivalent or more (e.g. 1.05 molar equivalents or more, 1.1 molar equivalents or more, 1.15 molar equivalents or more)].

  The raw material silver oxide may contain other components such as silver, but usually it may be substantially composed of only silver oxide.

  The form (shape) of the raw material silver oxide is not particularly limited, and may be a powder (powder, powder, granular) or a formed body (raw material formed body). Typically, the raw material silver oxide (silver oxide to be subjected to heat treatment) may be a powder molded body (powder molded product).

  Such a raw material molded body can be obtained by molding silver oxide (raw material silver oxide) by an appropriate method.

  For example, the powder compact may be obtained by pressure molding a raw material silver oxide powder. The pressure molding (method) is not particularly limited, but ship (CIP) molding (cold isostatic pressing) may be suitably used.

  Note that the raw material silver oxide powder may be temporarily molded before the pressure molding.

  The particle size of the powdered raw material silver oxide is not particularly limited, but may be, for example, an average particle size of 1 to 10 μm, preferably 2 to 8 μm, and more preferably about 3 to 5 μm.

  Further, the raw material silver oxide [for example, powdery raw material silver oxide (or powder compact)] may contain an appropriate binder component, but in the present invention, the raw material silver oxide does not contain such a binder component. May be suitably used.

  The shape of the raw material molded body is not particularly limited, and can be appropriately selected depending on the application. For example, it may be granular (particulate), pelletized, or the like.

In the heat treatment step, the raw material silver oxide is heat treated with water vapor as described above. By heat-treating with water vapor in this way, it is easy to efficiently obtain silver oxide having the above physical properties (for example, high open porosity, high bulk density, etc.).
Further, in the heat treatment step, heat treatment can be performed while maintaining the state of silver oxide even at a temperature at which silver oxide is decomposed and reduced to silver.

As long as the heat treatment can be performed in the presence of water vapor, the temperature is not particularly limited. For example, the temperature can be selected from a range of about 70 ° C. or higher (eg, 80 ° C. or higher), 100 ° C. or higher, preferably 120 ° C. or higher. More preferably, it may be 140 ° C. or higher, and may be 160 ° C. or higher (for example, 180 ° C. or higher).
In addition, the upper limit of temperature is not specifically limited, For example, 500 degreeC, 450 degreeC, 400 degreeC, 350 degreeC, 300 degreeC, 270 degreeC, 250 degreeC, 230 degreeC etc. may be sufficient.

  The heat treatment may be performed under normal pressure or under pressure, and particularly under pressure (pressurized steam, superheated steam, or hydrothermal conditions). When performed under pressure, the pressure (reactor internal pressure, internal pressure) depends on temperature, but may be, for example, 0.12 MPa or more, preferably 0.15 MPa or more, more preferably 0.2 MPa or more. , 0.3 MPa or more.

  When performed under pressure, the upper limit of the pressure is not particularly limited, but may be, for example, 22 MPa, 20 MPa, or the like. In order to efficiently obtain silver oxide having a relatively high open porosity and bulk density as described above, heat treatment may be performed without applying an extreme high pressure.

  The heat treatment may be performed under pressure or saturated water vapor pressure, or may be performed under non-saturated water vapor pressure.

The heat treatment may be performed in the presence of a component other than water as long as it can be performed in the presence of water vapor. For example, the heat treatment can be performed in a vapor of an aqueous solution containing components other than water (other components).
Examples of such other components include alkali components (for example, hydroxides such as sodium hydroxide and potassium hydroxide).

  However, it seems that the heat treatment in the presence of such other components tends to make the silver oxide (especially the silver oxide molded body) non-uniform (for example, the tissue grows densely depending on the site). . Therefore, even when heat treatment is performed in the presence of another component (for example, an alkali component), it is preferable that the other component is present to such an extent that such an influence does not occur. Is preferred.

  The container (reactor) for performing the heat treatment (step) is not particularly limited, and for example, a heatable (and pressurized) container such as an autoclave may be used.

In the heat treatment, the amount of water vapor is not particularly limited, and can be appropriately selected depending on whether it is in a saturated state or a non-saturated state, for example, 0.5% by volume or more of the volume in the container (volume in the system) as water The volume may be 1% by volume or more, more preferably 2% by volume or more, 5% by volume or more, 10% by volume or more, 15% by volume or more, 20% by volume or more, 25% by volume or more, 30% by volume. The above may be used.
The upper limit value is not particularly limited. For example, water may be 90% by volume, 80% by volume, 70% by volume, 60% by volume, 50% by volume, or the like of the volume in the container (volume in the system). Good.

  The heat treatment time can be appropriately selected according to the shape of the raw material silver oxide, the heat treatment conditions, and the like, and is not particularly limited. For example, it is 10 minutes or longer (for example, 30 minutes or longer), preferably 1 hour or longer (for example, 1.5 hours). Or more), more preferably 2 hours or more (for example, 2.5 hours or more).

  Note that the silver oxide after the heat treatment may be subjected to a washing treatment if necessary.

  Silver oxide is obtained as described above. In particular, when the raw material silver oxide is a molded body, silver oxide reflecting the form (shape) of the molded body is obtained.

[Use of silver oxide]
The use of the silver oxide of the present invention is not particularly limited, and can be used for various uses [for example, a regenerator material or a coolant (such as a regenerator material for a refrigerator), an electrode material, a catalyst, etc.).

  In particular, the silver oxide of the present invention often has a relatively large open porosity and bulk density (further high-purity and contains silver oxide), and is suitable for applications utilizing such physical properties. Can be used for

  Moreover, the silver oxide of this invention can be used not only when using as it is, but by reducing to silver.

  For example, in a catalyst application, the silver oxide of the present invention can be used as a catalyst as it is or in a silver state obtained by reducing silver oxide.

  Even if reduced to silver, the original physical properties (relatively large open porosity and bulk density) and shape are retained, so the silver oxide of the present invention is used as a silver raw material having such physical properties and shape. You can also.

  Next, the present invention will be described more specifically with reference to experimental examples and examples. However, the present invention is not limited to these examples, and many modifications are within the technical idea of the present invention. This is possible by those with ordinary knowledge in the field.

  Various physical properties and characteristics were measured or evaluated as follows.

(Open porosity)
The amount of open pores (P) was determined by the following formula from the dry weight (W ₁ ) of silver oxide (molded body), the weight in water (W ₂ ), and the weight when containing water (W ₃ ).
P (%) = 100 × (W ₃ −W ₁ ) / (W ₃ −W ₂ )
(The bulk density)
Measured by Archimedes method.
(Theoretical density ratio)
It was calculated from the bulk density measured by the Archimedes method and the theoretical density of silver oxide.
(Silver amount and crystal phase)
The intensity ratio I ₄₄ / I ₃₃ between the main peak (around 33 °) intensity I _{33 of} silver oxide and the second highest peak (around 44 °) intensity I _{44 of} silver was measured by X-ray diffraction (XRD). .
The crystal phase was determined to be a single phase of silver oxide when the value of I ₄₄ / I ₃₃ was 0.1 or less, and a phase containing silver oxide and silver when the value was more than 0.1.

(Examples 1-5, Reference Example 1)
2007.5 g of a silver nitrate aqueous solution with a concentration of 5.0% by mass is mixed with 707.5 g of a sodium hydroxide aqueous solution with a concentration of 0.4% by mass (1.2 mole times the reaction equivalent) over about 5 minutes and left for 15 minutes (aging). did. The obtained mixture was washed by decantation until neutral, and the obtained slurry was treated (aged) at 100 ° C. for 5 hours to obtain a silver oxide powder (average particle diameter of about 4 μm).

  The obtained silver oxide powder is temporarily formed by uniaxial pressing, and then formed into pellets (diameter: about 16 mm, thickness: about 3 mm) by cold isostatic pressing (CIP, pressure 150 MPa, time 4 minutes). did.

  The obtained pellets were placed in a Teflon-lined autoclave provided with a sample stage so as not to come into contact with the solution, and were subjected to heat treatment under the conditions shown in Table 1. After the heat treatment, it was washed with dilute nitric acid (concentration: 3.0% by mass) for 30 seconds to obtain pelleted silver oxide. In addition, about 4-5 micrometers void | hole was confirmed in the silver oxide (surface) obtained in Examples 1-5.

  The table below summarizes the conditions and physical properties of silver oxide after heat treatment.

  Moreover, the pellet before heat processing, the fine structure of the silver oxide obtained in Examples 1-5 and Reference Example 1 were confirmed with the scanning electron microscope (SEM). SEM photographs (5000 times) are shown in FIGS.

  As is clear from the results in Table 1 and the drawings, silver oxide having a high open porosity and the like were obtained in the examples.

  According to the present invention, novel silver oxide can be provided.

Claims (11)

  Silver oxide having an open porosity of 17% or more. The silver oxide according to claim 1, having a bulk density of 3 g / cm ³ or more. 3. The silver oxide according to claim 1, wherein an intensity ratio I ₄₄ / I ₃₃ between a peak intensity I ₃₃ near a diffraction angle of 33 ° and a peak intensity I ₄₄ near a diffraction angle of 44 ° is 0.1 or less. The open porosity is 18-25%,
The bulk density is 4-7 g / cm ³ ,
The intensity ratio I ₄₄ / I ₃₃ between the peak intensity I ₃₃ near the diffraction angle of 33 ° and the peak intensity I ₄₄ near the diffraction angle of 44 ° is 0.05 or less. Silver oxide.   The silver oxide according to any one of claims 1 to 4, which is a powder compact.   The silver oxide in any one of Claims 1-5 for using it for at least 1 sort (s) of application selected from a coolant, an electrode material, and a catalyst.   The method for producing silver oxide according to any one of claims 1 to 6, wherein the silver oxide is heat-treated in the presence of water vapor.   The manufacturing method of Claim 7 which heat-processes the powder compact of silver oxide.   The manufacturing method according to claim 8, wherein the compact is a ship compact of silver oxide powder.   The manufacturing method in any one of Claims 7-9 heat-processed above 120 degreeC under pressurization or saturated water vapor pressure.   A material comprising the silver oxide according to any one of claims 1 to 6, wherein the material is used for at least one application selected from a coolant, an electrode material, and a catalyst material.