JPH06346163A - Production of dendritic noble metal - Google Patents

Abstract

PURPOSE:To effectively produce a dendritic noble metal. CONSTITUTION:A noble metal is dissolved in a melt not forming a reaction product with a desired noble metal, the melt is rapidly cooled to crystallize the desired. dendritic noble metal in the melt, and the solidified material thus obtained is removed by the acid, hot water, etc., not dissolving or oxidizing the noble metal, and a dendritic noble metal is obtained. A dendritic noble metal which has not been produced is produced in this way. The temp. stability of the noble metal is improved and the noble metal is not deteriorated with time because its crystal defect is reduced, further unique catalysis is exhibited since a peculiar face is formed, and an efficient and selective catalytic reaction is expected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a dendritic noble metal, and more particularly to a method for producing a dendritic noble metal useful as a catalyst or various composite materials.

[0002]

2. Description of the Related Art Conventionally, precious metals such as platinum have been widely used as catalysts for various synthetic reactions. The specific surface area of the fine particles used as a catalyst greatly affects the catalytic activity, and it is desired that the specific surface area is large in terms of catalytic activity.

However, fine particles having a large specific surface area have the drawbacks of low temperature stability and large change over time, and it is difficult to obtain catalyst fine particles having high catalytic activity and excellent stability. Has been done. In addition, a fine-particle catalyst cannot obtain a specific selective catalytic action on a certain surface as seen in a single crystal.

By the way, conventionally, various methods have been proposed as a method for producing thin fibrous single crystals, that is, whiskers. Al ₂ O ₃ , C, SiC, Si ₃ N ₄ ,
Whiskers such as AlN are being used as constituent materials for composite materials, fireproofing and heat insulating materials.

However, there is no method for producing a noble metal that has crystallized into a dendritic form, and no noble dendritic metal has been provided so far.

[0006]

As described above, no dendritic noble metal has hitherto been provided, but when a dendritic noble metal is used as a catalyst, the specific surface area is slightly inferior, but it is considered that there are few crystal defects. Therefore, it is expected that the temperature stability and the change with time become good. In addition, it is considered that a dendritic noble metal having a unique surface has a unique catalytic action due to the uniqueness of the surface, which is expected to improve the efficiency of the catalytic reaction and a specific selective catalytic reaction. .

Under these circumstances, it is desired to develop an efficient production technique for dendritic precious metals.

The present invention has been made in view of the above conventional circumstances, and an object thereof is to provide a method for efficiently producing a dendritic noble metal expected to be used as a catalyst or various composite materials. To do.

[0009]

The method for producing a dendritic noble metal according to the present invention is a method for producing a dendritic noble metal by quenching and solidifying a melt containing a noble metal, which is non-reactive with the noble metal. After dissolving the noble metal in the melt of the substance, the melt is rapidly solidified to obtain a solidified product in which dendrites of the noble metal are crystallized, and the dendritic noble metal is separated from the solidified product. It is characterized by

That is, as described above, the present inventor focused on a noble metal having a dendritic morphology which is considered to be effective for a catalyst, and studied the production method thereof. As a result, the impurity distribution between the crystal and the melt was used. By doing so, it was found that a dendritic noble metal can be efficiently obtained, and the present invention was completed.

The present invention will be described in detail below.

In the method of the present invention, a substance which is non-reactive with the raw material noble metal of the target dendritic noble metal (hereinafter,
It is called "non-reactive substance". As), a substance that does not generate a reaction product with the noble metal, such as sodium borate or lithium borate, can be used.

Examples of the noble metal produced in the dendritic form by the method of the present invention include noble metals such as platinum, silver and palladium.

In order to dissolve the noble metal in the non-reactive substance, the non-reactive substance may be heated to a temperature above its melting point to form a melt of the non-reactive substance, and the noble metal may be added to the melt. . At this time, the noble metal may be added in powder form, or the noble metal pipe may be immersed in the melt of the non-reactive substance,
The precious metal may be dissolved while supplying oxygen through this pipe. Here, the supply of oxygen promotes the dissolution of the noble metal in the melt.

The melt obtained by dissolving the noble metal in this manner is then rapidly solidified. This rapid solidification can be carried out, for example, by letting the melt flow down on a ceramic substrate such as alumina at room temperature or cooled while blowing cooling air.

The solidified product thus obtained is one in which a non-reactive substance is used as a matrix and crystals of a dendritic noble metal are crystallized inside. Therefore, the dendritic noble metal can be separated by removing only the non-reactive substance from the solidified product.

In this case, if the non-reactive substance is water-soluble, the dendritic noble metal can be recovered by immersing the solidified product in water or warm water to dissolve the non-reactive substance.

Further, since the non-reactive substance is alkaline,
If it is acid-soluble, H that is obtained by heating the solidified product at room temperature or
The dendritic noble metal can be recovered by immersing the non-reactive substance in an aqueous acid solution that is not oxidizable with respect to the noble metal such as Cl.

The non-reactive substance can be removed by any method that does not dissolve, oxidize or modify the dendritic noble metal and is not particularly limited.

The dendritic noble metal obtained is a dendritic noble metal crystal grown, has a high purity and almost no crystal defects, and exhibits good properties as a catalyst or various composite materials.

[0021]

By dissolving the noble metal in the melt of the non-reactive substance and rapidly solidifying it, the noble metal can be crystallized in a dendritic manner inside the solidified substance of the non-reactive substance. Therefore,
The dendritic noble metal can be recovered from the solidified product by removing the non-reactive substance by a method that does not dissolve, oxidize or modify the dendritic noble metal.

[0022]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

Example 1 Dendritic platinum was produced according to the method shown in FIG. 100 g of sodium borate (melting point about 700 ° C.) 1 is put into a platinum crucible 2 and melted at 1000 ° C., and further a platinum pipe 3
Is immersed in a melt and oxygen (O ₂ ) gas is flowed in the melt at 800 ° C.
For 5 hours (Fig. 1 (a)). As a result, 2 g of platinum dissolved in the melt. After that, the melt 4 was poured onto a plate 5 of alumina (Al ₂ O ₃ ) at room temperature and was blown with air to be rapidly cooled and solidified (FIG. 1 (b)). Solidified product 6 at 60 ° C.
It was put into a Cl aqueous solution (HCl: water = 1: 10 (volume ratio)) to dissolve sodium borate (FIG. 1 (c)). This aqueous solution was filtered (FIG. 1 (d)), and 2 g of dendritic platinum 8 was separated as a residue.

A SEM photograph (1000 times) of the dendritic platinum obtained by this method is shown in FIG. Example 2 100 g of lithium borate (melting point 917 ° C.) was put into a platinum crucible and melted at 1100 ° C., a platinum pipe was immersed in the melt, an oxygen gas was flown therein, and the temperature was maintained at 1100 ° C. for 5 hours. As a result, 3 g of platinum dissolved in the melt. After that, the melt was poured onto a plate of alumina at room temperature, and air was blown on the plate to rapidly solidify it. The solidified product was put into a 60 ° C. aqueous HCl solution (HCl: water = 1: 10 (volume ratio)) to dissolve lithium borate. This aqueous solution was filtered, and 3 g of dendritic platinum was collected as a residue.

[0025]

As described in detail above, according to the method for producing a dendritic noble metal of the present invention, it is possible to easily and efficiently produce a dendritic noble metal in which the noble metal is crystallized in a dendritic form.

This dendritic noble metal is effective in improving the temperature stability as a catalyst and the change over time, and the shape specificity of the dendritic noble metal is expected to make the catalytic reaction efficient and a specific selective catalytic reaction. Further, this dendritic noble metal can be effectively used for various composite materials.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method of an example of a method for producing a dendritic noble metal of the present invention.

FIG. 2 is an SEM photograph of the dendritic platinum produced in Example 1.

[Explanation of symbols]

1 Sodium borate 2 Platinum crucible 3 Platinum pipe 4 Melt 5 Al ₂ O ₃ plate 6 Solidified substance 7 HCl aqueous solution 8 Dendritic platinum

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 5, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction content]

A schematic view of a SEM photograph (1000 times) of the dendritic platinum obtained by this method is shown in FIG. Example 2 100 g of lithium borate (melting point 917 ° C.) was put into a platinum crucible and melted at 1100 ° C., a platinum pipe was immersed in the melt, an oxygen gas was flown therein, and the temperature was maintained at 1100 ° C. for 5 hours. As a result, 3 g of platinum dissolved in the melt. After that, the melt was poured onto a plate of alumina at room temperature, and air was blown on the plate to rapidly solidify it. The solidified product was put into a 60 ° C. aqueous HCl solution (HCl: water = 1: 10 (volume ratio)) to dissolve lithium borate. This aqueous solution was filtered, and 3 g of dendritic platinum was collected as a residue.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

2 is an SEM photograph of dendritic platinum produced in Example 1. FIG.
FIG .

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

Claims (1)

[Claims] 1. A method for producing a dendritic noble metal by rapidly solidifying a melt containing a noble metal, which comprises dissolving the noble metal in a melt of a substance non-reactive with the noble metal, A method for producing a dendritic noble metal, which comprises rapidly cooling and solidifying a melt to obtain a solidified product in which dendrites of the noble metal are crystallized, and separating the dendritic noble metal from the solidified product.