JPS5842134B2 - Production method of red zinc oxide powder - Google Patents

Description

[Detailed Description of the Invention] ZnO powder is generally obtained by heating Zn metal or Zn ore and air oxidizing the evaporated Zn, and is white and used in paints, rubber additives, medicines, etc. has been done.

ZnO is also photoconductive and is used in electronic copying paper by coating it on paper.

However, general white ZnO absorbs only ultraviolet rays and does not absorb visible rays, so it is a photoconductor that is sensitive only to ultraviolet rays.

For this reason, sensitization is carried out by adding organic dyes to make the film sensitive to visible light.

However, this is sensitively affected by the surface properties of the ZnO powder and the composition of the resin used as a binder, making it difficult to obtain a stable product.

The present invention relates to obtaining a photoconductive ZnO powder which is sensitive to visible light and has a color to itself.

Colored ZnO can be obtained by dissolving other elements in ZnO.

For example, when a small amount of Mn is added, the color becomes yellow, and when lead is added, the color becomes pink.

However, solid solution of other elements involves reacting ZnO with an oxide or other substance containing the element, but since the reaction requires a high temperature, ZnO is sintered and its powder properties are lost.

Furthermore, colored metals may impair the harmlessness advantage of ZnO.

Therefore, a desirable manufacturing method is to color the ZnO powder at the time of making it, and moreover, the solid solution elements are harmless.

ZnO, which has a small amount of fixed nitrogen, exhibits a red or pink color, which is comparable to this.

When creating ZnO by calcining zinc hydroxide produced by adding ammonia water to a zinc salt aqueous solution, if cleaning is insufficient, ammonia will be adsorbed to the zinc hydroxide, and further heating will result in a pink color with solid solution of nitrogen. It is well known that colored ZnO is produced.

Furthermore, in order to obtain a certain red ZnO, a method has been adopted in which white ZnO powder is heat treated in a nitrogen-containing substance.

For example, there is a method in which white ZnO powder is heat treated in ammonium nitrate.

However, since this method uses the rapid heat generation of ammonium nitrate, it is difficult to control and is not suitable for mass production.

A method using ammonium carbamate (NI(4COON)L2) in place of ammonium nitrate has also been developed.

Since this reaction occurs at a relatively low temperature (150 to 200°C), agglomeration of the ZnO powder can be avoided, but the price is high because a special substance is used.

The present invention uses zinc oxalate as a raw material and thermally decomposes it to obtain ZnO, which is then fired in a nitrogen-containing gas to easily obtain ZnO powder in which nitrogen is dissolved in solid solution.

Zinc oxalate decomposes thermally at about 400°C.1. Changes to ZnO.

It is known that white fine powder can be obtained by firing in air.

It was found that when this was calcined in nitrogen gas, a slightly yellowish powder was obtained.

The present inventor has discovered that red ZnO powder can be obtained by calcining zinc oxalate in ammonia gas.

This is thought to be because ammonia gas is thermally decomposed to generate active nitrogen, which is easily dissolved in ZnO when zinc acetate is thermally decomposed.

The reason for using zinc oxalate is that its thermal decomposition temperature is 400°C, which is appropriate.

That is, if the decomposition temperature is low (less than 400°C), ammonia gas does not decompose, and the decomposition temperature is high (s o o'
c), sintering of ZnO occurs.

Therefore, the heat treatment temperature for zinc oxalate is also 400℃ or higher and 800℃.
°C is suitable, preferably 500 °C to 650 °C,
Most preferably it is 550°C to 600°C.

The method of the invention is carried out by heating the powder of zinc oxalate in a stream of ammonia gas, the flow rate of the ammonia gas being greater than or equal to, for example, 0,11 t.
It is sufficient if the flow is about / min or more, and the appropriate amount can be easily determined by observing the color of the produced ZnO.

It has been found that the red ZnO obtained by this method does not change color even after subsequent heat treatment in air.

Example 20g of oxalic acid powder was placed in a furnace, and 0.0% of ammonia gas was added.
It was heated at 550° C. with flowing water for 2117 minutes.

After 1 hour, a ZnO powder with a red color was obtained.

The spectral reflection characteristics of this powder are shown in the attached figure.

For comparison, the figure also shows the characteristics of powder treated in air at the same temperature and time.

When treated in air, the resulting powder is white and absorbs ultraviolet rays, but reflects visible light of 400 nm or more.

On the other hand, the powder treated in ammonia shows significant absorption in the visible region.

[Brief explanation of drawings]

The accompanying drawing is a graph showing a comparison of the spectral reflection characteristics of the red ZnO manufactured according to the example and the normal white ZnO.

Claims (1)

[Claims] 1. A method for producing zinc oxide powder that has a red color by thermally decomposing zinc oxalate in the presence of ammonia gas.