JPS63288914A - Production of globular zinc oxide - Google Patents

Abstract

PURPOSE:To obtain the title high-purity, superfine, and globular ZnO by bringing low-temp. and dilute zinc vapor into contact with oxygen. CONSTITUTION:A crucible 2 contg. ultrapure zinc is placed in an electric furnace 1, and heated to 550-950 deg.C to melt the Zn. An inert gas previously freed of oxygen is introduced into the furnace through a preheating pipe 3 to obtain low-temp. dilute zinc vapor contg. 0.06-1mol./m<3> Zn. The vapor is then introduced into an Elema thermal-element 4 kept at 1,000-1,100 deg.C, and brought into contact with oxygen. The formed ZnO is recovered through a filter 5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing spherical zinc oxide, and is applicable to conventional rubber vulcanization accelerators, cosmetics, additives to plastics, paints, ceramic products, etc. It provides useful materials for electrophotographic photosensitive materials, varistors, electronic component materials, etc., as well as additives.

[Prior Art] As a conventional IJ manufacturing method of zinc oxide, an oxidation combustion method of metallic zinc vapor, such as the so-called French method, is known. Zinc oxide obtained by this method has a high temperature and high zinc vapor density as a raw material, so fine zinc oxide particles produced by the oxidation reaction collide with each other and sinter, forming coarse zinc oxide particles. The particle size is 0.2 μm at the smallest, and 0.5 to 0.8 μm on average.

Due to the viscosity and cohesiveness of these zinc oxides, it is difficult to further refine them by mechanical grinding. However, in addition to the applications that have been used for a long time as mentioned above, in applications such as varistors that have been developed in recent years,
There is a growing demand for ultra-fine particles as well as higher purity than ever before.

Therefore, methods for producing ultrafine zinc oxide can be roughly divided into two types: a thermal decomposition method in which a fine zinc compound is generated and then heated and roasted, and a gas phase reaction method in which zinc vapor is directly oxidized and burned. There is.

The first example of the thermal decomposition method is to add oxalic acid, alkali oxalate, or ammonium oxalate solution to a zinc ion solution such as zinc chloride, zinc sulfate, or zinc nitrate to generate fine crystals of zinc oxalate, which are then filtered out. After drying, the powder is oxidized and roasted to produce zinc oxide (see Japanese Patent Application No. 56-90782), and the particle size of the resulting zinc oxide is said to be about 0.03 .mu.m.

The second example of the thermal decomposition method is a method in which alkali hydroxide or alkali carbonate is added to a zinc salt solution, the resulting zinc hydroxide or basic zinc is filtered, dried, and then oxidized and roasted.
The particle size of zinc oxide obtained by roasting zinc hydroxide is 0.
The amount is up to 1 .mu.l, and in the case of roasting basic zinc carbonate, it is said that 0.07 to 0.1 .mu.m is possible.

The third example of the pyrolysis method is to react a water slurry of zinc oxide with CO2 gas in a closed container to produce basic zinc carbonate, and then pyrolyze this basic zinc carbonate to form zinc oxide. method (see Japanese Patent Application No. 59-111720), the zinc oxide obtained has a specific surface area of 15 m 2 /! II, and when converted from this, the average particle size is 0.07 μm.

In addition, as an example of a gas phase reaction method, after spouting metallic zinc vapor into an oxygen-containing atmosphere to oxidize and burn zinc,
Acicular zinc is produced by rapidly cooling the immediately generated zinc oxide, and desired properties (particle size,
There is a method for obtaining nodular zinc oxide (particle size distribution, bulk density, adsorption characteristics, etc.) (see Japanese Patent Application No. 55-23516).

[Problems to be Solved by the Invention] In the first and second examples of the pyrolysis method described above, for example, by diluting the concentration of zinc salt and the concentration of alkali carbonate to be added, the basic carbonate produced can be reduced. Although it is possible to suppress the enlargement of zinc particles and obtain ultrafine zinc oxide particles with a diameter of about 0.1μ, there is a limit to how fine they can be made by simply adjusting the reaction conditions, and neither method can achieve the desired goal. Avoid the process of washing and removing residual zinc salts (e.g. zinc chloride, zinc sulfate, etc.) and by-products of the production system (e.g. sodium chloride, Glauber's salt, etc.) from the reaction product (basic zinc carbonate). Since the products are fine, this washing cannot be carried out easily and is a major economic disadvantage.

And if cleaning is insufficient, naturally Na,
There is a problem in that S and the like are mixed in as impurities, making it impossible to meet the demands for high purity.

The third example of the pyrolysis method discloses a method for producing basic zinc carbonate that does not contain impurities, and it is possible to make zinc oxide by pyrolyzing it free of impurities; There is a problem in that a container must be used.

In the example of the gas phase method, the purpose is essentially to produce acicular zinc oxide, and there is no disclosure of production of ultrafine zinc oxide. However, as new uses for zinc oxide are developed, ultrafine particles are desired, and a situation has arisen in which the shape of the particles is not acicular but spherical.

[Means for Solving the Problems] The purpose of the present invention is to solve the above-mentioned conventional problems and to produce highly pure, ultrafine, and spheroidized zinc oxide. The gist is a method for producing spherical zinc oxide, which is characterized by bringing low-temperature dilute zinc vapor into contact with oxygen.

In other words, in order to obtain fine zinc oxide, it is necessary to suppress the collision and sintering of zinc particles in the French method, etc., and to do this, it is necessary to lower the temperature of the oxidation reaction and reduce the amount of zinc vapor in the oxidation reaction. It was concluded that densification is effective.

In order to overcome the disadvantage of a reduction in processing speed that inevitably occurs when aiming to lower the temperature of the oxidation reaction and lower the density of zinc vapor, the amount of steam can be reduced by injecting preheated inert gas into the steam generation system. It was possible to satisfy both of the requirements of security and lowering the density of steam.

Incidentally, Table 1 shows the relationship among molten zinc temperature, zinc vapor pressure, and zinc vapor density. In Table 1, the zinc vapor density is the concentration of zinc saturated vapor as an ideal gas when the total pressure is balanced to 1 atmosphere with an inert gas.

Table 1 As is clear from the table above, there is a change in vapor density at 1.800°C. Since the density of zinc vapor at temperatures between 550° C. and 800° C. is low, low-temperature and dilute zinc vapor can be generated by blowing inert gas into molten zinc. The steam generated from high-temperature molten zinc has a high steam density, so it is diluted and cooled by blowing inert gas.

The dilution of zinc vapor that is brought into contact with oxygen is 0.06 to 1 m.
A range of ol/m 3 is preferred.

The oxidation reaction of zinc vapor is carried out with oxygen or air.

[Function] According to the present invention, collision and sintering of generated zinc oxide particles can be avoided.

[Example] Next, examples will be described.

Example 1 As shown in FIG. 1, a crucible 2 containing the purest zinc is placed in an electric furnace 1 and heated to a predetermined temperature. Nitrogen gas from which oxygen has been removed in advance is blown into the molten zinc in the crucible 2 through the preheating tube 3.

A voltage is applied to the Elema heating element 4 attached to the ceiling of the crucible 2, and the temperature of the heating pair is maintained at about 1000 to 1100°C, not for steam heating but to avoid condensation of zinc vapor.

In this way, diluted zinc vapor is released into the atmosphere from inside the crucible 2 to obtain zinc oxide. No flame due to oxidation reaction was observed. The generated zinc oxide is collected through a filter 5. 6 in the figure is a thermometer.

100 NI of nitrogen gas is injected through the preheating pipe 3.
/Hr, the temperature of the molten zinc is 550℃ to 700℃
The resulting white powder was identified as ZnO by X-ray diffraction.

Further, according to electron micrographs, the particle diameters at each molten metal temperature were as shown in Table 2. Among these, the temperature at 600°C and the temperature at 700°C are shown in FIGS. 3 and 4.

In the case of FIG. 3, some particles were seen in the form of nodules, but the diameter of each particle constituting the nodules was about 0.01 μm, which made them easy to separate and had a very large specific surface area.

In the one in Figure 4, some needle-like shapes can be seen, but most of them are spherical.

Table 2 Example 2 The experiment was carried out using the apparatus shown in FIG. Components in FIG. 2 with the same names as those in FIG. 1 are given the same reference numerals as in FIG. 1.

7 is a nitrogen supply pipe for dilution, and 8 is a cooling furnace.

In the molten zinc heated to over 800℃ in crucible 2,
Nitrogen gas from which oxygen has been removed is blown through the preheating tube 3.

Further, preheated nitrogen gas is blown into the hole at the top of the crucible 2 through the dilution nitrogen supply pipe 7 to dilute the zinc vapor generated from the molten metal. The diluted zinc vapor passes through the Elema heating element 4 and enters the cooling furnace 8. Then, dilute zinc vapor is released into the atmosphere from a nozzle attached to the ceiling of the cooling furnace 8. No flame associated with the oxidation reaction was observed. The generated zinc oxide is collected through a filter 5.

This method was carried out under conditions a and b shown in Table 3.

Table 3 In all cases, white powder was obtained, and the results of X-ray diffraction Z
It was identified as nO. Figure 5 is a microscopic photograph of zinc oxide produced under condition a. It appears to be agglomerated to some extent, but the diameter of each particle making up the agglomeration is 0.01μ.
It was easy to separate and had a very large specific surface area.

[Effects of the Invention] According to the present invention, ultrafine and spherical zinc oxide can be easily obtained. In particular, spherical materials have a high bulk density, good fluidity, are easy to handle, and are easy to cut out in a certain amount, making them effective for automating production processes. The ultrafine and spherical shape increases spreadability and uniform miscibility when used in cosmetics and other products. In addition, the characteristic values of fluorescence, piezoelectricity, and semiconductivity change, making it effective for new applications such as materials for electronic parts.

[Brief explanation of drawings]

FIGS. 1 and 2 are conceptual diagrams of an apparatus suitable for carrying out the present invention, and FIGS. 3 to 5 are GI microphotographs of zinc oxide obtained in Examples of the present invention. 1... Electric furnace 2... Crucible 3... Preheating tube 4... Elema heating element 5... Filter 6... Thermometer 7... Nitrogen feed pipe for dilution 8... Cooling Toga 3 diagrams x 606α Toga 4 diagrams X90. σD Fang 5 drawings x 90. αD Procedure book (method) % formula % 1, Indication of case 1986 Patent Application No. 1225
38 No. 2, Title of the invention: 11 Manufacturing method for spherical zinc oxide Name: Nikko Zinc Co., Ltd. (Delivery date: July 28, 1986) 6. Subject of amendment: A column for a brief explanation of the drawings in the specification. 7. Contents of correction

Claims (3)

[Claims] (1) A method for producing spherical zinc oxide, which comprises bringing low-temperature diluted zinc vapor into contact with oxygen. (2) The method for producing spherical zinc oxide according to claim (1), wherein the low-temperature diluted zinc vapor is generated by blowing an inert gas into molten zinc at a temperature of 550 to 800°C. (3) Low-temperature diluted zinc vapor is produced by evaporating zinc vapor from molten zinc at a temperature of 800 to 950°C, diluting and cooling it by blowing inert gas into it, as described in claim (1). Method for producing spherical zinc oxide.