JPS60186416A - Production of sn-doped in2o3 powder having low electrical resistance - Google Patents

Abstract

PURPOSE:To prepare SnO2-doped In2O3 powder having low electrical resistance, by adjusting the pH of an aqueous solution containing an indium salt and stannous chloride at a specific ratio with oxalic acid and ammonia, and sintering the resultant precipitate under a specific condition. CONSTITUTION:Oxalic acid is added to an aqueous solution containing a water- soluble indium salt such as chloride, sulfate, etc. and stannous chloride at a ratio to obtain a product having an Sn-content of 0.1-20%. After the reaction, ammonia is added to the reaction mixture to adjust the pH to 0-2. The obtained precipitate is separated by filtration, washed thoroughly, dried, and sintered at 400-800 deg.C in an oxidizing atmosphere such as air. An electrically conductive SnO2-doped In2O3 fine powder having an electrical resistance of as low as about <=100OMEGA.cm can be prepared by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing fine powder having electrical conductivity. Conductive fine powders are widely used for forming resistive layers in electrostatic copying paper, electrically conductive thermal copying paper, etc. (Japanese Patent Laid-Open No. 56-416
03). Conductive powder imparted with transparency by being made into fine powder is used to form a transparent conductive film (Japanese Unexamined Patent Publication No. 56-1566).
03), as a conductive filler for the production of antistatic resins, and as flexible electroluminescent display materials.

Examples of conductive powders include fine powders of metals such as Ag, Ni, and Cu, carbon black, and conductive ZnO1sb dope5.
n02. Sb-doped Sn 02 coated Ti 02, etc. are known, but Ag is expensive, Ni and Cu are easily oxidized, carbon black is black and has poor dispersibility, and conductive ZnO has a large particle size. Powders using sb lack moisture resistance, and powders using sb have the problem of sb toxicity. A satisfactory conductive powder exhibiting a transparent or nearly white color is not yet known. In addition, generally speaking, methods for producing powder for the purpose of electrical conductivity are not well known.

It is known that the Sn 02 doped In203M film, also known as an ITO film, exhibits electrical conductivity.

Therefore, it is expected that the powder is also electrically conductive. According to the findings of the present inventors, Sn 02 doped In2O3
In the manufacturing method, alkali is added to a mixed aqueous solution of tin chloride and indium chloride, and the resulting hydroxide is calcined. Although a fine powder can be obtained at a firing temperature of 800 O or less, it is possible that This seems to be because the and In are not mixed uniformly.
The resistance of the compacted powder at a pressure of Cm2 (all resistance values below were measured under this condition) is high, and when fired at a temperature exceeding 800℃, it becomes 100Ω・c.
m or less, but sintering of particles occurs and fine powder cannot be obtained.

Even by adding oxalic acid to a mixed aqueous solution of stannic chloride and indium chloride and thermally decomposing the resulting oxalate, only a powder with high resistance (iooΩ·81 or higher) can be obtained.

The present inventors have discovered that when stannous chloride is used as the tin salt in the oxalic acid method, a powder with low resistance can be obtained.

i.e., water soluble indium salts (chlorides, sulfates, etc.)
and water-soluble stannous salts (chloride, sulfate, etc.) are dissolved in a predetermined amount of water, and an aqueous oxalic acid solution is added to adjust the pH to 0~2.
tin oxalate/indium co-precipitate.

The obtained coprecipitate is washed, dried, and then calcined at a temperature of 400 to 800° C. to obtain Sn 02 -doped In2O3 powder with low resistance (100 Ω”cm or less).

The tin content in the product is between 0.1 and 20%, preferably between 1 and 15%. If it is less than 0.1%, the resistance is 100Ω5eff1 or more, and even if it exceeds 20%, there is no significant change in resistance.

Of course, in order to achieve such a tin content in the product, the stannous chloride and indium salt must be in a stoichiometrically equivalent relationship in the starting solution.

If the pH is below 0 during precipitate formation, no precipitate will be obtained, and if it exceeds 2, the filterability of the precipitate will be very poor.

If the firing temperature is less than 400°C, decomposition of oxalic acid will be insufficient, and if it exceeds 800°C, sintering will begin.

Next, the present invention will be specifically explained with reference to Examples.

44.2 g of stannous chloride was dissolved in a solution of indium chloride with a concentration of 125 g/l, and three solutions of oxalic acid with a concentration of 170 g/l were added to this mixed solution at room temperature to react. was added to adjust the pH to 1. The reaction was continued, and after 20 minutes had elapsed from the beginning, the precipitate produced was separated in the furnace and thoroughly washed.

The resulting crystals were roasted in a stream of air.

The temperature was raised to 300°C over 1 hour, then to 450°C over 0.5 hour, and then heated at 550°C for 5 hours.

The resulting powder was dissolved in acid and analyzed spectrophotometrically to determine S.
The n content was 10.5%, the specific surface area was 20 to 25 m2/g, and the specific resistance was 3 to 10×1O0Ω11CI11.

Patent applicant Mitsubishi Metals Corporation Agent: Patent Attorney Masahiro Matsui

Claims (1)

[Claims] 1. A method for producing low resistance 5n02 doped In2O3, in which indium salt and stannous chloride are combined in the product with Sn
Oxalic acid is added to an aqueous solution with a content of 0.1 to 20%, and then ammonia is added to adjust the pH to 0 to 2.The resulting precipitate is filtered, washed, and dried. and sintering at 400-800°C in an oxidizing atmosphere.