PROCESSES OF PRODUCTION Of a POWDER AND a BODY SINTERS Of OXIDE Of INDIUM AND OXIDE Of TIN AND POWDER THUS OBTAINED

The present invention relates to a method for producing a powder of indium oxide and tin oxide, a method for producing a sintered body of indium oxide and tin oxide from the powder, and the powder of indium oxide and tin oxide thus obtained.

Thin layers are used of indium oxide and tin oxide (indium tin oxide: referred to in the following as "ITO") containing 2 to 20% by weight of tin oxide as transparent conductive layers for liquid crystal display devices due to their high electrical conductivity and high transparency.

Methods to form thin films of ITO include a method comprising applying a paste containing a fine powder of the ITO on a substrate and a method of forming a layer of ITO on the surface of a substrate by sputtering using a target of ITO obtained by sintering. The method of applying a powder of ITO on a substrate is less than the sputtering method in such a way that the quality and the performance of ITO layers thus obtained.

In the method for producing thin layers of ITO by cathode sputtering using a target of ITO arises problems such as performance degradation sputtering (e.g. formation of nodules to the target surface from ITO, decrease the rate of formation of the layer) and degradation of the electrical conductivity and the transparency of the thin ITO layer when using a target of ITO low density, less than 90% of the theoretical density. Therefore, it has been necessary to develop a ITO sintered body of high density and an ITO powder for producing such a sintered body.

The Japanese Patent made available to the public (Kokai) n* 62-7 627 disclosed is a method for producing an ITO powder (co-precipitation method) in which tin oxide is uniformly distributed, which comprises mixing an aqueous solution of a salt of indium and a tin salt with a precipitating agent such as ammonia to obtain a precipitate containing indium and tin and drying the precipitate and its calcination, as a method for producing an ITO powder are a raw material for a sintered body of ITO.

In the production of an ITO powder by the coprecipitation conventional method it is not easy to collect the precipitate containing indium and tin by solid-liquid separation (such as filtration) because the precipitate, which is obtained in the form of precursor of the ITO powder, is in the form of a gel. The dried material obtained from the precipitate becomes a hard agglomerated mass and the ITO powder obtained by calcining the dried material contains a large amount of coarse agglomerate particles in which the primary particles are strongly adhered together such that a deagglomeration is delicate. When a ITO sintered body is formed by an ITO powder containing a large amount of agglomerated particles it is difficult to obtain ITO sintered body of high density greater than 90% of the theoretical density.

To solve these problems, for example, the Japanese Patent made available to the public (Kokai) n* 3-215 318 indicates that an ITO sintered body having a density greater than 75%, preferably 85%, of the theoretical density is obtained by means of an ITO powder formed by mechanical milling of an ITO powder comprising fine particles having a primary particle size of panel 1 or less, obtained by the co-precipitation method, by means of a mill vibration-type having a high crushing efficiency. According to the document, it is not possible to obtain an ITO powder for producing a sintered body of high density ITO when using a ball mill. A difficulty of this method is that some grinding media are liable to cause contamination by impurities because the ITO powders is comminuted by means of a mill vibration-type.

The methods of sintering to obtain a sintered body of high density ITO include, for example, hot pressing (hereinafter referred "DC") and hot isostatic pressing (hereinafter referred "CIP"). In these methods, sintering is conducted under pressure. However, as sintering is conducted in a reducing atmosphere, tin oxide is reduced when the sintering temperature is greater than or equal to 1100*C. Therefore, the solid solution of tin oxide in ITO becomes insufficient and heterogeneous such that are not producible a ITO sintered body having high strength. The methods have the disadvantage that the production cost is high because a expensive apparatus is required.

The Japanese Patent made available to the public (Kokai) n* 3-207 858 describes a sintering process in an atmosphere of oxygen under pressure to produce a sintered body of high density ITO. However, this method has the disadvantage that the production cost is high because a special sintering furnace capable of withstanding high pressures is needed to make the sintering in the atmosphere of oxygen under pressure. The method also presents a problem of security as sintering is carried out in a high-pressure oxygen atmosphere.

Following intensive studies on a production process of an ITO powder overcomes these disadvantages, it has been found that it is possible to produce a powder of ITO agglomeration small forces between the primary particles and for producing a sintered body of high density ITO by calcining a precipitate containing indium and tin which is obtained by reacting while the pH is maintained between 4 and 6. It has been found also that it is possible to obtain an ITO sintered body of high density by sintering the ITO powder under specific conditions of temperature.

Therefore, the present invention relates to a method for producing a powder of indium oxide and tin oxide which is characterized in that it comprises introducing into water at 40*C or more and less than 100*C and the reaction of an aqueous solution of an indium salt, an aqueous solution of a tin salt, or a mixture in aqueous solution of an indium salt and of a tin salt, and an aqueous alkali solution such that the pH during the reaction is maintained in the range of 4 to 6, the formation of a precipitate, washing the precipitate formed after the solid-liquid separation and calcining the precipitate at a temperature greater than or equal to 600^{# C} and less than or equal to 1,300 * C.

The present invention also provides a powder of indium oxide and tin oxide obtained by the above method, wherein the content of tin oxide is 2 to 20% by weight, the particle size, calculated from the BET specific surface area, is greater than or equal to 0.05 and less than or equal to [...][...] 1, the diameter at 50% in a cumulative distribution of particle size is less than or equal to 1 [...] and the halogen content is 0.2% by mass or less.

The present invention also relates to a method for producing a sintered body of indium oxide and tin oxide which is characterized in that it comprises molding the powder of indium oxide and tin oxide above to obtain a molded body and sintering the molded article at a temperature not less than 1,450^{# C} and less than or equal to 1,650^{# C}.

The present invention will be described in greater detail below.

The aqueous solution of indium salt used in the method for producing a powder of indium oxide and tin oxide according to the present invention may be a solution prepared by dissolving in water of salts such as the water-soluble indium indium chloride ( [...] (Π3), indium nitrate ( [...] ( [...] ) 3), indium sulfate (^ 2 (804) 3), for example, or a solution prepared by dissolving metallic indium in an aqueous hydrochloric acid solution or an aqueous solution of nitric acid, for example.

The aqueous solution of tin salt used in the method for producing a powder of indium oxide and tin oxide according to the present invention may be a solution prepared by dissolving in water of salts Water soluble tin such as tin chloride ( [...], SnCl2), tin sulfate ( [...] > 4), for example, or a solution prepared by dissolving tin metal in an aqueous hydrochloric acid solution, for example.

The mixture in aqueous salt solution of indium and tin salt which is used in the process for producing a powder of indium oxide and tin oxide of the invention can be a mixture prepared by dissolving water-soluble indium salts (for example indium chloride, indium nitrate) and tin water-soluble salts (for example tin chloride) in water, a mixture prepared by combining a mixture prepared by dissolving metallic indium in an aqueous hydrochloric acid solution or an aqueous solution of nitric acid and a mixture prepared by dissolving tin metal in an aqueous hydrochloric acid solution, or a mixture prepared by dissolving an alloy of indium and tin in an aqueous hydrochloric acid solution.

The concentration of the indium in the aqueous solution of indium salt and in the mixture in aqueous salt solution of indium and tin salt is not limited specifically but is preferably located in the range of about 20 to 400 g/l. When the concentration of the indium is less than 20 g/l, the production yield of the ITO powder can be lowered.

The concentration of tin in the aqueous solution of tin salt and in the mixture in aqueous salt solution of indium and tin salt can be determined by the relationship between the concentration of indium and the tin concentration which corresponds to the mass of tin oxide contained in the ITO powder which is obtained finally. The concentration of the indium salt and the tin salt in the aqueous solution may be adjusted so that the content of tin oxide in the ITO powder finally obtained is greater than or equal to 2% by mass and less than or equal to 20% by weight, based on the electrical conductivity of [...].

The aqueous solution of the salt of indium, the aqueous solution of the tin salt and the aqueous alkaline solution are introduced into water at a temperature greater than or equal to and less than 100*C 40*C such that the pH during the reaction is maintained in the range of 4 to 6, and the solutions are reacted to form a precipitate containing indium and tin.

Or, the mixture in aqueous salt solution of indium and tin salt and the aqueous alkaline solution are placed in water at a temperature greater than or equal to and less than 100*C 40*C such that the pH during the reaction is maintained in the range of 4 to 6, and the solutions are reacted for [...] a precipitate containing indium and tin.

Among the two above methods, preferred method of using the aqueous salt solution mixture of indium and tin salt because it is easy to maintain the pH between 4 and 6 during the reaction. Although only the method of using the aqueous salt solution mixture of indium and tin salt is explained in the following, it is also possible to use the method of using separately the aqueous solution of indium salt and the aqueous solution of tin salt by controlling the rate of delivery of each aqueous solution in accordance with the method of using the aqueous salt solution mixture of indium and tin salt.

The aqueous alkaline solution can be, for example, ammonia or an aqueous solution of sodium hydroxide. It is preferable to use ammonia free of metal ions so as to avoid the inclusion of metal ions in the precipitate containing indium and tin.

According to the method of the present invention, for example, a predetermined amount of water (for example distilled water or deionized water) having a predetermined temperature and pH is first introduced into a reactor and stirred. Furthermore, the mixture in aqueous salt solution of indium and tin salt and the aqueous alkaline solution is added to the water with agitation. Since the pH of the reaction system is lowered due to the supplying the mixture in aqueous salt solution of indium and tin salt, is added in an amount of aqueous alkaline solution sufficient to that the pH is maintained during the reaction between 4 and 6.

It is possible to maintain the predetermined pH by connecting a pH control device to the pump supplying aqueous alkaline solution and by operating the pump when the pH becomes less than the predetermined values.

To maintain the pH between 4 and 6 during the reaction, it is possible to also adjust the pH of the mixture being aqueous salt solution of indium and tin salt, for example between 0 and 2, so that a precipitate of indium and tin is not formed, before adding the aqueous alkaline solution, eg ammonia, to the mixture in aqueous solution, since the mixture in aqueous solution has a strong acidity.

The temperature of the water in the reactor is greater than or equal to and less than 100*C 40*C. When the temperature of the water is less than 40*C, recovering the precipitate by filtration requires much time (the filterability of the precipitate obtained is lowered) and further the dried material consisting of the precipitate becomes a hard agglomerated mass which is difficult to disintegrate, resulting in a degradation of the ability to deagglomeration.

The mixture in aqueous salt solution of indium and tin salt can be supplied at a flow rate of industrially advantageous. The delivery rate varies as a function of the extent of formation of the precipitate containing the indium salt and the tin salt. The time interval required to provide the total amount of mixture in aqueous salt solution of indium and tin salt is preferably greater than or equal to 10 min and less than or equal to 300 min, more preferably greater than or equal to 20 min and less than or equal to 200 min. When the supplying time of the aqueous salt solution mixture of indium and tin salt exceeds 300 min, the degree of agglomeration of the primary particles in the ITO powder finally obtained may become larger. In this case, it is also possible to perform the calcination after reducing the amount of agglomerated particles in deaggregating the dried material consisting of the precipitate obtained by solid-liquid separation and drying, in the manner described in the following.

The aqueous alkaline solution may be provided simultaneously that the pH during the reaction can be maintained in the range of 4 and 6, and the delivery rate is not limited specifically.

It is necessary that the pH during the reaction is maintained in the range of 4 to 6, preferably from 4.5 to 5.5. It is possible to obtain a precipitate containing indium and tin which has a uniform particle size, good filterability and deagglomeration after drying if the reaction is carried out by maintaining the pH in this field.

When the reaction is carried out by maintaining the pH to values above 6, the user may be provide a fine precipitate containing indium and tin. Therefore, not only a long time is required for the filtration but also it is formed after drying a hard agglomerated mass which is difficult to deagglomerate. When the reaction is carried out in the maintaining the pH at values below 4, there is no precipitate, the amount of indium dissolved in the solution becomes large and the final yield is lowered.

The variation range of pH during the reaction is preferably within the limits of + 1.0, more preferably ± 0.5, in the range from pH above.

At initial stage of the reaction, the pH is sometimes located outside the field of 4 to 6. In particular, it may occur a rapid decrease in the pH immediately after the start of the supply of the mixture by aqueous salt solution of indium and tin salt and it may occur a rapid rise in the pH after the start of the supply of the aqueous alkaline solution. If this phenomenon occurs only at the initial stage of the reaction, it does not affect the ability to filtration of the precipitate obtained containing indium and tin and the ability to deagglomeration of the dried material formed by the precipitate.

Therefore, a rapid change of the pH at the initial stage of the reaction is allowable. The reaction is operated so that the duration at the end of which the rapid variation of the pH at the initial stage of the reaction occurs is 10%, preferably 5%, of the total duration of reaction (time required to provide the total amount of the mixture in aqueous salt solution of indium and tin salt). Although the pH is sometimes located outside of the domain above, locally or instantaneously, in the reaction system, a low pH change can be admitted since the object of the present invention can be achieved.

After the end of the addition the mixture into aqueous salt solution of indium and tin salt, the precipitate formed, which contains indium and tin, is preferably subjected to a aging, such as by agitation or idle of the suspension containing the precipitate formed. The temperature of aging is the same as the reaction temperature and it is preferably greater than or equal to and less than [...] 40*C ' C. With the aging, the size of the particles becomes uniform and properties of filtering the precipitate and deagglomerating properties of the dried material consisting of the precipitate are improved further.

The precipitate containing indium and tin is caused to settle at the bottom of the reactor by ageing at rest. The volume of the sedimentation thus obtained is about 0.5 to 6 cm ^ / g ITO obtained theoretically, and it consists of solid particles of high density.

Furthermore, a solid-liquid separation is accomplished for example by filtration and the precipitate containing indium and tin is collected. The filtration method is not limited specifically and it may be for example a suction filtration or filtration using a filter press.

Since salts such as ammonium salts (for example ammonium chloride, ammonium nitrate) and alkali metal salts (for example sodium chloride, sodium nitrate), which are produced as by-products of the reaction of the salt of the indium and tin salt with the aqueous alkaline solution, adhere to the precipitate containing indium and tin after the solid-liquid separation by filtration, it is required to wash the precipitate. In particular, even if the ITO powder obtained by calcining the precipitate containing indium and tin to large amount of ammonium chloride is subjected to a treatment by washing dechlorinating described in the following, powder is obtained ITO containing a large amount of chlorine and it is not possible to obtain a sintered body of high density ITO having a relative density greater than 90%.

As a washing solvent water may be used (e.g. distilled water, deionized water) or ammonia which dissolves the being by-products. It is preferable to use ammonia as washing solvent because have the effect of reducing the duration of the wash. In this case, the pH of the ammonia is preferably 8 to 12, more preferably from 9 to 11. When the washing is accomplished with ammonia having a pH greater than 12, the precipitate containing indium and tin is capable of dissolving such that a resulting drop in the yield of the final ITO powder and a change in the composition of the tin oxide ITO powder in relation to the composition of the charge.

Furthermore, the precipitate containing indium and tin is calcined after the solid-liquid separation and an additional washing. After the solid-liquid separation and further washing, the precipitate containing indium and tin is preferably dried before the calcination. The drying process is not specifically limited and it may be for example of a heating process at a temperature at which the water which adheres to the precipitate containing indium and tin may be removed, for example, a temperature greater than or equal to and less than or equal to 90*C 200*C.

The dried material obtained is preferably deagglomerated. Since the volume of sedimentation of precipitate produced by supplying the mixture in aqueous salt solution of indium and tin salt then reacting decreases, the degree of agglomeration of the primary particles in the ITO powder finally obtained is low due to deagglomeration. The dried material can be easily deagglomerated because the degree of agglomeration is low even if the dried material is agglomerated. Deagglomerating The method is not limited specifically and it may be by example of a method using a ball mill or an atomizer.

The dried material consisting of the precipitate containing indium and tin obtained by the above process is then calcined to form an ITO powder.

It is necessary that the calcination temperature is greater than or equal to 600*C and less than or equal to 1,300 * C, preferably greater than or equal to 800*C and less than or equal to 1,200 * C. When the calcination temperature is less than 600*C, the decomposition of the remaining salts adhere to the precipitate containing indium and tin is insufficient and the primary particle size of TITO obtained is small so that the degree of agglomeration of the primary particles of the ITO powder increases to a large extent and that it is not possible to obtain a molded body high uniform density. As a result, the corresponding sintered body has difficulties such as cracking, fracture and warpage, for example.

When the calcination temperature exceeds 1,300 * C, the primary particles of ITO grow and some of them agglomerate so that the sinterability decreases and that it is not possible to obtain an ITO powder having good sintering properties.

The atmosphere for the calcination For it is preferable to use air, oxygen, nitrogen or a hydrogen halide (for example hydrogen chloride, hydrogen bromide, hydrogen iodide) or halogen (for example chlorine, bromine, iodine). It is preferred calcination in an atmosphere containing a hydrogen halide or halogen and being particularly preferred calcination in an atmosphere containing hydrogen chloride. When the calcination is performed in an atmosphere containing hydrogen chloride, the degree of agglomeration of the primary particles of the ITO powder is particularly low.

When the dried material consisting of the precipitate is calcined in an atmosphere containing a hydrogen halide or halogen, in particular in an atmosphere containing hydrogen chloride, the dried material is contained in an amount of preferably 1% by volume or more, more preferably in a proportion of from 5% by volume or more, and particularly preferred in an amount of 10% by volume or more, based on the total volume of the atmosphere. The upper limit of the concentration of the hydrogen halide or the halogen is not limited specifically and preferably 70% by volume or less, more preferably 50% by volume or less and particularly preferably 40% by volume or less, in view of industrial productivity. Preferred gases to dilute the hydrogen halide or the halogen, it is possible, for example, the use an inert gas (e.g. argon), nitrogen, oxygen, air or a mixture of these gases.

The atmosphere containing the hydrogen halide or halogen, in particular the atmosphere containing hydrogen chloride, is preferably introduced to 600*C or more. When the atmosphere containing the hydrogen halide is introduced at a temperature less than 600*C, volatilization losses ITO can become large and it can be a problem such as a decrease in the yield. After calcination at the predetermined temperature and during the predetermined period, the delivery of the atmosphere containing the hydrogen halide is interrupted and the atmosphere containing an inert gas (e.g. argon), nitrogen, oxygen, air or a mixture of these gases is provided, and cooling is accomplished.

The pressure of the atmosphere in which the calcination is is not limited specifically and it can be optionally selected in the domain that is used on an industrial scale.

The duration of calcination is not limited specifically because it depends on the concentration of the atmosphere and calcination temperature, and preferably 1 min or more, more preferably from 10 min or more.

The source of delivery and the delivery method the atmosphere are not limited specifically. It is preferable that the atmosphere can be introduced into the reaction system which contains the raw material containing indium, and tin.

The type of the calcining device is not specifically limited and it is possible to use a calciner. In particular, when using a hydrogen halide or halogen, the calciner is preferably made of a material which is not corroded by the hydrogen halide or halogen. Furthermore, it is desirable that the calciner is provided with a mechanism for adjusting the atmosphere. Preferably, the calciner is airtight when using a corrosive gas such as a hydrogen halide or halogen.

It is preferable to operate the calcination continuously industrially, such as by using a tunnel oven. When the the calcination is carried out in a corrosive atmosphere, the apparatus, or nacelle crucible used in the step of calcination is preferably alumina, quartz, acid-resistant bricks or graphite.

The ITO powder produced by the above method is composed of fine primary particles with a size, calculated from the BET specific surface area, is preferably greater than or equal to 0.05/ton and less than or equal to 1/is, more preferably greater than or equal to 0.1/year and less than or equal to 0.5 [...]. The diameter to 50% in a cumulative distribution of particle size (average size of the agglomerated particles) is greater than or equal to 1 [...] depending on the conditions used to obtain the precipitate containing indium and tin so that, sometimes, it is not possible to obtain a sintered body of high density ITO having a relative density greater than 90%, preferably greater than 95%. In this case, the ITO powder is preferably deagglomerated after calcination.

The method of deagglomeration of the ITO powder is not specifically limited and it may be by deagglomerating example of a method using a vibratory mill, a ball mill, a jet mill, which are normally used in the industry. As a method of deagglomeration of the ITO powder of the present invention it is possible to use a method of deagglomeration light (e.g. deagglomerating means of a ball mill or a jet mill) because the degree of agglomeration of the primary particles of the ITO powder is low. The deagglomeration In the case of using a ball mill, it is possible to use a wet or dry deagglomeration or a combination thereof.

For the container and the balls used for the deagglomeration of the ITO powder, it is possible to use a container or resin and alumina balls alumina, zirconia or resin. The deagglomeration In the case of using a ball mill, it is preferable to use a container made by a resin and balls zirconia highly wear-resistant, since contamination caused by the container and the balls is low.

When using a hydrogen halide or halogen as calcination atmosphere, there is sometimes a large amount of halogen in the ITO powder after calcination. When the residual amount of chlorine is particularly important, it is sometimes impossible to obtain a high density sintered body having a relative density greater than 90%, preferably greater than 95%. In this case, the residual amount of chlorine can be reduced preferably to 0.2% by mass or less, more preferably to 0.1% by mass or less, by washing with water or with an aqueous alkaline solution of the ITO powder after calcination or after calcination and deagglomeration, or by heat-treating the ITO powder in an atmosphere containing 0.1% by volume or more of at least one gas selected from the group consisting of water vapor and oxygen at a temperature greater than or equal to 600*C and less than or equal to 1,300 * C, or by a combination of the above treatment.

The ITO powder produced by the above method is an ITO powder easily sinterable wherein the particle size calculated from the BET specific surface area is greater than or equal to 0.05 [...] and less than or equal to 1/year, preferably greater than or equal to 0.1 [...] and less than or equal to 0.5/year, the diameter at 50% in a cumulative distribution of particle size is less than or equal to 1 [...] and the halogen content is 0.2% by mass or less, preferably 0.1% by mass or less, so that it is possible to obtain a high density sintered body having a relative density of 90% or more, preferably 95% or more.

The ITO powder obtained by the above method is molded to impart a specific shape such as a plate or disc, for example, and it is sintered. The method of molding is not specifically limited and it can be, for example molding under uniaxial pressure, a cold isostatic pressing (hereinafter referred "CIF"), wheel slip, of a filter press molding, extrusion molding or injection molding. The moulding methods above can be used alone or in combination.

Π is necessary that the sintering temperature is greater than or equal to 1,450 * C and less than or equal to 1,650 * C. When the sintering temperature is less than 1,450 * C, it is not possible to obtain a sintered body having a relative density of not less than 90%, preferably greater than or equal to 95%, and the solid solution of tin oxide in indium oxide is insufficient. On the other hand, when the sintering temperature exceeds 1,650 * C, there is a grain growth in the ITO sintered body and the mechanical strength of the ITO sputtering target obtained is lowered.

The sintering is accomplished preferably in an atmosphere containing an oxygen-containing gas at normal pressure (e.g., air), more preferably in a pure oxygen atmosphere. The pure oxygen atmosphere is an atmosphere containing oxygen and gaseous impurities inevitable. When the sintering is carried out in an atmosphere free of oxygen-containing gas (e.g. nitrogen, argon), indium oxide or tin oxide in TITO is sometimes disrupted indium, tin and oxygen.

According to the production method of the ITO sintered body of the present invention, it is possible to obtain a sintered body of high density ITO having a relative density greater than or equal to 90%, preferably greater than or equal to 95%. When used sintered body for sputtering, it is possible to reduce the formation of nodules, improve the efficiency of sputtering, reduce the formation of particles having an abnormal discharge and a thin layer of ITO high quality.

According to the present invention, it is possible to produce a powder of ITO upper sintering properties, capable of leading to the production of a high density sintered body whose density is more than or equal to 90%, more preferably greater than or equal to 95% of the theoretical density. The ITO powder of the present invention may be used in the production of transparent conductive fillers.

When using the ITO powder of the present invention as the raw material for producing a sintered body ITO a sintered body is obtained high density, when used as a sputtering target, can enhance the efficiency of sputtering.

The present invention will now be described by means of the following non-limiting examples.

In the examples, various properties were measured as follows.

(l) The diameter to 50% in a cumulative distribution of size of particles has been measured by means of a distribution analyzer particle size of centrifugal sedimentation type (SACP -2, manufactured by the company Shimadzu Corporation) based on the principle of the method to light transmission.

(2) The BET specific surface area was measured by means of an apparatus [...] -II, 2300 (manufactured by the company [...] ).

The particle size (D BET) has been derived from the and BET specific surface area calculated by the following equation:

D BET (um) = 6 / (S */ p)

(wherein S is the BET specific surface area (m^/g) and p is the theoretical density [...] (g/cm ^)) and the value obtained has been selected as a measure of the primary particle size.

In the case of an ITO containing 10% by weight of an oxide of tin, the value of the theoretical density of ITO has been determined from the theoretical density of indium oxide (7.18 g/cm ^) and that of tin oxide (6.95 g/cm3) according to the following equation, to obtain the value 7.16 g/cm3.

7,18 g/cm ^ (density of the indium oxide) (content) x 0.9+6.95 g/cm ^ (density tin oxide) (content) x 0.1 = 7.16 g/cm3 ( [...] density).

The tin content has been measured by spectroscopic analysis of transmission and converted into tin oxide content.

The chlorine content was determined by a titration method silver nitrate.

The density of the sintered body has been measured according to the principle of Archimedes according to the measuring method of JIS R 2205-1992.

Since value of the theoretical density of the ITO sintered body which is used to calculate the relative density of the sintered body, is 7.16 g/ [...] used in the case of an ITO containing 10% by weight of tin oxide.

A mixture in aqueous solution of an indium salt and a tin salt has been prepared by the following three types of methods so that the content of tin oxide in ITO powder obtained finally either of 10% by weight.

1. Mixture A salt in aqueous solution of indium and tin salt prepared an aqueous solution of indium salt by dissolving metallic indium (purity: 99.99%, 57.40 g) in an aqueous hydrochloric acid solution and 6N diluted to 11 with deionized water and 200 ml is taken from the resultant aqueous solution. On the other hand, is prepared 100 ml of an aqueous solution of tin salt by dissolving metallic tin (purity: 99.99%, 6.21 g) in a concentrated aqueous solution of hydrochloric acid and 21 ml was obtained the solution thus obtained. Furthermore, these solutions were mixed to prepare a mixture (221 ml) salt in aqueous solution of indium and tin salt.

In the mixture in aqueous solution thus obtained, the concentration of 51.95 g/l In is and the concentration of Sn is 5.91 g/l.

2. Mixture B salt in aqueous solution of indium and tin salt prepared 120 ml of an aqueous solution of indium salt by dissolving metallic indium (57.40 g) in a concentrated aqueous solution of hydrochloric acid and then was obtained 106 ml the solution thus obtained. On the other hand, is prepared 93 ml of an aqueous solution of tin salt by dissolving metallic tin (5.81 g) in a concentrated aqueous solution of hydrochloric acid and was obtained 90 ml of the resulting solution. Furthermore, these solutions were mixed to prepare a mixture in aqueous solution (196 ml) salt of indium and tin salt.

In this mixture in aqueous solution, the concentration of In is 258.69 g/l and the concentration of Sn is 28.68 g/l.

3. C mixture in aqueous solution of indium salt and tin salt prepared 680 ml of an aqueous solution of indium salt by dissolving metallic indium (252.60 g) in a concentrated aqueous solution of hydrochloric acid. On the other hand, is prepared 230 ml of an aqueous solution of tin salt by dissolving metallic tin (53.95 g) in a concentrated aqueous solution of hydrochloric acid and 117 ml was obtained the solution thus obtained. Furthermore, these solutions is mixed and added concentrated ammonia (63 ml) to prepare a mixture (860 ml) salt in aqueous solution of indium and tin salt.

The concentration of In in the mixture thus obtained was 293.72 g/l and the concentration of Sn was 31.91 g/l.

The precipitate containing indium and tin has been calcined according to the following two types of methods.

1. A method for calcination A

A precipitate containing indium and tin has been dried at 110*C as a raw material and then inserted into a nacelle of alumina or quartz. The introduction amount of dried material consisting of the precipitate is about 2 g to 18 and extended to a depth of about 10 mm. Roasting has been carried out in a cylindrical furnace (electric furnace MS manufactured by the company [...] Co., Ltd.) provided with a muffle of quartz (diameter: 58 mm, length:

1 200 mm). The heating rate was 10*C7min to 900*C and 5*C/min to 1100*C.

The atmosphere was formed by an air flow only, from room temperature to 1,000 * C. At temperatures above 1,000 * C, passed hydrogen chloride in a predetermined concentration. It has adjusted the concentration of the atmosphere by controlling the gas flow to the means of a flow meter. Since dilution gas hydrogen chloride is used air, and is adjusted to about 10 cm/min the linear speed of the gas flow that constitute the atmosphere.

Since hydrogen chloride using a hydrogen chloride contained in a bottle (purity: 99.9%, manufactured by the company Soda Tsurumi Co., Ltd.).

When the temperature has reached the predetermined temperature, the material is held at this temperature for a predetermined time. It has obtained the desired ITO powder in the nacelle of alumina in which has been introduced the dried precipitate containing indium and tin as a raw material, at the end of the predetermined holding time and cooling by means of a stream of air only.

2. A method for calcination B

It has dried at 110*C a precipitate containing indium and tin as raw material and introduced into a quartz boat. Sec The amount introduced material consisting of the precipitate is about 360 g and it extends to a depth of about 10 mm. The calcination was made in an electric furnace box high temperature (manufactured by the company [...][...] Co., Ltd.) inserted in a muffle of quartz (diameter:

160 mm, length: 1,600 mm). The heating rate was 5*C/min to 1100*C. The other operating conditions were the same as for the calcination process A above.

The ITO powder obtained by calcining has been washed with water to conduct dechlorination, dried, optionally subjected to a treatment deagglomerating and molded, then its sintering properties have been evaluated. The method of water washing the ITO powder comprises introducing 5 to 10 g of ITO powder after calcination in 500 ml of deionized water or the introduction of 280 g of ITO powder after calcination in 3,000 ml of deionized water, stirring for 30 min, filtering the solution by suction and repeating the washing with deionized water until no chlorine ion is detected upon introduction dropwise an aqueous nitrite solution of silver in the waste water.

The ITO powder was deagglomerated by the two kinds of the following methods.

1. Dry[...]

The ITO powder (5 g) and balls zirconia (500 g) of a diameter of 5 mm have been introduced in a pot of 500 ml polyethylene, and the powder of ITO has been agglomerated using a ball mill to 600 rpm for 6 hr.

2. Wet [...]

The ITO powder (250 g), balls (3,500 g) zirconia of a diameter of 5 mm and ethanol (500 ml) have been introduced in a polyethylene of 2,1, ITO and the powder has been agglomerated using a ball mill to 100 rpm for 6 h and dried under reduced pressure using a rotary evaporator.

The resulting powder has been subjected to molding under uniaxial pressure at 10 ^ Pa (100 kg/cm ^) and molding CIF under a pressure of 3 x 10 ^ Pa (t/cm ^ 3). Sintering has been produced by means of a heat treatment furnace ultra-high temperature (manufactured by the company [...][...] Co., Ltd.). First, the interior of the furnace wherein the molded body has been introduced has been evacuated with a vacuum pump, and the pressure has been returned to the normal pressure by the introduction of oxygen so that the atmosphere inside the oven has been replaced by an atmosphere with oxygen. Furthermore, the shaped body was sintered under a flow of oxygen, at normal pressure, at a temperature of 1500 to 1,600 * C for 10 hours to obtain a ITO sintered body. The heating rate was 20*C/min.

Example 1

Four hundred milliliters of water whose pH has been adjusted to 4.5 by addition of a dilute aqueous solution of hydrochloric acid to deionized water have been introduced in a beaker to 60*C 11 and held. As the deionized water was agitated (pH = 4.5,60 * C), a mixture in aqueous solution A of an indium salt and a tin salt and ammonia at 12.5% have been introduced simultaneously in 35 min so as to maintain the pH to 4.5 during the reaction. During the 2 min which have followed the start of the reaction, the pH varied in the range of 3.0 to 5.2. Two minutes after the start of the reaction, the reaction was performed while the pH was maintained in the range of 4.4 to 4.6 to form a precipitate containing indium and tin.

After the end of the reaction, the resulting solution has been stirred at 60*C during 30 min, allowed to stand at 60*C h during 6, and left to stand at room temperature for 14 h for subjecting the precipitate to an aging. The volume of settling the precipitate after the aging was 3.5 cm ^ / g ITO obtained theoretically.

The precipitate was collected by filtration by means of a Buchner filter having an internal diameter of about 76 mm (funnel-type filter Buchner manufactured by the company [...] Co., Ltd.), of a filter paper quantitative (filter paper quantitative n* 5C, manufactured by the company Toyo [...] Co., Ltd.) and aspirator ( [...][...], manufactured by the company Yamato Kagaku Co., Ltd.), and washed 10 times with about 120 ml of deionized water. The time required for filtration and washing was 1 h, the filterability was excellent, and the operation was extremely easy. This precipitate has been dried at 110*C and it has been found that the dried material was easily deagglomerated.

The dried material has been calcined at 1100*C during 30 min in a flow of hydrogen chloride to 20% by volume (diluted with air) from a temperature of 1,000 * C according to the calcination process A, washed with water and then dried to obtain an ITO powder.

The ITO powder obtained had a tin oxide content of 9.9% by mass, a BET specific surface area of 8.2 m ^ / g, a particle size calculated from the BET specific surface area of 0.10 [...] and a diameter at 50% in a cumulative distribution of particle size of 0.33 [...]. The ITO powder was observed by a scanning electron microscope (model [...] -T 220, manufactured by the company Nippon Denshi Co., Ltd.). It resulted in that the primary particle size of the ITO powder is about 0.1 [...] and that the degree of agglomeration of the primary particles is low.

Example 2

Four hundred milliliters of water whose pH has been adjusted to 4.5 by the addition of a dilute aqueous solution of hydrochloric acid to deionized water have been introduced in a beaker to 60*C 11 and held. As the deionized water was agitated (pH = 4.5,60 * C), the mixing in aqueous solution B of an indium salt and a salt of tin and aqueous ammonia to 12.5% have been introduced simultaneously in 69 min such that the pH is maintained at 4.5 during the reaction. During the 2 min which have followed the start of the reaction, the pH varied in the range of 3.1 to 5.4. Two minutes after the start of the reaction, the reaction was performed while the pH was maintained in the range of 4.4 to 4.6 to form a precipitate containing indium and tin.

After the end of the reaction, the resulting solution has been stirred at 60*C during 30 min, allowed to stand at 60*C during 6 h and left to stand at room temperature for 14 h for subjecting the precipitate to an aging. The volume of settling the precipitate after the aging was 1.3 cm ^ / g ITO obtained theoretically.

The precipitate was collected by filtration by means of a type filter Buchner from an inner diameter of about 135 mm, of a filter paper and quantitative n* 5C of a vacuum cleaner, and washed 10 times with about 120 ml of deionized water. The time required for filtration and washing was 1 h, the precipitate the filterability was excellent, and the operation was extremely easy. This precipitate has been dried at 110*C and it is found that the dried material was easily deagglomerated.

The dried material obtained was calcined at 1100*C during 30 min in a flow of hydrogen chloride to 20% by volume (diluted with air) from the temperature of 1,000 * C, according to the process of calcination A, washed with water and then dried to obtain an ITO powder.

The ITO powder obtained had a tin oxide content of 10.5% by weight, a BET specific surface area of 6.1 m ^ / g, a particle size calculated from the BET specific surface area of 0.14 ^ m and a diameter at 50% in a cumulative distribution of particle size of from 1.1 [...]. The ITO powder was observed by a scanning electron microscope. It resulted in that the primary particle size of the ITO powder obtained is about 0.1 [...] and that the degree of agglomeration of the primary particles is low.

The powder has been subjected to a treatment deagglomerating sec to obtain an ITO powder having a BET specific surface area of 8.7 m ^ / g, a particle size calculated from the BET specific surface area of 0.10/year and a diameter at 50% in a cumulative distribution of particle size of from 0.39 [...].

Example 3

A ITO powder was obtained in the same manner as described in the example 1, except that has been inserted a mixture in aqueous solution simultaneously A of an indium salt and a salt of tin and aqueous ammonia to 12.5% in 36 min so as to maintain the pH during the reaction to 5.0.

During the 2 min which have followed the start of the reaction, the pH varied in the range of 3.5 to 6.7. Two minutes after the start of the reaction, the reaction was conducted while the pH has been maintained in the range of 4.5 to 5.5.

After the end of the reaction, the resulting solution has been stirred at 60*C during 30 min, allowed to stand at 60*C during 6 h and left to stand at room temperature for 14 h for subjecting the precipitate to an aging. The volume of settling the precipitate after the aging was 4.6 g ^ [...] /ITO obtained theoretically.

The precipitate was collected by filtration by means of a type filter Buchner from an inner diameter of about 76 mm, filter paper and quantitative n* 5C of a vacuum cleaner, and washed 10 times with about 120 ml of deionized water. The time required for filtration and washing was 1 h, the precipitate the filterability was excellent, and the operation was extremely easy. This precipitate has been dried at 110*C and it is found that the dried material was easily deagglomerated.

The dried material obtained was calcined at 1100*C during 30 min under a stream of hydrogen chloride to 20% by volume (diluted with air) from the temperature of 1,000 * C, according to the process of calcination A, washed with water and then dried.

The ITO powder obtained by calcining had a BET specific surface area of 8.1 m ^ / g, a particle size calculated from the BET specific surface area of 0.10 [...] and a diameter at 50% in a cumulative distribution of particle size of 0.40 [...]. The ITO powder was observed by a scanning electron microscope and it has been found that the primary particle size of the ITO powder obtained is about 0.1 [...] and that the degree of agglomeration of the primary particles is low.

Example 4

The powder obtained in the example 3 has been calcined in air at 30 min 1100*C during electroless hydrogen chloride. The ITO powder obtained by calcining had a BET specific surface area of 7.3 m ^ / g, a particle size calculated from the BET specific surface area of 0.11 [...] and a diameter at 50% in a cumulative distribution of particle size of 0.50 ^ m. This ITO powder was observed by a scanning electron microscope and it has been found that the primary particle size of the ITO powder is about 0.1 [...] and that the degree of agglomeration of the primary particles is low.

Example 5

Two thousand milliliters of water whose pH has been adjusted to 5.0 by addition of a dilute aqueous solution of hydrochloric acid to deionized water have been introduced in a beaker to 60*C 5,1 and held. As the water was agitated (pH = 5.0,60 * Ç), a mixture in aqueous solution C of an indium salt and a salt of tin and aqueous ammonia to 12.5% have been simultaneously added in 84 min such that the pH is maintained at 5.0 during the reaction.

During the 2 min which have followed the start of the reaction, the pH varied in the range of 3.6 to 5.5. Two minutes after the start of the reaction, the reaction was performed while the pH was maintained in the range of 4.8 to 5.2 to form a precipitate containing indium and tin.

After the end of the reaction, the resulting solution has been stirred at 60*C during 30 min, allowed to stand at 60*C h during 6, and left to stand at room temperature for 14 h for subjecting the precipitate to an aging. The volume of settling the precipitate after the aging was 1.1 cm? ITO Ig obtained theoretically.

After the addition of concentrated aqueous ammonia to adjust the pH to 8.5 with stirring to the suspension containing the precipitate after a new aging, the precipitate was collected by filtration by means of a Buchner filter from an inner diameter of about 195 mm, filter paper and quantitative n* 5C of a vacuum cleaner, and washed 5 times with about 21 dilute aqueous ammonia whose pH has been adjusted to 10 by addition of aqueous ammonia de-ionized water. The time required for filtration and washing was 25 min, the precipitate the filterability was excellent, and the operation was extremely easy. This precipitate has been dried at 110*C and it is found that the dried material was easily deagglomerated.

The dried material obtained was calcined at 1100*C during 40 min under a stream of hydrogen chloride to 20% by volume (diluted with air) from the temperature of 1,000 * C, according to the process of calcination B, washed with water and then dried to obtain an ITO powder.

The ITO powder obtained had a BET specific surface area of 3.3 m^/g, a particle size calculated from the BET specific surface area of 0.25 [...] and a diameter at 50% in a cumulative distribution of particle size of 2.6 [...]. The ITO powder was observed by a scanning electron microscope and it has been found that the primary particle size of the ITO powder is about 0.1 to 0.2 [...] and that the degree of agglomeration of the primary particles is low.

The powder has been subjected to a treatment deagglomerating wet to obtain an ITO powder having a BET specific surface area of 5.1 m ^ / g, a particle size calculated from the BET specific surface area of 0,16/is and a diameter at 50% in a cumulative distribution of particle size of 0.48 [...]. The chlorine content of the ITO powder was 0.05% or less by mass.

Example 6

A ITO powder was obtained in the same manner as in the example 5, except that 2,000 ml water whose pH has been adjusted to 5.0 by addition of a dilute aqueous solution of hydrochloric acid to deionized water have been introduced in a beaker to 50*C 5,1 then held and as a mixture in aqueous solution C of an indium salt and a salt of tin and aqueous ammonia to 12.5% have been introduced simultaneously in 81 min so as to maintain the pH to 5.0 during the reaction while the water was agitated (pH = 5.0,50 * Ç).

During the 2 min which have followed the start of the reaction, the pH varied in the range of 3.6 to 6.5. Two minutes after the start of the reaction, the reaction was performed while the pH was maintained in the range of 4.8 to 5.3 to form a precipitate containing indium and tin.

After the end of the reaction, the resulting solution has been stirred at 60*C during 30 min, allowed to stand at 60*C during 6 h and left to stand at room temperature for 14 h for subjecting the precipitate to an aging. The volume of settling the precipitate after the aging was 1.7 cm ^ / g ITO obtained theoretically.

After the addition of concentrated aqueous ammonia to adjust the pH to 8.6 with stirring to the suspension containing the precipitate after a new aging, the precipitate was collected by filtration by means of a Buchner filter from an inner diameter of about 195 mm, filter paper and quantitative n* 5C of a vacuum cleaner, and washed 5 times with about 2,1 dilute aqueous ammonia whose pH has been adjusted to 10 by addition of aqueous ammonia de-ionized water. The time required for filtration and washing was 30 min, the precipitate the filterability was excellent, and the operation was extremely easy. This precipitate has been dried at 110*C and it is found that the dried material was easily deagglomerated.

The dried material obtained has been calcined by the calcination process B, washed with water and then dried to obtain an ITO powder that had a BET specific surface area of 3.2 m ^ / g, a particle size calculated from the BET specific surface area of 0.26/year and a diameter at 50% in a cumulative distribution of particle size of from 2,8/year. The ITO powder was observed by a scanning electron microscope and it has been found that the primary particle size of the ITO powder is about 0.1 to 0,2/year and that the degree of agglomeration of the primary particles is low.

The powder has been subjected to a treatment deagglomerating wet to obtain an ITO powder having a BET specific surface area of 5.1 m ^ / g, a particle size calculated from the BET specific surface area of 0.16/year and a diameter at 50% in a cumulative distribution of particle size of 0.52/year.

Example 7

[...] The powder obtained in the example 1, which had a content of tin oxide in of 9.9% by mass, a particle size calculated from the BET specific surface area of 0.1/year and a diameter at 50% in a cumulative distribution of particle size of 0.33/year, has been molded in the form of a disk having a diameter of 10 mm which was then sintered at 1,600 C for 10 * h. It resulted in a sintered body of ITO which had a density of 7.09 g/cm ^ and that was densified to 99.1% of the theoretical density.

Example 8

The ITO powder obtained in the example 1 which had a content of tin oxide in of 9.9% by mass, a particle size calculated from the BET specific surface area of 0.1/year and a diameter at 50% in a cumulative distribution of particle size of 0.33/year, has been molded in the form of a disk having a diameter of 10 mm which was then sintered at 1,500 C for 10 * h. Π resulted in a sintered body of ITO which had a density of 7.06 g/cm ^ and that was densified * to 98.5% of the theoretical density.

Example 9

The ITO powder obtained in the example 2 which had a tin oxide content of 10.5% by mass, a particle size calculated from the BET specific surface area of 0.1/is and a diameter at 50% in a cumulative distribution of particle size of 0,39/year, has been molded in the form of a disk having a diameter of 10 mm which was then sintered at 1,600 C for 10 * h. It resulted in a sintered body of ITO which had a density of 7.06 g/cm ^ and that was densified at 98.6% of the theoretical density.

Example 10

The ITO powder obtained in the example 5, which had a particle size calculated from the BET specific surface area of 0,16/is and a diameter at 50% in a cumulative distribution of particle size of 0.48/year, has been molded in the form of a disk having a diameter of 90 mm which was then sintered at 1,600 C for 10 * h. It resulted in a sintered body of ITO which had a density of 7.15 g/cm ^ and that was densified to 99.8% of the theoretical density.

Example 11

The ITO powder obtained in the example 6, which had a particle size calculated from the BET specific surface area of 0,16/is and a diameter at 50% in a cumulative distribution of particle size of 0,52/year, has been molded in the form of a disk having a diameter of from 20 mm which was then sintered at 1,600 C for¹⁰ # h. It resulted in a sintered body d ' [...] that had a density of 7.15 g/cm ^ and that was densified to 99.8% of the theoretical density.

Four hundred milliliters of water whose pH has been adjusted with 7.3 by adding dilute aqueous ammonia to deionized water have been introduced in a beaker of 11 and maintained at 60*C. As the water was agitated (pH = 7.3,60 * C), a mixture in aqueous solution A of an indium salt and a salt of tin and aqueous ammonia to 25% have been simultaneously added in 39 min such that the pH is maintained at 7.3 during the reaction. During the 3 min which have followed the start of the reaction, the pH varied in the range of 3.0 to 7.8. Three minutes after the start of the reaction, the reaction was performed while the pH was maintained in the range of 7.0 to 7.4 to form a precipitate containing indium and tin.

After the end of the reaction, ageing has been performed as described in the example 1. It resulted in that the volume of settling the precipitate after the aging was 11 cm-Vg [...] obtained theoretically.

In the same manner as in the example 1, the precipitate was collected by suction filtration and washed 3 times with about 120 ml of deionized water. The time required for filtration and washing was h 9 and the filtration process was delicate. After washing, the precipitate is dried at 110*C. This found that the dried material had become a hard agglomerated mass which was difficult to deagglomerate.

A precipitate containing indium and tin has been obtained in the manner described in the example 1, except that the temperature of the water in the reactor and the aging temperature have been adjusted to 28*C.

The volume of settling the precipitate after the aging was 8.7 cm ^ / g ITO theoretically obtained.

The precipitate was collected by suction filtration in the manner described in the example 1. It has been found that the time required for filtration was 7 the only h and that it was very difficult to perform the filtration operation. This precipitate has been dried at 110*C. It has been found that the dried material had become a very compact mass which was difficult to deagglomerate.

The ITO powder obtained in the example 2, which had a tin oxide content of 10.5% by weight, a BET specific surface area of 6.1 m ^ / g, a particle size calculated from the BET specific surface area of 0,14/and a diameter at 50% in a cumulative distribution of particle size of from 1.1/a, has been molded in the form of a disk having a diameter of 10 mm which was then sintered at 1,600 C for 10 * h. It resulted in a sintered body had a density of 6.34 g/cm ^ and that was densified to only 88.5% of the theoretical density.

The precipitate obtained in the manner described in the example 5 was collected by suction filtration and washed 3 times with about 21 of an aqueous solution of ammonium chloride to 2% by weight. The time required for filtration and washing was 23 min, the filtration properties were excellent and the operation was extremely easy. This precipitate has been dried at 110*C and it has been found that the dried material was easily deagglomerated.

The dried material obtained, which adhered ammonium chloride, has been calcined at 1100*C during 30 min under a stream of hydrogen chloride to 20% by volume (diluted with air) from the temperature of 1,000 * C, according to the process of calcination A, washed with water and then dried to obtain an ITO powder.

The ITO powder obtained had a BET specific surface area of 3.8 m ^ / g, a particle size calculated from the BET specific surface area of 0.22 [...] and a diameter at 50% in a cumulative distribution of particle size of from 1,2/is. [...] The powder was observed by a scanning electron microscope and it has been found that primary particle size of the ITO powder is about 0.1 to 0,2/a and that the degree of agglomeration of the primary particles is low. This powder was subjected to a dry treatment of deagglomeration to obtain an ITO powder having a BET specific surface area of 7.4 m ^ / g, a particle size calculated from the BET specific surface area of 0.11 [...] and a diameter of 50% in a cumulative distribution of particle size of 0.43 [...]. The chlorine content of the powder [...] was 0.28% by mass.

The powder [...] subjected deagglomerating dry has been molded in the form of a disk having a diameter of from 20 mm which has then been calcined at 1,600 C for 10 * h. The thus obtained sintered body had a density of 6.06 g/cm ^ and densified to only was 84.7% of the theoretical density.

A ITO powder was obtained in the manner described in the example 1, except that 25% aqueous ammonia was added dropwise to a mixture in aqueous solution A of an indium salt and of a tin salt, heated to 60*C, to adjust the final pH to 7.2.

The volume of settling the precipitate after aging was 2.3 cm ^ / g ITO obtained theoretically.

As described in the example 1, the precipitate was collected by suction filtration and washed 10 times with about 120 ml of deionized water. The time required for filtration and washing was 1 h, the precipitate the filterability was excellent, and the operation was extremely easy. This precipitate has been dried at 110*C and it is found that the dried material was easily deagglomerated.

The dried material has been calcined at 1,100 * C for 30 min under a stream of hydrogen chloride to 20% by volume (diluted with air) from the temperature of 1,000 * C, according to the process of calcination A, washed with water and then dried to obtain an ITO powder.

The ITO powder thus obtained had a BET specific surface area of 4.8 m ^ / g, a particle size calculated from the BET specific surface area and a diameter of 0.17[...] to 50% in a cumulative distribution of particle size of from 1, [...]. The ITO powder was observed by a scanning electron microscope and is thus found that the primary particle size of the ITO powder is about 0.1 to 0.2 m ^ and that it was comprises agglomerated particles whose primary particles strongly adhered to each other.