BEAD STRING OF TIN OXIDE CRYSTALLITE OR BEAD STRING OF COMPLEX OXIDE CRYSTALLITE OF TIN OXIDE AND TITANIUM OXIDE

Abstract

A bead string of tin oxide crystallite or a bead string of complex oxide crystallite of tin oxide and titanium oxide contains tantalum and has specific hue as well as a crystallite size on the order of nanometer, and exhibits excellent conductivity and improves the catalytic activity. A bead string includes a tin oxide crystal particle aggregate or a crystal particle aggregate of a complex oxide of tin oxide and titanium oxide, in which the crystal particle aggregate contains at least one particle having a crystallite size of 5 to 50 nm, and when the crystal particle aggregate is pressed under a pressure of 0.1 MPa to have a thickness of 1 cm, in the color of the resultant particle aggregate represented by Lab color space, a lightness L* value is 80 or less, a chromaticity a* value is 4 or less, and a chromaticity b* is 3 or less.

Claims

1. A bead string of tin oxide crystallite or bead string of complex oxide crystallite of tin oxide and titanium oxide, which is a bead string comprising a tin oxide crystal particle aggregate or a crystal particle aggregate of a complex oxide of tin oxide and titanium oxide, wherein the crystal particle aggregate contains at least one particle having a crystallite size of 5 to 50 nm, and wherein when the crystal particle aggregate is pressed under a pressure of 0.1 MPa so as to have a thickness of 1 cm, in the color of the resultant particle aggregate represented by the Lab color space, a lightness L* value is 80 or less, a chromaticity a* value is 4 or less, and a chromaticity b* is 3 or less.

Description

BRIEF DESCRIPTION OF DRAWING

[0027] FIG. 1 is a diagram of typical structure for explaining the structure of the bead string of tin oxide crystallite or bead string of complex oxide crystallite of tin oxide and titanium oxide.

DESCRIPTION OF EMBODIMENTS

[0028] The tin oxide crystallite or complex oxide crystallite of tin oxide and titanium oxide in the invention (hereinafter, the two types of crystallites are frequently collectively referred to simply as tin oxide crystallite) contains tantalum in the crystallite, and therefore the state of electrons in the tin oxide crystallite is changed, so that the tin oxide crystallite has not only specific hue but also improved conductivity.

[0029] In the invention, the Ta content is:

Ta(mol)/(Ta+Sn)(mol)1000.1 to 30 (mol %), or

Ta(mol)/(Ta+Sn+Ti)(mol)1000.1 to 30 (mol %),

and, when the Ta content is as mentioned above, the tin oxide crystallite has specific hue, and further is suitable for advantageously forming a bead string structure.

[0030] The bead string of tin oxide crystallite of the invention comprises a particle aggregate containing at least one particle having a crystal particle size of 5 to 50 nm, which is the above-mentioned tin oxide crystal particle.

[0031] In the bead string, as seen in the diagram of typical structure of FIG. 1, a tin oxide crystal particle 1 has a structure in which part of the particle is fused to form a chain or bunch structure (this structure is referred to as bead string), and, in the invention, at least one tin oxide crystal particle 1 in the bead string contains tantalum in the above-mentioned tin oxide crystal, and has the above-mentioned particle size.

[0032] Further, with respect to the bead string in the invention, the tin oxide crystal particle aggregate was pressed under a pressure of 0.1 MPa, and pressing was stopped at a point in time when the thickness became 1 cm, and hue of the pressed aggregate was measured by a specular reflected light removing optical system using a spectrophotometer (Model CM-5, manufactured by Konica Minolta, Inc.). In the hue represented by the Lab color space, a lightness L* value is 80 or less, a chromaticity a* value is 4 or less, and a chromaticity b* value is 3 or less. The bead string having the above-mentioned lightness and chromaticity has high specific surface area and excellent conductivity, porosity, catalytic activity, and durability.

[0033] The above-mentioned bead string of the invention is, for example, produced as follows. A mineral turpentine solution containing metal ions (tin, tantalum and/or titanium) as raw materials is preliminarily prepared, and a mist of the solution is formed by an atomizer using oxygen and/or nitrogen, and introduced into a chemical flame (chemical flame formed from propane, methane, acetylene, hydrogen, nitrous oxide, or the like), plasma, or the like at a high temperature.

[0034] By this procedure, in at least 80% of the tin oxide crystal particles, five or more particles are fused and bonded together, forming a bead string of a chain and/or bunch structure.

[0035] In view of improving the yield of the bead string, the temperature for the above procedure is suitably 600 to 2,000 C., preferably 1,200 to 1,800 C.

[0036] The above-mentioned mineral turpentine solution is prepared by dissolving an organotin compound (at least one member of organic acid tin salts, such as tin alkoxide and tin acetylacetonate, and the like) and an organotantalum compound (at least one member of organic acid tantalum salts, such as tantalum alkoxide, and the like) and/or an organotitanium compound (at least one member of organic acid titanium salts, such as titanium alkoxide, and the like) in an organic solvent (at least one member of turpentine oil, heptane, methanol, ethanol, and the like).

[0037] The concentration of the tin compound in the raw material liquid is suitably 1 to 50% by mass, preferably 3 to 14% by mass, in terms of an amount of tin, and, with respect to the concentration of the tantalum compound and/or titanium compound, the ratio of the tin compound and the tantalum compound and/or titanium compound in the raw material liquid may be controlled so that the Ta content of the final product, i.e., the structure material of the invention is consistent with the above-mentioned ratio.

[0038] The thus obtained raw material liquid (mineral turpentine solution) is fed to, for example, a chemical flame formed from fuel gas, such as propane, methane, acetylene, hydrogen, or nitrous oxide, to cause combustion, obtaining the bead string of tin oxide crystallite of the invention having a chain and/or bunch structure.

[0039] That is, immediately after the raw material liquid is fed to a chemical flame, a reaction and cooling are conducted, and primary particles are produced and, at the same time, the primary particles are partially fused and bonded together, so that the chain and/or bunch structure having high specific surface area in the invention is formed.

Example 1-1

[0040] Ta-doped SnO.sub.2 having a Ta content of 3 mol % was synthesized as described below, in which the Ta content is represented by: Ta/(Sn mol+Ta mol).

[0041] 20 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 0.59 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 60 g of turpentine oil were mixed to prepare a raw material solution.

[0042] Oxygen gas at a flow rate of 1 to 30 L/min (5 L/min in the present Example) and propane gas at a flow rate of 1 to 5 L/min (1 L/min in the present Example) were mixed and burned to form a pilot flame, and the above-adjusted solution at a flow rate of 1 to 10 g/min (5 g/min in the present Example) and carrier oxygen gas at a flow rate of 1 to 30 L/min (10 L/min in the present Example) were sprayed into the pilot flame to cause combustion, and the gas formed due to the combustion was recovered. The gas contained particles formed by flame synthesis (i.e., the bead string of tin oxide crystallite of the invention), and the particles were separated and recovered.

[0043] The recovered particles were observed by a transmission electron microscope, and, as a result, as seen in FIG. 1, it was found that the particles had a chain structure portion in which five or more particles having a crystallite size in the range of from 5 to 30 nm are linked in the form of a string of beads.

[0044] Further, the recovered particle aggregate was pressed under a pressure of 0.1 MPa so as to have a thickness of 1 cm, and hue was measured using a spectrophotometer (Model CM-5, manufactured by Konica Minolta, Inc.; by a specular reflected light removing optical system), and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 1-2

[0045] Ta-doped SnO.sub.2 having a Ta content of 10 mol % was synthesized as described below, in which the Ta content is represented by: Ta/(Sn mol+Ta mol).

[0046] 20 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 2.1 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 70 g of turpentine oil were mixed to prepare a raw material solution.

[0047] The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0048] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and, as a result, like Example 1-1, the particles had a chain structure portion in which five or more particles having a crystallite size in the range of 7 to 35 nm are linked in the form of a string of beads, and further the recovered particle aggregate was pressed under a pressure of 0.1 MPa so as to have a thickness of 1 cm, and hue was measured using a spectrophotometer and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 2-1

[0049] Ta-doped SnO.sub.2 having a Ta content of 3 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0050] 20 g of tin(II) acetylacetonate (manufactured by Sigma-Aldrich Co., LLC.; Sn=36.9% by mass), 0.78 g of tantalum ethoxide (manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 90 g of turpentine oil were mixed to prepare a solution.

[0051] The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0052] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 2-2

[0053] Ta-doped SnO.sub.2 having a Ta content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0054] 20 g of tin(II) acetylacetonate (manufactured by Sigma-Aldrich Co., LLC.; Sn=36.9% by mass), 2.81 g of tantalum ethoxide (manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 90 g of turpentine oil were mixed to prepare a solution.

[0055] The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0056] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 3-1

[0057] Ta-doped SnO.sub.2 having a Ta content of 3 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0058] 20 g of tin t-butoxide (trade name Tin(IV) t-Butoxide, manufactured by FUJIFILM Wako Pure Chemical Corporation; Sn=28% by mass), 0.59 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 60 g of turpentine oil were mixed to prepare a solution.

[0059] The prepared solution was sprayed in the same manner as in Example 1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0060] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 3-2

[0061] Ta-doped SnO.sub.2 having a Ta content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0062] 20 g of tin t-butoxide (trade name Tin(IV) t-Butoxide, manufactured by FUJIFILM Wako Pure Chemical Corporation; Sn=28% by mass), 2.13 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 70 g of turpentine oil were mixed to prepare a solution.

[0063] The prepared solution was sprayed in the same manner as in Example 1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0064] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 4-1

[0065] Ta-doped SnO.sub.2 having a Ta content of 3 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0066] 20 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 0.80 g of tantalum(V) butoxide (manufactured by Sigma-Aldrich Co., LLC.; Sn=36.9% by mass), and 60 g of turpentine oil were mixed to prepare a solution.

[0067] The prepared solution was sprayed in the same manner as in Example 1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0068] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 4-2

[0069] Ta-doped SnO.sub.2 having a Ta content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0070] 20 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 2.87 g of tantalum(V) butoxide (manufactured by Sigma-Aldrich Co., LLC.; Ta=33.1% by mass), and 70 g of turpentine oil were mixed to prepare a solution.

[0071] The prepared solution was sprayed in the same manner as in Example 1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0072] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 5-1

[0073] Ta-doped SnO.sub.2 having a Ta content of 3 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0074] 20 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 0.49 g of tantalum(V) methoxide (manufactured by Sigma-Aldrich Co., LLC.; Ta=33.1% by mass), and 60 g of turpentine oil were mixed to prepare a solution.

[0075] The prepared solution was sprayed in the same manner as in Example 1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0076] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 5-2

[0077] Ta-doped SnO.sub.2 having a Ta content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0078] 20 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 1.76 g of tantalum(V) methoxide (manufactured by Sigma-Aldrich Co., LLC.; Ta=33.1% by mass), and 70 g of turpentine oil were mixed to prepare a solution.

[0079] The prepared solution was sprayed in the same manner as in Example 1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0080] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 6

[0081] Ta-doped SnO.sub.2 having a Ta content of 30 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0082] 20 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 8.22 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 90 g of turpentine oil were mixed to prepare a raw material solution.

[0083] The prepared solution was sprayed in the same manner as in Example 1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0084] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-2 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 7-1

[0085] Ta+Ti-doped SnO.sub.2 having a Ta content of 3 mol % and having a Ti content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol+Ti mol), the Ti content is represented by: Ti (mol)/(Ti mol+Sn mol), and Ta:Ti (mol)=9:1.

[0086] 20 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 1.78 g of tetra-n-butoxytitanium (trade name B-1, manufactured by Nippon Soda Co., Ltd.; Ti=14.1% by mass) as a Ti source, 0.66 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 70 g of turpentine oil were mixed, and sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0087] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-2 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 7-2

[0088] Ta+Ti-doped SnO.sub.2 having a Ta content of 3 mol % and having a Ti content of 50 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol+Ti mol), the Ti content is represented by: Ti (mol)/(Ti mol+Sn mol), and Ta:Ti=5:5 (molar ratio).

[0089] 10 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 8.03 g of tetra-n-butoxytitanium (trade name B-1, manufactured by Nippon Soda Co., Ltd.; Ti=14.1% by mass) as a Ti source, 0.59 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 70 g of turpentine oil were mixed, and sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0090] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-2 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 8-1

[0091] Ta+Ti-doped SnO2 having a Ta content of 10 mol % and having a Ti content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)+Ti (mol)/(Sn mol+Ta mol+Ti mol), the Ti content is represented by: Ti (mol)/(Ti mol+Sn mol), and Ta:Ti=9:1 (molar ratio).

[0092] 20 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 1.78 g of tetra-n-butoxytitanium (trade name B-1, manufactured by Nippon Soda Co., Ltd.; Ti=14.1% by mass) as a Ti source, 9.13 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 90 g of turpentine oil were mixed, and sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0093] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-2 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

Example 8-2

[0094] Ta+Ti-doped SnO2 having a Ta content of 10 mol % and having a Ti content of 50 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)+Ti (mol)/(Sn mol+Ta mol+Ti mol), the Ti content is represented by: Ti (mol)/(Ti mol+Sn mol), and Ta:Ti=5:5 (molar ratio).

[0095] 10 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 8.03 g of tetra-n-butoxytitanium (trade name B-1, manufactured by Nippon Soda Co., Ltd.; Ti=14.1% by mass) as a Ti source, 8.22 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 90 g of turpentine oil were mixed, and sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite of the invention) were separated and recovered.

[0096] The recovered particles were observed by a transmission electron microscope in the same manner as in Example 1-1, and results similar to those in Example 1-2 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 1.

[Comparative Example 1-1] (which is an Example Corresponding to PTL 8 WO2011/65471, and which Applies to the Following Comparative Examples)

[0097] Ta-doped SnO.sub.2 having a Ta content of 3 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0098] 38 g of tin octylate (trade name Nikka Octhix Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 5 g of tantalum octylate (trade name Nikka Octhix Tantalum 10% (T), manufactured by Nihon Kagaku Sangyo Co., Ltd.; Ta=10% by mass), and 150 g of turpentine oil were mixed to prepare a solution.

[0099] The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite for comparison) were separated and recovered.

[0100] The recovered particles were observed by a transmission electron microscope, and, as a result, as seen in FIG. 1, it was found that the particles had a chain structure portion in which five or more particles having a crystallite size in the range of 5 to 50 nm are linked in the form of a string of beads, but it was also found that there were a number of particles which do not exist in FIG. 1 (a diagram is not shown).

[0101] Further, with respect to the recovered particles, in the same manner as in Example 1-1, the recovered particle aggregate was pressed under a pressure of 0.1 MPa so as to have a thickness of 1 cm, and hue was measured using a spectrophotometer (Model CM-5, manufactured by Konica Minolta, Inc.; by a specular reflected light removing optical system), and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 2.

Comparative Example 1-2

[0102] Ta-doped SnO.sub.2 having a Ta content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0103] 33.9 g of tin octylate (trade name Nikka Octhix Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 16.1 g of tantalum octylate (trade name Nikka Octhix Tantalum 10% (T), manufactured by Nihon Kagaku Sangyo Co., Ltd.; Ta=10% by mass), and 150 g of turpentine oil were mixed to prepare a solution.

[0104] The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite for comparison) were separated and recovered.

[0105] The recovered particles were observed by a transmission electron microscope in the same manner as in Comparative Example 1-1, and it was found that the particles had a bead string structure, but hue was measured using a spectrophotometer in the same manner as in Comparative Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 2.

Comparative Example 2-1

[0106] Ta-doped SnO.sub.2 having a Ta content of 3% (3 atm %) was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0107] 40 g of tin octylate (trade name Nikka Octhix Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 1.2 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 159 g of turpentine oil were mixed to prepare a solution.

[0108] The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite for comparison) were separated and recovered.

[0109] The recovered particles were observed by a transmission electron microscope in the same manner as in Comparative Example 1-1, and results similar to those in Comparative Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Comparative Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 2.

Comparative Example 2-2

[0110] Ta-doped SnO.sub.2 having a Ta content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0111] 45.2 g of tin octylate (trade name Nikka Octhix Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 4.8 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), and 159 g of turpentine oil were mixed to prepare a solution.

[0112] The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite for comparison) were separated and recovered.

[0113] The recovered particles were observed by a transmission electron microscope in the same manner as in Comparative Example 1-1, and results similar to those in Comparative Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Comparative Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 2.

Comparative Example 3-1

[0114] Ta-doped SnO.sub.2 having a Ta content of 3 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0115] 33.9 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 4.5 g of tantalum octylate (trade name Nikka Octhix Tantalum 10% (T), manufactured by Nihon Kagaku Sangyo Co., Ltd.; Ta=10% by mass), and 150 g of turpentine oil were mixed to prepare a solution.

[0116] The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite for comparison) were separated and recovered.

[0117] The recovered particles were observed by a transmission electron microscope in the same manner as in Comparative Example 1-1, and results similar to those in Comparative Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Comparative Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value were represented by the Lab color space as shown in Table 2.

Comparative Example 3-2

[0118] Ta-doped SnO.sub.2 having a Ta content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol).

[0119] 33.9 g of dibutyltin bisacetylacetonate (trade name NACEM Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 16.81 g of tantalum octylate (trade name Nikka Octhix Tantalum 10% (T), manufactured by Nihon Kagaku Sangyo Co., Ltd.; Ta=10% by mass), and 150 g of turpentine oil were mixed to prepare a solution.

[0120] The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite for comparison) were separated and recovered.

[0121] The recovered particles were observed by a transmission electron microscope in the same manner as in Comparative Example 1-1, and results similar to those in Comparative Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Comparative Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 2.

Comparative Example 4-1

[0122] Ta-doped SnO.sub.2 having a Ta content of 3 mol % and having a Ti content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)/(Sn mol+Ta mol+Ti mol), and the Ti content is represented by: Ti (mol)/(Ti mol+Sn mol).

[0123] 20 g of tin octylate (trade name Nikka Octhix Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 0.66 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), 1.78 g of tetra-n-butoxytitanium (trade name B-1, manufactured by Nippon Soda Co., Ltd.; Ti=14.1% by mass) as a Ti source, and 70 g of turpentine oil were mixed to prepare a solution. The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite for comparison) were separated and recovered.

[0124] The recovered particles were observed by a transmission electron microscope in the same manner as in Comparative Example 1-1, and results similar to those in Comparative Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Comparative Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 2.

Comparative Example 4-2

[0125] Ta+Ti-doped SnO2 having a Ta content of 3 mol % and having a Ti content of 50 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)+Ti (mol)/(Sn mol+Ta mol+Ti mol), the Ti content is represented by: Ti (mol)/(Ti mol+Sn mol), and Ta:Ti=5:5 (molar ratio).

[0126] 10 g of tin octylate (trade name Nikka Octhix Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 0.59 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), 8.03 g of tetra-n-butoxytitanium (trade name B-1, manufactured by Nippon Soda Co., Ltd.; Ti=14.1% by mass) as a Ti source, and 70 g of turpentine oil were mixed to prepare a solution. The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite for comparison) were separated and recovered.

[0127] The recovered particles were observed by a transmission electron microscope in the same manner as in Comparative Example 1-1, and results similar to those in Comparative Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Comparative Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 2.

Comparative Example 5-1

[0128] Ta+Ti-doped SnO.sub.2 having a Ta content of 10 mol % and having a Ti content of 10 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)+Ti (mol)/(Sn mol+Ta mol+Ti mol), the Ti content is represented by: Ti (mol)/(Ti mol+Sn mol), and Ta:Ti=9:1 (molar ratio).

[0129] 20 g of tin octylate (trade name Nikka Octhix Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 9.13 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), 1.78 g of tetra-n-butoxytitanium (trade name B-1, manufactured by Nippon Soda Co., Ltd.; Ti=14.1% by mass) as a Ti source, and 90 g of turpentine oil were mixed to prepare a solution. The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite for comparison) were separated and recovered.

[0130] The recovered particles were observed by a transmission electron microscope in the same manner as in Comparative Example 1-1, and results similar to those in Comparative Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Comparative Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 2.

Comparative Example 5-2

[0131] Ta+Ti-doped SnO2 having a Ta content of 10 mol % and having a Ti content of 50 mol % was synthesized by the method described below, in which the Ta content is represented by: Ta (mol)+Ti (mol)/(Sn mol+Ta mol+Ti mol), the Ti content is represented by: Ti (mol)/(Ti mol+Sn mol), and Ta:Ti=5:5 (molar ratio).

[0132] 10 g of tin octylate (trade name Nikka Octhix Tin, manufactured by Nihon Kagaku Sangyo Co., Ltd.; Sn=28% by mass), 8.22 g of tantalum ethoxide (trade name Tantalum ethoxide, manufactured by Hokko Chemical Industry Co., Ltd.; Ta=44.5% by mass), 8.03 g of tetra-n-butoxytitanium (trade name B-1, manufactured by Nippon Soda Co., Ltd.; Ti=14.1% by mass) as a Ti source, and 90 g of turpentine oil were mixed to prepare a solution. The prepared solution was sprayed in the same manner as in Example 1-1 into a pilot flame formed in the same manner as in Example 1-1 to cause combustion, and, from the recovered gas, particles (i.e., the bead string of tin oxide crystallite for comparison) were separated and recovered.

[0133] The recovered particles were observed by a transmission electron microscope in the same manner as in Comparative Example 1-1, and results similar to those in Comparative Example 1-1 were obtained. Further, hue was measured using a spectrophotometer in the same manner as in Comparative Example 1-1, and, as a result, the lightness L* value, chromaticity a* value, and b* value represented by the Lab color space were as shown in Table 2.

Evaluation Example

[Electrical Conductivity (Reduction of Cell Internal Resistance and Support Conductivity=Interfacial Resistance Between Particles+Resistance in Particles)]

[0134] With respect to the powders of bead string of tin oxide crystallite obtained in Examples and Comparative Examples above, the conductivity (reduction of cell internal resistance and support conductivity=interfacial resistance between particles+resistance in particles) was evaluated by an alternating current impedance method. Specifically, using an electrochemical measurement system SP-200, manufactured by Toyo Corporation, and a sample holder SH2-Z, in an atmosphere at a temperature of 20 to 30 C. and at a relative humidity of 30 to 70%, the space between parallel electrodes of the sample holder was filled with about 0.1 g of a sample, and a load of one megapascal was applied to the sample from the outside of the electrodes. In this state, an impedance was measured while changing the alternating current frequency from 7 to 10 millihertz. A resistance value of the sample was determined, based on fitting by an equivalent circuit composed of a resistance and a capacitor component for the Nyquist plot obtained by the measurement. From the determined resistance value, the thickness of the sample disposed between the parallel electrodes during the measurement of an impedance, and the area of the parallel electrode in contact with the sample, a conductivity of the sample was estimated. The results were as shown in Tables 1 and 2.

TABLE-US-00001 TABLE 1 Hue Chroma- Chroma- Crys- Conduc- Lightness ticity ticity tallite tivity Example L* value a* value b* value size (S/cm) 1-1 75 5 5 5 to 30 560 1-2 60 6 13 7 to 35 150 2-1 75 5 5 5 to 30 580 2-2 75 6 13 7 to 35 160 3-1 75 5 5 5 to 30 540 3-2 75 6 13 7 to 35 140 4-1 75 5 5 5 to 30 570 4-2 60 6 13 7 to 35 150 5-1 75 5 5 5 to 30 540 5-2 60 6 13 7 to 35 150 6 50 6 15 7 to 35 20 7-1 75 5 5 5 to 30 30 7-2 78 4 5 5 to 30 10 8-1 65 6 10 5 to 30 5 8-2 72 4 7 5 to 30 7

TABLE-US-00002 TABLE 2 Hue Chroma- Chroma- Crys- Conduc- Comparative Lightness ticity ticity tallite tivity Example L* value a* value b* value size (S/cm) 1-1 85 5 0 5 to 50 10 1-2 82 6 5 10 to 50 2 2-1 85 5 0 5 to 50 8 2-2 82 6 5 10 to 50 1.1 3-1 85 5 0 5 to 50 7 3-2 82 6 5 10 to 50 0.8 4-1 85 5 0 5 to 50 0.3 4-2 86 4 1 5 to 50 0.2 5-1 82 6 1 5 to 50 0.4 5-2 87 4 0 5 to 50 0.2

[0135] As is apparent from Tables 1 and 2, the conductivity of the Examples having such color that the L* is 80 or less, the a* value is 4 or less, and the b* is 5 or less is even higher than the conductivity of the Comparative Examples in which the a* value is equivalent to that of the Examples, but the L* is larger than 80 or the b* is larger than 5.

INDUSTRIAL APPLICABILITY

[0136] The bead string of tin oxide crystallite of the present invention exhibits specific hue and thus has various excellent properties, as compared to a bead string containing a metal oxide which contains the same dopant but does not exhibit specific hue, and can be extremely advantageously used as, for example, an electrode material for fuel cell.