US20110268599A1

US20110268599A1 - PROCESS FOR PREPARING ZnAl TARGET MATERIAL AND ZnAl TARGET MATERIAL MADE THEREBY

Info

Publication number: US20110268599A1
Application number: US13/143,359
Authority: US
Inventors: Shengcong Liufu; Hao Zeng
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 2009-01-12
Filing date: 2010-01-11
Publication date: 2011-11-03
Also published as: EP2376669A1; KR20110106923A; CN101775578B; JP2012515260A; WO2010081064A1; CN101775578A

Abstract

The present invention provides a process for preparing a ZnAl alloy target material by providing a mixture of zinc powder and aluminum powder and obtaining a ZnAl alloy by sintering the mixture of zinc powder and aluminum powder by using a spark plasma sintering process. The present invention also describes a ZnAl alloy target material prepared by the above-described process.

Description

FIELD OF THE INVENTION

The present invention relates to a process for preparing a ZnAl target material used for making transparent conductive oxide film.

BACKGROUND ART

Transparent conductive oxide (TCO) film has high transmittance in the range of the visible light spectrum and excellent conductivity, and has broad applications in such areas as flat liquid crystal display panels, field emission display units, electroluminescent display units, sunlight control films and transparent electrodes for thin film solar cells and the like. TCO film mainly includes film materials containing oxides of In, Sn, Zn and Cd, as well as their doped or composite multinary oxides, such as In₂O₃, SnO₂, ZnO, ITO (In₂O₃:Sn), FTO (SnO₂:F), In₂SnO₅, Zn₂SnO₄, CdIn₂O₄, GalnO₃, CdSb₂O₆, etc. However, taking its performance and cost into consideration, what has the broadest application at the present is ITO and FTO transparent conductive film. Usually, ITO film is prepared by a magnetron sputtering process. However, indium is a rare element and natural deposits of indium are very limited. Therefore, ITO target material is expensive, which leads to the high cost of ITO film and prevents it from being widely used. As to FTO film, its transmittance in a hydrogen plasma atmosphere can be attenuated, which limits its applications in some areas, particularly, in thin film solar cells. In addition, FTO film is usually prepared by chemical vapor deposition technology. Among the required raw materials, metal organic compounds (such as tetramethyl tin) as a precursor of Sn are expensive. That is why the price of FTO films remains high. Therefore, there is an urgent need to develop TCO films that not only have excellent comprehensive properties, but also have cost advantages. Currently, of the many TCO film compositions, aluminum doped zinc oxide (AZO) film has the best development potential.
To prepare AZO transparent conductive film via a sputtering process, it is necessary to have the corresponding target material. Depending on different raw materials, the target material for preparing AZO film may be categorized into two types: (1) ceramic target material consisting of ZnO and Al₂O₃; and (2) metal target material consisting of Zn and Al. Comparatively speaking, ZnAl metal target material has a lower sintering temperature, higher AZO film deposition rate, better controllability of oxygen content during film coating and lower cost, and therefore is more favorable. However, the target material obtained with existing preparation techniques of ZnAl target material can not simultaneously meet the requirements of high density, tiny crystal grain size and distribution uniformity in microstructure and chemical composition required by high quality AZO film. Currently, preparation techniques of ZnAl target material may be categorized into the following:
(1) Casting process: In the process, Zn and Al raw materials are molten and cast in molds. Because of a big difference in density between Zn melt (6.57 g/cm³) and Al melt (2.38 g/cm³), distribution of chemical composition inside the target material is not uniform, and the obtained crystal grain size of Zn and Al grains is relatively large (between 100 and 2000 μm);
(2) Spray deposition process: In the process, molten Zn and Al metals are atomized and then deposited while rapidly solidified. Density of the target material prepared by this process is not high, and it is difficult to reach above 90%;
(3) Atmospheric pressure sintering or hot press sintering process: In the process, Zn powder and Al powder are used as starting materials that are molded and then sintered in an atmospheric pressure sintering or hot press sintering process in an air, nitrogen or oxygen atmosphere. Although the process has avoided the problem of non-uniformity to some degree, it is possible to introduce impurities into the target material, and the process requires a long sintering time and high energy consumption. The obtained crystal grain size is usually from dozens of microns to several hundreds of microns. For example, Han Bin et al. have reported in Investigation on the Pseudo-eutectic Structure Formed by Solid Diffusion of Zn Powder and Al Powder (JOURNAL OF AERONAUTICAL MATERIALS, Volume 21, No. 2 Issue, June 2001) that Zn powder and Al powder were used as starting materials and sintered in an electric resistance furnace after being molded by cold pressing or hot pressing.
The entire sintering process needed 40˜140 hrs before densification could be started. The crystal grain size of the sintered compact is larger than dozens of microns; and
(4) Composite process: The Chinese Patent CN 1238543C involves a process for preparing ZnAl alloy, in which ZnAl alloy ingots obtained after melting are pressed in single-roller rapid solidification to obtain alloy belts. Then, the alloy belts are smashed, and ultimately sintered by a hot press sintering process. Although the process has solved the problem of non-uniformity of the casting process, the preparation process is more complicated and has a longer process flow. Meanwhile, it couldn't avoid the disadvantages existing in the hot pressing process.
Thus, there is an urgent need in the art to find a preparation process for ZnAl target material. It should provide a target material with a combination of high density, tiny crystal grain size and distribution uniformity in chemical composition and microstructure, which would be beneficial for obtaining AZO transparent conductive films having a large area, high quality and good distribution uniformity.

SUMMARY

A process for preparing a ZnAl alloy target material, wherein the process comprises the following two steps:
(1) providing a mixture of zinc powder and aluminum powder; and
(2) spark plasma sintering the mixture of zinc powder and aluminum powder wherein the ZnAl alloy target material is prepared.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an X-ray diffraction spectrum of the ZnAl alloy obtained in Example 1.

FIG. 2 illustrates a scanning electron photomicrograph of the ZnAl alloy obtained in Example 2.

FIG. 3 illustrates a temperature curve used in Example 3.

FIG. 4 illustrates a picture of actual ZnAl alloy obtained in Example 3.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, if not specifically specified, percentage (%) or “parts” refers to percentage by weight, or parts by weight.
In the present invention, if not specifically specified, individual components or preferred components in a composition may be combined with each other to form a new formulation.
In the present invention, if not specified to the contrary, the sum of contents of individual components in a composition is 100%.
In the present invention, if not specified to the contrary, the sum of numbers of parts of individual components in a composition may be 100 parts by weight.
In the present invention, unless otherwise specified, the numerical range “a-b” represents an abbreviated expression of any combination of real numbers within the range of a and b, in which both a and b are real numbers. For example, the numerical range “0-5” means that all real numbers in the range of “0-5” are listed herein. “0-5” is merely an abbreviated expression of any combination of these numbers and includes the end point numbers and all real numbers found between “0-5”.
In the present invention, unless otherwise specified, the numerical range of integers “a-b” represents an abbreviated expression of any combination of integers a and b and all integers between a and b, in which both a and b are integers. For example, the numerical range of integers “1-N” means 1, 2 . . . N, in which N is an integer.
In the present invention, unless otherwise specified, “a combination thereof” means a multi-component mixture of individual components, for example, a multi-component mixture of two, three, or four components, up to as many components as possible.
As disclosed herein, the term “range” is defined in the form of a lower limit and an upper limit. A range may have one or several lower limits and one or several upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a specific range. All the ranges that can be defined in this way are inclusive and combinable. In other words, any lower limit may be combined with any upper limit to form a range. For example, with regard to a particular parameter, if a range of 60-120 and a range of 80-110 are given, it should be construed that a range of 60-110 and a range of 80-120 can also be expected. Moreover, if the minimum range values are defined as 1 and 2, and the maximum range values are defined as 3, 4 and 5, all of the following ranges can be expected: 1-3,1-4, 1-5,2-3, 2-4, and 2-5.
In the present invention, the terms “alloy” and “target material” have the same meaning and both represent a substance having common metallic characteristics and consisting of a metal and another type (or several types) of metal or non-metal.
In the present invention, the term “chemical composition and microstructure are uniformly distributed” means that the Al phase is uniformly distributed among crystal grains in the Zn phase everywhere within the target material. There are no large areas of concentrated zones or unoccupied zones of the Al phase. The size of crystal grains in the Al phase is substantially consistent, and the size of crystal grains in the Zn phase is also substantially consistent.
The present invention provides a process for preparing ZnAl target material. The target material prepared by the process is characterized by its high density, tiny crystal grain size and distribution uniformity in chemical composition and microstructure. The AZO film made from the target material is a good substitute for ITO and FTO. Particularly, it has a promising prospect of applications in the area of transparent electrodes for solar energy conversion.
Another objective of the present invention is to provide a ZnAl target material, which is characterized by its high density, tiny crystal grain size and distribution uniformity in chemical composition and microstructure. The AZO film made from target material is a good substitute for ITO and FTO. Particularly, it has a promising prospect of applications in the area of transparent electrodes for solar energy conversion.
One aspect of the present invention provides a process for preparing a ZnAl alloy target material, wherein the process comprises the following two steps:
(1) providing a mixture of zinc powder and aluminum powder; and
(2) obtaining a ZnAl alloy by sintering the mixture of zinc powder and aluminum powder by a spark plasma sintering process.
In a preferred embodiment according to the present invention, the step of providing the mixture of zinc powder and aluminum powder is as follows:

- placing metallic Zn powder and Al powder into a ball mill pot for ball milling; and
- drying the powders at a temperature ranging from 20 to 90° C. and in vacuum for 0.5 to 24 hrs after the ball milling is completed.

In a preferred embodiment according to the present invention, the ball milling includes low temperature ball milling and wet ball milling and the like.
In a preferred embodiment according to the present invention, operating conditions of the ball milling include a rotation speed of 200 rpm to 1500 rpm and ball milling for 1 to 48 hrs.
In a preferred embodiment according to the present invention, the content of Zn powder is from 80% to less than 100%, the content of Al powder is from 20% to greater than 0%; preferably, the content of Zn powder is from 90% to 99.99%, and the content of Al powder is from 10% to 0.01%; more preferably, the content of Zn powder is from 95% to 99%, and the content of Al powder is from 5% to 1%, based on total weight of Zn powder and Al powder.
In a preferred embodiment according to the present invention, particle size of Zn powder and/or Al powder is from 100 to 1000 mesh, preferably from 100 to 500 mesh, more preferably from 300 to 500 mesh.
In a preferred embodiment according to the present invention, the spark plasma sintering process is carried out as follows: placing the mixture of zinc powder and aluminum powder into a graphite or metal mold, and then placing the mold into a spark plasma sintering furnace for spark plasma sintering in a vacuum.
The present invention also provides a ZnAl target material for preparing a transparent conductive oxide film, wherein the ZnAl target material is prepared by the process according to the present invention.
The present invention also provides a ZnAl target material for preparing a transparent conductive oxide film, wherein the relative density of the ZnAl target material is greater than or equal to 96%, and/or its crystal grain size is less than or equal to 10 microns.
In a preferred embodiment according to the present invention, the relative density is from 96% to 99.5%, more preferably from 97% to 98.5%, and most preferably from 98% to 98.5%; and/or the crystal grain size is from 0.1 to 10 microns, preferably from 1 to 8 microns, more preferably from 1 to 5 microns, and most preferably from 1 to 4 microns.
In a preferred embodiment according to the present invention, the ZnAl target material contains from 80% to less than 100% of Zn and from 20% to greater than 0% of Al; preferably the ZnAl target material contains from 90% to 99.99% of Zn and from 10% to 0.01% of Al; and more preferably the ZnAl target material contains from 95% to 99% of Zn and from 5% to 1% of Al, based on the total weight of the ZnAl target material.
In a preferred embodiment according to the present invention, the chemical composition and microstructure of the ZnAl target material are uniformly distributed.
The advantages of the present invention are in that the prepared target material has a combination of characteristics of high density (relative density greater than 96% as measured with Alfa Mirage SD-200L density meter by the drainage method), tiny crystal grain size (average crystal grain size less than 10 microns as observed with a FEI NOVA 200 NanoLab Dualbeam™ SEM/FIB system), and distribution uniformity in chemical composition and microstructure. Therefore, it has overcome problems existing in the prior art. Moreover, the preparation technique described in the present invention has a shortened sintering time and reduced sintering temperature, which has important significance in increasing efficiency and saving energy.
The present invention is mainly characterized in the use of a spark plasma sintering technique, which allows the target material to have high density, tiny crystal grain size and distribution uniformity in chemical composition and microstructure. The AZO film made from this target material is a good substitute for ITO and FTO. Particularly, it has a promising prospect of applications in the area of transparent electrodes for solar energy conversion.
The spark plasma sintering preparation technique of the ZnAl target material of the present invention is to directly apply a DC pulse current to the mold and sample, and produce instantaneous high-temperature plasma among particles of Zn and Al metal powder or in voids via a thermal effect and field effect. Such a highly active ionized gas is able to induce high-speed diffusion and migration of Zn and Al particles, and to facilitate rapid completion of sintering densification. The technique has several features such as low sintering temperature, short sintering time, high density of sintered materials, and can yield tiny crystal grains and materials with dense texture and uniform microstructure.
More particularly, a process for preparing a ZnAl alloy target material is described, wherein the process comprises the following two steps:
(1) providing a mixture of zinc powder and aluminum powder; and
(2) spark plasma sintering the mixture of zinc powder and aluminum powder wherein a ZnAl alloy is obtained by the sintering process.
In the process for preparing ZnAl target material of the present invention, the step of providing the mixture of zinc powder and aluminum powder is conventional. Those of ordinary skill in the art may directly obtain the method according to the description of the present invention in combination with the prior art. For example, a method for preparing the powder mixture is disclosed by Chen Hanbin et al., Microstructure of Nano-crystalline Al—Zn—Mg—Cu Alloy Prepared by Spark Plasma Sintering (Journal of Beijing University of Science and Technology. Volume 29, No. 3 Issue, March 2007).
In a preferred embodiment according to the present invention, the step of providing the mixture of zinc powder and aluminum powder is as follows:

- placing metallic Zn powder and Al powder into a ball mill pot for ball milling;
- ball milling the powders;
- drying the powders at a temperature ranging from 20 to 90° C. and in vacuum for 0.5 to 24 hrs after the ball milling is completed.

In the present invention, the ball milling method is conventional. Those of ordinary skill in the art may directly carry out the ball milling operation according to the description of the present invention in combination with the prior art. Usually, the ball milling includes low temperature ball milling and/or wet ball milling and the like.
In commonly used ball milling processes, grinding balls usually include, but are not limited to, alumina, zirconia, stainless steel, agate grinding balls or a combination thereof; and the ball milling medium includes, but is not limited to, methanol, ethanol, acetone or ethylene glycol and the like (in the case of wet ball milling) or liquid nitrogen and the like (in the case of low temperature ball milling).
In the present invention, the weight ratio of the grinding ball/powder/medium is conventional. Those of ordinary skill in the art may directly obtain their weight ratio according to specific applications based on the prior art. Usually, the weight ratio of grinding ball/powder/medium is 20:(2-20):(1-2.5).
In the present invention, operating conditions of the ball milling are conventional. Those of ordinary skill in the art may select the operating conditions of the ball milling according to the actual situations. In a preferred embodiment according to the present invention, the operating conditions of the ball milling include a rotation speed of 200 rpm to 1500 rpm and ball milling for 1 to 48 hrs.
In the present invention, the content of Zn powder is, but is not limited to, from 80% to less than 100%, the content of Al powder is from 20% to greater than 0%. In a preferred embodiment according to the present invention, the content of Zn powder is from 90% to 99.99%, and the content of Al powder is from 10% to 0.01%. In another preferred embodiment according to the present invention, the content of Zn powder is from 95% to 99%, and the content of Al powder is from 5% to 1%, based on the total weight of Zn powder and Al powder.
In the present invention, the particle size of Zn powder or Al powder is conventional. It may be any particle size commonly used in the art. In a preferred embodiment according to the present invention, the particle size of Zn powder and/or Al powder is from 100 to 1000 mesh, preferably from 100 to 500 mesh, more preferably from 300 to 500 mesh Therefore, prefereably, the particle size is in a range of 13 to 150 microns and may be any size found within the range.
In a preferred embodiment according to the present invention, the steps of providing the mixture of zinc powder and aluminum powder may further include screening. The screening is carried out with methods commonly used in the art, such as using a sieve for screening.
In the present invention, the steps to obtain ZnAl alloy by sintering the mixture of zinc powder and aluminum powder in the spark plasma sintering process is conventional. Those of ordinary skill in the art may directly obtain the method according to the description of the present invention in combination with the prior art. For example, a spark plasma sintering process is disclosed by Chen Hanbin et al., Microstructure of Nano-crystalline Al—Zn—Mg—Cu Alloy Prepared by Spark Plasma Sintering (Journal of Beijing University of Science and Technology. Volume 29, No. 3 Issue, March 2007).
In a preferred embodiment according to the present invention, the spark plasma sintering process is carried out as follows: placing the mixture of zinc powder and aluminum powder into a graphite or metal mold, and then placing the mold into a spark plasma sintering furnace for spark plasma sintering the mixture in a vacuum. In the present invention, operating conditions of the spark plasma sintering process are conventional. Those of ordinary skill in the art may directly determine its operating conditions according to actual situations. In a preferred embodiment according to the present invention, the operating conditions of the spark plasma sintering process are as follows: the vacuum pressure is 1-10 Pa; the axial pressure is above 10 MPa; the sintering temperature is 280-400° C.; the heating rate is 20° C./min to 300° C./min (controlled by regulating the pulse current); and the isothermal period is 1-30 min.
In the process of the present invention, post-treatment steps may be further included. For example, the sintered compact is cut, polished according to actual needs to provide the ZnAl target material.
The present invention also provides a ZnAl target material for preparing a transparent conductive oxide film, wherein the ZnAl target material is prepared by the process according to the present invention.
The present invention also provides a ZnAl target material for preparing a transparent conductive oxide film, wherein the relative density of the ZnAl target material is greater or equal to 96%, and/or its crystal grain size is less than or equal to 10 microns.
In a preferred embodiment according to the present invention, the relative density is from 96% to 99.5%, more preferably from 97% to 98.5%, and most preferably from 98% to 98.5%.
In a preferred embodiment according to the present invention, the crystal grain size is from 0.1 to 10 microns, preferably from 1 to 8 microns, more preferably from 1 to 5 microns, and most preferably from 1 to 4 microns.
In a preferred embodiment according to the present invention, the chemical composition and microstructure of the ZnAl target material are uniformly distributed.
In the ZnAl target material of the present invention, the amount of Zn and Al is conventional. Those of ordinary skill in the art may directly obtain the amount of Zn and Al according to the description of the present specification in combination with their professional knowledge.
In a preferred embodiment according to the present invention, the ZnAl target material contains from 80% to less than 100% of Zn and from 20% to greater than 0% of Al. In another preferred embodiment according to the present invention, the ZnAl target material contains from 90% to 99.99% of Zn and from 10% to 0.01% of Al. In another preferred embodiment according to the present invention, the ZnAl target material contains from 95% to 99% of Zn and from 5% to 1% of Al, based on the total weight of the ZnAl target material.
The present invention is further illustrated with the following examples. However, those of ordinary skills in the art should understand that the present invention is not limited thereto.

EXAMPLES

In the present invention, relative density refers to a ratio between actual density and theoretical density of the target material, as represented by percentage. Among them, the actual density of the target material is measured with an Alfa Mirage SD-200L density meter by the drainage method, and the theoretical density of the target material may be calculated according to the weight ratio of starting materials of the target material and the densities of Zn powder and Al powder.
In the present invention, the crystal grain size is directly read out on a scanning electron microscope (FEI NOVA 200 NanoLab SEM/FIB) when a cross-section of the sample is being observed. The sample is cut with an ion beam to ensure clear crystal boundaries and integrity of the crystal grains. Three hundred crystal grains are taken for statistic analysis to obtain the average crystal grain size of the target material.
In the present invention, the term “uniform” means that the Al phase is uniformly distributed among crystal grains in the Zn phase everywhere within the target material; that there are no large areas of concentrated zones or unoccupied zones of the Al phase; and that the size of crystal grains in the Al phase is substantially consistent, and that the size of crystal grains in the Zn phase is also substantially consistent.

Example 1

30.63 g of zinc powder with a purity of 99.9% and a particle size of 200 mesh (mesh hole size of the screen is approximately 75 micron) and 0.61 g of aluminum powder with a purity of 99.9% and a particle size of 300 mesh (mesh hole size approximately 48 micron) were weighed respectively and placed into a ball mill pot (a polyurethane ball mill pot provided by Nanjing University Instrument Plant) containing 70 g of alumina grinding balls, and then the mixture was milled at 250 rpm for 3 hrs after 6 ml of absolute ethanol (analytically pure) had been added and the ball mill pot had been sealed.
The resulted slurry was taken out and dried in air at 70° C. for 20 hrs, and then screened by a 200-mesh sieve to provide a powder mixture needed for sintering.
3 g of the above powder mixture was weighed and placed into a graphite mold of 12 mm in diameter, and then placed into a spark plasma sintering system (Model SPS-1050, SPS SYNTEX INC.) for sintering. When the vacuum reached 5 Pa, the system was heated at the rate of 100° C./min until the temperature reached 350° C., and then the temperature was maintained at that level for 90 sec. The axial pressure was 50 MPa during the sintering process. When the constant temperature period was over, the electric current was cut off, and the graphite mold was taken out after the furnace had been cooled down below 100° C. After being released from the mold, the sintered compact was polished as a post-treatment to provide the ZnAl target material.
The relative density was measured as 97.9% with a density meter (Model SD-200L, ALFA MIRAGE) by the drainage method. The X-ray diffraction spectrum (XRD; Model RINT 2000, Rigaku) of the target material is shown in FIG. 1. It can be seen from the figure that the sintered target material has a high purity, and no impurities such as oxides were introduced in the entire preparation process. The average crystal grain size of the target material is 2.3 microns.

Example 2

173.4 g of zinc powder with a purity of 99.9% and a particle size of 300 mesh and 3.6 g of aluminum powder with a purity of 99.9% and a particle size of 200 mesh were weighed respectively and placed into a ball mill pot containing 354 g of alumina grinding balls, and then the mixture was milled at 370 rpm for 20 hrs after 50 ml of absolute ethanol (analytically pure) had been added and the ball mill pot had been sealed.
The resulted slurry was taken out and dried in vacuum at 80° C. for 4 hrs, and then screened by a 500-mesh sieve to provide a powder mixture needed for sintering.
29.6 g of the above powder mixture was weighed and placed into a graphite mold of 36 mm in diameter, and then placed into a spark plasma sintering system for sintering. When the vacuum pressure reached 5 Pa, the system was heated at the rate of 50° C./min until the temperature reached 375° C., and then the temperature was maintained at that level for 10 min. The axial pressure was 40 MPa during the sintering process. When the constant temperature period was over, the electric current was cut off, and the graphite mold was taken out after the furnace had been cooled down below 100° C. After being released from the mold, the sintered compact was polished as a post-treatment to provide the ZnAl target material.
The relative density was measured as 98.5% with the SD-200L density meter by the drainage method. A scanning electron photomicrograph (FEI NOVA200 NanoLab SEM FIB) of the internal structure of the target material is shown in FIG. 2. In order to obtain a picture of real and clear microstructure of the target material, a cross-section of the target material was observed again after it was cut with an ion beam. It can be seen from the figure that the sintered target material has a high density and no voids. The average crystal grain size of the target material is 3 microns. The Al phase is uniformly distributed in the Zn phase.

Example 3

400 g of zinc powder with a purity of 99.9% and a particle size of 300 mesh and 3 g of aluminum powder with a purity of 99.9% and a particle size of 300 mesh were weighed respectively and placed into a ball mill pot containing 850 g of alumina grinding balls, and then the mixture was milled at 700 rpm for 24 hrs after 95 ml of absolute ethanol (analytically pure) had been added and the ball mill pot had been sealed.
The resulted slurry was taken out and dried in vacuum at 25° C. for 24 hrs, and then screened by a 500-mesh sieve to provide a powder mixture needed for sintering.
5.3 g of the above powder mixture was weighed and placed into a graphite mold of 12 mm in diameter, and then placed into a spark plasma sintering system for sintering. When the vacuum pressure reached 2 Pa, the system was heated at the rate of 30° C./min until the temperature reached 384° C., and then the temperature was maintained at that level for 5 min. The sintering temperature curve is shown in FIG. 3. The axial pressure was 30 MPa during the sintering process. When the constant temperature period was over, the electric current was cut off, and the graphite mold was taken out after the furnace had been cooled down below 100° C. After being released from the mold, the sintered compact was polished as a post-treatment to provide the ZnAl target material. FIG. 4 is a picture of the actual target material. The relative density was measured as 99.1% with the SD-200L density meter by the drainage method. The average crystal grain size of the target material is 3.9 microns.

Example 4

200 g of zinc powder with a purity of 99.9% and particle size of 500 mesh (hole size approximately 18 micron) and 3.1 g of aluminum powder with a purity of 99.9% and particle size of 300 mesh were weighed respectively and placed into a ball mill pot containing 390 g of alumina grinding balls, and then the mixture was milled at 900 rpm for 18 hrs after 25 ml of absolute ethanol (analytically pure) had been added and the ball mill pot had been sealed.
The resulted slurry was taken out and dried in vacuum at 70° C. for 6 hrs, and then screened by a 500-mesh sieve to provide a powder mixture needed for sintering.
57.2 g of the above powder mixture was weighed and placed into a graphite mold of 50 mm in diameter, and then placed into a spark plasma sintering system for sintering. When the vacuum reached 5 Pa, the system was heated at the rate of 50° C./min until the temperature reached 340° C., and then the temperature was maintained at that level for 15 min. The axial pressure was 60 MPa during the sintering process. When the constant-temperature period was over, the electric current was cut off, and the graphite mold was taken out after the furnace had been cooled down below 100° C. After being released from the mold, the sintered compact was polished as a post-treatment to provide the ZnAl target material. The relative density was measured as 97.1% with the SD-200L density meter by the drainage method. The average crystal grain size of the target material is 4.6 microns.

Example 5

400 g of zinc powder with a purity of 99.9% and a particle size of 800 mesh and 20 g of aluminum powder with a purity of 99.9% and a particle size of 500 mesh were weighed respectively and placed into a ball mill pot containing 850 g of alumina grinding balls, and then the mixture was milled at 1100 rpm for 24 hrs after 85 ml of absolute ethanol (analytically pure) had been added and the ball mill pot had been sealed.
The resulted slurry was taken out and dried in vacuum at 25° C. for 24 hrs, and then screened by a 500-mesh sieve to provide a powder mixture needed for sintering.
29.6 g of the above powder mixture was weighed and placed into a graphite mold of 36 mm in diameter, and then placed into a spark plasma sintering system for sintering. When the vacuum pressure reached 2 Pa, the system was heated at the rate of 30° C./min until the temperature reached 388° C., 391° C. or 394° C., and then the temperature was maintained at that level for 10 min. The axial pressure was 30 MPa during the sintering process. When the constant-temperature period was over, the electric current was cut off, and the graphite mold was taken out after the furnace had been cooled down below 100° C. After being released from the mold, the sintered compact was polished as a post-treatment to provide the ZnAl target material. The relative densities and average crystal grain sizes of the target materials are as shown in Table 1.

TABLE 1

		Relative	Average crystal
	Temperature	density	grain size
No.	(° C.)	(%)	(microns)

1	388	99.1	3.4
2	391	99.3	3.7
3	394	99.4	3.9

Claims

1. A process for preparing a ZnAl alloy target material, wherein the process comprises the following two steps:

(1) providing a mixture of zinc powder and aluminum powder; and

(2) spark plasma sintering the mixture of zinc powder and aluminum powder wherein the ZnAl alloy target material is prepared.

2. The process according to claim 1, wherein the step of providing the mixture of zinc powder and aluminum powder further comprises:

placing metallic Zn powder and Al powder into a ball mill pot for ball milling;

ball milling the powders; and

drying the powders at a temperature ranging from 20 to 90° C. and in vacuum for 0.5 to 24 hrs after the ball milling is completed.

3. The process according to claim 2, wherein the ball milling comprises low temperature ball milling or wet ball milling.

4. The process according to claim 2, wherein the ball milling is conducted at a rotation speed of 200 rpm to 1500 rpm for 1 to 48 hrs.

5. The process according to claim 1, wherein the content of Zn powder is from 80 to less than 100% and the content of Al powder is from 20 to greater than 0%.

6. The process according to claim 1, wherein the particle size of Zn powder and/or Al powder is from 100 to 1000 mesh.

7. The process according to claim 1, wherein the spark plasma sintering process is carried out as follows:

placing the mixture of zinc powder and aluminum powder into a graphite or metal mold; placing the mold with the mixture into a spark plasma sintering furnace; and spark plasma sintering the mixture in a vacuum.

8. A ZnAl target material for preparing a transparent conductive oxide film, wherein the ZnAl target material is prepared by the process according to claim 1.

9. A ZnAl target material for preparing a transparent conductive oxide film, wherein the relative density of the ZnAl target material is greater than or equal to 96%, or its crystal grain size is less than or equal to 10 microns; or the relative density of the ZnAl target material is greater than or equal to 96% and its crystal grain size is less than or equal to 10 microns.

10. The ZnAl target material according to claim 9, wherein the relative density is from 96 to 99.5% or the crystal grain size is from 0.1 to 10 microns.

11. The ZnAl target material according to claim 9, wherein the ZnAl target material contains from 80% to less than 100% of Zn and from 20% to greater than 0% of Al.

12. The ZnAl target material according to claim 9, wherein the chemical composition and microstructure of the ZnAl target material are uniformly distributed.