U.S. patent application number 15/365776 was filed with the patent office on 2018-01-25 for method of preparing tungsten metal material and tungsten target with high purity.
The applicant listed for this patent is NATIONAL CHUNG SHAN INSTITUTE OF SCIENCE AND TECHNOLOGY. Invention is credited to HUI-YUN BOR, KUAN-ZONG FUNG, CHIA-SHIH LIN, CUO-YO NIEH, CHAO-NAN WEI.
Application Number | 20180021857 15/365776 |
Document ID | / |
Family ID | 59688387 |
Filed Date | 2018-01-25 |
United States Patent
Application |
20180021857 |
Kind Code |
A1 |
LIN; CHIA-SHIH ; et
al. |
January 25, 2018 |
METHOD OF PREPARING TUNGSTEN METAL MATERIAL AND TUNGSTEN TARGET
WITH HIGH PURITY
Abstract
A method of preparing a tungsten metal material with high
purity, comprising the steps of (A) providing a tungsten metal
powder to mix with a metal nitrate to form a mixed powder slurry;
(B) ball-grinding the mixed powder slurry to obtain a uniformly
mixed powder; (C) sintering the uniformly mixed powder to obtain
the tungsten metal material with high purity. Accordingly, the
tungsten metal material with purity more than 99.9% can be
prepared, so as to prepare the tungsten metal target.
Inventors: |
LIN; CHIA-SHIH; (TAOYUAN
CITY, TW) ; WEI; CHAO-NAN; (TAOYUAN CITY, TW)
; NIEH; CUO-YO; (TAOYUAN CITY, TW) ; BOR;
HUI-YUN; (TAOYUAN CITY, TW) ; FUNG; KUAN-ZONG;
(TAOYUAN CITY, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL CHUNG SHAN INSTITUTE OF SCIENCE AND TECHNOLOGY |
Taoyuan City |
|
TW |
|
|
Family ID: |
59688387 |
Appl. No.: |
15/365776 |
Filed: |
November 30, 2016 |
Current U.S.
Class: |
75/369 |
Current CPC
Class: |
B22F 1/0003 20130101;
B22F 3/02 20130101; C22C 1/1084 20130101; B22F 3/1035 20130101;
B22F 2009/043 20130101; B22F 9/30 20130101; B22F 1/0085 20130101;
B22F 3/1017 20130101; C22C 1/05 20130101; B22F 2009/043 20130101;
B22F 2998/10 20130101; B22F 3/1017 20130101; B22F 9/04 20130101;
B22F 9/30 20130101; B22F 2301/20 20130101; B22F 2998/10
20130101 |
International
Class: |
B22F 9/30 20060101
B22F009/30; B22F 9/04 20060101 B22F009/04; B22F 1/00 20060101
B22F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 20, 2016 |
TW |
105122815 |
Claims
1. A method of preparing a tungsten metal material with high
purity, comprising the steps of: (A) providing a tungsten metal
powder to mix with a metal nitrate to form a mixed powder slurry;
(B) ball-grinding the mixed powder slurry to obtain a uniformly
mixed powder; (C) sintering the uniformly mixed powder to obtain
the tungsten metal material with high purity.
2. The method of preparing a tungsten metal material with high
purity as claimed in claim 1, wherein the purity of the tungsten
metal material with high purity is more than 99.9%, and the density
thereof is more than 99% of the density of pure tungsten.
3. The method of preparing a tungsten metal material with high
purity as claimed in claim 2, wherein the tungsten metal material
with high purity is used to prepare a tungsten metal target.
4. The method of preparing a tungsten metal material with high
purity as claimed in claim 3, wherein before the sintering step
(C), the uniformly mixed powder is further pressed and shaped to a
desired shape.
5. The method of preparing a tungsten metal material with high
purity as claimed in claim 1, wherein the metal nitrate is selected
from nickel nitrate, ferric nitrate, and a mixture thereof.
6. The method of preparing a tungsten metal material with high
purity as claimed in claim 1, wherein a solvent is added to the
mixed powder slurry in the ball-grinding step (B), and the solvent
is oleic acid.
7. The method of preparing a tungsten metal material with high
purity as claimed in claim 1, wherein the sintering treatment
include a plurality of stages of heating treatments.
8. The method of preparing a tungsten metal material with high
purity as claimed in claim 7, wherein the temperature in the first
stage of heating treatments of the sintering treatment is more than
200.degree. C.
9. The method of preparing a tungsten metal material with high
purity as claimed in claim 7, wherein the temperature in the last
stage of heating treatments of the sintering treatment is more than
1400.degree. C.
10. The method of preparing a tungsten metal material with high
purity as claimed in claim 1, wherein after the ball-grinding step
(B), a heating/drying process and a filtering process are further
performed.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This non-provisional application claims priority under 35
U.S.C. .sctn.119(a) on Patent Application No(s). 105122815 filed in
Taiwan, R.O.C. on Jul. 20, 2016, the entire contents of which are
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of preparing the
metal material and, more particularly, to a method of preparing the
tungsten metal material with high purity and a method of preparing
the tungsten target.
BACKGROUND OF THE INVENTION
[0003] Tungsten has the highest melting point among the metals.
Since tungsten has the properties such as high strength, high
density, good toughness of matrix phase, low coefficient of
expansion, and good wear-resistant ability, tungsten is usually
used in the fields of national defense and electronics industry. In
the military industry, particularly in the aspect used for
manufacturing weapons, tungsten exhibits good property. Tungsten is
principally used in manufacturing all kinds of warhead of armor
piercing shell in the weapon industry. With coming of nano-era
which requires that the electronic products have light weight and
thin volume, the applications of thin film sputtering develops
continuously, and so does the applications of tungsten sputtering
target that can be used in relevant industries such as optical
recording media, flat panel displays, semiconductors. Therefore,
for the application of the tungsten material used as target, the
industries have put a lot of labors and money in researching and
developing of the tungsten target in order to get good tungsten
sputtering thin film.
[0004] In addition to having good inherent properties, tungsten can
be subject to powder pre-treatment technique and large deformation
strengthening technique to fine the grains of the material and
elongate the orientation of the grains, and thus further enhance
toughness and erosion-resisting ability of the tungsten material.
Smelting casing technique is one of the methods of treating the
metal materials nowadays. Smelting casing technique is achieved by
melting the material under high temperature to turn into liquid
phase and then being poured into the sand mold or crucible for
being cooled and solidifying to get ingot, which can be classified
to include continuous casting, vacuum induction smelting, and
electron beam smelting. Continuous casting is accomplished by
continuously solidifying the melt liquid metal to become ingot by
continuous cooling of spray water tape, which has the advantages of
low cost, high purity, high yield, and can produce complicated
shapes of ingots that are not limited by the size. Since continuous
casting has the above-mentioned advantages, continuous casting can
become the normally used process of producing a large quantity of
bulks. However, continuous casting is not suitable for the metals
with high melting point such as tungsten, molybdenum, and tantalum.
Vacuum induction smelting is accomplished by heating the alloy raw
material with inductive coils under vacuum to make the alloy raw
material be fused and mixed in the liquid phase and then solidify
into shapes. Induction heating is operated at the temperature as
high as 1500-1600.degree. C., therefore induction heating can be
used for the metals with melting point of 1600.degree. C. or high
activity as long as appropriate crucibles are used. For example, TI
can be smelted by this method. However, this method cannot be used
for the metal materials with higher melting point or for achieving
purity>99% (2N) such as tungsten, molybdenum, and tantalum.
Besides, the degree of vacuum will seriously influence the smelting
purity. Electron beam smelting is accomplished by heating the raw
material by electron gun with huge energy to melt and solidify the
metals. This process requires higher degree of vacuum and heating
with high power of electron beam to melt the metal material with
high melting point of 1600-3300.degree. C. such as tungsten,
molybdenum, and tantalum, and get purity>4N. However, though the
purity of the raw material are high, the disadvantage of this
method is that the cost of the manufacturing equipment is
expensive. Moreover, the grains of the metal obtained by electron
beam smelting are rough and big which cannot be directly used as
target and have to be further treated.
[0005] For the above-said smelting processes for preparing the
metal material or target, to control the contents of the impure
elements in the material, smelting and casting are usually
proceeded under vacuum or protective atmosphere. But, in the
process of casting, there are some defects such as segregation of
the ingredients, porosity, and non-uniform microstructure which
appear after slow solidification. Therefore, all these processes
need further thermal treatments to lower the porosity.
[0006] Tungsten metal material or tungsten target can be prepared
by powder metallurgy. Powder metallurgy is suitable for preparing
ceramic compound materials which cannot be solid dissolved due to
thermodynamics factors or are easy to result in macroscopic
segregation during casting process. Besides, powder metallurgy is
suitable for preparing the metals with high activity or the metals
with high melting point such as Ti, Ta, Mo, and W, and the ceramic
materials such as Al.sub.2O.sub.3 and Zr.sub.2O.sub.3. Powder
metallurgy can be used to get the metal material and target with
high purity and high density. However, to prepare sintered body
with large area, the specification of the manufacturing equipment
has to be enhanced. For example, the capacity in tons of the
thermal compression furnace has to be increased, and the chamber of
the thermal compression furnace has to be expanded. But, all these
costs of investment for the equipment are very expensive, and thus
are not advantageous for the industry to carry out mass
production.
[0007] Therefore, there is a need in this industry to develop a
method for preparing the tungsten metal material and the tungsten
target with high purity in order to avoid using expensive
manufacturing equipment and to proceed with efficient treatment to
get tungsten metal material with high purity. In such way,
manufacturing cost and efficiency can be both satisfied for
preparing the tungsten metal material and the tungsten target with
high purity.
SUMMARY OF THE INVENTION
[0008] In view of the aforesaid drawbacks of the prior art, it is a
main objective of the present invention to provide a method of
preparing the tungsten metal material with high purity, which
includes the steps of a treatment of mixing a tungsten metal powder
with a metal nitrate, a ball-grinding treatment, and a sintering
treatment, for increasing the density of the tungsten-based metal
and thus obtaining the tungsten metal material with high
purity.
[0009] In order to achieve the above objective, the present
invention provides a method of preparing the tungsten metal
material with high purity, which can prepare the tungsten metal
material with purity more than 99.9%, includes the steps of: (A)
providing a tungsten metal powder to mix with a metal nitrate to
form a mixed powder slurry; (B) ball-grinding the mixed powder
slurry to obtain a uniformly mixed powder; (C) sintering the
uniformly mixed powder to obtain the tungsten metal material with
high purity.
[0010] The tungsten metal material with high purity has the
following properties: wherein the purity of the tungsten metal
material with high purity is more than 99.9%, and the density
thereof is more than 99% of the density of pure tungsten.
Therefore, the tungsten metal material with high purity is suitably
used to prepare a tungsten metal target. As long as the uniformly
mixed powder is further pressed and shaped to a desired shape for
the target before the sintering step (C), the tungsten metal
material can be used to prepare the tungsten metal target with high
purity and high density.
[0011] The tungsten metal powder of the present invention can be
prepared by solid state reaction, wherein the initiating material
is hexacarbonyl tungsten powder having an average particle diameter
of 1-5 .mu.m, and the metal nitrate in step (A) is selected from
nickel nitrate, ferric nitrate, and a mixture thereof. In step (A),
the tungsten metal powder is mixed with the metal nitrate to form a
mixed powder slurry. Then, oleic acid used as a solvent can be
further added into the mixed powder slurry to proceed with
ball-grinding treatment to obtain the uniformly mixed powder.
Thereafter, the uniformly mixed powder can be subject to a
heating/drying process and a filtering process to make the particle
diameter of the mixed powder more uniform.
[0012] The sintering treatment in step (C) can adopt Liquid Phase
Sintering (LPS) which is a method that can efficiently facilitate
the sintering rate and is usually suitable for the mixture of
elementary powders. When the sintering temperature is over the
melting point of one of the ingredients or over the eutectic
temperature or peritectic temperature of the ingredients, a liquid
phase formed. Since the capillary force of the liquid can cohere
the powders and the atom diffuses in the liquid faster than in the
solid, the sintering rate of liquid sintering is very fast. The
sintering treatment of the present invention can include a
plurality of stages of heating treatments. For example, the
sintering treatment can include four stages of heating treatments
(but is not limited thereto), wherein the temperature in the first
stage of heating treatments is more than 200.degree. C., and the
temperature in the last stage of heating treatments of the
sintering treatment is more than 1400.degree. C.
[0013] Both the above summary and the following description and
drawings aim to explain the techniques and means required to
achieve the predetermined objectives of the present invention as
well as the effects thereof. The other objectives and advantages of
the present invention are described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a flow chart of a method of preparing the tungsten
metal material with high purity according to the present
invention;
[0015] FIG. 2 is a schematic graph showing the temperature-raising
curve for the tungsten metal powder during sintering process
according to the present invention;
[0016] FIG. 3 shows relative density of the tungsten metal material
(having gone through 1400.degree. C. sintering temperature) with
metal nitrate being added thereinto to form different proportions
of solid phase to liquid phase according to the present
invention;
[0017] FIG. 4 is an XRD graph of the tungsten metal material
(having gone through 1400.degree. C. sintering temperature) at
different proportions of solid phase to liquid phase according the
present invention; and
[0018] FIG. 5 is the ingredients analyzing result of the tungsten
metal material with purity of 99.93 wt. % which is prepared at the
proportion that solid phase to liquid phase is 99.95:0.05 vol. %
according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] The following will illustrate the embodiments of the present
invention by specific examples. Any persons skilled in the art
could easily understand the advantages and the effects of the
present invention from the disclosed contents in the present
specification.
[0020] The present invention employs powder metallurgy to prepare
the material with high density by grain boundary diffusion of the
metals with high melting point (such as molybdenum, chromium,
tantalum, and tungsten). This process can make the material to have
the good properties such as fine grain size, uniform
microstructure, and isotropy. In the present invention, the
tungsten metal material and the tungsten-based metal target are
prepared by powder metallurgy, such as by hot isostatic pressing,
hot pressing, and cold isostatic pressing, which can all accomplish
the effect of increasing densification. However, the equipments of
hot pressing and hot isostatic pressing are limited by the heating
temperature and the size of the chamber, and thus they can only be
used to prepare the planar target no more than a specific size, and
cannot meet the requirement for the target in the semiconductor
industry, such as large size, rotary, and custom-made targets.
Regarding the present invention in applications, the embodiment
employs atmospheric pressure in powder metallurgy which adds
sintering aid. Although adding sintering aid can facilitate
diffusion under high temperature and is an effective method, it is
observed that inappropriate sintering aid, if added, will react
with tungsten metal and usually result in non-uniform distribution,
much impurities, or not good densification. Therefore, to solve the
problems encountered in the process for preparing tungsten alloy
with high melting point and to obtain tungsten metal and
tungsten-based metal target with good properties, the present
invention employs powder metallurgy by adding sintering aid of
nitrates in liquid phase (such as ferric nitrate and nickel
nitrate), where such method can make metal nitrates and tungsten
metal in solid phase to have uniform distribution, so that the
quantity of the sintering aid can be lowered and the disadvantage
caused by adding sintering aid can be avoided, and finally the
tungsten metal material and the tungsten-based metal target with
high purity and densification can be prepared.
[0021] Please refer to FIG. 1 which is a flow chart of a method of
preparing the tungsten metal material with high purity according to
the present invention. As shown, the method of preparing the
tungsten metal material with high purity according to the present
invention includes the steps of: (A) providing a tungsten metal
powder to mix with a metal nitrate to form a mixed powder slurry
(step S101); (B) ball-grinding the mixed powder slurry to obtain a
uniformly mixed powder (step S102); (C) sintering the uniformly
mixed powder to obtain the tungsten metal material with high purity
(step S103); wherein the tungsten metal material with high purity
can be used to prepare a tungsten metal target.
EMBODIMENT
[0022] The present embodiment mixes W(CO).sub.6 (hexacarbonyl
tungsten) with Ni(NO.sub.3).sub.2 (metal nitrate) to form a mixed
powder slurry, and illustrates the influence of different
proportions of solid phase to liquid phase on the target (final
product). The ingredients are shown in Table 1. According to Table
1, the present embodiment mixes W(CO).sub.6 (hexacarbonyl tungsten)
with Ni(NO.sub.3).sub.2 (metal nitrate) by different proportions of
solid phase to liquid phase to form a tungsten-based metal mixed
slurry, which is further mixed with oleic acid (solvent) and YSZ
grinding balls. After 24-hour ball grinding, the mixed slurry is
put into the furnace at 200.degree. C. After being completely dried
to become powder, it is filtered through the 325 mesh screen to
obtain uniformly mixed powder. The present embodiment further
adopts dry pressing to press and shape the powder into green body
of circular shaped disk (8 mm in diameter).
TABLE-US-00001 TABLE 1 Different proportions of solid phase to
liquid phase Proportion of solid phase to liquid phase W % Metal
nitrate % S/L = 88:12 88 12 S/L = 92:8 92 8 S/L = 96:4 96 4 S/L =
98:2 98 2 S/L = 99:1 99 1 S/L = 99.95:0.05 99.95 0.05
[0023] Please refer to FIG. 2 which is a schematic graph showing
the temperature-raising curve for the tungsten metal powder during
sintering process according to the present invention. As shown, the
present embodiment is to put the green body of circular shaped disk
(having different propositional ingredients) made by the above
process into the high temperature atmosphere furnace, and to
perform sintering by injecting reduction atmosphere. During
sintering, the furnace is firstly heated to 300.degree. C. at the
temperature-raising rate of 3.degree. C./min, and the temperature
is maintained at 300.degree. C. for one hour for completely
removing oleic acid. Then, the temperature is raised to
1000.degree. C. at the rate of 5.degree. C./min and the temperature
is further maintained at 1000.degree. C. for one hour, and
thereafter, the temperature is raised to 1200.degree. C. at the
rate of 5.degree. C./min and the temperature is maintained at
1200.degree. C. for one hour (where phase change occurs at each of
the two stages). Finally, the temperature is raised to 1400.degree.
C. at the rate of 5.degree. C./min and the temperature is further
maintained at 1400.degree. C. for five hours, and the furnace is
then cooled to room temperature to prepare the tungsten metal
target. It should be noted that the temperature-raising curve
during sintering process in the above embodiment is just an
example, and to prepare tungsten metal target having different
properties, the influencing parameters (such as the ingredients,
the maintained duration, and the sintering temperature) can be
adjusted.
[0024] According to the sintering treatment of the present
embodiment, there is liquid metal nitrate among the tungsten metal
powder particles which is quickly and uniformly distributed among
the powders to lower the surface energy, therefore the adjacent
powders are pulled towards one another because of capillary force.
In normal circumstances, since the capillary force is high, the
powder particles are easily to be re-arranged, and there is no need
to operate with long duration or at extreme high temperature and
the material can be densified. Effective control of the
temperature-raising curve is mainly to prevent the material from
shrinking unduly and thus cracking during the densification
process.
[0025] Please refer to FIG. 3, which shows relative density of the
tungsten metal material (having gone through 1400.degree. C.
sintering temperature) with metal nitrate being added thereinto to
form different proportions of solid phase to liquid phase according
to the present invention. Please refer to FIG. 4, which is an XRD
graph of the tungsten metal material (having gone through
1400.degree. C. sintering temperature) with metal nitrate being
added thereinto to form different proportions of solid phase to
liquid phase according the present invention. As shown, since the
present embodiment uses W(CO).sub.6 (hexacarbonyl tungsten) as the
initiating material that is dissolved in metal nitrate, liquid
metal nitrate (sintering aid) can be uniformly distributed in gel
form among the tungsten metal particles, so as to improve uniform
distribution of the sintering aid and remarkably lower the liquid
phase percentage to which contributed by the added sintering aid.
But, once the liquid phase percentage is over 2%, a second phase of
NiW is generated, and thus the density of the produced tungsten
metal material relative to pure tungsten is lowered.
[0026] Please refer to FIG. 4, which is an XRD graph of the
tungsten metal material (having gone through 1400.degree. C.
sintering temperature) at different proportions of solid phase to
liquid phase according the present invention. As shown, at
appropriate proportion of solid phase to liquid phase, the material
can be quickly densified and the microstructure with excellent
properties is formed.
[0027] The example prepared by the present embodiment is analyzed
by inductively coupled plasma mass spectrometry (ICP-MS) of the
National Science Council Instrument Center of National Cheng Kung
University to acquire the ingredients of the tungsten metal
material with high purity. FIG. 5 is the analyzing result of the
optimized tungsten metal material (tungsten metal target) according
to the present embodiment, wherein the parameters conducted on the
sample are listed as below: solid phase to liquid phase is
99.95:0.05 vol. %; and the sintering temperature is 1400.degree. C.
for the duration of four hours. It can be known from the analyzing
result that the tungsten metal material (tungsten metal target)
with purity of 99.93 wt. % can be obtained.
[0028] The above embodiments are just illustrated to explain the
characteristics and the effects of the present invention and are
not used to limit the scope of the substantial content of the
present invention. Any persons skilled in the art can make
modifications and changes to the above embodiments without
departing from the spirit and scope of the present invention.
Accordingly, the scope intended to be protected by the present
invention should be defined by the appended claims.
* * * * *