Patent Application
20180057912
This application claims the priority benefit of Korean Patent Application No. 10-2016-0108908, filed on Aug. 26, 2016 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
The present invention relates to a water-leachable alloy-melt-swapping (AMS) process in which a water-leachable alloy reacts with water and dissolves, and a porous metal manufactured using the same. More particularly, the present invention relates to a porous metal and a method of manufacturing the same, in which a precursor, including element groups that are selected in consideration of the relationship of heat of mixing with a water-leachable alloy composition to be subjected to an AMS process, is immersed in the water-leachable alloy melt, thus manufacturing a bi-continuous structure alloy including the water-leachable alloy due to a swapping process between the elements. The bi-continuous structure alloy is subjected to dealloying using only pure water instead of an etching solution, thus manufacturing the porous metal.
Porous metals have been actively studied as they are known to be applicable to structural materials, owing to mechanical properties such as excellent elongation, and functional materials having properties such as large surface area and low thermal conductivity. A chemical dealloying process using an etching solution has been actively studied as the most simple and effective method for manufacturing porous metals. However, conventional processes have been limited to the manufacture of only precious metal-based metals acting as positive electrodes due to the difference in corrosion potential between constituent elements.
In a liquid metal dealloying (LMD) process which has been studied recently as a solution to this problem, a high-temperature liquid metal is reacted with a precursor having a specific thermodynamic relationship with the metal to manufacture a bi-continuous complex structure alloy, and the bi-continuous complex structure alloy is subjected to dealloying using an etching solution, thus forming the porous structure of a metal having a low corrosion potential other than noble metals.
However, the conventional LMD process has problems in that pure metals such as magnesium (Mg) and bismuth (Bi), which are easily oxidized in a high-temperature atmosphere, must be maintained in a liquid phase at a high temperature for a long period of time, and in that a toxic etching solution such as a strong acid/strong base must be used in order to manufacture porous bodies. Accordingly, there is demand for the development of a more convenient and eco-friendly new process.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a porous metal and a method of manufacturing the same. The porous metal is manufactured using a more convenient and eco-friendly AMS process, and in the AMS process, the use of a pure metal liquid having low oxidation resistance, which is considered to be a drawback of a conventional LMD process, is avoided, a novel water-leachable alloy is designed so as to be more stably maintained in a liquid phase at high temperatures, and a water-leachable dealloying process is performed through a process using pure water instead of a process using an etching solution during the conventional LMD process.
In order to accomplish the above object, the present invention provides an AMS process. The AMS process includes preparing a water-leachable alloy having excellent oxidation resistance, preparing an AMS precursor including a composition having a relationship of both positive (+) and negative (−) heats of mixing with elements contained in the alloy, manufacturing a bi-continuous structure alloy by immersing the prepared precursor in a melt prepared by dissolving the water-leachable alloy prepared during the former step, and obtaining the porous metal by reacting the bi-continuous structure alloy in pure water instead of a toxic etching solution.
In addition, in the step of preparing the water-leachable alloy having the excellent oxidation resistance according to the present invention, metal elements (element group I) that are soluble in water are used, and the alloy is designed by controlling the composition thereof so as to be stably maintained in a liquid phase even in an oxidation atmosphere at a high temperature that is higher than a melting point thereof. The element group I constituting the alloy melt includes Ca and Mg which are known to have excellent water solubility. Particularly, the element group I is a Ca-based alloy and is represented by the composition of CaxMg100-x (55≦x≦82 at. %). Since the above-described composition region has a eutectic point having a relatively low melting point of about 445° C., the metal elements are very stable in a liquid phase, compared to a conventional pure metal, and include water-leachable alloy elements, thus being easily dissolved in pure water. Further, in the step of preparing the AMS precursor, an alloy is manufactured, which includes an element group II, having positive (+) heat of mixing with elements constituting the element group I, and an element group III, having negative (−) heat of mixing with elements constituting the element group I. Next, in the step of manufacturing the bi-continuous structure alloy, the AMS precursor including both the element groups II and III prepared during the former step is immersed in the melt of the alloy including the element group I and thus reacted, thereby manufacturing the bi-continuous structure alloy. Subsequently, in the step of manufacturing the porous metal, the porous metal is obtained by reacting the manufactured bi-continuous structure alloy in pure water to thus perform the dealloying process of the water-leachable alloy.
In the present invention, the AMS precursor to be immersed in the liquid metal is an alloy that includes one or more elements selected from the element group II including Ti, V, Cr, Mn, Fe, Co, Zr, Nb, Mo, Hf, Ta, W, and Re, which have positive (+) heat of mixing with both Ca and Mg of the element group I, and one or more elements selected from the element group III including Al, Si, P, Ni, Cu, Zn, Ga, Ge, As, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Tl, Pb, and Bi, which have negative (−) heat of mixing with both Ca and Mg of the element group I.
In addition, the AMS precursor according to the present invention is obtained by alloying one or more elements selected from the element group II, acting as the main element of the finally manufactured porous metal, and one or more elements selected from the element group III, which reacts with the alloy melt at high temperatures to dissolve and flow into the melt. The composition of the element groups II and III of the AMS precursor is represented by (element group II)100-y(element group III)y (5≦y≦95 at. %). In the above-described composition, when the value of y is less than 5, it is difficult to maintain the structure of the porous metal after dealloying. When the value of y is more than 95, it is difficult to form the structure of pores connected to each other through the dealloying process using water. In the step of preparing raw materials, it is possible to control the internal porosity of the finally obtained porous body by controlling the composition ratio of the element group II and the element group III, or it is possible to obtain microstructures having various shapes by controlling process conditions such as agitation conditions, immersion time, and the temperature of the melt to thus adjust a position exchange rate between the elements due to diffusion.
Finally, a porous metal manufactured using an alloy-melt-swapping process according to another aspect of the present invention includes a porous body that includes an alloy material including at least one element selected from among Ti, V, Cr, Mn, Fe, Co, Zr, Nb, Mo, Hf, Ta, W, and Re constituting the element group II as a main element, and has pores therein. The metal porous body exhibits a further characteristic of a porous structure due to the pores as well as characteristics of a conventional metal material, thereby securing specific physical properties.
The metal porous body may be obtained by performing dealloying of the bi-continuous structure alloy, which includes both a phase including the elements of the element group I undergoing swapping during the AMS process, as the main element, and another phase including the element group II, in water. It is possible to control the internal porosity by adjusting the composition ratio of constituent elements, or it is possible to obtain various porosities by controlling process conditions such as agitation conditions, immersion time, and the temperature of the melt to thus adjust the position exchange rate between the elements due to diffusion.
As described above, in a water-leachable alloy-based AMS process, porous structures of various metals having a low corrosion potential other than noble metals can be more conveniently and effectively provided than in a conventional dealloying process. Further, an alloy composition including Ca soluble in water as a main element according to the present invention can be completely dissolved in pure water within 72 hours (about 1.4 wt. % per hour), which is useful and eco-friendly, unlike a conventional dealloying process which is performed in a toxic etching solution such as a strong acid/strong base, and thus may create byproduct due to the toxic etching solution. Moreover, the alloy composition is manufactured by specifying surrounding compositions based on eutectic reaction so that oxidation resistance thereof is excellent at high temperatures. Accordingly, the alloy composition has excellent liquid-phase stability and excellent oxidation resistance in the atmosphere at high temperatures, compared to a melt of a single metal composition used in a conventional LMD process.
Furthermore, the porous metal provided in the present invention has a structure in which pores are distributed in a metal material. The porous metal has properties such as high elongation and large surface area due to its porous structure, in addition to excellent mechanical properties of a basic metal material, and the porosity and the shape of the ligament are controlled by controlling process conditions.
The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the present invention are shown so as to be easily understood by those skilled in the art. The present invention may be embodied in many different forms, but is not limited to the embodiments described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted in the drawings, and the same reference numerals are used for the same or similar components throughout the specification. In the case of publicly known technologies, a detailed description thereof will be omitted.
In the specification, when any portion “includes” any component, this means that the portion does not exclude other components but may further include other components unless otherwise stated.
The present invention relates to a water-leachable alloy-melt-swapping (AMS) process in which a water-leachable alloy reacts with water and dissolves in water, and a porous metal manufactured using the same. More particularly, the present invention relates to a porous metal and a method of manufacturing the same, in which an AMS precursor including element groups that are selected in consideration of the relationship of heat of mixing with a water-leachable alloy composition to be subjected to an AMS process is immersed in the water-leachable alloy melt, thus manufacturing a bi-continuous structure alloy, and the bi-continuous structure alloy is subjected to dealloying using water, thus manufacturing the porous metal.
The AMS process using the water-leachable alloy according to the present invention includes preparing the water-leachable alloy having excellent oxidation resistance, preparing the AMS precursor including a composition having a relationship of both positive (+) and negative (−) heats of mixing with the alloy elements, manufacturing the bi-continuous structure alloy by immersing the prepared precursor in a melt prepared by dissolving the water-leachable alloy prepared during the former step, and obtaining the porous metal by reacting the bi-continuous structure alloy in pure water instead of a toxic etching solution. The water-leachable alloy element having excellent oxidation resistance is designated by the element group I, the alloy elements having positive and negative heats of mixing with the elements constituting the element group I are designated by the element groups II and III, respectively, and the element groups I, II, and III are shown on the periodic table in
Manufacture of Water-Leachable Liquid Alloy Having Excellent Oxidation Resistance
In the present step, the water-leachable liquid alloy having excellent oxidation resistance for a water-leachable alloy-melt-swapping process will be described. The metal element constituting the alloy melt for the AMS process must satisfy the following conditions: 1) the metal element must have a low melting point so that the AMS precursor is not melted when the AMS precursor is immersed in the alloy melt, 2) the metal element must have excellent oxidation resistance so as not to be easily oxidized even when dissolved in the atmosphere, and finally 3) the metal element must include a water-leachable material so that dealloying is feasible even when the metal element is immersed in pure water, as in an etching solution environment.
For this purpose, Ca and Mg, which are known to actively react with water, are selected as the element group I constituting the water-leachable alloy. As shown in
In addition, for the water solubility evaluation of each liquid alloy, the water solubility of Ca—Mg alloys having various compositions is evaluated as shown in Table 1 below. Each water-leachable alloy is manufactured in a high-frequency melting furnace under a high-purity argon atmosphere, and is processed into a cubic shape so as to have a weight of 10 g, and the change in weight per hour in pure water is evaluated. With respect to the composition used, as shown in the table below, four compositions of pure Ca, pure Mg and eutectic points of the alloy of two metals are selected and compared.
The water-leachable liquid alloy according to the present invention is limited so that a water dissolution rate is at least 1.5 wt. % per hour, that is, a condition under which dealloying of the water-leachable alloy is completely performed within 72 hours due to the rapid reaction with pure water to thus dissolve the alloy in water. In fact, as can be seen from the table, the alloy of the Ca-based eutectic reaction composition, which is considered to be the least reactive among the liquid alloy compositions according to the present invention, is dissolved in water at a rate of 1.86 wt. % per hour. That is, it can be expected that the water-leachable liquid alloy according to the present invention exhibits excellent water solubility of at least 1.86 wt. % per hour even with pure water alone.
Manufacture of AMS Precursor
The manufacture of the AMS precursor for the AMS process, which is immersed in the liquid alloy to form the bi-continuous structure alloy, will be described below. The AMS precursor according to the present invention may be manufactured using an arc-melting method so that the AMS precursor includes a combination of the element group II and the element group III having a specific heat of mixing relationship with the composition of the liquid metal alloy. Since the arc melting method can offer elevated temperature easily to form a homogeneous solid solution, the precursor may be rapidly obtained in a bulk form, and impurities such as oxides and pores may be minimized, which leads to selection of the arc melting method. In addition to the above-described arc melting method, it is possible to manufacture the AMS precursor using an induction melting method exhibiting an agitation effect caused by an electromagnetic field during melting, a resistance heating method for precisely controlling a temperature, and a casting process such as a rapid solidification method which is useful to form a homogeneous solid solution. In addition to the casting method for directly melting a high-melting-point metal, it is possible to manufacture the AMS precursor according to spark plasma sintering using powder metallurgy, in which raw materials are shaped into powder, or using hot isostatic pressing sintering at a high temperature and pressure. The sintering method has merits in that the microstructures are precisely controlled and in that it is easy to manufacture a precursor having a desired shape.
Since the element group II (B) has a positive (+) heat of mixing with the elements constituting the element group I, which is the composition of the liquid metal alloy, its position is maintained in the precursor without reacting even in the high-temperature liquid metal. Accordingly, the element group II (B) constitutes the porous metal upon dealloying using water, which is a post-process. According to the present invention, Ti, V, Cr, Mn, Fe, Co, Zr, Nb, Mo, Hf, Ta, W, and Re are selected as the main constituent elements of the element group II (B). Further, the AMS precursor must include one or more elements among the element group II.
In addition, since the element group III (C) has a negative (−) heat of mixing with the element group I, the element group III easily reacts with the high-temperature liquid metal and diffuses. Accordingly, the element group III (C) may be exchanged in position with the constituent elements of the element group I in the precursor due to diffusion. According to the present invention, one or more among Al, Si, P, Ni, Cu, Zn, Ga, Ge, As, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Ti, Pb, and Bi must be included as the main constituent elements of the element group III (C).
In summary, when the AMS precursor manufactured under the above-described conditions is immersed in the high-temperature liquid metal of the alloy including the element group I, the element group II that is not reacted with the element group I may remain in the AMS precursor, and the element group I may occupy the space occupied by the element group III due to the reaction with the liquid metal, thus manufacturing a bi-continuous structure alloy including the element group I and the element group II.
Examples of the AMS precursors having various compositions according to the present invention is shown in Table 2 below, along with the crystal structure of the porous body, which is the final product. Each Example includes one to four types of elements among the elements of the element group II, and also includes elements of the element group III. The precursors of the Examples are manufactured using the arc melting method as described above, are reacted in the alloy melt of the Ca73Mg27 composition at 900° C. for 10 minutes, and are then dissolved in pure water for 72 hours.
50Ni50
50Ni50
50Ni50
50Cu50
50Ni47Pb3
50Ni47Bi3
50Ni47Cd3
75Ni25
50Ni50
25Ni75
75Cu25
50Cu50
25Cu75
As shown in the above-described table, the AMS precursor (B+C) may easily form a porous body (B) having a desired phase even when the AMS precursor is an alloy of a quinary or higher system having four or more types of elements selected from the element group II, including the case where the AMS precursor is an alloy of a simple binary system. In addition, the results shown in the table indicate that the AMS process may be successfully completed even if the elements selected from the element group III are changed to various element groups. Finally, even when the ratio between the element groups II and III is adjusted, the porous body, which is the final product, can be obtained.
Manufacture of Bi-Continuous Structure Complex Material Using AMS Process
In the present step, the alloy of the complex structure manufactured in the present invention through various Examples will be exemplified in more detail with reference to the drawings. Particularly, as shown in Table 3 below, Examples 1 to 3, 31 to 33, and 41 to 43, and Examples 2a, 2b, and 2c, in which the immersion conditions are changed relative to Example 2, will be described in detail in the present specification.
The AMS precursor of each Example is an alloy including both the element such as Ti, Fe, Mn, Co, and Cr, corresponding to the element group II, and Ni, which is the representative element of the element group III, and is comprised of elements having positive (+) and negative (−) heats of mixing with Ca and Mg, constituting the liquid alloy melt. The composition of the element group II and the element group III constituting the AMS precursor is represented by (element group II)100-y (element group III)y (5≦y≦95 at. %). When the value of y is less than 5, it is difficult to maintain the structure of the porous metal after dealloying in water. When the value of y is more than 95, it is difficult to realize the structure of pores connected to each other using a dealloying process. The composition of the melt that is used is Ca73Mg27, which is a Ca-based eutectic composition. The change of the composition is thoroughly observed while changing the temperature and the immersion time in the melt.
Meanwhile,
Further, from
Manufacture of Porous Alloy Using Dissolution in Water
A process of manufacturing a porous alloy will be described in detail. The step of manufacturing the porous alloy, which is the final step according to the present invention, is performed by dealloying of the bi-continuous structure complex material, manufactured via a series of steps in pure water.
These results show that the Ca-based alloy of liquid metal according to the present invention, effectively constitutes a bi-continuous structure alloy by reacting with the AMS precursor, and is easily dissolved in water by the dealloying process using water. A second phase may be completely removed by controlling a dealloying time, and a part thereof may remain in order to control the porosity. In addition, it can be seen that the porosity and the shape of the ligament are controlled depending on the concentration or the type of the etching solution used during the dealloying process.
In other words, it can be seen that the process of forming the bi-continuous structure between the alloy melt and the AMS precursor using the AMS process includes position swapping due to diffusion as a dominant process, and the rate of the diffusion process may be controlled so as to form the microstructure into a desired shape. For example, the porosity may be controlled by changing process conditions such as the immersion time in the alloy melt or the temperature of the melt. Further, a process for improving the diffusion rate in the melt, such as mechanical agitation, agitation using an electromagnetic field, or vibration of the melt using ultrasonic waves, may be additionally introduced during the AMS process, thereby reducing a process time.
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the technical idea of the present invention. Therefore, the scope of the present invention should be construed as being covered by the scope of the appended claims, rather than the specific embodiments, and all technical ideas falling within the scope of the claims should be construed as being included in the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2016-0108908 | Aug 2016 | KR | national |
