Patent Publication Number: US-2023144295-A1

Title: Apparatus and method of producing inorganic powder

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2021-0154264, filed on Nov. 10, 2021, and Korean Patent Application No. 10-2021-0154265, filed on Nov. 10, 2021, respectively, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entireties by reference. 
     BACKGROUND 
     1. Field 
     An embodiment of the present disclosure relates to an apparatus for producing inorganic powder, and a method of producing inorganic powder by using the apparatus and, more particularly, to a chemical vapor synthesis apparatus for producing inorganic powder by using chemical reaction between a gas-phase precursor and a reaction gas, and a method of producing inorganic powder by using the chemical vapor synthesis apparatus. 
     2. Description of the Related Art 
     A chemical vapor synthesis process is a process for producing a solid-phase material through chemical reaction between a gas-phase precursor and a reaction gas. The solid-phase material includes an inorganic material such as metal or ceramic. Powder of the inorganic material (hereinafter referred to as inorganic powder) may be produced using the chemical vapor synthesis process. A precursor in a gas phase at room temperature may be directly used, or a precursor in a solid or liquid phase at room temperature may also be used by vaporizing the same. 
     A liquid-phase precursor may be supplied using a pump, a sprayer, a bubbler, or the like. Using a pump, large-volume droplets need to be vaporized in a reactor but a long time is taken for vaporization due to a small specific surface area and poor heat transfer characteristics of the droplets. Using a sprayer, small droplets are produced but still have a small specific surface area, a large amount of gas is used to spray, and a reactor diameter is restricted due to a spray angle. Using a bubbler, although the precursor is easily injected at a constant amount compared to the pump or sprayer, a vaporized amount changes depending on a remaining solution amount, a gas flow rate, or the like. 
     A solid-phase precursor may be supplied by loading and vaporizing powder or pellets using a feeder or by loading and vaporizing a raw material in a furnace. When powder is loaded using a feeder, an error occurs in the feeder depending on characteristics of the powder, e.g., flowability or moisture content, and thus quantitative injection may not be easily achieved. When pellets are loaded using a feeder, a specific surface area changes as the pellets are vaporized, and thus a vaporized amount is not constant. Similarly, when a raw material is loaded in a furnace, a specific surface area changes as the raw material is vaporized, and thus a vaporized amount is not constant. 
     As described above, a precursor in a solid or liquid phase at room temperature may not be easily supplied at a constant amount and, when powder is produced using a chemical vapor synthesis process, the powder exhibits a wide particle size distribution due to the change in amount of the supplied precursor. Therefore, a method of quantitatively supplying a solid- or liquid-phase precursor in a chemical vapor synthesis process is required. 
     SUMMARY 
     An embodiment of the present disclosure provides a chemical vapor synthesis apparatus including a precursor supplier capable of quantitatively supplying a gas-phase precursor obtained by vaporizing a solid- or liquid-phase precursor, to a reaction part at a constant amount. An embodiment of the present disclosure also provides a method of producing inorganic powder having a uniform particle shape and a narrow particle size distribution, by using the chemical vapor synthesis apparatus. 
     However, the scope of embodiments of the present disclosure are not limited thereto. 
     According to an embodiment of the present disclosure, there is provided an apparatus for producing inorganic powder, the apparatus including a vaporization part where a condensed-phase precursor is vaporized to obtain a gas-phase precursor, a partial precipitation part where the gas-phase precursor obtained in the vaporization part is partially precipitated to a condensed phase, and a reaction part where the gas-phase precursor remaining after being partially precipitated to a condensed phase in the partial precipitation part reacts with a reaction gas to obtain inorganic powder. 
     An equilibrium vapor pressure of the gas-phase precursor in the partial precipitation part may be lower than a vapor pressure of the gas-phase precursor obtained in the vaporization part, and an equilibrium vapor pressure of the precursor in the reaction part may be equal to or higher than a vapor pressure of the gas-phase precursor partially precipitated to a condensed phase in the partial precipitation part. 
     A temperature of the vaporization part may be higher than a temperature of the partial precipitation part, and a temperature of the reaction part may be equal to or higher than the temperature of the partial precipitation part. 
     The partial precipitation part may include a precipitation induction member for inducing precipitation of the gas-phase precursor. 
     The apparatus may include a bottom-up type in which the vaporization part, the partial precipitation part, and the reaction part are sequentially provided in a direction opposite to a direction of gravity, a top-down type in which the vaporization part, the partial precipitation part, and the reaction part are sequentially provided in the direction of gravity, and a horizontal type in which the vaporization part, the partial precipitation part, and the reaction part are sequentially provided in a direction perpendicular to the direction of gravity. 
     The inorganic powder may include metal powder or ceramic powder. 
     The precursor may include at least one of metal acetate, metal bromide, metal carbonate, metal chloride, metal fluoride, metal hydroxide, metal iodide, metal nitrate, metal oxide, metal phosphate, metal silicate, metal sulfate, and metal sulfide. 
     The inorganic powder may include nickel (Ni), copper (Cu), silver (Ag), iron (Fe), aluminum (Al), cobalt (Co), platinum (Pt), gold (Au), tin (Sn), or an alloy thereof. 
     The inorganic powder may include an oxide, nitride, or carbide of Ni, Cu, Ag, Fe, Al, Co, Pt, Au, or Sn. 
     According to an embodiment of the present disclosure, there is provided an apparatus for producing inorganic powder, the apparatus including a precursor supplier including a channel, and a reaction part where a gas-phase precursor supplied from the precursor supplier reacts with a reaction gas to obtain inorganic powder. 
     The precursor supplier may include a vaporization part where a condensed-phase precursor is vaporized to obtain the gas-phase precursor, and a partial precipitation part where the gas-phase precursor obtained in the vaporization part is partially precipitated to a condensed phase. 
     The channel of the precursor supplier may be configured in such a manner that a fluid passes sequentially through the vaporization part and the partial precipitation part and then is discharged to the reaction part, and the gas-phase precursor remaining after being partially precipitated to a condensed phase in the partial precipitation part may be injected into the reaction part. 
     An equilibrium vapor pressure of the precursor in the partial precipitation part may be lower than a vapor pressure of the gas-phase precursor obtained in the vaporization part, and an equilibrium vapor pressure of the precursor in the reaction part may be equal to or higher than a vapor pressure of the gas-phase precursor partially precipitated to a condensed phase in the partial precipitation part. 
     The channel may be configured to include at least one downward channel through which a fluid flows downward, and at least one upward channel through which the fluid flows upward, and the downward and upward channels may be provided adjacent to each other in parallel. 
     A temperature of the vaporization part may be maintained higher than a temperature of the partial precipitation part, and a temperature of the reaction part may be maintained equal to or higher than the temperature of the partial precipitation part. 
     The apparatus may further include a quenching gas inlet for injecting a quenching gas into the partial precipitation part. 
     An end of the channel of the precursor supplier, where a fluid is discharged to the reaction part, may be increased in cross-sectional area along a direction in which the fluid moves. 
     The vaporization part may be included in the downward channel heated by a heat source, and the partial precipitation part may be provided between the upward channel extending from the downward channel including the vaporization part, and the downward channel extending to the reaction part. 
     The vaporization part may include a precursor vaporizer provided in a region through which a fluid moving downward along the downward channel heated by a heat source passes, and the partial precipitation part may be provided between the upward channel extending from the downward channel including the precursor vaporizer, and the downward channel extending to the reaction part. 
     The vaporization part may include a precursor vaporizer provided in a region through which a fluid moving upward along the upward channel heated by a heat source passes, and the partial precipitation part may be provided between the downward channel extending from the upward channel including the precursor vaporizer, and the upward channel extending to the reaction part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of embodiments of the present disclosure will become more apparent by describing in detail embodiments thereof with reference to the attached drawings in which: 
         FIG.  1    is a conceptual view of a chemical vapor synthesis apparatus for describing the concept of a partial precipitation part according to an embodiment of the present disclosure; 
         FIGS.  2 A to  4 B  show a vapor pressure of a precursor in a vaporization part and a vapor pressure of the precursor after partial precipitation, based on an injection rate of the precursor under each condition; 
         FIGS.  5 A to  5 C  are conceptual views of various types of chemical vapor synthesis apparatuses according to embodiments of the present disclosure; 
         FIG.  6    is a schematic diagram of a top-down chemical vapor synthesis apparatus according to an embodiment of the present disclosure; 
         FIGS.  7 A to  9 C  show embodiments of a top-down precursor supplier of the present disclosure; 
         FIGS.  10 A to  11 C  show embodiments of a bottom-up precursor supplier of the present disclosure; 
         FIGS.  12 A to  12 C  show embodiments of a horizontal precursor supplier according to an embodiment of the present disclosure; and 
         FIGS.  13  to  15    are scanning electron microscope (SEM) images of nickel (Ni) powder produced according to an inventive example and comparative examples. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, various embodiments of the present disclosure will be described in detail with reference to the attached drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to one of ordinary skill in the art. Like reference numerals denote like elements throughout. Various elements and regions are schematically illustrated in the drawings. Therefore, the scope of embodiments of the present disclosure is not limited by the sizes or distances shown in the attached drawings. 
     According to an embodiment of the present disclosure, a gas-phase precursor may be obtained by vaporizing a solid- or liquid-phase precursor, and the solid or liquid phase is defined as a condensed phase in distinction to the gas phase. 
     An embodiment of the present disclosure provides an apparatus and method of quantitatively supplying a gas-phase precursor at a constant amount to achieve a uniform particle shape and a narrow particle size distribution of inorganic powder produced through chemical vapor synthesis using reaction between the gas-phase precursor and a reaction gas. To this end, a configuration for partially precipitating the gas-phase precursor obtained by vaporizing a condensed-phase precursor, to a condensed phase before reacting with the reaction gas is provided. Then, the gas-phase precursor, which has reached a saturated vapor pressure through partial precipitation, is injected into a reaction part and reacts with the reaction gas to obtain the inorganic powder. 
     When the gas-phase precursor has reached the saturated vapor pressure at a specific temperature, it means that the gas-phase precursor vaporized to exceed the saturated vapor pressure has been entirely precipitated to a condensed phase. Because the saturated vapor pressure at the specific temperature is determined as a constant value, when the saturated vapor pressure is maintained at the specific temperature, it means that the gas-phase precursor is also maintained at a constant amount. Even when the precursor is vaporized to exceed the saturated vapor pressure, once a condition of the saturated vapor pressure is satisfied, an amount of the precursor exceeding the saturated vapor pressure is entirely precipitated to a condensed phase. In an embodiment of the present disclosure, the configuration for partially precipitating the gas-phase precursor to have the saturated vapor pressure is referred to as a partial precipitation part. The partial precipitation part includes a region or space through which a fluid may pass. The partial precipitation part may further include a precipitation induction member for inducing partial precipitation in the region or space. 
     In an embodiment of the present disclosure, a precursor corresponding to a raw material of inorganic powder is a condensed-phase metal compound which reacts with a reaction gas to obtain inorganic powder. The precursor may include one or more of metal acetate, metal bromide, metal carbonate, metal chloride, metal fluoride, metal hydroxide, metal iodide, metal nitrate, metal oxide, metal phosphate, metal silicate, metal sulfate, and metal sulfide, but is not limited thereto. 
     The inorganic powder may include nickel (Ni), copper (Cu), silver (Ag), iron (Fe), aluminum (Al), cobalt (Co), platinum (Pt), gold (Au), tin (Sn), or an alloy thereof. 
     The inorganic powder may include an oxide, nitride, or carbide of Ni, Cu, Ag, Fe, Al, Co, Pt, Au, or Sn. 
       FIG.  1    is a conceptual view of a chemical vapor synthesis apparatus  100  for describing the concept of a partial precipitation part according to an embodiment of the present disclosure. Referring to  FIG.  1   , the chemical vapor synthesis apparatus  100  includes a vaporization part E, a partial precipitation part C, and a reaction part R. 
     The vaporization part E provides a region where a condensed-phase precursor is vaporized to obtain a gas-phase precursor. For example, as shown in  FIG.  1   , a precursor vaporizer M for heating and vaporizing the precursor by using a heat source may be provided in the vaporization part E. The precursor vaporizer M may have a form of a furnace loaded with a powder- or pellet-type precursor or a liquid-phase precursor. In this case, a carrier gas CG injected into the vaporization part E is mixed with the gas-phase precursor vaporized by the precursor vaporizer M. A mixed gas of the carrier gas CG and the gas-phase precursor moves into the partial precipitation part C. An arrow  110  of  FIG.  1    represents that the mixed gas of the carrier gas CG and the gas-phase precursor is provided to the partial precipitation part C. 
     As another example, the vaporization part E may be heated by the heat source to a temperature equal to or higher than a precursor vaporization temperature. A powder-type precursor may be injected into the heated vaporization part E together with the carrier gas CG and be vaporized to a gas phase to obtain a gas-phase precursor. 
     The partial precipitation part C provides a region where the gas-phase precursor obtained in the vaporization part E is partially precipitated to a condensed phase. In this case, the precursor precipitated in the partial precipitation part C corresponds to an amount exceeding a precursor vaporization amount corresponding to an equilibrium vapor pressure at a corresponding temperature. The precursor precipitated to a condensed phase may fall to the bottom of the partial precipitation part C due to a self-weight or be condensed on the surface of a member provided on a path of the gas-phase precursor. An arrow  120  of  FIG.  1    represents that the mixed gas of the carrier gas CG and the gas-phase precursor remaining after being partially precipitated to a condensed phase in the partial precipitation part C is injected into the reaction part R. 
     The reaction part R provides a region where the gas-phase precursor remaining after being partially precipitated to a condensed phase in the partial precipitation part C reacts with a reaction gas to obtain inorganic powder. Although not shown in  FIG.  1   , the reaction part R includes a configuration through which the reaction gas is injected. Because the gas-phase precursor is already partially precipitated in the partial precipitation part C and is always injected into the reaction part R in a saturated state, the gas-phase precursor supplied to the reaction part R is maintained at a constant amount. As an effect of quantitatively supplying the precursor, the inorganic powder obtained in the reaction part R has a uniform particle shape and has a uniform particle diameter to exhibit a narrow particle size distribution. Therefore, an existing problem such as a non-uniform particle diameter or a wide particle size distribution of powder caused by irregular supply of a gas-phase precursor may be solved. 
     Embodiments of the present disclosure may be implemented by satisfying Conditions 1 and 2. 
     Condition 1: An equilibrium vapor pressure P C   eq  of a gas-phase precursor in a partial precipitation part is lower than a vapor pressure P E  of the gas-phase precursor obtained in a vaporization part. 
     Condition 2: An equilibrium vapor pressure P R   eq  of the precursor in a reaction part is equal to or higher than a vapor pressure P C  of the gas-phase precursor that remains after being partially precipitated to a condensed phase in the partial precipitation part. 
     When Condition 1 is satisfied, the precursor is precipitated by an amount corresponding to a difference between P C   eq  and P E . 
     Although Condition 1 is satisfied and the partially precipitated gas-phase precursor is injected into the reaction part, when the vapor pressure P C  of the gas-phase precursor injected into the reaction part is still higher than the equilibrium vapor pressure P R   eq  of the reaction part, the gas-phase precursor would also be partially precipitated to a condensed phase in the reaction part as in the partial precipitation part. Such precipitation in the reaction part causes impurities other than inorganic powder normally obtained by reaction with a reaction gas and thus greatly deteriorates the quality of the inorganic powder. 
     Therefore, P R   eq  needs to be at least equal to or higher than P C  in the reaction part. The above condition should be satisfied to prevent undesired precipitation of the gas-phase precursor to a condensed phase other than reaction with the reaction gas in the reaction part. 
     On the other hand, when P C  is lower than P R   eq , the gas-phase precursor injected into the reaction part is not precipitated before contacting the reaction gas, and participates in reaction after contacting the reaction gas. 
     A temperature in each part when a gas flowing from the vaporization part through the partial precipitation part to the reaction part is maintained at a constant flow rate will now be described. To satisfy Condition 1, the vaporization part E illustrated in  FIG.  1    has a temperature T 1  equal to or higher than a precursor vaporization temperature, and the partial precipitation part C has a temperature T 2  lower than the temperature T 1  of the vaporization part E. A temperature difference between T 1  and T 2  serves as a thermodynamic driving force by which the gas-phase precursor is partially precipitated to a condensed phase. To satisfy Condition 2, a temperature T 3  of the reaction part R is equal to or higher than the temperature T 2  in the partial precipitation part C. Therefore, a thermodynamic driving force by which the gas-phase precursor injected into the reaction part R is partially precipitated to a condensed phase is not present and thus precipitation to a condensed phase does not occur. 
     To verify an embodiment of the present disclosure, behaviors of a gas-phase precursor based on temperature in a vaporization part, a partial precipitation part, and a reaction part were simulated using the chemical vapor synthesis apparatus  100  illustrated in  FIG.  1   . 
     The precursor used for the simulation was solid-phase NiCl 2  for producing nickel (Ni) powder and, considering an equilibrium vapor pressure of NiCl 2  based on temperature, NiCl 2  was injected into a vaporization part maintained at a temperature equal to or higher than a vaporization temperature and then was vaporized. A carrier gas was used as nitrogen (N 2 ), and reaction was not considered to observe only vapor pressure changes of the precursor. The carrier gas was fixed at 15 liters per minute (LPM) for Comparative Example A and at 30 LPM for the others. A vapor pressure of vaporized NiCl 2  was calculated by multiplying a total pressure in the chemical vapor synthesis apparatus by a fraction occupied by gas-phase NiCl 2  in a mixed gas of gas-phase NiCl 2  and the carrier gas. Therefore, when the flow rate of the injected carrier gas is constant, the vapor pressure of NiCl 2  is determined based on temperature. 
     Table 1 shows process conditions used for the simulation, and  FIGS.  2 A to  4 B  show a vapor pressure P 1  of the precursor in the vaporization part, a vapor pressure P 2  of the precursor after partial precipitation, and an equilibrium vapor pressure P 3  of the precursor in the reaction part, based on an injection rate V of the precursor under each process condition. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Partial 
                   
               
               
                   
                   
                   
                 Carrier Gas 
                 Vaporization 
                 Precipitation 
                 Reaction 
               
               
                   
                 Condition 
                 Condition 
                 Flow Rate 
                 Part Temp. 
                 Part Temp. 
                 Part Temp. 
               
               
                   
                 1 
                 2 
                 (LPM) 
                 (° C.) 
                 (° C.) 
                 (° C.) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Embodiment A 
                 ◯ 
                 ◯ 
                 30 
                 950 
                 900 
                 900 
               
               
                 Embodiment B 
                 ◯ 
                 ◯ 
                 30 
                 950 
                 900 
                 1000 
               
               
                 Embodiment C 
                 ◯ 
                 ◯ 
                 15 
                 950 
                 900 
                 950 
               
               
                 Comparative 
                 X 
                 ◯ 
                 30 
                 950 
                 900 
                 950 
               
               
                 Example A 
               
               
                 Comparative 
                 X 
                 ◯ 
                 30 
                 900 
                 950 
                 950 
               
               
                 Example B 
               
               
                 Comparative 
                 ◯ 
                 X 
                 30 
                 950 
                 900 
                 850 
               
               
                 Example C 
               
               
                   
               
            
           
         
       
     
       FIGS.  2 A and  2 B  show simulation results of Embodiments A and B, and show a vapor pressure P 1  (kPa) of the precursor in the vaporization part and a vapor pressure P 2  (kPa) of the precursor after partial precipitation, based on an injection rate V (g/min) of the precursor over time. 
     Referring to Table 1, Embodiments A and B both satisfy Conditions 1 and 2. That is, when a flow rate of the carrier gas injected into the chemical vapor synthesis apparatus is maintained at 30 LPM, a temperature of the vaporization part is maintained higher than the temperature of the partial precipitation part, and temperatures of the partial precipitation part and the reaction part are maintained the same. Equilibrium vapor pressures of NiCl 2  at 850° C., 900° C., and 950° C. are 9.78 kPa, 24.97 kPa, and 58.46 kPa. Therefore, the maximum vapor pressure of NiCl 2  sufficiently vaporized in the vaporization part maintained at 950° C. is 58.46 kPa and, when NiCl 2  is provided to the partial precipitation part maintained at 900° C., precipitation occurs by an amount exceeding the equilibrium vapor pressure of the partial precipitation part, i.e., 24.97 kPa. In Embodiment A, because the temperature of the reaction part is 900° C. equal to that of the partial precipitation part, even when the partially precipitated gas-phase precursor is injected into the reaction part, no more precipitation occurs due to absence of a thermodynamic driving force. 
     Referring to  FIG.  2 A , the injection rate V of the precursor injected into the vaporization part refers to a weight of NiCl 2  injected per hour, and the vapor pressure P 1  of NiCl 2  in the vaporization part exhibits an increase or decrease in response to the increase or decrease in weight of injected NiCl 2 . However, it is shown that gas-phase NiCl 2  exceeding the equilibrium vapor pressure of NiCl 2  is precipitated to a solid phase in the partial precipitation part and thus the vapor pressure of NiCl 2  is constantly maintained at the equilibrium vapor pressure P 2  after partial precipitation regardless of the injection amount of NiCl 2 . This means that, even when the amount of NiCl 2  injected into the vaporization part of a reactor is irregular, the vapor pressure of vaporized NiCl 2  is always constantly maintained in the reaction part. 
       FIG.  2 B  shows a result of Embodiment B under the same process conditions as Embodiment A except that the temperature of the reaction part is 1000° C. When the temperature of the reaction part is 1000° C., the simulation result is the same as Embodiment A in that no more precipitation occurs in the reaction part. 
       FIGS.  3 A and  3 B  show simulation results of Comparative Example A and Embodiment C. Referring to  FIG.  3 A , in Comparative Example A, the injection rate V of NiCl 2  injected into the vaporization part has a large deviation, and this means that injected NiCl 2  greatly changes in weight over time. When the injection rate V of the precursor has the lowest value, the vapor pressure P 1  in the vaporization part is lower than the equilibrium vapor pressure in the partial precipitation part. In this state, when NiCl 2  is injected into the vaporization part, vaporized, and then provided into the partial precipitation part, because the vapor pressure P 1  of gas-phase NiCl 2  in the vaporization part which is lower than the equilibrium vapor pressure in the partial precipitation part is present, Condition 1 is not satisfied. Therefore, the effect that the vapor pressure P 2  of gas-phase NiCl 2  becomes constant to a saturated vapor pressure in the partial precipitation part as in Embodiment A does not occur. When gas-phase NiCl 2  is injected into the reaction part while the vapor pressure of gas-phase NiCl 2  is changing in response to the change in weight of NiCl 2  injected into the vaporization part as described above, this means that the amount of gas-phase NiCl 2  supplied to the reaction part irregularly changes over time. Ni particles obtained in the reaction part under the above condition have irregular diameters and thus exhibit a wide particle size distribution. 
     To solve the above problem, the vapor pressure of gas-phase NiCl 2  in the vaporization part needs to be increased to be higher than the equilibrium vapor pressure of the partial precipitation part. Embodiment C reduces the injection amount of the carrier gas to 15 LPM compared to Comparative Example A. By halving the injection amount of the carrier gas, a fraction of gas-phase NiCl 2  in the mixed gas of the carrier gas and vaporized NiCl 2  is relatively increased. As such, the vapor pressure of NiCl 2  in the vaporization part is higher than the saturated vapor pressure of gas-phase NiCl 2  in the partial precipitation part. Referring to  FIG.  3 B , it is shown that, when the vapor pressure P 1  of the NiCl 2  gas in the vaporization part is increased, the vapor pressure P 2  of gas-phase NiCl 2  in the partial precipitation part becomes constant to the saturated vapor pressure due to precipitation. 
       FIGS.  4 A and  4 B  show simulation results of Comparative Examples B and C. 
     Referring to Table 1, in Comparative Example B, a temperature of the partial precipitation part is maintained higher than the temperature of the vaporization part. Therefore, Condition 1 is not satisfied and thus the effect of partial precipitation caused when the vapor pressure P 1  of vaporized NiCl 2  in the vaporization part is higher than the equilibrium vapor pressure in the partial precipitation part does not occur. Therefore, the vapor pressure P 2  of gas-phase NiCl 2  in the partial precipitation part is substantially the same as the vapor pressure P 1  in the vaporization part, and the change in vapor pressure of gas-phase NiCl 2  in the reaction part over time occurs substantially the same as that in the vaporization part. This means that gas-phase NiCl 2  is not quantitatively supplied to the reaction part. 
     Referring to Table 1, in Comparative Example C, a temperature of the reaction part, i.e., 850° C., is lower than the temperature of the partial precipitation part, i.e., 900° C., and thus Condition 2 is not satisfied. Therefore, referring to  FIG.  4 B , although gas-phase NiCl 2  partially precipitated in the partial precipitation part is injected into the reaction part with a vapor pressure of P 2 , solid-phase NiCl 2  is precipitated by an amount exceeding the equilibrium vapor pressure P 3  in the reaction part. When solid-phase NiCl 2  is precipitated in the reaction part as described above, produced powder may not be used as a product. 
     According to an embodiment of the present disclosure, the partial precipitation part is enough as long as the partial precipitation part may be maintained at a specific temperature to satisfy Conditions 1 and 2 and includes a space through which a fluid may move.  FIGS.  5 A to  5 C  are conceptual views of various types of chemical vapor synthesis apparatuses according to embodiments of the present disclosure. A bottom-up type  500  in which the vaporization part E, the partial precipitation part C, and the reaction part R are sequentially provided in a direction opposite to the direction of gravity, a top-down type  510  in which the vaporization part E, the partial precipitation part C, and the reaction part R are sequentially provided in the direction of gravity, and a horizontal type  520  in which the vaporization part E, the partial precipitation part C, and the reaction part R are sequentially provided in a direction perpendicular to the direction of gravity are illustrated in  FIGS.  5 A to  5 C , respectively. 
     Referring to  FIGS.  5 A and  5 C , the bottom-up type  500  and the horizontal type  520  may include the precursor vaporizer M in the vaporization part E. A gas-phase precursor vaporized from the precursor vaporizer M may be mixed with a carrier gas CG injected into the vaporization part E, so as to form a mixed gas. The mixed gas moves to the partial precipitation part C and the reaction part R. Inorganic powder is obtained in the reaction part R by reaction with an additionally injected reaction gas RG. 
     Referring to  FIG.  5 B , in the top-down type  510 , when injected into the vaporization part E, a powder-type precursor SC carried by a carrier gas may be directly vaporized while falling in the vaporization part E heated to a high temperature. Inorganic powder is obtained in the reaction part R by reaction with an additionally injected reaction gas RG. 
       FIGS.  5 A to  5 C  are merely examples, and the precursor powder may also be injected into the vaporization part E together with the carrier gas in the bottom-up and horizontal types  500  and  520  whereas the vaporization part E may also include the precursor vaporizer M in the top-down type  510 . 
     In the partial precipitation part C of each type of chemical vapor synthesis apparatus, a precipitation induction member PIM capable of inducing partial precipitation of a gas-phase precursor may be additionally provided. In an embodiment, the precipitation induction member PIM may have one or more openings through which the gas-phase precursor passes. The precipitation induction member PIM may be maintained at a temperature lower than that of the vaporization part E to partially precipitate the gas-phase precursor supplied from the vaporization part E. In addition, a channel through which the gas-phase precursor passes may be provided in such a manner that the gas-phase precursor supplied from the vaporization part E moves to the reaction part R after partial precipitation occurs. A condensed-phase precursor obtained by partial precipitation, e.g., solid-phase particles or droplets, may be adhered to and accumulated on the precipitation induction member PIM. 
       FIG.  6    shows a top-down chemical vapor synthesis apparatus  600  including a vertical reaction chamber, as an example of an apparatus for producing inorganic powder, according to an embodiment of the present disclosure. 
     Referring to  FIG.  6   , the chemical vapor synthesis apparatus  600  includes a vertical reaction chamber  610  having a cavity extending in a vertical direction. A heater  640  for heating the reaction chamber  610  is provided on an outer circumferential surface of the reaction chamber  610 . The heater  640  may include, for example, a resistive heating element heated by electricity. The heater  640  may be divided into a plurality of heaters, temperatures of which are independently controlled. For example, as illustrated in  FIG.  6   , three heaters such as heater  1   641 , heater  2   642 , and heater  3   643  may be provided in a downward direction. The three heaters  641 ,  642 , and  643  may be controlled to different temperatures. Therefore, various temperature distributions may be implemented in portions of the reaction chamber  610  by controlling the temperature of each heater. For example, upper and lower portions in a precursor supplier S may be maintained at different temperatures. As another example, the reaction part R may be implemented to be gradually reduced in temperature in a downward direction. 
     The precursor supplier S for vaporizing a precursor and supplying the vaporized precursor to the reaction part R is provided in an upper portion of the reaction chamber  610 , and the reaction part R where a gas-phase precursor reacts with a reaction gas to obtain inorganic powder is provided under the precursor supplier S. The inorganic powder obtained in the reaction part R is collected by a collector G provided under the reaction part R and then is additionally processed, e.g., sorted and cleaned. 
     A first supplier  620  provided on the reaction chamber  610  supplies a raw material such as the precursor to the precursor supplier S together with a carrier gas. As another example, when the precursor supplier S includes a precursor vaporizer, the first supplier  620  may inject only a carrier gas for carrying a vaporized precursor. Additionally, the first supplier  620  may include a separate channel to further supply a quenching gas for cooing a partial precipitation part in the precursor supplier S. To vaporize the precursor, the precursor supplier S needs to be maintained at a high temperature equal to or higher than a certain temperature. In addition, to partially precipitate the gas-phase precursor, the precursor supplier S may have a local region with a low temperature. To this end, local portions in the precursor supplier S may be maintained at different temperatures by appropriately controlling the temperature of the heater  640  around the precursor supplier S. 
     A second supplier  630  is a channel through which a reaction gas reacting with the gas-phase precursor injected from the precursor supplier S is injected into the reaction part R, and is not particularly limited to any shape or path as long as it has a configuration for directly supplying the reaction gas to the reaction part R. 
     The precursor supplier S vaporizes the precursor to obtain a gas-phase precursor, and discharges the gas-phase precursor to the reaction part R. Therefore, a channel through which the gas-phase precursor may flow is provided in the precursor supplier S. The precursor injected through the first supplier  620  may be injected into and vaporized in the precursor supplier S to obtain the gas-phase precursor. As another example, a separate precursor vaporizer may be provided in the precursor supplier S and, in this case, the carrier gas injected through the first supplier  620  is mixed with the precursor vaporized from the precursor vaporizer and the mixed gas is discharged from the precursor supplier S and is injected into the reaction part R. 
     Various types of precursor suppliers according to embodiments of the present disclosure will now be described. 
     A precursor supplier according to an embodiment of the present disclosure includes a vaporization part where a condensed-phase precursor is vaporized to obtain a gas-phase precursor, and a partial precipitation part where the gas-phase precursor obtained in the vaporization part is partially precipitated to a condensed phase. In this case, a channel of the precursor supplier is configured in such a manner that a fluid passes sequentially through the vaporization part and the partial precipitation part and then is discharged to a reaction part. An equilibrium vapor pressure of the precursor in the partial precipitation part is lower than a vapor pressure of the gas-phase precursor obtained in the vaporization part, and an equilibrium vapor pressure of the precursor in the reaction part is equal to or higher than a vapor pressure of the gas-phase precursor partially precipitated to a condensed phase in the partial precipitation part. 
       FIGS.  7 A and  7 B  show embodiments of a top-down precursor supplier  700  of the present disclosure. 
     Referring to  FIG.  7 A , a channel of the precursor supplier  700  is configured to include at least one downward channel (e.g., downward channels  710  and  730 ) through which a fluid flows downward, and at least one upward channel (e.g., an upward channel  720 ) through which the fluid flows upward. The downward channels  710  and  730  and the upward channel  720  are provided adjacent to each other in parallel. 
     Specifically, the downward channel  710 , the upward channel  720 , and the downward channel  730  are sequentially provided adjacent to each other in a direction from both sides to a central axis of the precursor supplier  700 . The downward channel  710  and the upward channel  720  are symmetric with respect to the central axis, and the downward channel  730  is provided at the center of the precursor supplier  700  and extends along the central axis. 
     The channel in the precursor supplier  700  is configured in such a manner that the fluid passes sequentially through the vaporization part E and the partial precipitation part C and then is discharged to the reaction part R. The flow of the fluid is indicated by arrows in  FIG.  7 A . 
     The vaporization part E provides a region where a condensed-phase precursor injected into the downward channel  710  is vaporized, and includes the downward channel  710  heated by a heat source. The partial precipitation part C is provided between the upward channel  720  extending from the downward channel  710  including the vaporization part E, and the downward channel  730  extending to the reaction part R. A temperature of the partial precipitation part C is maintained lower than the temperature of the vaporization part E. As described above, such temperature control may be implemented by controlling a temperature of the heater  640  provided on an outer circumferential surface of the reaction chamber  610  in which the precursor supplier  700  is provided. 
     The vaporization part E is maintained at a temperature equal to or higher than a vaporization temperature of the precursor. When injected into the vaporization part E, a condensed-phase precursor SC carried by a carrier gas, e.g., precursor powder, is vaporized into a gas-phase precursor. In this case, the condensed-phase precursor SC needs to be injected at a sufficient amount in such a manner that a vapor pressure of the vaporized precursor is higher than a saturated vapor pressure in the partial precipitation part C. This is a process condition for satisfying Condition 1 described above. 
     The gas-phase precursor flows upward along the upward channel  720  at the sides and reaches the partial precipitation part C maintained at a temperature lower than that of the vaporization part E. In this case, the gas-phase precursor having reached the partial precipitation part C is partially precipitated to a condensed phase. The precipitated condensed-phase precursor falls along the upward channel  720  due to a self-weight. For example, when the condensed phase is a solid phase, the precipitated solid-phase precursor may fall downward along the upward channel  720  in the form of particles due to the self-weight and be accumulated on the bottom. The accumulated particles may be removed by a user after the process is completed. 
     The gas-phase precursor having passed through the partial precipitation part C is discharged along the downward channel  730  to the reaction part R and reacts with a reaction gas to obtain inorganic powder. Because the gas-phase precursor partially precipitated through the partial precipitation part C is injected into the reaction part R, the gas-phase precursor may always be constantly supplied. 
     The operational principle of  FIG.  7 B  is the same as that of  FIG.  7 A  except that the downward channel  710  including the vaporization part E is positioned at the center of the precursor supplier  700  and that the downward channel  710 , the upward channel  720 , and the downward channel  730  are sequentially provided adjacent to each other in a direction from the center to both sides of the precursor supplier  700 , and thus a repeated description therebetween is not provided herein. 
       FIGS.  8 A and  8 B  show other embodiments of a top-down precursor supplier  800  of the present disclosure. 
     Referring to  FIG.  8 A , the vaporization part E includes the precursor vaporizer M provided in a region through which a fluid moving downward along the downward channel  710  heated by a heat source passes. The carrier gas CG is injected into the downward channel  710 , and a gas-phase precursor vaporized from the precursor vaporizer M is mixed with the carrier gas CG and reaches the partial precipitation part C through the upward channel  720 . A description of a subsequent process has been already provided in relation to the previous embodiment, and thus is not provided herein. 
     The precursor vaporizer M may have a form of a furnace loaded with a powder- or pellet-type precursor or a liquid-phase precursor. The precursor vaporizer M may be refilled in real time by using a separate device. Alternatively, when a preset amount of the precursor is consumed after a certain time, the precursor vaporizer M may be replaced or be re-used by refilling the precursor. 
     According to an embodiment of the present disclosure, the gas-phase precursor participating in reaction may be maintained at a constant vapor pressure through the partial precipitation part C and thus, even when a solid-phase precursor loaded in the precursor vaporizer M exhibits a difference in particle shape or size, an irregular change in amount of the gas-phase precursor supplied to the reaction part R due to the difference may be suppressed as much as possible. 
     The operational principle of the precursor supplier  800  of  FIG.  8 B  is the same as that of  FIG.  8 A  except that the precursor vaporizer M is included in the downward channel  710  provided at the center, and thus a repeated description therebetween is not provided herein. 
       FIGS.  9 A to  9 C  show other embodiments of a top-down precursor supplier  900  of the present disclosure. The precursor supplier  900  according to the current embodiments includes a quenching gas inlet  910  for injecting a quenching gas QG into the partial precipitation part C. The quenching gas QG cools the partial precipitation part C to reduce a temperature of the partial precipitation part C and an equilibrium vapor pressure of a precursor in the partial precipitation part C, thereby facilitating partial precipitation. The quenching gas QG may use an inert gas, a nitrogen gas, or the like. 
     Referring to  FIGS.  9 A and  9 B , the quenching gas QG is provided to the partial precipitation part C through the quenching gas inlet  910  positioned at the top of the partial precipitation part C. Referring to  FIG.  9 C , the quenching gas QG is provided to the partial precipitation part C through the quenching gas inlet  910  positioned at sides of the partial precipitation part C. The injected quenching gas QG moves to the reaction part R together with other gases. 
       FIGS.  10 A and  10 B  show embodiments of a bottom-up precursor supplier  1000  of the present disclosure. 
     Referring to  FIG.  10 A , a channel of the bottom-up precursor supplier  1000  is configured to include at least one upward channel (e.g., upward channels  1010  and  1030 ) through which a fluid flows upward, and at least one downward channel (e.g., a downward channel  1020 ) through which the fluid flows downward. The upward channels  1010  and  1030  and the downward channel  1020  are provided adjacent to each other in parallel. 
     Specifically, the upward channel  1010 , the downward channel  1020 , and the upward channel  1030  are sequentially provided adjacent to each other in a direction from both sides to a central axis of the precursor supplier  1000 . The upward channel  1010  and the downward channel  1020  are symmetric with respect to the central axis, and the upward channel  1030  is provided at the center of the precursor supplier  1000  and extends along the central axis. 
     The channel in the precursor supplier  1000  is configured in such a manner that the fluid passes sequentially through the vaporization part E and the partial precipitation part C and then is discharged to the reaction part R. The flow of the fluid is indicated by arrows in  FIG.  10 A . 
     The vaporization part E includes the precursor vaporizer M provided in a region through which a fluid moving upward along the upward channel  1010  heated by a heat source passes. The partial precipitation part C is provided between the downward channel  1020  extending from the upward channel  1010  including the vaporization part E, and the upward channel  1030  extending to the reaction part R. A temperature of the partial precipitation part C is maintained lower than the temperature of the vaporization part E. The carrier gas CG is injected into the upward channel  1010 , and a gas-phase precursor vaporized from the precursor vaporizer M is mixed with the carrier gas CG, rises along the upward channel  1010 , and then falls through the downward channel  1020  to reach the partial precipitation part C. The gas-phase precursor partially precipitated in the partial precipitation part C flows upward along the upward channel  1030  and is discharged to the reaction part R. The condensed-phase precursor precipitated in the partial precipitation part C falls due to a self-weight and is accumulated on the bottom of the partial precipitation part C. The accumulated condensed-phase precursor may be removed later by a user after the process is completed. 
     The operational principle of  FIG.  10 B  is the same as that of  FIG.  10 A  except that the upward channel  1010  including the vaporization part E is positioned at the center of the precursor supplier  1000  and that the upward channel  1010 , the downward channel  1020 , and the upward channel  1030  are sequentially provided adjacent to each other in a direction from the center to both sides of the precursor supplier  1000 , and thus a repeated description therebetween is not provided herein. 
       FIGS.  11 A to  11 C  show other embodiments of a bottom-up precursor supplier  1100  of the present disclosure. The precursor supplier  1100  according to the current embodiments includes a quenching gas inlet  1110  for injecting a quenching gas QG into the partial precipitation part C. 
     Referring to  FIGS.  11 A and  11 B , the quenching gas QG is provided to the partial precipitation part C through the quenching gas inlet  1110  positioned at the bottom of the partial precipitation part C. Referring to  FIG.  11 C , the quenching gas QG is provided to the partial precipitation part C through the quenching gas inlet  1110  positioned at sides of the partial precipitation part C. 
       FIGS.  12 A to  12 C  show embodiments of a horizontal precursor supplier  1200  of the present disclosure. Referring to  FIG.  12 A , the precursor supplier  1200  may include a fluid rise induction member  1210  for inducing a gas-phase precursor to move upward when the gas-phase precursor is discharged from the partial precipitation part C to the reaction part R. A condensed-phase precursor, e.g., a powder- or droplet-type precursor, which is partially precipitated when the gas-phase precursor rises from the partial precipitation part C due to the fluid rise induction member  1210  and is discharged to the reaction part R, falls downward due to a self-weight and is accumulated on the bottom of the partial precipitation part C. Therefore, injection of the condensed-phase precursor into the reaction part R may be prevented as much as possible. 
     In the embodiment illustrated in  FIG.  12 A , the fluid rise induction member  1210  having a form of a barrier with a top opening is provided between the partial precipitation part C and the reaction part R. In the embodiment illustrated in  FIG.  12 B , a barrier with a bottom opening is further provided between the vaporization part E and the partial precipitation part C to serve as a fluid fall induction member  1220  for inducing the gas-phase precursor to be provided to the partial precipitation part C from below.  FIG.  12 C  shows a modified embodiment of the horizontal precursor supplier  1200  and, in the current embodiment, the partial precipitation part C is provided directly above the vaporization part E, and the gas-phase precursor rising from the vaporization part E and passing through the partial precipitation part C is injected into the reaction part R through the top opening of the fluid rise induction member  1210 . 
     TEST EXAMPLES 
     Test examples of the present disclosure will now be described. However, the following test examples are merely for better understanding of embodiments of the present disclosure, and embodiments of the present disclosure are not limited thereto. 
     Properties of inorganic powder depending on presence of a partial precipitation part were observed. To this end, a vertical top-down chemical vapor synthesis apparatus as shown in  FIG.  6    was used. Inventive Example 1 used a planar precursor supplier as shown in  FIG.  9 B . Comparative Examples 1 and 2 used the same apparatus as Inventive Example 1 except that a precursor was directly supplied into a reaction part instead of using the precursor supplier of the apparatus of  FIG.  6   . Temperatures of heaters  1  to  3  included in the heater  640  are shown in Table 2. In this test, Ni powder was produced and NiCl 2  was used as the precursor. A nitrogen gas (N 2 ) and a hydrogen gas (H 2 ) were used as a carrier gas and a reaction gas, respectively. Table 2 shows Ni powder synthesis conditions according to the inventive example and the comparative examples. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Precursor 
                 N 2   
                 H 2   
                   
                   
                   
                   
               
               
                   
                 Injection 
                 Flow 
                 Flow 
                 Precursor 
                 Heater 1 
                 Heater 2 
                 Heater 3 
               
               
                 Sample 
                 Rate 
                 Rate 
                 Rate 
                 Supplier 
                 Temp. 
                 Temp. 
                 Temp. 
               
               
                   
               
             
            
               
                 Inventive 
                 250 g/hr 
                 12 LPM 
                 4 LPM 
                 ◯ 
                 1050° C. 
                 1025° C. 
                 1000° C. 
               
               
                 Example 1 
               
               
                 Comparative 
                  15 g/hr 
                 12 LPM 
                 4 LPM 
                 X 
                 1050° C. 
                 1025° C. 
                 1000° C. 
               
               
                 Example 1 
               
               
                 Comparative 
                 250 g/hr 
                 12 LPM 
                 4 LPM 
                 X 
                 1050° C. 
                 1025° C. 
                 1000° C. 
               
               
                 Example 2 
               
               
                   
               
            
           
         
       
     
     Table 3 shows particle size distributions and average particle sizes of Ni powder according to the inventive example and the comparative examples. The particle size distributions and the average particle sizes were calculated using geometric standard deviation (GSD) and count median diameter (CMD) values, respectively. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Sample 
                 GSD 
                 CMD 
               
               
                   
                   
               
             
            
               
                   
                 Inventive Example 1 
                 1.19 
                 112.99 nm 
               
               
                   
                 Comparative Example 1 
                 1.34 
                 101.51 nm 
               
               
                   
                 Comparative Example 2 
                 N/A 
                 N/A 
               
               
                   
                   
               
            
           
         
       
     
       FIG.  13    is a scanning electron microscope (SEM) image of Ni powder according to Inventive Example 1.  FIGS.  14  and  15    are SEM images of Ni powder according to Comparative Examples 1 and 2, respectively. 
     Referring to  FIG.  13   , the Ni powder according to Inventive Example 1 has a GSD of 1.19 and a CMD of 112.99 nm and exhibits a narrow particle size distribution and very uniform-sized spherical particles. 
     On the other hand, referring to  FIG.  14   , the Ni powder according to Comparative Example 1 has a GSD of 1.34 and a CMD of 101.51 nm and exhibits a wide particle size distribution and a mixture of large-sized particles and small-sized particles. It is understood that this result is because the precursor was not constantly supplied to the reaction part. 
     Meanwhile, referring to  FIG.  15   , the Ni powder according to Comparative Example 2 exhibits a shape inappropriate for measuring the GSD and CMD values. NiCl 2  serving as the precursor was not completely volatilized and thus Ni powder reduced by H 2  from solid-phase NiCl 2  was observed. Compared to Inventive Example 1, it is understood that the result of Comparative Example 2 is because a time sufficient to completely vaporize the solid-phase precursor was not ensured due to absence of the precursor supplier. 
     In an embodiment, a method for producing inorganic powder includes: forming a gas-phase precursor, by vaporizing a condensed-phase precursor in a vaporization part, partially precipitating the gas-phase precursor to a condensed phase in a partial precipitation part, and forming the inorganic powder, by having the gas-phase precursor remaining after being partially precipitated to the condensed phase react with a reaction gas in a reaction part. A vapor pressure of the gas-phase precursor formed in the vaporization unit is higher than an equilibrium vapor pressure of the precursor in the partial precipitation part, such that the gas-phase precursor is partially precipitated in the partial precipitation part. After the gas-phase precursor is partially precipitated in the partial precipitation part, a vapor pressure of the remaining gas-phase precursor is equal to or less than the equilibrium vapor pressure of the precursor in the reaction part. 
     According to an embodiment of the present disclosure, inorganic powder having a uniform particle shape and a narrow particle size distribution may be produced by quantitatively supplying a gas-phase precursor to a reaction part at a substantially constant amount. The above-described effect is merely an example, and the scope of embodiments of the present disclosure is not limited thereto. 
     While some embodiments of the present disclosure have been particularly shown and described above, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention as defined by the following claims.