KR101335865B1 - Catalyst support for spececraft thruster and method for fabricating the same - Google Patents

Abstract

A catalyst carrier for a space vehicle thruster and a method of manufacturing the same are disclosed. The catalyst carrier for the spacecraft thruster according to the present invention contains 75 to 95% by weight of aluminum and 5 to 25% by weight of Group 2 or Lanthanon elements to maintain porosity and high strength and thermal stability at high temperatures of about 1473K to 1673K. It has a large specific surface area and can maintain the activity of the catalyst even when using an environmentally friendly propellant. In addition, the method of manufacturing a catalyst carrier for a space vehicle thruster according to the present invention comprises the steps of molding the alumina particles, the hexaaluminate particles containing the element by impregnating the alumina particles in a solution containing a Group 2 element or a lanthanide element It is possible to control the form and porosity of the particles to be produced simply and easily by including the step of preparing.

Description

Catalyst support for spacecraft thruster and method for preparing the same {Catalyst support for spececraft thruster and method for fabricating the same}

The present invention relates to a catalyst carrier for a space vehicle thruster and a method for manufacturing the same, and more particularly, to a hexaaluminate space vehicle capable of maintaining thermal stability at high temperature by adding a Group 2 element or a lanthanide element to the molded alumina particles. It relates to a catalyst carrier for the thruster and a method for producing the same.

A single propellant thruster using hydrazine as a fuel is a representative thrust system for attitude control of spacecraft such as satellites. It uses iridium catalyst as a catalyst for thrusters embedded in the engine and hydrazine as a liquid propellant to generate thrust due to the expansion of the gas generated through pyrolysis by the reaction of the catalyst with the propellant.

On the other hand, hydrazine single propellant thruster is the most widely used today because of its reliability and convenience, hydrazine is toxic and difficult to handle, it is necessary to develop an eco-friendly thrust system to replace it.

Hydroxylammonium nitrate (HAN), Hydrazinium nitroformate (HNF), ammonium dinitramide (ADM), and ammonium nitrate (AN) are being developed as alternatives to hydrazine. However, the heat of combustion upon decomposition of hydrazine is about 1273K, whereas the heat of combustion of HAN, HNF, ADM and AN is about 1473K to 1673K, which is higher than 200K. Therefore, it is necessary to develop a catalyst carrier having thermal stability so that the catalyst activity can be maintained even at a higher temperature.

The carrier uses a porous material having a large specific surface area to be highly dispersed and supported to increase the exposed surface area of the catalyst. In addition, since the carrier must be mechanically, thermally, and chemically stable, alumina is generally used as a carrier that satisfies these conditions. However, as the alumina increases in temperature to 1123K, 1327K, and 1473K, as the phase transition occurs from γ to δ, θ, and α types, the specific surface area decreases rapidly, resulting in a loss of function as a catalyst carrier.

In order to suppress the reduction of the specific surface area due to the phase transition, U.S. Patent Nos. 7,137 and 244 are added rare earth metals or transition metals such as lanthanum (La), barium (Ba), and the like, and a micro emulsion or A method for producing an alumina powder having a hexaaluminate phase using an alkoxide method is disclosed. In order to use the alumina powder on the hexaaluminate prepared by the above method as a catalyst carrier for a space vehicle thruster, a molding process in the form of particles is essential.

However, in order to form the alumina powder on the hexaaluminate prepared by the above method in the form of particles, use of an organic or inorganic binder is required, which leads to process inefficiencies such as complexity of manufacturing process and increase of manufacturing cost. . In addition, it was difficult to control the shape and porosity of the particles in the molding process. Therefore, in addition to the development of environmentally friendly propellants, there is a need for development of a catalyst carrier having mechanical, thermal and chemical stability even at high temperatures, and a manufacturing method that can more easily and easily control the form and porosity of the particles.

Accordingly, the first object of the present invention is to form alumina particles using self-adhesive alumina, and to add a Group 2 element or a lanthanide element to provide thermal stability and a constant specific surface area even at a high temperature of about 1473K to 1673K. Eggplant is to provide a catalyst carrier for the space vehicle thruster.

In addition, the second object of the present invention, by adding the Group 2 or lanthanide element to the alumina particles by using the impregnation method, it is possible to form directly into the particle form without going through the powder form, simply and easily form and It is to provide a method for producing a catalyst carrier for space vehicle thruster capable of controlling porosity.

The present invention for achieving the above first object is characterized by containing 75 to 95% by weight of aluminum, 5 to 25% by weight of a group 2 element or a lanthanide element.

In addition, the present invention for achieving the second object, the step of forming the alumina particles and impregnated with the alumina particles in a solution containing a Group 2 element or a lanthanide element to form the hexaaluminate particles containing the element Characterized in that it comprises the step of manufacturing.

The catalyst carrier for the space vehicle thruster according to the present invention has a large specific surface area even at high temperatures of 1473K to 1673K while maintaining the porosity and high strength characteristics, thereby maintaining the activity of the catalyst even when an environmentally friendly propellant is used.

In addition, the method for preparing a catalyst carrier for a space vehicle thruster according to the present invention has the effect of simplifying the manufacturing process and reducing the manufacturing cost by preparing a hexaaluminate catalyst carrier in the form of particles through a simple and easy method.

1 is an SEM image of alumina particles formed through an embodiment of the present invention.
2a and 2b is a view showing the pore volume and pore distribution of the alumina particles molded through an embodiment of the present invention.
Figure 3a is an X-ray diffraction graph measured after firing the alumina particles formed by the embodiment of the present invention at different temperatures.
3B to 3D are X-ray diffraction graphs measured after firing hexaaluminate particles in which lanthanum (La) is added at a predetermined ratio to alumina particles formed through one embodiment of the present invention at different temperatures.
4 is a graph showing specific surface areas measured after calcining alumina particles and hexaaluminate particles containing lanthanum (La) at a predetermined ratio at different temperatures.
FIG. 5 is an SEM image of lanthanum hexaaluminate particles prepared through one embodiment of the present invention. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments disclosed herein are provided so that the disclosure can be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. In describing the drawings, like reference numerals refer to like elements.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The method for preparing a catalyst carrier for a space vehicle thruster according to the present invention includes forming alumina particles, and impregnating the alumina particles in a solution containing a Group 2 element or a lanthanide element to prepare hexaaluminate particles. .

The alumina particles are calcined from the starting material to produce ρ-alumina having self-adhesion, adding and mixing the pore control material and distilled water to the ρ-alumina, injecting the mixture, alkali the injection molding Impregnating and heat-treating the solution, firing the heat-treated injection molding to remove the pore control material, and the fired injection molding is pulverized, separated and then surface treatment.

The starting material can be, for example, gibbsite. Gibbsite is well known as aluminum trihydroxide, and when it is pyrolyzed, phase transition occurs depending on the firing conditions. When the gibbsite is calcined within a temperature range of 500 to 600 ° C. within 5 seconds, phase transition occurs to produce amorphous alumina, which is ρ-alumina. The ρ-alumina has a property of containing about 4-6% water. Since ρ-alumina, which is a hydrated alumina, can be injection molded without an organic or inorganic binder because of its adhesiveness, ρ-alumina has various advantages in the field of catalysts and catalyst carriers.

Thereafter, a pore controlling material is added to the prepared p-alumina and mixed. The pore control material is added to control the pore size and pore distribution of the catalyst carrier, and the pore properties of the catalyst carrier are determined according to the size and content of the pore control material. For example, the pore control material may include micro-sized wood flour or organic matter, and is preferably added in the range of 1 to 5% by weight. At this time, distilled water may be further added and mixed. The distilled water serves to adjust the viscosity of the mixture of p-alumina and the pore control material, it is preferably added in the range of 60 to 70% by weight.

Thereafter, the mixture is injected. The injection is 120kg / cm ² By applying the above pressure can be made through the injection machine. The mixture may be injected into a rod shape, and the injected alumina is dried at 298 to 423 K for at least 24 hours.

Thereafter, the extrudate is impregnated with an alkaline solution and heat treated. The alkaline solution may be 1 to 10% by weight sodium hydroxide solution. It is preferable to immerse an injection product in the said sodium hydroxide solution, and to heat-process at 400-500K for 12 to 24 hours or more. This imparts adhesion, so that the starting material and the pore control material are fixed without flowing.

Thereafter, the injection molding is fired to remove the pore control material. At this time, after separating the injection-molded product from the alkaline solution, it may further comprise a step of washing in distilled water. The firing may be carried out at 700 to 800 K for 2 to 6 hours, through which the pore control material is removed and pores are formed in place to determine pore properties.

Thereafter, the calcined injection may be pulverized, separated, and then surface treated to adjust the shape and / or size of the alumina particles. For example, after pulverization through a pulverizer, the standard body (14-30 mesh (ASTM)) can be separated and separated using a high-speed abrasion for 12 to 24 hours or more to smooth the surface. By removing the surface roughness through the high-speed wear treatment to prevent the alumina particles from being continuously lost by the collision during the pyrolysis reaction for thrust generation. Through this, alumina is formed into granule-shaped granules having a predetermined size.

Thereafter, the alumina particles are impregnated into a solution containing a group 2 element or a lanthanide element. The Group 2 element may be at least one selected from barium (Ba), calcium (Ca), magnesium (Mg), and strontium (Sr), and the lanthanide element may be lanthanum (La) or cerium (Ce). The added element serves to maintain the activity of the catalyst by suppressing a decrease in the specific surface area that increases rapidly with increasing temperature.

The group 2 element or lanthanide element may be added to the alumina particles formed using the impregnation method. That is, a hydrate containing a Group 2 element or a lanthanide element may be dissolved in distilled water to prepare an aqueous solution, and the molded alumina particles may be impregnated therein. At this time, the Group 2 element or lanthanum element may be added in 5 to 25% by weight. Thereafter, the alumina particles taken out from the aqueous solution are dried, and then fired in two steps through the first and second firings. The drying process may be performed for 12 hours or more at 600K to 900K. The first firing is performed to remove organic matters in the particles, and may be performed at a temperature of 700K to 900K for 2 to 12 hours. In addition, the subsequent secondary firing converts the alumina particles into hexaaluminate particles containing a Group 2 element or a lanthanide element. At this time, the firing temperature is preferably 1200K ~ 1700K, it can be carried out for 6 hours to 12 hours.

Therefore, there is an advantage in that the hexaaluminate particles containing a Group 2 element or a lanthanide element can be produced simply and easily through the above process.

On the other hand, the catalyst carrier for the space vehicle thruster according to the present invention comprises 75 to 95% by weight of aluminum, 5 to 25% by weight of Group 2 elements or lanthanide elements. The Group 2 element may be at least one selected from barium (Ba), calcium (Ca), magnesium (Mg), and strontium (Sr), and the lanthanide element may be lanthanum (La) or cerium (Ce). The added element serves to maintain the activity of the catalyst by suppressing a decrease in the specific surface area that increases rapidly with increasing temperature.

For example, lanthanum hexaaluminate particles may be prepared by adding lanthanum, which is one of the lanthanide elements, to alumina particles in a predetermined ratio, and the lanthanum hexaaluminate particles may be represented by La _x (Al ₂ O ₃ ) _6-x . have. At this time, the range of x may be 0.1 to 3.0.

Hexahydro aluminosilicate containing a Group 2 element or a lanthanide element, such as the carbonate particles have a thermal stability at a high temperature of 1473K ~ 1673K, 10 ~ 15 kg · m · s - 2 of crush strength and, 10 ~ 30 m ² / has a specific surface area of g.

Therefore, when the hexaaluminate particles containing the Group 2 element or the lanthanide element are used as a catalyst carrier for the spacecraft thruster, thermal stability at the high temperatures is maintained even when an environmentally friendly propellant having a high temperature combustion heat of 1473K to 1673K is used. There is an advantage that can maintain the catalytic activity.

Hereinafter, preferred examples will be given to facilitate understanding of the present invention. It should be understood, however, that the following examples are intended to aid in the understanding of the present invention and are not intended to limit the scope of the present invention.

Alumina Particle Forming

Al (OH) ₃ is calcined in 773 K to 873 K within 5 seconds to prepare p-alumina. 1 to 5% by weight of micro-sized wood powder or organic matter is added to the prepared p-alumina and mixed, and then 60 to 70% by weight of distilled water is added thereto and mixed. The mixture is injected at a pressure of 120 kg / cm ₂ or more, and then dried at 298 to 423 K for at least 24 hours. The dried injection molded product is added to a 1-10% sodium hydroxide solution and heat-treated at 423K for 12 to 24 hours. The heat treated injection molded product is washed with distilled water 5 to 10 times and then calcined at 773 K for 2 hours. The fired extrudate is pulverized using a grinder and then separated using a standard body. The separated particles are surface treated through high-speed at least 12 to 24 hours to form? -Alumina particles having a macro-meso pore structure. The γ-alumina particles have a specific surface area of 180 to 250 m ² / g and have macro-mesoporous properties.

Lanthanum Hexaaluminate  Particle manufacturing

0.849 g (La / Al = 1/24), 1.698 g (La / Al = 2/24), 3.396 g (La / Al = 4/24) of La (NO ₃ ) ₃ · 6H ₂ O dissolved in distilled water Then, it is added to the alumina particles using the impregnation method. Thereafter, it is dried at 333 K for at least 12 hours and calcined at 823 K for 2 hours. The calcined alumina particles are calcined again at 1473K for 2 hours.

1 is an SEM image of alumina particles formed through an embodiment of the present invention.

Referring to FIG. 1, the γ-alumina particles formed through one embodiment of the present invention have a granule form, and it can be seen that many large and small pores exist. The plurality of pores facilitate material and heat transfer to favor the diffusion of gas, and has high thermal stability even in high temperature environments.

2a and 2b is a view showing the pore volume and pore distribution of the alumina particles molded through an embodiment of the present invention. In order to confirm the macro-meso pore characteristics of the molded alumina particles, the mercury penetration method using the mercury infiltration and removal was analyzed.

Referring to FIGS. 2A and 2B, peaks of mesopores at about 3 nm to 6 nm and macropore peaks at about 2 μm to 20 μm can be confirmed, and mesopores in a range of 2 nm to 50 nm and macropores at least 50 nm are present. You can check it. Therefore, it can be seen that the molded alumina particles through the embodiment of the present invention have a macro-meso pore structure in which a plurality of macropores and micropores exist. As described above, the continuous distribution of the macro-meso two different pore sizes facilitates the diffusion and adsorption of the reactants and the product, and has the advantage of widely dispersing the metal particles.

Figure 3a is an X-ray diffraction graph measured after firing the alumina particles formed by the embodiment of the present invention at different temperatures. (a) 773K, (b) 1173K, (c) 1373K, (d) 1473K, (e) 1573K, (f) 1673K, and as a reference material, (●) corundum, α- Alumina) (PDF # 10-0173) and (○) aluminum oxide (PDF # 04-0880) were used.

Referring to FIG. 3A, it is possible to observe a process of changing alumina through phase peaks indicated by X-ray diffraction analysis. It can be seen that the molded alumina particles through one embodiment of the present invention are changed to α phase at a temperature ((d), (e), (f)) of 1473 K or more. This results in the rapid calcination of the crystalline gibbsite and the phase transition to amorphous ρ-alumina. .

3B to 3D are X-ray diffraction graphs measured after firing hexaaluminate particles in which lanthanum (La) is added at a predetermined ratio to alumina particles formed through one embodiment of the present invention at different temperatures. 3B, 3C, and 3D show the case of (a) 773K, (b) 1173K, (c) 1373K, (d) 1473K, (e) 1573K, and (f) 1673K. 3B shows La / Al ratio of La / Al ₂ O ₃ , La / Al = 1/24, FIG. 3C shows La / Al = 2/24, and FIG. 3D shows La / Al = 4/24. As reference material, (●) corundum (α-alumina) (PDF # 10-0173), (○) aluminum oxide (PDF # 04-0880), (▼) lanthanum hexaalumina Nate (PDF # 34-0467) was used.

3b to 3d, the hexaaluminate particles to which a certain ratio of lanthanum is added are slightly different, but do not change to a pure α phase at temperatures of 1473 K or more ((d), (e), (f)), It can be confirmed that it has a lanthanum hexaaluminate phase.

4 is a graph showing specific surface areas measured after calcining alumina particles and hexaaluminate particles containing lanthanum (La) at a predetermined ratio at different temperatures. Each temperature is 773K, 1173K, 1373K, 1473K, 1573K, 1673K, and measured at 77K using hydrogen adsorption-desorption method.

Referring to FIG. 4, it can be seen that the specific surface area of the alumina particles and the hexaaluminate particles to which lanthanum is added at a predetermined ratio decreases with increasing temperature. Alumina particles without added lanthanum have a very rapid reduction in specific surface area at temperatures above 1473 K, compared to hexaaluminate particles with lanthanum added. Therefore, at a temperature of 773 K, pure alumina particles and hexaaluminate particles to which lanthanum is added in a predetermined ratio each have a nearly similar specific surface area of 180 to 250 m ² / g, while at a high temperature of 1473 K and above, lanthanum is respectively in a constant ratio. It can be seen that the added hexaaluminate particles have a specific surface area of 2 to 4 times larger at 10 to 30 m ² / g.

As a result, the phase transition occurs from γ-type to δ, θ, and α-type as the temperature increases to 1123K, 1327K, and 1473K of the conventional pure alumina particles. There is an advantage that can be solved to maintain the activity of the catalyst.

Table 1 shows the measured values of the fracture strength of the alumina particles molded through an embodiment of the present invention, and the hexaaluminate particles to which lanthanum is added in a predetermined ratio.

carrier
Crushing Strength (kgm · s ² ) 823K 1173K 1373K 1473K 1573K 1673K Al ₂ O ₃ 8 12 14 14 14 14 La / Al ₂ O ₃ 13 11 12 14 16 17 La / Al ₂ O ₃ 10 7 11 10 12 11

Each particle was measured 15 times using a tensile strength meter of 14 ~ 18 mesh (ASTM) size particles, and then the average value was calculated. Standard deviation for the intensity of ± 4 kg · m · s ^- in ^2. Referring to Table 1, the crush strength is on average 10 ~ 15 kg · m · s - can confirm the bars represent the high-strength properties having a value of ^2.

FIG. 5 is an SEM image of lanthanum hexaaluminate particles prepared through one embodiment of the present invention. FIG.

Referring to FIG. 5, the lanthanum hexaaluminate particles prepared according to an embodiment of the present invention may have a granule form and have large and small pores. The plurality of pores facilitate the material and heat transfer to favor the diffusion of the gas, there is an advantage to have a high thermal stability even in a high temperature environment. Therefore, the lanthanum hexaaluminate particles prepared according to one embodiment of the present invention have the advantage of pure γ-alumina particles, and the addition of 8% by weight of lanthanum has a specific surface area of 10 to 30 m ² / g, and fracture strength. 10 ~ 15 kg · m · s - 2 a shows the thermal stability and high strength characteristics.

Therefore, the catalyst carrier for the space vehicle thruster according to the present invention has a large specific surface area even at high temperatures of 1473K to 1673K while maintaining the porosity and high strength characteristics, thereby maintaining the activity of the catalyst even when using an environmentally friendly propellant.

Claims (12)

Shaping the alumina particles; And
Impregnating the alumina particles into a solution containing a group 2 element or a lanthanide element to produce hexaaluminate particles containing the element,
Forming the alumina particles,
Calcining the starting material to prepare p-alumina having self-adhesion;
Preparing a mixture by mixing the porosity controlling material and distilled water to the p-alumina;
Injecting the mixture to produce an injection product;
Impregnating the extrudate with an alkaline solution and heat treatment;
Firing the heat-treated injection molding to remove pore control material; And
The method of manufacturing a catalyst carrier for a space vehicle thruster, comprising the step of pulverizing the fired injection, separating and surface treatment. delete The method of claim 1,
Impregnating the alumina particles into a solution containing a Group 2 element or a lanthanide element to prepare hexaaluminate particles,
Preparing a hydrate containing a Group 2 element or a lanthanide element in the form of an aqueous solution;
Impregnating alumina particles into the aqueous solution;
Drying the alumina particles; And
And a second firing of the dried alumina particles after the first firing. The method of claim 3,
The primary firing temperature is a method for producing a catalyst carrier for a space vehicle thruster, characterized in that 600K ~ 900K. The method of claim 3,
The secondary firing temperature is a method for producing a catalyst carrier for a space vehicle thruster, characterized in that 1200K ~ 1700K. The method of claim 3,
The Group 2 element is a method for producing a catalyst carrier for a space vehicle thruster, characterized in that at least one selected from barium, calcium, magnesium and strontium. The method of claim 3,
The lanthanide element is a method for producing a catalyst carrier for a space vehicle thruster, characterized in that lanthanum or cerium. The method of claim 7, wherein
The ratio of the lanthanum and aluminum contained in the alumina particles is 1/24 to 4/24, characterized in that the method for producing a catalyst carrier for a space vehicle thruster. 75 to 95 weight percent aluminum; And
A catalyst carrier for a space vehicle thruster comprising 5 to 25% by weight of a group 2 element or a lanthanide element. 10. The method of claim 9,
The Group 2 element is a catalyst carrier for a space vehicle thruster, characterized in that at least any one selected from barium, calcium, magnesium and strontium. 10. The method of claim 9,
The lanthanide element is a catalyst carrier for a space vehicle thruster, characterized in that the lanthanum or cerium. 10. The method of claim 9,
The catalyst support is, 10 ~ 15 kg · m · s at a temperature of 1473K ~ 1673K ^- a crush strength of ^2, 10 ~ 30 m Spacecraft thruster catalyst carrier, characterized in that it has a specific surface area of ² / g.

Images