N-type Mg3 (Sb, Bi) 2 thermoelectric material with high thermal cycling stability and air stability and preparation method and application thereof

Abstract

The invention discloses an n-type Mg3 (Sb, Bi) 2 thermoelectric material with high thermal cycling stability and air stability and a preparation method and application thereof, and belongs to the technical field of thermoelectric material synthesizing.The Mg3 (Sb, Bi) 2-based thermoelectric material is prepared by adopting a mechanical alloying hot pressing sintering method, the material is good in crystallinity, compact in structure and high in repeatability, and the thermoelectric material can be applied to the field of thermoelectric materials. The chemical formula of the material is Mg < 3.4 > Bi < 1.3-x > Sb < 0.7 > Te < x > (0 < = x < = 0.03), by optimizing the sintering process and doping the element Te, the thermal cycling stability and the air stability of the Mg3 (Sb, Bi) 2-based thermoelectric material are remarkably improved, so that the temperature range and the service life of the material in practical application are widened.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoelectric material synthesis, and specifically relates to an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, a preparation method and an application thereof. Background Art

[0002] Thermoelectric conversion technology is an environmentally friendly energy conversion technology based on the Seebeck effect and the Peltier effect. It has the characteristics of small system size, noiseless operation, no emissions, high reliability, and long life. It has broad application prospects in technical fields such as multi-stage utilization of industrial waste heat, environmental energy recovery, special power supplies, and local refrigeration. The thermoelectric conversion efficiency of thermoelectric materials is determined by the thermoelectric properties of the materials, which is usually expressed by the dimensionless thermoelectric figure of merit ZT. However, the three parameters of the ZT value, namely, the electrical conductivity σ, the Seebeck coefficient S, and the thermal conductivity κ, are coupled with each other and are difficult to regulate individually, which brings challenges to the performance optimization of thermoelectric materials.

[0003] In recent years, Mg3(Sb / Bi)2-based thermoelectric materials have attracted extensive attention due to their excellent thermoelectric properties and good mechanical properties. The crystal structure of Mg3(Sb / Bi)2-based compounds is an inverse α-La2O3 type, with a space group of P-3m1, which is AB2X2 (where A is an alkaline earth or divalent rare earth element, and B is a d 0 , d 5 or 10 Mg3(Sb / Bi)2-based thermoelectric materials are a special case of Zintl phase compounds (transition metals, X is generally Sb or Bi). In Mg3(Sb / Bi)2-based compounds, Mg atoms occupy both A and B positions and exhibit two different properties: ionicity and covalency. Although Mg3(Sb / Bi)2-based thermoelectric materials have high thermoelectric properties and good mechanical properties, their thermal stability and oxidation resistance are poor, especially under high temperature and long-term service conditions. The high vapor pressure and high chemical activity of Mg element lead to serious deterioration of material performance or even failure, which limits its device application process.

[0004] In order to improve the thermal stability and antioxidant properties of Mg3(Sb / Bi)2-based thermoelectric materials, researchers have made various attempts. For example, Liang et al. obtained a more stable Mg-Mn bond by doping Mn at the Mg site, thereby enhancing the structural stability of the material, so that after testing at 673K ​​for 40h, the conductivity decreased by less than 5% (Acta Mater. 2023, 247, 118752.). Zhang et al. proposed a method of Mg vapor phase annealing at 873K to inhibit Mg loss and migration, which improved the thermal stability of the material compared to the conventional preparation method. However, after testing at high temperature for a long time, its conductivity decreased significantly, with a reduction of more than 50%. This method requires long-term annealing at a higher temperature, high energy consumption, and a long preparation cycle (ACS Appl. Mater. Interfaces. 2022, 14, 31024-31034.). The researchers also deposited a MgO protective layer on the surface of the material by magnetron sputtering to prevent the volatilization and oxidation of the Mg element, improving the stability of the material at high temperatures. The conductivity dropped by less than 5% under a 20-hour high-temperature test. Wu et al. obtained a stable Mg3(Sb,Bi)2 sample in the air by coating the Mg3(Sb,Bi)2 sample with polydimethylsiloxane to isolate H2O and O2 in the air. After being placed in the air for 7 days, the conductivity and Seebeck coefficient did not show a significant decrease, but the stability at high temperatures is unknown (ACS Appl. Mater. Interfaces. 2023, 15, 50216-50224.). Shang et al. prepared a BN coating on the surface of the Mg3(Sb,Bi)2-based material by chemical vapor deposition to improve the stability at high temperatures, but the BN coating is prone to cracking and falling off due to its small thermal expansion coefficient (Acta Materialsia 2020, 201, 572-579.). The above methods often have complex preparation processes and high costs, which seriously limits the further improvement of the practical application of Mg3(Sb,Bi)2 materials. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention aims to provide an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, a preparation method and an application thereof, wherein stable n-type conduction is achieved by doping with high-valence metals; a slow cooling strategy is adopted during the sintering process, which significantly improves the sintering quality and increases the thermal cycle stability and air stability of the material, thereby obtaining a Mg3(Sb / Bi)2 thermoelectric material with excellent thermal cycle stability and air stability, without the need for complex methods such as long-term annealing and complex processes for preparing coatings. The method has the advantages of being simple, rapid and low cost, and can simultaneously obtain excellent thermoelectric performance, with the room temperature ZT reaching 0.44, thereby meeting the preparation requirements of long-life semiconductor thermoelectric devices.

[0006] To achieve the above object, the present invention provides the following technical solution: an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, wherein the chemical formula of the thermoelectric material is Mg 3.4 Bi 1.3-x Sb 0.7 Te x , where x = 0.01~0.03.

[0007] Furthermore, the chemical formula of the n-type Mg3(Sb,Bi)2-based thermoelectric material is Mg 3.4 Bi 1.3-x Sb 0.7 Te x , where x=0.01.

[0008] Furthermore, the ZT value of the n-type Mg3(Sb,Bi)2-based thermoelectric material is 0.41-0.44 at 323K.

[0009] The present invention also provides a method for preparing the above-mentioned n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, comprising the following steps:

[0010] Under a protective atmosphere, metal Mg, metal Bi, metal Sb and metal Te with a purity greater than 99.9% are crushed to obtain a metal mixed powder with an average particle size less than 5 μm;

[0011] The metal mixed powder is hot pressed and sintered. After sintering, the temperature is cooled to 300°C at a cooling rate of 1°C / min to 3°C / min and then naturally cooled to obtain an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability.

[0012] Further, in a protective atmosphere, metal Mg, metal Bi, metal Sb, and metal Te with a purity greater than 99.9% are mixed and crushed to obtain a metal mixed powder with an average particle size of less than 5 μm:

[0013] Under the protection of high-purity argon, metal Mg, metal Bi, metal Sb, metal Te and grinding aids are mixed and high-energy ball milled. The rotation speed of the high-energy ball mill is 1200r / min~1400r / min, the ball milling time is 8h, and the ball-to-material ratio is 10:1 to obtain a metal mixed powder with an average particle size of less than 5μm.

[0014] Furthermore, during ball milling, metal Bi and metal Sb are pre-milled first, and then mixed with metal Mg and metal Te to continue ball milling.

[0015] Furthermore, the grinding aid is 1 wt% of stearic acid.

[0016] Further, in the step of hot pressing and sintering the metal mixed powder to obtain an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability:

[0017] The sintering temperature of hot pressing sintering is 800°C, the sintering heating rate is 10°C / min, the holding time is 2min, and the pressure is 60Mpa.

[0018] Furthermore, when the sintering temperature reaches 200°C, pressure is applied, and the pressure growth rate is 2 MPa / min. When the temperature reaches 500°C, the pressure reaches 60 MPa.

[0019] The present invention also provides a thermoelectric energy conversion device, which is prepared using the above-mentioned n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability.

[0020] The present invention also provides a temperature sensor, which is prepared by using the above-mentioned n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] The present invention discloses an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, which is composed of Mg 3.4 Bi 1.3-x Sb 0.7 Te x, where x=0-0.03, the carrier concentration and mobility of the material are increased by doping with high-valence Te, so that it can achieve stable n-type conduction; further, the present invention prepares Mg3(Sb,Bi)2 thermoelectric materials by a simple mechanical alloying: ball milling hot pressing sintering method. Compared with Mg3(Sb,Bi)2 thermoelectric materials prepared by other doping and preparation methods, the n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability prepared by the present invention significantly improves the sintering quality and increases the thermal cycle stability and air stability of the material by adjusting the sintering process and adopting a slow cooling strategy during the preparation process, and finally obtains n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability and high thermoelectric performance.

[0023] The results of the embodiments show that the n-type Mg3(Sb,Bi)2-based thermoelectric material provided by the present invention has excellent thermoelectric performance, with a room temperature ZT of 0.44 and a density of 91% to 95%. In 20 thermal cycle tests, the average conductivity of the cycle decreased by less than 5%, and the average Seebeck coefficient remained basically unchanged. In the air stability test, after the prepared Mg3(Sb,Bi)2-based thermoelectric material was exposed to air for 20 days, there was no obvious attenuation in the conductivity and Seebeck coefficient at room temperature and high temperature, which indicates that the material has excellent air stability.

[0024] The present invention also discloses the application of the above-mentioned Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability in the fields of thermoelectric energy conversion devices, temperature sensors, etc. When the Mg3(Sb,Bi)2 thermoelectric material prepared by the present invention is used in the above-mentioned fields, the high thermal cycle stability and air stability can further increase the service life, thereby reducing costs and improving the cost performance of thermoelectric devices, etc., and enhancing the application in the fields of thermoelectric energy conversion, temperature sensors, etc. The excellent thermoelectric performance and stability of the Mg3(Sb,Bi)2 thermoelectric material enable it to convert these large amounts of industrial waste heat into electrical energy, improve energy utilization efficiency, and thus reduce energy consumption and environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The n-type Mg obtained by mechanical alloying in Example 2 of the present invention 3.4 Bi 1.29 Sb 0.7 Te 0.01 Thermal cycling stability diagram of thermoelectric materials;

[0026] Figure 2 The n-type Mg obtained by mechanical alloying in Example 2 of the present invention 3.4 Bi 1.29 Sb 0.7 Te0.01 Air stability diagram of thermoelectric materials;

[0027] Figure 3 The n-type Mg obtained by mechanical alloying in Examples 1 to 4 of the present invention 3.4 Bi 1.3-x Sb 0.7 Te x , where x = 0 ~ 0.03 is the ZT diagram of thermoelectric materials. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0029] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0031] The present invention provides a method for preparing an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, comprising the following steps:

[0032] Step 1) According to the chemical formula, Mg 3.4 Bi 1.3-x Sb 0.7 Te x , wherein x=0-0.03, weigh 2g magnesium powder, 6.4226-6.5238g bismuth powder, 2.063g antimony powder, 0.0308-0.0926g tellurium powder and 0.1057-0.1061g stearic acid in an argon environment, put them into a ball mill, and mill them for 8h by high-energy ball milling at a speed of 1400rpm / min to obtain metal powder;

[0033] Preferably, the ball milling method is to rotate for 30 minutes, pause for 15 minutes, and repeat this process until the effective ball milling time is 8 hours.

[0034] Preferably, before ball milling, Sb powder and Bi powder are pre-milled for half an hour and then mixed and evenly ball-milled with Mg powder and Te powder to prevent side reactions and stably generate Mg3(Sb,Bi)2.

[0035] Step 2) The mixed metal powder obtained in step 1) is loaded into a hot-pressed graphite mold and sealed with carbon paper. The sintering temperature is 800°C, the sintering pressure is 60Mpa, the insulation time is 2min, and the cooling rate is 1-3°C / min to 300°C. After the pressure is removed, it is naturally cooled to finally obtain a bulk Mg3(Sb,Bi)2 thermoelectric material, which has excellent electrical conductivity and a density of 91% to 95%.

[0036] Preferably, the pressure is applied when the sintering temperature reaches 200°C, the pressure increase rate is 2Mpa / min, and when the temperature reaches 500°C, the pressure reaches 60Mpa.

[0037] The preparation process of the present invention is simple and low-cost, and effectively improves the thermal cycle stability and air stability of n-type Mg3(Sb,Bi)2 thermoelectric materials. Compared with other doping and preparation methods, the Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability prepared by this sintering process has an average conductivity drop of less than 5% in 20 thermal cycle tests, and the average Seebeck coefficient remains basically unchanged. In the air stability test, the conductivity and Seebeck coefficient of the prepared Mg3(Sb,Bi)2-based thermoelectric material at room temperature and high temperature have no obvious attenuation, which indicates that the material has excellent air stability.

[0038] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0039] Example 1

[0040] A method for preparing an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, wherein the chemical formula is Mg 3.4 Bi 1.3 Sb 0.7 , specifically including the following steps:

[0041] Step 1) Under an argon environment, 2 g of magnesium powder, 6.5711 g of bismuth powder, 2.063 g of antimony powder and 0.1074 g of stearic acid were weighed and put into a ball mill, and ball milled for 8 h using a high-energy ball mill at a speed of 1400 rpm / min to obtain a metal powder;

[0042] Step 2) The mixed metal powder obtained in step 1) is placed in a spark plasma sintering mold, the sintering temperature is 800°C, the sintering pressure is 60Mpa, the holding time is 2min, the cooling rate is 1°C / min to 300°C, and then naturally cooled to finally obtain a bulk Mg3(Sb,Bi)2 thermoelectric material.

[0043] like Figure 3 As shown, the Mg prepared in this embodiment 3.4 Bi 1.3 Sb 0.7 The ZT value of the thermoelectric material is 0.03 at 323K.

[0044] Example 2

[0045] A method for preparing an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, wherein the chemical formula is Mg 3.4 Bi 1.29 Sb 0.7 Te 0.01 , specifically including the following steps:

[0046] Step 1) Under an argon environment, 2 g of magnesium powder, 6.5238 g of bismuth powder, 2.063 g of antimony powder, 0.0308 g of tellurium powder and 0.1061 g of stearic acid were weighed and put into a ball mill, and ball milled for 8 h using a high-energy ball mill at a speed of 1400 rpm / min to obtain a metal powder;

[0047] Step 2) The mixed metal powder obtained in step 1) is placed in a spark plasma sintering mold, the sintering temperature is 800°C, the sintering pressure is 60Mpa, the holding time is 2min, the cooling rate is 1°C / min to 300°C, and then naturally cooled to finally obtain a bulk Mg3(Sb,Bi)2 thermoelectric material.

[0048] like Figure 3 As shown, the Te-doped Mg prepared in this embodiment 3.4 Bi 1.29 Sb0.7 Te 0.01 The ZT value of the thermoelectric material reached 0.43 at 323K.

[0049] Example 3

[0050] A method for preparing an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, wherein the chemical formula is Mg 3.4 Bi 1.28 Sb 0.7 Te 0.02 , specifically including the following steps:

[0051] Step 1) Under an argon environment, 2 g of magnesium powder, 6.4732 g of bismuth powder, 2.063 g of antimony powder, 0.0616 g of tellurium powder and 0.1059 g of stearic acid were weighed and put into a ball mill, and ball milled for 8 h using a high-energy ball mill at a speed of 1400 rpm / min to obtain a metal powder;

[0052] Step 2) The mixed metal powder obtained in step 1) is placed in a spark plasma sintering mold, the sintering temperature is 800°C, the sintering pressure is 60Mpa, the holding time is 2min, the cooling rate is 2°C / min to 300°C, and then naturally cooled to finally obtain a bulk Mg3(Sb,Bi)2 thermoelectric material.

[0053] The Te-doped Mg prepared in this example is characterized. 3.4 Bi 1.28 Sb 0.7 Te 0.02 The ZT value of the thermoelectric material reached 0.41 at 323K.

[0054] Example 4

[0055] A method for preparing an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, wherein the chemical formula is Mg 3.4 Bi 1.27 Sb 0.7 Te 0.03 , specifically including the following steps:

[0056] Step 1) Under an argon environment, 2 g of magnesium powder, 6.4226 g of bismuth powder, 2.063 g of antimony powder, 0.0926 g of tellurium powder and 0.1057 g of stearic acid were weighed and put into a ball mill, and ball milled for 8 h using a high-energy ball mill at a speed of 1400 rpm / min to obtain a metal powder;

[0057] Step 2) The mixed metal powder obtained in step 1) is placed in a spark plasma sintering mold, the sintering temperature is 800°C, the sintering pressure is 60Mpa, the holding time is 2min, the cooling rate is 3°C / min to 300°C, and then naturally cooled to finally obtain a bulk Mg3(Sb,Bi)2 thermoelectric material.

[0058] like Figure 3 As shown, the Te-doped Mg prepared in this embodiment 3.4 Bi 1.27 Sb 0.7 Te 0.03 The ZT value of the thermoelectric material reached 0.44 at 323K.

[0059] like Figure 1 As shown in FIG. 4 , in the 20 thermal cycle tests of Example 4, the average conductivity of the cycles decreased by less than 5%, and the average Seebeck coefficient remained basically unchanged. Figure 2 In the air stability test, the thermoelectric performance of the prepared Mg3(Sb,Bi)2-based thermoelectric material showed no obvious attenuation after being exposed to air for 20 days, which indicates that the material has excellent air stability.

[0060] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. An n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability, characterized in that: The chemical formula of the thermoelectric material is Mg 3.4 Bi 1.3-x Sb 0.7 Te x , where x = 0.01 to 0.03; The metal mixed powder of metal Mg, metal Bi, metal Sb and metal Te is hot pressed and sintered, and then slowly cooled after sintering to obtain an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability.

2. The n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability according to claim 1, characterized in that: The chemical formula of the n-type Mg3(Sb,Bi)2-based thermoelectric material is Mg 3.4 Bi 1.3-x Sb 0.7 Te x , where x=0.

01.

3. The n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability according to claim 1, characterized in that: The ZT value of the n-type Mg3(Sb,Bi)2-based thermoelectric material is 0.41-0.44 at 323K.

4. A method for preparing an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability according to any one of claims 1 to 3, characterized in that: The following steps are involved: Under a protective atmosphere, metal Mg, metal Bi, metal Sb and metal Te with a purity greater than 99.9% are crushed to obtain a metal mixed powder with an average particle size less than 5 μm; The metal mixed powder is hot pressed and sintered. After sintering, the temperature is cooled to 300°C at a cooling rate of 1°C / min to 3°C / min and then naturally cooled to obtain an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability.

5. The method for preparing an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability according to claim 4, characterized in that: In a protective atmosphere, metal Mg, metal Bi, metal Sb and metal Te with a purity greater than 99.9% are mixed and crushed to obtain a metal mixed powder with an average particle size less than 5 μm: Under the protection of high-purity argon, metal Mg, metal Bi, metal Sb, metal Te and grinding aids are mixed and high-energy ball milled. The rotation speed of the high-energy ball mill is 1200r / min~1400r / min, the ball milling time is 8h, and the ball-to-material ratio is 10:1 to obtain a metal mixed powder with an average particle size of less than 5μm.

6. The method for preparing an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability according to claim 5, characterized in that: When ball milling is performed, metal Bi and metal Sb are pre-milled first, and then mixed with metal Mg and metal Te and continued to be ball milled.

7. The method for preparing an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability according to claim 4, characterized in that: In the step of hot pressing and sintering the metal mixed powder to obtain an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability: The sintering temperature of hot pressing sintering is 800°C, the sintering heating rate is 10°C / min, the holding time is 2min, and the pressure is 60Mpa.

8. The method for preparing an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability according to claim 7, characterized in that: When the sintering temperature reaches 200°C, pressure begins to be applied, with a pressure increase rate of 2Mpa / min. When the temperature reaches 500°C, the pressure reaches 60Mpa.

9. A thermoelectric energy conversion device, characterized in that: The invention is prepared by using an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability as described in any one of claims 1 to 3.

10. A temperature sensor, characterized in that: The invention is prepared by using an n-type Mg3(Sb,Bi)2 thermoelectric material with high thermal cycle stability and air stability as described in any one of claims 1 to 3.

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