Germanium telluride-based thermoelectric material and preparation method thereof
By doping Si, Bi, and B into germanium telluride-based thermoelectric materials and constructing a multi-scale micro-defect structure, the problems of insufficient mechanical strength of the material and narrow zT value peak were solved, and the thermoelectric and mechanical properties were improved, especially the stability and reliability at high temperatures.
Patent Information
- Application Number
- CN202510804095.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-16
- Publication Date
- 2025-09-16
AI Technical Summary
Existing germanium telluride-based thermoelectric materials have weak mechanical strength and high brittleness. The doping concentration needs to be precisely controlled. Improper carrier concentration leads to a narrow zT value peak, strong temperature dependence, and easy performance degradation at high temperatures, which limits its reliability and thermoelectric performance.
A multi-scale micro-defect structure is constructed in germanium telluride-based thermoelectric materials. By doping Si, Bi, and B, the carrier concentration and electron transport are optimized, the local strain field and nano-strengthened structure are constructed, the interface scattering is enhanced, and point defects and strain fields introduced by appropriate amounts of Si/B are formed to improve the mechanical properties.
The thermoelectric and mechanical properties of the material are significantly improved, the zT value is increased, the thermoelectric performance at high temperature is stabilized, the negative impact of impurity scattering on carrier mobility is reduced, and the long-term operating stability and reliability of the material are enhanced.
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Abstract
Description
Technical Field
[0001] The present application relates to the technical field of thermoelectric materials, and in particular to a germanium telluride-based thermoelectric material and a preparation method thereof. Background Art
[0002] With rapid economic development, energy shortages and environmental pollution are becoming increasingly serious. Faced with this challenge, efforts are accelerating the development of new renewable energy sources, such as solar, wind, hydro, geothermal, and nuclear energy, to replace traditional fossil fuels. Meanwhile, researchers are striving to improve energy efficiency and achieve multi-level energy utilization. Thermoelectric technology not only effectively utilizes waste heat to convert thermal energy into electrical energy, improving energy efficiency, but also harnesses electrical energy for solid-state refrigeration. Due to its simplicity, sensitivity, high stability, and pollution-free nature, thermoelectric power generation and refrigeration technology has been widely used in aerospace applications such as specialty power supplies, small refrigerators, semiconductor refrigeration, and smart wearables.
[0003] The application of thermoelectric technology mainly depends on thermoelectric materials with good performance. The energy conversion efficiency of thermoelectric materials depends on the dimensionless thermoelectric figure of merit zT, zT = S 2 σT / κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. 2 σ, also known as the power factor (PF), determines the material's electrical performance. The various thermoelectric parameters are coupled, making simultaneous improvement difficult. Ideal thermoelectric materials require a high power factor and low thermal conductivity to maximize the zT value.
[0004] At present, germanium telluride (GeTe)-based thermoelectric materials have shown excellent thermoelectric performance in the medium and high temperature range. Many studies have shown that through doping (such as Bi, Sb) and nanostructure regulation, the Seebeck coefficient and electrical conductivity of GeTe can be significantly improved, the lattice thermal conductivity can be reduced, and the zT value can reach above 1.5. The synthesis process of this GeTe-based thermoelectric material is mature and low-cost, suitable for large-scale preparation and wide device application, and has good thermal and chemical stability, suitable for long-term operation. However, this GeTe-based thermoelectric material has weak mechanical strength and high brittleness, and the doping concentration needs to be precisely controlled. Otherwise, the carrier concentration is too high or too low, which will lead to a narrow zT value peak, strong temperature dependence, and easy performance decay at high temperatures, limiting reliability. Summary of the Invention
[0005] In view of this, the present application proposes a germanium telluride-based thermoelectric material and a preparation method thereof, aiming to effectively improve its thermoelectric and mechanical properties by constructing a multi-scale microscopic defect structure in the germanium telluride-based thermoelectric material.
[0006] The present application provides a germanium telluride-based thermoelectric material, the chemical formula of which is (Ge 0.95 Bi 0.05 Te) 1-X (Si 0.8 Ge 0.2 B 0.02 ) X , where 0.02≤X≤0.1.
[0007] In a preferred embodiment, the chemical formula of the germanium telluride-based thermoelectric material is (Ge 0.95 Bi 0.05 Te) 0.98 (Si 0.8 Ge 0.2 B 0.02 ) 0.02 .
[0008] The present application also provides a method for preparing the germanium telluride-based thermoelectric material as described above, the method comprising:
[0009] S1: Ge, Bi, and Te are weighed and mixed in a stoichiometric ratio of 0.95:0.05:1 to obtain a first mixture, the first mixture is placed in a quartz tube, the quartz tube is evacuated and sealed, and the quartz tube is placed in a rotary tube furnace to sinter the first mixture into an ingot;
[0010] S2: Si, Ge, and B were weighed and mixed in a stoichiometric ratio of 0.8:0.2:0.02 to obtain a second mixture, which was then placed in a ball mill and ground into a powder under an argon atmosphere;
[0011] S3: Weighing the ingot and the powder material according to the stoichiometric ratio of (1-X):X, putting them into a mortar and hand-grinding them into a uniformly mixed powder; and
[0012] S4: performing spark plasma sintering on the powder to obtain the germanium telluride-based thermoelectric material.
[0013] In a preferred embodiment, in step S1, the purity of Ge is greater than or equal to 99.999wt%, the purity of Bi is greater than or equal to 99.99wt%, and the purity of Te is greater than or equal to 99.99wt%;
[0014] And / or, in step S2, the purity of the Si is greater than or equal to 99.99wt%, the purity of the Ge is greater than or equal to 99.999wt%, and the purity of the B is greater than or equal to 99.99wt%.
[0015] In a preferred embodiment, in step S1, the vacuum degree of the quartz tube is controlled at 11 -1 Pa~9 - 1 Pa.
[0016] In a preferred embodiment, in step S1, after placing the quartz tube in the rotary tube furnace, the rotary tube furnace is controlled to heat from room temperature to 1223K~1323K, the heating time is 11h~13h, and then kept at the heated temperature for 11h~13h, and then cooled to room temperature, and the cooling time is 11h~13h.
[0017] In a preferred embodiment, in step S1, after placing the quartz tube in the rotary tube furnace, the rotary tube furnace is controlled to heat from room temperature to 1273K, the heating time is 12 hours, then kept at 1273K for 12 hours, and then cooled to room temperature, the cooling time is 12 hours.
[0018] In a preferred embodiment, in step S2, the rotation speed of the ball mill is set to 450 rpm to 550 rpm, and the ball milling time of the ball mill is set to 16 h to 24 h.
[0019] In a preferred embodiment, in step S4, the temperature for spark plasma sintering the powder is set to 793K-853K, the pressure is set to 25MPa-35MPa, and the time is set to 7min-13min.
[0020] In a preferred embodiment, in step S4, the temperature for spark plasma sintering the powder is set to 823K, the pressure is set to 30 MPa, and the time is set to 10 minutes.
[0021] In summary, the present application provides a germanium telluride-based thermoelectric material and a preparation method thereof. The main features are that the raw materials Ge, Te, and Bi are weighed in a stoichiometric ratio and then melted, and the raw materials Ge, Si, and B are weighed in a stoichiometric ratio and then ball-milled. Compared with the existing technology, the present application has at least the following advantages:
[0022] 1. This application is the first to dope Si, Bi, and B into GeTe to optimize carrier concentration and electron transport, construct local strain fields and nano-strengthening structures, and utilize multiphase precipitation to enhance interface scattering, effectively improving the zT value.
[0023] 2. The point defects, vacancies, and strain fields introduced by Si and B can partially passivate natural vacancies (such as Ge vacancies), reducing the negative impact of impurity scattering on carrier mobility μ. Furthermore, appropriate impurity concentrations can inhibit phase separation and migration under high-temperature operation, stabilize the material microstructure, and improve thermoelectric stability and mechanical reliability under long-term operating conditions.
[0024] 3. The preparation method of doping Si, Bi, and B in GeTe provided in this application has simple production process and production equipment, good controllability and repeatability, low production cost, and is suitable for application in large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 This is a schematic flow chart of the method for preparing germanium telluride-based thermoelectric materials of the present application.
[0026] Figure 2 The comparison curve of the conductivity of germanium telluride-based thermoelectric materials with different X values as the temperature changes.
[0027] Figure 3 Comparison curve of the Seebeck coefficient of germanium telluride-based thermoelectric materials with different X values as they change with temperature.
[0028] Figure 4 The power factor comparison curve of germanium telluride-based thermoelectric materials with different X values as the temperature changes.
[0029] Figure 5 Comparison curve of thermal conductivity of germanium telluride-based thermoelectric materials with different X values as the temperature changes.
[0030] Figure 6 Comparison curve of thermoelectric figure of merit zT of germanium telluride-based thermoelectric materials with different X values as the temperature changes. DETAILED DESCRIPTION
[0031] Before describing the embodiments in detail, it should be understood that the present application is not limited to the detailed structure or component arrangement described below or in the accompanying drawings in this application. The present application may be an embodiment implemented in other ways. Moreover, it should be understood that the words and terms used herein are for descriptive purposes only and should not be interpreted restrictively. The words "including", "comprising", "having" and similar words used herein are intended to include the matters listed thereafter, their equivalents and other additional matters. In particular, when describing "a certain element", the present application does not limit the number of the element to one, but may also include multiple elements.
[0032] The present application provides a germanium telluride-based thermoelectric material (GeTe-based thermoelectric material), the chemical formula of which is (Ge 0.95 Bi 0.05 Te) 1-X (Si0.8 Ge 0.2 B 0.02 ) X , where 0.02≤X≤0.1. Studies have shown that when the value of X is less than 0.02, the mechanical properties of the thermoelectric material will be too poor, and when the value of X is greater than 0.1, the zT value will be too small, affecting the thermoelectric performance of the thermoelectric material. The present application dopes the GeTe matrix with elements Si, Bi and B, optimizes the carrier concentration and electron transport through Bi, and constructs the local strain field and nano-strengthened structure through Si / B. The incorporation of an appropriate amount of Si or B can easily form micro-phase precipitation in the GeTe matrix, enhance interface scattering, achieve a high Seebeck coefficient and low lattice thermal conductivity, thereby greatly improving the zT value, and also obtaining better toughness, effectively improving the disadvantage of excessive brittleness of pure GeTe.
[0033] Preferably, X is 0.02, that is, the chemical formula of the germanium telluride-based thermoelectric material is (Ge 0.95 Bi 0.05 Te) 0.98 (Si 0.8 Ge 0.2 B 0.02 ) 0.02 .
[0034] Please refer to Figure 1 As shown, the present application also provides a method for preparing the germanium telluride-based thermoelectric material as described above, the preparation method comprising:
[0035] S1: Ge, Bi, and Te are weighed and mixed in a stoichiometric ratio of 0.95:0.05:1 to obtain a first mixture, the first mixture is placed in a quartz tube, the quartz tube is evacuated and sealed, and the quartz tube is placed in a rotary tube furnace to sinter the first mixture into an ingot;
[0036] S2: Si, Ge, and B were weighed and mixed according to a stoichiometric ratio of 0.8:0.2:0.02 to obtain a second mixture, which was then placed in a ball mill and ground into a powder under an argon atmosphere.
[0037] S3: Weigh the ingot and powder respectively according to the stoichiometric ratio of (1-X):X, put them into a mortar and grind them into a uniform powder by hand; and
[0038] S4: The powder is subjected to spark plasma sintering to obtain germanium telluride-based thermoelectric materials.
[0039] The raw materials Ge, Bi and Te are, for example, Ge powder, Bi powder and Te powder respectively, and the raw materials Si, Ge and B are, for example, Si powder, Ge powder and B powder respectively. In other embodiments, the raw materials may be in other forms, which is not limited in this application.
[0040] Among them, in step S1, the purity of Ge powder is greater than or equal to 99.999wt%, the purity of Bi powder is greater than or equal to 99.99wt%, and the purity of Te powder is greater than or equal to 99.99wt%; in step S2, the purity of Si powder is greater than or equal to 99.99wt%, the purity of Ge powder is greater than or equal to 99.999wt%, and the purity of B powder is greater than or equal to 99.99wt%.
[0041] In some embodiments, in step S1, the vacuum degree of the quartz tube can be controlled at 11 -1 Pa~9 -1 Pa. Preferably, the vacuum degree of the quartz tube is 10 -1 Pa.
[0042] In step S1, after placing the quartz tube in the rotary tube furnace, the rotary tube furnace is controlled to heat from room temperature to 1223K~1323K, the heating time is 11h~13h, then the temperature is kept at the heated temperature for 11h~13h, and then the temperature is cooled to room temperature, and the cooling time is 11h~13h. Preferably, in step S1, after placing the quartz tube in the rotary tube furnace, the rotary tube furnace is controlled to heat from room temperature to 1273K, the heating time is 12h, then the temperature is kept at 1273K for 12h, and then the temperature is cooled to room temperature, and the cooling time is 12h.
[0043] In some embodiments, in step S2, the speed of the ball mill is set to 450 rpm to 550 rpm, and the milling time of the ball mill is set to 16 h to 24 h. Preferably, in step S2, the speed of the ball mill is set to 500 rpm, and the milling time of the ball mill is set to 20 h.
[0044] In some embodiments, in step S4, the temperature for spark plasma sintering the powder is set to 793K to 853K, the pressure is set to 25MPa to 35MPa, and the time is set to 7min to 13min. Preferably, in step S4, the temperature for spark plasma sintering the powder is set to 823K, the pressure is set to 30MPa, and the time is set to 10min.
[0045] In a specific embodiment, in step S1, the purity of Ge powder is 99.999wt%, the purity of Bi powder is 99.99wt%, and the purity of Te powder is 99.99wt%; in step S2, the purity of Si powder is 99.99wt%, the purity of Ge powder is 99.999wt%, and the purity of B powder is 99.99wt%.
[0046] S1: Weigh and evenly mix the elemental raw materials Ge powder, Bi powder, and Te powder according to the stoichiometric ratio of 0.95:0.05:1 to obtain a first mixture, put the first mixture into a quartz tube, and vacuum seal it in a vacuum tube sealing machine. Control the vacuum degree of the quartz tube to 10 -1 Pa; placing the sealed quartz tube in a rotary tube furnace, slowly heating from room temperature to 1273K for 12 hours, then keeping it at 1273K for 12 hours, and finally slowly cooling it down to room temperature for 12 hours, and sintering to obtain an ingot;
[0047] S2: The elemental raw materials Si powder, Ge powder, and B powder were weighed and uniformly mixed according to the stoichiometric ratio of 0.8:0.2:0.02 to obtain a second mixed material, and then the second mixed material was placed in a ball mill jar filled with argon gas in a ball mill. The ball mill was operated at a speed of 500 rpm for 20 hours to form a nanopowder, i.e., a powder material;
[0048] S3: The ingot obtained in step S1 and the powder obtained in step S2 are weighed according to the stoichiometric ratio of (1-X):X (wherein the range of X is [0.02, 0.1]), and then put into a mortar and hand-grinded into a uniformly mixed powder;
[0049] S4: The powder obtained in step S3 is placed in a graphite mold and densified by spark plasma sintering (SPS) at a temperature of 823K and a pressure of 30MPa for 10 minutes to obtain a bulk germanium telluride-based thermoelectric material (Ge 0.95 Bi 0.05 Te) 1-X (Si 0.8 Ge 0.2 B 0.02 ) X .
[0050] Example 1
[0051] This embodiment provides a method for preparing a germanium telluride-based thermoelectric material. The chemical formula of the germanium telluride-based thermoelectric material prepared in this embodiment is (Ge 0.95 Bi 0.05 Te) 0.98 (Si 0.8 Ge 0.2 B 0.02 ) 0.02 At this time, X=0.02, and the specific preparation method includes the following steps:
[0052] The elemental raw materials Ge powder, Bi powder and Te powder were weighed and evenly mixed according to the stoichiometric ratio of 0.95:0.05:1 to obtain a first mixed material. The first mixed material was placed in a quartz tube and vacuum sealed in a vacuum tube sealing machine. The vacuum degree of the quartz tube was controlled to be 10 -1Pa; placing a sealed quartz tube in a rotary tube furnace, slowly heating from room temperature to 1273K for 12h, then keeping it at 1273K for 12h, and finally slowly cooling it down to room temperature for 12h, and sintering to obtain an ingot; weighing the elemental raw materials Si powder, Ge powder, and B powder according to the stoichiometric ratio of 0.8:0.2:0.02 and uniformly mixing them to obtain a second mixed material, and then placing the second mixed material into a ball mill filled with argon in a ball mill, and the ball mill was rotated at a speed of 500r The ingot and powder were weighed in a stoichiometric ratio of 0.98:0.02, and then hand-ground into a uniformly mixed powder in a mortar. The powder was placed in a graphite mold and densified by spark plasma sintering (SPS) at a temperature of 823 K and a pressure of 30 MPa for 10 min to obtain a bulk germanium telluride-based thermoelectric material (Ge 0.95 Bi 0.05 Te) 0.98 (Si 0.8 Ge 0.2 B 0.02 ) 0.02 .
[0053] Example 2
[0054] The preparation method of the germanium telluride-based thermoelectric material in this embodiment can refer to the first embodiment, except that: X=0.04, and the chemical formula of the obtained germanium telluride-based thermoelectric material is (Ge 0.95 Bi 0.05 Te) 0.96 (Si 0.8 Ge 0.2 B 0.02 ) 0.04 .
[0055] Example 3
[0056] The preparation method of the germanium telluride-based thermoelectric material in this embodiment can refer to the first embodiment, except that: X=0.08, and the chemical formula of the obtained germanium telluride-based thermoelectric material is (Ge 0.95 Bi 0.05 Te) 0.92 (Si 0.8 Ge 0.2 B 0.02 ) 0.08 .
[0057] Example 4
[0058] The preparation method of the germanium telluride-based thermoelectric material in this embodiment can refer to the first embodiment, except that: X=0.1, and the chemical formula of the obtained germanium telluride-based thermoelectric material is (Ge 0.95 Bi 0.05Te) 0.9 (Si 0.8 Ge 0.2 B 0.02 ) 0.1 .
[0059] Please also refer to Figures 2 to 6 As shown, Figure 2 The conductivity comparison curves of germanium telluride-based thermoelectric materials with temperature change when X is 0.02, 0.04, 0.08, and 0.1 respectively. Figure 3 The comparison curves of the Seebeck coefficient of germanium telluride-based thermoelectric materials as they change with temperature are obtained when X takes the values of 0.02, 0.04, 0.08, and 0.1, respectively. Figure 4 The power factor comparison curves of germanium telluride-based thermoelectric materials with temperature change are obtained when X takes values of 0.02, 0.04, 0.08, and 0.1 respectively. Figure 5 The comparison curves of thermal conductivity of germanium telluride-based thermoelectric materials as a function of temperature are obtained when X takes values of 0.02, 0.04, 0.08, and 0.1, respectively. Figure 6 The figure of merit zT of the germanium telluride-based thermoelectric material compared with temperature when X is 0.02, 0.04, 0.08, and 0.1, respectively. The temperature range of the above temperature change is 323K to 773K.
[0060] Based on the above tests, it can be concluded that the electrical conductivity, Seebeck coefficient, power factor, thermal conductivity, and zT value of germanium telluride-based thermoelectric materials decrease as the value of X increases. When the value of X is 0.02, the optimal zT value can be obtained, that is, the zT value is the highest at this time. Among them, the zT values of germanium telluride-based thermoelectric materials prepared when X is 0.02 and 0.04 are greater than the zT values of existing germanium telluride-based thermoelectric materials on the market, thereby improving the thermoelectric performance of germanium telluride-based thermoelectric materials.
[0061] In summary, the present application provides a germanium telluride-based thermoelectric material and a preparation method thereof. The main features are that the raw materials Ge, Te, and Bi are weighed in a stoichiometric ratio and then melted, and the raw materials Ge, Si, and B are weighed in a stoichiometric ratio and then ball-milled. Compared with the existing technology, the present application has at least the following advantages:
[0062] 1. This application is the first to dope Si, Bi, and B into GeTe to optimize carrier concentration and electron transport, construct local strain fields and nano-strengthening structures, and utilize multiphase precipitation to enhance interface scattering, effectively improving the zT value.
[0063] 2. The point defects, vacancies, and strain fields introduced by Si and B can partially passivate natural vacancies (such as Ge vacancies), reducing the negative impact of impurity scattering on carrier mobility μ. Furthermore, appropriate impurity concentrations can inhibit phase separation and migration under high-temperature operation, stabilize the material microstructure, and improve thermoelectric stability and mechanical reliability under long-term operating conditions.
[0064] 3. The preparation method of doping Si, Bi, and B in GeTe provided in this application has simple production process and production equipment, good controllability and repeatability, low production cost, and is suitable for application in large-scale industrial production.
[0065] The concepts described herein may be embodied in other forms without departing from their spirit and characteristics. The specific embodiments disclosed are to be considered illustrative rather than restrictive. Therefore, the scope of this application is to be determined by the appended claims, not by the preceding description. Any changes within the literal meaning and range of equivalents of the claims are intended to be within the scope of these claims.
Claims
1. A germanium telluride-based thermoelectric material, characterized in that: The general chemical formula of the germanium telluride-based thermoelectric material is (Ge 0.95 Bi 0.05 Te) 1-X (Si 0.8 Ge 0.2 B 0.02 ) X , where 0.02≤X≤0.
1.
2. The germanium telluride-based thermoelectric material according to claim 1, wherein The chemical formula of the germanium telluride-based thermoelectric material is (Ge 0.95 Bi 0.05 Te) 0.98 (Si 0.8 Ge 0.2 B 0.02 ) 0.02 .
3. A method for preparing a germanium telluride-based thermoelectric material according to any one of claims 1 to 2, characterized in that: The preparation method comprises: S1: Ge, Bi, and Te are weighed and mixed in a stoichiometric ratio of 0.95:0.05:1 to obtain a first mixture, the first mixture is placed in a quartz tube, the quartz tube is evacuated and sealed, and the quartz tube is placed in a rotary tube furnace to sinter the first mixture into an ingot; S2: Si, Ge, and B were weighed and mixed in a stoichiometric ratio of 0.8:0.2:0.02 to obtain a second mixture, which was then placed in a ball mill and ground into a powder under an argon atmosphere; S3: Weighing the ingot and the powder material according to the stoichiometric ratio of (1-X):X, putting them into a mortar and hand-grinding them into a uniformly mixed powder; and S4: performing spark plasma sintering on the powder to obtain the germanium telluride-based thermoelectric material.
4. The method for preparing germanium telluride-based thermoelectric material according to claim 3, wherein: In step S1, the purity of Ge is greater than or equal to 99.999 wt %, the purity of Bi is greater than or equal to 99.99 wt %, and the purity of Te is greater than or equal to 99.99 wt %; And / or, in step S2, the purity of the Si is greater than or equal to 99.99wt%, the purity of the Ge is greater than or equal to 99.999wt%, and the purity of the B is greater than or equal to 99.99wt%.
5. The method for preparing germanium telluride-based thermoelectric material according to claim 3, wherein: In step S1, the vacuum degree of the quartz tube is controlled at 11 -1 Pa~9 -1 Pa.
6. The method for preparing germanium telluride-based thermoelectric material according to claim 3, wherein: In step S1, after placing the quartz tube in the rotary tube furnace, the rotary tube furnace is controlled to heat from room temperature to 1223K~1323K, the heating time is 11h~13h, and then the temperature is kept at the heated temperature for 11h~13h, and then the temperature is cooled to room temperature, and the cooling time is 11h~13h.
7. The method for preparing germanium telluride-based thermoelectric material according to claim 6, wherein: In step S1, after placing the quartz tube in the rotary tube furnace, the rotary tube furnace is controlled to heat from room temperature to 1273K for 12 hours, then kept at 1273K for 12 hours, and then cooled to room temperature for 12 hours.
8. The method for preparing germanium telluride-based thermoelectric material according to claim 3, wherein: In the step S2, the rotation speed of the ball mill is set to 450 rpm to 550 rpm, and the ball milling time of the ball mill is set to 16 h to 24 h.
9. The method for preparing germanium telluride-based thermoelectric material according to claim 3, wherein: In the step S4, the temperature for spark plasma sintering the powder is set to 793K-853K, the pressure is set to 25MPa-35MPa, and the time is set to 7min-13min.
10. The method for preparing germanium telluride-based thermoelectric material according to claim 9, wherein: In step S4, the temperature for spark plasma sintering the powder is set to 823 K, the pressure is set to 30 MPa, and the time is set to 10 minutes.