Silver telluride and its preparation method

Abstract

The present invention belongs to the technical field of high-purity alloys, and discloses silver telluride and a preparation method thereof. In this preparation method, tellurium and silver are heated to 500-600 °C at a heating rate of ≤10 °C / min in an inert gas atmosphere, held for 30-60 min, then heated to 800-900 °C, held for 1-3 h, and then heated to 1000-1150 °C, held for 3-5 h to obtain silver telluride. By means of three-stage heating and holding, the present invention ensures complete reaction of silver telluride while reducing the loss of tellurium.

Description

Technical Field

[0001] The present invention relates to the technical field of high-purity alloys, and in particular to silver telluride and a preparation method thereof. Background Art

[0002] The chemical formula of silver telluride is Ag2Te, with a melting point of 955℃. It is widely used in optoelectronics, thermoelectricity and other fields. There are currently three methods to prepare it: 1. In a vacuum container, silver and tellurium are heated together until they turn slightly red to obtain silver telluride; 2. It is produced by reacting tellurium with hot silver nitrate solution; 3. Silver telluride can also be produced by reacting H2Te with a soluble silver salt solution.

[0003] The above three methods have high preparation costs. When used for large-scale production, a large amount of production costs will be generated, resulting in high product prices and lack of market competitiveness.

[0004] Therefore, the development of a method for preparing silver telluride using elemental silver and elemental tellurium as raw materials is currently a popular direction. Therefore, D1: Chinese patent 201810072149.9 discloses a high-performance silver-tellurium compound thermoelectric semiconductor material and a preparation method thereof. The chemical formula of the silver-tellurium compound thermoelectric semiconductor material is Ag 5-x Te3, -0.04≤x≤0.14; The material is prepared by using high-purity single substance as raw material, mixing ingredients according to the stoichiometric ratio in the above chemical formula, vacuum packaging, high-temperature melting, annealing heat treatment, grinding into powder, vacuum hot pressing sintering, and slowly cooling to obtain a sheet-like block material, which is the target product. Compared with the prior art, this invention has produced a thermoelectric semiconductor material with extremely low thermal conductivity and high thermoelectric performance, and explored the preparation process for obtaining high-quality polycrystalline samples. The lattice thermal conductivity of the thermoelectric material is as low as 0.18~0.25W / m·K in the full temperature range, and its thermoelectric figure of merit reaches 1.0 when the temperature reaches 650K. It is a type of thermoelectric material with great potential.

[0005] The above patent prepares high-performance silver telluride by multiple quenching and sintering methods, wherein the holding time for each quenching ranges from 6-8 hours to 2-4 days. The holding time process requires too much heat energy and does not solve the problem that the existing technology has high production costs and is not suitable for large-scale production. Further research and development is needed.

[0006] However, D2: Chinese Patent No. 202210012220.0 discloses a preparation method of high-strength and high-plasticity silver telluride. The room-temperature-phase silver telluride material is subjected to hot deformation treatment at 200-600 °C to obtain high-strength and high-plasticity silver telluride. Among them, during the hot deformation treatment, the compression deformation amount is in the range of 20-60%. The silver telluride bulk prepared by this method retains part of the high-temperature phase at room temperature, the grains become slender and are distributed in a specific direction, forming an obvious texture, and the mechanical strength and plasticity are significantly improved and the performance is stable.

[0007] The preparation method of high-strength and high-plasticity silver telluride disclosed in the above patent includes the following steps: 1) Using high-purity elemental silver and tellurium powder as raw materials, weighing an appropriate amount of raw materials according to the stoichiometric ratio of Ag and Te of 2:1, and synthesizing a silver telluride bulk at a reaction temperature of 200-600 °C, a pressure of 2-4 GPa, and a holding time of 5-20 minutes; 2) Subjecting the obtained silver telluride bulk to hot deformation treatment at 200-600 °C, with the compression deformation amount in the range of 20-60%, to obtain a high-strength and high-plasticity silver telluride bulk.

[0008] The above patent discloses a technical solution for synthesizing silver telluride by using elemental silver and tellurium powder as raw materials and holding at 200-600 °C and 2-4 GPa. Compared with other existing technologies, its production cost is relatively low.

[0009] However, there is a small problem with the technical solution of the above patent, that is, the reaction of silver telluride is not complete at 200-600 °C and a pressure of 2-4 GPa. Simply increasing the reaction temperature will cause tellurium to be lost due to excessive vapor pressure, resulting in a low yield of the prepared silver telluride. Summary of the Invention

[0010] One of the purposes of the present invention is to provide a preparation method of silver telluride to solve the technical problem that the prior art cannot effectively reduce the production cost while producing silver telluride with high conductivity, and to avoid the problems of more free tellurium at high temperature and more loss of tellurium due to vapor pressure resulting in incomplete reaction of silver.

[0011] Another purpose of the present invention is to provide a silver telluride, which is prepared by the preparation method of silver telluride provided by the present invention, and has a high yield and less free tellurium.

[0012] To achieve the above purpose, the present invention provides a preparation method of silver telluride. Under an inert gas atmosphere, elemental tellurium and elemental silver are heated to 500-600 °C at a heating rate of ≤10 °C / min, held for 30-60 min, then heated to 800-900 °C, held for 1-3 h, and then heated to 1000-1150 °C, held for 3-5 h to obtain silver telluride.

[0013] Preferably, the above preparation method of silver telluride includes the following steps:

[0014] Step 1: Load tellurium blocks and silver grains into a graphite boat according to a material ratio of 1.1 - 1.2:2 in terms of molar ratio;

[0015] Step 2: Load the graphite boat in Step 1 into a heating furnace, and introduce an inert gas to make the inside of the heating furnace in an inert gas atmosphere;

[0016] Step 3: Start heating up. The heating furnace heats up from room temperature to 500 - 600 °C at a heating rate of ≤10 °C / min, hold for 30 - 60 min, then heat up to 800 - 900 °C, hold for 1 - 3 h, and then heat up to 1000 - 1150 °C, hold for 3 - 5 h;

[0017] Step 4: Cool down with the furnace to obtain silver telluride.

[0018] Further, the specific operation of Step 1 is: place the silver grains at the bottom of the graphite boat, and place the tellurium blocks on top of the silver grains.

[0019] Further, the flow rate of the inert gas introduced in Step 2 is 3 - 10 L / min, and the introduction time is 30 - 40 min.

[0020] Further, the heating furnace in Step 3 is a horizontal tube furnace, and the heating rate is 5 - 10 °C / min.

[0021] Preferably, the purity of the tellurium element and the silver element is 5N. The tellurium element can be tellurium blocks or tellurium grains, and the silver element can be silver grains or silver powder; when the tellurium element is tellurium blocks, the silver element is silver grains; when the tellurium element is tellurium grains, the silver element is silver powder.

[0022] The present invention also discloses a silver telluride prepared by the above method for preparing silver telluride.

[0023] Beneficial effects

[0024] Compared with the prior art, the present invention has at least the following advantages:

[0025] (1) The present invention provides a method for preparing silver telluride. By means of three-stage heating and holding, while ensuring the complete reaction of silver telluride, the loss of tellurium is reduced;

[0026] (2) In the first-stage heating of the present invention, the heating temperature is controlled between 500 - 600 °C. Holding at this temperature ensures that all tellurium is heated and melted, and at the same time ensures that all the liquefied tellurium liquid penetrates into the silver grains or silver powder to wrap all silver particles, providing a more sufficient reaction environment for the subsequent heating reaction to generate silver telluride. And because the heating temperature in the first stage is relatively low and the holding time is short, tellurium is fully retained;

[0027] (3) In the second stage of heating up in the present invention, the heating temperature is controlled between 800 °C and 900 °C. This temperature is close to the melting point of silver. Therefore, keeping the temperature at this stage is to make the silver grains or silver powder fully softened, and the gaps between the grains are more easily squeezed by the liquid, making the penetration of the tellurium liquid more thorough, avoiding that some silver grains or silver powder at the bottom do not contact the tellurium liquid, providing a more sufficient reaction environment for the formation of silver telluride in the next stage of heating reaction, and not quickly heating up to above 1000 °C, which can effectively avoid the loss of tellurium;

[0028] (4) The present invention controls the heating rate to avoid excessive heating rate resulting in incomplete reaction of silver telluride and more generation of free tellurium. Detailed implementation mode

[0029] The following combines examples to further describe the present invention, but does not constitute any limitation to the present invention. Any limited number of modifications within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0030] In order to elaborate on the technical content of the present invention in detail, the following further explains in combination with the implementation modes.

[0031] Example 1

[0032] A kind of silver telluride is prepared by the following steps:

[0033] Step 1: Charge tellurium blocks and silver grains into a graphite boat according to a molar ratio of 1.2:2. Place the silver grains at the bottom of the graphite boat and place the tellurium blocks on top of the silver grains;

[0034] Step 2: Load the graphite boat in step 1 into a heating furnace, introduce an inert gas to make the heating furnace in an inert gas atmosphere. The flow rate of the introduced inert gas is 3 L / min, and the introduction time is 40 min;

[0035] Step 3: Start heating up. The heating furnace heats up from room temperature to 500 °C at a heating rate of 5 °C / min, keep the temperature for 60 min, then heat up to 800 °C, keep the temperature for 3 h, and then heat up to 1000 °C, keep the temperature for 5 h;

[0036] Step 4: Cool down with the furnace to obtain silver telluride.

[0037] Example 2

[0038] A kind of silver telluride is prepared by the following steps:

[0039] Step 1: Charge tellurium blocks and silver grains into a graphite boat according to a molar ratio of 1.1:2. Place the silver grains at the bottom of the graphite boat and place the tellurium blocks on top of the silver grains;

[0040] Step 2: Load the graphite boat from Step 1 into the heating furnace, introduce an inert gas to create an inert gas atmosphere inside the heating furnace. The flow rate of the introduced inert gas is 10 L / min, and the introduction time is 30 min;

[0041] Step 3: Start heating up. The heating furnace heats up from room temperature to 600 °C at a heating rate of 10 °C / min, hold for 30 min, then heat up to 900 °C, hold for 1 h, and then heat up to 1150 °C, hold for 3 h;

[0042] Step 4: Cool down with the furnace to obtain silver telluride.

[0043] Example 3

[0044] A silver telluride is prepared by the following steps:

[0045] Step 1: Charge tellurium ingots and silver grains into a graphite boat according to a molar ratio of 1.2:2. Place the silver grains at the bottom of the graphite boat and the tellurium ingots on top of the silver grains;

[0046] Step 2: Load the graphite boat from Step 1 into the heating furnace, introduce an inert gas to create an inert gas atmosphere inside the heating furnace. The flow rate of the introduced inert gas is 10 L / min, and the introduction time is 30 min;

[0047] Step 3: Start heating up. The heating furnace heats up from room temperature to 600 °C at a heating rate of 8 °C / min, hold for 30 min, then heat up to 900 °C, hold for 1 h, and then heat up to 1150 °C, hold for 3 h;

[0048] Step 4: Cool down with the furnace to obtain silver telluride.

[0049] Example 4

[0050] A silver telluride is prepared by the following steps:

[0051] Step 1: Charge tellurium ingots and silver grains into a graphite boat according to a molar ratio of 1.2:2. Place the silver grains at the bottom of the graphite boat and the tellurium ingots on top of the silver grains;

[0052] Step 2: Load the graphite boat from Step 1 into the heating furnace, introduce an inert gas to create an inert gas atmosphere inside the heating furnace. The flow rate of the introduced inert gas is 10 L / min, and the introduction time is 30 min;

[0053] Step 3: Start heating up. The heating furnace heats up from room temperature to 550 °C at a heating rate of 8 °C / min, hold for 50 min, then heat up to 850 °C, hold for 2 h, and then heat up to 1100 °C, hold for 4 h;

[0054] Step 4: Cool down with the furnace to obtain silver telluride.

[0055] Comparative Example 1

[0056] It is generally the same as Example 3, except that in Step 1, the molar ratio of tellurium blocks to silver grains is 1:2.

[0057] Comparative Example 2

[0058] It is generally the same as Example 3, except that Step 3 is changed to: Start heating up. The heating furnace heats up from room temperature to 1150 °C at a heating rate of 8 °C / min and holds for 4.5 h.

[0059] Comparative Example 3

[0060] It is generally the same as Example 3, except that Step 3 is changed to: Start heating up. The heating furnace heats up from room temperature to 1150 °C at a heating rate of 8 °C / min and holds for 3 h.

[0061] Comparative Example 4

[0062] It is generally the same as Example 3, except that Step 3 is changed to: Start heating up. The heating furnace heats up from room temperature to 900 °C at a heating rate of 8 °C / min, holds for 1.5 h, then heats up to 1150 °C and holds for 3 h.

[0063] Comparative Example 5

[0064] It is generally the same as Example 3, except that Step 3 is changed to: Start heating up. The heating furnace heats up from room temperature to 600 °C at a heating rate of 8 °C / min, holds for 1.5 h, then heats up to 1150 °C and holds for 3 h.

[0065] Comparative Example 6

[0066] It is generally the same as Example 3, except that the heating rate in Step 3 is changed to 12 °C / min.

[0067] Comparative Example 7

[0068] It is generally the same as Example 3, except that Step 3 is changed to: Start heating up. The heating furnace heats up from room temperature to 400 °C at a heating rate of 8 °C / min, holds for 30 min, then heats up to 900 °C, holds for 1 h, and then heats up to 1150 °C and holds for 3 h.

[0069] Comparative Example 8

[0070] It is generally the same as Example 3, except that Step 3 is changed to: Start heating up. The heating furnace heats up from room temperature to 700 °C at a heating rate of 8 °C / min, holds for 30 min, then heats up to 900 °C, holds for 1 h, and then heats up to 1150 °C and holds for 3 h.

[0071] Comparative Example 9

[0072] It is generally the same as Example 3, except that Step 3 is changed to: Start heating up. The heating furnace heats up from room temperature to 600 °C at a heating rate of 8 °C / min, holds for 30 min, then heats up to 700 °C, holds for 1 h, and then heats up to 1150 °C, holds for 3 h.

[0073] Comparative Example 10

[0074] It is generally the same as Example 3, except that Step 3 is changed to: Start heating up. The heating furnace heats up from room temperature to 600 °C at a heating rate of 8 °C / min, holds for 30 min, then heats up to 1000 °C, holds for 1 h, and then heats up to 1150 °C, holds for 3 h.

[0075] Performance test

[0076] Test method: The content of tellurium is measured by titration method, and free tellurium is tested by TG-DSC.

[0077] The silver telluride prepared in Examples 1-4 and Comparative Examples 1-10 was tested according to the above test method to obtain the content of free tellurium and the content of tellurium in silver telluride. The results are shown in Table 1;

[0078] Table 1 Test data results of silver telluride prepared in Examples 1-4 and Comparative Examples 1-10

[0079]

[0080]

[0081] It can be seen from the data in Table 1 that:

[0082] From the result comparison between Example 3 and Comparative Example 1, it can be seen that by using excessive tellurium to react with silver to form silver telluride in the present invention, it can effectively avoid the problem that the reaction of silver telluride is incomplete and the yield of the finished product is reduced due to the loss of tellurium caused by the vapor pressure.

[0083] From the result comparison between Example 3 and Comparative Examples 2-3, it can be seen that compared with the three-stage heating and holding technical solution of the present invention, directly heating up to the silver telluride production temperature will result in incomplete reaction of silver telluride, and due to the high vapor pressure state all the time, the loss of tellurium is large, and finally the yield of the obtained silver telluride finished product is low.

[0084] From the results of Example 3 and Comparative Example 4, it can be seen that in the case of lacking the holding at 500-600 °C in the first stage, tellurium quickly passes through the melting stage and starts to be heated and melted almost simultaneously with silver, resulting in that the tellurium liquid starts to enter the next stage of heating reaction without fully wrapping the silver particles, the reaction of silver telluride is not thorough, and at the same time, tellurium loss occurs due to the rapid change of vapor pressure, and finally the yield of the obtained silver telluride finished product is low.

[0085] From the result comparison between Example 3 and Comparative Example 4 and Comparative Example 5, it can be seen that in Comparative Example 5, in the absence of the second-stage heat preservation at 800-900 °C, the tellurium liquid did not penetrate into the silver grain layer to wrap the silver grains, so the reaction of silver telluride was not thorough enough; however, since Comparative Example 5 had the first-stage heat preservation at 500-600 °C compared with Comparative Example 4, the tellurium block was in a molten state for a long time to become tellurium liquid before the silver melted, and its contact with the silver grain layer was more sufficient. And because the vapor pressure generated by the heat preservation temperature in the first stage would not cause a large loss of tellurium, the yield of the obtained silver telluride finished product would be higher than that of Comparative Example 4; it shows that the three-stage heat preservation adopted in the present invention, with the first-stage heat preservation at 500-600 °C, the second-stage heat preservation at 800-900 °C, and the third-stage heat preservation at 1000-1150 °C, is indispensable. The combination of the three-stage heat preservation provides sufficient reaction space for the production of silver telluride while minimizing the loss of tellurium, and improves the yield of silver telluride finished product.

[0086] From the result comparison between Example 3 and Comparative Example 6, it can be seen that too fast heating rate will not have too much impact on the yield of silver telluride finished product, and even has some improvement effects. However, too fast heating rate will cause some tellurium to become free tellurium, and an additional process is needed to remove the free tellurium, increasing the additional production cost.

[0087] From the result comparison between Example 4 and Comparative Examples 7-10, it can be seen that in the three-stage heat preservation technical solution of the present invention, the temperature of each stage of heat preservation has a great influence on the final yield of silver telluride product; among them, if the heat preservation temperature in the first stage is too low, it is difficult for the tellurium block to melt into tellurium liquid, which will greatly affect the reaction environment between tellurium and silver, resulting in a low yield; while too high heat preservation temperature in the first stage will increase the vapor pressure and cause a large increase in the loss amount of tellurium, also affecting the yield; too low heat preservation temperature in the second stage will lead to insufficient penetration of the tellurium liquid into the silver grain layer and incomplete reaction, so it will affect the yield of silver telluride finished product, but compared with Comparative Examples 7 and 8, its influence is smaller; while too high heat preservation temperature in the second stage will only increase the loss of tellurium, so the influence is the smallest.

[0088] It should be noted that in actual production, when the content difference of tellurium in silver telluride ≥ 0.3%, it is already a large product quality difference.

[0089] The embodiments presented herein are only the implementation manners selected according to the combinations of all possible embodiments. The appended claims should not be limited by the implementation manners that illustrate the present invention. Some numerical ranges used in the claims include sub-ranges within them, and the changes in these ranges should also be covered by the appended claims.

Claims

1. A preparation method of silver telluride, characterized in that, It includes the following steps: Step 1: Charge tellurium blocks and silver grains into a graphite boat according to a molar ratio of 1.1 - 1.2:2; Step 2: Place the graphite boat from Step 1 into a heating furnace, and introduce an inert gas to make the inside of the heating furnace in an inert gas atmosphere; Step 3: Start heating up. The heating furnace heats up from room temperature to 500 - 600 °C at a heating rate of 5 - 10 °C / min, hold for 30 - 60 min, then heat up to 800 - 900 °C, hold for 1 - 3 h, and then heat up to 1000 - 1150 °C, hold for 3 - 5 h; Step 4: Cool down with the furnace to obtain silver telluride.

2. The preparation method of silver telluride according to claim 1, wherein, The specific operation of Step 1 is: Place the silver grains at the bottom of the graphite boat, and place the tellurium blocks on top of the silver grains.

3. The preparation method of silver telluride according to claim 1, wherein, In Step 2, the flow rate of the inert gas introduced is 3 - 10 L / min, and the introduction time is 30 - 40 min.

4. The preparation method of silver telluride according to claim 1, characterized in that, The heating furnace in Step 3 is a horizontal tube furnace.

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