Sulfur adding method of nanoscale nickel powder and sulfur-added nickel powder prepared by sulfur adding method

Abstract

The invention relates to the technical field of metal powder preparation, in particular to a sulfur adding method of nanoscale nickel powder and sulfur-added nickel powder prepared through the sulfur adding method, a post-sulfur adding mode is adopted, a rotary furnace is heated, inflated and the like, it can be guaranteed that the nickel powder in the rotary furnace is in a dispersed state when making contact with sulfur-containing steam, and the surfaces of particles can react / adsorb in all directions; the sulfur element is ensured to be uniformly distributed and stably exist on the surface of the nickel powder, and the change of the sulfur content caused by the influence of common physical or chemical factors is not easily caused; and the content of the added sulfur can be controlled, the obtained sulfur-added nickel powder is a finished product, and the change of the sulfur content of the nickel powder cannot be caused. The production cost is lower, and the process is high in flexibility in the aspects of adjusting the sulfur content of the product and developing products of different specifications (100-1500 ppm), especially in the case of trace addition; the method has the advantages in the aspect of 1000 ppm, and the batch processing period of the process is short.

Description

Technical Field

[0001] The invention relates to the technical field of metal powder preparation, and in particular to a sulfur-adding method for nano-grade nickel powder with a particle size of 200 nm or less and the sulfur-added nickel powder prepared therefrom. Background Art

[0002] The structure of MLCC capacitors is relatively simple, consisting of three layers: ceramic dielectric, inner electrode metal layer and outer electrode. The number of layers of MLCC determines the capacitance of MLCC. The more layers there are, the larger the layer area and the more total charge the capacitor can store. The trend of chip-based and miniaturized electronic components has caused the metal powder materials used in MLCC manufacturing to shrink from micron to nanometer. As the size of metal powder materials becomes smaller and smaller, the matching of thermal shrinkage during the co-firing process of the inner electrode metal layer and the ceramic dielectric is a key factor affecting the capacitance characteristics.

[0003] At present, adding sulfur to nickel powder can effectively delay the sintering of nickel powder, so the development of ultrafine sulfur-added nickel powder is one of the effective ways to improve the quality of high-order nickel powder. The pre-sulfurization process is widely used in the prior art, which is to add sulfur raw materials to co-evaporate when preparing nickel powder by evaporation and condensation, so that the sulfur sublimates and cools later than the nickel powder particles, thereby adhering to the surface of the nickel powder; this method has good effects, but there are still disadvantages, such as the uneven distribution of the sulfur content obtained. As we all know, the powder particles prepared by evaporation and condensation follow the normal distribution, and the large and small particles in the obtained raw powder are mixed, which cannot be directly applied to the client with high precision requirements. Therefore, the raw powder obtained after the powder making is generally subjected to multiple process treatments such as screening, grading, and spray drying to distinguish the powders of each particle size range; and in this process, the surface state of the sulfur-added nickel powder obtained by the pre-sulfurization process will be destroyed, resulting in uneven distribution, missing, and peeling of sulfur on the particle surface, and the final yield rate becomes low. In addition, since the fine powder has a larger specific surface area and a relatively higher sulfur content, there will be a difference in the sulfur content between the coarse powder and the fine powder obtained after classification, which deviates from the sulfur content design indicator of the previous sulfur addition process and leads to rework and other situations. Summary of the invention

[0004] In view of the problems in the background technology, the present invention develops a method for sulfurizing nano-grade nickel powder and the sulfurized nickel powder prepared therefrom, and adopts a post-sulfurization method to effectively improve the yield and reduce the development cost.

[0005] To achieve the above object, the present invention adopts the following technical solution: The method for adding sulfur to nano-grade nickel powder is carried out in a reaction kettle and a rotary kiln which are connected in an airtight manner through a pipeline, wherein the reaction kettle is provided with a carrier gas inlet and the rotary kiln is provided with a carrier gas outlet; The specific steps include: (1) placing a sulfur source in a reaction kettle and placing nickel powder in a rotary kiln; (2) Under a carrier gas protection atmosphere, the reaction kettle and the rotary kiln are heated to the required temperature respectively, and the sulfur-containing vapor obtained from the sulfur source is introduced into the rotary kiln through the carrier gas to contact with the nickel powder, thereby completing the sulfur addition process; (3) Keep the carrier gas flowing and cool the reactor and the rotary kiln to room temperature to obtain sulfur-added nano-sized nickel powder.

[0006] Preferably, in step (1), the sulfur source is at least one of sublimated sulfur, sulfur dioxide, sulfur trioxide, carbon disulfide, hydrogen sulfide, methyl mercaptan, methyl sulfide, ethyl mercaptan, ethyl sulfide, and thiourea; in step (2), the carrier gas is one of helium, argon, nitrogen, neon, and krypton, and the flow rate of the carrier gas is 0.5-10 Nm 3 / h; the temperature of the reactor is not less than 200°C, the temperature of the rotary kiln is 150-1200°C; the rotation speed ω of the rotary kiln is 0.5-60rpm.

[0007] Preferably, a heat-insulating layer is provided on the outside of the pipeline connecting the reactor and the rotary kiln to ensure that the sulfur-containing vapor effectively reacts when it enters the rotary kiln and contacts the surface of the nickel powder.

[0008] Preferably, in step (2), before the carrier gas is introduced, vacuum is firstly applied to make the absolute pressure inside the reactor and the rotary kiln no higher than 10 kPa, so as to prevent the oxidizing gas in the air from affecting the sulfur addition process; the above vacuum step can be repeated 2-3 times according to the specific situation.

[0009] Preferably, in step (2), the heating method of the heating kettle is at least one of resistance heating, electromagnetic induction heating, arc heating, microwave heating, infrared heating, and laser heating. The heating method is selected according to the different states of the sulfur source to ensure that the sulfur-containing vapor obtained from the sulfur source can react smoothly with the nickel powder. For example, when the sulfur source is a solid such as sublimated sulfur, arc plasma or laser heating can be selected to ensure the evaporation or decomposition of the sulfur source in the crucible to form the required sulfur-containing vapor. When the sulfur source is a gas such as hydrogen sulfide, resistance heating or magnetic induction coil heating can be selected to ensure the stability of the atmosphere temperature of the reactor. Generally, multiple heating methods can be used in combination.

[0010] Preferably, in step (2), the rotation speed ω and the filling rate φ of the rotary kiln satisfy the following relationship: 0.5≤ω≤30 / (0.55-φ) 1 / 2 rpm, the filling rate here refers to the ratio of the volume of nickel powder to the effective volume of the rotary kiln; when the rotary kiln rotates too fast, the nickel powder will adhere to the inner wall of the rotary kiln due to the influence of centrifugal force, affecting the contact reaction with sulfur-containing vapor, and the difference in the average particle size and bulk density of the nickel powder will also affect the centrifugal movement of the nickel powder in the rotary kiln.

[0011] Preferably, in step (2), when the sulfur source is sublimated sulfur, the hot spot temperature of the reactor is not less than 445°C, the atmosphere temperature is not less than 300°C, and the temperature of the rotary kiln is not less than 200°C.

[0012] Preferably, in step (3), an oxidizing gas is introduced while the carrier gas is introduced; the oxidizing gas is air or oxygen, and the flow rate of the oxidizing gas is 0.01-0.15 Nm 3 / h; through the above operation, the outer surface of the nickel powder is passivated to form an oxide layer, which can improve the oxidation resistance and dispersibility of the nickel powder.

[0013] The present invention also provides a sulfur-added nickel powder prepared by the method as described above, wherein the particles of the sulfur-added nickel powder are spherical, with a particle size of 10-200nm and a sulfur content of 100-1500ppm. Sulfur exists on the surface of the sulfur-added nickel powder in the form of a coating layer having sulfur-containing compounds, and the thickness of the coating layer is 2-8nm.

[0014] Preferably, the sulfur-containing compound is nickel sulfide.

[0015] Preferably, the coating layer further comprises nickel oxide, such as nickel oxide, nickel hydroxide, nickel carbonate, etc.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The configuration of the present invention can ensure that the nickel powder in the rotary kiln is in a dispersed state when in contact with the sulfur-containing vapor, and the particle surface can react / adsorb in all directions, ensuring that the sulfur element is evenly distributed and stably present on the surface of the nickel powder, and is not easily affected by common physical or chemical factors and causes changes in the sulfur content.

[0017] (2) The present invention can control the added sulfur content, and the obtained sulfur-added nickel powder is the finished product, which does not cause the sulfur content of the nickel powder to change due to the subsequent post-treatment steps as in the previous sulfur addition process.

[0018] (3) The present invention has lower production costs, and the process is flexible in adjusting the sulfur content of the product and developing products of different specifications (100-1500ppm), especially in trace addition, i.e., <1000ppm, and the process batch processing cycle is fast. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the device of the present invention.

[0020] Figure 2 This is the EDS energy spectrum of the sample obtained in Example 1. DETAILED DESCRIPTION

[0021] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0022] like Figure 1 As shown, the sulfur addition method of the nano-grade nickel powder of the present invention, through the selection of the sulfur source and the use of the rotary kiln, makes the sulfur element react with the nickel powder and uniformly adhere to the surface of the powder. The sulfur addition method is carried out in a reactor 1 and a rotary kiln 2 which are successively connected in an airtight manner through a pipeline, the reactor 1 is provided with a carrier gas inlet, a flow meter 3 is installed on the pipeline connecting the carrier gas inlet and the reactor, the rotary kiln 2 is provided with a carrier gas outlet, and an insulation layer is provided on the outer side of the pipeline connecting the reactor and the rotary kiln; specifically, the following operating steps are included: (1) placing a sulfur source in a reaction kettle and placing nickel powder in a rotary kiln; the sulfur source is at least one of sublimated sulfur, sulfur dioxide, sulfur trioxide, carbon disulfide, hydrogen sulfide, methyl mercaptan, methyl sulfide, ethyl mercaptan, ethyl sulfide, and thiourea.

[0023] (2) Before the carrier gas is introduced, the reactor and the rotary kiln are first evacuated to a vacuum so that the absolute pressure inside is not higher than 10 kPa; under the protective atmosphere of the carrier gas, the reactor and the rotary kiln are respectively heated to the required temperature, and the sulfur-containing vapor obtained from the sulfur source is introduced into the rotary kiln through the carrier gas to contact with the nickel powder to complete the sulfur addition process; the carrier gas is one of helium, argon, nitrogen, neon, and krypton, and the flow rate of the carrier gas is 0.5-10 Nm 3 / h; the temperature of the reactor is not less than 200°C, the temperature of the rotary kiln is 150-1200°C; the rotation speed ω of the rotary kiln is 0.5-60rpm.

[0024] (3) Keep the carrier gas flowing in and cool the reactor and the rotary kiln to room temperature to obtain the sulfur-added nano-sized nickel powder; while keeping the carrier gas flowing in, introduce an oxidizing gas; the oxidizing gas is air or oxygen, and the flow rate of the oxidizing gas is 0.01-0.15 Nm 3 / h.

[0025] Example 1 In this embodiment, sulfur is added to a batch of 180nm spray-dried spherical nickel powders, with a target sulfur content of 1000ppm. The reactor used is a muffle furnace, and a non-transferred arc plasma torch is provided above the crucible of the muffle furnace. The specific operating steps are as follows: (1) Preparation: Complete the equipment startup inspection, including appearance, power supply and grounding, fastening and airtightness, control panel and indicator device, etc.; then sieve the sublimated sulfur with an 80-mesh screen to remove impurity particles; (2) Feeding: Weigh 85 g of sublimated sulfur and place it in a crucible in a muffle furnace; weigh 80 kg of nickel powder and add it into a rotary furnace. During the powder addition, let the rotary furnace rotate slowly with the speed set to 5 rpm. After the powder addition is completed, close the feed port. Under this load, the filling rate φ of the rotary furnace is about 30%; (3) Ventilation: Vacuum the equipment until the internal pressure is 5-10 kPa, then open the nitrogen valve for ventilation and control the nitrogen flow rate at 10 Nm 3 / h, air intake time 5 minutes; repeat this step after the above operation is completed; (4) Sulfur addition: Turn on the equipment heating power supply, set the muffle furnace temperature to 300°C, the rotary furnace temperature to 210°C, and the rotary furnace wall temperature to 260°C; after the equipment is heated up, turn on the non-transferred arc plasma torch to evaporate the sublimated sulfur, and control the nitrogen flow rate at 10 Nm 3 / h, the rotary kiln speed is adjusted to 60 rpm, and the temperature is kept at 200-240℃ for 2 hours; (5) After the sulfur addition is completed, air is introduced into the rotary kiln and the air flow rate is adjusted to 0.15 Nm 3 / h, turn off the power of the equipment and let it cool naturally. After the end, samples were taken from the front section (denoted as 1-1), middle section (denoted as 1-2), rear section (denoted as 1-3) and furnace wall (denoted as 1-4) of the rotary furnace to obtain four components. The specific test data of each component are shown in Table 1: Table 1 180nm sulfur-added nickel powder test data It can be seen from the data in the table that a uniform reaction between sulfur-containing vapor and nickel can be achieved through a rotary kiln. After the same batch of nickel powder undergoes a sulfurization reaction in a rotary kiln, there is no significant difference in the sulfur content of the nickel powder obtained at each sampling point.

[0026] In addition, this embodiment also carried out EDS test on the obtained sulfur-added nickel powder, and the obtained image is shown in Figure 2 .Depend on Figure 2 It can be seen that the sulfur element is evenly distributed on the surface of the nickel powder particles, and there is no enrichment or deficiency in individual areas.

[0027] Example 2 In this embodiment, a batch of 80nm spray-dried spherical nickel powders are subjected to sulfur addition and airflow dispersion, with a target sulfur content of 500ppm. The reactor used is a muffle furnace, and the specific operating steps are as follows: (1) Preparation: Complete equipment startup inspection, including appearance, power supply and grounding, fastening and air tightness, control panel and indicator device, etc.; (2) Feeding: Weigh 105 g of sulfur trioxide and place it in a crucible in a muffle furnace; weigh 40 kg of nickel powder and add it into a rotary kiln. During the powder addition, let the rotary kiln rotate slowly with the speed set to 5 rpm. After the powder addition is completed, close the feed port. Under this load, the filling rate φ of the rotary kiln is about 18%; (3) Ventilation: Vacuum the equipment until the internal pressure is less than 1 kPa, then open the nitrogen valve for ventilation and control the nitrogen flow rate at 10 Nm 3 / h, air intake time 5 minutes; repeat this step after the above operation is completed; (4) Sulfur addition: Turn on the equipment heating power, set the muffle furnace temperature to 200°C, the rotary furnace temperature to 150°C, and the rotary furnace wall temperature to 220°C; after the equipment is heated up, control the nitrogen flow rate at 5 Nm 3 / h, the rotary kiln speed is adjusted to 40 rpm, and the temperature is kept at 150-200℃ for 2 hours; (5) After the sulfur addition is completed, switch the air intake to air and adjust the air flow rate to 0.01 Nm 3 / h, turn off the power of the equipment and let it cool naturally. After the end, take a sample to obtain the sulfur-added 80nm nickel powder (recorded as 2-1); (6) The sulfur-added 80 nm nickel powder obtained in the previous step was broken up by a jet mill to obtain a sulfur-added 80 nm nickel powder (denoted as 2-2). The specific test data of the obtained powder are shown in Table 2: Table 2 80nm nickel powder sulfur addition data It can be seen from the data in the table that the sulfur-added nickel powder obtained by rotary kiln treatment has good dispersibility, and the difference in dispersion degree of the powder before and after breaking up is small; in addition, the state of sulfur element on the surface of sulfur-added nickel powder particles is stable, and even if air flow milling is used to cause strong collision and friction of particles for physical dispersion, it is not easy for sulfur on the surface of particles to desorb or detach.

[0028] Example 3 In this embodiment, a batch of 200nm spray-dried spherical nickel powders were subjected to sulfur addition and airflow dispersion, with a target sulfur content of 100ppm. The reactor used was a conventional reactor with a heating jacket, and the specific operating steps were as follows: (1) Preparation: Complete the equipment startup inspection, including appearance, power supply and grounding, fastening and air tightness, control panel and indicator device, etc.; (2) Feeding: Connect the hydrogen sulfide gas source to the reactor; weigh 80 kg of nickel powder and add it into the rotary kiln. During the powder adding process, let the rotary kiln rotate slowly with the speed set to 5±0.3 rpm. After the powder adding is completed, close the feed port. Under this load, the filling rate φ of the rotary kiln is about 30%; (3) Ventilation: Vacuum the equipment until the internal pressure is 5-10 kPa, then open the nitrogen valve for ventilation and control the nitrogen flow rate at 10 Nm 3 / h, air intake time 5 minutes; repeat this step after the above operation is completed; (4) Sulfur addition: Turn on the equipment heating power supply, set the reactor temperature to 200°C, the rotary furnace temperature to 250°C, and the rotary furnace wall temperature to 300°C; after the equipment is heated up, control the nitrogen flow rate at 1.5 Nm 3 / h, the hydrogen sulfide gas flow rate is controlled at 1.5 Nm 3 / h, the rotary kiln speed is adjusted to 0.5 rpm, and the temperature is kept constant for 4 hours, during which the temperature in the rotary kiln is controlled at 240-270℃; (5) After the sulfur addition is completed, switch the air intake to air and adjust the air flow rate to 0.1 Nm 3 / h, turn off the power of the equipment and let it cool naturally. After the end, sulfur-added 200nm nickel powder is obtained.

[0029] Example 4 This embodiment is basically the same as Embodiment 2, except that the sulfur source used is carbon disulfide and the carrier gas used is argon.

[0030] Example 5 This embodiment is basically the same as Embodiment 2, except that the sulfur source used is methyl sulfide and the carrier gas used is krypton gas.

[0031] Example 6 This embodiment is substantially the same as embodiment 2, except that the sulfur source used is ethyl mercaptan.

[0032] Example 7 This embodiment is basically the same as embodiment 2, except that the sulfur source used is ethyl sulfide.

[0033] Example 8 This embodiment is basically the same as embodiment 2, except that the sulfur source used is thiourea.

[0034] Example 9 This embodiment is basically the same as Embodiment 3, except that the sulfur source used is sulfur dioxide, and the carrier gas used is helium.

[0035] Example 10 This embodiment is basically the same as embodiment 3, except that the sulfur source used is methyl mercaptan and the carrier gas used is neon.

[0036] Effect Example 1 In order to verify the stability of the distribution state of sulfur element on the surface of nickel powder, in addition to physical factors (the effect part of Example 2), this effect example uses strong acids such as sulfuric acid and alcohol to clean the surface of nickel powder with various sulfur contents obtained by applying the present invention, and determines whether the distribution amount of sulfur element changes due to chemical reactions. The results are shown in Table 4.

[0037] Table 4 Comparison of sulfur content of sulfur-added nickel powder after surface cleaning As shown in Table 4, the sulfur content on the surface of the sulfur-added nickel powder obtained by the method of the present invention is relatively stable, and the sulfur content will not change due to the influence of strong acid or conventional organic solvents.

[0038] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for adding sulfur to nano-grade nickel powder, characterized in that: The sulfur addition method is carried out in a reaction kettle and a rotary kiln which are connected in an airtight manner through a pipeline, wherein the reaction kettle is provided with a carrier gas inlet and the rotary kiln is provided with a carrier gas outlet; The specific steps include: (1) placing a sulfur source in a reaction kettle and placing nickel powder in a rotary kiln; (2) Under a carrier gas protection atmosphere, the reaction kettle and the rotary kiln are heated to the required temperature respectively, and the sulfur-containing vapor obtained from the sulfur source is introduced into the rotary kiln through the carrier gas to contact with the nickel powder, thereby completing the sulfur addition process; (3) Keep the carrier gas flowing and cool the reactor and the rotary kiln to room temperature to obtain sulfur-added nano-sized nickel powder.

2. The method for adding sulfur to nano-grade nickel powder as claimed in claim 1, wherein: In step (2), before the carrier gas is introduced, vacuum is first drawn to ensure that the absolute pressure inside the reactor and the rotary kiln is no higher than 10 kPa.

3. The sulfur adding method of nano nickel powder as claimed in claim 2, characterized in that: In step (1), the sulfur source is at least one of sublimated sulfur, sulfur dioxide, sulfur trioxide, carbon disulfide, hydrogen sulfide, methyl mercaptan, methyl sulfide, ethyl mercaptan, ethyl sulfide, and thiourea; the carrier gas is one of helium, argon, nitrogen, neon, and krypton, and the flow rate of the carrier gas is 0.5-10 Nm 3 / h; the temperature of the reactor is not less than 200°C, and the temperature of the rotary kiln is 150-1200°C.

4. The method for adding sulfur to nano-grade nickel powder as claimed in claim 3, characterized in that: In step (2), when the sulfur source is sublimated sulfur, the hot spot temperature of the reactor is not less than 445°C, the atmosphere temperature is not less than 300°C, and the temperature of the rotary kiln is not less than 200°C.

5. The method for adding sulfur to nano-grade nickel powder as claimed in claim 3, characterized in that: In step (2), the rotation speed ω of the rotary kiln is 0.5-60 rpm, and the rotation speed ω and the filling rate φ satisfy the following relationship: 0.5≤ω≤30 / (0.55-φ) 1 / 2 rpm.

6. The method for adding sulfur to nano-grade nickel powder as claimed in claim 3, characterized in that: In the step (3), an oxidizing gas is introduced while the carrier gas is introduced; the oxidizing gas is air or oxygen, and the flow rate of the oxidizing gas is 0.01-0.15 Nm3 / h.

7. The method for adding sulfur to nano-grade nickel powder as claimed in claim 1, characterized in that: The outer side of the pipeline connecting the reactor and the rotary kiln is provided with a heat-insulating layer.

8. A sulfur-added nickel powder prepared by the sulfur-added method for nano-grade nickel powder according to any one of claims 1 to 7, characterized in that: The sulfur-added nickel powder is spherical particles with a particle size of 10-200nm and a sulfur content of 100-1500ppm. Sulfur exists on the surface of the sulfur-added nickel powder in the form of a coating layer with sulfur-containing compounds, and the thickness of the coating layer is 2-8nm.

9. The sulfur-added nickel powder according to claim 8, characterized in that: The sulfur-containing compound is nickel sulfide.

10. The sulfur-added nickel powder according to claim 9, characterized in that: The coating layer further comprises nickel oxide.

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