Preparation method of silver powder with low ignition loss

Abstract

The invention discloses a preparation method of silver powder with low ignition loss, and belongs to the technical field of powder metallurgy. The preparation method comprises the following steps that silver powder is cleaned with deionized water under the heating condition, a settling agent is added into a water washing system, and ultrasonic treatment is assisted; the silver powder is cleaned with absolute ethyl alcohol under the normal temperature condition; the cleaned silver powder is subjected to vacuum gradient drying, the temperature ranges from 40 DEG C to 80 DEG C, the vacuum degree ranges from-0.06 MPa to-0.1 MPa, the time ranges from 3 h to 6 h, and the heating speed ranges from 1 DEG C / min to 4 DEG C / min; and the completely dried silver powder is blended with a silane coupling agent, the adding amount of the silane coupling agent is 0.2-2.0% of the mass of the silver powder, and the target low-ignition-loss silver powder is obtained. According to the preparation method, impurities on the surface of the silver powder are thoroughly removed by precisely regulating and controlling the cleaning, drying and surface treatment processes, the dispersity and sintering activity of the silver powder are improved, the ignition loss of the prepared silver powder in the high-temperature sintering process is smaller than 0.5%, and the preparation method is particularly suitable for the fields of high-temperature sintered electronic packaging, conductive coatings and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder metallurgy, and particularly relates to a method for preparing silver powder with low loss on ignition. Background Art

[0002] Silver powder is prone to loss during high-temperature sintering because impurities in the silver powder (such as Cl - , S 2- ) are prone to form volatile compounds at high temperatures. When the silver powder contains an organic dispersant, it will volatilize at high temperatures, resulting in mass loss and generating pores or contamination at the same time. The mass loss of silver powder during sintering will directly affect its final performance and application reliability, such as insufficient sintering densification, reduced mechanical strength, and decreased electrical conductivity. Based on this, the present invention aims to provide a method for preparing silver powder with low loss on ignition based on a composite cleaning and drying system and surface modification treatment, to improve the dispersibility and sintering activity of silver powder, reduce the loss on ignition of silver powder during high-temperature sintering, and meet the application requirements in fields such as electronic packaging and conductive coatings. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing silver powder with low loss on ignition.

[0004] The purpose of the present invention is achieved as follows: The method for preparing silver powder with low loss on ignition includes the following steps: Washing the silver powder with deionized water under heating conditions, adding a sedimentation agent to the water washing system, and assisting with ultrasonic treatment; Washing the silver powder with absolute ethanol at room temperature; The washed silver powder is dried by vacuum gradient drying, with a temperature of 40 - 80 °C, a vacuum degree of -0.06 - -0.1 MPa, a time of 3 - 6 h, and a heating rate of 1 - 4 °C / min; Mixing the completely dried silver powder with a silane coupling agent, and the addition amount of the silane coupling agent is 0.1 - 1.0% of the mass of the silver powder, thus obtaining the target silver powder with low loss on ignition.

[0005] Compared with the prior art, the technical solution of the present invention has the following advantages: Sodium dodecyl sulfate added to the water washing system in the technical solution of the present invention can adsorb on the surface of silver powder to form an electrostatic repulsion barrier, making the silver powder evenly dispersed in water. Polyethylene glycol can adjust the sedimentation rate of silver powder to achieve precise control of first dispersion and then sedimentation. The impact force formed when the cavitation bubbles generated by ultrasonic treatment burst can peel off the impurities on the surface of silver powder, and the accompanying ultrasonic shear force can break the agglomeration of particles, having an auxiliary dispersion effect. Combining with the pulsed ultrasonic mode can avoid over-dispersion and make it difficult to filter.

[0006] The silver powder after cleaning is dried by vacuum gradient drying. While achieving thorough drying, it can gradually decompose or volatilize the impurities remaining after alcohol washing, avoiding contamination and affecting the sintering conductivity. The temperature-varying treatment is also beneficial to optimizing the crystal nucleus size and regulating the particle morphology. In the low-temperature stage, it mainly makes the crystal nuclei of the silver powder contract orderly, avoiding crystal nucleus distortion and further causing particle fragmentation. In the high-temperature stage, it can promote the rearrangement of surface atoms of the silver powder crystal nuclei, while reducing the inter-particle force and preventing silver powder agglomeration.

[0007] The dried silver powder is surface chemically modified with a silane coupling agent, further enhancing the dispersibility and sintering activity of the silver powder, delaying oxidation during the sintering process, and reducing the interface resistance at the same time. The loss on ignition of the finally prepared silver powder during the high-temperature sintering process is <0.5%, which is especially suitable for fields such as high-temperature sintered electronic packaging and conductive coatings. Specific embodiments

[0008] The present invention will be further described below, but it is not limited to the present invention in any way. Any transformation or replacement based on the teachings of the present invention belongs to the protection scope of the present invention.

[0009] The preparation method of the low-loss-on-ignition silver powder includes the following steps: Clean the silver powder with deionized water under heating conditions. A sedimentation agent is added to the water washing system, and ultrasonic treatment is supplemented to improve the cleaning effect and remove impurities and organic substances on the surface of the silver powder; Clean the silver powder with absolute ethanol under normal temperature conditions to fully remove the remaining water, sedimentation agent and other impurities after water washing; The cleaned silver powder is dried by vacuum gradient drying at a temperature of 40-80 °C, a vacuum degree of -0.06 to -0.1 MPa, a time of 3-6 h, and a heating rate of 1-4 °C / min to control the formation of crystal nuclei, improve the drying uniformity and the sintering performance of the silver powder; Mix the completely dried silver powder with a silane coupling agent to enhance the dispersibility and sintering activity of the silver powder. Silicon enhances its high-temperature sintering performance. The addition amount of the silane coupling agent is 0.2-2.0% of the mass of the silver powder, and the target low-loss-on-ignition silver powder is obtained.

[0010] The particle size of the silver powder is 1 μm.

[0011] The temperature of the water washing is 40-60 °C, and the time is 2-3 h.

[0012] The mass ratio of the silver powder to deionized water is 1:2.5-1:3.

[0013] The sedimentation agent is any one or two of sodium dodecyl sulfate and polyethylene glycol. The molecular weight of polyethylene glycol is 400-2000, and the addition amount of the sedimentation agent is 0.1-0.3% of the mass of the silver powder.

[0014] The frequency of the ultrasonic treatment is 80 - 120 kHz, and the power density is 50 - 150 W / L. Pulse ultrasonic mode can be adopted for the ultrasonic treatment.

[0015] The time for ethanol cleaning is 25 - 35 min, preferably 30 min.

[0016] The mass ratio of the silver powder to absolute ethanol is 1:1 - 1:2.

[0017] The vacuum gradient drying includes: a low - temperature stage at 40 - 50 °C, a vacuum degree of - 0.06 - - 0.08 MPa, a time of 1 - 2 h, and a heating rate of 1 - 2 °C / min; a medium - temperature stage at 50 - 65 °C, a vacuum degree of - 0.08 - - 0.09 MPa, a time of 1.5 - 3 h, and a heating rate of 1 - 2 °C / min; a high - temperature stage at 65 - 80 °C, a vacuum degree of - 0.09 - - 0.1 MPa, a time of 0.5 - 1 h, and a heating rate of 2 - 4 °C / min.

[0018] The silane coupling agent is any one of amino - silane, epoxy - silane, and vinyl - silane.

[0019] The loss on ignition of the low - loss - on - ignition silver powder during high - temperature sintering is < 0.5%.

[0020] The high temperature is 600 - 900 °C.

[0021] Example 1

[0022] Using self - made silver powder as raw material, with a particle size of 1 μm.

[0023] Washing the silver powder with deionized water at 50 °C for 2.5 h, the mass ratio of the silver powder to deionized water is 1:3. First, add sodium dodecyl sulfate into the water - washing system at 0.1% of the silver powder mass, then add polyethylene glycol (molecular weight 400) into the water - washing system at 0.1% of the silver powder mass. Both are used as sedimentation agents, and ultrasonic treatment is supplemented, with a frequency of 100 kHz, a power density of 100 W / L, and pulse ultrasonic mode. Recover the washed silver powder by filtration and remove the cleaning solution.

[0024] Washing the silver powder with absolute ethanol at room temperature for 30 min, the mass ratio of the silver powder to absolute ethanol is 1:1.5. Then recover the washed silver powder by filtration.

[0025] The washed silver powder is dried by vacuum gradient drying. The low - temperature stage is at 45 °C, the vacuum degree is - 0.07 MPa, the time is 1.5 h, and the heating rate is 1 °C / min; the medium - temperature stage is at 60 °C, the vacuum degree is - 0.09 MPa, the time is 2 h, and the heating rate is 1 °C / min; the high - temperature stage is at 75 °C, the vacuum degree is - 0.1 MPa, the time is 1 h, and the heating rate is 3 °C / min.

[0026] Mix the completely dry silver powder with an epoxy-based silane coupling agent. The addition amount of the silane coupling agent is 1.0% of the mass of the silver powder, and the target silver powder with low loss on ignition is obtained. After sintering treatment at 750 °C, the loss on ignition of the silver powder is 0.2%.

[0027] Example 2

[0028] The source and particle size of the silver powder are the same as those in Example 1.

[0029] Wash the silver powder with deionized water at 40 °C for 3 h. The mass ratio of the silver powder to deionized water is 1:2.5. Add polyethylene glycol (molecular weight 2000) as a sedimentation agent into the water washing system according to 0.1% of the mass of the silver powder, and assist with ultrasonic treatment, with a frequency of 120 kHz, a power density of 150 W / L, and a pulsed ultrasonic mode. Recover the washed silver powder by filtration and remove the washing liquid.

[0030] Wash the silver powder with absolute ethanol at room temperature for 25 min. The mass ratio of the silver powder to absolute ethanol is 1:2. Then recover the washed silver powder by filtration.

[0031] The washed silver powder is dried by vacuum gradient drying. The low-temperature section is 40 °C, the vacuum degree is -0.08 MPa, the time is 1 h, and the heating rate is 1 °C / min; the medium-temperature section is 50 °C, the vacuum degree is -0.09 MPa, the time is 1.5 h, and the heating rate is 1 °C / min; the high-temperature section is 65 °C, the vacuum degree is -0.1 MPa, the time is 0.5 h, and the heating rate is 2 °C / min.

[0032] Mix the completely dry silver powder with a vinyl-based silane coupling agent. The addition amount of the silane coupling agent is 0.5% of the mass of the silver powder, and the target silver powder with low loss on ignition is obtained. After sintering treatment at 800 °C, the loss on ignition of the silver powder is 0.4%.

[0033] Example 3

[0034] The source and particle size of the silver powder are the same as those in Example 1.

[0035] Wash the silver powder with deionized water at 60 °C for 2 h. The mass ratio of the silver powder to deionized water is 1:3. Add sodium dodecyl sulfate as a sedimentation agent into the water washing system according to 0.3% of the mass of the silver powder, and assist with ultrasonic treatment, with a frequency of 80 kHz, a power density of 50 W / L, and a pulsed ultrasonic mode. Recover the washed silver powder by filtration and remove the washing liquid.

[0036] Wash the silver powder with absolute ethanol at room temperature for 35 min. The mass ratio of the silver powder to absolute ethanol is 1:1. Then recover the washed silver powder by filtration.

[0037] The cleaned silver powder is dried by vacuum gradient drying. The low-temperature section is at 50°C, the vacuum degree is -0.06 MPa, the time is 2 h, and the heating rate is 2°C / min; the medium-temperature section is at 65°C, the vacuum degree is -0.08 MPa, the time is 3 h, and the heating rate is 2°C / min; the high-temperature section is at 80°C, the vacuum degree is -0.09 MPa, the time is 1 h, and the heating rate is 4°C / min.

[0038] The completely dried silver powder is blended with an amino-silane coupling agent. The addition amount of the silane coupling agent is 1.5% of the mass of the silver powder, and thus the target silver powder with low loss on ignition is obtained. After sintering treatment at 850°C, the loss on ignition of the silver powder is 0.2%.

Claims

1. A method for preparing low loss on ignition silver powder, characterized in that: The steps include: The silver powder is washed with deionized water under heating conditions, a sedimentation agent is added to the washing system, and ultrasonic treatment is performed; Wash the silver powder with anhydrous ethanol at room temperature; The cleaned silver powder is dried in a vacuum gradient at a temperature of 40-80°C, a vacuum degree of -0.06-0.1 MPa, a time of 3-6 hours, and a heating rate of 1-4°C / min; The completely dried silver powder is mixed with a silane coupling agent, wherein the amount of the silane coupling agent added is 0.2-2.0% of the mass of the silver powder, and the target silver powder with low ignition loss is obtained.

2. The method for preparing low loss on ignition silver powder according to claim 1, characterized in that: The water washing temperature is 40-60°C and the washing time is 2-3h.

3. The method for preparing low loss on ignition silver powder according to claim 1, characterized in that: The mass ratio of the silver powder to deionized water is 1:2.5-1:

3.

4. The method for preparing low loss on ignition silver powder according to claim 1, characterized in that: The precipitant is any one or both of sodium lauryl sulfate and polyethylene glycol.

5. The method for preparing low ignition loss silver powder according to claim 1, characterized in that: The frequency of the ultrasonic treatment is 80-120 kHz, and the power density is 50-150 W / L.

6. The method for preparing low loss on ignition silver powder according to claim 1, characterized in that: The ethanol cleaning time is 30 minutes.

7. The method for preparing low loss on ignition silver powder according to claim 1, characterized in that: The mass ratio of the silver powder to anhydrous ethanol is 1:1-1:

2.

8. The method for preparing low loss on ignition silver powder according to claim 1, characterized in that: The vacuum gradient drying includes: a low temperature section of 40~50°C, a vacuum degree of -0.06~-0.08MPa, a time of 1~2h, and a heating rate of 1~2°C / min; a medium temperature section of 50~65°C, a vacuum degree of -0.08~-0.09MPa, a time of 1.5~3h, and a heating rate of 1~2°C / min; a high temperature section of 65~80°C, a vacuum degree of -0.09~-0.1MPa, a time of 0.5~1h, and a heating rate of 2~4°C / min.

9. The method for preparing low loss on ignition silver powder according to claim 1, characterized in that: The silane coupling agent is any one of aminosilane, epoxysilane and vinylsilane.

10. The method for preparing low loss on ignition silver powder according to claim 1, characterized in that: The ignition loss of the low ignition loss silver powder during high temperature sintering is less than 0.5%.