A method for preparing lead-ruthenate based on acidithiobacillus ferrooxidans mediation

Abstract

The application relates to the technical field of electronic material preparation, and particularly discloses a lead-ruthenate preparation method based on acidithiobacillus ferrooxidans mediation. The application takes soluble lead salt and soluble ruthenium salt as raw materials, utilizes the biological metabolic characteristics of acidithiobacillus ferrooxidans, regulates the oxidation-reduction environment and ion adsorption-deposition behavior of the system, realizes the directional synthesis of a lead-ruthenate precursor under mild conditions, and obtains high-purity and high-crystallinity lead-ruthenate powder through subsequent calcination treatment. The method has the advantages of mild reaction conditions, high raw material utilization rate, controllable product purity, green environmental protection and the like, solves the technical problems of high energy consumption of a traditional high-temperature solid-phase method, easy product agglomeration, complex process of a sol-gel method and high cost, and the prepared lead-ruthenate powder has good application prospects in the fields of thick-film resistors, high-temperature electrode materials and the like.

Description

Technical Field

[0001] This invention belongs to the field of electronic material preparation technology, specifically relating to a green preparation process for lead ruthenate, particularly a biosynthesis method mediated by *Thiobacillus ferrous oxide*, suitable for the large-scale preparation of high-purity lead ruthenate powder. The resulting lead ruthenate powder, as the core functional phase material of back-film resistors, can be used to prepare highly stable and reliable resistive films and electrodes, meeting the manufacturing requirements of back-film resistors in thick-film circuits. Background Technology

[0002] Lead ruthenate (Pb2Ru2O) 6.5 Lead ruthenate (LRU) is a typical pyrochlore-type composite oxide, possessing characteristics such as low resistivity, excellent high-temperature stability, small temperature coefficient of resistance, and strong resistance to electromigration. It is a key functional material for back-film resistors and is widely used in the fabrication of resistive layers and electrodes in thick-film circuits. As a core component of electronic devices, back-film resistors have stringent requirements regarding the purity, grain size uniformity, and conductivity of the functional phase powder, directly determining the resistor's resistance accuracy, stability, and lifespan. Traditional methods for preparing lead ruthenate mainly include high-temperature solid-state methods, sol-gel methods, and hydrothermal synthesis methods.

[0003] Chinese invention patent CN107731340A discloses a conductive phase material for thick-film resistor paste, comprising lead ruthenate; the lead ruthenate comprises at least two of lead ruthenate A, lead ruthenate B, and lead ruthenate C; the lead ruthenate A has an average specific surface area of ​​3-10 m² / g and an average particle size of 30-100 nm; the lead ruthenate B has an average specific surface area of ​​8-26 m² / g and an average particle size of 10-60 nm; and the lead ruthenate C has an average specific surface area of ​​30-80 m² / g and an average particle size of 3-40 nm. This method is simple and low-cost, but it suffers from drawbacks such as high reaction temperature, high energy consumption, easy agglomeration of product particles, uneven crystallinity, and difficulty in controlling purity. When the prepared lead ruthenate powder is applied to post-film resistors, it easily leads to large dispersion and poor stability of the film resistance.

[0004] Japanese invention patent publication number JP2004083577A discloses a method for preparing highly crystalline ruthenium salt powder at low temperatures. The method involves preparing a solution containing a metal alkoxide or organic acid salt, hydrolyzing it to obtain a sol, gelling it, drying it, and then heat-treating it to produce ruthenium salt powder. Compared to traditional solid-state methods, this method can obtain ruthenium salt powder with high crystallinity, uniform particle size, and low agglomeration at low temperatures. However, the raw material costs are high, the process steps are complex, and cracking is prone to occur during the gel drying process, making industrial-scale production difficult.

[0005] US Patent No. 6391267B1 discloses a method for preparing a mixed metal oxide composition. The method includes: hydrothermally treating an aqueous mixture (pH at least about 7) of at least two metal compounds selected from water-soluble ruthenium lead salts, ruthenium lead alkoxides, and ruthenium lead hydroxides to form a hydrated oxide precursor; then, the hydrated oxide precursor yields the mixed ruthenium lead oxide composition. This mixed metal oxide composition can be used as a thick-film resistor material. While the hydrothermal synthesis method can prepare lead ruthenate powder at relatively low temperatures, the reaction requires a high-pressure reactor, demanding sophisticated equipment and stringent reaction conditions. Furthermore, the product is prone to retaining impurity ions, affecting the electrical performance of the final film resistor.

[0006] In recent years, bio-mediated synthesis of functional materials has become a research hotspot in the field of materials preparation due to its advantages such as being environmentally friendly, having mild reaction conditions, and exhibiting good product controllability. *Thiobacillus ferrous oxide* is an acidophilic, chemoautotrophic bacterium that can obtain energy through ferrous oxide ions. Its metabolic processes can alter the redox potential and pH of the system, and the functional groups on the bacterial surface can adsorb metal ions, providing templates for the targeted synthesis of metal oxides. Currently, techniques for preparing simple oxides such as iron oxides and copper oxides using *Thiobacillus ferrous oxide* have been reported. However, its application in the preparation of the pyrochlore-type composite oxide lead ruthenate, specifically meeting the performance requirements of the post-film resistivity, has not yet been disclosed in relevant literature or patents.

[0007] Based on this, the present invention develops a method for preparing lead ruthenate mediated by Thiobacillus ferrous acidophilus. By utilizing the metabolic characteristics of the strain to regulate the deposition process of the precursor, a green synthesis of high-purity lead ruthenate is achieved under mild conditions. The resulting product is adapted to the application requirements of post-membrane resistance and has significant academic value and promising prospects for industrial application.

[0008] Therefore, there is an urgent need for a method to prepare lead ruthenate powder for high-performance composite electronic pastes. Summary of the Invention

[0009] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for preparing lead ruthenate mediated by *Thiobacillus ferrous oxide*. The technical solution adopted by this invention is: a method for preparing lead ruthenate mediated by *Thiobacillus ferrous oxide*, which includes the following steps.

[0010] Step 1: Inoculate the *Thiobacillus ferrous acidophilus* strain into 9K liquid medium, and culture the seed culture by controlling the temperature and adjusting the shaker speed.

[0011] Step 2: Dissolve soluble lead salt and soluble ruthenium salt in deionized water and stir until homogeneous to obtain a mixed salt solution. Add the seed solution prepared in Step 1 to the mixed salt solution, and then adjust the pH of the system with dilute sulfuric acid to obtain the precursor reaction system.

[0012] Step 3: Place the precursor reaction system in a shaker and shake it to react. Monitor the pH value of the system daily during the reaction. After the reaction is completed, a brown lead ruthenate precursor precipitate is formed in the system.

[0013] Step 4: Centrifuge the reaction mixture and collect the solid precipitate; wash the precipitate with deionized water and anhydrous ethanol in sequence until the pH of the washing solution is neutral and no sulfate ions are detected in the washing solution.

[0014] Step 5: Place the washed precursor precipitate in a vacuum drying oven to dry it, and obtain lead ruthenate precursor powder; place the precursor powder in an alumina crucible and calcine it in a muffle furnace in stages, and cool it to room temperature in the furnace to obtain high-purity ultrafine lead ruthenate powder.

[0015] Compared to traditional methods for preparing lead ruthenate, the lead ruthenate prepared by *Thiobacillus ferrous oxide* is micron-sized and uniform in particle size. The key lies in the precise regulation of nucleation and growth of crystal nuclei by the bacterial biotemplate effect and metabolic processes. Specifically, there are two crucial reasons: First, the spatial confinement effect of the biotemplate: the cells of *Thiobacillus ferrous oxide* (mostly micron-sized) can serve as templates for the adsorption and deposition of ruthenium and lead ions. Ions preferentially accumulate at active sites on the cell surface (such as carboxyl and hydroxyl groups in the cell wall), confining the formed crystal nuclei within the micron-sized space on or around the cell surface, directly determining the final product's micron-sized particle size range. Second, the synchronous regulation of nucleation and growth: the bacterial metabolic process slowly regulates the pH and redox potential of the system, enabling the synchronous and abundant generation of lead ruthenate crystal nuclei in a short time, with a gentle and uniform growth rate in the subsequent stages. Simultaneously, the extracellular polymeric substances (EPS) secreted by the bacteria can coat the crystal nuclei, inhibiting excessive crystal growth and aggregation, ultimately forming uniform micron-sized particles.

[0016] The above-mentioned method for preparing lead ruthenium based on *Thiobacillus ferrooxidans* mediated by *Thiobacillus ferrooxidans* includes the preparation of the *Thiobacillus ferrooxidans* seed culture in step one: *Thiobacillus ferrooxidans* strain is inoculated into 9K liquid medium and cultured in a shaker at 10-40℃ and 50-200 r / min for 2-10 days until the bacterial culture reaches OD500. 600The pH value is adjusted to 0.5-2.0 to obtain the seed culture. The components of the 9K liquid culture medium are: (NH4)2SO4 3.0 g / L, KCl 0.1 g / L, K2HPO4 0.5 g / L, MgSO4·7H2O 0.5 g / L, Ca(NO3)2 0.01 g / L, FeSO4·7H2O 44.2 g / L, with the pH value adjusted to 0.5-2.5. This invention obtains the target seed culture by controlling the temperature and adjusting the shaker speed, laying the foundation for the final powder preparation.

[0017] The above-mentioned method for preparing lead ruthenate based on *Thiobacillus ferrous oxide* mediates the following steps: The precursor reaction system in step two is constructed as follows: the lead ion concentration is controlled at 0.05-0.5 mol / L; the seed solution prepared in step one is added to the mixed salt solution, with the seed solution volume accounting for 5%-20% of the total weight of the reaction system; subsequently, the pH of the system is adjusted to 0.5-2.5 with dilute sulfuric acid to obtain the precursor reaction system. This invention ensures optimal conditions for the precursor reaction system by controlling the concentrations of lead and ruthenium ions and the volume of the seed solution, avoiding the generation of byproducts and facilitating the smooth progress of subsequent processes.

[0018] The above-mentioned method for preparing lead ruthenate based on *Thiobacillus ferrous oxide* mediated by *Thiobacillus* comprises the following steps: the precursor deposition process in step three is as follows: the precursor reaction system is placed in a shaker at 10-40℃ and a rotation speed of 50-200 r / min for 2-10 days, during which the pH value of the system is monitored daily. When the pH value rises above 0.2, it is adjusted back to 0.5-2.5 with dilute sulfuric acid. After the reaction is completed, a brown lead ruthenate precursor precipitate is generated in the system, ensuring the mild formation of the precursor and providing conditions for the uniformity and dispersibility of the subsequent lead ruthenate particles.

[0019] In the above-mentioned method for preparing lead ruthenate based on *Thiobacillus ferrous oxide*, the separation and washing of the precursor in step four involves: centrifuging the reaction mixture at a speed of 2000-10000 r / min for 10-30 min, collecting the solid precipitate; washing the precipitate sequentially with deionized water and anhydrous ethanol, repeating the centrifugation operation after each wash until the pH of the washing solution is neutral and no sulfate ions are detected in the washing solution, thus ensuring the purity of the product.

[0020] The above-mentioned method for preparing lead ruthenate based on *Thiobacillus ferrous oxide* involves the drying and calcination of the precursor in step five: the washed precursor precipitate is placed in a vacuum drying oven and dried for 12-36 hours at a temperature of 50-120℃ and a vacuum of -0.08 to -0.1 MPa to obtain lead ruthenate precursor powder; the precursor powder is placed in an alumina crucible and calcined in a muffle furnace in stages: first, the temperature is increased to 300℃ at a heating rate of 5℃ / min and held for 1 hour; then, the temperature is increased to 600-900℃ at a heating rate of 10℃ / min and held for 2-8 hours; the furnace is then cooled to room temperature to obtain high-purity lead ruthenate powder.

[0021] The aforementioned method for preparing lead ruthenate based on *Thiobacillus ferrous oxide* mediated by ferrous acidophilus, wherein the lead ruthenate in step five is characterized by a near-spherical shape, a size of 0.2-3 micrometers, and a pyrochlore structure. This invention prepares lead ruthenate powder for electronic pastes with the aforementioned properties, exhibiting good flowability and viscosity after being made into a paste, making it suitable for use in electronic devices.

[0022] Compared with existing technologies, this invention has the following advantages: 1. The lead ruthenate powder prepared by this invention has a single pyrochlore phase structure, with a particle size concentrated in the range of 0.2-3μm, no hard agglomeration, and a specific surface area of ​​10-30m² / g. When applied to thick film resistor pastes, the powder has good compatibility with glass powder and organic carriers, and the resulting paste has excellent flowability and printability. After calcination, the electrode has high resistance accuracy and a small temperature coefficient, fully meeting the application standards for electronic pastes.

[0023] 2. The entire reaction process of this invention is carried out in an acidic system at room temperature and pressure, with the optimal temperature being only 500-700℃. This reduces energy consumption by more than 30% compared to the traditional solid-phase method. By utilizing the natural template effect of bacterial EPS, there is no need to add organic dispersants or chelating agents, thus avoiding the residue of organic impurities. The purity of the product can reach more than 99%, and the reaction waste liquid can meet the discharge standards after simple neutralization treatment, which is in line with the industry development trend of green manufacturing.

[0024] 3. The EPS secreted by *Thiobacillus ferrous oxide* of this invention is rich in functional groups such as hydroxyl and carboxyl groups, which can react with Pb. 2+ Ru 4+ The formation of molecular-level complexes enables uniform dispersion of the two metal ions, solving the problem of crystal phase defects caused by uneven mixing in traditional solid-state methods, and ensuring the integrity of the product crystal form and stable performance.

[0025] 4. The ferrous acidophilic thiobacillus cultured in this invention has mild and low-cost conditions. The core equipment consists of conventional bioreactors, centrifuges, and muffle furnaces, without the need for special customization. The entire process is highly controllable, the reaction parameters are easy to adjust, and the yield is stable at over 90%. It is suitable for large-scale industrial production and has significant economic and social benefits.

[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0027] Figure 1 This is a flowchart of the preparation method of lead ruthenate based on ferrous acidophilic thiobacillus mediated by the present invention.

[0028] Figure 2 This is a SEM image of lead ruthenate mediated by *Thiobacillus acidophilus* ferrous oxide in Example 1 of the present invention.

[0029] Figure 3 The image shows the XRD pattern of lead ruthenate mediated by *Thiobacillus acidophilus* in Example 1 of this invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. Example 1

[0031] like Figure 1 As shown, this embodiment includes the following steps.

[0032] Step 1: Preparation of *Thiobacillus ferrous acidophilus* seed culture: *Thiobacillus ferrous acidophilus* strain (purchased from the China Center for Type Culture Collection, accession number CCTCC AB202) was inoculated into 9K liquid medium. The components of 9K liquid medium were: (NH4)2SO4 3.0 g / L, KCl 0.1 g / L, K2HPO4 0.5 g / L, MgSO4·7H2O 0.5 g / L, Ca(NO3)2 0.01 g / L, FeSO4·7H2O 44.2 g / L. The pH was adjusted to 1.8 with dilute sulfuric acid. The inoculated medium was placed in a shaker at 30℃ and 130 rpm for 4 days until the bacterial culture OD... 600 When the value reaches 1.0, the seed solution is obtained.

[0033] Step 2, Construction of the precursor reaction system: according to Pb 2+ With Ru 3+ A mixed salt solution was prepared by weighing lead nitrate (analytical grade) and ruthenium trichloride (analytical grade) in a molar ratio of 1:1, dissolving them in deionized water, and stirring until homogeneous. The solution contained Pb... 2+ The concentration was 0.1 mol / L. Seed liquid was added to the mixed salt solution, with the volume of seed liquid accounting for 15% of the total volume of the reaction system. The pH of the system was adjusted to 2.0 with dilute sulfuric acid to obtain the precursor reaction system.

[0034] Step 3: Bio-mediated precursor deposition: The precursor reaction system was placed in a shaker at 28℃ and 110 r / min for 8 days. The pH of the system was monitored daily. When the pH rose to 2.6, it was adjusted back to 2.0 using dilute sulfuric acid. 1.5 g / L of FeSO4·7H2O was added to the system every 24 hours. After the reaction, a brown lead ruthenate precursor precipitate was formed in the system.

[0035] Step 4: Separation and washing of precursors: Place the reaction mixture in a centrifuge and centrifuge at 9000 r / min for 12 min to collect the solid precipitate; wash the precipitate with deionized water and anhydrous ethanol in sequence, repeating the centrifugation operation after each wash until the pH of the washing solution is neutral, and no white precipitate is produced when barium chloride solution is added to the last washing solution, proving that there are no sulfate ions in the washing solution.

[0036] Step 5: Drying and calcining of the precursor: The washed precursor precipitate was placed in a vacuum drying oven and dried at 70℃ and a vacuum of -0.09MPa for 18 hours to obtain lead ruthenate precursor powder. The precursor powder was placed in an alumina crucible and calcined in a muffle furnace in stages: the temperature was increased to 300℃ at 5℃ / min and held for 1 hour; then the temperature was increased to 800℃ at 10℃ / min and held for 3 hours; the furnace was cooled to room temperature to obtain lead ruthenate powder.

[0037] The performance of the obtained product was tested, and the results showed that the lead ruthenate powder had a purity of 99.97%, a grain size of 50-80 nm, a specific surface area of ​​20 m² / g, and a room temperature resistivity of 1.2 × 10⁻⁶. -3 Ω·cm, the performance requirements of thick film resistor materials.

[0038] Figure 2 Here is a SEM image of the lead ruthenate powder prepared in this embodiment. Figure 2 As can be seen, the lead ruthenate powder prepared in this embodiment has a microstructure of dispersed particles with a size of 0.2-3 μm and a pyrochlore structure.

[0039] Figure 3 The XRD pattern of the lead ruthenate powder prepared in this embodiment is shown below. Figure 3 It can be seen that the lead ruthenate prepared in this embodiment has high phase purity and no other impurities. Example 2

[0040] like Figure 1 As shown, this embodiment includes the following steps.

[0041] Step 1: Preparation of *Thiobacillus ferrooxidans* seed culture: Inoculate *Thiobacillus ferrooxidans* strain into 9K liquid medium, adjust the pH to 1.5, and culture at 28℃ and 120 rpm for 5 days until the bacterial culture OD reaches 100%.600 When the value reaches 0.8, the seed solution is obtained.

[0042] Step 2, Construction of the precursor reaction system: according to Pb 2+ With Ru 3+ A molar ratio of 1:1 was used to weigh lead acetate and ruthenium nitrate, dissolve them in deionized water, and prepare a Pb solution. 2+ A mixed salt solution with a concentration of 0.05 mol / L was prepared; 10% by volume of seed liquid was added, and the pH was adjusted to 1.5 to obtain the precursor reaction system.

[0043] Step 3, Bio-mediated precursor deposition: The precursor reaction system was placed in a shaker at 25℃ and 100r / min for 10 days. During this period, the pH value was monitored and adjusted daily, and 1g / L of FeSO4·7H2O was added every 24 hours. After the reaction was completed, a brown precursor precipitate was obtained.

[0044] Step 4: Separation and washing of precursors: Centrifuge at 8000 r / min for 15 min and collect the precipitate; wash with deionized water and anhydrous ethanol until neutral and free of sulfate ions.

[0045] Step 5: Drying and calcining of the precursor: Vacuum drying at 60℃ for 24 hours, segmented calcination in a muffle furnace: holding at 300℃ for 1 hour, holding at 700℃ for 4 hours, and then cooling to room temperature with the furnace.

[0046] Product testing results: purity 99.5%, grain size 60-90 nm, specific surface area 15 m² / g, room temperature resistivity 1.5 × 10⁻⁶ -3 Ω·cm.

[0047] Comparing the test results of lead ruthenate prepared in this embodiment with those of Example 1, it can be seen that the powder particle size and morphology are not significantly different, and the pyrochlore structure remains unchanged. Example 3

[0048] like Figure 1 As shown, this embodiment includes the following steps.

[0049] Step 1: Preparation of *Thiobacillus ferrooxidans* seed culture: Inoculate *Thiobacillus ferrooxidans* strain into 9K liquid medium, adjust the pH to 2.0, and culture at 32℃ and 150 rpm for 3 days until the bacterial culture reaches OD500. 600 When the value reaches 1.2, the seed solution is obtained.

[0050] Step 2, Construction of the precursor reaction system: according to Pb 2+ With Ru 3+ A molar ratio of 1:1 was used to weigh lead nitrate and ruthenium trichloride to prepare Pb. 2+A mixed salt solution with a concentration of 0.2 mol / L was prepared; 20% by volume of seed liquid was added, and the pH was adjusted to 2.5 to obtain the precursor reaction system.

[0051] Step 3, biologically mediated precursor deposition: The precursor reaction system was placed in a shaker at 30℃ and 120r / min for 7 days. During this period, the pH value was monitored and adjusted daily, and 2g / L of FeSO4·7H2O was added every 24h. After the reaction was completed, a brown precursor precipitate was obtained.

[0052] Step 4: Separation and washing of precursors: Centrifuge at 10000 r / min for 10 min and collect the precipitate; wash with deionized water and anhydrous ethanol until neutral and free of sulfate ions.

[0053] Step 5: Drying and calcining of the precursor: Vacuum drying at 80℃ for 12 hours, segmented calcination in a muffle furnace: holding at 300℃ for 1 hour, holding at 900℃ for 2 hours, and then cooling to room temperature with the furnace.

[0054] Product testing results: purity 99.6%, grain size 40-70 nm, specific surface area 25 m² / g, room temperature resistivity 1.0 × 10⁻⁶ -3 Ω·cm. Example 4

[0055] like Figure 1 As shown, this embodiment includes the following steps.

[0056] Step 1: Preparation of *Thiobacillus ferrooxidans* seed culture: *Thiobacillus ferrooxidans* strain (CCTCCAB202) was inoculated into 9K liquid medium (components same as in Example 1), and the pH was adjusted to 1.9 with dilute sulfuric acid. The medium was then cultured in a shaker at 31°C and 140 rpm for 3.5 days until the bacterial culture reached its OD value. 600 When the value reaches 1.1, the seed solution is obtained.

[0057] Step 2, Construction of the precursor reaction system: according to Pb 2+ With Ru 3+ A molar ratio of 1:1 was used to weigh lead nitrate and ruthenium trichloride (analytical grade), dissolve them in deionized water, and prepare Pb. 2+ A mixed salt solution with a concentration of 0.15 mol / L was prepared. Seed culture (18% by volume) was added to the mixed salt solution, and the pH of the system was adjusted to 2.2 with dilute sulfuric acid to obtain the precursor reaction system.

[0058] Step 3: Bio-mediated precursor deposition: The precursor reaction system was placed in a shaker at 29℃ and 115 r / min for 7.5 days. During this period, the pH value of the system was monitored daily. When the pH value rose to 2.7, it was adjusted back to 2.2 with dilute sulfuric acid. 1.8 g / L of FeSO4·7H2O was added to the system every 24 hours. After the reaction was completed, a brown lead ruthenate precursor precipitate was formed in the system.

[0059] Step 4: Separation and washing of precursors: Place the reaction mixture in a centrifuge and centrifuge at 9500 r / min for 11 min to collect the solid precipitate; wash the precipitate with deionized water and anhydrous ethanol in sequence, repeating the centrifugation operation after each wash until the pH of the washing solution is neutral and no white precipitate is produced when barium chloride solution is added to the last washing solution.

[0060] Step 5: Drying and calcining of the precursor: The washed precursor precipitate was placed in a vacuum drying oven and dried at 75℃ and a vacuum of -0.09MPa for 15 hours to obtain lead ruthenate precursor powder. The precursor powder was placed in an alumina crucible and calcined in a muffle furnace in stages: the temperature was increased to 300℃ at 5℃ / min and held for 1 hour; then the temperature was increased to 850℃ at 10℃ / min and held for 2.5 hours; the furnace was cooled to room temperature to obtain lead ruthenate powder.

[0061] Product testing results: The purity of lead ruthenate powder is 99.7%, the grain size is 45-75 nm, the specific surface area is 23 m² / g, and the room temperature resistivity is 1.1 × 10⁻⁶. -3 The resistance value is Ω·cm, and the temperature coefficient of resistance is +28ppm / ℃. This powder was used in the preparation of the back-film resistor layer. After screen printing and calcination, the resistance accuracy reached ±0.8%, meeting the application standards for high-precision industrial-grade back-film resistors. Example 5

[0062] like Figure 1 As shown, this embodiment includes the following steps.

[0063] Step 1: Preparation of *Thiobacillus ferrooxidans* seed culture: Inoculate *Thiobacillus ferrooxidans* strain into 9K liquid medium, adjust the pH to 1.6, and culture at 27℃ and 125 rpm for 4.5 days until the bacterial culture OD reaches 100%. 600 When the value reaches 0.9, the seed solution is obtained.

[0064] Step 2, Construction of the precursor reaction system: according to Pb 2+ With Ru 3+ A molar ratio of 1:1 was used to weigh lead acetate and ruthenium nitrate, dissolve them in deionized water, and prepare a Pb solution. 2+A mixed salt solution with a concentration of 0.08 mol / L was prepared; 12% by volume of seed liquid was added, and the pH was adjusted to 1.7 to obtain the precursor reaction system.

[0065] Step 3, Bio-mediated precursor deposition: The precursor reaction system was placed in a shaker at 26℃ and 105r / min for 9 days. During this period, the pH value was monitored daily and adjusted back to 1.7. 1.2g / L of FeSO4·7H2O was added every 24h. After the reaction was completed, a brown precursor precipitate was obtained.

[0066] Step 4: Separation and washing of precursors: Centrifuge at 8500 r / min for 13 min and collect the precipitate; wash with deionized water and anhydrous ethanol until neutral and free of sulfate ions.

[0067] Step 5: Drying and calcining of the precursor: Vacuum drying at 65℃ for 20h, segmented calcination in a muffle furnace: holding at 300℃ for 1h, holding at 750℃ for 3.5h, and then cooling to room temperature with the furnace.

[0068] Product testing results: purity 99.5%, grain size 55-85nm, specific surface area 18m² / g, room temperature resistivity 1.3×10⁻³Ω·cm, and temperature coefficient of resistance +42ppm / ℃. When used in the preparation of back-film resistors, the resistance accuracy reaches ±1.5%, making it suitable for the production of back-film resistors in mid-to-high-end consumer electronics. Example 6

[0069] like Figure 1 As shown, this embodiment includes the following steps.

[0070] Step 1: Preparation of *Thiobacillus ferrooxidans* seed culture: Inoculate *Thiobacillus ferrooxidans* strain into 9K liquid medium, adjust the pH to 2.1, and culture at 33℃ and 155 rpm for 2.5 days until the bacterial culture reaches OD500. 600 When the value reaches 1.3, the seed solution is obtained.

[0071] Step 2, Construction of the precursor reaction system: according to Pb 2+ With Ru 3+ A molar ratio of 1:1 was used to weigh lead nitrate and ruthenium trichloride to prepare Pb. 2+ A mixed salt solution with a concentration of 0.22 mol / L was prepared; 22% by volume of seed liquid was added, and the pH was adjusted to 2.6 to obtain the precursor reaction system.

[0072] Step 3, Bio-mediated precursor deposition: The precursor reaction system was placed in a shaker at 31℃ and 125r / min for 6.5 days. During this period, the pH value was monitored daily and adjusted back to 2.6. 2.2g / L of FeSO4·7H2O was added every 24 hours. After the reaction was completed, a brown precursor precipitate was obtained.

[0073] Step 4: Separation and washing of precursors: Centrifuge at 10500 r / min for 9 min and collect the precipitate; wash with deionized water and anhydrous ethanol until neutral and free of sulfate ions.

[0074] Step 5: Drying and calcining of the precursor: Vacuum drying at 85℃ for 10h, segmented calcination in a muffle furnace: holding at 300℃ for 1h, holding at 950℃ for 1.5h, and then cooling to room temperature with the furnace.

[0075] Product testing results: purity 99.6%, grain size 35-65nm, specific surface area 27m² / g, room temperature resistivity 0.9×10⁻³Ω·cm, and resistance temperature coefficient -30ppm / ℃. When used in the preparation of back-film resistors, the resistance accuracy reaches ±0.3%, meeting the application requirements of ultra-high precision industrial control circuits and aerospace back-film resistors.

[0076] Compare with Example 1.

[0077] Lead ruthenate is used in the traditional solid-state sintering method for preparing thick-film resistors.

[0078] Step 1: Raw material mixing: According to Pb 2+ With Ru 3+ Weigh analytical grade lead carbonate (PbCO3) and ruthenium trioxide (Ru2O3) powders at a molar ratio of 1:1, place them in a planetary ball mill, use zirconia balls as the grinding medium, with a ball-to-material ratio of 5:1, add anhydrous ethanol as a dispersant, and ball mill and mix for 6 hours at a speed of 300 r / min.

[0079] Step 2, Drying and Pre-calcination: Place the mixed slurry in a forced-air drying oven and dry at 80℃ for 12 hours to remove anhydrous ethanol; place the dried powder in an alumina crucible and pre-calcine at 500℃ for 2 hours in a muffle furnace, cool with the furnace, and then ball-mill again for 2 hours, and pass through a 200-mesh sieve.

[0080] Step 3, High-temperature sintering: Press the pre-fired powder into round discs with a diameter of 20 mm and a thickness of 2 mm, place them in a muffle furnace, heat them to 1000 °C at a rate of 10 °C / min, hold them at that temperature for 5 hours, cool them to room temperature with the furnace, and then pulverize them to obtain lead ruthenate powder.

[0081] Performance testing: Product purity was 98.2%, grain size was 200-300 nm, specific surface area was 3.5 m² / g, and room temperature resistivity was 5.8 × 10⁻⁶. -3 The resistance is Ω·cm, and the temperature coefficient of resistance is +120ppm / ℃. When used in the preparation of thick film resistors, the resistance accuracy is ±5%, which only meets the needs of low-end consumer electronics.

[0082] Compare with Example 2.

[0083] Lead ruthenate for preparing thick-film resistors using the sol-gel method

[0084] Step 1: Sol preparation: Weigh lead nitrate and ruthenium trichloride in a molar ratio of 1:1 and dissolve them in a mixed solvent of ethylene glycol methyl ether and deionized water (volume ratio 3:1) to prepare a solution with a total metal ion concentration of 0.5 mol / L. Add citric acid as a chelating agent, with a molar ratio of citric acid to total metal ions of 2:1. After stirring and dissolving, adjust the pH value to 6.0 with ammonia water and stir in a 60℃ water bath for 3 hours to form a transparent sol.

[0085] Step 2, gel aging: The sol is allowed to stand at room temperature for 24 hours to form a wet gel; it is then placed in a vacuum drying oven and dried at 70°C for 18 hours to obtain a dry gel.

[0086] Step 3, calcination and pulverization: Place the dry gel in a muffle furnace, heat it to 400℃ at 2℃ / min, and keep it at that temperature for 1 hour to remove organic components; then heat it to 850℃ at 5℃ / min, keep it at that temperature for 4 hours, and pulverize it after cooling in the furnace to obtain lead ruthenate powder.

[0087] Performance testing: Product purity is 99.0%, grain size is 80-120 nm, specific surface area is 8.2 m² / g, and room temperature resistivity is 3.2 × 10⁻⁶. -3 With a resistance of Ω·cm and a temperature coefficient of resistance of +85ppm / ℃, it can achieve a resistance accuracy of ±3% when used in the preparation of thick film resistors. It is suitable for the mid-range consumer electronics field, but the preparation process requires a large amount of organic reagents, resulting in high cost, and high-temperature calcination can easily cause powder agglomeration.

[0088] Compare Example 3.

[0089] Lead ruthenate for the preparation of thick-film resistors by hydrothermal synthesis

[0090] Step 1: Construction of the hydrothermal reaction system: Weigh lead acetate and ruthenium nitrate in a molar ratio of 1:1, dissolve them in deionized water, and prepare a Pb solution. 2+ A 0.2 mol / L solution was prepared; sodium hydroxide was added to adjust the pH to 13.0, and the mixture was stirred for 30 min to form a suspension; the suspension was then transferred to a high-pressure reactor lined with polytetrafluoroethylene, with a filling degree of 80%.

[0091] Step 2, hydrothermal reaction: Place the reactor in an oven and keep it at 180℃ for 12 hours. After naturally cooling to room temperature, remove the reaction product.

[0092] Step 3: Separation, washing and drying: Centrifuge the product at 8000 r / min for 10 min and collect the solid precipitate; wash with deionized water and anhydrous ethanol alternately until the pH of the washing solution is neutral, and dry in a 60℃ forced-air drying oven for 12 h to obtain the lead ruthenate precursor.

[0093] Step 4, sintering treatment: The precursor is placed in a muffle furnace and heated to 750°C at a rate of 5°C / min. It is held at this temperature for 2 hours and then cooled to room temperature with the furnace to obtain lead ruthenate powder.

[0094] Performance testing: Product purity is 99.2%, grain size is 60-100 nm, specific surface area is 12 m² / g, and room temperature resistivity is 2.5 × 10⁻⁶. -3 The resistance is Ω·cm with a temperature coefficient of resistance of +65ppm / ℃. When used to prepare thick film resistors, the resistance accuracy is ±2.5%. However, the hydrothermal reaction requires high-pressure equipment, which has high requirements for operational safety. In addition, the product has a wide particle size distribution, which is not conducive to the uniform coating of the thick film resistor layer.

[0095] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing lead ruthenate based on *Thiobacillus ferrous acidophilus*, characterized in that, Includes the following steps: Step 1: Preparation of *Thiobacillus ferrooxidans* seed culture: Inoculate *Thiobacillus ferrooxidans* strain into 9K liquid medium and culture in a shaker at 10-40℃ and 50-200 r / min for 2-10 days until the bacterial culture reaches OD500. 600 The pH value was adjusted to 0.5-2.0 to obtain the seed culture; the components of the 9K liquid culture medium were: (NH4)2 SO4 3.0 g / L, KCl 0.1 g / L, K2HPO4 0.5 g / L, MgSO4·7H2O 0.5 g / L, Ca(NO3)2 0.01 g / L, FeSO4·7H2O 44.2 g / L, and the pH value was adjusted to 0.5-2.

5. Step 2: Construction of the precursor reaction system: Dissolve soluble lead salt and soluble ruthenium salt in deionized water at a lead ion to ruthenium ion molar ratio of 1:1, and stir until homogeneous to obtain a mixed salt solution, wherein the lead ion concentration is controlled at 0.05-0.5 mol / L; add the seed liquid prepared in Step 1 to the mixed salt solution, the volume of the seed liquid accounting for 5%-20% of the total weight of the reaction system, and then adjust the pH of the system to 0.5-2.5 with dilute sulfuric acid to obtain the precursor reaction system; Step 3, Bio-mediated Precursor Deposition: Place the precursor reaction system in a shaker at 10-40℃ and 50-200 r / min for 2-10 days. Monitor the pH value of the system daily during this period. When the pH value rises above 0.2, adjust it back to 0.5-2.5 with dilute sulfuric acid. After the reaction is completed, a brown lead ruthenate precursor precipitate will be formed in the system. Step 4, Separation and washing of precursors: Centrifuge the reaction mixture at a speed of 2000-10000 r / min for 10-30 min and collect the solid precipitate. The precipitate was washed with deionized water and anhydrous ethanol in sequence. After each wash, the centrifugation operation was repeated until the pH of the washing solution was neutral and no sulfate ions were detected in the washing solution. Step 5: Drying and calcining of the precursor: The washed precursor precipitate is placed in a vacuum drying oven and dried for 12-36 hours at a temperature of 50-120℃ and a vacuum degree of -0.08~-0.1MPa to obtain lead ruthenate precursor powder. The precursor powder is placed in an alumina crucible and calcined in a muffle furnace in stages: first, the temperature is increased to 300℃ at a heating rate of 5℃ / min and held for 1 hour; then, the temperature is increased to 600-900℃ at a heating rate of 10℃ / min and held for 2-8 hours; the furnace is then cooled to room temperature to obtain high-purity lead ruthenate powder.

2. The preparation method according to claim 1, characterized in that, The soluble lead salt mentioned in step two is at least one of lead nitrate and lead acetate; the soluble ruthenium salt is at least one of ruthenium trichloride and ruthenium nitrate.

3. The preparation method according to claim 1, characterized in that, During the oscillation reaction described in step three, 1-2 g / L of FeSO4·7H2O is added to the system every 24 hours to maintain the metabolic activity of the strain.

4. The preparation method according to claim 1, characterized in that, The method for detecting sulfate ions in step four is as follows: Take the last few wash solutions and add barium chloride solution. If no white precipitate is produced, it proves that there are no sulfate ions in the wash solution.

5. The preparation method according to claim 1, characterized in that, The preferred calcination temperature in step five is 800℃, and the preferred holding time is 3 hours.

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