CN113582703A - Method for preparing porous silicon nitride ceramic based on walnut shells - Google Patents

Method for preparing porous silicon nitride ceramic based on walnut shells Download PDF

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CN113582703A
CN113582703A CN202110743260.8A CN202110743260A CN113582703A CN 113582703 A CN113582703 A CN 113582703A CN 202110743260 A CN202110743260 A CN 202110743260A CN 113582703 A CN113582703 A CN 113582703A
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silicon nitride
powder
parts
walnut shells
porous silicon
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杜建周
艾多梅
宋继明
肖鑫
钟栋青
王路明
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Yancheng Institute of Technology
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Abstract

The invention discloses a method for preparing porous silicon nitride ceramics based on walnut shells, which comprises the following steps: calcining rice hulls at high temperature to obtain rice hull ash, directly nitriding to obtain silicon nitride, crushing and screening to obtain silicon nitride powder with different specifications. Weighing and dispersing 60-100 parts by mass of silicon nitride powder, 5-50 parts by mass of walnut shell powder, 1-20 parts by mass of sintering aid and 10-50 parts by mass of binder in a solvent according to a formula, and performing ball milling to obtain ceramic slurry; taking out the slurry, drying and grinding to obtain ceramic powder; pressing the ceramic powder into a biscuit in a dry pressing mode; and introducing nitrogen atmosphere, and sintering at 1600-1900 ℃ to obtain the porous silicon nitride ceramic material. The invention provides a green, low-cost and rapid method for preparing porous silicon nitride ceramics, and the prepared porous ceramics have high porosity, excellent mechanical properties and good acid and alkali resistance, and can be applied to high-temperature flue gas filtration.

Description

Method for preparing porous silicon nitride ceramic based on walnut shells
Technical Field
The invention relates to the technical field of preparation of ceramic materials, in particular to a method for preparing porous silicon nitride ceramic based on walnut shells.
Background
Silicon nitride ceramic materials have the characteristics of high strength, high hardness, high temperature resistance, wear resistance, thermal shock resistance and the like, and are considered to be one of the high-temperature structural ceramic materials with the greatest application prospect. The porous silicon nitride ceramic material has high porosity, excellent mechanical property, dielectric property and fracture toughness, and can be used for filtering high-temperature flue gas.
Pore-forming agents that have been reported to be useful for preparing porous ceramics include inorganic carbonates, organic polymers, and combustible biomass, including wood chips, rice hulls, coal particles, coal dust, plastic powder, etc. The walnut has rich nutrition value and huge annual consumption, the walnut shells are usually discarded as wastes, resource waste is caused, the main components of the walnut shells are lignin, cellulose and hemicellulose, the surfaces of the walnut shells are microporous, the adsorption effect is good, the main element in the walnut shells is C, H, O, N, S, and the walnut shells can be biodegraded and can be used as a pore-forming agent.
The rice hull has oligomeric amorphous silicon structure, has low impurity ion content, is easy to remove, and is calcined to obtain rice hull ash containing a large amount of free SiO2About 93.11% SiO2The powder has an amorphous structure, uniform particles and good dispersibility. In addition, the rice hulls contain rich silicon and carbon resources, the element composition is mainly C, O, H, Si, and the rice hulls can be used as a silicon source and a carbon source to prepare silicon nitride. The deep processing of the walnut shells and the rice husks can not only effectively treat the solid wastes, but also change wastes into valuables and improve the treatment effectAnd (4) value.
Disclosure of Invention
Aiming at the defects of the prior art, the invention discloses a method for preparing porous silicon nitride ceramics based on walnut shells, which uses rice hulls to prepare silicon nitride powder as a raw material, uses walnut shells with different specifications as pore-forming agents, and is added with a proper amount of sintering aids, so that the prepared sample has high porosity, uniform and easily controllable pore diameter and excellent mechanical properties.
The invention provides a method for preparing porous silicon nitride ceramics based on walnut shells, which comprises the following raw materials in parts by mass: 60-100 parts of silicon nitride powder, 5-50 parts of walnut shell powder, 1-20 parts of sintering aid and 10-50 parts of binder, wherein the silicon nitride powder is obtained by calcining rice hulls to obtain rice hull ash, directly nitriding the rice hull ash to obtain silicon nitride, crushing the silicon nitride, and passing the crushed silicon nitride through grading sieves with different meshes to obtain the silicon nitride powder with the particle size ranges of 1-50 microns, 60-150 microns and 160-500 microns.
Preferably, the sintering aid is one or a combination of any several of yttrium oxide, magnesium oxide and cerium oxide.
Preferably, the binder is a polyvinyl butyral (PVB) solution.
A method for preparing porous silicon nitride ceramics based on walnut shells comprises the following steps:
the first step is as follows: cleaning walnut shells, drying the walnut shells in a drying box to constant weight, crushing the walnut shells, and screening walnut shell powder with different particle sizes through grading sieves with different meshes;
the second step is that: cleaning rice hulls, soaking the rice hulls in dilute hydrochloric acid with the concentration of 5-15% for one month to dissolve organic matters and impurity ions, boiling the rice hulls in the dilute hydrochloric acid for 5-6 times, each time for 20min, cleaning the rice hulls with distilled water, and drying the rice hulls;
the third step: putting rice hulls in a sintering furnace, calcining to obtain rice hull ash, putting the rice hull ash in an atmosphere sintering furnace, introducing nitrogen to generate silicon nitride, crushing, and passing through grading sieves with different meshes to obtain silicon nitride powder with different specifications;
the fourth step: weighing 60-100 parts of silicon nitride powder, 5-50 parts of walnut shell powder, 1-20 parts of sintering aid and 10-50 parts of PVB solution according to the mass part, dispersing in absolute ethyl alcohol solution, taking silicon nitride balls as ball milling media, and ball milling to obtain ceramic slurry;
the fifth step: taking out the slurry obtained in the fourth step, drying, grinding and sieving to obtain ceramic powder;
and a sixth step: pressing the ceramic powder obtained in the fifth step into a biscuit in a dry pressing mode;
the seventh step: sintering the biscuit according to the following conditions: adding nitrogen atmosphere, keeping the temperature for 0.5-2 h at 300-400 ℃, heating to 500-650 ℃, discharging glue for 2-4 h, continuously heating to 1600-1900 ℃, keeping the temperature for 1-5 h, cooling to 700 ℃, and naturally cooling to room temperature to obtain the porous silicon nitride ceramic material, wherein the flow rate of introduced nitrogen is 3-5L/min.
Further, the temperature of the calcining process in the third step is 500-600 ℃, and the time is 0.5-2 hours; the flow rate of nitrogen introduced during direct nitridation is 3-5L/min, and the sintering temperature is 1000-1300 ℃.
Further, the mass ratio of the total mass of the silicon nitride powder, the walnut shell powder, the sintering aid and the PVB solution to the absolute ethyl alcohol solution is 1: 2-5; the ball milling medium is silicon nitride balls, the total mass ratio of the silicon nitride balls to the silicon nitride walnut shells, the walnut shell powder, the sintering aid and the PVB solution in the mixing process is 1-5: 1, the rotating speed is 200-400 r/min, and the ball milling time is 5-20 hours.
Further, the drying process in the fifth step is vacuum drying, and the temperature is 40-60 ℃.
Further, the pressure of the dry pressing in the sixth step is 2-10 MPa, and the pressure maintaining time is 0-30 s.
Has the advantages that:
compared with the prior art, the method for preparing the porous silicon nitride ceramic based on the walnut shells has the following advantages:
1. rice husk is used as raw material, and is pickled and calcined to obtain the product containing large amount of SiO2The rice hull ash is directly nitrided to prepare silicon nitride, and the silicon nitride is crushed and sieved by grading sieves with different meshesObtaining silicon nitride powder with the particle size ranges of 1-50 microns, 60-150 microns and 160-500 microns;
2. the walnut shells are loose and porous in surface, have good adsorption performance, are often used for filter materials of filters, waste gas treatment, sewage treatment and the like, are easy to decompose at high temperature, are pollution-free, are biomass raw materials with secondary utilization value, take the walnut shells with different specifications as pore-forming agents, and are added with sintering aids to prepare porous silicon nitride ceramics;
3. the preparation method provided by the invention is simple and easy to operate, the raw materials are easy to obtain, the cost is low, the industrial production is convenient to realize, and the preparation method has a good application prospect;
4. the solid waste is secondarily utilized, so that the environmental pollution is reduced, and the method has great significance in sustainable development;
5. the porosity of the product is as high as 55%, the pore diameter is uniform and easy to control, the mechanical property of the sample is excellent, and the flexural strength can reach 52.4 MPa.
Drawings
Fig. 1 is an XRD pattern of the silicon nitride powder obtained.
Fig. 2 is an SEM image of the silicon nitride powder produced.
FIG. 3 is an SEM photograph of the porous silicon nitride ceramic of example 4.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The preparation process of the present invention is formulated in view of the following considerations: the method comprises the steps of preparing silicon nitride powder by using rice hulls as raw materials, using silicon nitride as a raw material, using walnut shells as a pore-forming agent, adding a sintering aid, and changing the porosity and mechanical properties of a sample by changing the doping amount of the walnut shells and the sintering aid; the porosity and the pore diameter can be controlled by changing the particle sizes of the silicon nitride powder and the walnut shell powder.
The features and properties of the present invention will be described in further detail below with reference to the accompanying drawings and examples.
Example 1
The embodiment provides a method for preparing porous silicon nitride ceramic based on walnut shells, which comprises the following specific steps:
the first step is as follows: cleaning walnut shells to remove surface impurities, then placing the walnut shells in a drying oven to be dried to constant weight, crushing the walnut shells by using a crusher, and screening walnut shell powder with different particle sizes by using analysis sieves with different specifications, wherein the particle size ranges respectively comprise 1-10 microns, 30-80 microns and 100-300 microns;
the second step is that: picking out obvious impurities such as straws and sand grains in the rice hulls, washing to remove surface dust, soaking for one month in dilute hydrochloric acid with the volume fraction of 10%, dissolving organic matters and impurity ions, boiling for 5-6 times in the dilute hydrochloric acid, each time for 20min, washing with distilled water, and drying;
the third step: placing rice hulls in a sintering furnace, calcining for 30min at 520 ℃ to obtain rice hull ash, placing the rice hull ash in an atmosphere sintering furnace, generating silicon nitride at 1100 ℃ in a flowing nitrogen atmosphere of 3L/min, crushing by using a crusher, and passing through grading sieves with different meshes to obtain silicon nitride powder with different specifications, wherein the silicon nitride powder comprises 1-50 microns, 60-150 microns and 160-500 microns;
the fourth step: weighing 70 parts of silicon nitride powder, 30 parts of walnut shell powder, 4 parts of yttrium oxide and 10 parts of PVB solution according to the mass parts, wherein the particle size of the silicon nitride powder is 40 mu m, the particle size of the walnut shell powder is 10 mu m, weighing, dispersing in absolute ethyl alcohol, taking silicon nitride balls as a ball milling medium, and ball milling for 8 hours in a ball mill at the speed of 250r/min by taking the total mass of the silicon nitride balls, the silicon nitride, the walnut shell powder, the sintering aid and the PVB solution as 3: 1: 2.5;
the fifth step: taking out the slurry obtained in the fourth step, drying in vacuum at the temperature of 60 ℃, taking out after completely drying, grinding and sieving by a 50-mesh grading sieve to obtain ceramic powder;
and a sixth step: pressing the ceramic powder obtained in the fifth step into a biscuit in a dry pressing mode, wherein the forming pressure is 5MPa, and the pressure is maintained for 10 s;
the seventh step: placing the biscuit in a crucible, placing the crucible in an atmosphere sintering furnace, filling nitrogen with the flow rate of 3L/min, firstly preserving heat for 30min at 300 ℃, then discharging glue for 4h at 650 ℃, continuing to heat to 1700 ℃ and preserving heat for 2h, cooling to 700 ℃ and naturally cooling to room temperature to obtain the porous silicon nitride ceramic material.
Example 2
The embodiment provides a method for preparing porous silicon nitride ceramic based on walnut shells, which comprises the following specific steps:
the first step, the second step and the third step are the same as those in example 1;
the fourth step: weighing 65 parts of silicon nitride powder, 35 parts of walnut shell powder, 4 parts of magnesium oxide and 15 parts of PVB solution according to the mass parts, wherein the particle size of the silicon nitride powder is 80 mu m, the particle size of the walnut shell powder is 30 mu m, weighing, dispersing in absolute ethyl alcohol, taking silicon nitride balls as a ball milling medium, and ball milling for 8 hours in a ball mill at the speed of 250r/min by taking the total mass of the silicon nitride balls, the silicon nitride, the walnut shell powder, the sintering aid and the PVB solution as 3: 1: 3.
The fifth step: taking out the slurry obtained in the fourth step, drying in vacuum at the temperature of 60 ℃, taking out after completely drying, grinding and sieving by a 50-mesh grading sieve to obtain ceramic powder;
and a sixth step: pressing the ceramic powder obtained in the fifth step into a biscuit in a dry pressing mode, wherein the forming pressure is 5MPa, and the pressure is maintained for 10 s;
the seventh step: placing the biscuit in a crucible, placing the crucible in an atmosphere sintering furnace, introducing nitrogen with the flow rate of 3L/min, preserving heat at 300 ℃ for 30min, discharging glue at 650 ℃ for 4h, introducing nitrogen, continuing heating to 1750 ℃ and preserving heat for 2h, finishing the sintering process, cooling to 700 ℃ and naturally cooling to room temperature to obtain the porous silicon nitride ceramic material.
Example 3
The embodiment provides a method for preparing porous silicon nitride ceramic based on walnut shells, which comprises the following specific steps:
the first step and the second step are the same as those of example 1;
the third step: putting rice hulls in a sintering furnace, calcining at 540 ℃ for 30min to obtain rice hull ash, putting the rice hull ash in an atmosphere sintering furnace, generating silicon nitride powder at 1000 ℃ in a flowing nitrogen atmosphere of 3L/min, crushing by using a crusher, and passing through grading sieves with different meshes to obtain silicon nitride powder with different specifications, wherein the silicon nitride powder comprises 1-50 microns, 60-150 microns and 160-500 microns.
The fourth step: weighing 65 parts of silicon nitride powder, 25 parts of walnut shell powder, 3 parts of magnesium oxide, 2 parts of cerium oxide and 15 parts of PVB solution according to the mass parts, wherein the particle size of the silicon nitride powder is 100 micrometers, the particle size of the walnut shell powder is 50 micrometers, weighing, dispersing in absolute ethyl alcohol, taking silicon nitride balls as a ball milling medium, and ball milling for 6 hours at the speed of 300r/min, wherein the total mass of the silicon nitride balls, the silicon nitride, the walnut shell powder, the sintering aid and the PVB solution is 2.5: 1: 2;
the fifth step: taking out the slurry obtained in the fourth step, drying in vacuum at 50 ℃, taking out after completely drying, grinding and sieving by a 50-mesh grading sieve to obtain ceramic powder;
and a sixth step: pressing the ceramic powder obtained in the fifth step into a biscuit in a dry pressing mode, wherein the forming pressure is 5MPa, and the pressure is maintained for 10 s;
the seventh step: placing the biscuit in a crucible, placing the crucible in an atmosphere sintering furnace, introducing nitrogen with the flow rate of 4L/min, firstly preserving heat for 30min at 300 ℃, then discharging glue for 4h at 650 ℃, continuing to heat to 1750 ℃ and preserving heat for 2h, cooling to 700 ℃ and naturally cooling to room temperature to obtain the porous silicon nitride ceramic material.
Example 4
The embodiment provides a method for preparing porous silicon nitride ceramic based on walnut shells, which comprises the following specific steps:
the first step and the second step are the same as those of example 1;
the third step: putting rice hulls in a sintering furnace, calcining for 30min at 520 ℃ to obtain rice hull ash, putting the rice hull ash in an atmosphere sintering furnace, generating silicon nitride powder at 1200 ℃ in a flowing nitrogen atmosphere of 3L/min, crushing by using a crusher, and passing through grading sieves with different meshes to obtain silicon nitride powder with different specifications, wherein the silicon nitride powder comprises 1-50 microns, 60-150 microns and 160-500 microns.
The fourth step: weighing 75 parts of silicon nitride powder, 20 parts of walnut shell powder, 5 parts of cerium oxide and 20 parts of PVB solution according to the mass parts, wherein the particle size of the silicon nitride powder is 200 mu m, the particle size of the walnut shell powder is 100 mu m, weighing, dispersing in absolute ethyl alcohol, taking silicon nitride balls as a ball milling medium, and ball milling at the speed of 300r/min for 8 hours to obtain ceramic slurry, wherein the total mass of the silicon nitride balls, the silicon nitride, the walnut shell powder, the sintering aid and the PVB solution is 3: 1: 2;
the fifth step: taking out the slurry obtained in the fourth step, drying in vacuum at 50 ℃, taking out after completely drying, grinding and sieving by a 50-mesh grading sieve to obtain ceramic powder;
and a sixth step: pressing the ceramic powder obtained in the fifth step into a biscuit in a dry pressing mode, wherein the forming pressure is 5MPa, and the pressure is maintained for 10 s;
the seventh step: placing the biscuit in a crucible, placing the crucible in an atmosphere sintering furnace, introducing nitrogen with the flow rate of 4L/min, firstly preserving heat at 300 ℃ for 30min, then discharging glue at 650 ℃ for 4h, continuing to heat to 1800 ℃ and preserving heat for 2h, cooling to 700 ℃ and naturally cooling to room temperature to obtain the porous silicon nitride ceramic material.
Example 5
The embodiment provides a method for preparing porous silicon nitride ceramic based on walnut shells, which comprises the following specific steps:
the first step, the second step and the third step are the same as in example 4;
the fourth step: weighing 65 parts of silicon nitride powder, 35 parts of walnut shell powder, 3 parts of magnesium oxide, 1 part of yttrium oxide and 15 parts of PVB solution according to the mass parts, wherein the particle size of the silicon nitride powder is 250 micrometers, the particle size of the walnut shell powder is 100 micrometers, weighing, dispersing in absolute ethyl alcohol, taking silicon nitride balls as a ball milling medium, and ball milling for 6 hours at the speed of 300r/min, wherein the total mass of the silicon nitride balls, the silicon nitride, the walnut shell powder, the sintering aid and the PVB solution is 2.5: 1: 2;
the fifth step: taking out the slurry obtained in the fourth step, drying in vacuum at 50 ℃, taking out after completely drying, grinding and sieving by a 50-mesh grading sieve to obtain ceramic powder;
and a sixth step: pressing the ceramic powder obtained in the fifth step into a biscuit in a dry pressing mode, wherein the forming pressure is 5MPa, and the pressure is maintained for 10 s;
the seventh step: placing the biscuit in a crucible, placing the crucible in an atmosphere sintering furnace, introducing nitrogen with the flow rate of 3L/min, firstly preserving heat for 30min at 300 ℃, then discharging glue for 4h at 650 ℃, continuing to heat to 1850 ℃ and preserving heat for 2h, cooling to 700 ℃ and naturally cooling to room temperature to obtain the porous silicon nitride ceramic material.
The density and porosity of the porous silicon nitride ceramic obtained by the preparation method of the embodiment 1-5 are tested by an Archimedes drainage method; testing the flexural strength of the porous silicon nitride ceramic by adopting a three-point bending method; analyzing the phase composition of the sintered body by using an X-ray diffractometer; the microstructure of the cross section of the porous silicon nitride ceramic was observed with a scanning electron microscope. The results of these properties of density, porosity and flexural strength are shown in table 1.
TABLE 1 Properties of porous silicon nitride ceramics obtained in examples 1 to 5
Figure BDA0003143456080000081
Figure BDA0003143456080000091
The embodiments described above are some, but not all embodiments of the invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Claims (8)

1. The method for preparing the porous silicon nitride ceramic based on the walnut shells is characterized by comprising the following raw materials in parts by mass: 60-100 parts of silicon nitride powder, 5-50 parts of walnut shell powder, 1-20 parts of sintering aid and 10-50 parts of binder, wherein the silicon nitride powder is obtained by calcining rice hulls to obtain rice hull ash, directly nitriding the rice hull ash to obtain silicon nitride, crushing the silicon nitride, and passing the crushed silicon nitride through grading sieves with different meshes to obtain the silicon nitride powder with the particle size ranges of 1-50 microns, 60-150 microns and 160-500 microns.
2. The method for preparing porous silicon nitride ceramic based on walnut shells according to claim 1, wherein the method comprises the following steps: the sintering aid is one or the combination of any more of yttrium oxide, magnesium oxide and cerium oxide.
3. The method for preparing porous silicon nitride ceramic based on walnut shells according to claim 1, wherein the method comprises the following steps: the binder is a polyvinyl butyral (PVB) solution.
4. The method for preparing porous silicon nitride ceramic based on walnut shells according to claim 1, wherein the method comprises the following steps: the method specifically comprises the following steps:
the first step is as follows: cleaning walnut shells, drying the walnut shells in a drying box to constant weight, crushing the walnut shells, and screening walnut shell powder with different particle sizes through grading sieves with different meshes;
the second step is that: cleaning rice hulls, soaking the rice hulls in dilute hydrochloric acid with the concentration of 5-15% for one month to dissolve organic matters and impurity ions, boiling the rice hulls in the dilute hydrochloric acid for 5-6 times, each time for 20min, cleaning the rice hulls with distilled water, and drying the rice hulls;
the third step: putting rice hulls in a sintering furnace, calcining to obtain rice hull ash, putting the rice hull ash in an atmosphere sintering furnace, introducing nitrogen to generate silicon nitride, crushing, and passing through grading sieves with different meshes to obtain silicon nitride powder with different specifications;
the fourth step: weighing 60-100 parts of silicon nitride powder, 5-50 parts of walnut shell powder, 1-20 parts of sintering aid and 10-50 parts of PVB solution according to the mass part, dispersing in absolute ethyl alcohol solution, taking silicon nitride balls as ball milling media, and ball milling to obtain ceramic slurry;
the fifth step: taking out the slurry obtained in the fourth step, drying, grinding and sieving to obtain ceramic powder;
and a sixth step: pressing the ceramic powder obtained in the fifth step into a biscuit in a dry pressing mode;
the seventh step: sintering the biscuit according to the following conditions: adding nitrogen atmosphere, keeping the temperature for 0.5-2 h at 300-400 ℃, heating to 500-650 ℃, discharging glue for 2-4 h, continuously heating to 1600-1900 ℃, keeping the temperature for 1-5 h, cooling to 700 ℃, and naturally cooling to room temperature to obtain the porous silicon nitride ceramic material, wherein the flow rate of introduced nitrogen is 3-5L/min.
5. The method for preparing porous silicon nitride ceramic based on walnut shells according to claim 4, wherein: the temperature of the calcining process in the third step is 500-600 ℃, and the time is 0.5-2 h; the flow rate of nitrogen introduced during direct nitridation is 3-5L/min, and the sintering temperature is 1000-1300 ℃.
6. The method for preparing porous silicon nitride ceramic based on walnut shells according to claim 4, wherein: in the fourth step, the mass ratio of the total mass of the silicon nitride powder, the walnut shell powder, the sintering aid and the PVB solution to the absolute ethyl alcohol solution is 1: 2-5; the total mass ratio of the silicon nitride balls to the silicon nitride powder, the walnut shell powder, the sintering aid and the PVB solution in the mixing process is 1-5: 1, the rotating speed is 200-400 r/min, and the ball milling time is 5-20 h.
7. The method for preparing porous silicon nitride ceramic based on walnut shells according to claim 4, wherein: and in the fifth step, the drying process is vacuum drying, and the temperature is 40-60 ℃.
8. The method for preparing porous silicon nitride ceramic based on walnut shells according to claim 4, wherein: and in the sixth step, the pressure of dry pressing is 2-10 MPa, and the pressure maintaining time is 0-30 s.
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