CN114199719A - Specific surface area testing device and testing method - Google Patents
Specific surface area testing device and testing method Download PDFInfo
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Abstract
The invention provides a specific surface area testing device and a testing method, aiming at solving the problems that a specific surface area instrument on the market occupies a large area, is high in cost and complex in operation, and a sample chamber for storing a sample is small and cannot be disassembled, and has strict limitation on the volume and the quality of the sample, and the like; the transfer chamber is fixed on the frame through the mount for constitute pressure ladder buffer, seted up the gas vent on the transfer chamber, and install the evacuation mechanism to the inside evacuation of testing arrangement on the gas vent. The method is particularly suitable for quickly and accurately testing the gas adsorption rate of the low-temperature sample, and has higher social use value and application prospect.
Description
Technical Field
The invention relates to the technical field of gas adsorption rate detection, in particular to a specific surface area testing device and a specific surface area testing method.
Background
The specific surface area refers to the total area of the unit mass of the material, and the ideal non-porous material only has the external surface area, such as portland cement, some clay mineral powder particles and the like; the porous and porous material has an outer surface area and an inner surface area. The existing measuring method is mainly a BET measuring method, the adsorption volume of nitrogen under different partial pressures p is measured under given temperature, the adsorption volume is expressed by air pressure, and almost all domestic and foreign relevant standards are established according to a BET equation.
Although the specific surface area instruments on the market can carry out specific surface area test, the instruments are large-scale equipment, have large occupied area, high cost and complex operation, and meanwhile, a sample chamber for storing a sample is small and cannot be disassembled, so that the size and the quality of the sample are strictly limited (the diameter is less than 1cm), and the consumption of gas-liquid nitrogen for detection is large. Therefore, a specific surface area testing device and a testing method are provided.
Disclosure of Invention
It is an object of the present invention to solve or at least alleviate problems in the prior art.
In order to achieve the purpose, the invention is realized by the following technical scheme:
the invention provides a specific surface area testing device, which comprises a rack serving as a mounting base body, a high-pressure nitrogen bottle arranged on the rack to provide nitrogen, a transfer cavity arranged on the rack, a gas conveying system, a manifold, a sample chamber and a liquid nitrogen Dewar bottle, wherein the transfer cavity is connected with the gas conveying system;
the transfer cavity is fixed on the rack through a fixing frame and used for forming a pressure step buffer area, an exhaust port is formed in the transfer cavity, and a vacuumizing mechanism for vacuumizing the interior of the testing device is mounted on the exhaust port;
a gas delivery system for delivering and regulating the gas pressure of the measurement sample chamber and the manifold;
a manifold for storing nitrogen gas adsorbed by the sample;
a sample chamber for storing a test sample;
the liquid nitrogen Dewar bottle is movably sleeved on the outer side of the sample chamber and is used for storing liquid nitrogen and performing air suction test on the sample;
the high-pressure nitrogen cylinder, the transfer cavity, the manifold and the sample chamber are communicated through a gas delivery system, and a gas delivery path is adjusted as required.
Optionally, the gas delivery system comprises a first three-way valve, a first conduit, a second conduit, a third conduit, a fourth conduit, a four-way valve, and a second three-way valve;
the first valve port of the first three-way valve is communicated with the transfer cavity, the second valve port is communicated with the high-pressure nitrogen cylinder through a first pipeline, and the third valve port is communicated with one end of the second pipeline;
a first valve port of the four-way valve is communicated with a third valve port of the first three-way valve through a second pipeline, the second valve port of the four-way valve is communicated with a manifold, and the third valve port is communicated with one end of a third pipeline;
the first valve port of the second three-way valve is communicated with a third valve port of the four-way valve through a third pipeline, the second valve port of the second three-way valve is communicated with the sample chamber, and the third valve port is communicated with the transfer chamber through a fourth pipeline.
Optionally, a first control valve is installed on the first pipeline, a second control valve is installed on the second pipeline, and a third control valve is arranged between a second valve port of the second three-way valve and the sample chamber.
Optionally, a first pressure gauge for detecting a pressure value in the transfer chamber in real time is installed on the transfer chamber, and a second pressure gauge for detecting a pressure value in the manifold in real time is installed on a fourth valve port of the four-way valve.
Optionally, the first pipeline, the second pipeline and the fourth pipeline are of the same specification pipe diameter, and the pipe diameter of the third pipeline is 1/4-1/5 of the pipe diameter of the first pipeline.
Optionally, the detachable cover in the outside of sample room is equipped with the heating clothing that is used for the sample heating to get rid of aqueous vapor.
Optionally, the lower end of the liquid nitrogen dewar is provided with a lifting unit for lifting the liquid nitrogen dewar to continuously immerse the sample in the liquid nitrogen.
The invention also provides a testing method of the specific surface area testing device, which comprises the following steps:
s1, preheating the sample to remove water vapor, weighing and recording, then putting the sample from which the water vapor is removed into a sample chamber, filling the vacant space in the sample chamber with a filler which does not absorb gas, and reducing the dead volume;
s2, reheating the sample chamber, starting a vacuumizing mechanism to exhaust, removing water vapor (110-60 minutes),
s3, after exhausting, waiting for the sample to return to room temperature, then opening a high-pressure nitrogen bottle to carry out multiple air washing on the testing device, and replacing air in the testing device with high-purity nitrogen;
s4, closing the vacuumizing mechanism after vacuumizing the testing device, filling nitrogen into the transfer cavity, slowly filling the nitrogen in the transfer cavity into the manifold and the sample chamber, and regulating the air pressure in the manifold and the sample chamber to be stabilized at a required pressure value through a second control valve and recording;
s5, immersing the sample chamber in a liquid nitrogen Dewar bottle to cool the sample, gradually reducing the air pressure in the manifold after the sample adsorbs nitrogen, recording the air pressure value in the manifold for the second time after the air pressure is stable, and obtaining the actual volume V of the nitrogen adsorbed in the sample pores according to the difference of the two air pressure values;
s6, heating the sample in the sample chamber to restore the initial temperature, repeating the steps S1-S5 for a plurality of times, and calculating to obtain the volume Vm of the nitrogen adsorbed in the sample pore in the single layer;
s7, according to the calculation model:
wherein N is the Avogastron constant, Sigma is the cross-sectional area of a nitrogen molecule (0.162nm2), Vm is the volume of nitrogen adsorbed on the surface of a sample pore monolayer, W is the mass of the test sample, and the specific surface area S of the sample is calculatedg。
Optionally, in the step S4, the specific operation steps are as follows:
s4-1, vacuumizing the testing device to be within 0.01 atmospheric pressure through a vacuumizing mechanism, and filling nitrogen with 0.5 atmospheric pressure into the transfer cavity through a high-pressure nitrogen bottle;
s4-2, communicating the sample chamber with the manifold, slowly communicating the transfer chamber with the manifold, and slowly filling nitrogen in the transfer chamber into the manifold;
s4-3, stopping inflating after the pressure in the manifold reaches 0.05 atmosphere;
and S4-4, recording the air pressure value of the manifold after the air pressure is stabilized.
Optionally, in the steps S5-S7, the specific calculation process is as follows:
according to the relation formula between the volume V of the real adsorbed nitrogen in the sample and the Vm adsorbed by the monolayer:
wherein V is the actual volume of nitrogen adsorbed in the pores of the sample with unit mass, Vm is the single-layer adsorbed volume of nitrogen in the pores of the sample with unit mass, P is the nitrogen partial pressure, P0 is the saturated vapor pressure of nitrogen at the liquid nitrogen temperature, C is a constant related to thermal adsorption, and the larger the C value is, the stronger the adsorption capacity is;
several different sets of P/P0 values were taken during the test, the values being in the range of 0.05-0.35
To pair
In a linear relationship and
measuring different P/P0 values to obtain a linear curve of the nitrogen adsorption volume V, and calculating Vm through slope and intercept;
assuming that the nitrogen at the surface of the adsorbent is just a monolayer of molecules, the surface area of the material when in the standard state (one atmosphere, 0 ℃) is:
wherein S isgThe specific surface area of the sample is N, the Avogastron constant, the sigma is the cross-sectional area of one nitrogen molecule (0.162nm2), Vm is the volume of monolayer adsorption of nitrogen on the surface of a sample pore, and W is the mass of the test sample;
the specific surface area of the sample obtained by substituting the constant is:
the embodiment of the invention provides a specific surface area testing device and a testing method, which have the following beneficial effects:
1. the gas circuit system consisting of the sample chamber and the manifold can effectively measure the actual nitrogen adsorption volume of the sample, further repeat the test to obtain the single-layer adsorption volume of the nitrogen in the sample pore, and obtain the specific surface area of the sample according to the calculation model, compared with the traditional large-scale equipment, the testing device has the advantages of reducing the volume, occupying small area, being capable of moving flexibly, reducing the cost of the device and having the price of 1/10 of the traditional testing equipment.
2. The sample chamber and the manifold are detachably mounted, can be adjusted according to the sample and the test requirements, and have high adaptability; the transfer cavity is arranged to form a pressure step buffer zone, and the gas pressure of the manifold and the gas pressure of the sample chamber can be accurately and quickly controlled by matching with the second control valve, so that the gas pressure in the manifold can be quickly adjusted; the use/tubule between collocation sample room and the manifold, and the space outside the sample in the sample room uses the filler that does not absorb gas to reduce the dead volume, make the data of testing more accurate.
Drawings
The above features, technical features, advantages and implementations of a specific surface area test apparatus and test method will be further described in the following detailed description of preferred embodiments in a clearly understandable manner, with reference to the accompanying drawings.
FIG. 1 is a perspective view of the testing mechanism of the present invention;
FIG. 2 is an enlarged view of the front view of the testing mechanism of the present invention;
FIG. 3 is an enlarged view of the rear view of the testing mechanism of the present invention;
FIG. 4 is an enlarged left view of the testing mechanism of the present invention;
FIG. 5 is an enlarged view of the right side view of the testing mechanism of the present invention.
In the figure: the device comprises a frame 1, a fixed frame 2, a high-pressure nitrogen cylinder 3, a transfer cavity 4, a vacuumizing mechanism 5, a first pressure gauge 7, a first three-way valve 8, a first control valve 9, a first pipeline 101, a second pipeline 102, a third pipeline 103, a fourth pipeline 104, a second control valve 11, a four-way valve 12, a manifold 13, a second pressure gauge 14, a second three-way valve 15, a third control valve 16, a sample chamber 17 and a liquid nitrogen Dewar flask 18.
Detailed Description
The invention will be further illustrated with reference to the following figures 1 to 5 and examples:
example 1
A specific surface area testing device comprises a frame 1 used as a mounting base body, a high-pressure nitrogen bottle 3 which is mounted on the frame 1 and used for providing nitrogen, a transfer chamber 4 arranged on the frame 1, a gas delivery system, a manifold 13, a sample chamber 17 and a liquid nitrogen Dewar bottle 18;
the transfer chamber 4 is fixed on the frame 1 through the fixing frame 2 and used for forming a pressure step buffer area, an exhaust port is formed in the transfer chamber 4, a vacuumizing mechanism 5 for vacuumizing the interior of the testing device is mounted on the exhaust port, and redundant air in the transfer chamber 4 is exhausted during testing, wherein the vacuumizing mechanism 5 is a mechanical pump in the embodiment; a first pressure gauge 7 for detecting the pressure value in the transfer cavity 4 in real time is arranged on the transfer cavity 4;
the gas conveying system is used for conveying and regulating gas for measuring the specific surface area of the sample; the gas delivery system comprises a first three-way valve 8, a first pipeline 101, a second pipeline 102, a third pipeline 103, a fourth pipeline 104, a four-way valve 12 and a second three-way valve 15; the first pipeline 101, the second pipeline 102 and the fourth pipeline 104 have the same pipe diameter, and the pipe diameter of the third pipeline 103 is 1/4-1/5 of the pipe diameter of the first pipeline 101, in this embodiment, the first pipeline 101, the second pipeline 102 and the fourth pipeline 104 are 1/4 pipes, and the third pipeline 103 is 1/16 thin pipes;
wherein, the first valve port of the first three-way valve 8 is communicated with the transfer cavity 4, the second valve port is communicated with the high-pressure nitrogen cylinder 3 through a first pipeline 101, and the third valve port is communicated with one end of a second pipeline 102;
a first valve port of the four-way valve 12 is communicated with a third valve port of the first three-way valve 8 through a second pipeline 102, the second valve port of the four-way valve 12 is communicated with the manifold 13, the third valve port is communicated with one end of a third pipeline 103, and a fourth valve port of the four-way valve 12 is provided with a second pressure gauge 14 for detecting the air pressure value in the manifold 13 in real time;
a first valve port of the second three-way valve 15 is communicated with a third valve port of the four-way valve 12 through a third pipeline 103, a second valve port of the second three-way valve 15 is communicated with the sample chamber 17, and the third valve port is communicated with the transfer chamber 4 through a fourth pipeline 104;
a first control valve 9 is arranged on the first pipeline 101, a second control valve 11 is arranged on the second pipeline 102, and a third control valve 16 is arranged between a second valve port of the second three-way valve 15 and the sample chamber 17;
a manifold 13 for adjusting the pressure and fluctuations in nitrogen gas delivery;
the sample chamber 17 is used for storing a test sample, and a heating coat for heating the sample to remove water vapor is detachably sleeved on the outer side of the sample chamber 17;
the liquid nitrogen Dewar flask 18 is movably sleeved on the outer side of the sample chamber 17 and is used for performing air suction test on the sample; the lower end of the liquid nitrogen Dewar bottle 18 is provided with a lifting unit for lifting the liquid nitrogen Dewar bottle 18 so as to continuously immerse the sample chamber 17 in liquid nitrogen, in the embodiment, the lifting unit can be a lifting cylinder or an electric bracket so as to lift the liquid nitrogen Dewar bottle 18 to ensure the air suction test of the sample;
the high-pressure nitrogen cylinder 3, the transfer chamber 4, the manifold 13 and the sample chamber 17 are communicated through a gas delivery system, and the gas delivery path is adjusted as required.
The testing method of the specific surface area testing device is as follows:
s1, placing the sample into a sample chamber 17 and opening a third control valve 16, wherein in the embodiment, the sample chamber 17 can be a quartz tube, a second three-way valve 15 communicated between the sample chamber 17 and a transfer chamber 4 is used for air suction, a heating coat is wrapped outside the sample chamber 17 for heating and water vapor removal for 1h, after the water vapor removal is finished, the sample is transferred to an analytical balance for weighing and recording, then the sample with the water vapor removed is placed into the sample chamber 17, and the residual space in the sample chamber 17 is filled with a filler which does not absorb gas, so that the dead volume is reduced;
s2, heating the heating clothes outside the sample room 17 filled with the sample and the vacant space, simultaneously opening all valves of the gas delivery system and opening the vacuum-pumping mechanism 5 to remove water vapor (110-60 minutes)
S3, after exhausting, waiting for the sample to return to room temperature, then opening a high-pressure nitrogen bottle to carry out gas washing on the testing device for three times, and replacing air in the testing device with high-purity nitrogen;
s4, after the test device is vacuumized, the vacuumizing mechanism 5 is closed, the high-pressure nitrogen bottle 3 is opened to fill nitrogen into the transfer cavity 4, then the nitrogen in the transfer cavity 4 is slowly filled into the manifold 13 and the sample chamber 17, and the air pressure in the manifold 13 and the sample chamber 17 is regulated by the second control valve 11 to be stabilized at a required pressure value and recorded;
s4-1, vacuumizing the testing device to be within 0.01 atmospheric pressure through a vacuumizing mechanism 5, and filling nitrogen with 0.5 atmospheric pressure into a transit cavity 4 through a high-pressure nitrogen bottle 3;
s4-2, communicating the sample chamber 17 with the manifold 13, slowly communicating the transfer chamber 4 with the manifold 13, and slowly filling the gas in the transfer chamber 4 into the manifold 13;
s4-3, stopping inflating after the pressure in the manifold 13 reaches 0.05 atmosphere;
s4-4, after the air pressure is stable, recording the air pressure value of the manifold 13 through a second pressure gauge 14;
s5, immersing the sample chamber 17 in a liquid nitrogen Dewar flask 18 to cool the sample, adsorbing nitrogen by the sample, gradually reducing the air pressure in the manifold 13, recording the air pressure value of the manifold 13 for the second time by a second pressure gauge 14 after the air pressure is stable, and obtaining the actual volume V of the nitrogen adsorbed in the sample pore according to the difference of the air pressure values for the second time;
s6, heating the sample in the sample chamber 17 to restore the initial temperature, repeating the steps S1-S5 for a plurality of times, and calculating to obtain the volume Vm of the nitrogen adsorbed in the sample pore in the single layer;
s7, according to the calculation model:
wherein N is the Avogastron constant, Sigma is the cross-sectional area of a nitrogen molecule (0.162nm2), Vm is the volume of nitrogen adsorbed on the surface of a sample pore monolayer, W is the mass of the test sample, and the specific surface area S of the sample is calculatedg；
The specific calculation process in S5-S7 is as follows:
according to the relation formula between the volume V of the real adsorbed nitrogen in the sample and the Vm adsorbed by the monolayer:
wherein V is the actual volume of nitrogen adsorbed in the pores of the sample with unit mass, Vm is the single-layer adsorbed volume of nitrogen in the pores of the sample with unit mass, P is the nitrogen partial pressure, P0 is the saturated vapor pressure of nitrogen at the liquid nitrogen temperature, C is a constant related to thermal adsorption, and the larger the C value is, the stronger the adsorption capacity is;
several different sets of P/P0 values were taken during the test, the values being in the range of 0.05-0.35
To pair
In a linear relationship and
measuring different P/P0 values to obtain a linear curve of the nitrogen adsorption volume V, and calculating Vm through slope and intercept;
assuming that the nitrogen at the surface of the adsorbent is just a monolayer of molecules, the surface area of the material when in the standard state (one atmosphere, 0 ℃) is:
wherein S isgIs the specific surface area of the sample, N is the Avogastron constant, Sigma is oneThe cross-sectional area of the nitrogen molecule (0.162nm2), Vm is the volume of nitrogen adsorbed by the monolayer on the surface of the sample pore, and W is the mass of the test sample;
the specific surface area of the sample obtained by substituting the constant is:
example 2
The difference between the embodiment and the embodiment 1 is that the testing method of the specific surface area testing device of the invention further includes a test of changing the air pressure value, the test of changing the air pressure value is carried out on the premise that the testing device does not contain any impurity gas, the liquid nitrogen dewar 18 is taken down after the test is finished, the sample in the sample chamber 17 is heated by using a hot air gun or an electric hair drier to exhaust air, the value of the second pressure gauge 14 on the manifold 13 is recovered to the pressure value of the initial temperature, the steps S1-S5 are repeated, the air pressure value in the manifold 13 is changed, the sample chamber 17 is immersed in the liquid nitrogen dewar 18, the sample is cooled, the sample adsorbs nitrogen, the air pressure in the manifold 13 is gradually reduced, and the air pressure value of the manifold 13 is recorded for the second time through the second pressure gauge 14 after the air pressure is stabilized;
thereafter, calculation procedure with reference to S5-S7 of example 1, the adsorption values of the samples under the conditions of different air pressure values were measured.
Example 3
The present embodiment is different from embodiment 1 in that the testing method of the specific surface area testing apparatus of the present invention further includes a replacement sample test:
and after the test is finished, the liquid nitrogen Dewar bottle 18 is taken down, the sample in the sample chamber 17 is heated by using a hot air gun or an electric hair drier for exhausting, when the value of the second pressure gauge 14 on the manifold 13 is recovered to the pressure value of the initial temperature, the third control valve 16 is closed, the sample chamber 17 is taken down and replaced by a new sample in the sample chamber 17, and then the steps S1-S7 are repeated, so that the adsorption value of the new sample can be measured.
Other undescribed structures refer to example 1.
According to the specific surface area testing device and the testing method provided by the embodiment of the invention, the gas path system consisting of the sample chamber 17 and the manifold 13 can effectively measure the actual volume of nitrogen adsorption of the sample, and further repeat the test to obtain the volume of nitrogen adsorbed in a single layer in the sample pores, and the specific surface area of the sample is obtained according to the calculation model, so that compared with the traditional large-scale equipment, the testing device has the advantages that the volume is reduced, the occupied area is small, the testing device can flexibly move, the device cost is reduced, and the price is 1/10 of the traditional testing equipment;
meanwhile, the sample chamber 17 and the manifold 13 are detachably mounted, can be adjusted according to the sample and the test requirement, and have high adaptability; the arrangement of the transfer cavity 4 forms a pressure step buffer zone, and the gas pressure of the manifold 13 and the gas pressure of the sample chamber 17 can be accurately and rapidly controlled by matching with the second control valve 11, so that the gas pressure in the manifold 13 can be rapidly adjusted; 1/16 tubules are used between the sample chamber 17 and the manifold 13, and the space outside the sample inside the sample chamber 17 is filled with a filler that does not absorb gas, thereby reducing the dead volume and making the data tested more accurate.
In the description of the present invention, it should be noted that the terms "first", "second", and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
Finally, it should be noted that: the above-mentioned embodiments are only specific embodiments of the present invention, which are used for illustrating the technical solutions of the present invention and not for limiting the same, and the protection scope of the present invention is not limited thereto, although the present invention is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the embodiments of the present invention, and they should be construed as being included therein. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. A specific surface area testing device comprises a frame (1) used as a mounting base body and a high-pressure nitrogen cylinder (3) which is arranged on the frame (1) and used for providing nitrogen, and is characterized by also comprising a transfer chamber (4), a gas delivery system, a manifold (13), a sample chamber (17) and a liquid nitrogen Dewar flask (18) which are arranged on the frame (1);
the transfer cavity (4) is fixed on the rack (1) through a fixing frame (2) and is used for forming a pressure step buffer area, an exhaust port is formed in the transfer cavity (4), and a vacuumizing mechanism (5) for vacuumizing the interior of the testing device is mounted on the exhaust port;
and a gas delivery system for delivering and regulating the gas pressure of the measurement sample chamber and the manifold.
A manifold (13) for storing nitrogen adsorbed by the sample;
a sample chamber (17) for storing a test sample;
the liquid nitrogen Dewar flask (18) is movably sleeved on the outer side of the sample chamber (17) and is used for storing liquid nitrogen and performing air suction test on the sample;
the high-pressure nitrogen cylinder (3), the transfer cavity (4), the manifold (13) and the sample chamber (17) are communicated through a gas delivery system, and the gas delivery path is adjusted as required.
2. The specific surface area test apparatus according to claim 1, wherein: the gas conveying system comprises a first three-way valve (8), a first pipeline (101), a second pipeline (102), a third pipeline (103), a fourth pipeline (104), a four-way valve (12) and a second three-way valve (15);
wherein, a first valve port of the first three-way valve (8) is communicated with the transfer cavity (4), a second valve port is communicated with the high-pressure nitrogen cylinder (3) through a first pipeline (101), and a third valve port is communicated with one end of a second pipeline (102);
a first valve port of the four-way valve (12) is communicated with a third valve port of the first three-way valve (8) through a second pipeline (102), the second valve port of the four-way valve (12) is communicated with a manifold (13), and the third valve port is communicated with one end of a third pipeline (103);
the first valve port of the second three-way valve (15) is communicated with the third valve port of the four-way valve (12) through a third pipeline (103), the second valve port of the second three-way valve (15) is communicated with the sample chamber (17), and the third valve port is communicated with the transfer chamber (4) through a fourth pipeline (104).
3. The specific surface area test apparatus according to claim 2, wherein: a first control valve (9) is installed on the first pipeline (101), a second control valve (11) is installed on the second pipeline (102), and a third control valve (16) is arranged between a second valve port of the second three-way valve (15) and the sample chamber (17).
4. The specific surface area test apparatus according to claim 2, wherein: the transfer chamber (4) is provided with a first pressure gauge (7) for detecting the pressure value in the transfer chamber (4) in real time, and the fourth valve port of the four-way valve (12) is provided with a second pressure gauge (14) for detecting the pressure value in the manifold (13) in real time.
5. The specific surface area test apparatus according to claim 1, wherein: the first pipeline (101), the second pipeline (102) and the fourth pipeline (104) are of the same specification pipe diameter, and the pipe diameter of the third pipeline (103) is 1/4-1/5 of the pipe diameter of the first pipeline (101).
6. The specific surface area test apparatus according to claim 1, wherein: the detachable cover in outside of sample room (17) is equipped with the heating clothing that is used for the sample heating to get rid of aqueous vapor.
7. The specific surface area test apparatus according to claim 1, wherein: the lower end of the liquid nitrogen Dewar bottle (18) is provided with a lifting unit for lifting the liquid nitrogen Dewar bottle (18) so as to continuously immerse the sample into the liquid nitrogen.
8. A method for testing a specific surface area test device according to any one of claims 1 to 7, wherein: the method comprises the following steps:
s1, preheating the sample to remove water vapor, weighing and recording, then putting the sample with the water vapor removed into the sample chamber (17) and filling the empty space in the sample chamber (17) with filler which does not absorb gas;
s2, reheating the sample chamber (17), starting the vacuumizing mechanism (5) for vacuumizing, and removing water vapor;
s3, after the exhaust is finished, waiting for the sample to return to the room temperature, starting a high-pressure nitrogen bottle (3) to carry out multiple air washing on the testing device, and replacing the air in the testing device with high-purity nitrogen;
s4, after the test device is vacuumized, the vacuumizing mechanism (5) is closed, the transit cavity (4) is filled with nitrogen, then the nitrogen in the transit cavity (4) is slowly filled into the manifold (13) and the sample chamber (17), and the air pressure in the manifold (13) and the sample chamber (17) is regulated through the second control valve (11) to be stabilized at a required pressure value and recorded;
s5, immersing the sample chamber (17) in a liquid nitrogen Dewar flask (18) to cool the sample, gradually reducing the air pressure in the manifold (13) after the sample adsorbs nitrogen, recording the air pressure value in the manifold (13) for the second time after the air pressure is stable, and obtaining the actual volume V of the nitrogen adsorbed in the pores of the sample of unit mass according to the difference of the air pressure values for the second time;
s6, heating the sample in the sample chamber (17) to restore the initial temperature, repeating the steps S1-S5 for a plurality of times, and calculating to obtain the volume Vm of the nitrogen adsorbed in the single layer in the sample pores;
s7, according to the calculation model:
wherein N is an Avogastron constant,
the cross-sectional area of one nitrogen molecule (0.162nm2), Vm is the volume of nitrogen adsorbed by the monolayer on the surface of the sample pore, W is the mass of the sample to be tested, and the specific surface area S of the sample is calculatedg。
9. The method for testing a specific surface area test apparatus according to claim 8, wherein: in step S4, the specific operation steps are as follows:
s4-1, vacuumizing the testing device to be within 0.01 atmospheric pressure through a vacuumizing mechanism (5), and filling nitrogen with 0.5 atmospheric pressure into a transit cavity (4) through a high-pressure nitrogen bottle (3);
s4-2, communicating the sample chamber (17) with the manifold (13), slowly communicating the transfer chamber (4) with the manifold (13), and slowly filling nitrogen in the transfer chamber (4) into the manifold (13);
s4-3, stopping inflating after the internal pressure of the manifold (13) reaches 0.05 atmospheric pressure;
and S4-4, recording the air pressure value of the manifold (13) after the air pressure is stabilized.
10. The method for testing a specific surface area test apparatus according to claim 8, wherein: in step S6, the calculation model is as follows:
according to the relation formula between the volume V of the real adsorbed nitrogen in the sample and the Vm adsorbed by the monolayer:
wherein V is the actual volume of nitrogen adsorbed in the pores of the sample with unit mass, Vm is the single-layer adsorbed volume of nitrogen in the pores of the sample with unit mass, P is the nitrogen partial pressure, P0 is the saturated vapor pressure of nitrogen at the liquid nitrogen temperature, C is a constant related to thermal adsorption, and the larger the C value is, the stronger the adsorption capacity is;
several different sets of P/P0 values were taken during the test,
to pair
In a linear relationship and
measuring different P/P0 values to obtain a linear curve of the nitrogen adsorption volume V, and calculating Vm through slope and intercept;
assuming that the nitrogen at the surface of the adsorbent is just a monolayer of molecules, the surface area of the material when in the standard state (one atmosphere, 0 ℃) is:
wherein S isgIs the specific surface area of the sample, N is the Avogastron constant,
is the cross-sectional area of one nitrogen molecule (0.162nm2), Vm is the volume of nitrogen adsorbed by the monolayer on the surface of the sample pores, and w is the mass of the test sample;
the specific surface area of the sample obtained by substituting the constant is:
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111382773.7A CN114199719A (en) | 2021-11-22 | 2021-11-22 | Specific surface area testing device and testing method |
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