CN115639127A - Method and device for measuring porosity of porous material under pressure - Google Patents
Method and device for measuring porosity of porous material under pressure Download PDFInfo
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- CN115639127A CN115639127A CN202211100921.6A CN202211100921A CN115639127A CN 115639127 A CN115639127 A CN 115639127A CN 202211100921 A CN202211100921 A CN 202211100921A CN 115639127 A CN115639127 A CN 115639127A
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Abstract
The application provides a method and a device for measuring porosity of a porous material in a compressed state. The measuring method comprises the following steps: obtaining the apparent volume of a porous material sample to be detected; completely soaking a porous material sample to be detected in a wetting liquid; separating the porous material sample to be detected from the wetting liquid, allowing the porous material sample to be detected to stand still for dropping liquid in a non-pressurized state, and allowing all dropped wetting liquid to enter an impregnation tank; gradually extruding the porous material sample to be tested by adopting the pressurizing unit, moving the first pressurizing piece and/or the second pressurizing piece along the thickness direction of the porous material sample to be tested when each step of extrusion is executed, reducing the interval to the current interval, recording the current interval after each step of extrusion, and recording the current weight of the wetting liquid in the dipping tank when the porous material sample to be tested does not drip any more; and calculating the current porosity of the porous material sample to be tested in the current pressed state according to the apparent volume, the initial weight of the wetting liquid, the current weight and the density.
Description
Technical Field
The invention mainly relates to the technical field of porous material characterization, in particular to a method and a device for measuring porosity of a porous material in a compressed state.
Background
The porosity is a ratio of a total volume of interconnected minute pores in the porous material medium to an external volume of the porous material medium. The electrode in the flow battery is a porous material medium, the flow rate of electrolyte in the electrode plays a key role in the performance of the electric pile, and the porosity of the electrode material is a key parameter influencing the liquid transmission performance of the electrode. When the stack of the flow battery is assembled, the electrode needs to be compressed by an external fastening force, so that the electrode is tightly attached to the conductive pole plate to reduce the internal resistance of the stack. Along with the compression of the electrode, the porosity of the electrode also changes, and further the distribution and the transmission of the electrolyte in the reaction process are influenced. Especially under high current density, the electrochemical reaction speed is accelerated, and too low porosity can cause that the diffusion speed of reactants in the electrolyte cannot be matched with the consumption speed of the reactants on the surface of an electrode, namely concentration polarization is generated, and the voltage efficiency and the power density of the battery are greatly reduced. Therefore, it is necessary to determine the porosity of the electrode material under different compression states, to screen the electrode material, to determine the proper external fastening force, and to optimize the stack structure and the cell performance.
The porosity measuring method commonly used at present comprises mercury pressing method, gas adsorption method, weighing method, theoretical calculation method and the like. The mercury intrusion method is a relatively mature porosity testing method, but mercury is used as a non-wetting solvent, so that irreversible damage can be caused to materials, and safety accidents that mercury leaks and diffuses to cause poisoning of experimenters are very easy to occur. The gas adsorption method can accurately obtain the porosity of the porous material, but the method is mainly used for testing medium and small micropores of 2-100 nm, and the whole testing period is relatively long. More importantly, these methods are only suitable for measuring the porosity of a material in the non-stressed state, whereas the porosity under stress is often referenced to a measured value after decompression, which is subject to a large error compared to the true porosity of the porous material in the compressed state. For some porous materials with resilience, such as carbon felt and graphite felt electrode materials, the measured value after pressure relief does not reflect the porosity under actual working conditions.
Disclosure of Invention
The invention aims to provide a measuring method and a measuring device for measuring the true porosity of a porous material in a compressed state.
In order to solve the technical problem, the invention provides a method for measuring the porosity of a porous material in a compressed state, which is characterized by comprising the following steps: obtaining the apparent volume of a porous material sample to be detected; completely soaking the porous material sample to be tested in wetting liquid, wherein the wetting liquid has an initial weight and is loaded in an impregnation tank; separating the porous material sample to be tested from the wetting liquid, allowing the porous material sample to be tested to stand for dropping liquid in a non-pressurized state, allowing all dropped wetting liquid to enter the dipping tank, and recording the current weight of the wetting liquid in the dipping tank when the porous material sample to be tested does not drop liquid any more; gradually extruding the porous material sample to be detected by adopting a pressurizing unit, wherein the pressurizing unit comprises a first pressurizing part and a second pressurizing part, the porous material sample to be detected is positioned between the first pressurizing part and the second pressurizing part, and a distance is formed between the first pressurizing part and the second pressurizing part; when each step of extrusion is carried out, moving the first pressurizing piece and/or the second pressurizing piece along the thickness direction of the porous material sample to be tested, reducing the distance to the current distance, simultaneously keeping the porous material sample to be tested in the current pressure state, recording the current distance after each step of extrusion, allowing the porous material sample to be tested to stand still for dropping liquid under the current pressure state, allowing all dropped wetting liquid to enter the impregnation tank, and recording the current weight of the wetting liquid in the impregnation tank when the porous material sample to be tested does not drop liquid any more; and calculating the current porosity of the porous material sample to be detected in the current pressed state by adopting the following formula:
current porosity (%) = (m) 0 -m c )V 0 /ρ；
Wherein the current porosity (%) represents the porous material sample to be testedCurrent porosity, m, of the current state of compression 0 Represents the initial weight, m c Represents said current weight, V 0 Representing the apparent volume, p represents the density of the wetting fluid.
In an embodiment of the present application, the method further includes: calculating the current compression rate of the porous material sample to be detected in the current compression state by adopting the following formula:
current compression ratio (%) = (d-d) c )/d；
Wherein the current compression rate (%) represents the current compression rate of the porous material sample to be tested in the current compression state, d represents the original thickness of the porous material sample to be tested, d c Representing the current pitch.
In an embodiment of the present application, the method further includes: and establishing a relation curve between the compression rate and the porosity of the porous material sample to be tested according to the plurality of current compression rates and the plurality of current porosities.
In an embodiment of the present application, the wetting fluid comprises a non-polar hydrocarbon oil.
In an embodiment of the present application, the apparent volume is equal to the product of the original length, the original width and the original thickness of the porous material sample to be tested.
In an embodiment of the present application, the porous material sample to be tested is a carbon porous material.
The application also provides a device for measuring the porosity of the porous material in a pressed state, which is characterized by comprising a fixing unit, a pressurizing unit, a bearing piece and a weighing unit, wherein the fixing unit comprises a fixing frame extending along the vertical direction; the pressurizing unit comprises a first pressurizing piece and a second pressurizing piece, the first pressurizing piece and the second pressurizing piece are arranged on the fixed frame in a lifting manner, and the position of the first pressurizing piece and/or the second pressurizing piece along the horizontal direction is adjustable; the supporting piece is arranged between the first pressurizing piece and the second pressurizing piece in a penetrating mode, the supporting piece is provided with a liquid leakage through hole, and the supporting piece is used for bearing a porous material sample to be tested; the weighing unit comprises a weigher and an immersion tank for loading wetting liquid, the immersion tank is positioned on the weigher, and the projection of the support piece along the vertical direction is completely positioned inside the projection of the immersion tank along the vertical direction.
In an embodiment of the application, the fixed frame includes a first side frame and a second side frame, the first pressure piece is arranged on the first side frame in a liftable manner, and the second pressure piece is arranged on the second side frame in a liftable manner.
In an embodiment of the present application, the first side frame includes a first clamping groove and at least one first limiting member, the second side frame includes a second clamping groove and at least one second limiting member, the first pressure member is disposed in the first clamping groove through the first limiting member, and the second pressure member is disposed in the second clamping groove through the second limiting member.
In an embodiment of the present application, the pressing device further includes an adjusting rod, the adjusting rod penetrates through the fixing frame and is connected to the pressing unit, and the adjusting rod is used for moving the first pressing member and/or the second pressing member along the horizontal direction.
In an embodiment of the present application, the first pressing member includes a first through hole, the second pressing member includes a second through hole, and the support member is disposed through the first through hole and the second through hole.
In an embodiment of the application, the support is a fine wire mesh.
In an embodiment of this application, first pressor has first pressor face, the second pressor has the second pressor face, first pressor face with the second pressor face sets up relatively, when adopting the pressure unit progressively to extrude the porous material sample that awaits measuring, first pressor face with the second pressor face respectively with the porous material sample contact that awaits measuring, all have the hydrophobic wetting liquid coating on the first pressor face with on the second pressor face.
In an embodiment of the present application, the hydrophobic wetting liquid coating comprises polytetrafluoroethylene or silicone resin.
In an embodiment of the present application, the material of the first and second pressing surfaces is carbon steel or alloy steel.
In an embodiment of the present application, the fixing unit further includes an upper end plate extending in a horizontal direction, and the upper end plate includes a plurality of scales arranged in the horizontal direction for measuring a distance between the first pressing member and the second pressing member.
In an embodiment of the present application, the measuring apparatus is configured to measure the porosity of the porous material sample to be measured by using the measuring method as described above.
The measuring method and the measuring device have the advantages that the compression rate of the porous material sample to be measured is represented by the distance between the first pressurizing piece and the second pressurizing piece, so that wetting liquid dripped out of the porous material sample to be measured in different compression states returns to the impregnation tank, the change of the weight of the liquid in the impregnation tank is used for calculating the current porosity, the measuring method and the calculating method are simple and easy to implement, and the porosity of the sample in different compression states can be conveniently obtained. In practical application, the pressurizing unit is adopted to apply pressure to the sample to simulate the stress of the sample in the actual use process, such as the application of fastening force in the assembling process of the simulated stack, so that the obtained measurement result is more in line with the actual working condition, and the method has more guiding significance for stack structure design and battery performance optimization.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the principle of the invention. In the drawings:
FIG. 1 is an exemplary flow chart of a measurement method of an embodiment of the present application;
FIG. 2 is a graph of the relationship between porosity and compressibility of a carbon felt electrode obtained according to a measurement method of an embodiment of the present application;
FIG. 3 is a schematic structural diagram of a measuring device according to an embodiment of the present application;
fig. 4 is a schematic side view of a holder of a measuring device according to an embodiment of the present application.
Detailed Description
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings used in the description of the embodiments will be briefly described below. It is obvious that the drawings in the following description are only examples or embodiments of the application, from which the application can also be applied to other similar scenarios without inventive effort for a person skilled in the art. Unless otherwise apparent from the context, or otherwise indicated, like reference numbers in the figures refer to the same structure or operation.
As used in this application and in the claims, the terms "a," "an," "the," and/or "the" are not intended to be inclusive in the singular, but rather are intended to include the plural, unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" are intended to cover only the explicitly identified steps or elements as not constituting an exclusive list and that the method or apparatus may comprise further steps or elements.
The relative arrangement of the components and steps, the numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present application unless specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective portions shown in the drawings are not drawn in an actual proportional relationship for the convenience of description. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate. In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.
In the description of the present application, it is to be understood that the directions or positional relationships indicated by the directional terms such as "front, rear, upper, lower, left, right", "lateral, vertical, horizontal" and "top, bottom", etc., are generally based on the directions or positional relationships shown in the drawings, and are for convenience of description and simplicity of description only, and in the case of not making a reverse description, these directional terms do not indicate and imply that the device or element being referred to must have a particular orientation or be constructed and operated in a particular orientation, and therefore should not be construed as limiting the scope of the present application; the terms "inner and outer" refer to the inner and outer relative to the profile of the respective component itself.
For ease of description, spatially relative terms such as "over … …", "over … …", "over … …", "over", etc. may be used herein to describe the spatial positional relationship of one device or feature to another device or feature as shown in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures is turned over, devices described as "above" or "on" other devices or configurations would then be oriented "below" or "under" the other devices or configurations. Thus, the exemplary term "above … …" may include both orientations of "above … …" and "below … …". The device may be otherwise variously oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
It should be noted that the terms "first", "second", and the like are used to define the components, and are only used for convenience of distinguishing the corresponding components, and the terms have no special meanings unless otherwise stated, and therefore, the scope of protection of the present application is not to be construed as being limited. Further, although the terms used in the present application are selected from publicly known and used terms, some of the terms mentioned in the specification of the present application may be selected by the applicant at his or her discretion, the detailed meanings of which are described in relevant parts of the description herein. Further, it is required that the present application is understood, not simply by the actual terms used but by the meaning of each term lying within.
Flow charts are used herein to illustrate operations performed by systems according to embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed in the exact order in which they are performed. Rather, various steps may be processed in reverse order or simultaneously. Meanwhile, other operations are added to or removed from these processes.
The method and the device for measuring the porosity of the porous material under the compressed state are suitable for any porous material, and are particularly suitable for porous materials serving as electrode materials in flow batteries, such as carbon felts, graphite felts and the like.
Fig. 1 is an exemplary flowchart of a measurement method according to an embodiment of the present application. Referring to fig. 1, the measurement method of this embodiment includes the steps of:
step S110: and obtaining the apparent volume of the porous material sample to be detected.
For simplicity, the present specification will refer to the porous material sample to be tested as simply the "sample" in some places. Preferably, the porous material sample to be tested is an electrode material for a flow battery. Preferably, the porous material sample to be tested is a carbon porous material, such as carbon felt, graphite felt, and the like. In step S110, the porous material sample to be measured may be a piece of sample cut from the porous material to be measured, or may be a piece of complete electrode material in actual use.
The shape and size of the sample are not limited by the application. In some embodiments, the sample is rectangular with a certain thickness.
The present application does not limit how the apparent volume of the sample is obtained in step S110. In some embodiments, the apparent volume is equal to the product of the original length, the original width, and the original thickness of the porous material sample to be tested. It should be noted that in the original state, the sample is not compressed by an external force, and is in an uncompressed state, in which the sample has an original length, an original width, and an original thickness.
Step S120: and completely soaking the porous material sample to be detected in wetting liquid, wherein the wetting liquid has an initial weight and is loaded in the soaking tank.
In some embodiments, the wetting fluid comprises a non-polar hydrocarbon oil, such as kerosene, light diesel, and the like.
In step S120, the term completely wet means that the wetting fluid has sufficiently soaked the sample, and all or almost all of the pores in the sample are filled with the wetting fluid.
In some embodiments, after immersing the sample in the wetting fluid for a predetermined length of time, the sample is considered to have been completely wetted. In some embodiments, the preset time period is 5 to 15 minutes, and whether the sample is completely soaked is judged through the soaking time period. In some embodiments, a sample is considered to have been completely wetted when no bubbles visible to the naked eye appear on the surface of the sample, and the surface of the sample is observed to determine whether the sample is completely wetted.
The size and shape of the dipping tank are not limited in the present application.
The application is not limited as to how this initial weight is measured. The initial weight m of the wetting fluid may be measured using any suitable weighing instrument 0 。
Step S130: separating the porous material sample to be tested from the wetting liquid, allowing the porous material sample to be tested to stand for dropping liquid in a non-pressurized state, allowing all dropped wetting liquid to enter the impregnation tank, and recording the current weight of the wetting liquid in the impregnation tank when the porous material sample to be tested does not drop liquid any more.
The application does not limit how the sample is allowed to stand. For example, the sample may be placed on a plate having a plurality of through holes, the plate being disposed above the immersion tank, and the wetting fluid may drip through the plurality of through holes and into the immersion tank. To ensure that the drip is completely into the dipping tank, the dipping tank should be large enough and the projected position of the specimen when it is at rest is completely within the dipping tank.
The present application is directed to how to measure the current weight m c And are not intended to be limiting. Can adopt and measure the initial weight m 0 The same method is used for measurement. At the measuring stepCurrent weight m in S130 c The sample should remain uncompressed and the pressure to which it is subjected can be considered to be 0.
Step S140: the sample of the porous material to be detected is gradually extruded by a pressurizing unit, the pressurizing unit comprises a first pressurizing part and a second pressurizing part, the sample of the porous material to be detected is positioned between the first pressurizing part and the second pressurizing part, and a space is formed between the first pressurizing part and the second pressurizing part.
The present application does not limit the specific structure of the pressing unit, which includes at least a first pressing member and a second pressing member with a space therebetween. It will be appreciated that the smaller the spacing, the greater the squeezing force to which the sample is subjected. This application adopts the pressurization unit to exert pressure to the sample and simulates this sample atress in the in-service use process, for example the application of the fastening force of simulation pile equipment in-process to the measuring result that makes the acquisition accords with actual condition more, has more instructive meaning to pile structural design and battery performance optimization.
The step S140 of pressing by the pressing unit means that the pressing unit presses the sample for a plurality of times, and the sample is compressed each time to a greater extent than the previous time.
Step S150: when each step of extrusion is executed, the first pressurizing piece and/or the second pressurizing piece are/is moved along the thickness direction of the porous material sample to be tested, the distance is reduced to be the current distance, the porous material sample to be tested is in the current pressed state, the current distance after each step of extrusion is recorded, the porous material sample to be tested is enabled to be in a standing dropping liquid in the current pressed state, all the dropping wetting liquid enters the dipping tank, and when the porous material sample to be tested does not drop any more, the current weight of the wetting liquid in the dipping tank is recorded.
Step S150 further illustrates that the pressing action of the pressing unit is caused by the movement of the first pressing member and/or the second pressing member, and the thickness of the sample is compressed by the pressing. By this movement, the distance between the first and second pressing members is gradually reduced, and the degree of sample compression is also increased stepwise. After each extrusion step, the current spacing is maintained, and the sample is takenThis dropping liquid that stews under current pressurized state. It is conceivable that the wetting liquid impregnated in the porous material is squeezed out to form drops when further pressure is applied, and that the wetting liquid in the compressed pores is squeezed out and the wetting liquid in the dip tank increases when the sample no longer drips. Current weight m of the wetting fluid c And the compressed rate of the pores.
Step S160: and calculating the current porosity of the porous material sample to be detected in the current pressed state. Specifically, the following formula (1) is employed for calculation:
current porosity (%) = (m) 0 -m c )V 0 /ρ (1)
Wherein the current porosity (%) represents the current porosity of the porous material sample in the current state under pressure, m 0 Denotes initial weight, m c Denotes the current weight, V 0 Indicating the apparent volume and p the density of the wetting fluid. ρ is a known quantity.
In some embodiments, the following equation (2) is also used to calculate the current compressibility of the porous material sample to be tested:
current compression ratio (%) = (d-d) c )/d (2)
Wherein, the current compression rate (%) represents the current compression rate of the porous material sample to be tested in the current compression state, d represents the original thickness of the sample, d c Indicating the current pitch.
It should be noted that if the distance corresponding to the current weight of the wetting fluid obtained in step S130 is defined as d, the current compressibility of the sample in the non-pressurized state is 0.
Through the above-mentioned steps S110-S160, at least one current porosity and corresponding at least one current compression rate of the sample may be obtained. When the extrusion step in step S140 is greater than 1, a plurality of current porosities and a plurality of corresponding current compression ratios may be obtained through a plurality of extrusion steps, so as to further establish a relationship curve between the compression ratio and the porosity of the porous material sample to be tested.
Fig. 2 is a graph showing a relationship between porosity and compressibility of a carbon felt electrode obtained by a measurement method according to an embodiment of the present application. As shown in fig. 2, the horizontal axis represents compressibility and the vertical axis represents porosity. Obviously, the porosity and compressibility are in a negative correlation trend. By establishing the relation curve, the porosity of the carbon felt electrode in different compression states can be obtained for guiding the stack structure design and the optimization of the battery performance.
Fig. 3 is a schematic structural diagram of a measurement apparatus according to an embodiment of the present application. The measuring apparatus 300 can be used to perform the measuring method shown in fig. 1, and the above description of the measuring method can be used to describe the measuring apparatus 300, and the same will not be expanded.
Referring to fig. 3, the measuring device 300 includes a fixing unit, a pressurizing unit 320, a supporter 330, and a weighing unit 340. Wherein the fixing unit includes a fixing frame 310 extending in a vertical direction. The pressing unit 320 includes a first pressing member 321 and a second pressing member 322, the first pressing member 321 and the second pressing member 322 are disposed on the fixing frame 310 in a liftable manner, and a position of the first pressing member 321 and/or the second pressing member 322 in a horizontal direction is adjustable. The supporting member 330 is arranged between the first pressurizing member 321 and the second pressurizing member 322 in a penetrating manner, the supporting member 330 has a liquid leakage through hole, and the supporting member 330 is used for bearing a porous material sample to be tested. The weighing unit 340 includes a weigher 341 and a dipping tank 342, the dipping tank 342 resting on the weigher 341, and the dipping tank 341 for loading the wetting fluid.
As shown in fig. 3, in this embodiment, the first pressing member 321 and the second pressing member 322 both have an L-shaped structure, i.e., both are composed of two sides perpendicular to each other. The two sides of the first pressing member 321 are connected with supporting members 323, the two sides of the second pressing member 322 are connected with supporting members 324, and the L-shaped structure comprises a triangular structure by arranging the supporting members 323 and 324, so that the stability and the strength of the structure are improved. In the embodiment shown in fig. 3, the first pressing member 321 and the second pressing member 322 are provided separately from each other and are not directly connected. In other embodiments, the first pressing member 321 and the second pressing member 322 are connected with a variable distance therebetween, for example, a compression spring is provided therebetween, which is not limited in the present application.
Fig. 3 shows an example, and in other embodiments, the first pressing member 321 and the second pressing member 322 may be plate-shaped structures, column-shaped structures, block-shaped structures, and the like.
As shown in fig. 3, the fixing frame 310 includes a first side frame 311 and a second side frame 312, a first pressing member 321 is liftably disposed on the first side frame 311, and a second pressing member 322 is liftably disposed on the second side frame 312. Fig. 3 is a side view of the measuring apparatus 300, and since the fixing frame 310 is extended in a vertical direction, both the first side frame 311 and the second side frame 312 are extended in a vertical direction and can be erected on a horizontal plane.
Fig. 4 is a schematic side view of a holder of a measuring device according to an embodiment of the present application. Referring to FIG. 3, FIG. 4 shows a right side view of the first side frame 311. As shown in fig. 4, the first side frame 311 includes a first engaging groove 410 and at least one first limiting member, and the first pressing member 321 is disposed in the first engaging groove 410 through the first limiting member. Specifically, each first limiting member includes a limiting element 421 and a fastening element 422 which are matched with each other. For example, the fastening element 422 may be a screw, and the position limiting element 421 is a snap plate having a screw fitting hole, or the like. Fig. 4 can also be used to illustrate the second side frame 312, and the second side frame 312 includes a second locking groove and at least one second retaining member, and the second pressing member 322 is disposed in the second locking groove through the first retaining member. The second slot may be the same as or different from the first slot, and the second limiting member may be the same as or different from the first limiting member.
It is understood that the heights of the first and second pressing members 321 and 322 may be made equal by adjusting the heights thereof in the vertical direction.
As shown in fig. 3, in some embodiments, the measuring device 300 further includes an adjusting lever 350, the adjusting lever 350 is connected to the first pressing member 321 of the pressing unit 320 through the first side frame 311 of the fixing frame 310, and the adjusting lever 350 is used to move the first pressing member 321 in a horizontal direction. In one embodiment, the measuring device 300 includes an adjusting lever connected to the second pressing member 322 through the second side frame 312 for moving the second pressing member 322 in a horizontal direction. In one embodiment, the measuring device 300 includes 2 adjusting rods, one of which is connected to the first pressing member 321 through the first side frame 311, for moving the first pressing member 321 in a horizontal direction; another adjusting bar is connected to the second pressing member 322 through the second side frame 312 for moving the second pressing member 322 in a horizontal direction. The adjusting rod 350 gradually presses the porous material sample to be tested in step S150 of the method by moving the first pressing member 321 and/or the second pressing member 322 to change the distance therebetween.
The present application is not limited to the specific structure of the adjustment lever 350. For example, referring to fig. 3, the adjustment lever 350 may include a link 351 and a handle 352, and the link 351 may be moved in a horizontal direction by pushing or rotating the handle 352, thereby moving the first pressing member 321.
In some embodiments, the first pressing member 321 includes a first through hole, the second pressing member 322 includes a second through hole, and the supporter 330 is disposed through the first through hole and the second through hole. Referring specifically to fig. 3, a first through hole 327 is provided at a lower end of the vertical side 325 of the L-shaped first pressing member 321, and a second through hole 328 is provided at a lower end of the vertical side 326 of the L-shaped second pressing member 322. In this embodiment, the support 330 is a fine mesh screen, i.e., the openings are weep holes, through which fluid dripping from the sample can fall when the sample soaked with the wetting fluid is placed on the support 330. The first and second through holes 327 and 328 may also be aligned by adjusting the heights of the first and second pressing members 321 and 322 so that the surface of the susceptor 330 is parallel to a horizontal plane. As shown in fig. 3, in the step S150, although the distance between the first pressing member 321 and the second pressing member 322 is reduced, the position of the supporting member 330 may be kept unchanged or changed only slightly during the step-by-step pressing, which does not affect the pressing operation and does not press the sample.
As shown in fig. 3, in some embodiments, the first pressing member 321 has a first pressing surface 361, the second pressing member 322 has a second pressing surface 362, the first pressing surface 361 and the second pressing surface 362 are disposed opposite to each other, when the porous material sample to be tested is gradually pressed by the pressing unit 320, the first pressing surface 361 and the second pressing surface 362 respectively contact with the porous material sample to be tested, and the first pressing surface 361 and the second pressing surface 362 both have a hydrophobic coating. As shown in fig. 3, when measuring the porosity, the first pressing surface 361 and the second pressing surface 362 are actually in contact with the sample, and the lyophobic coatings are disposed at the two positions, so that the wetting liquid can be prevented from being absorbed by the pressing unit 320, and the accuracy of the measurement result can be affected.
In some embodiments, the hydrophobic wetting fluid coating comprises polytetrafluoroethylene or a silicone resin.
In order to perform effective pressing, the materials of the first pressing surface 361 and the second pressing surface 362 have high strength and high modulus characteristics. In some embodiments, the material of first and second pressing faces 361, 362 is carbon steel or alloy steel. In some embodiments, the material of both the first and second press members 321, 322 is carbon steel or alloy steel.
As shown in fig. 3, the fixing unit may further include a lower end plate 313 and an upper end plate 314, which form a rectangular frame structure, such as a box, together with the first side frame 311 and the second side frame 312. Both the upper end plate 314 and the lower end plate 313 extend in the horizontal direction. In some embodiments, the upper end plate 314 includes a plurality of scales arranged in a horizontal direction, and the plurality of scales are used to measure the distance between the first pressing member 321 and the second pressing member 322. As shown in fig. 3, a plurality of scales may be marked on the upper end plate 314, or a scale including a plurality of scales may be adhered to the surface of the upper end plate 314, which is not limited in the present application. If the upper end plate 314 is a plate having a certain thickness, as shown in fig. 3, a plurality of scales are provided on the side thereof. In other embodiments, a plurality of scales may be provided on the top surface of the upper end plate 314. By providing the scale, the distance between the first pressing member 321 and the second pressing member 322 can be visually read.
As shown in fig. 3, the weighing unit 340 may be fixedly disposed above the lower end plate 313. In some embodiments, the scale 341 is an analytical balance. During the measurement, the lower end plate 313 should be kept horizontal in order to ensure the accuracy of the analytical balance. The dipping tank 342 is located directly below the support 330 and is used for receiving the liquid dropped from the sample. In order to ensure that all drops enter the immersion tank 342, the projection of the support 330 in the vertical direction lies entirely within the projection of the immersion tank 342 in the vertical direction, on the basis of which the cross-sectional area of the immersion tank 342 can be as large as possible.
The following describes specific steps in performing the above-described measurement method using the measurement apparatus 300.
Step S510: obtaining a sample after regular cutting, and calculating the apparent volume V of the sample 0 . The immersion tank 342 is filled with a sufficient amount of wetting fluid, which should be greater than the amount of wetting fluid that the sample can absorb. The reading of the reading weigher 341 is registered as the initial weight m of the wetting fluid 0 . The initial weight m 0 May include the weight of the dip tank 342 or may be the net weight of the wetting fluid after peeling.
Step S520: the heights of the first and second pressing members 321 and 322 are adjusted to make the holder 330 horizontal, and the interval between the first and second pressing members 321 and 322, specifically, the interval between the first and second pressing surfaces 361 and 362 is adjusted by the adjustment lever 350 to be slightly larger than the original thickness d of the specimen, and the specimen is rested on the holder 330. At this point, the sample was an unimpregnated, squeezed sample.
Step S530: the heights of the first and second pressing members 321 and 322 are adjusted downward at the same time so that the sample is completely immersed in the wetting liquid.
Step S540: after the sample is completely soaked, the heights of the first pressing member 321 and the second pressing member 322 are simultaneously adjusted upward so that the sample is separated from the wetting liquid and is located above the dipping tank 342. The liquid dropping from the sample enters the dipping tank 342.
Step S550: after the sample no longer drips, the reading of the reading weigher 341 is registered as the current weight m of the wetting fluid 1 . The current porosity, which is (%) = (m), is calculated using equation (1) 0 -m 1 )V 0 And rho. Calculating the current compression ratio by formula (2), and setting the current distance d c = d, then the current compression ratio =0.
The first point of the graph of the relationship shown in fig. 2 for which the application compression rate is 0 can be obtained through step S550.
Step S560: turning the handle 352 controls the first pressure member321 moves the compressed sample leftward such that the distance between the first pressing surface 361 and the second pressing surface 362 is d 1 ，d 1 <d. The sample is allowed to stand by fixing the adjustment lever 350 so that the distance is constant, and the sample is dropped into the dipping tank 342. Read the scale of the upper end plate 314 to obtain d 1 Reading the weighing value of the weigher 341 to obtain the current weight m 2 . The current porosity, which is (%) = (m), is calculated using equation (1) 0 -m 2 )V 0 And rho. Calculating the current compression ratio by using the formula (2), wherein the current compression ratio (%) = (d-d) 1 ) D is calculated as the ratio of the total weight of the composition. Another point in the relation shown in fig. 2 may be obtained through one step S560.
Step S560 is repeatedly performed, and so on, a plurality of compression ratios and porosities and the correspondence relationship therebetween can be obtained.
Steps S510 to S560 are an example of performing the measurement method of the present application using the measurement apparatus 300. On the basis of the present application, the person skilled in the art should make appropriate adjustments to the respective measuring methods also when the measuring device differs from the measuring device 300.
A specific example is given below by taking the sample as a carbon felt electrode of a flow battery. In this example, the carbon felt electrode has a sample area of 50mm by 50mm and a thickness of 8.3mm. Calculating the apparent area V of the film in its natural state 0 Is 20.75cm 3 . The wetting liquid is kerosene, and the density rho is 0.8g/cm 3 . The initial mass of the wetting fluid was recorded as 53.05g. The heights of the first pressing member 321 and the second pressing member 322 were adjusted to completely immerse the carbon felt sample in kerosene, and after 10 minutes, the heights of the first pressing member 321 and the second pressing member 322 were adjusted to allow the carbon felt sample to stand for dripping. When no more drips were present, the scale reading was constant at 37.82g. According to the formula (1), the porosity in the natural state is approximately 91.7%. The handle 352 is rotated to control the first pressing member 321 to move leftward by 2mm, so that the compression rate of the carbon felt sample is about 24%, and the scale index is constant at 40.26g. The porosity in the compressed state is approximately 77.0% according to equation (1). By analogy, the displacement of the first pressurizing member 321 is further adjusted to ensure that the sample compression rates reach 35%,40%,50% and 60% in sequence, and each pressure receiving member is obtained by calculationThe porosity in the pressed state was 64.3%,61.5%,52.3% and 45.6% in this order. From the experimental results, the relationship shown in fig. 2 was obtained. The porosity can be measured without any pressure relief treatment on the carbon felt sample in the whole process, and the operation method is quick and convenient.
Having thus described the basic concept, it should be apparent to those skilled in the art that the foregoing disclosure is by way of example only, and is not intended to limit the present application. Various modifications, improvements and adaptations to the present application may occur to those skilled in the art, although not explicitly described herein. Such alterations, modifications, and improvements are intended to be suggested herein and are intended to be within the spirit and scope of the exemplary embodiments of this application.
Also, this application uses specific language to describe embodiments of the application. Reference to "one embodiment," "an embodiment," and/or "some embodiments" means a feature, structure, or characteristic described in connection with at least one embodiment of the application. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, some features, structures, or characteristics of one or more embodiments of the present application may be combined as appropriate.
Similarly, it should be noted that in the preceding description of embodiments of the application, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the embodiments. This method of disclosure, however, is not intended to require more features than are expressly recited in the claims. Indeed, the embodiments may be characterized as having less than all of the features of a single disclosed embodiment.
Where numerals describing the number of components, attributes or the like are used in some embodiments, it is to be understood that such numerals used in the description of the embodiments are modified in some instances by the modifier "about", "approximately" or "substantially". Unless otherwise indicated, "about", "approximately" or "substantially" indicates that the number allows a variation of ± 20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximations that may vary depending upon the desired properties of the individual embodiments. In some embodiments, the numerical parameter should take into account the specified significant digits and employ a general digit preserving approach. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the range are approximations, in the specific examples, such numerical values are set forth as precisely as possible within the scope of the application.
Claims (17)
1. A method for measuring the porosity of a porous material in a compressed state is characterized by comprising the following steps:
obtaining the apparent volume of a porous material sample to be detected;
completely soaking the porous material sample to be detected in wetting liquid, wherein the wetting liquid has an initial weight and is loaded in an impregnation tank;
separating the porous material sample to be tested from the wetting liquid, allowing the porous material sample to be tested to stand for dropping liquid in a non-pressurized state, allowing all dropped wetting liquid to enter the dipping tank, and recording the current weight of the wetting liquid in the dipping tank when the porous material sample to be tested does not drop liquid any more;
gradually extruding the porous material sample to be detected by adopting a pressurizing unit, wherein the pressurizing unit comprises a first pressurizing part and a second pressurizing part, the porous material sample to be detected is positioned between the first pressurizing part and the second pressurizing part, and a distance is formed between the first pressurizing part and the second pressurizing part;
when each step of extrusion is carried out, moving the first pressurizing piece and/or the second pressurizing piece along the thickness direction of the porous material sample to be tested, reducing the distance to the current distance, simultaneously keeping the porous material sample to be tested in the current pressure state, recording the current distance after each step of extrusion, allowing the porous material sample to be tested to stand still for dropping liquid under the current pressure state, allowing all dropped wetting liquid to enter the impregnation tank, and recording the current weight of the wetting liquid in the impregnation tank when the porous material sample to be tested does not drop liquid any more; and
calculating the current porosity of the porous material sample to be detected in the current pressed state by adopting the following formula:
current porosity (%) = (m) 0 -m c )V 0 /ρ；
Wherein the current porosity (%) represents the current porosity of the porous material sample to be tested in the current pressurized state, m 0 Represents the initial weight, m c Represents said current weight, V 0 Representing the apparent volume, p represents the density of the wetting fluid.
2. The measurement method of claim 1, further comprising: calculating the current compression rate of the porous material sample to be detected in the current compression state by adopting the following formula:
current compression ratio (%) = (d-d) c )/d；
Wherein the current compression rate (%) represents the current compression rate of the porous material sample to be tested in the current compression state, d represents the original thickness of the porous material sample to be tested, d c Representing the current pitch.
3. The measurement method of claim 1, further comprising: and establishing a relation curve between the compression rate and the porosity of the porous material sample to be tested according to the plurality of current compression rates and the plurality of current porosities.
4. The method of measurement according to claim 1, wherein the wetting fluid comprises a non-polar hydrocarbon oil.
5. The method of measurement according to claim 1, wherein the apparent volume is equal to a product of an original length, an original width, and an original thickness of the sample of porous material to be measured.
6. The measurement method according to claim 1, wherein the porous material sample to be measured is a carbon porous material.
7. A measuring device for porosity of porous materials under a compressed state is characterized by comprising a fixing unit, a pressurizing unit, a supporting piece and a weighing unit,
the fixing unit comprises a fixing frame extending along the vertical direction;
the pressurizing unit comprises a first pressurizing part and a second pressurizing part, the first pressurizing part and the second pressurizing part are arranged on the fixing frame in a lifting manner, and the position of the first pressurizing part and/or the second pressurizing part along the horizontal direction is adjustable;
the supporting piece is arranged between the first pressurizing piece and the second pressurizing piece in a penetrating mode, the supporting piece is provided with a liquid leakage through hole, and the supporting piece is used for bearing a porous material sample to be tested;
the weighing unit comprises a weigher and an immersion tank for loading wetting liquid, the immersion tank is positioned on the weigher, and the projection of the supporting piece along the vertical direction is completely positioned inside the projection of the immersion tank along the vertical direction.
8. The measuring apparatus according to claim 7, wherein the fixed frame includes a first side frame and a second side frame, the first pressing member is liftably provided on the first side frame, and the second pressing member is liftably provided on the second side frame.
9. The measurement device of claim 8, wherein the first side frame includes a first slot and at least one first stop, and the second side frame includes a second slot and at least one second stop, and wherein the first compression member is disposed in the first slot through the first stop and the second compression member is disposed in the second slot through the second stop.
10. The measuring device as claimed in claim 7, further comprising an adjusting lever connected to the pressurizing unit through the fixing frame, the adjusting lever being used to move the first pressurizing member and/or the second pressurizing member in the horizontal direction.
11. The measuring device of claim 7, wherein the first press member includes a first through hole, the second press member includes a second through hole, and the support member is disposed through the first through hole and the second through hole.
12. The measuring device of claim 7, wherein the support is a fine wire mesh.
13. The measuring device according to claim 7, wherein the first pressing member has a first pressing surface, the second pressing member has a second pressing surface, the first pressing surface and the second pressing surface are disposed to face each other, the first pressing surface and the second pressing surface are respectively in contact with the porous material sample to be measured when the porous material sample to be measured is gradually pressed by the pressing unit, and the first pressing surface and the second pressing surface each have a hydrophobic wetting liquid coating thereon.
14. The measurement device of claim 13, wherein the lyophobic coating comprises polytetrafluoroethylene or a silicone resin.
15. A measuring device as claimed in claim 13, wherein the material of the first and second pressing surfaces is carbon steel or alloy steel.
16. The measuring apparatus as set forth in claim 7, wherein the fixing unit further comprises an upper end plate extending in the horizontal direction, the upper end plate including a plurality of scales arranged in the horizontal direction for measuring a distance between the first pressing member and the second pressing member.
17. A measuring device according to claim 7, characterized in that the measuring device is adapted to measure the porosity of the sample of porous material to be measured using the measuring method according to any of claims 1-6.
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