Nickel ferrite solid reference electrode for concrete and design method of nickel ferrite solid reference electrode

Abstract

The invention discloses a nickel ferrite solid-state reference electrode for concrete and a design method thereof, the nickel ferrite solid-state reference electrode for concrete comprises a pipe body and a wire, a cement paste layer, an alkaline colloid layer, an electrode material layer, a conductive layer and a packaging layer are sequentially arranged in the pipe body, and one end of the wire penetrates through the packaging layer and is connected with the conductive layer. The design method comprises the following steps: calculating the resistivity of the cement paste layer, the alkaline colloid layer, the electrode material layer, the conductive layer and the packaging layer; determining the target resistance and the inner diameter size of the nickel ferrite solid-state reference electrode; calculating the thicknesses of the cement slurry layer, the alkaline colloid layer, the electrode material layer, the conductive layer and the packaging layer; and preparing the nickel ferrite solid reference electrode for concrete. According to the universal reference electrode prepared by the invention, the contact area of the electrode layer and the conductive layer is increased, and the conductivity of the conductive layer is obviously better than that of the electrode layer material, so that the potential stability and reproducibility of the reference electrode prepared by using the electrode material containing nickel ferrite are remarkably improved.

Description

Technical Field

[0001] The invention relates to a solid-state reference electrode and a design method thereof, in particular to a nickel ferrite solid-state reference electrode for concrete and a design method thereof. Background Art

[0002] Concrete durability refers to the ability of concrete to resist various destructive factors and maintain its strength and appearance integrity for a long time under working conditions. Monitoring the internal environment of concrete structures is of great significance for the study of concrete durability. Usually, reference electrodes and corresponding ion selective sensors, temperature sensors, pH sensors, and oxygen sensors are used to monitor the corresponding ion concentration, temperature, pH and oxygen content to understand the internal environment of concrete. Providing data support for the durability assessment and remaining life prediction of concrete structures, thereby formulating a scientific management and maintenance system to ensure the durability and service safety of concrete structures has great practical significance.

[0003] One of the important indicators of reference electrode performance is its electrochemical performance, which is closely related to the charge transfer resistance and external circuit impedance of the reference electrode. The external circuit impedance formed by the cement slurry layer, alkaline colloid layer and electrode material layer increases the high-frequency impedance of the solid reference electrode. The market has certain requirements for the comprehensive impedance of the reference electrode. For example, the external circuit impedance of the commercial ERE20 reference electrode is 109.7Ω·cm 2 In order to meet the different sensor size requirements, the sensor resistance is required and the size of the reference electrode must also be changed.

[0004] In general, there are many types of existing concrete monitoring sensors, with many requirements on the size and resistivity of the reference electrode, and there is no universal reference electrode. Summary of the invention

[0005] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a nickel ferrite solid reference electrode for concrete that can meet the requirements of different sensor sizes. Another purpose of the present invention is to provide a simple and convenient design method for a nickel ferrite solid reference electrode for concrete.

[0006] Technical solution: The nickel ferrite solid reference electrode for concrete described in the present invention includes a tube body and a conductor, wherein a cement slurry layer, an alkaline colloid layer, an electrode material layer, a conductive layer and a packaging layer are sequentially arranged in the tube body, and one end of the conductor passes through the packaging layer and is connected to the conductive layer.

[0007] Furthermore, the thickness ratio of the cement slurry layer, the alkaline colloid layer, the electrode material layer, the conductive layer and the encapsulation layer is 1:0.5-1.5:0.5-1.5:0.25-0.75:0.5-1.5.

[0008] Further, the electrode material layer is made of nickel ferrite, cerium oxide and graphite. Preferably, the mass ratio of nickel ferrite (NiFeO2), cerium oxide (CeO2) and graphite is 80:15:5.

[0009] Further, the tube body is a hollow cylinder made of PVC, with a height of 3 to 9 cm and an inner diameter of 3 to 10 mm. Preferably, the height is 3 to 9 cm, the inner diameter is 3 to 10 mm, and the thickness is 1 mm.

[0010] Furthermore, the cement slurry layer is formed by mixing silicate cement and distilled water. Preferably, the water-cement ratio is 0.4-0.6, which is equivalent to mixing 100 parts by weight of cement with 40-60 parts by weight of distilled water.

[0011] Furthermore, the alkaline colloidal layer is prepared by heating a saturated Ca(OH)2 solution to 80-90°C, adding sodium carboxymethyl cellulose, stirring, and cooling to room temperature. Preferably, 0.5 g sodium carboxymethyl cellulose is added to every 10 mL of saturated Ca(OH)2 solution and heated to 85°C.

[0012] Furthermore, the conductive layer is made of graphite powder or graphite conductive glue.

[0013] Furthermore, the encapsulation layer is formed by curing a mixed epoxy resin. Preferably, the mixed epoxy resin is an AB mixed epoxy resin, component A is an acrylic modified epoxy or epoxy resin, or contains a catalyst and other additives, and component B is a modified amine or other hardener, or contains a catalyst and other additives. The weight ratio of type A glue to type B glue is 3:1.

[0014] The design method of the nickel ferrite solid reference electrode for concrete comprises the following steps:

[0015] Step 1, calculating the resistivity of the cement slurry layer, the alkaline colloid layer, the electrode material layer, the conductive layer and the encapsulation layer;

[0016] Step 2, determining the target resistance and inner diameter size of the nickel ferrite solid reference electrode;

[0017] Step 3, calculating the thickness of the cement slurry layer, the alkaline colloid layer, the electrode material layer, the conductive layer and the encapsulation layer;

[0018] Step 4: prepare a nickel ferrite solid reference electrode for concrete.

[0019] Further,

[0020] Furthermore, in step 3, by determining the thickness of any two layers among the cement slurry layer, the alkaline colloid layer, and the electrode material layer, the thickness of another layer can be calculated, and the calculation formula is:

[0021]

[0022] Where r is the inner diameter of the reference electrode tube, R s is the target resistance, ρ1 is the resistivity of the cement slurry layer, L1 is the thickness of the cement slurry layer, ρ2 is the resistivity of the alkaline colloid layer, L2 is the thickness of the alkaline colloid layer, ρ3 is the resistivity of the electrode material layer, and L3 is the thickness of the electrode material layer.

[0023] Furthermore, in step 1, the resistance of the reference electrode wire and the conductive layer is very small and can be ignored. The resistance of each layer of the reference electrode cement slurry layer, alkaline colloid layer, and electrode material layer is measured in advance with a multimeter, and the resistivity is calculated. The calculation formula is as follows:

[0024]

[0025]

[0026] Where r is the inner diameter of the reference electrode tube, R s is the target resistance, ρ1 is the resistivity of the cement slurry layer, L1 is the thickness of the cement slurry layer, ρ2 is the resistivity of the alkaline colloid layer, L2 is the thickness of the alkaline colloid layer, ρ3 is the resistivity of the electrode material layer, and L3 is the thickness of the electrode material layer.

[0027] Working principle: Cement mortar is used at the bottom of the electrode to provide an ion diffusion channel to reduce the internal resistance of the reference electrode. An alkaline colloid layer is also added inside the reference electrode to maintain the internal pH of the electrode relatively stable and reduce the impact of pH changes on the electrode potential. On the other hand, it alleviates the change in electrode potential after chloride ions invade from the bottom cement mortar. Carboxymethyl cellulose is added to it, which has the characteristics of adhesion, water retention, salt and acid resistance.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0029] 1. A universal reference electrode is obtained, and the contact area between the electrode layer and the conductive layer is increased. At the same time, since the conductive performance of the conductive layer is significantly better than that of the material of the electrode layer, in addition, when using an electrode material containing nickel ferrite with a specific composition and proportion, the potential stability and reproducibility of the obtained reference electrode are significantly improved;

[0030] 2. A simple and convenient method for calculating the thickness of each layer of the solid reference electrode for concrete is provided to meet the resistance requirements of the solid reference electrode for concrete under different sensor size requirements, which is convenient and practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure of the present invention;

[0032] Figure 2 is an equivalent circuit diagram of the present invention;

[0033] Figure 3 It is the open circuit potential diagram of the present invention in concrete. DETAILED DESCRIPTION

[0034] In the following examples, the materials, reagents, instruments, etc. used, unless otherwise specified, can be obtained from commercial sources. Experimental methods without specific conditions in the examples are usually carried out under conventional conditions or under conditions recommended by the manufacturer. AB mixed epoxy resin was purchased from Wenzhou Yinghuoban Technology Co., Ltd.

[0035] Example 1

[0036] like Figure 1 The tube body 1 of the nickel ferrite solid reference electrode for concrete is a hollow cylinder made of PVC material, with a height of 3 to 9 cm, an inner diameter of 3 to 10 mm, and a thickness of 1 mm. PVC material does not react with metals and metal oxides, is acid-resistant and alkali-resistant, and has a certain strength. The tube body 1 is arranged from bottom to top with a cement slurry layer 2, an alkaline colloid layer 3, an electrode material layer 4, a conductive layer 5, and a packaging layer 6, and one end of a wire 7 passes through the packaging layer 6 and is connected to the conductive layer 5.

[0037] The cement slurry layer 2 is made of a mixture of P·O 42.5 type silicate cement and distilled water, with a water-cement ratio of 0.4-0.6, which is equivalent to 100 parts by weight of cement mixed with 40-60 parts by weight of distilled water. The alkaline colloid layer 4 is made by heating a saturated Ca(OH)2 solution to 85°C, then adding sodium carboxymethyl cellulose, adding 0.5g sodium carboxymethyl cellulose per 10mL saturated Ca(OH)2 solution, stirring and cooling to room temperature. The electrode material layer 4 is made of nickel ferrite (NiFeO2) powder, cerium oxide (CeO2) powder and graphite, and the mass ratio of the NiFeO2 powder, CeO2 powder and graphite is 80:15:5. It is fully mixed by a high-speed mixer and then pressed by a press. The conductive layer 5 is made of graphite powder or graphite conductive glue. The conductive layer 5 is in full contact with the electrode material layer 4, so that the wire 7 is better electrically connected to the electrode material layer 4, so that the reference electrode has better potential stability and reproducibility. The encapsulation layer 6 is formed by curing AB mixed epoxy resin, in which the weight ratio of type A glue to type B glue is 3: 1. Type A glue includes acrylic modified epoxy or epoxy resin, or contains catalysts and other additives, and type B glue includes modified amine or other hardeners, or contains catalysts and other additives.

[0038] Example 2

[0039] A method for designing a nickel ferrite solid reference electrode for concrete comprises the following steps:

[0040] (1) Use a multimeter to measure the resistance of each layer and calculate the resistivity.

[0041] Table 1 Resistivity of each layer

[0042] Layering Resistance (kΩ) <![CDATA[Cross-sectional area (mm 2 )]]> Thickness(mm) Resistivity (Ω·mm) Cement slurry layer 2 2.8 28 10 7840 Alkaline colloid layer 3 1.4 28 10 3920 Electrode material layer 4 2.1 28 10 5880

[0043] Through the equivalent circuit diagram inside the present invention, as Figure 2 In order to meet the overall resistance requirements of the present invention, by determining the thickness of any two layers of the reference electrode cement slurry layer 2, the alkaline colloid layer 3, and the electrode material layer 4, the thickness of another layer can be calculated. The calculation formula is as follows:

[0044] For example:

[0045] in,

[0046] r is the inner diameter of the reference electrode tube 1;

[0047] R s is the resistance of the reference electrode;

[0048] ρ1, ρ2, and ρ3 are the resistivities of the cement slurry layer 2, the alkaline colloid layer 3, and the electrode material layer 4, respectively;

[0049] R1, R2, and R3 are the resistances of the cement slurry layer 2, the alkaline colloid layer 3, and the electrode material layer 4, respectively;

[0050] L1, L2, and L3 are the thicknesses of the cement slurry layer 2, the alkaline colloid layer 3, and the electrode material layer 4, respectively.

[0051] The resistivities of the cement slurry layer 2, the alkaline colloid layer 3, and the electrode material layer 4 are calculated to be 7840, 3920, and 5880 Ω·mm, respectively.

[0052] (2) The sensor requires an electrode size of 6 mm in diameter and a reference electrode internal resistance no greater than 8 kΩ.

[0053] (3) The thickness of the electrode material layer 4 is determined to be 15 mm, the thickness of the alkaline colloid layer 3 is 10 mm, and it can be concluded that the thickness of the cement slurry layer 2 does not exceed 12.6 mm.

[0054] (4) Fix one end of the tube body 1 (with a diameter of 6 mm) on a fixing table, fill the other end of the tube body 1 with cement slurry and solidify it to form a cement slurry layer 2 with a thickness of 10 mm; introduce a mixture of calcium hydroxide, water and sodium carboxymethyl cellulose into the tube body 1 through the other end to form a calcium hydroxide colloidal layer 3 with a thickness of 10 mm; put electrode material into the tube body 1 through the other end to form an electrode material layer 4 with a thickness of 15 mm; introduce graphite powder or graphite conductive glue into the tube body 1 through the other end to form a conductive layer 5 with a thickness of 5 mm; insert the wire 7 into the conductive layer 5 through the other end; then introduce epoxy resin into the tube body 1 and solidify it to form a packaging layer 6 with a thickness of 10 mm.

[0055] Example 3

[0056] A method for designing a nickel ferrite solid reference electrode for concrete comprises the following steps:

[0057] (1) Use a multimeter to measure the resistance of each layer and calculate the resistivity. The resistivity of the cement slurry layer 2, the alkaline colloid layer 3, and the electrode material layer 4 are calculated to be 7840, 3920, and 5880 Ω·mm, respectively.

[0058] (2) The sensor requires an electrode size of 3 mm in diameter and a reference electrode internal resistance no greater than 8 kΩ.

[0059] (3) The thickness of the electrode material layer 4 is determined to be 3 mm, the thickness of the alkaline colloid layer 3 is determined to be 3 mm, and it can be concluded that the thickness of the cement slurry layer 2 does not exceed 3.6 mm.

[0060] (4) Fix one end of the tube body 1 (with a diameter of 6 mm) on a fixing table, fill the other end of the tube body 1 with cement slurry and solidify it to form a cement slurry layer 2 with a thickness of 3 mm; introduce a mixture of calcium hydroxide, water and sodium carboxymethyl cellulose into the tube body 1 through the other end to form a calcium hydroxide colloidal layer 3 with a thickness of 3 mm; put electrode material into the tube body 1 through the other end to form an electrode material layer 4 with a thickness of 3 mm; introduce graphite powder or graphite conductive glue into the tube body 1 through the other end to form a conductive layer 5 with a thickness of 3 mm; insert the wire 7 into the conductive layer 5 through the other end; then introduce epoxy resin into the tube body 1 and solidify it to form a packaging layer 6 with a thickness of 3 mm.

[0061] Example 4

[0062] A method for designing a nickel ferrite solid reference electrode for concrete comprises the following steps:

[0063] (1) Use a multimeter to measure the resistance of each layer and calculate the resistivity. The resistivity of the cement slurry layer 2, the alkaline colloid layer 3, and the electrode material layer 4 are calculated to be 7840, 3920, and 5880 Ω·mm, respectively.

[0064] (2) The sensor requires an electrode diameter of 10 mm and a reference electrode internal resistance of no more than 5 kΩ.

[0065] (3) The thickness of the electrode material layer 4 is determined to be 20 mm, the thickness of the alkaline colloid layer 3 is determined to be 20 mm, and it can be concluded that the thickness of the cement slurry layer 2 does not exceed 30 mm.

[0066] (4) Fix one end of the tube body 1 (with a diameter of 10 mm) on a fixing table, fill the other end of the tube body 1 with cement slurry and solidify it to form a cement slurry layer 2 with a thickness of 20 mm; introduce a mixture of calcium hydroxide, water and sodium carboxymethyl cellulose into the tube body 1 through the other end to form a calcium hydroxide colloidal layer 3 with a thickness of 20 mm; put electrode material into the tube body 1 through the other end to form an electrode material layer 4 with a thickness of 20 mm; introduce graphite powder or graphite conductive glue into the tube body 1 through the other end to form a conductive layer 5 with a thickness of 5 mm; insert the wire 7 into the conductive layer 5 through the other end; then introduce epoxy resin into the tube body 1 and solidify it to form a packaging layer 6 with a thickness of 10 mm.

[0067] Comparative Example

[0068] The rest of the structure of this comparative example is the same as that of Example 1, except that the material of the electrode material layer is replaced with graphene. Figure 3 .

[0069] The electrode potential of the present invention buried in the mortar is only in a relatively stable stage after about 30 days. After entering the stable period, the electrode potential fluctuates slightly. Within 25d to 45d, the maximum fluctuation potential of the present invention is 20mV, and the potential fluctuation variance is 7.25mV. However, when only the material is changed to graphene, the potential fluctuation is large, with a maximum fluctuation of 150mV. It can be seen that in the actual concrete system, the stability and reproducibility of the present invention are significantly improved.

Claims

1. A nickel ferrite solid reference electrode for concrete, characterized in that: The invention comprises a tube body (1) and a conductor (7), wherein a cement slurry layer (2), an alkaline colloid layer (3), an electrode material layer (4), a conductive layer (5) and a packaging layer (6) are sequentially arranged in the tube body (1), and one end of the conductor (7) passes through the packaging layer (6) and is connected to the conductive layer (5).

2. The nickel ferrite solid reference electrode for concrete according to claim 1, characterized in that: The thickness ratio of the cement slurry layer (2), the alkaline colloid layer (3), the electrode material layer (4), the conductive layer (5) and the packaging layer (6) is 1:0.5-1.5:0.5-1.5:0.25-0.75:0.5-1.

5.

3. The nickel ferrite solid reference electrode for concrete according to claim 1, characterized in that: The electrode material layer (4) is made of nickel ferrite, cerium oxide and graphite.

4. The nickel ferrite solid reference electrode for concrete according to claim 1, characterized in that: The tube body (1) is a hollow cylinder made of PVC, with a height of 3 to 9 cm and an inner diameter of 3 to 10 mm.

5. The nickel ferrite solid reference electrode for concrete according to claim 1, characterized in that: The cement slurry layer (2) is formed by mixing silicate cement and distilled water.

6. The nickel ferrite solid reference electrode for concrete according to claim 1, characterized in that: The alkaline colloid layer (3) is prepared by heating a saturated Ca(OH)2 solution to 80-90°C, adding sodium carboxymethyl cellulose, stirring, and then cooling to room temperature.

7. The nickel ferrite solid reference electrode for concrete according to claim 1, characterized in that: The conductive layer (5) is made of graphite powder or graphite conductive glue.

8. The nickel ferrite solid reference electrode for concrete according to claim 1, characterized in that: The encapsulation layer (6) is formed by curing a mixed epoxy resin.

9. The method for designing a nickel ferrite solid reference electrode for concrete according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1, calculating the resistivity of the cement slurry layer (2), the alkaline colloid layer (3), the electrode material layer (4), the conductive layer (5) and the encapsulation layer (6); Step 2, determining the target resistance and inner diameter size of the nickel ferrite solid reference electrode; Step 3, calculating the thickness of the cement slurry layer (2), the alkaline colloid layer (3), the electrode material layer (4), the conductive layer (5) and the encapsulation layer (6); Step 4: prepare a nickel ferrite solid reference electrode for concrete.

10. The method for designing a nickel ferrite solid reference electrode for concrete according to claim 9, characterized in that: In the step 3, by determining the thickness of any two layers among the cement slurry layer (2), the alkaline colloid layer (3), and the electrode material layer (4), the thickness of the other layer can be calculated.

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