Synthesis method of a NiCoFe-LDHGO binary mixture

Abstract

The synthesis method of the NiCoFe-LDHGO binary mixture of the present invention effectively weakens the skin effect by introducing NiCoFe-LDH with low conductivity. At the same time, NiCoFe-LDH is used to modify the graphene oxide flakes, which plays a bridging role between the graphene oxide flakes, significantly reducing the stacking of graphene oxide layers and providing more channels for electrons and microwaves. The combination of NiCoFe-LDH and graphene oxide through the synthesis of the method of the present invention generates multiple interfacial polarizations between the two with large conductivity differences, introducing an additional electromagnetic wave loss mechanism in the binary mixture, thereby improving the electromagnetic wave absorption performance of the binary mixture. The synthesized binary mixture LDH / G hybrid shows an overall effect of the perfect combination of GO and LDH flakes.

Description

Technical Field

[0001] The present invention relates to the technical field of synthesis methods, and particularly relates to a synthesis method of a NiCoFe-LDHGO binary mixture. Background Art

[0002] Water pollution, noise pollution, air pollution, and electromagnetic pollution are considered the four major main pollutions in current human society. Therefore, with the development and progress of modern science and technology, various energy-saving and emission-reduction technologies and pollution control means have been continuously developed and applied; although electromagnetic pollution was recognized by people later than the other three pollutions, its harm to humans is equally serious; as people's understanding of electromagnetic pollution becomes deeper and deeper, the research and development of electromagnetic shielding technology and microwave absorbing materials have also attracted more and more attention from academic and industrial circles around the world;

[0003] In recent years, while people have been enjoying the comfortable life brought by electronic products, they have also suffered serious harm caused by electromagnetic pollution; electromagnetic shielding is one of the effective methods to eliminate electromagnetic pollution; however, when the internal electrical equipment generates a strong electromagnetic field by itself, the shielding will fail because electromagnetic waves are completely reflected, and self-interference will cause serious potential dangers; therefore, finding an electromagnetic wave absorbing material with light weight, good thermal stability, strong absorption ability, and wide absorption bandwidth has become the focus of widespread attention of people;

[0004] According to the electromagnetic wave absorption principle, the electromagnetic wave absorption performance is determined by the complex permittivity, complex permeability, and impedance matching;

[0005] Graphene oxide in the prior art has good chemical and physical properties. Graphene oxide flakes are composed of randomly sized planar aromatic domains, interconnected by a network of chair-shaped cyclohexane-like units, and are easily modified by groups such as epoxy, hydroxyl, diol, ether, and ketone; the attachment of these groups to graphene oxide not only improves the water solubility but also generates more polarization points and polarization processes under an external electromagnetic field; thus enabling graphene oxide to have excellent electromagnetic wave absorption potential as an electromagnetic wave absorbing material;

[0006] However, under the prior art, graphene oxide also has some defects. On the one hand, graphene oxide is easily reduced by chemically removing part of the oxidized part in the flakes, greatly increasing its electrical conductivity; the high electrical conductivity is not conducive to the penetration of incident microwaves due to the skin effect; on the other hand, the p-p conjugation or van der Waals interaction between layers often leads to the self-restacking of two-dimensional graphene oxide flakes, seriously hindering its microwave dissipation ability;

[0007] Therefore, those skilled in the art are committed to developing a synthesis method of a NiCoFe-LDHGO binary mixture, aiming to solve the defect problems existing in the prior art. Summary of the Invention

[0008] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is that in the current prior art, graphene oxide is easily reduced by chemically removing part of the oxidized part in the flakes, greatly improving its electrical conductivity; the high electrical conductivity is not conducive to the penetration of incident microwaves due to the skin effect; the p-p conjugation or van der Waals interaction between layers often causes the two-dimensional graphene oxide flakes to re-stack themselves, seriously hindering their microwave dissipation ability, making it impossible to be a good electromagnetic wave absorbing material;

[0009] To achieve the above object, a method for synthesizing a NiCoFe-LDHGO binary mixture of the present invention includes the following steps:

[0010] Step 1: Dissolve a certain proportion of Ni(NO3)2·6H2O and Co(NO3)2·6H2O in deionized water;

[0011] Step 2: Stir an ammonia water solution with a certain concentration, and slowly drop the mixed solution obtained in Step 1 into the ammonia water solution, and continue to stir after dropping;

[0012] Step 3: Centrifuge the mixed suspension obtained in Step 2, take out the supernatant after centrifugation, and wash the precipitate with secondary distilled water;

[0013] Step 4: Place the precipitate obtained in Step 3 and graphene oxide together in a hydrothermal reaction kettle, and keep heating at a temperature of 115-125 °C in the reaction kettle for 12-16 h;

[0014] Step 5: After the product in the reaction kettle cools down, rinse the obtained product again, and dry it under the condition of 55-65 °C;

[0015] Step 6: Immerse the dried product obtained in Step 5 in a Fe(NO3)2·9H2O solution with a certain concentration for 12-16 h. After soaking, rinse it with methanol and secondary distilled water, and then perform vacuum dehydration;

[0016] Step 1: Dissolve a certain proportion of Ni(NO3)2·6H2O and Co(NO3)2·6H2O in deionized water;

[0017] In Step 1, the ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O is: 1:4-1:5;

[0018] The purity of both Ni(NO3)2·6H2O and Co(NO3)2·6H2O in Step 1 is greater than 99.5%;

[0019] Step 2: Stir an ammonia water solution with a certain concentration, and slowly add the mixed solution obtained in Step 1 to the ammonia water solution. After the addition is complete, continue stirring;

[0020] The concentration of ammonia water in Step 2 is 4 - 6 mol / L;

[0021] The stirring in Step 2 is carried out using a magnetic stirrer;

[0022] Before adding the mixed solution obtained in Step 1 in Step 2, it is necessary to stir the ammonia water solution to make it uniform;

[0023] After the addition in Step 2 is complete, the time for continued stirring is 10 - 14 h;

[0024] Step 3: Centrifuge the mixed suspension obtained in Step 2. After centrifugation, take out the supernatant and wash the precipitate with secondary distilled water;

[0025] The rotation speed for centrifugation in Step 3 is 8000 - 10000 r / min;

[0026] The time for each centrifugation in Step 3 is 4 - 6 min;

[0027] After washing the precipitate with secondary distilled water in Step 3, it is also necessary to perform the operations of centrifugation, removing the supernatant, and washing the precipitate with secondary distilled water multiple times. The number of repetitions is 3 - 5 times;

[0028] Step 4: Place the precipitate obtained in Step 3 and graphene oxide together in a hydrothermal reaction kettle, and maintain heating at a temperature of 115 - 125 °C in the reaction kettle for 12 - 16 h;

[0029] Before being placed in the reaction kettle in Step 4, the graphene oxide should be washed successively with solutions;

[0030] The solutions for successive washing in Step 4 are acetone, ethanol, and secondary distilled water respectively;

[0031] The washing of graphene oxide in Step 4 is carried out using ultrasonic cleaning, and the cleaning time for each solution is more than 10 min;

[0032] Step 5: After the product in the reaction kettle cools down, the obtained product is further rinsed and dried under the condition of 55 - 65 °C;

[0033] In Step 5, stop heating the reaction kettle to allow the product to cool naturally with the reaction kettle;

[0034] In step 5, when washing the product, first wash it with methanol and then with secondary distilled water. The washing needs to be repeated 3 to 5 times.

[0035] The drying time in step 5 is 0.5 h to 1 h.

[0036] Step 6: Immerse the dried product obtained in step 5 in a Fe(NO3)2·9H2O solution with a certain concentration for 12 to 16 h. After soaking, rinse with methanol and secondary distilled water, and then perform vacuum dehydration.

[0037] The concentration of Fe(NO3)2·9H2O in step 6 is 0.7 to 0.8 mol / L.

[0038] In step 6 during soaking, the Fe(NO3)2·9H2O solution needs to completely cover the dried product.

[0039] After soaking in step 6, the rinsing is first with methanol and then with secondary distilled water, and the number of rinsing times is 3 to 5 times.

[0040] The temperature during vacuum dehydration in step 6 is 55 to 65 °C.

[0041] Further, the preferred time for continuous stirring in step 2 is 12 h.

[0042] Further, the preferred drying temperature in step 5 is 60 °C.

[0043] Further, the preferred vacuum dehydration temperature in step 6 is 60 °C.

[0044] Further, the purity of methanol for rinsing in step 6 is above 99.99%.

[0045] Adopting the above scheme, the synthesis method of the NiCoFe-LDHGO binary mixture disclosed by the present invention has the following advantages:

[0046] (1) In the synthesis method of the NiCoFe-LDHGO binary mixture of the present invention, by introducing NiCoFe-LDH with low conductivity, the skin effect is effectively weakened; using NiCoFe-LDH to modify the graphene oxide flakes, NiCoFe-LDH plays a bridging role between the graphene oxide flakes, significantly reducing the stacking of graphene oxide layers and providing more channels for electrons and microwaves; moreover, the combination of NiCoFe-LDH and graphene oxide through the synthesis of the method of the present invention generates multiple interfacial polarizations between the two with large conductivity differences, introducing an additional electromagnetic wave loss mechanism in the binary mixture, thereby improving the electromagnetic wave absorption performance of the binary mixture.

[0047] (2) The synthesis method of the NiCoFe-LDHGO binary mixture of the present invention makes the binary mixture have an array structure, and part of the LDH nanosheets grow vertically towards the substrate without obvious aggregation and superposition; and the metal cations are first electrostatically adsorbed onto the surface of graphene oxide; the positively charged LDH laminate is adsorbed by the negatively charged graphene oxide through electrostatic attraction; thus, the binary mixture LDH / G hybrid synthesized by the method of the present invention presents an overall effect of perfect combination of GO and LDH flakes.

[0048] In summary, for the synthesis method of the NiCoFe-LDHGO binary mixture disclosed in the present invention, the skin effect is effectively weakened by introducing NiCoFe-LDH with low conductivity. At the same time, NiCoFe-LDH is used to modify the graphene oxide flakes, which plays a bridging role between the graphene oxide flakes, significantly reducing the stacking of graphene oxide layers and providing more channels for electrons and microwaves; the combination of NiCoFe-LDH and graphene oxide through the synthesis method of the present invention generates multiple interfacial polarizations between the two with large conductivity differences, introducing an additional electromagnetic wave loss mechanism in the binary mixture, thereby improving the electromagnetic wave absorption performance of the binary mixture; the binary mixture has an array structure, and part of the LDH nanosheets grow vertically towards the substrate without obvious aggregation and superposition, and the binary mixture LDH / G hybrid synthesized by the method of the present invention presents an overall effect of perfect combination of GO and LDH flakes.

[0049] The concept, specific technical solutions and technical effects of the present invention will be further described below in conjunction with specific embodiments to fully understand the purpose, features and effects of the present invention. Brief Description of the Drawings

[0050] Figure 1 is a schematic flow chart of the synthesis method of the NiCoFe-LDHGO binary mixture of the present invention;

[0051] Figure 2 is the XRD spectra of the (a) LDH, (b) LDH / G and (c) LDH+G samples of Example 1 of the present invention;

[0052] Figure 3 is the FT-IR spectra of the LDH, LDH / G and LDH+G samples of Example 1 of the present invention;

[0053] Figure 4 is the scanning electron microscope images of the LDH (a, d), LDH / G (b, e) and LDH+G (c, f) of Example 1 of the present invention;

[0054] Figure 5TEM images of LDH / G(a), LDH+G(b) and the corresponding EDS(c) and mapping(d) of LDH in Example 1 of the present invention;

[0055] Figure 6 is the XPS scanning spectrum of Example 1 of the present invention. Detailed implementation manners

[0056] The following introduces multiple preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments. These embodiments are described by way of example, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0057] Example 1: The binary mixture was prepared using the method of the present invention, and relevant properties were verified.

[0058] The binary mixture synthesis method implemented in Example 1 of the present invention is as Figure 1 shown. First, perform Step 1: Dissolve a certain proportion of Ni(NO3)2·6H2O and Co(NO3)2·6H2O in deionized water;

[0059] The ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O in Step 1 is: 1:4 to 1:5;

[0060] The purity of both Ni(NO3)2·6H2O and Co(NO3)2·6H2O in Step 1 is greater than 99.5%;

[0061] Specifically, in this Example 1, the ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O selected is specifically 1:4, and their purity is greater than 99.99%;

[0062] Subsequently, perform Step 2: Stir an ammonia water solution with a certain concentration, and slowly add the mixed solution obtained in Step 1 to the ammonia water solution. After the addition is complete, continue to stir;

[0063] The concentration of ammonia water in Step 2 of this Example 1 is 5 mol / L;

[0064] The stirring in Step 2 is carried out using a magnetic stirrer;

[0065] In Step 2, the ammonia water solution needs to be stirred before adding the mixed solution obtained in Step 1 to make the ammonia water solution uniform;

[0066] After the addition in Step 2 is complete, the time for continuing to stir is 12 h;

[0067] Next, perform Step 3: Centrifuge the mixed suspension obtained in Step 2. After centrifugation, take out the supernatant and wash the precipitate with secondary distilled water;

[0068] Specifically, in Step 3, the rotation speed for centrifugation is 9000 r / min, and the time for each centrifugation in Step 3 is 5 min;

[0069] After washing the precipitate with secondary distilled water in Step 3, the operations of centrifugation, removing the supernatant, and washing the precipitate with secondary distilled water need to be performed multiple times, and the number of repetitions is 3 times;

[0070] Step 4: Place the precipitate obtained in Step 3 and graphene oxide together in a hydrothermal reaction kettle, and keep heating at a temperature of 120 °C in the reaction kettle for 12 h;

[0071] Before being placed into the reaction kettle, the graphene oxide in Step 4 should be washed successively with solutions;

[0072] The solutions for successive washing in Step 4 are acetone, ethanol, and secondary distilled water respectively;

[0073] For the washing of graphene oxide in Step 4, ultrasonic cleaning is selected, and the cleaning time for each solution is greater than 10 min;

[0074] Step 5: After the product in the reaction kettle cools down, the obtained product is rinsed again and dried at 60 °C;

[0075] In Step 5, stop heating the reaction kettle so that the product cools down naturally with the reaction kettle;

[0076] In Step 5, when rinsing the product, first rinse with methanol and then rinse with secondary distilled water. Rinsing needs to be repeated, and the number of rinsing times is 3 times;

[0077] The drying time in Step 5 is 1 h;

[0078] Finally, perform Step 6: Immerse the dried product obtained in Step 5 in a Fe(NO3)2·9H2O solution with a certain concentration for 12 h. After soaking, rinse with methanol and secondary distilled water, and then perform vacuum dehydration;

[0079] Specifically, in Example 1, the concentration of Fe(NO3)2·9H2O in Step 6 is 0.7 mol / L

[0080] During soaking in Step 6, it is necessary to ensure that the Fe(NO3)2·9H2O solution completely covers the dried product;

[0081] After the soaking in Step 6 is completed, the rinsing is first carried out with methanol and then with secondary distilled water, and the number of rinsing times is 5 times;

[0082] The purity of the methanol used for rinsing in Step 6 is above 99.99%;

[0083] The temperature for vacuum dehydration in Step 6 is 60 °C, and the product after finally completing vacuum dehydration is the NiCoFe-LDHGO binary mixture obtained by synthesis and preparation;

[0084] Subsequently, the original layered iron cobalt nickel hydroxide (abbreviation: LDH), the simple composite of layered iron cobalt nickel hydroxide and graphene oxide (abbreviation: LDH / G), and the NiCoFe-LDHGO binary mixture (abbreviation: LDH+G) prepared by the synthesis method of the present invention are compared for relevant properties;

[0085] First, X-ray diffraction tests (i.e., XRD) are carried out on the three materials: the test results are as Figure 2 shown. It can be seen from Figure 2 that there are multiple diffraction peaks at 2θ = 11.5°, 22.9°, 34.5°, 59.8° and 61.2°, corresponding to the (003), (006), (012), (110) and (113) crystal planes [20, 21] respectively; the narrow and sharp peaks indicate that the synthesized LDHs compound has good crystallinity;

[0086] The diffraction peak of graphene oxide is around 2θ = 10.4°. The disappearance of the characteristic diffraction peak of graphene oxide in the composite material indicates less stacking of the composite material; this also indicates that the addition of graphene oxide does not cause any structural change; in addition, the diffraction peaks of other crystal planes such as (010) and (400) also indicate that the LDH crystal grows very completely;

[0087] FT-IR spectrum test: The FT-IR spectrum test results of the three materials are shown in Figure 3 as follows; the infrared vibrations of LDHs can be divided into three major categories: the molecular vibration of hydroxyl groups, the lattice vibration of octahedrons, and the vibration of interlayer anions; the strong absorption peaks at 3442 cm and 1647 cm are attributed to the vibration of interlayer water molecules and the bending and stretching vibrations of OH in OH-OH, indicating the presence of water between the hydrotalcite-like layers and in the interlayer; the absorption peak appearing at 1384 cm is the vibration absorption peak of NO3 in LDH; the asymmetric stretching vibration of CO32- is observed at 1352 cm; the peaks appearing below 1000 cm come from the absorption band of sodium nitrate groups, which play a role in charge balancing of anions in the interlayer region, and the peaks generated by the M-O stretching vibration are related to the M-O-M chain in the hydrotalcite;

[0088] SEM test: The SEM microstructures and detailed morphologies of the three materials are shown as follows Figure 4 ; It can be clearly seen from Figure 4 a that LDH is stacked in thin layers, and the morphology is typical LDH; The random polymerization, aggregation, and hybridization of microcrystals will affect the specific surface area and pore size of the material, thereby affecting the performance of the material; It can be seen from Figure 4 b that LDH / G shows an array structure, and some LDH nanosheets grow vertically towards the substrate without obvious aggregation and superposition, which is consistent with what Figure 2 shows; During the growth process, metal cations are first adsorbed onto the surface of graphene oxide through electrostatic attraction; The positively charged LDH laminate is adsorbed by the negatively charged graphene oxide through electrostatic attraction; Figure 4 c and Figure 4 f show that after the same reaction time, obvious graphene oxide flakes can be found exposed on the surface in the LDH+G mixture;

[0089] TEM test: The TEM microstructures and detailed morphologies of the three materials are shown as follows Figure 5 ;

[0090] In Figure 5 a, the LDH / G hybrid shows an overall effect of perfect combination of GO and LDH flakes; When observing the TEM image of the LDH+G mixture, obvious independent and separated combinations can be seen, as shown in Figure 4 b; The combination state and component distribution are detected by using EDS and Mapping techniques; It can be seen from Figure 4 c and d that within the measurement range, the distribution of LDH metal elements (Ni, Co, Fe) is basically consistent with the distribution of carbon;

[0091] XPS spectra: The test results of the XPS spectra of LDH / G and LDH+G are shown as follows Figure 6 ; The XPS spectra can also reflect the chemical bonding behavior in the microscopic electronic state; As shown in Figure 5 a, obvious characteristic peaks of Ni, Fe, Co, C, and O elements can be observed in both samples; The enlarged spectra of Ni 2p, Co 2p, and Fe 2p are shown in Figure 5 b, c, and d respectively; It is worth mentioning that the binding energies of these three elements have changed significantly; The displacement of the internal electron binding energy is almost the same under different valence states and structural environments; The XPS results are consistent with the TEM results;

[0092] In summary, the technical solution of this patent enables the binary mixture to have an array structure, with some LDH nanosheets growing vertically towards the substrate without obvious aggregation and superposition; and metal cations are first electrostatically adsorbed onto the surface of graphene oxide; the positively charged LDH laminate is adsorbed by the negatively charged graphene oxide through electrostatic attraction; thus, the binary mixture LDH / G hybrid synthesized by the method of the present invention exhibits an overall effect of perfect combination of GO and LDH flakes; by introducing NiCoFe-LDH with low conductivity, the skin effect is effectively weakened; using NiCoFe-LDH to modify the graphene oxide flakes, NiCoFe-LDH plays a bridging role between the graphene oxide flakes, significantly reducing the stacking of graphene oxide layers and providing more channels for electrons and microwaves; moreover, the combination of NiCoFe-LDH and graphene oxide through the synthesis of the method of the present invention generates multiple interfacial polarizations between the two with large conductivity differences, introducing an additional electromagnetic wave loss mechanism in the binary mixture, thereby enhancing the electromagnetic wave absorption performance of the binary mixture.

[0093] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. A method for synthesizing a NiCoFe-LDHGO binary mixture, characterized in that, It includes the following steps: Step 1: Dissolve a certain proportion of Ni(NO3)2·6H2O and Co(NO3)2·6H2O in deionized water; Step 2: Stir an ammonia water solution with a certain concentration, and slowly add the mixed solution obtained in Step 1 to the ammonia water solution. After the addition is complete, continue stirring; Step 3: Centrifuge the mixed suspension obtained in Step 2. After centrifugation, take out the supernatant and wash the precipitate with secondary distilled water; Step 4: Place the precipitate obtained in Step 3 and graphene oxide together in a hydrothermal reaction kettle, and keep heating in the reaction kettle at a temperature of 115 - 125 °C for 12 - 16 h; Step 5: After the product in the reaction kettle cools down, rinse the obtained product again, and dry it under the condition of 55 - 65 °C; Step 6: Immerse the dried product obtained in Step 5 in a Fe(NO3)2·9H2O solution with a certain concentration for 12 - 16 h. After soaking, rinse it with methanol and secondary distilled water, and then perform vacuum dehydration.

2. The synthesis method of the binary mixture as described in claim 1, characterized in that in Step 1, the ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O is: 1:4 - 1:5; the purity of both Ni(NO3)2·6H2O and Co(NO3)2·6H2O in Step 1 is greater than 99.5%; 3. The synthesis method of the binary mixture as described in claim 1, characterized in that the concentration of ammonia water in Step 2 is 4 - 6 mol / L; in Step 2, magnetic stirrer is used for stirring; in Step 2, the ammonia water solution needs to be stirred before adding the mixed solution obtained in Step 1 to make the ammonia water solution uniform; in Step 2, after the addition is complete, the stirring time is 10 - 14 h.

4. The synthesis method of the binary mixture as described in claim 1, characterized in that the rotation speed for centrifugation in Step 3 is 8000 - 10000 r / min; the time for each centrifugation in Step 3 is 4 - 6 min; in Step 3, after washing the precipitate with secondary distilled water, the operations of centrifugation, removing the supernatant, and washing the precipitate with secondary distilled water need to be carried out multiple times, and the number of repetitions is 3 - 5 times.

5. The synthesis method of the binary mixture as described in claim 1, characterized in that graphene oxide in Step 4 should be washed with solutions in sequence before being placed in the reaction kettle; the solutions for washing in sequence in Step 4 are acetone, ethanol, and secondary distilled water respectively; in Step 4, ultrasonic cleaning is used for washing graphene oxide, and the cleaning time for each solution is greater than 10 min.

6. The synthesis method of the binary mixture as described in claim 1, characterized in that in Step 5, stop heating the reaction kettle to make the product cool naturally with the reaction kettle; in Step 5, when rinsing the product, first rinse it with methanol, and then rinse it with secondary distilled water. Rinsing needs to be carried out repeatedly, and the number of rinsing times is 3 - 5 times; the drying time in Step 5 is 0.5 h - 1 h.

7. The synthesis method of the binary mixture according to claim 1, characterized in that, the concentration of Fe(NO3)2·9H2O in step 6 is 0.7 - 0.8 mol / L in step 6 during soaking, the Fe(NO3)2·9H2O solution needs to completely submerge the dried product; after step 6 is completed, the rinsing is first carried out with methanol, and then with secondary distilled water, and the number of rinsing times is 3 - 5 times; the temperature during vacuum dehydration in step 6 is 55 - 65 °C.

8. The synthesis method of the binary mixture according to claim 1, characterized in that, the continuous stirring time in step 2 is 12 h; the drying temperature in step 5 is 60 °C; the vacuum dehydration temperature in step 6 is 60 °C; the purity of the methanol used for rinsing in step 6 is above 99.99%.

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