A special additive for magnesium oxide used in BTTZ fire-resistant cables

Abstract

The present invention provides a special additive for magnesium oxide used in BTTZ fire-resistant cables, belonging to the technical field of the preparation of mineral insulated cables. The special additive for magnesium oxide used in BTTZ fire-resistant cables includes additive A. Additive A is based on zirconium silicate as the matrix, with calcium ions as doping ions, and is prepared into nano-scale fibers through the sol-gel method and the electrospinning method, and then a nano-scale additive is obtained. The special additive for magnesium oxide used in BTTZ fire-resistant cables of the present invention can increase the breakdown voltage of the magnesium oxide filling layer, and thus improve its electrical insulation performance.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of mineral insulated cables, and particularly relates to a special additive for magnesium oxide used in BTTZ fireproof cables. Background Art

[0002] The BTTZ cable is a copper-core copper-sheathed magnesium oxide insulated heavy-duty fireproof cable (also known as a heavy-duty mineral insulated cable). It is a new type of cable with a seamless copper tube sheath on the outer layer, magnesium oxide crystal powder filled in the middle as the insulating material, and the conductor is composed of a single-strand copper rod. It has the characteristics of high temperature resistance, fire prevention, explosion prevention, non-combustion (it can operate continuously for a long time at 250°C and can also operate for a short time of 30 minutes under the extreme state of 1000°C), large current-carrying capacity, small outer diameter, high mechanical strength, long service life, and generally does not require an independent grounding wire. It has high fire prevention performance and is widely used in nuclear power plants, metallurgy, airports, high-rise buildings and other places.

[0003] Magnesium oxide is an electrical insulator and a good thermal conductor. It has the characteristics of flame retardancy, high safety, low price, easy to purchase, and large storage capacity, so it has been widely and long-term used in cables. Its preparation process is that after magnesium oxide is refined, it needs to be melted at 2800°C to make its crystallization completely stable and then cooled into blocks. Due to the influence of internal cohesion, the middle part has a higher purity (specific gravity 3.58 - 3.6). It is crushed by a hammer and then the iron filings are removed and mixed in different meshes to form the magnesium oxide powder used as the filling material. The commonly used mesh specifications are 60 - 325 meshes.

[0004] When magnesium oxide is applied to mineral insulated cables, due to the density problem of magnesium oxide, it may be difficult to meet the electrical insulation performance standard. Usually, the original stirring method can be used to mix and calcine silicate synthetic oxides as additives to improve the electrical insulation performance. However, due to the poor resistance of the additive itself and the influence of high temperature, a relatively serious low-resistance effect is formed in the cable, which may cause a serious decline in the anti-electric breakdown ability of the cable during the heating process. On the other hand, since the method used for magnesium oxide in the production of cables is the vertical filling method, the uniformity and density of its filling and compaction are different, and the stability is poor. Summary of the Invention

[0005] In view of the above problems, the present invention provides a special additive for magnesium oxide used in BTTZ fireproof cables.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] A special additive for magnesium oxide used in BTTZ fireproof cables, including additive A, and the preparation method of additive A includes the following steps:

[0008] (1) Preparation of the precursor solution;

[0009] Weigh zirconium acetylacetonate and dissolve it in a mixed solvent. Add yttrium nitrate hexahydrate and calcium chloride, continue stirring until dissolved, then add a silicon source, and continue stirring and mixing until the mixed solution becomes transparent. Add polyethylene glycol ether, heat up to 60 - 70 °C and keep stirring and reacting for 1 - 2 h. After the reaction is completed, cool it to room temperature, and after defoaming treatment, the precursor solution is obtained;

[0010] Among them, the mixed solvent is a mixed solution of one or two of methanol, ethanol, and isopropanol and water; the silicon source is trimethoxysilane and / or triethoxysilane; the mass ratio of zirconium acetylacetonate to yttrium nitrate hexahydrate, calcium chloride, the silicon source, and polyethylene glycol ether is 10:(1 - 2.2):(1 - 1.8):(8 - 8.4):(0.05 - 0.08);

[0011] (2) Electrospinning;

[0012] (3) Heat treatment;

[0013] Heat the nanofibers obtained by electrospinning to 1000 - 1200 °C at a rate of 2 - 4 °C / min, keep heat-treating for 1 - 2 h, take it out after cooling to room temperature, and grind it to obtain the additive A.

[0014] In some preferred embodiments, the dissolution concentration of zirconium acetylacetonate in the mixed solvent is 20 - 25 wt%.

[0015] In some preferred embodiments, the nozzle specification of the electrospinning is 28G, the electrospinning rate is 2 mL / h, the electrospinning voltage is 25 kV, and the distance from the nozzle to the collector is 18 cm.

[0016] In some preferred embodiments, the addition amount of the additive A in magnesium oxide is 3 - 9 wt%.

[0017] In some preferred embodiments, the special additive further includes additive B, and the preparation method of the additive B includes the following steps:

[0018] S1. Weigh spherical silica powder and add it to an alkaline solution. After stirring and dispersing for 1 - 10 min, centrifuge and separate the spherical silica powder, then disperse the spherical silica powder in a mixed solution of aluminum ions and magnesium ions, stir and disperse for 10 - 60 min, centrifuge and separate the spherical silica powder, wash it by centrifugation with deionized water, and dry it to obtain the first modified powder;

[0019] S2. Heat the first modified powder to 300 - 500 °C at a rate of 1 - 5 °C / min, keep heat-treating for 0.5 - 1 h, take it out after cooling to room temperature to obtain the second modified powder;

[0020] S3. Disperse the second modified fine powder in a tetrahydrofuran solvent, add dimethylamine borane, stir and mix well, then transfer it into a high-pressure reactor with a polytetrafluoroethylene liner. Seal the reactor, heat it to 120 - 140 °C and keep it warm for 2 - 6 h. After the reaction, cool it to room temperature, centrifuge to separate the precipitate, wash it with tetrahydrofuran and absolute ethanol, and dry it under vacuum to obtain the additive B.

[0021] In some preferred embodiments, the purity of the spherical silica fine powder is greater than 99.5%, its sphericity is not less than 0.8, its particle size is less than 40 μm, its median diameter is 1 - 10 μm, and its bulk density is greater than 1.3 g / cm 3 .

[0022] In some preferred embodiments, the pH value of the alkaline solution is 8 - 10.

[0023] In some preferred embodiments, in the mixed solution of aluminum ions and magnesium ions, the concentration of aluminum ions is 0.01 - 0.1 mol / L, and the concentration of magnesium ions is 0.01 - 0.1 mol / L.

[0024] In some preferred embodiments, the addition amount of the additive A in magnesium oxide is 3 - 9 wt%.

[0025] In some preferred embodiments, the mass ratio of the second modified fine powder to the dimethylamine borane is 1:(9 - 10).

[0026] The beneficial effects of the present invention are as follows:

[0027] Aiming at the problem that the electrical insulation performance and stability of magnesium oxide as a filling material for BTTZ fireproof cables in the prior art need to be improved, the present invention provides a special additive for magnesium oxide used in BTTZ fireproof cables, which can effectively improve the insulation performance and filling performance. Specifically, on the basis of the existing silicate additives, the present invention uses zirconium silicate as the matrix, and prepares nano-scale fibers through the sol-gel method and the electrospinning method, and then obtains nano-scale additives. The present invention also uses calcium ions as doping ions to inhibit the secondary electron emission and surface charge accumulation on the surface of magnesium oxide filling particles, improve the breakdown voltage of the magnesium oxide filling layer, and thus improve its electrical insulation performance; further, the present invention uses high-sphericity ultra-fine silica fine powder as the precursor material, through surface micro-etching treatment with an alkaline solution and loading aluminum and magnesium ions to generate hydroxides, and then prepares a boronated product through pyrolysis and hydrothermal treatment in sequence. Based on the high sphericity of the ultra-fine silica fine powder and the low friction coefficient of the surface boronated product, it promotes the compactness and uniformity of the magnesium oxide powder during filling, and further improves the electrical insulation performance and stability of the insulation layer. Specific embodiments

[0028] The present invention will be further described in conjunction with the following embodiments.

[0029] Example 1

[0030] A special additive for magnesium oxide used in BTTZ fire-resistant cables, the special additive is Additive A, and the preparation method of Additive A includes the following steps:

[0031] (1) Preparation of precursor solution;

[0032] Weigh zirconium acetylacetonate and dissolve it in a mixed solution of ethanol and water (v / v = 1:2) according to a weight ratio of 1:5. Add yttrium nitrate hexahydrate and calcium chloride, continue to stir and dissolve, then add triethoxysilane, continue to stir and mix until the mixed solution becomes transparent. Add polyoxyethylene ether (weight average molecular weight is 1 million), heat up to 60 - 70 °C and keep stirring and reacting for 1 h. After the reaction is completed, cool to room temperature, and obtain the precursor solution after defoaming treatment;

[0033] Among them, the mass ratio of zirconium acetylacetonate to yttrium nitrate hexahydrate, calcium chloride, triethoxysilane, and polyoxyethylene ether is 10:1.8:1.4:8.2:0.06;

[0034] (2) Electrospinning;

[0035] Using a 28G nozzle, a spinning rate of 2 mL / h, a spinning voltage of 25 kV, and the distance from the nozzle to the collector is 18 cm to obtain nanofibers;

[0036] (3) Heat treatment;

[0037] Heat the nanofibers obtained by electrospinning to 1050 °C at a rate of 2 °C / min, keep heat-treating for 70 min, take out after cooling to room temperature, and grind to obtain Additive A.

[0038] Comparative Example 1

[0039] An additive for magnesium oxide used in BTTZ fire-resistant cables, the preparation method of the additive is the same as that in Example 1, the difference is that step (1) does not contain the calcium chloride.

[0040] Example 2

[0041] A special additive for magnesium oxide used in BTTZ fire-resistant cables, the special additive is Additive B, and the preparation method of Additive B includes the following steps:

[0042] S1. Weigh spherical silica powder and add it to an ammonia aqueous solution with a pH of 9. After stirring and dispersing for 2 minutes, centrifuge and separate the spherical silica powder. Then disperse the spherical silica powder in a mixed solution of aluminum ions and magnesium ions, stir and disperse for 30 minutes, centrifuge and separate the spherical silica powder, wash it by centrifugation with deionized water, and dry it to obtain the first modified powder;

[0043] Among them, the purity of the spherical silica powder is 99.8%, its sphericity is 0.86, its particle size is less than 40 μm, its median diameter is 7.8 μm, and its bulk density is 1.37 g / cm 3 ; the concentration of the aluminum ions is 0.08 mol / L, and the concentration of the magnesium ions is 0.07 mol / L;

[0044] S2. Heat the first modified powder to 450 °C at a rate of 4 °C / min, hold for heat treatment for 0.5 h, take it out after cooling to room temperature to obtain the second modified powder;

[0045] S3. Disperse the second modified powder in a tetrahydrofuran solvent, add dimethylamine borane, fully stir and mix, then transfer it to a high-pressure reaction kettle with a polytetrafluoroethylene lining, close the reaction kettle, heat it to 130 °C and hold for reaction for 4 h. After the reaction is completed, cool it to room temperature, centrifuge and separate the precipitate, wash it with tetrahydrofuran and absolute ethanol, and dry it under vacuum to obtain the additive B;

[0046] Among them, the mass ratio of the second modified powder to the dimethylamine borane is 1:9.5.

[0047] Comparative Example 2

[0048] An magnesia additive for BTTZ fire-resistant cables, and the additive is the spherical silica powder described in Example 2.

[0049] Example 3

[0050] A special magnesia additive for BTTZ fire-resistant cables, and the special additive is additive A and additive B, and the mass ratio of additive A to additive B is 1:1;

[0051] The preparation method of the additive A includes the following steps:

[0052] (1) Preparation of the precursor solution;

[0053] Weigh zirconium acetylacetonate and dissolve it in a mixed solution of ethanol and water (v / v = 1:2) at a weight ratio of 1:5. Add yttrium nitrate hexahydrate and calcium chloride, continue to stir and dissolve, then add triethoxysilane. Keep stirring and mixing until the mixed solution becomes transparent. Add polyethylene oxide (weight-average molecular weight is 1 million), heat up to 60 - 70 °C and keep stirring and reacting for 1 h. After the reaction is completed, cool to room temperature, and obtain the precursor solution after defoaming treatment;

[0054] Among them, the mass ratio of zirconium acetylacetonate to yttrium nitrate hexahydrate, calcium chloride, triethoxysilane, and polyethylene oxide is 10:1.8:1.4:8.2:0.06;

[0055] (2) Electrospinning;

[0056] Use a 28G nozzle, the spinning rate is 2 mL / h, the spinning voltage is 25 kV, and the distance from the nozzle to the collector is 18 cm to obtain nanofibers;

[0057] (3) Heat treatment;

[0058] Heat the nanofibers obtained by electrospinning to 1050 °C at a rate of 2 °C / min, keep heat-treating for 70 min, take them out after cooling to room temperature, and grind to obtain the additive A;

[0059] The preparation method of the additive B includes the following steps:

[0060] S1. Weigh spherical silica powder and add it to an ammonia water solution with a pH of 9. After stirring and dispersing for 2 min, centrifuge and separate the spherical silica powder. Then disperse the spherical silica powder in a mixed solution of aluminum ions and magnesium ions, stir and disperse for 30 min, centrifuge and separate the spherical silica powder, wash it by centrifugation with deionized water, and dry it to obtain the first modified powder;

[0061] Among them, the purity of the spherical silica powder is 99.8%, its sphericity is 0.86, its particle size is less than 40 μm, its median diameter is 7.8 μm, and its bulk density is 1.37 g / cm 3 ; the concentration of aluminum ions is 0.08 mol / L, and the concentration of magnesium ions is 0.07 mol / L;

[0062] S2. Heat the first modified powder to 450 °C at a rate of 4 °C / min, keep heat-treating for 0.5 h, take it out after cooling to room temperature to obtain the second modified powder;

[0063] S3. Disperse the second modified fine powder in a tetrahydrofuran solvent, add dimethylamine borane, stir and mix well, then transfer it into a high-pressure reaction kettle with a polytetrafluoroethylene liner. Seal the reaction kettle, heat it to 130 °C and keep the temperature for 4 h. After the reaction, cool it to room temperature, centrifuge to separate the precipitate, wash it with tetrahydrofuran and absolute ethanol, and dry it under vacuum to obtain the additive B.

[0064] Among them, the mass ratio of the second modified fine powder to the dimethylamine borane is 1:9.5.

[0065] Experimental Example

[0066] To further illustrate the technical effects of the present invention in combination with the embodiments of the present invention, the applicant measured the electrical properties of the additives described in Examples 1-3 and Comparative Examples 1-2. Among them, the addition amount of the additive in the filler is 8 wt%, and the chemical composition of the magnesium oxide powder is shown in Table 1. The measurement results are shown in Table 2:

[0067] Table 1 Chemical composition of the magnesium oxide powder

[0068] Component MgO CaO <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> Content ≥94％ ≤2.0％ ≤0.5％ ≤0.6％ ≤2.5％

[0069] Table 2 Electrical properties of magnesium oxide containing the additive

[0070]

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A special additive for magnesium oxide used in BTTZ fire-resistant cables, characterized in that, It includes additive A, and the preparation method of the additive A comprises the following steps: (1) Preparation of precursor solution; Weigh zirconium acetylacetonate and dissolve it in a mixed solvent, add yttrium nitrate hexahydrate and calcium chloride, continue to stir and dissolve, then add a silicon source, continue to stir and mix until the mixed solution becomes transparent, add polyethylene glycol ether, heat up to 60 - 70 °C and keep stirring and reacting for 1 - 2 h. After the reaction is completed, cool it to room temperature, conduct defoaming treatment to obtain the precursor solution; Among them, the mixed solvent is a mixed solution of one or two of methanol, ethanol, and isopropanol and water; the silicon source is trimethoxysilane and / or triethoxysilane; the mass ratio of zirconium acetylacetonate to yttrium nitrate hexahydrate, calcium chloride, the silicon source, and polyethylene glycol ether is 10:(1 - 2.2):(1 - 1.8):(8 - 8.4):(0.05 - 0.08); (2) Electrospinning; (3) Heat treatment; Heat the nanofibers obtained by spinning to 1000 - 1200 °C at a rate of 2 - 4 °C / min, keep heat-treating for 1 - 2 h, take it out after cooling to room temperature, and grind it to obtain the additive A; The special additive also includes additive B, and the preparation method of the additive B comprises the following steps: S1. Weigh spherical silica powder and add it to an alkaline solution. After stirring and dispersing for 1 - 10 min, centrifuge the spherical silica powder, then disperse the spherical silica powder in a mixed solution of aluminum ions and magnesium ions, stir and disperse for 10 - 60 min, centrifuge the spherical silica powder, wash it by centrifugation with deionized water, and dry it to obtain the first modified powder; S2. Heat the first modified powder to 300 - 500 °C at a rate of 1 - 5 °C / min, keep heat-treating for 0.5 - 1 h, take it out after cooling to room temperature to obtain the second modified powder; S3. Disperse the second modified powder in a tetrahydrofuran solvent, add dimethylamine borane, fully stir and mix, then transfer it to a high-pressure reaction kettle with a polytetrafluoroethylene inner lining, seal the reaction kettle, heat up to 120 - 140 °C and keep reacting for 2 - 6 h. After the reaction is completed, cool it to room temperature, centrifuge and separate the precipitate, wash it with tetrahydrofuran and absolute ethanol, and conduct vacuum drying to obtain the additive B.

2. The special additive for magnesium oxide used in BTTZ fire-resistant cables according to claim 1, characterized in that, The dissolution concentration of zirconium acetylacetonate in the mixed solvent is 20 - 25 wt%.

3. The special additive for magnesium oxide used in a BTTZ fire-resistant cable according to claim 1, characterized in that, The nozzle specification of the electrospinning is 28G, the spinning rate is 2 mL / h, the spinning voltage is 25 kV, and the distance from the nozzle to the collector is 18 cm.

4. The special additive for magnesium oxide used in a BTTZ fire-resistant cable according to claim 1, characterized in that, The addition amount of the additive A in magnesium oxide is 3 - 9 wt%.

5. The special additive for magnesium oxide used in a BTTZ fire-resistant cable according to claim 1, characterized in that, The purity of the spherical silica powder is greater than 99.5%, its sphericity is not less than 0.8, its particle size is less than 40μm, its median diameter is 1 - 10μm, and its bulk density is greater than 1.3g / cm 3 .

6. The special additive for magnesium oxide used in a BTTZ fire-resistant cable according to claim 1, characterized in that, The pH value of the alkaline solution is 8 - 10.

7. The special additive for magnesium oxide used in BTTZ fire-resistant cables according to claim 1, characterized in that, In the mixed solution of aluminum ions and magnesium ions, the concentration of aluminum ions is 0.01 - 0.1 mol / L, and the concentration of magnesium ions is 0.01 - 0.1 mol / L.

8. The special additive for magnesium oxide used in a BTTZ fire-resistant cable according to claim 1, characterized in that, The mass ratio of the second modified powder to dimethylamine borane is 1:(9 - 10).

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