阅读说明：本技术 一种增韧型无机纤维毡及其制备方法 (Toughening type inorganic fiber felt and preparation method thereof ) 是由 任大贵 张成贺 岳耀辉 王振宇 孟凡伟 于 2020-11-27 设计创作，主要内容包括：本发明提供了一种增韧型无机纤维毡,包括以下重量份数的制备原料：无机纤维：57～80份,黏土材料：0～5份,无机粘合剂：17～30份,增韧剂：2～5份,助滤剂：1～3份；所述增韧剂的原料包括氧化钙、氧化镁、氧化锌和无机酸。在本发明中的浆料体系中,金属氧化物和无机酸能够在所述无机纤维的表面反应得到一种呈鳞片状结构均匀包裹在所述纤维表面的连续相,同时金属阳离子在水中形成高度聚合的多羟基化合物,在絮凝剂的作用下能够吸附无机结合剂的胶体颗粒,最终使纤维毡具有质轻、保温、无机不燃、优良的压缩回弹性等特点。本发明还提供了一种增韧型无机纤维毡的制备方法。(The invention provides a toughened inorganic fiber felt which comprises the following preparation raw materials in parts by weight: inorganic fibers: 57-80 parts of clay material: 0-5 parts of inorganic binder: 17-30 parts of a toughening agent: 2-5 parts of filter aid: 1-3 parts; the raw materials of the toughening agent comprise calcium oxide, magnesium oxide, zinc oxide and inorganic acid. In the slurry system, metal oxide and inorganic acid can react on the surface of the inorganic fiber to obtain a continuous phase which is in a scale-like structure and uniformly wraps the surface of the fiber, and meanwhile, metal cations form a high-polymerization polyhydroxy compound in water, and can adsorb colloidal particles of an inorganic binding agent under the action of a flocculating agent, so that the fiber felt has the characteristics of light weight, heat preservation, inorganic non-combustibility, excellent compression resilience and the like. The invention also provides a preparation method of the toughened inorganic fiber felt.)

1. The toughened inorganic fiber felt comprises the following preparation raw materials in parts by weight:

inorganic fibers: 57-80 parts of clay material: 0-5 parts of inorganic binder: 17-30 parts of a toughening agent: 2-5 parts of filter aid: 1-3 parts;

the raw materials of the toughening agent comprise calcium oxide, magnesium oxide, zinc oxide and inorganic acid.

2. The toughened inorganic fiber felt according to claim 1, wherein the mass ratio of the calcium oxide, the magnesium oxide, the zinc oxide and the inorganic acid is (10-20): 10-20: (10-20): 50-60).

3. The toughened inorganic fiber mat of claim 1, wherein the inorganic fibers are one or more of aluminosilicate fibers, soluble fibers, glass fibers, basalt fibers, carbon fibers, and polycrystalline mullite fibers.

4. The toughened inorganic fiber mat according to claim 1, wherein the clay material is one or more of kaolin, attapulgite and wollastonite powder;

the particle size of the clay material is 800-1000 meshes.

5. The toughened inorganic fiber mat according to claim 1, wherein the inorganic binder is silica sol and/or water glass.

6. The toughened inorganic fiber felt according to claim 1, wherein the filter aid is polyacrylamide; the molecular weight of the polyacrylamide is 800-1200 ten thousand.

7. The method for preparing the toughened inorganic fiber felt according to any one of claims 1 to 6, comprising the following steps:

A) mixing inorganic fibers, clay materials, inorganic adhesives and toughening agents in water to obtain mixed slurry;

B) and adding a filter aid into the mixed slurry, flocculating and dehydrating to obtain the toughened inorganic fiber felt.

8. The preparation method according to claim 7, wherein the step A) is carried out under stirring conditions, wherein the stirring speed is 400-600 rpm, and the stirring time is 20-25 min.

9. The preparation method of claim 7, wherein the step B) is performed with vacuum suction filtration for dehydration after flocculation, and then is performed with drying, so as to obtain the toughening type inorganic fiber felt.

10. The method according to claim 9, wherein the drying temperature is 120 to 150 ℃ and the drying time is 5 to 15 hours.

Technical Field

The invention belongs to the technical field of inorganic fibers, and particularly relates to a toughened inorganic fiber felt and a preparation method thereof.

Background

In order to obtain excellent heat preservation effect and safety performance, a heat insulating material is generally used in an interlayer of a cabin wall of a locomotive, and the heat insulating material is required to have the characteristics of light weight, heat preservation, inorganic non-flammability, certain compression resilience and the like.

The traditional aluminum silicate fiber blanket or soluble fiber blanket has the characteristics of light weight, inorganic non-combustibility, certain compression resilience and the like, but has certain defects. The aluminum silicate fiber blanket or the soluble fiber blanket is completely the strength obtained by needling and high-temperature curing, and the fibers have no binding force, so that the fibers are easy to fall off; the aluminum silicate fiber blanket or the soluble fiber blanket is completely a flexible material, has no self-supporting property and has large construction difficulty; and the heat preservation effect of the product is poor due to long fibers and dense pinholes. The traditional aluminum silicate fiber felt (board) or soluble fiber felt (board) has self-supporting property, but generally contains organic components, can be combusted at high temperature to generate smoke, and has low safety.

Disclosure of Invention

The invention aims to provide a toughening type inorganic fiber felt and a preparation method thereof.

The invention provides a toughened inorganic fiber felt which comprises the following preparation raw materials in parts by weight:

inorganic fibers: 57-80 parts of clay material: 0-5 parts of inorganic binder: 17-30 parts of a toughening agent: 2-5 parts of filter aid: 1-3 parts;

the raw materials of the toughening agent comprise calcium oxide, magnesium oxide, zinc oxide and inorganic acid.

Preferably, the mass ratio of the calcium oxide to the magnesium oxide to the zinc oxide to the inorganic acid is (10-20): 50-60.

Preferably, the inorganic fiber is one or more of aluminum silicate fiber, soluble fiber, glass fiber, basalt fiber, carbon fiber and polycrystalline mullite fiber.

Preferably, the clay material is one or more of kaolin, attapulgite and wollastonite powder;

the particle size of the clay material is 800-1000 meshes.

Preferably, the inorganic binder is silica sol and/or water glass.

Preferably, the filter aid is polyacrylamide; the molecular weight of the polyacrylamide is 800-1200 ten thousand.

The invention provides a preparation method of the toughening type inorganic fiber felt, which comprises the following steps:

A) mixing inorganic fibers, clay materials, inorganic adhesives and toughening agents in water to obtain mixed slurry;

B) and adding a filter aid into the mixed slurry, flocculating and dehydrating to obtain the toughened inorganic fiber felt.

Preferably, the step A) is carried out under the condition of stirring, the stirring speed is 400-600 rpm, and the stirring time is 20-25 min.

Preferably, the step B) is performed with vacuum suction filtration for dehydration after flocculation, and then is dried, so as to obtain the toughening type inorganic fiber felt.

Preferably, the drying temperature is 120-150 ℃, and the drying time is 5-15 hours.

The invention provides a toughened inorganic fiber felt which comprises the following preparation raw materials in parts by weight: inorganic fibers: 57-80 parts of clay material: 0-5 parts of inorganic binder: 17-30 parts of a toughening agent: 2-5 parts of filter aid: 1-3 parts; the raw materials of the toughening agent comprise calcium oxide, magnesium oxide, zinc oxide and inorganic acid. In the slurry system, the metal oxide and the inorganic acid can react on the surface of the inorganic fiber to obtain a continuous phase which is in a flaky structure and uniformly wraps the surface of the fiber, the existence of the flaky structure of the continuous phase greatly improves the toughness of the inorganic fiber, and meanwhile, metal cations form a high-polymerization polyhydroxy compound in water, and can adsorb colloid particles of an inorganic binding agent under the action of a flocculating agent, so that the rigidity strength caused by drying of the pure inorganic binding agent is reduced, and finally, the fiber mat has the characteristics of light weight, heat preservation, inorganic incombustibility, excellent compression resilience and the like.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

Fig. 1 is an SEM electron micrograph of the inorganic fiber mat in example 1 of the present invention.

Detailed Description

The invention aims to provide a toughened inorganic fiber felt which comprises the following preparation raw materials in parts by weight:

inorganic fibers: 57-80 parts of clay material: 0-5 parts of inorganic binder: 17-30 parts of a toughening agent: 2-5 parts of filter aid: 1-3 parts;

the raw materials of the toughening agent comprise calcium oxide, magnesium oxide, zinc oxide and inorganic acid.

In the invention, the inorganic fiber is preferably one or more of alumina silicate fiber, soluble fiber, glass fiber, basalt fiber, carbon fiber and polycrystalline mullite fiber, the fiber diameters of the alumina silicate fiber, the soluble fiber and the polycrystalline mullite fiber are all 3-5 μm, the fiber diameter of the glass fiber is preferably 7-10 μm, the diameter of the basalt fiber is preferably 9-15 μm, and the fiber diameter of the carbon fiber is preferably 6-8 μm.

In the present invention, the weight part of the inorganic fiber is preferably 57 to 80 parts, more preferably 60 to 75 parts, and most preferably 65 to 70 parts, and specifically, in the embodiment of the present invention, it may be 57 parts, 70 parts, 75 parts, or 80 parts.

In the invention, the clay material preferably comprises one or more of kaolin, attapulgite and wollastonite powder; the particle size of the clay material is preferably 800-1000 meshes, and more preferably 850-950 meshes; the weight part of the clay material is preferably 0 to 5 parts, more preferably 1 to 4 parts, and most preferably 2 to 3 parts, and specifically, in the embodiment of the present invention, the weight part may be 0 part, 3 parts, 4 parts, or 5 parts.

In the invention, the inorganic binder is preferably silica sol and/or water glass, the mass concentration of the silica sol is preferably 30-40%, and the mass concentration of the water glass is preferably 20-30%. The inorganic binder is preferably 17 to 30 parts by weight, more preferably 20 to 25 parts by weight, and specifically, in an embodiment of the present invention, 30 parts, 20 parts, 21 parts, or 17 parts by weight.

In the invention, the raw materials of the toughening agent are preferably calcium oxide, magnesium oxide, zinc oxide and inorganic acid, wherein the calcium oxide is a white powdery substance and has the density of 3.32-3.35 g/cm³(ii) a The zinc oxide is white powdery substance with the density of 5.5-5.6 g/cm³(ii) a The magnesium oxide is white powdery substance with the density of 3.55-3.58 g/cm³。

In the invention, the inorganic acid is preferably one or more of hydrochloric acid, sulfuric acid and phosphoric acid, the mass concentration of the hydrochloric acid is preferably 36-37%, the mass concentration of the sulfuric acid is preferably 74-75%, and the mass concentration of the phosphoric acid is preferably 84-85%.

In the invention, the mass ratio of the calcium oxide, the magnesium oxide, the zinc oxide and the inorganic acid is preferably (10-20): 50-60; specifically, in the embodiment of the present invention, the amount of the calcium oxide may be in accordance with the weight parts, for example, the weight parts of the calcium oxide are preferably 10 to 20 parts, such as 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts, or any value of the above ranges is used as the upper limit or the lower limit; the weight portion of the magnesium oxide is preferably 10 to 20 portions, such as 10 portions, 11 portions, 12 portions, 13 portions, 14 portions, 15 portions, 16 portions, 17 portions, 18 portions, 19 portions or 20 portions, or the range value taking any value as the upper limit or the lower limit; the weight portion of the zinc oxide is preferably 10 to 20 portions, such as 10 portions, 11 portions, 12 portions, 13 portions, 14 portions, 15 portions, 16 portions, 17 portions, 18 portions, 19 portions or 20 portions, or the range value taking any value as the upper limit or the lower limit; the inorganic acid is preferably 50 to 60 parts by weight, such as 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts or 60 parts, or a range value taking any value of the above as an upper limit or a lower limit.

In the invention, the filter aid is preferably polyacrylamide, more preferably a polyacrylamide solution is used, and the mass concentration of the polyacrylamide solution is preferably 0.5-1%; the molecular weight of the polyacrylamide is preferably 800-1200 ten thousand, more preferably 900-1100 ten thousand, and most preferably 950-1000 ten thousand.

In the present invention, the amount of the filter aid, i.e. polyacrylamide, is calculated as the mass or molar amount of the pure substance of the filter aid, i.e. polyacrylamide.

The invention also provides a preparation method of the toughened inorganic fiber felt, which comprises the following steps:

A) mixing inorganic fibers, clay materials, inorganic adhesives and toughening agents in water to obtain mixed slurry;

B) and adding a filter aid into the mixed slurry, flocculating and dehydrating to obtain the toughened inorganic fiber felt.

In the present invention, the types and the amounts of the inorganic fiber, the clay material, the inorganic binder and the toughening agent primary filter aid are the same as those of the inorganic fiber, the clay material, the inorganic binder and the toughening agent primary filter aid, and thus, the description thereof is omitted.

Preferably, the calcium oxide, the zinc oxide and the magnesium oxide are added into water, then the inorganic acid is added under the condition of stirring, and the toughening agent solution is obtained after full reaction.

And then adding the inorganic fiber, the clay material, the inorganic adhesive and the toughening agent solution into water according to a ratio, and stirring to obtain mixed slurry.

In the invention, the stirring speed is preferably 400-600 rpm, more preferably 500-550 rpm; the stirring time is preferably 20-25 min.

The amount of water used for preparing the mixed slurry is not particularly limited, and the mixed slurry can provide a sufficient water environment for the raw materials and meet the subsequent flocculation and sedimentation environment conditions.

After the mixed slurry is obtained, adding a filter aid into the mixed slurry for flocculation until supernatant appears in the slurry; then vacuum suction filtration dehydration and hot air drying are carried out to prepare the inorganic fiber felt with certain thickness.

In the present invention, the vacuum filtration is a dehydration method commonly used by those skilled in the art, and the present invention is not described in detail again.

In the invention, the drying temperature is preferably 120-150 ℃, and more preferably 130-140 ℃; the drying time is preferably 5 to 15 hours, more preferably 8 to 12 hours, and most preferably 10 to 11 hours.

The invention provides a toughened inorganic fiber felt which comprises the following preparation raw materials in parts by weight: inorganic fibers: 57-80 parts of clay material: 0-5 parts of inorganic binder: 17-30 parts of a toughening agent: 2-5 parts of filter aid: 1-3 parts; the toughening agent comprises calcium oxide, magnesium oxide, zinc oxide and inorganic acid. In the slurry system, calcium oxide, magnesium oxide, zinc oxide and inorganic acid realize better interaction under the condition of a specific proportion, a continuous phase which is in a flaky structure and uniformly wraps the surface of the fiber is obtained through reaction, the toughness of the inorganic fiber is greatly improved due to the existence of the flaky structure of the continuous phase, and meanwhile, metal cations form a high-polymerization polyhydroxy compound in water, so that colloidal particles of an inorganic binding agent can be adsorbed under the action of a flocculating agent, the rigidity strength brought by drying of a pure inorganic binding agent is reduced, and finally, the fiber felt has the characteristics of light weight, heat preservation, inorganic non-combustibility, excellent compression resilience and the like.

In order to further illustrate the present invention, the following detailed description is provided with reference to the examples to illustrate a toughened inorganic fiber mat and a method for preparing the same, but the scope of the present invention should not be construed as being limited thereto.

Example 1

(1) Adding 15 parts by weight of calcium oxide, 15 parts by weight of zinc oxide and 15 parts by weight of magnesium oxide into water, starting a stirrer, adding 55 parts by weight of phosphoric acid into the stirrer after the materials are uniformly stirred, and fully reacting to obtain the toughening agent of the inorganic heat-insulating material;

(2) adding 57 parts by weight of aluminum silicate fiber, 5 parts by weight of attapulgite, 30 parts by weight of silica sol and 5 parts by weight of the toughening agent prepared in the step (1) into water, starting a stirrer, wherein the stirring speed is 400rpm, and the stirring time is 25 min;

(3) adding 3 parts by weight of 1% polyacrylamide solution with molecular weight of 800 ten thousand into the slurry prepared in the step (2), and continuing stirring for 3min until a supernatant appears;

(4) and (3) carrying out vacuum suction filtration dehydration and hot air drying to obtain an inorganic fiber felt with the thickness of 10mm, wherein the drying temperature is 150 ℃ and the drying time is 5 hours.

Example 2

(1) Adding 10 parts by weight of calcium oxide, 10 parts by weight of zinc oxide and 20 parts by weight of magnesium oxide into water, starting a stirrer, adding 60 parts by weight of sulfuric acid into the stirrer after the materials are uniformly stirred, and fully reacting to obtain the toughening agent of the inorganic heat-insulating material;

(2) adding 70 parts by weight of polycrystalline mullite fiber, 4 parts by weight of wollastonite powder, 20 parts by weight of water glass and 4 parts by weight of the toughening agent prepared in the step (1) into water, starting a stirrer, and stirring at the speed of 500rpm for 23 min;

(3) adding 2 parts by weight of 0.8% polyacrylamide solution with molecular weight of 900 ten thousand into the slurry prepared in the step (2), and continuing stirring for 4min until a supernatant appears;

(4) and (3) carrying out vacuum suction filtration dehydration and hot air drying to obtain an inorganic fiber felt with the thickness of 25mm, wherein the drying temperature is 130 ℃, and the drying time is 10 hours.

Example 3

(1) Adding 10 parts by weight of calcium oxide, 20 parts by weight of zinc oxide and 10 parts by weight of magnesium oxide into water, starting a stirrer, adding 60 parts by weight of hydrochloric acid into the stirrer after the materials are uniformly stirred, and fully reacting to obtain the inorganic heat-insulating material toughening agent;

(2) adding 75 parts by weight of carbon fiber, 3 parts by weight of kaolin, 20 parts by weight of water glass and 2 parts by weight of the toughening agent prepared in the step (1) into water, starting a stirrer, and stirring at the speed of 600rpm for 20 min;

(3) adding 1 part by weight of 0.8% polyacrylamide solution with the molecular weight of 1100 ten thousand into the slurry prepared in the step (2), and continuing stirring for 5min until a supernatant appears;

(4) and (3) carrying out vacuum suction filtration dehydration and hot air drying to obtain an inorganic fiber felt with the thickness of 40mm, wherein the drying temperature is 140 ℃ and the drying time is 11 h.

Example 4

(1) Adding 15 parts by weight of calcium oxide, 15 parts by weight of zinc oxide and 20 parts by weight of magnesium oxide into water, starting a stirrer, adding 50 parts by weight of phosphoric acid into the stirrer after the materials are uniformly stirred, and fully reacting to obtain the toughening agent of the inorganic heat-insulating material;

(2) adding 75 parts by weight of glass fiber, 21 parts by weight of water glass and 3 parts by weight of the toughening agent prepared in the step (1) into water, starting a stirrer, wherein the stirring speed is 600rpm, and the stirring time is 20 min;

(3) adding 1 part by weight of 0.5% polyacrylamide solution with the molecular weight of 1200 ten thousand into the slurry prepared in the step (2), and continuing stirring for 5min until a supernatant appears;

(4) and (3) dehydrating by vacuum suction filtration, and then drying by hot air to prepare the inorganic fiber felt with the thickness of 20mm, wherein the drying temperature is 125 ℃, and the drying time is 6 h.

Example 5

(1) Adding 20 parts by weight of calcium oxide, 10 parts by weight of zinc oxide and 10 parts by weight of magnesium oxide into water, starting a stirrer, adding 60 parts by weight of phosphoric acid into the stirrer after the materials are uniformly stirred, and fully reacting to obtain the toughening agent of the inorganic heat-insulating material;

(2) adding 80 parts by weight of basalt fiber, 17 parts by weight of silica sol and 2 parts by weight of the toughening agent prepared in the step (1) into water, starting a stirrer, wherein the stirring speed is 600rpm, and the stirring time is 20 min;

(3) adding 1 part by weight of 0.5% polyacrylamide solution with the molecular weight of 1100 ten thousand into the slurry prepared in the step (2), and continuing stirring for 4min until a supernatant appears;

(4) and (3) carrying out vacuum suction filtration dehydration and hot air drying to obtain an inorganic fiber felt with the thickness of 50mm, wherein the drying temperature is 140 ℃ and the drying time is 15 h.

Example 6

(1) Adding 15 parts by weight of calcium oxide, 15 parts by weight of zinc oxide and 15 parts by weight of magnesium oxide into water, starting a stirrer, adding 55 parts by weight of phosphoric acid into the stirrer after the materials are uniformly stirred, and fully reacting to obtain the toughening agent of the inorganic heat-insulating material;

(2) adding 75 parts by weight of soluble fiber, 20 parts by weight of silica sol and 3 parts by weight of the toughening agent prepared in the step (1) into water, starting a stirrer, and stirring at the speed of 600rpm for 20 min;

(3) adding 2 parts by weight of 0.5% polyacrylamide solution with the molecular weight of 1200 ten thousand into the slurry prepared in the step (2), and continuing stirring for 5min until a supernatant appears;

(4) and (3) carrying out vacuum suction filtration dehydration and hot air drying to obtain an inorganic fiber felt with the thickness of 50mm, wherein the drying temperature is 150 ℃ and the drying time is 10 h.

Comparative example 1

(1) Adding 35 parts by weight of calcium oxide, 15 parts by weight of zinc oxide and 15 parts by weight of magnesium oxide into water, starting a stirrer, adding 35 parts by weight of phosphoric acid into the stirrer after the materials are uniformly stirred, and fully reacting to obtain a toughening agent a;

(2) adding 57 parts by weight of aluminum silicate fiber, 5 parts by weight of attapulgite, 30 parts by weight of silica sol and 5 parts by weight of the material a prepared in the step (1) into water, starting a stirrer, wherein the stirring speed is 400rpm, and the stirring time is 25 min;

(3) adding 3 parts by weight of 1% polyacrylamide solution with molecular weight of 800 ten thousand into the slurry prepared in the step (2), and continuing stirring for 3min until a supernatant appears;

(4) and (3) carrying out vacuum suction filtration dehydration and hot air drying to obtain an inorganic fiber felt with the thickness of 10mm, wherein the drying temperature is 150 ℃ and the drying time is 5 hours.

Comparative example 2

(1) Adding 5 parts by weight of calcium oxide, 5 parts by weight of zinc oxide and 5 parts by weight of magnesium oxide into water, starting a stirrer, adding 85 parts by weight of sulfuric acid into the stirrer after the materials are uniformly stirred, and fully reacting to obtain a toughening agent b;

(2) adding 70 parts by weight of polycrystalline mullite fiber, 4 parts by weight of wollastonite powder, 20 parts by weight of water glass and 4 parts by weight of the material b prepared in the step (1) into water, starting a stirrer, and stirring at the speed of 500rpm for 23 min;

(3) adding 2 parts by weight of 0.8% polyacrylamide solution with molecular weight of 900 ten thousand into the slurry prepared in the step (2), and continuing stirring for 4min until a supernatant appears;

(4) and (3) carrying out vacuum suction filtration dehydration and hot air drying to obtain an inorganic fiber felt with the thickness of 25mm, wherein the drying temperature is 130 ℃, and the drying time is 10 hours.

Examples of the experiments

The inorganic fiber papers prepared in examples 1 to 6 of the present invention were sequentially numbered A, B, C, D, E, F, and the ceramic fiber mats, the soluble fiber boards, and the samples prepared in comparative examples 1 and 2 were respectively numbered G, H, I, J. The samples were tested for bulk density, spalling resistance, compression resilience and flammability separately, yielding the data shown in the following table:

TABLE 1 Performance data for inorganic fiber mats of examples 1-6

The data in table 1 show that the inorganic conjugate fiber mat (A, B, C, D, E, F) of the present invention has good peel resistance, good compression resilience, and excellent burn performance. The ceramic fiber blanket has poor anti-stripping performance and general compression resilience under the same detection condition; the soluble fiber board has poor compression resilience and poor combustion performance under the same detection condition; the compression resilience of the sample prepared in the comparative example 1 is lower than that of the sample prepared in the example 1, mainly because the metal oxide in the toughening agent a is excessive, the amount of the inorganic acid is small, the reaction is insufficient, the effective component in the toughening agent a is small, and the toughening effect is not obvious; the compression resilience of the sample prepared in the comparative example 2 is lower than that of the sample prepared in the example 2, mainly because the effective component of the toughening agent b is less and the toughening effect is not obvious due to less metal oxide in the toughening agent b and excessive inorganic acid.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.