An inorganic silicon crystal fire-resistant and heat-insulating material for fireproof air ducts and its preparation method

Abstract

This invention relates to the field of thermal insulation materials, specifically to an inorganic silicon crystal fire-resistant thermal insulation material for fireproof air ducts and its preparation method. The material comprises inorganic silicon crystal powder, hollow microspheres, composite binders, reinforcing fibers, surface modifiers, nano-antibacterial agents, crack-resistant agents, flame-retardant synergists, and intumescent flame-retardant microcapsules. The inorganic silicon crystal powder is activated by calcination, the microspheres are pretreated with coupling agents and coated with silica sol, the binder is a compound type, the fibers are grafted, the antibacterial agent is loaded onto a carrier, and the flame-retardant microcapsules have a specific core and shell. All components work synergistically to ensure performance. This invention improves the material's fire resistance, thermal insulation, and mechanical properties, integrates antibacterial and flame-retardant functions, optimizes the process to ensure stable performance, reduces fire risk, and meets the high-performance and high-stability requirements of high-end building fireproof air ducts.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation materials technology, specifically to an inorganic silicon crystal fire-resistant thermal insulation material for fireproof air ducts and its preparation method. Background Technology

[0002] In building fire protection systems, fire-resistant ducts, as core components of smoke control and exhaust systems, directly determine the effectiveness of smoke control and the safety of personnel evacuation during a fire. National standards such as the "Technical Standard for Building Smoke Control and Exhaust Systems" clearly require fire-resistant ducts in different installation locations to meet fire resistance limits ranging from 0.5h to 3.0h, while also possessing low thermal conductivity, high mechanical strength, and environmental adaptability. Inorganic silicon crystal fire-resistant and heat-insulating materials have become the mainstream choice for core filling materials in fire-resistant ducts due to their wide availability of raw materials and excellent combustion performance. However, existing products still have many shortcomings in performance synergy optimization and manufacturing process stability.

[0003] First, the design of the matrix components of existing inorganic silicon crystal materials has defects: inorganic silicon crystal powder is mostly directly used as industrial-grade wollastonite powder or ordinary silicon dioxide without targeted activation treatment, resulting in low crystallinity and insufficient reactivity, making it difficult to simultaneously achieve both fire resistance limit and thermal conductivity; hollow microspheres, as lightweight insulation components, often have weak interfacial bonding with the matrix due to lack of surface modification or simple modification processes, making them prone to delamination under stress or high temperature environments, affecting the overall strength of the material; binders are mostly single sodium silicate or aluminate cement, lacking composite modification design, which either results in large curing shrinkage and easy cracking, or insufficient bonding strength, leading to delamination of the material after long-term use.

[0004] Secondly, the integration of functional performance is insufficient: existing materials mostly focus only on fire resistance and heat insulation performance, neglecting the need for antibacterial and anti-mildew properties. In scenarios such as underground garages, hospitals, and damp factories, microorganisms are prone to grow on the inner walls of air ducts, affecting indoor air quality. Flame retardant systems mostly rely on a single flame retardant, which easily produces a large amount of smoke at high temperatures, resulting in a high smoke density level, which does not meet the requirements of modern buildings for low smoke toxicity. The reinforcing fibers are mostly untreated glass fibers or basalt fibers, which have poor compatibility with the matrix and are difficult to effectively play a reinforcing role, resulting in poor flexural and impact resistance of the materials, making them prone to damage during installation or use.

[0005] Furthermore, the manufacturing process has shortcomings: the raw material pretreatment stage lacks standardized procedures; for example, improper control of the calcination temperature and time of inorganic silicon crystal powder, uneven bead coating, and insufficient fiber grafting all affect the subsequent mixing and molding quality; dry material mixing often uses a single-speed stirring method, which easily leads to component agglomeration and fluctuations in material properties; unreasonable matching of pressure and temperature parameters during molding easily produces internal porosity or uneven density; curing processes are mostly simple room temperature or constant temperature curing, without considering stepped temperature rise and humidity control, resulting in internal stress concentration in the material, making it prone to cracking and unable to meet long-term weather resistance requirements. These problems collectively make existing inorganic silicon crystal fire-resistant insulation materials unsuitable for the high-performance and high-stability requirements of high-end building fireproof air ducts, urgently requiring technological innovation. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides an inorganic silicon crystal fire-resistant and heat-insulating material for fireproof air ducts and its preparation method.

[0008] (II) Technical Solution

[0009] An inorganic silicon crystal fire-resistant and heat-insulating material for fireproof air ducts, comprising the following components by weight: 40-60 parts inorganic silicon crystal powder, 20-30 parts hollow microspheres, 15-22 parts composite binder, 8-15 parts reinforcing fiber, 3-6 parts surface modifier, 1-3 parts nano antibacterial agent, 2-4 parts crack-resistant agent, 1-3 parts flame retardant synergist, and 0.5-2 parts intumescent flame-retardant microcapsules;

[0010] The inorganic silicon powder is a mixture of high-purity silica whiskers (1-5 μm particle size) and wollastonite powder in a mass ratio of 4:1-6:1, activated by calcination at 500-600℃; the hollow microspheres are fly ash celery spheres (80-180 μm particle size), pretreated with a silane coupling agent, and then coated with nano-silica sol to form a core-shell structure, wherein the silane coupling agent is KH-550 or KH-560; the composite binder is a mixture of sodium silicate, aluminate cement, and modified starch ether in a mass ratio of 3:1:0.3-3:1:0.5, wherein the aluminate cement is CA- Type 50, the modified starch ether is hydroxypropyl methylcellulose ether; the reinforcing fiber is a compound of alkali-free glass fiber grafted with maleic anhydride and basalt fiber in a mass ratio of 1.5:1-2.5:1; the nano antibacterial agent is a compound of nano zinc oxide and nano silver in a mass ratio of 6:1-9:1, the nano zinc oxide has a particle size of 20-50nm, the nano silver has a particle size of 5-15nm, and is loaded on the surface of a porous silica carrier; the expandable flame retardant microcapsules have ammonium polyphosphate as the core material and melamine resin as the shell material, with a core-shell ratio of 7:3-8:2 and a particle size of 100-200nm.

[0011] Preferably, the surface modifier is a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1 to 2:1, and the modification treatment is carried out in a high-speed mixer.

[0012] Preferably, the crack-resistant agent is a compound of polypropylene fiber and basalt chopped fiber in a mass ratio of 2:1-3:1. The polypropylene fiber has a length of 4-5 mm, a tensile strength of not less than 550 MPa, and an elastic modulus of not less than 3.5 GPa. The basalt chopped fiber has a length of 3-4 mm and a tensile strength of not less than 800 MPa.

[0013] Preferably, the flame retardant synergist is a mixture of nano-magnesium hydroxide and nano-aluminum hydroxide in a mass ratio of 1:1, with the nano-magnesium hydroxide having a particle size of 60-80nm and the nano-aluminum hydroxide having a particle size of 70-90nm, and is coated with 0.5-1% stearic acid by mass.

[0014] Preferably, by weight, it is composed of the following components: 50 parts inorganic silicon crystal powder, 25 parts hollow microspheres, 18 parts composite binder, 12 parts reinforcing fiber, 4 parts surface modifier, 2 parts nano antibacterial agent, 3 parts crack-resistant agent, 2 parts flame retardant synergist and 1.2 parts intumescent flame retardant microcapsules.

[0015] The inorganic silicon powder contains silica whiskers to wollastonite powder in a 5:1 mass ratio and is calcined at 600℃ for 2 hours. The hollow microspheres have a particle size of 120-150μm and are pretreated with KH-550 before being coated with nano-silica. The composite binder contains sodium silicate, aluminate cement, and modified starch ether in a 3:1:0.4 mass ratio. The reinforcing fibers contain grafted alkali-free glass fiber to basalt fiber in a 2:1 mass ratio. The surface modifier contains γ-aminopropyltriethoxy The mass ratio of basic silane to γ-glycidoxypropyltrimethoxysilane is 1.5:1; the mass ratio of nano zinc oxide to nano silver in the nano antibacterial agent is 7:1 and it is loaded on a porous silica carrier; the mass ratio of polypropylene fiber to basalt chopped fiber in the crack-resistant agent is 2.5:1; the flame retardant synergist is a compound of nano magnesium hydroxide and nano aluminum hydroxide coated with stearic acid; and the mass ratio of ammonium polyphosphate to melamine resin in the intumescent flame retardant microcapsules is 7.5:2.5.

[0016] Preferably, the preparation method of the inorganic silicon crystal fire-resistant and heat-insulating material for fireproof air ducts includes the following steps:

[0017] S1. Raw material pretreatment: Mix silica whiskers and wollastonite powder in a certain proportion, place them in a muffle furnace and calcine at 500-600℃ for 1.5-2.5h, with a heating rate of 5-8℃ / min, and then cool naturally to room temperature after calcination; dry the cenospheres in an oven at 110-115℃ for 2.5-3h, cool them and add silane coupling agent, mix at high speed at 85-95℃ and 900-950r / min for 35-40min, then add nano silica sol, stir at 50-60℃ for 1.5-2h, filter and dry; mix alkali-free glass fiber and basalt fiber in a certain proportion, cut them to a length of 5-8mm, soak them in a 3-5% maleic anhydride ethanol solution, react at a constant temperature of 80-85℃ for 2-2.5h, wash with water until neutral, and then dry at 105-110℃;

[0018] S2. Dry material mixing: Weigh the pretreated inorganic silicon crystal powder, modified cenospheres, nano antibacterial agent, crack-resistant agent, flame retardant synergist and intumescent flame retardant microcapsules according to the formula, add them to the double helix mixer, mix at 500-550 r / min for 18-22 min, stop the machine every 5 min and stir for 1 min to ensure uniform mixing, and obtain dry mixture;

[0019] S3. Preparation of wet material: First, add 70% of the composite binder to the dry mixture, stir at 650-700 r / min for 15-18 min, let stand for 5-8 min, then add the remaining 30% of the composite binder and deionized water. The amount of deionized water is 35-40% of the total mass of the dry mixture. Stir at 700-750 r / min for 25-30 min to form a viscous slurry with a viscosity of 15000-20000 mPa·s.

[0020] S4. Molding process: Inject the slurry into a mold preheated to 40-50℃. Coat the inner wall of the mold with a release agent. First, vibrate at a frequency of 50-60Hz for 10-15 minutes with an amplitude of 0.5-1mm. Then, use segmented pressure molding: first, pre-press at 5MPa for 25 minutes, then increase the pressure to 15-17MPa at a rate of 2MPa / min. Hold the pressure at 65-75℃ for 1.2-1.5 hours. During the holding period, the pressure fluctuation shall not exceed ±0.5MPa.

[0021] S5. Curing treatment: After demolding, the green body is first cured at room temperature for 30-36 hours at 22-25℃ and 65-75% relative humidity. Then it is transferred to a constant temperature curing chamber for step-by-step curing: from room temperature to 80℃ at a heating rate of 5℃ / h and held for 1.5h; then to 130-140℃ at a heating rate of 8℃ / h and held for 4.5-5h, with a relative humidity of 30-40% during the holding period; finally, it is cooled down to room temperature at a cooling rate of 3℃ / h to obtain inorganic silicon crystal refractory insulation material.

[0022] Preferably, in step S1, the solid content of the nano-silica sol is 20-30%, and the mass ratio of the nano-silica sol to the hollow microspheres is 1:10-1:8. The coating reaction is assisted by ultrasound with an ultrasound power of 300-400W, a frequency of 25-30kHz, and an ultrasound time of 30-40min.

[0023] Preferably, in step S1, the maleic anhydride grafting treatment of the reinforcing fiber is performed using ethanol as a solvent. The stirring rate of the maleic anhydride ethanol solution is controlled at 300-400 r / min. During the reaction, samples are taken every 30 minutes to detect the grafting rate, ensuring that the grafting rate reaches 3-5%. After grafting, the fiber needs to be dried at 105-110℃ until the moisture content does not exceed 0.5%.

[0024] Preferably, in step S4, the mold preheating is carried out by electric heating at a rate of 10°C / min. The release agent is polytetrafluoroethylene emulsion with a solid content of 30-40%. The coating thickness is 5-8 μm. After coating, it needs to be dried at 40-50°C for 10-15 min to form a uniform film. During the vibration treatment, the amplitude is gradually controlled. The initial amplitude is 0.5 mm, which is gradually increased to 1 mm and then reduced to 0.5 mm.

[0025] Preferably, during the room temperature curing period in step S5, deionized water is sprayed onto the surface of the billet once every 8 hours, with the spraying amount being 0.5-1% of the billet mass. After spraying, the billet is covered with a plastic film to retain moisture. During the 130-140℃ stage of the stepped temperature curing, an inert gas, namely nitrogen or argon, is introduced into the curing chamber at a flow rate of 0.5-1L / min. After curing, the temperature is reduced to room temperature at a rate of 3℃ / h.

[0026] (iii) Beneficial technical effects

[0027] Compared with existing technologies, the beneficial effects of this invention are:

[0028] 1. The reactivity of inorganic silicon crystal powder is significantly enhanced after low-temperature calcination activation. Combined with core-shell structure modified hollow microspheres, it can not only enhance the fire resistance of the material, but also optimize the heat insulation effect, ensuring that the fireproof air duct meets the higher fire resistance limit requirements while effectively reducing heat transfer. The composite binder introduces modified starch ether, which forms a synergistic effect with sodium silicate and aluminate cement, which can not only improve the bonding strength, but also inhibit curing shrinkage and prevent material cracking. Combined with grafted reinforcing fibers, the compatibility between the fibers and the matrix is ​​greatly improved, significantly enhancing the compressive, flexural and impact resistance of the material, reducing the risk of damage during installation and use.

[0029] 2. The introduction of nano-antibacterial agents integrates the antibacterial and antifungal functions of materials, effectively inhibiting the growth of microorganisms in humid environments and ensuring indoor air quality. This is especially suitable for scenarios with high hygiene requirements, such as hospitals and underground spaces. The combined use of intumescent flame-retardant microcapsules and flame-retardant synergists constructs a highly efficient and synergistic flame-retardant system, which not only improves the flame-retardant performance of materials but also significantly reduces smoke release at high temperatures, reduces the toxic hazards of smoke in fires, and enhances the safety of people escaping during building fires.

[0030] 3. Standardized raw material pretreatment processes ensure the stability of the properties of each component and avoid performance fluctuations caused by improper raw material processing; segmented dry material mixing and wet material preparation processes can effectively solve the problem of component agglomeration and ensure the uniformity of material mixing; vibration-assisted and segmented pressure molding can reduce the internal porosity of the material and improve density uniformity; stepped temperature curing process combined with humidity and inert gas control can effectively release the internal stress of the material, avoid cracking, improve the long-term weather resistance of the material, and ensure that the material can maintain stable performance under harsh environments such as temperature cycling. Attached Figure Description

[0031] Figure 1 This is a flowchart of a method for preparing an inorganic silicon crystal fire-resistant and heat-insulating material for fireproof air ducts, as disclosed in this invention.

[0032] Figure 2 This is a bar graph comparing the fire resistance limit and thermal conductivity of the embodiments and comparative examples;

[0033] Figure 3 This is a line graph comparing the limiting oxygen index and smoke density level of the examples and comparative examples;

[0034] Figure 4 This is a radar comparison chart created by standardizing the dimensions of the performance comparison data of the examples and comparative examples. Detailed Implementation

[0035] according to Figures 1 to 4 The specific embodiments of the present invention are as follows:

[0036] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples. All raw materials involved are qualified industrial-grade products, and all operations not specifically described are carried out in a conventional laboratory environment.

[0037] Raw material preparation

[0038] Inorganic silicon crystal powder: High-purity silica whiskers with a particle size of 1-5μm and a purity of not less than 99.5% are selected; wollastonite powder with a whiteness of not less than 93% is selected; the two are compounded in a specified mass ratio and then calcined and activated.

[0039] Hollow microspheres: fly ash cenospheres are selected, with a particle size range of 80-180μm and a bulk density of 0.4-0.6g / cm³. They are first pretreated with silane coupling agent KH-550 or KH-560, and then coated with nano silica sol. The solid content of the nano silica sol is controlled at 20-30%.

[0040] Composite binder: Sodium silicate with a modulus of 3.2-3.4 is selected; CA-50 aluminate cement with an initial setting time of not less than 45 min is selected; hydroxypropyl methylcellulose ether with a viscosity of 100,000 mPa·s is selected; the three are mixed in the specified proportion.

[0041] Reinforcing fibers: alkali-free glass fiber with a diameter of 10-15μm is selected; basalt fiber with a diameter of 8-12μm is selected; both are grafted with maleic anhydride, and the grafting rate is controlled at 3-5%.

[0042] Surface modifier: It is a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a specified ratio.

[0043] Nano antibacterial agent: Select nano zinc oxide with a particle size of 20-50nm and nano silver with a particle size of 5-15nm; the two are loaded onto a porous silica carrier in a specified ratio, and the specific surface area of ​​the porous silica carrier is not less than 300m² / g.

[0044] Crack-resistant agent: Polypropylene fiber with a length of 4-5 mm, a tensile strength of not less than 550 MPa, and an elastic modulus of not less than 3.5 GPa is selected; basalt short-cut fiber with a length of 3-4 mm and a tensile strength of not less than 800 MPa is selected; the two are compounded in a specified ratio.

[0045] Flame retardant synergist: Nano magnesium hydroxide with a particle size of 60-80nm and nano aluminum hydroxide with a particle size of 70-90nm are selected; the two are coated with stearic acid at a mass ratio of 0.5-1% and then compounded in a 1:1 mass ratio.

[0046] Expandable flame-retardant microcapsules: Ammonium polyphosphate is used as the core material, with a degree of polymerization of not less than 1000; melamine resin is used as the shell material; the core-shell ratio is controlled at 7:3-8:2, and the microcapsule particle size is 100-200nm.

[0047] Auxiliary materials: deionized water; ethanol, analytical grade; polytetrafluoroethylene emulsion, solid content 30-40%; nitrogen, purity not less than 99.9%; argon, purity not less than 99.9%. Example 1

[0048] Raw material ratio (by weight): 45 parts inorganic silicon crystal powder, 22 parts hollow microspheres, 16 parts composite binder, 10 parts reinforcing fiber, 3 parts surface modifier, 1 part nano antibacterial agent, 2 parts crack-resistant agent, 1 part flame retardant synergist, and 0.8 parts intumescent flame retardant microcapsules. Among them, the mass ratio of silica whiskers to wollastonite powder in inorganic silicon crystal powder is 4:1; the mass ratio of sodium silicate, aluminate cement, and modified starch ether in composite binder is 3:1:0.3; the mass ratio of grafted alkali-free glass fiber to basalt fiber in reinforcing fiber is 1.5:1; the mass ratio of γ-aminopropyltriethoxysilane to γ-glycidoxypropyltrimethoxysilane in surface modifier is 1:1; the mass ratio of nano zinc oxide to nano silver in nano antibacterial agent is 6:1; the mass ratio of polypropylene fiber to basalt chopped fiber in crack-resistant agent is 2:1; and the core-shell ratio of intumescent flame-retardant microcapsules is 7:3.

[0049] Preparation steps

[0050] S1. Raw material pretreatment

[0051] Activation of inorganic silicon powder: Silica whiskers and wollastonite powder were mixed evenly at a mass ratio of 4:1 and placed in a muffle furnace. The temperature was increased to 500℃ at a heating rate of 5℃ / min, and calcined at this temperature for 2.5 hours. After calcination, the mixture was allowed to cool naturally to room temperature. The cooled mixture was then ground and passed through a 200-mesh sieve to obtain activated inorganic silicon powder.

[0052] Hollow microsphere cenosphere modification: Hollow microspheres with a particle size of 80-120 μm were selected and dried in an oven at 110℃ for 3 hours. After drying, they were cooled to room temperature, and silane coupling agent KH-550 was added to the cooled cenospheres at a concentration of 1% of the cenosphere mass. The mixture was placed in a high-speed mixer and mixed at 85℃ and 900 r / min for 40 minutes. After mixing, nano-silica sol with a solid content of 20% and a mass ratio of 1:10 to the cenospheres was added. An ultrasonic device was turned on with an ultrasonic power of 300W and a frequency of 25kHz, and the mixture was stirred at 50℃ for 1.5 hours. After stirring, the mixture was filtered, and the filtered cenospheres were dried in an oven at 110℃ for 2 hours to obtain modified hollow microsphere cenospheres.

[0053] Reinforcing fiber grafting: Grafted alkali-free glass fiber and basalt fiber were mixed at a mass ratio of 1.5:1, and the mixed fibers were cut to a length of 5 mm. The cut fibers were immersed in a 3% (w / w) maleic anhydride ethanol solution with a bath ratio of 1:50. The mixture was stirred at a stirring rate of 300 r / min and reacted at a constant temperature of 80℃ for 2.5 h. During the reaction, samples were taken every 30 min to check the grafting rate, ensuring that the grafting rate reached 3%. After the reaction, the fibers were washed with deionized water until neutral, and then dried in an oven at 105℃ until the fiber moisture content did not exceed 0.5%, thus obtaining the grafted reinforcing fiber.

[0054] S2. Dry Mixing: Accurately weigh the pretreated inorganic silicon powder, modified hollow microspheres, nano-antibacterial agent, crack-resistant agent, flame retardant synergist, and intumescent flame-retardant microcapsules according to the above raw material ratio. Add all weighed materials to a twin-helix mixer and mix at 500 rpm for 22 minutes. During the mixing process, stop the machine every 5 minutes and manually stir for 1 minute to ensure that the materials are mixed evenly and without obvious agglomerates, thus obtaining a dry mix.

[0055] S3. Wet Mixture Preparation: First, add 70% of the total amount of composite binder to the obtained dry mix. Adjust the mixer speed to 650 r / min and stir for 18 min. After stirring, let it stand for 8 min, then add the remaining 30% of the composite binder and deionized water, with the amount of deionized water being 35% of the total mass of the dry mix. Adjust the mixer speed to 700 r / min and stir for 30 min. After stirring, use a rotational viscometer to test the viscosity of the material at 25°C to ensure the formation of a viscous slurry with a viscosity of 15000 mPa·s.

[0056] S4. Molding process

[0057] Mold preparation: Preheat the mold using electric heating at a rate of 10℃ / min to 40℃. Apply a 30% solids content polytetrafluoroethylene (PTFE) emulsion to the inner wall of the mold, with a coating thickness of 5μm. After coating, dry the mold at 40℃ for 15 minutes to allow the emulsion to form a uniform film on the inner wall of the mold.

[0058] Vibration and Molding: The prepared viscous slurry is injected into a preheated mold. The vibration equipment is turned on and vibrates at a frequency of 50Hz for 15 minutes. During vibration, the amplitude is gradually increased from 0.5mm to 1mm and then decreased back to 0.5mm. After vibration, segmented pressure molding is performed: first, a pre-pressure of 5MPa is applied for 25 minutes, and then the pressure is increased to 15MPa at a rate of 2MPa / min. The pressure is maintained at 65℃ for 1.5 hours, and the pressure is monitored in real time during the holding period to ensure that the pressure fluctuation does not exceed ±0.3MPa.

[0059] S5. Maintenance Treatment

[0060] Room temperature curing: After molding, the blank is demolded to obtain the green body. The green body is placed in an environment with a temperature of 22℃ and a relative humidity of 65% for room temperature curing for 36 hours. During the room temperature curing period, deionized water is sprayed on the surface of the green body every 8 hours, with the spraying amount being 0.5% of the green body mass. After spraying, the green body is covered with plastic film to retain moisture.

[0061] Step-by-step curing: After room temperature curing, the green body is transferred to a constant temperature curing chamber for step-by-step curing. First, the temperature is increased from room temperature to 80℃ at a rate of 5℃ / h, and held at 80℃ for 1.5h. Then, the temperature is increased to 130℃ at a rate of 8℃ / h, nitrogen gas is introduced into the curing chamber at a flow rate of 0.5L / min, and the relative humidity in the curing chamber is controlled at 30%. The temperature is held at 130℃ for 5h. Finally, the temperature is reduced to room temperature at a rate of 3℃ / h to obtain the finished inorganic silicon crystal refractory insulation material. Example 2

[0062] Raw material ratio (by weight): 50 parts inorganic silicon crystal powder, 25 parts hollow microspheres, 18 parts composite binder, 12 parts reinforcing fiber, 4 parts surface modifier, 2 parts nano antibacterial agent, 3 parts crack-resistant agent, 2 parts flame retardant synergist, and 1.2 parts intumescent flame retardant microcapsules. Among them, the mass ratio of silica whiskers to wollastonite powder in inorganic silicon crystal powder is 5:1; the mass ratio of sodium silicate, aluminate cement, and modified starch ether in composite binder is 3:1:0.4; the mass ratio of grafted alkali-free glass fiber to basalt fiber in reinforcing fiber is 2:1; the mass ratio of γ-aminopropyltriethoxysilane to γ-glycidoxypropyltrimethoxysilane in surface modifier is 1.5:1; the mass ratio of nano zinc oxide to nano silver in nano antibacterial agent is 7:1; the mass ratio of polypropylene fiber to basalt chopped fiber in crack-resistant agent is 2.5:1; and the core-shell ratio of intumescent flame-retardant microcapsules is 7.5:2.5.

[0063] Preparation steps

[0064] S1. Raw material pretreatment

[0065] Inorganic silicon powder activation: Silica whiskers and wollastonite powder were mixed evenly at a mass ratio of 5:1 and placed in a muffle furnace. The temperature was increased to 600℃ at a heating rate of 6℃ / min, and calcined at this temperature for 2 hours. After calcination, the mixture was allowed to cool naturally to room temperature. The cooled mixture was then ground and passed through a 200-mesh sieve to obtain activated inorganic silicon powder.

[0066] Hollow microsphere cenosphere modification: Hollow microspheres with a particle size of 120-150 μm were selected and dried in an oven at 112℃ for 2.8 h. After drying, they were cooled to room temperature, and silane coupling agent KH-550 was added to the cooled cenospheres at a concentration of 1.2% of the cenosphere mass. The mixture was placed in a high-speed mixer and mixed at 90℃ and 920 r / min for 38 min. After mixing, nano-silica sol with a solid content of 25% and a mass ratio of 1:9 to the cenospheres was added. An ultrasonic device was turned on with an ultrasonic power of 350 W and a frequency of 28 kHz, and the mixture was stirred at 55℃ for 1.8 h. After stirring, the mixture was filtered, and the filtered cenospheres were dried in an oven at 110℃ for 2 h to obtain modified hollow microsphere cenospheres.

[0067] Reinforcing fiber grafting: Grafted alkali-free glass fiber and basalt fiber were mixed at a mass ratio of 2:1, and the mixed fibers were cut to a length of 6 mm. The cut fibers were immersed in a 4% (w / w) maleic anhydride ethanol solution with a bath ratio of 1:50. The mixture was stirred at a stirring rate of 350 r / min and reacted at a constant temperature of 82℃ for 2.2 h. During the reaction, samples were taken every 30 min to check the grafting rate, ensuring that the grafting rate reached 4%. After the reaction, the fibers were washed with deionized water until neutral, and then dried in an oven at 108℃ until the fiber moisture content did not exceed 0.5%, thus obtaining the grafted reinforcing fiber.

[0068] S2. Dry Mixing: Accurately weigh the pretreated inorganic silicon powder, modified hollow microspheres, nano-antibacterial agent, crack-resistant agent, flame retardant synergist, and intumescent flame-retardant microcapsules according to the above raw material ratio. Add all weighed materials to a twin-screw mixer and mix at 520 r / min for 20 min. During the mixing process, stop the machine every 5 min and manually stir for 1 min to ensure that the materials are mixed evenly and without obvious agglomerates, thus obtaining a dry mix.

[0069] S3. Wet Mixture Preparation: First, add 70% of the total amount of composite binder to the obtained dry mix. Adjust the mixer speed to 680 r / min and stir for 16 min. After stirring, let it stand for 6 min, then add the remaining 30% of the composite binder and deionized water, with the amount of deionized water being 38% of the total mass of the dry mix. Adjust the mixer speed to 720 r / min and stir for 28 min. After stirring, use a rotational viscometer to test the viscosity of the material at 25°C to ensure the formation of a viscous slurry with a viscosity of 18000 mPa·s.

[0070] S4. Molding process

[0071] Mold preparation: Preheat the mold using electric heating at a rate of 10℃ / min to a temperature of 45℃. Apply a 35% solids content polytetrafluoroethylene (PTFE) emulsion to the inner wall of the mold, with a coating thickness of 6μm. After coating, dry the mold at 45℃ for 12 minutes to allow the emulsion to form a uniform film on the inner wall of the mold.

[0072] Vibration and Molding: The prepared viscous slurry is injected into a preheated mold. The vibration equipment is turned on and vibrates at a frequency of 55 Hz for 12 minutes. During vibration, the amplitude is gradually increased from 0.5 mm to 1 mm and then decreased back to 0.5 mm. After vibration, segmented pressure molding is performed: first, a pre-pressure of 5 MPa is applied for 25 minutes, and then the pressure is increased to 16 MPa at a rate of 2 MPa / min. The pressure is maintained at 70℃ for 1.3 hours, and the pressure is monitored in real time during the holding period to ensure that the pressure fluctuation does not exceed ±0.4 MPa.

[0073] S5. Maintenance Treatment

[0074] Room temperature curing: After molding, the blank is demolded to obtain the green body. The green body is placed in an environment with a temperature of 23℃ and a relative humidity of 70% for room temperature curing for 33 hours. During the room temperature curing period, deionized water is sprayed on the surface of the green body every 8 hours, with the spraying amount being 0.8% of the green body mass. After spraying, the green body is covered with plastic film to retain moisture.

[0075] Step-by-step curing: After room temperature curing, the green body is transferred to a constant temperature curing chamber for step-by-step curing. First, the temperature is increased from room temperature to 80℃ at a rate of 5℃ / h, and held at 80℃ for 1.5h. Then, the temperature is increased to 135℃ at a rate of 8℃ / h, nitrogen gas is introduced into the curing chamber at a flow rate of 0.8L / min, and the relative humidity in the curing chamber is controlled at 35%. The temperature is held at 135℃ for 4.8h. Finally, the temperature is reduced to room temperature at a rate of 3℃ / h to obtain the finished inorganic silicon crystal refractory insulation material. Example 3

[0076] Raw material ratio (by weight): 55 parts inorganic silicon crystal powder, 28 parts hollow microspheres, 20 parts composite binder, 14 parts reinforcing fiber, 5 parts surface modifier, 3 parts nano antibacterial agent, 4 parts crack-resistant agent, 3 parts flame retardant synergist, and 1.8 parts intumescent flame retardant microcapsules. Among them, the mass ratio of silica whiskers to wollastonite powder in inorganic silicon crystal powder is 6:1; the mass ratio of sodium silicate, aluminate cement, and modified starch ether in composite binder is 3:1:0.5; the mass ratio of grafted alkali-free glass fiber to basalt fiber in reinforcing fiber is 2.5:1; the mass ratio of γ-aminopropyltriethoxysilane to γ-glycidoxypropyltrimethoxysilane in surface modifier is 2:1; the mass ratio of nano zinc oxide to nano silver in nano antibacterial agent is 9:1; the mass ratio of polypropylene fiber to chopped basalt fiber in crack-resistant agent is 3:1; and the core-shell ratio of intumescent flame-retardant microcapsules is 8:2.

[0077] Preparation steps

[0078] S1. Raw material pretreatment

[0079] Activation of inorganic silicon powder: Silica whiskers and wollastonite powder were mixed evenly at a mass ratio of 6:1 and placed in a muffle furnace. The temperature was increased to 600℃ at a heating rate of 7℃ / min, and calcined at this temperature for 1.5 hours. After calcination, the mixture was allowed to cool naturally to room temperature. The cooled mixture was then ground and passed through a 200-mesh sieve to obtain activated inorganic silicon powder.

[0080] Hollow microsphere cenosphere modification: Hollow microspheres with a particle size of 150-180 μm were selected and dried in an oven at 115℃ for 2.5 h. After drying, they were cooled to room temperature, and silane coupling agent KH-560 was added to the cooled cenospheres at a concentration of 1.5% of the cenosphere mass. The mixture was placed in a high-speed mixer and mixed at 95℃ and 950 r / min for 35 min. After mixing, nano-silica sol with a solid content of 30% and a mass ratio of 1:8 to the cenospheres was added. An ultrasonic device was turned on with an ultrasonic power of 400 W and a frequency of 30 kHz, and the mixture was stirred at 60℃ for 2 h. After stirring, the mixture was filtered, and the filtered cenospheres were dried in an oven at 110℃ for 2 h to obtain modified hollow microsphere cenospheres.

[0081] Reinforcing fiber grafting: Grafted alkali-free glass fiber and basalt fiber were mixed at a mass ratio of 2.5:1, and the mixed fibers were cut to a length of 8 mm. The cut fibers were immersed in a 5% maleic anhydride ethanol solution (liquid ratio 1:50). The mixture was stirred at 400 rpm and reacted at a constant temperature of 85°C for 2 hours. Grafting rate was measured every 30 minutes during the reaction to ensure it reached 5%. After the reaction, the fibers were washed with deionized water until neutral and then dried in an oven at 110°C until the fiber moisture content did not exceed 0.5%, yielding the grafted reinforcing fiber.

[0082] S2. Dry Mixing: Accurately weigh the pretreated inorganic silicon powder, modified hollow microspheres, nano-antibacterial agent, crack-resistant agent, flame retardant synergist, and intumescent flame-retardant microcapsules according to the above raw material ratio. Add all weighed materials to a twin-screw mixer and mix at 550 r / min for 18 min. During the mixing process, stop the machine every 5 min and manually stir for 1 min to ensure that the materials are mixed evenly and without obvious agglomerates, thus obtaining a dry mix.

[0083] S3. Wet Mixture Preparation: First, add 70% of the total amount of composite binder to the obtained dry mix. Adjust the mixer speed to 700 r / min and stir for 15 min. After stirring, let it stand for 5 min, then add the remaining 30% of the composite binder and deionized water, with the amount of deionized water being 40% of the total mass of the dry mix. Adjust the mixer speed to 750 r / min and stir for 25 min. After stirring, use a rotational viscometer to test the viscosity of the material at 25°C to ensure the formation of a viscous slurry with a viscosity of 20000 mPa·s.

[0084] S4. Molding process

[0085] Mold preparation: Preheat the mold using electric heating at a rate of 10℃ / min to 50℃. Apply a 40% solids content polytetrafluoroethylene (PTFE) emulsion to the inner wall of the mold, with a coating thickness of 8μm. After coating, dry the mold at 50℃ for 10 minutes to allow the emulsion to form a uniform film on the inner wall of the mold.

[0086] Vibration and Molding: The prepared viscous slurry is injected into a preheated mold. The vibration equipment is turned on and vibrates at a frequency of 60Hz for 10 minutes. During vibration, the amplitude is gradually increased from 0.5mm to 1mm and then decreased back to 0.5mm. After vibration, segmented pressure molding is performed: first, a pre-pressure of 5MPa is applied for 25 minutes, and then the pressure is increased to 17MPa at a rate of 2MPa / min. The pressure is maintained at 75℃ for 1.2 hours, and the pressure is monitored in real time during the holding period to ensure that the pressure fluctuation does not exceed ±0.5MPa.

[0087] S5. Maintenance Treatment

[0088] Room temperature curing: After molding, the blank is demolded to obtain the green body. The green body is placed in an environment with a temperature of 25℃ and a relative humidity of 75% for room temperature curing for 30 hours. During the room temperature curing period, deionized water is sprayed on the surface of the green body every 8 hours, with the spraying amount being 1% of the green body mass. After spraying, the green body is covered with plastic film to retain moisture.

[0089] Step-by-step curing: After room temperature curing, the green body is transferred to a constant temperature curing chamber for step-by-step curing. First, the temperature is increased from room temperature to 80℃ at a rate of 5℃ / h, and held at 80℃ for 1.5h. Then, the temperature is increased to 140℃ at a rate of 8℃ / h, and argon gas is introduced into the curing chamber at a flow rate of 1L / min, while the relative humidity in the curing chamber is controlled at 40%, and the temperature is held at 140℃ for 4.5h. Finally, the temperature is reduced to room temperature at a rate of 3℃ / h to obtain the finished inorganic silicon crystal refractory insulation material.

[0090] Comparative Example

[0091] Raw material ratio (by weight): 50 parts ordinary wollastonite powder, 25 parts unmodified fly ash cenospheres, 18 parts sodium silicate binder, 12 parts untreated alkali-free glass fiber, 1 part stearic acid, and 2 parts nano-aluminum hydroxide. The ordinary wollastonite powder was not subjected to calcination activation treatment; the fly ash cenospheres were not pretreated with silane coupling agents or coated with nano-silica sol; the binder was sodium silicate alone; there were no nano-antibacterial agents, crack-resistant agents, flame-retardant synergists, or intumescent flame-retardant microcapsules; the alkali-free glass fiber was not grafted with maleic anhydride and was only cut to a length of 6 mm.

[0092] Preparation steps

[0093] S1. Raw material processing: Grind ordinary wollastonite powder and pass it through a 200-mesh sieve; select fly ash cenospheres with a particle size of 120-150μm, dry them in an oven at 110℃ for 3 hours, and use them directly after drying; cut untreated alkali-free glass fibers to a length of 6mm and use them directly after cutting; other raw materials do not require additional pretreatment.

[0094] S2. Mixing: Accurately weigh the following raw materials according to the above proportions: ordinary wollastonite powder, unmodified fly ash cenospheres, sodium silicate binder, untreated alkali-free glass fiber, stearic acid, and nano-aluminum hydroxide. Add all materials to a single-shaft mixer and mix at 400 rpm for 20 minutes. During mixing, add deionized water directly, with the amount of deionized water being 40% of the total dry material mass. Continue mixing at 600 rpm for 20 minutes to form a viscous slurry.

[0095] S3. Molding: The prepared viscous slurry is injected into a room temperature mold. The inner wall of the mold is not coated with a release agent and is not subjected to vibration treatment. Molding is performed directly at a pressure of 15 MPa and held at 70°C for 1 hour. Pressure fluctuations are not controlled during the holding period.

[0096] S4. Curing: After molding, the blank is demolded to obtain the green body. The green body is placed in an environment with a temperature of 23℃ and a relative humidity of 70% for room temperature curing for 72 hours. During the curing process, no water spraying or stepped temperature increase curing is performed; it is directly cured naturally to room temperature to obtain the comparison sample.

[0097] The basic performance and fire resistance / insulation of the examples and comparative examples are compared in the table below:

[0098] Table 1

[0099] Testing items Example 1 Example 2 Example 3 Comparative Example Testing standards Fire resistance rating (h) 1.5 2.5 2.0 0.3 GB / T 9978.1-2008 Thermal conductivity (25℃) (W / (m·K)) 0.035 0.030 0.032 0.060 GB / T 10294-2008 Bulk density (kg / m³) 680 650 700 820 GB / T 5486-2008 Compressive strength (MPa) 8.5 10.2 9.3 4.1 GB / T 5486-2008 Flexural strength (MPa) 2.8 3.5 3.1 1.2 GB / T 5486-2008 Linear shrinkage rate (at 1000℃) (%) 0.8 0.5 0.6 2.3 GB / T 7320-2018

[0100] The antibacterial properties and flame retardant toxicity index of the examples and comparative examples are compared in the table below:

[0101] Table 2

[0102] Testing items Example 1 Example 2 Example 3 Comparative Example Testing standards Antibacterial rate of Escherichia coli (%) 95.2 99.1 97.5 10.3 GB / T 21866-2008 Antibacterial rate against Staphylococcus aureus (%) 94.8 98.7 96.9 9.8 GB / T 21866-2008 Limiting Oxygen Index (LOI) (%) 32.5 35.2 33.8 25.1 GB / T 2406.2-2009 Smoke Density Rating (SDR) 38 30 35 75 GB / T 8627-2017 Peak release rate (HRRpeak) (kW / m²) 65 52 58 138 GB / T 16172-2007 Carbon monoxide release (peak) (mg / m³) 180 120 150 580 GB / T 16172-2007

[0103] Compared with the comparative example, this invention solves the problems of traditional inorganic silicon crystal materials such as imbalance of fire resistance and heat insulation, insufficient mechanical strength, single function and poor process stability by precisely optimizing the components, integrating functional innovation and standardizing the preparation process, and achieves comprehensive performance of high fire resistance, low thermal conductivity, strong mechanical strength, multifunctionality and long-term stability.

[0104] The fire resistance limit of the embodiment reaches 1.5-2.5h, far exceeding the 0.3h of the comparative example; the thermal conductivity is only 0.030-0.035 W / (m·K), which is 42%-50% lower than that of the comparative example; the compressive strength is 8.5-10.2MPa and the flexural strength is 2.8-3.5MPa, which are 2-2.5 times that of the comparative example; the linear shrinkage rate is only 0.5%-0.8%, which is far lower than the 2.3% of the comparative example. This is due to the activation of inorganic silicon powder by calcination at 500-600℃ to enhance its reactivity, combined with silane coupling agent pretreatment and core-shell structured cenospheres coated with nano-silica, which enhances the interfacial bonding.

[0105] The antibacterial rate of Escherichia coli and Staphylococcus aureus in the embodiment reached 94.8%-99.1%, while that in the comparative example was only 9.8%-10.3%, effectively solving the problem of microbial growth in humid environments; the limiting oxygen index was 32.5%-35.2%, the smoke density level was 30-38, and the peak carbon monoxide release was 120-180 mg / m³, which was far superior to the comparative example, achieving a balance between high flame retardancy and low smoke toxicity.

[0106] The embodiment exhibits uniform volumetric density and low linear shrinkage, making it less prone to cracking during long-term use. In contrast, the comparative embodiment, lacking raw material pretreatment, segmented mixing, and stepped curing, results in higher density, higher shrinkage, and greater susceptibility to breakage. This improvement is attributed to standardized raw material pretreatment, segmented dry material mixing and wet material preparation, vibration-assisted + segmented pressure molding, and stepped temperature curing, ensuring uniform material composition and a dense structure.

[0107] The comparative sample uses unactivated ordinary wollastonite powder, unmodified cenospheres and fibers, lacking key components such as composite binders and crack-resistant agents. Functionally, it can only meet basic heat insulation requirements, without antibacterial, low-smoke and flame-retardant functions. In terms of process, it adopts single-shaft stirring, room temperature molding and natural curing without vibration assistance and step heating, resulting in insufficient raw material reaction, component agglomeration and many internal pores. Ultimately, it exhibits extremely low fire resistance limit, weak mechanical strength and large shrinkage rate, which completely fails to meet the core requirements of the "Technical Standard for Building Smoke Control and Exhaust Systems" for fireproof air ducts.

[0108] In summary, the performance data from the embodiments fully demonstrate the three major beneficial effects of this invention: component optimization achieves synergistic improvement in fire resistance, thermal insulation, and mechanical properties; functional integration meets diverse needs for antibacterial properties and low smoke toxicity; and standardized processes ensure product stability and weather resistance. Ultimately, this results in a comprehensive advantage of "high fire resistance limit, low thermal conductivity, high mechanical strength, full functional coverage, and replicable process," providing a high-performance material solution for high-end building fireproof ducts that combines safety, reliability, and scenario adaptability.

[0109] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An inorganic crystalline silica refractory insulating material for fireproof ducts, characterized in that, By weight, it consists of the following components: 40-60 parts inorganic silicon crystal powder, 20-30 parts hollow microspheres, 15-22 parts composite binder, 8-15 parts reinforcing fiber, 3-6 parts surface modifier, 1-3 parts nano antibacterial agent, 2-4 parts crack-resistant agent, 1-3 parts flame retardant synergist and 0.5-2 parts intumescent flame retardant microcapsules; The inorganic silicon powder is a mixture of high-purity silica whiskers (1-5 μm particle size) and wollastonite powder in a mass ratio of 4:1-6:1, activated by calcination at 500-600℃; the hollow microspheres are fly ash celery beads (80-180 μm particle size), pretreated with a silane coupling agent, and then coated with nano-silica sol to form a core-shell structure, wherein the silane coupling agent is KH-550 or KH-560; the composite binder is a mixture of sodium silicate, aluminate cement, and hydroxypropyl methylcellulose ether in a mass ratio of 3:1:0.3-3:1:0.

5. The aluminate cement is CA-50 type; the reinforcing fiber is a compound of alkali-free glass fiber grafted with maleic anhydride and basalt fiber in a mass ratio of 1.5:1-2.5:1; the nano antibacterial agent is a compound of nano zinc oxide and nano silver in a mass ratio of 6:1-9:1, with nano zinc oxide particles of 20-50nm and nano silver particles of 5-15nm, and loaded on the surface of a porous silica carrier; the expandable flame-retardant microcapsules use ammonium polyphosphate as the core material and melamine resin as the shell material, with a core-shell ratio of 7:3-8:2 and a particle size of 100-200nm.

2. The inorganic silicate-based refractory thermal insulation material for fireproof air ducts according to claim 1, characterized in that, The surface modifier is a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1 to 2:1, and the modification treatment is carried out in a high-speed mixer.

3. The inorganic silicon crystal fire-resistant and heat-insulating material for fireproof air ducts according to claim 1, characterized in that, The crack-resistant agent is a compound of polypropylene fiber and basalt short-cut fiber in a mass ratio of 2:1-3:

1. The polypropylene fiber has a length of 4-5 mm, a tensile strength of not less than 550 MPa, and an elastic modulus of not less than 3.5 GPa. The basalt short-cut fiber has a length of 3-4 mm and a tensile strength of not less than 800 MPa.

4. The inorganic silicon crystal fire-resistant and heat-insulating material for fireproof air ducts according to claim 1, characterized in that, The flame retardant synergist is a mixture of nano magnesium hydroxide and nano aluminum hydroxide in a mass ratio of 1:

1. The nano magnesium hydroxide has a particle size of 60-80 nm, the nano aluminum hydroxide has a particle size of 70-90 nm, and the surface is coated with 0.5-1% stearic acid by mass.

5. The inorganic silicon crystal fire-resistant and heat-insulating material for fireproof air ducts according to claim 1, characterized in that, By weight, it consists of the following components: 50 parts inorganic silicon crystal powder, 25 parts hollow microspheres, 18 parts composite binder, 12 parts reinforcing fiber, 4 parts surface modifier, 2 parts nano antibacterial agent, 3 parts crack-resistant agent, 2 parts flame retardant synergist and 1.2 parts intumescent flame retardant microcapsules. The inorganic silicon powder consists of silica whiskers and wollastonite powder in a 5:1 mass ratio, calcined at 600℃ for 2 hours. Hollow microspheres with a particle size of 120-150 μm are pretreated with KH-550 and then coated with nano-silica sol to form a core-shell structure. The composite binder contains sodium silicate, aluminate cement, and hydroxypropyl methylcellulose ether in a 3:1:0.4 mass ratio. The reinforcing fibers consist of alkali-free glass fiber grafted with maleic anhydride in a 2:1 mass ratio to basalt fiber. Surface modification is also included. The mass ratio of γ-aminopropyltriethoxysilane to γ-glycidoxypropyltrimethoxysilane in the agent is 1.5:1; the mass ratio of nano zinc oxide to nano silver in the nano antibacterial agent is 7:1 and it is loaded on a porous silica carrier; the mass ratio of polypropylene fiber to basalt chopped fiber in the crack-resistant agent is 2.5:1; the flame retardant synergist is a compound of nano magnesium hydroxide and nano aluminum hydroxide coated with stearic acid; and the mass ratio of ammonium polyphosphate to melamine resin in the intumescent flame retardant microcapsules is 7.5:2.5.

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