Diatomite silicon nanodot composite material and preparation method and application thereof

Abstract

The invention discloses a diatomite-Si nanodot composite material which comprises the following components in parts by weight: 45-60 parts of a modified diatomite-Si nanodot material; 20 to 30 parts of bentonite; 10 to 15 parts of sand; 12 to 18 parts of a binder; 6-10 parts of a combustion improver; 6-10 parts of a fuming synergist; and 2-5 parts of an anti-moisture-absorption agent. The invention further discloses a preparation method of the diatomite-Si nanodot composite material and application of the diatomite-Si nanodot composite material to a smoke screen material.

Description

Technical Field

[0001] The present invention belongs to the field of material technology, and in particular relates to a diatomaceous earth silicon nanodot composite material, a preparation method thereof, and use thereof in smoke screens. Background Art

[0002] Smoke screens are an important means of camouflage in modern warfare. They interfere with enemy optical and electronic observations and shooting operations by artificially generating smoke barriers. They are widely used in tactical scenarios such as position concealment, target confusion, and breakthrough of defenses. The development of traditional smoke screen materials can be divided into three stages: 1. Early materials (from World War I to before World War II). They are mainly phosphorus-based (such as white phosphorus) and oil (such as diesel and kerosene). Phosphorus-based smoke screens produce phosphorus pentoxide smoke through combustion. Although it can effectively block visible light, phosphorus pentoxide is highly toxic (inhalation can cause pulmonary edema), and the combustion products easily absorb moisture to form acid mist, which corrodes equipment; oil smoke screens form oil mist through evaporation-condensation. When the smoke concentration is high but the combustion is incomplete, carbon black particles (PM2.5) are produced, which pollute the environment and have low smoke generation efficiency (the smoke generation per unit mass is about 300-500m 3 / kg). 2. Mid-term materials (WWII to the end of the 20th century). Metal powders (such as zinc powder, aluminum powder) and high molecular polymers (such as fuming ammonium nitrate) became the mainstream. Metal powder smoke screens require high temperature reactions (>600℃), consume a lot of energy (the amount of smoke per unit mass is about 200-400m 3 / kg), and metal particles easily absorb moisture and agglomerate (they cannot ignite if the moisture content is >5%). Polymer smoke screens (such as fuming ammonium nitrate) decompose to produce nitrogen oxides and water vapor. The smoke is light in color but short-lived (<10 minutes), and the decomposition products (such as nitric acid) are easily corrosive to equipment. 3. Recent Developments (21st century to present). With the prevalence of electro-optical guided weapons (such as laser-guided missiles) and drone reconnaissance, the demand for multifunctional smoke screens (visible light shielding, infrared jamming, radar stealth) is becoming increasingly urgent. Traditional materials are gradually being replaced by newer materials due to their limited functionality (only visible light shielding) and significant environmental hazards. Traditional smoke screen materials mainly include phosphorus-based (such as white phosphorus), oil (such as diesel), metal powder (such as zinc powder) and high molecular polymer (such as fuming ammonium nitrate), but they have the following significant defects: (1) Environmental and health hazards: the combustion of phosphorus-based smoke agents produces toxic phosphorus pentoxide, and oil smoke contains particulate pollutants, which can easily cause battlefield pollution and personnel injuries; (2) Low smoke generation efficiency: Traditional materials require high-temperature combustion or chemical reactions to release smoke, which consumes a lot of energy and has a limited amount of smoke per unit mass; (3) Poor storage stability: Some smoke agents (such as metal powder) are prone to moisture absorption and agglomeration, and oil-based smoke screens are prone to oxidation and deterioration, affecting long-term storage; (4) Single function: Most materials can only achieve a single shielding function, and it is difficult to take into account multiple task requirements such as blinding (reducing enemy shooting accuracy) and interference (failure of optoelectronic equipment).

[0003] Diatomite is a natural siliceous sedimentary rock, which is non-toxic, low-cost (my country's reserves exceed 300 million tons), easy to process and shape. Its main component is amorphous silicon dioxide (content 80% to 90%), with a porous structure (specific surface area 15 to 65m 2 / g) can absorb water to form aerosols, can absorb air at high temperatures and release quickly to form high-concentration aerosol particles; low density (0.3-0.5g / cm 3 ), high temperature resistance (melting point 1650-1750℃) and chemical inertness make it a potential new type of smoke screen material. However, in the existing technology, diatomaceous earth is only used as an auxiliary filler (such as adding 5%-10% to oil smoke screens). There is no technical solution to develop composite smoke screen materials using diatomaceous earth as the main component. The advantages of its porous structure are not fully utilized, and there is a lack of modification treatment for diatomaceous earth (such as surface hydroxylation) to improve hydrophilicity and reactivity. As a result, its application as the main smoke component alone is still blank; especially in improving smoke efficiency, optimizing smoke stability, and expanding multifunctional applications.

[0004] In recent years, the application of nanomaterials in the field of smoke screens has become a research hotspot. Si nanodots (size 2-10nm) have quantum confinement effects (fluorescence tunability), high specific surface area (≥300m 2 / g) and good biocompatibility, and has been proven to significantly enhance the light scattering and infrared interference properties of smoke. Related reports show that after diatomaceous earth is loaded with Si nanodots, its attenuation efficiency in the 8-14μm infrared band can be increased by more than 50%; the fluorescence characteristics of Si nanodots can effectively interfere with the target identification of laser-guided weapons. However, in existing technologies, Si nanodots are mostly synthesized independently through chemical vapor deposition (CVD) or hydrothermal methods, and then simply mixed with diatomaceous earth (weak binding force and easy agglomeration), and their surface activity is not optimized for the smoke generation requirements of the smoke screen (for example, insufficient hydrophilicity leads to low combustion efficiency).

[0005] Traditional smoke screen materials and existing diatomaceous earth applications also have the following drawbacks: A. Environmental and health hazards. Phosphorus-based smoke screens release toxic phosphorus pentoxide, oil smoke screens produce carbonaceous particulate pollutants, and metal powder smoke screens are easily oxidized to produce metal oxide dust, all of which will cause long-term pollution to soil and water sources and threaten the respiratory health of combatants. B. Low smoke generation efficiency. Traditional materials (oil, metal powder) have low smoke generation per unit mass (oil is about 300-500m 3 / kg, metal powder about 200-400m 3 / kg), a large amount of explosives is required to form an effective shield, which increases the logistical burden. C. Single function. Most existing smoke screens are "shielding type" and can only attenuate visible light (extinction coefficient <0.1m -1), it is difficult to interfere with infrared (8-14μm band attenuation <5dB), laser (1.06μm band attenuation <3dB) and other bands at the same time, and it is unable to cope with multi-modal reconnaissance. D. Poor storage stability. Oil is easy to oxidize and deteriorate (storage period <6 months), metal powder is easy to absorb moisture and agglomerate (cannot be ignited when the moisture content is >5%), and high molecular polymers are easily decomposed by ultraviolet rays (outdoor storage period <1 year). E. Poor controllability of release. Traditional smoke screens rely on combustion or chemical reactions, and are greatly affected by ambient temperature and wind speed (such as smoke dissipates quickly when the wind speed is >5m / s, and the reaction rate is reduced by 50% when the temperature is <-10℃), and it is difficult to accurately control the smoke concentration and duration. F. Single optical interference function. It only relies on the scattering effect of the porous structure of diatomaceous earth, and its efficient scattering ability for visible light (400-700nm) is insufficient (extinction coefficient <0.1m -1 ) and are unable to cope with modern optoelectronic reconnaissance (such as visible light cameras on drones); G. Poor dispersion of nanodots: Si nanodots have high surface energy and are prone to agglomeration to form large particles (>50nm), resulting in uneven distribution of nanodots in the smoke and large fluctuations in the interference effect in local areas. H. Low combustion efficiency. The surface of Si nanodots is highly inert (hydroxyl content <1%) and has weak bonding with diatomaceous earth. They are easily detached and lost during the combustion process, reducing the amount of smoke produced per unit mass (loss rate >20%). I. Weak functional synergy: The fluorescent properties of Si nanodots do not form synergy with the smoke-generating function of traditional diatomaceous earth, making it difficult to achieve the multi-task integration of "masking-interference-blinding".

[0006] To this end, the present invention is proposed. Summary of the Invention

[0007] The invention discloses a diatomite-Si nano-dot composite material and a preparation method thereof. The diatomite-Si nano-dot composite material of the invention is used for smoke screen materials to solve the defects of existing smoke screen materials.

[0008] The technical solutions of the present invention are as follows:

[0009] The first aspect of the present invention discloses a diatomite-Si nanodot composite material comprising the following components by weight: 45-60 parts modified diatomite-Si nanodot material; 20-30 parts bentonite; 10-15 parts sand; 12-18 parts binder; 6-10 parts combustion improver; 6-10 parts smoke enhancer; and 2-5 parts anti-hygroscopic agent. The modified diatomite-Si nanodot material can enhance light scattering and fluorescence interference.

[0010] The modified diatomite-Si nanodot material is a silane coupling agent-modified diatomite loaded with Si nanodot material, wherein the Si nanodot material accounts for 2-8wt% of the total amount of the modified diatomite-Si nanodot material; the particle size of the Si nanodot material is 2-8nm, and the agglomerate accounts for no more than 10%.

[0011] Preferably, the binder is one or more of hydroxypropyl methylcellulose (HPMC), sodium alginate, or polyvinyl alcohol; the combustion aid is one or both of potassium nitrate and ammonium perchlorate; the smoke enhancer is one or both of magnesium hydroxide and urea; and the anti-hygroscopic agent is one or both of calcium carbonate and silica powder. The binder improves particle formability and stabilizes the Si nanodots; the combustion aid lowers the ignition temperature to ≤300°C, promoting the synergistic combustion of diatomaceous earth and Si nanodots; the smoke enhancer decomposes at high temperatures to produce water vapor, promoting the dispersion of Si nanodots and inhibiting agglomeration; and the anti-hygroscopic agent reduces the material's hygroscopicity, preventing hydrolysis of the Si nanodots (Si + 2H2O → SiO2 + 2H2↑).

[0012] Preferably, the diatomaceous earth-Si nanodot composite material structure includes: a core layer, an intermediate bonding layer and an outer protective layer; the core layer is diatomaceous earth / Si nanodot material; the intermediate bonding layer is a combination of bentonite, sand and binder; the outer protective layer is a combination of anti-moisture absorbent, smoke enhancer and binder.

[0013] The second aspect of the present invention discloses a method for preparing the diatomite-Si nanodot composite material, comprising the following steps:

[0014] (1) Preparation of modified diatomite-Si nanodot materials;

[0015] (2) mixing the modified diatomite-Si nanodot material, bentonite, sand, a binder, and a combustion aid in proportion and at high speed to obtain a mixture;

[0016] (3) extruding and granulating the mixture to obtain cylindrical particles;

[0017] (4) rolling the cylindrical particles and spraying them with an anti-wetting agent and a smoke enhancer, and then drying them to obtain the diatomaceous earth-Si nanodot composite material.

[0018] Preferably, the method for preparing the modified diatomite-Si nanodot material comprises the following steps:

[0019] (11) Diatomite pretreatment: calcining the diatomite at high temperature for a period of time, then adding a silane coupling agent and ultrasonically treating it to obtain modified diatomite;

[0020] (12) In situ growth of Si nanodots on the surface of diatomite: the modified diatomite was dispersed in deionized water, sodium borohydride, anhydrous ethanol and ammonia were added, and ultrasonic dispersion was performed for a period of time; then hydrothermal reaction was performed for a period of time;

[0021] (13) After cooling to room temperature, the solid was separated and washed alternately with deionized water and ethanol for multiple times, and then vacuum dried to obtain the modified diatomite-Si nanodot material.

[0022] Preferably, in step (11), the diatomaceous earth is calcined at 600-800° C. for 2-3 hours; the silane coupling agent is KH-550; and the ultrasonic treatment is performed so that the contact angle of the diatomaceous earth is ≤30°.

[0023] Preferably, in step (12), the amount of modified diatomaceous earth added is 5-15 g / L, the amount of sodium borohydride is 0.4-0.6 mol / L, the amount of anhydrous ethanol is 10-30 mL / L, and the amount of ammonia added is such that the pH value of the solution is maintained at 9.5-10.5; and the hydrothermal reaction conditions are: reaction at 150-200° C. for 2-10 hours, and a heating rate of about 5° C. / min.

[0024] Preferably, step (2) is mixed at a rotation speed of 800-1000 rpm for 15-20 minutes to ensure that the Si nanodots are evenly dispersed on the surface of the diatomaceous earth without agglomeration; step (3) is extruded and granulated in a twin-screw extruder, with the temperature of the screw inlet zone set to 40°C, the temperature of the screw bonding layer zone set to 80-100°C, the temperature of the screw outlet zone set to 60°C, and the screw speed set to 20-30 rpm; cylindrical particles with a diameter of 3-5 mm and a length of 5-8 mm are extruded; step (4) is rolled on the cylindrical particles using a pressure of 6-10 MPa; the surface is rolled and densified, and then the particles are placed in a 60-80°C oven to dry for 4-6 hours to fully cross-link and solidify the binder, with a moisture content of ≤3%.

[0025] A third aspect of the present invention discloses the use of the diatomite-Si nanodot composite material as a smoke screen material. Preferably, the smoke screen material is used in a mobile smoke bomb or a fixed smoke generator; the mobile smoke bomb has a gradually diverging nozzle design; the fixed smoke generator is controlled by a temperature sensor and a fan.

[0026] The mobile smoke grenade features an optimized diffusion nozzle. Its structure includes a high-strength plastic shell, a charge chamber filled with 200-300g of composite smoke particles, an ignition fuse (impact explosion with a 3-second delay), and a porous ceramic diffusion nozzle with a pore size of 1-2mm. The surface is coated with a hydrophobic coating to prevent nanodot aggregation. Due to the fluorescent properties of Si nanodots, the nozzle is designed with a gradually expanding structure, such as from 5mm to 10mm in diameter. This reduces the initial smoke velocity to no more than 30m / s and prolongs the fluorescence scattering time.

[0027] The fixed smoke generator is a newly added temperature control module. Its structure includes a 5mm-thick stainless steel shell, a 10L particle charge chamber, a remote ignition controller with a temperature sensor for real-time combustion temperature monitoring, and an air vent with a diameter of approximately 5mm. A built-in micro-fan with a power of approximately 5W accelerates air flow during the initial combustion phase (e.g., the first 5 minutes), promoting contact between the Si nanodots and oxygen, and preventing incomplete combustion that could result in residual nanodots.

[0028] Application method. Meteorological condition selection: In order to balance the diffusion of smoke and the precipitation of nanodots to inhibit the hydrolysis of Si nanodots, it is preferred to select a wind speed of 3-5m / s, a temperature of 20-25℃, and a relative humidity of 60-70% (at this time, the hygroscopic expansion of diatomaceous earth can be enhanced to fix the nanodots). Release height control: The mobile smoke bomb launch elevation angle is 40-45°, which can cover the field of view of the enemy's optical camera; the fixed smoke generator is deployed at a height of 1.5-2 meters from the ground to avoid ground turbulence that destroys the dispersion of nanodots. Concentration adjustment: Adjust the ignition power to 50-150W and control the combustion rate to 5-15g / min, which can make the smoke mass concentration reach 0.5~1.56g / m 3 (corresponding to extinction coefficient 0.15~0.35m -1 ), achieving the coordinated interference coverage of visible light and infrared. Visible light shielding threshold: when the extinction coefficient is ≥0.15m -1 Targets 5 meters away cannot be identified. Infrared interference threshold: Attenuation ≥15dB in the 8-14μm band causes the thermal imager to be unable to identify the target. Fluorescence interference threshold: Fluorescence intensity ≥800a.u. in the 400-500nm band causes the laser detector to mistakenly identify it as background noise.

[0029] Beneficial effects of the present invention:

[0030] 1. The preparation principle of the Si nanodot material of the present invention is: sodium borohydride (NaBH4) is used as a strong reducing agent under alkaline conditions (ammonia water adjusts the pH value to about 10) to reduce SiO2 (Si 4+ ) is reduced to elemental silicon (Si 0 ) and hydrolyze to form Si nanodots; the reaction formula is: SiO2 + 2NaBH4 + 6H2O → Si + 2B(OH)3 + 4H2↑ + Na2B4O7; wherein ammonia provides OH- to promote hydrolysis, and ethanol acts as a dispersant to inhibit nanodot agglomeration. Diatomaceous earth is calcined at 600-800°C for 2-3 hours to remove organic matter while retaining the skeleton (porosity > 45%, shrinkage < 5%). KH-550 is then modified and amino groups are grafted to form a -Si-O-Si- fleece layer on the pore walls (loading rate reaches 95%). This is the first time that the diatomaceous earth carrier has been stably anchored to nanoscale Si quantum dots. The Si nanodot preparation method of the present invention can be replaced by a microwave-assisted reduction method, shortening the reaction time to 30 minutes. However, the sodium borohydride concentration must be adjusted to 0.3 mol / L, and the Si nanodot loading can be optimized to 3-5%, which can reduce material costs. However, the proportion of smoke enhancer must be increased to 10-12% to compensate for the loss in scattering efficiency. The binder is preferably HPMC or sodium alginate. If polyvinyl alcohol (PVA) is selected, the drying temperature should be adjusted not to exceed 80°C to avoid decomposition of PVA.

[0031] 2. The performance of the diatomite-Si nanodot composite material of the present invention is as follows: Smoke generation efficiency: 10g sample is ignited at 300℃, and the smoke volume generated in 3 minutes is ≥9L (under standard conditions), and the extinction coefficient is ≥0.15m -1 Dispersion of Si nanodots: Transmission electron microscopy (TEM) observations revealed a nanodot particle size ≤10nm and agglomerate proportion ≤10%. Fluorescence properties: Fluorescence spectrophotometer test (excitation wavelength 365nm) revealed a fluorescence intensity ≥1000a in the 400-500nm band, enhancing visible light interference. Storage stability: After two years of storage in a constant temperature and humidity chamber (25°C, 70% humidity), the Si nanodot loading decayed ≤5% (X-ray photoelectron spectroscopy XPS).

[0032] 3. The diatomite-Si nanodot composite material of the present invention has the following advantages when used as a smoke screen material: (1) Environmentally friendly: The combustion products are SiO2 particles (non-toxic and can settle naturally) and water vapor, and no toxic substances such as phosphorus and sulfur are emitted. (2) High smoke generation efficiency: The smoke generation per unit mass reaches 850-950m 3 / kg(traditional oil smoke screen 500m 3 / kg, increased by 70%-90%). (3) Multifunctional integration. Visible light shielding type (Mg(OH)2 content 10-15%): extinction coefficient ≥ 0.1m -1 , shielding distance ≥15 meters. Infrared interference type (urea content 15-20%): 8-14μm band attenuation ≥12dB. Blinding type (KNO3 content 8-10%): smoke particles with a diameter of 1-5μm account for ≥80%, and the dispersion error is expanded by 30%. (4) Storage stability: No agglomeration after 2 years of storage at room temperature (bulk density change ≤5%), and smoke efficiency attenuation ≤10%. (5) Controllable release: By adjusting the ignition power and environmental parameters, the smoke concentration (0.1-0.5m -1 ), diffusion range (diameter 15 meters - 800 square meters), and duration (15 seconds - 30 minutes). (6) Multi-dimensional optical interference: Achieve five-dimensional coordinated shielding of ultraviolet-visible light-near infrared-mid-far infrared-laser. (7) Improved visible light shielding efficiency: Diatomaceous earth porous structure scattering + Si nano-dot fluorescence scattering, extinction coefficient from 0.1m -1 Increase to 0.15-0.2m -1, shielding distance ≥ 20 meters. (8) Enhanced infrared interference: The hydroxyl group (-OH) on the surface of Si nanodots combines with water vapor to form aerosols, and the attenuation in the 8-14μm band is increased from 5dB to 15-20dB, and the detection distance of the thermal imager is shortened by 60%. (9) Fluorescence interference: The fluorescence intensity in the 400-500nm band is ≥1000a.u., which can interfere with the laser rangefinder (error ≥50m). (10) Enhanced functional synergy. Synergy between Si nanodots and diatomaceous earth combustion: The hydrophilicity of the Si nanodot surface is improved after reduction (contact angle ≤30°), and it is easier to absorb water to form aerosols during combustion, and the smoke emission per unit mass is increased from 850m 3 / kg increased to 950-1050m 3 / kg. Optimized blinding effect: The particle size of Si nanodots (2-8nm) is comparable to the wavelength of visible light (400-700nm), with a larger scattering angle (>90°), and the enemy's target position error is increased by 50% (the original solution was 30%). (11) Improved environmental adaptability. Storage stability: The Si nanodot loading decays by ≤5% in 2 years (the original diatomaceous earth material is only 3%), and the anti-hygroscopic agent (CaCO3) inhibits hydrolysis (the hydrolysis rate of Si nanodots is <2%). Controllable release: The fluorescent properties of Si nanodots can be used as "tracers" to monitor the smoke diffusion range in real time through drone ultraviolet imaging, with an accuracy of ±2 meters.

[0033] 4. Although the binders of traditional diatomite-based smoke screen particles (such as HPMC and sodium alginate) can ensure formability, they have low strength (compression resistance ≤ 3MPa) and unadjustable density (smoke retention < 30s). They are easily softened and broken under high humidity or mechanical impact, resulting in an increased particle breakage rate (> 10%) during storage or application. In addition, the density of pure diatomite-based particles is relatively low (0.4-0.6g / cm 3 ), it is easy to float in the air and it is difficult to form a stable smoke layer. The present invention introduces bentonite and sand to solve the above problems in a targeted manner, because bentonite has high expansibility (volume expands 10 to 30 times after absorbing water), strong adhesion (cation exchange capacity ≥80meq / 100g), and hydrophilicity. As an auxiliary binder, it can enhance the internal binding force of the particles; bentonite can also adjust hygroscopicity (can balance anti-caking and combustion efficiency); reduce costs (the price is only 1 / 5 of HPMC). Sand (SiO2) has high hardness (Mohs hardness 7), high temperature resistance (melting point 1710℃), inertness (does not participate in chemical reactions), low cost (abundant reserves); as a skeleton material, it improves the mechanical strength of the particles (compressive strength is increased by 30% to 50%); can adjust the bulk density (increased to 0.6 to 0.8g / cm 3), extending smoke hang time. The introduction of bentonite and sand in this invention optimizes the mechanical properties and storage stability of diatomite-based smoke screen particles. Through the synergistic "bonding-skeletal-protection" effect, the particles' engineering applicability is significantly enhanced.

[0034] 5. The diatomaceous earth-Si nanodot composite material of the present invention has a particle structure consisting of a core layer, an intermediate bonding layer, and an outer protective layer. Bentonite and sand are mainly distributed in the intermediate bonding layer and the outer layer. The core layer is the main smoke-generating component; it is composed of diatomaceous earth-Si nanodot material, which is the core smoke-generating unit of the particle, responsible for adsorbing moisture at high temperatures, releasing SiO2 aerosols, and the fluorescence interference of Si nanodots; the structural characteristics are: diatomaceous earth has a porous structure with a pore size of 5 to 20 μm, Si nanodots are loaded on the pore wall through amino grafting, diatomaceous earth is uniformly loaded with Si nanodots (particle size 2 to 8 nm), the surface is modified by hydroxylation, and the contact angle is ≤30°, and the bonding force with the binder is strong. Among them, the middle bonding layer is the key reinforcement unit; it is composed of bentonite, sand and binder (such as HPMC); because bentonite swells when it meets water to form a "colloidal network", which wraps the core layer, and the sand is embedded in it to form a support network, and fills the pores inside the particles, so that the porosity is reduced from 30% to 15% (pore filling rate >85%), which significantly improves the compressive strength of the particles, and the compressive strength is increased from 5MPa to 8-10MPa; sand acts as a rigid skeleton to disperse stress, preventing the core layer from being broken due to extrusion or collision, and the breakage rate is reduced from 10% to below 3%; the binder (such as HPMC) works together with bentonite to cross-link and solidify during the drying process at 60-80°C, forming a "physical + chemical" dual bond, which extends the gel time to about 15 seconds. Among them, the outer protective layer is a functional regulation unit; its composition is to add an anti-moisture absorption agent (such as CaCO3) and / or a smoke enhancement agent (such as Mg(OH)2); the anti-moisture absorption agent covers the surface of the particles, which can reduce the surface energy, increase the contact angle from 50° to 70°, inhibit the hydrolysis of Si nanodots, and reduce the hydrolysis rate by less than 2%; the smoke enhancement agent can decompose at high temperature to produce water vapor (such as 2Mg(OH)2→2MgO+2H2O↑), promote the water absorption and expansion of the porous structure of diatomaceous earth, increase the smoke concentration, and increase the extinction coefficient by 10% to 15%.

[0035] 6. The diatomite-Si nanodot composite material of the present invention has a particle structure of a core layer, an intermediate bonding layer and an outer protective layer. The key process parameters of the preparation method of the present invention play a role in ensuring the structure: First, gradient density control: in the mixing stage: diatomite (density 0.2g / cm 3 ), sand (1.5g / cm 3 ), bentonite (0.9g / cm 3) Automatic grading under 800-1000rpm centrifugal force, so that the diatomaceous earth forms the core layer in the center; during the extrusion stage: the screw shear gradient pushes the sand to migrate toward the central axis, so that the sand is precisely positioned in the middle layer. Second, interface bonding is strengthened: the bentonite is fully hydrated at a barrel temperature of 80-100℃, and the gel network penetrates the pores of the core layer, increasing the bonding force by 30%; 8MPa rolling pressure makes the protective layer particles embed more than 1μm and the shedding rate is less than 0.1%. Third, the ability to control layer thickness: core layer: diatomaceous earth feed ratio is controlled to achieve a diameter of 1-2mm; middle bonding layer: bentonite / sand ratio is controlled to achieve a thickness of 1.5-2mm; outer protective layer: spray solution concentration + rolling pressure is controlled to achieve a thickness of 0.05-0.1mm.

[0036] 7. The screw temperature zones for extrusion granulation in the preparation method of the present invention are controlled: 40°C in the inlet zone (preventing bentonite pre-gelation), 80-100°C in the bonding layer zone (bentonite fully hydrated and expanded), and 60°C in the outlet zone (setting the shape). The temperature gradient triggers the selective gelation of bentonite within the pores of the diatomite (gel volume expansion of 300%, pore filling rate >85%). The effect is: the interlayer bonding force is increased by 300% (peel strength reaches 8MPa), solving the interlayer debonding problem of traditional granulation. The preparation method of the present invention uses rolling embedding coating to solve the hydrolysis problem of Si nanodots. Under a rolling pressure of 6-10MPa, a suspension of anti-moisture agent and smoke enhancer (such as CaCO3 and Mg(OH)2) is simultaneously sprayed. The high pressure causes the anti-moisture agent particles (particle size 1-5μm) to be embedded in the surface layer to a depth of about 0.1mm, forming a mechanically interlocking protective layer (not simple surface adsorption) to ensure a shedding rate of less than 0.1%. The preparation method of the present invention realizes innovation in the steps of mixing, activation (extrusion), and coating (rolling, embedding and coating): in the mixing step, centrifugal force drives self-assembly to solve the problem of multi-component stratification; in the activation (extrusion) step, the adhesive layer is thermally activated in partitions to break through the bottleneck of interlayer bonding strength; in the coating (rolling, embedding and coating) step, high-pressure mechanical interlocking coating is used to solve the problem of hydrolysis of Si nanodots. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a scanning electron microscope image of the modified diatomaceous earth obtained in Example 1.

[0038] Figure 2 This is a cross-sectional SEM image of the composite smoke particles obtained in Example 1.

[0039] Figure 3 Schematic diagram of the granulation process of diatomaceous earth-Si nanodot composite materials.

[0040] Figure 4 This is the particle size distribution of diatomaceous earth-Si nanodot composite material after granulation.

[0041] Figure 5This is a schematic diagram of the structure of a mobile smoke bomb.

[0042] Figure 6 This is a schematic diagram of the fixed smoke generator structure.

[0043] Figure 7 Comparison of infrared attenuation performance. De-1 is a blank control, consisting of unmodified diatomaceous earth (no bentonite, sand, or Si nanodots); De-2 is an intermediate formulation that is not fully optimized, containing Si nanodots but no bentonite and / or sand; and De-3 is the granules obtained in Example 2. DETAILED DESCRIPTION

[0044] The technical scheme of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Where specific conditions are not specified in the examples, the conditions are carried out according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0045] Example 1: Preparation of high visible light shielding diatomite-Si nanodot composite material (composite smoke screen particles);

[0046] The weight ratio of each material is as follows: modified diatomaceous earth-Si nanodot material (wherein the Si nanodot loading accounts for 6wt% of the total amount of modified diatomaceous earth-Si nanodot material, and the particle size is 4nm) 50, bentonite 20, sand 10, HPMC binder 18, potassium nitrate combustion aid 8, magnesium hydroxide smoke enhancer 10, and calcium carbonate anti-moisture absorbent 4.

[0047] Preparation steps of diatomite-Si nanodot composite material:

[0048] Diatomaceous earth pretreatment: calcination at 700° C. for 2.5 hours, KH-550 ultrasonic treatment (3% ethanol solution, 30 minutes), moisture content 1.5%; modified diatomaceous earth was obtained. Figure 1 This is a scanning electron microscope image of modified diatomite. Figure 1 It can be seen that the three-dimensional porous skeleton structure of the modified diatomite is completely retained, and the pore penetration is significantly improved (pore diameter 5-20μm); the surface roughness is increased, forming densely distributed nanoscale protrusions (50-200nm), and the pore walls are covered with a uniform velvety Si-O-Si cross-linked network; this confirms the synergistic modification effect of calcination removal of impurities and surface modification with KH-550 silane coupling agent;

[0049] Synthesis of Si nanodots: 10 g of modified diatomite was dispersed in 1 L of deionized water, 50 mL of 0.5 mol / L NaBH4, 20 mL of ethanol, and ammonia water were added to adjust the pH to 10. After ultrasonication for 30 minutes, the reaction was hydrothermally reacted at 180 ° C for 6 hours, and the modified diatomite-Si nanodot material was obtained by centrifugation, washing, and drying.

[0050] Mixing and granulation: After the components (modified diatomaceous earth, sand, bentonite) are mixed at high speed (900 rpm × 18 minutes) to form a uniform composite material, they are fed into a screw extruder for extrusion granulation (diameter 4 mm, length 6 mm), such as Figure 3 As shown; then 8MPa rolling pressure is applied to shape and solidify, and anti-moisture agent calcium carbonate and smoke synergist magnesium hydroxide are sprayed simultaneously, and finally cylindrical particles with high mechanical integrity are obtained; drying and solidification: drying in an oven at 70℃ for 5 hours, with a moisture content of 2.2%.

[0051] Figure 2 This is a cross-sectional SEM image of the composite smoke screen particles obtained in Example 1. Figure 2 The composite smoke particles exhibit a highly developed and uniformly distributed through-pore network, with a pore size gradient ranging from 5 to 20 μm (matching the optimal smoke diffusion model). The three-dimensional skeleton structure is continuous and free of collapse (pore wall thickness > 1 μm), confirming the stability of the calcination-KH550 modification process. The nanoscale velvety surface coating (50-200 nm) significantly increases the specific surface area, supporting an ultra-high Si nanodot loading rate (> 95%). The fully interconnected pores are free of obstruction defects, ensuring a 300% increase in water vapor permeability during combustion, achieving instantaneous smoke coverage.

[0052] Performance testing:

[0053] Smoke generation efficiency: 10g sample ignited at 300℃, 3 minutes to generate smoke volume of 9.5L (standard state);

[0054] Visible light shielding: Targets 5 meters away cannot be identified, and the extinction coefficient is 0.18m -1 ;

[0055] Fluorescence characteristics: fluorescence intensity in the 450nm band under 365nm excitation is 1200a.u.;

[0056] After 2 years of storage: the Si nanodot loading was 5.7 wt%, attenuated by 5%; the smoke emission efficiency was 9.2 L / 10 g, attenuated by 3%.

[0057] Example 2: Preparation of infrared interference type diatomaceous earth-Si nanodot composite material (composite smoke particles):

[0058] Modified diatomaceous earth-Si nanodot material (wherein the Si nanodot loading accounts for 7wt% of the total amount of the modified diatomaceous earth-Si nanodot material, and the particle size is 5nm) 48, sodium alginate binder 1, bentonite 30, sand 15, ammonium perchlorate combustion aid 12, urea smoke enhancer 15, and silica micropowder anti-moisture absorption agent 5.

[0059] Preparation steps of diatomite-Si nanodot composite material:

[0060] Diatomite pretreatment: calcination at 800°C for 3 hours, KH-550 ultrasonic treatment (3% ethanol solution, 30 minutes), moisture content 1.2%; modified diatomite was obtained;

[0061] Synthesis of Si nanodots: Modified diatomite (10 g) was dispersed in 1 L of deionized water, and NaBH4 (0.5 mol / L × 50 mL), ethanol (20 mL), and ammonia water (pH = 10) were added. After ultrasonication for 30 minutes, the mixture was hydrothermally reacted at 180 ° C for 6 hours. The modified diatomite-Si nanodot material was washed and dried by centrifugation.

[0062] Mixing and granulation: The components were mixed at high speed (850 rpm for 20 minutes) and extruded into granules (3 mm in diameter, 5 mm in length, and rolled at a pressure of 7 MPa). The granules were then rolled and solidified at a pressure of 8 MPa, and then sprayed with silica powder, an anti-moisture agent, and urea, a smoke enhancer, to obtain cylindrical granules with high mechanical integrity. Drying and curing: Oven drying at 80°C for 4 hours, with a moisture content of 1.8%.

[0063] The particles obtained are Figure 4 As shown. Figure 4 The morphology, uniformity, and structure of the composite particles are shown to be complete. Twelve images, displayed side by side (four rows and three columns), demonstrate the morphological consistency and structural stability of the granulated particles. The particles have sharp edges and are free of breakage (consistent with the previously discussed conclusion of a "breakage rate <3% after adding bentonite / sand"). The particles are of similar size, with no lumps or debris, indicating excellent dispersion uniformity during the granulation process. This is directly related to the bentonite-assisted granulation and the sand's stress-dispersing effects. This indicates that after optimizing the "bentonite + sand" formula, the particles exhibit high consistency (size and shape) and low breakage, supporting the high reliability of the smoke screen material. The consistent morphology of the 12 parallel samples demonstrates the stable and reproducible production of the "bentonite + sand" formula. The particles exhibit no cracking or powdering, demonstrating satisfactory mechanical strength (storage breakage rate <3%). The uniform size allows for a controlled combustion rate, enabling fog shielding distances up to 25 meters.

[0064] Performance testing:

[0065] Smoke generation efficiency: 10g sample ignited at 300℃, 9.8L smoke volume generated in 3 minutes (standard state);

[0066] Infrared attenuation: 8-14μm band attenuates 18dB, and the detection distance of the thermal imager is shortened to 1 / 3 of the original (De-3 curve). Figure 7 As shown, the detection distance of enemy thermal imagers can be shortened to 1 / 3 of the original range; the peak attenuation in the 14-18μm far-infrared band exceeds 30dB, significantly improving the effectiveness of active protection on the battlefield. Figure 7Among them, De-1 is a blank control, that is, only unmodified diatomaceous earth (no bentonite, sand, Si nanodots); the attenuation is extremely low (≈2dB) and there is no fluctuation, lacking infrared interference ability, proving the ineffectiveness of the unmodified material; De-2 is an intermediate formula that is not fully optimized, that is, containing Si nanodots but no bentonite and / or sand; the attenuation is gentle (≈7dB), there is a certain infrared absorption, but the loose structure leads to unstable shielding performance; De-3 is the particle obtained in Example 2, and the attenuation increases significantly (peak value ≈35dB). The synergistic effect of bentonite + sand enhances infrared shielding, especially in the 14-18μm band, with an attenuation value (>20dB), and a visible light shielding distance of 25 meters, so that high infrared attenuation and high visible light shielding performance are synergistic; De-3 has a peak attenuation of 35dB in the 18μm band, which is because bentonite improves the compressive strength of the particles (8-10MPa) and sand increases the density (0.8g / cm 3 ), making the structure dense and extending the effective attenuation path. The introduction of bentonite + sand in the present invention significantly improves infrared shielding performance, resulting in a significant difference between De-3 and De-2 (35dB vs. 7dB); De-1, as a blank control, has the worst effect.

[0067] After 2 years of storage: Si nanodot loading 6.7 wt% (decayed 4.3%), smoke emission efficiency 9.5 L / 10 g (decayed 3.1%).

[0068] Example 3: Live-fire test of mobile smoke bombs, such as Figure 5 shown.

[0069] Device: 82mm mortar shell modified, loaded with 250g of composite smoke particles prepared in Example 1, diffusion nozzle aperture 8mm (gradual expansion structure), fuse with impact explosion + 3 seconds delay.

[0070] Test conditions: wind speed 4m / s, temperature 22℃, humidity 65%, launch elevation angle 42°, range 600 meters.

[0071] Test results:

[0072] Smoke coverage area: 2800m 2 (LiDAR scanning);

[0073] Visible light shielding time: 20 seconds (brightness of target area ≤ 0.05cd / m 2 );

[0074] Enemy optical sight test: Targets 5 meters away cannot be identified (clearly visible when there is no smoke screen);.

[0075] Fluorescence interference test: UAV ultraviolet imaging shows that the fluorescence intensity in the smoke area is 1000 a.u., which is close to the background noise (800 a.u.), and the target positioning error is ≥60 meters.

[0076] Example 4: Long-term storage test of fixed smoke generator, such as Figure 6 shown.

[0077] Sample: composite smoke particles prepared in Example 2 (sealed and stored in an environment of 25° C. and 70% humidity).

[0078] Test period: 0 months, 6 months, 12 months, 24 months.

[0079] Test indicators:

[0080] Bulk density: Initial 0.55g / cm 3 , 0.57g / cm after 24 months 3 (change ≤ 3.6%);

[0081] Smoke emission efficiency: 9.8 L / 10 g initially, 9.3 L / 10 g after 24 months (decay 5.1%);

[0082] Si nanodot loading: 7 wt% initially, 6.7 wt% after 24 months (decayed 4.3%);

[0083] Compressive strength: initial 6.2 MPa, 6.0 MPa after 24 months (decay 3.2%).

[0084] Conclusion: The material has stable performance after 2 years of storage and meets long-term equipment needs.

[0085] The above description is only used to introduce the specific embodiments of the present invention in detail, but the technical solutions proposed by the present invention are not limited to the above methods. Without departing from the basic principles of the present technology, equivalent modifications and variations made by those skilled in the art to the technology proposed by the present invention should be included in the scope of the claims of the present invention.

Claims

1. A diatomite-Si nanodot composite material, characterized in that: The invention comprises the following components by weight: modified diatomaceous earth-Si nano-dot material, 45-60; bentonite, 20-30; sand, 10-15; binder, 12-18; combustion improver, 6-10; smoke enhancer, 6-10; and anti-moisture absorption agent, 2-5.

2. The diatomite-Si nanodot composite material according to claim 1, characterized in that: The modified diatomite-Si nanodot material is a silane coupling agent-modified diatomite loaded with Si nanodot material; wherein the Si nanodot material accounts for 2-8wt% of the total amount of the modified diatomite-Si nanodot material, the particle size of the Si nanodot material is 2-8nm, and the agglomerate accounts for no more than 10%.

3. The diatomite-Si nanodot composite material according to claim 1, characterized in that: The binder is one or more of hydroxypropyl methylcellulose, sodium alginate or polyvinyl alcohol; the combustion aid is one or both of potassium nitrate or ammonium perchlorate; the smoke enhancer is one or both of magnesium hydroxide or urea; and the anti-hygroscopic agent is one or both of calcium carbonate or silicon dioxide powder.

4. The diatomite-Si nanodot composite material according to claim 3, characterized in that The diatomite-Si nanodot composite material structure includes: a core layer, an intermediate bonding layer and an outer protective layer; the core layer is a diatomite / Si nanodot material; the intermediate bonding layer is a combination of bentonite, sand and a binder; and the outer protective layer is a combination of an anti-moisture absorbent, a smoke enhancer and a binder.

5. The method for preparing the diatomite-Si nanodot composite material according to any one of claims 1 to 4, characterized in that: The steps include: (1) Preparation of modified diatomite-Si nanodot materials; (2) mixing the modified diatomite-Si nanodot material, bentonite, sand, a binder, and a combustion aid in proportion and at high speed to obtain a mixture; (3) extruding and granulating the mixture to obtain cylindrical particles; (4) rolling the cylindrical particles and spraying them with an anti-wetting agent and a smoke enhancer, and then drying them to obtain the diatomaceous earth-Si nanodot composite material.

6. The preparation method according to claim 5, characterized in that The preparation method of modified diatomite-Si nanodot material includes the following steps: (11) Diatomite pretreatment: calcining the diatomite at high temperature for a period of time, then adding a silane coupling agent and ultrasonically treating it to obtain modified diatomite; (12) In situ growth of Si nanodots on the surface of diatomite: the modified diatomite was dispersed in deionized water, sodium borohydride, anhydrous ethanol and ammonia were added, and ultrasonic dispersion was performed for a period of time; then hydrothermal reaction was performed for a period of time; (13) After cooling to room temperature, the solid was separated and washed alternately with deionized water and ethanol for multiple times, and then vacuum dried to obtain the modified diatomite-Si nanodot material.

7. The preparation method according to claim 6, characterized in that Step (11): calcining the diatomaceous earth at 600-800° C. for 2-3 hours; using KH-550 as the silane coupling agent; and ultrasonically treating the diatomaceous earth so that the contact angle thereof is ≤30°.

8. The preparation method according to claim 6, characterized in that In step (12), the amount of modified diatomaceous earth added is 5-15 g / L, the amount of sodium borohydride is 0.4-0.6 mol / L, the amount of anhydrous ethanol is 10-30 mL / L, and the amount of ammonia added is such that the pH value of the solution is maintained at 9.5-10.5; the hydrothermal reaction conditions are: reaction at 150-200° C. for 2-10 hours.

9. The preparation method according to claim 5, characterized in that Step (2) mixing at a rotation speed of 800-1000 rpm for 15-20 minutes; step (3) extruding granulation in a twin-screw extruder, setting the temperature of the screw barrel inlet zone to 40°C, the temperature of the screw barrel bonding layer zone to 80-100°C, the temperature of the screw barrel outlet zone to 60°C, and the screw speed to 20-30 rpm; extruding into cylindrical granules with a diameter of 3-5 mm and a length of 5-8 mm; step (4) rolling the cylindrical granules with a pressure of 6-10 MPa.

10. Use of the diatomite-Si nanodot composite material according to any one of claims 1 to 4 as a smoke screen material.

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