A lunar soil analogue polymer synergistically reinforced by particle size distribution and nanosilica and a preparation method thereof

Abstract

The application discloses a kind of granule gradation and nano-silica synergistic reinforced simulated lunar soil base polymer and preparation method thereof, it is related to deep space exploration in situ resource utilization technical field, including simulated lunar soil precursor, nano-silica, composite alkali activator and water, the simulated lunar soil precursor is non-continuous gradation TJ-1 simulated lunar soil;The nano-silica is added in the form of aqueous dispersion;The composite alkali activator is composed of sodium hydroxide, calcium hydroxide and sodium silicate nine water;The water-binder ratio of the simulated lunar soil base polymer is 0.27, and the total water consumption includes the moisture contained in nano-silica aqueous dispersion and composite alkali activator;The application realizes the comprehensive synergistic promotion of simulated lunar soil base polymer working performance, coagulation efficiency and mechanical property by the deep fusion of non-continuous gradation structure regulation and control and nano-silica chemical enhancement.

Description

Technical Field

[0001] This invention relates to the field of in-situ resource utilization technology for deep space exploration, specifically to a simulated lunar soil base polymer with synergistic enhancement of particle size distribution and nano-silica, and its preparation method. Background Technology

[0002] With the continuous advancement of global deep space exploration strategies, the Moon has become a crucial outpost for humanity to expand its living space and acquire space resources. Establishing a long-term, stable lunar research station is one of the core objectives for achieving manned lunar landings and deep space exploration. However, lunar surface construction faces harsh environments including extreme high and low temperature cycles, high vacuum, and strong cosmic radiation. Furthermore, the cost of transporting materials between Earth and the Moon is extremely high, and on-orbit resupply is extremely difficult. Relying on Earth to transport building materials is completely insufficient to meet the construction needs of large-scale lunar infrastructure. Therefore, in-situ construction using lunar soil as the primary raw material, based on In-Situ Resource Utilization (ISRU) technology, is widely recognized as the only feasible solution for achieving sustainable lunar base construction.

[0003] Geopolymers, as inorganic polymers formed from alkali-activated aluminosilicate precursors, possess core characteristics such as rapid strength development, resistance to high and low temperature cycling, excellent radiation resistance, and low dependence on water resources. Their raw material requirements are highly matched with the chemical composition of lunar soil, which is mainly composed of aluminosilicate oxides, and they are highly adaptable to the extreme lunar environment. They have become the most promising cementing material in the field of in-situ construction on the lunar surface. Preliminary research results have been achieved in the preparation and performance regulation of simulated lunar soil base polymers (SLSG).

[0004] However, while existing research has broken the inherent contradiction of the inability to balance flow properties and mechanical properties in traditional continuous gradation systems through the physical structure regulation of discontinuous gradation, and achieved synergistic optimization of the basic properties of materials, lunar soil minerals themselves are characterized by high crystallinity and low glass phase content. Their reactivity is far lower than that of conventional geopolymer precursors such as fly ash, slag, and metakaolin. Single physical structure regulation cannot overcome the inherent limitation of low reactivity of lunar soil. There are obvious ceilings to the improvement of material mechanical properties and the acceleration of reaction process, making it difficult to meet the stringent requirements of long-term load-bearing and rapid prototyping of lunar infrastructure.

[0005] Furthermore, existing research on SLSG modified with nano-silica (NS) has failed to integrate the chemical reinforcement of NS with the structural control of discontinuous gradation in its design. While NS modification alone can improve the mechanical properties of the material to some extent, the extremely high specific surface area of ​​NS adsorbs a large amount of free water, further exacerbating the problems of increased slurry viscosity and decreased fluidity, thus severely degrading the material's workability. If NS is combined with a fine-particle-dominated continuous gradation system, the slurry yield stress and plastic viscosity will surge, completely losing pumpability and extrudability, making it unsuitable for unmanned and intelligent construction processes such as pumping and casting and 3D printing in the low-gravity environment of the lunar surface. At the same time, existing research has not clarified the synergistic mechanism between NS and lunar soil particle gradation, nor has it optimized the appropriate dosage of NS for discontinuous gradation systems, failing to fully utilize the nano-filling effect, nucleation effect, and chemical activation effect of NS, thus significantly reducing the modification effect. Summary of the Invention

[0006] The purpose of this invention is to provide a simulated lunar soil-based polymer with synergistic enhancement of particle size distribution and nano-silica, and its preparation method, so as to solve the problem that the performance improvement of existing lunar soil-based polymers is limited by the intrinsic low reactivity of precursors.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] According to a first aspect of this disclosure, a simulated lunar soil base polymer with synergistic enhancement of particle size distribution and nano-silica is proposed, comprising a simulated lunar soil precursor, nano-silica, a composite alkali activator, and water, characterized in that the simulated lunar soil precursor is a discontinuously graded TJ-1 simulated lunar soil, wherein the discontinuously graded TJ-1 simulated lunar soil is a gradation system in which medium-sized particles in the range of 0.25 mm to 1 mm are removed, and only coarse-sized particles with a particle size > 1 mm and fine-sized particles with a particle size < 0.25 mm are retained;

[0009] The nano-silica was added in the form of an aqueous dispersion, and the dosage of nano-silica was 0.25 wt% to 1.50 wt%, based on the mass of the discontinuously graded TJ-1 simulated lunar soil.

[0010] The composite alkali activator is composed of sodium hydroxide, calcium hydroxide, and sodium silicate nonahydrate. Based on the mass of the discontinuously graded TJ-1 simulated lunar soil, the dosage of sodium hydroxide is 10 wt%, the dosage of calcium hydroxide is 6 wt%, and the dosage of sodium silicate nonahydrate is 6 wt%.

[0011] The water-cement ratio of the polymer in the simulated lunar soil base is 0.27, and the total water consumption includes the water contained in the nano-silica aqueous dispersion and the composite alkali activator.

[0012] Furthermore, the nano-silica is added at a rate of 0.75 wt%, based on the mass of the discontinuously graded TJ-1 simulated lunar soil.

[0013] Furthermore, the solid content of the aqueous dispersion of nano-silica is 15%, wherein the particle size of the nano-silica is 30 nm.

[0014] Furthermore, the purity of the sodium hydroxide is ≥99%, the purity of the calcium hydroxide and sodium silicate nonahydrate is ≥95%, and the modulus of the sodium silicate nonahydrate is 1.03±0.03.

[0015] According to the second aspect of this disclosure, a method for preparing a simulated lunar soil-based polymer synergistically reinforced by particle size distribution and nano-silica is also proposed, for preparing the simulated lunar soil-based polymer of the first aspect, comprising the following steps:

[0016] S1. Based on the mass of the non-continuously graded TJ-1 simulated lunar soil, take 10wt% sodium hydroxide, 6wt% calcium hydroxide, and 6wt% sodium silicate nonahydrate, mix with some water and stir continuously to obtain a uniform composite alkali activator solution.

[0017] S2. Add the discontinuously graded TJ-1 simulated lunar soil to the cement mortar mixer and stir at low speed to disperse the particles evenly.

[0018] S3. Based on the mass of the discontinuous graded TJ-1 simulated lunar soil, take 0.75wt% of the nano-silica aqueous dispersion, mix it evenly with the remaining water, and then slowly add it to the mixer along with the composite alkali activator solution. Mix it thoroughly with the discontinuous graded TJ-1 simulated lunar soil and continue to stir at low speed to obtain a uniform geopolymer slurry. The total amount of water added meets the requirement of a polymer water-cement ratio of 0.27.

[0019] S4. The geopolymer slurry is injected into the mold and vibrated to remove air. After high-temperature curing and demolding, it is cured at the same temperature until the target age is obtained to obtain the target simulated lunar soil base polymer.

[0020] Furthermore, in step S1, the stirring time is 20 minutes, and a uniform and transparent composite alkali activator solution is obtained after stirring.

[0021] Furthermore, in steps S2 and S3, the stirring speed is 140±5 r / min; the stirring time in step S2 is 1 min, and the stirring time in step S3 is 4 min.

[0022] Furthermore, in step S4, the high-temperature curing temperature is 100℃. After curing at this temperature for 24 hours, the product is demolded and then cured at 100℃ for 7 days.

[0023] Furthermore, in step S4, the vibration frequency of the tamping operation is 60 times / minute, and the tamping is performed continuously for 25 times until no visible air bubbles are visible in the slurry.

[0024] Compared with existing technologies, this invention provides a simulated lunar soil base polymer and its preparation method that is synergistically enhanced by particle size distribution and nano-silica. By deeply integrating the physical structure regulation of discontinuous particle size distribution with the chemical activity enhancement of nano-silica, the discontinuous particle size distribution solves the core contradiction between the flow properties of the slurry and the basic mechanical properties from a macroscopic structural perspective. The nano-silica stimulates the reactivity of lunar soil and optimizes the gel network structure from a microscopic level. The two work together to overcome the inherent limitation of low reactivity of lunar soil-based materials, and achieve comprehensive synergistic optimization of working performance, coagulation efficiency and mechanical properties, providing a cementing material with the best comprehensive performance for in-situ construction on the lunar surface. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0026] Figure 1 The diagram showing the influence of NS content on the flow properties of SLSG slurry provided by this invention;

[0027] Figure 2 The diagram showing the effect of NS dosage on the setting time of SLSG slurry provided by this invention;

[0028] Figure 3 The diagram showing the effect of NS content on the rheological properties of SLSG slurry provided by this invention;

[0029] Figure 4 The diagram showing the influence of NS content on the mechanical properties of SLSG slurry provided by this invention;

[0030] Figure 5 The diagram showing the influence of particle size distribution and NS doping amount on the reaction kinetics of SLSG provided by this invention; wherein, Figure 5 (a) is the evolution curve of the heat release rate; Figure 5 (b) is a magnified view of the heat release rate in the first 0.25 hours; Figure 5 (c) is the cumulative heat release curve; Figure 5 (d) is an enlarged view of the cumulative heat release in the first 0.25 hours;

[0031] Figure 6 The FT-IR test results of the PE-0, PG-0, PG-0.75 and PG-1.50 groups provided by this invention are shown in the figure.

[0032] Figure 7 The XRD diffraction patterns of the PE-0, PG-0, PG-0.75, and PG-1.50 groups provided by this invention; wherein, Figure 7 (a) is the full XRD diffraction spectrum of the sample; Figure 7 (b) is a magnified view of a portion of the XRD pattern;

[0033] Figure 8 The SEM microstructure images of PE-0, PG-0, PG-0.75, and PG-1.50 groups, magnified 2000x, provided by this invention; wherein, Figure 8 (a) is group PE-0; Figure 8 (b) is group PG-0; Figure 8 (c) is the PG-0.75 group; Figure 8 (d) PG-1.50 group;

[0034] Figure 9 This is a graph showing the EDS test results provided by the present invention; wherein, Figure 9 (a) is group PE-0; Figure 9 (b) is group PG-0; Figure 9 (c) is the PG-0.75 group; Figure 9 (d) PG-1.50 group. Detailed Implementation

[0035] The embodiments in this invention are technical extensions based on another application filed at the same time, "A geopolymer cementitious material based on discontinuous gradation simulated lunar soil and its preparation method". In order to enable those skilled in the art to better understand the technical solution of this invention, the invention will be further described in detail below with reference to the accompanying drawings.

[0036] 1. Test raw materials

[0037] The simulated lunar soil used in this embodiment and the comparative example is Tongji-1 (TJ-1) simulated lunar soil. This material has been widely used in the initial verification test of my country's Chang'e series and manned lunar landing project. Its parent material comes from the Cenozoic volcanic clastic rock layer in Jingyu County, Jilin Province, China. Its main mineral composition includes pyroxene, feldspar, olivine, etc., which is highly matched with the chemical composition of the real lunar soil retrieved by Apollo 14 and Chang'e 5.

[0038] The raw materials for the composite alkali activator are: flake sodium hydroxide (NaOH), purity 99%; calcium hydroxide [Ca(OH)2], purity 95%; sodium silicate nonahydrate (Na2SiO3・9H2O), purity 95%, modulus 1.03±0.03.

[0039] Nano silica: VK-Sp30W type aqueous dispersion, particle size 30nm, solid content 15%.

[0040] All water used in the experiments was purified water.

[0041] 2. Test Plan

[0042] The TJ-1 simulated lunar soil was sieved, yielding six particle aggregates with particle sizes of 3-2 mm, 2-1 mm, 1-0.5 mm, 0.5-0.25 mm, 0.25-0.075 mm, and <0.075 mm. Simulated lunar soil particles larger than 1 mm were defined as coarse-grained particles, and those smaller than 0.25 mm were defined as fine-grained particles. Five continuous gradations were established: gradation A (original gradation of TJ-1 simulated lunar soil), gradation B (removing 2-3 mm particles), gradation C (removing 1-3 mm particles), gradation D (removing 0.5-3 mm particles), and gradation E (removing 0.25-3 mm particles). Two discontinuous gradations were established: gradation F (removing 0.25-2 mm particles) and gradation G (removing 0.25-1 mm particles). The optimal particle size distribution was screened based on the flow properties, setting time, rheological properties, and mechanical properties of SLSG, and NS content was tested. The NS content was set to 0.25wt%, 0.50wt%, 0.75wt%, 1.00wt%, 1.25wt%, and 1.50wt%, respectively. The SH, CH, and SS contents were 10wt%, 6wt%, and 6wt%, respectively, and the water-cement ratio was 0.27.

[0043] The experimental protocol is shown in Table 1 below:

[0044] Table 1 Test Protocol

[0045]

[0046] Note: In PX-Y, X represents the particle size distribution selected during SLSG preparation, and Y represents the amount of NS doping. For example, PG-0.75 indicates that SLSG is prepared using G particle size distribution and 0.75wt% NS doping.

[0047] 3. Preparation process

[0048] Step 1: Based on the mass of the non-continuously graded TJ-1 simulated lunar soil, weigh out 10wt% sodium hydroxide, 6wt% calcium hydroxide, and 6wt% sodium silicate nonahydrate, respectively, mix them with some pure water, and stir continuously for 20 minutes to obtain a uniform and transparent composite alkali activator solution. The total water volume includes the water contained in the NS dispersion and the composite alkali activator.

[0049] Step 2: Pour the discontinuously graded TJ-1 simulated lunar soil into the cement mortar mixer and stir at a low speed of 140±5 r / min for 1 min to fully disperse the particles.

[0050] Step 3: Based on the mass of the discontinuous graded TJ-1 simulated lunar soil, take 0.75wt% of the nano-silica aqueous dispersion, mix it evenly with the remaining water, and then slowly add it to the mixer along with the composite alkali activator solution. Mix it thoroughly with the discontinuous graded TJ-1 simulated lunar soil and continue to stir at a low speed of 140±5r / min for 4min to obtain a uniform geopolymer slurry. The total amount of water added meets the requirement of a polymer water-cement ratio of 0.27.

[0051] Step 4: Inject the geopolymer slurry into the mold and vibrate to remove air. After high-temperature curing and demolding, continue curing at the same temperature until the target age to obtain the target simulated lunar soil base polymer. The high-temperature curing temperature is 100℃. First, cure at this temperature for 24 hours and then demold. Continue curing at 100℃ for 7 days. The vibration frequency of the vibration operation is 60 times / minute, and vibrate continuously for 25 times until there are no visible air bubbles in the slurry.

[0052] 4. Testing Methods

[0053] ① Flowability test: The test shall be conducted in accordance with the "Method for Determination of Flowability of Cement Mortar" (GB / T2419-2005). The specific implementation process is as follows: The freshly prepared SLSG slurry shall be placed on a standard vibration table with a vibration frequency of 60 times / minute and subjected to 25 consecutive vibrations. After the slurry stabilizes, the maximum diameter of its extended body in the orthogonal direction shall be measured, and the average value shall be calculated as the flowability index.

[0054] ② Setting Time Test: According to the "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement" (GB / T1346-2011), after the polymer of the target simulated lunar soil base was prepared, it was placed in the mold and the surface was smoothed. Then, the mold was moved to a 100℃ oven for curing. Starting from the moment water was added, the setting time of the SLSG slurry was measured using a Vicat apparatus at 5-minute intervals. When the slurry was close to initial setting, the measurement interval was shortened. The time when the needle sank freely to a distance of (4±1) mm from the bottom plate was the initial setting time. Afterward, the mold was flipped over, and the final setting needle was used to test the final setting time of the SLSG slurry at 5-minute intervals. When the slurry was close to final setting, the measurement interval was shortened. The time when the annular indentation left by the needle on the slurry surface did not exceed 0.5 mm was the final setting time.

[0055] ③ Rheological property testing: The shear stress-shear rate rheological curve of the SLSG slurry was determined using an NDJ-8T rotational viscometer from Shanghai Fangrui Company. The specific steps are as follows: Pour the freshly prepared SLSG slurry into a 500ml beaker and use an L4 rotor. The rotational viscometer was used at a speed of 6.42s... -1 After a pre-shear of 30 s, the shear rate drops to 0 s. -1 After the sample has returned to a flat state, shearing begins, with the shearing rate starting at 0.321 s⁻¹.-1 Gradually rising to 6.42s -1 After each rotational speed step of 10 seconds, the slurry viscosity, shear rate, and shear stress were recorded.

[0056] ④ Mechanical property testing: Referring to the "Test Method for Strength of Cement Mortar" (GB / T17671-2021), the SLSG mechanical property tests were conducted using a beam bending-shear loading and compression testing machine. Flexural strength was tested using the three-point bending method. The specimen size was 160mm×40mm×40mm, with a span of 100mm and a loading rate of 50N / s. Three specimens were tested in parallel per group, and the average value was taken as the flexural strength. Then, the fractured block formed after the flexural test was placed in the center of the compressive strength testing fixture, with a loading rate of 2.4kN / s. Six specimens were tested per group, and the average value was taken as the compressive strength.

[0057] ⑤ Reaction Kinetics Testing: The reaction kinetics of SLSG were tested using an ICC (Setaram-C80, France). First, the instrument was preheated to 100°C, the circulating cooling water flow rate was set to 2 L / min, and the purging nitrogen pressure was set to 0.8 bar. After the freshly prepared SLSG slurry was thoroughly stirred, approximately 10 g of representative sample was weighed and placed in the sample cell. Once the heat flow signal stabilized, the reaction kinetics evolution data were recorded.

[0058] ⑥ Microstructure analysis: The chemical structure of SLSG was analyzed using FT-IR (Shimadzu IRTracer 100, Japan), with a scan wavenumber of 4000-400 cm⁻¹. -1 Phase changes in SLSG were analyzed using XRD (Bruker D8 Advance, Germany), with diffraction patterns ranging from 5 to 90° at a scan rate of 2° / min. The microstructure of SLSG was analyzed using SEM (Zeiss Sigma 300). The elemental distribution of SLSG was analyzed using EDS (Oxford Energy Dispersive Spectroscopy UILTIMMAX40-Oxford EBSD C-SWIFT).

[0059] 5. Test Results

[0060] ① Flow Performance Test Results: Previous studies have shown that the flow performance of SLSG slurry gradually decreases with the removal of coarse-sized particles and the increase in the proportion of fine-sized particles in the simulated lunar soil; that is, the increase in the proportion of fine-sized particles in the simulated lunar soil has an adverse effect on the flow performance of SLSG. The reason for this is believed to be that the increase in the proportion of fine-sized particles in the simulated lunar soil significantly increases the specific surface area of ​​the particle system, adsorbing more free water, thus leading to a decrease in slurry flow performance. However, SLSG slurry prepared using discontinuously graded simulated lunar soil exhibits excellent flow performance. Through the synergistic design of coarse and fine-sized particles, the flow performance of SLSG can be significantly improved. This can be attributed to the ball bearing effect; the appropriate incorporation of coarse-sized particles can adjust the network structure formed between fine-sized particles, making it easier for particles to roll and slide, thereby improving the flow performance of the slurry. Figure 1 It can be seen that the flow properties of NS-SLSG slurry gradually decrease with increasing NS content. The flowability of the PG-0 group slurry is 215 mm. With increasing NS content, the flowability of NS-SLSG slurries in the PG-0.25, PG-0.50, PG-0.75, PG-1.00, PG-1.25, and PG-1.50 groups decreased to 190 mm, 183 mm, 182.5 mm, 174.5 mm, 180 mm, and 173 mm, respectively, which are 11.63%, 14.88%, 15.12%, 18.84%, 16.28%, and 19.53% lower than that of the PG-0 group. This indicates that increasing NS content has a negative impact on the flow properties of SLSG. The reason is that NS has a high specific surface area, and increasing NS content will adsorb more free water; at the same time, the hydroxyl groups on the NS surface enhance the interaction forces between particles through hydrogen bonding, significantly increasing the slurry viscosity and causing a further decrease in flow properties.

[0061] In summary, the discontinuous gradation method for preparing SLSG improves the fluidity of the slurry by 10.26%–32.31% compared to continuous gradation, better meeting the requirements for material flowability in lunar surface pumping, casting, and other construction processes. While the addition of natural gas (NS) reduces slurry fluidity, when the NS content is controlled below 0.75 wt% on a discontinuous gradation basis, the NS-SLSG slurry can still maintain a fluidity similar to the original gradation SLSG, and its overall flowability is significantly better than that of a continuous gradation system with an excessively high proportion of fine particles.

[0062] ② Setting Time Test Results: With the removal of coarse-sized particles from the simulated lunar soil and the increase in the proportion of fine-sized particles, the setting time of the SLSG slurry gradually decreased. The increase in the proportion of fine-sized particles had a more significant impact on the final setting efficiency of SLSG than on the initial setting efficiency. This is because the smaller-sized simulated lunar soil particles dissolve more completely, while when the content of coarse-sized particles is high, the reaction products on the particle surface easily form a coating layer, hindering the further dissolution of internal components and delaying the subsequent setting process. In contrast, fine-sized particles, due to their more complete contact efficiency with the alkali activator, exhibit a more sustained and efficient reaction process. Figure 2 It can be seen that with the increase of NS content, the setting time of NS-SLSG shows a trend of first decreasing and then slightly increasing. The initial setting time of the PG-0 group slurry is 56 min. With the increase of NS content, the initial setting times of NS-SLSG slurries in the PG-0.25, PG-0.50, PG-0.75, PG-1.00, PG-1.25, and PG-1.50 groups are 50 min, 46 min, 45 min, 47 min, 47 min, and 51 min, respectively, which are 10.71%, 17.86%, 19.64%, 16.07%, 16.07%, and 8.93% lower than those in the PG-0 group. The final setting time of the PG-0 group was 68 min. With the increase of NS doping, the final setting times of the NS-SLSG slurries in the PG-0.25, PG-0.50, PG-0.75, PG-1.00, PG-1.25, and PG-1.50 groups were 61 min, 57 min, 56 min, 60 min, 58 min, and 62 min, respectively, which were reduced by 10.29%, 16.18%, 17.65%, 11.76%, 14.71%, and 8.82% compared to the PG-0 group. This indicates that the incorporation of NS helps to achieve rapid SLSG setting. The reason is believed to be that NS can act as nucleation sites at the nanoscale, inducing the reaction of silicon-aluminum monomers with Na. + Ca 2+ Polycondensation forms NASH and C-(A)-SH gel networks, promoting the polymerization reaction. The high specific surface area and highly active surface hydroxyl groups of NS accelerate the polymerization kinetics, increasing the exothermic rate in the initial stage of the reaction and leading to accelerated solidification. Further analysis shows that when the NS content exceeds 0.75 wt%, the solidification time of SLSG increases slightly. This is because excessive NS incorporation causes agglomeration due to van der Waals forces, thereby weakening the reactivity of NS.

[0063] As shown above, while increasing the proportion of fine-grained particles significantly shortens the setting time of SLSG slurry, it severely impairs the slurry's flow properties. Using a discontinuous gradation method can reduce both the initial and final setting times compared to the original gradation while maintaining good flow properties. Furthermore, the addition of natural gas (NS) can further accelerate slurry setting, reducing the initial and final setting times by 8.93%–19.64% and 8.82%–17.65%, respectively. Therefore, through the combined regulation of discontinuous gradation and an appropriate amount of NS, the flow properties and setting efficiency of SLSG can be synergistically optimized, providing a material basis for rapid lunar surface construction.

[0064] ③ Rheological property test results: As shown in Table 2, with the removal of coarse-grained particles from the simulated lunar soil and the increase in the proportion of fine-grained particles, the yield stress of the SLSG slurry first decreases and then increases, while the plastic viscosity gradually increases. The yield stress and plastic viscosity of the PA-0 group decrease with the gradual removal of coarse-grained particles. The reason is that: coarse-grained particles generate mechanical interlocking, increasing the internal friction of the SLSG slurry, and at the same time generating a support effect similar to coarse aggregate; removing some coarse-grained particles weakens its skeletal effect, resulting in a decrease in yield stress; and with the increase in the proportion of fine-grained particles, the higher specific surface area of ​​fine-grained particles adsorbs more free water, and at the same time, fine-grained particles fill the pores to form a dense packing structure, which significantly increases the yield stress and plastic viscosity. Further analysis revealed that the yield stress of the PF-0 and PG-0 groups was significantly lower than that of the continuous gradation group. This indicates that the discontinuous gradation has good pumping ability. The reason is that an appropriate amount of coarse particles act as physical isolation points, which disrupts the connection between fine particle networks, weakens the bonding strength between particles, promotes the rolling and relative slippage of particle units in the SLSG slurry, and thus reduces the yield stress and plastic viscosity of the SLSG slurry.

[0065] Table 2 Rheological parameters of SLSG and NS-SLSG slurries

[0066]

[0067] Depend on Figure 3As shown in Table 2 above, the yield stress of NS-SLSG slurry first decreases and then increases with increasing NS content. The yield stress of NS-SLSG slurry in group PG-0 is 4.415 Pa. With increasing NS content, the yield stresses of NS-SLSG slurry in groups PG-0.25, PG-0.50, PG-0.75, PG-1.00, PG-1.25, and PG-1.50 are 2.385 Pa, 2.268 Pa, 2.134 Pa, 2.327 Pa, 2.361 Pa, and 3.654 Pa, respectively, which are 45.98%, 48.63%, 51.66%, 47.29%, 46.52%, and 17.24% lower than those in group PG-0. The reason for this is that under low NS content, NS can fill the pores in SLSG slurry, improve interfacial friction, and promote the relative slippage of slurry particles, thus leading to a decrease in yield stress. With increasing NS content, its high specific surface area leads to a gradual dominance of interparticle interactions, resulting in increased friction within the slurry. Furthermore, the negatively charged NS particles interact electrostatically with simulated lunar soil particles, potentially causing flocculation and agglomeration, which further contributes to a gradual increase in yield stress.

[0068] The plastic viscosity of NS-SLSG slurry gradually increased with increasing NS content. The plastic viscosity of the PG-0 group was 2.106 Pa·s. With increasing NS content, the plastic viscosities of NS-SLSG slurry in the PG-0.25, PG-0.50, PG-0.75, PG-1.00, PG-1.25, and PG-1.50 groups were 2.180 Pa·s, 2.210 Pa·s, 2.267 Pa·s, 2.291 Pa·s, 2.293 Pa·s, and 2.438 Pa·s, respectively, representing increases of 3.51%, 4.94%, 7.64%, 8.78%, 8.88%, and 15.76% compared to the PG-0 group. This is mainly attributed to the fact that the incorporation of NS accelerates the initial polymerization kinetics, and NS is a highly reactive particle that can promote the early polymerization reaction through chemical bonding effect, generating more gel products and enhancing the microstructure strength of SLSG slurry; at the same time, NS adsorbs more free water, resulting in a reduction of the water available for flow in SLSG slurry, making the relative sliding between particles more difficult, thus gradually increasing the plastic viscosity, which is consistent with the flow performance results.

[0069] As shown above, constructing a discontinuous gradation can effectively control the rheological properties of SLSG slurry. SLSG prepared with a discontinuous gradation effectively reduces the yield stress and plastic viscosity compared to a continuous gradation. Adding natural sulfur (NS) can further reduce the yield stress of the slurry. Although it slightly increases the plastic viscosity, at an appropriate dosage, its plastic viscosity is still significantly lower than that of a continuous gradation system dominated by fine-particle size. Using a discontinuous gradation combined with an appropriate amount of NS can achieve better yield behavior control while maintaining a low plastic viscosity, thereby synergistically optimizing the rheological properties of SLSG and providing a material performance basis for lunar pumping and molding processes.

[0070] ④ Mechanical Performance Test Results: Previous studies have shown that the mechanical properties of SLSG initially decrease and then increase with the removal of coarse-grained particles and the increase in the proportion of fine-grained particles in the simulated lunar soil. This indicates that different particle sizes of simulated lunar soil have different effects in the matrix. Coarse-grained particles mainly serve as the framework support, while fine-grained particles strengthen the matrix by increasing reactivity and filling. The synergistic effect of these two factors determines the mechanical properties of SLSG. Therefore, compared to the original gradation, discontinuous gradation can improve the mechanical properties of SLSG. By reasonably controlling the particle size distribution of the simulated lunar soil, the framework structure formed by an appropriate amount of coarse-grained particles can improve the load-bearing capacity of the matrix. Furthermore, the increased specific surface area due to the larger number of fine-grained particles further promotes the geopolymerization reaction. Therefore, the compressive strength of the PG-0 group is superior to that of the PA-0 group. Figure 4 It can be seen that the mechanical properties of NS-SLSG show a trend of first increasing and then decreasing with the increase of NS content. The compressive strength of the PG-0 group is 33.20 MPa. With the increase of NS content, the compressive strengths of NS-SLSG in the PG-0.25, PG-0.50, PG-0.75, PG-1.00, PG-1.25, and PG-1.50 groups are 34.85 MPa, 35.80 MPa, 37.80 MPa, 36.53 MPa, 29.82 MPa, and 31.68 MPa, respectively. The flexural strength of the PG-0 group is 7.50 MPa. With the increase of NS content, the flexural strengths of PG-0.25, PG-0.50, PG-0.75, PG-1.00, PG-1.25, and PG-1.50 groups are 34.85 MPa, 35.80 MPa, 37.80 MPa, 36.53 MPa, 29.82 MPa, and 31.68 MPa, respectively. The flexural strengths of NS-SLSG in the PG-0.50, PG-0.75, PG-1.00, PG-1.25, and PG-1.50 groups were 8.15 MPa, 9.47 MPa, 10.27 MPa, 8.38 MPa, 7.86 MPa, and 6.83 MPa, respectively. This indicates that there is a threshold for the enhancing effect of NS on the mechanical properties of SLSG, with the optimal dosage being 0.75 wt%. At this dosage, the compressive and flexural strengths of SLSG increased by 13.86% and 36.93% respectively compared to PG-0. The improvement effect of NS on the mechanical properties of SLSG is mainly manifested in the presence of a large number of active Si-OH on the NS surface, which can react with [Al(OH)4] dissolved from the simulated lunar soil. -The formation of condensation reactions optimizes the early geopolymerization kinetics and promotes the formation of a three-dimensional aluminosilicate gel network structure. Simultaneously, NS can generate a physical filling effect at the nanoscale, reducing porosity, sealing microcracks, and promoting structural densification. Moisture is an important medium for geopolymerization; NS particles adsorb free water within the system, slowing down the evaporation rate and creating more favorable conditions for the full progress of geopolymerization. However, excessive NS incorporation can easily lead to agglomeration, weakening the nano-reinforcing effect, and the sharp increase in the viscosity of the NS-SLSG slurry can hinder the effective migration of water and ions, thus impeding the geopolymerization process.

[0071] In summary, while a continuous gradation dominated by fine-particle size enables SLSG to achieve optimal mechanical properties, its flow properties and rheological behavior are poor, making it difficult to meet the requirements for lunar surface construction. Through discontinuous gradation design, SLSG's workability is superior to that of discontinuous gradations, while its compressive and flexural strengths are improved compared to the original gradation. Furthermore, the addition of natural sulfur (NS) can further enhance SLSG's compressive strength by 13.86% and flexural strength by 36.93%. Therefore, using a discontinuous gradation combined with an appropriate amount of NS is an effective way to achieve a coordinated improvement in the overall performance of SLSG.

[0072] ⑤ Results of reaction kinetics tests: Figure 5 (a) and (b) are the evolution curves of the heat release rate of SLSG. Figure 5 (c) and (d) are the corresponding cumulative heat release curves. From Figure 5 As shown in (a) and (b), the reaction kinetics curve of SLSG exhibits a continuous exothermic characteristic. This is because its kinetic process mainly includes the depolymerization of silicon aluminum oxide, the dissolution of metal oxide, and the condensation of silicon aluminum monomers. The polymerization reaction process of SLSG is shown in the following equation:

[0073]

[0074]

[0075]

[0076] The depolymerization reaction mainly involves the breaking of chemical bonds in silicon-aluminum oxides under alkaline conditions, requiring additional energy absorption and thus exhibiting an endothermic reaction; however, the dissolution of metal oxides and the condensation of silicon-aluminum monomers are exothermic reactions. Since the intensity and total amount of the exothermic reaction exceed the endothermic effect, the overall reaction kinetics of SLSG still exhibit continuous exothermic behavior. The reaction kinetics of materials such as cement and slag-based polymers typically include an initial reaction period, induction period, acceleration period, deceleration period, and steady-state period, exhibiting two exothermic peaks, corresponding to the initial reaction period and the inflection point of the acceleration-deceleration period, respectively. Analysis... Figure 5(a) It can be seen that in the early kinetic process, SLSG does not have an induction period and acceleration period with low exothermic rate. It mainly includes the initial reaction period, deceleration period and stabilization period. Moreover, the exothermic rate continues to decrease and there is no secondary peak. This is attributed to the fact that high temperature curing provides a large amount of initial energy, which accelerates the geopolymerization reaction rate of SLSG.

[0077] analyze Figure 5 As shown in (a) and (b), the early exothermic rates of PA-0, PE-0, and PG-0 groups are in the order of PG-0 > PE-0 > PA-0. Within the first 0.25 hours, the cumulative exothermic rates of PA-0, PE-0, and PG-0 groups are 0.318 J / g, 0.328 J / g, and 0.366 J / g, respectively. The cumulative exothermic rates of PE-0 and PG-0 groups are 3.14% and 15.09% higher than those of PA-0 group, respectively. The higher exothermic rates and cumulative exothermic rates of PE-0 and PG-0 groups in the early stages are due to their higher proportion of fine-particle size, which accelerates the polymerization reaction efficiency. However, the high viscosity of the slurry in the PE-0 group hinders water migration and diffusion, resulting in a lower initial exothermic rate compared to the PG-0 group. Figure 5 (c) It can be seen that the cumulative heat release of PA-0, PE-0 and PG-0 groups is PE-0 > PG-0 > PA-0. The cumulative heat release of PA-0, PE-0 and PG-0 groups after 48 hours is 24.154 J / g, 28.662 J / g and 28.255 J / g, respectively. The cumulative heat release of PE-0 and PG-0 groups is 18.66% and 16.98% higher than that of PA-0 group, respectively. This shows that the content of fine particles is still the key factor determining the cumulative heat release of SLSG reaction. Although the efficiency of PG-0 group is better than that of PE-0 group in the initial stage of reaction, the total cumulative heat release is still lower than that of PE-0 group.

[0078] Depend on Figure 5As shown in (b) and (d), the maximum exothermic rates of the PG-0.75 and PG-1.50 groups in the initial stage of the reaction were 1.752 mW / g and 1.843 mW / g, respectively, which were 19.18% and 25.37% higher than those of the PG-0 group. The cumulative heat release in the first 0.25 h were 0.396 J / g and 0.406 J / g, respectively, which were 8.20% and 10.93% higher than those of the PG-0 group (0.366 J / g). The initial exothermic rate and cumulative heat release of SLSG in the first 0.25 h after the addition of NS were higher than those of the PG-0 group, indicating that the addition of NS significantly accelerated the reaction kinetics of SLSG in the initial stage. The reason for this is that, because the Al-O bond energy is lower than that of the Si-O bond, Al sites dissolve before Si sites in the early stages of the polymerization reaction, resulting in a lower Si content in the gel network. Meanwhile, the highly active surface of NS has a large number of silanol groups (Si-OH), providing additional reaction sites and silicon sources, and serving as nucleation centers to effectively promote the formation and cross-linking of silicon-aluminum oligomers. Therefore, NS accelerates the early polycondensation process, leading to a significant increase in the exothermic rate.

[0079] Further analysis Figure 5 (c) It can be seen that the addition of NS reduced the exothermic rate and cumulative heat release in the later stage of the SLSG reaction. The cumulative heat release of the PG-0.75 and PG-1.50 groups after 48 hours was 21.121 J / g and 21.347 J / g, respectively, which were 25.25% and 24.45% lower than that of the PG-0 group. This phenomenon is closely related to the sustained endothermic effect of the depolymerization reaction. Existing studies have shown that the introduction of NS reduces the moisture recovery rate of SLSG within 24 hours, allowing the system to maintain a higher internal humidity for a longer period of time, thereby prolonging the duration of the depolymerization reaction, enhancing its endothermic effect, and ultimately reducing the overall heat release during the reaction process.

[0080] ⑥ Microstructure test results:

[0081] i. FTIR

[0082] like Figure 6 The figure shows the FT-IR test results for the PE-0, PG-0, PG-0.75, and PG-1.50 groups. The results indicate that particle size distribution and NS doping did not significantly affect the chemical structure of SLSG. The experimental groups showed a wavenumber of approximately 988 cm⁻¹. -1Strong absorption peaks were observed at all locations, corresponding to the asymmetric stretching vibrations of the Si-OT (T=Si / Al) bond. The peak intensity can be used to assess the degree of geopolymerization of SLSG. The peak intensities for each experimental group were, in descending order: PE-0 > PG-0.75 > PG-0 > PG-1.50. This indicates that increasing the proportion of fine-grained particles and incorporating an appropriate amount of NS promoted the formation of the gel phase, a trend consistent with its mechanical properties. The reasons for this are as follows: fine-grained particles, with their larger specific surface area, provide a more sufficient contact interface for the geopolymerization reaction, promoting the depolymerization process of the simulated lunar soil; the introduction of an appropriate amount of NS can provide nucleation sites through highly active surfaces, accelerating gel phase precipitation, and simultaneously participating in the construction of Si-OT bonds in the geopolymerization gel network through chemical bonding effects, increasing the amount of gel phase formed and the crosslinking density. However, excessive NS incorporation reduces its reinforcing effect due to agglomeration, leading to a decrease in its ability to promote the geopolymerization reaction.

[0083] Figure 6 Medium wave number 600-800cm -1 The absorption peaks in the specified range correspond to the bending vibrations of the Si-O-Al bonds, indicating that aluminum-bearing minerals in simulated lunar soil dissolved under alkaline conditions, with Al atoms replacing Si atoms to participate in coordination and construct a three-dimensional gel network, thus confirming the formation of C(N)-ASH gel. The wavenumber is approximately 735 cm⁻¹. -1 With 460 cm -1 The absorption peak at 1641 cm⁻¹ corresponds to the symmetrical stretching vibrations of Si-O-Si and O-Si-O bonds in the quartz phase, indicating that a quartz phase that is difficult to dissolve fully still exists in SLSG. -1 With 3437cm -1 The absorption peak at the point is attributed to the stretching and bending vibrations of hydroxyl groups, indicating that water molecules are fully connected to the three-dimensional gel network structure. Further analysis shows that the hydroxyl absorption peak intensity of the PE-0 group is higher than that of other experimental groups. This also indicates that the increase in the proportion of fine-sized particles promotes the retention of water bound to the geopolymer gel, which is beneficial to enhancing the stability of the gel network.

[0084] ii. XRD

[0085] like Figure 7The XRD diffraction patterns of the PE-0, PG-0, PG-0.75, and PG-1.50 groups are shown. The phase composition of their SLSGs mainly includes undissolved mineral phases from the simulated lunar regolith, such as olivine (Mg₂SiO₄), orthopyroxene (Mg,Fe)₂Si₂O₆, anorthite (CaAl₂Si₂O₈), and quartz (SiO₂), as well as zeolite phases formed under high-temperature alkaline conditions. The diffraction patterns show a broad diffraction peak at approximately 30.0° (2θ), corresponding to the NASH and C-(A)-SH gels generated by the geopolymerization reaction, indicating that the simulated lunar regolith particles formed an amorphous three-dimensional gel network after alkaline excitation.

[0086] analyze Figure 7 (b) It can be seen that the diffraction peak intensities of anorthite are in the order PE-0 < PG-0.75 < PG-1.50 < PG-0. This is attributed to the promoting effect of fine-grained particles and NS on the geopolymerization reaction. Since the PE-0 group has a higher proportion of fine-grained particles, the contact area with the alkali activator is increased, promoting the dissolution of anorthite. The incorporation of NS promotes the forward geopolymerization reaction by accelerating reaction kinetics and dissolving anorthite; however, excessive NS incorporation will weaken its reinforcing effect due to agglomeration. Therefore, the anorthite diffraction peak intensity of PG-1.50 is higher than that of the PG-0.75 group. Further analysis... Figure 7 (b) It can be seen that the PE-0 and PG-0 groups showed diffraction peaks of orthorhombic pyroxene at approximately 26.6–26.8° (2θ), while PG-0.75 and PG-1.50 did not produce such diffraction peaks. This indicates that the addition of NS promoted the complete depolymerization of orthorhombic pyroxene, which further confirms the promoting effect of NS on the geopolymerization reaction. The diffraction peaks at approximately 27.6–28.0° (2θ) are attributed to the quartz phase. It can be found that all experimental groups showed relatively obvious quartz diffraction peaks. This is because the crystal structure of quartz is relatively stable and difficult to be fully dissolved by alkaline activators.

[0087] Further observation revealed that sodalite (Na8Al6Si6O) was detected at approximately 24.5° (2θ). 24 The diffraction peaks of (OH)2(H2O) indicate that sodalite is an aluminum-rich zeolite phase, and its formation mechanism originates from Na. + The zeolite phase reacts with locally formed silicate oligomers and aluminum monomers, subsequently crystallizing and precipitating. The formation of the zeolite phase indicates that the simulated lunar soil particles underwent geopolymerization. However, the high crystallinity of the silica-alumina raw materials in the simulated lunar soil limited the efficiency of their transformation to the gel phase, causing some reaction products to precipitate in the form of the zeolite phase.

[0088] iii. SEM

[0089] like Figure 8The image shows the SEM microstructure of the PE-0, PG-0, PG-0.75, and PG-1.50 groups at 2000x magnification. The results indicate that the PE-0 group is dominated by a dense gel layer with only a small number of gel pores and microcracks. This is because the PE-0 group has a higher proportion of fine-sized particles, whose larger specific surface area significantly increases the reaction interface with the alkali activator. This allows for a more complete polymerization reaction, effectively filling the pore defects with the gel product, which is consistent with the higher mechanical properties of the PE-0 group.

[0090] analyze Figure 8 (b) It can be seen that the PG-0 group has a relatively loose structure with many pores and cracks. This indicates that although the mechanical properties of SLSG prepared by controlling the particle size distribution and using a discontinuous gradation of coarse-fine particle size composites are better than the original gradation, its microstructural integrity is still lower than that of the PE-0 group dominated by fine particle size. This further indicates that fine particle size plays a dominant role in the densification of the structure. Observation Figure 8 (b) It can be seen that the PG-0 group produces through cracks. As a primary defect, the through cracks can rapidly expand and extend under load, causing the bearing capacity of the SLSG to drop sharply, which is consistent with its low mechanical properties.

[0091] analyze Figure 8 (c) It can be seen that the microstructure of SLSG is significantly improved after incorporating an appropriate amount of NS compared to the PG-0 group, forming a smooth, uniform, and dense gel structure similar to the PE-0 group. This is attributed to the dual enhancement effect of NS at the physical and chemical levels: NS fills pores, seals microcracks, and prevents crack penetration at the nanoscale to reduce defects in SLSG; at the same time, through its highly active surface-optimized polymerization reaction, it promotes sufficient depolymerization of simulated lunar soil and increases the gel content of the product, thereby significantly improving the microstructure of SLSG. Further analysis shows that the PG-0.75 group is mainly composed of a dense gel layer, but a small number of weak gel particles are still distributed on its surface. This is because the effect of a small number of agglomerated nanoparticles on promoting the polymerization reaction is limited, resulting in the formation of some incompletely polymerized weak gel particles. However, due to their low agglomeration content, the impact on the overall material properties is small.

[0092] analyze Figure 8 (d) It is evident that the PG-1.50 group exhibits both a weak gel layer and a dense gel layer, forming a distinct interfacial transition zone (ITZ). This is due to the severe agglomeration caused by excessive NS incorporation. The aggregates adsorb silica-alumina monomers, forming a weak gel layer with a low degree of polymerization, leading to microstructural inhomogeneity and consequently, a significant ITZ. Existing research indicates that the presence of ITZ significantly reduces the fracture toughness of the material, which is consistent with the deterioration of the mechanical properties in the PG-1.50 group.

[0093] iv. EDS

[0094] To reveal the influence mechanism of particle size distribution and NS doping on the formation of SLSG gel phase, no less than 10 detection points were randomly selected in the relatively dense region of SLSG for EDS analysis. After taking the arithmetic mean of the test results of each element, the atomic ratios of Si / Al and Ca / Si were further obtained. Figure 9 Table 3 shows the typical EDS test results for the PE-0, PG-0, PG-0.75 and PG-1.50 groups. The table also shows the Na, Al, Si and Ca contents and the atomic ratio of each element in each experimental group.

[0095] Table 3 EDS Elemental Test Results

[0096]

[0097] Comparative analysis Figure 9 As shown in (a), (b), and Table 3, the Si, Al, and Ca contents in the PE-0 group were 15.44%, 6.92%, and 2.93%, respectively, representing increases of 52.27%, 16.11%, and 66.48% compared to the PG-0 group. This confirms the promoting effect of fine-particle size on the depolymerization reaction, as fine-particle size promotes the dissolution and condensation of silica, aluminum, and calcium minerals in the simulated lunar soil to form CASH gel. However, the Na content in the PE-0 group was 5.37%, a decrease of 55.06% compared to the PG-0 group. This is because Si, Al, and Ca mainly come from the depolymerization and dissolution of the simulated lunar soil, and can be partially supplemented by SS and CH; while Na depends on the external introduction of SH and SS. Therefore, the higher proportion of fine-particle size in the PE-0 group significantly increased the dissolution of Si, Al, and Ca components, resulting in a decrease in the relative proportion of Na in the system.

[0098] Comparative analysis Figure 9 As shown in (b), (c) and Table 3, the Si, Al, and Ca contents of the PG-0.75 group were 17.33%, 7.99%, and 3.68%, respectively, representing increases of 70.91%, 34.06%, and 109.09% compared to the PG-0 group. The Si / Al and Ca / Si ratios of the PG-0.75 group were 2.17 and 0.21, respectively, representing increases of 27.65% and 23.53% compared to the PG-0 group. These results indicate that the introduction of NS effectively promoted the geopolymerization reaction. Its surface active sites adsorbed aluminum monomers and alkali metal ions, promoting the formation of NASH and CASH gels, thereby significantly increasing the content of key elements in the gel network backbone.

[0099] Comparative analysis Figure 9As shown in (c), (d) and Table 3, excessive NS doping led to a decrease in the elemental content of the system. The Si, Al, and Ca contents of the PG-1.50 group were 14.67%, 7.75%, and 2.69%, respectively, which were 15.35%, 3.00%, and 26.90% lower than those of the PG-0.75 group. The Si / Al and Ca / Si ratios of the PG-1.50 group were 2.17 and 0.21, respectively, which were 12.90% and 14.29% lower than those of the PG-0 group. This is because excessive NS doping weakens the specific surface area due to particle agglomeration, reduces the content of surface active sites, and limits the enhancing effect of NS in the geopolymerization reaction.

[0100] 6. Conclusion

[0101] NS-SLSG was prepared by combining non-continuously graded TJ-1 simulated lunar soil with NS. With increasing NS content, the yield stress of NS-SLSG initially decreased and then increased, while the plastic viscosity continuously increased, the fluidity gradually decreased, the setting time initially decreased and then increased, and the compressive and flexural strengths initially increased and then decreased. The optimal NS content was 0.75 wt%. At this content, the compressive and flexural strengths of NS-SLSG were 37.80 MPa and 10.27 MPa, respectively, representing increases of 13.86% and 36.93% compared to the baseline group without NS. The yield stress decreased by 51.66%, and the initial and final setting times decreased by 19.64% and 17.65%, respectively. The maximum exothermic rate and cumulative heat release of SLSG and NS-SLSG were significantly lower than those of geopolymer materials such as fly ash and slag. Increasing the proportion of fine-particle size accelerated the reaction kinetics of SLSG and increased the cumulative heat release; however, an excessively high proportion of fine-particle size affected moisture migration, resulting in weaker initial reaction kinetics compared to the PG-0 group. The incorporation of NS significantly accelerates the initial reaction kinetics, but NS adsorption of water prolongs the depolymerization reaction, promotes a more complete geopolymerization reaction, and reduces the total cumulative heat release. The high specific surface area of ​​fine-diameter particles in the TJ-1 simulated lunar soil promotes geopolymerization and increases the packing density. The incorporation of an appropriate amount of NS can fill pores and promote gel network development through nucleation and chemical bonding effects. Increasing the proportion of fine-diameter particles and incorporating an appropriate amount of NS can both promote the dissolution of mineral phases in the simulated lunar soil, increase the content of Si, Al, and Ca elements in the gel network, optimize the Si / Al and Ca / Si atomic ratios, and promote the formation of Si-OT chemical bonds, thereby promoting geopolymerization and densifying the microstructure.

[0102] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A simulated lunar soil base polymer synergistically enhanced by particle size distribution and nano-silica, comprising a simulated lunar soil precursor, nano-silica, a composite alkali activator, and water, characterized in that, The simulated lunar soil precursor is discontinuously graded TJ-1 simulated lunar soil, which is a gradation system in which medium-sized particles in the range of 0.25 mm to 1 mm are removed, and only coarse particles with a particle size > 1 mm and fine particles with a particle size < 0.25 mm are retained. The nano-silica was added in the form of an aqueous dispersion, and the dosage of nano-silica was 0.25 wt% to 1.50 wt%, based on the mass of the discontinuously graded TJ-1 simulated lunar soil. The composite alkali activator is composed of sodium hydroxide, calcium hydroxide, and sodium silicate nonahydrate. Based on the mass of the discontinuously graded TJ-1 simulated lunar soil, the dosage of sodium hydroxide is 10 wt%, the dosage of calcium hydroxide is 6 wt%, and the dosage of sodium silicate nonahydrate is 6 wt%. The water-cement ratio of the polymer in the simulated lunar soil base is 0.27, and the total water consumption includes the water contained in the nano-silica aqueous dispersion and the composite alkali activator.

2. The simulated lunar soil base polymer with synergistic enhancement of particle size distribution and nano-silica as described in claim 1, characterized in that, The nano-silica is based on the mass of the discontinuously graded TJ-1 simulated lunar soil, with an addition amount of 0.75 wt%.

3. The simulated lunar soil base polymer with synergistic enhancement of particle size distribution and nano-silica as described in claim 1, characterized in that, The aqueous dispersion of nano-silica has a solid content of 15%, wherein the particle size of the nano-silica is 30 nm.

4. The simulated lunar soil base polymer with synergistic enhancement of particle size distribution and nano-silica as described in claim 1, characterized in that, The purity of the sodium hydroxide is ≥99%, the purity of the calcium hydroxide and sodium silicate nonahydrate is ≥95%, and the modulus of the sodium silicate nonahydrate is 1.03±0.

03.

5. A method for preparing a simulated lunar soil-based polymer synergistically reinforced by particle size distribution and nano-silica, characterized in that, The method for preparing the simulated lunar soil-based polymer according to any one of claims 1 to 4 comprises the following steps: S1. Based on the mass of the non-continuously graded TJ-1 simulated lunar soil, take 10wt% sodium hydroxide, 6wt% calcium hydroxide, and 6wt% sodium silicate nonahydrate, mix with some water and stir continuously to obtain a uniform composite alkali activator solution. S2. Add the discontinuously graded TJ-1 simulated lunar soil to the cement mortar mixer and mix at low speed to disperse the particles evenly. S3. Based on the mass of the discontinuous graded TJ-1 simulated lunar soil, take 0.75wt% of the nano-silica aqueous dispersion, mix it evenly with the remaining water, and then slowly add it to the mixer along with the composite alkali activator solution. Mix it thoroughly with the discontinuous graded TJ-1 simulated lunar soil and continue to stir at low speed to obtain a uniform geopolymer slurry. The total amount of water added meets the requirement of a polymer water-cement ratio of 0.

27. S4. The geopolymer slurry is injected into the mold and vibrated to remove air. After high-temperature curing and demolding, it is cured at the same temperature until the target age is obtained to obtain the target simulated lunar soil base polymer.

6. The method for preparing a simulated lunar soil base polymer synergistically reinforced by particle size distribution and nano-silica according to claim 5, characterized in that, In step S1, the stirring time is 20 minutes, and a uniform and transparent composite alkali activator solution is obtained after stirring.

7. The method for preparing a simulated lunar soil base polymer synergistically reinforced by particle size distribution and nano-silica according to claim 5, characterized in that, In both steps S2 and S3, the stirring speed is 140±5 r / min; the stirring time in step S2 is 1 min, and the stirring time in step S3 is 4 min.

8. The method for preparing a simulated lunar soil base polymer with synergistic enhancement of particle size distribution and nano-silica according to claim 5, characterized in that, In step S4, the high-temperature curing temperature is 100℃. After curing at this temperature for 24 hours, the product is demolded and then cured at 100℃ for 7 days.

9. The method for preparing a simulated lunar soil base polymer with synergistic enhancement of particle size distribution and nano-silica according to claim 5, characterized in that, In step S4, the vibration frequency of the tamping operation is 60 times / minute, and the vibration is repeated 25 times until no visible air bubbles are visible in the slurry.

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