Inorganic element incorporated high uniform mineral polymer and method for preparing the same

Abstract

This invention discloses a highly uniform mineral polymer incorporating inorganic elements and its preparation method. The preparation method of this invention involves mixing in a liquid state and molding at room temperature, which facilitates the homogenization of the incorporated elements in the matrix. The surface dissolution-gel rearrangement process in the mineral polymerization reaction increases the connectivity of the gel network and forms a gel network that restricts cation movement, thereby reducing element segregation during the curing process and improving the uniformity of the resulting sample. The optimized sample, verified by LA-ICP-MS analysis, exhibits good internal homogeneity, with a relative standard deviation of 3.82%–7.35% in LA-ICP-MS measurements, comparable to the measurement accuracy of NIM-4 samples prepared by the traditional fused glass method. The basic unit of the mineral polymerization reaction in this invention is [SiO4]. 4‑ and [AlO4] 5‑ The basic building blocks are the same as those of natural minerals, which helps to achieve matrix matching with actual samples. This is beneficial for subsequent practical analysis scenarios, providing an indication of rare earth mineral quantification and mineral deposit geology.

Description

TECHNICAL FIELD

[0001] The present application relates to an inorganic element-doped high-uniform mineral polymer and a preparation method thereof, and belongs to the technical field of 3D printing and mineral polymer. BACKGROUND

[0002] Rare earth materials, as a kind of strategic mineral resources with special performance, are widely used in military, industry, high-tech and other fields, and are called "industrial vitamin". Since the 1950s of last century, by using the relatively traditional geochemical research techniques of rare metal and rare earth ore deposit, China has obtained a large amount of data in the field of rare earth reserves and mineralization research, and thus established China's international position in rare earth mineral resources. However, after decades of exploration and exploitation, the mineral resources with shallow burial, large scale and simple prospecting conditions are becoming less and less. With the rapid development of China's economy, the demand for mineral resources is increasing, and the strategic resource status of rare earth materials as "China's advantage small metal" is increasingly prominent.

[0003] In recent years, modern micro-area in-situ analysis techniques represented by large-scale secondary ion mass spectrometry (SIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) can reveal important information of subtle changes hidden by conventional bulk analysis, and become the core technical support for solving many major scientific problems. However, with the development of in-situ micro-area analysis technology, the lack of micro-area analysis standard materials has become a bottleneck restricting the further development of related research, and has attracted widespread attention in the scientific community. In the development of micro-area analysis standard materials, the main challenges include sample matrix applicability, sample micro-area uniformity and accurate value of micro-area standard materials. In the past ten years, micro-area in-situ analysis technology has been widely valued by domestic and foreign geology experts as a new means in the exploration and utilization of strategic mineral resources. However, due to the lack of micro-area in-situ standard materials and the lack of standard material development technology, the development of related research is facing a series of technical bottlenecks, and it is urgent to establish in-situ micro-area analysis technology with higher accuracy and clearer traceability, and to develop micro-area analysis standard materials, to provide more effective methodological support for the exploration and utilization of strategic mineral resources.

[0004] Geopolymer is a kind of gel polymer prepared by using natural minerals or solid waste and artificial silicon-aluminum compounds as raw materials. The mineral polymerization reaction consumes water in the alkali activator, partially dissolves the solid silicate and aluminate raw materials, and generates silicon and aluminum tetrahedrons. At high pH value, the amorphous silicate and aluminate dissolves quickly, forming a supersaturated silicate and aluminate solution, and forming a gel. After gelation, the connectivity of the gel network increases, and the gel network is rearranged to form a new three-dimensional silicate and aluminate network. The gel forms a large network structure through polycondensation, and the process releases the water consumed in the dissolution process. The rearrangement process of the gel network determines the microstructure of the generated polymer. The structure composed of [SiO4] 4- and [AlO4] 5- tetrahedrons is similar to that of natural minerals, which is more conducive to matching the matrix of actual samples.

[0005] In addition, 3D printing, as a new forming technology, is praised as the "third industrial revolution" and is rapidly receiving more and more attention. Through slicing processing of a digital model, materials are layered and stacked to form a solid model. With this stacking method, 3D printing has great advantages in manufacturing complex structural components. Based on its high utilization rate of raw materials, customized forming, and lower cost, it has a wide application prospect. Its basic principle can be summarized as layer-by-layer additive manufacturing. This process divides the traditional macro-forming process into a simultaneous forming process at each point and each surface, which helps to realize micro-control of the forming process and greatly improves the uniformity of the formed sample. SUMMARY

[0006] The purpose of the present application is to provide an inorganic element-doped high-uniformity geopolymer and a preparation method thereof. By using the mineral polymerization technology and artificially adding target elements, the present application imitates the element composition and distribution of common silicate and aluminate minerals to prepare block standard materials of the corresponding system, so as to match the complex matrix of target minerals. Combined with 3D printing technology, the present application realizes the customized forming process of the above-mentioned standard materials and realizes the automatic production of the standard materials.

[0007] The preparation method of the inorganic element-doped high-uniformity geopolymer provided by the present application comprises the following steps:

[0008] S1, determining the amount of each raw material according to the equation group shown in formula (1);

[0009]

[0010] In the formula, n(NaOH) represents the molar amount of sodium hydroxide, n(Waterglass) represents the molar amount of water glass, n(metakaolin) represents the molar amount of metakaolin, n(Na) / n(Al) represents the molar ratio of sodium (Na) element and aluminum (Al) element in the system, and n(Si) / n(Al) represents the molar ratio of silicon (Si) element and aluminum (Al) element in the system.

[0011] M represents the modulus of alkali activator, which is used to describe the molar ratio of Si and Na oxides in the alkali activator, and the calculation formula is as follows:

[0012] M = n(SiO2) / n(Na2O)

[0013] S2, under the condition of stirring, the alkali activator solution is added to the mixture of metakaolin and target element mother liquor in multiple times, and the obtained slurry is solidified.

[0014] In the method, by giving three key ratios of M, n(Na) / n(Al) and n(Si) / n(Al), four unique component ratios can be solved, and the weighing mass can be calculated according to the relative molecular mass. In addition, the amount of pure water (MilliQ) added is used to simulate the mass of water introduced by the element mother liquor, which needs to be calculated by the sample drying loss, and the target concentration.

[0015] Preferably, n(Na) / n(Al) = 1.28, n(Si) / n(Al) = 2.50, and M = 1.83.

[0016] In the preparation method, the target elements include scandium, yttrium and lanthanide elements, including lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

[0017] In the preparation method, in step S2, after the alkali activator solution is added, stirring is carried out at a speed of 400-600 r / min for 26-38 h.

[0018] In the preparation method, in step S2, before the solidification, the slurry is subjected to degassing treatment; preferably vacuum degassing.

[0019] The time of the vacuum degassing is 15 min, and the vacuum degree is below 0.01 Mpa.

[0020] Through the degassing treatment, the defects such as air bubbles introduced in the stirring process of the sample are removed, so as to reduce the air voids in the sample after solidification.

[0021] By comparing the degassing effects of vacuum degassing, ultrasonic degassing and static methods, it is found that the vacuum degassing effect is much better than the other two degassing methods, and it is speculated that this phenomenon is related to the small particle size of the raw material. For similar powders, the main obstacle in the wetting process is the adsorption of gas on the surface of the powder. Therefore, under reduced pressure, the gas on the surface of the powder is discharged and completely wetted. This avoids the agglomeration of particles during the solidification process, thereby greatly improving the element uniformity of the solidified sample. Therefore, it is necessary to carry out the corresponding vacuum degassing (dissolution) step during the two processes of discharging gas from the powder sample, i.e. the mixing stage of the element mother liquor and the metakaolin powder and the sample after stirring.

[0022] In the preparation method of the present application, in step S2, the solidification method is 3D printing forming, preferably direct writing forming process.

[0023] The 3D printing forming is characterized by additive manufacturing, that is, by accumulating materials point by point, line by line and layer by layer on the substrate and solidifying on the printed sample, a three-dimensional entity is finally formed. When applied to the mineral polymerization system, it is different from the traditional integral injection molding, but is changed to form solid units one by one. The original centimeter-scale long-time solidification scale is divided into multiple short-time forming processes with a scale of hundreds of microns, thereby inhibiting the differentiation between the surface layer and the inner layer of the sample, and achieving the uniformity of the whole sample.

[0024] Based on the reaction mechanism of the mineral polymerization system involved in the present application, the slurry direct writing forming technology (DIW) can meet the demand of 3D printing. DIW technology, as a common technology for 3D printing ceramics, is to extrude the ceramic slurry from the extrusion device through the nozzle at the specified position, and move on the two-dimensional plane according to the path setting. After completing the slice pattern of this layer, the material cylinder is raised or the platform is lowered to the appropriate position for the next layer of printing. Repeat this process until the printing is complete, and a three-dimensional entity is obtained.

[0025] The whole process of direct writing forming process depends on the rheological properties of the slurry, that is, the slurry is transformed into a fluid during extrusion due to external force, and quickly "solidifies" to maintain the shape after extrusion, so as to maximize the retention of the forming shape and separate the extruded part from the subsequent slurry. And in order to make the most of the characteristics of the mineral polymerization system, the present application adopts SYNO 4070 ceramic printer (Henan Yuanchuang Gaokeli Technology Co., Ltd.), which has the function of environmental heating, which can open the internal hot air circulation during the solidification process, so that the extruded slurry can lose water faster. And the extrusion head part is equipped with a motor-driven stirring screw, which can provide shear force to temporarily reduce the kinematic viscosity of the gel system, so as to extrude more smoothly.

[0026] The 3D printing forming is performed within 4 hours after the slurry is stirred for at least 28 hours in the preparation method.

[0027] In the initial stage of the mineral polymerization reaction, the tetrahedron is gradually dissolved by the alkali activator in the system to form a loose gel network, and as the amount of dissolution gradually increases, the connectivity of the gel network is enhanced and the free water is reduced, causing the viscosity to gradually increase, and finally solidifying. In order to quantitatively describe the change of the rheological property of the slurry in this process, so as to determine the appropriate printing time and viscosity, the present application uses the ViscoQC100-H viscometer produced by Anton Paar to monitor the change of the sample viscosity with time, uses a V73 paddle, and the maximum test viscosity is 20.48 pa.s (200 r / min -1 ), and the accuracy is one thousandth. It is found through experiments that in order to make the slurry maintain a proper viscosity in the extrusion head without leakage, and at the same time to make as many raw material particles as possible to be dissolved, the most suitable printing starting time should be controlled between 26 hours and 38 hours after the sample is stirred, and after that, the viscosity of the sample will sharply increase, and it will be difficult to maintain the fluidity until the printing is completed.

[0028] In the preparation method of the present application, the uniformity of the mineral polymer is tested by using the LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometer) method.

[0029] The LA-ICP-MS can directly analyze solid samples under quasi-non-destructive conditions and obtain in-situ element concentration information with certain spatial resolution. In order to study the element composition in the nodule sample, the present application uses a 193 nm and 213 nm laser ablation system to analyze the total element content.

[0030] The present application is based on the mineral polymerization theory, combined with 3D printing forming technology, with the laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) measurement results as the evaluation standard, supplemented by laser particle size scattering, X-ray diffractometer, thermal gravimetric analyzer and other auxiliary characterization means, a series of related researches on the raw material composition, pretreatment process, important ratio parameters, mixing scheme and curing process parameters in the mineral polymerization system are carried out. The research method based on the mineral polymerization technology for developing the standard sample is established, the 3D printing of the mineral polymer with the target element added artificially at room temperature is realized, and the uniformity of the added element can meet the needs of micro-area in-situ analysis. The micro-area element concentration imaging of the prepared sample is carried out, and the results show that the micro-area uniformity is good, the relative standard deviation in the LA-ICP-MS measurement is 3.82%-7.35% (after internal standard correction), and the measurement precision reaches the same level as that of the standard sample prepared by the melting glass method. And according to the measurement requirements, the related measurement method is designed, and the measurement time is shortened.

[0031] Specifically, the present application has the following beneficial technical effects:

[0032] The present application provides a kind of inorganic element incorporated high uniform mineral polymer and its preparation method, its reaction condition is mixed in liquid state and is formed at normal temperature, it is helpful to mix in element in matrix Mix evenly. The surface dissolution-gel rearrangement process in mineral polymerization reaction makes the connectivity of gel network increase, and forms the gel network that limits the movement of cation, so as to weaken the element segregation in the curing process. The above advantages make the uniformity of the final cured sample be improved, the sample (GP-M4-LV-FINAL, example 3) after process route optimization is verified by LA-ICP-MS analysis that the internal uniformity of sample is good, the relative standard deviation in the LA-ICP-MS measurement is 3.82%-7.35% (after internal standard correction), and the measurement precision is at the same level as that of the NIM-4 sample prepared by the traditional melting glass method.

[0033] The basic unit of mineral polymerization reaction of the present application, [SiO4] 4- and [AlO4] 5- The same as the basic composition unit of natural mineral, it is beneficial to match with the matrix of actual sample. It is beneficial to subsequent actual analysis scene, for the quantitative analysis of rare earth mineral and the indication of ore deposit. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is the image and signal fluctuation of nodule in GP-3 in example 1 of the present application in the process of LA-ICP-MS analysis.

[0035] Figure 2 is the appearance of GP-2 sample in Example 1 of the present application.

[0036] Figure 3 is the state of slurry after adding alkali activator in Example 2 of the present application.

[0037] Figure 4 is the surface morphology of samples cured by three degassing methods in Example 2 of the present application.

[0038] Figure 5 is the line scan signal fluctuation of three degassing methods and NIM-4 in Example 2 of the present application.

[0039] Figure 6 is the longitudinal section of cured sample in Example 2 of the present application.

[0040] Figure 7 is the LA-ICP-MS signal fluctuation of samples in Vacuum group in Example 2 of the present application.

[0041] Figure 8 is the appearance of SYNO 4070 ceramic printer.

[0042] Figure 9 is the photo of 3D printer accessories (a) extrusion head (b) stirring screw.

[0043] Figure 10 is the coating and curing of GP-M1 to M10 in Example 2 of the present application.

[0044] Figure 11 is the signal fluctuation of La element in LA-ICP-MS analysis of GP-M1 to M10 slurry in Example 2 of the present application.

[0045] Figure 12 is the change of slurry viscosity with stirring time in Example 2 of the present application.

[0046] Figure 13 is the gcode slicing schematic diagram in Example 2 of the present application.

[0047] Figure 14 is the LA-ICP-MS signal stability of GP-M4-HV and GP-M4-LV in Example 2 of the present application.

[0048] Figure 15 is the sample ring and chimeric sample in Example 2 of the present application.

[0049] Figure 16 is the sample uniformity analysis strategy schematic diagram in Example 3 of the present application.

[0050] Figure 17 is the whole micro-area imaging figure of GP-M4-LV-FINAL sample in Example 3 of the present application.

[0051] Figure 18 is the local micro-area imaging figure of GP-M4-LV-FINAL sample in Example 3 of the present application. DETAILED DESCRIPTION

[0052] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0053] The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0054] The following examples use 193 nm and 213 nm laser ablation systems for full element content analysis. The 213 nm laser ablation system is LSX213-G2+ from the United States CETAC Technologies Company, which uses a five-fold frequency Nd:YAG laser to excite 213 nm laser, is equipped with a HelEx sample cell, and is attached with a CCD camera concentric cyclone extraction sample cup that can move to extract ablation aerosol in a large sample cell of 260x260mm, with a maximum output of 20Hz, 20.48J cm -2 , and a custom sample cell prepared by 3D printing can simultaneously measure multiple non-standard shape samples, and the sample cell allows transmission of light to pass through, so that part of the sample can maintain color without distortion under the CCD; the 193 nm laser ablation system is RESOlution M-50-LR—Coherent 102 (100Hz maximum repetition rate). The laser pulse width is 20ns, the pulse output energy is up to 200mJ; the laser wavelength is 193nm, the frequency is 1-20Hz, and can be continuously adjusted online, and the energy density is up to 30J cm -2 .

[0055] The laser ablation system is preheated for 20 minutes before use, during which the sample cup and ablation cell are vacuumed and purged with high-purity helium. Before analyzing the sample, the NIST610 glass standard is used to tune the instrument to obtain the maximum signal strength value and the smallest relative standard deviation (RSD) of the elements to be measured (mainly Sc, Y, La and other rare earth elements).

[0056] Example 1, determination of the ratio of mineral polymer

[0057] 1. Calculation of the ratio of the curing system

[0058] Al in the mineral polymer is provided only by metakaolin; Si in the mineral polymer is provided by metakaolin, water glass solution, quartz (part of the formula); Na in the mineral polymer is provided by water glass solution, sodium hydroxide; H2O in the mineral polymer is provided by sodium hydroxide, water glass solution, element mother liquor, pure water (part of the formula).

[0059] Therefore, according to the respective content of each atom, Table 1 can be listed:

[0060] Table 1: Element contribution table (in mol)

[0061] Relative molecular mass (M) 39.998 400 60.08 222.12 18.016 NaOH water glass quartz metakaolin MilliQ Na 1 1.368 - - - Si - 1.764 0.968 1.940 - Al - - - 1.462 - H2O 0.5 14 - - 1

[0062] In the table, NaOH, water glass, quartz, metakaolin, MilliQ represent sodium hydroxide, water glass, quartz powder, metakaolin powder, and additional pure water, respectively. In the test phase of the curing system, the element solution is not added temporarily.

[0063] Therefore, when designing the formula of the present application, it is assumed that n(Al) = 1 is the only source, combined with the calculation formula of M value, and the following equation group is obtained:

[0064]

[0065] By giving three key ratios of M, n(Na) / n(A), and n(Si) / n(Al), the unique four component ratios can be solved, and the weighing mass can be calculated according to the relative molecular mass. In addition, the amount of pure water (MilliQ) added is used to simulate the mass of water introduced by the element mother liquor, which needs to be calculated by the sample drying water loss and the target concentration.

[0066] 2. Mineral polymer curing formula research

[0067] According to equation group (1), the corresponding mineral polymer formula can be designed within the common formula key parameter range, and then three formulas are tried and tested, with the weighing results as follows, respectively marked as GP-1, GP-2 and GP-3, and the specific weighing data is shown in Table 2:

[0068] Table 2: Adding amount of each component of the prepared mineral polymer

[0069]

[0070] The three samples respectively simulate the possible situations that may be encountered in formula adjustment within the common ratio range. GP-1 represents the case of high silicon aluminum ratio and high alkalinity, GP-2 represents the case of low silicon aluminum ratio and high alkalinity, and GP-3 represents the case of low alkalinity.

[0071] After weighing each component of the three sample groups and adding them to plastic beakers, the samples were stirred using a dual-blade screw electric mixer at a speed of 700 rpm (500 rpm for GP-3 to prevent splashing) for more than 2 hours. After aging for more than 12 hours, the mixture was poured into molds. All three slurries exhibited fluidity and self-leveling properties in the molds, demonstrating that the slurries were relatively stable at room temperature. The molds were then placed in an oven at 80°C for continuous drying, and the weight loss of the samples was measured after 12 hours. The moisture content after constant weight drying is shown in Table 3.

[0072] Table 3. Drying weight loss (g) of GP-1, 2, and 3

[0073] Mold weight Slurry addition 12h 14h 16h 18h Moisture content GP-1 135.19 583.59 509.56 509.61 509.54 509.51 8.61％ GP-2 181.23 386.07 299.81 298.55 298.40 298.48 9.26％ GP-3 181.36 412.79 355.78 335.72 335.73 335.68 8.52％

[0074] It can be seen that all slurries reached a constant weight after drying at 80℃ for 14 hours. GP-3 samples were selected, and after drying to a constant weight, the drying temperature was increased to 110℃. After cooling, the weight fluctuation was less than one-thousandth, indicating that the slurry had stopped losing water. Therefore, the water loss rate of the slurry across the entire range was calculated to be 9.20% ± 1.09% (n = 3), and this water loss rate was used to calculate the expected elemental solution ratio in subsequent experiments.

[0075] 3. LA-ICP-MS analysis

[0076] The 213nm laser ablation system in this invention has advantages in processing non-standard shaped samples and identifying colors. Therefore, the nodular sample was fixed in a sample tray with Blu-Tack and analyzed by LA-ICP-MS. Figure 1 As shown.

[0077] Depend on Figure 1 As can be seen, the different colored spots on the nodule surface are clearly displayed under CCD, appearing as blue patches (20-100 μm) within a continuous brown-black matrix. To determine the relationship between this phenomenon and the elemental composition of the sample, a 100 μm spot was used to perform line scanning ablation on the sample under set laser parameters, and all elements of the sample were monitored during the process. Because the signal intensity of Na was too high, the detector saturated and could not be monitored. Therefore, the figure shows the signal fluctuations of the other two major elements in the sample, namely Si and Al. To compare the signal fluctuations of the two elements, the lower-intensity Si was amplified by 20 times to maintain a similar value.

[0078] The results showed that the fluctuation behavior of the two elements was basically the same, but the blue region generally had a higher Si / Al ratio, meaning that the Si content was higher in the patchy areas. This is related to the addition of quartz powder with a high Si content, as no patches were observed in the GP-2 sample.

[0079] And this phenomenon shows that in the traditional mineral polymerization system, quartz as ridge material failed to be completely dissolved, and it caused the relative enrichment of Si content in the final cured sample. This scale of patch, often referred to as a nugget in the study of the homogeneity of the relevant markers, this nugget is helpful to the development of the initial strength of the mineral polymer, because it provides additional sites for gel growth in the process of gel system from liquid to solid, and in the final cured product, as a composite particle in the continuous matrix, it plays a role in dispersing crack tip energy. But in this study, this mechanism has caused the gradient concentration of ions, making the element distribution uneven. Therefore, in order to avoid similar phenomena affecting the uniformity of the added elements, in the present invention, preferably, n(Qaurtz) = 0.

[0080] Example 2, preparation of mineral polymer

[0081] 1, mixed curing process

[0082] When the slurry is in the liquid mixing stage, the multi-element mother liquor is added, and mixed uniformly in the liquid state.

[0083] 1) Mixing method

[0084] At a predetermined concentration value, each rare earth element begins to precipitate when the pH value is greater than 8.5, so the element mother liquor should avoid mixing with the alkaline water glass solution or sodium hydroxide too early to avoid the generation of white precipitate.

[0085] For the same reason, in order to avoid the instantaneous high alkali concentration and local heating when the system is mixed, a high concentration solution of about 12.5M NaOH is prepared. The specific operation is: by increment method, weigh 202.89g of sodium hydroxide particles, and add 400ml of ultrapure water in a plastic beaker and place it in the sink. Then add the sodium hydroxide particles to the beaker and seal it with a plastic film. After the solution is completely clear and cooled, it is transferred to a disposable bottle. Therefore, the mass fraction of water molecules contributed by this solution is 73.9%.

[0086] Accordingly, the present invention provides the following mixing scheme:

[0087] A, in A plastic cup, weigh and add the predetermined weight of metakaolin powder, element mother liquor (some samples need to add extra ultrapure water), and mix uniformly with an electric mixer. Since the viscosity of the slurry is large at this time, it needs to be gradually accelerated and stabilized at 400r / min for 2h.

[0088] B, in B plastic cup, weigh and add the predetermined weight of water glass solution, sodium hydroxide solution, shake well and stand for 2h until the solution temperature returns to room temperature, which can be used as an alkali-activated solution.

[0089] C. Add the mixed alkali activator solution into the plastic cup in equal volume in 5 times under manual stirring. The viscosity should be observed to rise sharply at the second addition of alkali activator solution and gradually decrease at the following additions.

[0090] D. Increase the speed of the electric mixer to 600 r / min to ensure that all the slurry is stirred. After 2 h, inject the slurry into the mold for subsequent curing.

[0091] The slurry state during the addition of the alkali activator can be seen Figure 3 .

[0092] According to the above process, without adding quartz powder, the ratio range of GP1-3 is compromised to design the following formula, marked as GP-4, and the weighing process is shown in Table 4.

[0093] Table 4. Weighing weight of GP-4

[0094] MK+REE WG+NaOH Amount added Weighing Amount added Weighing Cup 50.18 Cup 49.8 MK 122.8 172.98 WG 215.62 265.42 REE 82.05 255.03 NaOH 11.92 277.34 Bar 102.37 357.4 MilliQ 29.7 387.1

[0095] It is calculated that Na / Al = 1.28, Si / Al = 2.50, and M = 1.83.

[0096] 2) Pre-curing treatment

[0097] After the stirring is completed, the slurry needs to be degassed to remove the defects such as air bubbles introduced during the stirring process, so as to reduce the air voids in the sample after curing. Therefore, the slurry is divided into three equal parts and injected into the plastic mold, and treated by vacuum degassing, ultrasonic degassing and standing for 20 min, respectively, and then placed in an oven at 80°C for curing.

[0098] After the sample is cured, the sample surface block is fixed on the blue tape and stuffed into the self-made sample ring to form a standard size sample block, and then placed under the 193 nm laser ablation system for testing to reveal the element distribution information of the sample under a smaller spot size. A 30 μm spot is used for testing, and the scanning speed is 5 μm s -1 .

[0099] It can be seen that the sample surface has reached visual smoothness through the self-leveling of the slurry. Three sets of line scans are measured for each sample, and the results of all samples after correction by the previously developed NIM-4 fusion glass external standard using internal Al element as internal standard are shown in Figure 5 .

[0100] It can be seen that the vacuum degassing effect is much better than the other two methods. It is speculated that this phenomenon is related to the small particle size of the raw material. For similar powders, the powder surface adsorbed gas is the main obstacle in the wetting process. Therefore, under the condition of reducing the gas pressure, the gas on the surface of the powder is discharged and completely wetted. This avoids the agglomeration of particles during the solidification process, thereby greatly improving the element uniformity of the solidified sample. Therefore, it is necessary to carry out the corresponding vacuum degassing (dissolution) step in the two processes of discharging gas from the powder sample, i.e. the mixing stage of the element mother liquor and the metakaolin powder and the sample after stirring. By comparing the element signal stability measured with the results of glass matrix NIM-4, it can be seen that the signal stability level of the Vacuum group sample is close to that of the fired glass sample, where the relative standard deviation (RSD) of the Si / Al signal ratio of NIM-4 is 1.2% (n=95, k=1), and that of the Vacuum group sample is 3.1% (n=96, k=1). The rest of the data is shown in Table 5.

[0101] Table 5 Signal stability comparison of Vacuum group samples and NIM-4 samples

[0102] NIM-4 Total number N RSD Vacumn Total number N RSD 29Si (IS) 95 1.25％ 29Si (IS) 96 3.11％ 45Sc (IS) 95 13.71％ 45Sc (IS) 96 7.22％ 89Y (IS) 95 5.06％ 89Y (IS) 96 8.31％ 139La (IS) 95 5.02％ 139La (IS) 96 6.59％ 140Ce (IS) 95 4.89％ 140Ce (IS) 96 7.57％ 141Pr (IS) 95 4.95％ 141Pr (IS) 96 7.38％ 146Nd (IS) 95 6.87％ 146Nd (IS) 96 10.19％ 147Sm (IS) 95 6.87％ 147Sm (IS) 96 12.87％ 153Eu (IS) 95 4.55％ 153Eu (IS) 96 7.78％ 157Gd (IS) 95 7.12％ 157Gd (IS) 96 12.53％ 159Tb (IS) 95 4.42％ 159Tb (IS) 96 7.68％ 163Dy (IS) - No addition 163Dy (IS) 96 9.95％ 165Ho (IS) 95 4.54％ 165Ho (IS) 96 7.38％ 166Er (IS) 95 5.66％ 166Er (IS) 96 9.23％ 169Tm (IS) 95 4.66％ 169Tm (IS) 96 6.85％ 172Yb (IS) 95 5.47％ 172Yb (IS) 96 10.18％ 175Lu (IS) 95 4.75％ 175Lu (IS) 96 6.85％

[0103] Among them, the Sc element has a low signal-to-noise ratio and the measurement effect is not good. As can be seen from other elements, the sample has a relatively low content, which may be the reason for the large RSD. However, the RSD of the Si / Al signal ratio is large, which indicates that the two components that constitute the matrix in the sample, i.e. metakaolin and water glass (Si gel), are not completely mixed. This indicates that there is room for improvement in the uniformity of the sample.

[0104] However, for the samples solidified in the mold, a visually observable boundary line between the surface and the interior of the sample can be observed in the longitudinal section, such as Figure 6 .

[0105] It can be seen that the internal structure of the sample is loose and accompanied by cracks, which is related to the capillary action of the sample slurry during the dehydration process. This phenomenon is similar to the slip casting process of ceramics, i.e. at the initial stage of solidification, the surface layer of the sample loses water at the fastest rate, thereby driving smaller particles to form a thin wall layer on the surface of the sample; when the thin wall layer is formed, water continues to evaporate, at which time the thin wall layer forms a filter plate, and as the thin wall layer thickens, the resistance to water diffusion gradually increases; when the internal dehydration of the system reaches a limit, the entire slurry begins to shrink and internal stress is generated due to the difference in shrinkage rate between the inner and outer layers, eventually forming cracks.

[0106] To confirm the difference between the surface and the interior of the sample, the part with different visual color was taken and fixed on the sample ring, and the same LA-ICP-MS analysis was carried out, and the results are shown in 7. It can be seen that as the structure of the sample is loose, more cavities are introduced, resulting in the decrease of the measurement stability, and more large particles generated during ablation can also be observed in the CCD camera of the laser ablation system. Therefore, to prepare a completely micro-homogeneous sample, a more microscopic forming process is required.

[0107] 2, 3D printing forming process

[0108] The present application adopts the 3D printing forming method, which is characterized by "additive manufacturing", that is, by accumulating materials point by point, line by line and layer by layer on the substrate and solidifying on the printed sample, a three-dimensional entity is finally formed. When applied to the mineral polymerization system, it is different from the traditional integral injection molding, but is changed to form solid units one by one. The original centimeter-level long-time curing scale is divided into multiple short-time forming processes with a scale of hundreds of microns, so as to suppress the differentiation phenomenon between the surface and the interior of the sample, so as to achieve the uniformity of the whole sample.

[0109] 1) Direct writing forming process

[0110] Considering the reaction mechanism of the above mineral polymerization system, the slurry direct writing forming technology (DIW) can meet the needs of 3D printing. DIW technology, as a common technology for 3D printing ceramics, is to extrude the ceramic slurry from the extrusion device through the nozzle, and move on the two-dimensional plane according to the path setting, complete the slice pattern of this layer, then raise the barrel or lower the platform to the appropriate position, and print the next layer, repeat the above process until the printing is completed, and a three-dimensional entity is obtained.

[0111] The whole process depends on the rheological properties of the slurry, that is, it is transformed into a fluid under the action of external force during extrusion, and quickly "solidifies" to maintain the shape after extrusion, so as to maximize the retention of the formed shape, and separate the extruded part from the subsequent slurry. And in order to make the most of the characteristics of the mineral polymerization system, the present application adopts SYNO 4070 ceramic printer (Henan Yuanchuang Gaokexue Technology Co., Ltd., Figure 8 ), which has the function of environmental heating, which can open the internal hot air circulation during the curing process, so that the extruded slurry can lose water faster. And in the extrusion head (a figure in the Figure 9 ) part of it, the motor-driven stirring screw (b figure in the Figure 9 ) is equipped, which can provide shear force to temporarily reduce the kinematic viscosity of the gel system, so as to extrude more smoothly. It can be seen that the slurry is tightly packed in the screw without cavities, and can remain moist inside the extrusion head, which helps to maintain the stability of the slurry before extrusion.

[0112] 2) Base-activation concentration optimization

[0113] The concentration of base-activator (alkalinity) determines the degree of dissolution of raw material particles (metakaolin powder), as well as the viscosity change and solidification rate of the slurry system. Therefore, to further improve the uniformity of the sample, it is necessary to increase the concentration of the base-activator. However, studies have shown that too high an alkali content will cause excessive residual alkali after solidification, and phenomena such as "alkali bleeding" will occur during storage, causing local elemental precipitation, which is not conducive to maintaining elemental uniformity. Therefore, the concentration of the base-activator needs to be optimized.

[0114] However, after confirming that the mineral polymerization system in the present application cannot add ridge material (quartz powder), the degree of freedom of the system is reduced, resulting in Si / Al, modulus M and Na / Al always having only two of them can be freely adjusted. Therefore, the Si / Al of the sample is fixed at 2.50, the concentration of NaOH is gradually increased, and the amount of water glass solution and metakaolin powder is reduced. In this way, the M value gradually decreases while not introducing additional free water into the system, but the Na / Al value inevitably increases.

[0115] Based on this scheme, the present application sets up samples with gradient base-activation concentrations as shown in Table 6, and labeled as GP-M1 to GP-M10.

[0116] Table 6 Mineral polymer ratio changes of different M values

[0117] NaOH solution amount added M S / L GP-M1 52.73 1.72 0.37 GP-M2 59.16 1.65 0.37 GP-M3 65.50 1.58 0.37 GP-M4 71.76 1.51 0.36 GP-M5 77.94 1.45 0.36 GP-M6 84.05 1.40 0.35 GP-M7 90.07 1.34 0.35 GP-M8 96.02 1.29 0.34 GP-M9 101.89 1.25 0.34 GP-M10 107.69 1.20 0.34

[0118] To exclude the influence of the reduction of solid-liquid ratio (S / L) on the solidification ability of the polymerization system, the samples were respectively cast in the mold. And a syringe was used to smear three parallel thin layers of slurry under the mold to simulate the slurry extrusion process in the 3D printing process, and then the whole was placed in an oven for 150 s to observe its solidification, as shown in Figure 10 .

[0119] It can be seen that from GP-M7, the thin layer sample cannot be solidified within the specified time and appears to be locally aggregated with liquid droplets, corresponding to the decrease in wettability and printing processing performance. The gel system formed by too high Na content and too low solid-liquid ratio is difficult to maintain and infiltrate the bottom of the mold, which will exacerbate shrinkage during solidification, thus leading to more internal cracks.

[0120] Subsequently, the slurry in the GP-M1 to GP-M10 mold was solidified, and then the surface sample was peeled off and placed in a self-made sample cell for LA-ICP-MS analysis. The signal stability of the lanthanum (La) element represents the rare earth elements, and the results are shown in Figure 11 .

[0121] As can be seen from the figure, consistent with the conclusion of the curing performance, the signal stability of GP-M5 to M10 slurry gradually deteriorates, and severe signal fluctuations occur in M10 slurry, which may be related to the severe shrinkage of the slurry itself, causing potential cracks in the internal of the final cured sample.

[0122] Based on the above conclusions, the GP-M4 ratio shows good curing performance and LA-ICP-MS signal stability, and is used for subsequent research.

[0123] 3) Shear viscosity change

[0124] In the early stage of mineral polymerization reaction, the tetrahedron is gradually dissolved by the alkali activator in the system to form a loose gel network. With the gradual increase of the dissolution amount, the gel network connectivity is enhanced and the free water is reduced, causing the viscosity to gradually increase, and finally curing. In order to quantitatively describe the change of the rheological property of the slurry in this process, so as to determine the appropriate printing time and viscosity, the ViscoQC100-H viscometer produced by Anton Paar Company was used to monitor the change of the sample viscosity with time. The V73 paddle was used in the experiment, and the maximum test viscosity was 20.48 pa·s (200 r / min -1 ), and the precision was one thousandth.

[0125] The GP-M4 ratio slurry was mixed, and the slurry was taken out from the slurry at intervals of 2h and placed in a PFA tube, continuously stirred at the maximum speed until the reading was stable, and the results were recorded three times, and the average value and standard deviation (1s) were as Figure 12 It can be seen that the viscosity of the slurry is about 0.32 Pa·s after 28h of continuous stirring, and a significant increase in viscosity is observed, and reaches 1.34 Pa·s after 36h, and then sharply rises to 8.76 Pa·s after 39.5h, and the sample is partially solidified at the speed of the viscometer, and cannot be accurately measured.

[0126] Through the experiment, the slurry can be kept in the extrusion head without leakage at a viscosity of 0.16 Pa·s, and in order to make the raw material particles dissolve as much as possible, the most suitable printing start time should be controlled between 26h and 38h after the sample is stirred, that is, at least 26h, at most 38h, and after that the viscosity of the sample sharply rises, and it will be difficult to maintain the flowability to the end of printing. Considering the time consumption of the subsequent 3D printing process, the preferred stirring time is 26h.

[0127] 4) 3D printing optimization

[0128] Even between 26h and 38h, the viscosity of the paste varies by 20 times, and for different viscosity pastes, the advantages and disadvantages are different. High viscosity paste can better retain the shape after extrusion, and the solidification time is shorter, but the disadvantage is that it needs more pressure and screw speed to extrude, and may cause pipe blockage, partial solidification before extrusion, etc. Low viscosity paste has relatively high free water content, and the forming precision is poor after extrusion during printing, and the solidification time is longer, but the advantage is that it is more tolerant to extrusion head heating, pipe blockage, etc. At the same time, it can be extruded at lower pressure and screw speed. Therefore, the printing paste is divided into 26h and 38h and marked as GP-M4-LV and GP-M4-HV to represent the printing effect of low and high viscosity paste.

[0129] The 3D printing model is built by solidworks 2018, exported as STL format, and imported into Ultimaker Cura software for slicing as gcode format file. The slicing path is shown in Figure 13 .

[0130] According to the density of the sample filled on the substrate, the key parameters in the slicing need to be designed to match, such as layer thickness, extrusion head aperture, wire width, filling density, extrusion flow, etc. After optimizing the optimal parameters for two different viscosity pastes, they are printed respectively. And the samples are analyzed by LA-ICP-MS to show the micro-area uniformity of elements.

[0131] Obviously, GP-M4-LV shows better signal stability, as shown in Figure 14 . Therefore, it is determined that the paste should be printed at a relatively lower viscosity, i.e. 26h is the best.

[0132] In addition, in order to facilitate the sample to be transferred from the substrate to the oven and subsequent storage, a standard size sample ring is designed. Finally, according to the optimized process route determined in each step, without oven drying, the chimeric printed sample is prepared, marked as GP-M4-LV-FINAL( Figure 15 ), and it can be seen that the sample surface is smooth and meets the needs of micro-area analysis.

[0133] Example 3, verification of micro-area uniformity of mineral polymerization sample

[0134] 1. Whole micro-area imaging of single piece sample

[0135] Example 2 GP-M4-LV-FINAL chimeric sample was prepared. The micro-area homogeneity of the sample needs to be characterized. However, due to the large difference between the size of the whole sample (cm) and the scale of in-situ analysis of micro-area (μm), the measurement time is too long if the adjacent measurement is performed on the whole sample, and the results will be greatly affected by the change of measurement conditions and the drift of instrument sensitivity. Therefore, in order to shorten the measurement time, a measurement strategy as shown in Figure 16 is designed:

[0136] The measurement process is carried out in the order of the numbers in the figure, and in this way the sample is divided into 12 equal areas every 30°. According to the measurement data on the 12 lines, the concentration values of the areas not actually measured within the same radius range are simulated by TPS (Thin Plate Spline) interpolation method. In addition, due to the fact that the laser ablation paths are too close at the center position of the sample, they inevitably interfere with each other. Therefore, the data at the middle position of the sample sheet are omitted.

[0137] The results of the GP-M4-LV-FINAL sample measurement are plotted as a polar coordinate heat map by Origin 2018 as shown in Figure 17 , where the elements are arranged in the order of the elements in Table 7, starting with Sc and ending with Pb; the coloring rule in the figure is that the high concentration end is blue, the low concentration end is red, and the intermediate color is green. The color blocks exceeding the upper and lower limits are gray and black respectively. Therefore, the homogeneity of the elements can be visualized by the color distribution in the figure. It can be seen that the added elements are uniformly distributed in the GP-M4-LV-FINAL sample.

[0138] Table 7 Concentration measurement results of rare earth element mother liquor

[0139]

[0140]

[0141] 2. Local micro-area imaging of the sample

[0142] After verifying the uniformity of the sample on a large scale, random sampling can be performed, and the smaller micro-area uniformity of the sample can be tested according to the traditional element concentration imaging method. That is, the LA-ICP-MS analysis of the regional sample is performed by the adjacent line scanning, and the signal intensity value of the corresponding element in the line scanning is used for color imaging. The scanning area covers a range of about 400*700 μm in the same position as the rectangular position in Figure 16 . The data uses NIM-4 as the quality control sample and performs time drift correction, and the rest of the arrangement and data processing method is the same as Figure 17 . The results are shown in Figure 18 .

[0143] It can be seen that the element concentration imaging results of the whole sample are consistent, and the elements exhibit good uniformity in the LA-ICP-MS analysis. However, some individual elements such as Yb and Pb show some "false" patches in the above LA-ICP-MS analysis, and this phenomenon gradually intensifies with the decrease of the relative signal intensity (compared with the internal standard element) and the signal-to-noise ratio. A more suitable correction scheme should be sought to weaken this effect. However, in the present application, there is no other internal standard element, so the RSD values of each element in the representative line scan are given for reference (Table 8).

[0144] Table 8 Fluctuation of each element in the representative line scan (n = 18)

[0145]

[0146]

[0147] Based on the above analysis, the present application establishes a process route for developing a target based on mineral polymerization technology, that is, based on three types of components of cementitious active ingredients, element mother liquor and alkali activator, through four main steps of raw material proportioning, component mixing, pre-curing treatment and curing forming to prepare a mineral polymerization sample artificially synthesized with target elements.

[0148] In the raw material proportioning stage, the element content of each raw material component needs to be determined, and the proportioning is carried out according to the results, so as to control the three key parameters of the silicon aluminum ratio (Si / Al), the sodium aluminum ratio (Na / Al) and the alkali activation modulus (M) in the formed sample. In the present study, the determined proportions are Na / Al = 1.28, Si / Al = 2.50 and M = 1.83 (3D printing curing).

[0149] The component mixing method should adopt a premixed way, and in the present application, metakaolin is mixed with the element solution, and the water glass solution is mixed with the sodium hydroxide solution, and then they are blended again after stabilization. And quartz (ridge material) component should be avoided to be added, because it cannot be completely dissolved in the gel polymerization process, resulting in the formation of nodules in the final cured sample, affecting the uniformity.

[0150] The pre-curing treatment process, that is, the degassing treatment of the sample slurry, is necessary, and the vacuum degassing method is obviously superior to ultrasonic degassing or standing degassing. In the curing forming stage, the injection molding method will cause the formation of a boundary line between the wall layer and the inner layer of the sample, and affect the uniformity of the sample. The 3D printing forming divides the slurry into small pieces, which can be printed into the sample ring at a lower viscosity, and the sample is formed into a smooth sheet sample.

[0151] The sample (GP-M4-LV-FINAL) after process route optimization was verified by LA-ICP-MS analysis to have good internal uniformity, with a relative standard deviation of 3.82%-7.35% (corrected by internal standard) in LA-ICP-MS measurement, which is at the same level as the measurement accuracy of the NIM-4 sample prepared by the fusion glass method.

Claims

1. A method for preparing an inorganic element-doped high-uniformity mineral polymer, comprising the following steps: S1. determining the amount of each raw material according to the equations shown in formula (1); （1） wherein represents the molar amount of sodium hydroxide, represents the molar amount of water glass, represents the molar amount of metakaolin, represents the molar ratio of sodium element and aluminum element in the system, represents the molar ratio of silicon element and aluminum element in the system; 0; M represents the modulus of alkali activator, which is used to describe the molar ratio of Si and Na oxides in the alkali activator, and the calculation formula is as follows: S2. under the condition of stirring, the alkali activator solution is added to the mixture of metakaolin and target element mother liquor in multiple times, and the obtained slurry is solidified; The target elements include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

2. The method of claim 1, wherein: =1.28， =2.50，M=1.83。 3. The production method according to claim 1 or 2, characterized by: In step S2, after the addition of the alkali activator solution is completed, the stirring is carried out at a speed of 400-600 r / min for 26-38 h.

4. The production method according to claim 1 or 2, characterized by: In step S2, before the solidification, the slurry is subjected to a degassing treatment.

5. The method of claim 4, wherein: The degassing treatment is vacuum degassing. The time for the vacuum degassing is 15 min, and the air pressure is extracted to below 0.01 MPa.

6. The production method according to claim 1 or 2, characterized by: In step S2, the solidification is 3D printing forming.

7. The mineral polymer prepared by the method according to any one of claims 1-6.

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