Patent Application
20220363597
The present disclosure generally relates to methods of forming synthetic aluminosilicate material. More particularly, examples of the disclosure relate to methods of forming aluminosilicate material using polymer solutions.
Industrial byproducts, such as fly ash and slag, metakaolin, and calinated clay, are aluminosilicate powders that are used in the production of inorganic cements and as a supplement in Portland cement concrete. It is expected that the national and global supply of fly ash will be decreasing over the next 10-50 years due to the closing of coal-fired power plants. During this time, demand for these materials is expected to increase at a high rate.
Accordingly, new methods of forming aluminosilicate material are desired.
Any discussion of problems and solutions set forth in this section has been included in this disclosure solely for the purpose of providing a context for the present disclosure and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.
This summary is provided to introduce a selection of concepts. This summary is not intended to necessarily identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
Various embodiments of the present disclosure relate to methods of forming an aluminosilicate material. The aluminosilicate material can be suitable for use in the production of inorganic cements and/or as a supplement in concrete. Additional embodiments of the disclosure relate to concrete or cement formed using the aluminosilicate material.
In accordance with exemplary embodiments of the disclosure, a method of forming aluminosilicate material includes forming a polymer solution, adding an aluminum precursor to the polymer solution, adding a silicon precursor to the polymer solution, forming a gel from the polymer solution, calcining the gel to form an aluminosilicate powder, and grinding the aluminosilicate powder to form ground aluminosilicate material. In accordance with examples of these embodiments, the step of forming a polymer solution comprises dissolving a polymer in water. By way of examples, a method can include dissolving polyethylene glycol (PEG), polyvinyl alcohol, or the like in water. An amount of polymer dissolved in water can be about greater than 0% to about 25%, about 0.1% to about 10%, or about 1% to about 5%. All percentages set forth herein are weight percentages, unless otherwise noted. A pH of the polymer solution can be about 1 to about 14 or about 1 to about 10. Exemplary methods can further include a step of passing the ground aluminosilicate material through a sieve, such as a 100 um mesh sieve. Exemplary methods can additionally or alternatively include a step of alkali activating the ground aluminosilicate material. A step of alkali activating the ground aluminosilicate material can include, for example, adding one or more of an NaOH solution, KOH solution, NaSi solution, Na2CO3 or the like solution to the ground aluminosilicate material. A concentration of the solution can be about 0.1M to about 15M, or about 0.1M to about 14M, or about 1M to about 10M alkali salt in solution. Exemplary methods can also include adding one or more additives to the polymer solution.
In accordance with further examples of the disclosure, a method can include a step of forming a cement using one or more aluminosilicate materials formed as described herein.
In accordance with additional examples of the disclosure, a method can include a step of forming a paste using one or more aluminosilicate materials formed as described herein.
In accordance with additional examples of the disclosure, a method can include a step of forming concrete (e.g., acid-resistant concrete) using one or more aluminosilicate materials formed as described herein.
In accordance with yet additional embodiments of the disclosure, concrete (e.g., acid-resistant concrete) including aluminosilicate material, as described herein, is provided.
These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the figures; the disclosure not being limited to any particular embodiment(s) disclosed.
A more complete understanding of exemplary embodiments of the present disclosure can be derived by referring to the detailed description and claims when considered in connection with the following illustrative figures.
It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure.
The description of exemplary embodiments provided below is merely exemplary and is intended for purposes of illustration only; the following description is not intended to limit the scope of the disclosure or the claims. Moreover, recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the stated features.
The present disclosure generally relates to methods of forming synthetic aluminosilicate material, to methods of forming other materials that include the synthetic aluminosilicate, and to concrete and other materials that include the synthetic aluminosilicate.
A synthetic aluminosilicate material (e.g., powder) may be used to make inorganic cements or as a supplement to, for example, Portland cement in concrete. The synthetic aluminosilicate powder can replace more conventional industrial byproduct materials that are used to make inorganic cements.
Synthetic aluminosilicate material as described herein can be created in such a way that it behaves, chemically speaking, identically (or substantially similar) to the natural and industrial byproduct aluminosilicates that are used today to form cement or concrete.
Polymer-assisted sol-gel synthesis—otherwise known as the organic steric entrapment (OSE) method—was first demonstrated in 1992 as a viable method to produce metal-oxide ceramics. Earlier, in 1931, conventional (i.e., non-polymer-assisted) sol-gel synthesis methods were used to produce ceramics using alkoxysilanes. The primary aim of sol-gel synthesis is typically to produce solid ceramics from a solution of liquid metal precursors via hydrolysis and subsequent polycondensation into a gel. By forming gels in a solution state, sol-gel synthesis methods facilitate atomic-level mixing, thereby circumventing challenges otherwise associated with solid-state chemistry (e.g., inhomogeneity, phase separation, low yield reactions). As a departure from conventional sol-gel synthesis, polymer-assisted sol-gel synthesis was first reported in a study that used polyethylene glycol (PEG) to synthesize nanocrystalline Perovskite materials. Soon thereafter, polyvinyl alcohol (PVA) was used to produce fine ferrite powders and mixed-metal-oxide materials. In 1999, polymer-assisted sol-gel synthesis was renamed the OSE method, due to the speculation that weak hydrog polymer and metal oxides was primarily responsible for sterically entrapping and structuring solvated cations in solution.
As set forth herein, OSE can be used to synthesize metal-oxide precursors for use as traditional ordinary Portland cement (OPC) cementitious binders, as well as alternative cementitious binders such as calcium- and sodium-stabilized aluminosilicate hydrates (i.e., C-N-A-S-H and N-A-S-H). Examples of synthesized OPC phases/precursors include calcium aluminate, dicalcium silicate, tricalcium silicate, tricalcium aluminate, and tetracalcium aluminate iron oxide. These synthesized cementitious components can be pure, nano- or sub-micron sized, and highly reactive. Furthermore, alternative cementitious binders (e.g., calcium aluminosilicate hydrates and sodium aluminosilicate binders) can be formed using techniques described herein. Production of alternative cementitious binders through OSE presents a unique opportunity to understand the atomic structure and material properties by stoichiometric control of the alternative cement chemistry. Despite advances in polymer-assisted sol-gel synthesis, heretofore, the effect of processing conditions to produce aluminosilicate precursors that yield structural variants of N-A-S-H cementitious binders was not well understood. N-A-S-H cementitious binders, or geopolymer cements, have gained popularity for their controllable chemistry and potential for increased durability, improved fire resistance, and reduced environmental impacts compared to OPC in some applications. Traditionally, geopolymer materials are composed of N-A-S-H binders, which have a standard composition of SiO2/Al2O3=3.3, Na2O/Al2O3=1.1, and H2O:Na2O=11, with modern N-A-S-H binders having SiO2/Al2O3 between 0.5 and 2.0 given the choice of low calcium precursor used. Multiple studies have been pivotal to understand the atomic structure and properties of N-A-S-H binders. However, little scientific understanding on process-structure effects of different N-A-S-H precursor synthesis conditions currently exists.
Process-structure relationships of synthetic aluminosilicate powders produced via polymer-assisted sol-gel synthesis, as well as process-structure relationships of resultant sodium-stabilized aluminum-silicate-hydrate (N-A-S-H) geopolymer cements are described herein. The influence of synthesis processing factors (i.e., polymer architecture, polymer content, and sol-gel aging pH) were explored using a 22 factorial design to reveal changes in atomic structure and variations in mineralogy in both synthetic aluminosilicate powders and resultant geopolymer cements. The mineralogy of geopolymer cements is also compared to that of alkali-activated metakaolin-based cements.
In accordance with various examples of the disclosure, a sol gel process is used to form (synthetic) aluminosilicate material.
During step 902, a polymer can be dissolved in a solvent. An amount of polymer (e.g., PVA and/or PEG) dissolved in the solvent (e.g., water) can be about greater than 0% to about 25%, about 0.1% to about 10%, or about 1% to about 5%. A molecular weight of the PVA, PEG, and/or other suitable polymer (e.g., having one or more alcohol (e.g., end) groups and/or one or more acetate groups) can range from about 1 to about 500, about 10 to about 100, or about 30 to about 50 Da. A temperature of the solution can be about 20 to about 90° C.
During step 904, the aluminum precursor is added to the solution. Aluminum can be added in ranges from about 1% to 100% or about 40% to 60% to by weight of solution.
Silicon precursor is then added to the solution and the silicon precursor is allowed to dissolve during step 906. A temperature of the solution during step 906 can be about 20 to about 90° C. Various additives, such as zeolites, alkali salts (e.g., magnesium hydroxide), and/or activated carbon, can be added to the polymer solution during step 902-906.
During step 908, the gelling process can occur by a reduction in temperature—e.g., from about 100° C. to about 20° C. The gel can then be dried to form a foamy mass prior to calcining.
During calcining (step 910), a phase change in the aluminosilicate material can occur. The calcined material can be ground to a desired size—e.g., less than 100 μm or about 50 μm to about 100 μm—during step 912. The ground particles can be activated (step 914) by adding an alkali or basic solution or material to the ground aluminosilicate material. For example, about 0.1M to about 15M, or about 0.1M to about 14M, or about 1M to about 10M basic or alkali solution (e.g., a solution comprising one or more of an NaOH solution, KOH solution, NaSi solution, or Na2CO3) can be added to the ground aluminosilicate material. A cement can be formed from the alkali activated ground aluminosilicate material. And, concrete can be formed using the cement. Or, a coating can be formed using the alkali activated ground aluminosilicate material. The coating can be applied to, for example, concrete.
In accordance with exemplary embodiments of the disclosure, an acid-resistant composite material is provided. The acid-resistant composite material can include a synthetic aluminosilicate material as described herein. Exemplary acid-resistant composite materials can include greater than 0% to about 75% or about 40% to about 60% SiO2; greater than 0% to about 75% or about 30% to about 50% Al2O3; about 1% to about 25% or about 1% to about 20% CaO; and greater than 0% to about 25%, or about 0.1% to about 10%, or about 1% to about 10% one or more monovalent, divalent, or polyvalent cationic metals. The one or more monovalent, divalent, or polyvalent cationic metals can include one or more group 2 and/or one or more transition metals. For example, the one or more monovalent, divalent, or polyvalent cationic metals can be selected from one or more group 2 and/or group 8-11 metals. By way of particular examples, one or more monovalent, divalent, or polyvalent cationic metals be selected from the group consisting of titanium, lithium, chromium, calcium copper, cobalt, iron, and magnesium. The acid-resistant composite material can include a plurality of the one or more monovalent, divalent, or polyvalent cationic metals. In accordance with various aspects of these embodiments, a ratio of silicon to aluminum in the acid-resistant composite material can be about 0.75 to about 3.0 or about 1.0 to about 2.5 or about 1.5 to about 2.0. A ratio of sodium to aluminum in the acid-resistant composite material can be about 1.0, or about 0.9 to about 1.1, or about 0.5 to about 1.5. In accordance with further examples of the disclosure, the one or more aluminosilicate precursors comprise a synthetic aluminosilicate precursor—e.g., formed using a method as described herein.
In accordance with further embodiments of the disclosure, a method of forming an acid-resistant composite material 1000 is provided. Method 1000 includes the steps of dissolving one or more alkaline metal salts in a solution (step 1002) and adding the solution to one or more aluminosilicate precursors and optionally other minerals to form a mixture (step 1004). The one or more aluminosilicate precursors comprise one or more of a synthetic aluminosilicate precursor, Metakaolin, fly ash, slag, pumice, basalt, glass, or other natural pozzolan. The method can optionally include filtering the mixture (step 1006). The method can also include a step of drying the mixture to form a dried material (step 1008). The drying can be performed using an oven or left to dry in ambient conditions. The dried material can be ground using a step of grinding (step 1010). The grinding can be performed using a mortar and pestle or an industrial grinder, which can also be used for step 912. Exemplary methods can further include adding an alkali additive to one or more of the mixture and the dried mixture (step 1012). The alkali additive can include, for example, one of more of sodium silicate, sodium hydroxide, potassium hydroxide, or sodium carbonate. The step of adding an alkali additive to one or more of the mixture and the dried material comprises adding a solid and/or a liquid. The alkali additive can include one or more of an NaOH solution, KOH solution, NaSi solution, Na2CO3. When in liquid form, a concentration of the solution can be about 0.1M to about 15M, or about 0.1M to about 14M, or about 1M to about 10M alkali salt in solution.
The examples provided below are merely exemplary and are not meant to limit the scope of the disclosure or invention described herein. Further, any values (e.g., temperature, times, percentages, molecular weights, sieve size, and the like) set forth below can be ±10 percent, ±5 percent, or ±2 percent of the stated values, unless noted otherwise.
Polyvinyl alcohol (PVA) and polyethylene glycol (PEG) polymers of molecular weight 31-50 kDa (Mw) and 35 kDa (Mn), respectively, were obtained from MilliporeSigma. Aluminum nitrate nonahydrate (99+%, analysis grade, Acros Organics), a 40% by weight colloidal silica suspension (LUDOX TM-40, Millipore), sodium hydroxide (NaOH) (10M, BioUltra grade, MilliporeSigma), and NaOH (reagent grade) were also acquired from MilliporeSigma. Metakaolin (Si:Al=1.0) was supplied by BASF Chemical Corporation (MetaMax).
The influence of both polymer architecture and sol-gel aging pH was investigated using a 22 factorial design of experiments. Additionally, the influence of polymer content was explored in combination with the aforementioned factors. In terms of polymer architecture, both PEG and PVA of similar molecular weights were used to elucidate the role of polymer architecture. Sol-gel aging at two different pH conditions (low pH ˜1.0, high pH ˜10) explored pH-dependent metal-polymer interactions. Polymer content was explored by varying the ion-to-polymer-oxide atomic ratios (I/O) in two levels (see supplementary information for calculation of I/O). The “ion” content refers to aluminum metal ions, while the oxide solely refers to the polymer oxide content. The aluminum content of aluminum nitrate nonahydrate salts was determined to be 9.28 wt. % via ICP-OES and used to calculate accurate I/O ratios. As seen in Table 1, PVA-derived precursors had I/O ratios of 4.0 (low) and 5.2 (high), while PEG-derived precursors had I/O ratios of 3.7 (low) and 4.4 (high). While similar ratios have been described as metal-to-hydroxide (M/OH) atomic ratios, in the present disclosure, PVA chain hydroxyls are compared to PEG chain ethers and, as a result, a redefinition of this atomic ratio was used to account for the differences in polymer architecture as an I/O ratio, where oxide (O) accounts for ethers or hydroxyls.
Aluminosilicate precursors were synthesized using a polymer-assisted sol-gel procedure—e.g., as described in connection with
Both PVA and PEG xerogels were calcined at 550° C. and at 900° C., respectively, with a hold time of one hour (ramp rate of 3° C./minute). The resultant white material was ground to form a powder and sieved through a No. 100 sieve. Samples of the synthetic aluminosilicate powders were saved for subsequent characterization. The Brunauer-Emmett-Teller (BET) nitrogen adsorption method was used to measure the surface area of the calcined powders. Samples were massed and degassed under vacuum in an inert nitrogen atmosphere at 100° C. for at least eight hours. After conducting a blank acquisition, samples were placed into the instrument and nitrogen gas was deposited atop the powder surface by varying the N2 pressure. For the measurement, eleven data points were collected with relative pressure (P/Po) ranging from 0.05 to 0.30 with a five second equilibration time. From the data, a BET plot was generated using a linear regression with a correlation coefficient of 0.99 for all data generated. The surface area of the resulting powders is reported in Table 1.
Aluminosilicate powders were alkali-activated via addition of NaOH (10M, BioUltra grade, MilliporeSigma) at a liquid-to-solid weight ratio of 0.75 to form synthetic geopolymer cements. Geopolymers were produced by manual mixing for one minute until a homogenous paste was obtained. Additionally, natural metakaolin-based geopolymer cements were utilized for mineralogical comparison. The mixing procedure included an initial one minute of manual mixing, followed by one minute of mechanical mixing using a Waring PDM112 mixer and one minute of additional manual mixing.
The natural metakaolin-based geopolymer cements were designed to exhibit equal chemical parameters as the synthetic geopolymer cements. More specifically, NaOH (reagent grade) was dissolved in deionized water to create activating solutions and yield Si:Al and Na:Al ratios of metakaolin-based geopolymer cements of 1.0 and 1.1, respectively. Both natural and synthetic geopolymer cements were cast in cylindrical molds (diameter: 1.26 cm, height: 3 cm) and cured at 35±5° C. and 100% relative humidity for 48±4 hours in a Quincy forced-air laboratory oven. Subsequently, samples were dried at 30° C. overnight (>12 hours).
Solid-state 29Si and 27Al MAS-NMR spectra were acquired using a Varian INOVA 400 MHz NMR spectrometer (magnetic field 9.39 T; operating frequency of 79.50 MHz for 29Si and 104.27 MHz for 27Al). Samples were packed into 4 mm zirconia rotors sealed at either end with Teflon end plugs, and all spectra were collected with magic-angle spinning (MAS) speed of 10 kHz using a broadband probe equipped with a 4 mm MAS spinning module designed and manufactured by Revolution NMR, LLC (Fort Collins, Colo.). 29Si chemical shifts were determined using the NMR signal from DSS (2,2-dimethyl- 2-silapentanesulfonate) referenced at 1.46 ppm. The spectra were acquired through a Bloch-decay experiment with 1600 scans using a pulse recycle delay of 5 s, a pulse width of 4.5 μs, and an acquisition time of ˜20 ms. These experimental parameters are sufficient for the qualitative analysis of the data, as presented herein. Cross-polarization (CP) MAS data were also collected using 1H and 29Si 90° pulse widths of 3.8 and 4.5 μs, respectively, with recycle delay of 2 s, CP spin-lock time of 3 ms, and 1600 scans. The 27Al chemical shifts were referenced to aluminum nitrate (0.0 ppm) and the Bloch-decay experiment was acquired using a pulse recycle delay of 5 s, a pulse width of 4.5 μs, an acquisition time of ˜20 ms, and 256 scans. For cross-polarization (1H—27Al CP) MAS experiments, 1H and 13C 90° pulse widths of 3.8 and 4.5 μs, respectively, were used with a recycle delay of 2 s, CP spin-lock time of 2 ms, and 256 scans. Peak identification and data processing was performed using MestReNova software.
Chemical characterization was determined with an ICP-OES (ARL 3410+) using an adapted protocol from a widely accepted technique developed by Farrell et al.
Five mL of a 7:3 mixture of hydrochloric acid and hydrofluoric acid were combined with 2 mL of nitric acid and placed in digestion tubes that were maintained at 95° C. in a digestion block (HotBlock by Environmental Express) for approximately two hours. Samples were then cooled and brought to 50 mL with a 1.5% boric acid solution (by mass). The samples were then reheated to 95° C. for 15 minutes and cooled for analysis. The samples were diluted 10× with deionized water and analyzed with an ICP-OES, as described above. An analytical blank, along with three standards that were made by accurately diluting certified standards, was used fc basaltic internal standard (Valmont Dike, Colo., , USA) of known chemical composition was digested and analyzed to ensure accuracy of the results.
Samples for analysis were ground in a slurry of ethanol using a McCrone micronizing mill with yttrium-stabilized zirconium (American Elements) grinding beads for five minutes to ensure particle sizes <5 μm. Collected slurries were dried overnight at 60° C. Next, 0.02±0.005 grams of each sample were mixed with 2.00±0.050 grams of potassium bromide (KBr) powder (dried at 70° C. overnight). Then, the powder mixtures were homogenized in a Spex Grinder mill and pressed into KBr disk pellets for analysis in a Thermo Scientific Nicolet iS10 FTIR Spectrometer. As a result, KBr disks with sample concentrations of 1% (by weight) were produced. Disks were analyzed against a blank background to remove the absorption spectra from the chamber purged with nitrogen.
To determine the mineralogy of (1) calcined precursors and (2) both synthetic and natural alkali-activated geopolymer binders, samples were first crushed into a powder with a mortar and pestle. The calcined precursor and synthetic geopolymer binder powders were well packed in XRD sample holders. Metakaolin-based geopolymer binders were prepared for mineral analysis using a modified method based on Eberl (2003). The former method was modified to employ corundum as an internal standard instead of zincite. All samples were analyzed in a Siemens D500 X-ray diffractometer to acquire X-Ray diffraction patterns for all samples. Samples were analyzed from 5 to 65 degrees 20 using Cu Ka X-ray radiation, with a step size of 0.02 degrees and a dwell time of two seconds per step. Mineralogy was identified using Jade software (MDI, Version 9) and the International Centre for Diffraction Data (ICDD) 2003 database.
Synthesized geopolymer cements herein have substantially uniform chemical formulations of Na1.22Si1.02Al.xH2O, see
Regardless of synthesis pH and I/O ratio, mineralogical differences were only observed in samples produced with different polymers, as illustrated in
To probe the molecular structure of all synthesized materials, Fourier-transform infrared spectroscopy (FTIR) was undertaken. FTIR was collected for each of the samples throughout the reaction (
In agreement with XRD diffractograms (
For PVA-derived uncalcined synthetic aluminosilicate precursors, regardless of pH or I/O, vibrational energy bands are observed with relatively the same peak location and peak intensity (
The analysis of the FTIR from PEG-derived systems indicates that, for a given processing condition, the material has similar vibrational energy, regardless of pH and I/O. However, key differences in the extent of geopolymer network formation (Si—O—Al) exist when compared to PVA-derived products. In the uncalcined state, vibrational energy bands for all samples are observed at relatively the same peak location and peak intensity (
29Si DP MAS-NMR technique (Bloch Decay) was used to study the silicon atomic structure of synthetic aluminosilicate materials.
Several other key differences exist between both synthesized geopolymer cements. For example, the average chemical shift in PEG-derived geopolymer cements (−83.67 ppm) was downfield-shifted to a greater extent than that of PVA-derived geopolymer cements (−89.01 ppm). Moreover, when compared to all geopolymer cements, PVA-L samples at low I/O ratio demonstrate a narrow linewidth (4.78 ppm) and further upfield shift (−89.95 ppm).
1H—29Si CP MAS-NMR experiments were conducted to study the presence of nearby hydrogen atoms to silicon nuclei. In general, PVA-derived and PEG-derived synthetic aluminosilicate precursors, as well as aluminosilicate powders, demonstrated a 29Si resonance of −105±5 ppm in 29Si CP MAS-NMR spectra, as expected, since cross-polarization techniques allow the resonances only from outer surface of the Al—O—Si network, which are near protons. Because of the inhomogeneous surface structure and nearby hydroxyl group, the peaks are downshifted in comparison to the bulk structure (−110 ppm vs −105 ppm). This downshift is more prominent in PEG-derived aluminosilicate powders as they exhibit 1H—29Si resonances between −100 ppm and −97 ppm, confirming the presence of single hydroxyl containing silica species (Q3). These differences may be explained by the fact that PEG-derived aluminosilicate powders at high polymer contents (low I/O ratio) do not undergo complete dehydroxylation and, thus, remnant single hydroxyls exist (Q3). Furthermore, adjacent water molecules may aid in the deshielding of Si atoms as evidenced by 29Si NMR spectra (
27Al MAS-NMR experiments were conducted to study the changes in aluminum atomic structure of synthetic aluminosilicate materials. All 27Al MAS-NMR spectra of uncalcined synthetic aluminosilicate precursors (PEG and PVA derived) show resonances at 0 ppm, confirming the presence of aluminum nitrate species (i.e., Al(VI)), which was added to prepare these precursors. Synthetic aluminosilicate powders demonstrated a peak at 8 ppm, indicating the presence of similar aluminum species with minimal environment differences (
Similarly, 1H—29Al CP-MAS NMR spectra of all uncalcined synthetic aluminosilicate precursors derived from PEG, as well as PVA, showed resonance near 0 ppm, indicating the presence of Al(VI) species. However, no 1H—29Al CP MAS-NMR signal was observed for all calcined synthetic aluminosilicate powders or geopolymer cements, regardless of polymer crosslinker used (
Hence, suggesting that Al(VI) species were incorporated in the network with oxygen, but they were very far from the nearby protons of water or hydroxyls. This observation suggests that water molecules were evaporated due to high temperature of calcination process, and polymers were volatilized from the Al—Si network in these calcined precursors, as expected from FTIR results. Similar results for geopolymers indicate the presence of Al(IV) species coordinated with SiO4 in a network with segregated Al(VI) phases as seen in the XRD data (
Differences in polymer architecture, more specifically, the absence of hydroxyls (i.e., PVA) and presence of ethers (i.e., PEG), result in phase segregation within the xerogel and, as a result, form γ-alumina in the synthetic aluminosilicate powder, as confirmed by XRD (
27Al δ
27Al-1H δ
27Al δ
27Al-1H δ
27Al δ
27Al-1H δ
Limited silicate incorporation into the gel 1→gel 2 evolution process within PEG-derived geopolymer cements may occur as observed by a higher 29Si NMR deshielding and higher variability of Si polymerization in FTIR results, when compared to PVA-derived samples as indicated in Table 2, Table 3 and Table 5. The gel 1 has been described as an initial Al-rich binder with a high content of Si—O—Al bonds relative to the bulk Si:Al ratio. This initial gel 1 is said to structurally evolve via condensation of silanols and incorporation of silicon metals, hence increasing the effective Si:Al ratio of the binder. The 29Si NMR resonances of PEG-derived geopolymer cements are downfield shifted between −80 ppm and −85 ppm, when compared to PVA-derived geopolymer cements as seen in Table 3. Deshielding of the 29Si nuclei may be due to next-nearest neighbor (Al) or structural distortions of the gel 2, which are hypothesized to be caused by limited silicate incorporation in the gel 1 precursor. Further confirming these results, FTIR results for PEG-derived geopolymer cements demonstrate geopolymer network formation as observed by peak shifts to lower wavenumbers corresponding to formation of Si—O—Si and Si—O—Al bonds (1120 cm−1→1060 cm−1), Table 3. Contrastingly, PVA-derived geopolymer cements exhibit greater extent of silicate incorporation in the gel 1→gel 2 evolution process as sharp and intense absorption peaks are observed to be centered around 1000 cm−1.
29Si δ
29Si-1H δ
29Si δ
29Si-1H δ
29Si δ
29Si-1H δ
(4A1)
(4A1)
(4A1)
(4A1)
(4A1)
(4A1)
(4A1)
(4A1)
indicates data missing or illegible when filed
Decreasing the polymer content (high I/O ratio) reduces Al metal-polymer coordination and results in partial γ-alumina formation for PEG-derived aluminosilicate powders (see
There are minimal differences in aluminosilicate powders synthetized with low or high pH sol-gel aging conditions, indicating that the order of chemical addition bears little effect on the synthesis procedure. For example, PVA-H aluminosilicate powders have slightly higher deshielding of their 29Si nuclei, as seen in Table 5. Moreover, when compared to samples synthesized with high PVA polymer contents, samples synthesized with a high pH sol-gel aging condition and low PVA polymer contents have a reduction in the absorption peak intensities associated with Si—O—Si and Si—O—Al bonds at ˜1060 407 cm−1.
However, when alkali-activated, synthetic aluminosilicate powders produced with low pH sol-gel aging conditions may improve the extent of geopolymerization and dictate the content of silanol groups in the resultant geopolymer cement. PEG-derived geopolymer cements synthesized with low pH sol-gel aging conditions exhibit higher absorption intensities for Si—O—Si and Si—O—Al bonds, when compared to PEG samples produced in high pH conditions (
All synthesized aluminosilicate precursors approximate the chemical composition of calcined clays (i.e., metakaolin) as evidenced by
29Si NMR (ppm)
27Al NMR (ppm)
The presence of extra-framework aluminum (EFAl) was reported in 2012 for metakaolin-based geopolymer cements with Si:Al and Na:Al atomic ratios of 1.6 and 1.0, respectively. The observed structural stability of these cements was attributed to the presence of these tetrahedrally coordinated aluminum ions (i.e., Al(IV)). More recently, EFAl with an Al(IV) resonance have been observed in geopolymer cements with Si:Al and Na:Al atomic ratios of 1.50 and 1.18, respectively.
Contrastingly, in the present examples, 27Al—1H NMR detected the presence of Al(IV) resonances at 60.5±1.5 ppm for PVA-derived geopolymer cements solely, which is in good agreement with results collected from the literature (Table 6). These cross-polarized nuclei resonances have been attributed in other studies to bridging hydroxyl groups (Si—OH+—Al, Brønsted-acid sites). Presence of these hydroxyl groups, both in Si and Al nuclei, have been shown to hydrogen bond with structural water molecules, resulting in the elongation of Al—O bonds. An important observation for the stability and durability of these cements.
Similar to studies of alkali-activated metakaolin, PEG-derived geopolymer cements have resonances at −107 ppm (Q4) from unreacted synthetic aluminosilicate powder (−103 ppm, attributed to Q3 Si-sheets, in metakaolin) and −85 ppm, indicative of Q4(4Al) aluminosilicate (
Data collected suggest three possible mechanisms by which the polymer-assisted sol-gel synthesis permits the incorporation of solubilized aluminum ions (Al+3). As depicted in
Architecture differences in polymer cross-linker oxide (i.e., ether, hydroxyl) may influence the polymer-metal interactions of Al+3 ions by inducing metal complexation or hydrogen bonding. Given that oxygen is a strong electron donor in both PVA and PEG systems, the electron-poor aluminum metal would tend to associate with these atoms to form complexes. Evidence for such metal-polymer complexes is observed for PVA-derived uncalcined synthetic aluminosilicate precursors, indicated by a shift of a vibrational peak centered around 1750 cm−1 in reagent PVA to 1730 cm−1 after polymer assisted sol-gel synthesis. The shift of this peak may indicate polymer-metal interactions between residual carbonyl groups on PVA polymer cross-linkers (an artifact from commercial fabrication of PVA from poly(vinyl acetate)) and the aluminum metal (at 1730 cm−1) (
For PEG-derived uncalcined synthetic aluminosilicate precursors, previous literature suggests that Al+3 polymer coordination occurs in the C—O—C stretching region between 1110-1105 cm−1. For this system, the 1100 cm−1 region corresponds to Si—O—Si vibrational stretching and bending frequencies, thus hindering the analysis of metal-polymer coordination for PEG-based systems. For both polymeric systems, it can be speculated that the hydration of components by water during the sol-gel aging would enable hydrogen bonding between water and pendant hydroxyl units, and, as the xerogels develop (i.e., dehydration), metal coordination may be enhanced, as with less volume the materials are more likely to interact. For both PEG and PVA systems, following calcination, the vibrational bands at 1730 cm−1, as well as broad vibrational bands from 3500-3000 cm−1 corresponding to O—H stretching frequency in both PVA and PEG-derived synthetic aluminosilicate powders, decrease in intensity. This decrease in intensity may indicate that the polymer, nitrate counter ion, and water were effectively removed following calcination, likely disrupting the Al+3 polymer coordination. Such disruptions may explain the absence of Al(IV) and distorted Al(VI) sites in the aluminosilicate powder, contrary to published literature.
29Si MAS-NMR (
Furthermore, narrow linewidths between 8.3 ppm and 17.4 ppm (
FTIR can be used to suggest mechanisms of inter- and intra-molecular coordination, such as hydrogen bonding in the xerogel. For both polymer architectures in the xerogel, the vibrational peak at 1650 cm−1 is attributed to H—O—H bending vibrations and is present in the FTIR of silica, aluminum nitrate, and PVA starting materials but at a lesser intensity than in the xerogel. The peak centered at 1650 cm−1 in conjunction with the broad stretching vibration of —OH centered at approximately 3400 cm−1 is often attributed to hydrogen bonding or water adsorption. For all xerogel materials, there is an increase in the intensity of these two vibrational frequencies. The increase in intensity may be attributed to hydrogen bonding between hydroxyl units between the polymers, silica, and bound water or to coordination of the silanol to aluminum following xerogel formation (
Contrary to previous publications, the presence of Al(IV) or distorted Al(VI) was not observed, likely due to differences in the polymer content (i.e., I/O ratio). As explained above, based on previous literature, it is known that Al+3 metal-polymer coordination occurs in the C—O—C stretching region between 1110-1105 cm−1. Consequently, polymer cross-linker complexation of Al+3 metal ions is expected to be the dominant mechanism for producing high-reactivity aluminosilicate powders, hence explaining the differences of results observed.
This disclosure described the effects of polymer architecture (i.e., PVA vs. PEG), polymer content (i.e., low vs. high ion-to-polymer-oxide (I/O) atomic ratio), and sol-gel aging pH conditions (i.e., low vs. high) on the atomic structure of resultant synthetic aluminosilicate powders and geopolymer cements.
Results have shown that polymer architecture is a primary factor in controlling phase segregation in synthetic aluminosilicate powders and the resulting mineralogy of geopolymer cements. The use of FTIR, XRD, and 29Si and 27Al single pulse and 1H cross-polarized MAS-NMR confirmed the effect of polymer architecture on the metal complexation of Al+3 ions, while PEG polymers yielded phase segregation during synthesis and formation of γ-alumina with a predominance of Al(VI) sites. Contrastingly, it is observed that the presence of hydroxyls in PVA may provide higher ion coordination competition, which results in synthetic aluminosilicate powders and geopolymer cements with single atomic environments. Moreover, PEG-derived synthetic aluminosilicate powders are most similar to the atomic environment of metakaolin (i.e., calcined clay).
A decrease of polymer content during synthesis is observed to improve reactivity of the precursor, improving the extent of binder formation in these samples, while sol-gel pH aging conditions (affected by order of reactant addition) reveals the ability to influence the content of Brønsted-acid sites (—OH groups) near the aluminum nuclei and geminal silanol groups within geopolymer cements. As a result, the molecular structure and mineralogy of resultant geopolymer cements is affected in the following order of significance: polymer type>polymer content>sol-gel pH aging condition. Finally, metakaolin-based geopolymers resemble the molecular structure and mineralogy of PVA-derived geopolymer cements. Thus, validating the further use of metakaolin as an aluminosilicate precursor to produce highly pure N-A-S-H cementitious binders.
Evidence collected supports three possible mechanisms by which the polymer-assisted sol-gel synthesis permits the incorporation of solubilized aluminum ions (Al+3) and formation of N-A-S-H (sodium-aluminum-silicate-hydrate) geopolymer binders. The proposed mechanisms are hypothesized to be related to: (1) complexation with polymer cross-linker, (2) hydrogen bonding with silanol, and (3) competition between polymer cross-linker coordination and silanol-based poly-condensation. It is expected that Al+3 metal-polymer competition dominates the mechanism for the production of high reactivity aluminosilicate powders.
The example embodiments of the disclosure described above do not limit the scope of the invention, since these embodiments are merely examples of the embodiments of the invention. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the disclosure, in addition to the embodiments shown and described herein, such as alternative useful combinations of the elements described, may become apparent to those skilled in the art from the description. Such modifications and embodiments are also intended to fall within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Application Ser. No. 62/885,748, filed on Aug. 12, 2019, and entitled Synthetic Aluminosilicate and of U.S. Provisional Application Ser. No. 62/914,887, filed on Oct. 14, 2019, and entitled Synthetic Aluminosilicate Material and Methods of Forming and Using Same.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2020/045804 | 8/11/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62885748 | Aug 2019 | US | |
| 62914887 | Oct 2019 | US |
