MgO Ratios Research Articles

1,3-Butadiene production from aqueous ethanol over ZnO/MgO-SiO2 catalysts: Insight into H2O effect on catalytic performance

A series of ZnO/MgO-SiO2 systems have been prepared and characterized by one-pass temperature-programmed desorption of CO2, NH3 and H2O, FTIR spectroscopy with adsorbed pyridine and CO2, temperature programmed surface reaction of ethanol and isopropanol, and reaction of isopropanol conversion. Effect of MgO:SiO2 ratio in the catalysts on catalytic performance in 1,3-butadiene production from aqueous ethanol have been investigated. The results indicate that hydrophilicity of ZnO/MgO-SiO2 are determined by MgO:SiO2 ratio, and chemisorption of water occurs preferably on Mg-containing sites. The presence of water in the initial ethanol leads to a decrease in formation of the CC coupling products. The hydrated sites formed in the interface of magnesia and silica remain active in the CC coupling reaction even in the presence of water. 1,3-Butadiene selectivity >60 % in the conversion of aqueous ethanol (80 vol%) is achieved in the presence of ZnO/MgO-SiO2 catalysts with the ratio of MgO:SiO2 = (1:1) and (3:1).

Preparation of Mg-Zr alloys through direct electro-deoxidation of MgO-ZrO2 in CaCl2-NaCl molten salt

The electro-deoxidation of MgO does not proceed efficiently due to the electrical insulation properties of MgO and large molar volume of metallic magnesium. In this experiment, an attempt was done to prepare Mg-Zr alloy from their oxides using the method of electro-deoxidation. The electrochemical mechanism of the deoxidation process of MgO, ZrO2 and MgO-ZrO2 composite was studied through cyclic voltammetry using metallic cavity electrode (MCE). There was an intermediate phase (Zr3O) in the reduction process of ZrO2. The electro-deoxidation of MgO occurred for MgO-ZrO2 composite in CaCl2-NaCl molten salt. Moreover, the electro-deoxidation of MgO was promoted by the addition of polyvinyl butyral (PVB). The formation of metal phase Mg was confirmed by XRD, EDS, Raman spectroscopy, and inductively-coupled plasma spectroscopy. The electro-deoxidation products showed significant differences with the concentration of PVB and the ratio between MgO and ZrO2. The electro-deoxidation of MgO and ZrO2 was favorable when the PVB concentration was 5.0% (wt.%). Pure metal phase of Mg-Zr alloys was formed when the molar ratio of MgO and ZrO2 was 1:2. The atomic fraction of Mg in the electrolytic product was ca. 28.0 mol.%. This work shows that MgO could be directly electro-deoxidized to Mg without the formation of intermediate phase oxide.

Chemically-Bonded Magnesium Phosphate Ceramics from Magnesium Oxide-Graphite Refractory Brick Waste

In Brazil, the production of each ton of steel generates approximately 621 kg of waste and direct co-products. One of the components that generates a high amount of waste is the refractory material used in the steel process. So, in this study, the possibility of using MgO-C refractory waste from steel casting pots after their deterioration for the formation of chemically bonded phosphate ceramics was investigated. This work aims to study the recovery of industrial solid waste from MgO-C refractories by determining the processing conditions necessary to obtain magnesium phosphate ceramics. Three mean particle size of the waste and three potassium monophosphate:MgO ratio in the mixture were adopted. All mixtures showed the formation of the K-struvite phase and a strong relationship between the compressive strength and porosity properties. The highest compressive strength value obtained, 7.51 ± 0.24 MPa, is sufficient for use in several areas of engineering. It was also possible to statistically represent, using a quadratic model, the variation in porosity in relation to the phosphate content and particle size of the waste, obtaining porosities ranging from 14% to 25%. Taking into account this study used a waste, the evaluation of its environmental impact assumed an important role. The waste showed no appreciable toxicity, while some samples W3-20 showed toxicity to Allium cepa L. and Artemia salina. Considering the presented properties, the obtained material could be used as a structural block, filters, support for catalysts, and repair element for cement-based structures and roadways.

Raw material ratio optimisation of magnesium oxychloride cement using response surface method

To improve the mechanical properties of magnesium oxychloride (MOC) cement, its raw materials ratio was optimized using the response surface method (RSM). The effects of the molar ratios of MgO/MgCl2 and H2O/MgCl2 on the compressive strength of MOC cement was were analysed using single-factor tests. Based on the results of the single-factor analysis, the factors and levels of the response surface test were determined. The response surface was established using a binary cubic equation, which fit well with the experimental data. It was predicted by RSM that when the molar ratio of MgO:MgCl2:H2O is 7.56:1:13.51, the compressive strength of the MOC cement would be the highest. The compressive strength of the samples fabricated according to the predicted ratio was 105.48 MPa, and the experimental value was 6.29% higher than the predicted value. The factors contributing to the high strength of the optimised samples were explained using X-ray diffraction and scanning electron microscopy, and it was proved that RSM had a guiding significance in optimising the performance of MOC cement.

Effect of volume ratio on optical and mechanical properties of Y2O3-MgO composites fabricated by spark-plasma-sintering process

The effect of Y2O3:MgO ratio on the microstructures, optical and mechanical properties of the Y2O3-MgO composites were investigated. Although the dense Y2O3-MgO composites were successfully fabricated in various Y2O3:MgO ratios using the spark-plasma-sintering (SPS) technique, the Y2O3:MgO ratio significantly influenced the microstructures and the optical/mechanical properties of the composites. Fine grain size was obtained in the composite with Y2O3:MgO = 50:50 owing to the effective pinning force caused by the homogenous two phase microstructure. The SPSed dense composites showed good transmittance in the wide wavelength range from visible to infrared (IR). The monolithic Y2O3 polycrystal, that is Y2O3:MgO = 100:0, showed the highest transmittance of 62.3 % at 600 nm and 84.3 % at 5 μm. Although the IR transmittance is independent of the Y2O3:MgO ratio, the visible transmittance decreased with the MgO particle dispersion. Among the Y2O3-MgO composites, the higher visible transmittance was obtained in the composite with Y2O3:MgO = 50:50 than those of the other two composites with Y2O3:MgO = 30:70 and 70:30 due to its smallest grain size. In contrast to the transmittance, the hardness Hv and toughness KIC tend to increase with increasing the MgO fraction irrespective of the grain size; both Hv and KIC increased from 9.6 GPa and 1.1 MPa m1/2 for the monolithic Y2O3 to 12.7 GPa and 2.5 MPa m1/2 for the composite with Y2O3/MgO = 30:70, respectively. The enhanced hardness and toughness of the composite can be interpreted dominantly by the mixture rule as a function of the volume fraction of the MgO phase.

Hot Pressed Si3N4 Ceramics Using MgO–Al2O3 as Sintering Additive for Vehicle Engine Parts

In an attempt to optimize a qualified ceramic material with enhanced and outstanding characteristics, the current work aims to study the processing of dense Si3N4 based ceramic composites by the hot pressing (HP) method. The proposed material consists of an equimolecular mixture of α- and β-Si3N4 with the addition of various amounts of MgO–Al2O3 spinel as sintering additive. Investigation of the different characteristics of the obtained ceramics with respect to densification parameters, hardness, fracture toughness, and bending strength and cold crushing strength was performed and correlated with their microstructure behavior. Results indicated that a dense, well distributed structure of silicon nitride ceramics was attained by the addition of various amounts of magnesium aluminate spinel. Moreover, insertion of MgO–Al2O3 mixtures into Si3N4 ceramics was established to enhance their grain growth demeanor and increase the elongated β-Si3N4 grains and their aspect ratio. Furthermore, it was revealed that increasing the MgO ratio relative to that of Al2O3 in the spinel structure was responsible for enhancing the different properties of the produced nitride ceramics. Results suggested that the obtained hot pressed Si3N4 ceramics seeded with β- Si3N4 particles can be a successful candidate in the automotive industry as alternative parts for vehicle engines.

Carbon sequestration of steel slag and carbonation for activating RO phase

Carbonation of Ca/Mg minerals in industrial alkaline residues is a technology to sequester CO2 and reduce its emissions to the atmosphere. In this work, BSE-EDS were used to determine the mineral phase in steel slag; compositions of RO phase were identified and simulated. The carbon sequestration of steel slag was studied, and RO phase was activated by carbonation. Result shows that the amount of CO2 sequestered in steel slag and RO phase increases as carbonation time increases. Under autoclaving condition, the hydration ratio of MgO in RO phase was 20.10%. Through carbonation, up to 58.83% of MgO in RO phase can be converted into MgCO3, and the activation of RO phase by carbonation was manifested. The mechanical properties and volume stability of carbonated steel slag were improved, proving that the positive effect of carbonation on steel slag when applied in cement and cementitious materials.

Effect of basicity and Al2O3 on viscosity of ferronickel smelting slag

The effect of the Al2O3 content and basicity (the molar ratio of MgO to SiO2) on the viscosity of a SiO2–MgO–FeO–Al2O3–CaO slag was studied to fully understand the smelting process of the ferronickel alloy. Experimental results show that the slag is a mixture of liquid and solid phases at the experimental temperature. The viscosity decreased as the basicity increased and increased as the Al2O3 content increased. To determine the effect of the Al2O3 content and basicity on the structure of the molten slag, Raman spectroscopy was performed on the slag sample, which was quenched from the high temperature with water. The Raman spectra showed that the fractions of the polymerization structural units decreased significantly as the basicity of the slag increased, resulting in a decrease in the apparent viscosity. However, Al2O3 acts as a network former in the slag system, thereby making the slag structure further polymerized and increasing the viscosity.

Hot pressed Si3N4 ceramics using MgO–Al<sub>2</sub>O<sub>3</sub> as sintering additive for vehicles engine parts

In an attempt to optimize a qualified ceramic material with enhanced and outstanding characteristics, the current work aims to study the processing of dense Si 3 N 4 based ceramic composites by hot pressing method. The proposed material consists of an equimolecular mixture of α and β-Si 3 N 4 with adding of variant amounts of MgO‒Al 2 O 3 spinel as sintering additive. Investigation of the different characteristics of the obtained ceramics with respect to densification parameters, hardness, fracture toughness, bending strength and cold crushing strength was performed and correlated to their microstructure behavior. Results indicated that dense well distributed structure of silicon nitride ceramics was attained by adding of variant amounts of the magnesium aluminate spinel structure. Moreover, insertion of MgO‒ Al 2 O 3 mixtures to Si 3 N 4 ceramics was established to enhance their grains growth demeanor, increased the elongated β-Si 3 N 4 grains and their aspect ratio. Furthermore, it was revealed that, increasing MgO ratio relative to Al 2 O 3 one in the spinel structure was responsible for enhancing the different properties of the produced nitride ceramics. Results suggested that the obtained hot pressed Si 3 N 4 ceramics seeded with β-Si 3 N 4 particles can be a successful candidate in automotive industry as alternative parts for the vehicle engines.

Geochemistry of the Villismán granite, associated aplite-pegmatites and surrounding Li-pegmatites, Sierra de Ancasti, Argentina

The Villismán pegmatite group belonging to the Ancasti district of the Pampean Pegmatite Province is geologically formed by banded schists of the Ancasti Formation which are intruded by the homonymous granitic stock and Li-pegmatites. It is located in the northern sector of the Sierra de Ancasti, Catamarca province, Argentina. The Villismán stock -VG- is a small, sub-rounded in shape two-mica-syenogranite. The VG hosts felsic aplitic and pegmatitic dykes -FDVG- with muscovite, black-tourmaline (schorl) ± garnet as main accessory minerals. The Li-pegmatites contain giant crystals of spodumene and are classified as of the Rare-Element class (REL) and REL-Li subclass pegmatites and belong to the LCT (Li–Cs–Ta) pegmatite family. They are more or less symmetrically zoned with outward zones composed of felsic aplite and coarse-grained to very coarse-grained granite -OZLiP-. The minerals of OZLiP are quartz, feldspars (secondary albite ‘cleavelandite’ predominant over K-feldspar), muscovite and scarce black-tourmaline (schorl), garnet and F-apatite. The VG, FDVG and OZLiP have high and similar SiO2 concentrations (72–78 wt %). They are peraluminous (ASIVG 1.10–1.16; ASIFDVG 1.23–1.77, ASIOZLiP 1.00–1.14). The VG has subalkaline-calc alkaline character with K2O > Na2O. Ferromagnesian elements (included Ti) and CaO have low concentrations in VG and the FeOt/FeOt + MgO ratio is low (0.80–0.82) classifying it as magnesian granite. High Rb/Sr (FDVG ~16; OZLiP ~19) and Rb/Ba (FDVG ~41; OZLiP ~ 7) and low K/Rb (FDVG ~107; OZLiP ~56) ratios clearly indicate that aplites and pegmatites are geochemically more evolved than the Villismán Granite (Rb/SrVG ~ 3; Rb/BaVG ~ 0.8; K/RbVG ~ 161). The Zr-saturation temperature in the granites, as expected, is higher than in the dykes and the outward zones of the Li-pegmatites. The VG is a post-orogenic granite developed in the easternmost sector of the Ordovician Famatinian active arc. All geological, mineralogical and geochemical features of the VG are comparable to typical S-type granites, probably originated from partial melting of the metasedimentary rocks of the Ancasti Formation. FDVG could have been formed by fractional crystallization from the VG parental-magma.

Effect of Structure and Composition of Non-Stoichiometry Magnesium Aluminate Spinel on Water Adsorption.

MgAl2O4 is used in humidity sensing and measurement, and as a catalyst or catalyst support in a wide variety of applications. For such applications, a detailed understanding of the surface properties and defect structure of the spinel, and, in particular, of the gas interactions at the spinel surface is essential. However, to the best of our knowledge, very limited experimental data regarding this subject is currently available. In this work, four spinel samples with an Al2O3 to MgO ratio (n) between 0.95 and 2.45 were synthesized and analyzed using X-ray photoelectron spectroscopy and water adsorption micro-calorimetry. The results showed that the spinel composition and its consequent defect structure do indeed have a distinct effect on the spinel-water vapor surface interactions. The adsorption behavior at the spinel-water interface showed changes that resulted from alterations in types and energetic diversity of adsorption sites, affecting both H2O uptake and overall energetics. Furthermore, changes in composition following appropriate thermal treatment were shown to have a major effect on the reducibility of the spinel which enabled increased water uptake at the surface. In addition to non-stoichiometry, the impact of intrinsic anti-site defects on the water-surface interaction was investigated. These defects were also shown to promote water uptake. Our results show that by composition modification and subsequent thermal treatments, the defect structure can be modified and controlled, allowing for the possibility of specifically designed spinels for water interactions.

Study on the effect of glass on the properties of Na2CO3-K2CO3 eutectic salt/MgO composite as phase change thermal storage materials

ABSTRACT The salt/ceramic phase change materials (PCMs) have a good thermal storage performance and high application temperature. In this paper, we studied the effect of glass as additive on the mechanical properties, thermal storage, and morphology of the Na2CO3-K2CO3 eutectic salt/MgO composite PCMs. The results show that glass can effectively improve the compressive strength of MgO matrix material. When the mass ratio of glass and MgO is 7:3, the compressive strength of the composite body can be up to 104.3 MPa. When the mass ratio of Na2CO3-K2CO3 eutectic salt, MgO, and glass is 55:25:20, the composite PCM body has a good stable form, and its total heat storage is 788 J/g, which increased by 6.7% compared with the total heat storage of composite PCMs without glass in the range of 150°C~750°C. When the mass ratio of Na2CO3-K2CO3 eutectic salt, MgO, and glass is 55:15:30, the composite PCM body cannot maintain stable form.

NaNO3 -Promoted Mesoporous MgO for High-Capacity CO2 Capture from Simulated Flue Gas with Isothermal Regeneration.

NaNO3 -promoted MgO composite materials have been prepared and their ability to sorb CO2 at a concentration relevant to CO2 capture from flue gas is explored. The uptake kinetics and capacities of sorbents of different NaNO3 /MgO ratios are measured at intermediate temperatures of 230-300 °C. The sorbent with a NaNO3 /MgO ratio of 0.10 has the highest 12 h sorption capacity among sorbents with different NaNO3 loadings, and the highest sorption capacity of 11.2 mmol g-1 is observed at 260 °C. Intriguingly, an induction period is observed in the initial stage of CO2 sorption. In situ XRD analysis, in situ FTIR spectroscopy, and a comparison of the CO2 sorption behavior under simulated flue gas conditions in comparison to prior studies employing pure CO2 indicated that the sorption of CO2 occurred through nucleation of MgCO3 crystallites in the material. The data indicate that the concentration of CO2 within the molten medium of NaNO3 , which is affected by both the solubility of CO2 in molten NaNO3 and the partial pressure of CO2 in the surrounding atmosphere, has a critical impact on the length of the induction period. A partially desorbed sample after sorption of CO2 displays much-improved sorption kinetics in the next cycle and was able to sorb and desorb CO2 over multiple cycles at isothermal conditions by simply switching the feed gas from CO2 to inert gas.

Zircon U–Pb ages, geochemistry, Sr–Nd–Hf isotopic compositions, and geological implications of the Shaziling pluton in the Nanling Orogenic Belt, southern China

Laser ablation–inductively coupled plasma–mass spectrometry zircon U–Pb ages indicate that the Shaziling pluton in the Jiuyishan area, Ningyuan County, Hunan Province crystallised at 151.9 ± 1.1 to 154.1 ± 1.2 Ma, indicating that it was emplaced during the Late Jurassic. The Shaziling pluton is metaluminous to peraluminous (A/CNK = 0.93–1.09), and has high silica and alkali contents, low Ca and Mg contents, and K2O/Na2O and FeO*/MgO ratios of 1.37–2.65 (mean = 1.80) and 5.43–15.33 (mean = 7.14), respectively. The total rare earth element (REE) content varies from 186.75 to 413.17 ppm, and the pluton is enriched in light REEs and shows negative Eu anomalies (0.095–0.224). It is enriched in the large‐ion lithophile elements Rb and Th, and depleted in Ni, Cr, Eu, Ti, V, P, and Sr. The pluton yields Ga/Al ratios of 245–582 ppm (mean = 350 ppm) and Zr + Nb + Ce + Y contents of 256.8–630.7 ppm (mean = 441.95 ppm), similar to A‐type granites. The Shaziling pluton has a high initial 87Sr/86Sr ratio (Sri = 0.71603–0.71817), and low εNd(t) (−6.8 to −7.4) and εHf(t) (4.8 to −14.2) values. The granitic magmas were produced by partial melting of crustal material, along with a mantle contribution. The Nd and Hf model ages are 1546–1498 and 1756–1061 Ma, respectively, suggesting that the source rocks separated from the mantle reservoir during the Mesoproterozoic. The Shaziling pluton was formed in an intracontinental extensional environment related to subduction.

Jet fuel and hydrogen produced from waste plastics catalytic pyrolysis with activated carbon and MgO

Catalytic pyrolysis of waste plastics to produce jet fuel and hydrogen using activated carbon and MgO as catalysts was studied. The effects of catalyst to waste plastics ratio experimental temperature, catalyst placement and activated carbon to MgO ratio on the yields and distributions of pyrolysis products were studied. The placement of catalysts played an important role on the catalytic pyrolysis of LDPE, and the pyrolytic volatiles first flowing through MgO and then biomass-derived activated carbon (BAC) could obtain an excellent result to produce H2 and jet fuel-rich products. The higher pyrolysis temperature converted diesel range alkanes into jet fuel range alkanes and promoted the aromatization of alkanes to generate aromatic hydrocarbons. BAC and MgO as catalysts had excellent performance in catalytic conversion of LDPE to produce hydrogen and jet fuel. 100 area.% jet fuel range products can be obtained in LDPE catalytic pyrolysis under desired experimental conditions. The combination of BAC and MgO as catalysts had a synergy effect on the gaseous product distribution and promoted the production of hydrogen, and up to 94.8 vol% of the obtained gaseous components belonged to hydrogen. This work provided an effective, convenient and economical pathway to produce jet fuel and hydrogen from waste plastics.

A Highly Stable and Efficient Co–Mg–Sr Mixed Oxide Catalysts for Hydrogen Production from Glycerol Steam Reforming

The production of hydrogen from glycerol steam reforming (GSR) was studied over a series of Co–Mg–Sr (CMS) mixed oxide catalysts. Co-precipitation method was adopted to prepare catalysts by varying the molar ratios of MgO–SrO and keeping Co3O4 content constant. The physico-chemical properties of the samples were investigated by BET surface area, X-ray diffraction, hydrogen chemisorption, temperature programmed reduction, temperature programmed desorption of CO2, Raman spectroscopy and CHNS analysis. The reforming activity depended on the composition of the metal oxides. The catalyst with Co–Mg–Sr molar ratio of 3:1:1 exhibited the highest catalytic activity at 700 °C. Glycerol was completely converted to gaseous products and showed 72% hydrogen yield. Catalytic activity of the catalysts was explained on the basis of cobalt particle size, basicity and metal oxides interaction. The catalysts basicity originating from MgO–SrO is also playing an important role in GSR. The present catalyst activity was unaltered even after 100 h of time on stream analysis.

Syngas production by catalytic pyrolysis of rice straw over modified Ni-based catalyst

Ni-xLa/Al2O3-MgO-sawdust char catalysts were prepared by modifying the Ni/Al2O3 catalyst from two aspects of support and active components. The effect of Al2O3, MgO, sawdust char molar ratio, and La content of catalysts on syngas (H2 + CO) production in the catalytic pyrolysis of rice straw was investigated in a horizontal fixed-bed quartz tube reactor. Furthermore, the stability of catalysts with the optimum catalytic performance was tested and compared with that of the Ni/Al2O3 catalysts. X-ray diffraction, X-ray fluorescence, field emission scanning electron microscopy, energy disperse X-ray, and Brunauer-Emmett-Teller analyses were applied to understand the physiochemical properties of the supports and catalysts. The study revealed that the supports were composed of many irregular flaky particles and thus formed many pores. Moreover, the addition of La decreased the particle size of NiAl2O4 and increased the active metal surface of the Ni/Al2O3-MgO-sawdust catalysts. When the molar ratio of Al2O3, MgO, and sawdust char was 1:1:1 and the La content was 10 wt% (dry weight basis), the catalysts presented the highest syngas concentration of 78.9 vol% and the most stable performance during the catalytic pyrolysis process.

Eu3+ -Eu2+ -doped xAl2 O3 -ySiO2 and xAl2 O3 -zMgO composites phosphors.

In this paper, the Eu3+ -Eu2+ (4%, molar ratio)-doped xAl2 O3 -ySiO2 (x = 0-2.5, y = 1-5) and xAl2 O3 -zMgO (x = 0-1.5, z = 0-3) composites phosphors with different Al2 O3 to SiO2 (A/S) and Al2 O3 to MgO (A/M) ratios were prepared using a high-temperature solid-state reaction under air atmosphere. The effects of the A/S and A/M on luminescence properties, crystal structure, electron spin resonance, and Commission Internationale de l'Eclairage chromaticity coordinates of the samples were systematically analyzed. These results indicated that the different A/S and A/M ratios in the matrix effectively affected the crystal phase, degrees of self-reduction of Eu3+ , and led the relative emission intensity of Eu2+ /Eu3+ to change and adjust.

A preliminary investigation of the properties of potassium magnesium phosphate cement-based grouts mixed with fly ash, water glass and bentonite

Water inflow in a karst area has the characteristics of a large water volume and a fast flow rate, which makes the water inrush of a karst conduit flow extremely difficult to treat. Ordinary inorganic grouting materials have weak bonding with the interface, long initial and final setting time intervals and high loss rates of dynamic water filling. Phosphate cement has good interfacial bonding and instantaneous final setting after the initial setting, which is suitable for dynamic water conduit plugging. In this work, we developed anti-scouring grouts based on light-burned magnesia, potassium dihydrogen phosphate, Class F fly ash, water glass, and bentonite. A condensate based on potassium magnesium phosphate cement (MKPC) is formed using Class F fly ash (0–30%) to replace some of the MgO and KH2PO4. Then, the three materials form a cementitious material system. The water-cement ratio is 1:1 and is then modified with bentonite (5%) and water glass (0–6%). The basic properties of the grouts were studied by measuring the setting time, viscosity, compressive strength (after 3 d, 7 d, and 28 d), and flow distance. The microscopic properties of the hardened stone were studied by using both X-ray diffraction (XRD) and scanning electron microscope (SEM). The experiments show that the molar ratio of MgO to KH2PO4 (M/P) along with the water glass and fly ash contents play a significant role in the setting time, compressive strength, and viscosity of the grouts. The addition of fly ash can reduce the fluidity of the grouts and the early strength; however, the 28-day compressive strength of the grouting material mixed with 30% class F fly ash is higher than that of the grouting material mixed with 10% and 20% Class F fly ash. Water glass can reduce the setting time and fluidity of the grouts and can increase the strength of the grouts.

An Inorganic Magnesium-based Consolidant for the Consolidation of Silica Sand (A Substitute for Weathered Sandstone): A Preliminary Exploration

ABSTRACT Sandstone is a common sedimentary rock that is easily carved due to its weakly cemented fine grains and relatively low strength. Therefore, numerous large-scale grottoes in China are made of sandstone. However, these sandstone cultural heritage structures are often seriously damaged due to temperature and humidity changes, air pollution, biodeterioration, and repeated dissolution and crystallization of soluble salts. In general, it is imperative that a consolidant capable of providing cohesion by infilling pores between the stone grains is synthesized. In recent years, it has been reported that using organic consolidation materials for sandstone protection comes with various negative effects, such as a short lifetime, poor compatibility, and preservation damage. Using inorganic consolidation materials to protect sandstone seems to be one of the research trends for the future. Herein, this paper introduces a permeable, inorganic magnesium-based material (MMH solution) for silica sand consolidation. To assess this consolidant, the paper investigates the influence of varying molar ratios of MgO:MgCl2·6H2O:H2O on properties such as penetration depth, consolidation weight, colour variation, and compressive strength. The results demonstrate that the molar ratios of MgO:MgCl2·6H2O:H2O can significantly affect the consolidation performance. Additionally, it is believed that the MMH solution of MgO:MgCl2·6H2O:H2O = 5:1:16 can be successfully used for the consolidation of silica sand, as the cubic specimens’ surface micrographs show good compatibility between the consolidation product and sand grains. Experiments (i.e. weight loss rate and mineralogical compositions analysis) are performed to evaluate the cubic specimens’ water resistance properties after being immersed in water. Furthermore, the consolidation material’s failure mechanism as a self-sacrificing material is preliminarily analyzed. Results indicate that MMH solution is a promising conservation material that shows great potential for consolidating severely weathered sandstone.