An organic solvent-saving method of preparing silica aerogel is reported. The silica aerogel was made from water glass (WG) and used as the solvent. Na+ was removed through ion exchange; prior to ...this ion exchange, concentrated hydrochloric acid (HCl) was added to the WG solution. The sol pH was adjusted to ~1 to suppress the condensation to the maximum extent. Ethanol was added to the sol after ion exchange. Surface modification was conducted with the assistance of hexamethyldisiloxane, which was catalyzed by HCl. The entire process can be finished in 6 h. The overall consumption of organic solvent is much lower than that in the previous preparation route. Characterization results indicate that the resulted silica aerogel has a uniform mesoporous structure and low thermal conductivity (0.0237–0.0245 W/m·K at 1 atm).
•Magnesium oxide modified by water glass prolongs the setting time of MKPC.•Modified magnesium oxide can promote the development of later strength of MKPC.•The effect mechanism of surface ...modification on the setting time of MKPC was studied.
In applying magnesium phosphate cement, controlling its setting time is of great importance, and the activity of the main raw material, magnesium oxide, is the key. In this study, dead-burned magnesia was modified with different amounts of water glass and different thermal treatment temperatures, and the effects of MgO on the macroscopic properties and microstructure of magnesium potassium phosphate cement (MKPC) were studied.The results show that the setting time of MKPC prepared with modified magnesia is prolonged, and the increase of the amount of water glass, the longer the setting time is.The setting time of the sample with 15% water glass and 300 °C treatment increased from 4.3 min to 17.5 min, an increase of 307%.The compressive strength results show that the surface modification of MgO decreased MKPC's early strength, which decreased with an increase in the water glass content and a decrease in the thermal treatment temperature.However, when the curing reached 7 days, the samples' compressive strength exceeded that of the reference group, and the strength development was optimum when the content of water glass was 5% with 300 °C treatment. The 28 d strength increased from 65.8 MPa of the reference group to 72.4 MPa, an increase of 10%.Through scanning electron microscopy (SEM), it was found that new phases were formed in the surface modified samples at the later stage of hydration. Combined with the results of energy-dispersive spectroscopy (EDS), it was confirmed that the magnesium silicate hydrate gels (M-S-H) were formed.The mercury intrusion porosimetry (MIP) test results show that these M-S-H gels can refine the pore size of MKPC, and the porosity of the sample with 5% water glass and 300 °C treatment was reduced from 6.6510% to 6.0429%, which explains the improvement in the MKPC compressive strength. Therefore, the surface modification of magnesium oxide can greatly extend its setting time without adversely affecting its later performance.
For thermal insulation to be sustainable, its performance and production efficiency must be considered. Foamed glass prepared from the mixture of waste cathode ray tube panel glass (CRT), Mn3O4 and ...carbon could become such a material assuming that its production efficiency could be improved. In light of this, the aim of the study was to engineer the transfer of the foaming process from inert to air atmosphere without drastically disturbing the primary mechanism of expansion. Foaming of carbon-containing mixtures in air atmosphere is normally a challenge due to premature oxidation of carbon by the oxygen from the air. Here, we systematically investigate how the addition of water glass (WG) affects the process by thermogravimetry coupled with mass spectrometry (TG/MS) and heating-stage microscopy analysis. Further, we propose an explanation about how WG protects the carbon and show that the addition of WG allows for the process to be successfully performed in air atmosphere. Two direct sources of expansion were identified (carbon-Mn3O4 reaction and WG) and quantitatively evaluated, allowing determination of an optimal addition of WG, 12 wt %, for the foaming temperature of 800 °C. The obtained foamed glass samples have a relatively low density and degree of open porosity, which reflects in their low thermal conductivity (λ). The lowest λ obtained was 39 mW m−1 K−1 at a density of 145 kg m−3, which is comparable to the samples prepared in inert atmosphere and best commercial products.
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•Water vapours displace the air and form less oxidative atmosphere within the sample.•Main expansion source identified from different combinations of additives.•Water glass content with minimum effect on primary foaming mechanism determined.•Obtained product with similar properties as in a controlled atmosphere.•Effective use of the process in the air atmosphere provides environmental benefits.
Converter steel slag, currently underutilized crystalline metallurgical residue, was investigated for use as a precursor for alkali activation. Water glass solution with various moduli (0.5, 1.0, 1.5 ...and 2.0) was used at the same Na
2
O dosage of 4% in order to investigate effect of modulus on hydration. Pure cement paste with the same ratio of water to binder was selected as the control sample. Results show that modulus has a significant impact on the hydration and mechanical strength development of alkali-activated steel slag. Similar to pure cement paste, alkali-activated steel slag paste has C–S–H gel and Ca(OH)
2
as its main hydration products. However, alkali-activated steel slag pastes have lower hydration heat and fewer amounts of hydration products. Additional silicate has a retarding effect on the hydration of steel slag. Hydration heat, Ca(OH)
2
contents and non-evaporable water contents reduce with increasing modulus. In addition, high silicate modulus fines the pore structure and improves compressive strength of the hardened paste.
Despite cement's superior performance and inexpensive cost compared to other industrial materials, crack development remains a persistent problem in concrete. Given the comparatively low tensile ...strength, when cracks emerge, a pathway is created for gas and water to enter the cementitious matrix, resulting in steel reinforcement corrosion which compromises the durability of concrete. Superabsorbent hydrogels have been developed as a novel material for enhancing the characteristics of cementitious materials in which they have been demonstrated to decrease autogenous shrinkage and encourage self-healing. This study will detail the design and application of polyelectrolyte hydrogel particles as internal curing agents in concrete and provide new findings on relevant hydrogel-ion interactions. When hydrogel particles are mixed into concrete, they generate their stored water to fuel the curing reaction that results in less cracking and shrinkage, thereby prolonging the service life of the concrete. The interaction of hydrogels with cementitious materials is addressed in this study; the effect of hydrogels on the characteristics and self-healing of cementitious materials was also studied. Incorporating hydrogel particles into cement decreased mixture shrinkage while increasing the production of particular inorganic phases within the vacuum region formerly supplied by the swollen particle. In addition, considering the control paste, cement pastes containing hydrogels exhibited less autogenous shrinkage. The influence of hydrogels on autogenous shrinkage was found to be chemically dependent; the hydrogel with a delayed desorption rate displayed significantly low shrinkage in cement paste.
► Calorimetry and strength gain of alkali-activated slag at various temperatures. ► NaOH activation is more effective at room temperature; water glass is at higher temperatures. ► Humidity is ...beneficial to mechanical property development at elevated temperatures. ► Effectiveness of KOH and NaOH appears dependent on curing temperature. ► Heat peaks associated with time of setting and strength gain are related, as is peak height to time.
Strength development of alkali activated slag (AAS) mortars, activated using alkali hydroxide and sodium silicate, was investigated at room and elevated temperatures. Heat evolution at room temperature was measured using isothermal calorimetry. Important differences were observed between critical activation parameters. Heat cured specimens gain strength rapidly, humid oven conditions being favorable, but given sufficient time room temperature curing yields comparable strengths. Both activators are needed for high strength at room temperature, NaOH solution is more critical and its concentration greatly influences strength. At 80
°C however, sodium silicate is essential and even sufficient. KOH is more effective than NaOH at 80
°C, but not at room temperature. Lower water-to-slag ratios give higher strength at early ages. AAS hydration evolves less heat than Portland cement hydration. Time to significant strength gain of mixtures can be predicted using their time and heat evolution at setting. Twenty eight-day strength of AAS mortars is roughly related to total evolved heat and increases nearly linearly with the amount of NaOH activator for fixed water glass content.
Silica aerogels are considered as promising materials for future energy saving buildings, however, their reliability remains questionable as commercially available aerogels can show relatively high ...standard deviations e.g. 22.2 ± 1.4 mW m−1 K−1. Therefore a synthesis protocol for silica aerogel powder with thermal conductivities having extremely reduced standard deviations was designed, compatible with mass production, i.e. reduced use of solvents and hydrophobization agents. Silica sols were prepared from non-ion exchanged water glass, while a combined solvent exchange, silylation and washing out of sodium ions was carried out using a hexane/trimethylchlorosilane/isopropyl alcohol solution with a molar ratio trimethylchlorosilane/pore water of only 0.11. The hexane amount was reduced 35 times compared to typical processes in literature. The aerogel powder was finally dried at ambient pressure at 150 °C. No notable shrinkage was observed for 8 wt% silica aerogel samples, having a thermal conductivity of 25.4 mW m−1 K−1 with a standard deviation of only 0.1. The 6 wt% silica aerogels had a thermal conductivity of 23.4 mW m−1 K−1 with a standard deviation of 0.3, but had shrunken 36%. By replacing trimethylchlorosilane with hexamethyldisiloxane, aerogels having a thermal conductivity of 22.4 mW m−1 K−1 with a standard deviation of 0.3 were obtained.
•Synthesis of silica aerogel powder dried at ambient pressure.•Fairly simple, more sustainable and cheaper protocol than more conventional methods.•Water glass as precursor without need for ion exchange or separate washing•Minimal amount of solvent and hydrophobization agent was used•High porosities and low thermal conductivities were measured
A more facile method was used to form the amorphous silica layer onto FeSiCr alloy powder, which can promote electromagnetic properties of SMC.
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•SiO2 coating onto FeSiCr alloy powder ...effects on electromagnetic properties was investigated.•A more facile method was used to form the amorphous silica layer.•Amorphous silica layer can promote electromagnetic properties of SMC.
The effects of amorphous SiO2 coating onto FeSiCr alloy powder on the electric and magnetic properties were investigated. FeSiCr alloy powder with an average particle size of 10 μm was coated with nano-sized silica powder to increase the resistivity and DC bias superposition characteristics. Inexpensive water glass (sodium silicate) was used as the raw material to form the amorphous silica layer onto the FeSiCr alloy powder surface acting as a binding and insulation layer. The amorphous silica layer thickness was about 20 nm to 50 nm. The thickness can be controlled by the amount of sodium silicate addition. The amorphous silica layer can significantly promote anti-oxidation, resistivity and DC bias superposition characteristic of the FeSiCr alloy.
Geopolymer recycled aggregate concrete (GRAC) was prepared by replacing cement with geopolymer and natural aggregate with waste concrete. The effect of the water-glass module on the mechanical ...properties of GRAC was studied. It was found that water-glass has a double-layer structure. The low module water-glass leads to a thicker diffusion layer and more Na+ and OH− in the solution, which activates more CaO, SiO2, and Al2O3 in the raw material, and improves the strength of GRAC. Moreover, two kinds of gel structures, namely layered C-A-S-H (calcium silicate hydrate) and networked N-A-S-H (zeolite), were found in the products of geopolymer. As the water-glass module changed, the phase of zeolite changed significantly, whereas the calcium silicate hydrate did not change, indicating that the decrease in the water-glass module contributes to the formation of more N-A-S-H gel. The compressive strengths of GRAC with the sizes of 200, 150, and 100 mm3 were in line with Bazant’s size effect theoretical curve. Through the segmented fitting method, the relationship of the size conversion coefficient of GRAC (α), the critical strength (fcr), the critical dimension (Dcr), and the water-glass module (ε) were determined. It was found that ε = 1.5 is the segmented point of the three equations. The elastic modulus and peak stress of GRAC are inversely proportional to the water-glass module, and the peak strain is proportional to the water-glass module, indicating that by reducing the water-glass module, the strength of GRAC can be improved, but the brittleness is increased. The constitutive equation of GRAC with only the water-glass module as a variable was also established. It was found that the polynomial mathematical model and rational fraction mathematical model are optimal for the rising-stage and falling-stage, respectively, and the relationship between the parameters of the rising-stage (a) and the falling-stage (b), and the water-glass module, is given.
To reduce the production costs of glass-ceramics and broaden the application field of solid waste in steel industry, low-density and high-strength glass-ceramics were produced by using blast furnace ...slag as the basic material, choosing glass fiber and water glass as the strengthening agents. The effects of glass fiber and water glass on the phase composition, microstructure, apparent density, water absorption and compressive strength of glass–ceramics were investigated. The results show that the rod structure of glass fiber can be retained in the sintered samples and high content of diopside and augite significantly improve the compressive strength of glass-ceramics. Tiny spherical crystalline phases can be obtained for the glass-ceramics soaked in the moderate concentration of water glass. The BGW-2 samples fabricated with 70% blast furnace slag, 30% glass fiber and 4% water glass, exhibit excellent comprehensive properties. The bulk density, water absorption and compressive strength of BGW-2 are 1.76g/cm3, 2.26% and 68MPa, respectively. Consequently, using blast furnace slag to prepare glass-ceramics can be another applicable way to utilize blast furnace slag efficiently.
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