Search Results (16)

Paint loss is one of the main forms of deterioration in historical wall paintings, generally restored by the application of chromatic reintegration. In the specific case of outdoor exposed paintings, it is essential to find a binder that will withstand diverse weather conditions. Since chromatic reintegrations have to be compatible with the original painting, fresco paint mock-ups were manufactured and compared to chromatic reintegrations made with an aqueous colloidal dispersion of silica nanoparticles as binder. The physical compatibility was studied by colour spectrophotometry and measurements of static contact angle, gloss, and roughness values, together with a peeling test, stereomicroscopy, and polarised light microscopy. They were also characterised from a mineralogical, chemical, and molecular point of view using X-ray diffraction, X-ray fluorescence and Fourier-transform infrared spectroscopy. The microtexture was studied by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Chromatic reintegrations showed similar roughness and lower gloss values than frescoes, and the nano-silica binder ensured the natural breathability of the wall. Overall, the chemical nature of pigments was highly influential. The reintegrations with silicate-based pigments were more homogenous, with hardly any fissures, while those carried out with sulphide- or oxide-based pigments were severely cracked. The use of verdigris is discouraged due to the lack of affinity between the binder and the pigment. Full article

Binder jetting is the most widely implemented additive technology for the fabrication of sand molds. However, the use of furan binder-jetting technology in the production of molds for vacuum casting is hindered by the thermal destruction of the furan binder accompanied by violent gas emission that occurs during the mold heating process. This investigation explores the potential of using the molds obtained via furan binder jetting 3D printing and further impregnation in colloidal silica binder and sintering. Two distinct sands, proppant and cenosphere, were utilized in the fabrication of the mold components exhibiting different thermal properties. An examination of the structure of the initial sands and samples produced via different impregnation and sintering regimes was conducted via scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray diffractometry, thermogravimetric analysis, and micro computed tomography. Furthermore, the bending mechanical properties and linear shrinkage of the samples were determined. The experimental findings demonstrated that the specific impregnation and sintering regimes examined in this study yielded sufficient mechanical properties for the casting molds and the structure with cristobalite bridges. The mold assembly, composed of proppant and cenosphere sands-based parts, was produced, and impeller nickel-based superalloy castings were fabricated. The findings of this study demonstrate that the utilization of a furan binder-jetting technique, in conjunction with impregnation in colloidal silica binder, is a promising technology for the manufacture of high-melting-temperature alloy casting. Full article

In the domain of metal casting, investment casting is recognized for its proficiency in producing high-quality castings. This method involves the utilization of a melt out, burnout, or soluble patterns to create ceramic molds. The present investigation explored the potential of utilizing fused deposition modeling (FDM) patterns fabricated from polyvinyl alcohol (PVA). An examination of the structural characteristics and properties of several commercially available PVA filaments, along with an evaluation of the as-printed samples, were provided in this study. It was demonstrated that commercial PVA filaments may contain additives that can lead to elevated ash content following pattern burnout and reduced strength in as-printed samples. Experiments on PVA dissolution in water revealed that, for high dissolution rates of the pattern, not only high temperature, but also water medium mixing was necessary. The colloidal silica binder, a common component in ceramic mold manufacturing, exhibited effective wetting properties of the patterns, while generally preventing significant dissolution, which can adversely impact pattern quality. The PVA filaments under investigation were utilized to fabricate patterns for the impeller cast parts. Subsequent to this, ceramic molds were obtained, and castings made of nickel superalloy were produced. The investigation revealed that the Bambu Lab filament, which is PVA without additives, exhibited the lowest defect rate in both the mold and the casting. In summary, this study demonstrates that the 3D printing of investment casting patterns holds considerable promise as a rapid casting technique. Full article

Novel Ni/SBA-15 catalysts were synthesised and their activity in the dry reforming of methane process was assessed. These materials were prepared into extrudates shaped like pellets and tested in a pyrolysis pilot plant fitted with a catalytic reactor for sewage sludge pyrolysis tar removal. The Ni/SBA-15 catalyst pellets remained highly active and stable throughout the test’s duration, converting 100% tar in the hot gas to smaller non-condensable gases, thereby increasing the pyrolysis gas fraction and eliminating the problematic tar in the vapour stream. Catalyst characterisation with Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray (EDX) analysis, Transmission Electron Microscopy (TEM), and Thermogravimetric Analysis (TGA) confirmed that both the Ni/SBA-15-powered catalyst and the pellets were resistant to sintering and carbon deposition and remained highly active even with relatively high-level sulphur in the feed stream. The Ni/SBA-15 catalyst extrudates were prepared by mixing the powdered catalyst with varied amounts of colloidal silica binder and fixed amounts of methyl cellulose and water. The highest mechanical strength of the extrudates was determined to be of those obtained with 36% of the inorganic binder. The physical properties and catalytic activity of Ni/SBA-15 pellets with 36% colloidal silica were compared with the original powdered Ni/SBA-15 catalyst to assess the binder inhibitory effect, if any. The results confirmed that colloidal silica binder did not inhibit the desired catalyst properties and performance in the reaction. Instead, enhanced catalytic performance was observed. Full article

Colloidal bonds are realized by sol–gel technology. The binder system of the refractory castable belongs to the Al₂O₃–SiO₂ binary diagram. Mullite is the most thermally stable mineral in this system. This work was motivated by an attempt to maximize the mullite content in the NCC binder system, because a high content of mullite is a guarantee of the long service life of refractories. Initially, the mineralogical composition of the pure gel was tested after drying and firing at temperatures between 1000 °C and 1600 °C. The behavior of the gel during drying was described. Subsequently, a method of minimizing gel shrinkage during drying was sought. To this aim, fine fillers (microfillers) of alumina and silica were tested. In particular, the reactivity of the microfillers, the ability of the microfillers to react with the sol to form mullite, and the drying shrinkage of the microfiller-doped gel were evaluated. The study showed that the least suitable source of Al₂O₃ in terms of its reactivity is tabular corundum, which produces the lowest amount of mullite. The internal structure of the prepared binder system when using different microfillers was described. Based on the results from the second stage of the work, several complete matrixes of the binder system were designed and the degree of their mullitization at different firing temperatures was studied. During this stage, it was shown that the degree of mullitization of the binder system depends mainly on the microsilica content. In the binder system, the maximum mullite content recorded was 76%. The effect of amorphous SiO₂ on the bulk density and internal structure of the binder system was also described. Full article

The increasing demand for lithium-ion batteries requires constant improvements in the areas of production and recycling to reduce their environmental impact. In this context, this work presents a method for structuring carbon black aggregates by adding colloidal silica via a spray flame with the goal of opening up more choices for polymeric binders. The main focus of this research lies in the multiscale characterization of the aggregate properties via small-angle X-ray scattering, analytical disc centrifugation and electron microscopy. The results show successful formation of sinter-bridges between silica and carbon black leading to an increase in hydrodynamic aggregate diameter from 201 nm to up to 357 nm, with no significant changes in primary particle properties. However, segregation and coalescence of silica particles was identified for higher mass ratios of silica to carbon black, resulting in a reduction in the homogeneity of the hetero-aggregates. This effect was particularly evident for silica particles with larger diameters of 60 nm. Consequently, optimal conditions for hetero-aggregation were identified at mass ratios below 1 and particle sizes around 10 nm, at which homogenous distributions of silica within the carbon black structure were achieved. The results emphasise the general applicability of hetero-aggregation via spray flames with possible applications as battery materials. Full article

We combined a nickel–aluminum–zirconium complex hydroxide (NAZ) with colloidal silica as a binder to prepare a granulated agent for adsorbing heavy metals from aqueous media. Three samples with different particle diameters were prepared to evaluate the effects on the properties: small (NAZ-S), medium (NAZ-M), and large (NAZ-L). We confirmed the granulation of the prepared samples at a binder content of 25%. NAZ-S had the largest specific surface area and number of hydroxyl groups, followed by NAZ-M and then NAZ-L. Regarding the adsorption capacity, NAZ-S adsorbed the most chromium(VI) ions followed by NAZ-M and then NAZ-L. The binding energy of Cr(2p) at 575–577 eV was detected after adsorption, and the effects of the temperature, contact time, and pH on the adsorption of chromium(VI) ions were evaluated. We identified the following adsorption mechanism: ion exchange with sulfate ions in the interlayer region of the NAZ samples. Finally, the chromium(VI) ions adsorbed by the NAZ samples were easily desorbed using a desorption solution. The results showed that NAZ offers great potential for the removal of chromium(VI) ions from aqueous solutions. Full article

Catalysts are very important in controlling the pollutant emissions and are used for hundreds of chemical processes. Currently, noble metal-based catalysts are being replaced for other kinds of materials. In this study, three lanthanum-based perovskite-like oxides were synthesized (LaCo, LaCoMn, and LaMn) by the glycine-combustion method. The powder catalysts obtained were supported onto cordierite ceramic monoliths using an optimized washcoating methodology to obtain the subsequent monolithic catalysts (LaCo-S, LaCoMn-S, and LaMn-S). Sample characterization confirmed the formation of the perovskite-like phase in the powder materials as well as the presence of the perovskite phase after supporting it onto the monolithic structure. The XPS analysis showed a general decrease in lattice oxygen species for monolithic catalysts, mainly caused by the colloidal silica used as a binder agent during the washcoating process. Additionally, some variations in the oxidation state distribution for elements in Co-containing systems suggest a stronger interaction between cordierite and such catalysts. The catalytic activity results indicated that powder and monolithic catalysts were active for single-component VOC oxidation in the following order: 2-propanol > n-hexane ≅ mixture > toluene, and there was no evidence of loss of catalytic activity after supporting the catalysts. However, LaMn-S had a better catalytic performance for all VOC tested under dry conditions, achieving oxidation temperatures between 230–420 °C. The oxidation efficiency for the VOC mixture was strongly affected by the presence of moisture linking the oxidation efficiency at wet conditions to the VOC chemical nature. Additionally, for higher VOC concentrations, the catalyst efficiency decreased due to the limited number of active sites. Full article

This article presents the results of research on the use of modern nondestructive methods such as 3D scanning, thermography and computed tomography (CT) to assess the quality of multilayer ceramic molds. Tests were performed on spherical samples of multilayer ceramic molds in the raw state. Samples were made of molding sands composed of quartz and molochite powders, the alcoholic binder hydrolyzed ethyl silicate (ZKE) and an aqueous binder based on colloidal silica. Thickness measurements of spherical forms were made using a 3D scanner. Porosity measurements were made using CT. Additionally, thermography observations of the mold cooling process were made with controlled temperature and humidity. The results of temperature measurements of samples were compared with measurements of thickness and porosity. The practical goal was to determine the possibility of using thermography, 3D scanning and CT as a quick method for detecting mold defects by varying their thickness, porosity and cracks and for final verification of the ceramic molds’ condition before casting. Full article

Powder bed 3D printing can be applied to sandcasting mold manufacturing to ensure high quality and economy through process innovation. In this study, refractory alumina cement was used as an aqueous binder to ensure high-temperature thermal stability to minimize the addition of organic matter to reduce gas generation. In addition, spherical silica sand, the study material, was selected to a size of 30 µm to improve the casting mold resolution. To improve the surface quality through the post-treatment process, we confirmed the change in the surface roughness of the mold depending on the surface treatment of colloidal silica and the presence or absence of heat treatment, and finally made the mold through actual casting. Changes in the surface roughness and flowability of the cast body after mold post-treatment were confirmed. For aluminum castings, the shrinkage rate and surface roughness were confirmed in a box-shaped mold via gravity casting, and the flowability of the molten metal in the mold was confirmed in a hand-shaped mold. There was a change in the roughness and porosity of the mold, owing to the post-treatment, and the influence of the surface roughness and flowability of the cast body during actual casting was confirmed. Full article

In this study, ultra-fine spherical particles of silica fume and reactive ultra-fine fly ash were added to a mixture of commercial ultra-high-performance grout (UHPG) with the aim of enhancing the rheological properties, compressive strength, compactness, and permeability. This commercial UHPG study was conducted in collaboration with Triaxis Corporation (Changsha city, Hunan province, China). A water-to-binder ratio of 0.21 and a binder-to-fine aggregates ratio of 1.17 were used as fixed parameters, and the binders were a combination of type-II Portland cement, sulphoaluminate cement, silica fume, and reactive ultra-fine fly ash (RUFA). Polycarboxylate superplasticizer powder was used to control the rheology. The results revealed excellent compressive strength, volume stability, and resistance to chloride penetration. Mercury intrusion porosimetry and scanning electron microscopy tests revealed that the medium-sized RUFA particles with small silica fume particles completely filled the spaces between large cement particles to achieve optimal densification. This mixture also produced dense hydration and calcium-silicate-hydrates colloids, which filled the microstructures of the UHPG resulting in excellent engineering properties and durability. This commercially available UHPG mix responded to excellent compressive strengths approaching 120 MPa and exhibited good workability with a loss of slump-flow rate up to 33% after 60 min. It also exhibited very low abrasion resistance (0.5%), stable shrinkage and expansion rates (stabilization over 10 days), very low chloride diffusion coefficient (less than 0.1 × 10⁻¹⁴ m²/s) with a denser microstructure. This commercial UHPG (UHPG-120) has been developed to meet the needs of the market. Full article

The purpose of this study was to comparatively investigate the behavior of silicate and sol-silicate coatings non-modified or modified with an organosilane on wood and on wood pre-coated with silica-mineralized primers. Adhesion strength, morphology, and water permeability and related damages were studied to evaluate the possibility of utilizing such inorganic-based coating systems for durable protection of wood without or with relatively cheap and water-borne primers. Potassium silicate and potassium methylsiliconate aqueous solutions and a colloidal silica were used for the preparation of the coatings. The white coating paints were brushed on beech wood substrates at a rate of 220 g·m⁻². The coatings exhibited good coverage ability. The pull-off adhesion strength values appeared to be related to pH following a polynomial law. The adhesion strength for the silicate coatings were adequate (above 3 MPa and up to 5 MPa) for wood, whereas the values for the sol-silicates were too low for practical applications. The adhesion values were in general higher for the samples cured in a climate room (23 ± 3 °C and 75 ± 2% relative humidity) than the samples cured in the ambient atmosphere of the laboratory (23 ± 3 °C and 25 ± 5% relative humidity). The presence of microdefects (cracks, holes) was revealed in the coating layers by optical and scanning electron microscopy. The surface roughness parameters assessed by confocal scanning laser microscopy were dependent on the magnification applied for their measurement. The arithmetic average roughness S_a was between 5 µm and 10 µm at magnification 5× and between 2.5 μm and 10 µm at magnification 20×. The maximum peak-to-valley height S_z confirmed the presence of open pores emerging through the coatings. The open pores constitute free pathways for water ingress through the coatings, and could explain the high water absorption of the coatings including the methysiliconate-containing silicate coating and despite the relatively high water contact angle and low wettability exhibited by this sample. The post-application of a hydrophobizing solution containing hexadecyltrimethoxysilane and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride considerably reduced the water permeability, while application of nanosilica-containing organic primers increased the adhesion for the coatings. Silicate coatings with adhesion great enough and resistance against water damages can be generated on wood even without a primer using low silica-to-alkali ratio binders and an organosilane additive. The sol-silicate coatings appear to be applicable only with a primer. The improvement of the paint formulations to control the formation of microcracks and open pores could be useful to reduce the liquid water permeability and increase durability. Otherwise, the application of a hydrophobizing treatment can be used for this purpose. Full article

Graphitic carbon nitride (g-C₃N₄) was supported on SrAl₂O₄:Eu,Dy-SiO₂ by a colloidal-sol coating method to improve its light absorption property. Transmission electron microscopy (TEM) revealed that the nanoparticles of g-C₃N₄ were coated on sub-micron phosphor particles and nanoscale surface roughness was imparted by the SiO₂-binder. Photoluminescence (PL) spectrum of the g-C₃N₄ supported on SrAl₂O₄:Eu,Dy exhibited a broadband emission from 400 to 650 nm. Increasing silica-binder in the g-C₃N₄/SrAl₂O₄:Eu,Dy composites suppressed the PL emission peak at 525 nm for SrAl₂O₄:Eu,Dy. Photocatalytic degradation activity was evaluated with 5 ppm methylene blue (MB) solutions under germicidal ultraviolet (UV) and visible (Vis) solar light illuminations. The UV/Vis photocatalytic efficiency was improved by supporting g-C₃N₄ on the SrAl₂O₄:Eu,Dy phosphor and with the addition of SiO₂ as a binder. In addition, low silica addition effectively improved the adhesiveness of the g-C₃N₄ coating on the SrAl₂O₄:Eu,Dy surface. Recyclability tests of photocatalysis for the SrAl₂O₄:Eu,Dy-0.01M SiO₂/50wt% g-C₃N₄ composites exhibited a remarkable stability by maintaining the degradation efficiencies above 90% in four cycles. Therefore, the composite of g-C₃N₄-supported SrAl₂O₄:Eu,Dy-SiO₂ is a prospective photocatalyst activating under UV/Vis light irradiation for the elimination of environmental pollutants. Full article

Colloidal nano-silica (NS) hydrosols are electrochemically stabilized, polymerized amorphous silica in low viscosity solutions, and in the form of hydrated gels, silica globules or pellicles. Compared to applications in concrete technology, the use of silica-based binders for groundwork applications has received little attention. Silica-based hydrosols impose no known direct risks to humans and are generally courteous to the soil health and ecosystem service functions. Their localized impact on microorganisms however needs to be further investigated. To this end, NS hydrosols have a scope for use as an alternative low-viscose material in groundworks. The current understanding of interactions between NS hydrosols and soil (sand) is, however, confused by the limited availability of experimental evidence concerning undrained static flow and large strain behavior. The contributions, presented in this paper, advance the knowledge through experimental testing, molecular modelling, and micro-analytical measurements. Four grades of colloidal NS (1–15 wt.%) were synthesized for grouting medium-dense sub-angular fine siliceous sand specimens. Consolidated-undrained triaxial compression testing was performed on the base and treated sand for isotropic consolidation over the effective stress range 100–400 kPa. Overall, silica impregnation produced improvements in yield and residual undrained shear strengths, restricted unwelcomed impacts of excess pore water pressure, and led to the formation of generally more dilative, strain-hardening behavior. Steady states and static flow potential indices are also studied as functions of confinement level and viscosity of the NS grout. Full article

This study applies a new method of mixing colloidal nano-silica (CNS). Previous studies have used powdered nano-silica or colloidal nano-silica and applied a binder weight substitution method. In this study, we tried to use ordinary Portland cement (OPC) as a binder and replace CNS with weight of mixing water. CNS was replaced by 10%, 20%, 30%, 40%, and 50% of the mixing water weight. The flow value, setting time, compressive strength, hydration reactant (X-ray diffractometer; XRD), pore structure (mercury intrusion porosimetry; MIP), thermal analysis, and scanning electron microscopy (SEM) analysis were performed. Experimental results show that the new substitution method improves the mechanical and microstructural properties through two effects. One is that the weight substitution of the mixing water shows a homogeneous dispersion effect of the nano-silica particles. The other is the effect of decreasing the w/b ratio when the CNS is substituted because the CNS is more dense than the mixing water. Therefore, we confirmed the applicability of mixing water weight replacement method as a new method of mixing CNS. Full article