Silicate Binder Research Articles

Slurry sprayed glass-ceramic coating for boiler tubes and its high temperature performance

Industrial boilers operate in extreme environments and are prone to degradation caused by high temperature oxidation, corrosion, and erosion. Protective coatings provide boiler components with protection to prolong their operation lifetime. Thus, a glass-ceramic coating has been developed using a slurry spray technique on carbon steel AS/NZS 3678 substrates. Microstructure, mechanical characteristics, and high temperature performance of the coating were investigated. The coating composed of chemically inert oxide ceramics dispersed in a glassy silicate binder matrix. The adhesion strength of the coating was 10.79 ± 0.86 MPa. Coating mass loss after abrasion test was 0.013 % of the tested specimen. The coating withstood at least 75 air quenched thermal shock cycles from 800 °C to the room temperature without any visible spallation and cracks. The coating mostly remained undamaged after cyclic oxidation at 800 °C for 10 cycles. However, minor iron oxide formation was observed, specifically, in relatively thin sections of the coating. The oxidation resistance of the boiler steel has been improved with the developed coating. The linear oxidation rate constant of the boiler steel has been statistically reduced from 6.90 × 10−4 mg cm−2 s−1 to 1.95 × 10−4 mg cm−2 s−1 for coated steel (p = 0.007). The developed slurry spray glass-ceramic coating is a potential candidate for boiler environments.

Improvement of Buildings’ Air Quality and Energy Consumption Using Air Purifying Paints

Among the existing techniques to mitigate the problem of contamination in the indoor environment, photocatalytic technology is considered to be the most promising solution in terms of effectiveness and cost. To that end, in the frame of the LIFEVISIONS project, a novel photocatalytic powder (photo-powder) was mixed in paints’ matrix, producing a photocatalytic building material (photo-paint) able to improve indoor air quality (IAQ), upon its application, without downgrading paint physical properties. As a result, of IAQ improvement, less energy will be needed from ventilation systems, addressing not only health issues related to air quality but also energy reduction targets. Many powder formulae were synthesized using different synthetic pathways, concentration of dopants, and TiO2 particles’ size. They were tested in a photocatalytic reactor (lab-scale tests), according to CEN TS 16980-1:2017, under visible light and the results showed that the most promising photocatalytic performance degrades 85.4% and 32.4% of nitrogen oxide (NO) and toluene, respectively. This one was used for the production of two different kinds of paints, organic (with organic binder) and inorganic (with potassium silicate binder), in an industrial scale. Both were tested in the Demo Houses’ prototype demonstrator (real-scale tests) with an ultimate scope to estimate their effectiveness to degrade air pollutants under real-world conditions. In addition, the reduced energy consumption as a result of less ventilation needs was calculated in Demo Houses. More specifically, the energy reduction based on simulation results on Demo Houses was more than 7%. Although lab-scale tests showed better photocatalytic performance than the real scale, the efficiency of the paints under a more complicated environment was very promising.

3D-printing of architected calcium silicate binders with enhanced and in-situ carbonation

ABSTRACT This paper investigates the use of architected cellular and solid designs of materials via additive manufacturing and in-situ CO2 circulation to augment the carbonation and mechanical properties of a calcium silicate-based cement (CSC) binder. A wollastonite-based binder was formulated for extrusion-based 3D-printing. Solid and cellular lamellar architectures were designed to probe the role of layered interfaces and higher surface area on the degree of carbonation (DOC), respectively. Two carbonation exposure scenarios, with and without in-situ carbonation were employed. The DOC, microstructural phases, and flexural strength were characterised using TGA, modified over-flow image analysis technique, and three-point-bending, respectively. By exploiting 3D-printing and harnessing the higher surface area of cellular architecture, the material obtained a significantly higher DOC (by 8.9-folds) and flexural strength (by 5.7-folds) compared to reference cast. In-situ carbonation of cellular architected materials can additionally improve early-stage deformation, DOC (by 12.9-folds) and flexural strength (by 16.5-folds), compared to cast.

Effects of surfactants on the physical properties of silicate binders and the mechanical properties of silicate-bonded foundry sand cores

In the foundry industry, casting sand cores require high and low peak and residual strengths, respectively, to achieve comprehensive optimal mechanical performance. The peak and residual strengths of sand cores are positively related, highlighting the criticality of balancing them. Thus, an innovative approach comprising the incorporation of anionic surfactants into the silicate binder was introduced to balance both factors. Additionally, the investigation of the effects of the anionic surfactants on the physical properties of the silicate binder, including its colloidal stability, surface tension and adhesion, revealed that four different anionic surfactants reduced the surface tension and adhesion of the silicate binders and reduced the residual strength of the silicate-bonded sand cores. Among them, 0.10 wt% lauryl ether phosphate reduced the surface tension and adhesion of the adhesive by 49.64 and 112 mN/m, respectively, and reduced the residual strength of the sand core by 0.035 MPa. However, increasing the dosage did not further reduce the residual strength of the sand core, although it continued to reduce its peak strength. Therefore, during silicate binder modification with anionic surfactants, the dosage of the anionic surfactant must be kept at ≤0.10 wt%, as this dosage exerted the most comprehensive optimal modification effect, which was attributable to the adsorption of anionic polymers onto the surface of the silicate aggregates. This adsorption weakened the network structure of the silicate aggregates and imparted the sand cores with appropriate mechanical properties during casting.

Research of the New Laboratory Methodology for Measuring the Disintegration of Mixtures with Inorganic Binders Hardened by Dehydration

The paper deals with the possibilities of using alkali silicate based inorganic binders for automotive industry aluminium castings production. In recent years, inorganic binders are coming back to the foreground and their manufacturers are developing new processes, which are starting to progressively supersede organic binder systems. Paper describes known knowledge about classic alkali silicate binders with focus on hardening processes and on improving their technological properties. Trends from the area of development and the use new alkali silicate based inorganic binders are also shortly described. As part of the experimental work, specific methods of producing samples were developed, with the help of which properties such as disintegration were subsequently evaluated by measuring abrasion and residual strengths. Characteristics such as residual compressive strength or shear strength at different thermal loads were also evaluated. When comparing the laboratory results with the results of de-coring in real conditions, a high degree of correlation was achieved, which makes it possible to determine the optimal recipe/procedure for the production of geometrically complex cores.

Effect of Additives on Heat Hardened Inorganic Solid Foundry Binder

AbstractRenewed interest in inorganic binders for sand molding has also intensified research on different forms of it. In this study, solid inorganic sodium silicate binder was tested with different additives to see how these affected the silica mold quality. The five additives used were: glucose, sucrose, boric acid, aluminum oxide and iron(III)oxide powders. The mold quality was assessed through tests like bending strength, tensile strength, hot distortion, wear resistance, gas evolution and collapsibility tests. In addition, SEM imaging was done on some select mold fracture samples. In the end, a casting trial was carried out followed by a surface roughness and defects analysis. A reduction in mold strength was noticed with glucose and boric acid, while collapsibility was improved by glucose, sucrose and boric acid additives. Casting trials have shown the best surface finish to be obtained with sucrose additive. All the casts in general showed some penetration; however, repeat casts have proven that altering some casting parameters could result in casts with excellent surface finish using solid silicates.

Energy-Technology Indicators of a Multi-Drum Electric Furnace for Firing Vermiculite Concentrates

The design and working process of a new electric drum furnace for heat treatment of vermiculite concentrates and conglomerates, as well as other bulk porous materials based on a silicate binder, are considered. The electric drum furnace is devoid of the disadvantages inherent in its predecessors – furnaces with a movable hearth platform: there are no oscillating elements, dynamic effects do not occur, and there is also no resonant mode of operation, since the working drums perform rotational motion with a constant angular velocity. Using the example of a six-drum furnace, the volumes of processed material located in the firing spaces are calculated, and the second and hourly productivity of the furnace (10 m3/h or 0.0029 m3/s) are determined. The temperature of the heating elements (1167 K) was calculated, the electric power of the furnace (95.2 kW) and the specific energy intensity of the firing process of vermiculite concentrate, with a dimension of 4 mm (0.004 m) from the raw materials of the Kovdorsky deposit – 44.2 MJ/m3, which makes the furnaces of the new design competitively capable, were determined.

Wettability, flowability and core bending strength of wet silica sand particles based on the interfacial properties of liquid silicate binders

The flowability of wet silica sand particles containing liquid binders, which are among the new moulding materials for green casting, must be further improved. Herein, we conducted an in-depth study on the interface characteristics of silicate binders with the addition of anionic surfactants. Through particle flow experiments and sand core bending fracture experiments, the influence of anionic surfactants on the flow characteristics of wet sand particles and the mechanical properties of silicate-bonded sand was explored. The experimental results showed that the addition of 0.10 wt% of an anionic surfactant significantly reduced the surface tension and contact angle of solutions, from 78.99 to 28.53 mN/m, and from 49.9° to 34.4°. Moreover, compared with unmodified wet particles, the flowability of wet particles modified with 0.10 wt% of the anionic surfactant was improved to some extent. However, the flexural strength of silicate-bonded sand was also reduced to a certain extent.

Effect of hydrogel on mitigating drying shrinkage induced cracking in carbonation cured calcium silicate binders

Carbonation cured calcium silicate binders can be considered an alternative material to reduce the carbon footprint of the construction industry. Carbonation at elevated temperatures is used to enhance carbonation reaction; however, it accelerates drying, which could result in drying shrinkage induced cracking. The effect of hydrogel on the microstructure and properties of carbonated wollastonite pastes was discussed in this paper. The teabag test and flow test showed that hydrogel absorption was notably higher in wollastonite paste than in OPC paste. The phase analysis based on Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), revealed calcite as the primary polymorph of calcium carbonate in the carbonated product. The micro-CT analysis showed crack formation in the control pastes while no or significantly fewer cracks were observed in the hydrogel modified pastes. The hydrogel modified pastes exhibited lower water loss and drying shrinkage compared to the control paste at early carbonation stage. The above results provided evidence that cracking was caused by drying shrinkage in the control carbonated pastes and hydrogel was effective in mitigating such cracking by lowering water loss at early stage of carbonation. The results of the nitrogen adsorption test indicated a higher specific surface area and pore volume in the hydrogel modified pastes. The hydrogel modified pastes exhibited a slightly reduced compressive strength due to the presence of hydrogel macrovoids in these pastes.

Wettability, adhesive performance and structural evolution of an environment-friendly modified silicate binder for foundry moulding and coremaking

For the manufacturing of sand cores, silicate inorganic binders have emerged as promising green casting binder materials; however, their adhesive performance requires further improvement. In this study, to evaluate the impact of using water-soluble polyols, i.e. polyethylene glycol (PEG) and xylitol, to modify silicate adhesives, the effect of the content and type of water-soluble polyol on the colloidal stability, wettability and adhesive performance of a silicate binder were investigated. The structural evolution of the modified silicate binder and the polysilicate bondswere studied using characterisation techniques including infrared spectroscopy and 29Si nuclear magnetic resonance (NMR) spectroscopy. Results revealed that PEG 400 and PEG 600 increased the size of polysilicate particles in the solution, resulting in flocculation of the silicate binders and easy precipitation or separation in a short period of time. However, PEG 200 and xylitol exerted little effect on the stability of the silicate solution. Moreover, 0.25 wt% PEG 200 reduced the surface tension of the solution from 78.93 to 54.15 mN/m and the equilibrium contact angle from 45.0° to 34.6°. The polyol promoted the dehydration and condensation of silicic acid gel to form a more stable three-dimensional network structure, improving the bonding strength of casting sand cores prepared using the silicate binder and silica sand from 2.42 to 3.02 MPa. This study not only unveils the role of PEG in improving the wettability and bonding behaviour but also provides an example of the rational use of environment-friendly water-soluble polyols to enhance the performance of green inorganic adhesive materials.

INFLUENCE OF BINDERS, MIX PROPORTIONS, AND FABRICATION METHOD ON THE CHARACTERISTICS OF FLY ASH AGGREGATE

In this paper, two types of lightweight fly ash (FA) aggregates: cold bonded fly ash (CFA) and sintered fly ash (SFA) aggregates were prepared through the cold bonding and sintering method. During the pelletization process, different ratios of binders to fly ash were used, i.e., 10:90, 15:85, 17:83, and 20:80 with a set amount of water. Cement, metakaolin, sodium silicate, urea-formaldehyde resin, bentonite powder, and phenol-formaldehyde resin were employed as binders. A comparative study on physicochemical, mechanical, phase identification, microstructure, and optical analysis of CFA and SFA was performed. The results showed that CFA (an alkali binder) had a higher water absorption (WA) value of 9,50 % with a crushing strength (CS) value of 6,30 MPa than SFA (sodium silicate binder) with a CS value of 5,80 MPa and a WA value of 10,28 %. Experimental observations also demonstrated that the leaching ability of SFA was considerably lower than that of CFA. Most notably, SFA can be used as a substitute for construction material and structural applications along with solving FA waste disposal and related problems to a considerable extent.

Controlling surface reconstruction of SrTiO3(100) with adhesive outgassing

We report on an unexpected effect of adhesives on the surface reconstruction of SrTiO3. We used two types of commercially available high-temperature adhesives, the platinum (Pt) and carbon (C) pastes, to mount two identical SrTiO3(100) substrates onto the sample holders, respectively. Two different surface reconstructions, namely 2 × 1 and (√13 × √13)-R33.7°, were obtained using Pt and C paste under nominally identical annealing conditions in ultrahigh vacuum (UHV). We show that the same two surface reconstructions can be obtained separately with annealing in UHV and in an O2 environment from identical substrates mounted without adhesives. Residual gas analysis of the adhesive outgassing suggests that the silicate binder in the C paste releases O2 at high temperatures while the Pt paste does not. Due to the limited amount of O2 that can be released from the C paste, a change of the surface reconstruction from (√13 × √13)-R33.7° to 2 × 1 was observed on the same substrate mounted with the C paste upon increasing the duration of annealing in UHV. Our study indicates that slight outgassing of certain adhesives may have a profound impact on the surface reconstruction of SrTiO3. This finding also provides an interesting new knob to tune the surface reconstruction of SrTiO3 in the same annealing environment.

Development of Zn2SiO4 and hexagonal BN inorganic thermal-control coatings with novel thermophysical property

Implementation of lightweight and long-lasting thermal-control coatings (TCCs) is vital for regulating the surface temperature and energy consumption of spacecraft. Herein, Zn2SiO4 and hexagonal boron nitride (hBN) based inorganic TCCs are developed with potassium silicate binder. The αs/εH (solar absorptance/ hemispherical emittance) ratio of the Zn2SiO4, ZnO and hBN coatings are 0.096, 0.190 and 0.107, respectively. Compared to the classical ZnO based Z-93 coating, both Zn2SiO4/K2SiO3 and hBN/K2SiO3 coatings show superior initial thermophysical properties. After vacuum-proton irradiation, the αs of Zn2SiO4, Z-93 and hBN coatings increased from 0.091, 0.167 and 0.098 to 0.193, 0.253 and 0.241, respectively. Apparently, the as-developed Zn2SiO4 coating exhibits exceptional heat-dissipation and radiation-resistance features in relation to the hBN and Z-93 TCCs.

Wetting characteristic and flow behavior of silicate binder at various sand particle-particle interfaces: Fine or coarse, circular or angular particles

This study presents an innovative investigation into the wetting characteristic and flow behavior of sand particles, which have different shapes, sizes, and textures, when they bonded with silicate binder. The results revealed that the apparent contact angles of fine and angular particles with the binder are higher than those of coarse and circular particles. In addition, after modifying the four systems with anionic surfactants, the equilibrium contact angles decreased by 42.8%, 26.7%, 26.5%, and 7%. These findings suggest that coarse and circular particles demonstrate stronger wetting properties with the binder compared to fine and angled particles. Additionally, the cohesion and internal friction angle of the wet sand mixture can be measured through the ring shear test. Moreover, the unconfined yield strength and main consolidation stress can be calculated using the Mohr Coulomb model to obtain the yield locus and quantify the flowability of the wet sand mixture. The yield trajectory of sand mixtures at specific consolidation stresses suggests that the most important factor affecting the flowability of wet sand particles is particle size distribution. Wet mixtures of coarse and circular particles exhibit lower cohesive forces, indicating higher fluidity.

Preparation of h‐BN microspheres for nanocomposites with high through‐plane thermal conductivity

AbstractIn recent times, electronics have been increasingly minimized, and hence, heat dissipation has become essential. Owing to its high thermal conductivity and superior electrical insulation, hexagonal‐boron nitride (h‐BN) has been regarded as an appropriate ceramic material to increase the thermal conductivity of polymer nanocomposites for effective heat dissipation. However, the poor through‐plane thermal conductivity of h‐BN severely restricts its practical uses, and it is favorable for heat to radiates in the in‐plane direction. In this study, densified spherical h‐BN (sph‐BN) microspheres, composed of as‐synthesized nano‐sized h‐BN (nano‐BN), were manufactured by a spray‐drying process with variations in organic and/or inorganic binders followed by sintering. After incorporating various sph‐BN particles as fillers into polydimethylsiloxane (PDMS), the through‐plane thermal conductivity of composites embedded with sph‐BN, assisted by a sodium silicate binder, enhanced the highest through‐plane and in‐plane thermal conductivities. The composites exhibited high thermal isotropy (through‐plane thermal conductivity/in‐plane thermal conductivity: ) of 0.77. The out‐of‐plane thermal conductivity of the composites was remarkably enhanced by over 2000% compared with pristine PDMS, which can be attributed to the synergy combined with the synthesis of the densified spherical BN initiated by nano‐BN, sintering, and the application of inorganic binders. This study proposes a simple method to prepare polymer composites with h‐BN that exhibit high through‐plane thermal conductivity and are promising materials for heat removal in electronics.

Properties of Cement-Based Composites Modified with Metal/Carbon Nanocomposite

The objective of this research is to study and analyse the properties of a cement-based composite modified with nickel/carbon nanocomposite (Ni/C NC). According to previous studies carried out by scientists in the field of nanostructures, it was assumed that metal/carbon nanostructures can increase the strength and impart electrically conductive properties to composite materials [9,12]. To confirm this hypothesis, in this research, mechanical strength tests and measurements of the electrical resistance of the modified samples were carried out. It was found that the addition of nickel/carbon nanocomposite in the amount of 0.05% increases the compressive strength of silicate composites by 35%. Moreover, by measuring the electrical conductivity of the samples, it was established that with the introduction of additives in the amount of 0.01-0.05% in relation to Portland cement, the resistance decreases by 80-84%. Further, the structural effect of Ni/C NC on the cement matrix was studied by the methods of IR spectral, differential thermal analyses, X-ray microanalysis. As a result of the analysis, it was revealed that the dispersions are crystallization centers during cement hydration and create chemical bonds with silicon oxide in the composition of the silicate composite. Ni/C NC has a structuring effect on the silicate binder matrix through the formation of a denser packing, which affects the mechanical properties and electrical conductivity of the material. The results of the study can be used to obtain electrically conductive materials with desired properties that can perform the functions of heating, monitoring the state of structures during operation, and protecting against an electromagnetic pulse.

Study on Laser Selective Curing Additive Manufacturing of Foamed Structural Ceramics

An additive manufacturing method for ceramic materials with internally formed foaming structure was proposed in this paper with the adoption of ceramic powder and sodium silicate binder to prepare sizing agent. The forming process on each layer consists of three basic processes, including spreading, freezing and laser scanning. Foaming structure arises due to the foaming effect of the frozen sodium silicate caused by laser gasification. After 3D printing, the support material in frozen state will be removed when it has been melt in water. Then finally the green ceramic parts internally filled with foaming structures will come into being. Experimental results show that the laser parameters, the content of ceramic, the scanning spacing and other factors affect the interior appearance of the green part. At the scanning speed of 100 mm·s-1, laser power of 20 W, and 0.3 mm scanning spacing, the ceramic parts are processed with a slurry with 50% solid content. The support materials in the deep fine structure can be quickly removed without mechanical damage or swelling in the water. This new process can be used to process thermal insulation ceramic parts.

Expansion and shrinkage of lightweight vermiculite material at high temperatures

Vermiculite materials are widely used as insulation material in the industry, fire protection systems, and fire stoves. The high dimensional stability of vermiculite boards ensures that thermal runways in the insulation lining are avoided. Vermiculite boards for high-temperature applications are produced from thermally expanded vermiculite and alkali silicate binder. Here, we show the impact of potassium silicate binder and vermiculite source on the dimensional stability of vermiculite boards. The vermiculite boards expand at 500–830 °C and shrink stepwise at 1000–1250 °C and 1400 °C, respectively, when heated at 10 °C min−1 in ambient air. The expansion process is discussed in relation to the boards containing non-expanded particles and metal carbonates. The evolved gas analysis indicates that the CO2 release from metal carbonates is the potential cause of the expansion of some vermiculite types. The shrinkage is initiated by the dehydroxylation of the clay structure. The binder promotes crystallisation during the shrinkage, ceasing the shrinkage process at higher temperatures. The expansion and shrinkage of vermiculite boards are anisotropic and depend on the board density and vermiculite origin. These findings provide new insights into the expansion and shrinkage behaviour of vermiculite boards.

Influence of iron ore concentrate quality on metallurgical properties of pellet

One of the important factors for improving the technical and economic performance of blast furnaces is the iron content in the iron ore part of the charge. At the same time, there is evidence that when using iron ore concentrate with an iron content of more than 66‒67% for the production of pellets, their strength decreases, and adjustments to the heating modes are required. In recent years, Russian mining enterprises have been implementing technological measures to increase the mass fraction of iron in the concentrate to 68‒70%. The results of a study of the influence of concentrate quality indicators (mass fraction of iron, specific surface value) on the pelletizing technology and metallur-gical properties of pellets are presented. Concentrates with a mass fraction of iron of 66.6, 68.0, 69.2% and a specific surface of 1576, 1999, 2015 cm2/g, respectively, were used as an object of study. It was found that increasing the iron content and specific surface area in the concentrate leads to an improvement in the raw pelletizing technology ‒ plasticity and the proportion of pellets with a size of 5‒16 mm increase. Roasting of laboratory pellets in baskets on a roasting machine showed a multidirectional change in the metallurgical properties of the pellets. The compressive strength index decreased, the hot strength changed little, the softening-melting temperature range (SMTR) decreased from 308 to 200‒290 °C. Mineralogical studies have established that the decrease in these indicators (strength and SMTR) was influenced by a decrease in the amount of silicate binder and the uneven distribution.

Development of sustainable alkali-activated binder for building products using sugarcane bagasse ash: A review

Industrial waste-based alkali-activated binders (AABs) can be a sustainable alternative to the cement industry. As the manufacturing of cement is accounting for over 8% of the world's CO2 emissions, using industrial byproducts in the production of alkali-activated construction materials (i.e. mortar, brick, and concrete) might reduce greenhouse gas emissions. The main chemical component of AAB is alumina-silicates, which is essential for alkali activation. Potassium or sodium hydroxide and silicates are common activators. The production of cement is minimised by completely replacing it with AAB using a polymerization method. Polymerisation process uses alkali activators to activate the aluminium–silicate binder and produce a 3D polymeric chain that helps with strength development. The emphasis of the current review is the use of Sugarcane Bagasse Ash (SCBA) in construction materials that have been alkali-activated. Burning bagasse, a type of agricultural waste, yields SCBA, which may be used to create AAB in place of cement. The use of various supplementary cementitious materials in combination with SCBA and their influence on the mechanical characteristics was analysed. Moreover, the influence of supplementary activator, activator concentration, mixing proportions and curing methods (ambient, heat, water etc.) were critically reviewed. The results of various researchers' analyses of SCBA using X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray fluorescence (XRF) technology was also evaluated in order to study the properties, content and morphology of bagasse ash. The sustainability and profitability of alkali-activated materials are greatly affected by the choice of alkali activator. Common activators include chemicals like sodium or potassium hydroxide or silicate, which have a relatively high carbon emission and are costly. As a result, several agro-industrial by-products have been studied as alternative alkali activators. Utilization of industrial waste-based materials will not only solve the waste disposal issue but also reduce CO2 emissions.