Optimization of colloidal nanosilica production from expanded perlite using Taguchi design of experiments

Colloidal nanosilica was prepared from perlite in two stages: production of wet gel and thermal peptization. The influence of acidic and alkaline solutions concentration, temperature and pH of the gel were investigated in wet gel production using Taguchi design of experiments. Effect of the temperature of the peptization process was studied by full factorial design. The purity of the obtained silica gel was analyzed using X-ray fluorescence (XRF) and the colloidal silica was characterized by dynamic laser scattering (DLS), field emission scanning electron microscope (FESEM) and N₂ sorption analyses. Results showed that pure colloidal nanosilica with purity of 99% was produced and the particle size of the product was in the range of 8 nm and 74 nm. Specific surface area of dried optimized mesoporous sample was 74.28 m²/g.     

Preparation and properties of foam ceramic from nickel slag and waste glass powder

The utilisation of nickel slag and waste glass powder as raw materials for preparing foamed ceramic was studied. The influences of the mixture design and foaming-agent dosage on the properties and microstructures of foamed ceramic were investigated in terms of the density, flexural strength, phase composition and micromorphology. Results showed that incorporating nickel slag improved the flexural strength and uniformity of the pore structure. However, owing to the high density of nickel slag, its excessive usage may impact the development of foamed ceramic density and porosity as a side effect. The Na₂CO₃ dosage was another crucial factor determining foamed ceramic properties. A nickel slag content of was 20% and a Na₂CO₃ content of 7% decreased the foamed ceramic density to 0.498 g/cm³, with a corresponding flexural strength of 2.66 MPa and a higher porosity of 80.06%.     

Production of alumino-borosilicate foamed glass body from waste LCD glass

A foaming process for waste LCD glass is presented, in which waste LCD glass is recycled to produce alumino-borosilicate foamed glass, which can eventually be used as a heat-insulating material, a light-weight aggregate for civil engineering applications, or a carrier for sewage treatment. The effects on waste LCD glass foaming of a variety of carbon foaming agents, metal salt foaming agents, and bonding agents are examined, as well as other factors such as chemical composition, foaming temperature, and grain size of the raw materials from the waste LCD glass. After examining all the variables that influence the foaming process, it was confirmed that the waste LCD glass is suitable as a raw material for producing alumino-borosilicate foamed glass. The alumino-borosilicate foamed glass has excellent physical properties, with density less than 0.14 g/cm³, heat conductivity less than 0.054 W/(mK) @20 °C, bending strength more than 35 N/cm², compressive strength more than 39 N/cm² and a coefficient of linear thermal expansion less than 4.5 × 10^?6 m/m °C. This clearly shows that the lightweight alumino-borosilicate foamed glass could be useful for various applications.     

Performance of glass powder as a pozzolanic material in concrete: A field trial on concrete slabs

Earlier laboratory work by the authors indicated satisfactory performance of glass powder (GLP) in concrete as a pozzolanic material. The powder was manufactured from mixed colour waste packaging glass comprising soda-lime glass. In order to investigate the performance of GLP in concrete under field conditions, a field trial was conducted using a 40 MPa concrete mixture, incorporating various proportions of GLP (0%, 20%, and 30%) as cement replacement. Ten mixture formulations, some of which also included sand-size crushed glass aggregate particles, were used to cast ten concrete slabs (1.5 × 2.5 × 0.25 m). Cylinders and prisms were also manufactured from the same batches at the time of casting for the measurement of compressive and splitting tensile strength, flexural strength, shrinkage, expansion, ultrasonic pulse velocity, volume of permeable voids, and chloride permeability. Core samples were drilled from the slabs at various ages for the same tests (except tensile and flexural), as well as for microstructural examination. Results showed that strength gain was slower in GLP-bearing concrete up to 28 days, but at the age of 404 days all the mixtures exceeded the 40 MPa target and achieved about 55 MPa strength.Mixtures containing GLP also performed satisfactorily with respect to drying shrinkage and alkali reactivity, and there were indications that GLP reduces the chloride ion penetrability of the concrete, thereby reducing the risk of chloride induced corrosion of the steel reinforcement in concrete. The results demonstrated that GLP can be incorporated into 40 MPa concrete at dosage rates of 20-30% to replace cement without harmful effects. The use of GLP provides for considerable value-added utilisation of waste glass in concrete and significant reductions in the production of green house gases by the cement industry.     

Synthesis of CaTiO3 and CaTiO3/TiO2 nanoparticulate compounds through Ca2+/TiO2 colloidal sols: Structural and photocatalytic characterization

CaTiO₃ and CaTiO₃/TiO₂ nanocompounds have been synthesized through a colloidal sol-gel route using Ca²⁺/TiO₂ nanoparticulate sols. The peptization time was determined so that as higher is the Ca²⁺ concentration, shorter is the peptization time. The obtained cryogels from the respective sols were calcined at different temperatures (300–900 °C) and the structural and morphological changes were characterized mainly by X-ray diffraction and transmission electron microscopy. In all cases, the formation of the CaTiO₃ phase was observed after calcination at temperatures as low as 500 °C. Mesoporous cryogels with nanoparticles with sizes below 50 nm were obtained and their photocatalytic activity changes as a function of the calcination temperature and the applied wavelength were determined. Quantum yield values revealed that either CaTiO₃ or the CaTiO₃/TiO₂ (0.4 M ratio) compound can be chosen as the most efficient photocatalyst at higher calcination temperatures and longer wavelengths, while TiO₂ is more effective at low calcination temperatures and shorter wavelengths.     

Optimisation of low temperature sinter crystallisation of waste derived glass

Abstract

Abstract

Mixtures of inorganic waste materials are commonly converted into glasses, in turn to be transformed into glass ceramics. Specific composition designs may lead to glasses with a low crystallisation temperature, useful for low cost ceramisation by bulk nucleation. This feature, however, may be disadvantageous if the same glasses are subjected to sintering, since intensive crystallisation hinders the viscous flow. This paper illustrates the optimisation of simultaneous sintering and crystallisation of a waste derived glass, originally intended for bulk nucleation, when coupled with recycled glasses, at a very low temperature (800°C). The mixing with secondary glasses did not merely enhance the densification (residual porosity of ～3%) but modified the crystallisation. Owing to the mechanical properties (e.g. Young’s modulus and bending strength exceeding 80 GPa and 90 MPa respectively), the obtained sintered glass ceramics may find profitable applications in the building industry.     

Experimental study on foam glass prepared by hydrothermal hot pressing-calcination technique using waste glass and fly ash

Foam glass is a lightweight and high-strength building and decoration material with superior performance in heat insulation, sound absorption, moisture resistance and fire protection. The use of waste glass powder and fly ash to prepare foam glass is one of the most important ways to utilize solid waste as a resource. In this study, waste glass powder and fly ash were used as raw materials to prepare foam glass by a hydrothermal hot pressing–calcination method. The effects of fly ash content (0 wt%, 10 wt%, 20 wt%, 30 wt%), heating rate (1 °C/min, 3 °C/min, 5 °C/min, 8 °C/min, 10 °C/min) and calcination temperature (600 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C) on the microscopic morphology, density, compressive strength, porosity and other properties of the foam glass samples were studied. Their microstructure and morphology were analyzed by thermogravimetric analysis–mass spectrometry, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. At a fly ash content of 10 wt%, the heating rate was 5 °C/min, the calcination temperature was 800 °C, the foam glass density was 0.3 g/cm³, the compressive strength was 1.65 MPa, the total porosity was 75.5%, and the effective thermal conductivity was 0.206 W/m·K. The effective thermal conductivity models of the composite materials were used to verify the experimental data. The relationship between the thermal conductivity of foam glass materials and the related influencing factors was investigated.     

Fabrication of superhydrophobic unplasticized poly(vinyl chloride)/nanosilica sheets using Taguchi design methodology

This study introduces a relatively simple technique for the manufacture of superhydrophobic coatings on polymeric surfaces. Plastics such as unplasticized poly(vinyl chloride) (UPVC ) do not have a strong hydrophobic nature that is characterized by their low contact angles. Techniques of both increasing surface roughness and lowering surface energy are required to change their hydrophilicity to superhydrophobicity. In the present study, a coating of a low‐surface‐energy thermoplastic polyurethane (TPU ) was spin‐coated with chemically treated nanosilica to reduce the surface energy of UPVC . Nanosilica particles were embedded on the surface using a hot‐press. Taguchi design was used to optimize multiple processing parameters. Samples spin‐coated with 10 g L^?1 nanosilica suspension in ethanol at a rate of 400 rpm for 5 s and then hot‐pressed at 155 °C under 2 atm (203 kPa ) for 4 min had a contact angle of ca 157° and sliding angle of ca 6°, which are characteristic of superhydrophobic surfaces. Atomic force microscopy (AFM) and scanning electron microscopy (SEM ) imaging showed that these superhydrophobic surfaces were highly rough with nanoscale features. Peel test and SEM analysis showed that silica nanoparticles embedded in the TPU coating were more stable than particles immobilized on UPVC sheet without TPU coating, proving that a layer of more flexible coating can improve the longevity of superhydrophobic surfaces manufactured using this facile method. © 2016 Society of Chemical Industry     

Properties of concrete containing waste glass

In our study, in which waste glass (WG) is considered as coarse aggregates in the concrete, WG was used reduced to 4-16 mm in proportions of 0-60% in the production of PKÇ/B 32.5/R type cement. The effects of WG on workability and strength of the concrete with fresh and hardened concrete tests were analyzed. As a result of the study conducted, WG was determined not to have a significant effect upon the workability of the concrete and only slightly in the reduction of its strength. Waste glass cannot be used as aggregate without taking into account its ASR properties. As for cost analysis, it was determined to lower the cost of concrete productions. Our study was an environmental one in consideration to the fact that WG could be used in the concrete as coarse aggregates without the need for a high cost or rigorous energy.     

Performance of glass-ceramic-based lightweight aggregates manufactured from waste glass and muck

Lightweight aggregates (LWAs) with microcrystalline diopside as the main constituent were prepared in this study. Waste glass and waste muck were used as the main raw materials, and the formula was designed according to the chemical composition of diopside, rather than using the Riley scheme. The effects of the glass content and nucleating agent on the mechanical properties, mineral composition, and microstructure of LWAs were studied. The results indicated that the presence of diopside crystallites can significantly improve the mechanical properties of LWAs. With an increase in the glass content from 0 wt % to 70 wt %, the strength of the LWAs increased from 12.21 MPa to 19.31 MPa with similar densities in the range of 1.667–1.687 g/cm³. The addition of a nucleating agent has a fluxing effect and promotes the formation and growth of diopside, which provides aggregates with high strength and low density. For example, the addition of CaF₂ decreased the density of the LWAs from 1.687 g/cm³ to 1.461 g/cm³ and increased the strength from 17.59 MPa to 20.81 MPa under the same calcination regime. The effect of the pore structure on the mechanical properties of the LWA in this experiment was far less than that of the crystal phase composition. With the addition of a nucleating agent, the diopside was co-precipitated from both the muck and glass. If no nucleating agent is added, diopside mainly precipitates from glass, and muck mainly forms a glass phase.     

Sintering and reactive crystal growth of diopside-albite glass-ceramics from waste glass

Diopside-albite glass-ceramics were fabricated by sintering the powder mixtures of crystallization promoters and waste glass. Two kinds of promoters were synthesized using kaolin clay, talc and chemical reagents. The crystalline phases were formed by a reactive crystallization between promoters and glass during sintering. The effect of promoter components, additions and sintering temperatures on the crystallizing and densifying behavior, microstructures and mechanical properties of glass-ceramics was investigated. The results showed that the higher densities and better mechanical properties were obtained for the glass-ceramics with 12-15% crystallization promoters sintered at 950 °C for 2 h.     

The sintering kinetics of porcelain bodies made from waste glass and fly ash

Porcelain is a material produced from kaoline, quartz and potassium-feldspar. Recently, research of new materials, for example non-hazardous wastes, that are able to replace traditional fluxing agents without changing the process or quality of the final products has been realized. The aim of this work is to study the possibility of the use of glass powder waste and fly ash together for manufacturing porcelain. Instead of quartz, fly ash was used at the selected porcelain composition. The waste glass was added partially and fully in replacement of potassium-feldspar. Samples were fired in an electric furnace with a heating rate of 10 °C/min at 1100, 1150 and 1200 °C for a period of 1, 2, 3 and 5 h. The sintered samples were characterised by XRD (X-ray diffraction) and SEM (scanning electron microscopy). Sintering activation energies were determined based on the bulk density result. At 10, 15, 20 and 25 wt.% glass waste addition, the apparent activation energies were calculated to be 145, 113.5, 70.4 and 53.74 kJ/mol, respectively. It was found that the sintering activation energy decreased with increasing waste glass addition.     

Reuse of glass waste in the manufacture of ceramic tableware glazes

Today, various studies are carried out to spread the understanding of sustainability. The sustainability of production processes gains importance in corporate areas. In this study, the use of glass waste instead of frit used in glaze compositions in the ceramic industry was evaluated. The chemical and physical properties of glass wastes on samples were examined. The glaze formulations were prepared using 3%, 5%, and 8% by weight of glass waste instead of frit. Glass wastes were added to glaze compositions and 12 different glaze formulation studies were carried out. Transparent, Opaque, and Matte test glazes were prepared with glass waste added glaze formulations, and these glazes were applied to ceramic bodies. SEM (scanning electron microscope) analysis of standard glaze and glass waste added glazes was performed to determine the microstructural and morphological characterizations. Also, surface whiteness, brightness, L*a*b values, glaze flows, harcort test results, and final water absorption values were compared. As a result of the studies, it has been determined that it is appropriate to use 3% glass waste by weight instead of the frit in the production of ceramic tableware.     

Preparation and characterization of foam glass from waste container glasses and water glass for application in thermal insulations

Glass foams are modern developed building materials which are now favorably competing with conventional materials for applications in thermal insulation. In this study, glass foams are synthesized solely from waste container glasses of mixed colors using sodium silicate (water glass) as foaming agent. Several glass foams of 150 × 150 × 30 mm were prepared from waste glasses of 75 μm, 150 μm and 250 μm size with addition of 15 wt % sodium silicate respectively and pressed uniaxially under a pressure of 10 MPa. The prepared glass foams were then sintered at temperatures of 800 °C and 850 °C respectively. Tests such as bulk density, estimated porosity, flexural strength, compressive strength and microstructure evaluation were used to assess the performance of the developed glass foams. The results showed that with increasing temperature and grain sizes, the percent porosity of the developed foams increased while the bulk density decreased. The microstructure evaluation showed that the finer the grain sizes used, the more homogenized are the pores formed and the higher the temperature, the larger the pores but are mostly closed. Both compressive and flexural strength were found to decrease with grain sizes and higher temperatures. The thermal conductivities of all the developed foam glasses satisfy the standard requirement to be used as an insulating material as their thermal conductivities did not exceed 0.25 W/m.K.     

Evaluation of locally available amorphous waste materials as a source for alternative alkali activators

The production of alkali-activated materials with excellent mechanical performance requires the use of water glass, which has a significant carbon footprint. Such materials can have a lower carbon footprint if we replace water glass with alternative activators sourced from waste. In this study, we assessed the suitability of locally available amorphous waste materials (stone wool, glass wool, bottle glass and cathode-ray tube glass) as a source for the preparation of alternative alkali activators. We quantified the amount of silicon and aluminium dissolved in the activator solutions via inductively coupled plasma-optical emission spectrometry. The alternative activators were then used to produce alkali-activated fly ash and slag. The compressive strength values of alkali-activated fly ash specimens upon the addition of NaOH, water glass and the most promising alternative activator were 38.98 MPa, 31.34 MPa and 40.37 MPa, respectively. The compressive strength of slag specimens activated with alternative activators with the highest concentration of dissolved silicon (21 g/L) was, however, 70% higher than the compressive strength of slag specimens activated with only 10 M sodium hydroxide. The compressive strength of slag specimens with the addition of the most promising alternative activator was significantly lower (3.5 MPa) than the compressive strength of those that had been activated by commercial water glass (34.3 MPa).     

Synthesis of beta-SiC powder from alkoxide precursor and study of its sintering behaviour

Abstract

Abstract

In this study, β-SiC powder was prepared using a pyrolysed spherical precursor derived from the hydrolysis mixture of phenyltrimethoxysilane and tetraethyl orthosilicate. Before the pyrolysed experiment, an alkoxide precursor was characterised using ²⁹Si solid nuclear magnetic resonance, Fourier transform infrared spectroscopy and thermogravimetric analysis. The alkoxide precursor was heated at 1800°C for 4 h under an Ar atmosphere. To examine the pyrolysed residue after heat treatment, the sample was collected and analysed with X-ray diffraction. The X-ray diffraction results for the sample show diffraction peaks at ～35, 60 and 73°, which correspond to the β-SiC phase. According to the results of chemical analysis, the SiC content of the powder that was prepared at 1800°C was determined to be 99·4%. The sintering behaviour of the prepared β-SiC powder was examined using B₄C and C as sintering additives in the temperature range of 1900–2200°C.     

Reuse of mineral wool waste and recycled glass in ceramic foams

Novel ceramic foams have been prepared by high temperature sintering of waste mineral wool and waste glass using SiC as a foaming agent. The aim of the research was to understand the effects of composition and sintering conditions on the properties and microstructure and produce commercially exploitable ceramic foams. Optimum ceramic foams were formed from 40 wt% mineral wool waste and 2 wt% SiC, sintered at 1170 °C using a heating rate of 20 °C/min with a 20 min hold at peak temperature. The ceramic foams produced had a bulk density of 0.71 g/cm³ and a uniform pore size distribution. The research shows that ceramic foams can be formed from waste mineral wool and these can be used for thermal insulation with associated economic and environmental benefits.     

Alkali-activation of marble sludge: Influence of curing conditions and waste glass addition

The use of marble sludge as precursor for new alkali activated materials was assessed studying three different curing conditions (air, humid and water immersion, respectively), after an initial curing at 60 °C for 24 h, and two glass powder fractions additions (2.5 and 5.0 vol%). Microstructural, physical (drying shrinkage, Fourier transform-infrared (FT-IR) spectroscopy, X-ray spectroscopy (XPS)), thermal (differential thermal analysis – thermogravimetric analysis, DTA-TGA) and mechanical (flexural and compressive strength) properties were investigated. Air curing was the most favourable atmosphere for mechanical properties development because it promotes Si-O-Si polymerization and gel densification, as demonstrated by FT-IR and FE-SEM observations, respectively. Satisfactory mechanical properties were achieved (18 MPa and 45 MPa, for flexural and compressive strength, respectively) in particular for glass containing mixtures. Moreover, glass powder addition significantly reduced drying shrinkage of air-cured samples because it operated as a rigid aggregate in the matrix and strengthened the formed gel.     

Effects of waste glass as a sand replacement on the strength and durability of fly ash/GGBS based alkali activated mortar

This study incorporates fine waste glass (GS) as a replacement for natural sand (NS) in fly ash (FA) and/or ground granulated blast furnace slag (GGBS) based alkali activated mortar (AAm). Tests were conducted on the AAm to determine the mechanical properties, water absorption, apparent porosity and the durability based on its resistance to Na₂SO₄ 5% and H₂SO₄ 2% concentrated solutions. Whereas the microstructure and chemical composition of AAm was analyzed by SEM-EDX to support results obtained from the experimental tests. The study revealed that the effects of GS depends on the ratio of binders used to synthesize the mortar. For high FA/GGBS mortar, an increase in strength and reduction of porosity was observed with increasing GS up to 50 wt%. For lower FA/GGBS mortar, increasing GS up to 100 wt%, increased strength and decreased porosity. The lower porosity attained with the incorporation of GS, improved the resistance of mortar to Na₂SO₄ solution thus increasing durability. The resistance of mortar to H₂SO₄ was also improved with lower porosity due to incorporation of GS. However, the durability of mortar was negatively impacted with the further reduction of porosity observed with increasing GS and GGBS above 50 wt% believed to be caused by the stress induced as a result of expansive reaction products created when the mortar reacted with acid.