Powder sintering and gel casting methods in making glass foam using waste glass: A review on parameters,performance, and challenges

The application of insulation materials in buildings and energy storage facilities is gaining global attention to reduce energy consumption, heat loss, and CO₂ emissions. Given the high insulation performance, glass foam is gaining popularity replacing combustible, high energy-consuming, and costly conventional insulation materials. The industrial process of glass foam manufacturing is an energy-consuming and non-ecofriendly process which requires the annealing of glass around its melting temperature. Therefore, researchers have developed powder sintering and gel casting methods to sinter glass foam mix at a temperature slightly above its glass transition point. However, research findings on these two methods are scattered because of the different parameters being used by researchers. The properties and performances of glass foam depend on the processing parameters, especially on the materials design and sintering conditions. Therefore, this study aimed to provide a comprehensive review on the key parameters for material selection and sintering of glass foams and provide necessary guidelines for the best practice and a direction for future research. Moreover, this review covers the current strategies and challenges associated with the powder sintering and gel casting methods including their sustainability and environmental performance.     

Integrated experimental and thermodynamic modeling study of phase equilibria in the ‘CuO0.5’-MgO-SiO2 system in equilibrium with liquid Cu metal for characterizing refractory-slag interactions

An integrated experimental and thermodynamic modeling study of the phase equilibria in the ‘CuO_0.5’-MgO-SiO₂ system in equilibrium with liquid Cu metal has been undertaken to better understand the reactions between MgO-based refractories and liquid slag in copper converting and refining processes. New experimental phase equilibria data at 1250–1680 °C were obtained for this system using a high-temperature equilibration of synthetic mixtures with predetermined compositions in silica ampoules or magnesia crucibles, a rapid quenching technique, and electron probe X-ray microanalysis of the equilibrated phase compositions. The system has been shown to contain primary phase fields of cristobalite (SiO₂), tridymite (SiO₂), pyroxene/protoenstatite (MgSiO₃), olivine/forsterite (Mg₂SiO₄), periclase (MgO), and cuprite (Cu₂O). Three regions of 2-liquid immiscibility were found—two in the high-silica range of compositions above the cristobalite primary phase field (close to ‘CuO_0.5’-SiO₂ and MgO–SiO₂ binaries) and one in the low-SiO₂, high-‘CuO_0.5’ compositional region above the periclase and olivine phase fields. The results obtained in this study indicate that silica in high-copper refining slags likely led to olivine and pyroxene phase formation, increased solubility of MgO in liquid slag, and decline in the performance of MgO-based refractories. New experimental data were used in the development of a thermodynamic database describing this pseudo-ternary system.     

A novel foam glass obtained from solid waste: A sustainable strategy for application in the degradation of an environmental pollutant

Foams glass were obtained from solid waste of flat glass and exhausted alkaline batteries. The physical, chemical, crystalline and morphological properties of the samples were obtained using the Archimedes principle, X-ray diffractometry (XRD), scanning electron microscopy (SEM). The results revealed glass foams with apparent porosities in the range of 55–64% and apparent densities in the range of 0.40–0.79 g cm^?3. The manganese oxide and graphite contained within the cathode of alkaline batteries acted as both oxidizing agents and as foaming agents. The zinc contained in the anode acted as a pore stabilizing agent and the zinc oxide as a semiconductor material. The foam glass that was composed of flat glass with an anode of Zn and ZnO, and a cathode of Mn₂O₃ and Mn₃O₄ (named An8), showed the greatest potential for heterogeneous photocatalysis, with a maximum efficiency of 95.9% after 3 h of treatment of solution containing dye. These results suggest the feasibility of producing foam glass from waste, as well as its potential application in photocatalytic systems, such as in the low-cost treatment of water.     

Werkstoffliche Aufbereitung von Wärmedämmverbundsystemen

Due to increasing energy requirements for buildings, thermal insulation composite systems (TICS) have been used to insulate building facades since the 1970s. In view of the longevity of these composite materials, there has been an increased amount of TICS waste in recent years. Since there is no current recycling concept for these systems, an enormous resource efficiency potential remains unused. Due to the complexity of composite materials this study focuses on the pretreatment and discusses different processing steps in detail.     

Enhanced UV- and visible-light driven photocatalytic performances and recycling properties of graphene oxide/ZnO hybrid layers

Light induced catalytic processes have attracted significant attention during the last years for wastewater treatment due to their efficiency in decomposition of organic contaminants. In this study we report the synthesis of graphene oxide (GO)/ZnO hybrid layers with high photocatalytic efficiency using laser radiation. The results show that the hybrid layers exhibit much improved photodecomposition efficiency as compared to pure GO or ZnO both under UV and visible-light irradiation. The enhanced photocatalytic efficiency of the hybrid as compared to the reference pure ZnO and GO layers was attributed to the contribution of GO to the separation and transport of the photogenerated charge carriers. Additionally, under visible light irradiation the organic molecules can act as first sensitizers in the degradation process. The recyclability of the layers was also investigated through repetitive photodegradation cycles under UV- or visible-light irradiation. After consecutive degradation runs, the hybrid photocatalyst layers were still stable and retained high degradation efficiency, ensuring reusability. The photocatalytic activity of the layers was correlated with the gradual change of their chemical structure during consecutive degradation cycles. Owing to the high photodegradation efficiency, reusability, and ease of recovery the synthesised hybrid layers consisting of easily available materials are suitable for environmental purification applications.     

Determining the mechanism controlling glass fibre strength loss during thermal recycling of waste composites

This paper presents an experimental investigation into the large reductions to the tensile fracture stress and the associated strength loss mechanism of E-glass fibres during thermal recycling. Fractographic analysis reveals the fracture process is controlled by surface flaws, irrespective of heat treatment temperature and duration. The fracture toughness is an important material property in order to understand possible changes in the strength–flaw relationship during heat treatment. Focussed ion beam (FIB) milling is used to artificially create a single nano-sized deep notch (between 30 and 1000 nm) in glass fibres. The strength loss, fracture toughness, fracture mirror constant and fracture mechanism observed for nano-notched and thermally recycled fibres are identical, indicating bulk property changes do not occur during thermal recycling. The study proves conclusively that surface flaw growth is the controlling mechanism reducing fibreglass strength during thermal recycling of waste polymer composites.     

Glass waste as supplementary cementing materials: The effects of glass chemical composition

Sustainable cements containing 25 wt% of different types of recycled glass have been investigated as a supplementary cementing material in order to highlight the role of glass chemical composition during the hardening process. Glass formers, stabilizers and modifiers regulate the glass dissolution in the alkaline environment during cement hydration. As a consequence, pozzolanic reaction and/or alkali–silica reaction are strictly related to the glass chemical composition. The mechanical and microstructure characterizations of mortar samples containing glass blended cements and un-reactive aggregates allow to determine which oxides in the glass have to be carefully monitored to avoid deleterious reactions.     

Recycling von marinen Sekundärrohstoffen

As a waste product, oyster shells pose a major environmental pollution problem and the reuse of the material is becoming increasingly important. Since the comminution process in the recycling of secondary raw materials defines the properties of the material, oyster shells were grinded using a planetary ball mill and an impact mill and the fractions obtained were analyzed in terms of size and shape and compared with each other. A comminuted material from the impact mill was used for a series of wetting experiments, which helped to demonstrate the surface free energy of the material.     

Klärschlammverbrennung in einer stationären Wirbelschicht mit integrierter Phosphor-Rückgewinnung

Currently, wet-chemical and thermochemical processes in particular are being discussed for the future obligatory recovery of phosphorus from sewage sludge. The coupling of phosphorus recovery with incineration in stationary fluidized bed incinerators, the dominant mono-incineration technology, offers potential advantages in terms of aftertreatment costs and economic efficiency. Tests have shown that by adjusting the incineration conditions and adding additives, an ash could be produced that corresponds to the fertilizer ordinance (DüMV) and can, therefore, potentially be used as phosphorus recyclate.     

Preparation of composite cathode material by using the extracted lead (Pb) of waste lead acid battery for LT-SOFC

The extraction of Pb from the waste lead acid batteries offers the conservation of energy resources and reduction of pollution load in the environment. The recycling of waste lead acid batteries than discarding by conventional methods is the best way. In the present studies, for LT-SOFC, three composite cathode materials (Pb_0.1Fe_0.4Co_0.5O_4-δ, Pb_0.2Fe_0.3Co_0.5O_4-δ and Pb_0.3Fe_0.2Co_0.5O_4-δ) were produced by extracting Pb from the waste lead acid batteries, cobalt nitrate [Co(NO₃)₃.6H₂O] and iron nitrate [Fe(NO₃)₃.9H₂O] using standard solid state reaction method. Thermal stability, morphological and structural characteristics were studied by TGA, SEM and XRD analyses. FTIR spectra were used to investigate the types of metal oxide bonding in the prepared ceramic composite cathode materials. Fuel cell testing and DC four probes were used to investigate electrochemical properties. The measurement of average crystalline size of the composites was found to be in the range of 12–37 nm.Scanning electron microscopy (SEM) images showed that composite materials are porous and suitable to diffuse the gases. The maximum conductivities of 1.6 Scm^?1, 2.05 Scm^?1 and 2.6 Scm^?1 have been obtained for Pb_0.1Fe_0.4Co_0.5O_4-δ, Pb_0.2Fe_0.3Co_0.5O_4-δ and Pb_0.3Fe_0.2Co_0.5O_4-δ, respectively. At 600 °C, the high OCV (0.95V) and the maximum power density (439 mW/cm²) have been achieved using hydrogen as the fuel. Lower value of activation energy (0.36ev) of Pb_0.3Fe_0.2Co_0.5O_4-δ confirms that it is the efficient material to convert electrochemically hydrogen fuel into valuable electricity.