Additive manufacturing (AM) technologies enable the fabrication of objects with complex geometries in much simpler ways than conventional shaping methods. With the fabrication of recyclable filters ...for contaminated waters, the present work aims at exploiting such features as an opportunity to reuse glass from discarded pharmaceutical containers. Masked stereolithography-printed scaffolds were first heat-treated at relatively low temperatures (680 and 730 °C for 1 h) and then functionalized by alkali activation, with the formation of zeolite and sodium carbonate phases, which worked as additional adsorbing centers. As-sintered and activated scaffolds were characterized in terms of the efficiency of filtration and removal of methylene blue, used as a reference dye. The adsorption efficiency of activated printed glass was 81%. The 3D-printed adsorbent can be easily separated from the solution for reuse.
The present COVID-19 emergency has dramatically increased the demand for pharmaceutical containers, especially vials. End-of-life containers, however, cannot be easily recycled in the manufacturing ...of new articles. This paper presents some strategies for upcycling of pharmaceutical glass into various porous ceramics. Suspensions of a fine glass powder (70 vol%) are used as a starting material. Highly uniform cellular structures may be easily prepared by vigorous mechanical stirring of partially gelified suspensions with added surfactant, followed by drying and firing at 550-650 °C. Stabilization of the cellular structures at temperatures as low as the glass transition temperature (T
) of the used glass is facilitated by thermal decomposition of the gel phase, instead of viscous flow sintering of glass. This finding enabled the preparation of glass membranes (∼78 vol% open porosity), by direct firing of hardened suspensions, avoiding any surfactant addition and mechanical stirring. The powders obtained by crushing of hardened suspensions, even in unfired state, may be used as a low-cost sorbent for dye removal.
Fiber glass waste (FGW) was subjected to alkali activation in an aqueous solution with different concentrations of sodium/potassium hydroxide. The activated materials were fed into a methane-oxygen ...flame with a temperature of around 1600 °C. X-ray diffraction analysis confirmed the formation of several hydrated compounds, which decomposed upon flame synthesis, leading to porous glass microspheres (PGMs). Pore formation was favored by using highly concentrated activating alkali solutions. The highest homogeneity and yield of PGMs corresponded to the activation with 9 M KOH aqueous solution.
Bi doped 2CaO-Al
2
O
3
-SiO
2
(gehlenite) glasses were prepared by conventional melting. The concentration of Bi
3+
was 0, 0.25, 0.50 and 1.50 mol. %. The prepared samples were X-ray amorphous except ...of the undoped sample and the sample with the highest content of Bi
3+
, for which XRD records revealed traces of crystalline gehlenite.
Differential thermal analysis (DTA) was used to study the thermal properties of prepared glasses, performed in the atmosphere of nitrogen at 5 different heating rates. The DTA records of all studied samples contained only one exothermic effect. Based on the results of XRD analysis, the exothermic effect was attributed to the crystallization of gehlenite. The XRD patterns of all samples measured after DTA analysis contained gehlenite as the main crystalline phase (01–074-164 COD). The DTA records measured at a heating rate of 10 °C.min
−1
revealed a significant decrease in the temperatures of maxima of the exothermic peaks (from 982 °C to 943 °C) with the increasing Bi doping. The model approach using the Johnson–Mehl–Avrami-Kolgomorov (JMAK) equations with six different values (1.5, 2, 2.5, 3, 3.5 and 4) of Avrami parameters (
m
) was used to study crystallization kinetics of gehlenite glasses. The model that best describes the experimental data was found, using the AIC (Akaike criterium) and wAIC (Akaike weight) criteria:
A
(frequency factor) and
E
app
(apparent activation energy) were determined. Based on kinetic parameters values, it is concluded that the nucleation rate is constant. Irrespective of the Bi content, the movement of the growth zone is controlled by diffusion and 3D growth is characteristic for the gehlenite crystals growth.
A porous membrane was developed through alkali activation of pharmaceutical boro-alumino-silicate glass powders suspended in diluted NaOH and KOH aqueous solutions (2.5 M). A consolidated porous ...structure was obtained by the binding of unreacted particles mediated by a surface gel, developed upon drying of the suspensions and their curing at 40 °C for 14 days. The binding phase was sufficiently stable to resist immersion in boiling water and in acidic solutions. Copper adsorption tests were carried out under acidic pH, immersing the membranes in a Cu(NO3)2 solution for different periods of time. To determine the effect of surface washing on capture of copper ions, adsorption experiments with washed and unwashed membranes were also carried out, at varying pH. It was determined that the adsorption kinetics follow the pseudo-second-order kinetic model. The main adsorption mechanism observed is the electrostatic interaction between the negative surface charge of the washed membrane and the Cu2+ ions present in solution. An adsorption higher than 60% was observed at pH = 5, while at pH = 2 the efficiency decreased due to the presence of H3O+ ions. To ensure immobilization of copper, the membranes were densified by viscous flow sintering at a moderate temperature (700 °C). Leaching tests on membranes demonstrated the efficiency of the process in terms of copper ions immobilization.
Additive manufacturing technologies, compared to conventional shaping methods, offer great opportunities in design versatility, for the manufacturing of highly porous ceramic components. However, the ...application to glass powders, later subjected to viscous flow sintering, involves significant challenges, especially in shape retention and in the achievement of a substantial degree of translucency in the final products. The present paper disclosed the potential of glass recovered from liquid crystal displays (LCD) for the manufacturing of highly porous scaffolds by direct ink writing and masked stereolithography of fine powders mixed with suitable organic additives, and sintered at 950 °C, for 1–1.5 h, in air. The specific glass, featuring a relatively high transition temperature (Tg~700 °C), allowed for the complete burn-out of organics before viscous flow sintering could take place; in addition, translucency was favored by the successful removal of porosity in the struts and by the resistance of the used glass to crystallization.
Novel and eco-friendly solutions are extensively needed for wastewater treatment. This work capitalizes on the combination of waste vitrification and additive manufacturing to produce an efficient ...photocatalyst for the specific purpose. Fine powders of waste-derived glass, containing Fe3O4 inclusions, by simple suspension (for a solid loading of 65 wt %) in alkaline solution (5 M NaOH), were transformed into pastes for direct ink writing. 3D-printed reticulated scaffolds were stabilized by the progressive hardening of a zeolite-like gel, formed by glass/solution interaction, at nearly room temperature. The printed scaffolds were successfully tested for the removal of methylene blue, realized by combining the high sorption capacity of the gel with the catalytic activity of magnetite inclusions, under UV light. A complete degradation of methylene blue is achieved by 90 min exposure, comparing favorably with other reported photocatalytic materials, requiring from 60 to 360 min. The photocatalytic activity was tested for several cycles, with no significant degradation. In other words, a waste-derived material can be reused for multiple times, to remediate wastewaters, with evident benefits on waste minimization.
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‘Silica-defective glasses’, combined with a silicone binder, have been already shown as a promising solution for the manufacturing of glass–ceramics with complex geometries. A fundamental advantage ...is the fact that, after holding glass powders together from room temperature up to the firing temperature, the binder does not completely disappear. More precisely, it converts into silica when heat-treated in air. A specified ‘target’ glass–ceramic formulation results from the interaction between glass powders and the binder-derived silica. The present paper is dedicated to the extension of the approach to the coating of titanium substrates (to be used for dental and orthopedic applications), with a bioactive wollastonite–diopside glass–ceramic layer, by the simple airbrushing of suspensions of glass powders in alcoholic silicone solutions. The interaction between glass and silica from the decomposition of the binder led to crack-free glass–ceramic coatings, upon firing in air; in argon, the glass/silicone mixtures yielded novel composite coatings, embedding pyrolytic carbon. The latter phase enabled the absorption of infrared radiation from the coating, which is useful for disinfection purposes.
The presence of residual carbon in powder precursors prepared using the sol-gel method can pose significant challenges in producing ceramics and glasses of high quality. In the case of glass, carbon ...dioxide formation during the glass-melt heating process leads to bubble/pore formation, while in the case of ceramics, residual carbon can significantly impair its optical properties. The present study aims to identify the reasons for the persistence of residual carbon in YAG and YAG ⁺ Al₂O₃ (YAGA) precursor powders prepared by the sol-gel Pechini method, even under high-temperature conditions exceeding 1400 °C. The study seeks to provide insights to aid in the development of strategies that mitigate the impact of residual carbon on the quality of ceramics and glasses produced using sol-gel techniques. It was found that even after the annealing of the precursor at a temperature of 1200 °C for two hours, a small amount of carbon remains in the precursor powder. The X-ray diffraction (XRD) analysis of the YAGA precursor powders showed that the crystallisation of alumina was delayed and began at 1200 °C. The amount of α-alumina, which corresponds to its actual addition, was identified at a temperature of 1500 °C. Additionally, as the alumina crystallises, the carbon is released from the precursor which is the reason for microspheres blowing in the flame, even when the precursor was burnt out at a temperature of 1400 °C.
The present study illustrates the manufacturing method of hierarchically porous 3D scaffolds based on åkermanite as a promising bioceramic for stereolithography. The macroporosity was designed by ...implementing 3D models corresponding to different lattice structures (cubic, diamond, Kelvin, and Kagome). To obtain micro-scale porosity, flame synthesized glass microbeads with 10 wt% of silicone resins were utilized to fabricate green scaffolds, later converted into targeted bioceramic phase by firing at 1100 °C in air. No chemical reaction between the glass microspheres, crystallizing into åkermanite, and silica deriving from silicone oxidation was observed upon heat treatment. Silica acted as a binder between the adjacent microspheres, enhancing the creation of microporosity, as documented by XRD, and SEM coupled with EDX analysis. The formation of 'spongy' struts was confirmed by infiltration with Rhodamine B solution. The compressive strength of the sintered porous scaffolds was up to 0.7 MPa with the porosity of 68-84%.
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