The effect of acrylate on the properties and machinability of alumina ceramics

Effect of methyl methacrylate (MMA) as a binder and heating treatment were investigated to improve green alumina compacts machinability. Properties of green compacts and their corresponding sintered samples prepared with and without MMA were compared. Investigation of green and sintered properties was performed on samples compacted at applied pressures up to 150 MPa. After pressing, samples with MMA were thermally treated at 115oC. The intention was to enhance the polymerization of MMA at a temperature a little higher than the glass transition temperature (Tg = 103oC) of poly (methyl methacrylate). Green compacts with MMA had higher green density values than those without MMA. Sintered samples with MMA had lower values of sintered density and higher values of total porosity; after sintering, relative linear shrinkage was around 15 % for the whole range of applied pressures. The possibility of easily machining the green compacts with MMA produces great possibilities for application in many field

The effect of hydrothermal synthesis parameters on cation-doped calciumhydroxyapatite

Calcium hydroxyapatite (HAP) presents the main mineral component of human bones and teeth, and thus is widely used bioceramic material for thehard tissue repair and regeneration. The biological HAP is never found pure in nature butdoped with multiple therapeutic ions, such as Cu, Mg, Sr, Zn, etc., which are found to play important roles in bone metabolism and growth. Hence, foreign cations have been introduced into the synthetic calcium hydroxyapatite, in order to induce a specific biological response after implementation, such as osteogenesis, angiogenesis, improved cell attachment and proliferation. However, the presence of the cations leads to the lattice distortion of the calcium-hydroxyapatite, resulting in different physico-chemical and mechanical properties. The hydrothermal synthesis of calcium hydroxyapatite leads to nanosized rod-like particles, which were found to possess properties close to those of the biological HAP. The aim of this study was to investigate the effect of hydrothermal synthesis parameters on physico-chemical and mechanical properties of mono- and binary cation-doped calcium hydroxyapatite by employing XRD, SEM and Hardness by Vickers tests. The temperature applied during the hydrothermal synthesis (150- 180 °C) was found to influence the hardness of the HAP based compacts sintered at 1200 °C.IX Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 20-21, 2021; Belgrad

Synthesis and deposition of MAPbBr3 perovskite on titania nanotube arrays

The organo-inorganic perovskites are materials that have recently revolutionized the field of photovoltaics due to their low-cost fabrication and high optical absorption. The hybrid organoinorganic perovskite absorbs the visible part of the spectrum resulting in the creation of electron-hole pair. To decrease the recombination of charge carriers, the construction of solar cells requires the existence of separate layers for holes and for electrons. TiO2 is usually used as an electron transport layer because its conduction band (CB) lies under the CB of perovskite. In that way, electrons diffuse from CB of perovskite to CB of TiO2. For these experiments, TiO2 nanotubular structure was used as an electron transport layer due to its advantages compared to nanoparticular TiO2. TiO2 nanotubes can provide a one-dimensional transmission channel for the charge carriers, so it will reduce the recombination rate of the carriers and provide a channel for fast carrier transport. However, there is a problem with the contact surface between perovskite and TiO2 nanotubes. The aim of this study is to increase the contact surface of perovskite and TiO2 nanotubes by filling the nanotubes with perovskite material in order to improve electron transport. Methylammonium lead bromide perovskite (MAPbBr3) was deposited on anodically synthesized TiO2 nanotubes which were annealed at 450 °C for 1 h. After degassation of the sample under high vacuum for 3 h at 200 °C, the cooled sample was put in a solution of MAPbBr3 in dimethylformamide (DMF) and it was treated with inert gas (N2), which enabled the filling of the nanotubes with perovskite material to some extent. FESEM and XRD analyses were used for morphological and chemical characterization of the sample. The diffuse reflectance spectroscopy measurement of the sample proved that deposition of MAPbBr3 improves the absorption properties of TiO2 nanotubes. By measuring the I-V characteristics of the sample in the dark and under visible light, a hysteresis curve was obtained

Supercritical CO2 assisted deposition of MAPbBr3 perovskite onto TiO2 nanotubes

Supercritical carbon dioxide (sCO2) is an ideal low-temperature cosolvent for perovskite deposition due to its relatively low critical point (31.2 °C, 73.8 bar), no surface tension, liquid-like density, gas-like viscosity, and diffusivity. It enables faster mass transfer which allows penetration of crystals in nanoporous structure. The study investigates the influence of time of deposition of perovskite assisted with supercritical carbon dioxide on the filling of nanotubes. Perovskite solar cell technology has been developed so fast due to several factors including a tunable band gap, high absorption coefficient, and low-cost fabrication. The quality of the perovskite film is important for the high efficiency of perovskite solar cells. Perovskite precursors are usually deposited from the solution onto a substrate using spin-coating followed by post-deposition treatments, but often it results in low-quality films that cannot provide good photovoltaic performances. Deposition of perovskite in the presence of sCO2 is a promising method for the formation of high-quality perovskite layers. In this work, methylammonium lead bromide perovskite (MAPbBr3) was deposited on TiO2 nanotubes from the solution in dimethylformamide (DMF) by application of sCO2 at 35 °C and 200 bar for 1 h, and 3 h. FESEM results show that TiO2 nanotubes were filled with perovskite material in both cases. The diffuse reflectance spectroscopy measurement of samples proved that the absorption edge of prepared TiO2 nanotubes/MAPbBr3 was extended to the visible range. Measurement of I-V characteristics showed that the sample made for 3 h had a higher value of current than the sample prepared for 1 h. The application of sCO2 during the deposition of perovskite has enabled the preparation of a photodiode with a better contact between TiO2 nanotubes and perovskite which is important for the future development of solar cells

Fabrication and applications of multifunctional nanostructured TiO2

Nanomaterials development is a rapidly emerging field of research with enormous potential for societal and economic benefits. In agro and food industries dimension-dependent properties or phenomena of nanomaterials may be used for various functional effects such as increased bioavailability or decreased toxicity of products, better detection of pathogens, improved food packaging materials, or improved delivery of nutrients. Since these effects may derive from altered or unique characteristics of materials in the nanoscale range that are not normally observed or expected in larger-scale materials with the same chemical composition, such changes raise questions about the safety, effectiveness, performance, quality or public health impact of nanotechnology products. In this article, we have reviewed the fabrication, properties, and selected applications of nanostructured TiO2 based materials. Special attention has been paid to TiO2 nanoparticles and nanotubes fabrication perspectives and applications in agriculture. We have shown that high photocatalytic disinfection and photobiological effects of nanostructured TiO2 coupled with its low price, nontoxicity, and stable performance especially provide new approaches for solving environmental pollution and pesticide residue problems in agriculture.Paper: [https://hdl.handle.net/21.15107/rcub_dais_5121

Mg/Cu co-substituted hydroxyapatite – Biocompatibility, mechanical properties and antimicrobial activity

The aim of this study was to improve the mechanical properties and to optimize antimicrobial activity of hydroxyapatite (HAP) by simultaneous doping with Mg and Cu ions in order to obtain material that would be able to assist in the bone/tooth healing process, prevent post-implementation infections and provide satisfying values of hardness and fracture toughness for biomedical application. Ion doping was done during the hydrothermal synthesis of HAP powders, whereby the content of Mg ions in the starting solution was varied between 1-20 mol. % with regard to Ca ions, while the amount of Cu ions was kept constant at 0.4 mol. %. The green compacts were sintered for 2 h at temperatures ranging 750–1200 °C depending on the Mg content, chosen in agreement with dilatometry results. Presence of Mg ions was found to favour transition from HAP to β−tricalcium phosphate phase (β−TCP), which enabled formation of biphasic HAP/β−TCP and pure β−TCP phase at 160 °C during hydrothermal synthesis. In vitro investigation of antimicrobial activity against Escherichia coli, Staphylococcus aureus and Enterococcus faecalis showed satisfactory antimicrobial activity. MTT assay performed on MRC-5 and L929 cell lines showed excellent cytocompatibility and cell proliferation. Maximum hardness by Vickers and fracture toughness values, 4.96 GPa and 1.75 MPa m1/2 respectively, were obtained upon addition of 5 mol. % Mg, as a consequence of the lowest grain size and porosity, as well as the highest densification rate. This is, to the best of our knowledge, the highest fracture toughness for HAP or β-TCP ceramics reported thus far.This is the peer-reviewed version ofthe article: Veljović, Đorđe, Matić, Tamara, Stamenić, Tanja, Kojić, Vesna, Dimitrijević Branković, Suzana, Lukić, Miodrag J., Jevtić, Sanja, Radovanović, Željko, Petrović, Rada, Janaćković, Đorđe, "Mg/Cu co-substituted hydroxyapatite – Biocompatibility, mechanical properties and antimicrobial activity" in Ceramics International, 45, no. 17, Part A (2019):22029, [https://doi.org/10.1016/j.ceramint.2019.07.219

Application of supercritical carbon dioxide for making perovskite photodiode

Perovskite solar cells reached high efficiency in a short period. When perovskite was applied for the first time as photovoltaics, power conversion efficiency (PCE) was less than 3 %. Up to now, PCE is over 29 %. In perovskite solar cells, the perovskite layer is an active layer that absorbs the visible part of the spectrum. To reduce the recombination of charge carriers, the construction of solar cells requires the existence of layers for holes and electrons. TiO2 is usually used as an inorganic electron transport layer because its conduction band (CB) lies under the CB of perovskite, so electrons could diffuse from CB of perovskite to CB of TiO2. For these experiments, TiO2 nanotubular structure was used due to its advantages compared to nanoparticular TiO2. TiO2 nanotubes provide a one-dimensional transmission channel for the charge carriers which will reduce the recombination of the carriers and provide a fast carrier transport. The TiO2 nanotubes were synthesized by anodization of Ti foil after which they were annealed at 450 °C for 1 h. Their inner diameter was ~ 103 ± 17 nm while the length was ~ 350 nm. Methylammonium lead bromide perovskite (MAPbBr3) was deposited on TiO2 nanotubes from the solution in dimethylformamide (DMF) by application of supercritical carbon dioxide at 35 °C and different pressures (100, 200, and 300 bar). It has been observed that supercritical CO2 improves the filling of nanotubes by the perovskite due to its stronger solubilizing power at higher pressures. A perovskite photodiode with an improved contact surface between TiO2 and perovskite was made, which is the basis for future solar cell construction. I-V characteristics show that the highest value of photocurrent under visible light reached 400 μA for the sample which was obtained at 35 ° C and 300 bar for 1 h. The absorption edge of prepared TiO2 nanotubes/MAPbBr3, determined by diffuse reflectance spectroscopy, was extended to the visible range. FESEM and XRD analyses also were done

Improving the contact surface between TiO2 nanotubes and MAPbBr3 to make perovskite solar cells

The organo-inorganic perovskites are extraordinary materials that have recently revolutionized the field of photovoltaics due to their low-cost fabrication and high optical absorption. In a short period, they reached great efficiency. Many parameters which affect the quality of perovskite films can be optimized, so the efficiency of these devices can be further improved. In perovskite solar cells, the perovskite layer is an active layer that absorbs the visible part of the spectrum, resulting in the formation of the electron-hole pair. To decrease the recombination of charge carriers, the construction of solar cells requires the existence of two additional layers in order to separate the holes and electrons. TiO2 could be used as an electron transport layer because its conduction band (CB) lies under the CB of perovskite. In that way, electrons diffuse from CB of perovskite to CB of TiO2. For these experiments, TiO2 nanotubular structure provides a one-dimensional transmission channel for the charge carriers, which resulting in faster carrier transport. Perovskite methylammonium lead bromide (MAPbBr3) was coupled with TiO2 nanotube arrays which were synthesized by anodization of Ti foil and annealed at 450 °C. The most used methods for deposition of perovskite materials on mesoporous and planar TiO2 are: one-step deposition, two-step sequential deposition, and vapor-assisted solution processing. Disadvantage of these methods is a small contact area between TiO2 and perovskite. The aim of this research was to increase the contact surface of the perovskite and TiO2 nanotubes by filling the nanotubes with the perovskite material in order to improve electron transport

[Characterization of deposited plasma spray nicralcoy2o3 coating layers on almg1 alloy substrates] [Karakterizacija deponovanih slojeva plazma sprej prevlake nicralcoy2o3 na podlogama od legure almg1]

In this paper, analyzed are the effects of the plasma spray distance on the microstructure and mechanical properties of the NiCrAlCoY2O3 coating layers deposited at atmospheric pressure. The microstructure and mechanical properties of the coating layers are under the influence of the interaction of plasma particles (ions and electrons) with powder particles, providing the transfer of velocity and temperature of the plasma particles onto the powder particles. The effect of the interaction is directly dependent on the time the powder particles were present in the plasma which is defined by distance of the plasma gun from the substrate, depending on the granulation of the powder, the melting point and specific gravity. In order to obtain homogeneous and denser coating layers with high adhesion, in the experiment three distances from the substrate were used: 95 mm, 105 mm and 115 mm. The layers were deposited on thin sheets of AlMg1 aluminum thickness of 0.6 mm. Evaluation of mechanical properties of the layers was carried out by examining microhardness using the HV0.1 method and the bond strength by tensile testing. The morphology of the powder particles was examined on the SEM, while the microstructure of the layers was evaluated under a light microscope in accordance with the Pratt Whitney standard. The results of the experiment showed that the distance from the substrate substantially influenced the structure and mechanical properties of the coating layers. The best deposited layers were examined in the system with the ZrO224%MgO ceramic coating, which have proved to be reliable protectionfrom high temperature and abrasive rocket jet fuel