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The present work demonstrates the microwave-assisted synthesis of two different structural morphologies containing nickel oxide nanoparticles (NiO NPs) embedded in nitrogen (N) and sulfur (S) co-doped reduced graphene oxide (NS-rGO) nanosheets. The synthesized NiO anchored on NS-rGO nanosheets (NS-rGO-NiO composites) and NiO covered by NS-rGO nanosheets (NS-rGO:NiO composites) were used as an application in electromagnetic interference (EMI) shielding effectiveness (SE). The EMI SE studies reveal that NS-rGO:NiO composites show improved performance as compared to NS-rGO-NiO composites. In NS-rGO:NiO composites, the covered surface of NiO NPs by conducting NS-rGO nanosheets helps to improve the EMI SE application. The synthesized composite materials were extensively characterized using various techniques including scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. Binding energy of N/S ...

Made available in DSpace on 2022-04-29T08:32:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Glass-ceramic materials were obtained by heat treatment (960°C for 2, 4, and 6 hs) of glasses with CaCO3 47.50 wt%-TiO2 23.75 wt%-SiO2 23.75-Al2O3 5.00 wt% formulation produced by the melt-quenching technique (melting at 1650°C and subsequent annealing at 650°C). The materials' structural characterization and crystallization kinetics (Kissinger method) indicate the presence of CaTiO3, CaSiO3, and CaTiSiO5 crystalline phases with activation energies 217, 281, and 446 kJ/mol, respectively. The structure refinement (Rietveld method) suggests metastability for the CaSiO3 and CaTiSiO5 phases as a function of the heat treatment time. The increase in time favors CaTiO3 crystallization, from 62.97 wt%, in the 2 hs treated sample, to 79.21 wt%, in the 6 hs treated sample. EDS and microstructure analyses confirm the glass-ceramic production and indicate segregation of the CaTiO3 phase for longer heat treatment times. Universidade Estadual Paulista (UNESP) Faculdade de Ciências e Tecnologia Departamento de Física Universidade Estadual Paulista (UNESP) Faculdade de Ciências Departamento de Química Universidade Estadual Paulista (UNESP) Faculdade de Ciências e Tecnologia Departamento de Física Universidade Estadual Paulista (UNESP) Faculdade de Ciências Departamento de Química

Made available in DSpace on 2021-07-14T10:26:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-10-30. Added 1 bitstream(s) on 2021-07-14T11:30:02Z : No. of bitstreams: 1 S0366-69132020000400413.pdf: 1427762 bytes, checksum: 101c416ef2eff63ec6e1bcc4c1cc8722 (MD5) A reciclagem tem sido apontada como alternativa ao descarte de resíduos em aterros industriais. No presente trabalho é mostrada a transformação de resíduos (areia descartada de fundição - ADF, grits e lama de cal) em materiais vitrocerâmicos. Os vidros foram obtidos pelo método de fusão/resfriamento. Os materiais precursores, compostos vítreos e vitrocerâmicos foram caracterizados pelas técnicas de difração de raios X (DRX), fluorescência de raios X (FRX) e calorimetria exploratória diferencial/análise termogravimétrica (CED/ATG). Os materiais vítreos foram moídos, pastilhados e tratados termicamente nas temperaturas de cristalização obtidas por CED para preparar os materiais vitrocerâmicos (885, 961 e 1090 ºC). As fases obtidas foram cristobalita, α-wolastonita (parawolastonita) e β-wolastonita (pseudowolastonita). As vitrocerâmicas apresentaram baixa absorção de água e porosidade aparente (0,26 até 0,88 wt% e 0,66 até 1,77 vol%, respectivamente). Os resultados confirmaram que os resíduos estudados podem ser utilizados como matéria-prima na fabricação de materiais vítreos e vitrocerâmicos. Recycling has been pointed out as an alternative to the disposal of waste materials in industrial landfills. In the present study, the transformation of residues (discarded foundry sand - DFS, grits, and lime mud) in glass-ceramic materials is shown. The glasses were obtained by the melting/cooling method. The precursor materials, glasses, and glass-ceramics were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), and differential scanning calorimetry/thermal gravimetric analysis (DSC/TGA). The glassy materials were milled, pelleted, and thermally treated at the crystallization temperatures given by DSC data to obtain the glass-ceramics (885, 961, and 1090 ºC). The main formed phases were cristobalite, α-wollastonite (parawollastonite), and β-wollastonite (pseudowollastonite). The glass-ceramics showed very low water absorption and apparent porosity (0.26 to 0.88 wt% and 0.66 to 1.77 vol%, respectively). The results confirmed that the studied residues can be used as raw materials for the manufacture of vitreous and glass-ceramic materials. Universidade Estadual Paulista, Faculdade de Ciências e Tecnologia Universidade do Oeste Paulista, Faculdade de Engenharia e Arquitetura Universidade Estadual Paulista, Faculdade de Ciências e Tecnologia

Eu-doped 1, 3 and 5 % CaZrO3 red-emitting phosphors were synthesized for the first time using the microwave-assisted hydrothermal method followed by heat treatment at 1200 °C. After the crystallization, the orthorhombic CaZrO3 and the non-stoichiometric cubic Ca0.15Zr0.85O 1.85 phases were identified for all samples, and the portion of the non-stoichiometric phase increases as the Eu3+ concentration increases. The excitation spectra of the phosphors display Eu3+ f-f excitation bands (namely at 395 nm and 464 nm) and the Eu3+→O2- charge transfer band at 250 nm, confirming that the CaZrO3 host acts as sensitizer for the Eu3+ luminescence. Likewise, the emission spectra feature the typical Eu3+ emission within the red spectral region, displaying CIE color coordinates of (0.642; 0.332), (0.663; 0.330) and (0.668; 0.327) for the 1, 3 and 5 % doped samples, respectively, indicating high emission color purity. By using Eu3+ as spectroscopic probe, the high-resolution selective emission spectra (14 K) confirm that Eu3+ replaces Ca2+ and Zr4+ local sites in both CaZrO3 and the Ca0.15Zr0.85O1.85 phases. Finally, the high absolute emission quantum yield of the 3 %-doped phosphor found at 393 nm (0.29 ± 0.03) confirms its potential application as red-emitting phosphor, especially in rapid identification of latent fingerprints, security ink or as red-emitting coating of near-UV LEDs for WLED applications.