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1.
Molecules ; 26(4)2021 Feb 18.
Artículo en Inglés | MEDLINE | ID: mdl-33670482

RESUMEN

In this paper, the structural and optical properties of ZnO-SiO2-based ceramics fabricated from oil palm empty fruit bunch (OPEFB) were investigated. The OPEFB waste was burned at 600, 700 and 800 °C to form palm ash and was then treated with sulfuric acid to extract silica from the ash. X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses confirmed the existence of SiO2 in the sample. Field emission scanning electron microscopy (FESEM) showed that the particles displayed an irregular shape and became finer after leaching. Then, the solid-state method was used to produce the ZnO-SiO2 composite and the samples were sintered at 600, 800, 1000, 1200 and 1400 °C. The XRD peaks of the Zn2SiO4 showed high intensity, which indicated high crystallinity of the composite. FESEM images proved that the grain boundaries were larger as the temperature increased. Upon obtaining the absorbance spectrum from ultraviolet-visible (UV-Vis) spectroscopy, the energy band gaps obtained were 3.192, 3.202 and 3.214 eV at room temperature, 600 and 800 °C, respectively, and decreased to 3.127, 2.854 and 2.609 eV at 1000, 1200 and 1400 °C, respectively. OPEFB shows high potential as a silica source in producing promising optical materials.


Asunto(s)
Frutas/química , Aceite de Palma/química , Dióxido de Silicio/síntesis química , Óxido de Zinc/síntesis química , Dióxido de Silicio/química , Análisis Espectral , Temperatura , Residuos , Difracción de Rayos X , Óxido de Zinc/química
2.
Molecules ; 26(11)2021 Jun 03.
Artículo en Inglés | MEDLINE | ID: mdl-34205014

RESUMEN

With the trend for green technology, the study focused on utilizing a forgotten herb to produce an eco-friendly coating. Andrographis paniculata or the kalmegh leaves extract (KLE) has been investigated for its abilities in retarding the corrosion process due to its excellent anti-oxidative and antimicrobial properties. Here, KLE was employed as a novel additive in coatings and formulations were made by varying its wt%: 0, 3, 6, 9, and 12. These were applied to stainless steel 316L immersed in seawater for up to 50 days. The samples were characterized and analyzed to measure effectiveness of inhibition of corrosion and microbial growth. The best concentration was revealed to be 6 wt% KLE; it exhibited the highest performance in improving the ionic resistance of the coating and reducing the growth of bacteria.


Asunto(s)
Andrographis/química , Materiales Biocompatibles Revestidos/farmacología , Extractos Vegetales/química , Agua de Mar/química , Acero Inoxidable/farmacología , Antiinfecciosos/química , Antiinfecciosos/farmacología , Antioxidantes/química , Antioxidantes/farmacología , Materiales Biocompatibles Revestidos/química , Corrosión , Tecnología Química Verde , Ensayo de Materiales , Hojas de la Planta/química , Agua de Mar/microbiología , Acero Inoxidable/química
3.
Molecules ; 23(4)2018 Apr 11.
Artículo en Inglés | MEDLINE | ID: mdl-29641443

RESUMEN

Willemite is a wide band gap semiconductor used in modern day technology for optoelectronics application. In this study, a new simple technique with less energy consumption is proposed. Willemite nanoparticles (NPs) were produced via a water-based solution consisting of a metallic precursor, polyvinylpyrrolidone (PVP), and underwent a calcination process at 900 °C for several holding times between 1-4 h. The FT-IR and Raman spectra indicated the presence of metal oxide bands as well as the effective removal of PVP. The degree of the crystallization and formation of the NPs were determined by XRD. The mean crystallite size of the NPs was between 18.23-27.40 nm. The morphology, particle shape and size distribution were viewed with HR-TEM and FESEM analysis. The willemite NPs aggregate from the smaller to larger particles with an increase in calcination holding time from 1-4 h with the sizes ranging between 19.74-29.71 nm. The energy values obtained from the experimental band gap decreased with increasing the holding time over the range of 5.39 eV at 1 h to at 5.27 at 4 h. These values match well with band gap obtained from the Mott and Davis model for direct transition. The findings in this study are very promising and can justify the use of these novel materials as a potential candidate for green luminescent optoelectronic applications.


Asunto(s)
Povidona/química , Puntos Cuánticos/química , Silicatos/química , Compuestos de Zinc/química , Cristalización , Luminiscencia , Tamaño de la Partícula , Espectroscopía Infrarroja por Transformada de Fourier , Espectrometría Raman , Termogravimetría
4.
Appl Opt ; 55(9): 2182-7, 2016 Mar 20.
Artículo en Inglés | MEDLINE | ID: mdl-27140551

RESUMEN

A series of MnO-doped zinc soda lime silica glass systems was prepared by a conventional melt and quenching technique. In this study, the x-ray diffraction analysis was applied to confirm the amorphous nature of the glasses. Fourier transform infrared spectroscopy shows the glass network consists of MnO4, SiO4, and ZnO4 units as basic structural units. The glass samples under field emission scanning electron microscopy observation demonstrated irregularity in shape and size with glassy phase-like structure. The optical absorption studies revealed that the optical bandgap (Eopt) values decrease with an increase of MnO content. Through the results of various measurements, the doping of MnO in the glass matrix had effects on the performance of the glasses and significantly improved the properties of the glass sample as a potential host for phosphor material.

5.
ScientificWorldJournal ; 2014: 726101, 2014.
Artículo en Inglés | MEDLINE | ID: mdl-25538962

RESUMEN

The artificial neural network (ANN) modeling of m-cresol photodegradation was carried out for determination of the optimum and importance values of the effective variables to achieve the maximum efficiency. The photodegradation was carried out in the suspension of synthesized manganese doped ZnO nanoparticles under visible-light irradiation. The input considered effective variables of the photodegradation were irradiation time, pH, photocatalyst amount, and concentration of m-cresol while the efficiency was the only response as output. The performed experiments were designed into three data sets such as training, testing, and validation that were randomly splitted by the software's option. To obtain the optimum topologies, ANN was trained by quick propagation (QP), Incremental Back Propagation (IBP), Batch Back Propagation (BBP), and Levenberg-Marquardt (LM) algorithms for testing data set. The topologies were determined by the indicator of minimized root mean squared error (RMSE) for each algorithm. According to the indicator, the QP-4-8-1, IBP-4-15-1, BBP-4-6-1, and LM-4-10-1 were selected as the optimized topologies. Among the topologies, QP-4-8-1 has presented the minimum RMSE and absolute average deviation as well as maximum R-squared. Therefore, QP-4-8-1 was selected as final model for validation test and navigation of the process. The model was used for determination of the optimum values of the effective variables by a few three-dimensional plots. The optimum points of the variables were confirmed by further validated experiments. Moreover, the model predicted the relative importance of the variables which showed none of them was neglectable in this work.


Asunto(s)
Cresoles/química , Manganeso/química , Modelos Químicos , Redes Neurales de la Computación , Procesos Fotoquímicos , Óxido de Zinc/química , Luz
6.
Int J Mol Sci ; 14(1): 1022-30, 2013 Jan 07.
Artículo en Inglés | MEDLINE | ID: mdl-23296276

RESUMEN

A systematic set of borotellurite glasses doped with manganese (1-x) [(B(2)O(3))(0.3)(TeO(2))(0.7)]-xMnO, with x = 0.1, 0.2, 0.3 and 0.4 mol%, were successfully synthesized by using a conventional melt and quench-casting technique. In this study, the remelting effect of the glass samples on their microstructure was investigated through density measurement and FT-IR spectra and evaluated by XRD techniques. Initial experimental results from XRD evaluation show that there are two distinct phases of glassy and crystallite microstructure due to the existence of peaks in the sample. The different physical behaviors of the studied glasses were closely related to the concentration of manganese in each phase. FTIR spectra revealed that the addition of manganese oxide contributes the transformation of TeO(4) trigonal bipyramids with bridging oxygen (BO) to TeO(3) trigonal pyramids with non-bridging oxygen (NBO).


Asunto(s)
Boro/química , Vidrio/química , Manganeso/química , Telurio/química , Compuestos de Boro/química , Compuestos de Manganeso/química , Óxidos/química , Oxígeno/química , Fenómenos Físicos , Espectroscopía Infrarroja por Transformada de Fourier , Difracción de Rayos X
7.
J Mech Behav Biomed Mater ; 143: 105889, 2023 07.
Artículo en Inglés | MEDLINE | ID: mdl-37150138

RESUMEN

This work investigates the role of sintering temperature on bioactive glass-ceramics derived from the new composition CaO-P2O5-Na2O-B2O3-SiO2 glass system. The sintering behaviour of the samples' physical, structural, and mechanical properties is highlighted in this study. The experimental results indicated that the sintering process improved the crystallization and hardness of the final product. Results from XRD and FTIR showed the existence of carbonate apatite, pseudo-wollastonite, and wollastonite phases. From the results, the bioglass-ceramics sintered at 700 °C obtained the highest densification and optimum mechanical results. It had the value of 5.34 ± 0.21 GPa regarding microhardness and 2.99 ± 0.24 MPa m1/2 concerning fracture toughness, which falls in the range of the human enamel. Also, the sintered samples maintained their bioactivity and biodegradability after being tested in the PBS medium. The bioactivity does not affect but slows down the apatite formation rate. Overall results promoted the novel bioglass-ceramics as a candidate material for dental application.


Asunto(s)
Silicatos , Dióxido de Silicio , Humanos , Dióxido de Silicio/química , Ensayo de Materiales , Vidrio/química , Cerámica/química
8.
Int J Mol Sci ; 13(12): 16812-21, 2012 Dec 07.
Artículo en Inglés | MEDLINE | ID: mdl-23222685

RESUMEN

We report on a recycling project in which α-Al(2)O(3) was produced from aluminum cans because no such work has been reported in literature. Heated aluminum cans were mixed with 8.0 M of H(2)SO(4) solution to form an Al(2)(SO(4))(3) solution. The Al(2)(SO(4))(3) salt was contained in a white semi-liquid solution with excess H(2)SO(4); some unreacted aluminum pieces were also present. The solution was filtered and mixed with ethanol in a ratio of 2:3, to form a white solid of Al(2)(SO(4))(3)·18H(2)O. The Al(2)(SO(4))(3)·18H(2)O was calcined in an electrical furnace for 3 h at temperatures of 400-1400 °C. The heating and cooling rates were 10 °C /min. XRD was used to investigate the phase changes at different temperatures and XRF was used to determine the elemental composition in the alumina produced. A series of different alumina compositions, made by repeated dehydration and desulfonation of the Al(2)(SO(4))(3)·18H(2)O, is reported. All transitional alumina phases produced at low temperatures were converted to α-Al(2)O(3) at high temperatures. The X-ray diffraction results indicated that the α-Al(2)O(3) phase was realized when the calcination temperature was at 1200 °C or higher.


Asunto(s)
Óxido de Aluminio/química , Aluminio/química , Precipitación Química , Residuos , Calor , Óxidos/química , Transición de Fase , Reciclaje , Difracción de Rayos X
9.
Int J Mol Sci ; 13(6): 7550-7558, 2012.
Artículo en Inglés | MEDLINE | ID: mdl-22837711

RESUMEN

This manuscript reports on the physical properties and optical band gap of five samples of soda lime silicate (SLS) glass combined with zinc oxide (ZnO) that were prepared by a melting and quenching process. To understand the role of ZnO in this glass structure, the density, molar volume and optical band gaps were investigated. The density and absorption spectra in the Ultra-Violet-Visible (UV-Visible) region were recorded at room temperature. The results show that the densities of the glass samples increased as the ZnO weight percentage increased. The molar volume of the glasses shows the same trend as the density: the molar volume increased as the ZnO content increased. The optical band gaps were calculated from the absorption edge, and it was found that the optical band gap decreased from 3.20 to 2.32 eV as the ZnO concentration increased.


Asunto(s)
Compuestos de Calcio/química , Vidrio/química , Óxidos/química , Hidróxido de Sodio/química , Óxido de Zinc/química , Rayos Ultravioleta
10.
Dent Res J (Isfahan) ; 18: 18, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-34104365

RESUMEN

BACKGROUND: The aim of this study was to investigate whether boron nitride (BN) and BN-chromium (BN-Cr) coatings applied with the sputtering method would change the characteristics of hardness and discoloration of the ceramic veneer surface. MATERIALS AND METHODS: In this experimental study, thirty disc-shaped cores (10 mm in diameter and 0.8 mm in thickness) were prepared. Three different ceramic systems, IPS Empress (E) (Ivoclar Vivadent, Schaan, Liechntenstein), IPS e.max Press (EP) (Ivoclar Vivadent, Schaan, Liechntenstein), and Turkom Cera (T) (Turcom-Ceramic SDN-BHD, Kuala Lumpur, Malaysia), were tested, each with n = 10. The specimens were divided into two subgroups (n = 5) according to the coating on the veneering ceramic: BN or BN-Cr. The Vickers hardness and color differences (ΔE) values were measured before and after coating. Surface analysis was performed with X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopic. The Wilcoxon signed-rank test was performed to compare hardness values. The Kruskal-Wallis test was performed to compare ΔE values among all groups. The post hoc tests was used after Kruskal-Wallis, with level of statistical significance set at P ≤ 0.05. RESULTS: BN-Cr coating statistically significantly increased the hardness of all types of ceramics (P < 0.05). BN coating did not change the hardness statistically significantly (P > 0.05). The mean ΔE values indicated clinically noticeable (over the limit of 3.7) color change in all groups except for the EP-BN and T-BN groups. CONCLUSION: Although BN-Cr coating in this thickness had a negative effect on color, it increased the hardness of the ceramics and could be useful in the palatal region.

11.
Dent Med Probl ; 58(2): 187-191, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-33982454

RESUMEN

BACKGROUND: If a temporary restoration is in the esthetic area and needs to be worn for a long time, the color stability of temporary materials becomes an important factor. OBJECTIVES: The aim of this in vitro study was to evaluate the long-term effects of various staining solutions on the color stability of different temporary materials produced with the computer-aided design and computer-aided manufacturing (CAD/CAM) technology. MATERIAL AND METHODS: In the study, the following materials were used: VITA CAD-Temp® (group 1); Ceramill® Temp (group 2); and Telio® CAD (group 3). Forty disk-shaped specimens (10 mm in diameter, 2 mm in thickness) of each material (N = 120) were produced with a CAD/CAM system. Staining solutions - of tea (A), of coffee (B) and cola (C) - and distilled water (D, control) were used, and color was evaluated before and after storing the samples in the solutions. Measurements were taken with a spectrophotometer and the color parameters (L*, a*, b*, and ΔE) were calculated according to the Commission internationale de l'éclairage system (CIELab). The results were evaluated with the two-way analysis of variance (ANOVA) and Tukey's tests (α = 0.05). RESULTS: Clinically perceivable (ΔE00 > 0.8) and statistically significant (p < 0.001) color differences were detected in all specimens. The highest ΔE00 value was found in the Ceramill Temp specimens. In addition, the highest ΔE00 values were noted for the specimens stored in cola and the coffee solution for all groups. The lowest ΔE00 value was observed for the groups stored in the tea solution. CONCLUSIONS: Clinically perceivable color changes were observed in all the specimens kept in the solutions. Color changes were greater for cola and coffee as compared to tea.


Asunto(s)
Diseño Asistido por Computadora , Estética Dental , Color , Humanos , Ensayo de Materiales , Propiedades de Superficie
12.
Materials (Basel) ; 14(5)2021 Feb 27.
Artículo en Inglés | MEDLINE | ID: mdl-33673655

RESUMEN

The contemporary market needs for enhanced solid-state lighting devices has led to an increased demand for the production of willemite based phosphors using low-cost techniques. In this study, Ce3+ doped willemite nanoparticles were fabricated using polymer thermal treatment method. The special effects of the calcination temperatures and the dopant concentration on the structural and optical properties of the material were thoroughly studied. The XRD analysis of the samples treated at 900 °C revealed the development and or materialization of the willemite phase. The increase in the dopant concentration causes an expansion of the lattice owing to the replacement of larger Ce3+ ions for smaller Zn2+ ions. Based on the FESEM and TEM micrographs, the nanoparticles size increases with the increase in the cerium ions. The mean particles sizes were estimated to be 23.61 nm at 1 mol% to 34.02 nm at 5 mol% of the cerium dopant. The optical band gap energy of the doped samples formed at 900 °C decreased precisely by 0.21 eV (i.e., 5.21 to 5.00 eV). The PL analysis of the doped samples exhibits a strong emission at 400 nm which is ascribed to the transition of an electron from localized Ce2f state to the valence band of O2p. The energy level of the Ce3+ ions affects the willemite crystal lattice, thus causing a decrease in the intensity of the green emission at 530 nm and the blue emission at 485 nm. The wide optical band gap energy of the willemite produced is expected to pave the way for exciting innovations in solid-state lighting applications.

13.
Materials (Basel) ; 14(22)2021 Nov 22.
Artículo en Inglés | MEDLINE | ID: mdl-34832475

RESUMEN

This study presents the utilization of mill scale waste, which has attracted much attention due to its high content of magnetite (Fe3O4). This work focuses on the extraction of Fe3O4 from mill scale waste via magnetic separation, and ball milling was used to fabricate a microwave absorber. The extracted magnetic powder was ground-milled using two different techniques: (i) a conventional milling technique (CM) and (ii) mechanical alloying (MM) process. The Fe3O4/CM samples were prepared by a conventional milling process using steel pot ball milling, while the Fe3O4/MM samples were prepared using a high-energy ball milling (HEBM) method. The effect of milling time on the structural, phase composition, and electromagnetic properties were examined using X-ray diffraction (XRD) and a vector network analyzer (VNA). XRD confirmed the formation of magnetite after both the magnetic separation and milling processes. The results revealed that Fe3O4 exhibited excellent microwave absorption properties because of the synergistic characteristics of its dielectric and magnetic loss. The results showed that the Fe3O4/CM particle powder had a greater absorption power (reflection loss: <-10 dB) with 99.9% absorption, a minimum reflection loss of -30.83 dB, and an effective bandwidth of 2.30 GHz for 2 mm thick samples. The results revealed the Fe3O4/MM powders had higher absorption properties, including a higher RL of -20.59 dB and a broader bandwidth of 2.43 GHz at a matching thickness of only 1 mm. The higher microwave absorption performance was attributed to the better impedance matching property caused by the porous microstructure. Furthermore, the magnetite, Fe3O4 showed superior microwave absorption characteristics because of the lower value of permittivity, which resulted in better impedance matching. This study presents a low-cost approach method by reutilizing mill scale waste to fabricate a high purity crystalline Fe3O4 with the best potential for designing magnetic nano-sized based microwave absorbers.

14.
Materials (Basel) ; 14(4)2021 Feb 18.
Artículo en Inglés | MEDLINE | ID: mdl-33670465

RESUMEN

Glass ionomer cement (GIC) is a well-known restorative material applied in dentistry. The present work aims to study the effect of hydroxyapatite (HA) addition into GIC based on physical, mechanical and structural properties. The utilization of waste materials namely clam shell (CS) and soda lime silica (SLS) glass as replacements for the respective CaO and SiO2 sources in the fabrication of alumino-silicate-fluoride (ASF) glass ceramics powder. GIC was formulated based on ASF glass ceramics, polyacrylic acid (PAA) and deionized water, while 1 wt.% of HA powder was added to enhance the properties of the cement samples. The cement samples were subjected to four different ageing times before being analyzed. In this study, the addition of HA caused an increment in density and compressive strength results along with ageing time. Besides, X-ray Diffraction (XRD) revealed the formation of fluorohydroxyapatite (FHA) phase in HA-added GIC samples and it was confirmed by Fourier Transform Infrared (FTIR) analysis which detected OH‒F vibration mode. In addition, needle-like and agglomeration of spherical shapes owned by apatite crystals were observed from Field Emission Scanning Electron Microscopy (FESEM). Based on Energy Dispersive X-ray (EDX) analysis, the detection of chemical elements in the cement samples were originated from chemical compounds used in the preparation of glass ceramics powder and also the polyacid utilized in initiating the reaction of GIC.

15.
Materials (Basel) ; 14(4)2021 Feb 03.
Artículo en Inglés | MEDLINE | ID: mdl-33546094

RESUMEN

This paper investigated the effects of Pr6O11 and Co3O4 on the electrical properties of ZnO-BaTiO3 varistor ceramics. The Pr6O11 doping has a notable influence on the characteristics of the nonlinear coefficient, varistor voltage, and leakage current where the values varied from 2.29 to 2.69, 12.36 to 68.36 V/mm and 599.33 to 548.16 µA/cm2, respectively. The nonlinear varistor coefficient of 5.50 to 7.15 and the varistor voltage of 7.38 to 8.10 V/mm was also influenced by the use of Co3O4 as a dopant. When the amount of Co3O4 was above 0.5 wt.%, the leakage current increased from 202.41 to 302.71 µA/cm2. The varistor ceramics with 1.5 wt.% Pr6O11 shows good nonlinear electrical performance at higher breakdown voltage and reduced the leakage current of the ceramic materials. Besides, the varistor sample that was doped with 0.5 wt.% Co3O4 was able to enhance the nonlinear electrical properties at low breakdown voltage with a smaller value of leakage current.

16.
Materials (Basel) ; 13(22)2020 Nov 18.
Artículo en Inglés | MEDLINE | ID: mdl-33218206

RESUMEN

Grog is an additive material that plays important roles in ceramic making. It improves the fabrication process of green bodies as well as the physical properties of fired bodies. Few low-cost materials and wastes have found their application as grog in recent years, thus encouraging the replacement of commercial grogs with cost-saving materials. Coal fly ash, a combustion waste produced by coal-fired power plant, has the potential to be converted into grog owing to its small particle sizes and high content of silica and alumina. In this study, grog was derived from coal fly ash and mixed with kaolin clay to produce ceramics. Effects of the grog addition on the resultant ceramics were investigated. It was found that, to a certain extent, the grog addition reduced the firing shrinkage and increased the total porosity of the ceramics. The dimensional stability of the ceramics at a firing temperature of 1200 °C was also not noticeably affected by the grog. However, the grog addition in general had negative effects on the biaxial flexural strength and refractoriness of the ceramics.

17.
Polymers (Basel) ; 12(2)2020 Feb 12.
Artículo en Inglés | MEDLINE | ID: mdl-32059368

RESUMEN

This paper presents the electromagnetic interference properties of multi-walled carbon nanotubes (MWCNTs) as a novel nano-reinforcement filler in poly (lactic acid) (PLA)/poly (ethylene glycol) (PEG) polymer matrix that was prepared via melt blending mode. Plasticization of PLA was first carried out by PEG, which overcomes its brittleness problem, in order to enhance its flexibility. A waveguide adapter technique was used to measure the dielectric properties εr, and S-parameters reflection (S11) and transmission (S21) coefficients. The dielectric properties, microwave attenuation performances, and electromagnetic interference shielding effectiveness (EMISE) for all the material under test have been calculated over the full X-Band (8-12 GHz) due to its importance for military and commercial applications. The prepared samples were studied while using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transforms infrared spectroscopy (FTIR), mechanical properties measurements, as well as thermogravimetric analysis (TGA). The results showed that the dielectric properties increased with increased multi-walled carbon nanotubes (MWCNTs) filler, as well as the shielding effectiveness of the MWCNT/PLA/PEG nanocomposites increased with the increasing of MWCNTs. The highest SE total value was found to be 42.07 dB at 12 GHz for 4 wt% filler content. It is also observed that the attenuation values of the nanocomposites increased with an increase in MWCNTs loading, as well as the power loss values for all of the samples increased with the increase in MWCNTs loading, except the amount of the transmitted wave through the nanocomposites.

18.
Sci Rep ; 10(1): 3135, 2020 Feb 21.
Artículo en Inglés | MEDLINE | ID: mdl-32081972

RESUMEN

Microwave absorption properties were systematically studied for double-layer carbon black/epoxy resin (CB) and Ni0.6Zn0.4Fe2O4/epoxy resin (F) nanocomposites in the frequency range of 8 to 18 GHz. The Ni0.6Zn0.4Fe2O4 nanoparticles were synthesized via high energy ball milling with subsequent sintering while carbon black was commercially purchased. The materials were later incorporated into epoxy resin to fabricate double-layer composite structures with total thicknesses of 2 and 3 mm. The CB1/F1, in which carbon black as matching and ferrite as absorbing layer with each thickness of 1 mm, showed the highest microwave absorption of more than 99.9%, with minimum reflection loss of -33.8 dB but with an absorption bandwidth of only 2.7 GHz. Double layer absorbers with F1/CB1(ferrite as matching and carbon black as absorbing layer with each thickness of 1 mm) structure showed the best microwave absorption performance in which more than 99% microwave energy were absorbed, with promising minimum reflection loss of -24.0 dB, along with a wider bandwidth of 4.8 GHz and yet with a reduced thickness of only 2 mm.

19.
Polymers (Basel) ; 11(4)2019 Apr 11.
Artículo en Inglés | MEDLINE | ID: mdl-30978935

RESUMEN

In this study, a nanocomposite of reduced graphene oxide (RGO) nanofiller-reinforcement poly(lactic acid) (PLA)/poly(ethylene glycol) (PEG) matrix was prepared via the melt blending method. The flexibility of PLA was improved by blending the polymer with a PEG plasticizer as a second polymer. To enhance the electromagnetic interference shielding properties of the nanocomposite, different RGO wt % were combined with the PLA/PEG blend. Using Fourier-transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM) and X-ray diffraction, the structural, microstructure, and morphological properties of the polymer and the RGO/PLA/PEG nanocomposites were examined. These studies showed that the RGO addition did not considerably affect the crystallinity of the resulting nanomaterials. Thermal analysis (TGA) reveals that the addition of RGO highly improved the thermal stability of PLA/PEG nanocomposites. The dielectric properties and electromagnetic interference shielding effectiveness of the synthesized nanocomposites were calculated and showed a higher SE total value than the target value (20 dB). On the other hand, the results showed an increased power loss by increasing the frequency and conversely decreased with an increased percentage of filler.

20.
Materials (Basel) ; 11(11)2018 Nov 06.
Artículo en Inglés | MEDLINE | ID: mdl-30404131

RESUMEN

This paper investigates the effect of the ratio of ammonium nitrate (AN) on the structural, microstructural, magnetic, and alternating current (AC) conductivity properties of barium hexaferrite (BaFe12O19). The BaFe12O19 were prepared by using the salt melt method. The samples were synthesized using different powder-to-salt weight ratio variations (1:3, 1:4, 1:5, 1:6 and 1:7) of BaCO3 + Fe2O3 and ammonium nitrate salt. The NH4NO3 was melted on a hot plate at 170 °C. A mixture of BaCO3 and Fe2O3 were added into the NH4NO3 melt solution and stirred for several hours using a magnetic stirrer under a controlled temperature of 170 °C. The heating temperature was then increased up to 260 °C for 24 hr to produce an ash powder. The x-ray diffraction (XRD) results show the intense peak of BaFe12O19 for all the samples and the presence of a small amount of the impurity Fe2O3 in the samples, at a ratio of 1:5 and 1:6. From the Fourier transform infra-red (FTIR) spectra, the band appears at 542.71 cm - 1 and 432.48 cm - 1 , which corresponding to metal⁻oxygen bending and the vibration of the octahedral sites of BaFe12O19. The field emission scanning electron microscope (FESEM) images show that the grains of the samples appear to stick each other and agglomerate at different masses throughout the image with the grain size 5.26, 5.88, 6.14, 6.22, and 6.18 µm for the ratios 1:3, 1:4, 1:5, 1:6, and 1:7 respectively. From the vibrating sample magnetometer (VSM) analysis, the magnetic properties of the sample ratio at 1:3 show the highest value of coercivity Hc of 1317 Oe, a saturation magnetization Ms of 91 emu/g, and a remnant Mr of 44 emu/g, respectively. As the temperature rises, the AC conductivity is increases with an increase in frequency.

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