Preparation and characterization of some ferromagnetic glass–ceramics contains high quantity of magnetite

Ferrimagnetic glass–ceramics are promising candidates for magnetic induction hyperthermia, which is one form of inducing deep-regional hyperthermia, by using a magnetic field. The aim of this work was to study the effect of increasing the amount of crystallized magnetite on the magnetic properties of glass–ceramic samples. Two different ferrimagnetic glass–ceramics with the composition based on wollastonite or hardystonite with high quantity (∼60%) of magnetite were prepared by melting the starting materials at 1450 °C for 2 h. The influences of chemical composition, amount of crystallized magnetite and microstructure of ferrimagnetic glass–ceramics on magnetic properties of ferromagnetic glass–ceramics were investigated using differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). The X-ray diffraction patterns show the presence of nanometric magnetite crystals in a glassy matrix after cooling from melting temperature. The amount of crystallized magnetite varies as a function of the chemical composition and heat treatment schedule. The presence of ZnO in the glass–ceramics was found to decrease the viscosity and so cases higher degree of mobility of ions leading to higher degree of crystallinity. The higher heat treatment parameters and so the lower viscosity of the glass containing ZnO are assumed to allow the magnetite to grow to larger crystallite size. Glass transition temperature and thermal stability were found to be functions of chemical composition. Magnetic hysteresis cycles were analyzed using a vibrating sample magnetometer (VSM) with a maximum applied field of 15 kOe at room temperature in quasi-static conditions. From the obtained hysteresis loops, the saturation magnetization (Ms), remanance magnetization (Mr) and coercivity (Hc) were determined. The results showed that these materials are expected to be useful in the localised treatment of cancer.     

Preparation and characterization of cordierite glass–ceramics for bonding solar thermal transmission pipelines

TiO₂ was employed to develop cordierite glass–ceramics for thermal transmission pipeline binders by a melt-quenching method. The effects of TiO₂ on the phase composition, microstructure, and physical properties of glass–ceramics were studied. In addition, the thermal shock resistance of the glass–ceramics based binder was investigated. The results showed the formation of α cordierite could be increased by adding 1.0 wt% TiO₂, thereby improving bending strength and decreasing the coefficient of thermal expansion. However, a 3-5 wt% TiO₂ additive resulted in massive generation of µ cordierite, which exhibited a negative effect on the above performances. After crystallization at 1000°C for 2 h, sample B1 (1 wt% TiO₂ additional) displayed the best overall properties. It was demonstrated that cordierite glass–ceramics were satisfactory materials as heat transmission pipeline binders when the C2 binder (40 wt% frit, 60 wt% as-prepared sample B1) was applied, which had a good thermal shock resistance.     

Preparation and characterization of crednerite glass–ceramics in the MnO·CuO·SiO2 system

Nanoscale crednerite (CuMnO₂) was prepared in the system MnO·CuO·SiO₂, using glass–ceramics technique for the first time. Based on obtained data from differential thermal analysis (DTA), the prepared samples were heat-treated at 700 and 800 °C for 2 h. The presence of crystalline phases after and before heat treatment was investigated by X-ray diffraction analysis. Crystallization of crednerite (CuMnO₂), manganese silicate (Mn₂SiO₄) and traces of cuprite (Cu₂O) and cristobalite (SiO₂) phases were recognized. Transmission electron microscopy showed nanoscale crystals in the range 5–10 nm. The prepared glass–ceramics showed ferrimagnetic properties with wide range coercivity from 53 to 2217 Hci and magnetization saturation from 0.21708 to 1.2 emu/g. From IR reflection data; the reflection intensity of the light is high in the range of orange–red color and violet–blue colors and low in the range of green color.     

Preparation,characterization, and giant dielectric permittivity of (Y3+ and Nb5+) co–doped TiO2 ceramics

The microstructure and giant dielectric properties of Y³⁺ and Nb⁵⁺ co–doped TiO₂ ceramics prepared via a chemical combustion method are investigated. A main rutile–TiO₂ phase and dense ceramic microstructure are obtained in (Y_0.5Nb_0.5)_xTi_1-xO₂ (x = 0.025 and 0.05) ceramics. Nb dopant ions are homogeneously dispersed in the microstructure, while a second phase of Y₂O₃ particles is detected. The existence of Y³⁺, Nb⁵⁺, Ti⁴⁺ and Ti³⁺ as well as oxygen vacancies is confirmed by X–ray photoelectron spectroscopy and X–ray absorption near edge structure analysis. The sintered ceramics exhibit very high dielectric permittivity values of 10⁴–10⁵ in the frequency range of 40–10⁶ Hz. A low loss tangent value of ≈0.08 is obtained at 40 Hz. (Y_0.5Nb_0.5)_xTi_1-xO₂ ceramics can exhibit non–Ohmic behavior. Using impedance spectroscopy analysis, the giant dielectric properties of (Y_0.5Nb_0.5)_xTi_1-xO₂ ceramics are confirmed to be primarily caused by interfacial polarization.     

Investigation of structural,magnetic and Mössbauer properties of Co2+ and Cu2+ substituted Ni–Zn nanoferrites

We investigated the effects of Co²⁺ and Cu²⁺ substitution on the super-exchange interactions in Ni–Zn nanoferrites. The cation distribution technique was taken into account to explain the results. To authenticate the cation distribution, we have estimated the cation distribution in the light of X-ray diffraction method, Mössbauer spectroscopic analysis, and magnetization study. Statistical model based on the cation distribution was used to calculate the Curie temperature. The values of magneton number n_B and Curie temperature T_C calculated by using the cation distribution is found to be in agreement with the experimentally obtained values.     

Synthesis and magnetic properties of La3+-Co2+ substituted strontium ferrite particles using modified spray pyrolysis–calcination method

The purpose of the research was to improve the intrinsic magnetic properties of strontium ferrite by substituting lanthanum and cobalt for strontium and iron. The salt-assisted ultrasonic spray pyrolysis (SA-USP) following calcination process were used to from La-Co substituted strontium ferrite particles (La_xSr_1-xFe_12-yCo_yO₁₉), and their compositional dependent magnetic properties systemically investigated. All the samples were calcined at 1050 °C for 1 h in an air atmosphere to yield single-phased hexagonal particles several hundred nanometers to microns in size. A saturation magnetization of 70.76 emu/g and a coercivity 7265 Oe were obtained at a composition of La_0.25Sr_0.75Fe_11.75Co_0.25O₁₉. The amount of Co was reduced to obtain an optimized saturation magnetization of 71.40 emu/g and a coercivity of 7572 Oe at a composition of La_0.25Sr_0.75Fe_11.8Co_0.2O₁₉.     

Preparation and characterization of MnOOH and β-MnO2 whiskers

MnOOH and β-MnO₂ whiskers are obtained for the first time in our work. MnOOH whiskers are chemically synthesized in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB). The product is obtained under extremely low surfactant concentrations under basic conditions, using MnSO₄·H₂O as the manganese source and ethylamine as the alkali source. After the subsequent heat treatment of MnOOH at 300 °C for 1 h, β-MnO₂ whiskers retaining the similar morphologies are obtained. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry analysis (TGA) are used to characterize the products.     

Preparation and characterization of ordered mesoporous Mg–Al–Co hydrotalcite based catalyst for decarboxylation of jatropha oil

This paper reported preparation of novel order mesoporous Mg–Al–Co hydrotalcite based catalysts through sol–gel procedure using precursors such Mg(NO₃)₂, Al(NO₃)₃ and Co(NO₃)₂ and Na₂CO₃. The catalyst also contained both acidity and basicity being very convenient for decarboxylation process of vegetable oil to green hydrocarbons. The alkaline media was maintained at pH 10 during the processes. Molar ratio of metal cations and temperature of the sol–gel processes were investigated for their effect in the mesoporous structure formation. The results showed that the procedure should be established at 70 °C with the molar Mg/Al/Co ratio of 1/5/0.2. Acidity and basicity of the mesoporous hydrotalcite based catalyst were demonstrated for their co-existence. The as-synthesized material at the suitable conditions was used as catalyst for decarboxylation of jatropha oil to obtain green hydrocarbons mainly belonging to diesel fraction. The decarboxylation was carried out at 400 °C for 3 h in closed auto-pressurized reactor exhibiting a yield of diesel involving hydrocarbons of over 70% after distillation and analysis. The result also confirmed that the acidity and basicity greatly accelerated the activity of the catalyst. Some techniques were used to characterizing the catalyst including XRD, SEM, TEM, TGA, NH₃-TPD, CO₂-TPD and BET, and GC–MS was also used to analyze the main product composition.     

Preparation and characterization of polyhedral oligomeric silsesquioxane–titania aerogels

The novel polyhedral oligomeric silsesquioxane (POSS)–titania aerogels which contain different contents of titania were successfully prepared by the sol–gel process and subsequently supercritical drying with carbon dioxide. All the aerogels are monolithic and the densities of those aerogels are low. The FTIR spectra of the aerogels showed the resulting POSS–TiO₂ composite aerogels had homogeneous Si–O–Ti bonds. The microstructure, surface composition and thermal stability were measured by FESEM, XPS and TGA. With the increasing of titania contents, the aggregated particles of the aerogels in the microstructure got larger and larger. The texture of the aerogels was measured by XRD and nitrogen adsorption/desorption and showed that they were amorphous and had high surface area (>500 m²/g).     

Preparation and luminescent properties of Eu-doped transparent mica glass–ceramics

Eu-doped transparent mica glass–ceramics were prepared, the influence of Eu-doping on the crystallization of the parent glasses was investigated and the luminescent properties of the parent glasses and the glass–ceramics were estimated. A small additive amount of Eu element was very effective in preparing transparent mica glass–ceramics. However, the excess addition led to the coarsening of phase separation in the glass phase and the separation of unidentified crystal phases and β-eucryptite during heating of the parent glasses, which caused white opaque at lower heating temperatures. When mica crystals were separated, Eu ions entered the interlayers of mica crystals. The observed emission and excitation spectra showed that parts of Eu³⁺ ions which were added as Eu₂O₃ were reduced to Eu²⁺ ions during melting of the starting materials and heating the parent glasses in air and the energy transfer from Eu²⁺ to Eu³⁺ ions occurred.     

Dielectric and magnetic properties of substituted Li–Zn ferrite thick films clouded over a half wavelength microstrip rejection filter

Li_0.35–0.5x Mg _x Zn_0.3Fe_2.35–0.5x O₄ nanoparticles (x = 0, 0.14, 0.28, 0.42, 0.56, and 0.70) were prepared by low-cost combustion synthesis at relatively low temperature. Thick films of Li–Mg–Zn ferrite were prepared by screen printing method and characterized by XRD and microwave characteristics at microwave frequencies (within X- and Ku-bands) by overlay technique using λ/2 rejection filter. The influence of magnesium content x on the resonance frequency, quality factor, effective dielectric constant, complex permittivity, complex permeability, microwave conductivity, and penetration depth was explored.     

Low temperature firing of Co2Y–NiCuZn ferrite composites

Hexagonal structure magnetoplumbite ferrites have revealed a higher dispersion frequency than that of nickel ferrites because of the magnetoplumbite's magnetic anisotropy. The magnetoplumbite ferrite densification temperature always exceeds 1000 °C and the initial low temperature firing permeability of magnetoplumbite ferrites with added glass is too low (μ_i = 2–4). Therefore, it is desirable to develop a material that has a higher permeability at above 300 MHz and can be densified at temperatures below 900 °C. The Bi₂O₃–B₂O₃–ZnO–SiO₂ (BBSZ) glass addition effects on the densification and magnetic properties of Co₂Y–NiCuZn ferrite composites with various Co₂Y/NiCuZn ferrite ratios were investigated. The densification of Co₂Y–NiCuZn ferrite composites was enhanced by the addition of glass at low sintering temperatures (<900 °C) due to the liquid phase sintering. Co₂Y–NiCuZn ferrite composites with 4 wt% BBSZ glass sintered at 900 °C show a relative density above 90%, a high-initial-permeability of 5–6, a quality factor of above 30 in the 200–300 MHz frequency and a resonance frequency above 1 GHz, which can be used in high frequency multilayer chip inductors.     

Physical,mechanical and microstructural characterization of TiC–ZrN ceramics

This study aims to investigate the impact of zirconium nitride (ZrN) additive on the microstructural features and physical-mechanical characteristics of TiC. For this objective, two different samples, namely monolithic TiC and TiC-5 wt% ZrN, were produced by spark plasma sintering method at 1900 °C for 10 min under 40 MPa. X-ray diffraction, field emission scanning electron microscopy, and thermodynamical evaluations confirmed the formation of a single solid solution of (Ti,Zr)(C,N), along with a carbon-rich secondary phase in the doped ceramic. The monolithic TiC provided a higher relative density (95.5%) than the ZrN-doped sample. The fractographical assessment revealed a change in the fracture mode of TiC from transgranular to intergranular with introducing the ZrN additive. Reinforcing TiC with ZrN resulted in a Vickers hardness of 2640 HV_0.1 kg, a flexural strength of 444 MPa, and a thermal conductivity of 14.9 W/mK. Furthermore, the TiC–ZrN sample presented a higher coefficient of friction (0.37 on average) compared to the monolithic TiC (0.34 on average).     

Preparation and characterization of equimolar SiO2–Al2O3–TiO2 ternary aerogel beads

Crack-free mesoporous equimolar SiO₂–Al₂O₃–TiO₂ ternary aerogel beads have been synthesized and characterized. Silica sol, alumina sol, and titania sol were synthesized individually to prevent the formation of inhomogeneous structure due to the different hydrolization and polymerization rate of individual precursor. After mixing these three types of acidic sols, SiO₂–Al₂O₃–TiO₂ ternary beads were prepared by the ball dropping method. The ternary aerogel beads were typically mesoporous, showing high surface area (305 m² g^?1), large pore volume (1.32 cm³ g^?1), and high surface acid amount (0.884 mmol NH₃ g^?1). Moreover, the acid sites of the ternary aerogel beads showed higher thermal stability than those of binary aerogel beads. Gradient drying (GD), supercritical drying (SD), ambient drying (AD), extended aging (EA) and hydrophobic modifying drying (HM) have been employed to investigate the effects of drying method on the characteristics of the aerogel beads. The surface areas of the ternary aerogel beads obtained by different drying methods decrease in the sequence EA > HM > GD > SD > AD. The ternary aerogel beads have been characterized by scanning electron microscopy, nitrogen adsorption, X-ray powder diffraction, Fourier-transform infrared spectroscopy (FTIR), solid-state NMR, temperature-programmed desorption measurements, pyridine adsorption FTIR, and differential scanning calorimetry.     

Preparation and characterization of wood-fiber-reinforced polyamide 6–polypropylene blend composites

In this study, we used lithium chloride (LiCl) as a modifier to decrease the melting temperature (T _m) of polyamide 6 (PA6), and then, we fabricated wood-fiber-reinforced PA6–polypropylene (PP) blend composites via hot pressing. From crystallization analysis, the composites exhibited a lower T _m and a lower processing temperature compared to PA6. Color and Fourier transform infrared analyses showed that severe thermal degradation and discoloration of the composites could be prevented by the incorporation of LiCl. LiCl had positive effects on the mechanical properties of the final product and the interfacial compatibility among PA6, PP, and wood fiber. The flexural strength increased by 8.5%. In addition, both maleic anhydride grafted PP and wood fiber improved the mechanical properties. The flexural strengths increased by 7.9 and 40%, respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47413.     

Preparation and characterization of PLLA–ESO/surface-grafted silica nanocomposites

Various amounts of surface-grafted silica (g-SiO₂) and un-grafted (SiO₂) nanoparticles were solution blended with a copolymer of l-lactide and epoxidized soybean oil (PLLA–ESO) or PLLA. Chemical reaction between the low molecular weight (LMW) PLLA and surface of silica nanoparticles is confirmed by FTIR and TGA analyses. The amount of grafted LMW PLLA investigated by thermal gravimetric analysis (TGA) was about 14.9%–28.2% in weight. g-SiO₂ nanoparticles can be easily dispersed into PLLA–ESO matrix to form a uniform PLLA–ESO/g-SiO₂ composite. Thermal properties of PLLA–ESO/g-SiO₂ and PLLA/g-SiO₂ nanocomposites were subsequently investigated by the differential scanning calorimeter measurements (DSC). DSC analyses indicated that g-SiO₂ nanoparticles can serve as a nucleating agent for the crystallization of PLLA–ESO in the composites, while the melting temperature (T _m) and the glass transition temperature (T _g) of PLLA–ESO/g-SiO₂ nanocomposites seemed to be independent of loading of g-SiO₂ particles. The DSC curves of PLLA/g-SiO₂ nanocomposite obviously showed double melting peaks, while that of PLLA–ESO/g-SiO₂ nanocomposites only a single melting peak. PLLA–ESO/g-SiO₂ composites exhibited a higher tensile strength and elongation than that of PLLA–ESO/SiO₂ composites.     

Preparation and properties of porous SiC–Al2O3 ceramics using coal ash

In this paper, we first reported that porous SiC–Al₂O₃ ceramics were prepared from solid waste coal ash, activated carbon, and commercial SiC powder by a carbothermal reduction reaction (CRR) method under Ar atmosphere. The effects of addition amounts of SiC (0, 10, 15, and 20 wt%) on the postsintering properties of as-prepared porous SiC–Al₂O₃ ceramics, such as phase composition, microstructure, apparent porosity, bulk density, pore size distribution, compressive strength, thermal shock resistance, and thermal diffusivity have been investigated. It was found that the final products are β-SiC and α-Al₂O₃. Meanwhile, the SEM shows the pores distribute uniformly and the body gradually contacts closely in the porous SiC–Al₂O₃ ceramics. The properties of as-prepared porous SiC–Al₂O₃ ceramics were found to be remarkably improved by adding proper amounts of SiC (10, 15, and 20 wt%). However, further increasing the amount of SiC leads to a decrease in thermal shock resistance and mechanical properties. Porous SiC–Al₂O₃ ceramics doped with 10 wt% SiC and sintered at 1600°C for 5 hours with the median pore diameter of 4.24 μm, room-temperature compressive strength of 21.70 MPa, apparent porosity of 48%, and thermal diffusivity of 0.0194 cm²/s were successfully obtained.     

Preparation and characterization of Al2O3–25 mol% ZrO2 composites

Al₂O₃–ZrO₂ (AZ_x), with 25 mol% ZrO₂ content, was prepared using the co-precipitation method. Synthesized powders were characterized by thermal reaction using a differential thermal analysis technique (TG–DTA) and were investigated by phase formation using X-ray diffraction. It indicated that the reaction occurred at 850 °C; cubic (c)-ZrO₂ phase and Al₂O₃ were obtained. By increasing temperature to 1100 °C, tetragonal (t)-ZrO₂ phase was detected. The Al₂O₃–25 mol% ZrO₂ was sintered for 2 h in the temperature range of between 1300 and 1600 °C. The majority phases of ceramics were m-ZrO₂ and α-Al₂O₃, although a t-ZrO₂ phase also appeared as a minor phase and decreased with higher temperature. Moreover, morphology and particle size evolution have been determined via the SEM technique. SEM showed that the particles of powder are agglomerated and basically irregular in shape. An SEM micrograph of ceramics exhibits uniform microstructure without abnormal grain growth.     

Crystallisation and characterisation of dielectric glass ceramics in Li2O–Al2O3–SiO2 system

Abstract

Glass ceramics in the Li₂O–Al₂O₃–SiO₂ system have been synthesised to produce bulk materials grown in a glass phase via quenching followed by controlled crystallisation. The crystallisation and microstructure of Li₂O–Al₂O₃–SiO₂ (LAS) glass–ceramic with nucleating agents (B₂O₃ and/or P₂O₅) are investigated by differential thermal analysis, X-ray diffraction and scanning electron microscopy and the effects of B₂O₃ and P₂O₅ on the crystallisation of LAS glass are also analysed. The introduction of both B₂O₃ and P₂O₅ promotes the crystallisation of LAS glass by decreasing the crystallisation temperature and adjusting the crystallisation kinetic parameters, allows a direct formation of β spodumene phase and as a result, increases the crystallinity of the LAS glass ceramic. Microstructural observations show that the randomly oriented, nanometre sized crystalline is found with residual glass concentrated at crystallite boundaries. Furthermore, it is interesting that codoping of B₂O₃ and P₂O₅ creates not much effect on the crystallisation temperature. The dielectric properties of the glass–ceramics formed through controlled crystallisation have a strong dependence on the phases that are developed during heat treatment. The dielectric constant is continuously increased and the dielectric loss is decreased with addition of additives where mobile alkali metal ions (e.g. Li⁺) are incorporated in a crystal phase and minimise the residual glass phase.     

Fabrication and characterization of anorthite–mullite–corundum porous ceramics from construction waste

In this work, anorthite–mullite–corundum porous ceramics were prepared from construction waste and Al₂O₃ powders by adding AlF₃ and MoO₃ as mineralizer and crystallization catalyst, respectively. The effects of the sintering temperature and time on open porosity, mechanical properties, pore size distribution, microstructure, and phase composition were characterized in detail. The results showed that the formation of the mullite whiskers and the properties of the anorthite–mullite–corundum porous ceramics depended more on the sintering temperature than the holding time. By co-adding 12 wt% AlF₃ and 4 wt% MoO₃, mullite whiskers were successfully obtained at sintering temperatures upon 1350 °C for 1 h. Furthermore, the resultant specimens exhibited excellent properties, including open porosity of 66.1±0.7%, biaxial flexural strength of 23.8±0.9 MPa, and average pore size of 1.32 µm (the corresponding cumulative volume percent was 37.29%).