Preparation and properties of ferrimagnetic glass–ceramic foams based on pyrite slag

By employing a melt-sintering method, we prepared a new type of ferrimagnetic glass–ceramic foam (FGCF) using ferrimagnetic glass–ceramic and foaming agent SrCO₃. The ferrimagnetic glass–ceramics were fabricated based on pyrite slag by a melt-quenching method. The effects of foaming agent content, sintering temperature and time on microstructure, magnetic properties, microwave absorption performance, compressive strength, and thermal conductivity of the as-obtained FGCF were analyzed. This foaming process at 1100°C for 40 min with 3-wt% SrCO₃ provided an FGCF with a bulk density of .693 g/cm³, a porosity of 63.60%, a specific saturation magnetic moment of 5.2 A m²/kg, a compressive strength of 2.61 MPa, a thermal conductivity of .241 W/(m K), and the calculated reflection loss of −12.1 dB for a layer thickness of 9 mm.     

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.     

Structural,piezoelectric and dielectric properties of PSLZT–PMnN ceramics

Pb_0.94Sr_0.05La_0.01(Zr_0.54Ti_0.46)_0.9975O₃–Pb(Mn_1/3Nb_2/3)O₃ (PSLZT–PMnN) ceramics with pure perovskite structure were prepared by conventional mixed oxide method. The influence of PMnN on the structural, dielectric and piezoelectric properties was investigated. The experimental results showed that the perovskite structure changed from tetragonal to rhombohedral symmetry and the Curie temperature decreased gradually with the increase of PMnN. The composition with 3 mol% PMnN exhibited favorable properties of Q_m (400), d₃₃(660 pC/N), k_p (0.60), K^T (1940), tan δ (0.90%) and T_C (247 °C), exhibiting potential usage for piezoelectric actuator and sensor applications.     

Physical properties and electrochemical performance of molybdenum–lead-germanate glasses and glass ceramics

Glasses and glass ceramics of the xMoO₃(100?x)[7GeO₂·3PbO] system where x=0–30 mol% MoO₃ were synthesized and characterized in order to obtain information about the structural correlations and the relationship between structure and physical properties in these materials. Changes of the FTIR, UV–vis and EPR data are discussed in view of the glass network structural changes determined by the evolution of molybdenum ions state, glass composition and MoO₃ concentration.The spectroscopic studies indicate that with increasing of MoO₃ content a fraction of the Mo⁶⁺ ions convert Mo³⁺ and Mo⁵⁺ ions. Accordingly, these modifications cause the depolymerization of the host network, the increase of the structural disorder and formation of GeO₂ and PbMoO₄ crystalline phases. The shape of EPR spectra is modified by the increase of the MoO₃ concentration indicating that molybdenum ions exists in glass and glass ceramics in more than one valence state. The EPR spectra contain a broad line located at g～5.2 and, for the samples with a MoO₃ content up to x≥15 mol%, the presence of the hyperfine structure characteristic for the Mo⁵⁺ ions can be observed, too.The electrochemical performances of the glass and glass ceramics samples with x=10 and 30 mol% MoO₃ were demonstrated by cyclic voltammetry.     

Preparation,structural and thermo-mechanical properties of lithium aluminum silicate glass–ceramics

Lithium aluminum silicate glasses of composition (wt%) 12.6Li₂O–71.7SiO₂–5.1Al₂O₃–4.9K₂O–3.2B₂O₃–2.5P₂O₅ were prepared by the melt quench technique. These glasses were converted to glass–ceramics based on DTA data. X-ray diffraction (XRD) and Fourier transform infra-red spectroscopy (FTIR) were used to discern the phases evolved in the glass–ceramics. Phase morphology was studied using scanning electron microscopy (SEM). Thermal expansion coefficient (TEC) and glass transition temperature (T_g) of all samples were measured using thermo-mechanical analyzer (TMA). It was found that 3 h dwell time at crystallization temperature yielded samples with good crystallinity with a TEC of 9.461 × 10⁻⁶ °C⁻¹. Glass–ceramic-to-metal compressive seal with SS-304 was fabricated using LAS glass–ceramic. The presence of metal housing and compressive stresses at the glass–ceramic-to-metal interface reduced average grain size and changed the overall microstructure.     

Structural and magnetic properties of erbium doped nanocrystalline Li–Ni ferrites

A series of nanocrystalline Li_0.25Ni_0.5Fe_2.25−xEr_xO₄ (x=0.00, 0.02, 0.06, 0.08, and 0.10) ferrite powders, having a cubic spinel crystal structure and a low value of coercivity, was synthesized by the sol–gel auto-combustion route. The structure, morphology and magnetic properties of the prepared nanoferrites were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the magnetic property measurement system (MPMS). A well-defined single phase spinel structure is confirmed in all the samples by X-ray diffraction analysis. The lattice parameters of the samples increase slightly with increasing the erbium content. The crystallite size of the Er-doped samples is smaller than that of pure Li–Ni ferrite, and decrease regularly in the range of 36.0–14.5 nm. It has been observed that the magnetic properties of these ferrites are strongly influenced by the added erbium content. The magnetic measurements indicate that saturation magnetization (M_s) and coercivity (H_c) decrease gradually with the increase of Er content in the lattice.     

Structural and electrical properties of magnetic ceramics of Co1−xCuxFe2O4 spinel nanoferrites

Abstract

Magnetic ceramics of the type of spinel nanoferrites of Co_1?xCu_xFe₂O₄ with Cu concentrations of x?=?0·00, 0·25, 0·50, 0·75 and 1·00 were prepared by chemical co-precipitation method. X-ray diffraction results confirmed the formation of a single spinel ferrite structure with crystallite size in the range of 20–63 nm. Scanning electron microscopy and EDS were used to study the morphological and compositional changes taking place with varying Cu concentration. DC electrical resistivity, activation energy and drift mobility are strongly influenced by both Cu concentration and temperature. Resistivities of the prepared magnetic ceramics were found to decrease with the increase in Cu concentration to follow Verwey mechanism. The semiconductor behaviour of the prepared nanoparticles was confirmed from the standard Arrhenius relation of resistivity versus temperature. The dielectric constants were measured in the frequency range of 100 Hz–3·0 MHz and are explained by the Maxwell–Wagner interfacial type of polarisation.     

Structural,dielectric and magnetic properties of Bi–Mn doped SmFeO3

We have studied the structural, magnetic, dielectric and impedance properties of the Sm_1-xBi_xFe_1-yMn_yO₃ [SmFeO₃ (SFO), Sm_0.9Bi_0.1FeO₃ (SBFO), Sm_0.9Bi_0.1Fe_0.9Mn_0.1O₃ (SBFMO)] polycrystalline samples synthesized by solid-state reaction method. Rietveld refinement of room temperature (RT) powder x-ray diffraction pattern confirms the orthorhombic crystal structure with Pnma/Pbnm space group. The average particle size of Bi doped and co-doped (Bi–Mn) samples determined from SEM analysis are 5.6 μm and 5.2 μm, respectively. Room temperature field-dependent magnetization increases, suggesting the presence of magnetic contribution due to the Rare earth-Fe ion interaction which persists even at RT. However, with co-doping of Bi and Mn, a decrease in magnetization is observed, which corresponds to the dilution of Fe³⁺-Fe³⁺ interactions due to the presence of Mn³⁺ ions. The observed values of magnetization at 90 kOe for Bi doped sample is (2.87 emu/g) approximately two times and for codoped (0.7 emu/g) sample is nearly half of that of pristine sample (1.51 emu/g). Dielectric measurements as a function of frequency/temperature and impedance analysis using equivalent circuit model reveal grain and grain boundary contributions of SBFO (at high temperature) and SBFMO (for all temperature) samples towards the electrical properties indicating the electrically heterogeneous nature of these samples. However, for SFO sample grain contribution is dominant. Observed value of dielectric constant varies from ~10³-10⁴ with Bi–Mn doping. The conduction mechanism of the studied samples has been explained by considering Jonscher power law. Arrhenius law fitting of AC conductivity data manifests two types of conduction mechanisms in these samples. The depressing nature of the semicircular arc observed in the Nyquist plot of all the samples indicates the presence of a non-Debye type of relaxation.     

Microstructure and properties of CaO–ZrO2–SiO2 glass–ceramics prepared by sintering

For the development of a new wear resistant and chemically stable glass-ceramic glaze, the CaO–ZrO₂–SiO₂ system was studied. Compositions consisting of CaO, ZrO₂, and SiO₂ were used for frit, which formed a glass-ceramic under a single stage heat treatment in electric furnace. In the sintered glass-ceramic, wollastonite (CaSiO₃) and calcium zirconium silicate (Ca₂ZrSi₄O₁₂) were crystalline phases composed of surface and internal crystals in the microstructure. The internal crystal formed with nuclei having a composition of Ca_1.2Si_4.3Zr_0.2O₈. The CaO–ZrO₂–SiO₂ system showed good properties in wear and chemical resistance because the Ca₂ZrSi₄O₁₂ crystals positively affected physical and mechanical properties.     

Effect of composition on sinter-crystallization and properties of low temperature co-fired α-cordierite glass–ceramics

This article investigates effect of composition, including SiO₂ and impurity defined to contain K₂O, Na₂O, Fe₂O₃, etc., from K-feldspar, on sinter-crystallization and properties of the low temperature co-fired α-cordierite glass–ceramics. Increasing impurity content from 5.72 wt% to 9.16 wt% leads to enhanced crystallinity, formation of leucite and more pores but the crystallinity and porosity decreased with a further increase to 10.8 wt%. The main impurity K₂O is critical for formation of α-cordierite and leucite. Only α-cordierite was precipitated from the glasses with different SiO₂ contents but an increase of SiO₂ content slightly improves their densification. The impurity and SiO₂ contents greatly affect the properties of glass–ceramics. Notably, some glass–ceramics from K-feldspar show high densification at low temperature, low dielectric constant (6–8), low loss (about 0.005), appropriate linear CTEs (4.32–5.87 × 10⁻⁶ K⁻¹) and flexural strength (above 100 MPa), all of which meet the requirements of LTCC substrates.     

Structural modification and evaluation of dielectric and ferromagnetic properties of Ce-modified BiFeO3–BaTiO3 ceramics

An investigation on Rare earth constituent Ce incorporated BiFeO₃–BaTiO₃ ceramics has been focused in the present study. The ceramic samples of (Bi₀.₇Ba_0.3)_1-xCe_x(Fe₀.₇Ti_0.3)O₃ (x = 0–0.12) were formulated adopting the cost-effective solid-state sintering method. The influence of aliovalent Ce ions on the structural, microstructural, dielectric, ferromagnetic, and optical properties of BiFeO₃–BaTiO₃ was evaluated in this paper. The coexistence of the Tetragonal and the Rhombohedral phases was established by the Rietveld refinement process. The refined crystallographic parameters showed maximum cell volume (V_cell) and the highest percentage of the Rhombohedral phase for x = 0.06; and consequently, the ceramic exhibited the topmost dielectric constant of 946 at x = 0.06. The scanning electron microscopy of the samples revealed the manifestation of polygonal grain morphology. Besides, remarkably improved ferromagnetic properties were evinced for Ce doped ceramics. The magnitude of saturation (M_s) and remnant (M_r) magnetizations were boosted from 0 emu/g and 0.0019 emu/g to 0.9186 emu/g and 0.3745 emu/g respectively with increasing x from 0 to 0.12. Additionally, the optical band gaps of all the samples were evaluated and found to be in the range of 2.941–3.077 eV.     

Structural and magnetic properties of Yb1−xSrxMnO3

The structural and magnetic properties of YbMnO₃ and Yb_0.82Sr_0.18MnO₃ multiferroics were studied by neutron powder diffraction (NPD), magnetometry and electron spin resonance (ESR) technics in a wide temperature range. Neutron diffraction measurements showed that the substitution of ytterbium ions with strontium ions in hexagonal h - YbMnO₃ (space group P6₃cm) leads to the destabilization of the crystal structure of the last compound and appearance of the mixture of three phases with different structure: hexagonal phase h - Yb_0.95Sr_0.05MnO₃ (space group P6₃cm), orthorhombic phase o - Yb_0.69Sr_0.31MnO₃ (space group Pbnm), hexagonal phase SrMnO₃ (space group P6₃cm). This fact was proved by the ESR measurements in which a several signals due to the phases of different structure were observed. NPD measurements showed that the magnetic structure of h - Yb_0.95Sr_0.05MnO₃ phase is similar to the magnetic structure of the pure h - YbMnO₃ and demonstrate the presence of the antiferromagnetic ordering in the samples. ESR and magnetization measurements of h - YbMnO₃ sample proved the presence of the antiferromagnetic correlations and also they showed the appearance of the ferromagnetically correlated nanoregions.     

Effect of MgO addition on the properties of PbO –TiO2–B2O3 glass and glass–ceramics

Glass samples with composition of (50?X) PbO–X MgO–25 TiO₂–25B₂O₃ (where X=0, 5, 10 and 15 mol%) were prepared using conventional quenching technique. The amorphous nature of glass samples were confirmed by XRD. The glass transition temperature, T_g and crystallization temperature T_c were determined from the DTA. It has been observed that the addition of MgO enhances the T_g. The rise in T_g with MgO content may be attributed to the greater field strength of Mg²⁺ cation (as compared to Pb²⁺) which leads to the formation of stronger bonds. These glass samples were converted to glass–ceramics by following a two-stage heat treatment schedule. It was observed that there was good correlation between the density and CTE results of the glass–ceramics. The XRD results revealed the formation of tetragonal lead titanate as a major crystalline phase in the glass–ceramics. The addition of MgO to the glass contributes to the formation of MgB₄O₇. The dielectric constant for all the glass–ceramic samples was observed to be higher than that of corresponding glass samples. Further, with addition of MgO the room temperature dielectric constant for glass–ceramic samples increases up to 10 mol% of MgO and then decreases for 15 mol%. It has been further observed that the variation of dielectric constant of glass–ceramic samples with MgO content is exactly opposite to the variation of crystallite size of PbTiO₃ embedded in the glass ceramic-samples.     

Modification of glass network and crystallization of CaO–Al2O3–MgO–SiO2 based glass ceramics with addition of iron oxide

Modification of glass network and crystallization process of a CaO–Al₂O₃–MgO–SiO₂ (CAMS) based glass ceramic to form diopside through addition of iron oxide were investigated using differential thermal analysis (DTA), Raman spectrum, X-ray diffraction, SEM and EBSD techniques. The experimental results showed that addition of Fe₂O₃ led to remarkable reductions in both the glass transition temperature (Tg) and crystallization temperature (Tp) of the CAMS glass ceramic. At addition level below 5 wt%, the Tg and Tp temperatures were 651°C and 903°C, respectively, and the crystallization only occurred on the surface of the glass ceramic samples. Increasing the addition level to 10 wt% and 15 wt%, not only led to reduction in the Tg and Tp temperatures to 643-641°C and 892-876°C, respectively, but also promoted the formation of crystalline diopside throughout the CAMS samples. Based on the results of Raman spectrums, it was confirmed that Fe₂O₃ addition reduced the strength of glass connection as a result of chemical reactions between the isolated Si–O tetrahedron and Fe³⁺ ion, forming Fe³⁺O₄–SiO₄, which can be regarded as Q₂ unit. And this is the first experimental evidence that proving the approach of Fe³⁺ mending glass network. Microstructural examination also identified the formation of large numbers of spherical Fe-enriched regions within the CAMS glass matrix as a result of the amorphous phase separation due to the Fe₂O₃ addition. The interfaces between the Fe-enriched regions and the glass matrix acted as preferred nucleation sites for the diopside, facilitating the crystallization. Crystallographic analysis using EBSD technique determined the <001> as the most favorite growth direction for the diopside crystals in the CAMS based glass ceramic.     

Optimized sintering and mechanical properties of Y–TZP ceramics for dental restorations by adding lithium disilicate glass ceramics

The novel dental ceramics can be fabricated at lower temperatures when sol–gel derived lithium disilicate glass ceramics (LDGC) was used as an additive for yttr...     

Mechanical properties and morphology of coal gasification fine slag glass bead-filled acrylonitrile–butadiene–styrene (ABS) composites

Coal gasification fine slag glass beads (CGFSGBs) were processed via an efficient pneumatic separation technique. CGFSGB products (CGFSGB-S1, CGFSGB-S2, and CGFSGB-S3) with different sizes were acquired. The heavy calcium carbonate (CaCO₃) was used as comparative filler. Effects of particle size and geometric shape on mechanical strengths, flow properties, and solid density of filled acrylonitrile–butadiene–styrene (ABS) were investigated. The mechanical strengths of composites decreased with increasing CGFSGB weight fraction, while MFR and solid density increased. The mechanical strengths were found to increase with decreasing CGFSGB size, and spherical surface of the CGFSGB is more beneficial to improve interface adhesion strength than square surface of the CaCO₃. The flow property analysis showed that the ABS/CaCO₃ composites have better fluidity and the advantages in the processing energy consumption. However, the incorporation of CaCO₃ resulted in the higher solid-state density. In summary, CGFSGBs have the potential to replace CaCO₃ in the ABS market. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48601.     

Structural and electric properties of polycrystalline Bi1−xErxFeO3 ceramics

Polycrystalline Bi_1?xEr_xFeO₃ ceramics were synthesized by the solid state reaction method followed by rapid liquid phase sintering. The effects of Er substitution on the structure, morphology and electrical properties of the BiFeO₃ multiferroic ceramics were investigated. X-ray diffraction and Raman studies reveal that the structure of BiFeO₃ is changed from rhombohedral to orthorhombic in the Er concentration range of 0.10–0.15, and the impurity phases decrease both due to Er substitution. The X-ray photoelectron spectroscopy shows that Fe²⁺ could be suppressed by Er substitution. The SEM investigations suggest that the Er substitution could significantly reduce the grain sizes and increase the density of the samples. The leakage current is found to be decreased with increasing Er concentration. The dielectric and ferroelectric measurements show that dielectric constant, dielectric loss and ferroelectric properties are strongly dependent on the Er concentration. Er substitution can significantly improve the dielectric constant and remnant polarization, and decrease the dielectric loss by reducing the leakage current.     

High temperature mechanical properties of laminated ZrB2–SiC based ceramics

Two laminated ZrB₂-SiC based ceramics were prepared by tape casting and subsequent hot pressing, with BN (LZB) and graphite (LZG ) as interface layers. The LZB specimen presents flexural strength of 381 MPa at room temperature and 111 MPa at 1500 °C; while the LZG specimen shows flexural strength of 414 MPa at room temperature and 377 MPa at 1500 °C. In addition, the flexural strength of LZG specimen is always higher than that of the LZB specimen in the temperature range from room temperature to 1500 °C. Such higher strength is attributed to the healing of surface microcracks and pores by the SiO₂ glass phase, producing less glass phase in graphite interface layers at high temperature.     

Fabrication and properties of cordierite based glass/AlN composites by sol–gel and pressureless sintering

In this study, the effect of AlN content on the crystallization behavior of cordierite based glass, was firstly investigated. Results show that μ-cordierite appeared in the composites with high AlN content even at high temperatures, which implied that the AlN may broad the crystallization temperature range of μ-cordierite and depress the transformation of μ→α-cordierite. The crystallization temperature of α-cordierite was about 980 °C for the pure glass and the temperature increased with AlN content for composites, but the crystallization temperature of μ-cordierite had reverse trend. The composites owned excellent bending strength when the AlN content was 20 wt%. With increasing of AlN content, the dielectric loss was increased which was caused mainly by the structural loss and the appearance of μ-cordierite, but the dielectric constant had crosscurrent. It was observed that the composites were beneficial in producing LTCC material which can be highlighted with high strength, low shrinkage and good dielectric properties at 1 MHz.     

Optimisation of sintered glass–ceramics from an industrial waste glass

Industrial plasma melting of municipal solid waste (MSW) incinerator fly ashes leads to a glass that may be easily crystallised to gehlenite glass–ceramics, by the sintering of fine glass powders. However, since the glass composition is not optimised for glass–ceramic manufacturing, the viscous flow is much hindered by a very significant surface crystallisation and dense glass–ceramics are feasible only by sintering above 1000 °C. This paper reports a new strategy for obtaining dense and strong glass–ceramics at 950 °C, with a holding time of only 30 min, consisting of the mixing of waste glass with a secondary recycled glass, such as soda-lime–silica glass or borosilicate glass. For an optimum balance between the two types of glass also the addition of kaolin clay, in order to favour the shaping, was found to be feasible. The approach had a positive effect, besides on the mechanical properties (e.g. bending strength exceeding 100 MPa), on the chemical stability.