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.     

Structural and magnetic properties of steel slag based glass–ceramics

Crystallisation of magnetite in multicomponent glass melts was investigated. Structural features and magnetic properties were tested using X-ray diffraction, scanning electron microscope techniques, vibrating sample magnetometer and Mössbauer spectroscopy at room temperature. The results show that the magnetite phase was detected in the glass–ceramic samples after heat treatment at higher crystallisation temperature (over 900°C). Fe²⁺ and Fe³⁺ ions contribute to the formation of magnetite crystal. Various crystal morphologies were observed. Isomer shift values suggest that Fe³⁺ and Fe²⁺ are in tetrahedral and octahedral coordination respectively. The saturation magnetisation tends to increase with the crystallisation temperature.     

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.     

Effect of ZnO nano-particulate modification on properties of PZT–BLT ceramics

This research was conducted to study the effect of ZnO nano-particulate modification on properties of Pb(Zr_0.52Ti_0.48)O₃ (PZT)–(Bi_3.25La_0.75)Ti₃O₁₂ (BLT) ceramics prepared by a mixed-oxide solid-state sintering method. ZnO nano-particulate was added into PZT–BLT ceramics to obtain PZT–BLT/xZnO (x = 0, 0.1, 0.5 and 1.0 wt%). The PZT–BLT/xZnO ceramics were investigated in terms of phase, microstructure, physical, electrical, and mechanical properties. Tetragonality of PZT–BLT crystal structure tended to increase with increasing ZnO content. ZnO addition obviously increased the density of PZT–BLT ceramics while the grain size slightly decreased. Intergranular fracture mode was observed for pure PZT–BLT ceramic while the samples contained ZnO nano-particles showed a mixed-mode inter-/trans-granular fracture. Addition of ZnO also affected hardness and fracture toughness values. Addition of ZnO nano-particulate into PZT–BLT ceramics was found to improve room temperature dielectric constant but did not have a significant effect on ferroelectric properties. These observed results were expected to be caused by the behaviors similar to a donor-doped system.     

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.     

Effects of La2O3–B2O3 on the flexural strength and microwave dielectric properties of low temperature co-fired CaO–B2O3–SiO2 glass–ceramic

The La₂O₃–B₂O₃ (LB) addition, synthesized using the traditional solid-state reaction process, was chosen as a novel sintering aid of the low temperature co-fired CaO–B₂O₃–SiO₂ (CBS) glass–ceramic. The effects of LB on the flexural strength and microwave dielectric properties have been investigated. The LB addition promotes the crystallization of the CaSiO₃ but high amount of the LB addition leads to the formation of more pores. The CBS sample with 4 wt% LB addition sintered at 850 °C for 15 min shows good properties: flexural strength = 193 MPa, ?_r = 6.26 and loss = 9.96 × 10^?4 (10 GHz).     

Effect of temperature on the structure and mechanical properties of SiC–TiB2 composite ceramics by solid-phase spark plasma sintering

SiC composite ceramics have good mechanical properties. In this study, the effect of temperature on the microstructure and mechanical properties of SiC–TiB₂ composite ceramics by solid-phase spark plasma sintering (SPS) was investigated. SiC–TiB₂ composite ceramics were prepared by SPS method with graphite powder as sintering additive and kept at 1700 °C, 1750 °C, 1800 °C and 50 MPa for 10min.The experimental results show that the proper TiB₂ addition can obviously increase the mechanical properties of SiC–TiB₂ composite ceramics. Higher sintering temperature results in the aggregation and growth of second-phase TiB₂ grains, which decreases the mechanical properties of SiC–TiB₂ composite ceramics. Good mechanical properties were obtained at 1750 °C, with a density of 97.3%, Vickers hardness of 26.68 GPa, bending strength of 380 MPa and fracture toughness of 5.16 MPa m^1/2.     

Sintering behavior of La2O3–B2O3–TiO2 glass powders prepared by spray pyrolysis for low temperature co-fired ceramics

Fine-sized La₂O₃–B₂O₃–TiO₂ glass powders with spherical shape were directly prepared by spray pyrolysis at a temperature of 1500 °C. The optimum flow rate of the carrier gas to prepare the glass powders with dense inner structure and fine size by complete melting was 10 L/min. The ratio of La/Ti was identified to be 2.06:1, which was close to the original starting ratio of La/Ti in mixture of the spray solution. The T_g and T_c of the powders were 614 and 718 °C. The crystal structures within the powders were observed from the sintered disc at 630 °C. The mean sizes of the powders changed from 0.24 to 0.71 μm when the concentrations of the spray solution were changed from 0.025 to 0.5 M. The BET surface areas of the powders changed from 4.4 to 1.6 m²/g. The grain sizes of the sintered discs increased with increasing the sintering temperatures. The main crystal structure of the sintered discs was LaBO₃.     

The effect of processing conditions,amount of additives and composition on the microstructures and mechanical properties of α-SiAlON ceramics

A series of samples with yttrium α-SiAlON compositions and different amounts of additive has been fabricated from α-Si₃N₄, AlN, Al₂O₃ and Y₂O₃ starting powders, using gas pressure sintering and three different sintering procedures. One series of samples was heated up to 1825°C and then held for 3 h, another group of samples was held at a lower temperature (1500 or 1600°C) for 1 h and then heated up to 1825°C and held for 3 h. The results of investigations using scanning electron microscopy showed the effect of composition and sintering procedure on the morphology of α-SiAlON grains. It was found that the amount of elongated grains increased with increasing amount of liquid phase. The mechanical tests showed that all of the samples exhibited HV10 values in the range of 1800–1976 kg/mm and K_IC values in the range of 3.9–6.3 MPam^1/2.     

Influence of hafnium oxide on the structure and properties of powders and ceramics of the YSZ–HfO2 composition

Using the X-ray diffraction, internal friction, 4-point bending, and electron microscopy methods we have studied the structural compatibility and influence of Y₂O₃ and HfO₂ dopants addition on the structure and phase composition of ZrO₂ powders and ceramics based on them. The mechanical properties of ZrO₂–Y₂O₃-HfO₂ (YSZ) system have been investigated.It was determined that the similarity of the structure and properties of yttrium and hafnium oxides is not complete. The individual structural features of ZrO₂, Y₂O₃, and HfO₂ oxides reviled themselves during the formation of ternary systems of the YSZ-Hf type. Studies of the nY₂O₃–ZrO₂ - mHf₂O₃ system in the range of hafnium amount from 1 to 15 wt% and yttrium oxide concentration from 0 to 12 mol% showed the possibility of increase in the values of physical and mechanical properties of common two-component zirconium ceramics by the forming ternary systems of the YSZ-Hf type.     

Effect of rare-earth oxide additives on transparency and fluorescence of α-SiAlON ceramics

Recently, novel transparent and fluorescent materials are in demand for various optical applications such as lasers, scintillators, and solid-state lighting. α-SiAlON, which has excellent thermal and mechanical properties, also exhibits photoluminescence depending on the stabilized doped rare-earth ions. Its transparency and fluorescence depend on the rare-earth oxide added as a raw material, particularly in conventional powder processing. In this study, we fabricated α-SiAlON ceramics by adding various rare-earth oxides to elucidate their effects on the transparency and fluorescence of these ceramics. High-transparency α-SiAlON ceramics were fabricated by adding rare-earth oxides whose rare-earth ions have small ionic radii: Y₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃. Because the fraction of α-SiAlON was high, the relative density was high, and the microstructure was composed of fine grains. In particular, α-SiAlON ceramics prepared by adding Ho₂O₃ showed lower light scattering than the other fabricated α-SiAlON ceramics because of the smaller α-SiAlON grains, resulting in higher in-line transmittance (48% at 600 nm). Furthermore, these transparent α-SiAlON ceramics exhibited fluorescence corresponding to the activated rare-earth ions: Ho³⁺, Er³⁺, Tm³⁺, and Yb³⁺ or Yb²⁺.     

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.     

Piezoelectric properties and temperature stabilities of Mn- and Cu-modified BiFeO3–BaTiO3 high temperature ceramics

The structures, microstructures, electrical properties and the thermal stability have been investigated for the MnO₂-doped (1 ? x)BF–xBT system and the MnO₂ and CuO-doped (1 ? x)BF–xBT system, where x ranges from 0.25 to 0.35. The XRD analysis shows that the two systems have a single perovskite phase, and the MnO₂ and CuO-doped (1 ? x)BF–xBT system has a morphotropic phase boundary (MPB) with the coexistence of rhombohedral and pseudo-cubic phases in the system about x = 0.325. The addition of small amount of CuO was quite effective to lower the sintering temperature. The diffusive phase transition characteristics were observed in the MnO₂-doped (1 ? x)BF–xBT system and a normal ferroelectric phase transition characteristics were observed in the MnO₂ and CuO doped (1 ? x)BF–xBT system. Compared with the MnO₂ doped (1 ? x)BF–xBT system, the ?_m, Curie temperature (T_c), depoling temperature (T_d), and piezoelectrical properties were improved evidently with the MnO₂ and CuO doping.     

Effect of acid treatment on the composition and structure of a natural aluminosilicate and on its catalytic properties in α-pinene isomerization

The article deals with the effect of the conditions of modification of a natural aluminosilicate catalyst with a 10% HCl solution on the chemical and phase compositions, porous and crystal structures, and acidity of the material and on its catalytic properties in α-pinene isomerization. Treatment of the aluminosilicate with 10% HCl (25–250 mL per gram of solid) causes cation exchange, increases the concentration of protonic sites on the aluminosilicate surface, and removes impurity calcite and dolomite. The specific surface area of the aluminosilicate increases from 52 to 68–82 m²/g. Treatment of the aluminosilicate with 175.0 or 250.0 mL/g of HCl removes a considerable amount framework Al³⁺, Fe^2+/3+, and Mg²⁺ cations, leading to a partial disruption of its structure and to a decrease in its acidity, specific surface area, and, as a consequence, catalytic activity relative to the same parameters of the samples treated with 50 or 100 mL/g of HCl. The highest catalytic activity is displayed by the aluminosilicate treated with 50 mL/g of HCl. The camphene and dipentene selectivity of the reaction (at 85% α-pinene conversion) with the original catalyst is 55 and 30%, respectively; modifying the aluminosilicate with HCl raises the camphene selectivity and reduces the dipentene selectivity by 5–6%. The catalyst considered here is more active than the commercial titanium catalyst.     

Effect of ultrasonic vibration on the structure and composition of the interface regions in Ва–W–Ti–O ceramics

A study of Ba–W–Ti–O ceramics has shown that the structure and composition of their interface regions differ from those in the grain bulk owing to the diffusion of tungsten atoms to the grain surface during sintering. They are determined by the conditions of compacting of dry nanopowders (compaction pressure and power of ultrasonic action) and vary in a nonmonotonic way. Increasing the pressure during dry static compacting and exposure to ultrasound result in the formation of a complex structure of fragments and boundaries between them, increase the acoustic density and lead to a decrease in the intergranular boundary thickness to the values that are sometimes comparable to the lattice constant of the boundary material.     

Densification behavior and properties of alumina–chrome ceramics: Effect of TiO2

Highly dense alumina–chrome bodies with low porosity are usually used as corrosion and thermal resistant refractories. Alumina–chrome refractory with molar ratio 1:1 was developed using chemical grade hydrated alumina and chromium (III) oxide by conventional sintering route. Batch materials were attrition milled, isostatically pressed and sintered in the temperature range from 1000 °C to 1700 °C with 2 h soaking at peak temperature. Phase development of the sintered materials with temperature was studied by X-ray diffraction. Sintering temperature, sintering condition and addition of sintering aid (TiO₂) have immense effect on the densification of the alumina–chrome refractory. Highly dense alumina–chrome refractory with almost nil apparent porosity was developed at 1500 °C in reducing atmosphere. Flexural strength of the sintered materials at room temperature and at 1200 °C was also measured. 1 wt% TiO₂ gives the optimum result with respect to densification and flexural strength.     

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 Kaolin on sintering and machinability of fluor–phlogopite glass ceramic

Abstract

The effect of kaolin on pressability, sintering, mechanical properties, and machinability of a fluor–phlogopite glass ceramic was investigated. Crystallinity and microstructure of specimens were determined by X-ray diffraction and scanning electron microscopy methods. Machinability of sintered specimen was investigated by visual assessment of chipping of the drilled specimen rims and measurement of the particle size distribution of chips obtained during drilling. The results indicated that while adding of kaolin improves pressability and hardness of samples, reduces their machinability and bending strength. Furthermore, in the high bearing kaolin specimens, beside fluor–phlogopite, sapphirin and spinel, mullite was also precipitated.