Preparation and characterization of multilayered ZrO<Subscript>2</Subscript> coatings on silicon carbide fibers for SiC/SiC composites

We have studied the surface morphology, phase composition, and oxidation resistance of multilayered tetragonal zirconia coatings produced on silicon carbide fibers by a sol-gel process and measured the tensile strength of individual fibers as a function of the number of layers in the coating. SiC-fiber-reinforced silicon carbide minicomposites have been prepared through pyrolysis of an organosilicon polymer, and their fracture surfaces have been examined. Using microindentation, we have determined the critical fiber-matrix debonding stress. The results demonstrate that the ZrO₂ coating on the fibers has the form of uniform, weakly bonded layers. The presence of a multilayered ZrO₂ interphase alters the fracture behavior of the SiC/SiC composites. The fiber debond stress in the composites markedly decreases with an increase in the number of layers in the interphase.     

Polymorphic transformation of ZrO<Subscript>2</Subscript> in the 75 wt % Al<Subscript>2</Subscript>O<Subscript>3</Subscript> + 25 wt % ZrO<Subscript>2</Subscript> alloy solidified under nonequilibrium conditions

This paper examines the α-ZrO₂ ↔ β-ZrO₂ polymorphic transformation in 75 wt % Al₂O₃ + 25 wt % ZrO₂ alloys solidified under nonequilibrium conditions and then heat-treated under various conditions. The strength of the alloys is shown to be more sensitive to β-ZrO₂ content than to the size of their microstructural constituents.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> on the properties of nanocrystalline ZrO<Subscript>2</Subscript> + 3 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> powder

We have studied the properties of nanocrystalline ZrO₂〈3 mol % Y₂O₃〉 and 90 wt % ZrO₂〈3 mol % Y₂O₃〉-10 wt % Al₂O₃ powders prepared via hydrothermal treatment of coprecipitated hydroxides at 210°C. The results demonstrate that Al₂O₃ doping raises the phase transition temperatures of the metastable low-temperature ZrO₂ polymorphs and that the structural transformations of the ZrO₂ and Al₂O₃ in the doped material inhibit each other.     

Specific absorption coefficient of chromium in (TeO<Subscript>2</Subscript>)<Subscript>0.80</Subscript>(MoO<Subscript>3</Subscript>)<Subscript>0.20</Subscript> glass

We have prepared (TeO₂)_0.80(MoO₃)_0.20 glass samples containing 0.01 to 0.11 wt % chromium and determined their optical transmission in the range from 450 to 2800 nm. The glasses have been shown to have a strong absorption band centered at 660 nm. From the attenuation coefficient as a function of Cr³⁺ concentration in the glasses, we have evaluated their specific absorption coefficient, which has been shown to be 190 ± 2 cm^–1/wt % at the maximum of the absorption band.     

Formation,thermal, optical and physical properties of GeS<Subscript>2</Subscript>–Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>–AgCl novel chalcohalide glasses

Novel GeS₂–Ga₂S₃–AgCl chalcohalide glasses had been prepared by melt-quenching technique, and the glass-forming region was determined by XRD, which indicated that the maximum of dissolvable AgCl was up to 65 mol%. Thermal and optical properties of the glasses were studied by differential scanning calorimetry (DSC) and Visible-IR transmission, which showed that most of GeS₂–Ga₂S₃–AgCl glasses had strong glass-forming ability and broad region of transmission (about 0.45–12.5 μm). With the addition of AgCl, the glass transition temperature, Tg decreases distinctly, and the short-wavelength cut-off edge (λ_vis) of the glasses also shifts to the long wavelength gradually. However, the glass-forming ability of the glass has a complicated evolutional trend depended on the compositional change. In addition, the values of the Vickers microhardness, H _v , which decrease with the addition of AgCl, are high enough for the practical applications. These excellent properties of GeS₂–Ga₂S₃–AgCl glasses make them potentially applied in the optoelectronic field, such as all-optical switch, etc.     

Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization behavior of SiO<Subscript>2</Subscript>–MgO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

A series of glass comprising of SiO₂–MgO–B₂O₃–Y₂O₃–Al₂O₃ in different mole ratio has been synthesized. The crystallization kinetics of these glasses was investigated using various characterization techniques such as differential thermal analysis (DTA), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Crystallization behavior of these glasses was markedly influenced by the addition of Y₂O₃ instead of Al₂O₃. Addition of Y₂O₃ increases the transition temperature, T _g, crystallization temperature, T _c and stability of the glasses. Also, it suppresses the formation of cordierite phase, which is very prominent and detrimental in MgO-based glasses. The results are discussed on the basis of the structural and chemical role of Y³⁺ and Al³⁺ ions in the present glasses.     

Fabrication of transparent polymer-matrix nanocomposites with enhanced mechanical properties from chemically modified ZrO<Subscript>2</Subscript> nanoparticles

Optically transparent nanocomposites with enhanced mechanical properties were fabricated using stable dispersions of sub 10 nm ZrO₂ nanoparticles. The ZrO₂ dispersions were mixed with a commercially available bisphenol-A-based epoxy resin (RIMR 135i) and cured with a mixture of two amine-based curing agents (RIMH 134 and RIMH 137) after complete solvent removal. The colloidal dispersions of ZrO₂ nanoparticles, synthesized through a non-aqueous approach, were obtained through a chemical modification of the ZrO₂ nanoparticle surface, employing different organic ligands through simple mixing at room temperature. Successful binding of the ligands to the surface was studied utilizing ATR–FT-IR and thermogravimetric analysis. The homogeneous distribution of the nanoparticles within the matrix was proven by SAXS and the observed high optical transmittance for ZrO₂ contents of up to 8 wt%. Nanocomposites with a ZrO₂ content of only 2 wt% showed a significant enhancement of the mechanical properties, e.g., an increase of the tensile strength and Young’s modulus by up to 11.9 and 12.5%, respectively. Also the effect of different surface bound ligands on the mechanical properties is discussed.     

Preparation of porous ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> macrobeads from ion-exchange resin templates

In this work, we will report a method to prepare porous ZrO₂ and ZrO₂/Al₂O₃ macrobeads using cation-exchange resins with sulfonate groups as templates. The preparation process involves metal ion-loading, ammonia-precipitation, and calcination at an appropriate temperature. Several characterization methods, such as TGA, XRD, SEM with EDX, TEM and N₂ adsorption and desorption, were used to characterize the ZrO₂ and ZrO₂/Al₂O₃ macrobeads. The results showed that the porous structures of the resin templates were negatively duplicated in the two kinds of macrobeads. We found the following interesting results: (1) The ZrO₂/Al₂O₃ macrobeads are composed of tetragonal zirconia nanocrystals that are more technologically important, while the pure ZrO₂ macrobeads consist of a mixture of tetragonal and monoclinic zirconia. (2) In the ZrO₂/Al₂O₃ macrobeads, the size of ZrO₂ nanocrystals is about 5 nm smaller than that (about 19 nm) found in the pure ZrO₂ macrobeads. (3) The ZrO₂/Al₂O₃ macrobeads have more mesopores and, therefore, have a larger surface area than the pure ZrO₂ macrobeads. These oxide macrobeads will have potential applications in catalysis by taking advantage of their macrobeads shape and pores structure.     

Electrical and physicochemical properties of some Ag<Subscript>2</Subscript>O-containing lithia iron silica phosphate glasses

The present paper reports the influence of Ag₂O addition at the expense of Li₂O on the local structure of xAg₂O·(30 − x)Li₂O·10Fe₂O₃·10SiO₂·50P₂O₅ glass matrix (with x = 0, 0.5, 1, 1.5 and 2 mol %). The phosphate structural units of the network former are assessed from Fourier transform infrared (FT-IR) spectroscopy. The addition of Ag₂O to the glass network matrix ≤1 mol % leads to the occurrence of a depolymerization process of the phosphate structure and consequently, to the appearance of a distortion of the PO₄ tetrahedra. When the content of Ag₂O is increased from 1.5 up to 2 mol %, a remarkable polymerization process has been observed. The density, molar volume, microhardness and chemical durability have been investigated in order to study the effect of Ag₂O/Li₂O replacements on the physicochemical properties the studied glasses. The AC electrical properties are affected to a great extent with composition. These results are related to the internal structure of the glass samples. The conductivity, dielectric constant and dielectric loss of the studied glasses were studied using the frequency response in the interval 100 Hz–100 kHz and the effect of compositional changes on the measured properties was investigated. Measurements showed that the electrical responses of glass samples were different and complex for interpretation. The increase of Ag₂O addition at the expense of Li₂O contents (from 0 to 1 mol %) led to increase the conductivity, dielectric constant and dielectric losses of samples. The addition of more Ag₂O at the expense of Li₂O (from 1.5 to 2 mol %), resulting into decreasing the conductivity, the dielectric constant and dielectric losses of the studied glasses. The experimental data of the glass samples were argued to the internal structure of the glasses and the nature and role-played by weakening or increasing the rigidity of the structure of the sample. It could be concluded, therefore, that the AC electrical properties of the samples were influenced by the distribution of its constituents, connectivity, and number of free charges.     

Mechanical properties of bovine hydroxyapatite (BHA) composites doped with SiO<Subscript>2</Subscript>, MgO,Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and ZrO<Subscript>2</Subscript>

Biologically derived hydroxyapatite from calcinated (at 850 °C) bovine bones (BHA) was doped with 5 wt% and 10 wt% of SiO₂, MgO, Al₂O₃ and ZrO₂ (stabilized with 8% Y₂O₃). The aim was to improve the sintering ability and the mechanical properties (compression strength and hardness) of the resultant BHA-composites. Cylindrical samples were sintered at several temperatures between 1,000 and 1,300 °C for 4 h in air. The experimental results showed that sintering generally occurs at 1,200 °C. The BHA–MgO composites showed the best sintering performance. In the BHA–SiO₂ composites, extended formation of glassy phase occurred at 1,300 °C, resulting in structural degradation of the resultant samples. No sound reinforcement was achieved in the case of doping with Al₂O₃ and zirconia probably due to the big gap between the optimum sintering temperatures of BHA and these two oxides.     

SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> fibers from titanium-modified polycarbosilane

We developed a process for preparing SiO₂/TiO₂ fibers by means of precursor transformation method. After mixing PCS and titanium alkoxide, continuous SiO₂/TiO₂ fibers were fabricated by the thermal decomposition of titanium-modified PCS (PTC) precursor. The tensile strength and diameter of SiO₂/TiO₂ fibers are 2.0 GPa, 13 μm, respectively. Based on X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) measurements, the microstructure of the SiO₂/TiO₂ fibers is described as anatase–TiO₂ nanocrystallites with the mean size of ~10 nm embedded in an amorphous silica continuous phase.     

Electrical properties of some Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and/or Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-containing lithium silicate glasses and glass-ceramics

The ac electrical properties of some lithium silicate glasses and glass-ceramics containing varying proportions of Y₂O₃ and/or Fe₂O₃ were measured to investigate their electronic hopping mechanism. There is a clear variation of these properties with composition. The obtained results were related to the concentration and role of Y₂O₃ and/or Fe₂O₃ in the lithium silicate glass structure. In crystalline solids the electrical properties data obtained were correlated to the type and content of the mineral phases formed as indicated by X-ray diffraction analysis (XRD). The conductivity, dielectric constant and dielectric loss of the studied glasses were studied using the frequency response in the interval 30 Hz–100 KHz and the effect of compositional changes on the measured properties was investigated. The measurements revealed that the electrical responses of the samples were different and complex. The addition of Y₂O₃ generally, decreased the ac conductivity, dielectric constant and dielectric losses of the lithium silicate glasses. The addition of Fe₂O₃ in Y₂O₃-containing glasses increases the conductivity, while, the dielectric constant and dielectric losses were found to be decreased. However, the addition of Fe₂O₃ instead of Y₂O₃ led to decrease the ac conductivity and increased their dielectric constant and dielectric losses. The obtained data were argued to the internal structure of the lithium silicate glass and the nature or role-played by weakness or rigidity of the structure of the sample. Lithium disilicate-Li₂Si₂O₅, lithium metasilicate-Li₂SiO₃, two forms of yttrium silicate Y₂Si₂O₇ & Y₂SiO₅, iron yttrium oxide-YFeO₃, lithium iron silicate-LiFeSi₂O₆ and α-quartz phases were mostly developed in the crystallized glasses. The conductivity of the crystalline materials was found to be relatively lower than those of the glass. At low frequency, as the Y₂O₃ content increased the ac conductivity, dielectric constant and dielectric loss data of the glass-ceramics decreased. However, the addition of Fe₂O₃ to the Y₂O₃ containing glass-ceramic led to increase the conductivity. The addition of high content of Fe₂O₃ instead of Y₂O₃ in the glass ceramic led to increase the ac conductivity.     

Solid state sintering of lime in presence of La<Subscript>2</Subscript>O<Subscript>3</Subscript> and CeO<Subscript>2</Subscript>

The sintering of lime by double calcination process from natural limestone has been conducted with La₂O₃ and CeO₂ additive up to 4 wt.% in the temperature range 1500–1650° C. The results show that the additives enhanced the densification and hydration resistance of sintered lime. Densification is achieved up to 98.5% of the theoretical value with La₂O₃ and CeO₂ addition in lime. Grain growth is substantial when additives are incorporated in lime. The grain size of sintered CaO (1600°C) with 4 wt.% La₂O₃ addition is 82 μm and that for CeO₂ addition is 50 μm. The grains of sintered CaO in presence of additive are angular with pores distributed throughout the matrix. EDX analysis shows that the solid solubility of La₂O₃ and CeO₂ in CaO grain is 2.9 and 1.7 weight %, respectively. The cell dimension of CaO lattice is 4.803 %C. This value decreases with incorporation of La₂O₃ and CeO₂. The better hydration resistance of La₂O₃ added sintered lime compared to that of CeO₂ added one, is related to the bigger grain size of the lime in former case.     

Effect of replacement of MgO by CaO on sintering,crystallization and properties of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system glass-ceramics

The effects of replacement of MgO by CaO on the sintering and crystallization behavior of MgO–Al₂O₃–SiO₂ system glass-ceramics were investigated. The results show that with increasing CaO content, the glass transition temperature firstly increased and then decreased, the melting temperature was lowered and the crystallization temperature of the glass-ceramics shifted clearly towards higher temperatures. With the replacement of MgO by less than 3 wt.% CaO, the predominant crystalline phase in the glass-ceramics fired at 900 °C was found to be α-cordierite and the secondary crystalline phase to be μ-cordierite. When the replacement was increased to 10 wt.%, the predominant crystalline phase was found to be anorthite and the secondary phase to be α-cordierite. Both thermal expansion coefficient (TCE) and dielectric constant of samples increases with the replacement of MgO by CaO. The dielectric loss of sample with 5 wt.% CaO fired at 900 °C has the lowest value of 0.08%. Only the sample containing 5 wt.% and10 wt.% CaO (abbreviated as sample C5 and C10) can be fully sintered before 900 °C. Therefore, a dense and low dielectric loss glass-ceramic with predominant crystal phase of α-cordierite and some amount of anorthite was achieved by using fine glass powders (D₅₀ = 3 μm) fired at 875–900 °C. The as-sintered density approaches 98% theoretical density. The flexural strength of sample C5 firstly increases and then decreases with sintering temperature, which closely corresponds to its relative density. The TCE of sample C5 increases with increasing temperature. The dielectric property of sample C5 sintered at different temperatures depends on not only its relative density but also its crystalline phases. The dense and crystallized glass-ceramic C5 exhibits a low sintering temperature (≤900 °C), a fairly low dielectric constant (5.2–5.3), a low dielectric loss (≤10⁻³) at 1 MHz, a low TCE (4.0–4.25 × 10⁻⁶ K⁻¹), very close to that of Si (∼3.5 × 10⁻⁶ K⁻¹), and a higher flexural strength (≥134 MPa), suggesting that it would be a promising material in the electronic packaging field.     

Effect of secondary heat treatment on the spectroscopic properties of Na<Subscript>2</Subscript>O-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

We have studied the optical absorption and luminescence spectra of 45Na₂O · xNb₂O₅ · (55 − x)P₂O₅ glasses containing 5, 10, 20, 25, 30, and 35 mol % Nb₂O₅. The results indicate that the absorption band around 26000 cm⁻¹, responsible for the yellow color of the glasses, is due to the [Nb^(5+)--O⁻] center and disappears upon secondary heat treatment. Heat treatment of europium-doped glasses increases the concentration of Eu³⁺ centers in an asymmetric environment, which is accompanied by an increase in luminescence efficiency. The reason for this is that the Eu³⁺ ions are located outside the niobate subsystem of the glass matrix. The europium in the glasses studied acts as a protector ion.     

A novel method for producing open-cell Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> ceramic foams with controlled cell structure

A novel method was introduced to prepare open-cell Al₂O₃–ZrO₂ ceramic foams with controlled cell structure. This method used epispastic polystyrene (EPS) spheres to array ordered templates and centrifugal slip casting in the interstitial spaces of the EPS template to obtain cell struts with high packing density. Aqueous Al₂O₃–ZrO₂ slurries with up to 50 vol.% solid contents were prepared and centrifuged at acceleration of 2,860g. The effect of the solid contents of slurries on segregation phenomena of different particles and green compact uniformity were investigated. In multiphase system, the settling velocities of Al₂O₃ and ZrO₂ particles were calculated. Theory analysis and calculated results both indicated segregation phenomenon was hindered for slurries with 50 vol.% solid content. The cell struts of sintered products had high green density (61.5%TD), sintered density (99.1%TD) and homogeneous microstructures after sintered at 1,550 °C for 2 h. The cell size and porosity of Al₂O₃–ZrO₂ ceramic foams can be adjusted by changing the size of EPS spheres and the load applied on them during packing, respectively. When the porosity increased from 75.3% to 83.1%, the compressive strength decreases from 3.82 to 2.07 MPa.     

Production of opaque frits with low ZrO<Subscript>2</Subscript> and ZnO contents and their industrial uses for fast single-fired wall tile glazes

The amounts of zirconium and zinc oxides, which raise the production costs of ceramic glazes, were decreased in fast single-fired wall tile frit compositions and an industrial frit production was conducted. Opacity of the fired frit-based glazes was accomplished by compositional modifications of frits with no other nucleating agent. It was determined that the ratios of Al₂O₃/ΣR₂O, Al₂O₃/ΣRO, and Al₂O₃/B₂O₃ have significant effects on decreasing ZrO₂ and ZnO levels in the frit composition. A reduction of 25% in both zirconia and zinc oxide contents of frit batches, with respect to the reference frit (R) containing 6–10% ZrO₂ and 6–10% ZnO for a glossy white opaque wall tile glaze, was achieved in the ZD glaze consisting of 4.5–7.5% zirconia and 4.5–7.5% ZnO in its frit composition. It was concluded that zircon was the main crystalline phase of the glaze contributing the opacity. The ZD frit-based glaze has a thermal expansion coefficient value of 61.13 ± 0.32 × 10⁻⁷ °C⁻¹ at 400 °C which well matches to that of the wall tile body. TS EN ISO 10545 standard tests were also applied to the final ZD glaze. It is confirmed that the production cost of a fast single-fired wall tile glaze can be decreased by 15–20% with the successful new frit developed.     

Characterization and electrical properties of semiconducting Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

Semiconducting glasses of the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system were prepared by the press-quenching method and their dc conductivity in the temperature range 223–393 K was measured. The glass transition temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The density for these glasses was consistent with the ionic size, atomic weight and amount of different elements in the glasses. Mössbauer results revealed that the relative fraction of Fe increases with increasing Fe₂O₃ content. Electrical conductivity showed a similar composition dependency as the fraction of Fe. The glasses had conductivities ranging from 10 to 10 Scm at temperatures from 223 to 393 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.     

Effect of impurities on characteristics of ZrO<Subscript>2</Subscript> and ZnO ceramic powders produced by spray pyrolysis

Previously it was observed that addition of impurities to a precursor solution may alter the size and morphology of the particles produced by spray pyrolysis. To investigate this further, the spray pyrolysis technique was used to prepare zirconia (ZrO₂) and zinc oxide (ZnO) ceramic powders, with addition of slight amounts of NaCl in various concentrations. The results show an increase in the percentage of nondisrupted particles which corresponds to an increase in the weight percentage of NaCl in the precursor in ZrO₂ powder produced at 400 °C. This effect is not repeated in ZnO powder produced at 400 °C, as the addition of NaCl to the precursor results in the disruption of individual particles into much smaller particles. As far as the morphology and strength of particles are concerned, it is concluded that the addition of NaCl to the precursor solution has a beneficiary effect on the morphology of ZrO₂ particles and an adverse effect on ZnO particles, both of which are negated at a higher reactor temperature of 600 °C.     

Study of structure and properties of ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Glasses of the ternary system ZnO–Bi₂O₃–P₂O₅ were prepared and studied in two compositional series 50ZnO–xBi₂O₃–(50 − x)P₂O₅ and (50 − y)ZnO–yBi₂O₃–50P₂O₅. Two distinct glass-forming regions were found in the 50ZnO–xBi₂O₃–(50 − x)P₂O₅ glass series with x = 0–10 and 20–35 mol.% Bi₂O₃. All prepared Bi₂O₃-containing glasses reveal a high chemical durability. Small additions of Bi₂O₃ (∼5 mol.%) improve thermal stability of glasses. All glasses crystallize on heating within the temperature range of 505–583 °C. Structural studies by Raman and ³¹P MAS NMR spectroscopies showed the rapid depolymerisation of phosphate chains within the first region with x = 0–15 and the presence of isolated Q⁰ phosphate units within the second region with x = 20–35. Raman studies showed that bismuth is incorporated in the glass structure in BiO₆ units and their vibrational bands were observed within the spectral region of 350–700 cm⁻¹. The evolution of properties and the spectroscopic data are both in accordance with a network former effect of Bi₂O₃.