Sharif Digital Repository

Nanocrystalline Y3-xMMxFe5O12 powders (MM denotes Misch-metal, x = 0.0, 0.25, 0.5, 0.75, and 1.0) were synthesized by a sol-gel combustion method. Magnetic properties and crystalline structures were investigated using X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), and a scanning electron microscope. The XRD patterns showed that the single-phase garnet of Y3-xMMxFe5O12 was formed at x values ≤ 1.0. The saturation magnetization of powders increased with decreasing MM content and reached the maximum value at Y3 Fe5O12. The crystallite size of powders calcined at 800°C for 3 h was in the range of 38-53 nm. © 2008 American Ceramic Society  

By a single-step supercritical hydrothermal synthesis method, yttrium oxide nanoparticles were successfully prepared without additional treatment. Yttrium oxide nanoparticles were employed as an adsorbent to study the adsorption of some heavy metal ions. This study revealed that nano structure yttrium oxide was an effective adsorbent for removal of lead ions from aqueous solutions  

The nitrate-citrate gels exhibit auto-catalytic behavior, which can be used to synthesize the nanocrystalline YIG powders. In this study yttrium iron garnet (Y3Fe5O12) nanocrystalline powders were prepared by a sol-gel auto-combustion process. The influence of pH value of the precursor solution on the combustion behavior and the garnet phase formation of synthesized powders were investigated by scanning electron microscopy (SEM), thermal analysis (DTA/TGA), infrared (IR) spectroscopy and X-ray diffraction technique (XRD). The results show that with increasing pH value, the combustion rate increases. The as-burnt powder prepared with pH 1 yielded a single phase YIG after calcination at 800... 

Y2 O3:Eu3+ nanostructures with bright red emitting phosphors have been synthesized by the combustion method using water and water/ethanol mixture as solvents. The effect of the solvents on nanostructure and luminescence properties of combustion synthesized Y2 O3:Eu3+ was explored. The synthesized nanostructures were calcined at 400 ° C and 1000 ° C to remove the organic phases and enhance the crystallinity. The crystal structures were characterized by an X-ray diffractometer and the particle size and morphology of the synthesized nanostructures were studies using a field emission scanning electron microscope and a transmission electron microscope. We found that the solvent choice has a... 

Pechini process was used for preparation of three kinds of nanocrystalline powders of yttria-stabilized zirconia (YSZ): doped with 1.5 mol% nickel oxide, doped with 15 mol% ceria, and doped with 1.5 mol% nickel oxide plus 15 mol% ceria. Zirconium chloride, yttrium nitrate, cerium nitrate, nickel nitrate, citric acid and ethylene glycol were polymerized at 80 °C to produce a gel. XRD, SEM and TEM analyses were used to investigate the crystalline phases and microstructures of obtained compounds. The results of XRD revealed the formation of nanocrystalline powder at 900 °C. Morphology of the powder calcined at 900 °C, examined with a scanning electron microscope, showed that the presence of... 

Yttrium Iron Garnet (YIG) powders were synthesized by a sol-gel auto-combustion method using cationic and anionic surfactants with different values and different calcination times and temperatures. The final products were characterized by DTA/TG, XRD, TEM and VSM techniques. The results showed a decrease in calcination temperature and crystallite size in the presence of a cationic surfactant, while no significant effect was observed using an anionic surfactant. Magnetic properties of YIG powders were improved as an optimum value of cationic surfactant was used  

Microstructural development and phase formation at the interface of yttria stabilized zirconia (3Y-TZP)/430L stainless steel composite layers produced by co-sintering method were studied by SEM, HRTEM, micro-focus XRD, and EPMA. Formation of a rich chromium boundary layer at the interface was noticed, which revealed Cr aggregation at the interface at the elevated temperatures. Misfit dislocations were also observed at the joint interface to tackle the mismatch crystallographic orientations between the ceramic and metal layer. The results of the micro-focus XRD showed formation of no new phases at the boundary zone. Microstructural studies also revealed a retarded grain growth in the... 

Joining of yttria-stabilized zirconia (YSZ) to stainless steels is considered for various applications such as solid oxide fuel cells, thermal barrier coatings, and medical implants. In the present work, a series of brazing pastes utilizing silver and nickel nanoparticles (∼80 nm) mixed with carboxymethyl cellulose as the organic phase were developed to join 5 mol% YSZ to AISI 420 steel. Effects of processing parameters including time and temperature of brazing and the composition of the nanopastes on the microstructure of joints and their shear rupture strength were studied. Elaboration of the joining mechanism by scanning electron microscopy and electron probe micro-analyzer showed... 

Zirconia Toughened Alumina (ZTA) Nanocomposites were prepared using Nano sized Zirconia (ZrO2) powders doped with 3% mol of yttria (Y 2O3) nanopowders. Diffusion of α-alumina (Al 2O3) nanoparticles as well as yttria into the Zirconia lattice network drives monoclinic - tetragonal martensitic transformation. Zirconia toughened alumina (ZTA) composites containing different amount of partially stabilized Zirconia (PSZ) 5, 10, 15 and 20% mol, were prepared via wet mixing and axial pressing. After sintering at different temperatures,1450, 1550 and 1650 °C, phase change in the samples were monitored. X-ray diffraction patterns showed that at constant composition, tetragonal zirconia was increased... 

Sintering is the most critical step in manufacturing of functional parts by co-powder injection molding. In the present work, we studied the sintering phenomena occurring during co-sintering of metal/ceramic composite layers. Nanostructured yttria-stabilized zirconia (3Y-TZP) was co-sintered with 430L stainless steel and chromium. The sintering response was studied by dilatometer analysis in isothermal and non-isothermal modes. The microstructure of the sintered specimens was studied by scanning electron microscopy (SEM), electron-probe microanalysis (EPMA) and micro-focused X-ray diffraction (MFXRD). The strength of the joint was also determined by a shear-punch method. It is shown that... 

The sintering behavior of commercially available granulated ZrO2-3 mol% Y2O3 (3Y-TZP) powder compacts with an aggregate size of 75 nm was studied. The shrinkage response of the powder compacts during non-isothermal sintering was measured in a sensitive dilatometer at different heating rates. Densification and grain growth were also studied after isothermal firing in air according to different sintering cycles. The sintering and grain growth activation energy was estimated to be QS = 485 ± 12 kJ mol-1 and QG = 546 ± 23 kJ mol-1, respectively. Using the estimated Q-values, the master curves for sintering and grain growth were established and used for prediction of the densification and... 

Holding U-bolts of an automobile wheels are manufactured from 10B21 boron steel rods. Changing the source of the rods from X to Y, with an identical manufacturing procedure, it was observed that parts fracture at the mechanical straightening stage (final stage of the manufacturing line). In this case study, microscopy techniques and mechanical tests were used to identify the cause of this failure. It was shown that higher contents of carbon and boron of the source Y rods promotes precipitation of boron containing carbides along the grain boundaries. These precipitates act as crack nucleation sites and are responsible for the fracture of the parts under the straightening stage stresses. Based... 

A pressureless sintering method was utilized to fabricate metal/ceramic joints out of yttria-stabilized zirconia (3Y-TZP) and stainless steels (SS). Ultrafine (150 nm) and nanoscale (75 nm) 3Y-TZP particles and micrometric 17-4PH, 316L, and 420 SS (<31 μm) powders were tested. Isothermal and nonisothermal sintering behaviors of the powders and composite layers in hydrogen, argon, and vacuum atmospheres were examined. It was found that the mismatch strain between the zirconia ceramic and SS during cosintering is significant, which leads to bond cracking and joint failure. Nevertheless, interlayer diffusion of Zr, Fe, and Cr and the formation of a reaction zone, particularly during vacuum... 

Two-step sintering (TSS) was applied on nanocrystalline yttria tetragonal stabilized zirconia (3Y-TZP) to control the grain growth during the final stage of sintering. The process involves firing at a high temperature (T1) followed by rapid cooling to a lower temperature (T2) and soaking for a prolonged time (t). It is shown that for nanocrystalline 3Y-TZP (27 nm) the optimum processing condition is T1 = 1300 °C, T2 = 1150 °C and t = 30 h. Firing at T1 for 1 min yields 0.83 fractional density and renders pores unstable, leading to further densification at the lower temperature (T2) without remarkable grain growth. Consequently, full density zirconia ceramic with an average grain size of 110... 

We report on the results of a YBa2Cu3O7−x (YBCO) superconductive transition edge bolometer (TEB) fabricated on a Ce0.9La0.1O2−7 (CLO) buffered single crystalline yttria-stabilized zirconia (YSZ) substrate. Metal organic deposition was used for the fabrication of both the YBCO thin film as well as CLO buffer layer, while standard photolithography was applied for TEB preparation. YBCO thin film properties were analysed using scanning electron microscopy (SEM), X-ray diffraction (XRD), AC susceptibility and resistance versus temperature measurements. Optical response of the TEB in terms of voltage amplitude and phase was analysed and measured through four-probe technique in a liquid nitrogen... 

We report on the results of a YBa2Cu3O7−x (YBCO) superconductive transition edge bolometer (TEB) fabricated on a Ce0.9La0.1O2−7 (CLO) buffered single crystalline yttria-stabilized zirconia (YSZ) substrate. Metal organic deposition was used for the fabrication of both the YBCO thin film as well as CLO buffer layer, while standard photolithography was applied for TEB preparation. YBCO thin film properties were analysed using scanning electron microscopy (SEM), X-ray diffraction (XRD), AC susceptibility and resistance versus temperature measurements. Optical response of the TEB in terms of voltage amplitude and phase was analysed and measured through four-probe technique in a liquid nitrogen... 

Recently, co-powder injection molding process (2C-PIM) has attained considerable interest to fabricate complex-shaped functional materials. The aim of this work is to study the sintering compatibility between nanocrystalline yttria-stabilized zirconia (3Y-TZP) and PIM grade 430L stainless steel (SS) powders, which is the utmost important step in the 2C-PIM process. To evaluate the mismatch strain development during the co-sintering, the isothermal and nonisothermal behaviors of the ceramic and metal powders were studied. Small bilayers of 3Y-TZP/430L were made by a powder metallurgy technique and the feasibility of simultaneous sintering and joining of the composite layer was examined....