نشریه علم و مهندسی سرامیک
سال هشتم شماره 4 (پیاپی 31، زمستان 1398)

In this study, the effect of two types of SiC powders consist of SiC-1 (β-SiC) and SiC-2 (β-SiC+α-SiC) and also different values of CaO additive consist of 0, 0.4 and 0.8 weight percent on sintering behavior of sintered SiC with pressureless technique in Al2O3-Y2O3-CaO additive system  was investigated. In all specimens, Al2O3:Y2O3 molar ratio was equal to 3:2 and all amounts of additive were equal to 9 weight percent. Specimens were sintered at 1900ºC for 1 hour in argon atmosphere. Results show that relative density, elastic modulus, micro hardness and fracture toughness of specimens sintered with SiC-2 is higher than specimens sintered with SiC-1. Also results showed that by adding CaO to 0.4 weight percent in both SiC powder types, sinterability increased and by increasing CaO amount to 0.8 weight percent, sinterability decreased. Maximum value of relative density and elastic modulus in specimens sintered with SiC-1 were respectively 80.86 % and 273.99±11 GPa and in specimens sintered with SiC-2 were respectively 92.34 % and 344.55±8.4 GPa. Also maximum amounts of micro hardness and fracture toughness in specimens sintered with SiC-2 powder and 0.4 weight percent of CaO were obtained 19.5± 0.82 GPa and 4.7± 0.5 MPa.   respectively.

Nowadays, suitable protective properties of tantalum nitride coatings, such as hardness, abrasion resistance and high corrosion resistance lead to increasing its application in medical engineering and improving the biological behavior of titanium and its alloys. In this research, nanostructured tantalum nitride coating was applied on the NiTi alloy by magnetron sputtering method. Then, the phase, structural and morphological properties of coating were investigated by using XPS, FESEM, AFM, respectively, as well as the nanomechanical properties of the coating were evaluated by using Nano-scanning and nano-scratch methods in different loads.
The results indicate that applying the uniform, homogeneous and crack free tantalum nitride coating with a thickness of 1050 nm. The hardness and elastic modulus of coating is 12.6 and 87.4 GPa under the applied force of 1000 μm and the penetration depth of 91 nm, respectively, which resulted in enhancing the hardness of NiTi alloy surface, about 34%. The coefficient of friction is 0.28 and the dominated wear mechanism of nanostructured tantalum nitride coating is abrasive wear with shearing mechanism.

In this research, the densification of magnesia nanopowder with a mean particle size of about 100 nm was investigated by spark plasma sintering undera pressures of 80 MPa and at temperature range from 1000 °C to 1400 °C and a heating rate of 50 °C/min for 20 minutes. The density of the samples slowly increased with increasing sintering temperatures to 1200 °C. Afterwards, with more increasing of temperature, decreasing density and increasing of grain growth were observed. Grain growth was analyzed during the sintering process with the classic grain growth theory. The results of the survey on the density showed that the highest densification rate occurred at 1100 ℃. The activation energy of grain growth was Obtained 452.24 kJ / mol. The MgO ceramic spark plasma sintered at 1200 °C for 20 min demonstrated the highest infrared transmittance of 67 % at the 5.6 μm wavelength.

CoAl2O4 nano pigments were fabricated using cobalt chloride and aluminum oxide as a ceramic blue pigment by co-precipitation . The product was calcinated at 1200°C. Three samples were made under different conditions and homogenized in a solvent using a milling system to prepare an ink. It has been printed on a ceramic by silk screen method. The powder was characterized by XRD, SEM and colorimetric tests to identify the structure, color parameters and microstructure. The results of XRD experiments show that CoAl2O4 nanoparticles were formed in all three samples. The results of the particle size distribution and SEM images of the manufactured powders show that with increasing milling time, the average particle size will decrease from 413 nm to 181 nm. Also, the printed ceramics were characterized by SEM and colorimetric tests.

In this investigation, bismuth tungstate (Bi2WO6) nanoparticles were synthesized by the hydrothermal method, and its surface modification was performed to increase photocatalytic property by palladium (Pd) and hydroxyapatite (Hap). The Pd / Bi2WO6 / Hap sample consists of two active components in visible light (Pd, Bi2WO6) and a hydroxyapatite adsorbent (Hap). The Pd / Bi₂WO6 / Hap sample activity is greater than that of an active component in visible light (such as Bi2WO6) to degrade phenol pollutants. 
In this study, the structural properties of Bi2WO6, Pd / Bi2WO6, Hap / Bi2WO6, Hap / Pd / Bi2WO6 samples were evaluated by the reflection spectroscopy (DRS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) imaging. The photocatalytic properties of the samples were also investigated in the degradation of phenol pollutants. The result of photocatalytic experiments showed that the photocatalyst Hap / Pd / Bi2WO6 has very good performance under visible light irradiation The results also showed that the photocatalytic degradation rate of the Hap / Pd / Bi2WO6 sample was significantly improved compared to the Bi2WO6 sample. This performance improvement is due to several factors, such as: increasing the special surface, the effective separation of electrons and cavities, the size of the energy gap, and also increase the absorption time by the hydroxyapatite.

Plasma electrolysis is a novel method for synthesis and processing of materials and nanomaterials, which uses plasma-solution interaction. In this paper, a simple setup of pin-to-solution electrical discharge with aqueous solution of silver nitrate in normal air is used. Experimental observations show that by start of electrical discharge and formation of air plasma between metal pin and solution surface, a black material is produced at the plasma-solution interface and gradually spreads throughout the electrolyte and finally precipitates at the bottom of the vessel and is separated. XRD analysis shows that the synthesized material is Ag2O2. From the FESEM images, it is inferred that the powder contains micrometer particles. Ultraviolet-Visible-Near Infrared (UV-Vis-NIR) absorption spectrum reveals that the sample is a semiconductor with energy gap of 0.9-0.94 eV.

In this study, zirconium carbide nanoparticles were synthesized by the sol-gel method in the alcoholic system. The sol was prepared in a three-component alkoxide-water-alcohol system based on the chemical sol-gel process under acidic conditions and at pH = 5. Zirconium n-propoxide, furfuryl alcohol were used as raw materials. After the hydrolysis process and formation of the gel, the initial powder was subjected to heat treatment and formed ZrC nanoparticles. The effects of pH and temperature parameters in the synthesis process of these nanopowder were investigated. To evaluate product properties, DLS SEM, DTA / TG-XRD-FTIR analyzes were used. The results for sol showed that by controlling pH in the range of 5, precursors particles containing Zr could be synthesized in sizes below 10 nm. In FTIR data, Zr-O and Zr-C bonds were identified in the range of 560 and 505 cm-1, respectively. The DTA / TG ​​analysis showed that the initial nucleates of ZrC particles were formed at a temperature of 1320 ° C, which confirmed  by the x-ray diffraction pattern. SEM microstructures showed that, zirconium carbide particles were formed in the range below 100 nm, and the distribution of particle size in a narrow and uniform range.

The purpose of this study was to fabricate and characterize nanocomposite powder from 45S5 bioactive glass/ fluorapatite. Nanocomposites containing 10, 15 and 20 wt.% of fluorapatite were synthesized by sol-gel method. XRD and FT-IR analyses were used to characterize and evaluate the produced nanocomposites. The results of XRD and FT-IR analysis indicated the successful synthesis of high purity bioactive glass nanocomposites. The results of compressive strength test showed an increase in strength of sample containing 15% fluorapatite. MTT (3-(4,5-Dimethylthiazol-2-Yl)-2,5-Diphenyltetrazolium Bromide) assay was used to evaluate cytotoxicity. The results of this section showed no cytotoxicity of the samples, which showed a decrease in the survival rate after seven days. The lowest survival rate was observed for pure fluorapatite.