نشریه علم و مهندسی سرامیک
سال هشتم شماره 2 (تابستان 1398)

The aim of this research was to study synthesize gamma aluminum oxynitride powder with cubic spinel structure. In order to carry out this process, carbothermal reduction and nitridation of α-alumina as starting powder was used. This process was carried out in two steps, that in the first step at 1550˚C, a portion of α-alumina was reacted with carbon and aluminum nitride (AlN) was formed, then in the second step at 1750°C, the residual alumina reacted with aluminum nitride, and aluminum oxynitride was formed. In order to achieve the dominant phase of aluminum oxynitride, different amounts of carbon (5, 10, 15 and 20 wt%) were used and the weight percentages of the middle phases at 1550°C, 1600°C and 1650°C were investigated for optimal sample. The results indicate that the highest percentage of aluminum oxynitride is present in 10 wt% of carbon.

Composites that are including silicide of tungsten and boride of tungsten intermetallic compound have properties such as high hardness, relatively good thermal shock, chemical stability and high strength at high temperature. The purpose of this investigation is evaluation of phase and microstructure of alumina base composite reinforced by boride and silicide of tungsten in three systems 1-Al+ Si+WO3, 2-Al+B2O3+WO3 and 3-Al+B2O3+Si+WO3 by combustion synthesis method in different thermal analysis experiments. In this study starting materials according to stoichiometric ratio were mixed by ball-milling under atmosphere of argon for 10 hours. The XRD results don’t show any new phase during ball-milling even up to 10 hours. Differential thermal analysis (DTA) and thermal gravity analysis (TGA) were conducted on different mixture of starting material. The results show a compact microstructure of WxBy (mostly WB) and WxSiy (mostly WSi2) as secondary phases in alumina matrix. There is a lower temperature for forming of tungsten silicide (WxSiy) compared with tungsten boride (WxBy). The presence of Si in the Al+B2O3+WO3 system facilitates the formation of tungsten borides. Tungsten boride grains are coarser and more elongated than silicide tungsten grains.

Injectable pastes are bioactive materials which are used in various forms in the living organism. The bioactivity of these materials are derived from calcium phosphate powder and/or a bio-glass composition. These materials are not individually injectable; however, they will be when suitable polymers such as chitosan, gelatin, sodium alginate, hyaluronic acid, etc. added to the paste. In this research, the authors have tried to prepare a bioactive injectable glass/polymer paste via mixing a sol-gel derived glass powder, based on the SiO2-CaO-P2O5 system, with polymer’s solution of gelatin. The rheological behavior and the injectability of the pastes were also investigated. The results showed that the paste was well-injected; however, it showed an undefined rheological behavior. The maximum viscosity of the paste was 8.88 × 10 Pa.s and it was washed out during it’s immersion in a simulated body fluid with time and reached to approximately 60wt.% of its initial weight after 48h. According to microstructural analysis, mineralogical phase analysis and Fourier Transform IR spectrometry analysis, the paste showed bioactivity after 14 days immersion in SBF solution.

Electrical conduction anomaly was observed in the mixed ion-polaron regime for xAg2O-40TeO2-(60-x)V2O5 glassy system with 0 ≤x≤ 50 mol%, which were prepared by common melt quenching method. For the understudied glasses, the temperature dependence of dc electrical conductivity was measured from a characteristic temperature to 380 K, which certified their semiconducting nature. The measured conductivity values at a typical temperature of 300 K were within the range of 5.88×10-7-3.33×10-3 Scm-1, which indicate the decreasing trend of electrical conductivity with increasing of silver oxide content for x=0- 30 and an increasing trend for x=40-50. With increase of Ag2O content within the range of 20 ≤x≤ 50, and especially for x≥40 mol%, the conduction mechanism changes from polaronic to ionic-polaronic, which is an evidence for the anomaly in conduction mechanism. For the present samples, at temperatures above a characteristic temperature, the electrical conduction mechanism obeys the non-adiabatic small polaron hopping (NASPH) between the vanadium ions, and the values of charge carrier mobility and charge carrier density, as important parameters in electrical investigations, were determined in NASPH regime. Also, the study of the density of non-bridging oxygens (NBOs) indicates the effect of Ag2O on the glass thermal stability and fragility, implying on the sample with critical x=20as the highest thermal stable glass.

Composite coatings with nickel matrix and ceramic reinforcement particles have high ability to improve surface properties, such as good corrosion and abrasion resistance. In this study, Ni-P composite coating was coated with ZrO2 and TiO2 ceramic particles on the AISI 316 steel substrate through direct current plating method. The effect of the current densities of 20, 30, 40 and 50 mA/cm2 on the microstructure and corrosion resistance was investigated. Scanning electron microscopy (SEM) was used to investigate the microstructure. In order to investigate the corrosion behavior of the coatings, potentiodynamic polarization test was used in aqueous NaCl solution of 3.5%. The results of SEM and EDX analysis showed that the coating produced at current density of 40 mA/cm2 was more uniform and had more deposition of titanium oxide and zirconium oxide particles. Also, the polarization results showed that the corrosion resistance of the coated specimen in the current density of 40 mA/cm2 (Rp = 12.3030 MΩ) was higher than that of the coated in current density of 20 (Rp = 12.1950 KΩ), 30 (Rp = 22.2710KΩ) and 50 mA/cm2 (Rp = 8.34020 KΩ). In the higher or less current densities, the coatings were not uniform.

h-BN is a multipurpose ceramic material, with exceptional properties and a wide area of application in industry. It is structurally similar to graphite and it resists oxidation to higher temperatures than graphite. It is used in powder form as a mold release agent in metal casting, as a high temperature lubricant or even in cosmetics. hBN can be shaped by hot-pressing and is used as molds or crucibles for liquid metal handling and as electrical insulator parts . Consumption of hBN has increased in the last decades as a result of its unique properties and its utilization in composite materials . hBN reduces the thermal expansion and friction coefficients, increases thermal conductivity and use temperatures of polymer matrix composites. hBN has also been widely used in ceramic matrix composites to improve thermal shock resistance and machinability . One of the uses of this material in the military industry is in the discussion of bullets and Khan light gun pillows that act as a friction and deviation reducer and increase the speed and point of a higher level as a coating on the surface of the bullet or Khan's gun barrel. Because of the high consumption of this ceramic, various inexpensive methods are under investigation. This paper covers a variety of methods for synthesizing hexagonal nitride powder with an emphasis on the carbetermal method and, in brief, the synthesis of other forms of boron nitride, such as hollow spheres, nanoparticles, nanoparticles, and two-dimensional nanostructures.

In this research, zinc-iron ferrite nanoparticles were synthesized by thermal treatment method. The presence of crystalline phases by X-ray diffraction (XRD) was determined by X-ray diffraction (XRD), which confirmed the presence of crystalline phases in all nanoparticles. The particle size and morphology of the nanoparticles were obtained using Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM), respectively. The magnetic properties of nanoparticles, such as saturation magnetization (Ms) and coercivity field (Hc), and remanent magnetization (Mr) were carried-out by vibrational sample magnetometer (VSM) at room temperature which showed that zinc and iron ferrite nanoparticles had superparamagnetic and ferromagnetic behaviors, respectively. The existence of metal oxides vibration modes were confirmed by a Fourier transform infrared spectroscopy (FT-IR) in all of nanoparticles. The band gap energies were estimated by UV–vis absorption in the range of 1.98 to 2.30 eV, which confirmed Zn1-xFexFe2O4 spinel nanostructures were semiconductors