نشریه علم و مهندسی سرامیک
سال ششم شماره 4 (پیاپی 23، زمستان 1396)

Boron carbide due to properties such as high hardness, high Young's modulus and low density is highly regarded; however its application is limited because of unsuitable sinterability, low fracture toughness and the low wettability of it with melt of most metals. In this study, the surface of B4C is coated with electroless method and the effect of ethylene diamine (C2H8N2) complexing agent at temperatures of 75 and 85 °C and a pH of 13 is examined. Scanning electron microscope equipped with EDS analyzer for investigation of microstructure and morphology of coated B4C powder and X-ray diffraction to determine the composition and phases were used. The results indicate that in the electroless coating process, the amount of the C2H8N2 complexing agent in the plating bath has significant effect on the quantity of coating and uniformity of it on the surface of the B4C particles. By increasing the C2H8N2 complexing agent in the electroless plating bath in each of the constant temperatures of 75 and 85 °C, the nickel coating is reduced. The phase analysis of coated B4C particles in the electroless nickel plating bath with different amounts of the C2H8N2 complexing agent as compared to nickel salt at a temperature of 85 °C showed that in all four composition of complexing agent, B4C and Ni phases are present. However, in ratios of 1: 1 and 1: 3 of C2H8N2 complexing agent to nickel salt, Ni(OH)2 phase is also visible.

In this study, nano yellow pigments were fabricated by doping of chromium and antimony elements into TiO2 using chemical precipitation and solid state method and after transforming them to ink, their printing performance on the ceramic surface were investigated. The precursor to doping antimony to white rutile structure of TiO2 was SbCl3, while Cr(NO3)3 and K2CrO4 were the precursors for chromium doping by solid state reactions. The fabricated nano pigments were characterization by x-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis which showed different morphology, structure and color. Particle sizes which were estimated by SEM image were between 50 to 170 nanometers which is appropriate for ink-jet printing on the ceramic. XRD results showed the pigment synthesized by Cr(NO3)3 (sample A) had a mono-phase compound while the sample synthesized by K2CrO4 (sample B) consisted of a multi-phase compound. The pigments were transformed to ink by milling method and using an ester media. After printing process, the ceramics were analyzed by Diffuse Reflectance Spectroscopy and colorimetric measurement (CIE L*a*b*). The h° value from colorimetric measurement of A nano pigment, was 76.59 while for B was 79.18. This shows better yellow color of B. After printing the prepared ink of each pigment, h° value changed to 69.59 for A and to 81.14 for B. Therefore, the ink of A nano pigment declined to golden yellow after printing while the ink of B nano pigment presented a pure and better yellow color.

In the present study, the role of morphology of nanoparticles (NP) of titanium and zinc oxide and nanorods (NR) of zinc oxide with graphene was investigated on the properties of the Dye-Sensitized Solar Cell, In this regard, TiO2 nanoparticles are deposited on ZnO nanorods and nanoparticles, covered on graphene (G) and reduced graphene oxide (RGO) on doped tin oxide glass with fluorine (FTO) using the Dip coating device respectively. Then, the thin-layer nanoparticles made into the N719 pigment solution for 24 hours were sensitized, and subsequently the thin-film nanocomposites (photo-anodes) were bonded with a platinum electrode, and the electrolyte was injected into the cell through the cavities contained in the platinum electrode. EIS, XRD, IV and FESEM techniques were employed for identification of phase analysis, microstructural, electrical properties and optical properties. The results showed that not only the morphology of the ZnO layer but also the type of TiO2 coating process affects the properties of the (G / RGO) -ZnO-TiO2 nanocomposites. According to the results, nanocomposite RGO-ZnO (NP) -TiO2 (NP), in which TiO2 was coated on ZnO nanoparticles, had higher yields than RGO-ZnO (NR) -TiO2 (NP) samples with the presence of ZnO nanorods. Also, the presence of functional groups on the photo-anode surface due to the presence of RGO in these specimens has lower electrical conductivity and efficiency, the results of the G-ZnO-TiO2 nanocomposite confirm the above result.

ZrB2­­-SiC-based ultrahigh temperature composites were fabricated by spark plasma sintering and reinforced with different amount of graphite nano-flakes (0, 2.5, 5, 7.5 and 10 wt%). Sintering process was performed at a temperature of 1900 °C for a dwell time of 7 min under an applied pressure of 40 MPa in a vacuum atmosphere. The effect of graphite nano-flake on the hardness and fracture toughness of samples were studied. The results showed that with increasing the nano-graphite content, the hardness of composites linearly decreased from 19.5 GPa for the graphite-free sample to 12.1 GPa for the composite reinforced with 10 wt% nano-graphite. An inverse trend was observed for the fracture toughness of ceramics, as it was increased from 4.3 MPa.m1/2 for the graphite-free sample to 8.2 MPa.m1/2 for the 7.5 wt% nano-graphite doped composite. The drop in hardness values, with increasing the nano-graphite content, was related to the intrinsic softness of graphite phase. However, an obvious enhancement in the fracture toughness values due to the addition of more graphite nano-flakes was attributed to the activation of several toughening mechanisms in such materials.

In this research the powders of TiO2, WO3 and graphite were mixed and after milling with WC balls, the reduction procedure was carried out separately under vacuum and nitrogen pressure. After blending the produced powder with Ni and the secondary carbides, (Ti0.93W0.07) C/C0.7N0.3-20 Ni based cermets were obtained through sintering at 1510 °C. To characterize the synthesized materials, XRD analyzer, SEM and EDS, STEM and hardness examiner were used. With the evaluation of core/rim included microstructures, it was observed that the addition of secondary carbide and also nitrogen in the reduction procedure, has a remarkable influence on the size of cermet microstructure. By the addition of nitrogen, the size of (Ti0.93W0.07) C microstructure was decreased about 3 µm. In this investigation it was shown that the increase of Mo2C from 2 to 8%, the amounts of tungsten and molybdenum elements were decreased in the core area. The weight percentages of W and Mo were changed from 20.01 to 19.5 and from 0.14 to 0.08, respectively. Also, in the rims, the weight percent of Mo, was significantly increased from 4.67 to 11.43. Furthermore, with the addition of just 2% Mo2C, the hardness of this composite material increased remarkably.

In recent years, SiC-TiC nano composite, attracted a lot of interest due to it's good electrical and mechanical property at high temperatures. In this study, nano composite powder of SiC-TiC using Titanium(IV) isopropoxide, Tetraethyl orthosilicate, Sucrose and nitric acid through Sol-gel method were synthesized. After mixing at 60 ℃, after 5 hours, the viscosity of the solution increased and the gel was fabricated. Produced gel heated at 110 ℃, then, the sample heated at 1500℃ under an argon atmosphere for 1 hour. Thermal analysis of the prepared gel from 25 ℃ to 1300℃, revealed decomposition of organic compounds in the temperature range between 200 ℃ to 400℃, In addition, sucrose carbonization was observed. XRD results showed that SiC and TiC have been formed because of reaction amorphous silica and titania with carbon at 1500 ℃. For evaluation of dimension and morphology of the synthesized powder, field emission scanning electron microscopy (FESEM) was used. The size of sample particles were between 20 and 70 nm.

In the current study, we have used solvothermal method to synthesize single phase calcium ferrite particles coated with polyethylene glycol (PEG) in ethylene glycol medium. Four samples, one of which with no PEG and three of which with different amounts of PEG, were synthesized and undergone several characterization analyses. The crystallite size, phase and morphology of the particles were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The XRD patterns are related to single phase calcium ferrite particles with cubic spinel structure. The elemental analysis results from the EDX analysis proved the presence of Ca, Fe and oxygen in the bare calcium ferrite sample. The presence of the PEG on the coated samples was confirmed using thermogravimetric (TG) analysis. The magnetic properties of the particles were measured by vibrating sample magnetometry (VSM) method. The presence of the PEG on coated samples was further confirmed by the decrease of saturation magnetization values in proportion to the coating agent amount. The heat generation capability of the particles using a high frequency alternative magnetic field indicated that the particles are able to dissipate remarkable heat amount, making them suitable for hyperthermia applications.