نشریه علم و مهندسی سرامیک
سال نهم شماره 1 (پیاپی 32، بهار 1399)

Improved magnetic characters of graphene oxides besides its unique biocompatibility make this compound as a theranostics agent could be so practical in the medicine fields. Oxygen functionalities with disturbing the symmetry of graphene sublattices could induce magnetic moments and improve magnetic properties in these structures . While that, vacancies and distortions, created by oxygen release, are also considered as factor disturbing the symmetry of graphene structure and increase its magnetic characters. To consider the effect of oxygen functionalities and deoxygenated defects on the magnetic properties of graphene structure, graphene oxide was synthesized by modified-Hummer method, reduced by distilled water and finally annealed in Argon furnaces. The variation in oxygen bond intensities and level of structural defects was evaluated by Fourier Inferred Transformer and Raman spectroscopy, respectively. And then, their results was matched by vibrating sample magnetometer. The result revealed that the competition between the effect of oxygen groups and deoxygenated defects on the graphene symmetry determinates the magnetic properties of RGOs.

In this study, B4C / SiC nanocomposite powder with 1 to 1 molar ratio was synthesized completely in situ, with high purity and at low temperature by mechanical activation volume combustion synthesis method. At first, raw materials consist of B2O3, Mg, C and Si were weighed. The weighed materials were mixed and milled for 9 hours by planetary ball mil and under argon atmosphere. Milled materials were poured into cylindrical graphite molds with a diameter of 1.5 and 3 cm. The molds are placed in the plasma spark instrument. The synthesis in vacuum occurred at a temperature of less than 300 ° C and less than 3 minutes. After synthesis, a step of acid leaching by 1 molar HCl was applied to remove magnesium oxide. XRD, SEM and EDS analyzes were used to study the samples at different stages. The results of XRD and EDS analysis showed that the sample synthesized in a mold with a diameter of 3 cm (sample with greater volume) and then acid leached had a higher purity (more than 95%). The average crystalline size was calculated by the Sherer equation for each of the components of B4C and SiC, 68 and 57 nm, respectively. Particles of B4C-SiC nanocomposite with a size between 100 and 600 nm were observed in SEM and TEM analysis.

Lead-free (Ba0.85Ca0.15)[(Zr0.1Ti0.9)]O3 (BCZT) piezoceramics were synthesized using solid-state ceramic processing. In order to improve the electrical properties CeO2 and CuO additives/dopants were used and two methods were employed to introduce theses oxides; one, in which 0.1 mol.% CeO2 was mixed with the raw materials and the composition was balanced for A-site substitution (BCCe0.1ZT) and the other where CuO (0.1mol%) was added to the raw materials in the same manner (BCCu0.1ZT) before calcination. After calcination at 1250 °C, sintering additives of CuO and CeO2 (0.04 wt.%) were added to the synthesized powders. The latter was added to BCCu0.1ZT to produce BCCu0.1ZT+0.04Ce and the former was used for BCCe0.1ZT powder to make BCCe0.1ZT+0.04Cu composition. These four samples together with pure BCZT were sintered at 1350°C for 4 h. The microstructure and phase composition were investigated by scanning electron microscopy and X-ray diffraction. Polarization and strain measurements were done using a modified Sawyer-Tower circuit and an optical displacement sensor and temperature and frequency dependence of dielectric permittivity were measured using an impedance analyzer. Our results revealed that BCCuZT+ 0.04 CeO2 sample had the best dielectric properties of ɛr=3585, Pr=15 μC/cm2, Smax=0.047, and d33*=967 pm/V, which was better than pure BCZT at this temperature. Accordingly, these ceramics can be regarded as good candidates to replace previous dielectric materials.

Sodium potassium niobate piezoceramics are considered as lead-free piezoelectric due to their good properties. In this study, the effect of titanium dioxide and molybdenum oxide as dopant on the densification behavior, piezoelectric and dielectric properties of lithium doped sodium potassium niobate ((K0.5Na0.5)0.94Li0.06NbO3, KNNL) was investigated. For this purpose, (K0.5Na0.5)0.94Li0.06Nb0.99X0.01O3 (KNNL-X, X= Mo, Ti) ceramics were synthesized by solid state reaction method. The results showed that the use of these dopants improves the densification of KNNL ceramic, which could be attributed to the increased diffusion due to creating the oxygen vacancy defect. The decrease in the piezoelectric coefficient of KNNL ceramic in the presence of dopants can be attributed to the hardening behavior of the piezoceramic due to the existence of oxygen vacancies. The increase in dielectric constant and decrease in dielectric loss of doped samples can be attributed to the increase in density and decrease in porosity. KNNL-Mo samples showed the lowest piezoelectric coefficient and the highest dielectric constant values.

Due to the conventional understanding of sintering phenomenon in ceramic materials, considering two words of “cold” and “sintering” together may arise a doubt to a ceramic engineer since the usual sintering process has been accompanied by a heating regime at elevated temperatures. Recently, a new technique called Cold Sintering Process (CSP) has been introduced and developed as an ultra-low temperature sintering technique for nano-structured ceramics. With the aim of this process, a variety of ceramic materials can be sintered under uniaxial pressure of 100-500 MPa and at temperatures up to 300 °C. The development of CPS helps to reduce the sintering time and temperature significantly. In addition, this is a promising method for reducing the economic costs, the amount of energy consumption and the environmental damages caused by the use of conventional sintering processes. Besides, some especial microstructures and properties can be expected from ceramics fabricated by CSP method due to such low-sintering temperatures. This review article aims to summarize the latest finding on the cold sintering process for the fabrication of nano-structured ceramics. The history of CPS, introduction of equipment and process components, proposed mechanisms for densification as well as opportunities and challenges are analyzed and discussed. Some ceramic materials which were produced using this method are briefly described with process parameters.

Nowadays, Because of daily reduction of fossil fuels and environmental problems caused by using them, Fuel Cells attracted a major attention as clean and efficient way of generating electrical power. Solid Oxide Fuel Cells (SOFCs) have many advantages to other fuel cell types. High working temperature of SOFCs caused serious challenges including high oxidation rate of interconnects, Spallation and cracks in oxide scale due to mismatch of Thermal Expansion Coefficient (TEC), Cathodic Poisoning and high Area Specific Resistance (ASR) of oxide scale. Manganese containing coatings have overcome these challenges successfully, having unique properties. The purpose of this project is, coating AISI-430 ferritic stainless steel with Cu-Mn Spinel for using as SOFCs interconnects. The coating was done, using Electrophoretic codeposition of CuO and MnO2 with subsequential oxidating thermal treatment for spinel synthesis. Thermal treatment for spinel synthesis was done in 40 hours at 750°C. Phase analysis and microscopic evaluation of coatings showed that Cu-Mn spinel synthesis was done successfully.

Calcium phosphate ceramics has been widely used in the present due to their chemical similarity to bone and good biocompatibility in the physiological environmental and a compatibility with synthetic and natural polymers Recent advancements in additive manufacturing have enabled the fabrication of 3D prototypes with controlled architecture resembling the natural bone. Binder jetting is a versatile method for production of bone scaffolds. In this method the solid is created by the reaction of a liquid selectively sprayed onto a powder bed. The article aims at understanding the link between powder parameters include flow ability, particle size and particle size distribution and printing quality. In this study the powder bed included hydroxyapatite and carboxymethyl chitosan as a mineral and organic constituent of bone respectively. For this purpose, we synthesized carboxymethyl chitosan which is a derivation of chitosan and it is soluble in water. Hydroxyapatite powder and carboxymethyl chitosan was mixed and the properties of the final mixture optimized.

In the area of ​​organizational behavior, leadership as one of the most prominent factors influencing the behavior of the organization's members toward brand performance. The present study aims to investigate the role of transformational leadership style in promoting brand citizenship behavior with the mediating role of employee-based trust to brand. The current study method is descriptive and correlation research project is a type of structural equation modeling. The statistical population consists of all sales and marketing staff of tile and ceramic companies linked with Iran Tile and Ceramic Association. Using random stratified sampling method, 210 individuals had selected as the statistical sample for the study. To collect data, three self-made questionnaires had used to evaluate leadership, brand trust and brand citizenship behavior. The collected data were analyzed using SPSS and AMOS software. The results of structural equation showed that direct effect of trust on brand citizenship behavior of employees is 0.574. The direct effect of leadership style on employee trust is 0.601, positive and significant, and the effect of trust mediator on relationship between leadership style and behavior Brand citizenship 0.84 is positive and significant.