فصلنامه مواد پیشرفته در مهندسی
سال چهل و سوم شماره 4 (زمستان 1403)

The sintering of ZrB2 presents significant challenges due to its covalent bonding and the high temperatures required for the process. Prior research has demonstrated that incorporating up to 20% by volume of SiC as an additive can enhance both the sintering process and the mechanical properties of ZrB2-based composites. The objective of this study was to fabricate and characterize an ultra-high temperature ceramic composite composed of ZrB2 containing 20 vol. % SiC, utilizing the Spark Plasma Sintering (SPS) method with a multi-step approach at various temperatures. Additionally, the study sought to investigate the influence of a TiC additive on the microstructural evolution and mechanical properties of the composite. The research focused on assessing the impact of sintering temperature, ranging from 1600°C to 1900°C under a pressure of 30 MPa, in the presence of a 10 vol. % TiC additive. The introduction of up to 10% by volume of TiC into the ZrB2-20 vol. % SiC composite, followed by sintering at 1800°C for 5 minutes, resulted in the formation of (Zr,Ti)B2 and (Ti,Zr)C solid solutions within the matrix. These solid solutions, along with reactions involving surface oxides such as ZrO2 and B2O3, contributed to a 15% increase in relative density. Furthermore, notable enhancement was observed in the mechanical properties, including a 14% increase in hardness, a 12% increase in elastic modulus, a 20% increase in fracture strength, and an 8% increase in fracture toughness. A comparative analysis with previous studies revealed that employing a multi-step SPS technique, as opposed to a single-step process, significantly reduced the temperature and time of the process to achieve a relative density exceeding 99%. However, it was also observed that increasing the maximum sintering temperature to 1900°C in the ZrB2-20 vol. % SiC-10 vol. % TiC composite resulted in excessive grain growth and a slight decrease in relative density by approximately 1%.

Titanium dioxide nanoparticles have been attention due to their biocompatibility, mechanical strength, photocatalytic properties, and affordability. In this research, green synthesis and optimization of the synthesis parameters of titanium dioxide nanoparticles by means of aloe vera extract were investigated. The synthesis parameters include the concentration of titanium dioxide precursor, solvent (deionized water), and aloe vera extract. Upon synthesis of titanium dioxide nanoparticles, a range of techniques were employed to characterize the resultant structure. These tests include X-ray diffraction, fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, zeta potential, scanning electron microscope, and X-ray energy dispersive analysis. The results showed that the synthesized titanium dioxide nanoparticles were formed in the crystalline phase of anatase. Also, according to the SEM images, titanium dioxide nanoparticles were spherical in shape with the size range of 31 ± 5 nm. The results of the ultraviolet-visible spectroscopy showed that all samples were in the ultraviolet and visible light ranges. The optimal sample of synthesized titanium dioxide nanoparticles was selected after accomplishment of the characterization tests. Cytotoxicity test was performed on fibroblast cells (L929) for 24 hours to investigate the biological performance of the optimized titanium dioxide nanoparticles. The results revealed the non-cytotoxic nature of titanium dioxide nanoparticles, further confirming their potential for medical applications.

The purpose of this paper is to investigate the manufacturing of a steel wall using gas metal arc welding (GMAW) process and to study its dimensional features, mechanical properties, and the microstructure. The selected parameters were the interpass dwell time, the welding speed, and the wire feeding speed. Based on the results, the average wall height and thickness decreases with increasing welding speed due to less weld deposition in the layer. A relationship between the wall thickness and height in terms of the welding speed and wire feeding speed was proposed. A longer interpass dwell time increased the wall height. The effective area percentage also increased with increasing welding speed. Tensile strength and elongation (%) were investigated based on the presence or absence of voids and microstructure. In high welding speed and long interpass dwell time, the microstructure included columnar grains with fine widmanstätten ferrite and intergranular pearlite. At low welding speed and short interpass dwell time, the microstructure consisted mostly of blocky ferrite and coarse pearlite. Both of these structures showed satisfactory strength and elongation. But in the other conditions, where the possibility of brittle phases in the heat-affected zone was higher, the strength and elongation decreased.

The aim of this research was to investigate the effect of milling time on the properties of HfB2-ZrB2-TiB2 ceramic. For this purpose, HfB2, ZrB2, and TiB2 powders with equal volume ratios were ground for 15, 30, and 45 hours and sintered using spark plasma sintering method at 2000 °C. X-ray diffraction was employed for phase identification. Microstructural studies were performed using a scanning electron microscope. The hardness and fracture toughness of the samples were evaluated using the Vickers hardness test and crack length measurement, respectively. The X-ray diffraction  results of the ground powders showed that the size of the crystallites decreased from 106.9  nm to 59.2 nm with increasing the grinding time from 15 to 45 hours. As a result of sintering process, the number and intensity of the peaks decreased significantly indicating the reduction of oxide impurities and the formation of a solid solution. Increasing the milling time led to the formation of further solid solution. The maximum values ​​of relative density, hardness, and fracture toughness in the sample milled for 45 hours were obtained to be 99.8%, 27.3 GPa, and 5.5 MPa.m0.5, respectively.

NO2 is known as one of the most dangerous air pollutants. Even extremely low concentrations of this gas could cause life-threatening diseases such as cancer. Ppb-level detection and measurement of this gas are still serious challenges for researchers. In current work, for the first time, K2CO3/Al2O3 composite material, was employed as solid electrolyte to fabricate a potentiometric sensor for the detection of extremely low NO2 concentrations (in the ppb range) at room temperature (RT). This material was chemically synthesized through a low-cost and facile process and then loaded into appropriate templates, forming rectangular-cube shaped ceramics. A thin layer of gold nano particles was sputtered on the both sides of ceramics’ top surface to provide external electrical connections. The sensor’s dynamic responses were recorded in the concentrations ranging from 15 to 1500 ppb at RT, and it was observed that its response variations corresponds the Nernst equation. This sensor’s limit of detection (LOD) was recorded as 15 ppb which is much lower than that of  the standard threshold for safe industrial environments (200 ppb). Tipically, the sensor’s response (ΔV = Vgas – Vair, where Vgas and Vair are its voltages in NO2 contaminated air and clean air, respectively) toward 60 ppb NO2 at RT is equal to 14 mV. In the entire evaluated concentration range the rise and recovery times did not exceed 80 s. Therefore, this sensor could be considered as a promising candidate for air quality control applications at RT.

The presence of lead as the first radiation shielding with a series of good features such as high density and having some flexibility and a series of inappropriate features such as toxicity, low physical and chemical stability, and high weight, has long made scientists think about alternatives. In this research, the protective properties against gamma radiation of polymer compounds with oxide (gadolinium-bismuth tellurium) (Gd2O3)x (TeO2)(30-x) - (resin)30 - (Bi2O3)40 (which here x is 10, 15, and 20% by weight percent) and (Gd2O3)x-(TeO2)(40-x) (resin)20 – (Bi2O3)40 (where x is 20, 25, and 30 by weight percent) was examined using the Monte Carlo simulation tool Gent4 in the range of 0.015 to 15  MeV. In this study, the quantities related to photon attenuation such as linear attenuation coefficient, mass attenuation coefficient, one-tenth-value layer, half-value layer, effective atomic number, effective electron density, the total atomic cross section, the total electron cross section, and the mean free path as well as the spectrum of secondary particles created according to their type and energy for different levels of incident gamma energy have been evaluated. The mass attenuation coefficient values ​​calculated from Geant4 were compared to the Phy-x results to validate the simulation results. The results showed a good agreement with each other. The agreement between the data revealed that the Geant4 tool was a good method to examin the properties of gamma ray shielding. The obtained results declared that the development of resins with the addition of oxides of transition metals such as gadolinium, tellurium, and bismuth increases the protective against gamma rays.