In this work, the electrochemical performance of various Membrane Electrode Assemblies (MEAs) using Nafion (R) membranes (NR211, XL, NR212 and N115) incorporating low platinum-loading electrodes (0.05 and 0.1 mgPt cm-2), developed with two different commercial catalyst 60% Pt/C and 40% Pt/C, have been evaluated. The electrodes were manufactured depositing the catalytic ink, prepared with catalyst HiSPEC4000 and HiSPEC9100, onto the gas diffusion layers, by wet powder spraying. In order to carrying out this study, a robust testing protocol for Proton Exchange Membrane Fuel Cells (PEMFCs) was designed, consisting of three steps: activation, polarization curve measurements (current-voltage), and Electrochemical Impedance Spectroscopy (EIS). Tests were repeated to assess the effects of oxidant (air or oxygen) and operating pressure, with parameters adjusted sequentially: air atmospheric -> air + 1 bar -> air + 2 bar -> O2 atmospheric -> O2 + 1 bar -> O2 + 2 bar. Results point out that, by the increasing of the back pressure consistently, the maximum power density across all four MEAs is improved, regardless of oxidant. Switching from air to oxygen led to significant power increases of 57.3, 56.6, 54.3, and 37.2% for MEAs with Nafion (R) NR211, XL, NR212, and N115, respectively. This suggests that thicker membranes result in higher PEMFCs performance due to lower internal resistance. The MEA with Nafion (R) NR211 (25 mu m thickness) achieved the highest performance, emphasizing that reducing membrane thickness enhances functionality. This insight will inform future research on optimizing membrane thickness. Additionally, reducing platinum content in the catalyst from 60 to 40% Pt/C in NR211 and NR212 membranes showed stable performance, confirming their suitability with lower Pt concentrations. The new catalyst formulation performed better than the previous one under H2/O2 and higher back pressures, where lower Pt loading limitations become more apparent.
This study focused on the development of insulating refractory bricks using quartzite, with a comprehensive analysis of their mechanical and thermal properties. The bricks were made from quartzite with 10% bentonite binder and water, added for mixing. Various tests were done (Xray Fluorescence, Thermogravimetric and Differential Thermal Analyses, apparent porosity, shrinkage, Loss on Ignition (LOI), compressive yield stress, and water absorption (WA)), following American Society for Testing and Materials' procedures. Microstructural analysis of the sample was observed using Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS). These results provided valuable insights into the stability of the developed refractory bricks at high temperatures. Analysis of chemical composition from quartz bricks revealed significant SiO2 content (94.303%), emphasizing the material's superior refractory properties. LOI (0.5%) and shrinkage (0.2%) results indicated enhanced performance with good thermal stability and strength. Compressive stress yield indicated that the material exhibits good strength relative to the amount of binder used. WA results confirmed that the brick sample is suitable for high-temperature applications. SEM/EDS analysis unveiled intricate microstructural features, affirming the bonding agent's influence on the material's composition.
This work sought to establish whether starting particle size (SPS) is an important parameter on the properties of hydroxyapatite (HAP) extracted from cattle bone (CB) waste material by heat treatment, for biomedical applications, such as temperature and holding time. CB was processed to obtain micron-sized particles of 50, 150, 250 and 350 & micro;m. The powders were heated to a constant temperature and holding time of 900 degrees C and 3 h, respectively, to enable their transformation into HAP. Evolved HAP was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR). Results indicated that physico-chemical properties were very sensitive to SPS of CB. XRD results revealed that crystallite size and degree of crystallinity of evolved HAP increased with greater SPS. Based on EDX results, concentration of essential elements of Ca, P, O and C in HAP also varied according to SPS increasing from 36.0 to 50.5 wt. % for Ca, decreasing from 13.7 to 9.9 wt. % for P, 36.2 to 29.6 wt. % for O and 12.6 to 9.3 wt. % for C. FTIR spectra indicated that concentration of functional groups is sensitive to SPS, with amounts of OH- and PO43- increasing, while CO32- decreased with an increase in SPS. Thus, SPS is an important parameter in evolution of HAP from CB waste via calcination process.
Residual stresses formed during quenching can significantly impact the integrity of engineering components. This study examined how varying immersion speeds in water affected both mechanical behavior and residual stress distribution in SAE 1025 steel. To achieve this, a hybrid approach combining finite element simulations (using ANSYS 2020 R1 and JMatPro) with controlled laboratory experiments was employed. The immersion speed control mechanism was developed and calibrated. Steel samples were quenched at five immersion speeds, ranging from 0.05 to 0.8 m/s. Metallographic analysis, Vickers microhardness testing and tensile testing were assessed and then compared to simulation predictions. A significant finding was the 83% reduction in maximum residual stress as immersion speed increased from 0.2 to 0.8 m/s. Furthermore, residual stress was significantly lower at the leading (first-contact) end of each sample and higher at the trailing end. Simulation results showed strong agreement with experimental findings, achieving an average error of 7.5% across the temperature range and a correlation coefficient (R2) of 0.97. Ultimately, the prediction of residual stress distributions achieved in this study will enable the production of safer and more durable components, critical for demanding engineering applications where performance and integrity are non-negotiable.
This study investigated theoretical methane potential (TMP)and biochemical methane potential (BMP) of Longkong (Lk) waste (peel and seed) and fruit pulp, and Napier grass (NG). TMP values were calculated using modified Buswell stoichiometric equation, while BMP assays were conducted to determine methane (CH4 ) production. TMP results showed that Lk waste had higher theoretical CH4 yield (0.5 L/g) of volatile solids (VS) than that from Lk pulp (0.39 L/g VS) and NG (0.46 L/g VS). BMP results showed that measured CH4 yield was 0.21, 0.3 and 0.33 L/g VS for Lk waste, Lk pulp and NG, respectively. Lk peel is a more suitable substrate for biogas production compared to its pulp, due to high moisture content, low alkalinity and high volatile fatty acid of the latter. CH4 potential of the three substrates compared favorably with those of others such as grapes and banana peels. The study recommends Lk peels and its leftover pulp for biogas production in regions with high cultivation.
