Synthesis and Sintering

Effect of welding polarity on iron dilution, clad chemistry, and interfacial microstructure in multilayer SMAW Inconel 625 overlays on

Majid Haghighi Borujeni, Iman Mohammadi, Fardin Nematzadeh — Thu, 10 Sep 2026 04:18:56 -0300

High-strength steels used in the oil and gas industry are susceptible to corrosion in harsh
environments. Although Inconel 625 offers excellent corrosion resistance, its high cost limits
large-scale application. Weld cladding with Inconel 625 provides a cost-effective alternative;
however, excessive dilution with the steel substrate increases iron content and degrades clad
chemistry. This study investigates the effect of welding polarity on iron dilution and clad
chemistry in multilayer SMAW Inconel 625 overlays deposited on SA-387 grade 11 steel.
Three-layer claddings were produced using direct current electrode negative (DCEN) and
direct current electrode positive (DCEP) polarities. Clad chemistry was characterized by
positive material identification (PMI) and scanning electron microscopy with energy-dispersive
X-ray spectroscopy (SEM-EDS). Iron dilution was calculated from measured iron contents.
Under the investigated conditions, the DCEN clad exhibited substantially lower iron content
(3.97 ± 0.12 wt%) compared with the DCEP clad (10.6 wt%). DCEN also permitted a lower
welding current (100–110 A versus 140–150 A for DCEP), resulting in reduced heat input.
These findings demonstrate that DCEN polarity can effectively minimize iron dilution and
produce clad chemistry closer to that of the Inconel 625 filler metal. Corrosion performance
was not directly evaluated in this study and remains a subject for future investigation.

In this study, an SA 387 Gr.11 CL2 steel plate was clad with three layers using the shielded metal arc welding (SMAW) process under two polarity conditions: Direct Current Electrode Negative (DCEN) and Direct Current Electrode Positive (DCEP). Qualitative and quantitative chemical analyses of the clad surface were determined using Positive Material Identification (PMI) alongside Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS). Subsequently, the iron dilution rate was calculated using standard dilution formulas. The results demonstrated that applying the three-layer SMAW process with DCEN polarity reduced the dilution rate from 10% (under DCEP) to approximately 3.9%, indicating lower penetration and a reduced dilution rate compared to DCEP. Furthermore, the use of negative polarity decreased the welding current from 140 A to approximately 110 A, thereby reducing the heat input into the component and mitigating the adverse effects associated with high heat input.

Engineering birefringence in polymers and polymer-based nanocomposites: Mechanisms, characterization, control, and applications

Ali Borchloo — Tue, 01 Sep 2026 10:13:30 -0300

Birefringence is a key optical property of polymers and polymer nanocomposites, influencing the performance of optical, photonic, and electro-optical devices. Precise control of birefringence is essential for polarization optics, optical communication, flexible electronics, smart materials, and stress analysis. Although previous reviews have addressed specific aspects of polymer birefringence, a framework linking molecular and structural origins to processing, nanofiller engineering, characterization, and material design remains limited. This review addresses this gap by providing an integrated and critical analysis of the mechanisms, theoretical models, processing-structure relationships, nanofiller effects, characterization approaches, and emerging applications of birefringence in polymeric systems. Attention is given to polymer chain orientation, crystallinity, molecular anisotropy, residual stress, phase morphology, and the effects of nanofiller dispersion, orientation, concentration, and surface functionalization on refractive-index modulation and optical anisotropy. Theoretical approaches, including the Lorentz-Lorenz equation, stress-optical relationship, and Abbe number, are examined to clarify the relationships among material structure, processing, refractive index, and birefringence. Advanced characterization techniques, including polarized optical microscopy, interferometry, ellipsometry, polarimetry, conoscopic analysis, and electro-optic and magneto-optic methods, are compared in terms of their principles, capabilities, and limitations. Recent advances in optical sensors, waveguides, optical films, liquid crystal displays, biomedical devices, and multifunctional smart materials are highlighted. Unlike earlier reviews that primarily emphasize individual mechanisms, materials, or applications, this review establishes an integrated structure-processing-property perspective. It further provides practical guidance on polymer architectures, processing conditions, nanofiller characteristics, surface-engineering strategies, and characterization methods to achieve targeted birefringence. Finally, current challenges, knowledge gaps, and future research directions are identified to support the rational design of next-generation high-performance optical and photonic polymer nanocomposites for emerging applications in high-performance optical and photonic devices.

Microstructural evolution and mechanical performance of TiO2 nanoparticle-reinforced Fe2O3–Al reactive composites

Mostafa Pasban, Ali Alizadeh, Hamid Reza Baharvandi — Tue, 01 Sep 2026 10:08:01 -0300

In this study, Fe₂O₃-Al reactive composite samples containing different concentrations of TiO₂ nanoparticles (0.1, 0.2, 0.3, 0.4, and 0.5 wt%) were prepared through ultrasonic mixing followed by thermite combustion in sand molds. Before nanoparticle incorporation, the optimum Fe₂O₃:Al ratio was determined as 3:1, which produced the highest iron yield (116.2 g) with a reaction time of 26.43 s, falling within the industrially desirable range of 23–28 s. X-ray diffraction (XRD) analysis revealed that the base sample primarily consisted of α-Fe and α-Al₂O₃ phases, while TiO₂-containing samples exhibited additional peaks associated with FeTi and Fe₂Ti intermetallic compounds. Field-emission scanning electron microscopy (FESEM) coupled with energy-dispersive spectroscopy (EDS) confirmed a uniform nanoparticle distribution up to 0.4 wt%, whereas noticeable agglomeration was observed at 0.5 wt%. Mechanical characterization demonstrated that the sample containing 0.4 wt% TiO₂ exhibited the highest density (7.81 g/cm³, corresponding to a 21.7% increase), hardness (293 HV, 36.3% increase), tensile strength (665 MPa, 35.2% increase), and compressive strength (732 MPa, 18.6% increase). Furthermore, the maximum impact energy (265 J, representing a 61.6% increase) and the highest wear resistance (30% reduction in wear depth) were achieved at the same nanoparticle content. The observed improvements are attributed to combined strengthening mechanisms including grain refinement, Orowan strengthening, crack deflection, and thermal mismatch effects.

Crystallinity control in covalent triazine frameworks: Synthetic approaches and mechanistic insights

Asieh Akhoondi, Bhaskar Bethi, Mohammed Muzibur Rahman — Sat, 27 Jun 2026 00:00:00 -0300

An important class of emerging porous organic materials is covalent triazine frameworks (CTFs), which have attracted much attention in wastewater treatment, energy conversion, and gas absorption due to their chemical and thermal properties and high nitrogen content. The synthesis of CTFs faces several challenges, including the reversibility of the reactions, which leads to structural defects and poor crystallinity. As a result, achieving high crystallinity is a major goal in the research and development of CTFs. This brief review focuses on the latest advances in the synthesis and control of crystallinity of these nitrogen-rich materials. The paper proceeds in order to review the principles governing crystal formation, the synthesis methods and factors affecting the reactions, and the final operations to prepare the product to enhance crystallinity. In addition, common crystallinity assessment techniques, including powder X-ray diffraction, Fourier transform infrared spectroscopy and advanced analysis, are reviewed. The effect of framework crystal structure on performance optimization is also discussed. Finally, challenges and future prospects in the development of synthesis techniques for the technological advancement of CTFs are presented.