Cement production, the primary material used in construction industry, accounts for around 8% of global CO2 emissions. In addition to the demand for materials that emit greenhouse gases, the sector generates approximately 50% of solid waste in Brazilian cities. Geopolymers, which utilise industrial by-products rich in chemically activated aluminosilicates, are emerging as a sustainable alternative to Portland cement. One of the main components of brazillian construction and demolition waste (CDW) is red ceramic, which, due to its firing temperature, contains a high proportion of metakaolinite, an amorphous, pozzolanic and highly reactive aluminosilicate. This study aims to develop a sustainable sealing brick using CDW as the main geopolymer precursor. CDW was activated with highly basic NaOH solutions to form the geopolymer paste. Pulverised CDW was analysed by XRF and XRD, confirming presence of Al and Si, as well as crystalline phases such as α-quartz (SiO2), hydrated calcium silicate (CaH2O4Si) and calcite (CaCO3). After determining the solid/liquid ratio (Casagrande apparatus), cylindrical test specimens were prepared using mixtures of CDW, hydrated lime and alkaline solution in four compositions. Compression tests on the probes exceeded the minimum compressive strength value specified by brazilian (>1.5 MPa) and european (>2.5 MPa) standards for fired ceramic bricks.
The effects of chemical zoning and radiation damage on U-Pb isotopic behavior were investigated in apatite from the Borborema Province and zircon from the Carajás Province, Brazil, using optical microscopy and LA-ICP-MS. Sample BJ19C, characterized by homogeneous fission-track distributions, yielded a concordia age of 569.6 ± 1.7 Ma, however, individual analyses showed 87.7 Ma of age dispersion and intra-grain offsets of up to 29.2 Ma. In contrast, chemically zoned CEBP035 yielded a concordia age of 538.6 ± 1.2 Ma and intra-grain age offsets of up to 85.6 Ma. A separate Raman case study of a single representative grain (CEBP035-G01) showed broader ν1 (PO4) bands in U-rich domains, with FWHM increasing from 3.2 to 4.4 cm−1, while the phosphate framework remained largely crystalline. For zircons, etched aliquots exhibited distinct spot distributions along similarly oriented discordia trends. Isotopic patterns were sample-dependent: sample C16 showed tighter regression alignment, C20 displayed a wider spatial distribution, and C23 showed no statistical change. Etched and unetched populations yielded equivalent upper-intercept ages. The results indicate that chemical heterogeneity and radiation damage contribute to U-Pb dispersion in apatite and zircon, while chemical etching modifies the analytical response of metamict zircon without systematically changing the inferred crystallization age.
In this work, Density Functional Theory (DFT) calculations were employed to investigate the structural stability and magnetic behavior of c-BN/h-BN heterostructures with different phase proportions (20/80, 40/60, 50/50, 60/40, and 80/20). The results reveal that heterostructures containing thin c-BN regions (20/80 and 40/60) undergo pronounced structural reconstruction toward hexagonal-like configurations during relaxation. In contrast, higher c-BN concentrations (50/50, 60/40, and 80/20) preserve the coexistence of sp2- and sp3-like arrangements, exhibiting enhanced structural stability and reduced interfacial distortions. Additionally, localized magnetic ordering emerges only in the heterostructures that preserve the cubic domains, indicating a strong correlation between the magnetic response and the stability of the sp3 network. These findings demonstrate that the structural and magnetic properties of c-BN/h-BN heterostructures are strongly governed by the cubic phase proportion.
Alpha particles emitted by the radioactive decay of uranium and thorium within zircon (ZrSiO4) grains produce latent damage trails in adjacent solid-state nuclear track detectors that can be made visible by controlled chemical etching. This work investigates the evolution of these alpha-particle tracks in CR-39 (allyl diglycol carbonate) detectors coupled to zircon grains from the Kawamoto Granodiorite (OD3) geochronological standard. Detectors were subjected to chemical etching in NaOH solution at 70 °C for durations of 90, 200, 300, and 400 minutes, enabling systematic characterization of track density and morphology as a function of etching time. Track density was quantified by optical microscopy and expressed as tracks per unit area (tr/cm2). Complementary microstructural characterization was performed by scanning electron microscopy (SEM) and cathodoluminescence (CL) imaging, enabling correlation between internal crystal heterogeneities and spatial track distributions. Raman spectroscopy using a Renishaw inVia confocal micro-Raman spectrometer provided additional quantitative characterization of radiation damage at the micrometer scale. The results demonstrate that track development follows a well-defined kinetic regime, with density increasing continuously from 90 to 300 minutes and stabilizing thereafter; the interval between 200 and 300 minutes is identified as the optimal etching window. The heterogeneous spatial distribution of tracks reflects the microstructural state of the host grain, particularly compositional zoning, radiation-induced structural damage (metamictization), and microfractures, all of which modulate alpha-particle emission and detection efficiency. Raman mapping further suggests that regions of elevated track density coincide with domains of broader Raman bands and lower peak positions. These findings have direct implications for the accuracy of (U–Th)/He thermochronology and for the broader use of CR-39-based alpha spectrometry in geochronological and materials science applications.
The combination of tungsten carbide (WC) and cobalt forms the most common cemented carbide on the market, as it is one of the most widely used materials industrially due to its excellent combination of properties. However, the search for a substitute binder is motivated by cobalt's high cost, toxicity, and low corrosion resistance. In this scenario, nickel (Ni) has stood out for meeting the necessary requirements and offering good corrosion resistance. However, its product presents a loss in mechanical properties. To improve these properties, the addition of alloying elements, such as aluminum (Al), was studied. This work aims to compare the micro-abrasive wear resistance of WC-Co and WC-Ni-Al cemented carbide. The micro-scale abrasion tests were carried out in a test rig with fixed-ball configuration, AISI 52100 steel ball and abrasive slurry composed of water and silicon carbide (SiC). The volume loss of the samples was the parameter used to determine micro-abrasive wear resistance. The samples were characterized before and after testing using scanning electron microscopy to identify the predominant wear mechanisms. WC-Ni-Al cemented carbide presented a microstructure similar to WC-Co, but pores and binder islands were observed. The micro-scale tests showed that WC-Ni-Al cemented carbide, despite its higher porosity, presented superior micro-abrasive wear resistance than WC-Co cemented carbide, indicating that the addition of Al contributed significantly to the increased wear resistance of this cemented carbide. This result also demonstrates the feasibility of using WC-Ni-Al cemented carbide as a substitute for WC-Co in applications involving abrasive wear.
