Structure and magnetic properties of Bi-doped calcium aluminosilicate glass microspheres

Bi-doped CaO–Al2O3–SiO2 glass microspheres with Ca2Al2SiO7 (gehlenite) composition were prepared by combination of solid-state reaction and flame synthesis. The concentration of Bi was 0.0, 0.5, 1 and 3 mol %. The chemical composition of prepared glass microspheres was determined by X-ray fluorescence (XRF). The structural and magnetic properties of prepared glass microspheres and their polycrystalline analogues were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectroscopy and SQUID magnetometry. The closer inspection of glass microspheres surface by SEM confirmed smooth surface and revealed no features indicating presence of crystalline phases. All Bi-doped microspheres are X-ray amorphous, however in case of undoped microspheres XRD detected traces of crystalline gehlenite. XRD analysis of samples crystallized at 1273 K for 10 h revealed the presence of gehlenite as the main crystalline phase. The presence of gehlenite in crystallized samples were also confirmed by Raman spectroscopy. All samples (glass microspheres and their crystalline analogues) showed diamagnetic or weak ferromagnetic behavior at room temperature, whereas paramagnetic or weak ferromagnetic behavior was observed at 2 K.

Application of Ceramsite Dust as an Active Pozzolan Additive in the Cement-Based Compositions

Ceramsite (expanded clay) dust is a waste material, obtained in large volumes all over the world as a by-product of ceramsite gravel production. With the development of the construction industry and the ever-growing amount of ceramsite dust disposed in the landfills, the recycling and rational use of this material is becoming a relevant issue. The currently available technologies for the ceramsite waste recycling are very limited, this is why it is necessary to develop a new effective way to involve this waste into the new production. The present research is based on the assumption that ceramsite dust can be applied effectively as an active pozzolanic mineral additive in the cement-based materials. In order to study the composition, structure and properties of the original clay used for the production of ceramsite, as well as the dehydrated clay dust, captured in the dust removing systems of kilns at ceramsite gravel plants, physical and chemical analysis methods were used. Based on the experimental data, the influence of ceramsite dust on the structure and properties of cement compositions was evaluated. Mechanical tests of the samples showed that the introduction of ceramsite dust as an additive in the amount of 3% by the cement weight leads to an increase in compressive strength by 23% in comparison with the reference composition. The paper also presents the results of microstructural analysis, IR spectral analysis and differential thermal analysis of samples modified with the optimal amount of this microadditive. The study of the microstructure of the modified samples shows that the introduction of ceramsite dust into the composition of the cement stone does not only change the morphology of new formations, thus increasing the density of the structure, but also varies the mineralogical composition of the cement matrix with the formation of stronger and more water-resistant minerals in the form of calcium silicate hydrates and calcium aluminosilicate hydrates. This technology allows the recycling of waste from the production of ceramsite stone, thus improving the environmental situation and contributing to the creation of a circular economy.

Effect of Sputter Deposition on the Adhesion and Failure Behavior between Cu Film and Glassy Calcium Aluminosilicate: A Molecular Dynamics Study

Understanding the physical vapor deposition (PVD) process of metallic coatings on an inorganic substrate is essential for the packaging and semiconductor industry. In this work, we investigate a Copper (Cu) film deposition on a glassy Calcium Aluminosilicate (CAS) by PVD and its dependence on the incident energy. Molecular dynamics simulation is adopted to mimic the deposition process, and pure Cu film is grown on top of CAS surface forming intermixing region (IR) of Cu oxide. In the initial stage of deposition, incident Cu atoms are diffused into CAS bulk and aggregated at the surface which leads to the formation of IR. When the high incident energy, 2 eV, is applied, 20% more Cu atoms are observed at the interface compared to the low incident energy, 0.2 eV, due to enhanced lateral diffusion. As the Cu film grows, the amorphous thin Cu layer of 1 nm is temporarily formed on top of CAS, and crystallization with face-centered cubic from amorphous structure follows regardless of incident energy, and surface roughness is observed to be low for high incident energy cases. Deformation and failure behavior of Cu-CAS bilayer by pulling is investigated by steered molecular dynamics technique. The adhesive failure mode is observed, which implies the bilayer experiences a failure at the interface, and a 7% higher adhesion force is predicted for the high incident energy case. To find an origin of adhesion enhancement, the distribution of Cu atoms on the fractured CAS surface is analyzed, and it turns out that 6.3% more Cu atoms remain on the surface, which can be regarded as a source for the high adhesion force. Our findings hopefully give the insight to understand deposition and failure mechanisms between heterogeneous materials and are also helping to further improve Cu adhesion in sputter experiments.

Effect of Calcium Hydroxide Content on Pozzolanic Reaction of Calcined Clays: Their Mechanical Properties and Microstructures

The research aimed to investigate the effect of calcium hydroxide content on pozzolanic reaction of calcined clays. Pozzolanic reaction of calcined clay was determined in terms of its mechanical properties, phase development and microstructures. Three clay minerals (two kaolinitic clays and kaolinite-montmorillonite clay) were chosen to produce pozzolanic materials via calcination at temperature of 700 °C to allow dehydroxylation of clay minerals. Ratios of calcium hydroxide to calcined clays were varied from 0.1 to 0.5. Mixing water contents or liquid to solid ratios (0.62, 0.75 and 0.80) and curing times (7 and 28 days) were also studied. It was found that calcium aluminosilicate hydrate (stratlingite) could be formed after pozzolanic reactions of all clay minerals. The development of stratlingite agreed with the strength development showing the highest compressive strength at 26 MPa (28 days) when kaolinite-montmorillonite clay was used as pozzolanic material and the ratio of calcium hydroxide to calcined clay was 0.5.

Strength and Durability of Cement-Treated Lateritic Soil

The transportation infrastructure, including low-volume roads in some regions, needs to be constructed on weak ground, implying the necessity of soil stabilization. Untreated and cement-treated lateritic soil for low-volume road suitability were studied based on Malaysian standards. A series of unconfined compressive strength (UCS) tests was performed for four cement doses (3%, 6%, 9%, 12%) for different curing times. According to Malaysian standards, the study suggested 6% cement and 7 days curing time as the optimum cement dosage and curing time, respectively, based on their 0.8 MPa UCS values. The durability test indicated that the specimens treated with 3% cement collapsed directly upon soaking in water. Although the UCS of 6% cement-treated specimens decreased against wetting–drying (WD) cycles, the minimum threshold based on Malaysian standards was still maintained against 15 WD cycles. On the contrary, the durability of specimens treated with 9% and 12% cement represented a UCS increase against WD cycles. FESEM results indicated the formation of calcium aluminate hydrate (CAH), calcium silicate hydrate (CSH), and calcium aluminosilicate hydrate (CASH) as well as shrinking of pore size when untreated soil was mixed with cement. The formation of gels (CAH, CSH, CASH) and decreasing pore size could be clarified by EDX results in which the increase in cement content increased calcium.