Synthesis of Niobium-Alumina Composite Aggregates and Their Application in Coarse-Grained Refractory Ceramic-Metal Castables

Niobium-alumina aggregate fractions with particle sizes up to 3150 µm were produced by crushing pre-synthesised fine-grained composites. Phase separation with niobium enrichment in the aggregate class 45–500 µm was revealed by XRD/Rietveld analysis. To reduce the amount of carbon-based impurities, no organic additives were used for the castable mixtures, which resulted in water demands of approximately 27 vol.% for the fine- and coarse-grained castables. As a consequence, open porosities of 18% and 30% were determined for the fine- and coarse-grained composites, respectively. Due to increased porosity, the modulus of rupture at room temperature decreased from 52 MPa for the fine-grained composite to 11 MPa for the coarse-grained one. However, even the compressive yield strength decreased from 49 MPa to 18 MPa at 1300 °C for the fine-grained to the coarse-grained composite, the latter showed still plasticity with a strain up to 5%. The electrical conductivity of fine-grained composite samples was in the range between 40 and 60 MMS/cm, which is fifteen magnitudes above the values of pure corundum.

Fabrication of transparent spinel by the reactive spark plasma sintering of spray-dried Magnesia-Alumina nanocomposite without sintering aid

In this project, magnesia-alumina composite granules were prepared using spray drying method. Next, the synthesized powder was sintered at 1400°C for 15 min under 100 MPa pressure through spark plasma sintering without using any sintering aid. The effect of two sintering temperatures of 1400 °C and 1500 °C was explored on the phase formation, density, fracture toughness, and optical transmission within visible and IR ranges. SEM results indicated that the magnesia-alumina composite granules had spherical morphology with the mean particle size of 21 micrometers. The XRD pattern showed that after the spark plasma sintering stage at 1400 °C and 1500 °C, the spinel phase of magnesium aluminate was obtained as in situ. The disc sintered at 1400 °C had greater maximum transmission compared to the samples sintered at 1500 °C (47% vs. ~70%) within the middle IR region because of lower porosity of the sample. The magnesium aluminate spinel sintered at 1400 °C had a density 99.98% of the theoretical density, hardness 18 GPa, and fracture toughness 1.6 MPam1/2.

Scientific Advances and Pharmacological Applications of Marine Derived-Collagen and Chitosan

This work is devoted to investigating the effect of arc welding energy on microstructures and mechanical properties of steel 316L. This later is very useful in industrial, infrastructure transportation, containers shipping, and almost logistic applications. For that reason, five samples of welded steel 316L were carried out based on many parameters to reveal some properties (microstructure, mechanical, corrosion resistance, etc.). To reveal the anticorrosion efficiency. The epoxy/Alumina composite coating on welded steel 316L is tested in 1M HCl acidic media. This manipulation shows excellent corrosion resistance thanks to epoxy/Alumina coated. The choices of this coating are based on the environment, cost and safety. The used epoxy is only degrading with fire but not toxic. Also, it is not a costly method, and it is widely used and performed. Impedance studies on samples of welded steel 316L were conducted in 1M HCl media. The results showed that transfer resistance is increasing with the increase of welding energy. This result was assessed by potentiodynamic polarization measurements indicating a noticeable reduction of current densities with welding energy decrease. The scanning electron microscope (SEM) micrograph was undertaken in order to check how far the studied samples are protected by the used coating in such aggressive media.

Epoxy/alumina composite coating on welded steel 316L with excellent wear and anticorrosion properties

The main purpose of this study is to elaborate anticorrosive coatings for the welded steel 316L, since this later is widely used in industrial field. Hence, within this work we have studied the electrochemical behaviour of different zones of the welded steel 316 in 1 M HCl media. The macrography study of the welded steel has revealed the different areas with a good contrast. We have stated three different zones, namely; melted zone (MZ), heat affected zone (HAZ) and base metal zone (BM). Impedance studies on welded steel 316L were conducted in 1 M HCl solution, coating of Epoxy/Alumina composite was applied on different zones, in order to reveal the anti-corrosion efficiency in each zone. Scanning electron microscopy (SEM) analysis was undertaken in order to check how far the used coating in such aggressive media protects the studied zones and these findings were assessed by water contact angle measurements. The choice of this coating is based on the cost and the safety. We concluded that the Epoxy/Alumina composite has a good protecting effect regarding welded steel in aggressive media.

Effect of hydroxyapatite/alumina composite coatings using HVOF on immersion behavior of NiTi alloys

Hydroxyapatite (HA) coatings have been widely used to improve biocompatibility of metal alloys. This paper discusses the effect of hydroxyapatite (HA) and HA/alumina coated NiTi on their corrosion and dissolution behavior in Phosphate Buffer Saline (PBS) and Ringer’s lactate solutions. The HA was synthesized from biogenic method and used as initial powder in High-Velocity Oxygen Fuel (HVOF) spray technique for the deposition of two coating types, fully HA and HA + 15 wt.% alumina composite coating. The as-synthesized HA had irregular porous structure with relatively low Ca/P ratio of 1.52. Tafel polarization curves obtained from electrochemical test had showed that both coatings increased the corrosion resistance of the NiTi substrates significantly. The ICP-MS analysis results that indicated a low nickel dissolved in both solutions after immersion in 21 days had supported these findings. The nickel levels in the solutions from all samples, either bared substrate or coated samples, in fact below the maximum limit for allergies of the human body. Immersion testing showed the stability of HA and HA/alumina layers as a barrier which maintains its morphology in PBS solution but slightly changed in Ringers.