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A nickel matrix with silicon carbide nanoparticles composite coating is prepared by electrodeposition on non-alloyed steel, assisted with an ultrasonic treatment of the galvanic bath. The abrasion and erosion wear resistance of the coating is determined, as well as its micro-hardness. The structure and the composition of the nickel nanocomposite coating is defined using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The corrosion behavior is investigated by the potentiodynamic polarization methods in the 3.5 wt% sodium chloride solution. The results show improved mechanical properties, wear and corrosion resistance as compared to the nickel metallic coating. [ABSTRACT FROM AUTHOR]

In the present study a biowaste, in the form of chicken eggshells, is used for producing a biomaterial - hydroxyapatite by a conventional chemical precipitation method. Hydroxyapatite is a major component of human hard tissues, such as bones and teeth, which makes it a paradigmatic bioactive material. The first step in the synthesis of hydroxyapatite from eggshells is the transformation of their main component calcium carbonate into calcium oxide at 1000 °C. Afterwards, calcium oxide is hydrated in order to produce calcium hydroxide. Hydroxyapatite is then synthesized by the addition of the phosphoric acid. The phase composition of the eggshells is examined by the powder X-ray diffraction. The surface morphology of the sintered product is determined by the scanning electron microscope equipped with the energy dispersive spectrometer. Powder X-ray diffraction and scanning electron microscope analyses confirmed hydroxyapatite as the main phase of the final product. The reuse of chicken eggshells reduces the amount of biowaste, as well as the need for the biowaste management. This investigation shows that the eggshells can be a useful raw material for the synthesis of valuable biomaterials. [ABSTRACT FROM AUTHOR]

The paper presents the preparation of biocomposites from waste seashells as reinforcement and poly(methyl methacrylate), abbreviated as PMMA as the matrix. The used seashells belong to the snow-white Bahamian species of tiger lucine (Codakia orbicularis) from the Island of Coco Cay. Seashells were grinded and homogenized with poly(methyl methacrylate) powder, with the seashell powder content ranging between 2 and 14 wt%, and finally hot pressed. Morphology of prepared composites was analyzed by scanning electron microscopy, and it was determined that the particle distribution was homogenous with no agglomeration. Mechanical properties (microhardness, compressive strength, Young's modulus) of biocomposite materials produced from different amount of waste seashells in poly (methyl methacrylate) were determined and analyzed. The best overall combination of mechanical properties was achieved when 6 wt% of seashell particles below 50 μm size were added to poly (methyl methacrylate). [ABSTRACT FROM AUTHOR]

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This study aims to evaluate the recycling potential of solid waste alumina powder (WAP) by utilization of the two-step sintering (TSS) process. For the study, WAP was collected as an industrial scrap after the machining process for the formation of green alumina compacts. The alumina samples were prepared according to the slip casting method by preparing suspensions containing commercial alumina with 0.8 μm average particle size and by adding up to 20 dwb. % (i.e., expressed on a dry weight basis) of WAP with 3.4 μm average particle size. The samples were sintered at optimized TSS conditions and compared with conventional one-step sintering (OSS) by conducting morphological analyses. The average grain size (AGS) was determined from the obtained field emission scanning electron microscopy (FESEM) images, while the sample porosity was calculated based on apparent densities. The obtained micrographs after TSS implementation revealed a partially textured microstructure. Furthermore, a comparison of the mechanical properties of alumina samples lacking or containing 20 dwb. % of WAP obtained after sintering is presented. The indentation fracture toughness (~3.2 MPa m 1/2 ) and Vickers hardness data (~14.5 GPa) showed a positive effect of adding WAP to alumina samples. The slightly improved mechanical properties of ceramic samples containing waste alumina are a consequence of lower porosity, which is due to the remaining sintering additives in WAP. The collected results demonstrate the possibility of using TSS for sintering ceramic materials that contain WAP.

In the present work, alumina (Al 2 O 3 ) foam was prepared by the replica method where a polyurethane (PU) foam (30 pores per inch (ppi)) template was impregnated with a 60 wt.% Al 2 O 3 suspension. Sintered Al 2 O 3 foam was used as substrate for the deposition of sol-gel derived titania (TiO 2 ) film using dip coating. For the preparation of TiO 2 sol, titanium(IV) isopropoxide (Ti-iPrOH) was used as the precursor. The common problem of qualification and quantification of a crystalline coating on a highly porous 3D substrate with an uneven surface was addressed using a combination of different structural characterization methods. Using Powder X-ray Diffraction (PXRD) and synchrotron Grazing Incidence X-ray Diffraction (GIXRD) on bulk and powdered Al 2 O 3 foam and TiO 2 -coated Al 2 O 3 foam samples, it was determined Al 2 O 3 foam crystallizes to corundum and coating to anatase, which was also confirmed by Fourier Transformed Infrared Spectroscopy (FTIR). Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDS) revealed the structural and microstructural properties of the substrate and coating. Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA) were used to clarify the evolution of the porous microstructure. The Al 2 O 3 -TiO 2 composite was evaluated as a photocatalyst candidate for the degradation of the micropollutant medication memantine. The degradation rate was monitored using a light-emitting diode (LED) lamp operating at electromagnetic (EM) wavelength of 365 nm. The photocatalytic activity of sol-gel-derived TiO 2 film immobilized on the Al 2 O 3 foam was compared with commercially available TiO 2 nanoparticles, P25-Degussa, in the form of a suspension. The levels of memantine were monitored by High-Performance Liquid Chromatography-Tandem Mass Spectrometry (HPLC-MS/MS). The efficiency and rate of the memantine photodegradation by suspended TiO 2 nanoparticles is higher than the TiO 2 -coated Al 2 O 3 foam. But, from the practical point of view, TiO 2 -coated Al 2 O 3 foam is more appropriate as a valuable photocatalytic composite material.

Alumina (Al 2 O 3 ) and zirconia (ZrO 2 ) have good overall properties and thus are widely used oxide technical ceramics. The biggest drawback of Al 2 O 3 is its low fracture toughness. In contrast, ZrO 2 is relatively tough, but is also much more expensive. In order to improve the alumina toughness, composite ceramics are being developed. Slip casting technology has economic advantages over the conventional hot isostatic pressure technology, but problems may arise when preparing stable highly-concentrated suspensions (slip) for filling the mold. The purpose of this study is to prepare aqueous suspensions using 70 wt. % α-Al 2 O 3 , with 0, 1, 5 and 10 wt. % of added t -ZrO 2 . Suspensions were electrosterically stabilized using the ammonium salt of polymethylacrylic acid, an alkali-free anionic polyelectrolyte dispersant. Also, magnesium oxide in form of magnesium aluminate spinel (MgAl 2 O 4 ) was used to inhibit the abnormal alumina grain growth during the sintering process. Minimum viscosities were used as stability estimators, where an increase in ZrO 2 content required adding more dispersant. After sintering, the Vickers indentation test was used to determine the hardness and the indentation fracture toughness from the measurement of the crack length. Also, the brittleness index ( B i , μm -1/2 ) was calculated from values of Vickers hardness and the Vickers indentation fracture toughness. It was found that with increasing ZrO 2 content the fracture toughness increased, while the hardness as well as the brittleness index decreased. Zirconia loading reduces the crystallite sizes of alumina, as confirmed by the X-ray diffraction analysis. SEM/EDS analysis showed that ZrO 2 grains are distributed in the Al 2 O 3 matrix, forming some agglomerates of ZrO 2 and some pores, with ZrO 2 having a smaller grain size than Al 2 O 3 .

The green machining of alumina (Al 2 O 3 ) green bodies generates a certain amount of waste alumina powder. Waste alumina ceramic powder should be disposed of as non-hazardous waste in a legally compliant manner. The influence of additives on the stability of 70 wt.% (≈40 vol.%) alumina-waste alumina water-based suspension was investigated in the presented research. A Box-Behnken three-factor response surface design was used for the preparation of stable highly-concentrated suspensions with the addition of three additives. The optimal amount of each additive was selected according to the obtained results of minimal apparent viscosity: 0.05 wt.% Tiron as dispersant, 0.1 wt.% poly (vinyl alcohol) as binder and 0.2 wt.% magnesium aluminate spinel as abnormal grain growth inhibitor. The analysis of variance was used to identify the contribution of each additive. The zeta potential and sedimentations tests were performed to confirm the suspension stability measurements at different pH values. Alumina particles were optimally dispersed at pH values between 8 and 11. According to the results, the investigated composition of 20 wt.% waste alumina powder (weight content, dry alumina powder), with the addition of optimal amounts of additives, shows a possible application in the production of ceramics by slip casting.