Aqueous slip casting of translucent magnesium aluminate spinel: Effects of dispersant concentration and solid loading

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Electric Field-Assisted Ion Exchange of Borosilicate Glass Tubes

In this work, DC electric field-assisted ion exchange was carried out to enhance the sodium-potassium inter-diffusion and improve the mechanical performance of borosilicate glass. Electric fields with intensity varying between 100 V cm-1 and 3000 V cm-1 were applied in both direct and inverted polarizations. Four point bending test and the Vickers indentation method were used to characterize the mechanical properties. Energy dispersion x-ray spectroscopy was carried out to determine the potassium concentration within the surface layers of the samples

Transparent LiOH-doped magnesium aluminate spinel produced by spark plasma sintering: Effects of heating rate and dopant concentration

The effects of LiOH doping of magnesium aluminate spinel powders and various Spark Plasma Sintering (SPS) schedules on densification behavior and final transparency of polycrystalline magnesium aluminate spinel were studied. Two commercial magnesium aluminate spinel powders, with different specific surface areas, were doped with up to 0.6 wt% of LiOH and consolidated using SPS with slow (2.75 °C/min) and fast (100 °C/min) heating rates. The slow heating rate was optimal for undoped magnesium aluminate spinel (LiOH-free) with the best real in-line transmittance (RIT) of 84.8% (measured at 633 nm on a disc 0.8 mm thick). For the magnesium aluminate spinel doped with 0.3 wt% of LiOH, the fast heating rate was beneficial, and an RIT of 76.5% was achieved. μ-Raman analysis confirmed that the addition of LiOH suppressed carbon contamination

Strengthening of Soda-Borosilicate Glasses by Ion Exchange Processes

Flexible electronics and displays rely on strong thin borosilicate glasses. Furthermore, borosilicate glass play a vital role in pharmaceutical packaging, particularly for the container of liquid medicine in the auto-injectors. Because of the risk of failure due to the fracture of the glass ampule the costumers need to purchase several units of auto-injector; also, the injector price increases dramatically. This renewed the interest in the strengthening of soda-borosilicate glass. Moreover, the applications of strong thin borosilicate glasses in flexible electronics attracted attention. Chemical strengthening is a practical means of improving the mechanical performance of soda borosilicate glasses. The chemical strengthening process involves the immersion of an alkali-silicate glass in a molten nitrate salt containing potassium ions at temperatures below the glass-transition temperature where the replacement of small alkali ions in the glass with larger potassium ions from the molten salt occurs. The glass composition, salts impurities, temperature and time, are crucial factors of the treatment. Furthermore, applying an electric field can speed up the process and improves the efficiency. This study investigates the impact of potassium for sodium ion exchange and its parameters on the final strength of alkali borosilicate glasses. Alkali borosilicate tubes, used in pharmaceutical packaging, were subjected to ion exchange in potassium nitrate salts containing different impurities. The initial surface flaws have a significant impact on the final strength due to the limited case depth of surface compression in alklai borosilicate glass subjected to ion exchange. Nonetheless, the results revealed that the sodium poisoning of salt has a limited influence on strengthening; conversely, even a small amount of calcium spoils the strengthening. The replacement of sodium ions with calcium is thermodynamically favoured with respect to Na/K ion-exchange. Calcium can penetrate into the glass surface and prevent the replacement of sodium with potassium and, consequently, the generation of compressive stress. Interestingly, performing electric field assisted ion exchange, EF-IE, for 10 min produces an ion-exchanged layer as deep as conventional strengthening for 4 hours in soda borosilicate glass. Electric field assisted ion exchange also augments the glass strength and makes the glass more damage resistant; however, the initial defects on the glass surface have an adverse influence on the efficiency, as expected. Applying an electric field changes the governing mechanism of ion exchange and accelerates the penetration of potassium ions into the glass; furthermore, the glass structure of the layer undergone electric field assisted ion exchange is modified during the process. Although EF-IE generates a strong surface compression in glass, the inhomogeneous distribution of residual stress is a drawback. Performing EF-IE using AC E-fields produces homogenous ion-exchanged layers in glass and is, probably, a practical approach to balancing the residual stress in glass. Chemical strengthening of a thin alkali-borosilicate glass ,D 263 Teco®, is also investigated in the present work. Na/K ion exchange improves the glass strength three times. Although the surface compression generated by ion-exchange in alkali borosilicate glasses is not as strong as typically used glasses for chemical strengthening ( alklai aluminosilicate), it can be used to improve the mechanical properties of borosilicate glass. Annealing prior to the ion exchange increases the compressive stress generated on the surface; however, its effect on strengthening is trivial. The compressive stress produced by Na/K ion exchange in thin alkali borosilicate glass improves the damage resistance and the bending strength of glass. Due to the limited thickness of samples, heat treatments with high heating and cooling rates can be conducted. Such heat treatments can be used to carry out surface relaxation and improve the strength of samples by “surface relaxation”. A fast heat treatment after ion exchange improves the finals strength samples about 40%

Densification of Magnesium Aluminate Spinel Using Manganese and Cobalt Fluoride as Sintering Aids

Highly dense magnesium aluminate spinel bodies are usually fabricated using pressure-assisted methods, such as spark plasma sintering (SPS), in the presence of lithium fluoride as a sintering aid. The present work investigates whether the addition of transition metal fluorides promotes the sintering of MgAl2O4 bodies during SPS. At the same time, such fluorides can act as a source of optically active dopants. A commercial MgAl2O4 was mixed with 0.5 wt% of LiF, MnF2, and CoF2 and, afterwards, consolidated using SPS at 1400 degrees C. Although MnF2 and CoF2 promote the densification as effectively as LiF, they cause significant grain growth

Improving corrosion protection of Mg alloys (AZ31B) using graphene-based hybrid coatings

[EN] In the present work, a study was carried out to compare the morphology and electrochemical properties of pure and graphene-modified hybrid silica sol–gel coatings deposited on anodized AZ31B magnesium alloys. The precursor solution was prepared using tetraethoxysilane (TEOS) and 3-glycidoxypropyl-trimethoxysilane (GPTMS), with the addition of chemically modified graphene nanosheets (GN-chem). Homogeneous and adherent coatings were obtained using GPTMS-TEOS (GT) and GPTMS-TEOS-GN-chem (GT/GN-chem) solutions with uniform thickness around 4 µm. Raman, SEM images and EDS analyses confirmed the presence of graphene nanosheets in the coatings. Potentiodynamic polarization results using 0.05 M NaCl electrolyte solution showed that graphene containing silica coatings significantly improve the corrosion resistance of AZ31B alloys. In addition, a significant passive region was observed for GT/GN-chem coatings.European Union’s Horizon2020 Research and Innovation program,Grant/AwardNumber:739566Peer reviewe

Sintering of Ce3+-doped yttria nanoparticles prepared by precipitation method

Cerium doped yttrium oxide nanoparticles with various Ce3+ concentrations between 0.001 and 0.010 at% have been synthesised by precipitation method using ammonium hydroxide as a precipitation agent. The synthesised powders are characterised by a mean particle size of ca. 55 nm. Highly dense specimens, with a relative density> 98.8%, were obtained by sintering the green compacts shaped by pressure filtration, at 1550 °C for 3 h in air. The sintering behaviour of Ce3+ doped Y2O3 was studied by constructing Master Sintering Curves (MSC); the results showed that the apparent activation energy of sintering for Ce3+ doped Y2O3 increases with the increase of cerium concentration. The segregation of larger Ce3+ cations in the grain boundaries is likely to be responsible for the increase in the sintering activation energy