The Improvement in Surface Properties of Metallic Implant via Magnetron Sputtering: Recent Progress and Remaining Challenges

Bioceramic coatings on metallic implants provide a wear-resistant and biocompatible layer, that own ability to develop bone-like apatite in physiological environments to ensure bonding with hard tissues. These bioceramics primarily belong to Calcium Phosphates (CaPs), bioactive glasses, and glass-ceramics. Several techniques are used to deposit these coatings such as; electrophoretic deposition (EPD), plasma spray (PS), and Radio frequency magnetron sputtering (RFMS). Most of these techniques require a high-temperature operation or sintering treatment. This causes either thermal decomposition of bioceramic or results in delamination and cracking of the bioceramic coating due to differences in thermal expansion behavior of metals and bioceramics. RFMS is primarily carried out either at room temperature. However, annealing is performed or substrate is heated at various temperatures ∼400–1,200°C for 2 or 4 h under dry argon (very low temperature compared to other techniques) to ensure crystallization of bioceramics and improve coating adhesion. Chemical composition stability and excellent surface finish are the premium features of RFMS, due to less heat involvement. Moreover, RFMS has the unique ability to develop one-unit/ multilayered composite coatings and the flexibility of in-situ reactions to yield oxides and nitrides. Single or multiple targets can be employed with the insertion of Oxygen and Nitrogen to yield versatile coatings. Due to this attractive set of features RFMS has a strong potential in the field of bioceramic coatings. In recent years, several multifunctional bioceramic coatings have been deposited on metallic substrates using RFMS for biomedical applications. This review focuses on the recent efforts made in order to deposit multifunctional bioceramic RFMS coatings with surface characteristics necessary for biomedical applications and highlights future directions for the improved biological performance of RFMS bioceramic coatings.

Crystallography relevant to Mars and Galilean icy moons: crystal behavior of kieserite-type monohydrate sulfates at extraterrestrial conditions down to 15 K

Monohydrate sulfate kieserites (M 2+SO4·H2O) and their solid solutions are essential constituents on the surface of Mars and most likely also on Galilean icy moons in our solar system. Phase stabilities of end-member representatives (M 2+ = Mg, Fe, Co, Ni) have been examined crystallographically using single-crystal X-ray diffraction at 1 bar and temperatures down to 15 K, by means of applying open He cryojet techniques at in-house laboratory instrumentation. All four representative phases show a comparable, highly anisotropic thermal expansion behavior with a remarkable negative thermal expansion along the monoclinic b axis and a pronounced anisotropic expansion perpendicular to it. The lattice changes down to 15 K correspond to an `inverse thermal pressure' of approximately 0.7 GPa, which is far below the critical pressures of transition under hydrostatic compression (Pc ≥ 2.40 GPa). Consequently, no equivalent structural phase transition was observed for any compound, and neither dehydration nor rearrangements of the hydrogen bonding schemes have been observed. The M 2+SO4·H2O (M 2+ = Mg, Fe, Co, Ni) end-member phases preserve the kieserite-type C2/c symmetry; hydrogen bonds and other structural details were found to vary smoothly down to the lowest experimental temperature. These findings serve as an important basis for the assignment of sulfate-related signals in remote-sensing data obtained from orbiters at celestial bodies, as well as for thermodynamic considerations and modeling of properties of kieserite-type sulfate monohydrates relevant to extraterrestrial sulfate associations at very low temperatures.

Determination of Tropical Belt Widening Using Multiple GNSS Radio Occultation Measurements

In the last decades, Global navigation satellite systems (GNSS) have provided an exceptional opportunity to retrieve atmospheric parameters globally through GNSS radio occultation (GNSS-RO). In this paper, data of 12 GNSS-RO missions from June 2001 to November 2020 with high resolution were used to investigate the possible widening of the tropical belt along with the probable drivers and impacts in both hemispheres. Applying both lapse rate tropopause (LRT) and cold point tropopause (CPT) definitions, the global tropopause height shows increase of approximately 36 m/decade and 60 m/decade, respectively. Moreover, the tropical edge latitude (TEL) estimated based on two tropopause height metrics, in the northern hemisphere (NH) and southern hemisphere (SH), are different from each other. For the first metric, subjective method, the tropical width from GNSS has expansion behavior in NH with ~ 0.41°/decade and a minor expansion in SH with ~ 0.08°/decade. In case of ECMWF Reanalysis v5 (ERA5) there is no significant contraction in both NH and SH. For Atmospheric Infrared Sounder (AIRS), there are expansion behavior in NH with ~ 0.34°/decade and strong contraction in SH with ~ −0.48°/decade. Using the second metric, objective method, the tropical width from GNSS has expansion in NH with ~ 0.13°/decade, and no significant expansion in SH. In case of ERA5, there is no significant signal in NH while SH has a minor contraction. AIRS has an expansion with ~ 0.13°/decade in NH, and strong contraction in SH with ~ −0.37°/decade. The variability of tropopause parameters (temperature and height) is maximum around the TEL locations at both hemispheres. The total column ozone (TCO) shows increasing rates globally, and the rate of increase at the SH is higher than that of the NH. There is a good agreement between the spatial and temporal patterns of TCO variability and the TEL location estimated from GNSS LRT height. Carbon dioxide (CO2), and Methane (CH4), the most important greenhouse gases (GHGs) and the main drivers of global warming, have a global increasing rate and the increasing rate of the NH is similar to that of the SH. The spatial pattern in the NH is located more pole ward than its equivalent at the SH. Both surface temperature and precipitation increase in time and have strong correlation with GNSS LRT height. Both show higher increasing rates at the NH, while the precipitation at the SH has slight decrease and the surface temperature increases. The surface temperature shows a spatial pattern with strong variability, which broadly agrees with the TEL locations. The spatial pattern of precipitation shows northward occurrence. In addition, Standardized Precipitation Evapotranspiration Index (SPEI) has no direct connection with the TEL behavior.

Synthesis and Characterization of Cr, Eggshell and Grinding Sludge Reinforced Aluminum Based Metal Matrix Composites: An Ingenious Experimental Approach

This investigation deals with the utilization of industrial waste to develop aluminum-based composite. Waste eggshell (ES) generated from the food industry has been used as primary reinforcement material. Waste grinding sludge (GS) produced from the iron forging sector was utilized as secondary reinforcement content. Cr content has been further encapsulated to the composite material to prevent the composite material's grain growth. The composite material was developed by the stir casting process. Experimental results concluded that tensile strength, compressive strength, and hardness of base material (AA5052 alloy) had been improved by about 18.02 %, 23.40 %, and 49.53 respectively, by adding 4.5 % of ES, 4.5 % of GS, and 1.5 % of Cr. Microstructural analysis of the AA5052/4.5 % ES/4.5 % GS/1.5 % Cr composite shows the fair distribution of reinforcement content. XRD of the Al/4.5 % ES/4.5 % GS/1.5 % Cr composite shows the occurrence of Al, Fe2O3, CaCO3, CaO, and Cr phases. Corrosion weight loss and thermal expansion behavior of developed composite have also been explored to observe the ES, GS, and Cr addition in the aluminum alloy.

The irreversible thermal expansion of an energetic material

The works deals with a macroscopically isotropic energetic material based on triamino-trinitrobenzene (TATB) crystals bonded with a small volume fraction of a thermoplastic polymer. This material is shown experimentally to display an irreversible thermal expansion behavior characterized by dilatancy and variations of its thermal expansion coefficient when heated or cooled outside a narrow reversibility temperature range. The analysis of cooling results suggests the existence of residual stresses in the initial state, attributed to the manufacturing process. Microstructure-level FFT computations including the very strong anisotropic thermoelastic TATB crystal response and temperature-dependent binder plasticity, show that strong internal stresses develop in the disoriented crystals under thermal load, either heating or cooling. Upon cooling, binder plastic yielding in hindered, thus promoting essentially brittle microcracking, while it is favored upon heating. Despite its low volume fraction, the role of the binder is essential, its plastic yielding causing stress redistribution and residual stresses upon cooling back to ambient.

Effect of Mixing Light-Burned MgO with Different Activity on the Expansion of Cement Paste

In mass concrete, shrinkage resulting from temperature drop and drying leads to cracking, which can seriously affect the strength and durability of cement-based materials. Fortunately, expansion agents can deter or prevent these effects, especially MgO expansion agents (MEAs). In this study, the effects of four MEAs of different activity on the expansion properties, strength, and hydration of cement paste were explored. The different expansion phenomena between the high activity and low activity MgO was especially explained by the hydration model and dynamic theory. The results indicate that when the other conditions were the same, higher curing temperature and dosage could improve the expansion to some extent. Moreover, the hydration of high activity MgO and the expansion behavior occurred mainly in the early hydration stage, while the hydration of low activity MgO and the expansion behavior had a high contribution rate in the later stage, and the final expansion of cement mixed with low activity MgO was larger.