HVOF-sprayed HAp/S53P4 BG composite coatings on an AZ31 alloy for potential applications in temporary implants

Bioactive thermal spray coatings produced via high-velocity oxygen fuel spray(HVOF)from hydroxyapatite(HAp)and bioactive glasses(BG)have the potential to be employed on temporary implants due to the ability of both HAp and BG to dissolve and promote osseointegration,considering that both phases have different reaction and dissolution rates under in-vitro conditions.In the present work,75%wt.HAp-25%wt.S53P4 bioactive glass powders were HVOF-sprayed to obtain HAp/S53P4 BG composite coatings on a bioresorbable AZ31 alloy.The study is focused on exploring the effect of the stand-off distance and fuel/oxygen ratio variation as HVOF parameters to obtain stable structural coatings and to establish their effect on the phases and microstructure produced in those coatings.Different characterization techniques,such as scanning electron microscopy,X-ray diffraction,and Fourier transform infrared spectroscopy,were employed to characterize relevant structural and microstructural properties of the composite coatings.The results showed that thermal gradients during coating deposition must be managed to avoid delamination due to the high temperature achieved(max 550℃)and the differences in coefficients of thermal expansion.It was also found that both spraying distance and oxygen/fuel ratio allowed to keep the hydroxyapatite as the main phase in the coatings.In addition,in-vitro electrochemical studies were performed on the obtained HAp/S53P4 BG composite coatings and compared against the uncoated AZ31 alloy.The results showed a significant decrease in hydrogen evolution(at least 98%)when the bioactive coating was applied on the Mg alloy during evaluation in simulated body fluid(SBF).

Application of a new reagent for analysis of oxygen presence in a lowcarbon steel wire rod

A microstructural analysis was performed to determine the presence of oxygen in a wire rod section of AISI 1008 steel with a surface mechanical failure produced during wire drawing.The failure zone was analyzed by comparison using three different attack reagents:alkaline sodium chromate(ASC),ASC with hydrogen peroxide and amyl alcohol,and a solution of nitric acid in ethyl alcohol.The reagents were applied in samples in the failure zone,showing different types of zones in regions with internal and superficial defects such as carbides,pores,cracks,deformation,and detachment zones,indicating the possible presence of oxygen.The areas identified were observed by means of an optical microscope and were correlated with the content of elements that were present in the region using a scanning electron microscope and a scattered X-ray energy spectrometer,which determined that the areas identified by chromate sodium correspond to regions with a high concentration of oxygen and slag-forming elements such as silicon,aluminum,and iron;this is associated with the presence of oxygen in the oxide form.It was also observed that the ASC and the modified ASC solution with hydrogen peroxide and amyl alcohol could identify areas with a high presence of oxides,while the nitric acid solution only identified the steel microstructure.The modified ASC solution is an alternative to identify the presence of chemical variants of oxygen because the conventional formulation is unstable and has a too short shelf life,and therefore,its application must be carried out at the time of preparation.

Ecological intensification of cropping systems enhances soil functions,mitigates soil erosion,and promotes crop resilience to dry spells in the Brazilian Cerrado

Water scarcity threatens global food security and agricultural systems are challenged to achieve high yields while optimizing water usage.Water deficit can be accentuated by soil physical degradation,which also triggers water losses through runoff and consequently soil erosion.Although soil health in cropping systems within the Brazilian Cerrado biome have been surveyed throughout the years,information about soil erosion impacts and its mitigation are still not well understood;especially concerning the role of cropping system diversification and its effects on crop yield.Thus,the aim of this study was to assess whether ecological intensification of cropping systems-inclusion of a consorted perennial grass and crop rotation-could promote soil coverage and consequently decrease water erosion and soil,water,and nutrient losses.This work studied the effects of crop rotation and consorted Brachiaria,along with different levels of investment in fertilization on soil physical quality and on soil,water,and nutrient losses,and crop yields.Results proved that soybean monoculture(SS)is a system of low sustainability even under no-till in the Brazilian Cerrado conditions.It exhibited high susceptibility to soil,water,and nutrient losses,causing low crop yields.Our results showed that water losses in SS cropping system were approximately 10%of the total annual rainfall,and total K losses would require an additional 35%of K application.Conversely,ecological intensification of cropping systems resulted in enhanced soil environmental and agronomic functions,increased grain yield,and promoted soil and water conservation:high soil cover rate,and low soil,water and nutrient losses.Ecological intensification proved to be an adequate practice to boost crop resilience to water deficit in the Brazilian Cerrado.