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Study of HVOF-sprayed hydroxyapatite/titania graded coatings under in-vitro conditions

Publication date: November–December 2020

Source: Journal of Materials Research and Technology, Volume 9, Issue 6

Author(s): John Henao, Oscar Sotelo-Mazon, Astrid L. Giraldo-Betancur, Juanita Hincapie-Bedoya, Diego G. Espinosa-Arbelaez, Carlos Poblano-Salas, Cecilia Cuevas-Arteaga, Jorge Corona-Castuera, Lorenzo Martinez-Gomez

Republished by Plato

Published

on

open access

Abstract

The present study concentrates on the bioactive behavior of HVOF-sprayed HAp/TiO2 graded coatings on a Ti-6Al-4V alloy. In-vitro bioactivity was evaluated by immersing graded coating samples in Hank’s solution at body temperature up to 28 days. Natural in-vitro bioactivity of the graded coatings was compared with in-vitro electrochemical analysis also performed for 28 days. Potentiodynamic polarization, open circuit potential, linear polarization resistance, and electrochemical impedance spectroscopy measurements in Hank’s solution, at body temperature, were performed to study the interaction of the HVOF-sprayed HAp/TiO2 graded coating with the simulated body fluid. Electrochemical in-vitro data of graded coatings were compared with those from an uncoated Ti-6Al-4V alloy. Graded coatings presented a rapid interaction with simulated body fluid during the first 4 days of immersion. The interaction between HAp/TiO2 graded coating and simulated body fluid led to the formation of a bone like-apatite layer on the top surface of the graded coating. This layer was not observed on the surface of the Ti-6Al-4V alloy. The growing kinetics of the apatite layer on the top surface of the graded coatings varied on time and provided useful information for future in-vivo studies focused on studying medical healing times. From a bioactive standpoint, the present study shows the advantages that a HVOF-sprayed HAp-based coating architecture has over an un-coated Ti-6Al-4V alloy, and how it represents a step forward in the development of bioactive coatings for implant technology.

Keywords

Graded coating

In-vitro behavior

Hydroxyapatite

Electrochemistry

Thermal spray

© 2020 The Authors. Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420318639?dgcid=rss_sd_all

Material

Study of the photocatalytic activity of CdS-ZnS nano-composite in the photodegradation of rifampin in aqueous solution

Publication date: Available online 2 December 2020

Source: Journal of Materials Research and Technology

Author(s): Fariba Soleimani, Alireza Nezamzadeh-Ejhieh

Republished by Plato

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The elimination of rifampin (RN) as a pollutant from an aqueous solution was performed via the photodegradation process by the coupled CdS-ZnS system under visible light irradiation. The catalyst was briefly characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and transmission electron microscope (TEM) techniques. The cubic ZnS structure and the hexagonal CdS structure with the crystallite size of 10 nm were detected from the XRD patterns. From the DRS results, the bandgap energies of 2.3, 3.9, and 2.4 eV were obtained for CdS, ZnS, and CdS-ZnS, respectively. The pH-values of 5.2 (5.25), 5.8 (5.8), and 5.9 (5.88) were obtained for the pHpzc of CdS, ZnS, and CdS-ZnS by two methods, respectively. Increased photocatalytic activity of the coupled ZnS-CdS system was achieved compared to the single systems and when the moles of CdS is 6 times higher than the ZnS component, the best activity was obtained. The optimal degradation conditions were the catalyst dose: 0.5 g/L, CRN: 8 mg/L, pH: 2, and irradiation time: 120 min. The rate constants of RN photodegradation and mineralization (from the chemical oxygen demand (COD) results) were 0.028 and 0.019 min-1, respectively. The mechanism pathway was similar to the type (II)-heterojunction system in which the accumulated holes in VB-ZnS, the accumulated electrons in CB-CdS, and hydroxyl radicals are more important reactive species in the photodegradation of RN molecules. Further, this mechanism is useful for hydrogen production by both the photogenerated electrons in CB-CdS and CB-ZnS positions. Another mechanism that can illustrate the photodegradation process is similar to the direct Z-scheme mechanism pathway in which the accumulated electrons in the CB-ZnS, the accumulated holes in the VB-CdS, and the superoxide radicals are more important active centers for the degradation of RN molecules. Also, the accumulated holes in the CB-CdS position are another active center to oxidize RN molecules. Besides, the accumulated holes in the CB-ZnS position are more suitable for hydrogen production. The photogenerated holes in the CB-CdS position are also capable to oxidize water molecules for oxygen evolution.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420320573?dgcid=rss_sd_all

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Material

A Control Volume Method Based Interface Movement Equation for One-Dimensional Stefan Problem Achieving Mass Conservation

Publication date: Available online 2 December 2020

Source: Journal of Materials Research and Technology

Author(s): Haitao Zhao, Jianjun Qi, Hongwei Chen, Zhiqiang Tian, Jian Sun, Zhonghua Sun

Republished by Plato

Published

on


Elsevier

Available online 2 December 2020

Journal of Materials Research and Technology

open access

Abstract

For heat-transfer-controlled or diffusion-controlled phase transformation simulations, the movement of the interface between different phases needs to be determined, which is commonly called the Stefan problem. Various numerical methods have been developed for this and the movement of the interface is conventionally calculated by a flux balance equation, which is usually called the Stefan condition equation. However, mass conservation errors have been reported in the literature for some of the numerical methods. In this research, a control volume method based interface movement equation was proposed to achieve mass conservation during calculation. The obtained maximum relative mass conservation error for the new interface movement equation is less than 10-13 and the total mass is constant to the machine precision. This is much smaller than that of the Stefan condition discrete equation, which is in the order of 10-2. It was also found that the mass conservation accuracy of the numerical methods partly depends on the choice of the interface movement equation. The mass change term in the Stefan condition discrete equation is only a part of the whole mass change during interface movement, leading to the mass non-conservation found in the literature. In contrast, the piecewise integration treatment in the proposed interface movement equation in this research gives a more accurate mass change description during the interface movement. The correctness of the proposed interface movement equation was also proved by a comparison with the analytical solutions.

Keywords

Stefan problem

control volume method

interface movement

mass conservation

© 2020 The Author(s). Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420320548?dgcid=rss_sd_all

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Material

Fe-bearing intermetallics transformation and its influence on the corrosion resistance of Al-Mg-Si alloy weld joints

Publication date: Available online 2 December 2020

Source: Journal of Materials Research and Technology

Author(s): Xia-Ming Chen, Qi-Peng Dong, Zhen-Guang Liu, Xiao-Nan Wang, Qing-Yu Zhang, Zeng-Rong Hu, Hiromi Nagaumi

Republished by Plato

Published

on


Elsevier

Available online 2 December 2020

Journal of Materials Research and Technology

open access

Abstract

This work investigated the transformation of Fe-bearing intermetallics and its influence on the corrosion behavior of Al-Mg-Si alloy weld joints. The results showed that the size and type of Fe-bearing intermetallics determined the pitting corrosion resistance of weldment regions. The partially melted zone (PMZ) suffered most serious corrosion attack, because of the formation of coarse needle-like β-AlFeSi. The heat-affected zone (HAZ) immediately behind the PMZ (HAZ-Ⅰ) experienced a complete transformation of β-AlFeSi into α-AlFeSi, but in the rest of the HAZ (HAZ-Ⅱ) was not sufficient for this transformation. Therefore, the HAZ-Ⅰ was more resistant to pitting corrosion than HAZ-Ⅱ.

Keywords

Corrosion behavior

Fe-bearing intermetallics

partially melted zone

fusion welding

Al-Mg-Si alloy

© 2020 The Author(s). Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420320445?dgcid=rss_sd_all

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