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13 pages, 7310 KiB

Open AccessArticle

Study of the Structural-Phase State of Hydroxyapatite Coatings Obtained by Detonation Spraying at Different O₂/C₂H₂ Ratios

and

Crystals 2023, 13(11), 1564; https://doi.org/10.3390/cryst13111564 - 02 Nov 2023

Viewed by 507

Abstract

This work studies the influence of the composition of an acetylene–oxygen explosive O₂/C₂H₂ mixture on the structure and properties of hydroxyapatite coatings obtained by detonation spraying. The molar ratios of O₂/C₂H₂ were 2.61; 3.03 and 3.35; the explosive charge was between 73 and 77%. The results of X-ray phase analysis showed partial conversion of the hydroxyapatite (HA) phase to the tricalcium phosphate (α-TCP) phase and formation of the amorphous phase during detonation sputtering. The formation of a small amount of the α-TCP phase during detonation spraying of HA is obviously due to structural transformations occurring during the heating of the material by detonation products. In addition, very rapid cooling of molten particles leads to the formation of the amorphous phase. The study results of the microstructure of the cross sections of the formed coatings, conducted using scanning electron microscopy, indicate that an increase in the O₂/C₂H₂ ratio leads to increased porosity in the coatings. Additionally, an increase in the explosive charge by 77% results in the appearance of transverse cracks in the coating. Full article

(This article belongs to the Special Issue Crystalline Materials: From Structure to Applications)

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19 pages, 9460 KiB

Open AccessArticle

Quantitative Analysis of the Geometrically Representative Volume Element of the Yellow River’s Granular Ice Microstructure during the Freezing Period

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Crystals 2023, 13(7), 1021; https://doi.org/10.3390/cryst13071021 - 28 Jun 2023

Cited by 1 | Viewed by 369

Abstract

As a naturally polycrystalline material, Yellow River ice exhibits complex mechanical properties that are closely related to its internal microstructure. To study the micromechanical properties of this ice, the geometrically representative volume element (RVE) and a method for determining it are proposed. By observing and quantifying trends in the microstructural characteristics of the granular ice, a micro-numerical model of Yellow River ice is established. Based on the calculations and analyses of randomness and similarity across model samples, the dimensions of a geometric RVE of granular ice in the Yellow River are quantitatively determined. The research shows that the geometric representation of Yellow River granular ice is 20–24 times larger than the average grain of Yellow River granular ice. These results provide a technique to accurately study, at a microscopic level, the relationship between the material properties of each phase and their macromechanical response. It also provides a theoretical basis for studying the fracture failure mechanism of Yellow River ice at multiple scales. Full article

(This article belongs to the Special Issue Crystalline Materials: From Structure to Applications)

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15 pages, 5416 KiB

Open AccessArticle

A 0D/2D Heterojunction Composite of Polymeric Carbon Nitride and ZIF-8-Derived ZnO for Photocatalytic Organic Pollutant Degradation

Vandana P. Viswanathan

Vaishak T. Balakrishnan

Nayarassery N. Adarsh

Binsy Varghese V

and

Suresh Mathew

Crystals 2023, 13(1), 47; https://doi.org/10.3390/cryst13010047 - 27 Dec 2022

Cited by 1 | Viewed by 1696

Abstract

Solar photocatalytic technology based on semiconducting materials has gained the attention of the scientific community to solve the energy crisis and environmental remediation. Zeolitic imidazolate frameworks (ZIFs) are a subfamily of metal–organic frameworks (MOFs) with the isomorphic topologies of zeolites and coordinative compositions of MOFs. Owing to high specific surface areas, tunable channels and high thermal stabilities, zeolitic imidazolate frameworks (ZIFs) have been used in catalytic applications. In this paper, ZIF-8 was used as a matrix to synthesize 0D/2D heterojunction photocatalysts, viz., ZnO/C₃N₄-x% (x = 2.5, 5 and 10), for the photocatalytic degradation study of rhodamine B (RhB). The synthesized composite materials were characterized using FTIR, PXRD, UVDRS, PL, TEM, and BET analyses. TEM images showed the nearby contacts between ZnO and C₃N₄ in the hybrid and the uniform distribution of ZnO on the surface of the C₃N₄ nanosheet, thus increasing the development of 0D/2D heterojunction. The hybrid system ZnO/C₃N₄-5% (ZCN-5) showed good photocatalytic activity for the degradation of RhB under sunlight. A possible mechanism for the improved photocatalytic activity of the ZnO/C₃N₄ composite is also suggested. This exploratory study demonstrates the effective separation and migration of photo-induced electron–hole pairs between the 2D C₃N₄ sheet and 0D ZnO for the improved performance of heterojunction photocatalysts. Full article

(This article belongs to the Special Issue Crystalline Materials: From Structure to Applications)

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