Structure formation of alloys of tin — zinc system during high-rapid solidification

The results of a study of the structure parameters of rapidly solidified foil of a hypoeutectic, eutectic, hypereutectic Sn—Zn system alloys containing 4.4; 8.8 and 15 mas. % Zn are presented Rapidly solidified foil consists of equiaxed zinc particles and a supersaturated tin solid solution. Zinc particles are distributed uniformly in the foil, that is caused by the formation of a supercooled and supersaturated liquid solution and its subsequent spinodal decomposition. The areas of the liquid solution enriched with tin and zinc are transformed into nuclei of crystalline phases. With an increase in the zinc concentration in the studied alloys, the volume fraction of zinc particles, the average chord of random secant sections at the sections of zinc particles, and the specific surface of the interphase formed by zinc and tin increase. The foil of Sn—Zn alloys has a microcrystalline structure in which the predominant grain orientation is observed. The formation of the texture of (100) tin and (0001) zinc occurs. Rapidly solidified alloy foils are in an unstable state, that results in the decomposition of a tin solid solution, the dissolution of small particles and the growth of large particles. Annealing at 180 °C for 22 hours causes an increase in the average chord of sections of zinc particles, volume of zinc particles and a decrease in the specific surface of the interface.

Influences of Ash-Existing Environments and Coal Structures on CO2 Gasification Characteristics of Tri-High Coal

Two kinds of tri-high coals were selected to determine the influences of ash-existing environments and coal structures on CO2 gasification characteristics. The TGA results showed that the gasification of ash-free coal (AFC) chars was more efficient than that of corresponding raw coal (RC) chars. To uncover the reasons, the structures of RCs and AFCs, and their char samples prepared at elevated temperatures were investigated with SEM, BET, XRD, Raman and FTIR. The BET, SEM and XRD results showed that the Ash/mineral matter is associated with coal, carbon forms the main structural framework and mineral matters are found embedded in the coal structure in the low-rank tri-high coal. The Raman and FTIR results show that the ash can hinder volatile matters from exposing to the coal particles. Those results indicate that the surface of AFC chars has more free active carbon sites than raw coal chars, which are favorable for mass transfer between C and CO2, thereby improving reactivity of the AFC chars. However, the gasification reactivity was dominated by pore structure at elevated gasification temperatures, even though the microcrystalline structure, functional group structure, and increase in the disorder carbon were improved by acid pickling.

High-temperature aluminum composite materials with special physical and mechanical properties produced by mechanical alloying

High-temperature aluminum composite materials with special physical and mechanical properties produced by mechanical alloying. The study is aimed at making high-temperature aluminum composite materials with special physical and mechanical properties. An effective way to solve the problem is to use a technology based on reactive mechanical alloying. The processes of phase composition formation, the structure and properties that occur at all stages of the technology implementation and the effect of alloying components on these processes have been analyzed, and the composition «aluminum (PA4) – surfactant (С17Н35СООН – 0.7 %)» has been found to be the most appropriate. The microcrystalline structure of its base, regardless of the composition of constituent materials, is preserved at subsequent stages of production of materials and determines high values of high-temperature strength, which are significantly higher than those of analogue materials. The microcrystalline structure of the base is characterized by a well-developed surface of grain and subgrain boundaries and is stabilized by nanosized inclusions of aluminum oxides and carbides formed during mechanical alloying. Additional alloying, which provides special properties, does not change the «structural phase» type of the developed materials. They are considered to be dispersion hardened composite microcrystalline materials.

Zn- or Cu-Containing CaP-Based Coatings Formed by Micro-arc Oxidation on Titanium and Ti-40Nb Alloy: Part I—Microstructure, Composition and Properties

Zn- and Cu-containing CaP-based coatings, obtained by micro-arc oxidation process, were deposited on substrates made of pure titanium (Ti) and novel Ti-40Nb alloy. The microstructure, phase, and elemental composition, as well as physicochemical and mechanical properties, were examined for unmodified CaP and Zn- or Cu-containing CaP coatings, in relation to the applied voltage that was varied in the range from 200 to 350 V. The unmodified CaP coatings on both types of substrates had mainly an amorphous microstructure with a minimal content of the CaHPO4 phase for all applied voltages. The CaP coatings modified with Zn or Cu had a range from amorphous to nano- and microcrystalline structure that contained micro-sized CaHPO4 and Ca(H2PO4)2·H2O phases, as well as nano-sized β-Ca2P2O7, CaHPO4, TiO2, and Nb2O5 phases. The crystallinity of the formed coatings increased in the following order: CaP/TiNb < Zn-CaP/TiNb < Cu-CaP/TiNb < CaP/Ti < Zn-CaP/Ti < Cu-CaP/Ti. The increase in the applied voltage led to a linear increase in thickness, roughness, and porosity of all types of coatings, unlike adhesive strength that was inversely proportional to an increase in the applied voltage. The increase in the applied voltage did not affect the Zn or Cu concentration (~0.4 at%), but led to an increase in the Ca/P atomic ratio from 0.3 to 0.7.