Evolution and Li Mineralization of the No. 134 Pegmatite in the Jiajika Rare-Metal Deposit, Western Sichuan, China: Constrains from Critical Minerals

The Jiajika rare-metal deposit located in western Sichuan Province (China) is renowned as the largest lithium deposit in Asia, and the No. 134 pegmatite dike is the largest lithium pegmatite under mining conditions in the area. On the basis of a detailed characterization of textures and minerals in the Jiajika No. 134 pegmatite, two zones (the barren Zone Ⅰ and the spodumene Zone Ⅱ) and three subzones (Zone Ⅱ was subdivided into microcrystalline, medium-fine grained and coarse-grained spodumene zones) have been identified. The detailed mineralogical characteristics of lithium minerals and other indicator minerals from each zone were evaluated by EPMA for illustrating the magmatic–hydrothermal evolution and the cooling path of the Jiajika No. 134 pegmatite. From the outer zone inwards, grain size gradually increased, the typical graphic pegmatite zone was absent, and spodumene randomly crystallized throughout nearly the whole pegmatite body. This evidence indicated a Li-saturated melt prior to pegmatite crystallization, which could be the main cause of the super-large-scale Li mineralization of the Jiajika No. 134 pegmatite. A comparison of the Cs content between primary beryl in the Jiajika No. 134 pegmatite and other important Li-Cs-Ta pegmatites in the world indicates that No. 134 pegmatite shows a high degree of fractional crystallization. The evolution of mica species from muscovite to Li-micas from Zone Ⅰ to Zone Ⅱ marks the transition from the magmatic to the hydrothermal stage in pegmatite evolution. The absence of individual lepidolite and the relatively limited scale of alteration of spodumene (<10 vol%) suggest that the activity of the hydrothermal fluids in the system is limited, which contributes to the preservation of the easily altered Li ores and is also an important controlling factor of the super-large-scale Li mineralization of the pegmatite. Spodumene–quartz intergrowth (SQI) usually occurs partly along the rims of the spodumene grains in the Jiajika No. 134 pegmatite. Combined with the pegmatite mineral equilibria, the results of fluid inclusion studies of the pegmatite and the metamorphic conditions in the area, a constrained P-T path of the magmatic–hydrothermal crystallization of the Jiajika No. 134 pegmatite is proposed. The unusual steeply sloped cooling path of the No. 134 pegmatite could be attributed to the fast pressure drop triggered by the intrusion of a pegmatitic melt along the fractures surrounding the Majingzi granite, which could also be the dominant evolution process for other spodumene pegmatites with similar SQI features in the world. The feature of limited internal geochemical fractionation suggested by mineral-scale geochemical analyses of spodumene and micas, combined with the clear textural zoning of the No. 134 pegmatite, can best be ascribed to the effect of undercooling during pegmatite formation. This effect might be one of the non-negligible rules of pegmatite petrogenesis, and would significantly upgrade the potential of Li mineralization by minimizing diffusional Li transfer to the country rocks.

Виготовлення тракту охолодження вдосконаленої конструкції для камери згоряння рідинного ракетного двигуна за допомогою адитивних технологій

The creation of complex structural elements of aircraft using additive technologies is promising and is widely used since such elements have many design and technological advantages over the collection of individual finished parts. However, it requires the solution of many scientific and technical problems to obtain products of high accuracy and density, develop a technological process, work out modes, and sometimes develop a new design of products. When the angles of inclination of the inclined surfaces are more than 45 °, in the manufacture of parts using the technology of selective laser melting, special conditions arise that cause some restrictions. Since the tracks that form the bottom layer (down-skin) of the inclined surface largely lie not on the previous layer of the metal part, but on the powder surrounding the part, the melt pool "falls through" into the powder, the melt pool breaks through, disrupting the track continuity. As a consequence, the bottom layer (down-skin) of the formed inclined at an angle of more than 45 °, and the horizontal surface has a high roughness. We studied samples of elements of the cooling path with an improved design (the shape of the channels in the form of parallelograms with an acute angle of 45 °) and with the original design (the shape of the channels in the form of rectangles) with a change in the angle of inclination of the channels relative to the Z-axis. According to the results of visual-optical analysis and determination of the down-skin roughness, it was found that at tilt angles to the Z-axis ≥75 ° with the original design of the channels, the transverse surface of the channel may not even form or have significant deviations from the specified geometry, and with the improved design of the channels, the roughness of the down-skin is only slightly increased. From the analysis of the change in roughness at tilt angles of the channels relative to the Z-axis in the range of 40…60 °, it was found that samples with an improved channel design have similar roughness values (5…6.5 μm), and for samples with an original channel design, the roughness changed significantly (6…22 μm). A model was developed and a combustion chamber cooling path was manufactured with channels of an improved design and an angle of inclination of the channels of 74 °. The possibility of manufacturing a combustion chamber cooling duct with an angle of inclination of the channels relative to the Z-axis using the technology of selective laser melting at a high metal density and low surface roughness of the inner channels is shown.

Effect of Cooling Path on Microstructures and Hardness of Hot-Stamped Steel

The final mechanical properties of hot-stamped steel are determined by the microstructures which are greatly influenced by the cooling process after hot stamping. This research studied the effect of the cooling path on the microstructures and hardness of 22MnB5 hot-stamped steel. The cooling path was divided into continuous and discontinuous (primary and secondary) processes. After cooling, the Vickers hardness along the thickness of the specimens was measured. The results indicate that, for a continuous cooling process, there was a critical cooling rate of 25 °C/s to obtain fully martensitic microstructure. For the discontinuous cooling process, the slower was the cooling rate, the higher was the degree of auto-tempering that occurred, and the greater was the amount of carbides that formed, regardless of the primary or secondary cooling rate. When the cooling rate was lower than the critical value, a higher primary cooling rate suppressed the auto-tempering of lath martensite and increased the quenched hardness. By contrast, the hardness was not sensitive to the cooling rate when it exceeded the critical value.

Prediction and Experimental of Yield Strengths of As-Quenched 7050 Aluminum Alloy Thick Plates after Continuous Quench Cooling

The aim of this study was to predict the yield strength of as-quenched aluminum alloys according to their continuous quench cooling path. Our model was established within the framework of quench factor analysis (QFA) by representing a quenching curve as a series of consecutive isothermal transformation events and adding the yield strength increments after each isothermal step to predict the yield strength after continuous quench cooling. For simplification; it was considered that the effective hardeners during quenching were the nanosized solute clusters formed at low temperatures, whereas the other coarse precipitates were neglected. In addition, quenching tests were conducted on aluminum plates with different thicknesses. The predictions were compared with the experimental measurements, and the results showed that the predictions fit the measurements well for the 40- and 80-mm-thick plates but overestimated the as-quenched yield strength at the mid-thickness of the 115-mm-thick plates.

Investigation of Propane and n- butane Hydrate Formation Condition and Determination of Equilibrium Pressure

The purpose of this study is to determine the equilibrium conditions for the formation of a mixture of propane and normal butane hydrates including temperature, pressure and mole fraction. In order to prevent the formation of hydrates in the cooling path, it is necessary to examine the conditions of hydrate formation and provide solutions. Modeling of hydrate formation conditions was performed using Hydoff software and compared with experimental results in this field, which obtained an acceptable error percentage. The range of temperature is between 267-276 &deg;C and the molar percentage of propane is 0.7,0.8 and 0.9 and the mathematical equation was presented to predict hydrate formation. By analyzing the results, it was found that by increasing the concentration of ethane in the presence of other compounds, hydrate growth increased and hydrates formed more stable, also by increasing the concentration of propane and normal butane the amount of equilibrium pressure will decrease.

Study of Hydraulic Characteristics of the Cooling Path of a Model Liquid Rocket Engine Manufactured using Additive Technology of Selective Laser Melting

The article discusses hydraulic tests of a model combustion chamber of a liquid-propellant rocket engine with a cooling path made using additive selective laser melting technology. The values of the coefficient of hydraulic resistance in the range of Re = 10--2500 are obtained and the influence of the design features of the cooling tract and its manufacturing technology on the hydraulic characteristics is determined. The results of the performed hydraulic tests confirm the possibility of using additive technologies based on selective laser melting technology for the manufacture of fire and power walls of combustion chambers of liquid rocket engines.