Influence of excess silicon phase on the thermal expansion behaviours of Al-Si binary casting alloys

Al-Si casting alloys are the most commonly used materials for piston alloys. The coefficient of thermal expansion is the key property of a piston material for improving the overall performance and service life of an engine. In the present study, the relationship between the morphology of the excess silicon phase and the coefficient of thermal expansion of Al-Si binary casting alloys was discussed. Optical and scanning electron microscopy were utilized to observe the morphology of the excess silicon phase in the Al-Si binary casting alloys before and after solution aging treatment. The results showed that the morphology of the excess silicon phase significantly influenced the coefficient of thermal expansion of the Al-Si binary casting alloys. After solution aging treatment, the coefficient of thermal expansion of the Al-Si binary casting alloys increased due to the rounding and granulating of the excess silicon phase precipitated during the casting process and decreased due to the precipitation of the finely dispersed Si phase in the α-Al matrix. The change in the coefficient of thermal expansion depended on which of the two kinds of morphological transformation of the excess silicon phase is dominant.

Study of Precipitation Hardening in Two Al-Mg-Si Alloys with and without Copper and Excess Silicon Using Kissinger and Boswell Methods

The precipitation of two 6xxx (Al-Mg-Si) alloys with and without copper (Cu) and excess silicon (Si) has been investigated by using the differential scanning calorimetry (DSC), transmission electron microscopic (TEM) and X ray diffraction (XRD) analysis. The analysis of the DSC curves found that the excess Si accelerate the precipitation. The values of activation energies for each peak of DSC curves were determined by using Kissinger–Akahira–Sunose (KAS) and Boswell isoconversional methods. The alloy which has an excess Si and copper require larger activation energy for precipitation despite the acceleration of the precipitation by the excess Si. TEM observation result shows there is smaller size and higher density of precipitate in excess Si alloy than those of excess-free.

Difference Analysis of Organic Matter Enrichment Mechanisms in Upper Ordovician-Lower Silurian Shale from the Yangtze Region of Southern China and Its Geological Significance in Shale Gas Exploration

The upper Ordovician-lower Silurian shale has always been the main target of marine shale gas exploration in southern China. However, the shale gas content varies greatly across different regions. The organic matter content is one of the most important factors in determining gas content; therefore, determining the enrichment mechanisms of organic matter is an important problem that needs to be solved urgently. In this paper, upper Ordovician-lower Silurian shale samples from the X-1 and Y-1 wells that are located in the southern Sichuan area of the upper Yangtze region and the northwestern Jiangxi area of the lower Yangtze region, respectively, are selected for analysis. Based on the core sample description, well logging data analysis, mineral and elemental composition analysis, silicon isotope analysis, and TOC (total organic carbon) content analysis, the upper Ordovician-lower Silurian shale is studied to quantitatively calculate its content of excess silicon. Subsequently, the results of elemental analysis and silicon isotope analysis are used to determine the origin of excess silicon. Finally, we used U/Th to determine the characteristics of the redox environment and the relationship between excess barium and TOC content to judge paleoproductivity and further studied the mechanism underlying sedimentary organic matter enrichment in the study area. The results show that the excess silicon from the upper Ordovician-lower Silurian shale in the upper Yangtze area is derived from biogenesis. The sedimentary water body is divided into an oxygen-rich upper water layer that has higher paleoproductivity and a strongly reducing lower water that is conducive to the preservation of sedimentary organic matter. Thus, for the upper Ordovician-lower Silurian shale in the upper Yangtze region, exploration should be conducted in the center of the blocks with high TOC contents and strongly reducing water body. However, the excess silicon in the upper Ordovician-lower Silurian shale of the lower Yangtze area originates from hydrothermal activity that can enhance the reducibility of the bottom water and carry nutrients from the crust to improve paleoproductivity and enrich sedimentary organic matter. Therefore, for the upper Ordovician-lower Silurian shale in the lower Yangtze region, exploration should be conducted in the blocks near the junction of the two plates where hydrothermal activity was active.

Division of shale sequences and prediction of the favorable shale gas intervals: an example of the Lower Cambrian of Yangtze Region in Xiuwu Basin

It is a common method to use sequence stratigraphic theory to identify favourable intervals in hydrocarbon exploration. The Lower Cambrian shale of Well Jiangye-1 in Yangtze Region in Xiuwu Basin was chosen as the research object. The content of excess silicon of siliceous minerals in shale was calculated quantitatively, and the concentration distribution of Al, Fe, Mn showed that the excess silicon is of hydrothermally origin and the shale deposited in an environment with hydrothermal activity. Using U/Th values in the study, combined with lithology and logging data, in order to divide sequences of the Lower Cambrian shale in Yangtze Region in Xiuwu Basin. The result shows that the shale of the Lower Cambrian shale is recognized as 1 2nd sequence (TST-RST, TST = Transgressive systems tract; RST = Regressive systems tract) and then further subdivided into 5 3rd sequences (SQ1-SQ5). During the deposition of SQ2 and SQ3, hydrothermal activity was active, and their excess silicon content was generally above 20%-30%. Rising sea level and active hydrothermal activity were beneficial for the enrichment of siliceous minerals and organic matter. Based on the comparison of the reservoir parameters, it tells that SQ2 and SQ3 have relatively higher content of TOC, higher content of brittle minerals (such as siliceous minerals, carbonate minerals and so on), larger effective porosity and higher content of gas, which make it as the most favourable intervals of the Lower Cambrian in Xiuwu Basin.

Effect of the hydrothermal activity in the Lower Yangtze region on marine shale gas enrichment: A case study of Lower Cambrian and Upper Ordovician-Lower Silurian shales in Jiangye-1 well

Finding favorable sites for the exploration of shale gas, is still one of the important areas of research that needs immediate attention. The content of organic matter in shale plays a crucial role in the hydrocarbon generation potential, reservoir space and gas-bearing capacity of shales. Therefore, studying the sedimentary environment of organic shale can provide a scientific basis for locating favorable exploration areas for shale gas. The article takes the Lower Cambrian and the Upper Ordovician-Lower Silurian shales in the Yangtze region as the research object and selects representative wells to quantitatively calculate the existence of excess silicon in shale siliceous minerals and the content of excess silicon. Then, the origin of excess silicon can be clarified by the Al, Fe and Mn elemental analysis. Finally, the sedimentary organic matter enrichment mechanism is analyzed from water oxidation-reduction environments and biological productivity. The results of the study show that the excess silicon in the Lower Cambrian and Upper Ordovician-Lower Silurian shales in the Lower Yangtze region is of hydrothermal origin. The hydrothermal activity improves biological fertility on the one hand; whereas on the other hand, it can enhance the reducing capacity of the bottom water conducive for the preservation of organic matter thereby enriching the sedimentary organic matter. The place near the junction of Yangtze plate and Cathaysian plate, where hydrothermal activities were more intense, provided favorable loci for shale gas exploration in the Lower Yangtze region. It was observed that, since the hydrothermal activity was stronger in the Early Cambrian than in the Late Ordovician-Early Silurian times, the total organic carbon (TOC) content of the Lower Cambrian shale was higher than that of the Upper Ordovician-Lower Silurian shales.