The use of the friction stir welding (FSW) process as a relatively new solid-state welding technology in the aerospace industry has pushed forward several developments in different related aspects of this strategic industry. In terms of the FSW process itself, due to the geometric limitations involved in the conventional FSW process, many variants have been required over time to suit the different types of geometries and structures, which has resulted in the development of numerous variants such as refill friction stir spot welding (RFSSW), stationary shoulder friction stir welding (SSFSW), and bobbin tool friction stir welding (BTFSW). In terms of FSW machines, significant development has occurred in the new design and adaptation of the existing machining equipment through the use of their structures or the new and specially designed FSW heads. In terms of the most used materials in the aerospace industry, there has been development of new high strength-to-weight ratios such as the 3rd generation aluminum–lithium alloys that have become successfully weldable by FSW with fewer welding defects and a significant improvement in the weld quality and geometric accuracy. The purpose of this article is to summarize the state of knowledge regarding the application of the FSW process to join materials used in the aerospace industry and to identify gaps in the state of the art. This work describes the fundamental techniques and tools necessary to make soundly welded joints. Typical applications of FSW processes are surveyed, including friction stir spot welding, RFSSW, SSFSW, BTFSW, and underwater FSW. Conclusions and suggestions for future development are proposed.

/pdf/friction-stir-welding-of-aluminum-in-the-aerospace-industry-ssxmh7z8.pdf

Friction Stir Welding of Aluminum in the Aerospace Industry: The Current Progress and State-of-the-Art Review

Alkali-activated materials (AAMs) are usually recognized having better acid resistance compared to ordinary Portland cement (OPC), however, the detailed mechanism has not been well studied due to the complexity of raw materials and hardened matrix. In this study, two typical binding gels in AAMs, sodium aluminum silicate hydrate (N-A-S-H) and calcium (sodium) aluminum silicate hydrate (C-(N)-A-S-H), were chemically prepared by laboratory synthesized aluminosilicate powders. The microstructure and composition evolution of the two gels exposed to sulfuric acid were investigated. The results showed that the C-(N)-A-S-H gel had higher degree of structural order than the N-A-S-H gel, while the N-A-S-H gel showed higher polymerization. The AlIV in N-A-S-H gel transferred completely to AlV during sulfuric acid attack, while trace amount of AlIV was still detected in the exposed C-(N)-A-S-H gels. Both gels had increased silica polymerization degree after exposure to sulfuric acid solution. Due to rapider dealumination of N-A-S-H gel than C-(N)-A-S-H gel, the Si/Al ratio increased much higher in the former. The molecular framework changes of N-A-S-H gel caused by dealumination was found to have less effect on the integrity though than that of C-(N)-A-S-H gel, in which coarse gypsum crystalline grains formed and led to destructive stress in hardened matrix. This paper provides an insight at microstructure level of the two typical gels, which is essential for the manufacturing and application of alkali-activated materials. 

Study of acidic degradation of alkali-activated materials using synthetic C-(N)-A-S-H and N-A-S-H gels

Intrinsic sulfuric acid resistance of C-(N)-A-S-H and N-A-S-H gels produced by alkali-activation of synthetic calcium aluminosilicate precursors

The adsorption of three food dyes, namely allura red AC, carmine and tartrazine, on a sweet potato residue-derived activated carbon (SPAC) was analyzed via experimental and theoretical tools. In a first step, SPAC was characterized by BET, FTIR and XRD to unravel its textural and surface properties. Adsorption isotherms of the three dyes were obtained at different temperatures ranging from 30 to 50 °C. Classical models were first applied to model the adsorption isotherms, but they were unable to describe the adsorption mechanisms. An alternative approach based on the application of mono- and multi-layer models from statistical physics theory was then used to better investigate the adsorption mechanisms. This alternative approach indicated that carmine and allura red AC adsorption followed a monolayer behavior, whereas the adsorption of tartrazine was a multi-layer process. These dyes were adsorbed via different configurations (horizontal, non-horizontal, horizontal and non-horizontal at the same time), depending on the system and the temperature. Tartrazine dye was removed via an aggregation process at different temperatures, while carmine was aggregated only at high temperatures. This aggregation process was absent for the allura red AC adsorption. Endothermic physisorption processes was observed for dye adsorption under these experimental conditions. The theoretical analysis indicated that SPAC is a promising material for the removal of these dyes, particularly in the case of allura red AC dye molecule. Overall, this study reports a combination of experimental and theoretical results to provide a new perspective at the molecular level of the removal of dye molecules using a low-cost activated carbon. 

Adsorption of food dyes from aqueous solution on a sweet potato residue-derived carbonaceous adsorbent: Analytical interpretation of adsorption mechanisms via adsorbent characterization and statistical physics modeling

Intrinsic Sulfuric Acid Resistance of C-(N)-A-S-H and N-A-S-H Gels Produced by Alkali-Activation of Synthetic Calcium Aluminosilicate Precursors

http://www.cell.com/article/S2405844022032285/pdf

Activated carbon from biomass precursors using phosphoric acid: A review

Ordinary Portland cement (OPC) is one of the most widely used binders in building materials. However, OPC production is related with high CO2 emission and high energy consumption. Currently geopolymer cements are found to be the alternative substitute for OPC. Geopolymers most commonly are covalently bonded alkali-aluminosilicates which are X-ray amorphous at ambient and medium temperatures. The current study focusses on fly ash which is a byproduct of coal combustion process and due to its amorphous nature and chemistry, it is considered an appropriate raw material for geopolymer synthesis. In this study the effect of alkali concentration and solid liquid ratio on the acid resistance of fly ash based geopolymer mortar was studied. The fly ash was obtained from ayka Addis Textile, Addis Ababa, Ethiopia. Samples were prepared with different solid to liquid ratio and NaOH molarity and were tested for mechanical and durability properties. It was found that as the molarity of NaOH solution and solid to liquid ratio increase the initial and final setting time become shorter. Compressive and flexural strength show that after 28 days of curing sample with high Liquid to solid ratio and higher molarity show higher strength and smaller water absorption percentage. Sample were immersed in a 2% H2SO4 solution for 25 days and the sample with higher strength with smaller water absorption percentage show higher resistance.

/pdf/effect-of-alkaline-concentration-and-solid-liquid-ratio-on-2o2o12nig7.pdf

Effect of Alkaline Concentration and Solid Liquid Ratio on the Acid Resistance of Fly Ash Based Geopolymer Mortar

Underwater friction stir welding (UWFSW) is an advancement of conventional friction stir welding, which is performed in air. The need for welding underwater calls for more information to be explored in the welding of different materials. The aim of this research is to investigate the UWFSW of 2 mm titanium sheet joints for their tensile and microstructural properties and compare them with the results of friction stir welding (FSW) performed in air. Also, nondestructive tests, such as radiography and dye penetrant tests, were carried out to identify the occurrence of any weld defects. The rotational speed of the FSW tool and its travelling speed were considered process parameters, while other parameters like the tilt angle of the tool, shape of the tool pin, etc. were kept constant. The results show that the welded joints with higher strengths were achieved at a lower travelling speed of 140 mm/min at a rotational speed of 400 and 500 rpm in FSW and UWFSW, respectively. The mechanical properties such as yield strength, tensile strength, and hardness are improved in UWFSW when compared with conventional FSW due to the proper mixing of the metal and effective cooling due to the water environment. In underwater FSW, the improved YS and TS values are observed, which are 95.9% and 75.1% of the base metal values, respectively, when the tool rotational speed is 400 rpm and the travelling speed is 140 mm/min. However, the elongation % is much lower in both FSW and UWFSW when compared with the base metal. These results are supported by microstructure and nondestructive test outcomes.

Evaluation of Pure Titanium Welded Joints Produced by Underwater Friction Stir Welding

Preparation and Characterization of Activated Carbon from Castor Seed Hull with H3po4

Castor seeds hull activated carbon impregnated with silver nanoparticles for removal of Escherichia coli from water

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