Formation of nanostructured surface layer, the white layer, through solid particles impingement during slurry erosion in a martensitic medium-carbon steel

The extremely altered topmost surface layer, known as the white layer, formed in a medium-carbon low-alloy steel as result of impacts by angular 10–12 mm granite particles during the slurry erosion process is comprehensively investigated. For this purpose, the characteristics, morphology, and formation mechanism of this white layer are described based on the microstructural observations using optical, scanning and transmission electron microscopies as well as nanoindentation hardness measurements and modelling of surface deformation. The white layer exhibits a nanocrystalline structure consisting of ultrafine grains with an average size of 200 nm. It has a nanohardness level of around 10.1 GPa, considerably higher than that of untempered martensitic bulk material (5.7 GPa) achieved by an induction hardening treatment. The results showed that during the high-speed slurry erosion process, solid particle impacts brought forth conditions of high strain, high strain rate, and multi-directional strain paths. This promoted formation of a cell-type structure at first and later, after increasing the number of impacts, development of subgrains following by subgrain rotation and eventually formation of a nanocrystalline structure with ultra-high hardness. The model confirmed that high strain conditions - much higher than required for the onset of plastic deformation - can be achieved on the surface resulting in severe microstructural and property changes during the slurry erosion test.publishedVersionPeer reviewe

Dynamic model of basic oxygen steelmaking process based on multi-zone reaction kinetics : model derivation and validation

A multi-zone kinetic model coupled with a dynamic slag generation model was developed for the simulation of hot metal and slag composition during the BOF operation. The three reaction zones, (i) jet impact zone (ii) slag-bulk metal zone (iii) slag-metal-gas emulsion zone were considered for the calculation of overall refining kinetics. In the rate equations, the transient rate parameters were mathematically described as a function of process variables. A micro and macroscopic rate calculation methodology (micro-kinetics and macro-kinetics) were developed to estimate the total refining contributed by the recirculating metal droplets through the slag-metal emulsion zone. The micro-kinetics involves developing the rate equation for individual droplets in the emulsion. The mathematical models for the size distribution of initial droplets, kinetics of simultaneous refining of elements, the residence time in the emulsion, dynamic interfacial area change were established in the micro-kinetic model. In the macro-kinetics calculation, a droplet generation model was employed and the total amount of refining by emulsion was calculated by summing the refining from the entire population of returning droplets. A dynamic FetO generation model based on oxygen mass balance was developed and coupled with the multi-zone kinetic model. The effect of post combustion on the evolution of slag and metal composition was investigated. The model was applied to a 200-ton top blowing converter and the simulated value of metal and slag was found to be in good agreement with the measured data. The post-combustion ratio was found to be an important factor in controlling FetO content in the slag and the kinetics of Mn and P in a BOF process

Effect of different waste filler and silane coupling agent on the mechanical properties of powder-resin composite

This study reports an innovative pathway for successfully synthesizing composite panels using various waste input. For this purpose, seven types of powder from waste or widely available filler i.e. Quartz off-cut, sand, waste seashell, dolomite, limestone aggregates, concrete waste and limestone dust were used. The study aims to assess the effectiveness and mechanical properties of the various waste powder in the production of powder-resin composites. The panels were then compared with the novel polymeric glass composite (PGC) in the previous study (Heriyanto et al., 2018). Following the same procedure in PGC, the filler was individually grounded to 64–108 μm and chemically treated with amino silane coupling agent (CA). The powder filler (untreated or treated) is then mixed with the resin binder with a ratio of 80/20 respectively, followed by hot pressing the mixture at the pressure of 550 bar at 65 °C for 1 h. The final composite slab is then further cut for mechanical testing. It was found in the study that when CA was not added, surface roughness of the powder particles affected the flexural strength of the final panel significantly. High surface roughness particles such as in Quartz, sand and seashell adhere effectively with the resin binder which led to higher strength. On the contrary, other factors like smooth particle morphology in glass, dolomite and limestone as well as porous structure in concrete and clump of very fine powder in limestone dust degrade the strength of the final panels. With CA addition, adhesion between resin and powder filler were improved significantly. Flexural strength after the CA treatment was found to be much affected by particle characteristics. Silica-based panels i.e. quartz, sand and glass which consist of high strength and hardness of silica particles perform better compared to that of calcium carbonate-based panels. Compression strength, toughness, stiffness, scratch resistance, density and water absorption were also reported in this study. The properties of all the treated panels are found to be comparable, or if not, much better than natural stones. These new approaches of using waste filler in powder - resin based composites can be a new alternative to produce green materials that deliver economic and environmental benefits

Effect of glass aggregates and coupling agent on the mechanical behaviour of polymeric glass composite

This study is the second in a series of papers on synthesizing polymeric glass composite (PGC)panels (Heriyanto, 2018)from mixed, contaminated and broken glasses that are not being recycled at present. The first series of the paper covered the composite production from powder glass, resin and coupling agent as well as investigated the mechanical properties of the powder-resin composite. In Part II, the study aims to incorporate glass aggregates as structural filler and decorative element. The lower surface area of glass aggregates compared to glass powder filler maximizes the waste glass input from 80 to 85–90% and minimize the resin used by 5–10%. Following similar process in previous study, the panel in this study was made by mixing waste glass filler and resin to a dough-like consistency, followed by hot-pressing the mixture at 550 Bar at 70 °C. The ratio of glass powder (GP), glass aggregates and resin are 50–55/35/15–10 respectively. The amount of glass aggregate was kept constant at 35% relative to the total weight, replicating a gap graded composite system in concrete where the intermediate size of aggregate is missing. Three different sizes of glass aggregates were used, ranging from 1 to 2, 2–4 and 4–6 mm, and their effect on the mechanical properties were reported in this study. The strength of the composites was inversely linear with the glass aggregate size. Small aggregate panels have higher strength compared to that with larger aggregates. Particle-resin interaction, continual interfacial region, and aggregate size were found to determine the average strength of the final composite panels. Effect of silane coupling agent (CA)was also reported. The CA helps to modify the glass surface and improve its wettability with the resin binder. The flexural and compression strength, as well as the water-resistant behaviour, were found to improve nearly double with 2% of CA addition. By using scanning electron microscope (SEM), rough surface and cracks was observed to occur at the fracture surface of the untreated panel, while massive shear deformation were found when silane were added. Except for fire-retardancy, most of the physical and mechanical performances of the silane-treated panels were found to offer equal or if not, superior performance compared to that of natural stones. These new approaches of using waste glass in resin-based composites can be a new alternative to produce green materials that deliver economic and environmental benefits

Synthesis of calcium silicate from selective thermal transformation of waste glass and waste shell

© 2017 Elsevier Ltd. This study details a new pathway for successfully synthesising calcium silicate compounds using 100% waste inputs and processing temperatures significantly lower than conventional approaches. Using a solid-state reaction of two common wastes - powdered float glass from building demolition and sea shells discarded by the food industry, wollastonite (β-CaSiO 3 ) and pseudo-wollastonite (α-CaSiO3) were obtained at 1100 °C and 1200 °C respectively. By comparison, a minimum processing temperature of 1436 °C has previously been required to achieve the same result. For both products, the optimum ratio of powdered glass to CaO derived from the mixed sea shell waste was 75:25. SEM analysis showed the wollastonite produced was dense with small sized porosity. By increasing the temperature to 1200 °C, smoother surface of pseudo-wollastonite was achieved with an acicular crystal structure observed at the fracture surface. Interactions between glass and CaO powder at 1000 °C, 1100 °C and 1200 °C were also studied using confocal microscopy. This revealed that the solubility and viscosity of the glass plays key roles in the production of the calcium silicate compounds. The hardness, flexural and compressive strength of the products increased in line with increases in temperature from 1100 to 1200 °C, with maximum values of 198.6 N/mm 2 , 30.1 and 110 MPa achieved, respectively. By measuring the mechanical properties of the calcium silicate compounds produced, we confirmed these 100% 'made from waste' slabs are potential low cost, energy-saving alternatives to ceramic tiles