Search Results (4)

Fast high-temperature gas-phase reactions occurring in the limited space of the arc cavity in the submerged arc welding (SAW) process limit the study of specific gas-phase behaviours. A low-temperature experimental method is applied to investigate gas-phase reactions in the reaction of oxy-fluoride slag with Al-Fe-Ni metal powders. The presence of nano-strands in the slag cavities confirms the vaporisation and re-condensation of gasses. Ti is the main element in nano-strands, although some nano-strands also contain Al-Mg-Si-Na oxy-fluoride. Nano-strand end-caps contain Mn-Fe-Si fluoride, and some contain Ni. The Ni in nano-strand end-caps is sourced from the added Ni powder and indicates gas-phase transfer. The Ti in the nano-strands is sourced from the flux. Themochemistry calculations identify KAlF₄, TiF₃, NaAlF₄, SiF₄, AlF₃, SiF₃, and Na in the gas phase. Increased Al reaction results in decreased TiF₃ in the gas phase, likely due to the displacement of Ti from TiF₃, resulting in the gas-phase transfer of Ti from the flux. Comparative diffusion flux calculations support Ti nano-strand formation via the vaporisation of TiF₃ and the re-condensation of Ti. The low-temperature simulation experiment applied here can be used to study the gas reaction behaviour in the reaction of oxy-fluoride flux with metal powders. Full article

Unconstrained metal powders of Cu, Cr, Ni and Al were applied to submerged arc welding (SAW) to clarify the chemical behaviour of copper in this modified SAW process. Aluminium metal is avoided in SAW because it is easily oxidised. Excessive aluminium oxides in the form of slag or inclusions in the weld metal will lead to poor weld metal materials properties. Aluminium is an effective deoxidiser and can be used to prevent Cr and Ni loss to the slag by preventing oxidation of these metals. The results show that carbon steel was alloyed to 5.3% Cr, 5.3% Ni, 3.6% Al and 5.2% Cu at 80% Cr yield, 81% Ni yield, 54% Al yield and 79% Cu yield. BSE (backscattered electron) images of the three-dimensional (3D) post-weld slag sample show 3D structures within the slag dome. The 3D structures contain features of vapour formation and recondensation. In addition, nano-strands appear in the 3D structures and confirm the vaporisation and recondensation of fluorides. The chemical behaviour of copper metal powder added in SAW is to vaporise as metallic copper and incorporate in the Al-Si-Mg-Ca-Mn-Fe-Cu-Na-Cr-Ni fluoride. Copper, in combination with aluminium, has a stabiliser effect in SAW due to its formation of an initial alloy melt of low liquidus temperature, thus decreasing the temperature required to melt high-melting-point metals such as Cr into the weld pool. Although Al and Cu have similar vapour pressures at specific temperatures, it appears that Cu does not substitute for Al in the gas phase. Gas-slag-alloy thermochemical equilibrium calculations confirm the partial oxygen pressure lowering effect of aluminium and the vaporisation of copper as metallic copper with very little copper-fluoride species expected to form. The quantity of metallic copper vaporisation calculated in the gas-slag-alloy thermochemical equilibrium is much higher than the vaporisation quantity measured in welding. This may be due to recondensation of vaporised copper which is not accounted for in the equilibrium calculation at the set arc cavity temperature, as well as the effect of surface-active elements such as sulphur and oxygen in limiting the vaporisation reaction of copper. Full article

In this research, Ni-Fe slag powder and mineral powder are blended into mineral admixtures and added to soil cement, with the aim of investigating the mechanical property of soil cement under a dynamic environment, and the dynamic properties of Ni-Fe slag powder soil cement after impact compression are obtained by conducting split-Hopkinson pressure bar (SHPB) test. The results show that under the same age and different admixture conditions, the dynamic stress of Ni-Fe slag powder soil cement increases first and then decreases and reaches the maximum when the admixture ratio is 40%, and the dynamic stresses at 7 d, 28 d and 60 d were 5.10 MPa, 9.73 MPa and 13.51 MPa, respectively. Under the same admixture ratio, Ni-Fe slag powder soil cement shows an increasing trend in dynamic stress with age, and its growth rate at the curing age from 7 d and 28 d is significantly higher than that at the curing age from 28 d to 60 d. After comparison, it is concluded that the best admixture ratio for Ni-Fe slag powder is 40%, which is close to the maximum value of 45% for mineral admixtures to replace cement as specified in the national standard. Full article

Slags from the remote Mota Farun locality above Casaccia (Val Bregaglia, Swiss Alps) have been analyzed with scanning electron microscopy, X-ray powder diffraction and microfocus synchrotron X-ray diffraction to determine mineralogical composition and microstructures. Non-magnetic slag samples are largely composed of euhedral and dendritic iron-rich olivine in a glassy matrix. Locally there are zones with globular inclusions rich in bornite ((Cu₅Fe)S₄) and locally metallic copper. Some regions display dendritic pentlandite ((Fe,Ni)₉S₈). Magnetic samples are mainly composed of fayalite (Fe₂SiO₄) and wüstite (FeO), with minor magnetite (Fe₃O₄). The mineralogical composition indicates that slags were the product of copper smelting. The slag compositions and morphologies are analogous to slags described from the Oberhalbstein (Graubünden, Switzerland) and the Trentino Alps (Italy) which are attributed to metallurgical exploitations of the Late Bronze Age. While the origin of the ore could not be determined, it may be related to ore deposits of chalcopyrite in greenschists and serpentinites in the vicinity, such as Alp Tgavretga (Septimer Pass) and Val Perossa (Val Bregaglia). Full article