Despite over ten years of research into the low-cost electrowinning of titanium direct from the oxide, the reduction sequence of TiO 2 pellets in molten CaCl 2 has been the subject of debate, particularly as the reduction pathway has been inferred from ex-situ studies. Here, for the first time white beam synchrotron X-ray diffraction is used to characterize the phases that form, in-situ during reduction and with ∼100 µm spatial resolution. It is found that TiO 2 becomes sub-stoichiometric very early in reduction facilitating the ionic conduction of oxygen ions, that CaTiO 3 persists to nearly the end of the process and that, finally, CaO forms just before completion of the process. The method is quite generally applicable to the in-situ study of industrial chemical processes. Implications for the industrial scale-up of this method for the low-cost production of titanium are drawn.

The FFC Cambridge process is a direct electrodeoxidation process used to reduce metal oxides to their constituent metals in a molten CanormalCl2 salt bath. NiTinormalO3 was used as a precursor (the first stable oxide to form upon blending and sintering NiO and TinormalO2 powders) and was successfully reduced using the FFC Cambridge process at 1173K and a constant cell voltage of −3.1V to produce a NiTi alloy. This work builds on the literature work [ Chinese Science Bulletin , 51 , 2535 (2006) ] through: (i) a predominance diagram calculated to show the regions of phase stability throughout the usable potential window of the CanormalCl2 salt; (ii) the investigation of a wide range of reduction times for a fixed cell voltage, elucidating several additional stable phases, to yield a complete and detailed reduction pathway. The reduction pathway for NiTinormalO3 was identified through the analysis of a series of partial reductions, with fully reduced NiTi formed after a period of 24h . The first stage of the reaction involved the rapid formation of Ni and CaTinormalO3 . The reduction then proceeded via the formation of the intermediate compounds normalNi3Ti and normalNi2normalTi4O . All the NiTinormalO3 and Ni were consumed after a period of 6h , while the intermediate compounds remained until the reaction was near completion. The experimental results related well to the thermodynamic predictions of the predominance diagram. A small variation in stoichiometry of the produced NiTi observed from the edge to the core of the samples was attributed to redeposition of Ti on the sample surface from the salt and a slightly Ti-rich NiTinormalO3 precursor material.

To date, the characterization of the reduction pathway for the Fray Farthing Chen (FFC) Cambridge process has been achieved through ex situ studies, leading to some ambiguities. This study employs a synchrotron X-ray diffraction technique to monitor in situ the FFC reduction of NiTiO3 to NiTi, yielding an unmatched level of detail on the electrochemical and chemical reactions involved. The reduction pathway consists of rapid initial reduction of NiTiO3 to form CaTiO3 and Ni, then the transformation of Ni to Ni3Ti , and finally the consumption of CaTiO3 and Ni3Ti to produce NiTi. The phases observed agree with thermodynamic predictions [ J. Electrochem. Soc. , 155 , E171 (2008) ] and allow the mapping of the reduction pathway on an electrochemical predominance diagram. Ni3Ti is a short-lived transient phase in the reduction pathway. Ni3Ti was found in significant quantities in ex situ studies [ J. Electrochem. Soc. , 155 , E171 (2008) ; Chin. Sci. Bull. , 51 , 2535 (2006) ]. The authors propose that Ni3Ti forms during furnace cooling to ambient temperature if extracted before a complete reduction. Neither Ni2Ti4O nor CaO was observed. The progression of the reduction front is clearly in line with existing observations and models [ Metall. Mater. Trans., B, Process Metall. Mater. Proc. Sci. , 35 , 223 (2004) ; J. Phys. Chem. B , 109 , 14043 (2005) ].

The electrochemical FFC Cambridge process is well suited for NiTi production as it avoids the Ni segregation associated with conventional manufacturing routes. A homogeneous low oxygen product can be produced through the direct electro-deoxidation of the mixed metal oxides in a molten CaCl2 salt bath. This work builds on previous literature concerning the reduction of NiTi [ J. Electrochem. Soc. , 155 , E171 (2008) ; Chin. Sci. Bull. , 51 , 2535 (2006) ] through the investigation of the effects of reduction temperature and the materials of construction on the phases formed. Previous work has shown that the use of a Ti cathodic current collector gave Ti enrichment, forming monoclinic B19′ monoclinic NiTi at ambient temperature [ J. Electrochem. Soc. , 155 , E171 (2008) ]. The use of a Ni current collector caused Ni enrichment in the product, stabilizing the high temperature B2 cubic form at ambient temperature. This was true for all reductions carried out from 1173 to 1273 K, but for 1123 K and below, monoclinic B19′ NiTi was formed. A NiTi current collector yielded Ni enrichment producing B2 cubic NiTi at ambient temperature. Mechanisms for the formation of these phases were proposed. The work also detailed the importance of good cell design and how sealing quality can dramatically affect the homogeneity of the products.

Current nondestructive examination (NDE) technology detection capabilities limit our ability to detect stress corrosion cracking (SCC) damage until it has progressed significantly. This work describes the continued development of an in-situ monitoring technique to detect and characterize mechanical damage caused by SCC, allowing the detection of the incipient stages of damage to components/piping. The application of this study is to prevent failures in the primary cooling loop piping in nuclear plants. The main benefit to the industry will be improved safety and component lifetime assessment with fewer inspections. The technique utilizes high resolution fiber optic strain gages mounted on the pipe outside diameter (OD). This technique has successfully detected changes in the residual stress profile caused by a crack propagating from the pipe inside diameter (ID). The gages have a resolution of less than 1 με. It has been shown experimentally for different crack geometries that the gages can readily detect the changes of approximately 10 to 60 με caused on the OD of the pipe due to crack initiation on the ID. This paper focuses on the latest in the development of the technology. Details of the previous work in this effort may be found in [1–3]. A short summary is provided in this paper. The main recent development was the full scale accelerated SCC cracking in boiling magnesium chloride (MgCl2) experiment. In conjunction with experimentation, both 2D and 3D finite element (FEA) models with thermal and mechanical analyses have been developed to simulate the changes in residual stresses in a welded pipe section as a SCC crack progresses.