During charging, tapping, hot repairing, and idling, the refractory lining also comes into direct contact with the air. Oxidation of MgO-C refractories containing 20 wt-% At the face opposite the hot face of the refractories, the graphite was conducted by measuring the weight loss temperature is low and the face may also come into contact at regular intervals at various temperatures from 800 with air which comes through cracks, crevices, etc. Besides to 1600°C in air. T he rate of decarburisation increased direct air oxidation, FeO present in slag plays a significant with rise in temperature from 800 to 1400°C and then role in the oxidation of carbon in MgO-C bricks. remained more or less constant from 1400 to 1600°C.Oxidation of carbon and its prevention is a subject of T he oxidation kinetics were analysed in detail and great interest in the field of BOF refractories. Different reaction rate models derived for the temperature range techniques1-6 have been used for studying air oxidation of 800-1400°C. T he reaction rate was found to be con-MgO-C samples. In the present work, it was studied under trolled by diVusion of oxygen through the decarburised isothermal conditions by measuring the weight loss at layer. At higher temperatures (>1400°C), oxidation regular intervals. One of the most important parameters is of graphite also takes place indirectly by the reacobviously the temperature. When heated in air, carbon is tion MgO(s)+C(s) Mg(g)+CO(g). T he magoxidised at temperatures from around 600-700°C to form nesium vapour thus produced is reoxidised at the outer CO or CO 2 . Oxidation studies were, therefore, conducted surface and redeposited as MgO. T his leads to a at various temperatures ranging from 800 to 1600°C. reduction in porosity in the decarburised outer shellAlthough MgO-C bricks can contain from 5 to 35 wt-% and, consequently, a reduction in the rate of oxidation. carbon, the amount of carbon usually ranges from 5 to BCT /364 20 wt-%. It was, therefore, thought appropriate to study the effect of temperature on MgO-C specimens containing At the time the research was carried out the authors 20 wt-% graphite.
Pd nanofilms were grown on Au(111) using the electrochemical form of atomic layer deposition (E-ALD). Deposits were formed by repeated cycles of surface-limited redox replacement (SLRR). Each cycle produced an atomic layer of Pd, allowing the reproducible formation of Pd nanofilms, with thicknesses proportional to the number of cycles performed. Pd deposits were formed with up to 30 cycles, in the present study, and used as a platform for studies of hydrogen sorption/desorption as a function of thickness. The SLRR cycle involved the initial formation of an atomic layer of Cu by underpotential deposition, followed by its galvanic exchange with PdCl4 2– ions at open circuit. The first three cycles were studied using in situ electrochemical scanning tunneling microscopy (EC-STM), which showed a consistent morphology from cycle to cycle and the monatomic steps indicative of layer-by-layer growth. Cyclic voltammetry was used to study the hydrogen sorption/desorption properties as a function of thickness in 0.1 M H2SO4. The results indicated that the underlying Au structure greatly influenced hydrogen adsorption, as did film thickness for deposits formed with fewer than five cycles. No hydrogen absorption occurred for the thinnest films, although it increased linearly for thicker films, producing an average H/Pd molar ratio of 0.6. Electrochemical annealing was shown to improve surface order, producing CVs that strongly resembled those characteristic of bulk Pd(111).
Electrochemical atomic layer deposition (E-ALD) is a method for the formation of nanofilms of materials, one atomic layer at a time. It uses the galvanic exchange of a less noble metal, deposited using underpotential deposition (UPD), to produce an atomic layer of a more noble element by reduction of its ions. This process is referred to as surface limited redox replacement and can be repeated in a cycle to grow thicker deposits. It was previously performed on nanoparticles and planar substrates. In the present report, E-ALD is applied for coating a submicron-sized powder substrate, making use of a new flow cell design. E-ALD is used to coat a Pd powder substrate with different thicknesses of Rh by exchanging it for Cu UPD. Cyclic voltammetry and X-ray photoelectron spectroscopy indicate an increasing Rh coverage with increasing numbers of deposition cycles performed, in a manner consistent with the atomic layer deposition (ALD) mechanism. Cyclic voltammetry also indicated increased kinetics of H sorption and desorption in and out of the Pd powder with Rh present, relative to unmodified Pd.
Nanofilms of Pd were grown using an electrochemical form of atomic layer deposition (E-ALD) on 100 nm evaporated Au films on glass. Multiple cycles of surface-limited redox replacement (SLRR) were used to grow deposits. Each SLRR involved the underpotential deposition (UPD) of a Cu atomic layer, followed by open circuit replacement via redox exchange with tetrachloropalladate, forming a Pd atomic layer: one E-ALD deposition cycle. That cycle was repeated in order to grow deposits of a desired thickness. 5 cycles of Pd deposition were performed on the Au on glass substrates, resulting in the formation of 2.5 monolayers of Pd. Those Pd films were then modified with varying coverages of Pt, also formed using SLRR. The amount of Pt was controlled by changing the potential for Cu UPD, and by increasing the number of Pt deposition cycles. Hydrogen absorption was studied using coulometry and cyclic voltammetry in 0.1 M H2SO4 as a function of Pt coverage. The presence of even a small fraction of a Pt monolayer dramatically increased the rate of hydrogen desorption. However, this did not reduce the films’ hydrogen storage capacity. The increase in desorption rate in the presence of Pt was over an order of magnitude.
Atomic layer deposition (ALD) is a group of methods for the formation of nanofilms of materials, an atomic layer at a time using surface limited reactions. The majority of those methods are based on use of the vacuum environment. However there are methods such as sequential ionic layer adsorption reaction (SILAR) which uses the condensed phase, that is, aqueous solutions of precursor ions. In addition, this group has been working on an electrochemical form of ALD for 25 years. That work is referred to as electrochemical atomic layer deposition (E-ALD) or electrochemical atomic layer epitaxy (EC-ALE), and is based on using underpotential deposition (UPD) for surface limited reactions. The problem with using an electrochemical methodology for the formation of nanofilms is that many compatible with the conductive substrates normally used for E-ALD. This has stimulated investigations into the growth of materials using an electroless form of ALD (EL-ALD). The processes being explored are based on use of an adsorbed layer of a precursor, where the solution is then exchanged for a reducing agent, or vis versa. This cycle is then repeated to desired thickness. One example is the use of an adsorbed (or absorbed) layer of hydrogen as the reducing agent (usually on Pd). This is then used for surface limited redox replacement (SLRR) of the desired element. Another example is the use of Sn2+ adsorption followed by Pd2+, which oxidizes the Sn2+ to Sn4+ and forms Pd on the surface. Studies are underway to build this into a cycle for EL-ALD.
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