Modeling of Thermo-Chemo-Mechanical Properties of Anode Mixture during the Baking Process

In the Hall–Héroult process, prebaked carbon anodes are utilized to produce primary aluminium. The quality of the anode plays a crucial role in the efficiency of electrowinning primary aluminium. In the production of anodes, the anode baking is considered as the stage most frequently causing anode problems. During the baking process, the anode undergoes complex physicochemical transformations. Moreover, the anode at a lower position, imposed by loading pressures from upper anodes, will creep during this process. Thus, the production of high-quality anodes demands efficient control of their baking process. This paper aims to investigate the thermo-chemo-mechanical properties of the anode paste mixture at high temperatures. These properties include kinetic parameters of pitch pyrolysis such as the activation energy and the pre-exponential factor, the thermal expansion coefficient (TEC) and relevant mechanical parameters related to the elastic, the viscoelastic and the viscoplastic behaviours of the anode. For this purpose, experiments consisting of the thermogravimetric analysis, the dilatometry and the creep test were carried out. Based on the obtained results, the forementioned parameters were identified. Relevant mechanical parameters were expressed as a function of a new variable, called the shrinking index, which is related to the volatile released in open and closed pores of the anode. This variable would be used to highlight the chemo-mechanical coupling effect of the anode mixture. New insights into the phenomena such as the expansion due to the increase of the pore pressure and the chemical shrinkage of the anode during the baking process were also gained in this work. These investigations pave the way for modeling the thermo-chemo-poromechanical behaviour of the anode during the baking process.

China’s aluminium sector and prospects of global aluminium industry

Using statistical data, this paper analyzes the evolution, current status and prospects of China’s aluminium industry: sufficiency of raw materials, bauxite mining, alumina production, capacity utilization, primary aluminium output, technological development. The analysis confirms that China will maintain its leading position at the global aluminium market in the long term. Thus, China will remain the world’s biggest importer of bauxites and alumina, the leading producer of alumina and primary aluminium, a big exporter of semi-finished products and aluminium compounds with a high added value. The growth of the country’s aluminium sector is a typical example of China’s global economic dominance policy — i. e. imports of raw materials, rising production and exports of final products, which are sweeping the national and international markets thanks to breakthrough technology and competitive prices. Being the key player at the global market for non-ferrous metals (primarily, aluminium), China, on one hand, generates an initial demand for them by using them in manufacturing and, on the other hand, the country is interested in low and stable prices. The main advantages of China’s aluminium industry include its large scale, low energy consumption, the capacity of the steadily growing internal market, available production facilities with a low wear level, a developed transport infrastructure and port facilities, an aggressive merge policy exercised at both the national and international markets, the government’s flexible currency policy, quick decision making, a high economic mobilization discipline. In the long run, only primary aluminium producers of comparable size and technology status (both the existing and the projected ones) will be able to survive the competition with their Chinese peers.

Effects on primary energy use, greenhouse gas emissions and related costs from improving energy end-use efficiency in the electrolysis in primary aluminium production

Primary aluminium production is energy- and GHG-intensive in which electrolysis is by far the most energy- and GHG-intensive process. This paper’s aim is to study the effects on (1) primary energy use, (2) GHG emissions and (3) energy and CO2 costs when energy end-use efficiency measures are implemented in the electrolysis. Significant savings in final and primary energy use, GHG emissions and energy and CO2 costs can be achieved by implementing the studied measures. Vertical electrode cells and the combination of inert anodes and wettable cathodes are among the measures with the highest savings in all three areas (primary energy use, GHG emissions and energy and CO2 costs). Direct carbothermic reduction is one of the measures with the highest savings in primary energy use and energy and CO2 costs. For GHG emissions, direct carbothermic reduction is the more beneficial choice in regions with a high proportion of coal power, while inert anodes are the more beneficial choice in regions with a high proportion of low-carbon electricity. Although a company potentially can save more money by implementing the direct carbothermic reduction, the company should consider implementing the vertical electrode cells together with other energy-saving technologies since this would yield the largest GHG emission savings while providing similar cost savings as the direct carbothermic reduction. It may be necessary to impose a price on GHG emissions in order to make inert anodes cost-effective on their own, although further evaluations are needed in this regard. There is a potential to achieve carbon-neutrality in the reduction of aluminium oxide to pure aluminium.

INDUSTRIAL SEMISOLID CASTING PROCESS FOR SECONDARY ALUMINIUM ALLOYS FOR DECARBONISING LIGHTWEIGHT PARTS IN AUTOMOTIVE SECTOR

The life cycle holistic approach for the automotive sector highlighted how much important is working on decarbonisation of Al casting processes to produce vehicle components. Broadening the use of recycled aluminium alloys, instead of high energy intensive primary aluminium alloys, is key for environment preservation. While primary aluminium alloys are preferred by automotive original equipment manufacturers (OEMs) because impurities (mainly Fe) present in secondary aluminium alloys might cause fatigue properties decay, a new semisolid state process route has been developed at Brembo to drastically reduce the sensitivity of cast aluminium to Fe impurities. Based on these premises, during the CRAL European project in the framework of the LIFE Programme, an industrial prototype machinery - a vertical high pressure die casting machine - has been designed and constructed to inject secondary aluminium in the semisolid state. A number of A357 Fe-enriched brake callipers manufactured via the new process route have been fully investigated by fatigue tests, SEM and OM analyses in order to validate the new eco-sustainable product compared to conventional ones manufactured with primary aluminium by gravity casting.