Economic and Environmental Optimization of Ornamental Stone Block Cutting with a 3D Algorithm

This thesis focuses on finding the optimum block cutting dimensions in terms of the environmental and economic factors by using a 3D algorithm for a limestone quarry in Foggia, Italy. The environmental concerns of quarrying operations are mainly: energy consumption, material waste, and pollution. The main economic concerns are the block recovery, the selling prices, and the production costs. Fractures adversely affect the block recovery ratio. With a fracture model, block production can be optimized. In this research, the waste volume produced by quarrying was minimised to increase the recovery ratio and ensure economic benefits. SlabCutOpt is a software developed at DICAM–University of Bologna for block cutting optimization which tests different cutting angles on the x-y-z planes to offer up alternative cutting methods. The program tests several block sizes and outputs the optimal result for each entry. By using SlabCutOpt, ten different block dimensions were analysed, the results indicated the maximum number of non-intersecting blocks for each dimension. After analysing the outputs, the block named number 1 with the dimensions ‘1mx1mx1m’ had the highest recovery ratio as 43% and the total Relative Money Value (RMV) with a value of 22829. Dimension number 1, also had the lowest waste volume, with a value of 3953.25 m3, for the total bench. For cutting the total bench volume of 6932.25m3, the diamond wire cutter had the lowest dust emission values for the block with the dimension ‘2mx2mx2m’, with a value of 24m3. When compared with the Eco-Label standards, block dimensions having surface area values lower than 15m2, were found to fit the natural resource waste criteria of the label, as the threshold required 25% of minimum recovery [1]. Due to the relativity of production costs, together with the Eco-Label threshold, the research recommends the selection of the blocks with a surface area value between 6m2 and 14m2.

Characterization of innovative kerfless cutting of monocrystalline silicon wafers for photovoltaic applications

Nowadays renewable energies are a hot research topic, and the goal is to improve cell efficiency and reduce production costs, aiming to make the use of photovoltaics increasingly widespread and convenient. Monocrystalline silicon solar cells are leaders in the photovoltaic market. However, market-established cutting techniques produce a consistent amount of material waste when cutting ingots into wafers. The“Stress-induced LIft-Off Method” (SLIM) is emerging in recent years as an alternative, more sustainable separation technique, which reduces material loss and can lead to obtaining increasingly thinner wafers, further reducing the required amount of silicon. This thesis presents the micro-characterization of the separated wafers with the SLIM technique. The wafers were obtained with a two-step procedure. First, a layer of defects was induced in the silicon using ultra-short medium-infrared laser pulses. Then, the material was deposited on one of the sides and induced stress in the silicon, such as to further weaken it. In this way, only rapid cooling is required for detachment to occur. The obtained results indicate that the SLIM-cut technique halves the minority carriers’ lifetime. There is no amorphization, crystal disorder or high-pressure phases. However, changes in the Raman spectra suggest that tensile stress may have been produced on these surface layers by the separation process. The AFM topography highlights surface irregularities, which may be removed with a polishing step. The surface also shows laser-modified regions, which are evident in SEM images, but not in AFM topographies, suggesting a charging effect due to electron bombardment. Lastly, the electrical characterization by conductive AFM lacks any changes in the conductive behaviour of the material where the laser-modified areas should be located. In conclusion, these preliminary results are promising to carry out a systematic characterization of this technique of this innovative SLIM technique.