## 3 Results and Discussion
### Behaviour of Upscaled Biocarbon Briquettes at High Temperature  
The experimental conditions are summarized in Table 6. Five trials were conducted for biocarbon Briquettes and compared to CBB and industrial foundry coke (FC). Figure 11 shows the procedure for changing the gas flow rates and variation of temperature in the experiments. In the first three experiments, the biocarbon Briquettes were tested in a pure N\({}_{2}\) atmosphere and the samples disintegrated; therefore, the weight change is not presented in Table 6. Examples of a foundry coke reference sample and a biocarbon Briquette before and after the experiment are shown in Figure 12. Development of cracks in the biocarbon Briquette and oxidation on the surface of the sample is clearly seen in the picture, while the changes in the foundry coke were minor. Slight weight changes were observed in the reference samples, while in all biocarbon Briquettes, the average weight loss was around 35% due to the higher content of moisture, volatiles and binders. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Test No.** & **Sample** & \multicolumn{2}{c}{**Gas Composition (vol\%)**} & \multicolumn{2}{c}{**Total Load**} & \multicolumn{1}{c}{**Total Weight**} \\ \cline{3-8}  & **CO** & **CO\({}_{2}\)** & **N\({}_{2}\)** & **(/m\({}^{2}\))** & **Loss (\%)** \\ \hline
1, 2, 3 & M5 & - & - & 100 & 0 & - \\
4 & M5 & - & - & 100 & 8 & 35.3 \\
5, 6 & M5 & 34 & 7 & 59 & 8 & 36 \\
7 & CBB & 34 & 7 & 59 & 8 & 5.3 \\
8, 9 & Foundry coke (FC) & 34 & 7 & 59 & 8 & 0.6 \\
10 & M11 & 34 & 7 & 59 & 8 & 36.5 \\
11 & M13 & 34 & 7 & 59 & 8 & 34.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Test conditions for high temperature performance of biquettes. Figure 11: Changes in temperatures and gas flow rates during experiments. Figure 10: Energy density of briquettes in all recipes. During the high-temperature tests, opening of cracks and disintegration of biocarbon biquettes took place even in nitrogen atmosphere and without application of load. The cracks followed a similar pattern to the initial fine cracks seen in the briquettes after drying. In general, three types of cracks were identified: (i) surface cracks caused by friction between the material and the die wall during compaction and during ejection of biquettes from the die, (ii) vertical cracks developed during drying of biquettes and moisture evaporation, and (iii) cracks developed from the pressure gradient during compaction, resulting in the formation and separation of a cone cap. It is expected that changes in mechanical stresses during the compaction cycle such as compression, decompression and ejection of biquettes from the mould play an important role in the formation of the cone shape cap in briquettes. Similar behaviour has been observed in the work reported by [PERSON] et al., on the compaction of pharmaceutical powders [16]. Using modelling and calculation of the mechanical stresses in the compacts, they showed a clear correlation between the separation of cone and stress gradients during removal of sample from the die in the cylindrical compacts [16]. Efforts were made to decrease the formation of cracks by improving die surface quality, testing finer charcoal particles, and curing the briquettes in closed containers with high moisture content to slow down the drying process. Major improvement was obtained by slowing down the drying process. Although the briquette qualities were improved, it was clear that the cracks are caused by a combination of different parameters. Therefore, further investigation of the bonding mechanisms, compaction method and microstructure of the compacted material is necessary. The occurrence of a density gradient in the briquettes is inevitable in one punch die pressing method; therefore, using this compaction technique for producing materials with suitable dimensions for cupola demands are still needed for further improvements in material selection and compaction conditions.