Figures (6)  Tables (6)

    • Figure 1. 

      SEM images of pine biochar (a) produced at 1,000 °C in axial, and (b) transverse orientations.

    • Figure 2. 

      Hardness of maple and pine biochar produced at 600, 800, and 1,000 °C in axial and transverse directions.

    • Figure 3. 

      Hardness of biochar in axial and transverse directions for different wood species pyrolyzed at 1,000 °C.

    • Figure 4. 

      Relationship between transverse hardness and bulk density of biochar for different species produced at 1,000 °C.

    • Figure 5. 

      Relationship between axial hardness and bulk density of biochar for different species produced at 1,000 °C.

    • Figure 6. 

      Axial hardness of biochar pyrolyzed at 1,000 °C vs carbon fraction.

    • Parameter Uncertainty source Mitigation Magnitude
      Micro-indentation Epoxy infiltration Vacuum impregnation + SEM exclusion ΔHV ≈ 0.116 GPa
      Nano-indentation Surface roughness Calibration of indentation positions + low indentation depth ± 3%
      Orientation Cutting angle deviation Sample preparation + surface parallelism check (optical) < 5°
      Carbon fraction SEM threshold sensitivity Multi-operator validation ± 5% RSD
      Statistical significance (p < 0.05) was assessed via ANOVA in OriginPro 2023.

      Table 1. 

      Uncertainty management for various types of tests

    • Sample Temperature
      (°C)      		 Transverse
      hardness (GPa)      		 Axial hardness
      (GPa)
      Maple 600 0.246 ± 0.029 0.251 ± 0.047
      800 0.364 ± 0.042 0.443 ± 0.058
      1,000 0.472 ± 0.084 0.914 ± 0.040
      Pine 600 0.086 ± 0.002 0.121 ± 0.019
      800 0.096 ± 0.012 0.279 ± 0.029
      1,000 0.184 ± 0.008 0.473 ± 0.043

      Table 2. 

      Hardness of maple and pine biochar produced at 600, 800, and 1,000 °C in axial and transverse directions from micro-indentation testing

    • Wood species Axial hardness
      (GPa)      		 Transverse
      hardness (GPa)      		 Anisotropy
      (A/T)
      African ironwood 2.251 ± 0.201 0.731 ± 0.046 3.08
      Redwood 0.987 ± 0.034 0.574 ± 0.132 1.72
      Maple 0.914 ± 0.040 0.472 ± 0.084 1.94
      Yew 0.823 ± 0.065 0.082 ± 0.011 10.04
      Pine 0.473 ± 0.043 0.184 ± 0.008 2.57
      Bamboo 0.441 ± 0.066 0.074 ± 0.013 5.96
      Hemlock 0.485 ± 0.065 0.017 ± 0.006 28.53

      Table 3. 

      Hardness of biochar in axial and transverse directions for different wood species pyrolyzed at 1,000 °C

    • Species Pyrolysis
      temperature (°C)      		 Bulk density (g/cm3) Wood density (g/cm3)
      Maple 600 0.4125 0.78
      800 0.4423
      1,000 0.5474
      Pine 600 0.3002 0.41
      800 0.3509
      600
      Pine 1,000 0.3647
      African ironwood 1,000 0.9260 1.35
      Redwood 1,000 0.3983 0.68
      Yew 1,000 0.5521 0.72
      Bamboo 1,000 0.3898 0.76
      Hemlock 1,000 0.4490 0.55

      Table 4. 

      Bulk density of different wood biochar under different pyrolysis temperature

    • Biochar species Carbon fraction
      African ironwood 0.5967
      Maple 0.5116
      Yew 0.4532
      Pine 0.4373
      Redwood 0.4268
      Bamboo 0.3274
      Hemlock 0.3144

      Table 5. 

      Summarized carbon fraction of different biochar species

    • Species Pyrolysis
      temperature (°C)      		 Axial hardness
      (GPa)      		 Transverse
      hardness (GPa)
      Maple 1,000 4.04 ± 0.16 −
      Pine 1,000 4.41 ± 0.05 4.38 ± 0.71
      Bamboo 1,000 − 3.64 ± 0.52

      Table 6. 

      Intrinsic hardness measured using nano-indentation technique for maple, pine, and bamboo biochar created at 1,000 °C