Graphitization is a core process that transforms amorphous, disordered carbonaceous materials into an ordered graphitic crystalline structure, with its key parameters directly influencing graphitization degree, material properties, and production efficiency. Below are the critical process parameters and technical considerations for graphitization:
I. Core Temperature Parameters
Target Temperature Range
Graphitization requires heating materials to 2300–3000℃, where:
- 2500℃ marks the critical point for significant reduction in graphite interlayer spacing, initiating ordered structure formation;
- At 3000℃, graphitization nears completion, with interlayer spacing stabilizing at 0.3354 nm (ideal graphite value) and graphitization degree exceeding 90%.
High-Temperature Holding Time
- Maintain target temperature for 6–30 hours to ensure uniform furnace temperature distribution;
- An additional 3–6 hours of holding during power supply is required to prevent resistance rebound and avoid lattice defects caused by temperature fluctuations.
II. Heating Curve Control
Staged Heating Strategy
- Initial heating phase (0–1000℃): Controlled at 50℃/h to promote gradual release of volatiles (e.g., tar, gases) and prevent furnace eruption;
- Heating phase (1000–2500℃): Increased to 100℃/h as electrical resistance decreases, with current adjusted to maintain power;
- High-temperature recombination phase (2500–3000℃): Held for 20–30 hours to complete lattice defect repair and microcrystalline rearrangement.
Volatile Management
- Raw materials must be mixed based on volatile content to avoid localized concentration;
- Ventilation holes are provided in top insulation to ensure efficient volatile escape;
- The heating curve is slowed during peak volatile emission (e.g., 800–1200℃) to prevent incomplete combustion and black smoke generation.
III. Furnace Loading Optimization
Uniform Resistance Material Distribution
- Resistance materials should be distributed evenly from furnace head to tail via long-line loading to prevent bias currents caused by particle clustering;
- New and used crucibles must be mixed appropriately and prohibited from being stacked in layers to avoid localized overheating due to resistance variations.
Auxiliary Material Selection and Particle Size Control
- ≤10% of auxiliary materials should consist of 0–1 mm fines to minimize resistance inhomogeneity;
- Low-ash (<1%) and low-volatile (<5%) auxiliary materials are prioritized to reduce impurity adsorption risks.
IV. Cooling and Unloading Control
Natural Cooling Process
- Forced cooling by water spraying is prohibited; instead, materials are removed layer by layer using grabs or suction devices to prevent thermal stress cracking;
- Cooling time must be ≥7 days to ensure gradual temperature gradients within the material.
Unloading Temperature and Crust Handling
- Optimal unloading occurs when crucibles reach ~150℃; premature removal causes material oxidation (increased specific surface area) and crucible damage;
- A 1–5 mm thick crust (containing minor impurities) forms on crucible surfaces during unloading and must be stored separately, with qualified materials packed in ton bags for shipment.
V. Graphitization Degree Measurement and Property Correlation
Measurement Methods
- X-ray Diffraction (XRD): Calculates interlayer spacing d002 via the (002) diffraction peak position, with graphitization degree g derived using Franklin’s formula:
g=0.00860.3440−2c0×100%
(where c0 is the measured interlayer spacing; g=84.05% when d002=0.3360nm).
- Raman Spectroscopy: Estimates graphitization degree via the intensity ratio of D-peak to G-peak.
Property Impact
- Every 0.1 increase in graphitization degree reduces resistivity by 30% and increases thermal conductivity by 25%;
- Highly graphitized materials (>90%) achieve conductivity up to 1.2×10⁵ S/m, though impact toughness may decline, necessitating composite material techniques to balance performance.
VI. Advanced Process Parameter Optimization
Catalytic Graphitization
- Iron/nickel catalysts form Fe₃C/Ni₃C intermediate phases, lowering graphitization temperature to 2200℃;
- Boron catalysts intercalate into carbon layers to promote ordering, requiring 2300℃.
Ultra-High-Temperature Graphitization
- Plasma arc heating (argon plasma core temperature: 15,000℃) achieves surface temperatures of 3200℃ and graphitization degrees >99%, suitable for nuclear-grade and aerospace-grade graphite.
Microwave Graphitization
- 2.45 GHz microwaves excite carbon atom vibrations, enabling heating rates of 500℃/min with no temperature gradients, though limited to thin-walled components (<50 mm).
Post time: Sep-04-2025