Fluorine Production Carbon Plates: Why Does a Row of Copper Rods Pierce the Edge of That Thick Carbon Plate in the Electrolytic Cell?

XRD Graphite · Fluorine Production Carbon Plates · Technical Column

Fluorine Production Carbon Plates: Why Does a Row of Copper Rods Pierce the Edge of That Thick Carbon Plate in the Electrolytic Cell?

The items in the photo are fluorine production carbon plates: regular thick rectangular plates, stacked in groups, with a row of copper rods neatly inserted along the edge of each plate, evenly spaced and uniformly oriented. These plates do not hold materials, bear loads, or serve as insulation in a furnace chamber—they work in the fluorine electrolysis process as anodes inside the cell. The carbon plate participates in the anodic reaction and withstands attack by fluorine-containing media, while the copper rods conduct current from outside the cell to the plate. This article explains what they are, why carbon materials are used for fluorine production anodes, the design considerations on the plate, where machining is difficult, what to look for in the material, and the operating boundaries.

Written by: XRD Graphite · Technical Column

I. What Are Fluorine Production Carbon Plates?

Fluorine production carbon plates are carbon plates used as anodes in the fluorine electrolysis process. Their role has two aspects: first, to serve as the anode and participate in the electrochemical reaction; second, to conduct current from outside the cell to the reaction surface. Therefore, they must be connected to conductors—the row of copper rods in the photo serves this current-leading function, with the rods inserted into the plate body and the other ends led out to the conductive system outside the cell.

The perspective for evaluating this component is completely different from that for furnace components. Graphite parts in vacuum furnaces focus on temperature resistance, thermal shock resistance, load-bearing, and insulation. Fluorine production carbon plates focus on electrical conductivity, structural density, ash and impurity content, and resistance in fluorine-containing media. They are electrode materials for chemical electrolysis, with a separate set of evaluation criteria and acceptance concerns.

One more distinction should be made: although they are all called “plates,” the directions differ considerably. Graphite plates are mostly used for heating, load-bearing, flow guiding, and partitioning. Flow battery bipolar plates require conductivity and medium separation. Fluorine production carbon plates face a strongly corrosive fluorine-containing system, and their material structure and purity requirements differ from the above categories. Similar names, different material selection logic—the specific application depends on what medium the plate is installed in.

II. Why Are Carbon Materials Used for Fluorine Production Anodes?

To understand this plate, one must first understand the environment it is placed in. Fluorine production is a process of electrolysing fluorine-containing molten salts to evolve fluorine at the anode. The anode remains in a fluorine-containing medium for extended periods and must meet requirements for both conductivity and structural stability. This position is demanding for materials.

Metals are difficult to use here. Metals such as copper and iron are noticeably corroded in fluorine-containing media and hydrogen fluoride environments, and neither dimensions nor surface condition can be maintained. Nickel can be used in some systems but has a limited range of adaptability to operating conditions and other factors. Precious metals, while stable, are not practical as a single large plate. Carbon materials combine conductivity, corrosion resistance, the ability to be made into large plates, and relatively controllable cost—hence their long-standing use in fluorine production anodes.

Next is a key dividing line within this class of materials: among carbon-containing materials, why do fluorine production anodes mostly use carbon materials with a lower degree of graphitisation rather than graphite with a higher degree?

The reason relates to the crystal structure of carbon. Materials with a high degree of graphitisation have regularly arranged carbon layers with consistent interlayer spacing. Active species such as fluorine can, under certain conditions, enter between the layers to form intercalation compounds, accompanied by volume expansion and layer separation, causing surface blistering and flaking—what the industry often refers to as expansion and powdering. Amorphous carbon materials with a lower degree of graphitisation have a structure closer to a disordered, turbostratic stacking, and this interlayer entry behaviour is relatively weaker, so their resistance in fluorine-containing environments is generally better. Therefore, fluorine production carbon plates often do not follow the path of “the purer the graphite, the better,” but rather the route of a dense structure, low porosity, low ash, and a lower degree of graphitisation. The specific grade depends on the operating conditions and the customer’s material specifications.

This boundary should be stated clearly: the carbon anode is gradually fluorinated during operation—the surface structure slowly changes, the plate body gradually thins, and flaking carbon mud appears. This is normal for this type of electrode, not an anomaly. How long it lasts depends on the material’s density, pore structure, and ash control, as well as the electrolysis conditions. Therefore, the replacement cycle and loss allowance should be factored in at the design stage, rather than expecting it to remain unchanged.

III. Breaking Down the Actual Component: Plate, Holes, Rods, Surfaces

1. Plate body – thickness uniformity and flatness

The plates in the photo are considerable in thickness, regular in shape, and straight on all four sides. Two things should be monitored on the plate body: the uniformity of thickness across the entire plate, and the flatness of the plate surface. Uneven thickness has two consequences: first, different conductive cross-sections at different locations lead to uneven current distribution, and areas with higher local current also wear faster; second, during assembly, gaps or interference may occur between the plate and the conductive copper busbar or backing plate, resulting in inconsistent contact. An uneven plate surface tends to form local contact points, where resistance and heating are more concentrated.

2. Hole positions – the relative positioning of the row of copper rod holes

Each plate requires a row of copper rods, which means a set of holes: hole diameter, hole spacing, perpendicularity, insertion depth, and the positional relationship of the hole axis relative to the plate surface. The key to this set of holes is not the precision of any single hole, but consistency from hole to hole. Cumulative deviation in hole spacing will cause the entire row of copper rods to skew, failing to align with the lead-out positions on the cell during assembly. Poor perpendicularity means the copper rod goes in at an angle, and the contact surface inside the hole becomes a line rather than an area. Hole positioning is one of the links in machining these plates with the least tolerance for error.

3. Hole interior and hole openings – the source of contact quality and a high-risk area for chipping

Conduction between the copper rod and the plate relies on contact between the hole wall and the rod. A rough hole wall, chipping, or residual dust all reduce the actual contact area and raise contact resistance. During operation, the connection point runs hotter, which in turn accelerates wear on both the carbon and copper sides. At the same time, carbon materials are brittle, and the entry and exit points during drilling are high-risk areas for chipping. Once the hole opening chips, it affects both contact and becomes a stress concentration point under load. Therefore, chamfering the hole opening, deburring, and cleaning the hole interior are not simply a matter of “tidying up”—they directly affect how well the plate performs once installed.

4. Copper rod assembly – insertion depth must be consistent

The copper rods in the photo appear uniform in length and insertion depth, and there is a reason for this. Each rod, together with the section of plate it contacts, forms a branch circuit. If the contact resistance and conductive length of each branch differ, the current distribution across the rods will be uneven, and individual rods and hole positions will bear higher loads. In the assembly stage, the fit method between rod and hole (gap filling with conductive material, compression, bonding, or other methods) also directly affects contact resistance and thermal stability. The specific form depends on the drawing and the user’s requirements.

5. Plate surface cleaning and edge treatment

These plates are “feed-in components” in the electrolysis system. Dust on the plate surface, oil, and residues from machining can all enter the system and become sources of impurities. Therefore, thorough cleaning after machining is essential: clear debris from each hole individually, remove dust and oil from the plate surface, and chamfer or lightly finish the edges to prevent sharp corners from chipping during handling and assembly.

To summarise the key points for this component: the plate body is about thickness and flatness, hole positions are about spacing consistency, hole interiors are about contact and cleanliness, copper rods are about uniform insertion depth, and edges are about whether there is chipping. Together, these determine the conductive state and service cycle—not how good it looks.

IV. Where Is Machining Difficult?

Machining these plates may look like “drilling a row of holes in a thick plate,” but the actual process is more complex than it appears:

• Flatness and thickness control on large plate surfaces: The larger and thicker the plate, the more pronounced the effects of clamping and cutting during machining. To achieve uniform thickness across the entire surface and meet flatness requirements, the clamping method and machining sequence must be planned in advance.
• Relative positional accuracy of a row of holes: Hole diameter, spacing, perpendicularity, and depth must all be consistent, and spacing deviation must not accumulate along the row. The locating datum must be unified; changing datums repeatedly during processing will cause deviations to grow larger toward the end.
• Carbon materials are brittle and prone to chipping during drilling: The entry and exit points are high-risk areas for chipping. Chipping at the hole opening affects both contact quality and structural integrity, so the feed method and drill bit selection must account for this.
• Difficult hole cleaning: When holes are blind or deep, dust and debris tend to remain inside. Residual powder on the hole wall can become trapped between the copper rod and the hole wall, creating a hidden risk of poor contact.
• Consistency control of insertion depth: With multiple rods in a row, any deviation in insertion depth means the resistance of each branch differs, leading to uneven current distribution after assembly. Depth control must be verified at both the machining and assembly stages.
• Handling and packaging protection: Thick carbon plates are heavy, and edges and corners are brittle points. Care must be taken to prevent impact during workshop transfer, stacking, and packaging. The grouped stacking shown in the photo is itself a space-saving practice, but cushioning and securing must be adequate.
• Cleaning and protection throughout the process: From machining to packaging, dust, oil, and moisture should not be introduced into the finished product. Cleaning is not a final step but a requirement throughout.

V. What to Look for in the Material

• Density and pore structure: The denser the structure, the less opportunity for media to penetrate into the plate body. Porosity is a pathway for corrosion and penetration. For anode carbon plates, porosity and pore morphology are indicators more worth attention than strength.
• Ash and impurity elements: Ash is the residue of inorganic impurities in carbon materials. In electrolysis systems, impurities can participate in or interfere with the reaction process and may also enter the product side. Therefore, ash and impurity element control requirements are stricter than for general graphite parts. Specific limits are subject to the user’s technical requirements.
• Degree of graphitisation: As mentioned earlier, in fluorine-containing systems, amorphous carbon materials with a lower degree of graphitisation generally perform more steadily in terms of interlayer entry and expansion. This is usually determined by the material’s inherent structure and is a direction to establish at the material selection stage.
• Resistivity: As an electrode material, resistivity directly relates to voltage drop and heating along the current path, and is one of the basic indicators for these plates.
• Mechanical strength: Carbon materials are brittle. Flexural strength and compressive strength relate to resistance to cracking during cell installation, tightening, and operation.
• Thermal expansion and thermal conductivity: When used with copper rods, differences in thermal expansion cause the contact state to change with temperature. This is needed in the design of assembly clearances.

It should be noted that the density, resistivity, strength, thermal conductivity, and other indicators of the above materials vary with grade and specification. Different grades under the same name can differ considerably. For specific values, refer to the technical conditions for the corresponding grade and the user’s technical requirements. When selecting, it is not advisable to draw conclusions based on a name alone.

VI. Where Are They Mainly Used?

The approach to selecting these plates and determining dimensions is to start with the operating conditions: what the medium is, the concentration and temperature range, the anode layout and lead-out method, and the expected replacement cycle. Once these four are defined, the plate thickness, hole layout, insertion method, material grade, and ash limits have a basis. Different medium systems may result in considerably different material resistance. In such cases, small-batch verification before scaling up is more prudent than ordering directly based on assumptions.

VII. Operating Boundaries: Medium, Contact, and Assembly

The boundary for these components is not “heat” but “medium.” They face a strongly corrosive fluorine-containing system, and material consumption is part of their service. The key to evaluating them is keeping the consumption rate within expectations.

Several points require attention in use and design:

• Medium attack and structural change: Carbon plates are gradually fluorinated in fluorine-containing media, resulting in surface structural changes, thickness reduction, and flaking. When the plate body thins to a certain extent, it affects the conductive cross-section and structural strength. Therefore, replacement should be determined periodically based on measurement results, rather than waiting for obvious anomalies.
• The copper portion and the medium: Copper is not stable in strongly corrosive fluorine-containing media. Therefore, the connection and lead-out sections of copper rods are usually designed to avoid direct contact with the medium or to incorporate isolation and protection measures. The specific approach is directly related to the cell design and is subject to drawings and user requirements.
• Contact resistance and heating: The contact state between copper and carbon directly affects the temperature at the connection during operation. Poor contact leads to local heating, which in turn accelerates wear on both sides of the contact surface. Doing a solid job on hole cleaning, insertion depth, and fit method during assembly is easier than dealing with it after operation begins.
• Assembly and thermal expansion: Carbon and copper differ considerably in thermal expansion, so contact pressure changes with temperature. The fit and clearance should be calculated for the operating temperature range during design to avoid loosening or excessive interference in the hot state.
• Mechanical damage and handling: Carbon materials are brittle. During installation and removal, do not pry, hammer, or force-twist. Copper rods should not be driven in with excessive force. Before installing in the cell, check the plate surface and hole openings for chipping and cracks. Damaged plates are prone to further propagation at hole openings or edges after being put into service.
• Safety note: The fluorine production process involves toxic and strongly corrosive media. Related process design, operation, and maintenance should be carried out in accordance with professional regulations and safety requirements. This article discusses only materials and machining, not the determination of specific process parameters.

VIII. About XRD Graphite’s Fluorine Production Carbon Plates

With 30 years of experience in graphite product R&D and machining, XRD Graphite specialises in manufacturing fluorine production carbon plates and various carbon plate materials. We have accumulated extensive process expertise in machining to drawings, including flatness and thickness control on thick plates, hole spacing and depth consistency for row holes, hole opening treatment, and hole interior cleaning. We machine precisely to customer drawings and strictly control tolerances on critical dimensions such as plate thickness consistency, hole positions, and insertion depth. Our products offer relatively long service life under normal use and maintenance and have gained recognition from many industry clients.

For fluorine production carbon plates, we typically recommend clarifying four things first: the operating medium and concentration range, the installation and lead-out method, the requirements for ash and impurities, and the specific dimensional relationships for hole positions and insertion depth. Once these are defined, the blank grade, plate thickness, hole layout, and assembly fit method have a basis. If the operating conditions are uncertain, small-sized test plates or single-piece samples can be used for verification first, and scaling up after a successful trial run keeps trial-and-error costs relatively controllable. The factory can machine carbon plates of different specifications to drawings, with capabilities for cutting, surface grinding, drilling, chamfering, and clean packaging. We also accept evaluation from drawings and samples.

Final Thoughts

A fluorine production carbon plate is an “electrode component,” not a “structural component.” Its value lies not in load-bearing or insulation, but in stable conductivity, dense structure, low impurities, and resistance in fluorine-containing media. Whether a plate performs well depends on whether the thickness is uniform, the surface is flat, the spacing and depth of the row of holes are consistent, the holes are clean, and the copper rods are inserted straight. These details are reflected in current distribution and contact temperature, and ultimately in the service cycle. When selecting such components, discuss the medium and operating conditions first, then the material grade and dimensions. Where the medium system is unclear, small-batch verification is more cost-effective than direct scale-up. For specific operating conditions, confirmation based on actual parameters is still recommended.