Polygranular Graphite Production via Anthracite Puffing Inhibition
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Solution Overview
Problem
The production of polygranular graphite bodies, such as graphite electrodes and nipples, faces challenges due to 'puffing' – an irreversible rapid volume expansion during graphitization, primarily caused by nitrogen and sulfur release, leading to mechanical stresses and reject products, especially with pitch-based needle cokes, which increases production costs and risks.
Innovation Solution
Incorporating high-temperature treated anthracite with a high vitrinite content into the mixture of petroleum- and/or pitch-based needle cokes and a binder coke precursor, which acts as a puffing inhibitor, particularly for nitrogen puffing, by forming a green body and then carbonizing and graphitizing it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If pitch-based needle cokes are used in the production of polygranular graphite bodies, then the mechanical properties and electrical resistance can be improved, but nitrogen puffing occurs during graphitization causing mechanical stresses and micro- and macro-tears
Solution Approach 1:
Iron oxide is introduced as an intermediary substance that mediates between the nitrogen-containing pitch-based needle cokes and the graphitization process. The iron oxide reacts with the released nitrogen to form iron nitride, preventing direct nitrogen puffing and its harmful effects on the graphite body structure.
Solution Approach 2:
The harmful nitrogen release during graphitization is converted into a beneficial effect by using iron oxide to capture the nitrogen and form iron nitride. This transforms the harmful puffing phenomenon into a controlled chemical reaction that actually strengthens the graphite body by forming a reinforcing phase.
2Manufacturing precision
If the process curves for graphitization are adapted precisely to the parameters of needle cokes with strong puffing behavior, then the quality of graphite bodies can be maintained, but the process time increases leading to higher production costs
Solution Approach 1:
Iron oxide is added to the coke mixture before graphitization begins, preparing the system in advance to handle nitrogen release. This preliminary action allows the graphitization process to proceed without requiring extended process curves, as the nitrogen capture mechanism is already in place.
Solution Approach 2:
The addition of iron oxide changes the chemical parameters of the graphitization process, specifically how nitrogen is handled. This parameter change allows for more aggressive and faster heating curves without compromising quality, as the iron oxide continuously captures nitrogen throughout the process.
3Object-affected harmful factors
If iron oxide is added to diminish sulfur puffing, then sulfur-related expansion can be reduced, but nitrogen puffing remains unaffected
Solution Approach 1:
The invention changes the chemical parameters by using iron oxide, which has the capability to react with both sulfur and nitrogen. This single additive approach provides versatile protection against both types of puffing by altering the chemical interaction pathways during graphitization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method significantly reduces or prevents nitrogen puffing, resulting in reduced mechanical stresses, fewer rejects, and lower production costs, with improved operational characteristics of the graphite bodies, such as lower thermal expansion and electrical resistance.
Implementation Method 1
high-temperature treated anthracite with a high vitrinite content into the mixture of petroleum- and/or pitch-based needle cokes and a binder coke precursor, which acts as a puffing inhibitor, particularly for nitrogen puffing
Implementation Method 2
c) Carbonizing and graphitizing the green body from step b)
Implementation Method 3
c) Carbonizing and graphitizing the green body from step b)
Implementation Method 4
Puffing is understood to be the irreversible rapid volume expansion during graphitization in a temperature range of 1500 to 2000° C. that is caused by nitrogen- and sulfur release.
Data Source
AI summary
A method for the production of polygranular graphite bodies including the step of provisioning a mixture including a high-temperature treated anthracite having a high vitrinite content and a petroleum-based needle coke and/or a pitch-based needle coke, and provisioning at least one binder coke precursor. The method also includes the steps of forming a green body from the mixture from the provisioning step, and carbonizing and graphitizing the green body.