Boron-Free Nitride-Bonded SiC Refractory for Oxidation Resistance
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Solution Overview
Problem
Refractory products made of nitride-bonded silicon carbide (SiC) are vulnerable to oxidation and water vapor, particularly in waste incineration plants, and existing solutions like adding boron components pose environmental and toxicological concerns.
Innovation Solution
A boron-free dry and fresh batch composition for producing nitride-bonded SiC products with a sufficient content of silicon oxynitride (Si2ON2) and magnesium (Mg) that provides excellent oxidation resistance, using SiC grains, Si powder, SiO2 powder, and a Mg component, with Mg-containing binders like magnesium lignin sulfonate or magnesium stearate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If boron components are added to improve oxidation resistance, then the oxidation resistance of nitride-bonded SiC products is improved, but environmental and toxicological concerns arise
Solution Approach 1:
The patent removes boron components from the batch composition entirely, extracting the harmful substance while maintaining oxidation resistance through alternative means (nitrogen-containing binding system and controlled atmosphere firing). This directly resolves the contradiction by eliminating the harmful factor while preserving the beneficial property.
Solution Approach 2:
The patent changes the chemical composition parameters by using a nitrogen-containing binding system (silicon nitride, silicon oxynitride) instead of boron-based binders. The firing process parameters are also optimized (1300-1500°C in nitrogen or inert atmosphere) to achieve oxidation resistance without boron, thus resolving the environmental concern while maintaining reliability.
2Ease of manufacture
If conventional binding systems are used for nitride-bonded SiC, then manufacturing is simplified, but vulnerability to oxidation and water vapor increases
Solution Approach 1:
The patent uses a composite binding system comprising silicon nitride (Si3N4), silicon oxynitride (Si2ON2), and free silicon in specific proportions. This composite material provides both ease of manufacture (as a ceramic-binding system) and superior resistance to oxidation and water vapor, resolving the contradiction between manufacturing simplicity and reliability.
Solution Approach 2:
The patent specifies firing in a nitrogen or inert gas atmosphere to prevent oxidation during processing. This creates a protective environment that maintains the vulnerability-free properties of the nitride-bonded SiC product while keeping the manufacturing process straightforward, thus resolving the contradiction between ease of manufacture and oxidation resistance.
3Reliability
If SiO2 content is maintained to form protective layer, then oxidation resistance is improved, but SiO2 may be lost during processing without proper control
Solution Approach 1:
The patent incorporates SiO2 into the batch composition beforehand (0.5-5.0% by weight) and uses a nitrogen-containing binding system that forms additional SiO2 during firing. This preliminary preparation ensures sufficient SiO2 is available to form the protective layer during the firing process, maintaining composition stability while achieving oxidation resistance.
Solution Approach 2:
The patent carefully controls the SiO2 content parameter within a specific range (0.5-5.0% by weight) and adjusts the firing temperature (1300-1500°C) to optimize SiO2 layer formation without excessive loss. This parameter optimization resolves the contradiction between forming a protective layer and maintaining composition stability.
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 boron-free nitride-bonded SiC products exhibit superior oxidation resistance, maintaining SiO2 content to form a protective layer, ensuring stability in steam atmospheres and reducing oxidation, while being environmentally harmless.
Implementation Method 1
the added free silicon of the silicon powder reacts with the nitrogen in the furnace atmosphere to form the respective nitride phase(s)
Implementation Method 2
Silicon carbide materials with a nitrogen-containing binding system (=nitride-bonded SiC or nitride-bonded silicon carbide) have SiC grains or silicon carbide grains that are connected to one another by means of a nitride-containing binding matrix
Implementation Method 3
the oxidation product SiO2 usually only forms a self-glaze on the SiC grains above these temperatures, which significantly slows down the oxidation progress
Data Source
AI summary
The present invention relates to a dry refractory material and a fresh refractory material for the production of a coarse ceramic, shaped refractory product, in particular a pipe protection plate, made of silicon carbide material with a nitrogen-containing binder system, such a product, a method for its production, and a waste incineration plant with such a pipe protection plate. The refractory material has a SiC granulate in an amount of 73.0 to 82.0 wt.%, Si powder in an amount of 10.0 to 15.0 wt.%, SiO₂ powder in an amount of 0.5 to 5.0 wt.%, and at least one powdery Mg component from a Mg-containing raw material, characterized in that the refractory material has an MgO content of 0.1 to 1.0 wt.% and that the refractory material is boron-free. The binder matrix contains 6.5-12 wt.% Si₃N₄ and 8-18 wt.% Si₂ON₂.