Sealing Pressurized Ceramic Structures with Ceramics
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Solution Overview
Problem
Existing methods for joining and sealing ceramic structures in high-temperature, corrosive environments, such as nuclear reactors, face challenges in maintaining structural integrity and hermetic sealing while allowing internal pressurization, especially when components like nuclear pellets and retaining springs cannot withstand high operating temperatures.
Innovation Solution
A multi-step process involving the use of preceramic polymers with inclusions, chemical vapor infiltration (CVI), and chemical vapor deposition (CVD) to form a crystalline matrix with a gas impermeable sealing layer, utilizing a ceramic end plug with a fill hole for controlled gas composition and pressure, and applying localized heat with induction coils to solidify a high-melt-temperature material within the fill hole for sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ceramic structure is sealed with a traditional sealing method, then the joint strength may be sufficient, but the hermetic sealing at elevated internal pressure cannot be maintained
Solution Approach 1:
The patent applies chemical vapor infiltration (CVI) and chemical vapor deposition (CVD) processes to transform the sealing material from a preceramic polymer state to a crystalline ceramic state through controlled temperature and chemical environment parameters. This parameter change creates a sealing layer with enhanced impermeability and mechanical strength capable of withstanding elevated internal pressures while maintaining hermetic sealing.
Solution Approach 2:
The patent creates a composite sealing structure consisting of a preceramic polymer matrix with embedded inclusions that transforms into a crystalline ceramic composite. This composite material combines the flexibility of the polymer during application with the strength and impermeability of the crystalline ceramic after processing, enabling the joint to maintain hermetic sealing under pressure.
2Temperature
If high-melt-temperature material is used for sealing, then the temperature resistance is improved, but the complexity of the sealing process increases
Solution Approach 1:
The patent replaces traditional mechanical sealing methods with a chemical-based sealing approach using preceramic polymers that undergo pyrolysis and crystallization. Instead of relying on mechanical compression or physical barriers, the sealing is achieved through chemical transformation of the polymer into a temperature-resistant crystalline ceramic material that inherently resists high temperatures.
Solution Approach 2:
The patent utilizes phase transitions of the preceramic polymer material, transforming it from a flexible polymer state through pyrolysis to a rigid crystalline ceramic state. This phase transition enables the sealing material to achieve high-temperature resistance while the process is controlled through staged heating and chemical vapor infiltration, managing the overall process complexity.
3Reliability
If the end plug is completely sealed, then the structural integrity is improved, but the ability to fill with desired gas composition is lost
Solution Approach 1:
The patent incorporates a fill hole in the end plug that allows gas composition to be controlled before the final sealing operation. The preceramic polymer sealing material is applied and processed while the fill hole remains open, enabling the ceramic structure to be filled with the desired gas composition. Only after gas filling is complete is the fill hole sealed through the same CVI/CVD process, ensuring both gas composition control and final structural integrity.
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
This method creates a hermetic, resilient joint that maintains elevated internal pressure, provides corrosion and temperature resistance, and ensures structural integrity, addressing the limitations of existing technologies by forming a strong, impermeable seal that can withstand the harsh conditions of nuclear reactors.
Implementation Method 1
The sealing material can be cured at a first temperature and pyrolized at a second temperature higher than the first temperature to form the solid ceramic
Implementation Method 2
crystallizing the solid ceramic to form a crystalline matrix comprising a same ceramic polymorph as the ceramic structure and the end plug
Implementation Method 3
strengthening the joint under the low pressure, before the filling of the desired gas composition, by applying to the crystalline matrix a substantially gas impermeable sealing layer
Implementation Method 4
heating a material into a molten form using a heat source; and directing the material into the hole, wherein the material solidifies to seal the end plug
Data Source
AI summary
This patent document relates to systems, structures, devices, and fabrication processes for ceramic matrix composites suitable for use in a nuclear reactor environment and other applications requiring materials that can withstand high temperatures and/or highly corrosive environments. In one exemplary aspect, a method of joining and sealing ceramic structures is disclosed. The method comprises forming a joint of a ceramic structure and an end plug using a sealing material, wherein the end plug has a hole that goes through a top surface and a bottom surface of the end plug; filling the ceramic structure with a desired gas composition through the hole; heating a material into a molten form using a heat source; and directing the material into the hole, wherein the material solidifies to seal the end plug.