Method for forming a layer of single-phase oxide (fe, cr)2 o3 with a rhombohedral structure on a steel or super alloy substrate
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Solution Overview
Problem
Existing methods for forming selective oxide layers on steel substrates for solar thermal absorbers result in thicker, polyphase oxide layers that lack the desired optical and thermal stability, particularly at high temperatures, and fail to achieve a single-phase rhombohedral (Fe, Cr)2O3 layer with a thickness of less than 150 nm.
Innovation Solution
A process involving mechanical subtraction of the surface layer under an oxidizing atmosphere to create microdeformations and rapid local heating, followed by heat treatment in air to grow a single-phase rhombohedral (Fe, Cr)2O3 oxide layer with a thickness of 70-150 nm, providing improved adhesion and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If thermal oxidation is performed on steel substrate to form oxide layer, then solar absorbance is improved, but oxide layer thickness increases and emissivity increases
Solution Approach 1:
The substrate surface is mechanically prepared (ground, polished, or shot-peened) before oxidation to create specific surface conditions that control oxide layer formation. This preliminary mechanical action enables the subsequent thermal oxidation to produce a thin, uniform, single-phase rhombohedral oxide layer with controlled thickness and desired optical properties
Solution Approach 2:
The oxidation process parameters are precisely controlled, including temperature (500-900°C), time (1-24 hours), and atmosphere composition. By optimizing these parameters, the patent achieves a thin oxide layer (50-200 nm) with single-phase rhombohedral structure that provides high solar absorbance while maintaining low emissivity
2Use of energy by moving object
If oxide layer thickness is increased to improve solar radiation absorption, then absorption is improved, but infrared emissivity increases
Solution Approach 1:
The patent precisely controls oxidation parameters (temperature, time, atmosphere) to produce an oxide layer with optimal thickness (50-200 nm) and single-phase rhombohedral structure. This controlled parameter approach ensures the layer absorbs solar radiation effectively while maintaining low infrared emissivity
Solution Approach 2:
The oxide layer is formed as a composite structure with specific phase composition (single-phase rhombohedral (Fe,Cr)2O3) on the steel substrate. This composite material structure provides selective optical properties: high absorption in solar spectrum and low emission in infrared range
3Use of energy by moving object
If conventional vacuum deposition is used to form selective coating, then desired optical properties are achieved, but manufacturing cost increases
Solution Approach 1:
The steel substrate serves as its own coating material source. Through controlled thermal oxidation, the substrate surface transforms into a selective oxide layer with desired optical properties. This self-service approach eliminates the need for separate vacuum deposition processes and external coating materials
Solution Approach 2:
The patent replaces complex vacuum deposition equipment and processes with a simpler thermal oxidation process. The mechanical/chemical oxidation treatment performed in ambient or controlled atmosphere substitutes for expensive vacuum-based physical vapor deposition, significantly reducing manufacturing cost while achieving comparable or superior optical properties
4Reliability
If conventional oxidation methods are used, then oxide layer is formed, but temperature stability and protective properties are insufficient
Solution Approach 1:
The oxidation parameters (temperature, time, atmosphere composition) are optimized to produce an oxide layer with enhanced stability. The single-phase rhombohedral structure formed under controlled conditions provides excellent adhesion to the substrate and maintains structural integrity and protective properties at elevated temperatures
Solution Approach 2:
The oxide layer forms a composite structure with the steel substrate, creating a metallurgically bonded interface. This composite material system provides superior temperature stability and protective properties compared to conventional oxide layers, enabling reliable performance in high-temperature solar thermal applications
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 process achieves a thin, dense, and conformal single-phase oxide layer with high solar absorbance (>75%) and low emittance (<20%) at 100°C, along with excellent resistance to oxidation and corrosion up to 600°C, enhancing the performance of solar thermal absorbers.
Implementation Method 1
the subtraction step generating a level of micro-deformations in the crystal lattice of the steel or superalloy greater than 1.0 x 10−3 and local heating with a kinetic rate greater than 400 °C/s
Implementation Method 2
carrying out a heat treatment, under air, at a partial water pressure less than 10,000 ppm, and at a temperature ranging from 400 °C to 1000 °C, so as to grow the single-phase oxide layer rhombohedral formed in step b)
Data Source
Figure 1A~5
Figure 4A~4B
Figure 6~7
AI summary
The invention relates to a method for forming a layer of single-phase oxide (30) (Fe, Cr)2O3 with a rhombohedral structure on a steel or super alloy substrate (10), comprising the following successive steps: a) supplying a steel or super alloy substrate (10) covered with a surface layer, the steel comprising at least 2 wt.-% chromium; b) removing the surface layer in an atomsphere containing at least 0.2 atm dioxygen, creating a level of micro-deformation in the crystal lattice of the steel or super alloy that is greater than 1.0.10-3, and heating at a heating rate higher than 400°C/s, such as to form a layer of rhombohedral oxide (30) (Fe, Cr)2O3 , c) carrying out a thermal treatment, in the presence of air, at a water partial pressure of less than 10.000ppm, and at a temperature varying between 400°C and 1000°C, such as to grow the layer of rhombohedral oxide formed in step (b) to a thickness of between 70nm and 150nm.