Multilayer Coating for Process Sensor Corrosion
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Solution Overview
Problem
Field devices used in process and automation technology face challenges with corrosion when exposed to aggressive media, particularly at high temperatures and pressures, leading to reduced service life due to limitations in existing coating materials and methods, including corrosion of sensitive components and diffusion of molecules through plastic coatings.
Innovation Solution
A media-resistant multi-layer coating comprising a densely packed first layer with corrosion protection and a chemically resistant plastic second layer, where the first layer is approximately 10 μm thick and elastic, and the second layer is about 300 μm thick, providing enhanced corrosion protection and mechanical robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a plastic coating (PEEK, PTFE, PFA, ECTFE) is applied to provide chemical resistance and electrical insulation, then corrosion protection and non-stick properties are improved, but the coating allows diffusion of small molecules (water, acid, HF, HCl) and requires thickness that may not be compatible with flexible diaphragms
Solution Approach 1:
The patent combines a plastic coating layer with a metal or ceramic coating layer to create a composite coating system. The plastic layer provides chemical resistance and electrical insulation, while the metal/ceramic layer acts as a diffusion barrier to prevent molecule penetration. This composite structure resolves the contradiction by integrating the advantages of both material types.
Solution Approach 2:
The coating is divided into multiple functional layers: an inner layer (metal or ceramic) that provides the diffusion barrier function, and an outer plastic layer that provides chemical resistance and electrical insulation. This segmentation allows each layer to specialize in one function, overcoming the limitations of single-material coatings.
2Reliability
If the plastic coating thickness is increased to reduce diffusion rate, then corrosion protection is improved, but the coating becomes less flexible and incompatible with thin diaphragms (25-150 μm) required for pressure sensors
Solution Approach 1:
By using a composite coating with a thin metal or ceramic barrier layer combined with a plastic layer, the system achieves sufficient corrosion protection without requiring a thick plastic coating. The metal/ceramic layer provides the diffusion barrier function at minimal thickness, allowing the overall coating to remain flexible and compatible with thin diaphragms.
Solution Approach 2:
Different regions of the coating system have different thicknesses and material properties optimized for their specific functions. The metal/ceramic layer is thin but dense for diffusion blocking, while the plastic layer is thicker for chemical resistance but the overall structure remains flexible due to the thin total thickness.
3Reliability
If a precious metal coating (gold, platinum) is applied via electroplating or PVD to provide excellent corrosion protection, then corrosion resistance is improved, but severe and rapid corrosion of other components occurs due to redox reactions with less noble metals
Solution Approach 1:
The patent uses a plastic coating layer as an intermediary barrier between the precious metal coating and the medium. This plastic layer prevents direct contact between the precious metal and corrosive substances, eliminating the redox reactions that would otherwise occur between the precious metal and less noble metal components. The intermediary layer isolates the two materials.
4Reliability
If a hard material coating (SiC, DLC, BN) is applied via CVD to provide corrosion resistance, then chemical resistance is improved, but the coating contains microscopic defects (microperforations, pinholes) that allow corrosion penetration
Solution Approach 1:
The patent combines a hard material coating (SiC, DLC, or BN) applied via CVD with a plastic coating layer. The hard material layer provides excellent chemical resistance and hardness, while the plastic layer acts as a complementary barrier that can seal or cover the microscopic defects inherent in the hard material coating, preventing corrosion penetration through pinholes and microperforations.
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 multi-layer coating offers superior corrosion resistance and diffusion barrier performance, even with thin layer thicknesses, effectively protecting components from mechanical damage and extending the service life of field devices under extreme conditions.
Implementation Method 1
a first layer (4) consisting of a material which is composed of a densely packed atomic arrangement and which first layer (4) provides corrosion protection for the medium
Implementation Method 2
the first layer (4) has a thickness of about 10 μm and is elastic
Data Source
Figure 1
Figure 2a~2b
AI summary
Field device (7, 12) used in process and/or automation engineering for monitoring at least one chemical or physical process variable of a medium (16) in a component (17) carrying a medium at least partially and temporarily and comprising at least an electronic unit (14) and a sensor unit (15), wherein at least one portion of at least one component (3) of the sensor unit is in contact with the medium at least temporarily, the at least one portion of the component (3) in contact with the medium is provided with a chemically resistant multilayered coating (2) consisting of at least two layers, wherein a first layer (4) is made of a material consisting of a densely packed atomic arrangement which provides a protection against corrosion by said medium, and a second layer (5) consisting of a chemically resistant plastic material is arranged around the first layer (4) and protects the first layer against outer damage and corrosion.