In applications where hydrogen is measured, pressure transmitters or differential pressure transmitters usually use stainless steel diaphragms. However, when handling and measuring hydrogen, it is common practice to gold-plate stainless steel diaphragms. The reason behind this involves the physicochemical properties of hydrogen and its interaction with metallic materials. Here's how:
1. Characteristics and permeability of hydrogen
Hydrogen (H₂) is one of the smallest molecules in nature and is extremely permeable. Its extremely small molecular size allows it to easily penetrate many solid materials, including metals such as stainless steel. When hydrogen penetrates the stainless steel diaphragm, it can cause the following problems:
Hydrogen Embrittlement: Hydrogen atoms can diffuse into the lattice of stainless steel, causing the material to become brittle. Hydrogen infiltration will cause stress concentration, resulting in brittle fracture or damage of stainless steel under mechanical stress.
• Measurement error: Hydrogen permeates the back of the diaphragm, affecting the strain characteristics of the diaphragm, which in turn affects the measurement accuracy of the transmitter.
2. The necessity of gold plating
Gold plating is used to reduce or prevent the penetration of hydrogen. Gold is a high density and chemically inert metal with excellent permeability resistance. The specific reasons are as follows:
Low permeability: The permeability of gold to hydrogen is much lower than that of stainless steel. This is because gold has a tighter lattice structure and a dense array of atoms, which can effectively prevent hydrogen molecules from passing through.
Corrosion resistance: Gold does not react with hydrogen and is therefore able to maintain its physicochemical stability so that it does not deteriorate or corrode when exposed to hydrogen.
• Reduce hydrogen embrittlement: Because gold can block the penetration of hydrogen, the stainless steel substrate is not susceptible to the diffusion of hydrogen atoms, thereby reducing or preventing hydrogen embrittlement.
3. Mechanism of gold-plating treatment
When the stainless steel membrane is gold-plated, the gold layer acts as a physical barrier, preventing hydrogen molecules from penetrating the bottom layer of the stainless steel. This treatment significantly reduces hydrogen penetration, protects the structure inside the diaphragm, maintains the mechanical strength and elastic properties of the stainless steel diaphragm, and ensures that the pressure transmitter provides stable and accurate readings when measuring hydrogen.
Technical details include:
• Thickness of the gold plating: The thickness of the gold plating needs to be thin enough not to affect the sensitivity of the diaphragm, but also thick enough to prevent hydrogen from penetrating. Usually the thickness ranges from a few microns to tens of microns.
• Gold plating process: Using technologies such as electroplating or physical vapor deposition (PVD) to ensure that the gold layer is uniform and void free to enhance its permeability resistance.
4. Application examples and practical experience
In industrial applications, hydrogen is widely used in chemical industry, energy and other fields, pressure transmitter is the key measurement equipment. If there is no gold-plated protection, the stainless steel diaphragm will gradually fail after long-term exposure to hydrogen. Therefore, when measuring the pressure in high-purity hydrogen or hydrogen-containing environments, the choice of gold-plated diaphragm can significantly improve the service life and measurement stability of the instrument.
Sum up
Stainless steel diaphragms need to be gold-plated when measuring hydrogen because of the high permeability of hydrogen and the potential hydrogen embrittlement effect on stainless steel. By gilding the membrane, an anti-permeability barrier is formed to prevent the hydrogen molecules from penetrating, ensuring the measurement accuracy and long-term stability of the device.
Thank you
