The key difference between cathodic protection and sacrificial protection is that cathodic protection is the process of protecting a metal surface by making it the cathode in the electrochemical cell whereas sacrificial protection involves the protection of the desired metal surface by a sacrificial anode.

1. Apocalypto Sacrificial Procession
2. Sacrificial Princess

Cathodic protection and sacrificial protection are two related electrochemical processes. Cathodic protection involves the protection of a metal surface by making it a cathode. Sacrificial protection involves the same process, but it describes the role of the anode that makes the desired metal surface a cathode.

Blood from the male animal sacrifice was sprinkled on the brazen altar by the priests. Peace Offerings were usually voluntary and were a kind of thanksgiving to the Lord. The male or female animal was eaten by the priests and worshiper, although sometimes the offering would consist of unleavened cakes, which were eaten by the priests except for. ‘Sacrificial carbon anodes have been used in aluminum production since the process was invented in 1886.’ ‘A 2.75 - in.-thick latex layer of concrete is placed on top to act as a short-term sacrificial layer that soaks up winter road salts and chemicals.’. Libations poured and prayers made in conjunction with sacrifices will be discussed as part of the sacrificial process, but those performed without animal sacrifice, such as Akhilleus’ libation and prayer for the safety of Patroklos (Iliad XVI 220–255), are best left for a separate study. Digital Integrated Circuits Manufacturing Process EE141 CMOS Process Walk-Through p+ p-epi (a) Base material: p+ substrate with p-epilayer p+ (c) After plasma etch of insulating trenches using the inverse of the active area mask p+ p-epi SiO 2 3 SiN 4 (b) After deposition of gate -oxide and sacrificial nitride (acts as a buffer layer).

CONTENTS

1. Overview and Key Difference
2. What is Cathodic Protection
3. What is Sacrificial Protection
4. Side by Side Comparison – Cathodic Protection vs Sacrificial Protection in Tabular Form
5. Summary

What is Cathodic Protection?

Cathodic protection is a type of electrochemical process that is useful in protecting a metal surface by making it the cathode in the electrochemical cell. This term is denoted as CP. Cathodic protection is important to prevent metal surfaces from corrosion. We can observe different types of cathodic protection methods such as galvanic protection or sacrificial protection, impressed current systems and hybrid systems.

In the cathodic protection method, the sacrificial metal undergoes corrosion instead of the protected metal. Moreover, if we use cathodic protection for large structures such as long pipelines, galvanic protection technique is not enough. Therefore, we need to provide sufficient current using an external DC electrical power source. Apart from that, we can use this technique to protect fuel or water pipelines made of steel, storage tanks, ships and boat hulls, galvanized steel, etc.

What is Sacrificial Protection?

Sacrificial protection is a type of electrochemical process in which the metal of desire is protected by a sacrificial anode. Sacrificial anodes are highly active metals or metal alloys that can protect the less active metal surface from corrosion. The term galvanic anode is also used to name these anodes. Sacrificial anodes can supply cathodic protection. Generally, anodes are consumed during the protection process, so the protection has to be replaced and maintained.

Figure 02: Use of a Sacrificial Anode

We can use different materials as sacrificial anodes. Generally, they are pure metals such as zinc and magnesium. However, we can also use alloys of magnesium or aluminium. Moreover, these sacrificial anodes provide protection by being more electronegative or much more anodic than the protected metal. During this protection, a current passes from the sacrificial anode to the protected metal, and the protected metal becomes a cathode. Therefore, this process creates a galvanic cell.

When placing the sacrificial anodes, we can use either lead wires (attached to the metal surface we are going to protect via welding) or use cast-m straps (either by welding or using the straps as locations for attachment). There are many applications of sacrificial anodes, including the protection of hulls of ships, water heaters, pipelines, underground tanks, refineries, etc.

What is the Difference Between Cathodic Protection and Sacrificial Protection?

Cathodic protection and sacrificial protection are important electrochemical processes. The key difference between cathodic protection and sacrificial protection is that cathodic protection is the process of protecting a metal surface by making it the cathode in the electrochemical cell whereas sacrificial protection involves the protection of the desired metal surface by a sacrificial anode.

Below infographic summarizes the difference between cathodic protection and sacrificial protection.

Summary – Cathodic Protection vs Sacrificial Protection

Cathodic protection and sacrificial protection are important electrochemical processes. The key difference between cathodic protection and sacrificial protection is that cathodic protection is the process of protecting a metal surface by making it the cathode in the electrochemical cell whereas sacrificial protection involves the protection of the desired metal surface by a sacrificial anode.

Reference:

1. “Cathodic Protection.” Wikipedia, Wikimedia Foundation, 15 July 2020, Available here.

Image Courtesy:

1. “Cathodic Protection diagram” By Cafe Nervosa – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Anodes-on-jacket” – original uploader was Chetan at English Wikipedia. – Transferred from en.wikipedia to Commons by Armando-Martin using CommonsHelper (CC BY-SA 2.5) via Commons Wikimedia

Surface micromachining builds microstructures by deposition and etching structural layers over a substrate.^[1] This is different from Bulk micromachining, in which a silicon substrate wafer is selectively etched to produce structures.

Layers[edit]

Generally, polysilicon is used as one of the substrate layers while silicon dioxide is used as a sacrificial layer. The sacrificial layer is removed or etched out to create any necessary void in the thickness direction. Added layers tend to vary in size from 2-5 micrometres. The main advantage of this machining process is the ability to build electronic and mechanical components (functions) on the same substrate. Surface micro-machined components are smaller compared to their bulk micro-machined counterparts.

As the structures are built on top of the substrate and not inside it, the substrate's properties are not as important as in bulk micro-machining. Expensive silicon wafers can be replaced by cheaper substrates, such as glass or plastic. The size of the substrates may be larger than a silicon wafer, and surface micro-machining is used to produce thin-film transistors on large area glass substrates for flat panel displays. This technology can also be used for the manufacture of thin film solar cells, which can be deposited on glass, polyethylene terepthalate substrates or other non-rigid materials.

Fabrication process[edit]

Micro-machining starts with a silicon wafer or other substrate upon which new layers are grown. These layers are selectively etched by photo-lithography; either a wet etch involving an acid, or a dry etch involving an ionized gas (or plasma). Dry etching can combine chemical etching with physical etching or ion bombardment. Surface micro-machining involves as many layers as are needed with a different mask (producing a different pattern) on each layer. Modern integrated circuitfabrication uses this technique and can use as many as 100 layers. Micro-machining is a younger technology and usually uses no more than 5 or 6 layers. Surface micro-machining uses developed technology (although sometimes not enough for demanding applications) which is easily repeatable for volume production.

Sacrificial layers[edit]

A sacrificial layer is used to build complicated components, such as movable parts. For example, a suspended cantilever can be built by depositing and structuring a sacrificial layer, which is then selectively removed at the locations where the future beams must be attached to the substrate (i.e. the anchor points). A structural layer is then deposited on top of the polymer and structured to define the beams. Finally, the sacrificial layer is removed to release the beams, using a selective etch process that does not damage the structural layer.

Many combinations of structural and sacrificial layers are possible. The combination chosen depends on the process. For example, it is important for the structural layer not to be damaged by the process used to remove the sacrificial layer.

Examples[edit]

Apocalypto Sacrificial Procession

Surface Micro-machining can be seen in action in the following MEMS (Microelectromechanical) products:

• Surface Micro-machined Accelerometers^[2]
• 3D Flexible Multichannel Neural Probe Array^[3]

See also[edit]

References[edit]

1. ^Bustillo, J.M.; R.T. Howe; R.S. Muller (August 1998). 'Surface micromachining for microelectromechanical systems'. Proceedings of the IEEE. 86 (8): 1552–1574. CiteSeerX10.1.1.120.4059. doi:10.1109/5.704260.
2. ^Boser, B.E.; R.T. Howe (March 1996). 'Surface Micro-machined Accelerometers'. IEEE Journal of Solid-State Circuits. 31 (3): 366–375. Bibcode:1996IJSSC..31..366B. doi:10.1109/4.494198.
3. ^Takeuchi, Shoji; Takafumi Suzuki; Kunihiko Mabuchi; Hiroyuki Fujita (October 2003). '3D Flexible Multi-channel Neural Probe Array'. Journal of Micro-machines and Micro-engineering.

Sacrificial Princess