graphite Archives

February 14, 2023 by Kat Griffin Kat Griffin

Why is graphite used for electrodes?

Electrodes can be made from any conductive material. Depending on the nature of the application, electrodes are typically from graphite. Noble metals like gold, silver or platinum can be used but are very expensive. Copper, titanium and brass are other options, but they are also costly.

Graphite is used as an electrode material because it is a good conductor of electricity, is chemically stable, and can withstand high temperatures. It also has a low reactivity and thermal expansion coefficient, making it suitable for electrode use in electrochemical cells.

Graphite is a Good Conductor of Electricity

Graphite’s unique structure, with layers of carbon atoms arranged in hexagonal, allows the electrons to move freely, making it a good conductor of electricity and useful as an electrode material.

In graphite, the carbon atoms are arranged in layers, retaining their structure through covalent bonds. A significant feature of graphite’s structure is the number of delocalized electrons present. Graphite requires only three of its outer energy electrons to bond, leaving the fourth free to act in a delocalized manner. Delocalized electrons are not readily associated with a particular atom and move freely. These electrons enable graphite to exhibit a high level of conductivity, explaining why the material is frequently used for electrodes.

Graphite Electrode Materials

Check out MWI’s EDM Graphite Product Guide that contains information for our Electro-Carb “EC” family of graphite electrode materials. Graphite grades include EC-4, EC-12, EC-14, EC-15, EC-15C. EC-16, EC-17, HK-6, and HK-6C.

November 30, 2022 by Kat Griffin Kat Griffin

What are the Structure and Properties of Graphite?

Carbon-graphite offers a unique combination of physical, chemical and mechanical characteristics found in no other material. One particular characteristic is its structure.

Graphite has a layered structure. In each layer, each carbon atom is bound to three others. This results in a two-dimensional network of hexagons. Within each layer, there are strong bonds, but between the different layers, the bonds are fragile. Thus, the layers can easily be shifted against each other and separated. This structure is why graphite is very soft and even used as a lubricant. But graphite has other unique characteristics as well:

Electrical Conductivity of Graphite

The fact that graphite is electrically conductive results from its atomic structure. Each carbon atom in a graphite crystal has four valence electrons, also called outer electrons, which can form bonds with neighboring atoms. However, only three of the four valence electrons enter into a bond, while the fourth electron remains freely mobile and thus allows electricity to be conducted.

Thermal Conductivity of Graphite

Graphite has excellent thermal conductivity combined with high-temperature resistance. Graphite does not have a melting point; it changes from the solid state directly into the gaseous state. This process is called sublimation. In an inert gas atmosphere, graphite becomes plastically deformable starting at 2500 °C. At temperatures above 3750 °C, graphite sublimates even without oxygen.

Chemical Resistance of Graphite

Graphite is one of the most chemically resistant materials. It is resistant to almost all media of organic chemistry. These typically include the intermediate and/or end products in the petrochemicals, coal refining, plastics industry, the production of paints, coatings, refrigerants, and antifreeze, but also in the cosmetics and food industries. In addition, graphite is resistant to most inorganic media, such as non-oxidizing acids, alkalis, aqueous salt solutions, and most technical gasses.

Important Chemical Reactions

Reaction with Air
Carbon in the form of Graphite, burns in the air to form Carbon Monoxide and Carbon Dioxide depending upon the availability of air or oxygen.

C(s)+O2→CO2(g)
2C(s)+O2(g)→2CO(g)

Reaction with Water
Carbon in the form of Graphite doesn’t react with water in normal conditions. Under certain circumstances, the given reaction becomes possible and forms water gas which is a mixture of carbon monoxide and hydrogen gas.

C+H2O→CO+H2

November 3, 2022 by Kat Griffin Kat Griffin

What is Graphite?

Graphite is a naturally occurring modification of the element carbon (C). Its atoms arrange themselves in the hexagonal pattern typical for carbon and thus form a hexagonal layered lattice. As a result, graphite gets its typical gray color from its opaque gray to black crystals.

Natural graphite is mainly used for refractories, batteries, steelmaking, brake linings, foundry facings, lubricants in pinewood derby, and headphones. Graphene, a one-atom-thick layer of graphite, is used to make the 40mm acoustic drivers that deliver sound to the ear in your headphones.

Graphite is also in pencils. In pencils, graphite particles are packed together inside a core made from wax or plastic. It’s most suitable for making pencils because graphite is soft and slippery. This makes it easy to rub off, leaving a mark on your paper. A soft pencil is about 90% graphite, while a harder one is around 20% graphite. To harden graphite, you need to mix graphite and clay with water and leave it out for about three days to dry and harden completely. Graphite of various hardness or softness results in different qualities and tones when used as an artistic medium.

Natural Graphite

Graphite occurs naturally on earth but can also be produced synthetically. Natural graphite is mainly mined underground and above ground in Brazil, China, India, Mexico, and Ukraine. The production process of synthetic graphite, on the other hand, is highly complex – but simultaneously offers the possibility of modifying the properties of graphite as desired.

Flexible graphite (expanded or exfoliated graphite) is produced from natural graphite flakes. The flakes are mixed with a highly oxidizing acid in the manufacturing process to produce graphite intercalation compounds. A sudden application of high temperature expands these. The resulting product, called expanded graphite, is mechanically compressed to shaped products, mainly graphite foil. Although still showing the unique properties of natural graphite, e.g., its excellent conductivity, expanded graphite foil is also flexible, soft, and easy to process in contrast to the raw material.

There are three types of natural graphite:

High crystalline
Amorphous
Flake

Synthetic Graphite

The manufacturing processes for synthetic graphite are comparable to those for ceramic materials. First, the solid raw materials coke and graphite are ground and mixed in mixing units with carbonaceous binders such as pitches to form a homogeneous mass. This is followed by shaping. Various processes are available for this purpose: isostatic pressing, extrusion, vibration molding, or die molding. The pressed “green” bodies are then heated under the exclusion of oxygen at about 1000 °C. During this process, binder bridges are formed between the solid particles. Graphitization – the second thermal processing step – converts the amorphous carbon into three-dimensionally ordered graphite at about 3000 °C. The graphitized molded parts are then mechanically processed into complex components. Optionally, these can be further refined by additional cleaning processes and coating steps, such as silicon carbide (SiC) coating. The grain size of the graphite powder and the pressing method plays an important role.

The synthetic production of graphite has been technically possible since the end of the 19th century. In December 1895, a patent for the graphitization of carbon was registered in the USA. The electrographite obtained in this manufacturing process was then used as a current-transmitting element in the form of electrodes and graphite, thus becoming increasingly important for a wide range of industries.

Synthetic graphite is formed by two raw materials: a carbon carrier that is as pure as possible, usually coal from crude oil, and pitch as a binder. The two raw materials are mixed to form a homogeneous mass and then processed and refined in complex high-temperature processes. The processes vary depending on the desired properties and type of synthetic graphite. This way, a process can be reproduced in the shortest possible time, for which nature takes several million years.

Advantages

Heat resistant
Super lightweight
Increased strength at higher temperatures
Low thermal expansion (3 times lower than copper), which guarantees the stability of electrode geometry during electro-discharge machining
Density is 5 times lower than that of copper, which results in lighter electrodes
Provides a higher metal removal rate than copper, with less wear
Good thermal conductivity
Good electrical conductivity
Self-lubricating
Easy to machine
Very resistant to thermal shock
Available in large blocks

January 21, 2015 by rMcMahon rMcMahon

Democrat & Chronicle Features MWI, Inc.

On the machine shop floor sits a six-foot-wide slab of round graphite. Imagine the lead for a mechanical pencil the size of a skyscraper.

Each day at MWI, Inc. in Henrietta, a manufacturer of polysilicon composite, almost every shape and dimension of graphite stock imaginable is worked into molds for high-temperature applications.

“It’s one-tenth the weight of steel, yet it withstands temperatures greater than 1,000 degrees Celsius,” said Brian McMahon, MWI vice president of operations.

An easy-to-mill product and an excellent conductor of electricity, graphite is a commodity for several industries. Because it strengthens when heated, it is no surprise that one of the most interesting industries happens to be aerospace technology. MWI has been commissioned to make molds that form huge satellite reflectors.

“We’re also working on experimental airplane components,” McMahon said, “and heat-treat tooling for ongoing space programs.”

Graphite molds can also be used for the medical industry, to create parts for the coating of heart valves, the LED market for processing wafers, fuel cell flow fields and solar applications.

“Because the product is inert, it won’t decompose in a certain chemical environment,” said McMahon. “That makes it very useful in applications where most materials would break down. Graphite actually doubles in strength at temperatures where metals have since vaporized.”

The company spends a great deal of effort to keep the facility free from dust, which helps maintain a contaminant-free process. To enable this, MWI operates two enormous furnaces that operate in excess of 2,000 degrees Celsius.

“We’re using basing chemistry to vaporize any molecules that aren’t carbon,” McMahon said. “The process is to ensure that our customers receive the purist, uncontaminated product, because impurities will affect their process.”

MWI employs 110 people, about half in administration, sales, and support, and the rest in operations. It has manufacturing facilities in Massachusetts, Indiana, and California. Other offices are located in Oregon, Texas, and Michigan. Because machinists are difficult to come by, the company has established its own machinist’s program, and has hired graduates of National Technical Institute for the Deaf and Monroe Community College.

McMahon said the company is constantly reinvesting in the business, and will spend $2 million in the next year, mostly in equipment. He recently returned from Italy, where he had a hands-on demonstration of some prospective machines.

“I love working with the employees, the customers, the vendors — all of it,” he said. “Not every day can be a gem, but when we work hard to ship tangible product that was made by hand and machine, it’s very rewarding.”

Russo is a freelance writer covering the Rochester area.

Brian McMahon’s Five Must-Do’s

1. Hire and retain great employees.

2. Listen to employees and empower them to make change at every level.

3. Invest in technology to enhance your service and increase morale.

4. Eliminate all obstacles to gain and retain your customers’ business.

5. Manage cash flow.

Check out the feature story in the Democrat & Chronicle.