What is Carbon Black?
Carbon Black is a form of amorphous carbon which exists in various types, such as Channel black( Gas Black), furnace black, lamp black and acetylene black. In its purest form, it exists in a very fine powder state. It is obtained through the unfinished combustion process of heavy petroleums like coal tar, ethylene cracking tar.
Approximately 90% of carbon black is used in rubber applications, 9% as a pigment (For Paints & Coatings, Printing inks, Plastics, Polymer), and the remaining 1% as an essential ingredient in hundreds of diverse applications.
Carbon Black Manufacturing Process – furnace black and Channel black (Gas Black ), Acetylene Black and Lamp black
1.) The furnace black process uses heavy aromatic oils as feedstock. The production furnace uses a closed reactor to atomize the feedstock oil under carefully controlled conditions (primarily temperature and pressure). The primary feedstock is introduced into a hot gas stream (achieved by burning a secondary feedstock, e.g., natural gas or oil) where it vaporizes and then pyrolyzes in the vapor phase to form microscopic carbon particles. In most furnace reactors, the reaction rate is controlled by steam or water sprays. The carbon black produced is conveyed through the reactor, cooled, and collected in bag filters in a continuous process. Residual gas, or tail gas, from a furnace reactor includes a variety of gases such as carbon monoxide and hydrogen. Most furnace black plants use a portion of this residual gas to produce heat, steam, or electric power.
2.) The Channel black ( Gas Black ) process uses natural gas, consisting primarily of methane or heavy aromatic oils, as feedstock material. The process uses a pair of furnaces that alternate approximately every five minutes between preheating and carbon black production. The natural gas is injected into the hot refractory lined furnace, and, in the absence of air, the heat from the refractory material decomposes the natural gas into carbon black and hydrogen. The aerosol material stream is quenched with water sprays and filtered in a bag house. The exiting carbon black may be further processed to remove impurities, pelletized, screened, and then packaged for shipment. The hydrogen off-gas is burned in air to preheat the second furnace.
3.) Acetylene Black Process
This process obtains carbon black by thermally decomposing acetylene gas. It provides carbon black with higher structures and higher crystallinity, and is mainly used for electric conductive agents.
4.) Lamp black Process
This method obtains carbon black by collecting soot from fumes generated by burning oils or pine wood.This method has been used since the days before Christ, and is not suitable for mass production. However, it is used as raw material for ink sticks as it provides carbon black with specific color.
Applications of Carbon Black
Carbon black are used for Tires and Rubber, hoses, conveyor belts, Plastics, Printing Inks, Paints & Coatings( Automotive Coatings, Industrial Coatings, Powder Coatings, Architectural Coatings, Decorative Paints, Wood Coatings), Sealant, Fertilizer, Construction material ( Cement, Concrete,Brick) , And also as UV stabilizer, and conductive or insulating agent.
Main Physical Property of Tire and Rubber Carbon.
Carbon black is used with natural rubber and synthetic elastomers; carbon black acts as a reinforcer, strengthening the material. This involves mixing carbon black with elastomers and sulfur, along with multiple processing oils and chemicals. These are then heated to produce a wide variety of products.
Use Carbon Black, The benefits for both natural and synthetic elastomers: Economical reinforcing agent; Improves material’s resilience; Keeps material from tearing; Promotes conductivity; Reinforces material
Properties of Specialty Carbon Black
The properties of carbon black include: Particle Size, Structure, Porosity, Surface Activity, Physical Form, Particle Size. These propertie are important for pigment carbon black ( specialty carbon black ).
For specialty carbon blacks, smaller particle diameter gives rise to higher surface area and tinting strength. High surface area is usually associated with greater jetness, higher conductivity, improved weatherability, and higher viscosity, but requires increased dispersion energy.
For rubber, Carbon Black Particle size impacts both coloration and properties of rubber, with smaller particles offering higher conductivity and viscosity, improved weathering capabilities, stronger reinforcement, increased tensile strength and improved abrasion resistance.
To disperse finer particles size requires increased mixing time and energy. Typical particle sizes range from around 8 nanometers to 100 nanometers for furnace blacks. Surface area is utilized in the industry as an indicator of the fineness level of the carbon black and, therefore, of the particle size.
This is a measure of the three-dimensional fusion of carbon black particles to form aggregates, which may contain a large number of particles. The shape and degree of branching of the aggregates is referred to as structure.
Highly structured carbon blacks provide higher viscosity, greater electrical conductivity and easier dispersion for specialty carbon blacks. Measures of aggregate structure may be obtained from shape distributions from EM analysis, oil absorption (OAN) or void volume analysis.
This is a fundamental property of carbon black that can be controlled during the production process. It can affect the measurement of surface area providing a total surface area (NSA) larger than the external value (STSA).
Conductive Carbon Black tend to have a high degree of porosity, while an increase in porosity also allows a rubber compounder to increase carbon black loading while maintaining compound specific gravity. This leads to an increase in compound modulus and electrical conductivity for a fixed loading.
This is a function of the manufacturing process and the heat history of a carbon black and generally refers to the oxygen-containing groups present on a carbon black’s surface.
For specialty carbon black, oxidized surfaces improve pigment wetting, dispersion, rheology, and overall performance in selected systems. In other cases, oxidation increases electrical resistivity and makes carbon blacks more hydrophilic. The extent of surface oxidation is measured by determining the quantity of the “volatile” component on the carbon black. High volatile levels are associated with low pH.
While difficult to measure directly for rubber, surface chemistry manifests itself through its effects on such in-rubber properties as abrasion resistance, tensile strength, hysteresis, and modulus. The effect of surface activity on cure characteristics will depend strongly on the cure system in use.
The physical form (beads or powder) can affect the handling and mixing characteristics.
The ultimate degree of dispersion is also a function of the mixing procedures and equipment used. Powdered carbon blacks are recommended in low-shear dispersers and on three-roll mills. Beaded carbon blacks are recommended for shot mills, ball mills, and other high energy equipment. Beading provides lower dusting, bulk handling capabilities, and higher bulk densities, while powdered carbon blacks offer improved dispersibility.