In modern industry and defense, you may often hear the name “black diamond”. Yes, this unique name refers to boron carbide ceramics (B4C). It is a very critical advanced ceramic material. Read on to learn all about boron carbide ceramics.
Quick Links
- What is Boron Carbide Ceramic?
- Characteristics of Boron Carbide Ceramics
- Production Process of Boron Carbide Ceramics
- Application of Boron Carbide Ceramics
- Boron Carbide Product Forms and Specifications
What is Boron Carbide Ceramic?
Boron carbide ceramic is a non-oxide technical ceramic material that occupies a very important position in the field of materials. You need to know that it is one of the hardest materials known so far, second only to diamond and cubic boron nitride. In addition to high hardness, it also has the characteristics of low density, with a density of only 2.52 g/cm³. A variety of superior performance combinations make it unique in many high-performance applications.
Is Boron Carbide a Metal?
You may be curious, “Is Boron Carbide a Metal, a Ceramic, or a Polymer?”
Boron carbide is not a metal or a polymer. It is a member of the ceramic material family. More specifically, it is a covalently bonded non-oxide ceramic. This material has the following characteristics:
Structural characteristics: Boron carbide has a typical crystal structure of ceramic materials, and boron atoms and carbon atoms are connected by covalent bonds.
Performance: Boron carbide has the characteristics of typical ceramic materials, such as high hardness, high melting point, and good chemical stability, but its toughness is relatively low.
Although boron carbide is not a metal, it has some metal-like properties (such as conductivity). Due to its basic properties and preparation process, it is still classified as a ceramic material.
Chemical structure and molecular formula of boron carbide
The chemical formula of boron carbide is B4C. It has a unique crystal structure, and its basic structural unit is composed of B12 icosahedron and C-B-C chain. In this structure, twelve boron atoms form an icosahedral cage structure, and carbon atoms and boron atoms form linear chains connecting the icosahedrons. This special structure gives boron carbide a unique crystal structure.
Boron Carbide Structural Elements
You need to note that boron carbide can form non-stoichiometric compounds within a certain range, such as (B12+xC3-x, 0≤x≤0.1). This flexible combination allows you to optimize specific properties by adjusting the components.
Characteristics of Boron Carbide Ceramics
Boron carbide ceramics have many superior characteristics. Before fully understanding boron carbide ceramics, we recommend that you first understand the basic characteristics of boron carbide as a material. These characteristics determine the specific performance of boron carbide ceramics in various applications and are the objects you need to focus on.
Density and hardness
As we mentioned earlier, boron carbide has a very low density of 2.52 g/cm3. In addition, its hardness is also very high, second only to diamond. These two superior properties make it very advantageous as an engineering material.
Theoretical density: 2.52 g/cm³
Vickers hardness: 28-35 GPa
Mohs hardness: 9.5-9.75
This low density and high hardness make it an excellent lightweight protective material. In some armor designs, boron carbide ceramics can provide excellent protective strength and are much lighter than many traditional materials.
Thermal properties
Boron carbide also performs very well in high-temperature applications. The following are the main thermal properties of boron carbide:
Melting point: 2450℃
Thermal conductivity: 30-35 W/(m·K)
Coefficient of thermal expansion: 5.5×10⁻⁶/K (room temperature to 1000℃)
Specific heat capacity: 950-1200 J/(kg·K)
These superior properties allow boron carbide to maintain good stability even in harsh high-temperature environments.
Electrical properties
As a ceramic material, boron carbide also has some semiconductor properties:
Resistivity: ranges from 0.1-10 Ω·cm
Band gap: about 2.09 eV
Conduction type: P-type semiconductor
These excellent electrical properties make boron carbide very promising in some high-temperature electronic devices.
Chemical stability
Boron carbide has very stable chemical stability and has good resistance in some acidic and alkaline environments. The following are some chemical stabilities of boron carbide:
Oxidation resistance: It has excellent oxidation resistance and can maintain good stability below 1000℃
Acid resistance: It can resist corrosion from most inorganic acids.
Alkali resistance: It can remain stable in alkaline environments
Hydrolysis resistance: It will not undergo hydrolysis at room temperature
Although the chemical properties of boron carbide are very stable, you still need to pay attention that in high temperature (>1000℃) oxidizing environments, boron carbide will gradually oxidize to form B2O3. When you use boron carbide ceramics at extremely high temperatures, you need to consider this factor and take precautions.
Production Process of Boron Carbide Ceramics
In the preparation process of boron carbide ceramics, the control of the process will directly affect the final performance of the product. Below we will analyze in detail the key processes of boron carbide ceramics from powder to final molding.
Powder preparation
The preparation of boron carbide powder is the basis of the entire production process. Currently, there are two main process routes:
1. Carbon thermal reduction method
This is the most commonly used commercial production method. In this process, you only need to react B2O3 with carbon in an arc furnace at a high temperature of 2400℃ to generate boron carbide.
2B2O3 + 7C → B4C + 6CO
The advantage of this method is that the cost of raw materials is relatively low and the process is mature.
2. Magnesium thermal reduction method
Magnesium thermal reduction method can be carried out at a lower temperature:
2B2O3 + 6Mg + C → B4C + 6MgO
With this method, you can get finer powder, but the cost will be relatively high.
Molding sintering process
Hot pressing sintering
Hot pressing sintering is one of the most commonly used densification methods. In this step, you need to apply pressure (30-40MPa) and temperature (2100-2200℃) at the same time. Through this process, you can obtain a dense body with a relative density of up to 99%.
Pressureless sintering
Pressureless sintering is a more economical densification method, but the process requirements are higher. The sintering temperature of this process needs to reach 2300-2400℃, and it is carried out in an inert atmosphere or vacuum. This process usually requires the addition of sintering aids (such as Al2O3, Cr, Co, etc.).
For some large-scale production and large-sized complex parts, this process is very suitable, but the density of the finished product produced may be slightly lower than that of hot pressing sintering.
Isostatic pressing sintering
Isostatic pressing sintering combines the advantages of isostatic pressing and high-temperature sintering. First, you need to wait for cold isostatic pressing, and the pressure usually needs to be 200-300MPa and the temperature is 2200-2300℃. You can use this process to make larger, more complex parts with a more even density distribution.
Application of Boron Carbide Ceramics
Military protection
In modern society, the importance of the protection system is becoming more and more popular. Boron carbide ceramics play an irreplaceable role in the field of protection due to their excellent comprehensive properties.
Personal protective equipment
In personal protection, boron carbide ceramic plates are the core material of high-end bulletproof equipment. Compared with traditional armor steel, you can get better weight advantages by using boron carbide ceramics.
Research shows that a set of standard boron carbide bulletproof plates can provide protection level up to SK4, and its weight is only 30 kg/m², while the weight of steel bulletproof plates of the same protection level is more than 42 kg/m².
In actual applications, boron carbide ceramics are usually combined with high-performance composite materials, such as Dyneema or Kevlar. This combination not only provides excellent multi-strike protection capabilities, but also ensures comfort and mobility.
Vehicle Armor
In vehicle protection systems, boron carbide ceramics can also demonstrate their unique advantages. When dealing with various threats, a variety of boron carbide ceramic components in different shapes (plates, hexagons or cylinders) can help you protect against various fragments and blast impacts.
It is particularly important for vehicle chassis protection, and boron carbide ceramics can play an important role. The boron carbide ceramic composite armor system can effectively protect against mine explosions and improvised explosive devices, and its lighter weight can also reduce the total weight of the vehicle and improve maneuverability.
Aircraft protection
In the field of aviation protection, the weight control of materials is extremely strict. Boron carbide ceramics can be seen in some helicopter seats and key parts protection. The use of customized boron carbide ceramic plates can provide pilots with maximum protection and effectively control the increase in weight.
Boron carbide bulletproof sheet characteristics
Boron carbide bulletproof sheet has the following outstanding characteristics:
Thickness: between 8-20mm according to the protection level
Surface density: less than 30 kg/m², reaching SK4 level
Multiple strike capability: can withstand multiple violent impacts within a specified distance
Lifespan: reasonable storage can reach more than 10 years
Comparison with other protective materials
When faced with the choice of different protective materials, you need to consider multiple factors. The following is a comparison of boron carbide ceramics with other common protective materials:
Protective performance (SK4 level surface density comparison):
Boron carbide composite system: <30 kg/m²
Alumina ceramics: 42 kg/m²
Armor steel: >50 kg/m²
Extended reading: The best bulletproof material
Industrial Applications
In the industrial field, boron carbide ceramics still have many wide applications. Its unique physical and chemical properties make it an ideal material choice for many harsh working environments.
Grinding and polishing
In the field of precision machining, boron carbide powder and slurry are the first choice for machining superhard materials. As an efficient grinding medium, you can use boron carbide to process various difficult-to-process materials, including cemented carbide, non-ferrous metals, titanium alloys and ceramics.
Boron carbide grinding slurry can be used for the processing of a variety of precision parts, such as grinding of mechanical parts, finishing of tools, surface treatment of various molds, etc. This slurry has the following characteristics:
Different types of boron carbide slurries have different use temperatures. Water-soluble boron carbide slurries can be used below 200°C, while oil-based boron carbide slurries can be used at temperatures up to 350°C. This temperature adaptability enables it to meet your different working conditions. It is worth noting that if you use petroleum or motor oil as a diluent, it will provide more convenience for process adjustment.
Sandblasting nozzles
In sandblasting operations, the service life of the nozzle directly affects the operating efficiency and cost. Boron carbide ceramic nozzles can provide you with the best solution with their excellent wear resistance. Compared with other materials, boron carbide nozzles show a more superior cost advantage.
You can also use boron carbide nozzles in many occasions, such as part deburring, surface treatment, glass etching, etc. Even when using high-hardness abrasives (such as corundum, silicon carbide), boron carbide nozzles can still maintain stable spraying performance and a long service life.
Cutting tools
In the field of cutting tools, boron carbide is mainly used to make special cutting tools and abrasives. When you need to process high-hardness, brittle materials, boron carbide tools can provide you with excellent cutting performance:
For processing cemented carbide
Precision cutting of ceramic materials
Cutting of hard and brittle materials such as sapphire
Boron Carbide Product Forms and Specifications
With the continuous advancement of modern technology, boron carbide ceramic products have developed a variety of forms to meet the needs of your various application scenarios.
Powder products
Boron carbide powder is the most basic product form and the raw material basis for other product forms.
Grinding grade powder
The particle size distribution range of grinding grade powder is generally 0.8-20μm, and the purity is required to be above 99.5%. You need to note that the uniformity of particle size distribution will directly affect the grinding effect of the final product. For some precision grinding applications, we recommend that you choose fine powder with D50 less than 2μm, which can help you get better surface finish.
Sintering grade powder
Sintering grade powder is generally controlled between 0.8-2μm, and the purity is required to reach above 99.9%. When using this type of powder, you need to pay attention to the control of agglomeration, because this will directly affect the subsequent densification process.
Plate products
Boron carbide plate is also one of the most widely used product forms. Depending on the application scenario, it has a variety of specifications for you to choose from:
Protective plate
The thickness of the protective plate is usually between 8-20mm, and the size can reach 500×500mm. The dimensional accuracy and surface quality of the plate have an important impact on the improvement of protective performance.
Boron carbide plate is one of the most widely used product forms. Depending on the application scenario, you can choose different specifications.
Industrial plate
Industrial plate has a wider range of specifications, with thickness ranging from 1mm to 50mm, and the size can be customized according to your needs. When choosing, you need to consider the requirements of the use environment and make the best choice based on cost factors.
Special-shaped parts
The preparation of special-shaped parts requires very high boron carbide manufacturing and molding technology. Such products are usually designed and produced by customers according to drawings.
Due to the brittle characteristics of boron carbide ceramics, overly complex shapes or sharp edges should be avoided during the design process. Secondly, during the hot pressing and sintering process, about 20% shrinkage will occur, so you need to pay attention to the design of the mold.
Composite Materials
Boron carbide composite materials are made by combining boron carbide with other materials to optimize performance.
Composite materials for protection
Composite plates made of boron carbide and high-performance fibers (such as Kevlar and Dyneema) can significantly improve toughness while maintaining the superior protective properties of boron carbide.
Industrial composite materials
The composite materials used in the process are more extensive. Boron carbide can be compounded with other ceramic materials or with metals to achieve better performance. For example, the composite materials of boron carbide and silicon carbide can have better grinding and wear resistance performance; while the composite materials with metals can be used as special cutting tools.
Summary
Boron carbide ceramics have excellent performance and a wide range of applications. I hope you will find this article helpful.