月: 2023年1月

What Is Diethyl Carbonate?

Diethyl carbonate, a neutral ester of carbonic acid, emits an ethereal odor and appears as a colorless liquid at room temperature. Due to its low flash point, it is classified as a hazardous and inflammable substance under various safety laws, necessitating careful handling.

Uses of Diethyl Carbonate

This compound finds application as a solvent for nitrocellulose, and synthetic resins, and as a reaction solvent, cleaning, and stripping agent. It is notably used as an electrolyte solvent for lithium-ion batteries, in organic synthesis for ethoxycarbonylation, and as a raw material in the production of polycarbonates and polyurethanes. Additionally, it facilitates C-alkoxycarbonylation reactions and the formation of 2-oxazolidinone from 1,2-amino alcohols.

Properties of Diethyl Carbonate

With a melting point of -43°C and a boiling point between 126-128°C, diethyl carbonate is insoluble in water yet soluble in organic solvents like ethanol, chloroform, and ether. It boasts a flash point of 25°C, an ignition point of 445°C, and a molar mass of 118.13 g/mol. Its density is 0.975 g/cm³.

Other Information on Diethyl Carbonate

1. Synthesis with Phosgene or Urea

Diethyl carbonate can be synthesized through the reaction of phosgene and ethanol, producing hydrogen chloride as a byproduct. Alternatively, it can be generated from urea and ethanol, with ethyl carbamate forming as an intermediate. This process requires a heterogeneous catalyst that acts as both a Lewis acid and a base.

2. Other Synthetic Methods

Other methods include the reaction of silver carbonate with ethyl iodide, oxidative carbonylation with carbon monoxide and ethanol, and transesterification from dimethyl carbonate. Additionally, it can be produced using ethyl nitrite and carbon monoxide with a palladium catalyst.

3. Related Compounds

As a type of carbonate ester, diethyl carbonate is related to dimethyl carbonate, diphenyl carbonate, and cyclic esters like ethylene carbonate and propylene carbonate.

What Is Boron Carbide?

Boron carbide, a compound of boron and carbon with the chemical formula B₄C, is a grayish-black powder known for its exceptional hardness—second only to diamond on the modified Mohs scale—and excellent wear resistance. This material is notable for its chemical stability, being resistant to attack by both acids and alkalis.

Uses of Boron Carbide

Due to its superior hardness and wear resistance, boron carbide is utilized in various applications requiring durability. It is commonly found in cutting tools, abrasives, cermets, mortars, and bulletproof materials. Its high electrical insulation and thermal conductivity make it suitable for use in high-temperature industrial environments, including in electronic components and hard disk heads. Additionally, its high neutron absorption capacity, thanks to the natural abundance of boron-10, allows its use in nuclear reactors for fission reaction control and neutron shielding.

Properties of Boron Carbide

With a molecular weight of 55.25, a density of 2.51, and a melting point of 2350℃, boron carbide boasts a high melting point, low specific gravity, and remarkable heat and chemical resistance. It begins to oxidize at 570℃ and reacts with chlorine at high temperatures to form boron trichloride, although it is generally resistant to acids and alkalis except when exposed to alkali fusion or hydrofluoric acid.

Structure of Boron Carbide

The rhombohedral crystal structure of boron carbide features three carbon atoms on the diagonal of a unit lattice, with boron atoms forming an icosahedron at each vertex. This structure allows for the substitution of carbon with boron, affecting the material’s properties minimally due to the unchanged crystal backbone.

Types of Boron Carbide

Available in both bulk and powder forms, boron carbide is processed into various ceramic products such as plates, nozzles, and seals, utilized in bulletproofing, sandblasting, and mechanical sealing. Its particulate form serves as an abrasive, antioxidant for refractory materials, and a sintering aid for silicon carbide, with applications determined by particle size uniformity.

Other Information on Boron Carbide

How Boron Carbide Is Produced

Industrially, boron carbide is synthesized by heating a mixture of boron oxide and carbon in an electric furnace. This thermal carbon reduction method uses boric acid or boron oxide and activated carbon or petroleum coke, offering a cost-effective and safe mass synthesis approach. Alternative methods include direct boron and carbon reaction, synthesis from composite carbides using TiO₂-SiO₂-B₂O₃ glass, and a low-temperature synthesis involving boric anhydride or borax, magnesium, and carbon.

What Is Titanium Carbide?

Titanium carbide (TiC) is a face-centered cubic lattice crystal, part of the NaCl-type structure, where metal and carbon atoms are alternately arranged. It has a molar mass of 59.9 g/mol, melts at 3,170℃, and has a density of 4.9 g/cm³. Identified by CAS number 12070-08-5, titanium carbide appears as a black powder at room temperature. Its production, which began in the 20th century, was aimed at replacing expensive tungsten in filaments.

Naturally occurring as khamrabaevite [(Ti,V,Fe)C], it is a rare mineral with crystals typically ranging from 0.1mm to 0.3mm in size.

Properties of Titanium Carbide

With its insolubility in water, solubility in nitric acid and aqua regia, high electrical conductivity, and a Vickers hardness of around 3,200, titanium carbide is notable for its exceptional properties. It is produced through various industrial methods, including vacuum carbonization and plasma processes, among others. Recent research has shown that a titanium-to-carbon ratio of 2:1 allows for the creation of high-strength sintered bodies at around 1500℃ in just minutes.

Uses of Titanium Carbide

1. Cutting Tools

Due to its extreme hardness and high melting point, titanium carbide is integral to cutting tools. It is typically combined with cobalt, nickel, and molybdenum, providing a cost-effective alternative to tungsten-based cemented carbides. Its addition to tungsten carbide enhances wear and oxidation resistance, making it ideal for high-speed steel machining. Despite its hardness, its brittleness under impact and rapid cooling requires careful handling.

2. Coating Materials

As a coating, titanium carbide offers metal-like surface characteristics, enhancing the wear resistance of precision parts and instruments, including machine components and watch elements. Its application in arc electrolysis and as a welding aid for aluminum alloys showcases its versatility. Known for its low friction coefficient and excellent heat resistance among the various ceramic coatings, it is a preferred material for high-temperature component coatings.

3. Other Applications

Beyond coatings, titanium carbide is utilized in the mold-release processes for steel and resins, benefiting press molding, cold forging, and plastic molding. Its hypoallergenic and lightweight nature also makes it a popular choice for jewelry, such as necklaces.

Uses of Tantalum Carbide

Tantalum carbide, with the formula TaC, is a compound of tantalum metal and carbon. It has a high melting point of 3,740℃ to 3,880℃ and is extremely hard, with a Mohs hardness of 9-10, second only to diamond.

This material is resistant to water, dilute acids, and alkalis, but reacts slightly with sulfuric acid and hydrogen fluoride. Despite being a compound, tantalum carbide conducts electricity similarly to metals.

Its high heat resistance and electrical conductivity make it suitable for various applications. However, it usually exists in powder form and requires sintering for industrial use. Due to its high melting point, traditional hot-pressing methods are ineffective. However, new techniques like discharge plasma sintering are promising for producing high-quality sintered bodies.

Applications of Tantalum Carbide

Tantalum carbide’s high heat resistance and hardness enable its use in various applications. It’s often sintered into a cermet material and used in refractory ceramics, cutting tool parts, cemented carbide tools, cutting tools, and wear-resistant tools. It’s increasingly popular in machining automotive parts.

Additionally, its high melting point makes it suitable for coating high-temperature heating elements in the manufacture of high-temperature furnaces.

What Is Tungsten Carbide?

Tungsten carbide, a compound of tungsten and carbon, is known for its exceptional hardness, high modulus of elasticity (Young’s modulus), and excellent corrosion resistance. It combines the properties of both metals and ceramics, making it extremely rigid and durable.

Discovered in Chusum County, Shannan City, Tibet Autonomous Region, China, natural tungsten carbide was named Qusongite in 2007. Exposure to tungsten carbide dust can cause pulmonary fibrosis, similar to silicosis, and WC-Co alloys are considered potential carcinogens.

Uses of Tungsten Carbide

Primarily, tungsten carbide serves as a crucial material for cemented carbides, particularly in WC-Co alloys, which exhibit outstanding mechanical properties upon mixing and sintering with cobalt (Co). These alloys, alongside WC-Ni alloys containing nickel (Ni), are renowned for their rigidity, hardness, and wear resistance. They find extensive use in cutting tools, wire drawing dies, rolling rolls, and various types of dies.

Enhancements in oxidation and corrosion resistance are achieved by adding titanium carbide (TiC) and tantalum carbide (TaC) to WC-Co alloys.

Properties of Tungsten Carbide

With a melting point of 2,870°C and a boiling point of 6,000°C, tungsten carbide appears as a gray or black solid. Its Young’s modulus is approximately 550 GPa, making it significantly more rigid than steel, and its hardness rivals that of α-aluminum oxide.

Structure of Tungsten Carbide

The chemical formula of tungsten carbide is WC, featuring a molar mass of 195.851 g/mol. It exists in two forms: hexagonal α-tungsten carbide and cubic β-tungsten carbide, with distinct structural properties and a high density of 15.63 g/cm³ for the α form.

Other Information on Tungsten Carbide

1. Synthesis of Tungsten Carbide

Tungsten carbide is synthesized through high-temperature reactions between carbon and tungsten, utilizing various methods such as the fluidized bed technique or direct heating with graphite and tungsten(VI) oxide. Alternative methods include reactions involving tungsten hexachloride or tungsten hexafluoride with suitable carbon sources and reducing agents.

2. Reaction of Tungsten Carbide

This compound exhibits strong resistance to acids and is insoluble in water, hydrochloric acid, and sulfuric acid. It dissolves in nitric hydrofluoric acid and aqua regia. Tungsten carbide begins to oxidize at temperatures between 500-600°C and reacts with fluorine and chlorine under specific conditions. In fine powder form, it oxidizes in aqueous hydrogen peroxide solutions and reacts with sodium carbonate at elevated temperatures and pressures.