Aluminum nitride (AlN), with the chemical formula AlN, is a covalent bonded nitride consisting of [AlN₄] tetrahedra as structural units. It belongs to the hexagonal crystal system and has characteristics such as low molecular weight, strong atomic bonding, simple crystal structure, and high lattice vibration coordination.

 

Due to the unique crystal parameters, AlN exhibits excellent properties such as high thermal conductivity, high strength, high volume resistivity, high insulation withstand voltage, low dielectric loss, and a thermal expansion coefficient that matches silicon. These properties make AlN an ideal material for high thermal conductivity ceramic electronic substrates and packaging materials. It is often considered the most ideal electronic substrate material.

 

Tip 1: Thermal Conductivity and Other Applications of AlN

 

The theoretical thermal conductivity of AlN single crystals is 320 W/(m·K), while the thermal conductivity of polycrystalline AlN ceramics can range from 140 to 200 W/(m·K), which is approximately 10 times that of conventional resin substrates and alumina ceramics. In addition, AlN has a direct bandgap structure and can theoretically emit light across a wide range of wavelengths, from deep ultraviolet to deep infrared. It is an indispensable material in GaN-based light-emitting diodes, field-effect transistors, and other devices.

 

1. Why Modify the Surface of Aluminum Nitride Powders?

The surface of AlN powders is highly reactive and easily reacts with moisture in the air. AlN initially transforms into an amorphous AlOOH phase, which may further convert into Al(OH)₃ under certain temperature, pH, and ion activity conditions. This leads to the formation of Al(OH)₃ or AlOOH (aluminum hydroxide) films on the surface of the powders. The increase in oxygen content significantly reduces the thermal conductivity of AlN ceramics. Due to this characteristic, handling, storage, transportation, and post-processing of AlN powders can be problematic.

 

Tip 2: Methods for producing Aluminum Nitride Powders

 

The primary methods for producing high-purity, fine-grained, and narrowly distributed AlN powders include the direct nitridation of aluminum powder, the carbothermic reduction of aluminum oxide, self-propagating high-temperature synthesis (SHS), chemical vapor deposition (CVD), and high-energy ball milling. Industrial production mainly uses the first two methods, while the others are primarily employed in experimental research.

 

Tip 3: Methods for Determining the Hydrolysis Degree of AlN Powders

 

The degree of hydrolysis of AlN powders can be determined through various techniques, including X-ray diffraction (XRD) analysis to examine phase changes, scanning electron microscopy (SEM) to observe changes in the shape of AlN powder particles before and after hydrolysis, and transmission electron microscopy (TEM) to analyze the crystal structure of the products. Additionally, the hydrolysis degree can be determined by monitoring the ammonia gas produced during hydrolysis, which results in the formation of NH₄⁺ and OH⁻ ions, leading to changes in the pH of the solution.

 

Moreover, the primary forming method for AlN-based ceramic substrates, often referred to as the "king of ceramic substrates," is the slip casting method. This method is efficient and cost-effective. However, the hydrolysis of AlN powders severely hinders the development of water-based slip casting processes for AlN ceramics. Non-water-based slip casting methods, while viable, are expensive, lead to poor uniformity of samples, and generate organic vapors that cause environmental pollution.

 

In addition, new applications of AlN, such as in thermally conductive plastics and thermally conductive adhesives, require AlN powders with improved hydrolysis resistance, compatibility with organic materials, and low interface thermal resistance.

Thus, improving the hydrolysis resistance and stability of AlN powders has become a hot topic in research on surface modification methods for AlN powders. The following will briefly explore the methods of surface modification for AlN.

 

2. Surface Modification Methods of Aluminum Nitride (AlN)

 

There are various surface modification techniques for AlN powder, with the basic principle being to perform physical adsorption or chemical treatment on the powder's surface. This results in the coating of AlN particles or the formation of a thin reactive layer, preventing AlN powder from hydrolyzing when it interacts with water. The main methods include coating modification, surface chemical modification, and heat treatment, among others.

 

1. Coating Modification Method of AlN 

Coating modification is a traditional method that has been applied for a long time. It involves coating AlN powder with inorganic or organic compounds to reduce or shield particle agglomeration. Furthermore, the coating generates steric hindrance, making it difficult for the particles to re-agglomerate, thus achieving surface modification. The modifiers used for coating include surfactants, inorganic materials, dispersants, etc.

 

a. Surfactant Method

Surfactant modification relies on the surface charge characteristics of AlN particles. By adding cationic or anionic surfactants, the interfacial tension between the powder dispersion system (gas-liquid, solid-liquid) is altered, and a coating layer is formed on the powder surface with carbon-oxygen chains extending outward. The surfactant's hydrophilic group can adsorb onto the solid surface, alter chemical reactivity, and lower surface tension, which can control the hydrophilicity, lipophilicity, and surface activity of the nanomaterial. This process modifies the surface properties of the powder or imparts new characteristics to the powder.

 

This is reflected in three aspects:

 

The hydrophilic group reacts with the surface group to form a new structure, which provides new activity to the powder surface.

The reduction of the surface energy stabilizes the powder.

The hydrophobic groups of the surfactant form steric hindrance on the surface, preventing powder re-agglomeration, thereby improving the dispersion of the nanomaterial in different media.

Example: Research by Guo Xingzhong et al. found that AlN powder modified with organic carboxylic acids and polyethylene glycol showed no significant Al(OH)3 phase after soaking in water for 48 hours, indicating that the organic carboxylic acids coated the surface of the AlN powder, thereby preventing water molecules from eroding the AlN powder surface.

 

b. Inorganic Coating Modification

Inorganic surface modification of AlN powder involves depositing inorganic compounds or metals on the surface through specific methods to form a coating film or a core-shell composite particle, improving surface properties. This process utilizes physical or chemical adsorption principles to ensure that the coating material is uniformly attached to the coated object, forming a continuous and complete coating layer. The modified powder's surface then exhibits the properties of the coating material.

 

c. Dispersant Method

Dispersants, which have amphiphilic structures similar to traditional surfactants, use anchoring groups and solvated chains to replace the hydrophilic and hydrophobic groups of surfactants. The anchoring groups can strongly adsorb onto the particle surface through ionic bonds, covalent bonds, hydrogen bonds, or van der Waals forces, either at single or multiple points. The solvated chains are selected by varying the polymer monomer or adjusting the copolymer composition to regulate compatibility with the dispersion medium. Additionally, increasing the molecular weight of the solvated chain ensures the formation of a sufficiently thick space layer on the particle surface.

 

When selecting dispersants, two main factors are considered:

 

The polarity of the dispersion medium and its solubility for the solvated chains of the dispersant. Typically, a medium with a high ability to dissolve the solvated chain and a low ability to dissolve the anchoring group is preferred.

The surface polarity, surface functional groups, and acid-base properties of the particles to be dispersed. Low-polarity particles require dispersants with multiple anchoring groups. Different functional groups have varying reactivity and interaction methods, and the absorption sites on the particle surface can select anchoring groups based on their acid-base properties.

 

Surface Chemical Modification

 

Surface chemical modification is accomplished through chemical reactions or adsorption between surface modifiers and the particle surface. Polymer long chains are grafted onto the surface of the powder, and the long chains containing hydrophilic groups in the polymer extend and form a steric barrier in aqueous media. This helps to disperse and stabilize the AlN powder in the medium, relying not only on electrostatic repulsion but also on steric hindrance, which is highly effective.

 

The selection of surface modifiers must aim to lower the surface energy of the particles, eliminate surface charges, and reduce surface attraction. To achieve good surface modification, organic substances used for modification should also provide the maximum degree of wetting with the particles, forming a uniform and dense coating. This is primarily dependent on the physical and chemical adsorption of the organic modifier on the particle surface. Physical adsorption occurs through van der Waals forces, electrostatic attraction, and other physical interactions between the modifier and the particles. Chemical adsorption relies on the reaction between functional groups on the particle surface and the modifier to achieve the surface coating of the particles by the surfactant.

 

Thermal Spray Method for Surface Coating of AlN Powder

 

The surface properties of AlN particles differ significantly from those of organic matrices, and common surface chemical modifiers (such as organosilicon, titanates, and aluminates) are used to modify the surface of AlN to increase its compatibility with the matrix. After treatment, the powder exhibits strong non-wettability to water. These small particles, with their non-wetting nature, float in water like an oil film without sinking. Based on this phenomenon, the activation index is used to characterize the degree of hydrophobicity. A higher activation index indicates better hydrophobicity, while a lower index indicates poorer hydrophobicity. When the unmodified nano-AlN powder is strongly hydrophilic, it sinks entirely when in contact with water, resulting in an activation index of R = 0. The activation index R is defined as the mass of the floating portion of the sample divided by the total mass of the sample.

 

Coupling Agent Modification of AlN

 

A coupling agent is a compound that contains both a polar group that can react with the surface of inorganic particles and an organic functional group that can react with or be compatible with organic materials. The role of the coupling agent is that one end can bind to the surface of the powder, while the other end can strongly interact with the dispersion medium. This improves the affinity of AlN powder with polymer materials, facilitating the dispersion of the powder in the polymer matrix.

 

Common coupling agents include the following types:

 

a) Silane Coupling Agents: Organic silane coupling agents are the most commonly used and widely applied coupling agents. Their general structural formula is Y-(CH2CH2-Si)-X3, where n is typically 2-3. In this structure, Y is the organic functional group, such as vinyl, methacryloxy, epoxy, amino, or hydrophobic groups, and X is the functional group bound to the silicon atom. Silane coupling agents are often classified based on the X group, which includes types like hydrolyzed silane, peroxysilane, and polysilane.

 

b) Titanate Ester Coupling Agents: These coupling agents are a new type developed by Kenrich Petroleum Company in the mid-1970s. They exhibit good modification effects for many inorganic particles.

 

c) Aluminate Ester Coupling Agents: Aluminate ester coupling agents are a new class of coupling agents.

 

b) Hydrophobization Treatment: Hydrophobization treatment involves selecting organic substances with hydrophobic groups (such as long-chain alkyl, aliphatic hydrocarbon, or cycloalkyl groups) to surround the surface of AlN powder. These hydrophobic groups firmly bond to the powder surface, resulting in a strong hydrophobicity.

 

c) Surface Grafting Modification: Surface grafting polymerization is a chemical method that links high-molecular polymers to the surface of AlN powder, significantly improving the dispersion of particles in organic solvents or polymer matrices.

 

d) Inorganic Acid Modification: Inorganic acids, such as phosphoric acid or mono-dihydrogen phosphate, are used to treat the surface of AlN powder. This treatment not only enhances the hydrolysis resistance of AlN but also improves the dispersion of the powder. The relationship between the suspension stability of AlN and time, as well as the stability of AlN in water, depends on the specific inorganic acid used.

 

Heat Treatment Method

The heat treatment method involves heating the powder to induce oxidation on its surface, forming a dense alumina protective film, thereby enhancing its hydrolysis resistance. Li Yawei and other researchers studied the effect of heat treatment on the hydrolysis resistance of aluminum nitride (AlN) in the temperature range of 700-1050°C in air. They found that AlN started to oxidize at 700°C in the air, and as the temperature increased, further oxidation occurred. At 1050°C, the AlN was completely oxidized. After heat treatment, the hydrolysis resistance of the AlN powder was found to be temperature-dependent, with the resistance decreasing as the water temperature increased.

 

Other Modification Methods

There are several other modification methods, such as high-energy treatments, ultrasound, and encapsulation, which can also be used to modify the surface of AlN powders. Typically, combining these methods with others yields better surface modification results.

 

Factors Affecting the Surface Modification of AlN Powder

 

Several factors influence the surface modification of AlN powder, such as temperature, time, and the amount of modifier used. The modifier works by interacting with the surface groups of the nano powder to achieve modification. However, the chemical structure of the modifier and the length of the molecular chains can impact the dispersion of the nano powder in the polymer matrix. The molecular weight of the modifier has a significant effect on surface modification. If the molecular weight is too low, the coating layer will be thin and unable to provide sufficient steric hindrance, leading to poor dispersion of the modified powder. On the other hand, a higher molecular weight modifier will form a thicker coating on the surface, which can better interact with the organic matrix, as shown in Figure 4.

 

When using silane coupling agents to modify the surface of AlN powder, a small amount of anhydrous ethanol or other solvents is often added to accelerate the reaction between the coupling agent and the powder. However, the presence or absence of the solvent can affect the interaction between the AlN powder and the coupling agent.

 

Reference: Baidu Wenku

Polyacrylamide is a widely used chemical compound that has various applications in industries such as wastewater treatment, agriculture, mining, and paper production. While it is generally safe when handled properly, there are certain safety considerations to keep in mind when working with polyacrylamide. Here are some important safety knowledge points:

 

1. Personal Protective Equipment (PPE): When handling polyacrylamide, it is recommended to wear appropriate PPE, including gloves, safety glasses, and protective clothing. This helps to protect the skin and eyes from direct contact with the chemical.

 

2. Handling and Storage: Polyacrylamide should be stored in a cool, dry, and well-ventilated area away from incompatible substances. Avoid exposure to heat, open flames, and direct sunlight. Follow proper handling procedures to prevent spills, leaks, and accidents.

 

3. Inhalation and Dust Control: Polyacrylamide can sometimes generate dust particles, especially when in powdered form. Inhalation of these particles may cause respiratory irritation. It is important to work in well-ventilated areas or use local exhaust ventilation systems to control dust.

 

4. Skin and Eye Contact: Direct contact with polyacrylamide can cause mild to moderate irritation to the skin and eyes. In case of contact, immediately rinse with plenty of water for at least 15 minutes. If irritation persists, seek medical attention.

 

5. Environmental Considerations: Polyacrylamide can be harmful to aquatic organisms if released into water bodies. Take precautions to prevent spills or leaks into the environment. Follow local regulations for proper disposal of polyacrylamide waste.

 

6. Health Effects: While acute exposure to polyacrylamide is generally low risk, prolonged or repeated exposure may have adverse health effects. Some studies suggest that polyacrylamide may be a potential skin sensitizer or respiratory sensitizer. It is important to follow good hygiene practices and minimize unnecessary exposure.

 

7. Emergency Procedures: In the event of a spill or accidental release of polyacrylamide, contain the area, prevent further spread, and clean up the spill using appropriate methods and equipment. If a large spill occurs or if there is a risk of exposure to a significant amount of the substance, contact the appropriate emergency response authorities.

 

It is important to note that the safety considerations may vary depending on the specific form and concentration of polyacrylamide being used. Always refer to the safety data sheet (SDS) and follow the manufacturer's instructions and safety guidelines for the particular product you are.

Choosing the right type of polyacrylamide is crucial for various applications such as wastewater treatment, enhanced oil recovery, papermaking, and mining. With a wide range of polyacrylamide types available, selecting the most appropriate one requires careful consideration of several factors. Here are some key points to help you make the right choice:

 

1. Polymer Structure: Polyacrylamides come in different structures, including linear, branched, or cross-linked. Linear polymers offer higher viscosity and are effective in flocculation and sedimentation processes. Cross-linked polymers have superior resistance to shear degradation and are commonly used in applications requiring increased stability.

 

2. Charge Type: Polyacrylamides can be classified as nonionic Polyacrylamides , anionic Polyacrylamides, or cationic Polyacrylamides depending on their charge characteristics. Nonionic polymers are typically used for flocculation processes where the suspended solids have no charge. Anionic polymers are effective in neutralizing positively charged particles, while cationic polymers are suitable for negatively charged particles.

 

3. Molecular Weight: The molecular weight of polyacrylamide affects its performance in terms of viscosity, flocculation efficiency, and shear resistance. Higher molecular weight polymers are generally preferred for applications involving solid-liquid separation, while lower molecular weight polymers are suitable for thinning and dispersing applications.

 

4. Application Requirements: Consider the specific requirements of your application. Factors such as pH, temperature, salinity, and the presence of other chemicals can influence the effectiveness of polyacrylamides. It is essential to choose a polymer that can withstand the conditions and provide optimal performance.

 

5. Compatibility: Ensure that the chosen polyacrylamide is compatible with other chemicals or coagulants that may be used in your process. Compatibility issues can lead to decreased efficiency or even flocculation failure.

 

6. Environmental Considerations: Evaluate the environmental impact of the polyacrylamide you choose. Look for products that are non-toxic, biodegradable, and produced using environmentally friendly methods.

 

7. Technical Support: If you are unsure about the appropriate type of polyacrylamide for your application, consult with experts or suppliers who can provide technical guidance and support. They can help you select the right product based on your specific needs.

 

By considering these factors and seeking expert advice, you can choose the right type of polyacrylamide that will optimize the performance of your application while ensuring cost-effectiveness and environmental.

If non-transparent TPU (Thermoplastic Polyurethane) is changed to a transparent form without altering the incorporation of colorants, it can lead to a few potential problems:

 

 

Inconsistent or altered color appearance:The colorants used in non-transparent TPU are typically designed for its opaque nature. When the TPU becomes transparent, the interaction between light and the colorants changes, which can result in an inconsistent or altered color appearance. The color may appear less vibrant or distorted, and the intended hue may not be achieved.

 

 

 

Loss of opacity: Non-transparent TPU is engineered to block or reduce the transmission of light, resulting in its opacity. When it becomes transparent, light can pass through more easily, leading to a loss of the desired opacity. This can be problematic if the material's intended purpose requires a certain level of light blocking or privacy.

 

To overcome these problems, manufacturers would need to modify the colorant formulation for transparent TPU. They would typically use transparent colorants specifically designed for transparent materials to achieve the desired color appearance. Additionally, adjustments may be needed in the material's composition and processing parameters to address changes in properties such as opacity and compatibility with surrounding.

 

Polyacrylamide (PAM) is a synthetic polymer composed of repeating units of acrylamide. It is widely used as a flocculant, thickener, and binder in various industrial processes, including water treatment, papermaking, mining, and petroleum production. Here is an introduction to the physical and chemical properties of polyacrylamide:

 

1. Molecular Structure: Polyacrylamide is a linear polymer with a molecular weight ranging from a few thousand to several million Daltons. It consists of long chains of acrylamide monomers linked together by amide bonds (-CONH-). The structure of polyacrylamide can be modified by copolymerization with other monomers to incorporate specific properties.

 

2. Solubility: Polyacrylamide is highly soluble in water, forming clear and viscous solutions. It has the ability to absorb and retain large amounts of water, which contributes to its excellent water treatment properties. The solubility of PAM can be affected by factors such as molecular weight, ionic strength, and pH.

 

3. Ionic Character: Polyacrylamide can be classified into two main types based on its ionic character: nonionic and anionic/cationic. Nonionic PAM is electrically neutral, while anionic PAM carries negative charges and cationic PAM carries positive charges along the polymer chain. The ionic character determines the interactions of PAM with other substances and its performance in different applications.

 

4. Flocculation and Dispersion: Polyacrylamide exhibits flocculation properties, meaning it can cause the aggregation of suspended particles in a liquid. The polymer chains form bridges between particles, leading to the formation of larger, settleable flocs. This property is extensively used in water and wastewater treatment processes.

 

5. Rheological Properties: Polyacrylamide solutions display high viscosity, which is desirable in applications such as thickening and emulsion stabilization. The viscosity is influenced by factors like molecular weight, concentration, and temperature. PAM solutions can form gels under specific conditions, allowing them to act as thickening agents.

 

6. Stability: Polyacrylamide is stable under normal conditions, but its stability can be affected by factors such as temperature, pH, and the presence of oxidizing agents. High temperatures can cause the degradation of PAM, leading to a decrease in its performance.

 

7. Biocompatibility: Polyacrylamide is generally considered safe for use in industrial applications. However, its use in certain consumer products, such as cosmetics, may require additional scrutiny to ensure safety. It is important to follow proper handling and disposal practices to minimize environmental impacts.

 

Overall, the physical and chemical properties of polyacrylamide make it a versatile polymer with a wide range of applications in various.

Bismaleimide powder, a game-changing material in the industrial world, has taken the manufacturing sector by storm. Its exceptional properties and versatility have made it a popular choice among various industries, including the automotive, aerospace, and electronics sectors. In this article, we will delve into the introduction of Bismaleimide powder manufacture, the benefits of using it, and its various applications.

Bismaleimide Powder Manufacture: Breaking New Grounds

The manufacturing process of Bismaleimide powder involves meticulous steps that ensure its quality and performance. With cutting-edge technology, manufacturers employ advanced techniques to produce high-grade Bismaleimide powder, meeting the stringent demands of modern industries.

Bismaleimide Powder Wholesales: Meeting Industry Demands

As the demand for Bismaleimide powder continues to rise, wholesalers play a vital role in distributing this remarkable material. By connecting manufacturers to end-users, wholesalers bridge the gap between supply and demand, facilitating smooth transactions and ensuring a constant flow of Bismaleimide powder in the market.

PDM/HA-8/HVA-2 Powder Manufacturer: Offering a Wide Range of Options

Not all Bismaleimide powders are created equal. Manufacturers understand the need for diversity, providing various options like PDM (Phenylene diamine), HA-8 (Hexamethylenediamine), and HVA-2 (Hexamethylenedianiline). These powders offer unique characteristics, enabling industries to choose the most suitable Bismaleimide powder for their specific applications.

Crosslinking Agent Manufacturer: Enhancing Performance and Durability

Bismaleimide powder alone boasts exceptional properties, but its potential can be further unlocked through the introduction of crosslinking agents. Manufacturers of crosslinking agents tailor their products to complement Bismaleimide powder, enhancing its performance, strength, and durability. This crucial partnership between Bismaleimide powder manufacturers and crosslinking agent manufacturers fuels innovation and opens new frontiers.

Vulcanizing Agent Powder Manufacturer: Enabling Seamless Processing

To optimize the processing of Bismaleimide powder, manufacturers produce vulcanizing agents in powder form. These agents aid in improving flowability, reducing agglomeration, and achieving homogeneous mixtures for hassle-free processing. Vulcanizing agent powder manufacturers contribute significantly to the seamless utilization of Bismaleimide powder in various manufacturing processes.

Conclusion: Invaluable Contributions to Modern Industries

The emergence of Bismaleimide powder, coupled with the efforts of its manufacturers and associated industries, has revolutionized manufacturing processes. With the ever-expanding range of applications and continuous advancements in its production, Bismaleimide powder is rapidly becoming an indispensable material across numerous sectors. As innovation persists, we can expect further breakthroughs, propelling industries towards new levels of efficiency, reliability, and performance.

With Bismaleimide powder manufacture, wholesale operations, PDM/HA-8/HVA-2 powder manufacturing, crosslinking agent production, and vulcanizing agent manufacturing in full swing, industries worldwide are poised to unleash the full potential of this remarkable material. The future has never seemed brighter for manufacturers as they harness the power of Bismaleimide powder to shape tomorrow’s world.

The preparation of polyacrylamide involves a polymerization reaction of acrylamide monomer using a suitable initiator. Here are the main steps involved in the preparation process:

 

1. Monomer Selection: Acrylamide (CH2=CHCONH2) is chosen as the primary monomer for polyacrylamide synthesis due to its reactivity and ability to form long polymer chains.

 

2. Initiator Selection: A chemical initiator is required to initiate the polymerization reaction by generating free radicals. Common initiators for polyacrylamide include ammonium persulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TEMED).

 

3. Polymerization: The polymerization reaction usually takes place in an aqueous solution. Here are the steps involved:

 

   a. Preparation of Monomer Solution: Acrylamide monomer is dissolved in water to create a monomer solution. Depending on the desired polymer properties, co-monomers or crosslinkers may be added to the solution.

 

   b. Initiator Addition: The initiator, such as APS and TEMED, is added to the monomer solution. APS decomposes in water to generate sulfate radicals, while TEMED helps initiate the reaction.

 

   c. Initiation: After adding the initiator, the reaction mixture is typically heated to a suitable temperature, often around 60-70°C. This initiates the formation of free radicals.

 

   d. Polymerization: Free radicals produced by the initiator react with acrylamide monomers, causing them to join together and form long polymer chains. The reaction proceeds until all the monomers are consumed or until terminated by adding a termination agent, such as ammonium persulfate or hydrogen peroxide.

 

   e. Post-Reaction Treatment: After the desired reaction time, the reaction mixture is often cooled and subjected to further processing steps, such as filtration, precipitation, or drying, to obtain the final polyacrylamide product.

 

It's important to note that the polymerization process can be modified by adjusting various parameters such as monomer concentration, initiator concentration, reaction temperature, reaction time, and the addition of crosslinking agents or functional groups, to achieve specific properties and tailor polyacrylamide for applications.