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Alumina Or Zirconia Ceramic Milling Jars Cleaning solution

The ball mill machine stands as one of the most advanced powder grinding apparatuses currently available, widely employed across industries such as electronics, building materials, ceramics, chemicals, light industry, medicine, beauty, and environmental protection. Its innovative design, compact footprint, and multifunctional capabilities render it indispensable in various departments. However, achieving fine grinding outcomes relies significantly on the operational integrity of Milling Jars. Over time, users may encounter a buildup of materials on the surfaces of the zirconia ceramic ball mill jars tank, presenting a persistent challenge. Presented below are several professional cleaning methods to address this issue effectively.

Water Washing:

The simplest and gentlest method involves rinsing with water and incorporating a mild detergent, ensuring thorough cleaning without compromising the integrity of the grinding balls or the tank body.

Detergent Washing:

For substances resistant to water-based cleaning, such as oils and solvents, a combination of laundry detergent or soapy water with the grinding balls and water can be rotated within the ball mill, effectively dislodging stubborn residues without causing damage.

Ultrasonic or Plasma Cleaning Machine:

Employing mechanical means, ultrasonic or plasma cleaning proves effective against oils, viscous substances, and other tenacious residues, utilizing their powerful capabilities to disintegrate attachments and achieve optimal cleanliness.

Acidic Washing with Sulfuric or Nitric Acid:

In instances where particularly stubborn residues persist, a judicious application of dilute acids, such as sulfuric or nitric acid, can be employed. This method, albeit aggressive, is reserved for specific circumstances and necessitates careful handling to ensure safety and equipment integrity.

Solvent-Based Cleaning:

Tailored to materials processed in a wet ground state, solvent-based cleaning aligns with the principle of using compatible solvents for effective residue removal, thereby restoring the milling environment to its original state.

Primarily applicable in mechanical alloying studies, where alloy layers may form on tank walls and grinding balls, this method employs a combination of construction sand, quartz sand, or small corundum balls with water for comprehensive cleaning. This approach is particularly effective in addressing challenging residues.

Mastering these six cleaning methods for Alumina ceramic or zirconia ceramic Mill Jars ensures optimal equipment maintenance and longevity. Regular cleaning following each grinding session is imperative to preserve the operational efficiency of the ball mill and enhance its service life.

If you have any questions or inquiry about ceramic ball milling jars,welcome to contact us by email sales@inlabs.cc and we will reply you soon.

Precautions For Using Alumina Crucibles

To improve the service life of alumina crucibles and reduce the losses caused by improper use of alumina crucibles, the following suggestions are proposed for user reference:

Small ball mills exhibit compact dimensions, high operational efficiency, and ease of maintenance, rendering them indispensable equipment for powder grinding, mixing, and dispersion in laboratory and small batch production settings following material crushing. Their versatile nature enables the processing of materials spanning the spectrum from soft to hard, brittle to tough. Moreover, these mills can be tailored to various capacities, accommodating grinding tasks ranging from a few grams to several tons per operation. Below, we delve into the distinctive features of horizontal and planetary ball mills to facilitate informed decision-making.

1. The maximum operating temperature of the alumina crucibles should not exceed 1750℃, and the long-term operating temperature should be below 1700℃. In order to improve the service life, it is recommended raising the temperature at a rate of less than 3°C per minute. If the alumina crucible size is large and there is a lot of material to be loaded, it can be insulated for 30 minutes at the 300°C and 600°C nodes to achieve uniform heating; Efforts should be made to avoid sudden temperature rise and uneven heating, especially to avoid directly inserting the alumina crucible into the high-temperature furnace. If the process allows for cooling, natural will slow cooling with the kiln should be used, and air cooling or indirect cooling with cooling water should be avoided as much as possible.

2. To reduce the cracking of alumina crucibles local sudden cooling and heating should be avoided, especially for hot alumina crucibles, which should not be directly placed on refractory bricks or refractory fiber blankets at room temperature, otherwise they are prone to cracking. Try to avoid uneven heating caused by open flames and cracking.

3. Alumina crucibles are brittle and hard materials. The service life of Alumina crucibles varies depending on different usage conditions and process methods. They are greatly affected by factors such as usage temperature, temperature rise and fall rate, atmosphere, vocalization of wintered materials, and ambient temperature. We hope that the manufacturer can combine their own process characteristics to summarize a set of operating standards that are most suitable for the usage conditions. The above is for reference only.

Alumina ceramics: the “quality gatekeeper” of wafer polishing

In recent years, silicon carbide (SiC) with high breakdown electric field and high thermal conductivity has been increasingly used as a material for electric vehicle inverters. As the voltage of electric vehicle batteries increases from 400V to 800V, the demand for faster charging speed and higher power density also increases. However, the strong market demand for electric vehicles has not improved the production efficiency of SiC substrates manufactured using physical vapor transfer (PVT) methods.

CMP and CMP post cleaning processes play a crucial role in reducing surface roughness, scratches, and contamination of SiC wafers. At the same time, CMP combines the advantages of chemical and mechanical grinding, and can achieve surface roughness at the nanoscale to atomic level. If global planarization at the nanoscale cannot be achieved during wafer manufacturing, key processes such as photolithography, etching, thin film, and doping cannot be repeated, and process nodes cannot be reduced to advanced fields at the nanoscale. The CMP equipment is mainly divided into two parts, namely the polishing part and the cleaning part. The polishing part consists of four parts, namely three polishing turntables and a disc loading and unloading module. The cleaning section is responsible for cleaning and drying the wafers, achieving the “dry in and dry out” of the wafers. In the entire polishing equipment, alumina ceramics are ubiquitous.

1. Alumina Wafer Polishing Disc

At present, using ceramic grinding discs to grind semiconductor wafers is the most advanced grinding method. The double-sided grinding process is used to grind the cut wafers, and the quality of the grinding discs is improved by improving the grinding process (disc material, grinding fluid, grinding pressure, and grinding speed, etc.); Especially when using ceramic discs instead of cast iron discs, it avoids causing scratches or pollution to the main surface of the wafer during grinding, reduces the introduction of metal ions, reduces the subsequent processing volume of the wafer, shortens the subsequent process (corrosion) time, improves production efficiency, and reduces the loss of wafer processing, greatly improving the utilization rate of the wafer.

Alumina ceramics are usually used to prepare wafer polishing discs, which require high purity, high chemical durability, and good control of surface shape and roughness.

2. Alumina Ceramic Mechanical Handling Arm

In CMP equipment, the wafer is first picked up from the mechanical wall of the wafer box, accurately positioned and aligned onto the platform below the polishing head. The polishing head usually has a vacuum adsorption function. When the wafer is placed below it, the polishing head moves downward and firmly adsorbs the wafer onto the polishing head through vacuum adsorption. Once the wafer is fixed, the polishing head moves the wafer onto the polishing pad for the polishing process.

To avoid contamination of the wafer, it is generally carried out in a vacuum environment. The handling arm needs to be resistant to high temperature, wear, and high hardness. Both alumina ceramics and silicon carbide ceramics have physical properties such as density, high hardness, and high wear resistance, as well as good heat resistance, excellent mechanical strength, good insulation and corrosion resistance in high temperature environments, It is an excellent material for making semiconductor equipment robotic arms.

3. Alumina Vacuum Suction Cup

The common materials for vacuum suction cups are Alumina and silicon carbide. The ceramic forms a hollow structure inside, which adsorbs and fixes the adsorbed material by applying negative pressure to the porous matrix. The preparation process of this integrated hollow structure ceramic has a high technical threshold and is mainly used as a fixed fixture for wafer thinning programs (grinding machines, polishing machines, CMP), various types of measuring devices, and fixed fixtures for inspection devices Fixed fixtures for processing thin film sheets and metal substrates, etc.

Ceramic Heat Sinks for Aerospace Use

The application prospects of ceramic heat sinks in the aerospace field are very broad. With the continuous development of aerospace technology, the complexity of spacecraft is increasing, and the requirements for heat dissipation performance are also becoming stricter. Ceramic heat sinks have broad application prospects in the aerospace field due to their excellent high-temperature resistance, corrosion resistance, high thermal conductivity, and low coefficient of thermal expansion. It is expected to play a more important role in the future development of aerospace technology. With the continuous development of technology, the performance and reliability of ceramic heat sinks will be further improved, providing strong support for the development of aerospace technology.

Specific Applications of Ceramic Heat Sinks in the Aerospace Field:

1. Heat Dissipation in Rockets:

Ceramic radiators are widely used for heat dissipation in the combustion chamber and tail nozzle of rocket engines due to their characteristics of high temperature resistance, corrosion resistance, and high thermal conductivity. By quickly transferring the high-temperature heat generated by the engine to the cooling medium, the engine temperature is maintained within a safe range, thereby improving the reliability and service life of the engine.

Ceramic radiators have multiple specific application scenarios in rockets, including but not limited to the following aspects:

Engine combustion chamber heat dissipation: Ceramic radiators can be used for engine combustion chamber heat dissipation, by transferring the high-temperature heat generated by combustion to the cooling medium, to maintain the engine temperature within a safe range. This is one of the most typical application scenarios of ceramic heat sinks in rockets.

Heat dissipation of propellant supply system: In the rocket propellant supply system, various equipment and pipelines need to dissipate heat to maintain normal working conditions. Ceramic heat sinks can be used for the heat dissipation of these devices and pipelines, providing efficient thermal management solutions.

Electronic device heat dissipation: Effective heat dissipation is required in rocket electronic devices to prevent overheating and damage. Ceramic heat sinks have the characteristics of high thermal conductivity and low coefficient of thermal expansion, which can provide stable heat dissipation and ensure the normal operation of electronic devices.

Thermal protection system heat dissipation: In the thermal protection system of a rocket, efficient heat dissipation is required to prevent heat accumulation and erosion.

2. Satellite Thermal Management:

Effective thermal management is required in satellites to prevent overheating or supercooling. Ceramic radiators are widely used in satellite heat pipes and radiators due to their lightweight and high thermal conductivity characteristics, providing reliable heat dissipation support for the normal operation of satellites.

3. Space Detector Heat Dissipation:

In space detectors, efficient and reliable heat dissipation is required to ensure the normal operation of the detector. Ceramic heat sinks are widely used in the heat dissipation system of space detectors due to their excellent characteristics of high temperature resistance, corrosion resistance, and lightweight.

4. Heat Dissipation of Spacecraft Electronic Equipment:

Effective heat dissipation is required for electronic equipment in spacecraft to prevent overheating and damage. Ceramic heat sinks, due to their high thermal conductivity and low coefficient of thermal expansion, can provide stable heat dissipation and ensure the normal operation of electronic devices.

Opening up the Development Window of Advanced Ceramic Materials in the 100 Billion Market of Optical Communication

With the advent of the digital age, optical communication technology has developed rapidly as an important branch in the field of information and communication. Driven by emerging technologies such as smartphones, 5G networks, cloud computing, and the Internet of Things, the optical communication industry is facing new development opportunities.Advanced ceramic materials, with their excellent performance, have already entered the optical communication industry chain and play a crucial role. The optical communication industry chain consists of optical chips, optical devices, optical modules, and optical equipment. Among them, optical chips and optical components are the basic components for manufacturing optical devices. At present, China is the world”s largest producer of optical components, and the market competition is fierce. Advanced ceramics have a place in the optical communication industry chain due to their excellent performance.

Optical Messenger: Fiber Optic Ceramic Insert

The emergence of fiber optic ceramic inserts has met the demand for high capacity, low loss, and low-cost technology in the field of high-speed information transmission, and has become a key component used in the connection of optical communication devices. Fiber optic ceramic inserts are mainly made of zirconia powder, and are processed through processes such as raw material mixing, granulation, injection molding, high-temperature sintering, and precision grinding. Ceramic inserts made from nano zirconia raw materials have the following excellent properties: Good coaxiality and dimensional accuracy, with small fiber docking errors; High strength, wear resistance, aging resistance and long service life; Low insertion loss and return loss, high insertion and extraction frequency; The end is easy to machine.

Fiber optic ceramic plug ceramic sleeve

Fiber optic ceramic inserts are usually used in conjunction with fiber optic ceramic sleeves. The fiber optic connectors made of ceramic inserts are detachable and classified fiber optic active connectors, making the connection and conversion scheduling of optical channels more flexible. Ceramic inserts used in fiber optic connectors account for 72% of the entire ceramic insert market, with approximately 25% of ceramic inserts used in optical passive devices such as splitters and transceivers, and a small portion of about 3% used in other optical active devices, such as semiconductor lasers.

The development space of ceramic shells is vast

Long distance transmission of optical communication requires airtight packaging, and electronic ceramic casing is the preferred material for airtight packaging. It is packaged with multi-layer ceramic insulators and adopts a multi-layer co fired ceramic insulation structure, providing electrical signal transmission channels and optical coupling interfaces for devices, providing mechanical support and airtight protection, and solving the interconnection between chips and external circuits. There are usually two ways to package optical devices: airtight packaging and non airtight packaging. Gas tight packaging, as the name suggests, is a type of packaging that cannot be penetrated by gas. Its purpose is to prevent external water vapor and other harmful gases from entering the interior of sealed optical devices, affecting the performance of optical chips and related components. Compared to metal materials, electronic ceramic shells have advantages such as high temperature resistance, corrosion resistance, good moisture resistance, as well as good thermal properties such as thermal expansion rate and thermal conductivity, high mechanical strength, and stable chemical properties, with excellent comprehensive performance.

Ceramic shell

The growth of the optical module market is also driving the demand for optical module casings, which are one of the key components. According to Yole data, the global market size of optical modules in 2022 is approximately 11 billion US dollars, a year-on-year increase of 9.09%.Light counting predicts that the global optical module market will have a compound annual growth rate of 11% in the next 5 years, and predicts that the global optical module market will exceed 20 billion yuan by 2027.Yole expects a compound annual growth rate of 12% from 2022 to 2028, and predicts that it will reach $22.3 billion by 2028.

Inventory the Ceramic Components in Plasma Etching Equipment

Plasma etching technology is an indispensable processing technology in the preparation of ultra large scale integrated circuits. As the size of semiconductor transistors sharply decreases and the energy of halogen like plasma increases, the problem of wafer contamination becomes increasingly prominent. The requirements for the material”s resistance to plasma corrosion in the cavity of plasma etching equipment under high-density plasma conditions during wafer processing are becoming increasingly stringent. The new generation of etching technology requires stronger and more reliable materials to solve problems such as plasma corrosion, particle generation, metal pollution, and oxygen decomposition.

Ceramics are Key Materials for Plasma Etching Equipment Components

Compared to organic and metal materials, ceramic materials generally have good physical and chemical corrosion resistance, as well as high operating temperatures. Therefore, in the semiconductor industry, ceramic materials have become the core component manufacturing material for semiconductor wafer processing equipment. The components of ceramic materials used in plasma etching equipment mainly include window mirrors, focusing rings, electrostatic chucks, nozzles, cavities, gas dispersion discs, etc.

The main characteristics of plasma etched ceramic materials inside the etching machine cavity are:

1. High purity and low metal impurity content;
2. The chemical properties of the main components are stable, especially the chemical reaction rate with halogen corrosive gases is low;
3. High density with few open pores;
4. Fine grain size and low content of grain boundary phases;
5. Has excellent mechanical properties and is easy to produce and process;
6. Some components may have other performance requirements, such as good dielectric performance, conductivity, or thermal conductivity. In a plasma environment, the selection of ceramic materials depends on the working environment of the core components and the quality requirements for the process products, such as plasma etching resistance, electrical performance, insulation, etc.

Application of Ceramics in Core Components of Plasma Etching Equipment

1. Cavity

The material of the etching machine chamber is the main source of wafer contamination, and the degree of influence of plasma etching on it determines the yield, quality, and stability of the etching process of the wafer. High purity alumina ceramics are a good plasma corrosion resistant material, which can provide reliable plasma impedance as a chamber material. However, the alumina ceramic cavity in the plasma etching machine equipment belongs to large-sized ceramics. The production of such large-sized and ultra-high purity alumina ceramics has problems such as easy deformation, cracking, and difficulty in sintering and densification. To obtain high-density and high-purity alumina ceramics, high requirements are placed on the purity of the powder and the preparation process.

2. Focusing Ring

The focusing ring aims to improve the etching uniformity around the edges or periphery of the wafer, fix the wafer in place to maintain plasma density and prevent contamination of the wafer sides. When used with electrostatic suction cups, the wafer is placed on the focusing ring and secured in place by electrostatic charges. Due to the direct contact between the focusing ring and the plasma in the vacuum reaction chamber, it is necessary to use materials that are resistant to plasma corrosion and have conductivity similar to that of silicon wafers. The materials of the focusing ring include conductive silicon and silicon carbide.

Conductive silicon, as a commonly used focusing ring material, has a conductivity almost similar to that of silicon wafers. However, its disadvantage is poor corrosion resistance in fluorinated plasma. After a period of use, the material of etching machine components often exhibits severe corrosion, seriously reducing its production efficiency. Silicon carbide has similar electrical conductivity and good ion resistance to silicon. The sub etching performance is suitable for focusing ring materials. Usually, the focusing ring is formed by depositing the silicon carbide generated by chemical reactions into a certain shape through vapor deposition, and then mechanically processing the silicon carbide into a focusing ring according to specific usage conditions.

3. Electrostatic chuck (ESC)

During the entire etching process of the chip, it is adsorbed and fixed by the electrostatic chuck (ESC) in the lower electrode system, and RF is introduced to the electrostatic chuck, which forms a DC bias (DC bias) on the chip.This facilitates the etching reaction of plasma on the chip. At the same time, the electrostatic chuck will achieve temperature control on the chip to promote the uniformity of chip etching. The interior of the electrostatic chuck mainly consists of a dielectric layer, a base, and a heating layer. Aluminum oxide and aluminum nitride are commonly used as dielectric layer materials in the production of electrostatic chucks due to their high thermal conductivity and low coefficient of thermal expansion.

4. Nozzles

The nozzle is used for precise gas flow rate and uniform control to evenly disperse gas into the etching process chamber. These components require high plasma resistance, dielectric strength, and strong corrosion resistance to process gases and by-products. The commonly used ceramic materials include aluminum nitride ceramics and aluminum oxide ceramics. At present, ceramic 3D printing technology can also be used to produce ceramic nozzles in the etching chamber, improving product manufacturing efficiency and usage stability.

Silicon Nitride Ceramics: Hard Core Basic Materials In The New Energy Era

1. Tesla leads the wind vane for silicon nitride ceramic substrates

With Tesla taking the lead in using a large number of silicon nitride ceramic substrates in Model 3 SIC MOSFET devices to solve module heat dissipation problems, silicon nitride ceramic materials have once again entered the industry”s sight. Recently, with the vigorous promotion of 800V high-voltage fast charging technology in new energy vehicles, the issue of corrosion of steel ball bearings in traditional drive motors has received attention. Tesla has adopted Japanese NSK hybrid ceramic bearings in the motor output shaft, with bearing balls composed of 50 silicon nitride bearing balls.

2. Mainstream application products of silicon nitride

The rapid growth in downstream demand for new energy, energy storage, and new energy vehicles will further drive the rapid growth of the domestic market for mainstream application products such as silicon nitride structural components (such as silicon nitride ceramic balls, silicon nitride valve balls, and silicon nitride grading wheels) and silicon nitride ceramic substrates.

1). Silicon nitride ceramics as the application trend of future bearings

At present, traditional steel bearings are still the main type, and silicon nitride ceramic bearings, as a new type of application material in the future, have broad potential for substitution. Rolling bearings are composed of rings, rolling elements, retainers, lubricating grease, and sealing elements. Silicon nitride all ceramic ball bearings refer to rolling elements and rings made of silicon nitride material. Under the wave of electrification, steel ball bearings are currently facing problems such as inability to break through the limitations of higher speed requirements, inability to meet the low noise requirements of users for whole vehicles, and corrosion under higher voltage and high switching frequency requirements. Compared with traditional steel balls and other ceramic materials, silicon nitride ceramics have the characteristics of lightweight, high hardness and heat resistance, low friction, corrosion resistance, self-lubricating, etc., and are considered the best material for manufacturing ceramic bearings in the future.

2). Silicon nitride ceramic substrate is the ceramic substrate material with the best comprehensive performance

With the increasing power density of IGBT and third-generation semiconductor power devices, mainstream aluminum oxide substrates with low thermal conductivity, low mechanical strength, poor toughness, high dielectric constant, and high thermal expansion rate can no longer meet the needs of the new energy vehicle market. Silicon nitride ceramics are considered to have the best comprehensive performance as ceramic substrate materials due to their excellent mechanical strength, good chemical stability, and thermal shock resistance. At the same time, with a thermal expansion coefficient close to that of the third-generation semiconductor substrate silicon carbide crystal, it has become the preferred material for high thermal conductivity substrates in third-generation silicon carbide semiconductor power devices. At present, silicon nitride ceramic substrates are widely used in power modules, heat sinks, LEDs, wireless modules, etc. Driven by the growth in demand for power modules, the sales of silicon nitride ceramic substrates in 2024 are about 136.6 million US dollars, with a compound annual growth rate of about 6.45% from 2018 to 2024.

Ceramic Substrate: Optimal Selection Of High-End Probe Card Core Components

A probe card is a testing interface composed of probes, electronic components, wires, and printed circuit boards (PCBs). Depending on the situation, there may also be requirements for reinforcement boards, mainly for testing bare cores. According to different application scenarios and requirements, probe cards can be divided into various types, such as cantilever probe cards, vertical probe cards, MEMS probe cards, etc. Widely used in integrated circuit testing, semiconductor manufacturing, automotive electronics and other fields.

Ceramic substrate in probe card

The STF substrates are the core component of the entire probe card. The spatial conversion matrix plays a role in electronic connection spacing conversion and electrical signal transmission throughout the probe card, while providing sufficient mechanical/mechanical strength to support the applied force of several hundred to several thousand Newtons during the testing process.

The adapter board in high-end probe cards often uses ceramic substrates. Precision ceramic substrates have excellent electrical insulation, high thermal conductivity, high adhesion strength, and large current carrying capacity. And it has high strength, high hardness, and a wide temperature range, which can reach -55 ℃ to 850 ℃. The coefficient of thermal expansion is close to that of silicon chips. In a multi temperature testing environment, it is one of the effective solutions to solve deformation.

The ceramic substrate used for probe cards is generally a single-layer or multi-layer ceramic substrate with metallization. The multi-layer ceramic substrate is made by co firing high-temperature or low-temperature ceramics through multi-layer lamination and co firing, commonly referred to as a multi-layer ceramic space conversion matrix (MLC).

Type of ceramic substrate material for probe cards

1. High alumina porcelain

High alumina porcelain is a ceramic material mainly composed of aluminum oxide. It has excellent electrical performance and high-temperature stability, so it has been widely used in probe cards. High alumina ceramics have high strength and hardness, but high brittleness. Therefore, in the manufacturing process, it is necessary to pay attention to controlling process parameters such as sintering temperature and time.

2. Silicon nitride ceramics

Silicon nitride ceramic is a ceramic material mainly composed of silicon nitride. It has excellent electrical performance, high temperature stability, and oxidation resistance, so it can replace high alumina porcelain as a substrate material in some application fields. Previously, Kyocera launched a Starceram N3000 P high-performance silicon nitride ceramic plate, which combines the necessary strength, low wear, and the ability to slide back and forth in the guide hole, with the best characteristics suitable for producing probe cards.

3. Other material types

In addition to high alumina ceramics and silicon nitride ceramics, there are also some other types of materials that can be used to manufacture ceramic substrates for probe cards. For example, magnesium oxide ceramics have excellent electrical properties and high temperature stability; Boron nitride ceramics have excellent high-temperature resistance and oxidation resistance; Silicon carbide ceramics have excellent characteristics such as strength and hardness. These material types can also be applied in certain application fields, but they need to be selected based on specific usage environments and performance requirements.

What Important Role Does Beryllium Oxide Play In The Nuclear Industry

In advanced ceramic materials, toxicity is the inherent “label” of beryllium oxide, and in many applications, beryllium oxide is the first to be excluded. But this ceramic material that talks about color change can conquer a “difficult” industry – the nuclear industry.

Since the first nuclear reactor was established in the United States in 1942, the nuclear industry has been developing for nearly eighty years. During this period, the development center of the nuclear industry shifted from nuclear weapons to nuclear energy applications, and the materials used in the nuclear industry were constantly being updated. Among them, ceramic materials for nuclear reactors are one of the important materials used in reactors. In reactors and fusion reactors, ceramic materials receive high-energy particles and γ Radiation from radiation, therefore, in addition to high temperature and corrosion resistance, ceramic materials also need to have good structural stability. The fission reaction in a nuclear fission reactor is caused by neutron bombardment of 235U. In light water reactors, heavy water reactors, and high-temperature gas cooled reactors, slow neutrons are more likely to cause 235U fission compared to fast neutrons produced by neutron fission. Therefore, materials that can slow down neutron velocity are needed in these reactors, which are called moderators. At present, the commonly used moderators internationally include water, graphite, beryllium, beryllium oxide, etc. Among them, beryllium oxide as a ceramic material is considered as a future moderator.

Beryllium oxide is a refractory material that is very stable and dense. Its high temperature vapor pressure and low evaporation rate can be used for a long time in an inert atmosphere, even if the temperature reaches 2000 ℃. However, due to the reaction between beryllium oxide and water vapor to generate beryllium hydroxide, it evaporates significantly when the temperature reaches 1800 ℃ in an oxidizing atmosphere, and a large amount of volatilization occurs when the temperature reaches 1500 ℃ in water vapor. The main performance of BeO ceramic pellets differs from theory. It is worth noting that as the temperature increases, the specific heat capacity of BeO increases sharply, the thermal conductivity decreases sharply, and the coefficient of thermal expansion slightly increases.

In terms of mechanical strength, BeO is about 1/4 of Al2O3, but it has good high-temperature strength. In addition, BeO has good nuclear performance, strong neutron deceleration ability, and high penetration ability for X-rays. At high temperatures, BeO only reacts weakly with carbon, silicon, and boron.

In addition, ceramic particles formed by beryllium oxide and uranium oxide can be combined to form a new type of nuclear fuel. In nuclear fuel neutron source assemblies, both initial and restart of the reactor require a neutron source to “ignite”. Polonium (PO) beryllium source is commonly used in primary neutron source rods, while antimony beryllium source is commonly used in secondary neutron source rods. Currently, the Korean Nuclear Research Institute uses beryllium oxide ceramics to act on the startup control rods of primary neutron source reactors, which is very rare.

In addition, compared with graphite materials, beryllium oxide ceramics have excellent comprehensive properties such as oxidation resistance, corrosion resistance, high thermal conductivity, better neutron slowing and breeding ability, and are expected to play important roles as structural materials, moderators, and matrix materials in small nuclear reactors for deep-sea deep space exploration, land-based mobile nuclear power, and thermonuclear propulsion in the future.

Common Materials, Characteristics, And Accuracy Levels Of High-End Ceramic Balls

In the development and application process of engineering ceramic products, ceramic ball bearings are a typical example of the widespread application of engineering ceramics in the industrial field. Ceramic ball bearings have excellent comprehensive performance such as long service life (2-5 times that of steel bearings), high speed, good overall accuracy and stiffness, good thermal stability, and no magnetism. They have a very broad application prospect in working conditions such as high temperature, high speed, high precision, acid alkali corrosion, electrical corrosion, strong magnetic field, no lubrication or medium lubrication. In high-speed precision ceramic ball bearings, the most commonly used is hybrid ceramic ball bearings, where the ball is made of ceramic balls and the bearing ring is still made of steel. This type of bearing has a relatively high degree of standardization and will not make significant changes to the machine tool structure, making it easy to maintain and especially suitable for high-speed operation. The assembled high-speed electric spindle has advantages such as high speed, high stiffness, high power, and long service life.

Compared with traditional bearing steel, precision ceramic balls have excellent comprehensive properties such as low density, high hardness, high elastic modulus (stiffness), wear resistance, low coefficient of thermal expansion, good thermal and chemical stability, insulation, and no magnetism. Silicon nitride is considered the best material for manufacturing bearing rolling elements and has achieved great success in the application of ceramic ball bearings. Ceramic ball bearings can operate without adding any grease, avoiding the occurrence of premature bearing damage caused by grease drying in ordinary bearings. At present, ceramic balls have been widely used in various fields such as aerospace, military, petroleum, chemical, and high-speed precision machinery.

1. Common materials and characteristics

The ceramic balls used in the market mainly include silicon nitride ceramic balls (Si₃N₄), zirconia ceramic balls (ZrO₂), silicon carbide ceramic balls (SiC), and high-purity alumina ceramic balls (Al₂O₃ ). Si₃N₄ has become the most widely used variety due to its superior comprehensive performance. The reason why precision ceramic balls can replace steel balls is that they have characteristics such as low density, medium elastic modulus, low thermal expansion coefficient, and excellent internal chemical properties. The most important feature is that their failure mode, like bearing steel, occurs in a pre existing peeling mode, while ZrO₂ and Al₂O₃ both occur in a destructive failure mode such as fragmentation. Therefore, ZrO₂ and Al₂O₃ are relatively less applied. The following table provides a brief comparison of the main properties of the four materials.

Table 1- Performance Comparison of Four Materials

A. Silicon Nitride Ceramic Balls
Silicon nitride ceramic material has light weight, fine surface, high moisture content, wear resistance, high toughness, high temperature resistance of 1400 ℃, and is not easily deformed. Compared to ZrO₂ material, Si₃N₄ all ceramic bearings are suitable for higher speeds and load capacities, as well as for higher ambient temperatures. The thermal expansion coefficient of silicon nitride ceramics is only 1/4 of that of bearing steel, reducing the sensitivity of bearings to temperature changes and helping to prevent jamming. At the same time, it can be used as a precision ceramic bearing for high-speed, high-precision, and rigid spindles, with a maximum manufacturing accuracy of P4 to UP levels.

B. Zirconia Ceramic Balls
Zirconia ceramics are not oxidized, not easily corroded, non magnetic, resistant to high temperatures of 1000 ℃, not easily deformed, and have a thermal expansion coefficient similar to that of metals in the industrial environment, but have weak resistance to strong acid and alkali corrosion. The density per cubic centimeter can reach as high as 5.95-6.05g/cm³. Among the four commonly used materials for making ceramic spheres (Si₃N₄, SiC, Al₂O₃, ZrO₂), zirconia ceramics have a higher toughness, reaching over 10MPa · m^1/2. The thermal expansion coefficient is close to that of metals, which can meet the needs of good bonding with metals. Zirconia ceramics have self-lubricating properties, which can solve problems such as pollution caused by lubricating media and inconvenience in addition; Good corrosion resistance, can also be used in medium acid, medium alkali, seawater and other media; High temperature resistance, zirconia ceramics have almost no change in strength and hardness at 600 ℃; Non magnetic, insulating, and can also be used in magnetic fields. However, dimensional stability varies greatly with temperature, and the form of rolling fatigue contact failure is destructive fragmentation, which is not as stable as silicon nitride materials in some critical situations.

C. Silicon Carbide Ceramic Balls
Silicon carbide ceramics have the highest usage limit temperature, high strength at high temperatures, highest thermal conductivity, best thermal shock resistance, highest elastic modulus, and lowest density among the four types, and have the best corrosion resistance. They can withstand a mixture of concentrated hydrofluoric acid and heated strong acids, and can be used in extremely strong corrosion resistant environments.

D. Alumina Ceramic Balls

The main component of alumina ceramic balls is high-quality alumina, with a bending strength of up to 250MPa. Hot pressed products have a bending strength of up to 500MPa, and have excellent wear resistance. They are widely used in the manufacturing of grinding wheels, ceramic nails, bearings, etc.

2. Precision level of ceramic balls

The accuracy of ceramic balls has been graded in the market, and Table 3 and Table 4 respectively list the explanations of professional evaluation standard terms and international general grade standards. Ceramic balls usually have an accuracy of G100 or higher for bearings, and between G3-G20 for high-precision bearings.

Table 2 Important Indicators of Precision Level

Table 3 International Standard (ISO3290-1:2014) (Unit: μ M)