illustrate

The characteristics and technical specifications of high-purity and standard alumina ceramics, such as high-temperature compressive strength, hardness, and wear resistance, are described. The powder preparation, forming methods (including slip casting, extrusion, and hot pressing), sintering techniques, and subsequent precision machining steps, such as precision grinding, cutting, and surface treatment, are then detailed. These processes enable alumina ceramics to be suitable for high-precision applications in the mechanical, electronic, and medical fields.

Part 1: Features and Technical Specifications

Alumina ceramics are mainly divided into two categories: high-purity and ordinary. High-purity alumina ceramic materials have an Al2O3 content of over 99%. Due to their high operating temperature (up to 1650℃ or even higher), compressive strength (20°C) of 2000MPa, Vickers hardness (Hv50) of 15.7 (GPa), and kJ/mm², they are widely used in machinery, chemical, and petroleum industries to manufacture various mechanical parts. In the electronics industry, they can be used as integrated circuit substrates and high-frequency insulating materials. Ordinary alumina ceramics are classified according to their Al2O3 content into 98%, 95%, 90%, and 85% types, and sometimes those with an Al2O3 content of 80% or 75% are also included in the ordinary alumina ceramic series.

Durezza: Mohs hardness is 9, second only to diamond (10), far exceeding wear-resistant steel and common steel.

Excellent wear resistance: Wear resistance is 266 times that of manganese steel and 171.5 times that of high-chromium cast iron. According to our customer tracking survey over the past ten years, under the same working conditions, the service life of equipment can be extended by at least ten times.

Lightweight: The density of alumina ceramic is 3.85 g/cm³, only half that of steel, which can greatly reduce the load on equipment. The main technical indicators of our alumina ceramic are: alumina content ≥99%, density ≥3.85 g/cm³, Vickers hardness (Hv50) ≥15.7 (1600) Gpa (Kg/mm²), compressive strength ≥2000 MPa, fracture toughness ≥4 MPa·m1/2, bending strength ≥330 MPa, thermal conductivity 27.5 W/mK, etc.

Among them, 99% alumina ceramic material is used to manufacture various precision ceramic structural components, such as ceramic flanges, irregularly shaped ceramic structural components, and ceramic protective sleeves. Alumina ceramics are mainly used as corrosion-resistant and wear-resistant parts. 85% alumina ceramic often incorporates talc powder to improve its electrical properties and mechanical strength, and can be sealed with metals such as molybdenum, niobium, and tantalum. It is sometimes used in electrovacuum devices.

Part 2: Powder Preparation

Alumina powder is produced according to different product requirements and molding processes, with a particle size below 1μm. Manufacturing high-purity alumina ceramics requires not only an alumina purity of over 99%, but also ultrafine grinding and uniform particle size distribution. When using extrusion or injection molding, 10-30% binder and plasticizer, usually thermoplastic or resin, need to be added to the powder. The organic binder should be mixed with the alumina powder at 150-200℃ to facilitate molding. Hot-pressed powder materials do not require the addition of binders. If semi-automatic or fully automatic dry pressing is used, special requirements apply to the powder. Spray granulation requires the powder to be spherical to improve its flowability and facilitate automatic filling of the mold wall during molding. Furthermore, to reduce friction between the powder and the mold wall, 1-2% lubricant, such as stearic acid or PVA, needs to be added.

Part 3: Molding Method

Forming methods for alumina ceramics include dry pressing, slip casting, extrusion, cold isostatic pressing, injection molding, tape casting, hot pressing, and hot isostatic pressing. In recent years, some other forming technologies have been developed, such as pressure filtration molding, direct solidification molding, gel molding, centrifugal slip casting, and free solid molding. Different shapes, sizes, complex shapes, and precision requirements necessitate different forming methods. The following is an introduction to common forming methods:

Cold isostatic pressing: In isostatic pressing, powder is uniformly pressed from all directions under the same pressure. This uniform pressure distribution ensures that the pressed ceramic blank has a consistent density. Uniform density helps maintain a consistent shrinkage rate during sintering or hot isostatic pressing, thus minimizing warping or deformation. Furthermore, the high blank strength obtained through isostatic pressing ensures excellent durability and performance in the final product.

Part 4: Sintering Technology

Sintering is a technique for densifying granular ceramic blanks into solid materials. The sintering process removes pores, small amounts of gas, impurities, and organic matter from the blank, allowing the particles to grow and solidify. Electric furnaces are commonly used for sintering. Besides atmospheric pressure sintering, there are also hot pressing sintering and hot isostatic pressing (HIP). While continuous hot pressing sintering increases production output, it is expensive in terms of equipment and molds, and the length of the finished product is limited due to axial heating. Currently, many high-value-added alumina ceramic products or special components required for national defense, such as ceramic bearings, mirrors, nuclear fuel, and cylindrical products, are mostly produced using HIP or high-vacuum pressureless sintering methods.

Part 5: Subsequent Processing

After sintering, alumina ceramics require a series of precision machining steps to meet the demands of various high-precision applications. The subsequent processing of precision ceramics includes the following key steps:

Precision Grinding and Polishing: Sintered alumina ceramic blanks require precision grinding and polishing to achieve the desired surface finish and dimensional accuracy. This process is performed step-by-step, from coarse grinding to fine grinding, culminating in final polishing.

Precision Cutting and Shaping: Based on customer requirements, sintered alumina ceramics can be further cut and shaped into complex geometries and intricate structures. Advanced laser cutting technology is widely used to ensure cutting precision and finished product quality.

Inspection and Quality Control: Processed precision ceramic components undergo multiple inspections and rigorous quality control to ensure product quality and performance. Common inspection methods include dimensional measurement, hardness testing, and thermal stability testing. During inspection, specialized equipment and tools are used, and relevant inspection standards and specifications are followed.

Through these precision machining steps, alumina ceramics can be made into precision ceramic parts that meet various high-tech requirements and are widely used in electronics, machinery, medical and other fields.