In recent years, ceramic technology has been advancing rapidly, especially in the field of sintering technology. In addition to traditional special sintering techniques such as hot pressing and hot isostatic pressing, new sintering technologies like cold sintering, flash sintering, and Spark Plasma Sintering (SPS) have emerged. Although these technologies sound very advanced, their application in actual production is not widespread due to limitations in cost and technological maturity. In contrast, pressureless sintering is more common in ceramic production because of its simple operation and lower cost, with gas kilns, coal kilns, wood kilns, and electric kilns being typical examples.
Against the backdrop of pressureless sintering, it is particularly important to study how to prepare high-performance ceramics under these conditions. The terms "pressureless sintering" and "unpressurized sintering" are often used interchangeably, but they actually differ in strict terms. Unpressurized sintering specifically refers to pressureless sintering conducted under electric heating conditions, while other methods using natural gas, coal gas, coal, heavy oil, or wood are not included.
Electric heating sintering is classified separately because it fundamentally differs from other pressureless sintering methods in terms of heating. Electric heating does not rely on chemical reactions; it only requires controlling the power supply, making it simple and precise. As a result, the temperature control in electric heating kilns is more accurate, and the kiln chamber is cleaner, making it suitable for the production of high-value ceramics.
In unpressurized sintering, electric heating specifically refers to the process where heat is generated by electrical resistance and radiated to the green body, causing it to heat up from the outside in and sinter. This sintering method's temperature field is similar to that of traditional pressureless sintering, which is why resistance wire furnaces, silicon carbide rod furnaces, or molybdenum disilicide rod furnaces are considered unpressurized sintering. Microwave ovens, on the other hand, are not considered unpressurized sintering due to their different heating mechanisms.
Unpressurized sintering is important not only for its application in the production of special ceramics but also for its role in theoretical research. During the sintering process, temperature is the most critical factor, and unpressurized sintering provides an environment free from other interferences, facilitating the study of the effects of temperature on sintering. Such research findings can be widely applied to various pressureless sintering technologies to improve and optimize sintering systems. This is also why unpressurized sintering is frequently mentioned in ceramic sintering literature.
