Glass can be made by sintering, a process that involves forming a solid mass of material through heat and pressure without melting it to the point of liquefaction. This method is used for various types of glass materials, including ceramic glazes, silica glass, and lead glass, as well as sintered glass slabs made from fused silica glass powder.
Summary of the Process: Sintering of glass typically involves compression molding, where the glass powder is placed into a mold and pressed to form a green body. This body is then heated at high temperatures to fuse the ceramic particles, significantly reducing the porosity of the material.
Detailed Explanation:
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Preparation of the Glass Powder: The process begins by mixing water, binder, deflocculant, and unfired ceramic powder (in this case, glass powder) uniformly to form a slurry. This slurry is then spray dried to create a powder suitable for sintering.
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Formation of the Green Body: The spray-dried powder is placed into a mold and pressed under high pressure to form a green body. This step is crucial as it determines the initial shape and density of the final product.
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Heating and Sintering: The green body is heated at a low temperature to burn off the binder. Subsequently, it is sintered at high temperatures, which is typically below the melting point of the glass. During sintering, the glass phase flows as it reaches its transition temperature, incorporating the powder structure and reducing porosity. This process involves the atoms in the materials diffusing across the particle boundaries and fusing together into one piece.
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Characteristic Temperatures: By observing the expansion-temperature curve using an optical dilatometer, all characteristic temperatures occurring during the sintering cycle can be identified. These include phase transition temperature, glass transition temperature, and melting point, which are critical for optimizing the sintering process.
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Shrinkage and Final Properties: Sintering is associated with significant material shrinkage as the glass phase consolidates the powder structure. The final sintered product is a dense, monolithic material whose properties are influenced by the grain size, pore size, and grain boundary shape and distribution, all of which are affected by the sintering process.
In conclusion, sintering is a viable method for making glass, particularly suitable for materials that are difficult to melt due to their high melting points. This process allows for the creation of dense, strong glass products through controlled heating and pressure application, without the need for complete liquefaction.
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