Fly ash from a thermal power plant and waste plate glass are the main raw materials, while auxiliary materials include a blowing agent such as carbon powder, a foaming agent like manganese oxide, and a flux such as boric acid. Coke is selected as the foaming agent due to the high Al₂O₃ content in the fly ash, which requires a relatively high foaming temperature.
On the upper part of the 100-mesh sieve, there is a small amount of large particles mainly consisting of unburnt carbon, which can negatively affect the foaming process by interfering with the ceramic fiber board. Therefore, the fly ash remaining on the 100-mesh screen is removed. The weight ratio of fly ash to waste glass is set between (303-8) to (70-62), and the foaming agent dosage ranges from 0.2% to 3.0%. After adding the appropriate amounts of flux and foam stabilizer, all the raw materials are weighed and thoroughly mixed before being placed into the mold. Before firing, a small portion of the well-mixed material is taken for differential thermal analysis to determine the optimal firing temperature regime for producing foam glass.
The particle size and quantity of the blowing agent play a crucial role in the foaming process. Carbon powder has very low chemical affinity with molten glass and is hardly wetted by it. This property helps in forming closed vesicles that do not interconnect, improving the insulation properties of the final product. When the particle size and amount of carbon powder are properly controlled, an insulating foam glass with large, uniformly distributed pores can be produced, resulting in a low bulk density and reduced thermal conductivity.
Carbon powders with the same concentration but different particle sizes have varying effects on the pore structure. Smaller particle sizes are more favorable for foaming, leading to more uniform pore sizes. Additionally, smaller particles require less blowing agent to achieve the desired effect. In the experiment, the toner content was set between 0.3% and 0.8%, allowing for fine control over the foaming process and the final microstructure of the foam glass.
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