Preparation And Sound Absorption Characteristic Of Foamed Alumina Ceramics Fabricated By Gelcasting-foaming Process

With the increasing effect of noise pollution on the working and living environment,it has become a research hotspot to solve the problem of noise pollution,especially the low-frequency noise pollution in transformer substations.Most sound absorbption materials have good absorption capacity for high-frequency noise,but poor for low-frequency noise.And flammable and conductive materials are also not suitable for transformer substations.To solve the problem of the application of sound absorption materials in transformer substations,high-purity alumina（Al₂O₃）powder is used as raw material,and isobam#104 was used as dispersant to prepare foamed ceramics with high porosity by gelcasting-foaming method.The properties of slurry and green body with different mixing processes were also explored.The effects of the process parameters:solid loading,dispersant content and foaming agent content on the micromorphology,open porosity,compressive strength were studied.The sound absorption properties with different air-gap depths of 0-80 mm fabricated by different process parameters were studied,and the sound absorption properties at low frequency of the combinations of two ceramics with different porosity and space depths between the two ceramics were studied.The main research results are as follows:（1）The mixing process with mixing speed of 700 r/min,830 r/min,950 r/min and mixing time of 1 min,2 min,3 min respectively were used to make foamed slurry.Slurry fluidity,filling degree of mold and integrity degree of green bodies of different mixing processes were found.Increasing stirring speed and stirring time excessively would reduce the fluidity of slurry.After pouring slurry into the mold,it was easy to generate bridging,and green body was easy to be damaged and generate hole.（2）The ceramics with solid loading of 42%,46%,50%and 54%respectively were prepared.It showed that with the increase of solid loading,the number of large pores in foamed ceramics decreased,the open porosity decreased from 74.30%to 68.98%,and the compressive strength increased from 4.66 MPa to 14.77 Mpa;The ceramics with dispersant contents of 0.1 wt%,0.3 wt%,5 wt%and 0.7 wt%respectively were prepared.It showed that with the increase of dispersant content,the number of large pores in foamed ceramics decreased slightly,the open porosity decreased from 73.15%to 70.83%,and the compressive strength increased from 10.91 MPa to 14.50 Mpa;The ceramics with foaming agent contents of 0.15 wt%,0.20 wt%,0.25 wt%and 0.30 wt%respectively were prepared.It showed that with the increase of foaming agent content,the number of large pores in foamed ceramics increased,the open porosity increased from 77.42%to 82.66%,and the compressive strength decreased from 12.66 MPa to 6.25 MPa.（3）With the increase of solid loading the sound absorption peak shifted towards lower frequency and the maximum absorption coefficient increased first and then decreased.The noise reduction coefficient also increased first and then decreased slightly.With the increase of dispersant content the sound absorption peak shifted towards lower frequency,and the maximum absorption coefficient decreased.The noise reduction coefficient also increased first and then decreased slightly.With the increase of foaming agent content the absorption peak shifted towards higher frequency,and the maximum absorption coefficient increased first and then decreased slightly.The noise reduction coefficient also increased first and then decreased.The foamed ceramics with moderate porosity have better sound absorbtion properties.（4）The combination of two ceramics with different porosity had better sound absorption properties than a single ceramics on lower frequency.The frequency corresponds to the maximum absorption coefficient was located between 200-400 Hz,while that of a single ceramic was mainly located between 400-1000 Hz.The absorption peak shifted towards higher frequency with the increase of the porosity of foamed ceramics on both sides.The sound absorption peak shifted towards lower frequency with the increase of porosity of the ceramics in the combination,and the width of the peaks increased first and then decreased.The combinations of two ceramics with moderate porosity had better sound absorbtion properties.（5）Increasing the air-gap depths between the foamed ceramic and the rigid wall and increasing the space depths between the two ceramics would significantly improve the sound absorption performance at low frequency.The sound absorption peak shifted towards lower frequency with the increase of air-gap and space depths,and the maximum absorption coefficient also increased.The noise reduction coefficient increased with the increase of air-gap depth.In this paper,the process to fabricate foamed ceramic with good sound absorption performance and mechanical properties was obtained through the control group experiment.The effects of the porosity and different space depths between two ceramics on the sound absorption properties of ceramics were studied.This is also helpful to research ceramics for sound absorption,especially in the field of low-frequency sound absorption.