Preparation And Characterization Of Porous Sound Absorption Materials Based On Expanded Perlite

Noise pollution not only affects people's work efficiency,normal life and rest,but also does harm to people's physiological system of the human body.Moreover,it affects the accuracy and service life of mechanical equipment.Therefore,the development of high-efficiency,economical,environmentally friendly and widely used sound absorption materials is a quite meaningful subject.However,traditional sound absorption materials have a series of problems.For example,organic fiber materials have poor fire resistance,moisture resistance and moth resistance.Metal sound absorption materials provide excellent sound absorption and mechanical performance,but expensive costs limit their widespread application.Expanded perlite,as a porous material processed from natural volcanic aluminosilicate lava,has a lot of great properties including flame-resistant,environmentally friendly,harmless,sound insulation and low-cost.Hence,using expanded perlite as aggregate to develop a sound absorption product is a subject of great application value.In addition,since discovered in 1991,carbon nanotubes(CNTs)have been favored by researchers in the field of acoustics due to their extremely high specific surface area and good mechanical properties.Some researchers have added them to polyurethane foam and alumina foam materials to improve the sound absorption performance.In this thesis,in order to explore the influence of CNTs'introduction on the performance of expanded perlite sound absorption materials,CNTs/perlite composites were prepared by CVD method.CNTs/perlite mortar was synthesized by the preparation method of coating and coated on the expanded perlite sound absorption bricks as sound absorption composite materials.Effects of preparation technology and formula parameters were also studied systematically.First of all,the preparation process and formula for preparing expanded perlite sound absorption slurry were studied.Different test methods were used to investigate the influence of the content and particle size of expanded perlite,the type and dosage of fillers,the type and dosage of emulsion in preparation process on drying time,storage stability,adhesion,open porosity and dry density of sound absorption slurry.The conclusions were as follows:70-90mesh expanded perlite was the best choice,the mortar prepared with 70-90 mesh expanded perlite had a higher open porosity,and the coating surface was smoother than that of 50-70mesh.Pure acrylic emulsion had better adhesion,and the content of 10-12wt%was most suitable.Besides,the influence of the type and dosage of the adhesive,the particle size of expanded perlite and thickness on the performance of the sound absorption brick was explored by measuring the bulk density,effective porosity,fracture load and sound absorption coefficient of the sound absorption brick.The results showed that Epoxy resin adhesive had higher bulk density and fracturing load compared to other adhesives.There was a steady and significant degradation on average sound absorption coefficient of sound absorption perlite bricks with incremental grain size.Besides,the sound absorption coefficients of the sound absorption bricks with different thickness(3 cm,5 cm,8 cm)were 0.4721,0.5771,0.5807,respectively,which revealed that the sound absorption coefficient increased with thickness.Secondly,CNTs were prepared on the surface of expanded perlite via chemical vapor deposition(CVD)by using camphor as carbon source and ferrocene as catalyst,which called CNTs/perlite.And then it was made into CNTs/perlite slurry.Finally,the expanded perlite sound absorption brick coated with the slurry were prepared as sound absorption composite material.Different characterization methods containing SEM,TEM,TG,Raman,BET,MIP,etc.were employed to investigate the influence of the preparation method,the growth temperature and time of CNTs,the size of expanded perlite,and the amount of camphor on the microstructures,growth density and quality of CNTs.The optimal synthesis conditions were as follows:based on the two-step method,CNTs/perlite were developed by using 70-90mesh expanded perlite as substrate,2 g camphor as carbon source under 800?growing temperatures for 40 min.Under this optimal synthesis conditions,the specific surface area of the(CNTs/perlite)was 18.68 m~2/g,more than 300 times higher than that of the expanded perlite.The sound absorption test results showed that the average sound absorption coefficient of sound absorption bricks coated with sound absorption slurry were all above 0.6,compared to 0.5807 of pure sound absorption brick,which indicated that the sound absorption slurry coating was beneficial to rise the flow resistance of the sound absorption brick,thereby improving the sound absorption performance.In addition,the average absorption coefficient of the sound absorption brick coated with CNTs/perlite slurry(two-step method)reached the highest(0.6607).Due to the introduction of CNTs modified the structures of the expanded perlite,which increased the structural factor of the material and reduced the pore size of the expanded perlite.At the same time,the introduction of CNTs increased the viscous damping at the interface,which was conducive to more sound energy converting into heat,and in turn improve the sound absorption coefficient of the composite material.