Preparation Of Silica Aerogels By Ambient Pressure Drying

Silica aerogel is a new type of functional material.As a mesoporous material,silica aerogel has broad prospects in the fields of heat preservation,catalysis and sound insulation.However,the following disadvantages are presented for the common silica aerogels:The advantages and disadvantages of silica aerogel are significantly.The preparation cost is high,the mechanical property is poor,and the drying period is long.All of this restricting the development of the aerogels.In this work we used both TEOS and nine hydrated sodium silicate as the silica source to prepare silica aerogels.Preparing wet gel by sol-gel method and after aging.Silica aerogels were successfully prepared by microwave drying and high temperature drying.The main conclusions of the study are as follows:In this paper,we prepared aerogels with TEOS as raw material.The best condition for preparing wet gel is to choose the two step method by adjusting the pH value to 2-3 first,then adjusting the pH value to 6 after hydrolysis.The molar ratio of TEOS,water and ethanol was 1:4:8.The prepared wet gel needs aging treatment.It is found that the aging time can be shortened and the aerogel performance can be improved when the aging temperature is 40 degrees Celsius.We used wet gel for microwave drying and high temperature drying.The optimum condition of microwave drying was 30 days or 40 days and in high fire power of 700W with the time of 3 minutes.The sample density is 0.11 g/cm3,the specific surface area is 765 m2/g,the total pore volume is 4.1 cm3/g,and the average pore size is 21 nm.The optimum condition of high temperature drying is 40 days and 700 degrees Celsius with the drying time is 90 seconds.The sample density is 0.11 g/cm3,the specific surface area of the sample is 765 m2/g,the total pore volume of the aerogel is 3.8 cm3/g and the average pore diameter is about 22 nm.Microwave drying and high temperature drying time are a few minutes of about 1 to 3 minutes.Silica aerogels are amorphous structures.We used nine sodium silicate as raw material to prepare aerogel.With the washing method of desalination.The mass fraction of sodium silicate was determined to be 6%.The best condition for preparing wet gel is to choose the two step method by first adjusting the pH value of the solution for 2-3,and then adding ammonia to pH 6.Wait for the gel and to be washed.The aging temperature is 25 degrees Celsius and 40 degrees Celsius.The aging time is 10 days to 40 days.We used wet gel for microwave drying and high temperature drying.When the aging temperature is 40 degrees Celsius,The optimum condition of microwave drying was 20 days and medium fire positionhigh.The power is 450W and the drying time is 5 minutes.The sample density is 0.11 g/cm3,the specific surface area is 530 m2/g,the total pore volume is 3.3 cm3/g,and the average pore size is 22 nm.The optimum condition of high temperature drying is 30 days and 700 degrees Celsius with the drying time is 2 minutes.The sample density is 0.11 g/cm3,the specific surface area of the sample is 520 m2/g,the total pore volume of the aerogel is 3.2 cm3/g and the average pore diameter is about 22 nm.Microwave drying and high temperature drying time are a few minutes about 2 to 5 minutes.We used nine sodium silicate as raw material to prepare aerogel.We use the method of ion exchange resin to remove the salt.Other conditions are the same as above.The optimum condition of microwave drying was 10 days and medium fire positionhigh.The power is 450W and the drying time is 3 minutes.The sample density is 0.12 g/cm3,the specific surface area is 556 m2/g,the total pore volume is 2.5 cm3/g,the average pore size is 16 nm.The optimum condition of high temperature drying is 20 days and 500 degrees Celsius.The drying time is 4 minutes.The sample density is 0.11 g/cm3,the specific surface area of the sample is 444 m2/g,the total pore volume of the aerogel is 2.3 cm3/g and the average pore diameter is about 22 nm.Microwave drying and high temperature drying time are a few minutes about 3 to 4 minutes.Compared with the drying at normal temperature,the performance is improved greatly.Silica aerogels are amorphous structures.