Effect of aging on surface properties of silica powders produced by plasma-arc vaporization

Add time:07/14/2019    Source:sciencedirect.com

Submicron, nonporous silica powders were prepared by vaporization of powdered quartz in a plasma-arc apparatus. Physical and surface chemical properties were measured for silica powders prepared by rapidly cooling the hot N2SiO2 plasma with either (a) dry N2, (b) N2—water vapor, or (c) N2—O2—water vapor. Freshly prepared powders had surface areas ranging from 250 to 750 m2/g and 0.5 to 7 surface silanol groups per nm2. With normal handling and storage in closed containers, the silicas showed substantial aging effects. In one year, surface areas decreased 25 – 60% and chemisorption of atmospheric moisture resulted in nearly complete surface silanol coverage. Continuous exposure to ambient air produced these surface area changes within 5 to 6 weeks, but storage in dry N2 drastically reduced the rate of change. Thickening and thixotropic character of all of these silicas in polyester resin decreased after one year of normal storage.

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