The minimum pore size obtainable in a silica gel during drying
- Sandia National Labs., Albuquerque, NM (United States)
- New Mexico Univ., Albuquerque, NM (United States). Center for Micro-Engineered Ceramics
The pore size r{sub p} in a gel is determined by the extent of shrinkage of the gel network during drying. Shrinkage is driven by the collapse of the gel network in response to the capillary pressure P{sub c} exerted by the pore fluid. The extent of shrinkage depends on the balance between the capillary pressure P{sub c} in the pore fluid and the bulk modulus K{sub p} of the gel. The hydraulic pore radius, r{sub H} = 2V{sub p}/S{sub a}, where V{sub p} is the pore volume and S{sub a} is the apparent N{sub 2} BET surface area, is often used to characterize the pore size of a gel. A series of acid catalyzed silica gels dried in pore fluids with different {gamma}{sub lv}, showed that there is a limit to the minimum apparent r{sub H} obtainable in a gel, and when the volume fraction of porosity {phi} {le} 0.37, r{sub H} becomes constant and {approximately}0.8 nm. In contrast, experimental data show that the true pore size r{sub p} of gels continues to decrease when {phi} {le} 0.37. Analysis of their adsorption isotherms show that while r{sub H} apparently stays constant: (a) the BET C constant continues to increase, (b) the width and average of their pore size distributions continue to decrease, and (c) as shrinkage continues the gels eventually become non-porous to N{sub 2} at 77K but are still porous to CO{sub 2} at 273K. This paper reviews these results and addresses micropore formation in silica gels with the goal of determining how P{sub c} influences the final r{sub p}, and why r{sub p} and r{sub H} diverge when {phi} {le} 0.37.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States); National Science Foundation, Washington, DC (United States); Gas Research Inst., Chicago, IL (United States)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 32597
- Report Number(s):
- SAND-95-0391C; CONF-941144-86; ON: DE95008162; CNN: CDR-8800532; 5091-222-2306
- Resource Relation:
- Conference: Fall meeting of the Materials Research Society (MRS), Boston, MA (United States), 28 Nov - 9 Dec 1994; Other Information: PBD: [1994]
- Country of Publication:
- United States
- Language:
- English
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