%PDF-1.2 %âãÏÓ 10 0 obj << /Length 11 0 R >> stream BT 90 710.25 TD 0 0 0 rg /F0 9.75 Tf 0 Tc -0.1875 Tw ( ) Tj 0 -15.75 TD /F0 14.25 Tf -0.0599 Tc 0.2474 Tw (Guidelines For Selecting The Appropriate Adsorptive) Tj 325.5 0 TD /F1 14.25 Tf 0 Tc 0.1875 Tw ( ) Tj -325.5 -16.5 TD ( ) Tj 0 -15.75 TD /F1 12 Tf -0.3211 Tc 0.2742 Tw (The type of adsorptive gas selected for a surface area analysis depends upon the objective of ) Tj 0 -15 TD -0.3659 Tc 0.3659 Tw (the analysis. The gas chosen to characterize the surface may not be the best gas to use if the ) Tj T* -0.4315 Tc 0.4315 Tw (objective is) Tj 51 0 TD -0.3704 Tc 0.3704 Tw ( to study adsorption phenomenon. Guidelines for selecting the appropriate ) Tj -51 -15 TD -0.3849 Tc 0.3849 Tw (adsorptive are offered here. The bases of these guidelines may involve the gas) Tj 352.5 0 TD -0.246 Tc 0 Tw (-) Tj 4.5 0 TD -0.4214 Tc 0.4214 Tw (solid interaction, ) Tj -357 -15 TD -0.3736 Tc 0.3736 Tw (the instrument system, or the data reduction method.) Tj 235.5 0 TD 0 Tc 0 Tw ( ) Tj -235.5 -15 TD ( ) Tj 0 -15 TD /F0 12 Tf -0.3003 Tc 0.3003 Tw (Krypton or Nitrogen?) Tj 108 0 TD /F1 12 Tf 0 Tc 0 Tw ( ) Tj -108 -15 TD -0.3713 Tc 0.3713 Tw (Some materials, such as organic materials, powdered metals, and certain geological samples ) Tj 0 -15 TD -0.2875 Tc 0.2875 Tw (have surface areas below 1 m) Tj 134.25 5.25 TD /F1 7.5 Tf 0 Tc 0 Tw (2) Tj 3.75 -5.25 TD /F1 12 Tf -0.4276 Tc 0.3699 Tw (/g and adsorb a very small quantity of gas. When working with ) Tj -138 -15 TD -0.3677 Tc 0.3677 Tw (these materials, it is advantageous to increase the difference between the quanti) Tj 354.75 0 TD -0.277 Tc 0.277 Tw (ty of gas dosed ) Tj -354.75 -15 TD -0.4236 Tc 0.4236 Tw (and the quantity of gas remaining after equilibrium. Krypton has a saturation pressure ) Tj 0 -15 TD -0.3976 Tc 0.3399 Tw (approximately 1/300 that of nitrogen at liquid nitrogen temperature \(krypton: 2.5 torr; nitrogen: ) Tj T* -0.2987 Tc 0.2987 Tw (760 torr\). Therefore, compared to nitrogen, there is in the free space above the sample about ) Tj T* -0.3366 Tc 0.3366 Tw (1/300 the number of krypton molecules present at the same relative pressure. Since about the ) Tj T* -0.4102 Tc 0.4102 Tw (same number of krypton and nitrogen molecules are required to form a monolayer, this number ) Tj T* -0.2242 Tc 0.2242 Tw (represents a far greater prop) Tj 129 0 TD -0.4004 Tc 0.4004 Tw (ortion of the quantity dosed than in the case of nitrogen. ) Tj 252.75 0 TD 0 Tc 0 Tw ( ) Tj -381.75 -15 TD /F0 12 Tf ( ) Tj 0 -15 TD -0.1703 Tc 0.1703 Tw (Nitrogen or Argon for Micropore Analysis?) Tj 216.75 0 TD /F1 12 Tf 0 Tc 0 Tw ( ) Tj -216.75 -15 TD -0.4193 Tc 0.4193 Tw (Argon is inert, and its molecule is spherical, monatomic, and nonpolar. Nitrogen is diatomic, ) Tj 0 -15 TD -0.3984 Tc 0.3407 Tw (nonspherical, and has a quadrupole moment which may lead to localized adsorption, particularly ) Tj T* -0.4097 Tc 0.3656 Tw (on adsorbents with polar sites. Argon and nitrogen molecules are similar in size and, other than ) Tj T* -0.3955 Tc 0.3955 Tw (for nitrogen adsorption on polar sites, adsorb with similar heats of adsorption. The boiling point ) Tj T* -0.2876 Tc 0.2876 Tw (of argon at standard ) Tj 93.75 0 TD -0.2471 Tc 0.2471 Tw (pressure is 87.29 K and of nitrogen is 77.35 K.) Tj 215.25 0 TD 0 Tc 0 Tw ( ) Tj -309 -15 TD ( ) Tj 0 -15 TD -0.3818 Tc 0.3818 Tw (Argon at liquid argon temperature is preferable to nitrogen or argon at LN) Tj 333 -1.5 TD /F1 7.5 Tf 0 Tc 0 Tw (2) Tj 3.75 1.5 TD /F1 12 Tf -0.2597 Tc 0.2597 Tw ( temperature as a ) Tj -336.75 -15 TD -0.4029 Tc 0.4029 Tw (probe molecule in studies of microporosity. Being inert is an advantageous attribute in regard to ) Tj 0 -15 TD -0.5317 Tc 0.5317 Tw (the solid) Tj 37.5 0 TD -0.246 Tc 0 Tw (-) Tj 4.5 0 TD -0.384 Tc 0.384 Tw (surface interaction because there are fewer specific interactions. Being at a higher ) Tj -42 -15 TD -0.4058 Tc 0.4058 Tw (temperature provides the experimental advantage of shorter equilibrium times. In addition, the ) Tj 0 -15 TD -0.4825 Tc 0.4825 Tw (argon pressure at which a given pore width fills is higher than with nitrogen a) Tj 341.25 0 TD -0.3702 Tc 0.3702 Tw (nd therefore is ) Tj -341.25 -15 TD -0.3408 Tc 0.3408 Tw (easier to measure accurately.) 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