表面与界面化学试卷(a)2007

Fig.2 An adsorbed structure on an fcc (100) surface Fig.3 adsorption isotherms

At 77K a 1.5g sample of a porous solid showed the following results for the adsorption of nitrogen:

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课程名称—表面与界面化学—— （ A 卷）

1. ① surface tension: Surface tension is defined as the force acting at right angles to any line of unit length on the liquid surface or surface tension is the work required to increase the area of a surface isothermally and reversibly by unit amount. (3 points)

②CMC: CMC is the concentration above which micelle formation becomes appreciable. (3 points)

③solubilisation: Surfactant solutions above the CMC can solubilise otherwise insoluble organic material by incorporating it into the interior of the micelles. This is known as micellar solubilisation. (3 points)

④ interface: The point, area, or surface along which two substances or other qualitatively different things meet. (3 points)

⑤coverage: a measure of the extent of adsorption of a species onto a surface. Usually defined as , Where N ads is the number of adsorbate atoms per unit area and N m is the number of atoms adsorbated per unit area to produce one complete layer on the surface. (3 points)

⑥unit mesh: the unit cell of a two-dimensional surface structure. (3 points) ⑦surface atom density: the number of atoms per unit surface area 。 (3 points) ⑧ surface activity: The strong adsorption of such materials at surfaces or interfaces in m ads

N N /=θ

the form of an orientated monomolecular layer is termed surface activity. (3 points)

⑨Krafft point: Micelle-forming surfactants exhibit another unusual phenomenon in that their solubilities show a rapid increase above a certain temperature, known as the Krafft point.

⑩surface excess: The difference in concentration between surface and inner due to the adsorption is termed “surface excess”.

2.P/(V(P0-P))⨯104(cm-3) 4.17 16.67

P/P00.04 0.2

The slop and the intercept are 0.0078125, 0.0001045 respectively. (3 points) Vm=1/(0.0078125+0.0001045)=126.31 cm3 (3 points)

The specific sruface area

A=N0σV m/m22400=6.02⨯1023⨯16.2⨯10-20⨯126.31/1.5/22400

=367m2/g (4 points)

3.Read off a number of pairs of values of pressure (P) and temperature (T) which yield the

same surface coverage, (5 points) and then plot a line of ( ln P ) v's (1/T), the slope of which yields the adsorption heat. (5 points)

The unit cell is illustrated below - note, this cell contains only one repeat unit and is the primitve unit cell for the adsorbate.

It is rectangular in shape and shows no rotational misalignment with the substrate unit cell. Using the substrate vectors given on the diagram we have the following relations: b1 = a1; b2 = 3.a2

Hence, this structure is a M(110)(1x3) structure.

The ratio of the areas the unit cells of the adsorbate and substrate is 3:1 and the adsorbate cell contains only one adsorbed entity - consequently

Coverage = ( 1 / 3 ) x 1 = 0.33