氮气吸附法研究偏高岭土基地聚合物孔结构特征

Pore Structure Characteristics of Metakaolin-based Geopolymers by Nitrogen Adsorption Method

为揭示偏高岭土基地聚合物的微观孔结构特征并探索介孔地聚合物制备和微孔结构调控途径,采用氮气吸附法研究了偏高岭土基地聚合物的吸附/脱附等温曲线和微观孔结构特征(包括总孔体积、比表面积、孔形状和孔径分布等),并讨论了水玻璃模数和水用量对地聚合物孔结构的影响。结果表明:偏高岭土基地聚合物吸附/脱附等温曲线为IV型,迟滞回线为H1和H3混合型;总孔体积为0.141 8~0.313 6 cm^3/g,比表面积为28.87~53.25 m^2/g,孔径为2~92 nm,其中孔径为2~50 nm的介孔分别占总孔体积和比表面积的97.82%和98.87%;地聚合物中的孔以两端开放的圆柱形孔、平行板狭缝孔为主,同时存在少量一端封闭的圆柱形孔、平行板狭缝孔或墨水瓶孔。调整水玻璃模数和水用量均可在一定范围内调控偏高岭土基地聚合物孔结构。水玻璃模数由1.2增至1.8时,其总孔体积由0.225 3 cm^3/g降至0.141 8 cm^3/g,最可几孔径在13.91~19.56 nm范围;水用量由15.5增至18.5时,其总孔体积从0.221 9 cm^3/g逐渐增至0.313 6 cm^3/g,孔径分布先由水用量为15.5的单峰分布变为双峰分布;水用量增至18.5时,孔径分布显著宽化,最可几孔径消失。水用量比水玻璃模数对偏高岭土基地聚合物孔结构具有更强的调控效应。

To reveal the microscopic pore structure of metakalin-based geopolymers and explore the effective ways to prepare mesoporous geopolymers and regulate its pore structure, the adsorption-desorption isotherms, microscopic pore structure of metakaolin-based geopolymers （i.e., total pore volume, specific surface area, morphology and pore size distribution） were investigated by nitrogen adsorption method. The influences of soluble sodium silicate modulus and water content on the pore structure of geopolymers were discussed. The results show that the adsorption-desorption isotherms of metakaolin-based geopolymers belong to type IV, and its adsorption hysteresis loop is a mixture of H1 and H3. The total pore volume and specific surface area are 0.141 8-0.313 6 cm3/g and 28.87-53.25 m2/g, respectively. The pore size distribution range is from 2 nm to 92 nm, among which, mesopores with the sizes of 2-50 nm are dominant, accounting for 97.82% of the total pore volume, and 98.87% of the pore surface area. Moreover, massive pores in geopolymers are mainly the two-side open cylindrical pores and parallel wall pores, while a small amount of pores are one side opened pores, like cylindrical pores, slited-shaped pores with parallel or ink bottle-shaped pores. The mesopore structure can be modulated by changing sodium silicate modulus and water content in a certain range. The total pore volume of metakalin-based geopolymers decreases from 0.225 3 cm3/g to 0.141 8 cm3/g, while the most probable pore diameter varies from 13.91 nm to 19.56 nm with the increase of sodium silicate modulus from 1.2 to 1.8. The total pore volume increases from 0.221 9 cm3/g to 0.313 6 cm3/g, while the pore size distribution varies from single peak at water content of 15.5 to double peaks, and eventually broadens to disappear at water content of 18.5 with the increase of water content from 15.5 to 18.5. Water content shows a stronger effect than the modulus of water glass in modulating the mesopore structure of metakaolin-based geopolymers.