Journal of Porous Materials 6, 95–99 (1999) c  1999 Kluwer Academic Publishers. Manufactured in The Netherlands. Neutron Diffraction Study of Cement M.P. FANG AND P.E. SOKOL Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA J.Y. JEHNGAND W.P. HALPERIN Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA Received ; Revised April 3, 1998 Abstract. Neutron diffraction studies of the static structure factor S( Q) of water confined in the pore space of cement samples have been carried out for temperatures from 170 to 293 K. At high temperatures, when the water in the pores is liquid, a fraction of the water molecules are strongly bound to specific adsorption sites on the crystalline components of the cement. On cooling, the water in the pore space solidifies at 245 K into a cubic structure different from that of bulk water at similar temperatures. Keywords: cement, structure, water, phase transition, diffraction Cements are porous materials with obvious techno- logical significance. The complex pore structure in ce- ment, consisting of interconnecting pore networks with different sizes, plays a large role in determining the properties of the material, such as mechanical strength, permeability, and durability [1]. In addition, the porous structure provides a unique framework for studying the effects of confinement and interconnections on the phase transitions and structure of adsorbed liquids such as water. Neutron scattering measurements provide a power- ful probe of the microscopic structural and dynamics of condensed systems since the wavelength of ther- mal neutrons is well matched to characteristic inter- particle separations of atoms or molecules [2]. In a liquid or amorphous solid, neutron scattering provides information on the local environment and short range structure. In a crystalline solid, the spatial arrangement of the atoms or molecules composing the solid can be obtained from the location and width of the diffrac- tion peaks, the appearance of which are characteristic of long range order. Thus, neutron scattering provides unambiguous information on the nature of the phase transitions and structure of condensed systems and has been used to probe the large scale structure of cement [3–8], the crystalline structure of the cement powders [9, 10] and the hydration kinetics [11]. In this paper we report measurements of the static structure factor, S( Q), of both wet and dried cements. These measurements show that the microscopic struc- ture of the cement changes little during the drying pro- cess. The structure of the water in the cement pores, however, is significantly modified by confinement. A depression of the liquid-solid phase transition tempera- ture, known as supercooling, is observed and the struc- ture of the water in the pores is different from that of bulk water. The neutron diffraction measurements were carried out using the High Intensity Powder Diffractometer (HIPD) at the Intense Pulse Neutron Source, Argonne National Laboratory. HIPD is a high-intensity low- resolution time-of-flight powder diffractometer with detector banks located at 30 and 90 ◦ allowing a wide range of momentum transfers Q to be covered. The data were converted to S( Q) using standard tech- niques [12]. Corrections for sample attenuation, mul- tiple scattering and inelasticity have not been applied. These corrections only affect the overall intensity of