The maximum crystal radius Rn of ice in hollow wet chrysotile tubes is established by thermoporometry to be between 2.8 and 3.2 nm, and the internal pore volume Vn of the tubes to be between 0.008 and 0.02 ml/g. The hollow tubes of chrysotile and, for comparative reasons, small plates of talc, are hydrothermally synthesized at temperatures between 563 and 600 K and at pressures between 75 and 120 hPa. Size and shape of the pores can be varied by changing the Mg/Si molar ratios in steps of 3/1.5 and 3/2 for chrysotile and 3/3.6 and 3/4 for talc. The tubular morphology of the aggregates dried at 393 K is investigated by 1) transmission electron microscopy (TEM), 2) nitrogen adsorption and desorption at 77 K, and 3) diffuse reflectance infrared fourier transformed spectroscopy (DRIFTS). The radius within the hollow tubes, Ri, is between 2.5 and 4.0 nm as measured by TEM, and between 2.8 and 3.2 nm as determined by nitrogen adsorption and desorption. The measured radii agree well with the value calculated from crystallographic data, which is smaller than 5.3 nm. Within the dried aggregates the tubes are clustered in regular patterns, in which each tube is surrounded by six other tubes. The external radius, Ro, between the clustered tubes is from 1.6 to 2.9 nm as observed by TEM, and from 1.8 to 2.3 nm by N2 adsorption and desorption. The external radius is not measured by thermoporometry. Where thermoporometry only measures the average pore size and pore volume within the tubes, TEM and N2 adsorption and desorption additionally provide the corresponding values between the tubes. A third pore radius, 5 to 20 nm between the clusters of chrysotile tubes, is established with N2 adsorption and desorption.

A version of thermoporometry dedicated to analyzing the pore network of expanding clays is proposed here. The blurred, wide Differential Scanning Calorimetry (DSC) peak obtained upon the melting of a frozen clay sample is processed by means of a deconvolution analysis based on searching for such a temperature distribution of “pulse-like heat events” which, convolved with the apparatus function, gives a minimal deviation from the observed heat flux function, i.e. the calorimetric signal. As a result, a sharp thermogram was obtained which can be transformed easily into the pore-size distribution curve. Results obtained for samples of two Clay Minerals Society Source Clays (montmorillonites SWy-2 from Wyoming and STx-1b from Texas) at different water contents indicate a greater resolution and sensitivity than that achieved by classical thermoporometry using the unprocessed DSC signal. Phenomena corresponding to the evolution of the pore network as a function of the water content have been detected in samples with large water contents subjected to free drying prior to the experiments.