Ultrasonic sound speed of hydrating calcium sulphate hemihydrate; part 2, the correlation of sound velocity to hydration degree
In this article the sound velocity through a mix is correlated to the hydration degree of 
the mix. Models are presented predicting the sound velocity through fresh slurries and 
hardened products. These two states correspond to the starting and finishing point of the 
hydration process. The present research shows that a linear relation between the amount 
of hydration-product (gypsum) formed (Smith et al., 2002) and sound velocity can be 
used to describe this process. To this end, the amount of hydration-product formed is 
determined by the using the equations of Schiller (1974) for the hydration process and 
of Brouwers (2010) for the volume fractions of binder, water and hydration products 
during the hydration process. The presented model shows that the induction time and 
gypsum growth rate are linear related to the water/gypsum-ratio.
Correlation between hydration mechanism and ultrasonic measurements in an aluminous cement: effect of setting time and temperature on the early hydration
Abstract Early hydration (0–24 h) of Secar 71, a calcium aluminate cement, has been examined in-situ by ultrasonic testing for pastes prepared at 20 °C (W/C=0.33, 0.38 or 0.40) and at 5 °C, 40 °C and 60 °C (W/C=0.33). The ultrasonic measurements consist of following the velocity of the longitudinal ultrasonic wave, V L (frequency=1 MHz), transmitted inside the specimen and also the reflection coefficient, R , at the interface between the cement and the container of the paste, which is a polymethylmethacrylate mould. The variations of V L as a function of setting time can be described by a dissolution-precipitation mechanism. Lastly, the changes in R can be linked with morphological changes occurring inside the cement paste, especially the progressive formation of crystallised hydrates.
Phase formation during mechanical alloying in the Ti–Si system
Abstract Mechanical alloying of Ti–Si powder mixture or TiH 1.924 –Si powder mixture was performed by high-energy ball milling, in which the Ti to Si mole ratio was 1:2. The phase formations in both mixtures during milling were investigated by X-ray diffraction. Mechanical alloying a mixture of elemental powders led to the formation of TiSi 2 equilibrium compound, while when starting from Si + TiH 1.924 , a metastable phase was formed. The metastable phase completely transforms to TiSi 2 when the mechanically alloyed powder is annealed at temperatures above 800 °C. Two different pathways of phase transitions during mechanical alloying are attributed to the existence of hydrogen atoms, i.e., when starting from Si + TiH 1.924 compared to Si + Ti, the kinetics for the formation of the TiSi 2 intermetallic compound slows down. The kinetics related to the different phase transitions depending on the starting powder mixture are discussed.