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.
Kinetics of hydration of calcium sulphate hemihydrate
The kinetics of hydration of α-CaSO4·0.5H2O has been studied by calorimetry, analysis of the liquid phase, measurement of the combined water, and electron microscopic observations. Hemihydrate particles dissolve immediately after mixing with water and subsequently form hydrated layers on their surfaces by intrusion of water molecules, which grow to a thickness of ca. 0.09 µm according to a parabolic law and then undergo destruction, when the dihydrate nuclei are generated for the first time. At this point in time, the induction period terminates, and subsequent hydration of hemihydrate proceeds in accordance with the previously proposed rate equation based on the dissolution–crystallization mechanism.
Study on urea-modified phenol formaldehyde resin adhesive
A reasonable technology to synthesize Urea-Modified Phenol Formaldehyde resins is realized by reacting phenol,urea and formaldehyde.The resin's feasibility is explored.The experiment result of shows that storable stability of the modified resin is good.The curing temperature of PUF resins was 25 ℃,lower than that of PF resins.The curing speed of PUF resins is faster than that of PF resins at the same curing temperature.The physical properties of the birch plywood bonded with PUF resins is similar to that of the birch plywood bonded with normal PF resins.The mechanical properties of the birch plywood bonded with PUF resins can achieve the demands of GB/T9846-1988.Free formaldehyde content of plywood is lower than the E1 level set by GB18580-2001.The cost of the adhesive is lowered for the use of urea,and its comprehensive properties is better than that of PF resins.