Cement contact models

Atomic force microscope (AFM). Sample solutions at 100 ng/ml or less were cemented onto mica and imaged in a model Nanoscope Ilia scanning probe microscope with TESP cantilevers (Veeco/Digital Instruments, Santa Barbara, CA) operated in the intermittent contact mode on an atomic force microscope. 

The surface topography of the obtained MDF cement specimens was studied by AFM (NT-MDT model NTGRA PREVIA EC), operated at ambient atmosphere. AFM data were collected in semi contact mode using a silicone cantilever (CSG 10, force constant 0.15 N/m, tip radius 10 nm). The average roughness was calculated with the AFM manufacturer s provided software on images of 5 x 5 pm scan size. 

For plastic materials, a conical plastometer can be used. The immersion of a cone with a defined apex angle into the body down to a depth h due to the action of force F can yield an area of contact, 5( and the tangential component of the force, f,. If the ratio FJS,=t is invariant with respect to the force applied, then the rheological behavior can be interpreted in terms of the Coulomb model and t = Inv is a critical shear stress. This is a common way to study the rheology of cement, flour, soils, etc. A conical plastometer was used in the evalnation of the mechanical properties of the surface of the Moon. 

A third important alteration process in cement/rock interaction is the precipitation of calcite and other carbonates and sulphates. This happens when calcium hydroxide-rich cement fluids come into contact with various sources of carbonate and sulphate, such as local ground-waters or carbonate and sulphate phases already present in the rock which may dissolve when the highest pH fluids are encountered. Calcite precipitation due to these processes has been predicted by models (Jefferies et al. 1988 Lunden Andersson 1989 Eikenberg Lichtner 1992 Steefel Lichtner 1994). Calcite has also precipitated in some experiments, even if attempts were made to keep carbonate and CO2 out of the system (e.g. Pusch 1982 Jefferies et al. 1988). 

Figure 5a shows an original McKee-Farrar metal-on-metal hip implant, fixed to the pelvis with bone cement, and Figure 5b shows the corresponding finite elemait model employed to perform contact mechanics and lubrication analysis (Jin et al 2002). 

In the category of diluent, nonreactive adhesives, one example is model airplane cement (often cellulose nitrate in a mixture of ketones and aromatic solvents). As a coating we would call it a lacquer. Aqueous solutions of natural and synthetic gums are used in library paste. Some of the popular white glues for paper and wood are simply poly(vinyl acetate) emulsions with a small amount of plasticizer. All of these materials solidify after contacting the surface as a liquid by loss of solvent or diluent. Evaporation or diffusion into a porous substrate may be involved. 

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