Spherical cement

The adsorption of superplasticizer to spherical cement particle surface decreases by 40% because of a decrease of the specific surface area and localization of the intestitial phase with gypsum. 

The initial heat evolution amount of spherical cement is smaller by 25% than that of normal Portland cement. This low activity at initial hydration contributes to the creation of high fluidity. 

Random coil conformations can range from the spherical contracted state to the fully extended cylindrical or rod-like form. The conformation adopted depends on the charge on the polyion and the effect of the counterions. When the charge is low the conformation is that of a contracted random coil. As the charge increases the chains extend under the influence of mutually repulsive forces to a rod-like form (Jacobsen, 1962). Thus, as a weak polyelectrolyte acid is neutralized, its conformation changes from that of a compact random coil to an extended chain. For example poly(acrylic acid), degree of polymerization 1000, adopts a spherical form with a radius of 20 nm at low pH. As neutralization proceeds the polyion first extends spherically and then becomes rod-like with a maximum extension of 250 nm (Oosawa, 1971). These pH-dependent conformational changes are important to the chemistry of polyelectrolyte cements. 

Particulate Composites. Particulate composites encompass a wide range of materials, from cement reinforced with rock aggregates (concrete) to mixtures of ceramic particles in metals, called cermets. In all cases, however, the particulate composite consists of a reinforcement that has similar dimensions in all directions (roughly spherical), and all phases in the composite bear a proportion of an applied load. The percentage of particulates in this class of composites range from a few percent to 70%. 

The appearance of the individual microcapsules is shown in Fig. 1. Most individual microcapsules are approximately spherical and show a surface made up of deposited plates of poly(DL-lactic acid) in which the drug is embedded. Many of the larger microcapsules are cemented together by further plates of poly(DL-lactic acid). The effect of compression on these microcapsules is shown in Fig. 2. At a compressive force of 2 kN (Fig. 2(a)) the electron micrograph of the tablet fracture surface shows that the microcapsules, while distorted, remain essentially intact and rounded, with a relatively open porous structure to the tablet as a whole. At 10 kN force (Fig. 2(b)) the microcapsules at the fracture are flattened, cracked and distorted so that the fracture surface shows a far less open, porous aspect. Both of these microcap tablets have a very different appearance from that produced by the simple mixture (Fig. 3), where the individual plates of poly(DL-lactic acid) are mixed with the drug crystals in an open structure from which release would be easily... 

The effects of various formulation factors on the in vitro release characteristics of spherical polymethylmethacrylate implants were studied. Physical and mathematical models were proposed to describe the in vitro release profiles. The in vitro release data could be described by a biexponential equation of the following type fraction of tobramycin remaining in the implant at time t=Aerai+BQ, where a, and P represent the rate constants for the initial rapid and subsequent slow phases of release. The influence of drug loading, volume of dissolution medium, implant size and type of cement and the incorporation of water-soluble additives on the release profiles and a and P rate constants is described. 

A routine operation usually proceeds as follows. First the head of the femur is sawn off. The socket in the pelvis (the acetabulum) is then made deeper with a cutting machine and subsequently the metal socket is stamped into the hip. This metal is then lined with plastic to facilitate sliding movements. The femur is scooped out with a rasp and filled with cement. This cement is a mixture of plastics which automatically polymerizes in the femur. Since 1997 it has been becoming customary to grind up old hip heads and use the bone shreds together with the cement as a filler for the shaft of the prosthesis. The stem of the prosthesis is hammered into the femur, the spherical head is attached to it and inserted into the plastic socket. 

When a portion of the rock is well-cemented while the material around it is not, this can result in differential erosion as the weaker material is worn away. Concretions are masses of well-cemented sediment that often form around a core, sometimes a fossil or a fragment of rock. These structures are often spherical or rounded and occur in many different types of sedimentary rocks. 

Influence of Grain Form on the Strength of Sulfur Concrete. When the influence of the grain form on the strength of sulfur concrete is examined, complete analogies to cement concrete are found. Because of its spherical form gravel can be compacted more easily and therefore has a lower grain heap porosity. Because of its smooth surface and its spherical form the binder demand is lower. 

Since the surface-volume diameter is inversely proportional to S, the constant of proportionality being a minimum of six for spherical particles, Martin s diameter is systematically different to the surface-volume diameter. Experiments confirm that, on the whole, d/ shape function. For example dp/dj = 1.2 for Portland cement and 1.3 for ground glass [65]. 

Nodular Term synonymous with glaebular and refers to soft to highly indurated concretions of carbonate, or carbonate cemented host material. The margins may be gradational to sharp, and internally the nodules may be uniform, showing concentric laminae or septarian cracks or veins. The nodules can range in shape from spherical to elongate. The nodules typically consist of micrite or less commonly microsparite. Nodular calcrete develops primarily in siliciclastic host material... 

Figure 45(c) shows in principle the adhesive method for the determination of tensile strength. 3 Cylindrical agglomerates with two parallel, flat ends are centrically cemented between two so-called adapters. To eliminate bending stresses it is necessary to machine spherical or nonsymmetrical agglomerates into cylindrical specimens using a special method (Figure 47). This sample is fastened to thin wires and subjected to tensile forces in a conventional testing machine (Figure 48). The tensile strength of the agglomerate is defined as the tensile force P at failure divided by the cross section of the cylindrical specimen.

A solid feed of j-in. spherical particles of pure B is to be reacted in a rotary kiln (such as a lime or cement kiln). The gas A in contact with the solids is of uhifbraT composition.- The-whole process- is-isothermal. The reaction is. first. order with respect to A, irreversible, and follows the stoichiometry... 

The concept of the same tan cp value for corresponding void ratios in the case of various gradation ranges of particles possessing the same degree of sphericity and the same coefficient of material friction appears to be quite well justified by experience with Portland cement concrete but appears to be contrary to experience in soil stabilization. The difference lies in the different... 

The ARC calorimeter jacket and sample system are shown in Figure 11.49 (168). A spherical bomb is mounted inside a nickel-plated copper jacket with a swagelok fitting to a 0.0625 in. tee, on which is attached a pressure transducer and a sample thermocouple. The jacket is composed of three zones, top, side, and base, which are individually heated and controlled by the Nisil/Nicrosil type N thermocouples. The thermocouples are cemented on the inside surface of the jacket at a point one quarter the distance between the two cartridge heaters. The point is halfway between the hottesl and coldest spots of the jacket. The same type of thermocouple is clamped directly on the outside surface of the spherical sample bomb. All the thermocouples are referenced to the ice point that is designed to be stable to within 0.01°C. Adiabatic conditions are achieved by maintaining the bomb and jacket temperatures exactly equal. The sample holder has a capacity of 1-10 g of sample. Pressure in the system is monitored with a Serotec 0-2500 psi TJE pressure transducer pressure is limited in the vessel to 2500 psi. The maximum temperature of the system is 500°C. 

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