Bulk fill materials

S. Flury, S. Hayoz, A. Peutzfeldt, J. HUsler, A. Lussi, Depth of cure of resin composites is the ISO 4049 method suitable for bulk fill materials Dent. Mater. 28 (2012) 521-528. 

Notice that all the answers are very short. Do not try to fill all the space provided on the exam. You score points by saying specific things, not by the bulk of material. The graders look for certain keywords or phrases. The answers should not contain statements that contradict each other. 

In the 1970s a model for semi-crystalline polymers was presented by Struik (1978) it is reproduced here as Fig. 2.13. The main feature of this model is that the crystalline regions disturb the amorphous phase and reduce its segmental mobility. This reduction is at its maximum in the immediate vicinity of the crystallites at large distances from the crystallites will the properties of the amorphous phase become equal to those of the bulk amorphous material. This model is similar to that of filled rubbers in which the carbon black particles restrict the mobility of parts of the rubbery phase (Smith, 1966). 

The principle of photocatalysis is often explained with an illustration like Fig. 2, a schematic representation of the electronic structures of semiconducting materials, a band model. An electron in an electron-filled valence band (VB) is excited by photoirradiation to a vacant conduction band (CB), which is separated by a forbidden band, a band gap, from the VB, leaving a positive hole in the VB (Section III.B). These electrons and positive holes drive reduction and oxidation, respectively, of compounds adsorbed on the surface of a photocatalyst. Such an interpretation accounts for the photocatalytic reactions of semiconducting and insulating materials absorbing photons by the bulk of materials. In the definition of photocatalysis given above, however, no such limitation based on the electronic structure of a photocatalyst is included. For example, isolated... 

Diluent To act as a bulking agent or filling material Sugars, lactose, mannitol, sorbitol, sucrose Inorganic salts, primarily calcium salts Polysaccharides, primarily microcrystalline celluloses... 

Me2Sn(C = C-Fc)2 showing two different tin sites [Siso —144.0 (minor), —150.5 (major) are marked by filled circles S Sn (CD2CI2 solution) —152.8]. In contrast to the bulk crystalline material, the crystal studied by X-ray diffraction had only one type of molecule in the unit cell, as shown. (Adapted from Reference 228, with permission from Wiley-VCH.)... 

These proeesses modify surfaee layers of both interacting materials (filler and matrix) and form an interphase which differs in properties from the bulk matrix. The formation of the interphase is responsible for changes in the physical and mechanical properties of filled materials and usually improves material reinforcement. ... 

Bulk fill. Lime improvement (partial lime treatment) is used to dry and/or reduce the plasticity of materials, such as silts or clays. It makes such materials more suitable for placing and compacting, whether in landBll or embankments. The Moisture Condition Value (MCV) test [26.11] and [26.13] is used to assess the suitability of a material for handling and compaction. 

Thermal conductivity of a bulk of material filled with air can be estimated by the equation... 

When single-screw extruders are starve fed (Fig. 5.12d), plastic particles do not immediately fill the screw channel. As a result, the first few channels of the feed zone lack the pressure required to compact the polymer particles. Particle conveyance in the imfilled channels is not as steady as transport with filled channels. Consequently, metered feeding is seldom used with single-screw extruders. Such feeding can be used to reduce the motor load, limit temperature rises, add several components through the same hopper, improve mixing in singlescrew extruders, control flow into vented barrel extruders, and feed low-bulk-density materials. 

A low-bulk-density material leads to the use of less mass of proppant for a given volume of reservoir bed or storage tank to fill. 

It is essential with suction nozzles to avoid filling the inlet tube solidly with material, and to maintain an adequate flow of air through the conveying line at all times. To avoid blocking the inlet pipe, sufficient air must be available at the material feed point, even if the suction nozzle is buried in the bulk solid material. Indeed, the vacuum off-loading system must be able to operate continuously with the nozzle buried in the material in order to maximise the material flow rate. Sufficient air must also be available for conveying the material through... 

During dredging, transport and placement of fill material a change in volume occurs. This is caused by a change of density (bulking) and by loss of fine material. This is schematically shown in Figure 5.1. 

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