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Porous materials, consolidation

Efflorescence. The solvent properties of water also causes efflorescence, a phenomenon whereby soluble or slightly soluble substances migrate from the interior of porous solids to the surface, where they precipitate. Efflorescence is an important factor in the decay and disintegration of many rocks, and of human-made porous materials such as ceramics, and even of some types of glass. On archaeological objects, efflorescence generally occurs mostly as a white, powdery, but sometimes consolidated accretion on the surface of the objects. Calcite, a form of calcium carbonate, is one of the most common substances to effloresce on archaeological ceramics. [Pg.441]

Turner (T14) has proposed two detailed models of packed beds which try to closely approximate the true physical picture. The first model considers channels of equal diameter and length but with stagnant pockets of various lengths opening into the channels. There is no flow into or out of these pockets, and all mass transfer occurs only by molecular diffusion. The second model considers a collection of channels of various lengths and diameters. We will briefly discuss each of these models, which are probably more representative of consolidated porous materials than packed unconsolidated beds. [Pg.145]

Magnetic resonance imaging (MRI) has been applied to the study of the distribution of fluid components (i.e., water or a polymer used as consolidant) in a porous material such as stone or waterlogged wood by a direct visualization of the water or fluid confined in the opaque porous medium [13]. [Pg.15]

Powders are porous materials and their bulk and relative densities can change with consolidation (6). However, a powder s true density is the density of its solid phase only and thus is independent of the state of consolidation. The true density of organic excipients typically ranges from 1.0 to 1.6g/cm3 while inorganic excipients (e.g., calcium phosphate) show values greater than 2g/cm3. True density is used to determine powder or compact solid fraction (SF) (see below) and it may be a consideration when selecting excipients if segregation is a concern. True density is often determined by gas pycnometry. [Pg.130]

Ilic, M. and Turner, I.W. Convective drying of a consolidated slab of wet porous material, Int. JHeat Mass Transfer, 32 (12),[1989). [Pg.108]

The pore properties of cast bulk porous material and coating layers from the same suspension become different above sinter temperatures where intermediate stage sintering in the bulk starts (see Section 6.2.5). At lower temperatures pore properties of free casts determined with Hg porosimetry can be used to compare the pore properties of consolidated dispersion coatings. [Pg.207]

Some dry archaeological wood may be riddled by insect activity and require consolidation. Hillman and Florian (24) have described a sandwich type of deterioration of boards of a bentwood box. The boards are virtually a sandwich of paper-thin outer surfaces between which the wood is completely riddled with lyctid beetle galleries and tunnels filled with frass. This porous material is easily, consolidated. [Pg.28]

Biot, M.A. (1956). General solutions of the equations of elasticity and consolidation for a porous material, i. Appl. Mech., Trans. Am. Soc. Mech. Engrs., Vol. 78, pp. 91-96. [Pg.586]

In 2000, we have begun our research on this topic paying particular attention to the possibility of finding new chemical systems able to frontally polymerize and new FP applications. Specifically, we have studied polyurethanes (19, 20), polyester tyrene resins (21), polydicylopentadiene (22) and its BPNs with polyacrylates (23), Furthermore, we were able to prepare films (24) and to apply FP to the consolidation of porous materials (i.e. stones, woods, flaxes, papers), in particular -but not only- those having a historical-artistic interest (24), In this chapter we present a brief overview of these recent findings. [Pg.123]

AppUcation of the Frontal Polymerization Technique to the Consolidation of Porous Materials... [Pg.131]

FIGURE 5.5 A guide to the application of consolidant to an object If the application is carried out under vacuum, the container should be evacuated before the addition of the liquid consolidating material. A cova- should be placed over the container to prevent premature evaporation or reaction with atmospheric moisture. The object is lifted off the bottom of the container to reduce the pos-sibiUty of air pockets (a). A small amount of polymer in Uquid form is added to start the penetration process. This Uquid is drawn up into the porous material by capillary absorption (b). The object is soaked in consoUdant aUowing time for trapped air to dissolve and the diffusion of the various components in the Uquid to approach equdibrium. Any vacuum that has been applied is broken slowly and carefully to prevent sudden stresses being appUed to the object (c). Excess consolidant is allowed to drain out before the drying ot setting takes place. This reduces excess consoUdant and reduces the fomation of a surface skin with solvent-appUed polymers. [Pg.127]

Many data exist on measured permeability and hydraulic conductivity of both consolidated and unconsolidated porous material. These data represent the geological material consisting of sand, silt, and clay particles that form the sediment bed plus the sandstone, limestone, and other aquifer material along the flow pathways. Selected data from various sources that represent bank and stream-bed materials appear in Table 11.1. A study of these data indicates that the range of values for any particular... [Pg.310]

The term porosity refers to the fraction of the medium that contains the voids. When a fluid is passed over the medium, the fraction of the medium (i.e., the pores) that contributes to the flow is referred to as the effective porosity of the media. In a general sense, porous media are classified as either unconsolidated and consolidated and/or as ordered and random. Examples of unconsolidated media are sand, glass beads, catalyst pellets, column packing materials, soil, gravel and packing such as charcoal. [Pg.63]

Recently, a new porous crystalline matrix ( Gubka ) has been prepared on the basis of fly ash from power stations to incorporate complex ACT-containing wastes by means of repeated saturation-drying-calcining cycles. This matrix can accommodate up to 50 wt% nitrate salts (after drying) and 35 wt% calcine. The waste-loaded material can be consolidated by hot pressing with a 35% volume reduction (Aloy et al. 2000 Tranter et al. 2002). [Pg.54]

Parylene-C is of potential interest in conservation because of the unique application method that can result in the formation of thin, uniform, and strong films within porous or fibrous materials. However, the polymer has the disadvantages of being a non-reversible consolidant that is sensitive to ultraviolet-induced oxidation. [Pg.111]

Those comprising consolidated mare material (porous and unshocked, F—1)... [Pg.106]

The sol-gel process is a versatile solution process for making ceramic and glass materials involving the transition of a system from a colloidal suspension (sol) into a solid phase (gel) ". The resulting porous gel can be chemically purified and consolidated at high temperatures. In the classical sol-gel process, the precursor (e.g. a metal enolate or a metal aUcoxide) is exposed to a series of hydrolysis and polymerization reactions to form... [Pg.936]

When the electrode is completely immersed in the electrolyte solution, only a two-phase interface (i.e., liquid-solid) is present in the electrode structure. In form it may be either a consolidated powdered active carbon or a confined but unconsolidated bed of carbon particles. These are u.sed for flow-through porous electrodes in many electrochemical systems. The other mode of operation is the gas-diffusion electrode, in which the electrode pores contain both the electrolyte solution and a gaseous phase. Numerous publications [29-31] have reported on a theoretical analysis of flow-through porous electrodes and gas-diffusion electrodes, which takes into account the physicochemical characteristics of carbon electrode materials. There does not seem to be a uniform explanation for the effects of structural and chemical heterogeneity in carbons. [Pg.128]


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