Porous calcium carbonate

Recently, the LbL technique has been extended from conventional nonporous substrates to macroporous substrates, such as 3DOM materials [58,59], macroporous membranes [60-63], and porous calcium carbonate microparticles [64,65], to prepare porous PE-based materials. LbL-assembly of polyelectrolytes can also be performed on the surface of MS particles preloaded with enzymes [66,67] or small molecule drugs [68], and, under appropriate solution conditions, within the pores of MS particles to generate polymer-based nanoporous spheres following removal of the silica template [69]. 

In this example, a simple mechanism for breaking a colloid was chosen. The eggshells are made of porous calcium carbonate, their surface covered with innumerable tiny pores. The particles of fat in the broth accumulate in these small pores. Removing the eggshells from the broth (each with oil particles adsorbed on their surfaces) removes the dispersed medium from the broth. One of the two components of the colloid is removed, preventing the colloid from persisting. 

Sukhorukov GB, Volodkin DV, Gunther AM et al (2004) Porous calcium carbonate microparticles as templates for encapsulation of bioactive compounds. J Mater Chem 14 2073-2081... 

Parameter Non-porous calcium carbonate Porous calcium carbonate ... 

Petite, H., Kacem, K., Triffitt, J.T., 1996. Adhesion, growth and differentiation of human bone marrow cells on non porous calcium carbonate and pastic substrata effects of dexametha-sone and 1,25 dihydroxyvitamin D3. Mater. Med. 7, 665-671. 

Filter aids should have low bulk density to minimize settling and aid good distribution on a filter-medium surface that may not be horizontal. They should also be porous and capable of forming a porous cake to minimize flow resistance, and they must be chemically inert to the filtrate. These characteristics are all found in the two most popular commercial filter aids diatomaceous silica (also called diatomite, or diatomaceous earth), which is an almost pure silica prepared from deposits of diatom skeletons and expanded perhte, particles of puffed lava that are principally aluminum alkali siheate. Cellulosic fibers (ground wood pulp) are sometimes used when siliceous materials cannot be used but are much more compressible. The use of other less effective aids (e.g., carbon and gypsum) may be justified in special cases. Sometimes a combination or carbon and diatomaceous silica permits adsorption in addition to filter-aid performance. Various other materials, such as salt, fine sand, starch, and precipitated calcium carbonate, are employed in specific industries where they represent either waste material or inexpensive alternatives to conventional filter aids. 

Sedimentary rocks (like sandstone) have a microstructure rather like that of a vitreous ceramic. Sandstone is made of particles of silica, bonded together either by more silica or by calcium carbonate (CaCOj). Like pottery, it is porous. The difference lies in the way the bonding phase formed it is precipitated from solution in ground water, rather than formed by melting. 

Bone is a porous tissue composite material containing a fluid phase, a calcified bone mineral, hydroxyapatite (HA), and organic components (mainly, collagen type). The variety of cellular and noncellular components consist of approximately 69% organic and 22% inorganic material and 9% water. The principal constiments of bone tissue are calcium (Ca ), phosphate (PO ), and hydroxyl (OH ) ions and calcium carbonate. There are smaller quantities of sodium, magnesium, and fluoride. The major compound, HA, has the formula Caio(P04)g(OH)2 in its unit cell. The porosity of bone includes membrane-lined capillary blood vessels, which function to transport nutrients and ions in bone, canaliculi, and the lacunae occupied in vivo by bone cells (osteoblasts), and the micropores present in the matrix. 

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. 

Insulation materials contain more air and have an lower apparent density than ordinary refractory materials. In the case of insulation bricks the desired porosity is obtained by making use of additives which produce gases when heated (e.g. calcium carbonate), or of porous raw materials. In figure 11.3. 2 the effect of the appplication of insulation bricks is represented. 

Figure 6 shows the CTL spectra observed during the catalytic oxidation of ethanol on y-alumina, calcium carbonate, and barium sulfate. The profiles of these broad spectrum components are similar to each other, and they peak in the vicinity of 420 nm. The profiles of the CTL spectra from the excited species depend on the kind of catalyst. Fine spectra are observed in the non-porous BaSC>4 catalyst. In Fig. 6b, the thin curves denote the fine spectrum components obtained by the peak-fitting technique. 

Ripamonti, U., The morphologenisis of bone in replicas of porous hydroxapatite obtained from conversion of calcium carbonate exoskeletons of coral. J. Bone Jt. Surg. 73A, 692-703 (1991). 

Tensile properties of PVC filled with precipitated calcium carbonate particles having two different mean sizes were studied. The particles were porous agglomerates of spherical primary particles. 10-50 parts of the particles were mixed with 100 parts PVC and 3 parts lead stearate using a mixing roll. Tensile tests were carried out using dumbbell test specimens. 20 refs. 

Limestones vary in physical characteristics from compact rocks of low porosity to friable and highly porous ones, such as chalk, which may contain up to 25% of water. All consist essentially of calcium carbonate, normally in the polymorphic form of calcite. Other naturally occurring forms of CaCOj, such as shell deposits, are sometimes used. Many limestones contain significant amounts of minor components, either as substituents in the calcite or in accessory phases, some of which are deleterious if present in amounts exceeding a few per cent (e.g. MgO, SrO), a few tenths of a per cent (e.g. P2O5, CaF2, alkalis) or even less (some heavy metals). 

Artificial saltpetre earths can be prepared by allowing stable refuse to nitrify in contact with a porous soil containing calcium carbonate, the nitrate being isolated by lixiviation and purified by crystallization. The salt is also manufactured from sodium nitrate by the action of potassium chloride, since it crystallizes out from a hot concentrated solution of these two substances as the temperature falls. When prepared from Chile saltpetre, it often contains sodium nitrate, and chloride, chlorate, and perchlorate of potassium. 

Typically, bone has a solid outer portion called cortical bone and a porous inner part called cancellous bone. The amounts of each vary with location in the body. The cortical bone is a ceramic containing calcium compounds and viscous liquids, a protein called collagen , and an organic polymer. In addition to HAP, bone consists of calcium carbonate and calcium phosphate. HAP is 69 wt.% of total calcium phosphate compounds [4]. Part of the Ca in these compounds is substituted by Na, K, Mg, and Sr. Hydroxyl ions in the HAP are also substituted by F, CO3, or Cl, which makes the apatite a fluoroapatite, dahllite or chloroapatite, respectively. These substitutions are considered to play significant roles in the structure and mechanical properties of bones. 

What is the chemistry of the deterioration of marble by sulfuric acid Marble is produced by geological processes at high temperatures and pressures from limestone, a sedimentary rock formed by slow deposition of calcium carbonate from the shells of marine organisms. Limestone and marble are chemically identical (CaC03) but differ in physical properties because limestone is composed of smaller particles of calcium carbonate and is thus more porous and more workable. Although both limestone and marble are used for buildings, marble can be polished to a higher sheen and is often preferred for decorative purposes. 

Dollimore and co-workers [47] in later investigations found wide variations in A and d(s). Dollimore and Horridge [69] found A = 20.2 for china clay. Thompson [cit. 45] found 24.3calcium carbonate in aqueous sodium chloride Dollimore and Owens [70] found 4 = 81 and A = 206 for non-porous silica in water and n-heptane respectively. 

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