Spherical calcium carbonate

A carboxylate derivative of a fully aromatic, water-soluble, hyperbranched polyphenylene is considered as a unimolecular micelle due to its ability to complex and solubilize non-polar guest molecules [23]. The carboxylic acid derivative of hyperbranched polyphenylene polymer (HBP) (My,=5750-7077, Mn=3810-3910) consists of 40-60 phenyl units that branch outward from a central point forming a roughly spherical molecule with carboxylates on the outer surface. The free acid form of HBP was suspended in distilled water and dissolved by adding a minimum quantity of NaOH. The solution was adjusted to pH 6.2 with aqueous HCl. Calcium carbonate crystals were growth from supersaturated calcium hydrogencarbonate solution at room temperature. HBP gave... 

The geometry and surface chemistry of the dendrimer assemblies can be varied through the addition of surfactants. These dendrimer/surfactant aggregates can be tuned to template the formation of the different phases of calcium carbonate [40]. In combination with hexadecyltrimethylammonium bromide (CTAB), small spherical aggregates were formed that induce the formation of vaterite. Over a period of five days, the vaterite was transformed into calcite. The use of the negatively charged surfactant, sodium dodecylsulfonate (SDS), result-... 

Spherical vaterite crystals were obtained with 4-mercaptobenzoic acid protected gold nanoparticles as the nucleation template by the carbonate diffusion method [51]. The crystallization of calcium carbonate in the absence of the 4-MBA capped gold nanoparticles resulted in calcite crystals. This indicates that the polymorphs of CaCOj were controlled by the acid-terminated gold nanoparticles. This result indicates that the rigid carboxylic acid structures can play a role in initiating the nucleation of vaterite as in the case of the G4.5 PAMAM dendrimer described above. 

The nano-sized particles of calcium carbonate and barium carbonate have specific characteristics. They are important materials for the industry. The main object of this investigation is to obtain nanoparticles of calcium carbonate and barium carbonate by chemical reaction carried out in microemulsion of water in oil. The nanoparticles obtained are spherical. Their sizes vary from 20 to 30 nm. The shape and size of particles are determinated by electron microscopy. 

Nano-sized particles of barium and calcium carbonate were obtained by a chemical reaction in a microemulsion. The particles were studied by electron microscopy and were found to possess spherical shape and diameters from 20 to 30 nm. 

The droplets crystallize and condense into hard, spherical prills that are dried, cooled, and sized for shipment. If calcium ammonium nitrate (CAN or nitro chalk) is made, ground calcium carbonate (limestone or dolomite) is added to the melt prior to the formation of the droplets when CAN is being made103 10S. 

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. 

Haruta, S. Hanafusa, T. Fukase, H. Miyajima, H. Oki, T. An effective absorption behavior of insulin for diabetic treatment following intranasal dehvery using porous spherical calcium carbonate in monkeys and healthy human volunteers. Diabetes Technol. Ther. 2003, 5 (1), 1-9. 

Four (PtS/AlA) bilayers were formed on the calcium carbonate cores as described above. The initial cores are monodisperse and have a spherical form with the diameter of approximately 3 pm (Fig. la). A direct evidence for polyelectrolyte (PtS/AlA)4 coating of the matrix is provided in the corresponding fluorescence image (Fig. lb). It shows the distribution of fluorescence due to rhodamin C, which is adsorbed in the polyelectrolyte shell. The appearance of fluorescent rings confirms that the dye molecules interact only with the (PtS/AlA)4 multilayer coating and do not penetrate into the interior of the CaC03 cores. The multilayer coatings on the carbonate cores were stable for several days when stored in the aqueous medium at pH 5.5. 

The soluble form of calcium can be precipitated in the marine environment to form rock by some physical conditions such as warming of the water (carbon dioxide is less soluble in warm water than in cold water and thus calcium carbonate is precipitated), by the use of carbon dioxide by marine plants, or by alterations in the pH of water by ammonia-producing bacteria which also lowers the solubility of calcium carbonate. However, the majority of calcium carbonate deposits are formed from skeletal fragments of organisms living in the marine environment. Some of these organisms inhabit reefs but the majority float free in water. Figure 2.13 shows various shapes of shells formed by Coccolithophorides which can be spherical coccospheres some, such as dicoaster, are star shaped. 

Calcium hydroxide is a product new to the market. There have been, in past, positive scientific reports of its usefulness. The benefits of calcium hydroxide over calcium carbonate are its functionality, particle shape (more spherical and thus less abrasive to the equipment) (Figure 2.18), its lower density (decreases the density of product and lowers the price), a refractive index closer to many polymers, and its lower cost (approximately half of the price of calcium carbonate). The manufacturing equipment includes an excitement chamber, metered conveying, pneumatic transportation, flash drying, classification, and silo storage. The manufacturer delivers product to customers by its own silo-trucks. 

The performance expected from a sealant and the polymer used in its production determine the type of fillers used. From the point of view of performance, sealants can be divided into these having plastic behavior and these with elastomeric behavior. Sealants which have plastic behavior are low-cost and low-performance products which are being gradually eliminated from the market. These sealants use inexpensive fillers to lower cost and regulate non-sag properties. Typical fillers used in these products are calcium carbonate and some fibrous materials which are used as replacement for asbestos which was very popular in the past. This combination of fibrous and spherical particles provided a useful tool to the sealant formula-tor to regulate non-sag properties which are very important in sealants. Fibers have also been used to reinforce these products because the properties of polymers were poor. 

Ash particles are formed through the thermal decomposition or dehydration of inorganic minerals associated with the coal. Calcium carbonate and clay are the most abundant mineral impurities, with lesser amounts of sulfides, chlorides and oxides also present. The shape of the ash particle is dependent on many factors, two of which are the amount of time and temperature to which the coal is exposed in the combustion chamber (Fisher et al., 1978). The spherical shape, most commonly associated with fly ash particles, shows that complete melting of silicates occurs at high temperature. These spheres may be solid, hollow (cenospheres) or encapsulating spheres (plerospheres). 

It is the length of a particle divided by its diameter. For spherical or cubical particles, the aspect ratio equals to one. For calcium carbonate particles, the aspect ratio is typically 1-3. For talc, the aspect ratio is typically in the range of 5-20. For milled glass fiber, it is between 3 and 25. For mica, it is 10-70. For wollastonite, it is between 4 and 70. For chopped glass fiber, it is between 250 and 800. For natural fibers, such as cellulose, the aspect ratio can be from 20-80 to thousands. Low aspect ratio is below 10. However, the above figures are given for fillers not processed in a compounder and/or an extruder. Upon processing, aspect ratio can decrease from dozens and hundreds to as low as 3-10. 

The effect of organics on calcium carbonate precipitation was also confirmed. While in the absence of organics large calcite crystals deposit, in the presence of organics the precipitates are smaller and of spherical shape. At the low pH, where calcium carbonate is more soluble, a very smooth deposit formed. 

Quite original is the attempt to obtain porous materials, for example, from crystalline calcium carbonate (aragonite) similar to the natural material chalk of a certain porosity [192]. Another attempt was made to synthesize macro-porous aragonite with a structure similar to the cocco-spheres of certain marine algae [295]. For this purpose, oil-water-surfactant microemulsions supersaturated with calcium bicarbonate were obtained. The pore size was determined by the water and oil concentration ratio. Microemulsions were applied on the substrate of micrometersized polystyrene beads. Hollow spherical shells of finished structure were produced as a result of a rapid mineralisation. The authors suggest that such materials could gain widespread use in materitils chemistry. 

Chem. Descrip. Calcium carbonate (99.7%) coated by stearine acid CAS 471-34-1 EINECS/ELINCS 207-439-9 Uses Filler for paints (primers, undercoats), plastics (PVC rigid extrusion, PVC foam extmsion, PVC calendered sheet, PVC inj. molding), rubber, adhesives, sealing compds., and fire extinguishers Properties Spherical crystals 30% < 2 p sp.gr. 2.7 bulk dens. 1.1 g/ml (packed) surf, area 3.5 m /g oil absorp. 14/100 g dry brightness 93% pH 9 ref. index 1.58 hardness (Mohs) 3 < 0.2% moisture MT Binder ENB 02 [Bayer AG]... 

Kerosene has been used as a binding agent for the production of spherical agglomerates of precipitated inorganic substances, e.g. calcium carbonate (Bos and Zuiderweg, 1985 Kawashima et al., 1986). 

Kawashima, Y., Handa, T., Takeuchi, H., Takenaka, H. and Lin, S.Y. (1986) Spherical agglomeration of calcium carbonate dispersed in aqueous medium containing sodium oleate. Powder Technology, 46, 61-66. 

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