Clinkerization

Ferrogenous minerals have been used as fluxes to form the melt and to facilitate the clinkerization at lower temperatures. The t5T3es of minerals used inelude hematite, magnetite, goethite, limonite, siderite, and ankerite. Thermal methods may be used to identify them. 

Mineralizers are added to the raw feed to aeeelerate the kinetics of reactions by modifying the solid and liquid state sintering. The temperature of decomposition of calcium carbonate is lowered in the presence of mineralizers. In the synthesis of C3S and C2S, DTA has shown that some phosphates, earbonates, sulfates, and ehlorides deerease the deearbonation temperature and that of the formation of the silieates.[ °l Caleium fluoride acts both as a flux and a mineralizer in promoting the formation the tricalcium silicate phase. DTA thermograms have been applied to study the effect of mineralizers on the melting behaviors and crystallization temperatures of clinker. Early formation of liquid can be established by thermal techniques. 

DTA-TG techniques have been applied to study calcination kinetics of raw materials, quantification of raw materials, determination of total heat for clinker formation, and prediction of material temperature profile in 

An assessment of the bumability of raw mix is important because it denotes the amount of mass transfer of its constituents to the clinker phase. It is measured by determining the amount of uncombined lime after a certain time and a particular temperature. The high temperature thermal 

Specific heat is an important thermodynamic parameter needed for determining the heat balance of a reaction. The specific heat of crude cement and clinker has been measured by The results demon- 

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The model allows to perform thermal calculation of a multi-layer annular structure of a kiln body with a granular mixture-clinker, roasted inside it (Fig 1). 

For a cell, located close to an internal kiln surface without clinker and for a cell with clinker and contacting with a kiln gas the same equation can be written in tbe form ... 

The process of the clinker mass transport is simulated as follows ... 

All the cells of the same radial section, containing clinker, are shifted by one angular step... 

An average temperature of cells, that have left a zone of stability, is calculated (clinker in these cells is rolling down along a line of the greatest angle). 

The cells, that occupy a zone of stability, but free of clinker due to mechanical translation, are again filled with clinker with an averaged temperature. 

Cement clinker Cement-composites Cement copper Cemented carbide... 

Cling control agents Cbnical analyses Clinical chemistry Clinical performance Clinical trials Clinique aromatics Clinker... 

A second form of limestone is finely pulverized limestone for masonry cement. This form is achieved by intergrinding roughly equal parts of limestone and cement clinker in a bad mill to which an air-entraining agent is added. 

The western WetheriU. furnace is like the eastern furnace except that a block of 12 or more furnaces has a common combustion chamber. This results in improved control and uniformity of product. Clinker usually contains 8—15 wt % zinc, which is often recovered in a Waelz kiln (24). 

The traveling-grate furnace requires less labor, increases the output per unit of grate area, and produces more uniform product than the WetheriU. furnaces. The traveling grate is an endless chain of cast-iron bars, driven by sprockets, which traverses a firebrick chamber. Anthracite briquettes are fed to a depth of ca 15 cm. After ignition by the previous charge, the coal briquettes are covered by 15—16.5 cm of ore/coal briquettes. The latter are dried with waste heat from the furnace. Zinc vapor evolves and bums in a combustion chamber and the spent clinker faUs into containers for removal (24,25). 

Tetracalcium aluminoferrite acts as a processing aid by reducing the clinkering temperature. It hydrates rapidly but does Htde for any performance property of the cured concrete. It does, however, cause most of the color effects in the cured concrete. 

Pordand cement clinker is formed by the reactions of calcium oxide and acidic components to give C S, C2S, C A, and a ferrite phase approximating... 

Phase Equilibria. During burning ia the kiln, about 20—30% of Hquid forms ia the mix at clinkering temperatures. Reactions occur at surfaces of soHds and ia the Hquid. The crystalline siHcate phases formed are separated by the iaterstitial Hquid. The iaterstitial phases formed from the Hquid ia normal clinkers duting cooling are also completely crystalline to x-rays, although they may be so finely subdivided as to appear glassy (optically amorphous) under the microscope. 

In the relatively small Pordand cement 2one almost all modem cements fall in the high lime portion (about 65% CaO). Cements of lower lime content tend to be slow in hardening and may show trouble from dusting of the clinker by transformation of to especially if clinker cooling is... 

The theoretical energy requirement for the burning of Portiand cement clinker can be calculated from the heat requirements and energy recovery from the various stages of the process. Knowledge of the specific heats of the various phases, and the heats of decomposition, transformation, and reaction then permits calculation of the net theoretical energy requirement of 1760 kj (420 kcal) for 1 kg of clinker from 1.55 kg of dry CaCO and kaolin (see Clays) (8). 

The reaction of C2S with CaO to form C S depends on dissolution of the lime Hi the clinker Hquid. When sufficient Hquid is present, the rate of solution is controUed by the size of the CaO particles, which depends Hi turn on the sizes of the particles of ground limestone. Coarse particles of siHca or calcite fail to react completely under commercial burning conditions. The reaction is governed by the rate of solution (10) ... 

Phases Formed in Pordand Cements. Most clinker compounds take up small amounts of other components to form soHd solutions (11). Best known of these phases is the C S soHd solution called aHte. Phases that may occur Hi Portiand cement clinker are given Hi Table 1. In addition, a variety of minor phases may occur Hi Portiand cement clinker when certain minor elements are present Hi quantities above that which can be dissolved Hi other phases. Under reducHig conditions Hi the kiln, reduced phases, such as ferrous oxide [1345-25-17, FeO, and calcium sulfide [20548-54-3] CaS, maybe formed. 

The primary phases all contain impurities. In fact these impurities stabilize the stmctures formed at high temperatures so that decomposition or transformations do not occur during cooling, as occurs with the pure compounds. For example, pure C S exists in at least six polymorphic forms each having a sharply defined temperature range of stability, whereas alite exists in three stabilized forms at room temperature depending on the impurities. Some properties of the more common phases in Portland clinkers are given in Table 2. 

Table 2. Properties of the More Common Phases in Portland Cement Clinker ...

Fig. 4. Photomiciogiaph of polished and etched sections of Poidand cement clinkers. The C A appears as dark interstitial material, the C AF as light...

Portiand cement clinker structures (18,19) vary considerably with composition, particle size of raw materials, and burning conditions, resulting in variations of clinker porosity, crystallite sizes and forms, and aggregations of crystallites. Alite sizes range up to about 80 p.m or even larger, most being 15—40 )J.m. 

Raw Material Proportions. The three main considerations in proportioning raw materials for cement clinker are the potential compound composition the percentage of Hquid phase at clinkering temperatures and the bumabiUty of the raw mix, ie, the relative ease, in terms of temperature, time, and fuel requirements, of combining the oxides into good quaUty clinker. The ratios of the oxides are related to clinker composition and bumabiUty. For example, as the CaO content of the mix is increased, more C S can be formed, but certain limits cannot be exceeded under normal burning conditions. The lime saturation factor (LSF) is a measure of the amount of CaO that can be combined (20) ... 

An LSF of 100 would indicate that the clinker can contain only C S and the ferrite soHd solution. Time saturation factors of 88—94 are frequentiy appropriate for reasonable bumabiUty low LSF indicates insufficient C S for acceptable early strengths, and higher values may render the mix very difficult to bum. Several other weight ratios such as the siUca modulus and the iron modulus are also important (21). 

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