#

 n

*<sup>G</sup> <sup>K</sup> RT*

( ) exp exp exp

*Ea BkT S H kT A*

The approach is known as the "Congruent dissociative vaporization mechanism" (CDV). In the case of a solid compound *S* decomposed into gaseous products *A* and *B* with simultaneous condensation of low-volatility of species *A*, that is [89,369]:

$$S(\mathbf{s}) \to a \,\, A(\mathbf{g}) \,\stackrel{\downarrow}{\cdot} + b \,\, B(\mathbf{g})\tag{121}$$

The theoretical value of activation energy *E*<sup>a</sup> T should be different for equimolar (in the absence of gaseous product *B* in the reactor atmosphere) and isobaric (in the presence of the excess of gaseous product B) modes of decomposition. The relations for the equimolar (*E*<sup>a</sup> Te) mode are:

$$E\_a^{Tc} = \frac{\Delta\_{rc}H^{\bullet}(T)}{\nu} = \frac{\Delta\_rH^{\bullet}(T)}{a+b} \tag{122}$$

and for the isobaric mode (*E*<sup>a</sup> Ti) they are:

$$E\_a^{T\bar{}} = \frac{\Delta\_{rc}H^{\mathfrak{O}}(T)}{\nu - b} = \frac{\Delta\_rH^{\mathfrak{O}}(T)}{a} \tag{123}$$

$$
\Delta\_r H^\bullet(T) = \sum \nu\_i \Delta\_f H^\bullet\_{\,i} \tag{124}
$$

*ν* denotes total number of moles of gaseous product (*a+b*) and *Δ*r*H*° is the reaction enthalpy for given temperature (Eq.124). The temperature dependence of enthalpy is given by Eq.21 in Chapter 4. In both cases, the *E*<sup>a</sup> T parameter corresponds to the specific enthalpy, i.e. the enthalpy of the decomposition reaction reduced to one mole of primary products without including components present in excess.

In order to take into account the partial transfer of energy released in the condensation of lowvolatility product *A* to the reactant, the calculations of enthalpy of decomposition reaction 121 require an additional term (*τ* a *Δ*c*H*°(A,T)) where the coefficient *τ* corresponds to the fraction of condensation energy transferred to the reactant at the interface. The reaction enthalpy is then given by the relation:

$$\begin{aligned} \Delta\_{rc}H^{\mathfrak{O}}(T) &= a \, \Delta\_f H^{\mathfrak{O}}(A,T) + b \, \Delta\_f H^{\mathfrak{O}}(B,T) \\ -c \, \Delta\_f H^{\mathfrak{O}}(C,T) &+ \tau a \, \Delta\_c H^{\mathfrak{O}}(A,T) \end{aligned} \tag{125}$$

**Chapter 2**

2-triangles which are placed

2-ions are

¯ where A

**Raw Materials for Production of SrAC**

**1. Raw Materials and Raw Material Treatment**

strontium (SrO) and aluminium oxide (Al2O3).

[92,93].

The structure of strontianite (Fig.1(a)) is based on isolated [CO3]

found [91].

eral **strontianite**<sup>1</sup>

tween these layers.

Strontian in Scotland.

group R3

the group of aragonite2

For the synthesis of strontium aluminate cement it is necessary to find the proper source of

Two major strontium minerals are its carbonate, strontianite (SrCO3) and more abundant sulfate mineral celestite (SrSO4). William Cruickshank in 1787 and Adair Crawford in 1790 independently detected strontium in the strontianite mineral, small quantities of which are associated with calcium and barium minerals. They determined that the strontianite was an entirely new mineral and was different from barite and other barium minerals known in those times. In 1808, Sir Humphry Davy isolated strontium by the electrolysis of a mixture of moist strontium hydroxide or chloride with mercuric oxide, using mercury cathode. The element was named after the town Strontian in Scotland where the mineral strontianite was

The **strontium oxide** (SrO) is the first substantial component of strontium aluminate clinker. Therefore, the strontium carbonate (SrCO3) is the most appropriate input material for the synthesis of strontium aluminate clinker. In nature SrCO3 occurs as rare orthorhombic min‐

(CaCO3), witherite (BaCO3) and cerussite (PbCO3) it belongs to anhydrous carbonates from

oriented in the opposite direction. Cations with the coordination number of 9 are placed be‐

Natural and artificially synthesized binary (**aragonites** up to 14 mol. % Sr [94], **strontianites** up to 27 % Ca [94], **witherites** [94], **baritocalcites** [95]) or ternary solid-solutions (**alstonites** [94]) of these carbonates are intensively studied in order to elucidate the mechanism of their formation, their structure, the thermodynamic stability and the luminescence properties.

1 Discovered in 1787 (Strontian, Scotland). Originally was considered the barium bearing mineral; which was dis‐ proved by Crawford and later by Klaproth and Kopp. Named in 1791 by Friedrich Gabriel Sulzer after the locality

2 There are three main groups of anhydrous carbonates without additional anions. The group of calcite (trigonal, space

and Pb) has the composition given by general formula ACO3. The trigonal group of dolomite (space group R3

= Ca and B = Mg, Fe, Mn and Zn) has general composition given by the general formula AB(CO3)2.

¯c, A = Ca, Mg, Mn, Fe, Co, Ni, Zn and Cd) and aragonite (orthorhombic, space group Pmnc, A = Ca, Sr, Ba

© 2014 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

in layers perpendicular to *c*-axis. The layer has two structural planes where [CO3]

(space group *Pcmn*) and together with isostructural minerals aragonite

For the majority of substances, the condition *τ*=0.5 can be applied [89,90].

An essential difference between the CDV mechanism and the Arrhenius activation mechanism is that during the interface reactions, a proportion of the energy released on condensation of a non-volatile product is transferred to the solid reactant, reducing the energy barrier for further reactant volatilization. Thus, 'recycled' energy is responsible for the autocatalytic behaviour, justifying the following important generalizations [70]:


The simplest presumption for the energy redistribution at an interface is that the condensation energy is shared equally between the reactant and the solid products, which is expressed as τ=0.5. The deviations, where *ΔcH*° is distributed unequally between the solid reactant and the product phases in the ratio *τ*/(1-*τ*), are ascribed to the degree of supersaturation of the nonvolatile vapor.

The Arrhenius model is often represented by the familiar graph of energy variations as the reaction progresses by the "Advance along the Reaction Coordinate". This shows an initial rise to a maximum value, to form the 'transition complex', being followed by a decline thereafter. The activation energy is then the energy required for forming the 'activated' tran‐ sition complex in an assumed "rate-determining step". However, in CDV theory, the value of parameter *E* represents the vaporization enthalpy [70].
