Twinning belite

Photograph 7-41 Slowly cooled kiln buildup from the transition zone containing, for the most part, polysynthetically twinned belite (Type II, Insley) in lower left and slightly splintery gamma belite (upper right) in matrix of coarsely microcrystalline ferrite and aluminate. (S A6661)... 

Photograph 7-44 Polysynthetically twinned belite (Type II, Insley) in slowly cooled kiln buildup. (S A6664)... 

Belite crystals have been observed that show only one set of striations. whose behaviour in transmitted light between crossed polars shows them to be twin lamellae. Such crystals are typically irregular in shape they have been called Type II belites, and are rare in modern clinkers. The striations arise from the aY to p transformation. Such crystals can form either by... 

Different 38 phases, in the case of low content of belite in clinker, is most convenient to identify using light microscopy. Among others, Metzger [161] applying this method found the presence of phase a. The striations of belite crystals always observed in industrial ehnkers due to polysynthetic twinning, are distinctly differentiate this phase from alite crystals and are formed in the polymorphic transformation process. 

Tavasci classified belite into three morphological types I, II, and III. Belite I was said to show striations, sometimes like twinning, prevalently in two directions. The striae were described as being relatively... 

Beta dicalcium silicate is metastable below 670°C and monoclinic, with an n ofl.717,an n ofl.722,and of 1.736 and parallel to b birefringence is 0.019. The (h-) 2 Vis 64° to 69°, with the axial plane (010). The beta form exhibits very close polysynthetic twinning (Chromy, 1970). It comprises most of belite in clinker. Cleavage is poor on (100) and (010). Colors range from colorless to yellow or brown. Density is 3.28 Mg/m. Boikova (1980) reported a typical yellow color and spotty surface (not striated). 

Maki (1994) stated that belite contains six sets of twinned lamellae. Polymorphic varieties formed as a function of temperature with the alpha polymorph prevailing when the mix was quenched above a temperature of 1280 C. Slowly cooled belite, showing... 

The cross striations of Type I belite have been called polysynthetic twinning. However, this structure is not polysynthetic twinning but a skeleton structure, consisting of beta and alpha forms of belite. 

If the clinker is burned below the temperature of alpha prime inversion, and belite is cooled from the temperature region of alpha prime, belite has only the alpha prime to beta inversion texture. This texture is ob served as one set of parallel striations, which is polysynthetic twinning and parting on (100) and (010) after the crystal axes of the alpha prime. Rarely occurring are polysythetic twins on (110), (oil), and (011). 

Ono (1975) stated that the structure of Type I belite is skeletal instead of polysynthetically twinned. Thus, confusion, and perhaps some disagreement, in the literature exists as to the description and origin of the microstructure of Types I and II belites. The above pullout presents Ono s argument (1975), with only slight editing, in support of a largely skeletal interpretation of belite and a brief statement of polymorph origins. 

Application of modern microscopical equipment, such as the transmission electron microscope, to the problem of belite microstructure appears to be aprom-ising field of research and may, as Groves (1982) stated, provide data on belite twinning types relating to the temperature at which the belite formed. 

Polysynthetic twinning in belite Formed during very slow cooling as a result of alpha prime to beta transition (Hofmanner, 1973)... 

Belite with polysynthetic twinning Normal cooling rate (Kramer, 1960)... 

Photograph 7-27 Ragged belite crystals and belite coating on alite, one of which is twinned. Note abundant dotlike impurities in alite. Coarsely crystalline matrix with gray aluminate and relatively bright ferrite. Slowly cooled clinker. (S A6647)... 

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