Iwao Maki

Phase identification of alite in portland cement clinker

Abstract Unequivocal phase identification of alite in portland cement clinker has been made by combined use of microscopy during heating, X-ray powder diffraction, and differential thermal analysis. Alite thus far assigned to M 1b by X-ray powder diffractometry, in reality, gives every indication of being M 3 . Only M 1a should therefore be denoted simply as M 1 . The M 1 form of alite in clinker has long been mistake for R because of an apparent trigonal character of its cell. It is M 3 that gives the monoclinic cell as first described by Jeffery.

Factors influencing the phase constitution of alite in portland cement clinker

Abstract The phase constitution of alite in portland cement clinker highly depends not only in the chemical composition of a raw mix but also on the kinetics of crystallization from the interstitial melt. From the melt of high supersaturation alite can be crystallized so quickly as to take up foreign ions in quantities in favor of the occurrence of M 3 at ambient temperature. The reverse is the case for the crystallization from the melt low in supersaturation, where M 1 tends to be formed. The formation of zoned alite can be explained by the change in the degree of supersaturation during crystallization. The phase constitution of alite can be correlated with its crystal size in terms of the supersaturation of the melt. The SO 3 in clinker considerably lowers the viscosity of the interstitial melt and thus encourages the formation of M 1 along with the grain growth of alite. The relation between the phase constitution of alite and the quality of cements has been remarked in conjunction with the Onos method.

Nature of the prismatic dark interstitial material in Portland cement clinker

Abstract The prismatic dark interstitial material in Portland cement clinker is essentially identical with the stable solid solution phase in the system C 3 A-NC 8 A 3 ; with rapid cooling, however, metastable extension of the solid solution series takes place, which is the prevailing mechanism of formation of the prismatic phase in works clinkers of low alkali content. The presence of SiO 2 in the interstitial material favors the metastable formation by enhancing the supercooling of the liquid phase in clinker.

Microscopic study on the polymorphism of Ca3SiO5

The polymorphism of Ca3SiO5 has been studied microscopically by following changes in optic properties and modes of twinning of the crystal as a function of temperature. Besides the six modifications already established, a hitherto-unidentified monoclinic phase M3, which can be characterized only by microscopy at present, has been found to exist just below the rhombohedral phase (R). The transitions T2 ⇇ T3etM1 ⇇ M2 that give clear thermal effects on the DTA curve show no corresponding change under the microscope.

Orientation of β-Ca2SiO4 solid solution lamellae formed in the host α-phase

Abstract The cystalline textures of belite consisting of multidirectional lamellae of the β-phase with the α-phase as host (what is called the Type I belite) have been studied by means of the optical microscope, TEM and XRD. The orientation relationship the β- and α-phases is, in agreement with the results of previous studies, {11 2 0} α // {100} β and α // β. From combined use of X-ray diffraction and optical microscopy all the lamellae have been found to occur in parallel with the aα∗-axes and make an angle of 27±3° with {0001}α. The most probable face indices of the habit planes are {11 2 5} α and different from {10 1 2} α by Yamaguchi and Ono (1).

Effect of prolonged heating at elevated temperatures on the phase composition and textures of portland cement clinker

Abstract Two kinds of portland cement clinker with widely different MgO and SO3 content were reheated for a long time at elevated temperature. With the clinker rich in MgO and SO3, alite increased while belite decreased in quantity after reheating. The alite crystals, overgrown with new precipitates, gave zonal structures. Thin platy hexagonal crystals were occasionally nucleated and grown separately in the bulk liquid. High degree of supercooling produced dismembered dendritic crystals of belite. The C/S ratio of the interstitial phase decreased with reheating. The above changes occur in association with the process in which the interstitial liquid, initially variable in basicity, is transformed to the uniform and most acidic one. This process is controlled by the counterdiffusion of CaO and SiO2, the rate of which is such that, in normal clinker processing, the clinkering reaction terminates before reaching this stage. Rise in firing temperature increases the concentration of SiO2 in the interstitial liquid and leads to higher solid C3S/C2S ratio in clinker. The presence of MgO and SO3 in abundance lowers the viscosity of the liquid and hence accelerates the changes. No appreciable change could be recognized for the clinker low in MgO and SO3 content.

Morphology of the so-called prismatic phase in Portland cement clinker

Abstract This study deals mainly with the morphology of the so-called prismatic phase in Portland cement clinker and some characteristic microstructures of the interstitial material. Crystals of the prismatic phase as well as those of the solid solution in the system C 3 A-NC 8 A 3 are usually composed of the forms: bipyramids {112}, {111}, pinacoids {100}, {010}, {001}, being square tablets on {001}. A description has been given on parallel growths between the constituent minerals of the interstitial material. Zonal structure within crystals of the prismatic phase has been confirmed experimentally.

Mechanism of glass formation in portland cement clinker

Abstract In the system C 3 AC 4 AFSiO 2 MgO, the glass formation region that is closely similar in composition to the interstitial material of portland cement clinker has been determined. The interstitial melt that exists in equilibrium with the silicates at the clinkering temperature contains a little silica. This forms clusters, which increase the viscosity of the melt and cause the latter to supercool appreciably. Crystallization of C 3 A and C 4 AF increases the concentration of clusters, which progressively interlock in the residual liquid, thus giving a glass on quenching. The presence of SiO 2 in the interstitial melt also enables the metastable formation of the orthorhombic aluminate and the oriented overgrowth of the ferrite on the aluminate to occur through encouraging supercooling of the melt.

Clinker grindability and textures of alite and belite

Abstract Superior in fracture toughness to the other constituents of portland cement clinker, belite, when clustered, deteriorates the grindability of clinker to a considerable degree and appears in the ground product mostly as angular fragments of clusters. When belite exists separately throughout clinker without forming clusters, spherical single grains of belite result from grinding and the grindability of clinker is much improved. Belite clusters thus play a much more important role in grinding than pores, especially in relation to fine grinding. Microcracks within alite crystals occur mainly through the volume shrinkage during crystallization of the interstitial liquid and hence depend on the rate and extent of crystallization during cooling. Quenching in air from just above the crystallization temperature of the interstitial liquid produces microcracks in abundance.

Formation of belite clusters from quartz grains in portland cement clinker

Abstract The conversion process of quartz grains into belite clusters in portland cement clinker has been followed under isothermal heating conditions at 1400 °C. On heating, quartz grains are surrounded by layers consisting of belite and liquid, which continue to grow thick with the progress of conversion (outer layers of belite). The conversion process has been divided into three stages considering the chemical composition of the liquid phase formed in each stage. In the first stage are formed two kinds of liquids the compositions of which lie across the primary phase field of wollastonite from each other. The belite crystals precipitated constitute thin, dense layers (inner layers of belite). At the beginning of the second stage, the inside of the belite layers is completely converted into a liquid without quartz and wollastonite. The inner layers extend inward and grow thick; the impurity concentration is lowest for this part of the belite layers. With further progress of diffusion, belite crystals nucleate and grow independently inside the layers. The composition of the coexisting liquid, rich in alkalies, moves on the primary phase field of C 2 S toward that of C 3 A. In the third stage the conversion is completed and the liquid phase, enriched with Al 2 O 3 and Fe 2 O 3 , is similar in composition to the interstitial liquid in portland cement clinker. The belite crystals, especially those of the inner layers, undergo grain growth with an increase in impurity content with duration of heating. Three kinds of belite crystals different in origin, texture and composition are thus distinguishable in the belite clusters.