MICROSTRUCTURE AND MORPHOLOGY OF INDUSTRIAL CLINKERS – AN INDIAN PERSPECTIVE

By

Praseeja Shankaran, A K Rai and S P Pandey Dalmia Cement, New Delhi-110001 India

The Clinker Microscopy is a powerful tool for process and product evaluation and also to characterize and improve clinker quality and kiln performance. It is a tool for analyzing and assessing the impacts that are caused during cement production in cement industry, or in other words Microscopy analysis has influence on all the operational areas, from quarry to the final cement production. It often gives evidence of the causes of the disturbances that occur in clinker manufacturing and while working with cement. All those concerned with Cement industries must be familiar with its application and its potential in order to improve the production and product by making optimum use of this tool. Also this tool has some limitations. This paper gives a synopsis of effective use of microscopy for effective process & quality control of industrial Portland cement clinker. Recently Clinker Microscopy is being very commonly used as an improvement tool for process and product evaluation in India. Along with clinker Microscopy, concrete microscopy and raw material microscopy are also getting matured in cement industries. In case of clinker, Microscopic can give an idea regarding the reactions taking place within the kiln. Clinker nodules are used to assess production conditions such as raw material fineness, kiln temperature profile and cooling rate. The information obtained can then be used to predict the likely performance of cement made from the clinker or perhaps indicate the cause of production difficulties such as poor combination. 1.0 Introduction

This paper presents an assessment of the microscopy of nominally similar cement clinkers from cement production facilities in India. Chemical analysis alone can never give the cause of enhanced or diminished clinker quality. Hence we need to study the morphological characters of clinker. Clinker samples were collected from various cement plants for microscopic evaluation. The samples were crushed and moulds prepared for analysis. Along with microscopy the same samples went through chemical and physical tests also. This test helped us to relate different morphological parameter’s to the quality of clinker. With the study carried out here we can easily observe the impact of morphological characteristics of clinker on strength development or quality of clinker. Hence with this result one can have an idea about the cement properties. The results of these tests were related to the chemical and physical parameters of the corresponding cement clinkers. The results indicate a clear relation between the morphology, chemical and physical data of clinker. The study here mainly reveals the relation between the rawmeal residue and phase % quantified by Microscopy, also the impact of clusters over phase %. It also gives evidence regarding the relation between phase size and the chemical composition. It gives idea about the impact of size on 1 day strength of clinker. The experimental results indicate that clinker microstructure along with mineralogy and chemical composition could be used effectively for controlling the cement manufacturing process.

2.0 Experimental Method of Research Clinker Samples were collected for microscopic study from different parts of the country India. These samples were analyzed in R&D lab of Dalmia. 2.1 Test Methods

X-ray fluorescence: XRF was used to determine the chemical composition of the clinkers. The analyses were conducted using ground clinker samples. This analysis was conducted in the plant from where the samples were collected where XRF is used with their own calibration for their routine quality control purpose.

Physical test: All tests related to physical were carried out but only strength results are taken in account for a better understanding of relation between the clinker morphology and clinker strength.

Optical microscopy: A geological polarizing microscope with reflected light capability was used to assess the structure and morphology of polished and etched samples of each of the clinker. Alite, Belite, Aluminate and ferrite are the major four compounds of normal Portland cement clinker. Of which, Alite and belite are formed essentially from solid state reaction whereas aluminates and ferrites are crystallized from molten state on cooling. The percentage and morphology of all the four phases varies in wide range. Beside these major phases, a normal clinker contains so called minor phases like free lime, Periclase and alkali Sulphates. The percentage of all major & minor phases can be detected by some or the other methods but the reason behind that can only be drawn out by microscopy.

3.0 Microstructure and Morphological study for Clinker

Poor combinability and

feed related issues Short diffusion distance Alite decomposition

Large Cannibalistic Belite

Round to sub round cross lamellar Belite

Ragged / finger Belites Well differentiated

Aluminates and Ferrite Free lime and Belite inclusions in Alite

Large Belite cluster with a pore at center

Belite and freelime crystals in direct contact

Amoeboid or Irregular shaped Alite

Belite precipitation in matrix

4.0 Results and Discussions The features observed in above images are due to some or the other changes in process parameters. These features have direct impact on quality of clinker. The features witnessed in above table are the combine effect of following parameters:

• Mixing of kilnfeed. • Kilnfeed Residue. • High temperature maintained in kiln. • Flame length in kiln. • Kiln RPM. • O2% in kiln • Coal used. • Cooling conditions.

5.0 Conclusion The study discussed here tells the story about how microscopy can be favorable for a cement plant and how its data can be related for improvements. To make a good clinker or reactive clinker, the morphological study of clinker is quite helpful in taking corrective actions. Proper microscopic clinker examination provides invaluable textural and morphological information that are pertinent from the point of view of raw mix, clinkering parameters, i.e. pyro-processing and cooling conditions. The shape and size of Alite and Belite crystals, nature of grain boundary, Belite lamellas, interstitial matrix phases, presence/absence of grain agglomeration, all reflect on the process carried out during the clinker formation. It would be more appropriate to apply such techniques for better process and quality optimization. 6.0 References

• Arthur Harrisson, Importance of cooling, Cement technology, May 2011, pages 78-80.

• Angel Rodriguez Rey, Modesto Montoto, Lope Calleja Vicente G. Ruiz De Argandona Proposed

textural indexes to quantify the distribution of tine Portland cement clinker phases, , materials de

construction, vol. 38, 1988

• Campbell, D. H. Microscopical Examination and Interpretation of Cement and Clinker, Second

Edition, Portland cement Association, 1999.