The Alite still have mysteries awaiting be solved them!

Introduction

With some frequency I read articles about the cement industry in which says things like this "The process of heating limestone and clay to create “clinker” has changed little since its 19th-century expansion" January 2021- by Financial Times, or statements more or less like "exists little to discover/develop in an Old Industry as the Cement one" . I completely disagree with both concepts: the Cement industry have changed a lot in the last 150 years, in process, equipment, technology and management strategy. Our knowledge increased around the process and chemistry but still are a lot to discover and invent. Actually we are facing challenges to reduce the CO2 emissions and costs, both issues will trigger the innovation in the search of new cements, process, savings, materials and equipment.

"In other words the Cement Industry is in the face a great wave of R&D, and innovation is the key and the constant. All the people will be involve in this cascade of innovations, even if you are working in the shop or in a science lab."

Luis Fuentes

Introduction

After Le Chatelier identified the 4 elements that exists in the clinker and Törnebohm named the Alite. The Scientifics after a long controversy of 50 years concluded that the Alite is majority C3S.

In that moment started the search to know how the atoms were placed in the Alite, the discoveries in this path still are in develop. This is the theme of this article.

The Alite Crystal

Alite is found mainly as idiomorphic crystals in industrial clinker.

• 1966.- Yamaguchi & Ono have made an extensive crystallographic study of alite.
• 1968.- Guinier & M Regourd made a detailed study of the trigonal rhombohedral form
• 1992.- In The Ninth International Symposium on the Chemistry of Cement, M Regourd and Boikova made a comprehensive review of the crystal chemistry of alite.
• 1992.- The zoning of works clinkers was examined by Uchikawa. Alite is mostly found as idiomorphic crystals in industrial clinker.
• The following sketch (Yamaguchi and Ono, 1966) of a single crystal illustrates the principal crystal sections, W and L denote the dimensions necessary to define the crystal size

Twinning may be observed in Section I of the sketch and Section II shows polarising properties. The optical vector a is parallel to the C axis and the mineral is optically negative.

The crystal habit shown in the sketch belongs to the trigonal system with basis and two rhombohedral faces developed.

The Alite Polymorphic transformations

The crystal structure of alite exhibits seven polymorphs depending on temperature and impurities, which have been identified by a combination of DTA, high temperature XRD and high-temperature light microscopy studies.

For pure 3Ca0.Si02 the sequence of polymorphic transformations upon heating is:

Where letters indicate the formal crystallographic symmetry; T= triclinic, M = monoclinic, R = rhombohedral and the subscript numbers designate variants of a particular symmetry.

• The M1 or M3 form is normally present in Portland cement clinker and T2 rarely due to the incorporation of impurities.

Development of the Alite Crystal structure

• 1952 The first determination of the crystal structure was made by Jeffrey using rotation, Laue and Weissenberg photographs.
• 1975 Later on the structures of the T1 form by Golovastikov
• 1985 the M3 and M1 form by Nishi
• 1984 the R form by Nishi & Takéuchi
• 1985 Il’inets & Malinovski, R form was determined more in detail.
• 1995 Mumme determined the crystal structure of alite out of a Portland cement clinker and described a structure similar to the M1 unit cell of Nishi (1985). 

Pure Alite Structure

Isolated SiO4 tetrahedra are linked with five and six-coordinated calcium ions, or seven and eight-coordinated calcium ions.

The C3S alite corresponds to the nesosilicate mineral hatrurite (Gross, 1977) named after the Hatrurim Formation in Israel. 

The Hatrurim Formation or Mottled Zone is a geologic formation with outcrops all around the Dead Sea Basin: in the Negev Desert in Israel, in the Judean Desert on the West Bank, and in western Jordan. It includes aged impure limestone along with coal bearing chalk and marl. The rocks have been subjected to pyro metamorphism. The formation contain 5 unusual minerals and other minerals more common to Portland cement.

The Alite Mysteries

No structural model is actually available for

the T2, T3 and M2 polymorphs.

The known structures are closely similar as regards the positions of the calcium silicon and oxygen ions but differ markedly in the orientations of the SiO4 tetrahedra.

The forms now known as M1

the R, T1 and the M3

appeared to have very similar structures.

A good overview and discussion about the crystal structure of the known polymorphs of C3S can be found in Dunstetter (2006).

We have still a lot for investigate, invent, discover, develop in the cement industry, this is just an example of many!

If you liked this article please share it between your contacts!

Luis Fuentes

Bibliography

• Geology of the Hatrurim Formation ("Mottled Zone") in the Hatrurim basin. Article  in  Israel Journal of Earth Sciences · January 1991 
• SCI Lecture Papers Series Reflections on the History of the Chemistry of Cement by RG Blezard.1998 Society of Chemical Industry. 
• Portland cement and other calcareous hydraulic binders: History, production and mineralogy Article  in  European Mineralogical Union Notes Mineralogy August 2011 
• https://www.cementkilns.co.uk/ckr_phase.html
• https://en.wikipedia.org/wiki/Alite