Mineralogical and physical behaviour of solid bricks with additives

Dolomite, wollastonite and calcite as different CaO sources in anorthite-based porcelain

Focused on uncoated ceramics, this tutorial paper is divided into two main sections. The first section deals with the operational phases required prior to firing (drying, piling, fuel supply). Then, the second chapter deals with the transformations that occur in the clayey paste during firing. An overall understanding of the firing process includes several issues to be considered and properly investigated. Thereafter, the thermal behaviour of several mineralogical phases (calcite and dolomite; quartz and cristobalite; K-feldspar and plagioclase; rutile and anatase; haematite, maghemite, hercynite and metallic Fe; illite, muscovite, biotite and chlorite; wollastonite, melilite, anorthite and monticellite; diopside and kaolinite) is described. Four brief chapters are further dedicated to the development of the amorphous/glassy component, to the matrix and its porosity, to the colour and the organic matter and to the variations in chemical composition, respectively. The concluding remarks provide a short list of the analytical techniques that have been commonly applied to the investigation of firing conditions and a concise summary of the state of the art of the “firing issue”. The method to be applied in future experimental reproductions and the opportunity itself to investigate the “firing issue” in various contexts are further discussed.

Ceramic technology. How to reconstruct the firing process

Ancient mortars used in the construction of the church of Santa Maria de Irache monastery have been studied. With the aim to characterise their binder and aggregate fractions, a complete characterisation has been carried out including chemical (rapid analysis, soluble salts and trace elements), mineralogical (structural characterisation and X-ray diffraction, XRD) and thermal studies (simultaneous differential thermal and thermogravimetric analysis, DTA-TGA). Lime binder, lime with dolomitic phases and mixed mortars (lime and gypsum) have been determined. The approximate orginal composition of these classes of mortars has been presented. Advice about, the employment of repair materials in a restoration work is given.

/pdf/mineralogical-chemical-and-thermal-characterisations-of-506b7md269.pdf

Mineralogical, chemical and thermal characterisations of ancient mortars of the church of Santa María de Irache Monastery (Navarra, Spain)

Kaolinite mixed with calcite was sintered at low temperature (1100 °C; 5 °C/min). The successive phase transformations are metakaolinite to gehlenite and then anorthite, although the available phase diagram indicates a direct anorthite recrystallization. Transmission electron microscopy and electron diffraction studies of nanocrystallites revealed that the transformation path is favored by the structural similarities of phases. In particular, the pseudolayers of gehlenite have a major orientation relationship with the initial metakaolinite layers. The gehlenite axis, [001]G, is parallel to the metakaolinite axis, [001]A. This direct transition is favored by the existence of Si tetrahedral units and 4–fold–coordinated Al in both structures. Ca atoms, initially in the interlayer spacing of metakaolinite, remain in the interlayers of gehlenite. During the second transformation step, anorthite recrystallizes from gehlenite with axis [020]A parallel to [210]G. It is proposed that this orientation relationship is favored by the orientation and shape of Ca-atom channels through both structures, along [001]G and [100]A axes.

Structural transformation of a kaolinite and calcite mixture to gehlenite and anorthite

New building material composed of clay and dolomite at the variable mass ratio C D = 1/9−9/1 is developed. At the firing temperature of 720 °C the interaction between the components takes place resulting in the formation of structure which ensures high mechanical strength of the material obtained. The structure is composed of both the ‘old’ structure of carbonates and new formations such as calcium silicates, calcium aluminates and MgO in fine crystalline or amorphous state permeating through the ‘old’ structure. The mechanical strength of the fired material subjected to hydraulic hardening with following drying increases per 200–300%.

S. Lagzdina

Papers

Low temperature dolomitic ceramics

Dolomitic lime containing hydraulic additive

Low Temperature Dolomitic Ceramics.