Engobes for ceramic brick

Abstract

Engobing is used to expand the color range for the facial surface of brick. A light-colored engobe composition has been developed, using red-fire clays followed by the addition of various pigments, to regulate color. The rheological properties of the engobe slips are studied and the quantity of electrolytes is optimized.Additional methods of finishing a brick surface are needed in order to expand the color range of the facial surface of bricks. One such method is engobing. Together with increasing the architectural -artistic advantages, engobing makes it possible to eliminate surface defects of brick, such as "salting out" and color nonuniformity.On account of the capability of engobes to form a fired surface film that is sufficiently dense so that water from air and dissolved salts cannot pass through the film, such brick does not show seasonal discoloration, and the ability of coloring engobe materials with stable inorganic natural or synthesized pigments makes it possible to expand the color range of articles.The color of a composition can be regulated in a desired manner only if the matrix has a light color. Consequently, the first problem of the present investigation was to develop an engobe composition with a light color based on the red-firing low-melting clay from the Novokubanskoe deposit "Khutorok," the same clay that was used to make the brick itself. Similar materials must be used so that the CLTE of the ceramic base matches that of the coating.It is well known that the decrease of the intensity of the red color of red-firing clays can be regulated by introducing carbonate materials, such as chalk, into the mixes [1]. But, in addition to bleaching, at brick firing temperatures near 1000°C carbonates decrease substantially the capability of the mixes to sinter, since at these temperatures only intense decarbonization of chalk occurs and the alkali-earth components do not act as fluxes. Consequently, cullet was added to the engobe mixes in order to intensify sintering.Mathematical methods of planning, specifically, accumulation analysis, were used to work out the optimal composition of a light-colored engobe and subsequent experiments [2]. The contents of clay, chalk, and cullet (X1, X2, X3) were chosen as the factors controlling the compositions of the engobes.Three-dimensional plots with the ability to project a two-dimensional triangle onto a plane were used as the coordinate system. Scheffe's simplex-centroid plan was chosen to analyze the results.Since the engobe must form on the brick surface a dense, fired, 0.1 -0.3 mm thick layer with low porosity and minimal water absorption, the water absorption, the Mohs hardness of the engobe, and the intensity of red color were chosen as the response functions. The sum of the components for each mixture was equal to 1, so that their values were interpreted as proportions, since the coordinate of any vertex of a component equals 1 (100%) and 0 for all other components. On this basis it is possible to calculate the position of each point inside the triangle a...

Designing engobe coatings for ceramic bricks

“…Unlike most works on engobe construction products [6-9, 11, 17, 18], where coatings for thin ceramics are developed, this paper reveals the algorithm for developing engobe coatings for building ceramics, which has a rough structure, which greatly complicates the coordination of coating and ceramics. In contrast to the few works on engobing bricks [19,20], which offer engobe compositions with limited use, our paper formulates a systematic approach to the development of engobe. That has made it possible to establish the dependences «property -structure -composition», to reveal the possibilities of their regulation and adaptation of engobe coatings to brick production.…”

“…Engobe coatings can be relevant not only for expanding the color gamut of ceramic bricks [20] but also for creating self-cleaning facades of buildings [21].…”

Development of the technology for obtaining engobed construction articles with the "antiquity" effect

“…Among the variety of raw materials for the production of engobes as fine ceramic material, the following groups can be conditionally distinguished [3,4,6]: the basic clay component, as well as the leaning and fluxing component. For the white anode basis, it is advisable to choose semi-refractory or refractory clay or kaolin as the main clay component.…”

“…Paper [6] presents the results of the development of engobe coatings for ceramic facing brick. It is shown, that red clay is used to obtain the basis for manufacturing the engobe, and the necessary colors are provided by the introduction of pigments.…”