Assessment of technological properties of calcareous and non-calcareous clays used for the brick-making industry of Zaragoza (Spain)
The granulometric, mineralogical, and geochemical features of two different types of clayey raw materials (carbonated clays, CC; and non-carbonated clays, NCC) used for the brickmaking industry near Zaragoza (Spain) have been studied. Their particle-size distribution suggests that they may be classified as silty clays and are suitable for use as thin-walled hollow bricks. For technological testing, prismatic bars obtained by extrusion under vacuum conditions from raw materials were fired from 800 to 1050 °C. Technological determinations, such as linear shrinkage, bulk density, hydric tests, and an accelerated decay test, indicate that both CC and NCC are suitable to be used as bricks for building, although bricks made of NCC would be of better quality. In addition, pore-size distribution suggests that the durability of the highest temperature fired products will be higher because of an increase both in the dominant pore access radius and in the percentage of larger pore sizes.
Potentiality of Clay Raw Materials from Northern Morocco in Ceramic Industry: Tetouan and Meknes Areas
This study aims at evaluating the potential suitability of Tetouan and Meknes (central Morocco) clay material as raw materials in various ceramic applications by investigating their textural, chemical, thermal and firing characteristics. Textural properties were identified by specific surface area, cation exchange capacity (CEC) and bulk density (ρs). Chemical and thermal properties were assessed using XRF and TG/DTA techniques, respectively. Firing characteristics at temperatures from 800℃ to 1100℃ were determined by linear firing shrinkage, loss on weight and water absorption capacity. The Meknes clays are characterised by medium cation exchange capacity (CEC) and specific surface area (SSA) values due to their moderate smectite content. The Tetouan clays have medium to low CEC and medium SSA values. The main oxides in the clayey samples are SiO2 (35 - 54.3 wt%), Al2O3 (20.6 - 43.9 wt%), and Fe2O3 (9.7 - 22.4 wt%). The amount of CaO in Meknes clays ranges from 8 to 12 wt%, whereas CaO is only present in some Tetouan clay (TE4, TE7, TN4 and TN5). A significant densification of ceramic behaviour could be noticed for most of Tetouan clays at firing temperatures above 1000℃. Meknes clays show earlier densification from 800℃. The chemical, textural and ceramic properties of Tetouan and Meknes clays indicate their suitability as raw materials for the production of structural ceramics. The high amount of Fe2O3 in all clays makes them inappropriate in fine ceramics.
Firing transformations of mixtures of clays containing illite, kaolinite and calcium carbonate used by ornamental tile industries
Abstract In this work were studied the firing transformations undergone by mixtures of illitic-kaolinitic clays containing CaCO 3 , free quarts, iron oxides and other impurities, with other kaolinitic and illitic clays also including some impurities but no CaCO 3 . Such mixtures yielded no mullite on heating from room temperature to 950 and 1100°C. This process involves the formation of calcium silicates such as wollastonite in medium to high proportions or calcium aluminosilicates such as gehlenite and anorthitic plagioclases. The proportion in which the last were obtained increased considerably with the firing temperature; on the other hand, the proportion of wollastonite only increased moderately and that of gehlenite decreased with increasing temperature. Some thermodynamic considerations on the formation of these crystalline phases and the absence of mullite were made. Such phases influence the technical properties of the fired products.