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Processing and Application of Ceramics 9  (2015) 117123
Augite-anorthite glass-ceramics from residues of basalt quarry andceramic wastes
Gamal A. Khater1,, Mamduh O. Abu Safiah2, Esmat M.A. Hamzawy1
1Glass Research Department, National Research Centre, Dokki, Cairo 12622, Egypt2Saudi Geological Survey, Saudi Arabia
Received 27 April 2015; Received in revised form 14 June 2015; Accepted 27 June 2015
Dark brown glasses were prepared from residues of basalt quarries and wastes of ceramic factories. Addi-tion of CaF2, Cr2O3 and their mixture CaF2-Cr2O3 were used as nucleation catalysts. Generally, structureswith augite and anorthite as major phases and small amount of magnetite and olivine phases were developedthrough the crystallization process. In the samples heat treated at 900 C the dominant phase is augite, whereasthe content of anorthite usually overcomes the augite at higher temperature (1100 C). Fine to medium homoge-nous microstructures were detected in the prepared glass-ceramic samples. The coefficient of thermal expan-sion and microhardness measurements of the glass-ceramic samples were from 6.1610-6 to 8.9610-6 C-1 (inthe 20500 C) and 5.58 to 7.16 GP, respectively.
Keywords: crystallization, anorthite, augite, glass-ceramics, basalt, ceramic waste
Since the early 1960s, using waste to prepare glass-ceramics has developed in Russia, by employing slagof ferrous and non-ferrous metallurgy, ashes and wastesfrom mining and chemical industries . Lately, thewaste of coal combustion ash, fly ash and filter dustsfrom waste incinerators, mud from metal metallurgy,pass cement dust, different types of sludge and glasscullet or mixtures of them have been considered for theproduction of glass-ceramics . Using waste to pre-pare glass-ceramics is significant for industrial applica-tions as well as for environment protection and scientificimportance with proper correction of the chemical com-position [5,6].
Basalts are the main raw materials for the iron-richglass and glass-ceramic materials. They are character-ized by low viscosity, which allows production of poly-crystalline materials by applying short production cy-cles at low temperature. For these reasons, many re-searchers continue to study the melting and the crys-tallization behaviour of different igneous rocks, and tocharacterize the obtained materials .
Because glass and glass-ceramics are known to havemany commercial applications, the transformation of
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waste into glass or glass-ceramics provides the oppor-tunity of making useful, marketable products.
Ceramic waste materials used in this investigation areformed as waste materials from Saudi Ceramic plantSaudi Arabia formed during the manufacturing of san-itary ware ceramics. This waste accumulates in largequantities and possesses serious problems to the sur-rounding environment.
The use of waste materials such as ceramic waste,glass cullet, blast-furnace slag and by-pass cement dustfor the production of glass-ceramic materials is ofgreat economic technological and scientific importancethrough proper correction of chemical batch composi-tion.
Research and development pertaining to glass-ceramic materials have been underway for more thanthree decades . The fabrication technology of glass-ceramics, the glass composition, the nature of the nucle-ating agent and the thermal history, all greatly affect themicrostructure and properties of these materials . Theinternal crystallization can usually be achieved with asimple two-step heat treatment. In the first step, namelythe nucleation step, the mobility of atoms in the glassis sufficient for embryo formation and subsequent nu-clei stabilization. In the second step, the nuclei growto crystals of desired sizes homogenously dispersed inthe glass volume . It is obvious that internal crys-
G.A. Khater et al. / Processing and Application of Ceramics 9  (2015) 117123
Table 1. Base glass composition
Raw materials [wt.%] Calculated oxides constituents of base glass G0 [wt.%]Basalt waste Ceramic waste SiO2 Al2O3 Fe2O3 TiO2 CaO MgO Na2O K2O
80.00 20.00 50.75 17.28 9.62 1.31 9.01 6.71 3.08 1.07
tallization will be greatly facilitated by using suitablenucleating agents. Some investigations carried out inthe field of nucleation in the ternary SiO2-MgO-CaOand related systems have shown the relative difficultyof initiating internal nucleation and bulk crystallizationin some glass-ceramic compositions of this system .
The composition of the above-mentioned glass-ceramics can mainly be located in the SiO2-Al2O3-CaO-MgO system. Many investigators have studied thenucleation process in the SiO2-Al2O3-CaO-MgO andrelated glass system. Cr2O3 is one of the most rec-ommended oxides which according to the reports ofmany researchers is able to induce effective bulk nu-cleation in the glasses of SiO2-Al2O3-CaO-MgO andrelated systems. Rezvani et al.  found that Cr2O3,Fe2O3 and TiO2 are more effective in inducing bulkcrystallization and Omar et al. [13 ] suggested thatCr2O3 favours pyroxene crystallization in quartz sand-dolomite-magnesite mixtures. Khater et al. [14,15]found that Cr2O3 and CaF2 and their mixtures are moreeffective in SiO2-Al2O3-CaO-MgO system based on in-dustrial waste.
The use of raw materials, such as igneous or sedimen-tary rocks, for the production of glass-ceramics materi-als is of great economic, technological and scientific im-portance. With proper batch formulation, different typesof igneous and sedimentary rocks can be successfullyused for the production of crystalline-glass materialsof different microstructures and mineralogical constitu-tions having a wide range of properties. Furthermore,the study of crystallization process taking place in rockmelts and their corresponding glasses has a great con-tribution in petrology field. Minerals capable of wideisomorphs substitutions in their crystal structures, andhaving the desired properties, may be the bases for theproduction of many valuable crystalline-glass materials.
Due to the high chemical durability of natural basalts,basalt-like glass-ceramic materials were developed fornuclear waste disposal  and for vitrification of vari-ous hazardous industrial wastes .
In the previous paper , preparation of glass-ceramics materials from basaltic rocks and some indus-trial wastes was investigated. The aim of the presentstudy is the preparation of glass-ceramics based on ce-ramic waste materials and basaltic rocks. The effect of
different additions of the nucleating agents Cr2O3, CaF2and their mixtures on the crystallization ability, phaseassemblages and microstructure was investigated.
II. Experimental procedure
2.1. Glass preparation and batch calculation
Wastes basaltic rocks and ceramic waste from SaudiCeramic Company, Saudi Arabia, were used as startingmaterials for the preparation of the investigated glassand glass-ceramics. Their chemical compositions aregiven in Table 1. The base glass (G0) was prepared bymixing of 80 wt.% of the basaltic rocks with 20 wt.% ofthe ceramic waste and their compositions are given inTable 2.
Nucleation agents such as CaF2, Cr2O3 and their mix-ture, were used for the control of crystallization pro-cess and formation of augite-anorthite glass-ceramics.Different amounts of additives were incorporated in thebase glass G0 and five different samples were obtained:G2F with 2 wt.% of CaF2, G4F with 4 wt.% of CaF2,G0.5C with 0.5 wt.% of Cr2O3, G1C with 1 wt.% ofCr2O3 and G2F0.5C with CaF2-Cr2O3 mixture contain-ing 2 wt.% CaF2 and 0.5 wt.% of Cr2O3.
The weighed batch materials, after thorough mixingwere melted in Pt crucibles in an electrically heatedfurnace at temperatures ranging from 1400 to 1450 Cfor 1.5 to 2 h depending upon the nucleant involved.The melts containing Cr2O3 were rather more viscousthan those containing CaF2 and their mixtures there-fore required higher temperatures and longer periods ofmelting. The homogeneity of the melt was achieved byswirling of the melt-containing crucible several timesat about 20 min. intervals. After melting and refining,the bubble-free melt was cast onto a hot steel marverinto buttons and rods. The hot glass samples were thentransferred to a preheated electric muffle furnace for an-nealing.
2.2. Differential thermal analysis
Differential thermal analysis (DTA) was carried outby a Shimadzu DTG60 micro differential thermo-analyser. 60 mg of powdered glass sample, of grain sizeless than 0.60 mm and greater than 0.2 mm, were usedagainst Al2O3 powder as a reference material. A heatingrate of 10 C/min was maintained for all runs. The heat-
Table 2. Chemical composition (wt.%) of the raw materials used for batch preparation
Raw material SiO2 Al2O3 Fe2O3 TiO2 CaO MgO Na2O K2O L.O.I.a
Residue of basaltic rocks 45.90 16.55 11.8 1.49 10.85 8.30 3.24 0.76 0.41Ceramic waste 70.14 20.20 0.88 0.60 1.63 0.33 2.45 2.30 1.17
a loss of ignition at 1000 C
G.A. Khater et al. / Processing and Application of Ceramics 9  (2015) 117123
Figure 1. DTA curves of the investigated glasses
treatment of the glass samples were heated in a mufflefurnace from room temperature to the required temper-ature and kept at the intended temperature for 2 h, af-ter which the furnace was switched off and the sampleswere allowed to cool inside it to room temperature. Theprepared glass samples were first soaked at 700 C for1 h and then at 900 and/or 1100 C for 2 h.
2.3. X-ray diffraction analysis
Identification of crystalline phases precipitating inthe course of crystallization was done by X-ray diffrac-tion analysis