PROCESS FOR PRODUCING CERAMIC-TYPE MATERIALS BY PROCESSING WASTE CONTAINING ASBESTOS AND CLAY

Abstract: According to the process for producing ceramic-type materials by processing asbestos-containing waste, pre-ground asbestos-containing waste with clays are mixed, thus obtaining a mixture which is fired at temperatures between 650 and 1200 DEG C, the firing process leading to the complete elimination of the asbestos fibres and to the conversion of the mixture into ceramic materials having characteristics that are dependent on the parameters of the mixture and on the starting waste materials, containing asbestos.

Description: Process for producing ceramic-tvpe materials bv processing waste containing asbestos and clay The present invention relates to a process for disposing of waste containing asbestos by means of a reaction of thermal transformation type and subsequent conversion of the inert products thus obtained in order to produce various grades of ceramics. Asbestos-containing waste is one of the most significant types of materials needing to be disposed of, not only in Italy but also throughout the rest of the industrialized world, given that asbestos has been widely used for almost a century and forms a part of more than 3000 products. On account of the carcinogenicity which has been ascertained for asbestos and products containing it, the problem of the safe disposal of the said materials has been encountered in many parts of the world. The term asbestos refers to any mineral phase which, when suitably prepared, gives non-combustible fibres that can be spun into a thread. Five minerals come under this definition: coiled asbestos (chrysotile) Mg 3 Si 2 0 5 (OH) 4 amphibole amosite asbestos (mixtures of cummingtonite- grunerite) (Mg, Fe, Mn) 7 (Si 8 0 22 )(OH) 2 amphibole crocidolite asbestos (mixtures of glaucophane- riebeckite) Na 2 Fe 5 (Si 8 θ 22 )(OH) 2 amphibole tremolite asbestos Ca 2 Mg 5 (Si 8 0 22 )(OH) 2 amphibole actinolite asbestos Ca 2 (Mg, Fe) 5 (Si 8 0 22 )(OH) 2 Besides their ability to be spun into a thread, the common feature of all of these mineral phases is the presence of water, as hydroxyl ions, inside the crystalline structure. In particular, detailed analysis of the structure of asbestos compounds reveals that chrysotile (coiled asbestos) cluster consists of a layered book of atoms in which Si0 4 groups are alternated with MgO 6 ' groups. OH ions are found in this sandwich. These layers roll up, in a very similar way to a carpet, thus forming the elongated fibre structure. In the case of the amphibole asbestos compounds, their structure is formed of a regular alternation of layers containing silica and oxygen with layers containing Mg, Fe or other cations and oxygen. Water in the form of hydroxyl ions is found in the cavities left by the cations. The fibres are formed by elongation along a growth axis (generally the c-axis) of the layers described above. It is known that asbestos compounds have ranges of thermal and mechanical stability, which have been studied by many authors, in which the various phases known as asbestos survive. Beyond these ranges, in particular when the dehydroxylation temperatures are exceeded, asbestos compounds gradually lose their properties and tend to become converted into phases of varying composition that are harmless from the point of view of health. As regards methods of disposing of asbestos compounds, besides dumping them, which obviously does not eliminate the problem but merely hides it, many methods exist for processing asbestos-containing waste, which, for the sake of brevity, will be referred to as ACW (Table 1). Table 1 Comparative Analysis of the Costs and Benefits of ACW Methods Method Costs Benefits Product Value (It.lira/kg ACW) % asbestos converted (It.lira/kg) Dumping 250 (asbestos cement) 0 0 600-1600 (friable) Encasement 300-350 (asbestos cement) 0 0 in cement 800 (friable) Vitrification 1800-2500 100 0 by plasma Vitrification with 800-1800 100 0 or without additives Clinkerization 400-100 100 20 Ceramizing 400-600 100 from 200 to 700 depending on product The techniques of encasement and dilution in cement matrices, vitrification by plasma, vitrification by conventional fusion, clinkerization, vitroceramizing and ceramizing are reviewed briefly below. Although relatively inexpensive, as industrially developed, the technique of encasement in cement does not eliminate the problem of the presence of breathable asbestos fibres but merely dilutes it, at the same time increasing the volume of materials to be dumped. For this reason, in the long term this technique is expensive and does not in fact solve anything. Vitrification by plasma is an extremely interesting technique since it involves fusing the ACW using a plasma arc at temperatures above 1600°C. The products thus obtained are quite clearly free of fibres since the asbestos melts at much lower temperatures; this is the most expensive method for disposing of ACW. Vitrification in conventional ovens can be carried out with or without fluxes. In the first case, the process is performed at temperatures close to 1150-1200°C with all of the components of the mixtures melting to produce a vitreous slag. In the second case, fusion without fluxes is achieved by working at temperatures above 1400°C, again producing a harmless and useless vitreous slag. Either way, vitrification techniques are very expensive and do not always enable all of the waste to be digested, since this depends on the residence times in the ovens and on the temperatures used, which, however, for fusion without fluxes, must necessarily be above 1400°C. As regards ceramizing techniques, many authors have explored the possibilities of processing different types of waste materials by heating them to temperatures below their melting point but above their dissociation point. In the field of asbestos minerals, Russian studies relating to the conversion of chrysotile and Canadian studies on the conversion of residues from the chrysotile asbestos industry for producing forsterite (refractory ceramics) will be recalled. Other techniques envisage the firing and subsequent conversion of asbestos compounds and of ACW without additives in order to convert them into inert materials for use in cement materials and roadbuilding. The techniques which exploit ceramizing processes are effectively amongst the safest and most economical since they make use of thermal transformation reactions, which are present in nature in many geological situations, in order to convert asbestos minerals completely. It is more difficult to convert chrysotile directly into enstatite since this requires a higher activation energy and thus a higher temperature (MacKenzie and Mainhold, 1994). There are also structural considerations which suggest that coiled asbestos is converted into forsterite via a topotactic conversion; studying the sizes of the unit cells of coiled asbestos and forsterite reveals the following correspondences: coiled asbestos forsterite 2a = 10.62 A -> b = 10.20 A 2b = 18.40 → 3c = 17.94 2[001] = 14.64 -> 3a = 14.27 Forsterite thus preferentially forms with the c-axis of the crystal parallel to the b-axis of coiled asbestos, so as to become aligned with the tetrahedra of the structure (Ravaglioli and Rajewski, 1989). Total loss of structural OH takes place between 680°C and 780°C. During the conversion of chrysotile into forsterite, some of the forsterite is also converted into enstatite, magnesium pyroxene. Enstatite coexists, as clinoenstatite, with forsterite up to temperatures of 1557°C, at which temperature the clinoenstatite melts. If during the reaction, in the range between 600 and 900°C, an aluminium-donating component is placed in the mixture and reacts rapidly, stable Si-Mg-Al phases are produced. In particular, by studying the Schreyer diagram (Schreyer, 1988) it is seen that there is a range of phases, and in particular cordierite, on the line connecting the "coiled asbestos" and "kaolinite" extremes. As is known, this phase is formed in nature in the transformation of argillaceous sediments, in particular of chlorites and metapelites, according to the following reaction: (OH) 8 (Mg,Fe) 4 Al 4 Si 2 O 10 + 5Si0 2 → (Mg,Fe) 2 Al 4 Si 2 0 18 + 2(Mg,Fe)Si0 3 + 4H 2 0 Chlorite + Silica = Cordierite + Enstatite + Water Vapour The temperature at which this conversion takes place depends on the temperature and on the partial pressure of water. Thus, in order to convert chrysotile into cordierite, since there is no aluminium present in its structure the conversion reaction can take place only by introducing an Al-rich reactant which will participate in the reaction in the same temperature range. Such introduction has been attempted by introducing kaolinite, which reaches the stage of metakaolinite at about 650-700°C, becoming amorphous and converting into a material of very high reactivity (Sergeev and Goncharev, 1987-1990, Plescia et al., 1995). The reaction conjectured to take place is thus as follows: Mg 3 Si 2 0 5 (OH) 4 +2Al 2 Si 2 0 5 (OH) 4 + n0 2 → Mg 2 Al 4 Si 2 0 18 +l/2Mg 2 Si0 4 +3Si0 2 +8H 2 0 Chrysotile + Kaolinite + Oxygen → Cordierite + Olivine + Silica + Water Vapour One process for converting waste containing chrysotile asbestos and then recycling the inert products for the production of cordierite- containing ceramics is described in the Italian patent application in the name of the present Applicant, No. RM 95 A 000269, filed on 28 April 1995. Amosite is the commercial name of a class of fibrous amphiboles of ferro-magnesium type, the end-members of which are cummingtonite and grunerite. The characteristic formation of these phases is linked to the thermal and dynamothermal transformation of ferromagnesium rocks in the presence of water. The thermal stability of amosite differs from that of chrysotile. It can melt at 1400°C, although its structure already disintegrates at much lower temperatures and the asbestos loses its properties. In particular, certain studies (Fonarov and Korolkov, 1980) demonstrate that in the presence of air amosite tends to lose OH, converting into an oxyamphibole, and loses mechanical strength at temperatures as low as 600°C. The dissociation of grunerite (experimentally determined by Ross and Papike, 1969) has been placed at about 600°C and increases as the magnesium content increases and as the iron content decreases. The conversion products are generally forsterite/fayalite olivine and silica. By increasing the magnesium content there is a tendency to form the corresponding pyroxene. All of these reactions depend critically not only on temperature but also on the fugacity of oxygen, on the total pressure and on the pressure of H 2 0. Among the asbestos minerals, crocidolite is the phase which has the lowest melting point (1190"C). The conversion of crocidolite can thus take place at substantially lower temperatures than those of the other asbestos minerals. In particular, Addison et al. (1962) examined the oxidation of crocidolite by heating it in an air atmosphere and analysed the products generated. He found that the OH of crocidolite tends to recombine as water vapour with simultaneous oxidation of Fe + and OH according to the reaction: 4Fe 2+ + 4(OH) " + O 2 → 4Fe 2+ + 4O 2 " + 2H 2 0 with a secondary reaction on the surface: 4Fe 2+ + O 2 - → 4Fe 3+ + 20 2 " In reality, the presence of iron may in some way control the dehydroxylation of the amphibole, as demonstrated by the studies carried out by Rouxhet et al. (1972); Addison shows that a 1:1 relationship exists between the FeO content and the OH content of the sample. In grunerite (amosite) there is a 3:2 relationship between the FeO content and the OH content (Ernst and Wai, 1970). The object of the present invention is to provide a process for producing ceramic-type materials by processing waste containing asbestos and clays, in particular, but not exclusively, kaolinitic clays. According to the present invention, the process under consideration envisages mixing pre-ground asbestos-containing waste with kaolinite- type clays having a kaolinite content of between 55% and 100%, thus obtaining a mixture which is fired at temperatures between 650 and 1200°C, the firing process leading to the complete elimination of the asbestos fibres and to the conversion of the mixture into ceramic materials having characteristics that are dependent on the parameters of the mixture and on the starting waste materials. Preferably, according to the invention, the asbestos-containing waste materials are ground, by techniques that are known per se, down to a particle size of between 500 μm and 10 μm, and preferably between 200 μm and 50 μm. The present invention will now be described with reference to its currently preferred embodiments, given by way of non-limiting illustration, and with reference to the figures in the appended drawings, in which: Figure 1 schematically shows the SiO 2 -MgO-FeO- Al 2 O 3 compositional tetrahedron which illustrates the composition of the main types of asbestos and of the conversion products obtained with the addition of kaolin; Figure 2 shows the changes in the products during heating, starting with a 1:1 ratio of an amosite/kaolinite mixture; Figure 3 shows the changes in the products during heating, starting with a 1:1 ratio of a chrysotile/kaolinite mixture; Figures 4, 5, 6 and 7 are photographs showing that the residual fibres are rich in particles with oxidized surfaces. The process according to the invention, briefly outlined above, can be summarized as follows from a chemical point of view. As is already known, a common feature of the so-called asbestos minerals is the presence of water, in the form of hydroxyl ions, which is contained in specific sites in the mineral. In the case of chrysotile, these sites consist of the cavities between the silicon and oxygen tetrahedra which form the layered framework, whereas in the amphibole compounds the hydroxyl ions are inserted inside the double- chain of silicon-oxygen tetrahedra which form the structural framework of the minerals. Heating leads to the progressive loss of hydroxyl ions and thus to weakening of the crystal structure. At temperatures of about 650°C for chrysotile and of about 850°C for the amphibole compounds, the structure of the minerals dissociates into its fundamental components. In particular, immediately after losing hydroxyl ions, chrysotile tends to become converted into metachrysotile (partially amorphous), whereas the amphibole compounds become oxidized and their iron crystallizes separately as magnetite and haematite (iron oxides). During the thermal reaction of the amphibole compounds, magnesium silicate (olivine, pyroxene) also separates out. If, during the dehydroxylation phase, an argillaceous phase is added, which in turn reacts, becoming converted and losing water, a vigorous solid-state reaction takes place, with amalgamation of the two components: the asbestos with the amorphous kaolinite. The phase which is formed is thus a new, synthetic mineral of intermediate composition, and as such it can readily be distinguished from its precursors. A few tests of inertization carried out on pure asbestos compounds and on various types of asbestos-containing waste will now be described. The main aspects of the process according to the invention are summarized in Table 3 given later according to type of asbestos and of asbestos-containing waste. Mixtures of pure chrysotile - Mg 3 Si 2 θ 5 (OH) 1 - and kaolinite - The firing tests on chrysotile/kaolinite Mg 3 Si 2 0 5 (OH) 4 - Al 2 Si 2 0 5 (OH) 4 mixtures made it possible to identify a series of reactions and products which form in a temperature range between 600 and 1100°C, which are variable depending on the type of mixture (Table 2). Table 2 Kaolinite/chrysotile mixtures Kaolinite/chrysotile ratio Products formed 1:2 l En + 2 01 1:1 I Cor + 1 Mul+01 2:1 I Cor + 1 Mul Cor = Cordierite Mg 2 Al 4 Si 5 0 18 01 = Olivine Mg 2 Si0 4 Mul = Mullite Al 2 Si0 5 The reaction of kaolinite with chrysotile takes place according to a scheme which may be indicated as follows: chrysotile + kaolinite - metakaolinite + "metachrysotile" -> cordierite + enstatite/olivine/mullite. An in-depth study of the reactions of chrysotile at different temperatures was recently published by MacKenzie and Meinhold, which shows that at a temperature of about 650°C, chrysotile tends to lose its structure and adopt a metastable phase which is probably amorphous. The fact that at the same temperature kaolinite also is converted into metakaolinite means that the two minerals are extremely reactive (increase in the specific surface and decrease in the free energy of crystallization) and can react together. From the study carried out on the 1:1 chrysotile/kaolinite mixture, carried out both with direct heating to the maximum temperature and with stepwise heating, it is observed that the heating cycle strongly influences the temperature of formation of the Mg-Al-Si phases. In particular, whereas in the "direct" reactions, such as during rapid heating to a temperature of 1050-1100°C, cordierite is obtained in coexistence with mullite, in the cycles involving intermediate steps the temperatures of formation of cordierite increase. From Figure 3, which shows combined XRD spectra of the products obtained by stepwise heating, it is seen that the chrysotile/ kaolinite mixture is again completely amorphous at 650°C, with few reflections derived from olivine. After that, between 750 and 850°C, the mixture becomes enriched in olivine; at 950°C the pyroxene enstatite increases, while mullite appears between 950°C and 1100°C. Cordierite appears between 1050°C and 1100°C and becomes predominant at 1150°C; at 1200°C the mullite disappears, traces of olivine remain and the enstatite also reduces in amount. At 1300°C the main phase present is cordierite. The melting point of the cordierite- containing product is about 1360°C, which can vary by about 10°C depending on the iron content. The electron microscope photographs show how the chrysotile fibres are replaced by squat objects of vaguely fibrous or flattened and elongated appearance, often with clear traces of sintering, immersed in a porous paste (Figures 4, 5, 6 and 7). In an earlier study (Plescia et al., 1995), it was observed that the density of the products obtained varied significantly as the temperature increased, rising from a minimum of 1.4 g/cm 3 at 950°C to 2.8 g/cm 3 at 1300°C. Mixtures of pure amosite (Mg,Fe) 6 Si 8 θ 2 (OH) 2 and kaolinite Al Si 2 θ 5 (OH) 1 and of pure crocidolite Na 2 Fe 5 Si 8 0 22 (OH) 2 with kaolinite Al 2 Si 2 θ 5 (OH) 1 The conversion of amosite mixed with kaolinite was attempted from 750 to 1200°C. The X-ray spectral plots (Figure 2) show that the reflections relating to the structure of the amphibole are stable to temperatures of about 850°C, after which a sudden transformation takes place: the amphibole tends to split into spinel-type oxides (magnetite and haematite), whereas the silicate phase is converted into mullite and clinoenstatite. If there is sufficient calcium (>8%) in the structure of the amphibole, a mixture rich in calcium-magnesium feldspar is obtained, with a structure similar to that of plagioclase. From the electron microscope photographs it is observed that the residual fibres are rich in particles that have oxidized surfaces (Figures 4, 5, 6 and 7). These particles represent the conversion which has taken place, at temperatures of about 900°C, which may be described schematically in the following way: amosite + kaolinite → Fe Si0 3 (enstatite) + (Mg, Fe)Si0 4 (olivine) + Al 2 Si0 5 (mullite) + H 2 0 + α-Fe 2 0 3 (haematite) +/- α-, Fe 5 0 4 (magnetite) At temperatures of more than 900°C, the components tend to recombine as in the reactions described in the above paragraph, forming ferro-cordierite. This phase, which is very rich in iron from the cordierite which is formed from the chrysotile, is found to have a lower melting point, of about 1330°C. The conversion of crocidolite takes place at temperatures slightly lower than that of amosite: the absence of peaks derived from crocidolite can already be established at 780°C. The crocidolite tends to split into pyroxene, olivine, magnesium spinel and haematite. The conversion of this phase is closely linked to the presence of oxygen, since it is known that in the presence of a gentle stream of heated air, the crocidolite tends to be converted more rapidly and to react with the kaolinite. Tests with clay-ACW mixtures Mixtures of asbestos cement with kaolinite clav Asbestos cement is an industrial composite product formed from Portland cement and asbestos in fibres 0.1 to 1 cm in length, predominantly of chrysotile type, with small percentages of amosite and crocidolite. Asbestos cement contains an average of 12-15% asbestos and about 1.85% cement. Direct firing of asbestos cement leads to the production of phases of calcium silicate type (dioxide, akermanite) and magnesium calcium silicate type (pyroxene, olivene). The material thus obtained can be used as inert material. Mixing properly ground asbestos cement with clay produces a mixture with a higher aluminium content. During firing, the composition tends to shift towards phases of magnesium aluminium silicate and calcium aluminosilicate type, in particular of the anortite-akermanite type, which are harmless and can be used as inert materials in the ceramics industry. Mixtures containing asbestos boards or asbestos and clav papers The results are identical to those which may be obtained using pure chrysotile: excellent cordierites are obtained, which can be used for refractory materials and the cores of catalytic filters. As in the case of pure chrysotile mixed with clay, the minimum conversion temperature is found to be 650°C. At 1100°C cordierite forms, mixed with mullite. Mixtures containing cords and fabrics of chrysotile cords asbestos and clay Mixtures composed of cords and fabrics of chrysotile asbestos and clay also lead to the production of refractory materials mainly containing cordierite. The conversion temperatures are the same as those in the above example. Mixtures containing friable asbestos of the amosite or crocidolite type and clavs The products and the conversion temperatures are identical to those relating to the test using amosite and pure crocidolite mixed with kaolin. Table 3 Processing of various types of ACW (asbestos containing waste) Type of % Asbestos Asbestos/ Cost of Estimated Type of Value of ACW (range) kaolin ratio disposal treatment material product to the in the mixture (dumping) cost producer (range) It.Lιra g It.Lirakg It. Lira kg Pure chrysotile 100 1:1-1.3 cordierite 2500-5000 (refractories, filters) Pure amosite 100 1:1-1.2 cordierite 2500-5000 (retractones, filters) Pure crocidolite 100 1:1-1.2 cordierite 100-500 (refractories, inerts) Asbestos ceramic and similar materials 12-20 1:1-1:5 200-350 350-600 merts. ceramics 20-100 fired mateπale Threads, fibres 80-100 1 1-1:3 1600-1800 350-600 cordierite 2500-6000 (refractories, filters) Papers, 80-90 1:1-1.3 1600-1800 350-600 cordieπte 2500-6000 boards (refractories, filters) Pannelling 30-60 1:1-1:5 1600-1800 350-600 Sprayed asbestos 80-90 1:1-1:2 1600-1800 350-600 refractories, 100-500 fired materials N,B. Values in Italian Lira Example 1 An asbestos-containing waste (friable amosite originating from railway thermal insulating material) was ground and then mixed with kaolinite clay, in ratios ranging from 1:1 to 1:3. The mixture was fired at 950°C in a muffle furnace, using a heating cycle as follows: 25-150°C at 10°C/min and stationary at 150"C for two hours 150-650°C at 5°C/min and stationary at 650°C for two hours 650-950"C at 5°C/min and stationary at 950°C for two hours The material was then cooled and analysed. No traces of asbestos are found in the final fired product, but ferrous cordierite is predominantly present, along with traces of pyroxene, mullite, olivine and iron oxides. The material may be used for firebricks up to 1200 <> C and as inert material. Example 2 Asbestos-containing waste (Eternit ® [asbestos]) was ground and mixed with kaolinite clay. The mixture was prepared in a 1:5 asbestos/kaolinite ratio. The heating process is the same as that in the above example. The final products are: anortite wollastonite olivine (traces) mullite. The material obtained can be used in the cement and refractory materials industries at up to 1300°C. Example 3 Asbestos-containing waste (chrysotile from an electricity power station) was ground and mixed with kaolinite clay. The 1:1 mixture was fired at 750°C and then analysed. The composition is made up as follows: amorphous material (75%) olivine The heating cycle used was as follows: 25-150°C at 10°C/min and stationary at lSOT for two hours 150-750°C at 5°C/min and stationary at 750°C for two hours This product contains no asbestos, is extremely friable, porous and reactive and may be sold without further processing to the refractory materials industry as a starting material for the production of simple cordierites and cordierites supplemented with mullite. Indeed, if the product formed is subjected to a new cycle of firing and sintering, magnesium cordierite forms between 1000 and 1150°C. Example 4 The same waste material as in the previous example was fired up to 1150°C using the following heating cycle: 20-1150°C at 5°C/min and stationary at 1150"C for two hours The material recovered is 80% cordierite with about 15% mullite, and has the characteristics illustrated above. Bibliography Addison CC, Addison W.E., Neal G.H., Sharp J.H. (1962) J. of Chem. Soc, 1468-1471 Ernst W.G., Wai CM. (1970) Amer. Mineral. 55, 1226-1258 Fonarev V.I., Korolkov G. Ya (1980) Contrib. Mineral. Petroli. 73, 413- 420 McKenzie K.J:D., Meinhold R.H. (1994) Amer. Mineral. 79, 48-50 Plescia P., Maccari D., Marabini A. Acqua Aria, No. 10, 1041-1046 Ravaglioli, A., Krajeski A. (1989) in "Chimica, Fisica tecnica e Scienza dei materiali antichi ceramici e vetrosi" Museo Internazionale della Ceramica, Faenza Ross M., Papike J.J., Shaw K.W. (1969) Min. Soc. Amer. Spec. Paper 2, 279-299 Rouxhet P.G. Gillard J.L., (1972) Mineral Magazine 38, 538-592 Schreyer W., Shair F. (1958) Ann. Rep. Dir. Geophys. Lab., Carnagie Inst. W.D.C Schreyer W. (1988) Mineral Mag., 52, pp. 1-26 Sergeev N.E., Goncharov Yu. I. (1990) Steklo Keram. No. 5, 5-7 C.N.R, patent application No. RM 95 A 000269 of 28 April 1995.

Claims: Claims: 1. Process for producing ceramic-type materials by processing asbestos-containing waste, characterized by mixing pre-ground asbestos-containing waste with clays, thus obtaining a mixture which is fired at temperatures between 650 and 1200°C, the firing process leading to the complete elimination of the asbestos fibres and to the conversion of the mixture into ceramic materials having characteristics that are dependent on the parameters of the mixture and on the starting waste materials, containing asbestos. 2. Process according to Claim 1, characterized in that the clays consist of kaolinite-type clays. 3. Process according to Claim 2, characterized in that the kaolinite- type clays have a kaolinite content of between 55% and 100%. 4. Process according to any one of the preceding claims, characterized in that the asbestos-containing waste materials are ground, by techniques that are known per se, down to a particle size of between 500 μm and 10 μm, and preferably between 200 μm and 50 μm. 5. Ceramic- type material obtained by processing asbestos- containing waste and clay according to any one of the preceding claims. 6. Use of the ceramic-type material according to Claim 5 as inert material for refractory materials in general and in particular for firebricks.

Inventors: BELARDI GIROLAMO, MACCARI DANTE, MARABINI ANNA MARIA, PLESCIA PAOLO, BELARDI, GIROLAMO, MACCARI, DANTE, MARABINI, ANNA, MARIA, PLESCIA, PAOLO
Applicants: BELARDI GIROLAMO, CONSIGLIO NAZIONALE RICERCHE, MACCARI DANTE, MARABINI ANNA MARIA, PLESCIA PAOLO, BELARDI, GIROLAMO, CONSIGLIO NAZIONALE DELLE RICERCHE, MACCARI, DANTE, MARABINI, ANNA, MARIA, PLESCIA, PAOLO
Application year: 1997
Main classification: C04B35
IPC codes: B09B3, C04B35