Foamed glass-ceramic materials based on oil shale by-products. Alexander V. ... properties, having maiiy advantages over other types of porous insulating ...
Short Communication Foamed glass-ceramic materials based on oil shale by-products Alexander V. Gorokhovsky, Yose lvan Escalante-Garcia and Juan Mendez-Nonell Center for Research and Advanced Studies icinvestav), Saltillo, Coahuila (Mexico) V(adilen A. Gorokhovsky and Drnitrii V. Mescheryakov Saratov State Technical University,Saratov (Russia)
The feasibility and features oí' the production of foanxd glass-ceramic inaterials baved o11 oil shale ash were investigated. The optimal regime of synthesis f'ound involved the followinp steps: glass fusionat 1400°C. preparation of the glass powders and blending with the foaming agent. The foaming was carried out at 900 to Y20CC:witti a further one-stage crystallization at 790 to 820°C. It was noted that the admixtiire of calcium carbonate. as ü foaining agent, changed the phase composition of the resulting giassceramics by an increased rate of the crystallization process arid the intensive fomation of gehlenite simultaneoiisly with diopside.
1. lntroduction The analysis of publications related to tlie production of glass and glass-ceramic materials suggests the extended interest towards the use of different slag and asli wnstes of metallurgy and hcat powcr stations [ l t« S]. These wastes and by-products can be considered as quite prornising raw materials for the production of glass-ceramics of the diopside type that are effective in thc manufactunng of difyerent coiistruction materials [ S to 61. The base system of R20-Mg0-Ca0-Fe203AI2O3-Si02 is characterized by a very wide isoinorphism and allows varying the chemical composition of raw materials without significani changes on the final product properties. The chemical composition of the aforementioned oxide system is close to the composition of industrial wastes of oil shale mining and thermal treatrnent. lt has been shown [7] that various glass and glass-cerümic rnaterials can be produced on the base of such wastes. However the high variability of the oil shale chernical ccin~position, even from the sanie depositioi-i, Icads towarcis research related to the rnanufacturing oS glass-cerñmic inaterials of not very ctrong requiremeiits, such as the technologies of application for traditional glass. Foained glass-ceramics based on oil shale are rnost pronlising matenals showing good heat and noise insulation properties, having maiiy advantages over other types of porous insulating materials, suc1.i as lower density arlti Received 17 September 2001. revised rnsinuscript 25 Febriiary 2002.
Glass Sci. Technol. 75 (2002) No. 5
water absorption, and higher heat capacity, fire resistance and chemical durability in aggressive conditions. However, for the production of iiisulating foamed material~special requirements niust be considered, such as tlie optiinal ratio of viscosity to siirface energy in the foarning teinperature interval, which favors the effective forniation of gas bubbles and solidification of the foanied material. Another interesting characteristic of thc oil shale ash is the low alkali concentration, which can increase the electric conductivity of the h a 1 material. The ohjective of this research was the investigation of thc optinial coiiditioi~sfor the manufacture of foanied glass-ceramic materials of the pyroxene type based on oil shale ash.
2. Experimental Oil shale ash produced by the heat power station of Syzmnskaya (Russia) was iised as the raw material, its chciiiical composition (in wt'!h) was the following: 41.8 Si02, 12.5 A1203. 8.5 FexOr 31.3 CaO, 2.0 MgO, 0.7 T'i02, 0.8 P205. 0.8 NazO, 1.6 K 2 0 , 7.7 SO3 and 2.3 H20. Somc adn~ixtureswere employed in the batches as follows: sodium srilts to favor glass rnelting, sand and carbon to regulate the crystallization properties and C r 2 0 3(0.7 wt%) as a nucleation agent. 'lable 1 presents the hatch composit~ons,which were nielteci ai 1400°C during 1.5 h. The molteii glass, cooled down to 1200°C, was used in the diff'erent ways for the following piirposcs. Preforms were prnduced by casting 259
A. V. Gorokhovsky; J. l. Escalante-Garcia;J. Mendez-Nonell: V. A. Gorokhovskv: D. V. Meschewakov:
Table 1. Composition of batches (in wt%) and technological propei ties of obtaintld glasses batch no.
raw material o11shale ash soda ash Nd2S04
1
2
3
8O 17
80
80 12 8
-
16
-
sand carbon
3
technological property temperature at the beginiiing of fusion proce~sin "C Littleton temperature in 'C: interval of bulk crystallBation temperature iii "C interval of surface crystallization temperature III "C:
1180
1150
870 850 t» 900 XOO i» 850
920 750 to 820 750 to 820
onto a metal plate to investigate the optimal crystallization regime; fibers werc drawn and used to deiermine the Littleton temperature by method of English (Col viscometer, Kussia), and fritted glass was produced by water quenching for the production of foained glass-ceramics. Prior to the foaining processing, the latter was ball-milled to a specific surface area of 4500 to 4800 cm2/g (as mcasured by the RET rriethoci, Kiissiati equipment LHM-XMD). The foaniiiig agcrits ernployed were limestone, sodium meta-silicate and oil shale (48 %, mineral part), added in the rangc of 1 to 5 wt% of the glass powder. The mixtures of glass powder and foaming agent were furthcr ball-milled togethsr riuritig ?O min. During the thermal treatment of the afcmmentioned rnixtures the volume variation was sclected as the foaming parameter and monitored onlinc fcir exprri~rientsat different tempcratiircs. The device used for this purpose comprised a stainless steel cyliiider (3 cin diameter) partially filled with the powder mixtures; an iriiier stainless steel plate (thickness 0.32 mm) was placed onto tlic powder and its other face was c«iinectixl, witti a riickel-chromium wire, to an electro-magrietic serisor to detect the movement of the wire as a result of the voliime chztnge. The expansion (AV/ Ló)oS samples at different tenipcratures in the range of 700 to 1 0 0 ° C was investigated. In accordance with previous rescarch [7] an irttensive one-stage bulk crystalli7ation of pyroxene glass compositions took place at 790 to 820°C The foanied xmiples were treated at 800°C for onc hour and cooled to room temperature at a rate of 300K/ii Slandard tcst methods of ASTM C240-97 wcre used to measure density, tlexural strength and thcrnial conductivity of the obtaincd foamed glass-ceramic wnples The structure and chemical composition of thc giitssceramics were investigated by scanriing electron microscopy (Jeol, nlodcl 6300 (.J;ipan)) equi pped wit li Xray microanalysis and also by X-ray ditrraction (Philips, model X'Pert- MPD (Netherlands)). The 3-point tlexural strength of foamed glass-ceramic rods, S inm dimi260
4 -
'Iable 2. Cornparativc inci-case of volume AMI',, (deviation 2 i2 ';,Íij For the rnixtiires oí' glass powder with dill'creiir foarning agerits ( 5 u.t'i:i~attcr tlic thermal treatmeni during 0.25 h (batch no. 2.) teniperature of thermal treatrnent 111"C'
limestone sodium oil shale mela-siliute
eter nnd 100 miri of length, w
