Encyclopedia of Glass Science, Technology, History, and Culture. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

Автор: Группа авторов
Издательство: John Wiley & Sons Limited
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Жанр произведения: Техническая литература
Год издания: 0
isbn: 9781118799499
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when water reacts with other volatile components of the batch.

      Without taking into account the formation of intermediate products, the overall meltability of the raw materials is highly variable [3]: H2O is released at around 100 °C; the deshydroxilation of OH‐bearing minerals takes place at 400–800 °C; carbonates release large quantities of CO2 at 700–900 °C; feldspars melt below 1200 °C; the other silicates are dissolved in the pre‐existing glass melt above that range; bauxite has an even stronger refractory character, needing temperature above 1300 °C to be digested by the surrounding liquid (cf. the DSC thermogram of Figure 3, in Chapter. 1.5).

      Suppliers of raw materials process their products through several steps to match their customers' specifications [4]. First, rocks containing the desired raw material(s) are blasted or excavated. The bulk material so extracted is then retrieved, crushed, ground, screened, and sorted to achieve the required grain size, washed, dried, or dewatered before being stockpiled and transported in big bags or in bulk. In some cases a physical and/or chemical beneficiation stage may be needed to achieve the required specifications, especially to remove unwanted impurities. All these steps can have an impact on the final quality of the raw materials in terms of presence of impurities and heterogeneities.

      2.2 Grain Size

      The particle (or grain) size distribution (PSD) is a crucial parameter of individual raw materials. The required PSD may be costly to achieve. It primarily depends on the hardness of the bulk material, which in turn roughly correlates with its melting temperature [5]. As examples, K‐feldspar has a hardness of 6 (out of a maximum of 10) on the Mohs scale and melts at about 1200 °C, quartz has a hardness of 7 and melts above 1700 °C (in the form of cristobalite), whereas corundum (α‐Al2O3) has a hardness of 9 and melts above 2000 °C. Hence, the glassmaker determines the final PSD of the raw material as a compromise between meltability, furnace technology, and price (cost) while also limiting the unnecessary fines that generate dust and furnace carryovers. For specific applications, the glassmaker may in addition request the supplier of raw material to cut the lower end of the PSD to get totally rid of dust from fines.

Oxide Raw material Bulk chemistry Overall mineralogy Sp – Fr – It – De Price €/T*
SiO2 Quartz‐sand >95 % SiO2; H2O, Al2O3, RO, R2O, Fe2O3 Quartz, free‐water, mica, feldspars Arena – Sable – Sabbia – Sand 20–200€/T
Sandstone >95 % SiO2; H2O, Al2O3, RO, R2O, Fe2O3 Quartz, mica, feldspars, FeTi‐oxides, free‐water Arenisca – Grès – Arenaria – Sandstein
Quartzite >95 % SiO2; H2O, Al2O3, RO, R2O, Fe2O3 Quartz, mica, feldspars, FeTi‐oxides Cuarcita – Quartzite – Quarzite – Quarzit
Al2O3, R2O Feldspar (concentrates from greywacke, arkose, pegmatite, granite, etc.) 17–20 % Al2O3; 11–15 % R2O; <65 % SiO2; H2O; Fe2O3, TiO2, CaO Alkali‐feldspars [(K,Na)AlSi3O8: orthoclase, microcline, sanidine, albite, and their solid solutions], quartz (15–20%), micas. Li‐rich (up to 1.5 wt %) contain spodumene, petalite, or lepidolite (Li‐mica), mainly. Feldespato – Feldspath – Feldspato – Feldspat 80–150€/T
Nepheline(−syenite) 20–26 % Al2O3; 15–18 % R2O; <56 % SiO2; H2O; Fe2O3, TiO2, CaO Alkali‐feldspars [(K,Na)AlSi3O8: microcline, sanidine, albite, and their solid solutions], alkali‐feldspatoids [(K,Na)AlSiO4: nepheline, kalsilite, and their solid solutions], micas, titanite, perovskite, garnet, zircon, apatite, REE‐silicates. Silica undersaturated = no quartz Nefelina – Néphéline – Nefelina – Nephelin 100–130€/T
Phonolite 20–26 % Al2O3; 15–18 % R2O; <56 % SiO2; H2O; Fe2O3, TiO2, CaO Alkali‐feldspars [(K,Na)AlSi3O8: sanidine, albite, and their solid,solutions], alkali‐feldspatoids [(K,Na)AlSiO4: nepheline, kalsilite, and their solid,solutions], leucite KAlSi2O6, sodalite, haüyne, carnegeite, micas, amphibole, pyroxene, titanite, ilmenite, perovskite. Silica undersaturated = no quartz Fonolita – Phonolite – Fonolite – Phonolith 60–70€/T
Anorthosite <30 % Al2O3, <15 % CaO, <45 % SiO2, Fe2O3, R2O, MgO Anorthite CaAl2Si2O8, pyroxene, amphibole
Al2O3 Bauxite (raw or calcined) 40 % < Al2O3 < 80 %; 10–15 % Fe2O3; H2O; SiO2 Gibbsite Al(OH)3, diaspore α‐AlO(OH), boehmite y‐AlO(OH), bayerite, corundum, goethite, hematite, kaolin, anatase Bauxita – Bauxite – Bauxite – Bauxit 250–400€/T
Hydrated alumina >60 % Al2 O3

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