Seminar chm801


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silicates general introduction

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Seminar chm801

  1. 1. SILICATES Presented by- Aysha fatima M.Sc
  2. 2. •Silicates occur in the earth’s crust in the form of silicates minerals and aluminosilicate clays. •The silicates are the largest, the most interesting and the most complicated class of minerals than any other minerals. • Approximately 30% of all minerals are silicates and some geologists estimate that 90% of the Earth's crust is made up of silicates, SiO4- based material. 4 •oxygen and silicon are the two most abundant elements in the earth's crust.
  3. 3. -Very Common - 95% of All Minerals - Silicon (Si) and Oxygen (O) bond Easily SILICATES Minerals Containing Silicon and Oxygen Si O SINGLE SILICA TETRAHEDRON SiO4
  4. 4. • Sodium silicates is the only common silicate which is soluble in water • Most of the silicates are insoluble in water .this is due to great strength of Si-O bond this bond can be broken only on treatment with strong reagents like hydrofluoric acid. • The Si-O bond – 50% covalent, 50% ionic • Electronegativity of O is 3.5 and of Si is 1.9 difference is 1.6. 4- tetrahedra which • All silicates comprises of SiO4 are formed by sp3 hybrisidisation of Si orbitals.Si forms 4 bonds with oxygen atoms.
  5. 5. All silicates contains the tetrahedral SiO4 4- units.
  6. 6. PREPARATION Sodium silicate is commonly manufactured using a reaction in liquid phase or in solid phase. Both processes use alkaline and quartz sand as raw materials A mixture of caustic soda, quartz sand, and water are prepared in a mixing tank, then fed into a reactor, where steam is introduced. The reaction is n SiO2 + 2 NaOH → Na2O•nSiO2 + H2O
  7. 7. • This process uses quartz sand with either sodium carbonate or sodium sulfate. The feed materials are heated in a reflection furnace. The reaction is Na2CO3 + x SiO2 → (Na2O)•(SiO2)x + CO2 2 Na2SO4 + C + 2 SiO2 → 2 Na2SiO3 + 2 SO2 + CO2
  8. 8. Talc is primarily formed via hydration and carbonation via the following reaction; serpentine + carbon dioxide→ talc+ magnesite+ water 2 Mg3Si2O5(OH)4 + 3CO2 → Mg3Si4O10(OH)2 + 3 MgCO3 + 3 H2O Talc can also be formed via a reaction between dolomite and silica, dolomite+ silica+ water → talc + calcite+ carbon dioxide 3 CaMg(CO3)2 + 4 SiO2 + H2O → Mg3Si4O10(OH)2 + 3 CaCO3 + 3 CO2
  9. 9. ZSM-5 is a synthetic zeolite. There are many ways to synthesize ZSM-5, a common method is as follows: SiO2 + NaAlO2 + NaOH + N(CH2CH2CH3)4Br + H2O → ZSM-5 + analcime + alpha-quartz ZSM-5 is typically prepared at high temperature and high pressure in a Teflon-coated autoclave and can be prepared using varying ratios of SiO2 and Al containing compounds.
  10. 10. Different types of silicates  Orthosilicates  Pyrosilicates  Ring and chain silicates  Double chain silicates  Silicates with sheet structures  Silicates with 3-dimensional framework
  11. 11. Orthosilicates • Orthosilicates are minerals consisting of only single SiO4 4- units. The cations are some other metals. • the following minerals are orthosilicates:The Be and Zn ions are tetrahedrally bonded to the oxygen of the silicate in these two minerals: phenacite, Be2SiO4 and willemite, Zn2SiO4 ,zircon.
  12. 12. • In olivine, (Fe, Mg)2SiO4, the cations are either Fe2+ or Mg2+. • This formula suggests that this mineral is a mixed salt of iron and magnesium silicates. • These cations are octahedrally coordinated to the oxygen atoms of the silicate. • Pure salt Fe2SiO4 is called fayalite, and Mg2SiO4 is called forsterite.
  13. 13. Pyrosilicates 4- units are linked together, they • When two SiO4 6-. For example, form the pyrosilicate group, Si2O7 thortveitite, Sc2Si2O7 is a pyrosilicate, hemimorphite [Zn4(OH)2Si2O7 ]
  14. 14. Ring and chain silicates 4- units share with other SiO4 • When two oxygen of SiO4 4- units, the silicates form a ring or an infinite chain. • The stoichiometry of the silicates becomes (SiO3)n 2n- Benitoite BaTi(SiO3)3 contain three silica rings. • The precious stone beryl Be3Al2(SiO3)6 contain six-silica rings.
  15. 15. • Single chain silica are called pyroxenes. • Some synthetic silicates Na2(SiO3) have been shown to contain the simple chain silicates (SiO3)n, • in which the Si-O bonds of the type Si-O-Si are 168 nm, with the Si-O-Si angles of 137o. The Si=O bonds are shorter, 1.57 nm. • The natural pyroxenes include enstatite, MgSiO3, diopside, CaMg(SiO3)2, and jadeite, NaAl(SiO3)2, Spodumene LiAl(SiO3)2
  16. 16. Double chain silicates • Double chain silicates are called amphiboles, chains have a stoichiometry of (Si4O11)n 6n. • Tremolite, Ca2Mg5(Si4O11)2(OH)2, is such a mineral. • crocidolite Na2Fe3 IIFe2 IIISi8O22(OH)2 or blue asbestos consist of double chain silicates. • Asbestoses have been identified as carcinogens, and its application has since been limited due to a ban to limit its exposure to the public. • Most comercial asbestoses are chrysotile, which contain layers of silicate sheet
  17. 17. Structure of Double chain silicates basic unit is (SiO)6n- 411n
  18. 18. Silicates with sheet structures • Sheet slilicates are called phyllosilicates (phyllo means leaflike). • These silicates are easy to cleave (as does graphite). • Talc is a typical sheet silicate, Mg3(OH)2(Si2O5 ). Talc is a main ingredient of the soapstone (steatite). • Formed by sharing 3 bridging O per Si atom. • Sometimes Si atoms are partly replaced by Al atoms. Eg-Biotite K(MgFe)3(OH)3(AlSi3O10), miscoviteKAl(OH)2(AlSi3O10)
  19. 19. Silicates with 3-dimensional framework • the SiO4 4- units can share every oxygen with other units to form a three dimensional network, and quartz has such a structure. • In this arrangement, the stoichiometry is reduced to SiO2, which is often called silica. A collection of small pieces of quartz is sand.
  20. 20. Aluminosilicate • when some of the Si4+ ions in silicates are replaced by Al3+ ions. • For each Si4+ ion replaced by an Al3+, the charge must be balanced by having other positive ions such as Na+, K+, and Ca2+ ions. • Radius ratio is .43 close to CN 4 to 6 • Sanidine, [(K,Na)AlSi3O8]4 Orthoclase, [(K, Na)AlSi3O8]4 Albite, [NaAlSi3O8]4 Anorthite, Ca[Al2Si2O8]
  21. 21. • The alkali ions are held in place to balance the charges due to the presence of Al3+ ions instead of Si4+ ions. • The Al3+ ions replace Si4+ ions in the chains of corner shared tetrahedra of SiO4 groups. • However, the bonding between Al and Si can be different. • Silicon atoms or ion tend to be bonded to 4 oxygen atoms in a tetrahedral fashion, but aluminum ions tend to be bonded to 6 oxygen atoms in an octahedral fashion.
  22. 22. IMPORTANT ALUMINOSILICATES • Micas • Clay • Fuller’s earth • Talc • zeolites
  23. 23. MICA 4- SiO4  Micas are amphiboles made up of sheets of 4- is replaced by (AlO4)5- tetrahedre in which SiO4 tetrahedra. They are chemically inert and thermally stable have high dielectric constant.  Due to which micas are used in furnance windows and electrical appliances.  powdered mica is used as a filters for rubbers plastics and insulation boards
  24. 24. CLAY • Produced by weatering and decomposition of ignious rocks. • Eg- china clay Al2(OH)4Si2O5,.e kaoline has sheet structure sheets are hald by OH bridges. • Used in making chinaware, fire bricks etc • At 900°C clay forms multite Al6SiO2O13. this has glassy appearance.
  25. 25. FULLER’S EARTH • It is montmorillonite in which principle exchangable ion is Ca+2. • Ii has strong absorbtive power and cation exchange properties. • Used as adsorbent and cation exchanger.
  26. 26. ZEOLITES • is a class of hydrated aluminosilicates found in certain volcanic rocks. • Once upon a time, geologists thought these minerals were interesting because they consist of large cage-like structures with open channelways. • Today, these materials are highly valued for their applications.
  27. 27. • Zeolites have a porous structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+ and others. These positive ions are rather loosely held and can readily be exchanged for others in a contact solution. • An example mineral formula is: Na2Al2Si3O10·2H2O, the formula for natrolite.
  28. 28. • The name 'zeolite' is said to have its origin in the two Greek words zeo and lithos which mean 'to boil' and 'a stone'. • The phenomena of melting and boiling at the same time is a novel property. • The name 'zeolite' was first used by the Swedish mineralogist Axel Fredrik Cronsted , the first recognized mineral zeolite, which was discovered in 1756.
  29. 29. • Zeolites are the aluminosilicate members of the family of microporous solids known as "molecular sieves." • The term molecular sieve refers to a particular property of these materials, i.e., the ability to selectively sort molecules based primarily on a size exclusion process. • At present over 150 synthetic zeolites & zeotypes and 40 natural zeolites are known. Synthesis of zeolite is a very active field of study
  30. 30. • industrially important zeolites are produced synthetically. • Typical procedures heating aqueous solutions of alumina and silica with sodium hydroxide. • Equivalent reagents include sodium aluminate and sodium silicate. • Further variations include changes in the cations to include quaternary ammonium cations.
  31. 31. APPLICATIONS • there are many different kinds of zeolites, each with a definite structure and associate with it are unique properties. • In terms of applications, we are assuming zeolites as porous aluminosilicates with large tunnels and cages for a fluid (gas and liquid) to pass through. • The applications are based on the interactions between the fluid phase and the atoms or ions of the zeolites.
  32. 32. IN GENERAL TERMS, ZEOLITES HAVE MANY APPLICATIONS: • As selective and strong adsorbers: remove toxic material, selective concentrate a particular chemical, as Molecular Sieve. • As selective ion exchangers: for example used in water softener. • Superb solid acid catalysts, when the cations are protons H+.
  33. 33. • As catalysts, their environmental advantages include decreased corrosion, improved handling, decreased environmentally toxic waste and minimal undesirable byprducts. • As builder a material that enhance or protecting the cleaning power of a detergent. • Sodium aluminosilicate is an ion exchange builder often used in lundary detergent as a builder. • A builder inactive the hardness of water by either keeping calcium ions in solution, by precipitation, or by ion exchange.
  34. 34. APPLICATIONS OF SILICATES Microchips • Unique properties of silicates include the ability to conduct electricity, produce a high-frequency vibration and provide thermal insulation. • Silicon is the central component of silicates. • It is a very hard crystal that can be cut to minuscule sizes, and it conducts electricity. • It is because of these characteristics that silicon is the perfect material to make microchips, which run every computer, cell phone and gaming device.
  35. 35. QUARTZ CRYSTALS • Quartz crystals are another silicate with a unique ability to produce a rhythmic high-frequency vibration. • For this reason, these crystals are used to make oscillators used in watches, radios and pressure gages.
  36. 36. Glass • Silicates are also used to make glass and ceramics. • To do so, hard, formless material like sand or ceramic clay is heated to high temperatures, turning it into malleable material that can be formed to make drinking glasses,
  37. 37. Ceramics • Silicate ceramics have clearly defined thermal properties and, as such, are particularly useful for advanced engineering and technology. • For example, silicate ceramic tiles are used on the space shuttle to shield it from the extreme temperatures of the outer atmosphere.
  38. 38. High and Low Technology • Silicates are the most abundant mineral class on Earth. • In general, they are hard and cut easily to micro pieces, produce a rhythmic high-frequency vibration, and provide thermal insulation properties. • These unique characteristics make them highly useful for myriad high- and low-tech products, from microchips to watches
  39. 39. thank you