slide1 l.
Skip this Video
Loading SlideShow in 5 Seconds..
Contents PowerPoint Presentation
Download Presentation

Loading in 2 Seconds...

play fullscreen
1 / 23

Contents - PowerPoint PPT Presentation

  • Uploaded on

Corrosion of Inorganic Non-Metallic Materials part 2 Corrosion of ceramics Enamels Corrosion of concrete Ale š Helebrant Department of Glass and Ceramics I CT Prague , Czech Republic Contents Main categories of ceramics Corrosion of refractories in melts

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Corrosion of Inorganic Non-Metallic Materialspart 2 Corrosion of ceramicsEnamelsCorrosion of concreteAleš HelebrantDepartment of Glass and Ceramics ICT Prague, Czech

Corrosion of Materials Course

  • Main categories of ceramics
  • Corrosion of refractories in melts
  • Corrosion of refractories in furnace atmosphere
  • Corrosion of non/oxide ceramics
  • Protection of metals by enamels
  • Corrosion of concrete

Corrosion of Materials Course

  • Porcelain, chinaware
  • Pottery
  • Bricks, roof tiles, tiles, sanitary ceramics
  • Advanced (engineering) ceramics - Al2O3, ZrO2, UO2
  • Refractories
  • Non-oxide ceramics (nitrides, carbides)

Corrosion of Materials Course

  • Polycrystalline material
  • Usually prepared by high-temperature processes
  • typical HT reaction kaolinite – mullite
  • Al2O3.2SiO2.2H2O3 Al2O3.2SiO2 + SiO2 + H2O
  • sintering process

Corrosion of Materials Course

ceramics microstructure
Ceramics - microstructure

Corrosion of Materials Course

main types of r efractories
Main types of refractories
  • silica r.
  • fireclay r. (grog, chamotte)
  • corundum r.
  • magnesite r.
  • chrome-magnesite r.
  • fusion-cast
  • refractoriness – technical property

refractoriness test

tip touching support (3-5°C.min-1)

Corrosion of Materials Course

refractories composition properties
Refractories – composition, properties
  • silica r. (dinas)(refractoriness 1710-1750°C)
    • >93% silica quartz, tridymite, cristobalite, glass
  • fireclay r. (grog, chamotte) (1600-1750°C)
    • 15-46% Al2O3 - SiO2, mullite 3Al2O3.2SiO2
  • corundum (1850-2000°C)
    • a-Al2O3
  • magnesite r. (>2000°C)
    • MgO periclase
  • chrome-magnesite r. (1920-2000°C)
    • MgO.Cr2O3
  • fusion-cast corundum/badelleyite r. (no open pores!)
    • a-Al2O3,ZrO2, SiO2 glass phase




Corrosion of Materials Course


Corrosion of refractories in melts





influence of density or surface tension gradient



Corrosion of Materials Course


Testing of corrosion resistance

Corrosion of Materials Course


Corrosion of refractories in atmosphere

  • corrosion leading to mechanical degradation
  • regenerators in gas heated glass melting furnaces – preheating of gas by products of combustion
  • 3Al2O3.2SiO2 + Na2O  Na2O.Al2O3.2SiO2 + 2Al2O3
  • nepheline
  • 3(Na2O.Al2O3.2SiO2) + 2Na2O + 2SO3 5Na2O.3Al2O3.6SiO2.2SO3
  • noselite
  • mullit  nepheline  noselite = volume expansion  mechanical stress
  • similar effect - changing oxidation/reduction atmosphere
  • MgO.Fe2O3and MgO-FeO or oxidation of FeO.Cr2O3and FeO.Fe2O3

Corrosion of Materials Course


Corrosion of non - oxide ceramics

active or pasive mechanism

pasive – high pO2, lower T

Si3N4(s) + 3O2 3SiO2(s) + 2N2

controlled by diffusion

active – low pO2, higher T

2Si3N4(s) + 3O2 6SiO(g) + 4N2

controlled by chemical reaction






Corrosion of Materials Course

  • glassy layers on metals (glazes on ceramics)
    • protecting metals
    • improving appearance
  • mostly on Fe - steel sheets, cast iron (low content of C in the form of free cementite Fe3C)
  • other applications
    • Al – building industry
    • Cu, Ag, Au, Pt - jewellery
    • Ti - biomaterials

Corrosion of Materials Course

  • Main criteria for enamelling
    • similar thermal expansion coefficient
    • adhesion (physical, chemical)
    • wettability of metal by enamelling suspension

Three steps of enamelling

  • the manufacture of enamel frits
  • treatment of the metal materials
  • preparation of enamelling slips (suspensions) and the enamelling itself

Corrosion of Materials Course

enamels 3 main steps
Enamels - 3 main steps

1) the manufacture of enamel frits

  • glass melting (1000-1400°C) in gas fired furnaces
  • quenching in water  granulation
  • (rotating cylinders  glass ribbon crushed into scales)
  • low silica glasses (about 50-47%), B2O3 (16-11), Al2O3 (7) Na2O+K2O (20-15) fluorides (6-20) different composition for ground and cover layers
  • other components 0.5% CoO (ground), SnO2 in mill (cover)
  • TiO2 enamels – nucleation (anatase)  opacity, thinner layer

Corrosion of Materials Course

enamels 3 main steps15
Enamels - 3 main steps

2) treatment of the metal materials

  • degreasing (trichlorethylene or alkaline solutions
  • or anneling at approx 750°C – burning off organic substances
  • removing iron oxides from the metal surface
    • cold bath 5-20% HCl
    • or 6-17% H2SO4 at 50-70°C
    • inhibitors needed (e.g. phenols) – Fe dissolution without them faster then oxides dissolution

Corrosion of Materials Course

enamels 3 main steps16
Enamels - 3 main steps

3) preparation of enamelling slips and the enamelling itself

  • frit is ground in ball mills (<0.1 mm) (in wet or dry process)
  • adding other ingredients during wet process
    • quartz, MgO etc. – adjusting the firing interval
    • colorants or opacifiers
    • NaNO2 for preventing the metal from rusting
    • clays and electrolytes to adjust rheological properties of the slip
  • dipping or pouring, electrostatic wet spraying
  • dry process for large cast-iron objects – application of dry powdered frit onto a preheated product
  • drying, firing (780-900°C)

Corrosion of Materials Course


Special enamels

  • acid-resitant for food or pharmaceutical industry (higher content of SiO2 and ZrO2, lower of alkaline oxides
  • non-alkaline enamels for engines – resistant to T changing
  • enamels for Al – low firing temperatures (550°C) – higher content of PbO


  • in organic acids – enamels for household or food industry
  • in mineral acids – enamels for technical reasons

General chemical durability of enamels and corrosion mechanisms – same as for glass

Corrosion of Materials Course

corrosion of concrete
Corrosion of concrete
  • Concrete = material prepared by chemical reaction between inorganic binder (cement) and water
  • other components – gravel aggregate (stones), quartz...
  • corrosion of concrete – corrosion of binder
  • cement – fine grain hydraulic binder
  • Portland cement – mixture of Ca silicates and alumosilicates

Corrosion of Materials Course

corrosion of concrete19
Corrosion of concrete

Manufacture of cement

  • raw materials CaCO3, clays, bauxit...
  • firing in rotary cement kilns (1400°C)  clinker  milling (particles <0.1 mm)
  • theoretical clinker composition: C3S, C2S, C3A, C4AF

Reaction cement + water

  • hydrosilicates CSH phase (near to tobermorite) main connecting gel phase
  • other phases Ca(OH)2, open and closed pores

Corrosion of Materials Course

corrosion of concrete20
Corrosion of concrete

3 basic groups of concrete corrosion

  • dissolution and leaching
  • corrosion with chemical reaction – soluble products
  • corrosion with chemical reaction – insoluble products

Corrosion of Materials Course

corrosion of concrete21
Corrosion of concrete
  • dissolution and leaching
  • Ca(OH)2 dissolution
  • increase of porosity, increase of contact surface with corrosive environment
  • decrease of pH in concrete – dissolution of CSH phase + influence of Fe corrosion in concrete
  • Ca, (Na, K) sulphates and carbonates on the concrete surface
  • in “soft“ waters
  • “hard“(earthy) waters - densifying of concrete

Ca(OH)2 + Ca(HCO3)2 = 2CaCO3 + H2O

Corrosion of Materials Course

corrosion of concrete22
Corrosion of concrete
  • corrosion with chemical reaction – soluble products
  • dissolution in acid solutions: pH<6 dissolution of all cement phases – CSH, Ca(OH)2, CaCO3
    • treatment – decrease porosity, protective layers (water glass, pure cement mortar)
  • corrosion by ammonium salts
  • Ca(OH)2 + 2NH4 = 2NH3 + CaCl2 + 2H2O

Corrosion of Materials Course

corrosion of concrete23
Corrosion of concrete
  • corrosion with chemical reaction – insoluble products
  • sulphate corrosion – most dangerous
  • product ettringite 3CaO.Al2O3.3CaSO4.32H2O
  • volume expansion (400%) increase  mechanical degradation
  • seawater, waste waters


    • low content of aluminates
    • active silica in cements – reaction with Ca(OH)2 to silicates – no Ca2+ for ettringite

Corrosion of Materials Course