Chemical properties of
glass, ceramics, and
refractories
Ing. Milena Pavlíková, Ph.D.
K123, D1045
224 354 688, [email protected]
tpm.fsv.cvut.cz
Overview
Terminology
Silicates and aluminates
Glass
Ceramics
Refractories
Technicals
„
Polymorfism
„
Modification
„
Glass
„
Sintering
„
Rheology
„
Ceramics
„
Refractories
Aluminates and silicates
{
Silica dioxide SiO2
{
Aluminium oxide Al2O3
Silica dioxide
{
{
{
The chemical compound silicon dioxide, also known as silica or silox (from the
Latin "silex"), is an oxide of silicon, chemical formula SiO2.
Silica is the most commonly found in nature as sand or quartz, as well as in the
cell walls of diatoms.
Sources: crystalline as a quartz, tridymit a crystobalit
z Crystalline:
{
Mountain crystal, rock crystal – pure silica glass
z
{
quartz sands
z
{
Ceramics, cement, sand filters
quartzite
z
{
Optics, chemical dishes
Milling stones and support if milling apparatus
quartzy sandstones
z
glass production
Silica dioxide
z
Amorphous (vitreous silica):
{ Diatomaceous
z Thermal
earth (soil)
and sound insulator, filtering materila
{ opal
{ Synthetic
gels
z Grouting,
z
z
z
injection, facade coating
Semiprecious stones
rocks – quarzite, sandstone, granite, gneiss
Gravel (ballast) and sand soils
In the vast majority of silicates, including silicate minerals, the Si atom
shows tetrahedral coordination by 4 oxygens. In different minerals the
tetrahedra show different degrees of polymerization: they occur singly,
joined together in pairs, in larger finite clusters including rings, in
chains, double chains, sheets, and three-dimensional frameworks. The
minerals are classified into groups based on these anion structures.
a)
isolated
tetrahedrons
b) holms – b,c, d, e
c) linear– f, g
d) 3D – h, i
Nesosilicates (lone tetrahedron) - [SiO4]4−, eg olivine.
Sorosilicates (double tetrahedra) - [Si2O7]6−, eg
epidote.
Cyclosilicates (rings) - [SinO3n]2n−, eg tourmaline
group.
Inosilicates (single chain) - [SinO3n]2n−, eg pyroxene
group.
Inosilicates(double chain) - [Si4nO11n]6n−, eg
amphibole group.
Phyllosilicates (sheets) - [Si2nO5n]2n−, eg micas and
clays.
Tectosilicates (3D framework) - [AlxSiyO2(x+y)]x−, eg
quartz, feldspars, zeolites.
Phase modifications
- guartz
- guartz
melt
Volume changes during polymorhic transformations of SiO2
Volume change (%)
transformation
- quartz
- quartz
- quartz
- quartz
Volume change
Volume changes during polymorhic transformations of SiO2
Properties of silica dioxide
{
good abrasion resistance
{
electrical insulation
{
high thermal stability
{
insoluble in all acids with the exception of
hydrogen fluoride (HF).
{
slowly soluble in hot alkaline solutions
{
UV permeable
Compounds of silicon
{
{
Silicic acid, [SiOx(OH)4-2x]n , H4SiO4),
z
formed by acidification of silicate salts (such as sodium silicate) in
aqueous solution
z
when heated they lose water to form silica gel (M=6000 g/mol) - an
active form of silicon dioxide
Silicones [R2SiO]n
z
largely inert compounds with a wide variety of forms and uses
z
typically heat-resistant, nonstick and rubberlike
z
frequently used in cookware, medical applications, sealants, lubricants
and insulation
hypothetical silicone group, such species do not exist
Compounds of silicon
{
{
{
{
{
Silicate - an anion in which one or more central silicon atoms are surrounded by electronegative ligands
z
hexafluorosilicate ("fluorosilicate"), [SiF6]2−
z
silicon with oxygen as the ligand
Silicide - silicon with more electropositive elements
z
Examples:
{ sodium silicide, Na2Si
{ magnesium silicide, Mg2Si
Silicon carbide, SiC
{ used as an abrasive (trademark carborundum) semiconductor and diamond simulant of gem quality
Silicon nitride, Si3N4
{ ceramics, which have relatively good shock resistance
{ insulator layer to electrically isolate different structures or as an etch mask in bulk micromachining
{
used as a dielectric between polysilicon layers in capacitors in analog chips
Silane, SiH4
z
used as:
{ coupling agents to adhere glass fibers to a polymer matrix, stabilizing the composite material
{ water repellents, masonry protection
Aluminium
{
the most abundant metal in the Earth's crust, and the third most
abundant element therein, after oxygen and silicon. It makes up
about 8% by weight of the Earth’s solid surface.
{
too reactive chemically to occur in nature as the free metal
{
is found combined in over 270 different minerals
{
chief source of aluminium - bauxite ore
{
silvery white and ductile
{
nontoxic, nonmagnetic, and nonsparking
{
good thermal and electrical conductor
Aluminium oxide, Al2O3
{
{
{
{
{
also alumina or aloxite
electrical insulator but has a relatively high thermal conductivity
resistance to weathering
produced by the Bayer process from bauxite
Sources:
{
{
{
crystalline form - corundum or α-aluminium oxide (α-Al2O3) - rubies
and sapphires are gem-quality forms
main component of bauxite
Used:
{
{
{
{
in the production of aluminium metal
as an abrasive due to its hardness
as a refractory material due to its high melting point
industrial diamond
Coumpounds of aluminium
{
{
{
{
{
{
{
Aluminium ammonium sulfate ([Al(NH4)](SO4)2) - is used as a mordant, in
water purification and sewage treatment, in paper production, as a food additive,
and in leather tanning
Aluminium borate (Al2O3 B2O3) - used in the production of glass and ceramic.
Aluminium chloride (AlCl3) - used in paint manufacturing, in antiperspirants, in
petroleum refining and in the production of synthetic rubber.
Aluminium fluorosilicate (Al2(SiF6)3) - used in the production of synthetic
gemstones, glass and ceramic.
Aluminium hydroxide (Al(OH)3) – used as an antacid, as a mordant, in water
purification, in the manufacture of glass and ceramic and in the waterproofing of
fabrics.
Aluminium phosphate (AlPO4) - used in the manufacture: of glass and ceramic,
pulp and paper products, cosmetics, paints and varnishes and in making dental
cement.
Aluminium sulfate (Al2(SO4)3) - used in the manufacture of paper, as a mordant,
in a fire extinguisher, in water purification and sewage treatment, as a food
additive, in fireproofing, and in leather tanning.
Glass
„
an inorganic product of fusion which has been cooled to yield an amorphism of
rigid condition without crystallizing
„
In the scientific sense the term glass is often extended to all amorphous solids.
„
The optical and physical properties of glass make it suitable for applications
such as flat glass, container glass, optics and optoelectronics material,
laboratory equipment, thermal insulator (glass wool), reinforcement fiber
(glass-reinforced plastic, glass fiber reinforced concrete), and art.
„
Properties:
„
hard, brittle, transparent solid
„
prevalent due to its transparency to visible light
„
brittle at normal temperature, at 500-1000°C plastic and workability, over 1400°C liquid
„
resistance to weathering
„
electric and heat insulator
Glass structure
[Gedeon, Macháček]
Chemical resistance of glass
„
„
„
insoluble in water and all acids with the exception of hydrogen
fluoride (HF).
slowly soluble in hot alkaline solutions
possibility of glass leaching (alkalies, Pb)
Production
„
„
Glass ingredients:
„ fused quartz
„ sodium carbonate (Na2CO3), which lowers the melting point to about 1500
°C (2700 °F) in soda-lime glass;
z "soda" refers to the original source of sodium carbonate in the soda ash
obtained from certain plants
z lime (calcium oxide (CaO), generally obtained from limestone), some
magnesium oxide (MgO) and aluminium oxide are added to provide for
a better chemical durability
„ recycled glass ("cullet")
Contemporary glass production in glass batch preparation:
„ mixing the raw materials → batch
„ transportation to the furnace (gas fired units, electric melters, pot furnaces or
day tanks)
„ melting at 1000-1200°C
„ homogenization and refining (removal of bubbles) at 1400°C
„ annealing for the removal of stresses at 900-1200°C
„ surface treatment
Glass forming techniques
Commercial
Float glass process · Blowing and pressing (containers) ·
techniques
Extrusion / Drawing (fibers, glasswool) · Drawing (optical
fibers) · Overflow downdraw method · Pressing · Casting ·
Cutting · Flame polishing · Diamond turning · Rolling
Artistic and
Beadmaking · Blowing · Blown plate · Broad sheet ·
historic
Caneworking · Crown glass · Cylinder blown sheet ·
techniques
Etching · Fourcault process · Fusing · Lampworking ·
Machine drawn cylinder sheet · Millefiori · Polished plate ·
Slumping · Stained glass fusing · Stained glass production
In addition, glass can be formed by other techniques that are common for
ceramics or metals, including polishing, sintering, sawing, grinding, drilling,
cutting, and bending. For application to glass these techniques may need to
be adjusted.
Float glass process
Drawing and rolling
Blowing and pressing
Main industrial glasses
„
Silica glass:
z
„
Water glass:
z
„
60 SiO2 – 26 PbO – 14 K2O (PbO between 24-36)
3.3 glass (Pyrex, Simax):
z
„
72 SiO2 – 12 CaO – 14 Na2O
Crystal glass:
z
„
70 SiO2 – 30 Na2O (wt.%)
Flat glass, bottles:
z
„
SiO2
80 SiO2 – 15 B2O3 – 5 Na2O
Glass fibres:
z
53 SiO2 – 15 Al2O3 – 16 CaO – 4 MgO – 10 B2O3
Glass types according to the chemical composition
„
Soda-lime glass:
„
„
„
„
„
Borosilicate glass(Pyrex):
„
„
„
„
„
„
„
„
„
much higher index of refraction than normal glass, and consequently much greater "sparkle"
much more difficult to form crystal during manufacturing
Lead crystal typically contains 24–35 percent lead oxide
Chalcogenide glass (sulfur, selenium or tellurium)
„
„
„
„
manufactured by melting naturally occurring quartz crystals of high purity at approximately 2000°C
used to make optical fiber for telecommunications
used as the envelope of halogen lamps
used to make various refractory shapes such as crucibles, trays, shrouds, and rollers for many high temperature thermal processes
including steel making, foundries, and glass manufacture
Lead crystal glass
„
„
having very low coefficient of thermal expansion (~ 3 x 10-6 / C at 20°C), making them resistant to thermal shock
superior durability, chemical and heat resistance
use in chemical laboratory equipment, cookware, lighting, and in certain cases, windows.
Fused quartz and fused silica:
„
„
the most prevalent type of glass
prepared by melting the raw materials, such as soda, lime, silica, alumina, and small quantities of fining agents (e.g., sodium
sulfate, sodium chloride) in a glass furnace at temperatures locally up to 1675°C
Green and brown bottles are obtained from raw materials containing iron oxide. For lowering the price of the raw materials, pure
chemicals are not used, but relatively inexpensive minerals such as trona, sand, and feldspar
used for windowpanes, and glass containers (bottles and jars) for beverages, food, and some commodity items
ideal for incorporation into laser and other active devices
optical discs
sandwiched between dielectric layers
Fluorosilicate glass (FSG)
„
dielectric used in between copper metal layers during silicon integrated circuit fabrication process
„
„
Photochromic glass:
„ embedding of microcrystalline silver halides (usually silver chloride), or
molecules in a glass substrate
„ darken substantially in response to UV light in less than one minute, and then
continue to darken very slightly over the next fifteen minutes
„ Used as eyeglass lens
To control the amount of heat and light that passes through the glass. Three types of glass
designed for this purpose are:
z
z
z
„
Reflective Glass - clear or tinted glass that has a very thin layer of metal or metallic oxide on the
surface. The reflective coating reduces heat gain and glare from the outside while allowing visible
light to enter
Low Emissivity Glass- with very thin metallic coatings that reduce visible light transmission by
about 10 percent compared to uncoated glass, reduces heat loss through windows
Insulating Glass - made from two or more lites of glass separated by a sealed air space. The
metal tube around the perimeter of the insulated unit which seperates the two lites of glass is
called the spacer
Specialty Glass:
„ Mirrors - made from high quality annealed float glass, depositing a layer of
silver on one surface of the glass
„ Spandrel Glass - must be either heat strengthened or fully tempered because the
frit causes the glass to absorb heat
„ Laminated Glass - used as the inboard lite in skylights, varying the thickness and
color, can be used to reduce the transmission of solar energy, control glare, and
screen out ultraviolet radiation
„ Art Glass - opalescent, cathedral or stained glass, usually produced in small
batch operations
„
Fiberglass (fibreglass or glass fibre):
„
material made from extremely fine fibers of glass
„
used as a reinforcing agent for many polymer products;
the resulting composite material, properly known as
fiber-reinforced polymer (FRP) or glass-reinforced
plastic (GRP), is called "fiberglass" in popular usage
„
uses for regular fiber glass - mats, insulation,
reinforcement, sound absorption, heat resistant fabrics,
corrosion resistant fabrics and high strength fabrics
„
the main source of material used by the modern
automobile industry
Sintering
method for making objects from powder, by heating the material
(below its melting point - solid state sintering) until its particles adhere
to each other
traditionally used for manufacturing ceramic objects, and has also
found uses in such fields as powder metallurgy
some ceramic raw materials have a lower affinity for water and a lower
plasticity index than clay, requiring organic additives in the stages
before sintering
sinterisation is associated to a remarkable shrinkage of the material due
to the fact that glass phases flow, once their transition temperature is
reached, and start consolidating the powdery structure and
considerably reducing the porosity of the material
There are two types of sintering: with pressure (also known as hot
pressing), and without pressure.
Rheology
study of the deformation and flow of matter under the influence of an
applied stress, which might be, for example, a shear stress or extensional
stress
rheometry - the experimental characterisation of a material's rheological
behaviour
Theoretical aspects of rheology are:
the relation of the flow/deformation behaviour of material and its internal
structure (e.g. the orientation and elongation of polymer molecules)
the flow/deformation behaviour of materials that cannot be described by
classical fluid mechanics or elasticity
This is also often called Non-Newtonian fluid mechanics in the case of
fluids.
Ceramics
z
Porcelain, chinaware
z
Pottery
z
Bricks, roof tiles, tiles, sanitary ceramics
z
Advanced (engineering) ceramics - Al2O3, ZrO2,
UO2
z
Refractories
z
Non-oxide ceramics (nitrides, carbides)
Ceramics
z
Polycrystalline material
z
Usually prepared by high-temperature processes
z
typical HT reaction kaolinite – mullite
Al2O3.2SiO2.2H2O →3 Al2O3.2SiO2 + SiO2 + H2O
z
sintering process
z
derived from the Greek word κεραμικός (keramos)
z
The term covers inorganic non-metallic materials which are
formed by the action of heat.
z
Raw materials
z
z
z
z
plastic – clays, soils, tills
nonplastic – grog (inert filler) – sand, corund, mullit
addition – alkaline feldspar
Many ceramic materials are hard, porous, and
brittle
Kaolinite
z
Al2Si2O5(OH)4, Aluminum Silicate
Hydroxide
z
White or colored with impurities
z
above 1200°C mullite formation –
Al6Si2O13
z
The most important phase in ceramic
microstructure – high strength,
refractoriness, durability
z
Needlelike shape
z
important to the production of ceramics and
porcelain.
z
used as a filler for paint, rubber and plastics
since it is relatively inert and is long lasting
Types of ceramic materials
z
Structural
z
z
Whitewares
z
z
includes tiles used in the Space Shuttle program, gas burner nozzles,
ballistic protection, nuclear fuel uranium oxide pellets, bio-medical implants,
jet engine turbine blades, and missile nose cones
Refractories
z
z
including tableware, wall tiles, decorative art objects and sanitary ware
Technical (Engineering, Advanced, Special, and in Japan, Fine
Ceramics)
z
z
including bricks, pipes, floor and roof tiles
as kiln linings, gas fire radiants, steel and glass making crucibles
Frequently the raw materials do not include clays.
Structural ceramics
z
z
z
Construction bricks.
Floor and roof tiles.
Sewage pipes
Whiteware ceramics
z
z
Bone china:
z
type of porcelain body first developed in Britain,
z
calcined ox bone (bone ash) - major constituent
z
characterised by high whiteness, translucency and strength
z
Production usually involves a two stage firing where the first, bisque, is without a glaze at 1280 °C
(2336 °F), which gives a translucent product and then glaze, or glost, fired at a lower temperature
below 1080 °C (1976 °F).
Earthenware:
z
common ceramic material, which is used extensively for pottery tableware and decorative objects
z
generic composition is 25% ball clay, 28% kaolin, 32% quartz, and 15% feldspar
z
commonly bisque, or biscuit, fired to temperatures in the range of 1000 and 1150 degrees Celsius
(1800 and 2100 degrees Fahrenheit, and glost fired from 950 to 1050°C (1750 to 1925°F)
z
After firing the body is porous and opaque with colours ranging from white to red depending on the
raw materials used
z
less strong, less tough, and more porous than stoneware - but its low cost and easier working
compensate for these deficiencies.
z
Due to its higher porosity, earthenware must usually be glazed in order to be watertight
Ceramic glaze
z
layer or coating of a vitreous substance
z
fired to fuse to a ceramic object to color, decorate,
strengthen or waterproof it
z
important for earthenware vessels
z
may be applied by dry dusting a dry mixture over the
surface of the clay body
z
Liquid glazes - suspensions of various powdered
minerals, and metal oxides - can be applied by dipping
pieces directly into the glaze, pouring the glaze over
the piece, spraying it onto the piece with an airbrush or
similar tool, with a brush, or with any tool that will
achieve the desired effect
z
z
Porcelain:
z
ceramic material made by heating raw materials, generally including clay in the form of
kaolin, in a kiln to temperatures between 1,200 °C (2,192 °F) and 1,400 °C (2,552 °F)
z
toughness, strength, and translucence of porcelain arise mainly from the formation of
glass and the mineral mullite within the fired body at these high temperatures
z
used to make table, kitchen, sanitary, and decorative wares; objects of fine art; and
tiles. Its high resistance to the passage of electricity makes porcelain an excellent
insulator. It is also used in dentistry to make false teeth, caps and crowns.
Stoneware:
z
category of clay
z
distinguished primarily by its firing and maturation temperature (from about 1200°C to
1315 °C)
z
man-made stone
z
dense, impermeable and hard enough to resist scratching by a steel point
z
coloured grey or brownish because of impurities in the clay used for its manufacture,
and is normally glazed
Technical ceramics
z
Oxides
z
z
z
alumina
zirconia - zirconium dioxide (ZrO2),
z white crystalline oxide of zirconium
z used as a refractory material, in insulation, abrasives,
enamels and ceramic glazes
z high ionic conductivity (and a low electronic conductivity)
makes it one of the most useful electroceramics
Composites
z
z
particulate reinforced
combinations of oxides and non-oxides
z
Non-oxides
z
Carbides - compound of carbon with a more electronegative element
z
z
Borides
z
z
z
generally high melting and are not ionic in nature
exhibit very useful physical properties (high melting and inert, super
conductivity)
Nitrides
z
z
z
z
z
z
z
z
SiC
refractory materials
lubricant BN
cutting materials e.g. silicon nitride, Si3N4
insulators e.g. boron nitride, BN, silicon nitride, Si3N4
semiconductors e.g. gallium nitride, GaN
metal coatings e.g. titanium nitride, TiN
hydrogen storage e.g Lithium nitride, Li3N
Silicides
z
z
inert to aqueous solutions of everything with exception of hydrofluoric acid
react with more aggressive agents, eg. melted potassium hydroxide, or
fluorine and chlorine
Examples of technical ceramics
z
z
z
z
z
z
z
z
z
z
z
z
z
z
Barium titanate (often mixed with strontium titanate) displays ferroelectricity, meaning that its mechanical,
electrical, and thermal responses are coupled to one another and also history-dependent. It is widely used in
electromechanical transducers, ceramic capacitors, and data storage elements. Grain boundary conditions can
create PTC effects in heating elements.
Bismuth strontium calcium copper oxide, a high-temperature superconductor
Boron nitride is structurally isoelectronic to carbon and takes on similar physical forms: a graphite-like one used as
a lubricant, and a diamond-like one used as an abrasive.
Ferrite (Fe3O4), which is ferrimagnetic and is used in the magnetic cores of electrical transformers and magnetic
core memory.
Lead zirconate titanate is another ferroelectric material.
Magnesium diboride (MgB2), which is an unconventional superconductor.
Sialons / Silicon Aluminium Oxynitrides, high strength, high thermal shock / chemical / wear resistance, low
density ceramics used in non-ferrous molten metal handling, weld pins and the chemical industry.
Silicon carbide (SiC), which is used as a susceptor in microwave furnaces, a commonly used abrasive, and as a
refractory material.
Silicon nitride (Si3N4), which is used as an abrasive powder.
Steatite (magnesium silicates) is used as an electrical insulator.
Uranium oxide (UO2), used as fuel in nuclear reactors.
Yttrium barium copper oxide (YBa2Cu3O7-x), another high temperature superconductor.
Zinc oxide (ZnO), which is a semiconductor, and used in the construction of varistors.
Zirconium dioxide (zirconia), which in pure form undergoes many phase changes between room temperature and
practical sintering temperatures, can be chemically "stabilized" in several different forms. Its high oxygen ion
conductivity recommends it for use in fuel cells. In another variant, metastable structures can impart
transformation toughening for mechanical applications; most ceramic knife blades are made of this material.
z
Each one of these classes can develop
unique material properties
z
Manufacturing:
z
Properties are influenced due to
ƒ
Composition and granularity of raw
materials
ƒ
Temperature, time and medium of firing
z
20-200°C drying
z
200-450°C water evaporation
z
450-600 °C metakaolinite formation
z
Above 1000°C mullit formation and
sintering
The general procedure of creating
ceramic objects
z
z
z
z
z
Mixing water, binder, deflocculant, and unfired
ceramic powder to form a slurry
Spray-drying the slurry
Putting the spray dried powder into a mold and
pressing it to form a green body (an unsintered
ceramic item)
Heating the green body at low temperature to burn
off the binder
Sintering at a high temperature to fuse the ceramic
particles together
Furnace, kiln, heater
Chamber furnace (storey)
Circular kiln
Tunnel kiln
Refractories
z
material to withstand temperatures above 1100 °C without
softening
z
must be strong at high temperatures
z
resistant to thermal shock
z
chemically inert
z
have low thermal conductivities and coefficients of expansion
z
Bricks are pre-sintered forms which can hold their shape.
z
Monolithics are loose material which can be formed into complex
shapes, or sprayed into place, and have to be sintered before
use.
Main types of refractories
z
silica r.
fireclay r. (grog, chamotte)
corundum r.
magnesite r.
chrome-magnesite r.
fusion-cast
z
refractoriness – technical property
z
z
z
z
z
refractoriness test
tip touching support (3-5°C.min-1)
Refractories – composition,
properties
z
silica r. (dinas) (refractoriness 1710-1750°C)
z
z
Fireclay r. (grog, chamotte) (1600-1750°C)
z
z
MgO periclase
chrome-magnesite r. (1920-2000°C)
z
z
a-Al2O3
magnesite r. (>2000°C)
z
z
15-46% Al2O3 - SiO2, mullite 3Al2O3.2SiO2
corundum (1850-2000°C)
z
z
>93% silica quartz, tridymite, cristobalite, glass
MgO.Cr2O3
fusion-cast corundum/badelleyite r. (no open pores!)
z
a-Al2O3, ZrO2, SiO2 glass phase
acid
neutral
basic
Literatura
http://en.wikipedia.org/wiki/Glass
http://www.azom.com/details.asp?ArticleID=1114
http://en.wikipedia.org/wiki/Brick
http://en.wikipedia.org/wiki/Tile
http://en.wikipedia.org/wiki/Pipe_%28material%29
http://en.wikipedia.org/wiki/Silicon_carbide