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 Institute of Mineral EngineeringDepartment of Ceramics and Refractory MaterialsUniv.-Prof. Dr. rer. nat. R. Telle

Testing of Refractories For more than 45 years the Aachen Institute of Mineral Engineering has been successful in

testing and developing refractory materials. During that time requirements for these materials

increased due to both higher processing temperatures and tightening up production efficiency

demands. This guided into optimized conventional refractory products which can only be

achieved by applying high grade, oxide as well as non-oxide, synthetic raw materials and

innovating production technologies. Major impulses in developing high performance materials

have been initiated by process innovations out of steel industries, waste incinerators dispose

and coal gasification.

In order to meet with this specific requirements new test methods have been developed to

assess the suitability and reliability of these materials under extreme operating conditions.

The Aachen Institute of Mineral Engineering intensively participated in development and

approvement of new testing procedures being involved in various expert organisations

and boards. So, tests after DIN, EN-DIN, ASTM, AFNOR and BS -standards, as well as

non-standard tests which simulate special operating conditions are available.

Range of application of refractory materials  

Iron making industry• blast furnaces

• hot blast stoves

• blast tyeres

• hot blast main systems

• blast furnace runners 

Steel making industry • pig iron transport vessels

• pig iron collector vessels

• oxygen steel converter 

• electric arc furnaces

• steel casting laddles 

• treatment laddle for secondary metallurgical

 processes

• steel degassing vessels

• refractory parts in continuous casting systems

• refractories for heating and heat treatment

furnaces: soaking pits, pusher type furnaces,

rotary hearth furnaces, walking beam furnaces,

walking hearth furnaces, roller-hearth furnaces 

Iron- and steel-casting foundry • cold and hot blast cupolas

• crucible and channel induction furnaces

• transport and casting laddles

• nozzles 

Coke ovens

Metallurgical treatment and casting

of nonferrous metals• anode-baking furnaces

• melting-holding furnaces for Al

• refractory parts in continuous casting systemsfor Al

• reverberatory furnaces for Cu

• Pierce-Smith-converters

• anode-drum furnaces for Cu

• slag-cleaning furnaces for Cu

• Cu-melting furnaces

Boilers and power plants, fireboxes • municipal incinerators

• special refuse incinerators

• melting chamber boilers

• combustion chambers, burner rigs

Coal gasification plants• refractories for hot gas purifyers

Ceramic and enamelling industry• tunnel kilns

• bugie hearth furnaces

• enamelling kilns

• roller furnaces 

Cement and alkaline earths industry• rotary kilns for cement, dolomite and magnesite

•shaft kilns

Glass industry 

• glass melting tanks

• regenerators for glass melting tanks

• electric furnaces 

Refractory heat-insulation materials 

Chemical industry• combustion chambers

• hot gas generators

• rotary kilns

• liquid waste incinerators

• sulfur incinerators

• crackers

• reformers

• carbon black generators

•

petrol chemistry plants

Refractory and heat resistant materials  

Shaped refractory products 

SiO2-rich products --------------------

fireclay products ----------------------

high alumina products ---------------

products on base of sesquioxides --

-

products on base of zirconium -----

- silicate and zirconia

forsterite bricks -----------------------

-

basic bricks -----------------------------

silica bricks, fused silica products

commercial (groups A 25 - A 40);

silica-rich, acid-resistant, graphite-containing, SiC-

and cordierite-containing, kaoline-products;

groups I and IIalumina-rich fireclay, sillimanite, andalusite, cyanite,

mullite (sintered and fused), corundum (calcined

alumina, sintered and fused alumina), bauxite

products

alumina, chromium oxide

ZrO2, ZrSiO4 

forsterite, olivine

magnesia, magnesia-chrome-, chrome-magnesia,

magnesia-spinel, chromite, dolomite-magnesia

products

spinel refractories -----------------------

chromium oxide based refractor -----

pitch-/tar-impregnated products -----

resin- and pitch-bonded products ----

fusion cast products

graphite containing bricks

nonoxide refractory products ---------

MgAl2O4-, picrochromite-refractories

Cr2O3 

based on periclase, dolomite corundum

with and without the addition of graphite resp. antioxidants; magnesia-

graphite and dolomite-graphite bricks

based on mullite, corundum, periclase,

spinel, baddeleyite/corundum, sesqui-

oxides (Al2O3, Cr2O3, Fe2O3)

based on SiC: silicate, oxidic, Si3N4- or

BN-bonded. Si3N4-products 

Unshaped refractory materials Refractory insulating materials

For monolithic linings, repairs, prefabricated refractory parts, as laying and jointing

materials, plastic mixes, ramming, gunning, slinging and fritting mixes; refractory castables.

Unshaped refractory and semi-refractory materials for laying, jointing and sealing shaped and

unshaped products: mortars, mastics, adhesives

bonding: hydraulic, ceramic, chemical, organic

grogs: oxidic: SiO2, Al2O3, Cr2O3, MgO, CaO; non-oxidic: SiC, Si3N4;C

refractory castables : regular castables (RC), liquefied (DCC), medium cement (MCC), low

cement (LCC), ultra low cement (ULCC), no-cement (NCC) 

• insulating materials up to 1100°C -----

• refractory lightweight bricks up to ----

1900°C

• ceramic fibre products up to 1800°C -- 

based on perlite, vermiculite, expanded

clay, calcium silicate

based on silica, fireclay, sillimanite,

bubble alumina

alumosilicate fibres, Al2O3 and ZrO2-

based fibres, with or without organic

and inorganic additives 

Testing of Refractories and Refractoring

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  Microstructural Characterisation of Raw Materials and Refractory Products

Mechanical and Thermo-mechanical Properties

Corrosion Behaviour(Reaction with gases, volatile dusts, ashes, slag, metallicmelts, vapor and acids) 

Chemical analysis• x-ray fluorescent analysis

• atomic absorption spectrometry (AAS)

• ion chromatography

• infrared spectrometry

• wet chemistry

• coulometry

X-ray diffraction analysis(qualitative and quantitative)

• powder diffraction

• low-angle diffraction

• high-temperature diffractometry up to 2000°C

Light microscopy 

• polarization microscopy in reflected light

• fluorescence microscopy in reflected light

• polarization microscopy in transmitted light

• wetting microscopy up to 1700°C 

Scanning electron microscopy• including x-ray microanalysis:

- energy-dispersive (EDX, semi quantitative)

- wavelength-dispersive (WDX)

Transmission electron microscopy (TEM, 300 kV) • high resolution, EDX, STEM

• sample heater up to 1200°C

Analysis of macrostructure

of mono- and polyphase polycrystalline structures

Determination of density and porosity• true density (pycnometer)

• bulk density, shaped or granular materials (fluid displacement and

measure method)

• open porosity (permeable and impermeable)

• true porosity (calculated from density and bulk density)

• closed pores (difference between true and open porosity)

• permeability to gases (open permeable pores), gas diffusion

• pore size distribution

- mercury displacement method

- water-air displacement method

- systems for the analysis of microstructures

Specific surface• single point of adsorption processing (areameter)

• gas adsorption, BET-method

• air penetration

Grain size analysis• laser granulometry

• sedimentation analysis

• air separator

• screen analysis, particle size analysis

Strength at ambient temperatures• crushing strength

• MOR: transverse strength (3- and 4-point bending)

• Weibull statistics

• tensile cleavage strength

• static E-modulus

• Young´s modulus

- Grindo Sonic number

- determination of first grade longitudinal resonance

frequency (according to Kottas)

• mechanical fracture behaviour

- K IC-factor (fracture toughness)

- determination of work of fracture

• determination of hardness of surfaces

• abrasion resistance

- Böhme grinding machine

- sand blasting method (by impact of quartz-, corundum-

or SiC- grains) 

High Temperature Strength• hot crushing strength

• hot transverse strength HMOR (3- and 4-point bending)

• tensile cleavage strength

• hot abrasion resistance

- by grinding

- by sand blasting impact

Stress/deformation behaviour at high temperatures

• thermal expansion (dilatometry)

constant heating rate, without stress, dilatation as a function

of temperature

•refractoriness under loadconstant heating rate, constant stress, dilatation as a

function of temperature

• creep in compression at constant temperature

heated at a constant rate and given stress up to required

test temperature, dilatation as a function of both

temperature and time

• creep under transverse/flexural stress

constant temperature and stress, compliance as a function of 

temperature and time

• permanent change in dimensions (shrinkage and expansion)

after thermal impact, with and without load

Refractoriness- determination of thermal softening behaviour by

pyrometric cone equivalent

- melting behaviour determined by hot stage microscope up to

(1700°C)

Thermal properties

thermal conductivity: hot wire method up to 1300°C- parallel- and cross-wire method

- 2 devices 

Carbon desintegration(reaction in CO-atmosphere at 500°C / 200 h)

Carbon desintegration(reaction in CH4-atmosphere at 900°C / 200 h)

SiC-materials(reaction in steam-saturated atmosphere, up to 1250°C /

500 h)

SiC-materials(reaction in CO- and CO / hydrogenous atmosphere, up

to 1500°C)

Reaction of alkalies in vapor with

refractories up to 1100°C

Corrosion by melt or slag• cup test  • modified cup test

• stirring method  ("tumbling method")

• rod test  • rotary kiln test

• induction furnace test

Resistance to acids

Wetting behaviourrefractory and ceramic materials:

metallic melts and oxide slags:

sessile drop method

Thermal shock resistance

• - air quenching method

- water quenching method• thermal shock between two high temperatures

(array of practical conditions):

maximum quenching temperature: 1550°C

minimum quenching temperature: 450°C

• Peeling test

• determination of crack formation depending on

heating rate by measuring thermal expansion

Thermal Analysis

for

• thermal decomposion reactions, vapourisation

• solid reactions

• sintering

• melting and softening behaviour

• forming of new phases and alternating modifications

• thermal effects

- differential thermo-analysis (DTA)

- differential calorimetry (DSC)

- thermo gravimetry (TG, DTG)

Tests on Specific Refractory Product Types and Raw MaterialsUnshaped Products Chemical Bonded Basic Bricks Ceramic Fibre Materials

chemical analysis

distribution of grain size

workability, consistency

sample preparation

- refractory castables vibrating, tamping, casting with and

without vibration

- light refractory castables vibrating, poking

- ramming mixes ramming, pneumatic tamping

- plastic mixes ramming, pneumatic tamping- gunning mixes pneumatic or mechanical gunning

Tests on prefabricated refractory parts

Properties at ambient temperature• bulk density

• transverse strength

• crushing strength

Properties during or after firing• bulk density, porosity

• permanent linear change

• cold transverse strength

• hot transverse strength

• softening under load

• creep in compression

• sticking ability (refractory mortars)

density, bulk density, permeability to gases

cold crushing strength after preliminary firing

determination of interzonar strength

determination of volatile contents and residual carbon

contents

Raw Materials

determination of suitability of quartz sands andgravels for refractory production according to §3, 4

"Bundesberggesetz" (Bberg G, "german federal

mining law")

•  pyrometric cone equivalent

•  determination of quartz and quartzite contents by x-ray

diffraction and picking methods

determination of suitability of clay and feldspar for

proceramic production, not to be considered as tile

products according to §3, 4 of Bberg G•  pyrometric cone equivalent

•  resistance to acids

diameter of ceramic fibres - light microscopic methods

- SEM

shot content

bulk density, thickness

permanent change in dimensions on heating

classification temperature

resilience and compressibilitytensile strength

Emission measurements of natural and

man made fibres

Measurements of synthetic fibre dusts

emission in production plants 

•  Measurements of inorganic fibrous

particles in ambient and industrial air

according to VDI 3492, 1 guideline by

scanning electron microscopy

•  Investigations characterizing respireable

fibre dusts - application of light microscopy

in accordance to ZH1/120.31 

Department of Ceramics and Refractory Materials Please contact:

Mauerstrasse 5, D-52064 Aachenphone: +49-(0)241-8094968fax: +49-(0)241-8092226www.ghi.rwth-aachen.de

Dr.-Ing. Th. Tonnesenphone: +49-(0)241-8094988fax: +49-(0)241-8092226e-mail: tonnesen@ghi.rwth-aachen.de

Institute of Mineral Engineering