Refractory Materials

Refractory materials must be chemically and physically stable at high temperatures. Depending on the operating environment, they need to be resistant to thermal shock, be chemically inert, and/or have specific ranges of thermal conductivity and of the coefficient of thermal expansion.

• Refractory Bricks
• Fire Bricks
• Shape Bricks
• Refractory Castables
• Refractory Mortars
• Insulating Bricks
• Insulating Castables
• Ceramic Blanket
• Calcium Silicate Blocks
• Acid Proof Bricks

Insulation materials

These fall into two broad categories: organic foams; and inorganic materials. The organic foams include polystyrene, polyurethane, phenolic foam, polyethylene foam etc. The inorganic material include mineral wool, calcium silicate, cellular glass, microporous silica, magnesia, ceramic fibre, vermiculite and perlite.

Types of refractory

Acidic refractories
These are used in areas where slag and atmosphere are acidic. They are stable to acids but attacked by alkalis. The main raw materials belongs to the RO2 group, ex- silica (SiO₂), zirconia (ZrO₂), etc.

Neutral refractories
These are used in areas where slags and atmosphere are either acidic or basic and are chemically stable to both acids and bases. The main raw materials belongs to, but not confined to, R₂O₃ group. The common examples of these materials are alumina (Al₂O₃), chromia (Cr₂O₃) and carbon.

Basic refractories
These are used on areas where slags and atmosphere are basic, stable to alkaline materials but reacts with acids. The main raw materials belong to the RO group to which magnesia (MgO) is a very common example. Other examples include dolomite and chrome-magnesia.

Types of tests

	Modulus of elasticity, rigidity and Poisson’s ratio
	Abrasion resistance
	Density and porosity
	Pyrometric Cone Equivalent (PCE)
	Particle Size Determination (PSD)
	Cold crushing strength
	Modulus of rupture

Chemical

	XRF (X-Ray Fluorescence)o
	XRD (X-Ray Diffraction)

Thermomechanical

	Compressive stress/strain up to 1550°C
	Abrasion resistance
	Flexural stress/strain up to 1550°C
	Thermal Conductivity
	Thermal shock resistance
	Creep in compression up to 1550°C
	Thermal expansion up to 1600°C
	Specific Heat
	Refractoriness under Load (RUL)
	Permanent Linear Change (PLC)

Microstructural Evaluation

	Optical microscopy
	SEM/EDA (Scanning Electron Microscopy/Energy Dispersive Analysis).

Creep Test
Creep testing of materials at high temperatures is a very important field of study at many levels of industry. Accurate high temperature creep data is absolutely essential for the proper design and construction of any structural element operating at elevated temperatures. As such, ways of improving upon conventional creep testing methods at high temperature are highly sought after.

Permanent Linear Change
This test helps in determining the critical linear markings and measurements in green condition, after drying and after firing. The permanent change in dimensions is measured as permanent linear change.

Pyrometric Cone Equivalent
This test helps in determining the fireclay variations, mining control, and developing raw material specifications.

Refractories Under Load
This test helps in determining the deformation behavior of refractory ceramic products subjected to a constant load and increasing temperature.

Abrasion Test
This test helps in determining the relative abrasion resistance of refractory brick at room temperature. This test method can also be applied to castable refractories.

Air permeability Test
This test helps in determining the measurement of the air permeability of textile fabrics. This test method applies to most fabrics including woven fabrics, nonwoven fabrics, air bag fabrics, blankets, napped fabrics, knitted fabrics, layered fabrics, and pile fabrics. The fabrics may be untreated, heavily sized, coated, resin-treated, or otherwise treated.

Petrographic analysis by Optical Microscopy
This test helps in determining the microscopic analysis of materials using thin sections or polished surfaces.

Acid Resistance Test
This test helps in determining the acid resistance capacity of the refractory material.

Thermal Conductivity
Thermal conductivity depends upon the chemical and mineralogical compositions as well as the glassy phase contained in the refractory and the application temperature. The conductivity usually changes with rise in temperature. In cases where heat transfer is required though the brick work, for example in recuperators, regenerators, muffles, etc. the refractory should have high conductivity. Low thermal conductivity is desirable for conservation of heat by providing adequate insulation.

Particle Size
This test helps in determining the percentile quantity of particles of known diameter within a sample. The specimen can be either passed through a set of standard sieves in its natural state, or if a significant amount of binding matThis test helps in determining the strength of a brick. It tells us how much load that refractory can bear in cold conditions. The concept of testing CCS of a refractory material has perhaps, come from metallurgy. This is because for any refractory brick it is rather; rare that it would fail simply due to load on it in cold condition and therefore, the determination of cold crushing strength does not appear to be important from that point of view. erial is present, such as clay, then the sample can first be washed over a small aperture sieve to remove the binding material.

Water absorption
The amount of water that a refractory can absorb is measured by the water absorption test. The results of water absorption tests are used for quality assurance.

Apparent Porosity
Apparent porosity, water absorption, apparent specific gravity, and bulk density are primary properties of burned refractory brick and shapes. These properties are widely used in the evaluation and comparison of product quality and as part of the criteria for selection and use of refractory products in a variety of industrial applications.

Cold Crushing Strength
This test helps in determining the strength of a brick. It tells us how much load that refractory can bear in cold conditions. The concept of testing CCS of a refractory material has perhaps, come from metallurgy. This is because for any refractory brick it is rather; rare that it would fail simply due to load on it in cold condition and therefore, the determination of cold crushing strength does not appear to be important from that point of view.

Bulk Density
A useful property of refractories is bulk density, which defines the material present in a given volume. An increase in bulk density of a given refractory increases its volume stability, its heat capacity, as well as resistance to slag penetration.

Modulus of Rupture
The modulus of rupture (MOR) is the maximum surface stress in a bent beam at the instant of failure. One might expect this to be exactly the same as the strength measured in tension, but it is always larger because the volume subjected to this maximum stress is small, and the probability of a large flaw lying in the highly stressed region is also small.

Dimensional check
Refractory materials must maintain dimensional stability under extreme temperatures (including repeated thermal cycling) and constant corrosion from very hot liquids and gases. The standard for refractory materials restricts compressive creep (deformation at a given time and temperature under stress) for normal working conditions to no more than 0.3 percent in the first 50 hours.