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 The impact of Nano-technology on recent advances in monolithic refractories: A review  
Heidar Ali* 1Department of Materials Science, UNSW University, Australia
*Corresponding Author, Tel: +98
9133330848, E-mail address: [email protected]      
Abstract: In recent years, the use of Nano-technology (Nano-particles,
Nano-material and Nano-additives) has attracted attention of scholars,
engineers, and scientists in all scientific fields such as chemistry, medicine,
material, agriculture, electric, and etc. The use of Nano-technology has also
become widespread in the refractories products (which mainly used by
various industries such
as steel, casting, cement, glass, and etc.). Therefore, many researchers
have evaluated the effect of using different types and contents of
Nano-materials (oxides and non-oxides) on the properties of shaped (bricks) and
un-shaped (monolithic) refractories products andthey have achieved very interesting results.  One of the most consumable refractory products in various industries is monolithic refractories, which has been widely used because of their
great benefits to the other refractories products (bricks). Hence, in this paper, recent advances in monolithic refractories by Nano-technology are presented. Thisarticle can be considered as a complete
reference and guidance for researchers, students and
artisans in order toeasy access
to experimental research
results of the impact of Nano-technology
on monolithic refractories. Keywords: Nano-technology, Nano-particles, Refractory, Monolithic
                    
                                   
         
                                    
 
                                                         
  1.    Introduction:
1.2.        Nanotechnology(Introduction )
  The Nano-technology phrase originating from two words consist of
the Greeknumerical prefix nano referring to a billionth and the technology word 1-3. As an outcome,
Nano-technology or Nano-scaled technology is commonly considered to be at a
size under 100 nm (a Nano-meter is 10-9 m) 1-2.  
2.      Refractories: 2.1. Introduction:  
According to the ASTM C 71 , the refractories are a “non-metallic
materials having those physical and chemical properties that lead to them applicable
for structures or as components of systems that are exposed to environments
above 1000 °F (538°C) 11,
16. Also, some references mentioned that refractories are in-organic non-metallic material which can
withstand high temperature without changing in their chemical or physical properties while
remaining in contact with molten slag, metal and gases 11-13, 16-20.
As well as, according to the operating situation, they should to have high thermal shock resistant, be chemically inert, and  have definedranges of thermal conductivity and thermal expansion coefficient 11- 21, 22. It is clear that refractories have an
important role in glassmaking, metallurgical, and ceramic industries, where they are generated into a variety of shapes to line the interiors of furnaces or kilns or other devices for processing the materials at
high temperatures 23-25. Some of the technological and scientific inventions and progresses would
not have been possible withoutrefractory materials.
Producing 1Kg of any metal without
utilize of refractory is almost quite impracticable 26-29.The history of using refractory materials dates back to since mankind start to develop metallurgical process. The
firstrefractor raw material was clay. Up to the nineteenth century, refractory products were made of natural ores, such asmagnesite, dolomite stones and clay.it
was at the end of the eighteenth century and beginning of nineteenth century
that the basis of modern metal beneficiation, the development of Portland
cement and of modern glass processes started to inflict higher requirements to the refractory
industry 30-33. The main
materials used in the
producing ofrefractories are based
to Fig.1 34-36. In recent years, with the changing trends in steelmaking, the
high performing shaped refractories are
on an increasing demand. The
higher campaign lives and the mutability
of the newer steelmaking operations are decided by the accessibility
and performance of such shaped
refractories with superiorhigh-temperature mechanical strength, erosion and corrosion resistance the selection of refractories to be utilized is often according to the conditions dominating in the application zone 36-40.  
2.2.        Classification : Generally,refractories are divided based on chemical composition, manufacturing method,
and physical shape or based
on their applications (Fig.2) 11-20, 40-55.
2.2.1. Based on chemical
composition: a) Acidic refractories:
These types of refractories are used
in region that slag and atmosphere are acidic. They have high resistance to acids but corroded by alkalis.
The main raw materials belong
to the RO2 category, such as SiO2, ZrO2 and etc. b) Neutral refractories: These
categories of refractories are used in
area that atmosphere and
slags are chemically resistant to both acids andbases. The
major raw materials related to, but not confined to, R2O3 category. The general examples
of thesematerials are Al2O3, Cr2O3 and
carbon(C). c) Basic refractories: These categories of refractories are used in area that atmosphere and slags are basic; these categories high
resistance to alkaline materials but
corroded by acids. Themajor raw materials related to the RO
category to which MgO is a very general example. Also,
(Mg.Ca (CO3)2 and (MgO-Cr2O3) are in these categories.   2.2.2. according to
producing method: a) Dry press. b) Fused cast. c) Handmolded. d) Formed (normal, fired or chemically bonded). e)
Un-formed (monolithic- plastic,
ramming and gunningmass,
castables).   2.2.3. according to
physical shape: a) Formed: These types have determined shapes and size. These types divided into standard shapes and special shapes. The
first type has size that is confirmed by mostrefractory
producer and is generally suitable to furnaces or kilns of the same types. The second type specifically
made for special furnaces or kilns. b) Un-formed:
These categories are without clear format and are only given shapeupon application. Un-formed are known as monolithic refractories. The common
examples castables are, plasticmasses, gunning
masses, ramming masses, fettling
mix, mortars etc.   Monolithic
Refractories: Monolithic refractoryphrase is the name usually
given to all un-shaped refractory products, the word “monolithic” extracted from the
word monolith which means ‘big stone’56-58.
Monolithic refractories are specific batches
or blends of dry granular or cohesive
plastic materials utilized to form nearly joint free
linings. Monolithic refractory are un-shaped products which are installed as some form of suspension that finally harden to create a solid shape. Most monolithicformulations are made of three constituent such as: large refractory particulates (an aggregate), fine filler materials(which fill the inter
particle voids) and a binder phase (that gels the particulates together in the green state) Fig
359-65. Monolithic refractories show a great range of mineral
compositions and vary greatly in their physical andchemical properties. Some of them have low melting point (low refractoriness) whiles others approach high purity brick compositions in their
ability to tolerate severe
environments. Monolithic refractories are replacing theconventional type fired refractories at a much faster rate in many applications including
those of industrial furnaces53-55,
66-68. These refractories are
used to advantage compare to brick construction in different type of furnaces.
Their use enhanced fast installation. Utilize of monolithic refractories often delete difficult brick laying tasks, whichmay be accompanied with looseness in
construction. Protect of furnaces is
very importance because substantial repairs can be made with a minimum loss of
time 69-74. Sometimes, monolithic refractories linings of the same
composition as firebrick provide better insulation, lower
diffusion and enhanced spalling resistance to the effects of repetitive thermal shock. Other
major benefits of monolithic refractory linings are as
follows 75-80: ü Removingjoints which is an inherent weakness. ü Easier and faster application.  ü Better properties
than pressed (sintered or tempered) bricks. ü Simpler transportation and handling. ü Better volume stability. ü
Possibility to install in hot
standby state. ü Higher mechanical resistance to vibration and impact. ü
confirming shrinkage and expansion to the application. Different methods are used in the placement of monolithic refractories such as
ramming casting, spraying, gunning, sand slinging and etc. Heat setting monolithic
refractories have a very low cold
strength values and rely on relatively high temperatures to progress a ceramic bond 81-83. Furnaces wall having the usual temperature
drop across its thickness, the temperature in
the cooler part is
generally not enough to
progress aceramic bond. However with the use of a proper insulating material as backup, the temperature of the lining can behigh enough to
progress a ceramic bond throughout its entire thickness. In order to the installation and curing,
monolithic refractories need
an intently controlled dry-out
program. This led to the filler, binder and aggregate
to firegenerating a high strength material 84-86.   3.1. Types of monolithic refractories Usually the
monolithic refractories are divided
according to Fig.4 56-60, 65-88 a) Castable refractories  Materials with hydraulic setting
in nature are name of
Castables. These refractories are containing cement binder (commonly aluminate
cement), which creates hydraulic setting properties when blended with water. By
heat-up temperature, the material and binder either transforms or volatilizes
simplifying the generation of a ceramic bond. The most common
binder used in castables is
high alumina cement. Other binders are
consisting of hydratable alumina and colloidal silica. These materials are
installed by casting and are
also known as refractory
concretes. Insulating castables are specialized monolithic refractories that
are used on the cold surfaces
of applications. These monolithic castables are composed of lightweight
aggregate aggregates such as vermiculite,
bubble alumina, perlite and expanded clay. The main function of castables is to create thermal insulation. Also,
they are generally had low
density and low thermal conductivity. The
castables are classified according to following 48-58: ü Conventional Castable. ü Low Cement
Castables (LCC). ü Ultra Low Cement Castable
(ULCC). ü No Cement Castable (NCC). ü Light Weight Castables. ü Self-Flow
Castables (SFC). ü Insulating Castable.
  b) Plastic refractories Plastic refractories are used to form refractory monolithic linings in
different types of furnaces. These refractories are suitable for making quick, economical emergency repairs and they are easily rammed to any shape or contour. Plastic refractories are consisting of refractory
aggregates and adhesive clays which are prepared in stiff plastic condition at the proper consistency for use without more
preparation. During utilization, the blocks are tasked into pieces and are
rammed or casted into place
with pneumatic rammer.  These refractories can also be casted into place
with a mallet. These refractories suitable for many important applications due
to the high melting point (high refractoriness), the range ofcompositions, and the ease with which plastic
refractories are rammed into
place make them. Also, they have often highly spalling resistant. Plastic
refractories can consist of all the, clay-graphite, fireclay, high alumina, high aluminagraphite
and chrome types adapted for
many various operating situations. Specific gunning types are also accessible. These are in granulated
shape and are produced at the
proper consistency, ready to use. Some examples
of plastic refractories are
65-69, 76-80: ü Heat setting super duty fireclay plastic, ü Super duty heat setting plastics with graphite, ü Plastics in
the 50 % alumina class, ü Heat setting 60 % alumina class plastics, ü Air setting highalumina plastics in 80 % alumina class, ü Phosphate
bonded high alumina plastics with alumina content ranging from 70 % to 90 %, ü Phosphate bonded alumina chrome plastics, ü And silicon carbide based phosphate bonded
plastics.   c) Ramming mixes Ramming mixes composed essentially of ground
refractory aggregates, with a
semi-plastic bonding matrix.  These
refractory materials are like
to plastic refractories but are much harder. They need some sort of form to maintenance them when formed. The grain sizes are carefully classified and the final product is usually rendered
dry and then mixed with a
little content of water just before
utilization. Other ramming products arerendered in wet state and are ready for use immediately upon opening.
Ramming mixes are placed with
pneumatic rammer in layers of 25 mm to 40 mm. Steel making, burner blocks,
ports and similar
applications used of High purity ramming mixes based on
mullite grain. Ramming mixes consist of 80wt. % alumina content have good shrinkage resistance and thermal spalling at high
temperatures. Some ramming mixed such as, stabilized high alumina air
setting, have good thermal spalling
resistance at high temperatures and volume stability up to their temperature
limit. Also, phosphate-bonded alumina-chrome ramming mixes typically have very
high strength at high temperatures and very good resistance to acid and neutral slags consist of coal
ash slags. Alumina-graphite ramming mixes have mixture of high alumina grain and slag inhibitors which give them
well slag resistance to acidic and slightly basic slags. In
steel making industry, the dry ramming mixes based on high purity MgO and a sintering aid
are useful. Magnesite ramming mixes of exceptional purity and stability are used firstly as lining materials forcoreless type induction kilns. Magnesia-Chrome fused
grain ramming mixes can create special strength and density 52-60, 64-73.
d) Gunning mixes The install method of more monolithic refractories is gunning. The constitution
material of gunning mixes are different particles sized of refractory aggregate, a bonding compound, and maycontain plasticizing agent to enhance their stickiness when pneumatically
placed onto a kiln surface.  These refractory materials are sprayed on
application surfaces using a gun device. Usually gunning refractory mixes are supplied dry. In order
to application, they are pre-damped in a batch mixer, and
then continuously poured into a gundevice. Water is added to the mix at the nozzle to achieve the
proper consistency. Typically, Gun mixes are
including high alumina, siliceous, fireclay, dead burned magnesite and chrome types. Magnesite and hot gun
mixes are not pre-damped and are placed in a batch pressure gun. Gun mixes should provide good coverage
in a variety of applications 40-52, 61-68. Some types of gunning mixes are: ü
Fireclay gunning mixes of multipurpose hard firedfireclay and standard calcium-aluminate
cement compositions. ü Fire clay gunning mixes with high purity calcium-aluminate bonding system. ü Gunning mixes based on vitreous silica. ü High
purity alumina mixes which combine high fired alumina aggregate. ü High purity
calcium aluminate binder. ü Basic refractory gunning mixes with magnesia
content ranging from 60 % to 95 % with or without a phosphate bond. e) Patching refractories
 These typerefractories materials are like to plastic refractories though
have a very soft plasticity let
them to be casted into place
35-43, 71-76. F) Coating refractories
 These types of refractories materials are used to maintain refractory liningsusually against chemical attack. Coating refractories are usually intended to
coat just the working surface of a
lining. They tend to be justly thin layers 60-76. g) Mortars  Generally, mortars are neither classified
as refractory brick nor monolithic refractories. They are very fine refractory materials, which become plastic when mixed with water. These are used to bond the brickwork into solid unit, to provide cushion among the slightly
irregular surfaces of the brick, to fill up spaces created by a deformed shell, and to make a wall gas-tight to
prevent penetration of slag into the joints. Mortars should have good water keeping properties and must not foul. In this
way, premature penetration of water in
the refractory bricks after laying, causing the mortar to dry out, can be avoided. Different types of refractorymortars are consisting of 50-58: Ø Mortars with ceramic bonding
(bonding starting at 800 C) Ø Mortars With
chemical bonding Ø Mortars with hydraulic
bonding (bonding starting at 20 C) Also, the important properties of the mortars are
consisting of: ü Composition and characteristics of the mortar materials, ü Grain size ü Consistency   e) Fettling mixes
 Fettling mixes are also granular refractory materials, with function like
to gunning mixes, but areapplied
by shoveling into the kilns needing patching 43-51. f) Tap-hole mixes
Tap-hole mixes are resin bonded. In
these mixes the higher
strength which is normally desired
for monolithic refractory products, is not that important. Some criteria are necessary for all tap-hole mixes. These criteria are consisting of: correct consistency,
setting, and carbonization at the right time, precisely controllable PLC, and above all
drilling capability 72-78.  

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 3.      Application
of Nano-technology in refractory industrial:  Nano-technology is usually
introduced by size and consistof
the visualization, properties, production and manipulation of structures which
are lower than 100 nm 89-
90.Specific mechanical, optical, electrical,
and magnetic properties which can
differ substantially from the properties of the same materials at larger
dimensions can show for the structures that the dimensions of which range from
100 nm down to approx. 0.1 nm. Hence, nano-technology is a very active research field and has applications in
a number of areas. Today, considerable attention has been paid to the use of
nano-technology in the progress of refractories products 91-93.
Nano-technology has been entered to
refractories. It has been
expressed that the efficiency of therefractories
was extremely improved for the well dispersion of nano-sized grain in the
microstructure and reaction activity. Some efforts have been done by different
researchers to enhance the properties of refractories
(bricks andmonolithic) by using
Nano-particles. The application of nano-technology is aimed at achieving the
following specific properties of brick and monolithic refractories 90-95: ü
Ultra-high compressive strength, ü Relatively high tensile strength and ductility,
ü More efficient cement hydration, ü Increased aggregate-paste bond
strength, ü High corrosion resistance ü Control of cracks and self-healing ü High thermal shock
resistance and   ü High Abrasionresistance ü High chemical corrosion résistance  
4.      The Use of Nano technology in monolithic
refractories: According to the above, in this section, the results of carried out
activities by various researchers using nano-technology in monolithic
refractories have been expressed (Table
1). It is observed that the use of Nano-technology has been heavily used by researchers in recent years. Conclusion: Recently, Nano-technology
is used for production to
refractory products and it is a necessary tool included in many activities. A
lot of research has been working on
theadding of different types
of additives in ceramic goods,
and some of them have concentrated their
investigations on the use of Nano-additives, because of the mentioned advantageous of adding
nano-particles to the ceramic goods.  In this review article, all
researches which done to enhance the performance of monolithic refractories is
reported and it was concluded that the application of nano-additives has the
best results. Results show that recently, researchers have been using
nano-technology and have reached interesting results.