https://edubirdie.com/plagiarism-checker The impact of Nano-technology on recent advances in shapeless refractories: A review Heidar Ali* 1Department of Materials Science, UNSW University, Australia*Corresponding Author, Tel: +989133330848, E-mail address: [email protected]
com 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 alsobecome widespread in the refractories products (which mainly used byvarious industries suchas steel, casting, cement, glass, and etc.). So, some researchershave examined the effect of using different types and contents ofNano-materials (oxides and non-oxides) on the properties of shaped (bricks) andun-shaped (shapeless) refractoriesproducts and they have attained very interesting results.
One of the most consumable refractory goods in different industries is shapeless refractories, which has been widely used because of theirgreat advantages to the other refractories goods (bricks). Hence, in this research, recent progresses in shapeless refractories by Nano-technology are mentioned. This article can be used as a complete reference and guidance for Scientific’s, students andartisans for easy access to experimental research results of theimpact of Nano-technology on shapeless refractories. Keywords: Nano-technology, Nano particles, Refractory, shapeless 1.
Introduction: 1.2. Nanotechnology(Introduction): The Nano-technology phrase originating fromtwo words consist of the Greek numerical prefix nano referring to a billionth and the technology word 1-2.
As an outcome,Nano-technology or Nano-scaled technology is commonly considered to be at asize 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-metallicmaterials having those physical and chemical properties that lead to themapplicable for structures or as components of systems that are exposed toenvironments above 1000 °F (538°C)11, 16. Also, some references mentionedthat refractories arein-organic non-metallic material which can withstand high temperature withoutchanging in their chemical or physicalproperties 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 animportant 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 athigh temperatures 23-25.
Some of the technological and scientific inventions and progresses wouldnot have been possible withoutrefractory materials.Producing 1Kg of any metal withoututilize of refractory is almost quite impracticable 26-29.The history of using refractory materials dates back to since mankind start to develop metallurgical process. Thefirstrefractor raw material was clay. Up to the nineteenth century, refractory products were made of natural ores, such asmagnesite, dolomite stones and clay.itwas at the end of the eighteenth century and beginning of nineteenth centurythat the basis of modern metal beneficiation, the development of Portlandcement and of modern glass processes started to inflict higher requirements to the refractoryindustry 30-33. The mainmaterials used in theproducing ofrefractories are basedto Fig.
1 34-36. In recent years, with the changing trends in steelmaking, thehigh performing shaped refractories areon an increasing demand. Thehigher campaign lives and the mutabilityof the newer steelmaking operations are decided by the accessibilityand performance of such shapedrefractories with superior high-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 basedon their applications (Fig.
2) 11-20, 40-18.104.22.168. Based on chemicalcomposition: a) Acidic refractories:These types of refractories are usedin region that slag and atmosphere are acidic.
They have high resistance to acids but corroded by alkalis.The main raw materials belongto the AO2 category, such as Silica, zirconia and etc. b) Neutral refractories: Thesecategories of refractories are used inarea that atmosphere andslags are chemically resistant to both acids andbases. Themajor raw materials related to, but not confined to, A2B3 category. The generalexamples of these materials are alumina, chromiaand carbon(C). c) Basic refractories: These categories of refractories are used in area that atmosphere and slags are basic; these categories highresistance to alkaline materials butcorroded by acids. Themajor raw materials related to the ROcategory to which MgO is a very general example. Also,(Mg.
Ca (CO3)2 and (MgO-Cr2O3) are in these categories. 2.2.2. according toproducing method: a) Dry press. b) Fused cast.
c) Handmolded. d) Formed (normal, fired or chemically bonded). e)Un-formed (shapeless – plastic,ramming and gunningmass,castables). 2.2.
3. according tophysical shape: a) Formed: These types have determined shapes and size. These types divided into standard shapes and special shapes. Thefirst type has size that is confirmed by mostrefractoryproducer and is generally suitable to furnaces or kilns of the same types.
The second type specificallymade 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 shapeless refractories. The commonexamples castables are, plasticmasses, gunningmasses, ramming masses, fettlingmix, mortars etc.
shapeless Refractories:Monolithic refractory phrase is the name usually given to all un-shaped refractory products, the word “monolithic” extracted from theword monolith which means ‘big stone’56-58.Monolithic refractories are specific batchesor blends of dry granular or cohesiveplastic materials utilized to form nearly joint freelinings. Monolithic refractory are un-shaped products which are installed as some form of suspension that finally harden to create a solid shape. Most shapeless formulations are made of three constituent such as: large refractory particulates (an aggregate), fine filler materials(which fill the interparticle voids) and a binder phase (that gels the particulates together in the green state) Fig359-65. shapeless refractories show a great range of mineralcompositions 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 theirability to tolerate severeenvironments.
shapeless refractories are replacing theconventional type fired refractories at a much faster rate in many applications includingthose of industrial furnaces53-55,66-68. These refractories areused to advantage compare to brick construction in different type of furnaces.Their use enhanced fast installation.
Utilize of shapeless refractories often delete difficult brick laying tasks, whichmay be accompanied with looseness inconstruction. Protect of furnaces isvery importance because substantial repairs can be made with a minimum loss oftime 69-74. Sometimes, shapeless refractories linings of the samecomposition as firebrick provide better insulation, lowerdiffusion and enhanced spalling resistance to the effects of repetitive thermal shock. Othermajor benefits of shapeless refractory linings are as follows 75-80: ü Removingjoints which is an inherent weakness. ü Easier and faster application.
ü Better propertiesthan pressed (sintered or tempered) bricks. ü Simpler transportation and handling. ü Better volume stability. üPossibility to install in hotstandby state. ü Higher mechanical resistance to vibration and impact.
üconfirming shrinkage and expansion to the application. Different methods are used in the placement of shapeless refractories such asramming casting, spraying, gunning, sand slinging and etc. Heat setting monolithicrefractories have a very low coldstrength values and rely on relatively high temperatures to progress a ceramic bond 81-83.
Furnaces wall having the usual temperaturedrop across its thickness, the temperature inthe cooler part isgenerally not enough toprogress aceramic bond. However with the use of a proper insulating material as backup, the temperature of the lining can behigh enough toprogress a ceramic bond throughout its entire thickness. In order to the installation and curing,shapeless refractories need an intentlycontrolled dry-out program. This led to the filler, binder and aggregate to firegenerating a high strength material 84-86. 3.1. Types of shapeless refractoriesUsually the shapeless 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 containingcement binder (commonly aluminate cement), which creates hydraulic settingproperties when blended with water. By heat-up temperature, the material andbinder either transforms or volatilizes simplifying the generation of a ceramic bond. The most commonbinder used in castables ishigh alumina cement. Other binders areconsisting of hydratable alumina and colloidal silica.
These materials areinstalled by casting and arealso known as refractoryconcretes. Insulating castables are specialized shapeless refractories that are used on the cold surfaces of applications. These shapelesscastables 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 lowdensity and low thermal conductivity.
Thecastables are classified according to following 48-58: ü Conventional Castable. ü Low CementCastables (LCC). ü Ultra Low CementCastable (ULCC). ü No Cement Castable (NCC).
ü Light Weight Castables. ü Self-FlowCastables (SFC). ü Insulating Castable. b) Plastic refractories Plastic refractories are used to form refractory shapeless linings indifferent 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 refractoryaggregates and adhesive clays which are prepared in stiff plastic condition at the proper consistency for use without morepreparation. During utilization, the blocks are tasked into pieces and arerammed or casted into placewith pneumatic rammer. These refractories can also be casted into placewith a mallet. These refractories suitable for many important applications dueto the high melting point (high refractoriness), the range ofcompositions, and the ease with which plasticrefractories are rammed intoplace make them. Also, they have often highly spalling resistant. Plasticrefractories can consist of all the, clay-graphite, fireclay, high alumina, high aluminagraphiteand chrome types adapted formany various operating situations.
Specific gunning types are also accessible. These are in granulatedshape and are produced at theproper consistency, ready to use. Some examplesof plastic refractories are65-69, 76-80: ü Heat setting super duty fireclay plastic, ü Super duty heat setting plastics with graphite, ü Plastics inthe 50 % alumina class, ü Heat setting 60 % alumina class plastics, ü Air setting highalumina plastics in 80 % alumina class, ü Phosphatebonded high alumina plastics with alumina content ranging from 70 % to 90 %, ü Phosphate bonded alumina chrome plastics, ü And silicon carbide based phosphate bondedplastics. c) Ramming mixes Ramming mixes composed essentially of groundrefractory aggregates, with asemi-plastic bonding matrix.
Theserefractory materials are liketo 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 rendereddry and then mixed with alittle content of water just beforeutilization. Other ramming products arerendered in wet state and are ready for use immediately upon opening.Ramming mixes are placed withpneumatic rammer in layers of 25 mm to 40 mm. Steel making, burner blocks,ports and similarapplications used of High purity ramming mixes based onmullite grain. Ramming mixes consist of 80wt.
% alumina content have good shrinkage resistance and thermal spalling at hightemperatures. Some ramming mixed such as, stabilized high alumina air setting,have good thermal spallingresistance at high temperatures and volume stability up to their temperaturelimit. Also, phosphate-bonded alumina-chrome ramming mixes typically have veryhigh strength at high temperatures and very good resistance to acid and neutral slags consist of coalash slags. Alumina-graphite ramming mixes have mixture of high alumina grain and slag inhibitors which give themwell slag resistance to acidic and slightly basic slags. Insteel making industry, the dry ramming mixes based on high purity MgO and a sintering aidare useful. Magnesite ramming mixes of exceptional purity and stability are used firstly as lining materials forcoreless type induction kilns. Magnesia-Chrome fusedgrain ramming mixes can create special strength and density 52-60, 64-73.
d) Gunning mixes The install method of more shapeless refractories is gunning. The constitutionmaterial of gunning mixes are different particles sized of refractory aggregate, a bonding compound, and maycontain plasticizing agent to enhance their stickiness when pneumaticallyplaced onto a kiln surface. These refractory materials are sprayed onapplication surfaces using a gun device. Usually gunning refractory mixes are supplied dry.
In orderto application, they are pre-damped in a batch mixer, andthen continuously poured into a gundevice. Water is added to the mix at the nozzle to achieve theproper consistency. Typically, Gun mixes areincluding high alumina, siliceous, fireclay, dead burned magnesite and chrome types. Magnesite and hot gunmixes are not pre-damped and are placed in a batch pressure gun. Gun mixes should provide good coveragein a variety of applications 40-52, 61-68. Some types of gunning mixes are: üFireclay gunning mixes of multipurpose hard firedfireclay and standard calcium-aluminatecement compositions.
ü Fire clay gunning mixes with high purity calcium-aluminate bonding system. ü Gunning mixes based on vitreous silica. ü Highpurity alumina mixes which combine high fired alumina aggregate. ü High puritycalcium aluminate binder.
ü Basic refractory gunning mixes with magnesiacontent ranging from 60 % to 95 % with or without a phosphate bond. e) Patching refractories These typerefractories materials are like to plastic refractories thoughhave a very soft plasticity letthem to be casted into place35-43, 71-76. F) Coating refractories These types of refractories materials are used to maintain refractory liningsusually against chemical attack. Coating refractories are usually intended tocoat just the working surface of alining. They tend to be justly thin layers 60-76. g) Mortars Generally, mortars are neitherclassified as refractory brick nor shapelessrefractories. They are very finerefractory materials, which become plastic when mixed with water. These are used to bond the brickwork into solid unit, to provide cushion among the slightlyirregular surfaces of the brick, to fill up spaces created by a deformed shell, and to make a wall gas-tight toprevent penetration of slag into the joints.
Mortars should have good water keeping properties and must not foul. In thisway, premature penetration of water inthe 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 Withchemical bonding Ø Mortars with hydraulicbonding (bonding starting at 20 C) Also, the important properties of the mortars areconsisting 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 liketo gunning mixes, but areappliedby shoveling into the kilns needing patching 43-51. f) Tap-hole mixesTap-hole mixes are resin bonded. Inthese mixes the higherstrength which is normally desiredfor 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 alldrilling capability 72-78. 3. Application of Nano-technology in refractoryindustrial: Nano-technology is usually introduced by size and consistof the visualization, properties, production andmanipulation 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 thesame materials at larger dimensions can show for the structures that thedimensions of which range from 100 nm down to approx. 0.1 nm. Hence,nano-technology is a veryactive research field and has applications in a number of areas. Today,considerable attention has been paid to the use of nano-technology in theprogress of refractories products 91-93. Nano-technology has been entered to refractories.
It has been expressed that the efficiency oftherefractories was extremely improved for thewell dispersion of nano-sized grain in the microstructure and reactionactivity. Some efforts have been done by different researchersto enhance the properties of refractories(bricks and shapeless) by usingNano-particles. The application of nano-technology is aimed at achieving thefollowing specific properties of brick and shapeless refractories 90-95: üUltra-high compressive strength, ü Relatively high tensile strength and ductility,ü More efficient cement hydration, ü Increased aggregate-paste bondstrength, ü High corrosion resistance ü Control of cracks and self-healing ü High thermal shockresistance and ü High Abrasionresistance ü High chemical corrosion résistance 4. The Use of Nano technology in shapelessrefractories: According to the above, in this section, the results of carried outactivities by various researchers using nano-technology in shapelessrefractories have been expressed (Table1). It is observed that the use of Nano-technology has been heavily used by researchers in recent years. Conclusion: Recently, Nano-technologyis used for production torefractory products and it is a necessary tool included in many activities.
Alot of research has been working ontheadding of different typesof additives in ceramic goods,and some of them have concentrated theirinvestigations on the use of Nano-additives, because of the mentioned advantageous of addingnano-particles to the ceramic goods. In this review article, allresearches which done to enhance the performance of shapeless refractories is reported and it was concluded thatthe application of nano-additives has the best results. Results show thatrecently, researchers have been using nano-technology and have reachedinteresting results.