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Materials are usually classified in threebroad classes; metals & alloys, ce-

ramics & polymers. Every class of materi-als exhibits a unique set of properties. Ce-ramics are inorganic materials either crys-talline or amorphous in nature. Among theclass of materials, ceramics displayed awide range of properties because of its di-versified bonding, lattice-structure and mi-crostructure, relationship. It is a stone-agematerial which evolved over time as Tech-nical ceramics and finds its usage in vari-ous structural and functional applicationsfor development and progress of econo-my.Technical ceramics are oxides (e.g. alumi-na, zirconia, titanates), non-oxides (e.g.carbides, nitrides, oxy-nitrides) and com-posites which are often made with syn-thetic raw materials with controlled speci-fications, manufactured under a controlledprocess to deliver products for appropriatestructural and functional applications.

Product portfolio of CUMI – Industrial Ceramics DivisionCUMI IC-division operating in design anddevelopment, manufacture and supply ofadvanced sintered ceramic products forcritical and demanding applications.

It is broadly classified into three segmentsnamely• Wear resistant ceramics• Engineered ceramics• Metallized ceramics

Technical Ceramics and itsApplication – CUMI PerspectiveThe usage of sintered technical ceramics has been one of the provensolutions in wear, corrosion resistance, thermal/thermal shockresistance, electrical insulation, dielectrics and ballistic applications.

Calcined alumina is used as a major rawmaterial for the production of high-alumi-na technical grade of ceramics for struc-tural application. The performance of highalumina sintered products are determinedby the alumina grade used, quality andcomposition of sintering additives/aidsand the sintering process. The degree ofsintering to manufacture a defect-freeproducts are related to the whole chain ofthe manufacturing process such as extentof uniform mixing and milling, uniformityin preparation of the deflocculated slip forspray-drying, quality of spray-drying forthe production of ceramic granules for thesubsequent forming process, uniformity insintering etc. CUMI – IC manufacturestechnical ceramics products by variousforming processes such as isostaticpressing, extrusion, ceramic injectionmoulding (CIM), slip casting other thanthe conventional uni-axial pressing. The selection of the right quality of alumi-na with uniform crystal size, particle size,α-alumina content, low alkali content adreactivity and compatible sintering aids re-lated to applications are the critical toquality. CUMI uses the best classes of se-lective calcined alumina and compatibledifferent kind of sintering additives tomanufacture 90 % to 99,8 % high aluminasintered products for diversified applica-tions. It uses a very high optimum temper-ature sintering process to develop theright kind of microstructure with the helpof various tunnel and batch kilns or vacu-um sintering processes in conjunctionwith on-line process control. CUMI-IC also has partially/fully stabilizedzirconia, reaction sintered aluminiumti-tanate, reaction bonded SiC products. Theapplications include wear-resistant, corro-

sion-resistant, thermal resistant, thermalshock-resistant, electrical insulation andballistic application for diversified indus-tries. CUMI-IC has a unique technology ofceramic to metal seals for manufacturingvarious metallized ceramic products forelectrical and dielectric applications.

Wear Resistant CeramicsWear ceramic products are used in miner-al and ore processing, power genera-tion/distribution, cement, coal-processing,steel, non-ferrous, fluid-handling indus-tries. CUMI-IC manufactures high-end sin-tered alumina (various application specificcomposition ranging from 90 % to 99,8 %alumina).There are five grades of products namely;CUMITUFF 90, CUMITUFF 92, CUMITUFFCSP, CUMITUFF 96 and CUMITUFF 995which are being used for wear and corro-sion application depending upon the cus-tomer's expectation and application de-mands.High alumina (> 90 % Al2O3) sinteredstructural-grade of ceramics manifests asuperior wear resistance due to high hard-ness value because of its hexagonal close-packed crystal structure. It also possessesa high specific strength (per unit mass),moderate fracture toughness, high tem-

Keywordsmetallized ceramics, reaction bonded silicon carbide (RbSiC) ceramics,alumina, zirconia and aluminiumtitanateceramics

Santanu Mandal, Suresh KumarChatakonda, Ritendu Ganguly, S. Prabu, Shyam S. RaoCarborundum Universal Limited,Industrial Ceramic DivisionHosur 635126, Tamil NaduIndiawww.cumiceramics.com

mandalsananu@cumi.murugappa.com

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perature resistance and an exceptional im-pact resistance property next to zirconiaamong oxide ceramics. Sintered aluminaceramics also exhibits a very good corro-sion resistance property in most of theacidic and alkaline environment because ofits chemical inertness due to amphoteric

fore a value-for-money for the customer asfar as the cost to performance is con-cerned.The microstructures (Fig. 1) of CUMIproducts are close-packed and uniform re-sulting one of the best and performance

in nature. Therefore, sintered high alumina(> 90 % Al2O3) ceramic-based compo-nents are the most diversified used mate-rials due to its excellent mechanical properties, wear and corrosion resistanceand good manufacturing ability of even complex and large shapes and there-

Tab. 1 Products, features and its applications

Formulation Salient features Products and its applications

Cumituff 90/ 92 Excellent wear resistanceStandard and pre-engineered Tiles, small/ dimple tiles, iso-pressed components, lined equipment, rubberized ceramics

Cumituff CSP Excellent wear and corrosion resistance

Cumituff 96 Premium wear and corrosion resistance

Cumituff 94Excellent mechanical and di-electric strength, metallizedceramics

Metallized cylinders for vacuum interrupters and metallizeddevices for electrical applications

Cumituff 95 Excellent corrosion resistance Igniters and water pump seals

Cumituff 98 Good ballistic performance Monolithic armor plates for personnel protection, inserts forvehicle armor

Cumituff 995 Excellent wear, corrosion resistance and outstandingballistic performance

Mechanical seal parts and inserts for personal and vehiclearmor

Cumituff 998 Excellent thermal and corrosion resistance Lab-ware, ferrules, furnace parts and components

Cumituff YSZ/ MgSZ Excellent impact, wear and corrosion resistant toughceramics

Battery tooling, wire drawing dies, mud-pump liners, step cone pulleys

Fully Stabilized Zirconia Excellent thermal shock resistance, Oxygen conductivity Oxygen sensor applications

975 M/ 995 M Excellent di-electric strength, metallized ceramics Metallized devices for X-ray tubes, night vision cameras andmicrowave

CUMITHERM Excellent thermal shock resistance, Non-wettability tomolten non-ferrous metal and insulating ceramics

Dosing tube, riser tube, sprue bushes, tapping plugs andplates, spout and other non-ferrous melts, holding andconveying parts

RbSiC Excellent wear, mechanical, thermal and corrosionresistance

Thrust bearings, mechanical seals and shrink fittedcomponents for chemical pump industry

Fig. 1 SEM of etched CUMITUFF 92

Fig. 2 Weibull Modulus of CUMITUFF 92

fracture stress

fract

ure

prob

abili

ty

grad

ient

b

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consistency, which are evident from thehigh Weibull Modulus value (Fig. 2). Wear Model and SimulationThe following erosion models have beenproposed [1] for non-ductile material likehigh-alumina ceramics for differentprocess conditions.

Gas/Particle “low” concentrationE ∝ Vp

2,8 dp0,66 ρp

1,3 KIC-1,33 H·-0,25 sin2α

(1)Gas/Particle “high” concentrationE ∝ Vp

2,8 dp0,66 ρp

1,3 ρtKIC-1,33 H·-0,25 sin2α

(2)Slurry/particle “high” concentrationE ∝ (vρpf)·-0,3551 (sin α)1,623 (3)

E: Erosion Rate (gm/s)Vp: velocity of the particle (m/s)v: slurry velocity (m/s)

dp: dia of particle (cm)ρp: density of particle (g/cm3)ρt: density of target (g/cm3)KIC: fracture toughness of target

(MPa.√m)H: Vickers micro-hardness (kg/mm2)f: particle volume fractionα: angle of impingement (deg)

It takes long time to understand the per-formance of ceramic under trial in a givensets of condition, therefore it is required todevelop the method of simulation of per-formance under such conditions to predictthe same quickly. CUMI is working to de-velop the method of simulating the wearperformance for given set of parametersby CFD [2]. The proposed wear model (eq.1, 2 and 3) was used as inputs for the sim-ulation of wear in CFD model. The “CFX”-

software was used for simulation wear-patterns of bends (Fig. 3) and “Fluent” wasused for simulation of wear-patterns of cy-clone (Fig. 4). The Eulerian-Lagrangian ap-proach was fused for pneumatic convey-ing of coal particles in bends and Eulerian-Eulerian approach was used for slurries incyclone.

Engineered ceramicsAlumina CeramicsCUMI – IC manufactures customized highpurity alumina ceramics for wear protec-tion, corrosion protection, electrical resist-ance and ballistic protection. The productscan be used in diverse applications suchas fluid handling equipment, power distri-bution industry, defence (personnel andvehicle armor) applications. High-aluminatechnical ceramics also finds applicationsas various wear resistant nozzle, machinecomponents, applications in paper indus-try as well as in textile industry because ofits high wear resistance and corro-sion/contamination-free in nature.

Aluminiumtitanate (CUMITHERM) ceramicsCUMI – IC manufacture and supply a reac-tion-sintered aluminiumtitanate (CUMI-THERM), which is ideally suited for casthouses and foundries for non-ferrous (NF)metal handling applications. It has extraor-dinary properties high thermal shock re-sistance due to near-zero expansion coef-ficient (Fig. 5), low thermal conductivityand non-wettability to most NF-moltenmetal. These properties are achieved byreaction sintering of high-purity alumina

Fig. 3 CFD-analysis of wear-pattern in bends

Fig. 4 CFD-analysis of wear-pattern in Cyclone

Fig. 5Typical Thermal Expansion Curve of CUMITHERM

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and titania in a precision reaction-sinteringprocess to engineer a unique micro-struc-ture. The aluminium titanate phase hasbeen sufficiently stabilized with the help ofcertain additives to prevent the decompo-sition of otherwise unstable aluminium ti-tanate at high temperature. CUMI – IC sup-plies dosing tubes for HPDC, metal pour-ing tubes/nozzles, sprue bushes, connec-tors, metal tapping plate/plug with reac-tion sintered aluminium titanate products.

Zirconia ceramicsZirconia and zirconia-toughened aluminafind their applications wherein fracturetoughness is one of the key requirementsother than wear and corrosion resistancein applications such as battery-tooling in-dustry, extrusion dies, pump seal andparts for petrochemical industries. MgPSZis a preferred ceramic material for pumpseal and parts applications in petrochemi-cal industries. Other than structural appli-cations CUMI-IC also makes fully stabi-lized zirconia sleeves for oxygen sensorapplications.

Reaction bonded silicon carbide (RbSiC) ceramicsSintered technical ceramics also finds var-ious usages other than bulk wear applica-tions. CUMI – IC supplies various productslike rotating impellers, pistons andplungers, thrust bearing, mechanical sealsbased on 99,5 % alumina or reaction-bonded SiC (RbSiC) for pump industry inchemical applications. Shrink-fitted RbSiCcomponents also find various applicationsin pump industry. CUMI RbSiC productshave lower content of free-silica(~ 9 – 10 %) and finer SiC-grain structure(Fig. 6), which results in improving themechanical, thermal and corrosion resist-ance properties. One of the large marketsfor ceramics is automotive water pump

These brazed assemblies are used in highvoltage feed-through, vacuum feed-through applications.

ConclusionThe usage of sintered technical ceramicshas been one of the proven solutions inwear, corrosion resistance, ther-mal/thermal shock resistance, electricalinsulation, dielectrics and ballistic applica-tions. However, it has the limitation in theapplication where high fracture toughness,impact resistance and failure predictabilityare in demand. Therefore, the search of ce-ramics/composites with high fracturetoughness in combination with high hard-ness at the competitive cost is on the wayto open up a new horizon for the user in-dustry. Research is also on for varioussmart ceramics such as self-healed glassand ceramics devoid of catastrophic fail-ure to improve its reliability for structuralapplication. Thus, technical-grade of ceramics hasbeen playing and would continue to play aprogressively important role in variousstructural and functional applications be-cause of its diversified engineered proper-ties and tailored microstructure.

seals. Tungsten carbide seals cannot with-stand certain corrosion resistant additivesused to protect aluminium engine blockstherefore alumina and SiC-based superiorautomotive water pump seals are beingused because of their wear and corrosionresistance.

Metallized ceramicsCUMI - IC has state-of-the-art technologyfor making hermetically sealed metallizedceramics. CUMI manufactures metallizedceramics with 94 % alumina, 97,5 % alu-mina and 99,5 % alumina products. Suchzero-porosity sintered high-purity aluminaceramics has very good mechanical aswell as good dielectric strength and henceelectrical insulation properties. It has highthermal conductivity, very good volumeresistivity and low di-electric loss value.Metallized ceramics with 94 %-aluminaare used in vacuum interrupters. The mi-crostructure of sintered alumina has beenengineered for making it suitable for sub-sequent metallization. The metallized layerare often consists of Mo-Mn coating withNi-plating to make it compatible for subse-quent brazing process. The Mo-Mn layerwith high pull strength value makes it suit-able for high temperature brazed assem-blies. In many cases, special high-temper-ature impervious glazes are applied onmetallized ceramics for prevention of sur-face flashovers.High alumina metallized ceramics productsinclude vacuum interrupters, feed-throughinsulators, X-ray tubes, power switches,power grid tubes and other various devicesfor electrical insulation application.At CUMI metallized ceramics are brazedonto special alloys. High pure vacuum-grade brazed materials like copper-silver,copper, gold-nickel are used for brazing.

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Fig. 6Typical Optical Photograph of RbSiC, 200X

Reference:

[1] K. R. Gopi, R. Nagarajan, S. S. Rao, S.Mandal, “Erosion model on alumina ceramics: A retrospection, validation &refinement”, Wear, 264 (2008) [3-4], pp211-218

[2] Report – Joint Research Programme on“Erosion model and CFD-analysis ofwear patterns for gas/liquid-laden parti-cle flow for certain applications” be-tween Carborundum Universal Limited &IIT-Madras (2006).

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