High Temperature Concrete / Monolithics For Application In Kiln And Furnace: Role Of Chemistry

The conventional high temperature concrete for application in kiln and furnaces is a mixture of refractory aggregate and calcium aluminate cement binder. The CaO-Al2O3 binary equilibrium diagram provides useful information regarding existence of various calcium aluminates, out of which CA(CaO.Al2O3), CA2(CaO.2Al2O3) and C12A7(12CaO.7Al2O3) are considered to be the most important hydraulic phases having wide applications as binder to produce high temperature concretes. In the present study, high temperature concretes were prepared utilizing different types of refractory aggregates and synthetically prepared CA, CA2, C12A7 binders in single or in combination and allowed the samples to undergo hydration at different temperatures and different periods of time. It has been observed that water converts anhydrous calcium aluminates into different hydrated phases and the hydration reaction scheme has been different for each of the calcium aluminates. The major hydraulic phases were identified as CAH10, C2AH8, C3AH6 (C=CaO, H=H2O) which contribute towards strength development. A distinct change in crystal morphology was seen in each individual calcium aluminates and also when they were mixed in certain proportions. The chemistry of refractory aggregate has a considerable influence upon the quality of castable product for high temperature applications in kiln and furnaces. The paper discusses some of these issues. The process of making high temperature concrete utilizing commercially available tabular alumina aggregate, reactive alumina fines and calcium aluminate cement binder will also be demonstrated along with their main testing methods

Geopolymer Research In India For Sustainable Green Technology

It is widely accepted that geopolymer binders and concretes would be ushering in an era of real green construction technology as low CO2 footprint based substitute for ordinary portland cement. There are two main constituents of geopolymers, namely the source materials and the alkaline liquids. The source materials should be rich in silicon and aluminium namely naturally occurring minerals like kaolinite, clays etc. Alternatively, it can be by-product materials such as fly ash, slag, silica fume, meta kaolin, rice husk ash, red mud etc. The choice depends on availability, cost and type of application. The alkali liquids are from soluble alkali metals that are usually sodium or potassium based. The most common alkaline liquid used in geoploymerization is a combination of NaOH or KOH and Na2SiO3 or K2SiO3. In India, CSIR- National Metallurgical Laboratory started a comprehensive programme on fly ash (a by-product of Thermal power plant) based geopolymers encompassing both basic and applied aspects of geopolymerisation. After several laboratory experimentation, a number of novel geopolymer based building and construction materials have been developed by CSIR-NML. The process flow sheet developed at lab scale consists of mixing fly ash, milled granulated blast furnace slag (a by-product of Iron and steel plant ), sand and aggregate with alkali solution, vibro compaction into desired shapes using PVC mould and curing at 27OC in controlled condition for different periods. The paper discusses the scientific aspects of this laboratory development and process modification done during up-scaling of the technology in a fully automated pilot plant. The paper also highlighted the African connections with CSIR-NML regarding geopolymer research under CV Raman and CSIR-TWAS scholarship programme. Other Indian academic and research institutions are also engaged in geopolymer research with different kinds of source materials and alkaline activator. The paper briefly reviews the same

NLO QCD corrections to the resonant Vector Diquark production at the LHC

With the upcoming run of the Large Hadron Collider (LHC) at much higher center of mass energies, the search for Beyond Standard Model (BSM) physics will again take center stage. New colored particles predicted in many BSM scenarios are expected to be produced with large cross sections thus making them interesting prospects as a doorway to hints of new physics. We consider the resonant production of such a colored particle, the diquark, a particle having the quantum number of two quarks. The diquark can be either a scalar or vector. We focus on the vector diquark which has much larger production cross section compared to the scalar ones. In this work we calculate the next-to-leading order (NLO) QCD corrections to the on-shell vector diquark production at the LHC produced through the fusion of two quarks as well as the NLO corrections to its decay width. We present full analytic results for the one-loop NLO calculation and do a numerical study to show that the NLO corrections can reduce the scale uncertainties in the cross sections which can be appreciable and therefore modify the expected search limits for such particles. We also use the dijet result from LHC to obtain current limits on the mass and coupling strengths of the vector diquarks.Comment: Published in JHE

Failure of evaporator tubes initiated by lamellar tearing during the commissioning of a waste heat recovery boiler

Successive failures of several new evaporator tubes during commissioning and trial run of a waste heat recovery boiler has been analyzed. The evaporator tubes are cold bent into U-shape and subsequently TIG welded to a 24-mm thick wear plate on either sides of the tube immediately adjacent to the bend. The failed samples showed stepped longitudinal cracks along the rolling direction and parallel to the weld fusion boundary at the fireside surface of the inner bend of the tube,prominently at the center of the bend. It was found that the failure of the evaporator tubes at the tube bends was initiated by lamellar tearing because of inherent defects in the material (segregation leading to banded structure), improper processing of material (inclusions with high aspect ratios along the rolling direction) and accelerated by high transverse shrinkage stresses over the entire bend portion of the tube introduced by the weld. The pre-existing fine cracks in the welded evaporator tube initiated by lamellar tearing have subsequently opened up during service when the total strain in the region increased because of steam pressure resulting in catastrophic failure of the tubes. Contrary to expectation, many of the elongated inclusions were found to be iron oxide scales and only few were manganese sulfide stringers enveloped by iron oxide scales. The iron oxide inclusions were resolved from the manganese sulfide by scanning electron microscopy and EDS spot analysis of the inclusions

Colonization behaviour of arbuscular mycorrhizal fungi and phosphorus uptake pattern of mycorrhizal sensitive upland paddy using hydroponics culture

Three upland rice cultivars namely Vandana, Brown Gora and Kalinga collected from the Central Rainfed Upland Rice Research Station (CRURRS), Hazaribag, Jharkhand of the Central Rice Research Institute, are mycorrhiza sensitive genotypes. Their affinity towards mycorrhizal colonization varied. The cv. Kalinga had the highest colonization followed by Vandana and Brown Gora. Variation of arbuscular mycorrhizal fungi affinity of the rice genotypes might be due to the variable demands of phosphorus nutrition of the different genotypes. To justify these variable demands of phosphorus among these three cultivars of rice, four different doses of phosphorus (5, 10, 15 and 20 ppm) were imposed to them in a system of hydroponics. Overall, among the three cultivars, the highest uptake efficiency (34% at 30 days, 57% at 45 days, 68% at 60days and 70% at 75 days interval) throughout the growth period was noticed in the cv. Brown Gora, followed by Kalinga and Vandana. The physiological demands of phosphorus of these cultivars were finally estimated as the contribution of uptake phosphorus to the total dry matter production of the plants with respect to available phosphorus. The overall results of these estimations gave the highest value in cv. Kalinga followed by the cv. Vandana and Brown Gora. Therefore, the cultivars Brown Gora and Kalinga could be recommended for the cultivation of the vast upland rain-fed areas of the country for higher yield and increased phosphorus use efficiency which could ultimately contribute significantly to the food grain production of the country

Evaluation of Nigerian Source of Kaolin as a Raw Material for Mullite Synthesis

In the present study, a new source of kaolinitic clay (Al2O3.2SiO2.2H2O) collected from Abule Onikosin Road in Abeokuta area of Ogun State, Nigeria was first processed to remove the stony materials adhered to its surface and subsequently characterized with respect to its chemical analysis, TG-DTA, particle size spectrum and identification of mineralogical phases by XRD technique. The identified endothermic peak at 516.39oC for dehydroxylation in the DTA curve and observed deformed XRD profile confirm that the clay belongs to disordered kaolinitic clay. The high SiO2 content (59.26 wt%) compared to theoretical value (46.54 wt%) of well-ordered kaolinite is due to excess silica and this has been revealed in XRD pattern as quartz peak. The compact samples of this processed clay powder on heating in the temperature range of 1400-1600oC resulted almost densified and impervious sample at 1600oC. The densification occurred by viscous flow mechanism. Silica together with impurity oxides (Fe2O3, TiO2) in the clay forms glassy phase in the above temperature range and that accompany the formation of mullite (3Al2O3.2SiO2) crystals. The XRD and FESEM studies conducted on heated samples revealed the formation of mullite needle, the amount and aspect ratio of which increases with increase in heating temperature. The EDAX studies confirm the presence of Al, Si, O as major elements which also support mullite formation in the heated compact samples. This new sources of kaolinitic clay identified in Nigeria is found to be suitable for mullite synthesis and it is advantageous due to its low temperature mullitization unique microstructure

Some studies on olivine fines and clay mixtures

Olivine is a mineral composed of forsterite (2 MgO.SiO2) as major and fayalite (2 FeO.SiO,) as minor phases. During pro¬cessing of olivine minerals for foundry and other uses, lot of fines (around -100 mesh) are generated. The present study has been carried out on the olivine fines collected from the Salem district of Tamil Nadu to explore the possibilities of converting these fines into value added ceramic products by reaction sintering with clan Different combinations of olivine fines and clay have been formulated and the mixtures are heated at various tempera¬tures in the form of pellets. The sintering kinetics and physical properties have been studied and discussed in this paper. XRD & SEM and studies are also carried out to confirm the phases formed

Effect of plasma ion implantation on the hydrogen embrittlement of Cu strengthened HSLA-100 steel

The effect of low dosage plasma ion implantation on hydrogen embrittlement was studied for an HSLA steel using notched tensile samples. The plasma treatment caused an enhancement in the linear strain to failure under embrittling conditions. This was however not reflected in the fracture surfaces of the treated samples which had similar fractographic features as those of untreated samples. The plasma treatment delayed the process of embrittlement without causing any alteration in the basic mechanism of embrittlement. This was due to introduction of residual compressive stresses as well as reduction in the hydrogen permeation flux. Implantation in pure nitrogen seemed most beneficial while implantation in pure argon caused very little improvement

Effect of heating rates on the synthesis of Al2O3–SiC composites by the self-propagating high-temperature synthesis (SHS) technique

Various aspects of insitu formation of Al2O3–SiC composites by the self-propagating high-temperature synthesis (SHS) technique have been investigated using thermal analyses (TG/DTA) of a powder mixture (4Al, 3SiO2, 3C) and pellets in an argon atmosphere at different heating rates. Both the reaction initiation and peak temperatures are found to increase with the heating rates. At lower heating rates, the powder samples do not reveal any exothermic peak possibly because of poor reactivity and sluggish exothermic reaction. The appearance of exothermic peaks in the DTA plots after melting of aluminum indicates reduction of silica by liquid aluminum. Conversion of aluminum is found to decrease marginally with an increase in heating rates. The apparent activation energy of the process compares well with the interdiffusion activation energy of silicon and oxygen, indicating that oxygen diffusion in Si formed at the reaction front may be the rate-controlling factor for this SHS process. From SEM studies it appears that the formation of SiC whiskers is through liquid-phase mass transfer