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Research Activities
The
Chemistry Group is primarily engaged in basic research in thrust areas
of radiation and photochemistry, superconductivity, metal hydrides, catalysis,
solid state reactions and chemical synthesis and studies of organometallics,
bioactive catalysts, chirons, peptides and bioactive compounds. Applied
research is being actively pursued in thermodynamic studies particularly
with reactor applications, diamond film deposition, dry combustion plasma,
pheromones for pest control applications, radio pharmaceuticals, solvents
for fuel reprocessing, etc. Basic and applied research is being carried
out in analytical chemistry to develop newer and improved analytical methodologies.
Facilities
have been set up for investigation of the dynamics of ultrafast chemical
reactions in the femto second regime, and for generation and study of atomic
clusters. The necessary capability for ultra trace analysis of high purity
materials exists in the Group.
The
Chemistry Group has an active reactor-oriented programme on decontamination
studies, activity transport studies, studies related to biofouling etc.
Collaboration,
consultancy and analytical services are being offered by the Chemistry
Group to various units of BARC and DAE, government and private sector organisations,
academic institutions and advisory bodies/organisations.
The
Chemistry Group gives extensive help to Training and Management Division,
BARC in teaching and practicals on several advanced topics.
1. Radiation and Photochemistry
& Laser Induced Chemistry
The
major facilities for studying these include pulse radiolysis equipment
based on 7 Mev electron linear accelerator, laser flash photolysis equipments
in nano, pico and femtosecond time domains. Using recently developed ultrafast
pump-probe spectrometer based on CPM dye laser (see under Facilities),
work on vibronic relaxation in laser dyes is in progress. Studies on electron
transfer processes with dissociative electron transfer, inter and intramolecular
H-bonding effects and their influence on photoprocesses in hydroxy substituted
benzophenones have been carried out. Photophysical processes in substituted
fullerenes (e.g. halo, hydroxy) is another area of intense activity. Gas
phase dynamics studies on O (3P) with nitromethane and reactions of NO2
with free radicals like CF2Br and Br. are in progress.
Pulse
radiolysis studies in nano and microsecond time domains are being carried
out on biologically important systems like antioxidants (derivatives of
curcumin, vanillin), substituted quinones, bilrubin and lysozyme in microemulsions,
peroxy radical reactions with proteins. Investigations on nanoparticles
of Tl, Cu, Co, Ag, Pd generated by radiolysis and their properties are
being pursued. Studies on radical cation generation in organic halo and
sulphur compounds and on 2 centre - 3 electron bonds are in progress.
Work
has been carried out on the oxidative photodegradation of model pollutants
such as aromatic amines in aqueous solutions and carbon dioxide formed
was estimated by gas chromatography. In this context, pulse radiolysis
technique was employed to study one-electron oxidation of 2, 3, 4-amino
phenols and 1-napthyl amine 4-sulphonic acid in order to understand the
mechanism of photodegradation of these compounds in aqueous solutions.
Radiation chemistry of ammonia and hydrazine in aerated aqueous solutions
was studied in the context of their use as `oxygen scavengers' in the primary
coolant circuits of VVERs. The radiolysis products were identified and
the mechanism of oxygen removal was elucidated. A new colorimetric method
for estimation of hydrazine in presence of ammonia was standardised.
A
lot of applied work on radiation polymerization and hydrogels is being
carried out.
2. Solid State Reactions
& Thermodynamic Studies
Solid
state reactions in a number of systems are being investigated to understand
the basic mechanism and to evolve alternative routes to the synthesis of
useful materials. They include preparation of chromium ferrite using an
alternative oxalic acid route, synthesis and magnetic properties of parent
and substituted scandium manganates, preparation of KMgF3 and KCuF3, phase
transition and bulk thermal expansion studies on La1-xMxCrO3[M = Sr, Nd;
x = 0.10 to 0.30], synthesis of VO, synthesis and characterisation of Sr++
doped Mn2O3, mixed fluorides etc. Other areas pursued include preparation
and characterisation of ß-Li3MF6 (M = Ga and Mn), M7Er6F32 (M = Ba,
Sr).
Thermodynamic
studies center around reactor applications and include investigation of
CaO-TeO2 system , thermodynamic properties of UTeO5 and UTe3O9, characterisation
and thermal stability of uranium tellurites and tellurates [UTe3O5, UTeO4
UTe3O9 and UTe3O8], vapour pressure of uranium-iron alloys, determination
of standard Gibbs energy of formation of Th2Mo2O8, standard enthalpies
of formation of BaTe2O5 and BaTeO3 and phase diagram of the pseudo binary
BaO-TeO2 system. Differential thermal analysis study of phase transitions
in BaCO3 and SrCO3 and several other compounds recommended as standards
in thermal analysis is also carried out.
3. Diamond Film Deposition
The laboratory set up of the HFCVD equipment set up in the previous years has been scaled up to coat larger samples. Diamond films have been successfully coated on 5 cm diameter samples of zircaloy, molybdenum, silicon (on the 100 crystallographic plane) etc. P-30 tool inserts have also been coated which are being tested in the Central Workshop.
4. Dry Combustion
Plasma
Investigations
have shown that dry combustion plasma and its precursor fuels offer such
technological and economical advantages that electricity generation by
magnetohydrodynamic process, presently globally discounted, can be reconsidered
as highly possible. High thermal to electrical conversion, use of conventional
saturated ion core magnet instead of cryogenic magnet in the channel, easy
availability and low cost of fuels are the main advantages envisaged.
5. Chemical Synthesis
Several
organometallic compounds of palladium, gallium, indium, arsenic and antimony
which would be potential candidates for the preparation of advanced materials
like catalysts/ semiconductors have been synthesised and characterised.
A series of bi- and tri- nuclear palladium and platinum organochalcogenides
were prepared which showed interesting pyrolytic decomposition resulting
in the formation of respective selenides and sulpho-selenides.
6.
Superconductivity
A
synthesis protocol was developed for making Bi-2223 tapes by powder in
tube method starting from lead doped Bi-2122 and infinite layer compound
Ca0.85Sr0.15CuO2. In order to identify phase responsibe for superconductivity
in the multiphase sample of nominal composition (Nd4/6Th1/6)2[Nd1/3(Ba0.67Sr0.33)2/3]2
Cu3O9, a number of compounds with T* - and 223-type structures not containing
Ce were prepared. Their properties are being studied.
7.
Studies on Metal Hydrides
Effect
on the H2 absorption on the structural, magnetic and superconducting characteristics
of Zr, rare earth annd uranium based intermetallics is being investigated.
8.
Catalysis studies
Using
hydrogen TPD method the metal surface area of a polycrystalline ruthenium
catalyst and a 2% Ru/TiO2 catalyst was evaluated. Enthalpy changes involved
during adsorption/interaction of He, H2 and O2 over Au/Fe2O3 catalysts
were evaluated at adsorption temperature of 300 K. Irrespective of the
nature of pretreatment an almost similar fraction of CO2- (55%) was found
to adsorb/interact over both the catalysts during exposure to successive
CO2 pulses. The methods based on D2O/OH group isotopic exchange and NH
temperature programmed description were used to evaluate the concentration
of the hydroxyl groups in ZSM-5 and HZSM-5 zeolites as a function of heat
pretreatment in the temperature range 573-1173 K. A deuterated ZSM-5 catalyst
was prepared by ion exchange method using 10 % solution of ND4NP3.
Simulated
gas adsorption/ desorption experiment on dehydrated molecular sieve-5 A
and Fe-doped and Fe free alumina were carried out to evaluate the H2/D2
exchange phenomenon noticed in gas chromatographic analysis with D2 carrier
gas using these column packings.
9.
Analytical Chemistry
Research
on various aspects of analytical chemistry is pursued. These include: a
systematic study on the permeation of various metal ions like silver and
zinc through Nafion ionomer membrane as well as the transport of halides
through modified membranes; thermal analysis study of ammonium uranyl carbonate
coprecipitated with gadolinium carbonate; X ray diffraction of copper tellurium
intermetallic compound; fabrication of biosensors; cyclic voltammetric
behaviour of Pd on biotin; investigation on the effect of magnetic field
on the manifestation of anomalous phenomena during electrolytic charging
of deuterium into palladium and nuclear transmutation reactions in the
cold by means of Patterson Power Cell.
Applied
research is pursued to develop newer and improved analytical methodologies.
These include determination of traces of uranium in zircaloy, assay of
trace metals in calcium, estimation of Mg and Zn in semen samples, determination
of nitrogen and trace metals in hydrogel, analysis of trace impurities
in diverse materials like calcium sulphate TLD powder, lithium pentaborate,
environmental sample solutions etc. A Electroanalytical procedure for determination
of palladium in recombiner catalysts was developed. Methods were standardised
for characterisation of several trace impurities in high purity arsenic
using DCPAES, GFAAS and electroanalytical techniques. NAA methods were
developed for the analysis of platinum group metals in rock samples and
copper plant tailings. Work was pursued on the potentiality of charged
particle activation analysis (CPAA) for the determination of rare earth
elements in geological samples and determination of light elements in high
purity materials. Thin layer activation analysis (TLA) was applied for
surface wear studies in zircaloy-2.
10.
Biocatalysts
To
cater to the demand for compounds with varied molecular structure, design
of new synthetic strategies is an important activity. Use of biocatalysts
(enzymes) is likely to contribute significantly in future. Efforts were
directed to design novel asymmetric synthesis of high value, low volume
bioactive compounds such as agrochemicals and pharmaceuticals. The specificity
of the enzymes could be altered by solvent enginnering thereby increasing
their utility.
11.
Chirons
Due
to importance of optically pure compounds in chemical industries, several
asymmetric methodologies (chirotechnology) were developed. Using readily
available carbohydrates as starting materials, highly functionalised chirons
were prepared; these would be useful for synthesis of drug intermediates
and other bioactive compounds. A highly convergent protocol which allows
enantiocontrol of three stereogenic centres has been developed and used
in enantiomeric synthesis of antifungal compound.
2-alkenyl-4-chromanones
are attractive substrates for intramolecular arene-alkene photoadditions.
Using suitably designed substrates highly strained (energy rich) multicyclic
systems, with hitherto unknown carbon framework with defined stereochemistry
could be synthesised. A low valent titanium mediated protocol for low temperature
carbonyl coupling (McMurray Reaction) which is the backbone of nuclear
medicine has been developed.
12.
Peptides
Peptides
containing non-natural amino acids have been synthesised. Some of these
show strong chiral recognition as evidenced by NMR studies. These studies
will be useful in the design of peptides of therapeutic value. Molecular
interactions of fullerenes (C60) with different classes of compounds were
studied using 1H an 13C NMR spectroscopy. The solubility trends of fullerenes
could be rationalised on the basis of charge transfer complexes and resulted
in the discovery of new solvents.
13.
Pest Control
Integrated
pest management programmes based on the use of insect pheromones provide
an eco-friendly alternative to toxic pesticides. Additional amount of the
pheromone which is useful for control of the weevil menace of the sweet
potato crop has been synthesised and field trials have been continued in
collaboration with Central Tuber Crop Research Institute. Repeated trials
revealed excellent efficacy of the synthetic pheromone both in the control
of the pest as well as improvement of the quality of the crop. Pink bollworm
(Pectinophora gossypiella) and American bollworm (Helicoverpa
armigera) are the two major pests of cotton. Pheromones of these pests
were made available by synthesis and trials for their control were continued
for the third successive year. Prediction of the population build-up of
pests could be made by careful monitioring the extent of infestation. Studies
on mating disruption have also been carried out against pink bollworm.
A pheromone mimic was evaluated for mating disruption of pink bollworm.
14.
Radiopharmaceuticals
Improvement
in the methods for the preparation of known radiopharmaceuticals and design
of new ones are some important goals of the IAEA Coordinated Research Programme.
Expertise gained from the basic work on bioorganometallics was utilised
towards the development of new generation of organic ligands which are
likely to find use in the radiopharmaceuticals as well as in chelation
therapy and biochemistry. The reaction is based on single electron transfer
induced reductive dimerisation of imines. More than fifteen ligands with
rigid, multidentate and macrocyclic frameworks have been synthesised. These
allow modulation of physical characteristics (e.g. hydrophobicity) and
altering the chelate ring size to the desired stability by using appropriate
substrates.
15.
Solvent for Fuel Reprocessing
Solvent
extraction is used in nuclear fuel reprocessing. Work on CMPO (n-octyl-phenyldiisobutylcarbomoylmethyl
phosphine oxide) has been supported by synthesising the ligand in sufficient
quantities. Studies on radiolytic degradation of TRUEX solvent were continued
using GC and GC-MS (in collaboration with RCD). Interpretation of the mass
spectra shows that CMPO undergoes fragmentation at different sites giving
various products. An understanding of the nature of the radiolytic products
will be useful for their removal so that CMPO can be repeatedly recycled.
Use of alkyl malonamides as extractants for actinides offers advantages
owing to their ready incineratibility. Several malonamides have been synthesised.
16.
Bio Active Compounds
Studies
towards isolation and characterisation of the immunomodulatory principle
from Gulvel were continued. Composition of the monosachharides of
the active principle was determined by GC-MS. The linkages between the
monosachharides have been partly established. Chemotherapeutic potential
of two alkaloids, pergularine annd tylophorinidine were evaluated. Both
compounds showed significant inhibition against thymidylate synthase activity
of leukaemia leukocytes. Ecdysoids and precocenoids (the insect growth
regulators) have been isolated from plant sources. Some of the growth regulators
have been found to be toxic to marine fouling organisms. Some synthetic
analogs of garlic constituents were found to inhibit HMG CoA reductase
activity and were evaluated for hypolipidemic activity. Significant reduction
in triglyceride and cholesterol levels were observed in cholesterol induced
hypercholesterolemic rats. In addition, the synthetic compound showed antioxidant
properties. It exhibited significant in vitro inhibition of CCl4
or Fe2+ induced lipid peroxidation.
FACILITIES
1.
Femto second Laser Spectrometer
An
important equipment to investigate the dynamics of ultrafast chemical reactions,
the Femto second Laser Spectrometer for measurement of transient optical
absorptions of extremely short lived chemical species in the time scale
of 10-15 second (femto second, fs) has been set up in the Group. The desired
chemical species are generated by the interaction of 100 fs pulses of a
colliding pulse mode locked (CPM) dye laser pumped by Argon ion laser.
This output is then amplified in a 5 stage dye amplifier pumped by seeded
Nd-YAG laser to give amplified pulses of 300 µJ energy at 30Hz rep
rate. The spectrometer is based on pump-probe configuration, the white
light probe continuum pulses being generated by focussing part of the amplified
output of CPM laser on a jet of ethylene glycol. The range of the spectrometer
is 0-6600 fs and is achieved by using an ultrafine optical delay with a
resolution of 1 fs.
2.
Laser Vapourisation Cluster Equipment
The
equipment for generation of atomic clusters of metals and for study of
their reactions has been set up in the laboratory. The clusters are generated
by laser pulses and are characterised by a captive time of flight mass
spectrometer. Trial experiments with aluminium are being carried out to
evaluate the performance of the unit.
The
ultra trace analytical facilities at HRD Complex, BARC have been refurbished
to cater to the needs for the analysis of high purity materials. A sophisticated
AAS unit with provision for flame and electrothermal atomisation and vapour
and hydride generation measurements has been procured and installed.
REACTOR
ORIENTED ACTIVITIES
1.
Decontamination of BWR surfaces
Studies
on decontamination of BWR surfaces is under way. A comparative assessment
of LOMI and EAC formulations has been completed. A feasibility report for
carrying out chemical decontamination of the clean-up system of TAPS Unit
# 2 is being prepared and the details regarding ion exchanger column size,
quantity of chemicals needed and operational procedure are being worked
out.
2.
Decontamination of PHWRs
Water
and Steam Chemistry Laboratory, Kalpakkam in collaboration with MAPS has
successfully decontaminated the PHT systems of MAPS-1 and MAPS-2. The technology
for this was developed in-house and employs a decontaminant formulation
to remove the oxide deposits from the PHT system surfaces.
Recently
a repeat decontamination of MAPS-1 PHT system was carried out in November
1997 using the same methodology. 160 Ci of Co and 40 Ci of fission produts
were removed. Decontamination factors ranging from 2 to 15 were achieved
on the system surfaces thereby bringing down the radiation fields significantly
and resulting in considerable man-rem savings for carrying out maintenance
jobs.
3.
Chemical Cleaning of Steam Generators
Fouling
of nuclear steam generators by the oxides and scale forming impurities
transported from the feed water systems is not uncommon. To prevent the
occurence of steam generator tube failures by the aggressive ions which
may get concentrated in the sludge pile, it is desirable to periodically
remove the fouling sludge deposits. Detailed investigations have been carried
out to evaluate EDTA based chemical cleaning formulations for their efficacy
in dissolving the copper and iron containing sludge and their compatibility
with the Monel-400 steam generator tubes. Electrochemical evaluation has
shown that the formulations do not cause any localised attack on the SG
tube materials. Based on these studies it is shown that a two stage chemical
cleaning process using EDTA as the complexant can be used to chemically
clean the MAPS steam generators.
4.
SIM Loop Commissioning
A
modular simulated test facility (SIM LOOP) has been constructed out of
stainless steel for testing of decontamination formulations at pilot plant
scale. SIM loop can also be used to carry out component decontaminnation,
corrosion studies, ion exchange behaviour related to decontamination etc.
This loop has recently been commissioned.
5.
Studies Related to Biofouling
In
the area of biofouling, investigations are carried out on evaluation of
water quality, rearing of barnacle larvae for laboratory biofouling studies,
microbiological studies in fresh water and sea water, biofilm development
and its dependence on plant nutrients, chlorination and biofouling studies
at MAPS etc. As a part of these studies a Biofouling Test Loop is being
set up at MAPS site and is nearing completion.
6.
Activity Transport Studies
A
computer code is being developed to calculate the build-up of mass and
activity on PHWR primary transport system surfaces. As a firt step, a simplified
model of a single metal pipe closed loop with three different diameter
has been chosen. This loop also has a sink for corrosion products. It utilises
variable parameters such as deposition coefficient, release coefficient
and purification factor. The model at present calculates the build-up of
iron on surface and in the coolant as a function of time.
R
& D studies for understanding the corrosion and ion exchange behaviour
in dilute decontaminant formulation are being pursued. Besides dissolution
of corrosion product oxides such as mixed ferrites and iron oxides in other
prospective decontaminant formulations such as pyridine di carboxylic acid
(PDCA), picolinic acid and nitrilo triacetic acid was investigated for
understanding mechanism of oxide dissolution in these media.
COLLABORATION,
SERVICES AND CONSULTANCY
Analysis
of samples emanating from various Divisions of BARC, units of DAE and Government
and private sector organisations constitutes the analytical service support.
The number of samples analysed every year averages 2500 involving more
than 7500 determinations. The samples analysed include materials of nuclear
importance, organic and inorganic compounds, rocks and minerals, biological
and environmental specimens, transformer oils, and diverse materials like
molecular sieves, glass powder, PTFE etc. Besides, a number of solution
samples are also analysed. Analytical techniques like UV/VIS spectrophotometry,
AAS, GFAAS, DCPAES, CHN and elemental analyser, gas and ion chromatography,
XRF, nuclear analytical techniques like INAA, RNAA and charged particle
activation analysis are employed to provide the best service support to
users. Specialised services like determination of particle size, surface
area and thermoanalytical properties are provided. To cater to the increasing
demand for fast and accurate analyses, it is proposed to modernise the
analytical laboratory by aquiring state of the art equipments. Analytical
services (XRD, HTXRD, TG, DTA) are provided to other Divisions/DAE units.
In
collaboration with Central Forensic Science Laboratory, the Division has
contributed to the solution of several forensic cases. Irradiation facilities
are being offered to Geological Surey of India for the analysis of rock
samples. Cooperation is extended to various academic institutions for training
in sophisticated analytical methods. Consultancy is rendered to various
Advisory Bodies/ organisations viz. COSWAC, DST, BIS etc.
Consultancy
services to Nuclear Power stations/ reactors/ Heavy Water Plants are being
provided.
The
Group gives extensive help to Training and Management Services Division
by giving lectures, tutorials, practicals on several topics such as Thermodynamics,
Radiation & Photochemistry, Reactor Chemistry, Chemical Dynamics and
Rate Processes, Material Science, Analytical Chemistry, Molecular Structure
and Spectroscopy etc. to Chemistry Trainees of BARC Training School.
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