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Co–28Cr–6Mo alloy was prepared by vacuum induction melting process and tested for electrochemical corrosion behavior in a neutral Hank’s solution at 37±1 ○ C. The hot deformation behavior of the as cast alloy was studied using uniaxial compression tests carried out in vacuum to a true strain value of 0.4, in the temperature range of 1000 to 1200 °C and for the strain rate of 0.002, 0.01 and 0.1 s -1 . The measured open circuit potential, corrosion current density and corrosion potential values for the as cast samples were -0.191 V, 4.08 x 10 -6 A/cm 2 and -0.301 V, respectively. Whereas, the corresponding values for the homogenized samples were -0.148V, 1.12 x 10 -7 A/cm 2 and -0.109 V, respectively. Scanning electron microscopy and energy dispersive X-ray spectroscopy measurement techniques were used to study the microstructure of the alloy before and after the electrochemical corrosion tests and, also to know the effect of heat treatment on the mechanical and electrochemical properties of Co-28Cr-6Mo alloy.

This paper presents the results of investigations carried out on processing and characterization of CrB2-based novel composites. Niobium metal powder was used as additive to form new composites. Hardness and fracture toughness of chromium boride increased by addition of niobium. CrB2 composites were prepared by addition of 2.5, 10 and 20 wt.% Nb. Density of higher than 95% ρ th was achieved in all the samples. Hot pressed samples were analyzed to contain reaction products of NbB2, Cr2B3 and Cr3B4 phases along with CrB2. Hardness of CrB2 composite was increased from 18.46 GPa to 21.89 GPa by increasing the Nb content from 2.5 to 10 wt.%. Fracture toughness of composites prepared by addition of 2.5 and 10% was measured as 3.11 and 3.38 MPa.m1/2 respectively. Addition of 20% Nb resulted in increased fracture toughness of 4.32 MPa.m1/2 .

Isothermal oxidation behavior of the single layer NbSi2 and the double layered (NbSi2 + Nb5Si3) silicide coated Nb–1Zr–0.1C (wt.%) alloys has been studied between 800 and 1300 °C in static laboratory air. The single layer coated alloy shows a lower weight gain as compared to the double layer coatings at all temperatures. The formation of amorphous silica scale embedded with Nb2O5 oxide particles is observed beyond 1100 °C, and a superior oxidation resistance is detected between 1100 and 1300 °C. A kinetic equation relating the thickness of the coating layer with the various process parameters for pack siliconizing of Nb-alloy has been established.

Palladium selective ligand, N , N , N ′, N ′-tetra-(2-ethylhexyl)-dithiodiglycolamide (DTDGA), was encapsulated in polymeric composite beads under simple laboratory conditions. The composite beads were evaluated for separation and recovery of palladium from simulated spent automobile catalyst dissolver (SSACD) solution. Batch extraction studies were carried out to understand the influence of various parameters on the sorption behavior of palladium. The beads showed maximum uptake of Pd at 3.0 M HCl. Pd sorption kinetics is found to be fast, and the kinetics data fit well in to the pseudo second-order equation model for the sorption of palladium ions onto the composite beads. Different sorption isotherm models were applied to the experimental data. Equilibrium data are represented well by the Langmuir isotherm equation, with a monolayer sorption capacity of 1.37 mg/g for the swollen beads. The process mechanism is found to be complex, consisting of both intraparticle diffusion and film diffusion. More than 99% of palladium was back extracted in single contact using 0.01 M thiourea in 0.1 M HCl. Batch extraction studies with SSACD solution showed negligible uptake of Fe, Cr, Ni and Pt thus showing very high selectivity and extractability of the composite beads for palladium.

A new solid supported ionic liquid (SSIL) has been synthesized and evaluated for the separation of uranium from acidic aqueous streams. SSIL has provided an opportunity to exploit the anchored task specific ionic liquid (TSIL) moiety for the sorption of uranium from aqueous streams and thus overcoming the limitations encountered during liquid–liquid extraction processes involving the use of TSILs.

The electrodeposition of thick metallic molybdenum coating from aqueous electrolyte considered difficult for a long time owing to high reactivity with oxygen. In the present study, a successful attempt was made to electrodeposit thick (~ 25 μm), metallic bright Mo coating by DC electrolysis from a water deficient aqueous electrolyte containing molybdate ions. Energy-dispersive spectroscopic (EDS) analysis confirmed the presence of Mo along with low content of oxygen on top surface. The crystal structure of as-deposited Mo coating was amorphous in nature, as monitored by in situ XRD investigation, which transformed into crystalline BCC structure upon vacuum annealing. The surface morphology of Mo coatings as investigated by scanning electron microscopy (SEM) revealed the presence of several cracks without any grain structure. Transmission electron microscope micrographs showed the featureless microstructure of amorphous molybdenum, which was further ascertained by the appearance of a continuous ring pattern in the selected area electron diffraction pattern (SAED). XPS analysis confirmed deposition of reduced Mo(0) metal and the top layer converted to Mo oxides upon keeping in ordinary atmosphere. Nanoindentation measurements showed a drastic improvement of nanohardness of as-deposited (2186 ± 455 MPa) to coatings (4187 ± 910 MPa) after annealing at 700 °C.

Imino diacetamide styrene divinyl benzene (IDAA SDVB) resin was synthesized and evaluated for separation of molybdenum (Mo) from simulated dissolver solution of irradiated uranium–aluminium alloy. Detailed studies were carried out to understand the influence of various parameters on sorption of Mo. The kinetics of Mo sorption is found to be fast and the kinetics data fit well to the pseudo-second order kinetic equation. Sorption of Mo is found to decrease with the increase of feed acidity. The loading capacity of resin is determined to be 30 mg g−1, the sorption isotherm data fit well to the Langmuir model. Batch sorption experiments with simulated dissolver solution showed quantitative uptake of Mo along with some co-extraction of iodine (I). Column runs have demonstrated that co-extracted ‘I’ could be scrubbed easily with solutions of feed acidity. Finally, sorbed Mo could be eluted with 3.0 M HNO3. XAFS and FT-IR studies of Mo sorbed on to IDAA SDVB resin have shown that Mo is sorbed in the +6 oxidation state (in the form of MoO42−), wherein the complex attains octahedral geometry with contribution from four oxygen atoms of the molybdate anion and two oxygen atoms of the amidic moiety of the imino-diacetamide ligand.

The synergistic extraction of uranium from phosphoric acid solutions with di-nonyl phenyl phosphoric acid (DNPPA) and bidentate n -octyl (phenyl)- N , N -di-isobutyl carbamoyl methyl phosphine oxide (CMPO) in n -dodecane has been investigated and effect of varying concentrations of phosphoric acid, phosphate ions, DNPPA and CMPO on the extraction of uranium were determined. The results demonstrated that synergistic combination of DNPPA with bidentate CMPO significantly enhances the extraction efficiency when compared to monodentate extractant TOPO (tri- n -octyl phosphine oxide). Stoichiometry of complex obtained by slope analysis method indicated the formation of neutral species of the type [UO 2 (HA 2 ) 2 · CMPO], where (HA) 2 is the dimer form of DNPPA. Extraction reaction was found to be exothermic with enthalpy change (ΔH) of 43.3 kJ/mol. A mole ratio of DNPPA/CMPO = 2 was found to be suitable for effective extraction of uranium. Under comparable condition, the extraction of uranium from phosphoric acid with various synergistic reagents followed the order: DNPPA/CMPO > DNPPA/TOPO > DIDPA (di-isodecyl phosphoric acid)/CMPO > DIDPA/TOPO > D2EHPA (di-2-ethyl hexyl phosphoric acid)/CMPO > D2EHPA/TOPO. The loading capacity of DNPPA/CMPO was found to be greater than DNPPA/TOPO for both WPPA (wet process phosphoric acid) and MGA (merchant grade phosphoric acid). Stripping of uranium with various reagents was in the order: Na 2 CO 3 > H 3 PO 4 + Fe > H 3 PO 3 > HCOOH. DNPPA and CMPO solvent mixture was found to be stable even after 20 cycles of repeated extraction and stripping operations.

The paper deals with the microstructure and wear properties of the Mo-30W alloy, coated with silicide based oxidation resistant coatings using pack cementation technique. The microstructure of the coating revealed that the coating was free of cracks or pores, adherent to the substrate and comprised of either single layer or double layer depending the coating temperature. Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) was used to determine diffusion profiles for Mo, W and Si. Reciprocating sliding wear and friction experiments were performed on the uncoated and coated alloy. Double layer coating showed an improved friction coefficient as compared to base alloy as well as a single layer coated alloy. The wear tests also showed a marked improvement of wear resistance of coated alloy as compared to uncoated alloy. The coating was found to be wear resistant at 7 N.

This paper presents the result of investigation carried out on the synthesis, densification and oxidation studies of LaB 6 . LaB 6 was synthesized by boron carbide reduction of La 2 O 3 . Effect of temperature on product quality was investigated. Pure LaB 6 powder was obtained at 1500 °C, in vacuum. Pressureless sintering at 1950 °C of LaB 6 powder resulted in a density of only 85.1% of the theoretical value. Hot pressing resulted in near theoretical density at the same operating temperature. Hardness and fracture toughness of the dense LaB 6 was measured as 20 GPa and 3.02 MPa m 1/2 respectively. Oxidation study by thermogravimetry revealed that oxidation starts slowly at 500 °C and accelerates at 700 °C. Isothermal oxidation study revealed that protective oxide layer forms on LaB 6 surface on oxidation at 900 °C. The presence of protective continuous oxide layer on the surface was observed even after 64 h exposure in air atmosphere.

Novel ligand, namely, N , N , N ′, N ′-tetra-(2-ethylhexyl)-dithiodiglycolamide (DTDGA) has been evaluated for separation and recovery of palladium from simulated spent catalyst dissolver (SSCD) solution. Liquid–liquid batch extraction studies were carried out to understand the influence of various parameters on the extraction behavior of palladium. Extraction equilibrium studies showed near complete extraction of palladium within 5 min. With the increase in hydrochloric acid concentration, the extraction of palladium increased up to 3.0 M HCl and then remained constant on further increase in acidity. Stoichiometry of the extracted species was determined to be PdCl 2 ⋅DTDGA by mole ratio plot. The effect of various diluents on the extraction of palladium was studied and it was found that there is quantitative uptake in n -paraffinic diluents and the extraction decreases with increase in polarity of diluent. More than 99% of palladium was back extracted in single contact using 0.01 M thiourea in 0.1 M HCl. Extraction studies with SSCD solution showed negligible uptake of Fe, Cr, Ni, and Pt, thus showing very high selectivity and extractability of DTDGA for palladium.

Friction and wear properties of the hot pressed composite of pre-alloyed (TiCr)B2 + 20%MoSi2 (4.81 g/cm3) were studied at different loads and frequencies under reciprocative sliding, using a counter body of cemented tungsten carbide (WC-Co) ball. Coefficient of friction, wear volume and wear rate were measured. Optical microscopy and SEM-EDS analysis were carried out to understand the wear mechanism and chemistry of debris. A lowest value of coefficient of friction (COF) was measured as 0.38 at 10 N load and 10 Hz frequency. At 15 Hz frequency, the increase in load from 3 N to 10 N results in reducing the COF from 0.56 to 0.39. One order decrease in magnitude of specific wear rate was observed with an increase in load from 3 N to 10 N. Abrasive wear was the main mechanism identified in both flat and counter body materials. Severe wear was seen in counter body material (WC-Co) compared to base material of (Ti0.85Cr0.15)B2 + 20%MoSi2 composite.

Detailed liquid–liquid extraction studies of Pu(IV) with BenzoDODA have been carried out to evaluate the efficacy of BenzoDODA in the separation and recovery of Pu(IV) from acidic solutions. Acid uptake constant (KH) was determined to be 0.44. Incorporation of tertiary butyl group in the aromatic moiety of BenzoDODA resulted in the increase in extractability of Pu(IV) but at the expense of decrease in the selectivity for Pu(IV) vis a vis other metal ions. Among the various diluents studied, the normal paraffinic hydrocarbons, namely, n-dodecane/kerosene were found to be the most preferred diluents. BenzoDODA was found to be stable in radiation environment, with good extraction ability up to 20 MRad. Number of stages required for the effective recovery of plutonium from the feed solution has been determined by McCabe Thiele’s plot. It was found that even at higher loadings of Pu(IV), there is no third formation which is remarkable since at these loading TBP/n-dodecane solvent system has shown considerable third phase formation. Thus, BenzoDODA/n-dodecane solvent system can be used for recovery of Pu(IV) from concentrated processing streams as well.

Niobium diboride (NbB 2 ) is synthesized and consolidated by the spark plasma sintering technique. Elemental reactants such as niobium (Nb) and boron (B) were subjected to two stage heat treatment, initially at 1200 °C for synthesis and followed by densification at the temperatures in the range of 1700 °C to 1900 °C. High dense NbB 2 (~ 97.7%ρ th ) is obtained at 1900 °C after 15 min holding period. Load application during heat treatment stage is found to improve the sinterability of the niobium diboride compacts. Hardness, elastic modulus and indentation fracture toughness of the high dense NbB 2 are measured as 20.25 GPa, 539 GPa and 4 MPa m 1/2 respectively.

The 25,27-di(octyloxy)calix[4]arenebenzocrown-6 (CBC) in 1,3-alternate conformation was synthesized indigenously starting from its intermediates in good yield and purity. The extraction studies of CBC were carried out by using two different phase modifiers namely isodecyl alcohol and ortho-nitrophenyl hexyl ether. Detailed investigations on the effect of various parameters like, concentration of phase modifiers, aqueous phase acidity, ligand concentration, nitrate ion concentration and effect of temperature on extraction of cesium have been carried out. The concentration of phase modifiers was optimized to be 30 % in n-dodecane to ensure optimum extraction of cesium. Stoichiometry of the extracted complex determined by slope analysis method reveals 1:1:1 molar ratio for CsNO3:CBC:HNO3. The extraction process was found to be exothermic as determined from the plot of log K ex versus 1/T. The solvent system with a composition 0.01 M CBC/30 % phase modifier/n-dodecane was found to be effective for selective separation of cesium from simulated high level liquid waste solution.

The densification behavior of boron carbide without sintering additives is reported for temperatures in the range of 1100 °C to 1800 °C by spark plasma sintering (SPS) technique together with the sintering parameters (Holding Time and Pulsed DC). The influence of porosity on mechanical properties (hardness, fracture toughness and elastic modulus) of boron carbide prepared by SPS is measured. Pulsed DC current is found to play a dominant role in the densification of boron carbide and in achieving near theoretical density at lower sintering temperature compared to conventional sintering techniques. Hardness, fracture toughness and elastic modulus of fully dense B 4 C are measured as 37.2 GPa, 2.8 MPa.m 1/2 and 570 GPa respectively. Microstructural analysis indicates the presence of deformation twins in boron carbide grains.

A series of novel calix[4]arene-benzocrown-6 amide (CBCA) ligands in 1,3-alternate conformation having an amide group attached to the aromatic ring of the polyether ring network have been synthesized and evaluated for the extraction of cesium at varying concentrations of aqueous nitric acid. Amide substituted calix-crowns modified with isodecyl alcohol (IDA) and o-nitrophenylhexyl ether (o-NPHE) in n-dodecane have been used for the extraction of cesium and compared to their non-amide analogue viz. calix-benzocrown (CBC). It was observed that the presence of the amide group enhanced the uptake of cesium at high nitric acid concentrations as compared to CBC . This behavior may be attributed to an internal buffering effect of the amide group present in the calix-crowns.

A novel ligand, namely, N , N , N ′, N ′-tetra-(2-ethylhexyl)dithiodiglycolamide (DTDGA) has been explored as a carrier across a supported liquid membrane (SLM) to study the transport behavior of Pd(II) from nitric acid medium. Almost quantitative transport of Pd(II) was observed in ~2 h time interval using 0.025 M DTDGA in n-dodecane as carrier from 4.0 M HNO 3 feed solution with 0.01 M thiourea in 0.2 M HNO 3 as strippant. During this time interval almost negligible transport of other fission products present in high level waste (HLW) solution was observed. Various parameters were optimized to achieve maximum transport rate viz., feed acidity, DTDGA concentration in membrane phase, membrane porosity etc. Highest permeability co-efficient value of 2.37×10 −3 cm/s was observed for 0.025 M DTDGA as carrier keeping the feed acidity at 4 M HNO 3 and using 0.2 µm PTFE as membrane support. The membrane was found to be stable over six cycles of operation.

Effect of WSi2 addition on densification and properties of ZrB2 has been investigated. Samples of the following composition with controlled addition of WSi2 were prepared by hot pressing (1) ZrB2, (2) ZrB2+2·5%WSi2, (3) ZrB2+5%WSi2 and (4) ZrB2+10%WSi2. Hot pressing of monolithic ZrB2 at 1750°C resulted in achieving a density of only 80·1% ρth. Addition of WSi2 enhanced the densification and resulted in near theoretical density. Microstructural investigations revealed the presence of reaction product containing Si and Zr. An increase in WSi2 content led to an increase in hardness of the product. A slight increase in fracture toughness was observed with WSi2 addition. Crack deflection was observed in the microstructure. Oxidation study of the composite samples revealed that the oxidised layer is not adherent and resulted in spallation at the end of the test.

This paper presents the experimental results on synthesis of boron carbide from its elements. Boron to carbon ratio of 4:1 and a synthesis temperature of 1850°C was found optimum to obtain stoichiometric B4C. Higher boron in charge resulted in the formation of boron rich phase B8C along with B4C but was not effective in eliminating free carbon in the product. Effect of hot pressing parameters on densification of boron carbide was investigated and the optimum operating parameters to obtain B4C pellets with a density of ≥95% TD were identified. Mechanical and thermal properties were characterized and compared with literature values.

This paper presents the result of the investigation carried out on the synthesis and densification of Europium hexaboride. EuB 6 was synthesized by boron carbide reduction of Eu 2 O 3 . Effect of temperature on product quality was investigated. Pure EuB 6 powder was obtained at 1400 °C, in vacuum. Hot pressing of EuB 6 powder at 1750 °C and 32 MPa resulted in a density of only 86% of theoretical value. Addition of 10% TiSi 2 resulted in 96% of theoretical density at the same hot pressing conditions. The higher density achieved is attributed to liquid phase sintering due to low melting TiSi 2 . Hardness and fracture toughness of the composite was measured as 18.49 GPa and 3.2 MPa m 1/2 respectively. Fractured surface of the composite reveals the mode of fracture to be transgranular. SEM and EDS analyses indicate the presence of TiSi 2 in EuB 6 matrix. Isothermal oxidation study revealed that EuB 6 + TiSi 2 composite has good oxidation resistance at 900 °C in air.

This paper presents the results of detailed studies carried out on synthesis of starting materials and densification of (TiCr)B 2 with MoSi 2 as sinter additive by hot pressing. Dense compacts were characterized by measurement of density, hardness, indentation fracture toughness, flexural strength, coefficient of thermal expansion, hot hardness and electrical resistivity. Oxidation studies were investigated up to 1000 °C and isothermal oxidation kinetics in the temperature range of 750 to 950 °C. Phase identification and surface morphology analysis of hot pressed and oxidized samples were done using XRD, SEM–EDS and EPMA. (TiCr)B 2 composite of 4.81 g/cc density was obtained with the addition of 20% MoSi 2 by hot pressing at 1800 °C with 35 MPa pressure. Hardness values of composites were close to 27 GPa and fracture toughness was in the range of 3–5 MPa·m 1/2 . Coefficient of thermal expansion was measured and found to be in the range of 6.6–7.5 × 10 − 6 K − 1 from room temperature to 900 °C and electrical resistivity of the composite as 2.1, 2.6 and 3.0 μΩ·cm at 25, 500 and 1000 °C respectively. Observed nature of oxidation was parabolic for all composites. Formation of continuous and thick glassy film was observed with increased proportion of CrB 2 content in the composite. TiO 2 , SiO 2 and Cr 2 O 3 phases were mainly identified on the oxidized surface, which are responsible for the improved oxidation resistance of this composite.

The extraction properties of N,N,N',N'-tetra-(2-ethylhexyl) dithiodiglycolamide (DTDGA) have been evaluated for separation and recovery of palladium from simulated high-level liquid waste (SHLW) solution. Extraction of Pd was found to increase with increase in nitric acid concentration up to 4.0 M, above which the extraction remains almost constant. Acid uptake studies show 1:1 stoichiometry between DTDGA and HNO3 at nitric acid concentration above 3.0 M. The acid uptake constant (KH) was found to be 0.60 which could be due to the presence of two carbonyl groups of amidic moiety. DTDGA has shown very high extractability and selectivity for Pd over other metal ions present in SHLW. The separation factor (SF) for Pd over other metal ions was found to be more than 104. Almost complete back extraction of palladium from organic phase was achieved with 0.01 M thiourea in 0.1 M nitric acid. Reusability studies of the extractant indicate that DPd remains almost constant even after five successive cycles of extrac...

Titanium diboride (TiB 2 ) composite with MoSi 2 and CrB 2 has been prepared and tested to possess excellent oxidation resistance. Dense composite pellets were fabricated by hot pressing of powder mixtures. Microstructural characterization was carried out by XRD and SEM. Hardness and fracture toughness values were measured. Extensive oxidation studies of the composites were also carried out. Density of ≥ 96% ρ th was obtained by hot pressing at 1800 °C under a pressure of 35 MPa for 1 h. Hardness and fracture toughness were in the range of 18–24 GPa and 3.5–4 MPa·m 1/2 respectively. Crack branching, deflection and bridging mechanisms were observed in the crack propagation paths. Isothermal and continuous oxidation studies of these composites up to 1000 °C showed improved oxidation resistance with the formation of protective glassy layer. TiO 2 , Cr 2 O 3 and SiO 2 phases were identified on the oxidized surface. Diffusion controlled mechanism of oxidation was observed in the composites.

DTDGA solvent system was evaluated for hydrolytic and radiolytic stabilities to ascertain its application in separation and recovery of palladium from High Level Liquid Waste (HLW) solutions. Hydrolysis of DTDGA solvent system was not observed when it was kept in contact with 3.0 M nitric acid solution for two weeks. Moreover, contrary to other ‘S’ donor extractants used for the said purpose, the oxidation of thioetheric sulphur to sulphoxide or sulphones was also not observed. On the other hand, radiolysis of DTDGA solvent system was notably observed, which was found to increase with increase in absorbed dose. At gamma radiation dose of 0.2 MGy, no significant loss of DTDGA was observed. Aliphatic diluent namely n-dodecane was found to have sensitization effect on degradation of DTDGA. The degradation products were identified by GC-MS, the major ones were found to be formed by cleavage of thioetheric and amidic bonds of DTDGA molecule. The liquid–liquid extraction studies of palladium with irradiated solvent indicate that there was no significant change in D Pd up to an absorbed dose of 0.2 MGy above which it decreases gradually. Further, the radiolysis does not affect the stripping behavior of palladium. Extraction studies of Simulated High Level Liquid Waste (SHLW) elements with irradiated solvent system showed that, except palladium, any other element is hardly extracted thus retaining its remarkable selectivity.

Effect of EuB 6 addition on densification and properties of ZrB 2 have been investigated. Samples of the following composition were hot pressed. (1) ZrB 2 + 2.5% EuB 6 , (2) ZrB 2 + 5% EuB 6 and (3) ZrB 2 + 10% EuB 6 . EuB 6 addition helped in densification of ZrB 2 at a lower hot pressing temperature of 1750 °C. Microstructural investigations revealed the formation of ZrB 2 –EuB 6 solid solution. The mode of fracture was seen to be intergranular. Hardness slightly increased with 2.5% EuB 6 addition but decreased with 5 and 10% EuB 6 addition. Fracture toughness of the composite was better than the monolithic ceramic. Crack deflection and crack branching were observed in the microstructure. The composite samples were found to be resistant to oxidation at 900 °C in air. The nature of oxidation for the composite was near parabolic in nature.

This paper reports on the development of HfB2 reinforced B4C composite prepared through reaction hot pressing of B4C and HfO2. These composites were characterized for phase composition, microstructure, mechanical and physical properties. Full dense composites were obtained by hot pressing at 1900 °C and a pressure of 40 MPa. HfB2 phase was identified as a reaction product in the composites by XRD analysis. Hardness of all the composites was measured to be in the range of 28–35 GPa. High elastic modulus (525 GPa) and shear modulus (196 GPa) were measured for composite corresponding to 10 wt.% HfO2. Fractography of the composites indicates transgranular mode of fracture. Fracture toughness of the composites was in the range of 4–7 MPa.m1/2 which is higher than that of monolithic B4C (2.43 MPa.m1/2). Microstructural observation of crack propagation patterns indicates the major toughening mechanism as crack deflection, crack arrest and crack bridging.

Amberlite XAD-16 has been functionalized with 2-acteyl pyridine by coupling it with 2-chloro pyridine after acetylation. The resulting resin (AP-XAD 16) has been characterized by various techniques like FT-IR, TGA, elemental analysis, etc. and has been evaluated for the solid phase extraction of palladium and other metal ions present in high level waste (HLW) solution. Sorption equilibrium was attained within 30–45 min. The pseudo-second order kinetics model yielded the best fit for the experimental data of sorption kinetics. Pd sorption was found to decrease gradually with increase in aqueous phase acidity. The sorption process involves the complex formation between Pd(II) and the resin which contains the carbonyl group and soft ‘N’ atom of pyridine moiety with lone pair of electrons. The loaded palladium can be effectively eluted using acidic thiourea solutions. The adsorption isotherm data fitted well with Langmuir as well as Freundlich models. The maximum sorption capacity of the resin was found to be 8 mg/g which is in agreement with the equilibrium adsorption capacity. Sorption studies carried out with simulated high level waste solution have shown very high uptake of palladium as compared to the other elements, thus showing the potential for possible use of the resin for efficient separation and recovery of palladium from HLW solution.

The extractant N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (TEHDGA) has been evaluated for extraction of strontium from the raffinate solution of TEHDGA-actinide partitioning process. Actinide partitioning of HLW using 0.2 M TEHDGA + 30% isodecyl alcohol/n-dodecane, carried at our unit at engineering scale, selectively separates trivalent ‘f’ group elements from HLW leaving all the elements including strontium in the raffinate. Strontium from the raffinate was extracted using 0.3 M TEHDGA + 5% isodecyl alcohol/n-dodecane, isodecyl alcohol has been used as a phase modifier whose concentration was optimized to 5% (v/v) to obtain maximum extraction of strontium (D3.1–3.8 M = 23) without third phase formation in the given extraction conditions. The stoichiometry of the extracted complex was found to depend on initial aqueous nitric acid concentration and obtained as Sr(NO3)2(TEHDGA)2(HNO3)2. Fission products, such as Mo, Pd, and Zr, co-extracted during extraction process were scrubbed with 3.5 M nitric acid containing 0.2 M oxalic acid and 0.05 M HEDTA. Complete stripping of strontium was achieved with 0.01 M nitric acid. Quantitative recovery of strontium was obtained in a single contact of extraction, two contacts of scrubbing and two contacts of stripping each at O/A = 1.

A novel carrier, N,N,N',N'-tetra-(2-ethylhexyl) thiodiglycolamide, T(2EH)TDGA has been studied for transport of Pd(II) from nitric acid medium across a supported liquid membrane (SLM). Pd(II) was found to be almost quantitatively transported (≈ 99.9%) within 2h from 3.0M HNO(3) medium using 0.05 M T(2EH)TDGA in n-dodecane as carrier and 0.01 M thiourea in 0.2M HNO(3) as strippant. Pd(II) transport was also studied against various parameters like feed acidity, carrier concentration, membrane pore size, etc. Palladium transport was found to be diffusion controlled and the diffusion co-efficient value was found to be 3.56 × 10(-5)cm(2)/s. Selectivity of T(2EH)TDGA for palladium over other fission products was found to be quite high, with the separation factors for Pd, with respect to different fission products being >10(3). With respect to leaching out of carrier from the membrane support, the membrane was found to be stable for six consecutive cycles. Thus, T(2EH)TDGA can be used as an efficient carrier of Pd(II) from nitric acid medium.

This paper reports on the densification of TiB2 by hot pressing using WSi2 as sinter additive. The dense pellets were evaluated for mechanical, physical and thermal properties. Isothermal oxidation studies were carried out at 850 °C. Thermal shock resistance of this composite was evaluated by repeated heating/cooling cycles between 850 °C and 150 °C. Microstructural observations of hot pressed and oxidized samples were made using SEM-EDAX and XRD. Pellets of near theoretical density were obtained by hot pressing of the powder mixtures at 1600 °C and a pressure of 30 MPa with ≥ 5% addition of WSi2. W5Si3 phase was identified as a reaction product of hot pressing. Hardness values of the composite with varying WSi2 were measured and these were found to be in the range of 24–26 GPa. Fracture toughness was in the range of 4–6 MPa.m1/2 which is higher than that of monolithic TiB2 (3–4 MPa.m1/2). Crack deflection and bridging mechanisms were responsible for the higher fracture toughness. Coefficient of thermal expansion was measured up to 900 °C. Improved oxidation behavior was observed in the TiB2 + WSi2 composite as compared to that of monolithic TiB2. TiO2 and SiO2 phases were identified on the surface of the oxidized samples. Excellent thermal shock resistance was observed in TiB2 + 15%WSi2 composites even after 800 cycles.

Solvent extraction separation of divalent cobalt and nickel from sulphate solutions was studied using OPPA dissolved in n -dodecane and the optimum conditions for separation of cobalt and nickel were determined. It was found that extraction of both the metal ions increases with increase in equilibrium pH. Cobalt was preferentially extracted over nickel in all pH range, ΔpH 0.5 value of 1.8 indicates the possible separation of both the metal ions from each other. Almost complete extraction of cobalt is observed at pH 4.5 where separation factor ( β = D Co / D Ni ) is approximately 1400, above this pH co-extraction of nickel increases and reduction in separation factor was observed. The composition of extracted species determined by slope analysis of the plots of log D vs. log [OPPA] 2 and log D vs. equilibrium pH indicates formation of the species MA 2 (HA) 2 for both the metal ions. Temperature dependence studies of the extraction constant K ex , showed that the extraction is enthalpy driven with unfavorable entropy. OPPA/dodecane was employed for cobalt/nickel separation from raffinate solution obtained during solvent extraction process of spent ammonia cracker catalyst leach solution. 1.0 M OPPA/dodecane in counter-current extraction at O / A of 1.0 was efficiently used to separate cobalt from nickel.

Effect of CrSi 2 and HfB 2 addition on densification and properties of ZrB 2 has been investigated. Dense samples of ZrB 2 + 10%CrSi 2 and ZrB 2 + 10%CrSi 2 + 10%HfB 2 were prepared by hot pressing. Addition of CrSi 2 assisted in densification of ZrB 2 at lower hot pressing temperature (1650 °C) and pressure (20 MPa). During sintering, formation of ZrSi 2 took place which helps in densification by liquid phase sintering. Hardness of ZrB 2 with silicide was measured to be lower than the monolithic ceramic, but the fracture toughness was higher. CrSi 2 addition improved the oxidation resistance of ZrB 2 in the temperature range of 800–1000 °C due the formation of silica based glassy layer on the surface. Addition of HfB 2 to this composite has been found to increase the hardness. Oxidation resistance of the composite containing 10%HfB 2 was found superior compared to other samples. Thus a composite having a higher fracture toughness and better oxidation properties than monolithic ZrB 2 has been developed with the addition of CrSi 2 and HfB 2 .

Hydrolytic and radiolytic stability of T(2EH)TDGA solvent system has been investigated to establish its application in separation and recovery of palladium from High Level Liquid Waste (HLW) solutions. Hydrolysis of T(2EH)TDGA solvent system with nitric acid was not observed. Moreover, unlike other “S” donor extractants used for the said purpose, the oxidation of thioetheric sulphur to sulphoxide or sulphones was also not observed. However, radiolytic degradation was notably observed and found to increase with increase in absorbed dose. n-dodecane was found to sensitize the degradation of T(2EH)TDGA. At gamma radiation dose of 0.2 MGy, no significant loss of T(2EH)TDGA was observed. The degradation products were identified by GC-MS. The major products were found to be formed by cleavage of thioetheric and amidic bonds of T(2EH)TDGA molecule. The extraction studies of palladium with irradiated solvent indicate that with 0.025 M T(2EH)TDGA/n-dodecane, there was no significant change in D Pd up to an absorbed dose of 0.2 MGy above which it decreases significantly. However, with 0.05 M T(2EH)TDGA/n-dodecane, there is gradual decrease in D Pd with increase of absorbed dose. Further, the radiolysis does not affect the stripping behavior of palladium. Extraction studies of Pd(II) and other fission products from simulated high level liquid waste (SHLW) solutions to irradiated solvent system showed that, except palladium, any other element is hardly extracted thus retaining its remarkable selectivity.

Boron carbide is one of the potential neutron-shielding materials and its use can be maximized for structural shielding application by dispersing it into metal matrixes such as aluminum. Dispersion of B4C and its interfacial stability is a major issue during its processing. This investigation is on the synthesis of B4C-reinforced 6061 aluminum matrix composite by liquid–metal stir-casting technique under optimized conditions after solving the issues related to the processing, and evaluation of the structural, mechanical, and interfacial characteristics. During processing of composites, pretreatment of B4C particles is necessary to improve its dispersion. However, higher preheating temperatures above 300°C lead to particle agglomeration in the matrix due to the formation of B2O3 phase during preheating. B2O3 is formed due to the surface oxidation of B4C particles above 300°C and this glassy phase leads to particle sintering and lump formation. Incorporation of particles preheated at 250°C has shown uniform distribution of particles in the composite. Interfacial characterization of the composite and the extracted B4C particles from the matrix has shown the presence of interfacial reaction products such as AlB2, Al3BC, AlB12, and AlB10.

The extraction properties of N,N,N′,N′-tetra(2-ethylhexyl)thiodiglycolamide T(2EH)TDGA have been evaluated for the separation and recovery of palladium from simulated high-level liquid waste (SHLW). T(2EH)TDGA has shown very high selectivity for Pd (II) over other metal ions present in SHLW. The separation factor (SF) for Pd (II) over other metal ions was found to be more than 105. Reusability studies of the extractant indicate that DPd remained almost constant even after five successive cycles of extraction and stripping. Palladium was quantitatively recovered from thiourea strip solution by treating it with ammonia and filtering the precipitate of palladium sulphide. The acid uptake constant (KH) was found to be 0.62 which could be due to the presence of two carbonyl groups of amidic moiety. To account for very high extractability of palladium with T(2EH)TDGA over other ‘S’ donor extractants, namely Bis-(2-ethylhexyl)sulphoxide (BESO), FTIR, as well as Raman studies were carried out. FTIR and Raman stud...

Electrorefining is a very effective technique for transforming impure vanadium to a state of high purity. Besides being semi-continuous in nature, this process removes all the interstitial impurities to well below their respective tolerable limits, together with a number of commonly associated metallic impurities. Among different types of vanadium materials used for anode feed, carbothermic vanadium is not only relatively, less costly and easy to prepare, but also could be electrorefined into high purity vanadium. However, the presence of relatively high amount of carbon in the anode feed critically affects the electrorefining process resulting in lesser purity and poorer recovery of the vanadium. In the present study, a low-cost vanadium intermediate, essentially a solid solution of vanadium, nitrogen, carbon and oxygen was studied for electrorefining. The anode feed, containing {approx}94% vanadium, was prepared by nitridation-cum-denitridation of a mixture, comprised of V{sub 2}O{sub 5} and petroleum coke powders. The electrorefining was carried out in a LiCl-KCl-VCl{sub 2} bath at 893 K under high purity argon atmosphere. The current efficiency, vanadium recovery and purity were 90, 86, and 99.85%, respectively.

A process to upgrade the nickel-rich fraction of the chromite ore overburden, mined from the Sukinda belt of Orissa state on the eastern coast of India, has been developed. The composition of this fraction is similar to that of the lateritic nickel ore deposits of this region. It was possible to upgrade the nickel content from an initial value of ∼ 1 wt.% to a final value of 3 wt.% NiO by selectively removing iron from the overburden, through a combination of sulphurization and chlorination processes. The optimum parameters to ensure maximum removal of iron have been established.

A novel extractant, namely, Benzodioxodiamide (BenzoDODA) has been synthesized and evaluated for its extraction behaviour towards plutonium and other elements present in the spent nuclear fuel. High separation factors for plutonium over other elements were observed, indicating the high selectivity of the extractant for plutonium. The extractant is quite promising for the selective separation of plutonium from dissolver solution and various acidic waste streams.

Review: evaluation of various liquid-liquid extraction processes for Pd separation from liquid waste generated during reprocessing of spent nuclear fuels; 63 refs.

Boron carbide and its composites find a wide range of applications such as armour material, p-type semiconductor in electronic industries, as a neutron detectors and absorbers in nuclear industry and as a thermo-electric device for space applications, due to their unique physical, thermal and thermo-electric properties. This work discusses about the development of B4C-HfB2 ceramic-ceramic composites. Nearly full dense B4C-HfB2 ceramic composites were fabricated by in situ processing using B4C, HfO2 and CNT, as starting materials. The effect of HfO2 and CNT content on microstructure and mechanical properties of B4C composite has been investigated. Additions of 2.5–30 wt% HfO2 and 0.2–2.5 wt% CNT resulted in improvement in density and fracture toughness of the material. On increasing the additive contents, the fracture toughness of the composite increased more than twice that of monolithic B4C, whereas hardness decreased by about 12 %. Elastic Modulus of the composites was measured to be in the range of 570–625 GPa. Crack deflection observed in the composites was found to be the major toughening mechanism due to the existence of residual thermal stress. The maximum value of hardness, fracture toughness and elastic modulus were 36 GPa, 6.6 MPa m1/2, and 625 GPa, respectively.

The kinetics of cobalto-cobaltic oxide (Co3O4) dissolution in sulphuric acid have been investigated. The dissolution rate is significantly enhanced by the use of Na2SO3 in aqueous media for the reduction of Co3+ to Co2+. The dissolution was studied as a function of rate of agitation, leaching time, acid concentration, temperature and Na2SO3 concentration. The reaction has a 12 order of dependence on acid concentration between 1.0 and 4.0 M. The rate of dissolution appears to be independent of the SO2−3 concentration above 0.025 M. Primary identification of the rate-controlling step has been accomplished by close fitting experimental data to the predicted reduced time plots for diffusion of the reactant species across the unreacted solid layer. The activation energy for the temperature range 303–343 K was found to be 25 kJ/mol, thereby confirming diffusion as the rate-controlling step.

Oxidation of millerite by cupric chloride in sodium chloride solutions has been studied as a function of: rate of agitation; leaching time; temperature; acid concentration; and total initial cupric concentration. The reaction has a 0.5 order of dependence on initial cupric concentration in the range 0.0 – 0.5 M . The activation energy for the temperature range 333–363 K was found to be 65.2 kJ/mol with chemical reaction at the mineral surface as the rate-controlling step. The rate expression, for initial cupric concentrations between 0.0 and 0.5 M , is: {1−(1−α) 1 3 } = {9.27 × 10 3 ·[ Cu(II) ] 0.5 · r 0 −1 exp ( −7.847 × 10 3 T ) }·t according to the shrinking-core model.

A precise, sensitive and selective method for the spectrophotometric determination of palladium (II) using N , N , N ′, N ′-tetra(2-ethylhexyl) thiodiglycolamide T(2EH)TDGA as an extractant is described. Palladium (II) forms yellow colored complex with T(2EH)TDGA which exhibits an absorption maximum at ∼300 nm. The colored complex obeys Beer's law in the concentration range 1.0–15.0 μg ml −1 of palladium with a molar absorptivity of 1.29 × 10 5 M −1 cm −1 . The effects of various experimental parameters have been studied to establish the optimum conditions for the extraction and determination of palladium. The precision of the method has been evaluated and the relative standard deviation has been found to be less than 0.5%. The method has been successfully applied to the determination of palladium in simulated high level liquid waste (SHLW) solution.

The present paper provides a review of the various processes/schemes developed for the separation and recovery of palladium from high level liquid waste (HLLW) generated during reprocessing of spent nuclear fuel. This separation is necessary in view of various problems posed by the presence of palladium during vitrification of HLLW. Further, to meet the ever increasing demand for palladium in various applications, HLLW can be considered as one of the possible secondary sources of this valuable metal. In this regard several processes are proposed involving liquid–liquid extraction, solid phase extraction, precipitation electro-deposition, for recovering palladium from HLLW. The focus of the present review is to evaluate various liquid–liquid extraction processes proposed for palladium separation from HLLW.

The structure of the extraction complexes of palladium(II) with novel ligands, namely, N,N,N′,N′-tetra-(2-ethylhexyl) thiodiglycolamide (T(2EH)TDGA) and N,N,N′,N′-tetra-(2-ethylhexyl) dithiodiglycolamide (DTDGA), have been determined by extended X-ray absorption fine structure spectroscopy (EXAFS). The interpretation of the EXAFS data is well supported by theoretical calculations of the complex geometry based on density functional theory (DFT). T(2EH)TDGA, having one thioetheric ‘S’ atom, forms a square planar complex with the Pd(II) ion, exhibiting 2 : 1 stoichiometry with one sulphur atom and one carbonyl oxygen atom from each T(2EH)TDGA molecule interacting with Pd(II) at distances of 2.24 and 2.04 A, respectively. On the other hand, DTDGA, having two ‘S’ atoms in addition to two carbonyl groups, forms a square planar complex with Pd(II), exhibiting 1 : 1 stoichiometry, wherein both the sulphur atoms and the carbonyl oxygen of DTDGA interact with Pd(II) at distances of 2.29 and 2.05 A, respectively. The slight distortion from the perfect square planar geometry could be attributed to the steric hindrance imposed by the bulky alkyl group of the amidic moieties. DFT calculations for the Pd–ligand complexes show that the Pd(II)–DTDGA complex with 1 : 1 stoichiometry is energetically more stable than the Pd(II)–T(2EH)TDGA complex with 1 : 2 stoichiometry. Among the two possible Pd(II)–T(2EH)TDGA complex geometries, the cis configuration appears more favorable. The methodology of fitting the EXAFS data has been validated by fitting the EXAFS data of a Pd(II)–aquo complex which showed square planar geometry with two axial water molecules constituting the secondary hydration sphere.

The paper reports leaching studies on a nickel-copper sulphide mineral concentrate with cupric chloride in a strong brine solution under a moderate pressure of oxygen. Oxygenation not only helps to maintain a high cupric to cuprous ion ratio in the leaching medium but also facilitates rejection of iron as insoluble goethite. A single step thus gives rise to a relatively iron-free nickel-copper-bearing solution. The influence of the amount of cupric chloride, pulp density, time, temperature, oxygen pressure, concentration of hydrochloric acid and particle size of the feed material on the leaching process have been studied. On this basis it has been possible to define a suitable combination of process parameters for leaching out most of the associated nickel and copper values and to generate a solution low in iron.

This paper describes a ferrous chloride-oxygen leach process for recovery of nickel and copper values from sulphide concentrates available in India. The sulphide concentrates aareleached with a stirred solution of ferrous chloride in a glass-lined reactor operated at various temperatures and oxygen pressures. In this single step process, copper and nickel are converted into their water soluble chloride forms, whereas iron is rejected as hydrated iron oxide with simultaneous generation of sulphur in the non-polluting elemental form. The influence of various parameters such as (i) amount of ferrous chloride (60–100% stoichiometric), (ii) oxygen pressure (0.308–0.515 MPa), (iii) leaching temperature (90–120°C) and (iv) duration of leaching (2–10 h) on the leaching process has been examined. It has been possible to recover 94–99% nickel and 98% copper with low iron contamination by using optinum conditions, such as a stoichiometric amount of ferrous chloride, a temperature of 110°C, an oxygen pressure of 0.377 MPa and a duration of 8 h.