Thermodynamic and kinetic analysis of CrB_(2) and VB_(2) formation in molten Al−Cr−V−B alloy

Transition metal impurities such as chromium(Cr)and vanadium(V)in solution deteriorate electrical conductivity of smelter grade aluminium(Al).These impurities can be removed from solution via boron treatment in which borides form upon their in-situ reaction with boron(B)-bearing substances.However,Cr removal from smelter grade Al solution is not well understood.A disagreement related to chromium boride(CrB_(2))formation in molten Al in the presence of other transition metals(V,Ti,Zr,Fe)by adding Al−B master alloy has been reported in literatures.This study presents an effort to understand the mechanism of Cr removal from Al−0.50%Cr−0.50%V(mass fraction)alloy by adding Al−B(AlB_(12))master alloy at 1023 K in the Al alloy solution.Results indicate that Cr removal from molten Al−0.50%Cr−0.50%V alloy by forming stable borides cannot be achieved at 1023 K;whereas excess of B in the solution preferentially forms aluminium boride(AlB2)over CrB_(2) during boron treatment of molten Al.The underlying kinetics of V removal from molten Al−0.50%Cr−0.50%V alloy revealed that early reaction stage is controlled by[B]/[V]mass transfer through liquid phase and mass transfer coefficient(km)was measured to be 9.6×10^(−4) m/s.The later reaction stage was controlled by[B]/[V]diffusion through boride(VB_(2))ring.This study,therefore,advocates to investigate alternative ways to remove Cr from molten Al.

Effect of Plant Growth-Promoting Rhizobacteria on Growth,Nodulation and Nutrient Accumulation of Lentil Under Controlled Conditions

Application of plant growth-promoting rhizobacteria （PGPR） has been shown to increase legume growth and development under field and controlled environmental conditions. The present study was conducted to isolate plant growth-promoting rhizobacteria （PGPR） from the root nodules of lentil （Lens culinaris Medik.） grown in arid/semi-arid region of Punjab, Pakistan and examined their plant growth-promoting abilities. Five bacterial isolates were isolated, screened in vitro for plant growth-promoting （PGP） characteristics and their effects on the growth of lentil were assessed under in vitro, hydroponic and greenhouse （pot experiment） conditions. All the isolates were Gram negative, rod-shaped and circular in form and exhibited the plant growth-promoting attributes of phosphate solubilization and auxin （indole acetic acid, IAA） production. The IAA production capacity ranged in 0.5-11.0μg mL-1 and P solubilization ranged in 3-16 mg L-1. When tested for their effects on plant growth, the isolated strains had a stimulatory effect on growth, nodulation and nitrogen （N） and phosphorus （P） uptake in plants on nutrient-deficient soil. In the greenhouse pot experiment, application of PGPR significantly increased shoot length, fresh weight and dry weight by 65%, 43% and 63% and the increases in root length, fresh weight and dry weight were 74%, 54% and 92%, respectively, as compared with the uninoculated control. The relative increases in growth characteristics under in vitro and hydroponic conditions were even higher. PGPR also increased the number of pods per plant, 1 000-grain weight, dry matter yield and grain yield by 50%, 13%, 2870 and 29%, respectively, over the control. The number of nodules and nodule dry mass increased by 170% and 136%, respectively. After inoculation with effective bacterial strains, the shoot, root and seed N and P contents increased, thereby increasing both N and P uptake in plants. The root elongation showed a positive correlation （R2 = 0.67） with the IAA production and seed yield exhibited a positive correlation （R2 = 0.82） with root nodulation. These indicated that the isolated PGPR rhizobial strains can be best utilized as potential agents or biofertilizers for stimulating the growth and nutrient accumulation of lentil.