Optimization of casting process parameters for synthesis of Al-Nb-B master alloy

Al-Nb-B master alloys were synthesized using commercial pure aluminum, niobium, and KBF4 salts. Two different sources of Nb (pure Nb powder and Al-60%Nb powder) were used to prepare the master alloy. Casting process parameters such as reaction time and melt stir time interval were varied to enhance the formation of in situ intermetallic particles in the master alloys. The size, shape and distribution of intermetallic particles in these master alloys were studied using microscopy techniques. The results show that the Al-5Nb-1B master alloy prepared with Al-60%Nb powders has a uniform distribution of intermetallic particles as compared to the master alloy prepared with pure Nb powders. Increase in boron content from 1 wt.% to 2 wt.% in the master alloys resulted in a higher fraction of intermetallic particles. Among all the master alloys synthesized, Al-5Nb-2B was observed to have the highest number of well-distributed intermetallic particles which could act as potential grain refiners of aluminum alloys

Periodontal Considerations in Adult Orthodontic Patients

The relationship between periodontology and orthodontics consists of a highly complex, bidirectional and close interaction that is nowadays characterized by controversial scientific opinions and clinical approaches. The relevant increasing number of adult orthodontic patients which in most cases present already-compromised periodontal tissues has markedly highlighted the potential of orthodontic treatment in enhancing or deteriorating periodontal health and also the outmost relevance of peculiar periodontal planning prior and during orthodontic treatment. Since the progress in adult orthodontics trend is rapid, there is also an increasing need for evidence-based protocols that might guide clinicians through a comprehensive, interdisciplinary and successful treatment. This chapter has been compiled with the aim of providing orthodontists, periodontists and general practitioners with sound evidence-based protocols and valid clinical approaches that have proven to be successful for numerous patients over long follow-ups. It is structured following the steps for a correct therapy management, starting from comprehensive examination and diagnosis to before and during orthodontic treatment considerations, and finally analysing the present state of new adult orthodontic technologies

A Large-scale Analysis of the Marketplace Characteristics in Fiverr

Crowdsourcing platforms have become quite popular due to the increasing demand of human computation-based tasks. Though the crowdsourcing systems are primarily demand-driven like MTurk, supply-driven marketplaces are becoming increasingly popular. Fiverr is a fast growing supply-driven marketplace where the sellers post micro-tasks (gigs) and users purchase them for prices as low as $5. In this paper, we study the Fiverr platform as a unique marketplace and characterize the sellers, buyers and the interactions among them. We find that sellers are more appeasing in their interactions and try to woo their buyers into buying their gigs. There are many small tightly-knit communities existing in the seller-seller network who support each other. We also study Fiverr as a seller-driven marketplace in terms of sales, churn rates, competitiveness among various subcategories etc. and observe that while there are certain similarities with common marketplaces there are also many differences

Physico-chemical investigations on the sintering behaviour of red mud - flue dust composites

Two industrial waste products namely red mud and flue dust have been utilised to form composites and their sintering behaviour was investigated in this study. It has been observed that red mud alone can be sintered around 1250°C. Addition of flue dust can reduce the sintering temperature and bring it in the range of 1150 - 1200°C depending on the extent of flue dust addition (10-30%). The sintering kinetics initially follows the Johnson - Mehl model of nucleation and grain growth and subsequently beyond fractional conversion of 0.7. follows the three dimensional contracting geometry model. XRD studies reveal that there are at least 6-8 phases in the sintered product. Some of these are Fe,O, Ca,Fe,Si,Ofz, SiO,. NaAlSiO4, FeT(O,, 710, and Na,Si,O, EPMA studies show that apart from the above phases, smaller amounts of ZrSiO, and a few other rare earth compounds were also present in the sintered product. The silicate phases are essentially present in the grain boundaries of other non-silicate phases and these phases are responsible for reduction in the sintering temperature. These glassy phases are also responsible for inter-particle bonding in the composites. This conclusion has also been verified through scanning electron microscopy (SEM). The sintering temperature and fraction of the flue dust in the composites have been optimised at 1200°C and 20% respectively

Sensing properties of germanate and tellurite glass optical fibres

Strain and thermal sensitivities of germanate and tellurite glass fibres were measured using a fibre Fabry-Perot (FFP) interferometer and fibre Bragg gratings (FBG). The strain phase sensitivity for germanate and tellurite fibre were 5900×103 rad/m and 5600×103 rad/m respectively at a central wavelength of 1540nm using FFP interferometer, which is consistent with the value of 1.22pm/µepsilon obtained for a germanate fibre FBG. The Young's modulus for germanate and tellurite fibre were also measured to be 58GPa and 37GPa. The thermal responses of germanate fibre were examined as 24.71 and 16.80 pm/°C at 1540nm and 1033nm wavelength using the FBG

Fiber Bragg gratings inscribed using 800nm femtosecond laser and a phase mask in singleand multi-core mid-IR glass fibers

For the first time, Fiber Bragg grating (FBG) structures have been inscribed in single-core passive germanate and three-core passive and active tellurite glass fibers using 800 nm femtosecond (fs) laser and phase mask technique. With fs peak power intensity in the order of 10(11)W/cm(2), the FBG spectra with 2nd and 3rd order resonances at 1540 and 1033 nm in the germanate glass fiber and 2nd order resonances at approximately 1694 and approximately 1677 nm with strengths up to 14 dB in all three cores in the tellurite fiber were observed. Thermal responsivities of the FBGs made in these mid-IR glass fibers were characterized, showing average temperature responsivity approximately 20 pm/ degrees C. Strain responsivities of the FBGs in germanate glass fiber were measured to be 1.219 pm/microepsilon

Phase equilibria in the metal-sulfur-oxygen system and selective reduction of metal oxides and sulfides : Part I. The carbothermic reduction and calcination of complex mineral sulfides

Copyright 2006 Elsevier B.V., All rights reserved.The difference in the standard Gibbs free energy for the formation of any two oxides or sulfides is the chemical potential for selective reduction of metals from complex minerals. The magnitude of the Gibbs free energy difference is shown by plotting the univariant relationships for relevant sulfides and oxides. In this investigation, three examples of mineral sulfides are considered, and the experimental results are compared with the predicted thermodynamic calculations. These examples include the reduction conditions for nickel and iron sulfides and pentlandite (Fe,Ni)S and chalcopyrite (CuFeS) minerals. The reduction behavior of mineral sulfides, such as those of nickel, cobalt, iron, and copper, is illustrated by referring to both the sulfide and alloy phase equilibria. In particular, the solution thermodynamic properties of the metallic phase equilibria are featured for determining the physical chemistry of preferential or selective reduction of the metal oxides and sulfides. The mechanism for the reduction of the aforementioned sulfide minerals is explained with the aid of the governing phase equilibria for the calcination process. The results from the carbothermic reduction of sulfide minerals are also compared. The important roles of lime and calcium sulfate in controlling the emission of sulfurous gases during the reduction reaction are explained. A qualitative analysis of reduction reactions of nickel and iron sulfides is reviewed to provide a comparison of the mechanism for complex nickel-bearing minerals. The importance of these results in producing alloy and pure metallic phases is also examined.Peer reviewe