Dipentaerythritol: a novel additive for the precipitation of dispersed Ni particles in polyols Angshuman Pal, a Igor Sevonkaev, a Brandon Bartling, b Job Rijssenbeek b and Dan V. Goia * a Highly dispersed uniform Ni particles ranging in size from 0.1 to 1.2 mm were synthesized by reducing nickel carbonate in polyols in the presence of dipentaerythritol (DPE) and noble metal salts. DPE was essential in preventing the aggregation of nickel particles, while the noble metal (‘seeding’ approach) effectively tailored their size. Ferromagnetic particles with a cubic closed packed (ccp) crystal habit were obtained using short reduction times at temperatures below 200  C. Non-magnetic particles with hexagonal closed packed (hcp) structure were obtained after extended heating times (>16 hours) at temperatures above 220  C. The temperature of the reduction and heat-treatment process was adjusted by using polyols with different boiling points. Introduction Dispersed nickel particles are widely used in conducting 1 and magnetic inks, 2 ferrouids, 3,4 as well as in the manufacturing of optical, 5 catalytic, 6 and electronic devices. 7 In these applications a precise tuning of powder properties is critical for optimum performance. Developing methods that offer the ability to tailor the size, dispersion, and structure of particles is a challenging task, particularly when attempting to prepare powders at industrial scale. Hydrothermal growth, 8,9 ethanol–water extrac- tion, 10 electrochemical, 11,12 sol–gel, 13,14 microwave-assisted, 15 and polyol reduction 16,17 are some of the techniques used to produce such particles. Among these methods, liquid phase precipitation via polyol reduction stands out as a versatile, environmentally friendly, and cost effective approach well- suited to industrial scale manufacturing. Since the pioneering work of Fievet et al. 18 on the polyol system, extensive research has been carried out to obtain nely dispersed metal powders with controlled properties. 19–22 The nature and concentration of metal salt, the chemical structure of the polyol, and the reduction temperature have been found to play important roles in the particle formation. Additionally, the use of dispersing agents to keep the metallic particles dispersed at high metal concentration has been extensively investigated. Since high molecular weight organic compounds are oen detrimental, low molecular weight dispersants similar in structure to the polyols have been considered. Prior studies have shown that sorbitol (a small linear polyalcohol molecule) has a benecial effect on the dispersion and uniformity of precipitated metallic particles. 23 Goia et al. 24 showed that pentaerythritol (a branched polyalcohol) effectively prevents the aggregation of nickel particles at high nickel concentration. In this work, we report that larger branched polyol molecules, such as dipentaerythritol, are even more effec- tive in maintaining the nickel particles dispersed at very high metal concentrations (>15 wt% nickel). This study also reveals that at these high concentrations, the size of highly dispersed nickel particles can be readily adjusted in the 0.1 to 1.2 mm range by using noble metal salts as ‘seeding’ agents. Finally, processing conditions that convert magnetic cubic closed packed (ccp) Ni particles (typically formed in the conventional polyol system) to nonmagnetic hexagonal closed packed (hcp) particles are described. The ability to obtain highly dispersed uniform Ni particles with controlled size and magnetic properties using a concentrated, easily scalable, and cost effective precipitation process is of signicant importance for many practical applications. Experimental Reagents Nickel basic carbonate (54% Ni) was purchased from Sheppard Chemical Co. 1,2-Propylene glycol was obtained from Pharmco- aaper (Brookeld, CT). Tetraethylene glycol was purchased from Sigma-Aldrich. Pentaerythritol (PE) and dipentaerythritol (DPE) were received from Alfa Aesar. Hexachloroplatinic acid (H 2 PtCl 6 , 33.57 wt% platinum) and palladium chloride (PdCl 2 , 24.29 wt% palladium) solutions were supplied by Umicore (South Plaineld, NJ, USA). All reactants were used as received. Characterization The size and shape of nickel particles were determined by eld emission scanning electron microscopy (FESEM JEOL-7400). a Center for Advanced Materials Processing, Clarkson University, Potsdam, NY 13699-5814, USA. E-mail: goiadanv@clarkson.edu b GE Global Research, One Research Circle, Niskayuna, NY 12309, USA Cite this: RSC Adv. , 2014, 4, 20909 Received 19th February 2014 Accepted 29th April 2014 DOI: 10.1039/c4ra01464b www.rsc.org/advances This journal is © The Royal Society of Chemistry 2014 RSC Adv. , 2014, 4, 20909–20914 | 20909 RSC Advances PAPER Published on 29 April 2014. Downloaded by Clarkson University on 13/05/2014 18:00:40. View Article Online View Journal | View Issue