Contemporary Chemistry of Berkelium and Californium

The merging of small-scale syntheses and rapid crystallization methods have provided access to crystalline samples of berkelium (Z=97) and californium (Z=98) coordination complexes and compounds that can be interrogated with a suite of spectroscopic tools and structural elucidation approaches that have come online over the last 20 years. The combination of this experimental data with relativistic theoretical methods that capture the effects of spin-orbit coupling and scalar relativistic effects have allowed us to understand the electronic structure of berkelium and californium compounds at a level of detail that was not previously possible. The harbinger of this new era of post-curium chemistry was the synthesis and characterization of [Cf{B₆O₈(OH)₅}]. This compound possesses a structure type that is distinct from earlier actinide borates, a reduction in coordination number for californium, contracted Cf−O bond lengths, a substantially reduced magnetic moment with respect to the calculated free-ion moment and, most importantly, vibronically coupled broadband photoluminescence. Ligand-field analysis also showed that the splitting of the ground state was larger than typically found in the f-block elements, and when taken together places its overall electronic structure as a hybrid of d- and f-block components. The discovery of the unusual properties of this compound has led to the development of large families of 4f and 5f coordination complexes, in an effort to uncover the underlying origin of the electronic structure oddities, and whether there really is a sharp onset of these changes at californium. This in turn pushed the development of far more challenging berkelium chemistry (from a radiologic standpoint) because the half-life of the isotopes decreases from 351 years for ²⁴⁹Cf to 330 days for ²⁴⁹Bk. This short review details some of the chemistry that has been reported over the last 15 years, and its consequences for understanding the periodic table.     

Biomedical neutron research at the Californium User Facility for Neutron Science

The Californium User Facility for Neutron Science has been established at Oak Ridge National Laboratory (ORNL). The Californium Use Facility (CUF) is a part of the larger Californium Facility, which fabricates and stores compact²⁵²Cf neutron sources for worldwide distribution. The CUF can provide a cost-effective option for research with²⁵²Cf sources. Three projects at the CUF that demonstrate the versatility of²⁵²Cf for biological and biomedical neutron-based research are described: future establishment of a²⁵²Cf-based neutron activation analysis system, ongoing work to produce miniature high-intensity, remotely afterloaded²⁵²Cf sources for tumors therapy, and a recent experiment that irradiated living human lung cancer cells impregnated with experimental boron compounds to test their effectiveness for boron neutron capture therapy.     

First Structural Determination of a Trivalent Californium Compound with Oxygen Coordination.

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Evidence of Alpha Radiolysis in the Formation of a Californium Nitrate Complex

Well-characterized complexes of transplutonium elements are scarce because of the experimental challenges of working with these elements and the rarity of the isotopes. This leads to a lack of structural and spectroscopic data needed to understand the nature of chemical bonds in these compounds. In this work, the synthesis of Cf(DOPO^q)₂(NO₃)(py) (DOPO^q=2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazin-9-olate; py=pyridine) is reported, in which the nitrate anion is hypothesized to form through the α-radiolysis-induced reaction of pyridine and/or the ligand. Computational analysis of the electronic structure of the complex reveals that the Cf^III–ligand interactions are largely ionic.     

Zinc-cobalt alloy: electrodeposition and characterization

Zinc-cobalt alloy electrodeposits offer enhanced corrosion protection to steel, compared to zinc deposits. A near neutral zinc-cobalt alloy sulfate bath was developed. In the absence of β-naphthol and sodium lauryl sulfate (SLS), only a light grey and non-uniform deposit was obtained. Addition of boric acid yielded a grey and uniform deposit. To obtain the grey uniform alloy deposit, the optimum bath composition was: 0.5 M ZnSO₄, 0.5 M CoSO₄, 40 g/L H₃BO₃, 0.865 g/L SLS and 0.345 g/L β-naphthol. The current efficiency for alloy deposition was 50% in the current density range 0.5–2.5 A/dm². X-ray fluorescence studies on the alloy deposit formed on steel revealed 58–75% zinc on the surface. Anodic stripping voltammetric studies were carried out on zinc-cobalt alloy films formed on glassy carbon to identify the phases formed in the alloy. Zn-Co alloy film dissolution peaks suggested the existence of β, β₁ and γ phases of the alloy. Electronic Publication     

Separation and electrodeposition of226Ra

The chemical behavior of calcium, barium and radium in the ion exchange resins Dowex 50W-X8, AG 50W-X8 and Merk I in the presence of ammonium tartrate, EDTA, and citrate has been studied. No differences were observed in results while using any one of the three resins. Calcium, barium and radium were fixed to the exchange column at pH 4.8 EDTA solution. Calcium was eluted in an EDTA solution at pH 5.3, barium and radium between pH 8–11. Elution in citrate media for calcium was achieved at pH 6.1 and for radium at pH 10. In ammonium tartrate, calcium was eluted at pH 6, barium and radium at pH 11.5. Radium was also eluted from the ion exchange resins with a 2M nitric acid solution. The radium free of calcium was electrodeposited onto a stainless steel disc cathode using a 0.1 M potassium fluoride solution, pH 12–14, with a yield of >50%. The energies of²²⁶Ra were analyzed through high resolution -spectra. The²²⁶Ra utilized for these experiments was separated from Mexican carnotite.     

UV curable electrodeposition systems

This article reviews the development of a UV curable electrodeposition system. Tailor-made acrylic functionalized polyurethane resins, which have been designed, are described and basic properties of the final e-coat system are shown. In addition several fundamental studies have been performed in order to analyze as well the homogeneity of the deposition as the efficiency of the UV curing process.     

Simultaneous electrodeposition of actinides

A new system for simultaneous electrodeposition of U, Np, Pu, Am and Cm has been developed. The system consists of (NH₄)₂C₂O₄–H₂SO₄–HCl. The effects on recovery of pH, current density, interfering ions and the amount of added HCl have been studied. The optimum condition for simultaneous electrodeposition of actinides has been recommended. Under the recommended condition recoveries of U, Np, Pu, Am and Cm have been obtained by using²³²U,²³⁷Np,²⁴¹Am,²⁴²Pu and²⁴⁴Cm. The counting sources prepared are uniform, adherent and suitable for -spectrometry.     

Structure and electrokinetic study of nickel electrodeposition

Electrodeposited layers of nickel show different growth characteristics depending on the composition of the electrolyte, namely the type of the anion, the presence or the absence of boric acid and the pH. These process parameters are examined in the present work in order to elucidate their influence upon the growth texture and the related surface morphology of the electrodeposits. The relationship between process and structure is investigated by studying the transient electrochemical behavior during deposition, in order to discriminate between different interface conditions corresponding to different growth modes. The observed preferred orientations can be in this way linked to different reactive species, which are assumed to be present at the surface, and to their stability. The correlation between kinetics and structure in nickel electrodeposition reported in the present work and the similar correlation found in cobalt electrodeposition suggest a rationalization of the growth modes of ECD inert metals, based on the correspondence between the transient Tafel parameter and the growth texture observed in defined conditions. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 6, pp. 771–783. The text was submitted by the authors in English.     

Direct electrodeposition of aluminium nano-rods

Electrodeposition of aluminium within an alumina nano-structured template, for use as high surface area current collectors in Li-ion microbatteries, was investigated. The aluminium electrodeposition was carried out in the ionic liquid 1-ethyl-3-methylimidazolium chloride:aluminium chloride (1:2 ratio). First the aluminium electrodeposition process was confirmed by combined cyclic voltammetry and electrochemical quartz crystal microbalance measurements. Then, aluminium was electrodeposited under pulsed-potential conditions within ordered alumina membranes. A careful removal of the alumina template unveiled free standing arrays of aluminium nano-rods. The nano-columns shape and dimensions are directly related to the template dimensions. To our knowledge, this is the first time that direct electrodeposition of aluminium nano-pillars onto an aluminium substrate is reported.     

Spontaneous oscillations in gold electrodeposition

We report the appearance of spontaneous oscillations during the electrodeposition of gold along the surface of aqueous hydrogen tetrachloroaurate solutions coated by a positively charged dimethyldioctadecylammonium monolayer, when a current ramp with a rate comprised between 1 and 1.5 nA s⁻¹ is applied to the working electrode. Alternating sequences of two-dimensional (2D) growth and three-dimensional (3D) thickening of the deposits leading to gold films with a well-defined terraced structure are observed. Such a phenomenon appears to be produced by the competition between two mechanisms controlling the current density J₁: one is the current ramp which tends to increase J₁ and the other one is the growing of the gold deposit which induces a decrease of J₁.     

The process chain of electrodeposition

The electrochemical processes on a growing metal layer can be described as a chain of processes consisting of nucleation and formation of a stable grain, growth of the active grain, and death of the active grain. Considering the statistical nature of the process chain, mean growth rate, mean lifetime, mean death rate, mean density and mean size of the active grains can be defined. Equations for the rate of nucleation are given in the literature. Stationary growth of the metal film is achieved if the rate of nucleation is equal to the death rate of active grains. From the condition of stationary growth an equation for the dependence of the average grain size on the experimental parameters can be derived. Several situations of metal deposition with different process parameters are discussed and compared with experimental results.     

Patterned self-assembled film guided electrodeposition

Conjugated polymers can be the alternatives to metals to manufacture the integrated circuit in nano/micro electromechanical systems (NEMS/ MEMS)[1], while patterning is the basis for such an application. It has been well known that the electro-deposition on a template[2—10] represents the simplest method to construct a patterned conducting polymer structure as compared with the conventional ap-proaches such as photolithography, e-beam writing, screen-printing, and ink-jet printing[11]. For…     

Shape-controlled electrodeposition of gold nanostructures

A one-step, nontemplated, low-cost electrochemical method for the growth of gold nanostructures with different shapes is reported here. It is the first time that nanopyramidal, nanorod-like, and spherical gold nanostructures were fabricated on polycrystalline gold substrates through electrochemical overpotential deposition (OPD) by easily manipulating the deposited potentials and concentrations of HAuCl4. X-ray diffraction and electrochemical analyses revealed that the pyramidal structures are more extensively dominated by (111) facets in comparison with the other nanostructures. The nanopyramids, which have anisotropic structures, exhibited broad extinction over the visible region, most likely due to plasmon resonance. Oxygen reduction activity of a gold electrode with the pyramidal structures was lower than those of the electrodes with the other nanostructures since the activity at the gold (111) surface is lower than that at the (100) and (110) surfaces.     

Copper electrodeposition into ion-exchange materials

Electrodeposition of copper into spherical granules of ion-exchange materials KU-23 and KU-2 out of acid sulfate solutions is studied by a method of cyclic voltammetry. It is discovered that the discharge of copper ions in an ion-exchange matrix is characterized by a cathodic overvoltage that is higher than the overvoltage of the same process on a graphite substrate by 0.08 V, which is most probably connected with a limited mobility of ions localized at fixed groups [RSO ₃ ^? ]. The cyclic voltammogram exhibits an additional cathodic peak in the potential region corresponding to the reduction of single-charged copper ions that form as a result of their accumulation inside pores of the ion-exchange matrix during anodic dissolution of metal deposited previously. It is fixed microscopically that the process of deposition begins at the graphite substrate/ion-exchanger interface and passes into bulk upon the formation of an electron-conducting layer saturated with copper. Preliminary saturation of the ion-exchanger by copper deposited chemically facilitates uniform electrodeposition of copper over the entire volume of pores of the ion-exchange matrix.     

Magnetic nanowires via template electrodeposition

The magnetic NiFe_x nanowires were prepared via template-guided electrodeposition. Anodized nanoporous aluminum was used as a template. The pore density and dimensions of alumina templates can be controlled by anodization conditions. Magnetic nanorods (or nanowires) with various aspect ratios were prepared by controlling the electrodeposition time. SEM and TEM micrographs revealed the wire and rod shape morphologies with 50 nm in diameter and 1.5 ~ 10 μm in length. Elemental analysis and ESCA studies suggested that NiFe₃ magnetic alloy was formed. The X-ray diffraction pattern indicates that all the nanowires are stabilized in a BCC structure with a [1 1 0] texture oriented along the long axis of the nanowires. The magnetic measurement showed no hysteresis loops for the whole aspect ratios of the nanowires. Nevertheless, the magnetization is more temperature sensitive for nanowires with lower aspect ratio. This is caused by the fact that the easy magnetization axis is always parallel to the long axis of the nanowires.     

Chitosan-mediated and spatially selective electrodeposition of nanoscale particles

Nanoscale particles offer a variety of interesting properties, and there is growing interest in their assembly into higher ordered structures. We report that the pH-responsive aminopolysaccharide chitosan can mediate the electrodeposition of model nanoparticles. Chitosan is known to electrodeposit at the cathode surface in response to a high localized pH. To demonstrate that chitosan can mediate nanoparticle deposition, we suspended fluorescently labeled latex nanoparticles (100 nm diameter spheres) in a chitosan solution (1%) and performed electrodeposition (0.05 mA/cm2 for several minutes). Results demonstrate that chitosan is required for nanoparticle electrodeposition; chitosan confers spatial selectivity to electrodeposition; and nanoparticles distribute throughout the electrodeposited chitosan film. Additionally, we observed that the deposited films reversibly swell upon rehydration. This work indicates that chitosan provides a simple means to assemble nanoparticles at addressable locations and provides further evidence that stimuli-responsive biological materials may facilitate fabrication at the microscale.     

钛酸钙的电沉积法制备及表征

采用硝酸钙为钙源,钛酸丁酯为钛源,通过电极沉淀法制备钛酸钙.利用红外光谱仪对制备所得的钛酸钙进行表征.结果显示,在室温条件下,于外加5 V的电场中反应3 h,所得前驱体在800℃下焙烧2 h可得到纯度较高的钛酸钙产品.