Fluoborate electrolyte

Use Production of fluoborates, electrolytic brightening of aluminum, throwing power aid in electrolytic plating baths, esterification catalyst, metal cleaning, making stabilized diazo salt. 

The FLUBOR process is an electrochemical process for electrowinning lead from impure Pb metal and/or PbS based raw materials. This process is based on a ferric fluoborate leaching medium which is used to dissolve the Pb. The generated fluoboric electrolyte is fed to the cathodic compartment of an electrolytic cell, divided into two compartments by a diaphragm, where Pb is deposited. In the anodic compartment ferric fluoborate is regenerated, and is sent to the leaching reactor closing the electrolysis circuit. 

The disadvantage of the use of a chloride system is the production of lead powder or sponge at the cathode rather than a dense deposit as with fluosilicate and fluoborate electrolytes. In this case such an output would facilitate recycle to the leaching stage, but the bulk of the cathode deposit must be compressed by briquetting or roll extrusion prior to melting to minimise oxidation. 

For a process based on the chloride system rather than fluoborates, electrolytic power will increase from 600 to 950 kWh/t and the total energy input will increase from 10 390 MJ/t of lead to 14 400 MJ/t. 

Electrodeposited chromium, both decorative and hard , is produced with the use of a solution of chromic acid containing a small amount of catalyst which is usually sulphuric acid, although fluosilicic or fluoboric acid may be used. A typical electrolyte contains 250-400 g/1 of chromic acid and... 

The composition of the codeposition bath is defined not only by the concentration and type of electrolyte used for depositing the matrix metal, but also by the particle loading in suspension, the pH, the temperature, and the additives used. A variety of electrolytes have been used for the electrocodeposition process including simple metal sulfate or acidic metal sulfate baths to form a metal matrix of copper, iron, nickel, cobalt, or chromium, or their alloys. Deposition of a nickel matrix has also been conducted using a Watts bath which consists of nickel sulfate, nickel chloride and boric acid, and electrolyte baths based on nickel fluoborate or nickel sulfamate. Although many of the bath chemistries used provide high current efficiency, the effect of hydrogen evolution on electrocodeposition is not discussed in the literature. 

Fluoroboric (or Fluoboric) Acid, HBF , mw 87.83 colorless clear, strongly acid liq bp 130° (dec) miscible with w ale. Can be prepd by action of boric + sulfuric acid on fluorspar. Used for prepn of fluoboraces and stabilized diazo sales. Its specially purified so In used in patented process for electrolytic brightening of Al... 

Cyclic voltammetry can be used to estimate the charge transfer rate and also evaluate how this rate depends on parameters such as morphology and the chemical structure. The cyclic voltammetric examination of electroactive polymers is usually done in monomer-free solutions containing only the solvent and supporting electrolyte. In order to avoid the complication of mixed electrolytic equilibria, the supporting electrolyte and the solvent are usually the same as employed for the polymerization. Figure 3 shows the cyclic voltammogram (CV) of a polypyrrole film prepared in acetonitrile/tetra-w-butyl ammonium fluoborate medium. The anodic peak corresponds to polypyrrole oxidation, while the cathodic one corresponds to the reduction of this species. 

Dithionic acid tends to decompose at normal cell operating temperatures to H2SO4 and SO2. The sulfate will then precipitate lead and SO2 wiU be reduced at the cathode to H2S, which in turn will precipitate PbS. Sulfamic acid is also unstable at higher current densities and tends to break down to form ammonium sulfate, in turn precipitating lead sulfate. Hence, the most suitable practical alternative electrolytes are fluosilicic and fluoboric acid systems. 

In this case batteries are fully separated, metallic components are simply melted and drosses from that operation together with desulfurised battery pastes are subjected to hydrometaUurgical extraction of lead followed by electrowinning from the leach solution. As detailed in Chapter 9, solutions used for lead electrolytes are fluosilicates as used in the Betts refining process, fluoborates and chlorides. 

In the Engitec process, based on a fluoboric acid electrolyte, hydrogen peroxide is used according to Equation 11.17 during leaching with HBE4. 

For electrolytic refining, an electrolyte is required that has a reasonable lead solubility, is stable, has a high electrical conductivity and will yield a smooth compact deposit of lead. Various organic acids have good lead solubility and conductivity but tend to be unstable. It was found during the early development of the process that fluosilicic acid, fluoboric acid and sulfamic acid were most suitable and fluosilicic acid was the least costly. Sulfamic acid systems were also used, but showed instability at high current densities. Consequently, most electrolytic refining operations are based on a fluosilicate electrolyte. 

Commonly used electrolytes, such as tetra-n-butylammonium perchlorate (TBAP), tetra-n-butylammonium fluoborate (TBABF4), tetra-n-butylammonium hexafluorophos-phate (TBAPFg), tetraethylanunonium perchlorate (TEAP), can be purchased from... 

The chemistry most commonly employed in spin-dependent liquid-electrolyte reserve batteries has been the lead/fluoboric acid/lead dioxide cell represented by the following simplified reaction ... 

Since the individual cells of a spin-dependent liquid-electrolyte reserve battery are generally annular in shape and are filled by centrifugal force, the periphery of the cell must be sealed to keep electrolyte from leaking out. This sealing is typically accomplished by a plastic barrier formed around the outside of the electrode-spacer stack. For lead/fluoboric acid/lead dioxide batteries, this barrier is formed by fish paper (a dense, impervious paper) coated with polyethylene that melts at a relatively low temperature (similar to that used on milk cartons). Cell spacers are punched from the coated fish paper and placed between the electrodes. The stack is then clamped together and heated in an oven at a temperature sufficient to fuse the polyethylene, which then acts as an adhesive and sealer between the electrodes. 

Operating Temperature Limits. Like most other batteries, the performance of liquid-electrolyte reserve batteries is affected by temperature. Military applications frequently demand battery operations at all temperatures between -40 and 60°C, with storage limits of -55 to 70°C. These requirements are routinely met by the lead/fluoboric acid/lead dioxide systems and, with some difficulty at the low-temperature end, by the lithium/thionyl chloride and zinc/potassium hydroxide/silver oxide systems. Provision is occasionally made to warm the electrolyte prior to the activation of the two latter systems. 

Lead/Fluoboric Acid/Lead Dioxide Battery. Discharge curves for a typical lead/fluoboric acid/lead dioxide liquid-electrolyte reserve battery employed to power the proximity fuze of an artillery shell are given in Fig. 19.6. The slight rise in the low-temperature curve is due to its gradual rise in temperature in a room-temperature spinning tester. Similarly, the high-temperature curve is falling faster than it would in a true isothermal situation. 

The beneficial effect of fluoroborates lies in the efficiency at higher current densities which is better than that of sulfate electrolytes. The preparation of the appropriate metal salts starts with the dissolution of metal oxides, -hydroxides or -carbonates in fluoboric acid. The quantities vary with bath type and metal used, between 100-400 g/1 of fluoroborates depending on the application [55]. KBF4 has been also used as a conducting salt in nonaqueous electrolytes for secondary lithium-ion batteries [56]. 

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