Juha Tikkanen

Characteristics of the liquid flame spray process

Liquid flame spraying (LFS) is a new thermal spray process. Liquid feedstock is injected and atomized in an oxygen-hydrogen flame where the liquid phase is evaporated and thermochemical reactions are completed to produce fine particles. Production of nanoparticles requires a thorough understanding of the process. Therefore, various process stages were studied; i.e., the atomization of liquid feedstock, and characterization of the flame and flame-droplet interactions. Experimental techniques included laser diffraction anemometry for droplet size distribution, laser doppler velocimetry for particle velocity, pulsed laser Rayleigh back scattering for flame temperature and Schlieren photography for flame structure. Atomization is optimized with an organic solvent, such as isopropanol, nebulized with hydrogen gas at a high flow rate. Liquid droplets injected into the flame are subjected to a maximum temperature of 2600°C and are accelerated to about 160 m s−1. The flame length can be controlled by flame velocity and the solvent type. Water produces a shorter flame whereas ispropanol extends the flame. Injection of the aerosol produces a “pencil-like” region which does not experience turbulence for most of the flame length. Experimentation with manganese nitrate and aluminium isopropoxide or aluminium nitrate showed conversion to a

Liquid flame spraying for glass coloring

The liquid flame spraying process has been developed to uniformly color hot glass objects. A solution consisting of a metal nitrate dissolved in alcohol or water is fed to an oxyfuel torch and atomized in the flame. The liquid evaporates from the droplet, and subsequent reactions produce metals or metallic oxides that impact the hot glass surface. Flame spraying of Co, Cu, and Ag solutions onto soda-lime silica glass at 900 to 1000 °C have produced blue, blue-green, and yellow colors. Typical spraying times are 5 to 20 s. Other colors have been produced by using a combination of transition metal ions. This method has found application in studio production and in volume manufacturing of glassware.

An electrical sensor for long-term monitoring of ultrafine particles in workplaces

Pegasor Oy Ltd. (Finland) has developed a diffusion charging measurement device that enables continuous monitoring of fine particle concentration at a low initial and lifecycle cost. The innovation, for which an international process and apparatus patent has been applied for, opens doors for monitoring nanoparticle concentrations in workplaces. The Pegasor Particle Sensor (PPS) operates by electrostatically charging particles passing through the sensor and then measuring the current caused by the charged particles as they leave the sensor. The particles never touch the sensor and so never accumulate on its surfaces or need to be cleaned off. The sensor uses an ejector pump to draw a constant sample flow into the sensing area where it is mixed with the clean, charged pump flow air (provided by an external source). The sample flow containing charged particles passes through the sensor. The current generated by the charge leaving the detection volume is measured and related to the particle surface area. This system is extremely simple and reliable – no contact, no moving parts, and all critical parts of the sensor are constantly cleaned by a stream of fresh, filtered air. Due to the ejector pump, the sample flow, and respectively the sensor response is independent of the flow and pressure conditions around the sampling inlet. Tests with the Pegasor Particle Sensor have been conducted in a laboratory, and at a workplace producing nanoparticles for glass coatings. A new measurement protocol has been designed to ensure that process workers are not exposed to unusually high nanoparticle concentrations at any time during their working day. One sensor is placed inside the process line, and a light alarm system indicates the worker not to open any protective shielding or ventilation systems before concentration inside has reached background levels. The benefits of PPS in industrial hygiene are that the same monitoring technology can be used at the source as well as at the worker breathing zone. Up to eight sensors can be installed in series for centralized monitoring of the whole process in real time.

Coating glass by flame spraying

Abstract In this project, flame spraying was used on glass. Metal and coloured glass powders were sprayed onto a hot glass surface. Copper and coloured glass were found to have good adhesion on the glass surface. The sintering of the sprayed glass particles can be improved by using smaller particle size and special coating glass with low viscosity at spraying temperatures. Good sintering of sprayed glass powder makes for an efficient way of colouring glass.