ENERGY APPLICATION
Low-E Glass Coating
Pyrolytic deposition of low-emissivity (low-E) and transparent conductive coatings such as fluorine-doped tin oxide (SnO₂:F) on hot glass — with the droplet-size control needed to manage the Leidenfrost effect and hold deposition in its ideal regime.
The Challenge
A pyrolytic low-E coating has to deliver uniform emissivity and neutral optics across every square meter of glass, deposited in seconds onto a substrate held at 400–500 °C. At those temperatures the process lives on the edge of the Leidenfrost regime: droplets that are too small decompose in-flight and arrive as powder, droplets that are too large punch through the vapor cushion and splash, and only a narrow size band vaporizes right at the surface where the precursor can react into a dense, adherent film. Pneumatic spray guns produce a broad droplet-size scatter, so every spray event samples all three regimes at once — showing up as haze, pinholes, and emissivity drift on the finished glass.
Our Solution
MicroSpray ultrasonic nozzles set droplet size by operating frequency rather than air pressure, delivering a narrow 18–45 µm distribution that can be tuned into the ideal near-Leidenfrost deposition window — and kept there run after run. The soft, low-velocity mist lets shaping air, not atomization energy, control how droplets approach the hot surface, and the nozzle stands off above the heated substrate with air cooling and thermocouple monitoring for continuous pyrolysis operation. The same nozzle scales from a benchtop hot-plate feasibility study to linear arrays over conveyorized glass.
The Leidenfrost Effect in Spray Pyrolysis of Low-E Glass Coatings
When an atomized precursor droplet approaches glass held at the 400–500 °C substrate temperatures typical of SnO₂:F deposition, a cushion of vapor can form beneath it before it ever wets the surface — the Leidenfrost effect. In spray pyrolysis of low-emissivity coatings, that vapor layer is a regime to control, not a mechanism that produces the film: a droplet in full Leidenfrost levitation skates across the surface and is swept away by the gas stream without depositing anything, while a droplet far below the regime splashes, wets, and leaves haze-producing residue.
The best films grow in the narrow window just below full levitation, where the droplet vaporizes at the surface and the precursor decomposes on contact in a CVD-like reaction. Published work on In₂O₃ and ZnO transistor films attributes exceptionally smooth, highly crystalline growth to exactly this near-Leidenfrost regime — and which regime any given droplet lands in depends strongly on its size.
This is where ultrasonic atomization earns its place: droplet size is set by nozzle frequency, not by air pressure, so the spray arrives as a narrow distribution — roughly 18–45 µm depending on frequency — instead of the broad scatter of a pneumatic gun. With every droplet in nearly the same size class, the entire spray can be held in the vaporize-at-the-surface window, yielding uniform, adherent, optically consistent low-E films.
Why Ultrasonic Spray?
- ✓Narrow droplet distribution keeps the whole spray in one deposition regime — no mixed splash, powder, and levitation behavior
- ✓Uniform emissivity and neutral optics across the coated area
- ✓Droplet size selected by frequency (18–45 µm), independent of flow rate
- ✓Nozzle stands off above 400–500 °C substrates with air-cooled body and thermocouple monitoring
- ✓High transfer efficiency cuts waste of organotin and fluorine precursor chemistry
- ✓Non-clogging design handles dissolved precursor salts in continuous operation
- ✓Scales from single-nozzle R&D rigs to linear arrays for wide glass
- ✓Same process suits related pyrolytic TCO films — ITO, AZO, In₂O₃, and ZnO
Supporting Research
Peer-reviewed publications and technical literature relevant to this application area. Links open the publisher's site.
- A self-driving laboratory optimizes a scalable process for making functional coatings
C. C. Rupnow, B. P. MacLeod, et al. — Berlinguette Group, University of British Columbia
Cell Reports Physical Science ·
Open access · no paywall
Spray deposition in this work was performed using a MicroSpray ultrasonic spray system.
- Study of fluorine-doped tin oxide thin films deposited by pneumatic spray pyrolysis and ultrasonic spray pyrolysis: a direct comparison
R. Ramírez-Amador, J. J. Alvarado-Pulido, H. P. Martínez-Hernández, et al.
Materials Research Express ·
Open access · no paywall
- Exploring the Leidenfrost Effect for the Deposition of High-Quality In₂O₃ Layers via Spray Pyrolysis at Low Temperatures and Their Application in High Electron Mobility Transistors
I. Isakov, H. Faber, M. Grell, G. Wyatt-Moon, et al.
Advanced Functional Materials ·
- Effects of droplet diameter on the Leidenfrost temperature of laser processed multiscale structured surfaces
A. Hassebrook, C. Kruse, C. Wilson, et al.
Proceedings of the 14th IEEE ITherm Conference ·
- Comparison of spray pyrolyzed FTO, ATO and ITO coatings for flat and bent glass substrates
H. Bisht, H.-T. Eun, A. Mehrtens, M. A. Aegerter — Institut für Neue Materialien (INM), Saarbrücken
Thin Solid Films ·
Recommended Equipment
ThermalSpray™ High-Temperature Ultrasonic Nozzle
Built for heated environments above pyrolysis-temperature substrates, with air cooling and tip thermocouple monitoring
View details →SprayBlade™ Air Knife
Flat fan-shaped spray with linear-array capability for uniform coverage across wide glass
View details →Common Questions from Research Groups
What substrate temperature window applies to SnO₂:F low-E deposition?
Most published SnO₂:F work deposits at roughly 400–500 °C, where the precursor decomposes fully and the film crystallizes; modified processes have demonstrated films down to about 250–340 °C. The right point inside that window depends on your precursor and solvent system — and because droplet size shifts the effective Leidenfrost threshold, a narrow droplet distribution makes the window meaningfully wider in practice.
How do I know whether my droplets are hitting the Leidenfrost regime?
The deposit tells you. Powdery, poorly adherent material means droplets decomposed in-flight; splat marks and haze mean droplets wetted the surface below the regime; little or no deposition with precursor exhausting past the substrate means full levitation. With a pneumatic gun all three signatures appear at once, which makes diagnosis ambiguous — a narrow ultrasonic distribution produces one behavior at a time, so temperature and standoff adjustments have readable effects.
Can the nozzle operate above a 450 °C substrate?
Yes. The ThermalSpray™ nozzle is built for heated environments, with integrated air cooling ports and a tip thermocouple so you can verify the nozzle temperature in your geometry. Because the nozzle sits at a standoff above the hot glass, the substrate can run considerably hotter than the nozzle body itself. Tell us your substrate temperature and standoff and we'll confirm the configuration.
Can I develop the process on a benchtop rig before committing to a line?
Yes — most research customers purchase only the nozzle and its generator/controller and integrate them over their own hot plate or tube furnace. A process developed at benchtop scale transfers directly, because droplet size is set by frequency rather than by rig-specific air pressures, and the same nozzles can later be mounted as a linear array over conveyorized glass.
Developing a pyrolytic low-E or TCO coating process? Contact us about droplet-size control and Leidenfrost-regime feasibility.
Let's discuss your specific coating requirements.