ambient pressure laser heating and melting of pt foil—validating bl 12.2.2 temperature...

Ambient Pressure Laser Heating and Melting of Pt Foil—Validating BL 12.2.2 Temperature Measurements

• Wed Feb 21-Fri Feb 23• Pt foil (4 m thin) cut in thin strip and mounted in “Wire melting chamber”. Chamber

flooded with Ar gas.• Laser Power setting at 25 Amps. Waveplate value upon melting 1.90-2.04 Volts. This

means the laser power at the sample was approx.5 Watts (combined upstream and downstream)

• Melt determination made by visual observation of “melt pool” and/or flicker of sample. Neutral density filters greatly aid in visual observations.

• Simultaneous diffraction aided in melt determination, but diffraction signal from sample after heating is very weak due to texturing. Detailed discussion of diffraction signal given below.

Pre&Post Heat Pt Foil

~25m

Post-heating observations support melting with appearance of holes in foil, and foil having a different (glassy?) texture.

PreHeating PostHeating

Ambient Pressure Laser Heating and Melting of Pt Foil

• Temperature calculation is done by fitting data (corrected for system response) to the Planck function in a wavelength range of 600-800 nm. No wavelength dependent emissivity was applied to the data.

• The melting temperature is calculated as the average of the last temperature when a “solid” observation is made and the first determination when a “melt” observation is made.

• For 3 separate runs with observations made both upstream and downstream, the average melt temperature is determined as 2052+/-29 K. This is close to the literature value of 2041 K.

Pt Foil Ambient P Laser Melting:Raw Data

Temperature Profile during melt observation of ambient pressure Pt foil

Temperature Vs Laser Power• Temperature vs total power at sample

position (upstream + downstream)

• Plot levels off at Pt Tm

• Another supporting piece of evidence for melt indication

Diffraction signal from Pt foil at ambient condition right after mounting foil before any heating

20 keVDist: 316.974 mm

X-ray diffraction during laser heating of Pt foil

Diffraction signal almost completely disappears on a mm-area after heating to moderate temperatures (barely coupling).

1 single diffraction spot left.

Zoom in on diffraction spot

Most intense D-value corresponds to (111) of Pt. ~ 2.27 Å

(unsure of why spot is split into 3 peaks) residual strain?

In vicinity of melting. Spot broadens and loses intensity

During HeatingRoom Temperature

Integrated Pt Spot During Heating

T =~2000K~1e-5d/d ~ 2e-5d ~ 2.25 => d + d = 2.295

Spot broadens and shifts to higher dsp.Confirms the alignment of x-ray and laser(diffraction from laser heated spot)

Peak sharpens up upon quenching.

After melting most intensity recovered to the lowest of the 3 peaks