Construction of a chamber to measure liquid lithium alloy vapor pressures and measurement of the lead-lithium eutectic vapor pressure

Diaz, Gio

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https://hdl.handle.net/2142/129336 Copy

Description

Title

Construction of a chamber to measure liquid lithium alloy vapor pressures and measurement of the lead-lithium eutectic vapor pressure

Author(s)

Diaz, Gio

Issue Date

2025-05-08

Director of Research (if dissertation) or Advisor (if thesis)

Ruzic, David N

Committee Member(s)

Andruczyk, Daniel

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• lithium
• lead
• lead-lithium
• fusion
• vapor pressure
• knudsen effusion

Abstract

This thesis discusses the design and construction of the Lithium Alloy Vacuum Appliance (LAVA) chamber made to measure the vapor pressures of liquid lithium alloys. The chamber was made of three sections. The first section was a suitcase was made to transport air sensitive samples (such as lithium) between LAVA and storage in a glove box. The second section was a load lock that allows the transfer of samples into or out of the lower chamber. The third section could then be kept at high or ultra-high vacuum almost continuously. Keeping the lower section at this low pressure minimized the turnaround time between tests; although, bringing this section up to atmosphere is sometimes unavoidable. This section housed the stage for the sample holders and the heating coils. To measure the lithium alloys— Pb83Li17 is the alloy of interest in this thesis— in LAVA, the Knudsen effusion technique is used. This involves placing the alloy into a so-called Knudsen cell, which maintains a stable vapor pressure of the alloy, while allowing a small amount of evaporate to escape through an orifice. To do this the cell must: be compatible with the samples used (lithium, lead, and tin), be at a uniform temperature during testing, and have a properly designed effusion orifice. To address the compatibility and temperature uniformity, molybdenum was chosen as the cell material. The shape of the effusion orifice was chosen to be that of a cone rather than a cylinder with the small hole facing outward (a diameter of 3 mm for the small side and 12.66 mm for the larger side). In addition to a Knudsen cell, the Knudsen effusion technique requires the measurement of the change in sample mass from an evaporation run. In LAVA this was done using a dual Quartz Crystal Microbalance (QCM). The QCM was centered over the Knudsen cell, and given the cosine distribution of the evaporate, the viewing factor of the QCM crystal can be calculated and used to determine the total mass loss of the sample in the cell. However, to accurately determine the vapor pressure from the change in mass, the species of the evaporate must be known as well as how much of the evaporate it makes up. So, to modify the Knudsen effusion technique to work for multi species evaporate, and to determine the composition of the evaporate, witness plates were used to capture some evaporate material. These silicon wafers were positioned above the Knudsen cell to allow for the evaporate to deposit onto them. To make the lithium alloys produce a measurable amount of evaporate for this setup, they must be molten. The approach to this in LAVA was to use an induction heater. The induction heater allowed for volumetric heating and thus a simple heating design. Another benefit of induction heating (over something like resistive heating) is that it can heat a workpiece very quickly. Over the course of data collection, there were issues with having the QCM too close to the evaporate source, which caused jumps in the frequency measured. This was fixed by moving the QCM farther away, but that lowered the evaporate signal to background ratio, meaning that higher temperatures would be required to be able to make meaningful measurements. Data collection began with measurement of lithium vapor pressure to confirm that vapor pressures could be measured correctly in LAVA. This was done before and after the issue with the QCM was found. With the confirmation of the lithium runs prior to lead-lithium, it was necessary to adapt the Knudsen effusion technique to work with the expected two evaporate species of lead-lithium. The approach taken with this was to collect the evaporate onto witness plates, remove the plates and analyze them. One of the few techniques available that could even detect lithium was TOF SIMS. In addition to being able to detect lithium, a composition of the evaporate was also able to be made. This composition was used to weigh the data from the QCM to determine ”partial vapor pressures” of lead and lithium to calculate a total vapor pressure. Before the QCM issue became significant, the lead-lithium vapor pressures overestimated the literature vapor pressures by at least one order of magnitude. The lead-lithium vapor pressures measured appear to be uniform over the temperature range (500 K to 750 K). These values hover around 1 × 10^−5 Torr. Along with the vapor pressures, the cell mass loss rate was calculated from the QCM data. Over the same temperature range, the values ranged from 250 ng s^−1 to 1400 ng s^−1. The values did not have a clear relationship with temperature. Further converting the cell mass loss rate to particle flux from the cell did not appear to create any trends with temperature and ranged in value from 1 × 10^16 cm^−2 s^−1 to 1 × 10^17 cm^−2 s^−1. All of this data also was dependent on the composition of the evaporate, which was found to have significant amounts of lead across the temperature range (in atomic percentages: 11 % to 100 %). Like with the mass rate and particle flux, there was no apparent trend in composition. After the QCM issue was addressed, the overestimation of lead-lithium vapor pressure became at least an order of magnitude larger. The temperature range was increased to 550 K to 800 K due to the induction heater not being able to maintain temperature at the lower end of the previous temperature range. The values for vapor pressure ranged from 1 × 10^−4 Torr to 1 × 10^−2 Torr, with the highest point around 700 K. Unlike the previous iteration, the evaporate composition results showed that the evaporate was all lithium. Because no lead was detected in the Time of Flight Secondary Ion Mass Spectrometry (TOF SIMS) machine, X-Ray Fluorescence (XRF) was also done on the samples to confirm this and did not detect any lead. Because this disagrees with the previous data, there may be some issue with re-evaporation or the repeatability of the measurements at these temperatures. To address the issues with overshooting vapor pressure and disagreement of composition results of the previous two data sets, an increased cell temperature and therefore the vapor pressure was used. The new temperature range was 800 K to 1200 K. This ended up working, as the experimental lead-lithium vapor pressures were within one order of magnitude of the experimental data. The measured vapor pressures were in the range 1 × 10^−3 Torr to 1 × 10^−1 Torr. The particle flux data also made more sense than in either previous iteration. The overall particle flux did increase with increasing temperature. The particle fluxes ranged from 1 × 10^20 cm^−2 s^−1 to 1 × 10^21 cm^−2 s^−1. Composition results remained significantly lead heavy with samples having 70 % to 100 % (atomic) lead concentrations.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129336

Copyright and License Information

Copyright 2025 Gio Diaz

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