Development of an alkali chloride vapour-generating apparatus for calibration of ultraviolet absorption measurements

Abstract

A novel design of alkali chloride vapour-generating cell has been developed, which can serve as a calibration cell for quantitative ultraviolet absorption concentration measurements and meticulous spectral investigations of alkali compounds. The calibration cell was designed to provide alkali vapour of well-controlled concentrations and temperatures, and consisted of a sealed quartz cell measuring 0.4 m in length with a temperature-controlled reservoir containing solid alkali salt. The cell was placed in a furnace and the alkali vapours generated from the reservoir have direct access to the measuring chamber. Investigations of potassium chloride (KCl) were made on sublimated vapour at temperatures 650, 700, 750, 780, and 800 °C while the reservoir temperature was kept 50 °C lower to avoid condensation. The cell provides stable KCl vapour pressures, and the furnace provides a homogenous temperature profile along the cell. KCl vapour pressures are well characterised and conform the base for determination of the KCl concentration in the cell. The alkali chloride levels matched the concentration range of the absorption setup and indicated a previously employed calibration method to overestimate KCl concentrations. The KCl absorption cross sections for wavelengths λ=197.6 nm and λ=246.2 nm were calculated to be 3.4 × 10−17 and 2.9 × 10−17 cm2/molecule, respectively. The absorption cross section spectra did not show any structural differences with increasing temperature, which could indicate influence of dimers or significant changes of the population in the KCl vibrational states. The KCl absorption cross sections thus did not show any temperature dependence in the temperature region of 700–800 °C. Moreover, the applicability of the calibration cell for measurement of other alkali chlorides and hydroxides is discussed.

Ultraviolet Absorption Cross Sections of KOH and KCl for Nonintrusive Species-Specific Quantitative Detection in Hot Flue Gases

“…The present value is ∼20% lower than the value from Leffler et al 20 measured at a temperature of ∼1000 K, which is ∼28% higher than the values from Davidovits et al. 19 and Forsberg et al 18 at a temperature of ∼1100 K. In the measurements by Leffler et al 20 and Davidovits et al, 19 sealed quartz cells generating controlled amounts of KCl vapor were used, in which the evaluation of the KCl cross sections strongly relied on the determination of the KCl vapor pressure in the cell. The accuracy of the calculated KCl vapor pressure was directly affected by the accuracy of the salt reservoir temperature.…”

“…Rowland and Makide 21 estimated the absorption cross sections of NaOH in flames based on the measurement of Daidoji, 22 but the values relied on the calculated amount of NaOH seeded into the flame, which introduced a severe uncertainty. Recently, Weng et al 23 measured the UV absorption spectrum of KOH and KCl in flame environments, and the UV absorption cross sections were evaluated based on the KCl absorption data presented by Leffler et al, 20 which were obtained at 1073 K. In the study of Weng et al, 23 the influence of even higher temperature on the absorption cross-section values was assumed to be negligible.…”

Spectrally Resolved Ultraviolet (UV) Absorption Cross-Sections of Alkali Hydroxides and Chlorides Measured in Hot Flue Gases

“…20 Quantitative measurements, however, require accurate and precise UV absorption cross-section data obtained at well-defined conditions. 21 This data is also required for other online measurements techniques, such as laser-induced photofragmentation spectroscopy and differential absorption light detection and ranging (LIDAR). 22,23 Previous works have been targeted on the measurements of UV absorption cross-section of alkali chlorides.…”

“…25 Related to the UV absorption spectra, photolysis cross-section spectra of alkali chlorides have also been investigated. 13 Recently, a more reliable measurement of the spectrally resolved UV absorption cross-sections of KCl at temperatures between 973 K and 1073 K was reported by Leffler et al 21 In their work, a novel quartz calibration cell was developed, which was characterized by a closed design with accurate control of the temperature homogeneity to ensure well-defined and reproducible alkali vapor pressure. The cell was made with a relatively large diameter to avoid wall effects.…”

“…In the present work, laminar flames from a specially designed burner were used to prepare NaCl, KCl, NaOH, and KOH in the hot flue gases with known temperature and concentrations. The absorption crosssections were determined for NaCl, KOH, and NaOH in the hot flue gas at temperatures $1400 K. Their absolute cross-section values were calibrated based on the results for KCl reported by Leffler et al 21 In addition, the temperature dependence of the absorption spectra was investigated between 1200 K and 1850 K.…”