Characteristics of hollow cathode lamps and hollow cathode lamps
1. Cathode hollow cathode lamp
The cathode is made of the element being analyzed or a substance containing the element being analyzed. If the metal is stable in air and has a high melting point, a pure metal (e.g. silver) is generally used as the cathode material. If the metal itself is brittle, a sintered metal powder (e.g.manganeseTungsten). Metal oxides or halides (e.g. cadmium, sodium) are generally used if the metal itself is more reactive in air or has a high relative vapor pressure. Powder technology is also used to make multi-element lamps containing a variety of the metals being analyzed.
The diameter of the cathode is also very important because the emission intensity of the lamp depends on the current density.
2. Enclosed gas
The sealed gas must be a single molecule gas to avoid the molecular vibration spectrum, so an inert rare gas is generally used. The sealed gas generally uses neon or argon, and neon is the best choice. This is due to its higher ionization potential for higher emission intensity. Argon is only used when the emission line of neon is very close to the emission line of the measured element. The lower mass number used for helium not only results in a significantly smaller sputtering effect, but also shortens the life of the lamp due to the rapid depletion of the gas.
The depletion of the sealed low-pressure gas is caused by the absorption of the surface material of the lamp. When the sealed gas pressure is lower than the specified value, the continuous discharge cannot be carried out, and the life of the lamp reaches the end. Although the lamp can still be lit, it can no longer emit the resonance line of the measured element.
3. Anode hollow cathode lamp
The anode is a simple ordinary electrode that can provide a discharge bombardment voltage. The anode material is generally made of zirconium because it is a "getter". This feature is explained in the "5 Processes" section below.
4. Envelope
Electrodes are usually enclosed using glass containing a light path window made of quartz or special borosilicate glass. The material of the light path window is determined by the emission line of the element lamp. Since the emission line of most elements is below 300 nanometers, quartz material must be used at this time. Borosilicate glass is generally used for wavelengths higher than this.
5. Processing
The treatment step is the key to manufacturing high-performance lamps. The main purpose of treatment is to remove contamination for purification.
The processing steps mainly include vacuuming and maintaining a suitable high temperature outside the lamp.
The treatment step can reverse the polarity so that the zirconium anode turns into a cathode. For impurity gases oxygen and hydrogen zirconium electrodes are a good "getter", so using this electrode can remove impurity gases. A layer of zirconium rests on the envelope of the lamp during discharge.
Near the anode, there will be a black film. This active film absorbs the impurity gas and purifies the gas in the lamp. Until the final pure gas fills the entire lamp, it is then sealed. The finished lamp still needs to be tested for a few hours.
