Direct measurement of dissolved hydrogen in aluminum alloys
What is AlproH palm?
AlproH palm is a portable instrument designed for the rapid determination of dissolved hydrogen content in molten aluminum alloys. By employing a direct electrochemical measurement method, it provides the fastest measurement among commercially available hydrogen analysis techniques.
The system comprises of a probe, an analyzer (includes connecting line), and a personal measuring aid gear. The probe can use indefinitely until it breaks a part; leaching out of metal frame or broken electrical line inside.
A patented PARK sensor, housed at the tip of the probe, provides an EMF output which depends purely on the hydrogen partial pressure (pH2) and temperature in the melt. The sensor is housed in a robust, impact-resistant probe constructed from special high temperature alloy and porous graphite, which ensures that the AlproH palm is able to withstand the harsh environments in the Al foundry.
The sensor EMF and temperature outputs are fed into the analyzer, which when combined with the alloy interaction parameters, gives the dissolved hydrogen concentration in units of ml/100g Al.
How it works
▲ AlproH palm test
The technology is based on a novel solid electrochemical hydrogen sensor, so called Park sensor, which, at an elevated temperature, is able to measure hydrogen content with reference to oxygen in the air through the adoption of proton conductor/oxygen ion conductor hetero- junction electrolytes. The principle behind how it can be used to measure hydrogen concentration is described as follows:
An impervious section of Park sensor is coated with Pt electrodes on both faces. The inside of the sensor (reference electrode) is exposed to the oxygen-containing air and the other side (working electrode) is to the hydrogen gas in the melt. For this arrangement, the measured EMF of the sensor, E is expressed as
E = E0 + 9.921x10-5 T log[H2]
, i.e. it depends logarithmically on the hydrogen partial pressure in the melt. Here Eo, and T are sensor constant, and absolute temperature, respectively. Thus the hydrogen concentration can be calculated from the measured EMF. To work out the dissolved hydrogen content in the melt, the relation between the gas partial pressure of hydrogen and its solubility for Al melt must be known. From Sievert’s law, the dissolved hydrogen content in Al melt for a given hydrogen partial pressure, S is expressed as
where S has units of ml/100gAl and T, f are absolute temperature H and alloy interaction parameter, respectively
Probe
The sensor features a heterojunction structure consisting of an oxygen-ion conductor and a proton conductor, both fabricated from high-temperature ceramic materials. This design provides excellent resistance to harsh operating environments and thermal shock.
The ceramic sensor is brazed to a KOVAR fitting, which is laser-welded to a stainless-steel tube to ensure a hermetic seal and prevent hydrogen leakage. The working electrode (WE) is protected from direct contact with the molten aluminum by a porous graphite cover, while an aluminum seal prevents oxidation of the electrode during cooling. The probe responds rapidly, requiring approximately 2.5 minutes to complete a measurement.
The probe is designed for a long service life and may be used until it reaches the end of its operational life. However, calibration is recommended every six months or after approximately 300 measurements, whichever comes first. If the probe malfunctions or an abnormal operating condition is detected, the analyzer automatically recognizes the fault and displays an error message to the user.
The sensor probe is approximately 20 cm long and is fitted with a 20 cm or 40 cm handle, which provides both mechanical support and the electrical connection to the analyzer. A thermocouple integrated into the handle continuously measures the melt temperature, allowing accurate temperature compensation during hydrogen measurement.
Specifications
| Measuring Range | 0.01-0.72 ml/100gAl |
| Accuracy | ±0.02 ml/100gAl or ±15% (whichever is greater) |
| Reproducibility | <0.02 ml/100gAl or ± 10% (whichever is greater) |
| Measuring Time | <2.5 min |
| Max. depth of Immersion | 150mm |
| Sensor Operating Temp. | 640-790 ℃ |
| Size | 120x244x46 mm |
| Weight | 600g |
Probe Stand
For improved safety and ease of operation, the use of the dedicated probe handling stand is strongly recommended. It allows the probe to be inserted into the molten aluminum safely and helps maintain a constant immersion depth throughout the measurement.
The stand consists of a secure probe holder and a cooling pad. The probe holder firmly supports the probe during operation, while the cooling pad provides a safe location for the hot probe immediately after measurement and rapidly cools the sensor. Rapid cooling is important to minimize oxidation of the sensor after it is withdrawn from the molten aluminum, thereby helping to maintain measurement performance and extend probe life.
The stand is manufactured from aluminum alloy, making it lightweight, durable, and easy to transport and deploy in the foundry.
Fast, Accurate, Easy to handle and Long Life
By combining a patented air-reference electrochemical sensor with a proprietary direct measurement method and advanced signal-processing algorithm, AlproH Palm delivers reliable hydrogen measurements in less than 2.5 minutes.
The probe features a robust sensor structure that provides excellent resistance to mechanical stability, thermal shock, and the harsh operating conditions encountered in aluminum foundries. The analyzer is equipped with a clear and intuitive display, allowing users to read and interpret measurement results quickly and easily.
