I have a customer who uses silicon tetrachloride and germanium chloride in his production process. If the gases are released in air they form a dangerous chloride gas. He has an exhaust chamber where the gases could potentially be present, and needs a portable instrument he can use to sample the chamber before opening the door. Are we able to detect or measure these gases?


Both silicon tetrachloride (SiCl4) and germanium chlorides (GeCl4 and GeCl2) can be detected by using a hydrochloric acid (HCl) sensor.

When these highly reactive gases are released into the atmosphere, they react with the humidity in the air to produce hydrogen chloride (HCl) gas.

SiCl4 + 2 H2O → SiO2 + 4 HCl

GeCl4 + 2 H2O → GeO2 + 4 HCl

Besides being able to detect the original gas, we are also able to detect the primary HCl reaction byproduct when it hits the air.

HCl is an extremely toxic and corrosive gas, with a TLV® (Ceiling) of 2.0 ppm. The OSHA PEL and NIOSH REL exposure limit (Ceiling) is 5.0 ppm.

The other byproducts, silicon dioxide (SiO2) and germanium oxide (GeO2), are normally stable, and in moderate concentrations, not very toxic. It’s the HCl that is the big concern.

GfG technical note TN 2015, “Electrochemical (EC) sensors: gases measured, ranges and resolution,” provides a complete list of the EC sensors that are available for use with GfG products, as well as optional ranges and resolutions (Table 1). The note also includes a list of additional gases that are reliably detectable by means of our standard available sensors based on relative response (Table 2). Both germanium chloride and silicon tetrachloride are on the list.

You can use the HCl sensor to detect a number of other common semi-conductor gases. The list in Table 2 is actually pretty extensive. For the chloride gases we generally use the HCl sensor. For the fluoride gases we use the HF sensor.

GfG has the ability to support many different sensors. In addition, we are often able to customize the range and resolution in order to optimize the sensor for a specific application. Not all of the available sensors, ranges and resolutions are listed in our data sheets, nor even (in some cases) in our price list. We just don’t have the space, and we don’t want to add additional complexity to the product ordering structure.

The GfG Customer Service Department can provide a special part number, and add the additional configuration details when you place the order.

One word of caution about these particular gases. Silicon and germanium are both catalytic LEL sensor poisons. If you need to include an LEL sensor in the same instrument as the HCl sensor used to measure these gases, you should consider using our infrared (IR) LEL sensor. IR LEL sensors are not harmed by exposure to sensor poisons. Also, since hydrogen (H2) is almost always a concern in semi-conductor applications, and hydrogen cannot be measured with an IR LEL sensor, you should also include an electrochemical hydrogen sensor in the same instrument.

Thanks again for asking the question!

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