Read More
Date: 12-2-2018
1654
Date: 11-3-2017
1557
Date: 5-5-2019
1766
|
Sensing gases
Detecting the presence of toxic gases can be carried out by IR spectroscopic means, but such techniques do not lend themselves to a domestic market. Capitalizing on the ntype semiconducting properties of SnO2 has led to its use in gas sensors, and sensors that detect gases such as CO, hydrocarbons or solvent (alcohols, ketones, esters, etc.) vapours are commercially available and are now in common use in underground car parking garages, automatic ventilation systems, fire alarms and gas-leak detectors. The presence of even small amounts of the target gases results in a significant increase in the electrical conductivity of SnO2, and this change is used to provide a measure of the gas concentration, triggering a signal or alarm if a pre-set threshold level is detected. The increase in electrical conductivity arises as follows. Adsorption of oxygen on to an SnO2 surface draws electrons from the conduction band. The operating temperature of an SnO2 sensor is 450–750K and in the presence of a reducing gas such as CO or hydrocarbon, the SnO2 surface loses oxygen and at the same time, electrons return to the conduction band of the bulk solid resulting in an increase in the electrical conductivity. Doping the SnO2 with Pd or Pt increases the sensitivity of a detector. Tin(IV) oxide sensors play a major role in the commercial market and can be used to detect all the following gases, but other sensor materials include:
|
|
للتخلص من الإمساك.. فاكهة واحدة لها مفعول سحري
|
|
|
|
|
العلماء ينجحون لأول مرة في إنشاء حبل شوكي بشري وظيفي في المختبر
|
|
|
|
|
قسم الشؤون الفكرية يحتفي بإصدار العدد الألف من نشرة الكفيل
|
|
|