Liquefied the volumes of the vaporized gas and the

Liquefied petroleum gas is an inflammable mixture of hydrocarbon
gases used as a fuel in heating appliances
and vehicles. It is increasingly used as an aerosol propellant and a refrigerant,
replacing chlorofluorocarbons in an effort to reduce
damage to the ozone layer. Varieties of LPG bought and sold include mixes
that are primarily propane, mixes that are primarily butane, and – most
common – mixes including both propane C3H8 and butane C4H10,
depending on the season: in winter more propane, in summer more butane. Propylene
and butylenes
are usually also present in small concentration. A powerful odorant,
ethanethiol,
is added so that leaks can be detected easily. In the United States, thiophene
or ethyl mercaptan
is also approved odorants. LPG has a typical specific calorific value
of 46.1 MJ/kg compared with 42.5 MJ/kg for fuel-oil and
43.5 MJ/kg for premium grade petrol (gasoline).  However, its energy density per volume unit
of 26 MJ/l is lower than either that of petrol or fuel-oil. LPG will evaporate
at normal temperatures and pressures and is supplied in pressurised steel cylinders. They are
typically filled to between 80% and 85% of their capacity to allow for thermal
expansion of the contained liquid. The ratio between the volumes of
the vaporized gas and the liquefied gas varies depending on composition,
pressure, and temperature, but is typically around 250:1. The pressure at which
LPG becomes liquid, called its vapour pressure,
likewise varies depending on composition and temperature; for example, it is
approximately 220 kilo Pascal’s (2.2 bar) for pure butane at 20 °C
(68 F), and approximately 2.2 mega Pascal’s (22 bar) for pure propane
at 55 °C (131 F). LPG is heavier than air, and thus will flow
along floors and tend to settle in low spots, such as basements. This can cause
ignition or suffocation hazards if not dealt with.

A gas sensor is a
chemical sensor that provides an electrical output in response to the chemical
interactions with gases. From the literature, it is observed that presently
available sensors have two major shortcomings; first, low sensitivity and
second, high operating temperature. We have to compromise with either
sensitivity or operating temperature. A highly sensitive sensor mostly works at
a very high operating temperature which increases the power consumption. On the
other hand, sensors which operate at low temperatures are not sensitive for
tracing small concentrations of LPG. Liquefied Petroleum Gas is one of the most
harmful gases due to its inflammable and explosive nature which presents many
hazards to humans as well as environment. The leakage of LPG is a serious
problem. So nowadays the LPG sensor has become very interesting topic in view
of the fundamental research as well as industrial applications. Nanostructured
materials can enhance the performance of LPG sensor because of their much
higher surface-to-volume ratio as compared to coarse micro grained materials.
In addition to the enhanced sensitivity demonstrated by the nanostructured
material based sensors, the sensors can give a quick response too. Grain size
and porous structure have a major effect on the gas-sensing properties of
polycrystalline materials and their full characterization should be the first
step in the study of materials. Therefore the development of portable LPG
sensors that are robust, small sized, have long lifetimes, are quick in
response and have sufficient sensitivity in the ambient environment is
necessary and demanded in order to prevent the explosion accidents in homes and
industries for safety requirements. Solid-state LPG sensors using metal oxide
are the most promising for the detection of LPG because of their compact structure,
high selectivity, low cost, and the ability of continuous monitoring. The need
for reliable, cheap and user-friendly gas sensors for the detection of LPG is
industrially important and has led to a considerable expansion in the field of
sensor research and development. For this reason efforts are made nowadays by
scientific research communities in leading laboratories all over the world to
focus on the investigation of novel LPG sensitive materials suited for
solid-state gas sensors. Consequently, their performances have to be improved
dramatically by adopting preparation conditions and by controlling deposition
processing. Several types of LPG sensors such as chemical sensors, the
resistive and conductive type sensors using semiconductors and sensors based on
metal polymer complexes have been investigated by different research groups in
various parts of the world. Therefore, a great attention has been recently paid
to the development of new material “architectures” at the nano-scale.

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The
strategies followed to maximize the sensor response involve the use of
catalytic additives. The additives are chosen on the basis of their ability for
enhancing the interactions between the gas modulus and the sensing surface.
There are few studies concerning the use of additives for increasing the gas
sensor response. However, no clear information about the chemical state and
effects of the additives is shown and thus, their role in the sensing mechanism
is not yet clarified. From a fundamental point of view, it is interesting to
achieve a better understanding of the interaction mechanism between the sensing
material and the target-gas. This knowledge will provide information regarding
the conditions under which better sensor responses may be obtained and thus, it
would facilitate further improvements in design and fabrication of sensors.