Atmospheric pressures

The Earth is approximately a sphere with a radius of 3950 miles. If the air pressure is around 14.7 psi, we can estimate the total weight of the atmosphere. First, let s change the radius from miles to inches  

let s calculate the approximate surface area of Earth, using the surface area of a sphere equaling 4Ttr2  

plugging in the pressure of 14.7 psi applied over an area of 787 quadrillion square inches gives us a total weight of the atmosphere of 11.6 quintil-lion pounds, or 5.79 quadrillion tons. 

The gravitation of the earth attracts the gaseous components of the air, which exert a force, known as atmospheric pressure, on the surface of the pianet. The pressure on any particuiar piace on the earth s surface depends on the amount of air above the piace. it foiiows that the atmospheric pressure decreases at high aititudes, increases at iow aititudes and beiow sea ievei, and is aiso affected by changes in weather. Measuring the atmospheric pressure is usuaiiy done with physicai instruments known as barometers (see Fig. 83). 

Nitrogen. Nitrogen, a colorless, odorless, and tasteless gaseous element, is the main component of the atmosphere, which makes up about 78% of its volume since it is also an important constituent of living organisms. 

a gas that makes up just xmder 1% by volume of the atmosphere, is an inert element and a noble gas, that does not combine with other elements. 

Carbon Dioxide. Carbon dioxide, also a colorless and odorless gas, makes up about 0.03% of dry air. Carbon dioxide is introduced into the atmosphere by several natural processes it is released from volcanoes, from burning organic matter, and from living animals as a byproduct of the respiration process. It is for this latter reason that carbon dioxide plays a vital role in the carbon cycle (see Fig. 62), which makes possible one of the more important scientific tools in archaeology, radiocarbon dating (see Textbox 52). 

Water generally occurs in air in low or relatively low concentrations, mostly in the form of atmospheric moisture. Its importance cannot, however, be overemphasized, since atmospheric moisture, xmique to the surface of the earth, is a determining factor in the water cycle (see below) and in living and other processes. Moisture is, therefore, one of the most important and probably the most relevant atmospheric components for the majority of living processes. 

Notice that we did not specify the diameter of the barometer tube. If the mercury in a 1-cm diameter tube rises to a height of 760 mm, the mercury in a 2-cm diameter tube will rise to that height also. The weight of mercury is greater in the wider tube, but the area is larger also thus the pressure, the ratio of weight to area, is the same. 

Since the pressure of the mercury column is directly proportional to its height, a unit commonly used for pressure is mmHg, the height of the column in millimeters (mm). At sea level and 0°C, normal atmospheric pressure is 760 mmHg at the top of Mt. Everest (29,028 ft, or 8848 m), the atmospheric pressure is only about 270 mmHg. Thus, pressure decreases with altitude the column of air above the sea is taller and weighs more than the column of air above Mt. Everest. 

Laboratory barometers contain mercury because its high density allows the barometer to be a convenient size. For example, the pressure of the atmosphere would equal the pressure of a column of water about 10,300 mm, almost 34 ft, high. Note that, for a given pressure, the ratio of heights (h) of the liquid columns is inversely related to the ratio of the densities (d) of the liquids  

Pressure results from a force exerted on an area. The SI unit of force is the newton (N) 1 N = I kg m/s. The SI unit of pressure is the pascal (Pa), which equals a force of one newton exerted on an area of one square meter 

A much larger unit is the standard atmosphere (atm), the average atmospheric pressure measured at sea level and 0 C It is defined in terms of the pascal  

Silicon dioxide films have been an essential factor in the manufacture of integrated circuits from the earliest days of the industry. They have been used as a final passivation film to protect against scratches and to getter mobile ion impurities (when doped with phosphorus). Another application has been as an interlayer dielectric between the gate polysilicon and the aluminum metal-ization. Initially, most such films were deposited in atmospheric pressure systems. In recent years, low pressure processes have assumed greater importance. We will begin by examining the atmospheric process. 

Although the atmospheric pressure Si02 film deposition process was the first CVD process used, it continues in use today because it can be run success- 

If SiH4 is mixed with 02, using an oxygen to SiH4 ratio above 3 1, and this mixture is heavily diluted with an inert gas, then Si02 will be deposited on a hot plate at temperatures above 240°C.2 The typical reactor is a cold-wall type where the wafer holder is heated. The walls are cooled to try to minimize the deposition on them so that reactor cleaning is kept to a minimum. Several commercial reactors are available that implement this process, and they will be reviewed in Chapter 6. 

If the SiH4/02 mixture is not sufficiently diluted with an inert gas, then gas phase nucleation typically occurs and Si02 particulates are formed. Generally, N2 is used as the diluent, but some work has been done with Ar, C02, and He. Depending on the reactor configuration, an inert gas effects the deposition rates in different ways. 

The low-temperature depositions described in the present section can be used for either interlayer dielectrics or final passivation films. Their primary disadvantage is one of film quality, because the process is susceptible to gas-phase nucleation and incorporation of particles into the film. 

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This is an endothermic reaction accompanied by an increase in the number of moles. High conversion is favored by high temperature and low pressure. The reduction in pressure is achieved in practice by the use of superheated steam as a diluent and by operating the reactor below atmospheric pressure. The steam in this case fulfills a dual purpose by also providing heat for the reaction. 

Solution The fraction of liquid vaporized on release is calculated from a heat balance. The sensible heat above saturated conditions at atmospheric pressure provides the heat of vaporization. The sensible heat of the superheat is given by... 

Gattermann-Koch reaction Formylation of an aromatic hydrocarbon to yield the corresponding aldehyde by treatment with CO, HCl and AICI3 at atmospheric pressure CuCl is also required. The reaction resembles a Friedel-Crafts acylation since methanoyl chloride, HCOCl, is probably involved. 

Commercial equipment is available which automatically switches from atmospheric distillation to vacuum distillation and calculates the distillation curve as temperatures under atmospheric pressure conditions as a function of weight or volume per cent recovery. 

The results are presented as a distillation curve showing the boiling temperature (corrected to atmospheric pressure) as a function of the distilled volume. 

Recently, chromatographs and their associated columns have been able to elute components with boiling points up to 700°C under atmospheric pressure. 

This is the average boiling temperature at atmospheric pressure (1.013 bar abs). This characteristic is obtained by direct laboratory measurement and is expressed in K or °C. 

This is the most common method. It is used for gasolines, kerosenes, gas oiis and similar products. The test is conducted at atmospheric pressure and is not recommended for gasolines having high dissolved gas contents or solvents whose cut points are close together. 

T = temperature equivalent at atmospheric pressure T = experimental temperature taken at pressure P P = pressure log = common logarithm (base 10)... 

Conversion of the Low Pressure Distillation Results into Equivalent Results for Atmospheric Pressure... 

To convert low pressure distillation results into those of atmospheric pressure, the Maxwell and Bonnel (1955) equations are used. 

Crude oil is generally characterized by a TBP analysis whose results are expressed as temperatures equivalent to atmospheric pressure as a function of the fraction of volume and weight distilled... 

At atmospheric pressure, hydrocarbon viscosities can be estimated by two methods the ASTM method and that of Mehrotra (1990). 

The error of this method is about 10% at atmospheric pressure. The accuracy becomes lower as the pressure increases. 

Chamber B is filled with partially degassed sample material at 0°C. Chamber A is filled with air at 37.8°C and at atmospheric pressure. 

The flash curve at atmospheric pressure can be estimated using the results of the ASTM D 86 distillation by a correlation proposed by the API. For the same volume fraction distilled one has the following relation ... 

This calculation starts from the TBP at atmospheric pressure. The API recommends a relation established by Riazi (1982) ( oj j... 

Note that the RVP is a relative pressure that is a difference compared to the atmospheric pressure. The RVPs for gasolines are generally between 350 and 1000 millibar. The level corresponding to European specifications are shown in Table 5.6 the fuel must be simultaneously within minimum and maximum limits, identical for each type of fuel, gasoline and premium, but... 

Fluid Coking", developed in 1953. The reaction proceeds at atmospheric pressure, at about SOO-SSOT, in a reactor whose feed is mixed in a fluidized bed of hot coke which maintains the desired temperature. 

Certain curves, T = f(% distilled), level off at high temperatures due to the change in pressure and to the utilization of charts for converting temperatures under reduced pressure to equivalent temperatures under atmospheric pressure. 

Edmister, W.C. and K.K. Okamoto (1959), Applied hydrocarbon thermodynamics. Part 13 equilibrium flash vaporization for heavy oils under sub-atmospheric pressures . Petroleum Refiner, Vol. 38, No. 9, p. 271. 

As anode and cathode of the tube have to share the same vacuum envelope, and the insulating material has to insulate the high tension between these respective electrodes, the material is always part of the vacuum envelope of the tube. Therefore, the insulator has to be vacuum tight and must be able to carry the atmospheric pressure, which loads this envelope. 

The material is brittle. There are relatively large radii to be obeyed to enable the vacuum envelope to withstand atmospheric pressure, and tubes must be handled carefully. 

Here a - surface tension pa - atmospheric pressure 9 - contact angle of crack s wall wetting by penetrant n - coefficient, characterizing residual filling of defect s hollow by a penetrant before developer s application IT and h - porosity and thickness of developer s layer respectively W - minimum width of crack s indication, which can be registered visually or with the use of special optical system. The peculiarity of the case Re < H is that the whole penetrant volume is extracted by a developer. As a result the whole penetrant s volume, which was trapped during the stage of penetrant application, imbibes developer s layer and forms an indication of a defect. 

Let us consider one more physical phenomenon, which can influence upon PT sensitivity and efficiency. There is a process of liquid s penetration inside a capillary, physical nature of that is not obvious up to present time. Let us consider one-side-closed conical capillary immersed in a liquid. If a liquid wets capillary wall, it flows towards cannel s top due to capillary pressure pc. This process is very fast and capillary imbibition stage is going on until the liquid fills the channel up to the depth l , which corresponds the equality pcm = (Pc + Pa), where pa - atmospheric pressure and pcm - the pressure of compressed air blocked in the channel. 

Most ion-molecule techniques study reactivity at pressures below 1000 Pa however, several techniques now exist for studying reactions above this pressure range. These include time-resolved, atmospheric-pressure, mass spectrometry optical spectroscopy in a pulsed discharge ion-mobility spectrometry [108] and the turbulent flow reactor [109]. 

The importance of low pressures has already been stressed as a criterion for surface science studies. However, it is also a limitation because real-world phenomena do not occur in a controlled vacuum. Instead, they occur at atmospheric pressures or higher, often at elevated temperatures, and in conditions of humidity or even contamination. Hence, a major tlmist in surface science has been to modify existmg techniques and equipment to pemiit detailed surface analysis under conditions that are less than ideal. The scamiing tunnelling microscope (STM) is a recent addition to the surface science arsenal and has the capability of providing atomic-scale infomiation at ambient pressures and elevated temperatures. Incredible insight into the nature of surface reactions has been achieved by means of the STM and other in situ teclmiques. 

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