Luminous gas treatment

GENERAL PRINCIPLES IN MEMBRANE APPLICATION OF LUMINOUS CHEMICAL VAPOR DEPOSITION AND LUMINOUS GAS TREATMENT... 

Luminous chemical vapor deposition (LCVD) and luminous gas treatment (LGT), which does not yield the primary deposition, could be used in the preparation and modification of membrane and barrier [1]. The term primary deposition refers to the direct deposition of material from the luminous gas (LCVD) in contrast to secondary deposition that results from the deposition of ablated material in LGT. It should be emphasized, however, that both methods are nanofilm technologies and require the substrate membrane on which LCVD nanofilm is deposited or the surface is modified. Accordingly, their use should be limited to special cases where such a nanofilm could be incorporated into membrane or the LGT of surface is warranted. 

Luminous Gas Treatment of Nonporous Membrane to Increase the Selectivity... 

No deposition of materials occurs in most cases however, the deposition of plasma polymer could occur depending on the nature of substrate polymer. Such a deposition of materials can be viewed as PP of organic vapors, which emanated from the substrate, by the interaction with plasma. Because the major player is the luminous gas phase, the surface treatment is included in this book under the term luminous chemical vapor treatment (LCVT). 

All of the postdeposition treatments, even treatment with the more inert gas plasmas, leave the surface of the films in a silica-like state. This is thought to be due to the creation of free radicals in the luminous gas phase, which are quickly oxidized upon exposure to the atmosphere prior to analysis. 

The creation of reactive species that cause ablation is essentially the same process as that occurs in LCVD, except that the final result is completely opposite, i.e., ablation vs. deposition. In this context, ablation by luminous gas could be described as luminous chemical vapor treatment (LCVT). Therefore, the dependence of ablation on operational parameters in LCVT is very similar to that of LCVD, which is discussed in more detail in Chapter 4. The chemical ablation of polymeric materials by O2 plasma [6] is described here to demonstrate how oxidative ablation is influenced by the operational parameters of discharge. 

As far as plasma polymerization and plasma treatment of materials, particularly organic polymers, are concerned, the luminous gas phase (low-pressure plasma) can be divided into three major groups based on the mode of consumption of the gas used to create the plasma (1) chemically nonreactive plasma (2) chemically reactive plasma and (3) polymer-forming plasma. The terms chemically reactive and chemically nonreactive are based strictly on whether the gas used in glow discharge is consumed in chemical processes yielding products in the gas phase or being incorporated into the solid phase by chemical bonds. 

These findings clearly show that the principle of CAP also applies to glow discharge treatment, which is not intended to deposit plasma polymers, in a similar manner with respect to the interaction of luminous gas with materials. 

In the continuous processing, a steady-state flow of luminous gas is established and maintained for the duration of operation, e.g., 1 month, without interruption. Due to the factors described above, it takes some time, e.g., 30 min, to establish a steady-state flow of luminous gas. Once a steady state is established, it can be maintained it for sufficient time to allow continuous processing. Substrates are fed into the steady-state flow of luminous gas in a cross-flow pattern. The rate of transport of substrate and the length of the path in the luminous gas phase determine the treatment time. 

A single monoatomic gas, e.g., argon or helium, is used as the carrier gas of the cascade arc discharge. When the luminous gas is injected into an expansion chamber under low pressure, e.g., 1 torr or less, the flame extends a significant length (e.g., 1 m), which depends on the fiow rate, input power, diameter of the nozzle, and pressure of the expansion chamber. This mode of cascade arc torch is termed low-pressure cascade arc torch (LPCAT), which is useful in the surface modification by means of low-pressure cascade arc torch treatment and low-pressure cascade arc torch polymerization. 

As seen in Figure 16.3, the LPCAT fiame is relatively narrow, implying that a uniform diffused luminous gas phase is not created in the expansion chamber. Consequently, the treatment that can be achieved by an LPCAT is governed by the... 

The relative motion of substrate with respect to the luminous gas jet is more or less mandatory for the uniform treatment. Figure 16.4 depicts a reactor equipped with three cascade arc generators, of which two are used to treat substrates placed on a rotating plate. 

The treatment by secondary plasma reactor utilizes chemically reactive species created in glow discharge without influences of electron and ion bombardments and luminous gas phase. In-glow LPCAT treatment, on the other hand, utilizes luminous gas phase without the influence of ion and electron bombardment, and chemically reactive species are created on PTFE by energy transfer from the luminous gas phase. Thus, surface treatment by secondary plasma works only with gases that produce relatively long-lived chemically reactive species. Most secondary plasma treatments appear to be surface modifications by air or oxygen. 

Luminous vapor treatment without depositing film (LGT) could be used to modify the surface characteristics of membranes. Type B plasma polymer also could be used for this purpose. General schemes of membrane application of LGT and LCVD are schematically depicted in Figures 34.2 and 34.3, respectively [2]. Since the luminous gas interacts with the substrate material, the selection of the membrane material and the gas to be used in these possible schemes is important, and it should not be considered that any combinations of gas and material could be used in any mode of application. 

The functionalization of membrane surface could be achieved by the grafting of functional groups created by luminous gas. Such a treatment has been used to attach amino groups to polymer surfaces. The luminous gas of ammonia, a mixture of... 

As seen in Fig. 3, the LPCAT flame is relatively narrow implying that a uniform luminous gas phase is not created in the expansion chamber. Consequently, the treatment that can be achieved by an LPCAT is governed by the line of sight process, regardless of whether the substrate touches the luminous gas flame or not, and limited to a relatively small area that is exposed to the flame or near the tip of flame. When a substrate is placed along the line of the jet stream, the well-identifiable flame is destroyed, and gaseous species scatter in the downstream of the substrate. The scattered species could cause surface treatment effects however, their extents are much smaller than that by the jet. 

It is common that a substrate or a section of continuous substrate, such as fibers and films, passes multiple sets of luminous gas flow. Fig. 16 depicts a schematic diagram of continuous operation of plasma polymerization with two sets of luminous gas flow. A chamber that is pumped individually to avoid cross-contamination separates the two sets of luminous gas flow. Thus, multiple plasma polymerizations or treatments can be applied on a substrate according to this principle. A continuous substrate, such as fibers, tubes, and films, is fed vertically. The horizontal feeding of substrates, shown in Fig. 16, requires multiple substrates holding devices that travel through the reactor. 

One gram of radium produces about 0.0001 ml (stp) of emanation, or radon gas, per day. This is pumped from the radium and sealed in minute tubes, which are used in the treatment of cancer and other diseases. One gram of radium yields about 4186 kj per year. Radium is used in producing self-luminous paints, neutron sources, and in medicine for the treatment of disease. Some of the more recendy discovered radioisotopes, such as Co, are now being used in place of radium. Some of these sources are much more powerful, and others are safer to use. Radium loses about 1% of its activity in 25 years, being transformed into elements of lower atomic weight. Lead is a fintil product of disintegration. Stored radium should be ventilated to prevent build-up of radon. Inhalation, injection, or body exposure to radium can cause cancer and other body disorders. The maximum permissible burden in the total body for Ra is 7400 becquerel. 

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