Controlled atmospheres

Metal organic decomposition (MOD) is a synthesis technique in which metal-containing organic chemicals react with water in a nonaqueous solvent to produce a metal hydroxide or hydrous oxide, or in special cases, an anhydrous metal oxide (7). MOD techniques can also be used to prepare nonoxide powders (8,9). Powders may require calcination to obtain the desired phase. A major advantage of the MOD method is the control over purity and stoichiometry that can be achieved. Two limitations are atmosphere control (if required) and expense of the chemicals. However, the cost of metal organic chemicals is decreasing with greater use of MOD techniques. 

Simple gravimetry of the sample is likely to be an integral component of the determination of, e.g., the concentration of, or exposures to, airborne dust. Care is required to avoid errors arising from absorption of atmospheric moisture. Tliis can be avoided by using blank filters, by conditioning the filters in an atmospherically-controlled room, or use of a desiccator. 

Before powdered carbon can be used commercially or reused for tertiary treatment of sewage effluents, a method of regeneration is required. The use of the fluidized bed for regeneration offers the key advantages of excellent temperature and atmosphere control and the ability to process the powdered solids conveniently and continuously. 

The second method, based on measurements of IR reflection spectra, is simpler and enables working with larger volumes of molten salt. No special problems involving temperature and atmosphere control exist. The method was used successfully by Fordyce and Baum [336-338] in the investigation of fluoride melts containing tantalum and niobium. 

Atmosphere control, e.g. controlling dust concentrations or inerting. 

Are emissions and discharges to atmosphere controlled by regulations Provide details of the relevant regulations. Provide details of the specific emission standards required. Identify the risk category. 

Low concentrations of VOCs in ambient ah of 1 to 1,000 ppmv (parts per million based on volume) are often harmful to human health. VOCs also promote the photochemical formation of ozone and other contaminants, and in high concentrations are a fire hazard. These severe environmental implications have resulted in increasingly stringent legislation in the U.S.A. and elsewhere to limit release of VOCs into the atmosphere. Control technologies for VOCs release include combustion and vapor recovery. Vapor recovery is preferred as combustion may result in the production of other air pollutants, and destroy valuable VOCs. 

For the practical use of ferrite it is necessary to get high-density material. In the firing process, the starting compound mixture has to be ferritized and densified by solid -solid and solid-gas reactions. In this process, the value of (5 and the grain size also have to be controlled. For this purpose, a heat-treatment, which was called atmosphere controlled two step firing by Tanaka, was devised, as shown schematically in Fig. 3.12 and in detail in Table 3.1. For reference, the usual heat-treatment for preparation of ferrites is shown in Fig. 3.12(b). The new heat treatment is composed of the following six processes. In process (1), the starting mixed compounds are heated to... 

Fig. 3.12 Manufacturing processes for the ferrites (a) atmosphere controlled two step firing (b) usual heat-treatment (in Nj gas). In the hatched regions (1) and (6) in (a), the samples are heated or cooled under flowing N2 gas. In the other regions, Po. has to be controlled to obtain the required oxygen content.

The schematic set-up for a thermogravimetric experiment is shown in Figure 16-2. The device is a combination of a sophisticated high temperature furnace (with temperature and gas atmosphere control) and a micro-balance. Since it is meant to... 

All experiments were done in an atmospheric control chamber (initially nearly 100% Ar, <60 ppm 02, and undetectable levels of 002) Aliquots of the Np(IV) stock solution were adjusted with NaOH to an approximate pH value of 12 to precipitate the brown Np(IV) hydrous oxide(11). These suspensions were centrifuged and the supernatants were discarded. The Np solids were resuspended and the pH of the suspensions (approximately 10 mg Np solid/30 ml solution) were adjusted with HC1 or NaOH to pH values between 4 to 12. No further adjustments in the pH values were made. Some of the freshly precipitated Np(IV) hydrous oxide was redissolved in acid and the Np oxidation state was analyzed by the TTA extraction procedure. As before, approximately 90% of the Np was measured to be in the reduced state. 

Figure 4.8 A modification of the Gibbs (1970) plot shows that evaporation-controlled rivers are in arid regions, rock-controlled rivers are in intermediate rainfall areas, and atmospheric-controlled rivers are in high rainfall areas. (Modified from Gibbs, 1970.)...

Other wastes generate H2 and loss of ventilation may cause an explosive atmosphere. Control systems are needed to ensure concentrations are maintained at safe levels. 

The atmosphere controls the planet. The effective temperature of the modem Earth (the temperature without the greenhouse warming of the... 

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