Ambient humidity

When the surface conditions are acidic or the ambient humidity is low enough to affect the cure significantly, a surface accelerator may be used to promote the reaction. Available from most manufacturers, these basic solutions may be dip, wipe, or spray appHed. Recentiy, new additive chemistry has been developed that accelerates the cure under adverse conditions without the need for a separate accelerator. 

Properties. Ammonium bifluoride, NH4HF2, is a colorless, orthorhombic crystal (2). The compound is odorless however, less than 1% excess HF can cause an acid odor. The salt has no tendency to form hydrates yet is hygroscopic if the ambient humidity is over 50%. A number of chemical and physical properties are Hsted in Table 1. 

These ate the main reactions ia Pordand cements because the two calcium siHcates constitute about 75% of the cement. The average lime—silica ratio (C S) may vary from about 1.5 to about 2.0 or even higher, the average value is about 1.7. The water content varies with the ambient humidity, the three moles of water being estimated from measurements ia the dry state and stmctural considerations. As the lime—silica ratio of the C—S—H iacreases, the amount of water iacreases on an equimolar basis, ie, the lime goes iato the stmcture as calcium hydroxide, resulting ialess free calcium hydroxide. 

Ambient humidity corrections to generator output and heat rate... 

When dimensional accuracy is required in a specific application the effect of water absorption should also be considered. Manufacturers commonly supply data on their products showing how the dimensions change with the ambient humidity. 

FIGURE 5.12 Perceived ambient humidity by sedentary subjects. 

Where human occupancy or wet process plant is present, the emission of water vapor will occur. Depending on external conditions and building fabric constmction, the attendant potential for excessive ambient humidity or surface condensation may exist. 

Moisture precipitation Apart from wetting by sea-spray, moisture may either be deposited on a surface by rainfall or dew formation. For a known ambient humidity the dew point can be calculated, using the expression given previously, from standard tables giving the saturated vapour pressure of... 

Chemical condensation This occurs when soluble corrosion products or atmospheric contaminants are present on the metal surface. When the humidity exceeds that in equilibrium with a saturated solution of the soluble species, a solution, initially saturated, is formed until equilibrium is established with the ambient humidity. The contaminants have already been detailed and of the corrosion products, obviously sulphates, chlorides and carbonates are most important in this context. However, in some cases there is a lack of reliable data on the vapour pressure exerted by saturated solutions of likely corrosion products. The useful data was summarised in Table 2.7. 

SPFM experiments were performed on sulfuric acid deposited on the surface of aluminum films on silicon. A macroscopic droplet was first deposited and then rapidly dispersed using a jet of gas. This produced submicrometer-sized droplets. The initial concentration of the sulfuric acid ranged from 20 to 98 wt.%. However, the acid droplets equilibrate rapidly with the ambient water vapor. For example, at room temperature and RH = 30%, the concentration of sulfuric acid is 55 wt% at 90% RH, it is 20 wt%. The increase in droplet volume as they equilibrate with the ambient humidity is shown in Figure 35. 

Figure 262. Comparison of cooled (Pi) and uncooled (A) absorption process. Treg indicate the equilibrium regeneration temperatures at ambient humidity for different concentration C...

FIG. 4. Many STM experiments performed under ambient conditions incorporate SECM phenomena associated with water adsorption on surface due to the ambient humidity. In some instances the SECM signal may be dominant as in the case of imaging bulk insulators such as mica. (From Ref. 50.)... 

Figure 6. MaxEnt reconstruction of SAXS data from as-received Nafion equilibrated under (a) ambient humidity and (b) 100% RH. (Reprinted with permission from ref 63. Copyright 2000 American Chemical Society.)...

A major part of Taguchi s philosophy centers around the separation of effects caused by noise factors and effects caused by control factors. Control factors are variables that are under the control of the experimenter flow rate, pH, concentration, reactor temperature, etc. In contrast, noise factors are variables that are not under the control of the experimenter ambient temperature, ambient humidity, identity of process operator (Joe or Jane), source of raw material, etc. Control factors are sometimes called process factors noise factors are sometimes called environmental factors. 

Figure 14.8. The inner array exists in the three-dimensional space of control factors x X2, and X3 these might represent temperature, flow rate, and pH, respectively. The outer array is represented by the small fractional factorial designs shown at each factor combination of the inner array. It is important to understand that this inner outer does not exist in the control factor space - it exists in a separate three-dimensional space of noise factors, designated for our purposes here as z Zj, and Z3 these might represent ambient humidity, source of raw material, and identity of process operator.

Suppose viscosity, y, is the quality response of interest. Then at one of the four factor combinations in the inner array (i.e., in the control factor space), experiments can be carried out at the four factor combinations in the outer array (i.e., in the noise factor space). Frequently the outer array experiments are adventitious experiments in the sense that the experimenter has to wait until, say, the ambient humidity approaches the desired value then the appropriate source of raw material and the appropriate process operator can be brought in and the experiment can be carried out. 

The parameter estimates a, Oj, and represent the noise factor effects. In this example, they represent how much influence the ambient humidity, source of raw material, and name of person running the process have on the viscosity. Ideally, for a rugged system, we would like Oi, a, and to be zero. 

It states that the effect of the ambient humidity is a function of the control factors This inforpiation can be tremendously useful because it offers a quantitative means of adjusting the control factors jCi, jCj, and jCj in such a way as to cause the value of tti to approach zero. In short, there might be a combination of the control factors that will cause the system to be rugged with respect to ambient humidity. 

Fig. 5. SFM images of chicken erythrocyte chromatin fibers. (A) Untrypsinized, linker histone-containing control fibers, and (B) linker histone-stripped fibers. The stripping of linker histones destroys both the three-dimensional interactions of adjacent nucleosomes and the zig-zag arrangement of consecutive nucleosomes. Trypsinization of the N-terminal histone tails of the linker histones and core histone H3 result in the loss of the three-dimensional association of the consecutive nucleosomes, but does not destroy the zig-zag configuration. Imaging of fibers deposited onto mica was performed in air under conditions of ambient humidity and temperature (from Ref. [32]). Full width of each image corresponds to 500 nm.

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