Strength, mechanical

The mechanical strength of many compositions of LaCrOa is low compared to YSZ (see Table 7.4) and appears to be variable. This low strength and variability 

Since that initial work, a number of other liquid promoters have been Investigated and several systems have been rather successful. For example, Koc showed that compositions within the system (La,Ca)(Co,Cr)03 sintered well and yielded nearly theoretically dense structures at temperatures as low as 1350°C [6], These compositions are stable in a fuel atmosphere at 1000°C and therefore are potential interconnect candidates. The main problem with these compositions is that Ca and Co tend to react with other cell components and therefore their long time stability is suspect [21]. 

An initial qualitative assessment of the mechanical strength can made with a simple fingernail test (an acceptable catalyst should not be powderable between the thumbnails) or a simple drop test from a certain height. A quantitative measure of the mechanical strength is the lateral strength of the catalyst particles, which should exceed 15 N cm l 

Due to the brittleness and elasticity of glass, its mechanical strength is not an intrinsic property but greatly depends on 

As a consequence, strength data given under laboratory conditions have to be transferred properly to strength data under life conditions. A concept for predicting life data is, for example, given by Exner [3.10]. 

Because there is a certain randomness to the kind and distribution of surface flaws that are typical for a certain material as well as for its production process, strength measurement data are statistical data and have to be treated in a statistical way. In most cases the strength is adequately described using the Weibull distribution. 

The physical behavior of glass-ceramic panels under impact varies depending on the contact situation. Accordingly, standards distinguish between flat impact (pot impact) and sharp -edged impact (steel ball impact and Norwegian hammer). 

It is important to realize that the mechanical load resistance of cooktop panels is entirely determined by the strength of the bottom side. Assuming the small thicknesses of cooktop panels as usual, bending forces (caused by 

Engineering Aspects of MIEC Hollow Fiber Membranes for Oxygen Production 265 

---

In certain alloys and under certain environmental conditions, selective removal of one metal (the most electrochemically active) can occur that results in a weakening of the strength of the component. The most common example is dezincification of brass [164, 165]. The residual copper lacks mechanical strength. 

Corrosion problems are particularly important when two metals are in contact. The more reactive metal becomes the cathode of the cell and goes into solution when the cell is activated by an electrolyte. A typical cell is shown in Figure 13.7. When the metal in contact with iron is more reactive than iron itself, the iron is protected from corrosion. This is important when mechanical strength... 

This is simUar to (a) except that it is provided with a ring neck, which increases the mechanical strength, prevents breakage when a stopper is inserted, and provides a means for wiring a stopper in place. The upper rim is ground flat. 

Type B thermocouples (Table 11.56) offer distinct advantages of improved stability, increased mechanical strength, and higher possible operating temperatures. They have the unique advantage that the reference junction potential is almost immaterial, as long as it is between 0°C and 40°C. Type B is virtually useless below 50°C because it exhibits a double-value ambiguity from 0°C to 42°C. 

Capillary Tubes Figure 12.42 shows a cross section of a typical capillary tube. Most capillary tubes are made from fused silica coated with a 20-35-)J,m layer of poly-imide to give it mechanical strength. The inner diameter is typically 25-75 )J,m, which is smaller than that for a capillary GC column, with an outer diameter of 200-375 )J,m. 

Fig. 31. An acrylic terpolymer designed for chemically amplified resist applications. The properties each monomer contributes to the final polymeric stmcture are for MMA, PAG solubility, low shrinkage, adhesion and mechanical, strength for TBMA acid-cataly2ed deprotection and for MMA, aqueous...

Crystallinity. The crystallinity of the parylenes determines two of their most important practical characteristics mechanical strength at elevated temperatures (see Fig. 5) and solvent resistance. 

SiHcon nitride (see Nitrides) is a key material for stmctural ceramic appHcations in environments of high mechanical and thermal stress such as in vehicular propulsion engines. Properties which make this material uniquely suitable are high mechanical strength at room and elevated temperatures, good oxidation and creep resistance at high temperatures, high thermal shock resistance, exceUent abrasion and corrosion resistance, low density, and, consequently, a low moment of inertia. Additionally, siHcon nitride is made from abundant raw materials. 

Polymer-based rocket propellants are generally referred to as composite propellants, and often identified by the elastomer used, eg, urethane propellants or carboxy- (CTPB) or hydroxy- (HTPB) terrninated polybutadiene propellants. The cross-linked polymers act as a viscoelastic matrix to provide mechanical strength, and as a fuel to react with the oxidizers present. Ammonium perchlorate and ammonium nitrate are the most common oxidizers used nitramines such as HMX or RDX may be added to react with the fuels and increase the impulse produced. Many other substances may be added including metallic fuels, plasticizers, stabilizers, catalysts, ballistic modifiers, and bonding agents. Typical components are Hsted in Table 1. 

Electrical Properties. Polytetrafluoroethylene is an excellent electrical insulator because of its mechanical strength and chemical and thermal stabihty as well as excellent electrical properties (Table 6). It does not absorb water and volume resistivity remains unchanged even after prolonged soaking. The dielectric constant remains constant at 2.1 for a temperature range of —40 to 250°C and a frequency range of 5 Hz to 10 GHz. 

---