Selective hardening

We have demonstrated that vegetable oils and fatty acid esters can be selectively hardened in liquid, near-critical, or supercritical C02 or propane and in mixtures thereof at temperatures between 60 °C and 120 °C and at a total pressure up to 20.0 MPa. Table 14.2 summarizes the results for the selective hydrogenation of vegetable oils in supercritical C02 in comparison with hydrogenation reactions performed in a discontinuous (i.e., batch or semibatch) stirred-tank reactor and in a continuous trickle-bed reactor. 

Table 14.2. Selective Hardening of Vegetable Oils in Liquid Phase (Slurry, Trickle Bed) and in Supercritical C02... 

Figure 14.4. Hydrogenation activity in the selective hardening of fatty acid esters using Deloxan AP II / 1 % Pd fixed-bed catalyst.

Edible oils and fatty acid esters were selectively hardened in sc CO2 at temperatures between 60°C and 90°C and at a total pressure of 10.0 MPa. In order to get different degrees of hardening, we investigated activated carbon and different DELOXAN supported precious metal fixed bed catalysts at space velocities (LHSV) between 5 and 60 h1. 

Selective hardening of edible oils in discontinuous stirred tank reactors (STR), continuous trickle bed reactors and in continuous flow reactors operating with supercritical CO2... 

Blanco, L Cicala, G. Motta, O. Recca, A. (2004). Influence of a selected hardener on the phase separation in epoxy/thermoplastic polymer blends. Journal of Applied Polymer Science, Vol.94, No. 1, (September 2004), pp. 361-371, ISSN 1097-4628. 

Fig. 13.7 Step and Flash Nano Imprint Lithography a wafer coated in photoresist b master stamp imprinted into resist c UV curing flash step to selectively harden resist d stamp retracted from resist...

Surface hardening involves selective hardening of just the surface of a part or changing the composition of the surface by diffusing a small atom into the surface (usually C or N), followed by heat treatment of the surface. An example is case hardening of steel by increasing the carbon content of the surface by heating the part for about one hour in contact with some source of carbon (such as methane gas) followed by heat treatment. 

Selective hardening treatments, for example, flame hardening... 

The enhanced strength and corrosion properties of duplex stainless steels depend on maintaining equal amounts of the austenite and ferrite phases. The welding thermal cycle can dismpt this balance therefore, proper weld-parameter and filler metal selection is essential. Precipitation-hardened stainless steels derive their additional strength from alloy precipitates in an austenitic or martensitic stainless steel matrix. To obtain weld properties neat those of the base metal, these steels are heat treated after welding. 

The laser spray process uses a high power carbon dioxide laser focused onto the surface of the part to be metallized. A carrier gas such as belium blows metal particles into the path of the laser and onto the part. The laser melted particles may fuse to the surface, or may be incorporated into an aHoy in a molten surface up to 1-mm thick. The laser can be used for selective aHoying of the surface, for production of amorphous coatings, or for laser hardening. 

Selenium and precious metals can be removed selectively from the chlorination Hquor by reduction with sulfur dioxide. However, conditions of acidity, temperature, and a rate of reduction must be carefliUy controlled to avoid the formation of selenium monochloride, which reacts with elemental selenium already generated to form a tar-like substance. This tar gradually hardens to form an intractable mass which must be chipped from the reactor. Under proper conditions of precipitation, a selenium/precious metals product substantially free of other impurities can be obtained. Selenium can be recovered in a pure state by vacuum distillation, leaving behind a precious metals residue. 

The mechanical and electrical properties of selected high strength aUoys in cast and wrought forms are provided in Table 5. A similar compilation for the high conductivity aUoys is given in Table 6. The mechanical properties shown in the tables correspond to standard hardening times and temperatures and therefore are close to peak conditions. Considerable latitude exists for achieving a wide variety of special mechanical and electrical property combinations. 

Elements that can dissolve in copper, such as zinc, tin, and nickel for example, increase annealed strength by varying amounts depending on the element and the quantity in solution. The effect of selected solution hardening elements on tensile properties of annealed copper aUoys is iUustrated by the data in Table 4, where the yield strength is the stress at 0.2% offset strain in a tensile test. 

Use for heat treating is also small compared to the past. It has been supplanted to a large extent by furnaces using special atmospheric conditions. Heat treatment salts containing sodium cyanide are used for small metal parts when selective case hardening is required. 

Cement and Concrete Concrete is an aggregate of inert reinforcing particles in an amorphous matrix of hardened cement paste. Concrete made of portland cement has limited resistance to acids and bases and will fail mechanically following absorption of crystalforming solutions such as brines and various organics. Concretes made of corrosion-resistant cements (such as calcium aluminate) can be selected for specific chemical exposures. 

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