Deposition, heat

The stmcture of the polysihcon depends on the dopants, impurities, deposition temperature, and post-deposition heat annealing. Deposition at less than 575°C produces an amorphous stmcture deposition higher than 625°C results in a polycrystalline, columnar stmcture. Heating after deposition induces crystallization and grain growth. Deposition between 600 and 650°C yields a columnar stmcture having reasonable grain size and (llO)-preferred orientation. 

There are several means by which boiler water can become highly concentrated. One of the most common is iron oxide deposition on radiant wall tubes. Iron oxide deposits are often quite porous and act as miniature boilers. Water is drawn into the iron oxide deposit. Heat appHed to the deposit from the tube wall generates steam, which passes out through the deposit. More water enters the deposit, taking the place of the steam. This cycle is repeated and the water beneath the deposit is concentrated to extremely high levels. It is possible to have 100,000 ppm of caustic beneath the deposit while the bulk water contains only about 5—10 ppm of caustic. 

As discussed in the introduction, disruptions cause the most severe thermomechanical loading experienced in a tokamak. In each of the 500 or so disruptions expected in ITER, approximately 10-20 MJ/m will be deposited onto the first wall in 0.01 to 3 seconds. Such a disruption will cause very high thermal stresses and significant material erosion (Section 4). As these events are transient in nature, the ability of the PFC to withstand the disruption depends on the material s ability to both conduct and to absorb the deposited heat, before reaching a temperature or stress limit. For comparative purposes, a disruption figure of merit takes this into account ... 

Extensive work has been reported on the deposition of individual cell layers and of full anode-electrolyte-cathode fuel cells on metallic interconnect substrates, much of it by VPS, with no sintering or other post-deposition heat treatments required [112]. However, so far relatively thick YSZ electrolytes, approximately 25 to 35 pm, have been needed to provide sufficient gas tightness [108, 114], so further optimization of the process is required to produce thinner, gas-tight electrolytes. Peak power densities of 300 mW/cm2 have been reported at 750°C for APS single cells [114], with four-cell stacks exhibiting power densities of approximately 200 mW/cm2 at 800°C [55],... 

To 25 gms. of absolute alcohol contained in a flask provided with a reflux condenser, 2-3 gms. of sodium are added, and when the metal has dissolved, 16 gms. of ethyl malonate are added. The sodio-derivative of the ester is precipitated as a white solid. The flask is shaken while 20 gms. of ethyl iodide are slowly run in from a dropping funnel the precipitate gradually reacts and sodium iodide is deposited. Heating is conducted on a water bath (1—2 hours) until the product ceases to show an alkaline reaction. The alcohol is distilled off, the residue diluted with water and extracted with ether. The extract is dried over calcium chloride, the ether distilled off, and the residue fractionated, when the product passes over at 200°—210°. 

We have included the summation because there may be more than one heat reservoir in the surroundings that is involved in the process. For example, in the Carnot cycle engine, we remove heat from a hot reservoir and deposit heat in a cold reservoir. 

In the first stage, the chamber is evacuated to a high vacuum and the source of material to be deposited heated to its melting point. Additional heat is applied so that the vapour pressure exceeds the pressure within the chamber and the vaporized molecules of material travel in straight lines from the source—to be deposited on the work pieces, the walls of the chamber, etc. Subject to correct adjustment of pressure the vapour molecules do not collide with any molecules remaining from the air and take the mean free path (the average distance a molecule will travel between two successive collisions)— which for a given vapour is inversely proportional to the vapour pressure. 

The surface temperature excursion during an plasma exposure is shown in Fig. 13.8. The plasma was heated auxiliary by two neutral beams of 1.5 and 1.3MW/m2. The resulting load on the test limiter amounted to 4MW/m2. The 170 pm thick B4C layer was rapidly heated up to 1300 K and cooled down, as the pyrometer signals show. The surface layer withstood such an exposure and did not detach from the copper. Increasing the deposited heating power above 8MW/m2 led to melting of the B4C coating (see Fig. 9 in [33]). 

Fig. 4b demonstrates that under UHV conditions, electro-pumped Na is identical in behaviour and in chemical state with Na supplied by vacuum deposition firom a Na evaporation source. Spectrum (1) shows the XPS of the catalyst film when Na was vacuum-deposited. Heating to 400 K under open circuit conditions caused no change- spectrum (2). 

The multiphoton absorption cycle was confirmed by a comparison of the temporal profile of the fluorescence of anthracene-doped polystyrene films with computational results based on the cyclic process [97]. In the computational studies, the ground state, first excited singlet state, and lowest triplet state have been included. The calculated temperature rise during the laser pulse depends nonlinearly on the laser intensity. Rapid internal conversion within the triplet manifold is the most effective mechanism for depositing heat at the irradiated surface. 

Electrochemical methods applied to deposit calcium phosphate coatings require an electrical conductor as a substrate as well as post-depositional heat treatment (Abe, Kokubo and Yamamuro, 1990). Hence, they are not well suited to coat non-conducting ceramics and heat sensitive polymers. 

Non-thermal deposition methods are defined as those ones carried out at temperatures much below the incongruent melting point of hydroxyapatite, in particular at or near ambient temperature. However, frequently post-depositional heat treatment must be applied to either crystallise amorphous calcium phosphate (ACP), transform (dehydrated/dehydroxylated) precursor phases such as octacal-cium phosphate (OCP) to hydroxyapatite, and/or to remove organic compounds used in coating preparation, for example during sol-gel, dip coating, electrochemical and EPD. 

Similar problems arise in connection with the electrolysis of dilute NaCl solutions (seawater). NaOCl produced by electrolysis is used to kill marine life in cooling systems in industrial plants using seawater. Interestingly, amorphous Pd-Ir-P alloys have lower activity in dilute solutions, and Pd-Rh-P samples prove to be more suitable under these conditions (102,103). In order to further increase their activity, surface activation by the Zn deposition-heat treatment-Zn leaching method was used (63). 

The surface activation consisting of zinc deposition, heat treatment, and subsequent leaching of zinc (63, 64) was applied to different amorphous iron-, cobalt-, nickel-, and palladium-based alloys (63, 64). SEM measurements indicated the formation of a porous surface layer. Cyclic voltammetric examinations suggested an increase of surface area by about two orders of magnitude. Heat treatments at higher temperatures resulted in thicker, more porous surface layers and higher electrocatalytic activities (Table II). Palladium-phosphorus alloys with Ni, Pt, Ru, or Rh proved to be the best specimens. Pd-Ni-P with 5% Ni, after treatment at 573 K, exhibited even higher activity than that of the Pt-Pt electrode (Table II). These amorphous alloy electrodes were active in the oxidation of methanol, formaldehyde, and sodium formate. 

Macbeth, R.V., 1971, Boiling on surfaces overlaid with a porous deposit Heat transfer rates obt nable by capillary action. Report AEEW-R711. AERE Winfiith Heath, UK. 

ZnS nanotubes have been prepared by sulfidizing ZnO templates obtained in columnar form by electrochemical deposition. Heating the ZnO column in H2S above 400 gave the ZnS coated ZnO columns. The ZnO cores were then etched out giving hollow ZnS tubes. 

Formula weight 250.47. Butay-red crystals. d 1.783. Solubility in H3O 0.0089 (0°C) 0.0225(25°C) 0.040(50°C) moles/liter. The presence of HCl lowers the solubility at 25°, 10% HCl dissolves 0.00067 moles/liter. Neutral aqueous solutions decompose when boiled, and Co(OH)3 is deposited. Heating to higher temperatures produces Cod3. Crystal type orthorhombic-bipyramidal. 

A FIGURE 5.12 Endothermic and exothermic processes, (a) An endothermic process (AH > 0) deposits heat into the system, (b) An exothermic process (AH < 0) withdraws heat from the system. 

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