Hot injection techniques

CoPt3 nanoparticles earn interest as representatives of alloy-hke species. Furthermore, they are less sensitive towards oxygen and so are somewhat easier to be prepared and to be handled. They become available by simultaneous reduction of platinum acetylacetonate and thermal decomposition of Co2(CO)g. As stabilizing agents, adamantanecarboxyhc acid and hexadecylamine (HAD) are used. Practically, the hot injection technique is applied. The recipient vessel contains the platinum salt, dissolved in 1,2-hexadecanediol, and the stabilizers, whereas Co2(CO)g in 1,2-dichlorobenzene is injected into the hot stock solution. In order to obtain well crystallized nanoparticles, annealing of the reaction mixture at 275 285 °C for about an hour is necessary. The crystalhnity can be checked by TEM andXRD. Figure 7 shows... 

Figure 3.114 Schematic representation of the hot injection technique usually employed in the organometallic synthesis of magnetic nanocrystals. A thermocouple (TC) controls the...

In spite of the many advantages of the cold injection system, in practice there are also limits to its use. These exist both between different cold injection techniques and in comparison with hot injection techniques (Table 2.23). These include the analysis of thermally labile substances. Because of the low injection temperature a cold injection is expected to be particularly suitable for labile substances. However, during the heating phase, the residence times of the substances in the insert are long enough to initiate thermal decomposition. In this case, only on-column injection can be used because it completely avoids external evaporation of the sample for transfer to the column (see Section 2.2.6.3). A test for thermal decomposition was suggested by Donike with the injection of a mixture of the same quantities of fatty acid TMS esters (CIO to C22 thermolabile) and n-alkanes (C12 to C32 thermally stable). If no thermal decomposition takes place, all the substances appear with the same peak intensity. 

Fig. 2 Schematic representation of the hot injection technique employed in the organo-metallic synthesis of nanocrystals (adapted from reference [61]).

Worldwide demand for blast furnace coke has decreased over the past decade. Although, as shown in Figure 1, blast furnace hot metal production (pig iron) increased by about 4% from 1980 to 1990, coke production decreased by about 2% over the same time period (3). This discrepancy of increased hot metal and decreased coke production is accounted for by steady improvement in the amounts of coke required to produce pig iron. Increased technical capabihties, although not universally implemented, have allowed for about a 10% decrease in coke rate, ie, coke consumed per pig iron produced, because of better specification of coke quaUty and improvements in blast furnace instmmentation, understanding, and operation methods (4). As more blast furnaces implement injection of coal into blast furnaces, additional reduction in coke rate is expected. In some countries that have aggressively adopted coal injection techniques, coke rates have been lowered by 25% (4). 

Adsorption or catalytic decomposition of labile substances by the syringe needle can be a problem for some compounds using hot vaporizing injectors [25]. For open tubular columns deactivated fused silica syringe needles and cold on-column Injection techniques are used to minimize this problem. Alternatively, syringes fitted with a needle shroud for cold-needle injection can be used [26]. 

Certainly, the precision and accuracy of the PTV techniques are generally superior to those of the classical hot split and splitless techniques and approach those obtained by cold on-column Injection [ 34,36,37, -54-57,62,64]. However, less is known concerning optimization of PTV injection and probably more parameters have to be considered than for cold on-column injection. The latter is, consequently, the preferred injection technique for most samples, except those contaminated by larg< amounts of involatile Impurities and for headspace vapors. 

Figure 3.3 Discriaination of n-alkanes depending on injection technique. A, filled needle B, hot needle C, cold on-coluan. A and B were obtained using a 1 40 split. Saaple n-alkanes 1 10,000 in hexane. (Reproduced with peraission froa ref. 24. Copyright Dr. Alfred Huethig Publishers). ...

The organic cellulose ester plastics are versatile materials and can be processed by almost any hot-processing technique used for thermoplastics. The principal techniques for all three plastics are injection molding and extrusion. Blow molding is also possible. Butyrate and propionate powder are used in tluidized-bed and electrostatic coating processes, as well as in the rotational molding process. 

Direct injection simply transfers the entire sample to the analytical column. Direct injection techniques include direct flash vaporization (hot direct injection) and cold on-column. Direct flash vaporization has become popular used with wide-bore capillary columns (> 530 /xm ID) having phase ratios less than 80 and high sample volume capacity and can easily accommodate injections of up to 10 /xl of sample. 

H. Stan and H. Muller, Evaluation of automated and manual hot splitless, cold-splitless (PTV) and on-column injection technique us-... 

RIM and TIM is that in the case of RIM the components are mixed shortly before injection into the mold and are cured by polymerization in the mold. On the other hand, in the TIM method a uniform molding compound is heated above its glass transition temperature to produce a material that can be injected into the mold where it resolidifies as the temperature decreases. We wish to stress that the hot embossing technique for thermoplastics is particularly suitable... 

The SPME sampling device can be immersed directly into an aqueous sample such as groundwater for a finite period of time, then withdrawn, the fiber and rod retracted back into the needle, brought to the hot-injection port of a gas chromatograph, and then inserted into the septum, the fiber and rod extended into the injection port for a finite period of time in which thermal desorption is accomplished. For analysis of aqueous samples for VOCs, the fiber is inserted into the headspace, sampled, retracted, and then injected directly into the injection port. For solids, wastewater, sludge, etc. this headspace technique is appropriate provided that analytes can partition... 

Thiol stabilization also proved to offer a very successful route towards the creation of monosized nanoparticles of various compounds however, as it has also attracted widespread interest it will be outlined separately in Chapter 3.2.1.2. In this chapter, from this point onwards, attention will be focused on recent developments that differ from the hot injection synthesis and from the thiol technique. 

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