Transition powders

Figure 10. NMR spectra (without MAS) of AIPO4 cristobalite taken just below (473 K) and above (523 K) the a-f transition, with y-axis scaling proportional to absolute intensity. Spectrum of the a-phase contains only the central transition, whereas that for the f-phase contains also the satellite transitions, indicating Cq = 0 (cf Fig. 4) and consistent with cubic point symmetry. For the a-phase, the central transition comprises 9/35 of the total intensity the remainder occurs in the satellite transition powder spectrum that spans a wide frequency range according to Equation 3, with Cq = 0.9 MHz. Origin of the frequency scale is arbitrary. [Redrawn from data of Phillips et al. (1993).]...

Figure Bl.12.1. (a) Energy level diagram for an/= nueleus showing the effeets of the Zeeman interaetion and first- and seeond-order quadnipolar effeet. The resulting speetra show statie powder speetra for (b) first-order perturbation for all transitions and (e) seeond-order broadening of the eentral transition, (d) The MAS speetnim for the eentral transition. ...

Physical background. MAS will narrow the inliomogeneously broadened satellite transitions to give a series of sharp sidebands whose intensity envelopes closely follow the static powder pattern so that the quadnipole interaction can be deduced. The work of Samoson [25] gave real impetus to satellite transition spectroscopy by showing that both the second-order quadnipolar linewidths and isotropic shifts are fiinctions of / and Some combinations of / and produce smaller second-order quadnipolar effects on the satellite lines than... 

Apphcations of ultrasound to electrochemistry have also seen substantial recent progress. Beneficial effects of ultrasound on electroplating and on organic synthetic apphcations of organic electrochemistry (71) have been known for quite some time. More recent studies have focused on the underlying physical theory of enhanced mass transport near electrode surfaces (72,73). Another important appHcation for sonoelectrochemistry has been developed by J. Reisse and co-workers for the electroreductive synthesis of submicrometer powders of transition metals (74). 

Although a few simple hydrides were known before the twentieth century, the field of hydride chemistry did not become active until around the time of World War II. Commerce in hydrides began in 1937 when Metal Hydrides Inc. used calcium hydride [7789-78-8J, CaH2, to produce transition-metal powders. After World War II, lithium aluminum hydride [16853-85-3] LiAlH, and sodium borohydride [16940-66-2] NaBH, gained rapid acceptance in organic synthesis. Commercial appHcations of hydrides have continued to grow, such that hydrides have become important industrial chemicals manufactured and used on a large scale. 

Trialkyl- and triarylarsine sulfides have been prepared by several different methods. The reaction of sulfur with a tertiary arsine, with or without a solvent, gives the sulfides in almost quantitative yields. Another method involves the reaction of hydrogen sulfide with a tertiary arsine oxide, hydroxyhahde, or dihaloarsorane. X-ray diffraction studies of triphenylarsine sulfide [3937-40-4], C gH AsS, show the arsenic to be tetrahedral the arsenic—sulfur bond is a tme double bond (137). Triphenylarsine sulfide and trimethylarsine sulfide [38859-90-4], C H AsS, form a number of coordination compounds with salts of transition elements (138,139). Both trialkyl- and triarylarsine selenides have been reported. The trialkyl compounds have been prepared by refluxing trialkylarsines with selenium powder (140). The preparation of triphenylarsine selenide [65374-39-2], C gH AsSe, from dichlorotriphenylarsorane and hydrogen selenide has been reported (141), but other workers could not dupHcate this work (140). 

Iron carbide (3 1), Fe C mol wt 179.56 carbon 6.69 wt % density 7.64 g/cm mp 1650°C is obtained from high carbon iron melts as a dark gray air-sensitive powder by anodic isolation with hydrochloric acid. In the microstmcture of steels, cementite appears in the form of etch-resistant grain borders, needles, or lamellae. Fe C powder cannot be sintered with binder metals to produce cemented carbides because Fe C reacts with the binder phase. The hard components in alloy steels, such as chromium steels, are double carbides of the formulas (Cr,Fe)23Cg, (Fe,Cr)2C3, or (Fe,Cr)3C2, that derive from the binary chromium carbides, and can also contain tungsten or molybdenum. These double carbides are related to Tj-carbides, ternary compounds of the general formula M M C where M = iron metal M = refractory transition metal. 

The expressions provide the limiting transition. When d Q for all j-phases, g rTf and the above expression transforms to the expression for a homogeneous sample. In case of the two-component powder, consisting of fluorescent and non-fluorescent par ticles, when size of the non-fluorescent par ticles d - Q, the above expression transforms to the expression for slurrylike substance (A.L. Finkelstein, T.N. Gunicheva, e. a. // X-Ray Spectrom. 1992. V. 21. p. 287-292). In case of the multicomponent powder with the equal size particles the expression transforms to the well-known Berry-Fumta-Rhodes formula. 

Zincon disodium salt (o-[l-(2-bydroxy-5-sulfo)-3-pbenyl-5-formazono]-benzoic acid di-Na salt) [135-52-4, 56484-13-0] M 484.4, m -250-260 (dec). Zincon soln is prepared by dissolving 0.13g of the powder in aqueous N NaOH (2mL diluted to lOOmL with H2O). This gives a deep red colour which is stable for one week. It is a good reagent for zinc ions but also forms stable complexes with transition metal ions. [UV-VIS Bush and Yoe Anal Chem 26 1345 1954 Hunter and Roberts J Chem Soc 820 1941 Platte and Marcy Anal Chem 31 1226 1959] The free acid has been recrystd from dilute H2SO4. [Fichter and Scheiss Chem Ber 33 751 1900.]... 

Strict control of the fusion process is imperative. In addition to thickness, hardness, continuity and adhesion checks, correct cure may be assessed by differential scanning calorimetry techniques, which are designed to measure any difference in the glass transition temperature of a laboratory-cured powder and the cured coating taken from the factory-coated pipe. 

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