Alpha-phase

Pigment Blue 15 [147-14-8] 74160 copper phthalocyanine condensation of phthaUc anhydride with urea, in presence of copper ions, with or without added chlorophthahc anhy-dride subsequent conversion to alpha-phase and stabili2ation, if necessary... 

The Zn—A1 system permits manipulation of the mechanical properties by suitable heat treatment. The aluminum-rich alpha phase is especially suitable for solution hardening since it can be supersaturated by as much as 30 wt % zinc. Furthermore, both alpha and beta phases can be strengthened by precipitation because of decreasing solute solubiUty with decreasing temperature. 

Support-phase changes or loss of surface area are, of course, irreversible, and replacement of the catalyst may be appropriate. Catalyst damage may take the form of phase changes to the alumina support from gamma to theta or alpha phase. The last is catalyticaky inert because of insignificant surface area. Theta alumina has a low surface area (< 100 /g) relative to gamma alumina (180 m /g) and has poor halogen retention. 

Fig. 7.13. The conversion of theta- to alpha-phase alumina was found to be strongly affected by shock modification in work of Beauchamp and co-workers [90B01]. Whereas the unshocked powder showed evidence for an incubation period of 60 min, the shock-modified materials show immediate conversion typical of the presence of shock-formed nuclei.

Thermal treatment of shock-modified theta-phase alumina, which initially contained about 30% alpha phase, showed a dramatic change in the rate of transformation to the alpha phase [90B01]. As shown in Fig. 7.13, the shocked sample showed no evidence for an incubation period and displayed a rapid conversion to the alpha phase, in sharp contrast to the unshocked sample. Such behavior clearly indicates that the shock process resulted in formation of larger concentrations of alpha-phase nuclei. 

Half-life is the time taken to decrease the concentration of a drug to one-half its original value. There may be several phases in the elimination, and the most common is the so-called beta-phase. Alpha-phase is a distribution phase and gamma-phase is the terminal phase when the drug is finally leaving the tissues. 

For bi-exponential accumulation kinetics the contribution of the fast alpha phase (Ralpha = 1/(1 - exp(-alpha Tau))) decreases (Ralpha Ca Rbeta Cb) as compared with the contribution of the slow beta-phase (Rbeta = 1/(1 - exp(-beta Tau))). 

Materials. THF and ethyl ether were purified by distillation from LiAlH in an argon atmosphere. Toluene and petroleum ether (b.p., 20-40 C) were stirred overnight with CaH2 and filtered before use. Alpha-phase plutonium metal pieces, prepared at Rocky Flats (Rockwell International, Golden, Colorado), were cleaned with a THF solution of C2H I2 before use. 

Alumina, present in the gamma modification, is the most suitable high surface area support for noble metals. The y-Al203 in washcoats typically has a surface area of 150-175 m g However, at high temperatures y-alumina transforms into the alpha phase, and stabilization to prevent this is essential. Another concern is the diffusion of rhodium into alumina, which calls for the application of diffusion barriers. 

Perhaps even more noteworthy is the effect of crystallographic phase. While one phase of a specific composition may readily incorporate from a particular bath composition, another phase of the same composition may incorporate to a much lower extent or not at all. For instance, in the alumina particle system, the alpha phase has been found to readily incorporate from an acidic copper bath while the gamma phase incorporates at less than one tenth the amount of alpha, if at all, as shown in Table 1 [2, 11, 27, 31, 33],... 

X-ray diffraction conducted on the codeposited powder revealed that the deposit obtained from a suspension of gamma alumina, which had been partially converted to the alpha phase, contained both phases of alumina. Whereas, the powder codeposited from a suspension having a 50 50 mixture of alpha to gamma alumina powder, consisted only of the alpha phase. Using a parallel plate electrode configuration, Chen et al. [31] concluded that only alpha alumina can be codeposited. Chen also observed a difference in codeposition with copper when using two different phases of the titanium oxide particle system rutile readily codeposited but anatase titania did not... 

The work by Chen et al. also resulted in no measurable incorporation with particle diameters of 0.05 and 0.02 pm gamma alumina in copper [31]. When the 0.02 pm gamma particles were calcined to obtain a mix of gamma and alpha alumina, codeposition increased to 2.9 vol.%, under the same codeposition conditions. Furthermore, when the 0.02 pm gamma powders were completely converted to the alpha phase of alumina, incorporation rose to 3.3 vol.% [31]-... 

Black tetragonal crystal exhibits two allotropic modifications—a stable alpha phase, occurring in tetragonal crystalline form (as hausmannite) and an unstable beta modification density 4.85 g/cm Moh s hardness 5.5 melts at 1,567°C insoluble in water soluble in hydrochloric acid. 

The alpha phase is made up of ice-hke needles having polymeric cross-linked structure. It melts at 62.3°C and has a vapor pressure of 73 torr at... 

The metal exists in three crystal forms an orthorhombic alpha phase, density 18.97 g/cm3 and stable to 667°C a tetragonal beta phase of density 18.11 g/cm3, stable between 688 to 776°C and a body-centered cubic form of density 18.06 g/cm3 and stable in the range 776 to 1,132°C. Other physical properties are listed below ... 

Silvery lustrous metal soft, malleahle and ductile the metal exists in two allotropic forms an alpha form, which has a face-centered cubic structure and is stable at room temperature, and a beta form, a body-centered cubic modification that forms when the alpha form is heated to 798°C. Density of the alpha modification is 6.98 g/cm and that of beta form is 6.54 g/cm. Alpha phase exhibits metallic-type conductivity at ordinary temperatures and pressures, but becomes semi-conductive above 16,000 atm. At about 40,000 atm it again becomes metallic-type conductor. (In some texts, the term beta form refers to the alpha phase). 

The preparation of precious metal supported catalysts by the HTAD process is illustrated by the synthesis of a wide range of silver on alumina materials, and Pt-, Pt-Ir, Ir-alumina catalysts. It is interesting to note that the aerosol synthesis of alumina without any metal loading results in a material showing only broad reflections by XRD. When the alumina sample was calcined to 900°C, only reflections for a-alumina were evident. The low temperature required for calcination to the alpha-phase along with TEM results suggest that this material was formed as nano-phase, a-alumina. Furthermore, the use of this material for hexane conversions at 450°C indicated that it has an exceptionally low surface acidity as evidenced by the lack of any detectable cracking or isomerization. 

URANIUM. [CAS 7440-61-1], Chemical element symbol. U, at. no. 92, at. wt, 238,03, periodic table group (Actinides), mp 1,131 to i. 33°C, bp 3,818°C, density 18.9 g/cm3 (20UC). Uranium metal is found in three allotropic forms (1) alpha phase, stable below 668°C, orthorhombic (2) beta phase, existing between 668 and 774°C. tetragonal and (3) gamma phase, above 774°C, body-centered cubic crystal structure. The gamma phase behaves most nearly that of a true metal. The alpha phase has several nonmetallic features in its crystallography. The beta phase is brittle. See also Chemical Elements. 

ZIRCONIUM. [CAS 7440-67-7]. Chemical element symbol Zr. at. no. 40, at. wt. 91.22, periodic table group 4. mp l,853°C, bp 4,376°C, density 6.44 g/cm3, 6.47 g/cm3 (single crystal). Metallic zirconium is allotropic. Up to about 863°C, the alpha phase (hexagonal close-packed) is stable above this temperature, the metal assumes the beta phase (body-centered cubic). The most common impurity, oxygen, tends to stabilize the alpha phase. 

SmB SmC SmC SmCA SmCPA SmCPp SmCo, SmIA SmX UCST XRD Smectic B phase Smectic C phase (synclinic tilted smectic C phase) Chiral (synclinic tilted) smectic C phase Chiral anticlinic tilted (antiferroelectric switching) SmC phase Antiferroelectric switching polar smectic C phase Ferroelectric switching polar smectic C phase Chiral smectic C alpha phase Chiral antiferroelectric switching smectic I phase Smectic phase with unknown structure Upper critical solution temperature X-ray diffraction... 

A typical kinetic profile is divided into alpha and beta phases. The alpha phase occurs rapidly (in the first 24 h) and is considered to be the period in which the administered antibody reaches equilibrium. The beta phase then continues for several days in a direct log-linear relationship of serum concentration to time. It is this beta phase that is considered to be the most reliable indicator of antibody half-life in circulation. To establish beta phase kinetics, we take blood samples (25-75 xl depending on the frequency of sampling) at 1-4 days following administration, followed by... 

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