Cobalt thermal properties

Thermal Properties. The thermal stabiUty of cellulose esters is deterrnined by heating a known amount of ester in a test tube at a specific temperature a specified length of time, after which the sample is dissolved in a given amount of solvent and its intrinsic viscosity and solution color are deterrnined. Solution color is deterrnined spectroscopically and is compared to platinum—cobalt standards. Differential thermal analysis (dta) has also been reported as a method for determining the relative heat stabiUty of cellulose esters (127). 

Thermal Properties. Each of the polyimide film samples was evaluated by differential scanning calorimetry to determine the glass transition temperature (Table I). The general observation is that the BTDA-ODA polyimide films have a higher glass transition temperature than the BDSDA-ODA polyimide films whether they are nonmodifled or are modified with cobalt chloride. This is in agreement with the work of Frye ( ) in which the dianhydride moiety, not the dieunine, was found to control the polyimide glass transition temperature. 

Recently, two pyrazine (pz)-linked hetero-triads of cobalt phthalocyanine (CoPc) and ZnTPP, namely (CoPc)-pz-(ZnTPP)-pz-(CoPc) (15) and (ZnTPP)-pz-(CoPc)-pz-(ZnTPP) (16), have been prepared [30], The thermal properties of these triads and related macrocyclic components have been studied by thermal gravimetric analysis and differential scanning calorimetry. It has been found that the thermal stability of axial coordination increases in the order ZnPc(pz)2 < ZnTPP(pz)2 sa CoPc(pz)2, and the thermal decomposition of the triads 15 and 16 proceeds firstly via the degradation of the spacer ligand. 

The thermal properties of diastereomers of mixed cobalt(III) complexes with aromatic amino acids and diamine were studied by Miodragovi and coworkers [140] to obtain information about stereochemical effects on their thermal stability. The thermal decompositions of these complexes were shown to be multi-step degradation processes, some of which can be satisfactorily separated into individual steps, depending on the molecular symmetry. For diastereomers which crystallize with water molecules, preliminary dehydration occurs. 

Upon reduction, the inserted metal ions, may partially leave layered stacks and reduction may occur on the outer surface of graphite. Nanosize particles of titanimn are inserted into the imperfect lattice of graphite in this matmer. Many metals are inserted into graphite under high pressure in combination with shear deformation. Nanosize cobalt particles inserted into the graphite lattice in this way exhibit imusual magnetic and thermal properties. " ... 

The effects of three different cobalt 60 gamma irradiation doses between 267 and 641 rad L on cryogenic (77°K) mechanical and thermal properties were measured. 

Cobalt(II) chloride was dissolved in poly(amide acid)/ N,N-dimethylacetamide solutions. Solvent cast films were prepared and subsequently dried and cured in static air, forced air or inert gas ovens with controlled humidity. The resulting structures contain a near surface gradient of cobalt oxide and also residual cobalt(II) chloride dispersed throughout the bul)c of the film. Two properties of these films, surface resistivity and bullc thermal stability, are substantially reduced compared with the nonmodified condensation polyimide films. In an attempt to recover the high thermal stability characteristic of polyimide films but retain the decreased surface resistivity solvent extraction of the thermally imidized films has been pursued. 

The data indicate that the properties of the lower glass transition temperature metal ion modified polyimides are altered more than the properties of the higher glass transition temperature metal ion modified polyimides. Extraction removes both cobalt and chlorine from the films and slightly increases bulk thermal stability and both surface resistivity and bulk electrical resistivity. Details pertaining to the structure, analysis and properties of these novel gradient composites are discussed. 

Certain alloys of iron, nickel, and cobalt (Kovar, Fernico, etc.) have thermal expansion curves which nearly match those of borosilicate glasses, and a good bond may be formed between the two. Kovar is similar to carbon steel in its chemical properties. For example, it oxidizes when heated in air and is not wet by mercury. It may be machined, welded, copper brazed, and soft soldered. Silver solders should not be used with Kovar since they may cause embrittlement. At low temperatures Kovar undergoes a phase transformation, and the change in expansion coefficient below this temperature may be sufficient to cause failure of a glass-to-Kovar seal. The transformation temperature usually is below... 

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