The Crystallization of Modified Cis-Polybutadiene

1960 ◽  
Vol 33 (3) ◽  
pp. 699-702
Author(s):  
G. S. Trick
Keyword(s):  
Melting Point ◽  
Crosslink Density ◽  
Fixed Temperature ◽  
Trans Isomerization

Abstract From a sample of polybutadiene of high cis-1,4 content, the microstructure is modified by cis-trans isomerization or by crosslinking. Measurements of rates of crystallization and melting point are made on the modified samples. An increase in irons content or crosslink density markedly decreases the rate of crystallization at a fixed temperature. It is found, however, that this retardation in rate may usually be accounted for by the depressed melting point of the modified samples.

Polybutadiene Vulcanization. Chemical Structures from Sulfur-Donor Vulcanization of an Accurate Model

1984 ◽  
Vol 57 (5) ◽  
pp. 1056-1097 ◽  
Author(s):  
Earl C. Gregg ◽  
Robert P. Lattimer
Keyword(s):  
Network Structure ◽  
Crosslink Density ◽  
Hydrogen Transfer ◽  
Reaction Products ◽  
Volatile Substances ◽  
Chemical Structures ◽  
Trans Isomerization ◽  
Polybutadiene Rubber ◽  
Configurational Isomerism ◽  
Crosslinking Agents

Abstract Only 1,5-polyenes with three or more double bonds crosslinked in a curing recipe with 2-benzothiazolyl-N-morpholyl disulfide (BMD) or bis(dimethylthiocarbamyl) disulfide (TMTD) as the crosslinking agents. A suitable chemical model for 1,4-polybutadiene (PB) is cycIohexadeca-1,5,9,13-tetraene (CHT). The preparation of CHT is described. The crosslink density of a CHT vulcanizate agreed well with the chemical crosslink density of cis- 1,4-polybutadiene rubber, similarly cured. The crosslink density of the CHT vulcanizate was measured by isolating, identifying, and weighing the various crosslink structures. The non-crosslink structures of the network and the extranetwork structures were also identified and quantified. Various amounts of curative fragments attach to the PB network structure, as exemplified by the amount of curative fragments attached to CHT. About 16% of the lauric acid attached to the network structure. The curing agent, BMD, divided into three fragments: 2-thiobenzothiazole, morpholyl, and thio groups. About 67% of the thio groups, 25% of the 2-thiobenzothiazole groups, and about 6% of the morpholyl groups attached to the network structure. About 57% of the thio groups formed crosslinks. The main crosslink structure was 85% bis(allylic) monosulfide and 15% bis(allylic) disulfide. The length of the disulfide crosslink was only 60 pm greater than the length of the monosulfide crosslink. This compares with the 0.2 nm length of a sulfur atom. Very little cis-trans isomerization occurred in the unreacted CHT as a result of vulcanization. This indicated almost no cis-trans isomerization of unreacted segments of PB in PB vulcanizates. However, extensive cis-trans isomerization occurred in the CHT that crosslinked, which indicates that cis-trans isomerization in PB vulcanizates is confined to the reaction sites of the PB molecules. The configurational isomerism was essentially exclusively cis-to-trans. No trans-to-cis isomerism was observed. The insoluble solid in the vulcanizate was a mixture of cadmium bis(2-thiobenzothiazole), cadmium sulfide, and morpholinium sulfate. Material balances of the reaction products with the curatives showed that 90% by weight of the reaction products of the vulcanization of CHT were identified. The hydrogen transfer balance showed that CHT is the main hydrogen donor during crosslink formation. The morpholyl group from BMD was the main hydrogen acceptor and formed morpholine and morpholinium sulfate. Escape of volatile substances during vulcanization of PB resulted in much reduced crosslinking. For this reason, a hydraulic reactor for vulcanization of liquids, such as CHT, without loss of volatile substances was described.

Voids in Irradiated Tungsten and Molybdenum

1969 ◽  
Vol 27 ◽  
pp. 190-191
Author(s):  
Robert C. Rau ◽  
Robert L. Ladd
Keyword(s):  
Melting Point ◽  
Fast Neutron ◽  
Neutron Irradiation ◽  
Elevated Temperatures ◽  
Irradiation Temperature ◽  
The Body ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Cubic Metals ◽  
Face Centered

Recent studies have shown the presence of voids in several face-centered cubic metals after neutron irradiation at elevated temperatures. These voids were found when the irradiation temperature was above 0.3 Tm where Tm is the absolute melting point, and were ascribed to the agglomeration of lattice vacancies resulting from fast neutron generated displacement cascades. The present paper reports the existence of similar voids in the body-centered cubic metals tungsten and molybdenum.

The observation of nano-voids in Au thin films

1987 ◽  
Vol 45 ◽  
pp. 366-367
Author(s):  
William Krakow
Keyword(s):  
Thin Films ◽  
Melting Point ◽  
Present Author ◽  
Stacking Faults ◽  
Damage Threshold ◽  
Ionic Species ◽  
Rare Gases ◽  
Chain Defects ◽  
Vacancy Chains ◽  
Au Thin Films

It has long been known that defects such as stacking faults and voids can be quenched from various alloyed metals heated to near their melting point. Today it is common practice to irradiate samples with various ionic species of rare gases which also form voids containing solidified phases of the same atomic species, e.g. ref. 3. Equivalently, electron irradiation has been used to produce damage events, e.g. ref. 4. Generally all of the above mentioned studies have relied on diffraction contrast to observe the defects produced down to a dimension of perhaps 10 to 20Å. Also all these studies have used ions or electrons which exceeded the damage threshold for knockon events. In the case of higher resolution studies the present author has identified vacancy and interstitial type chain defects in ion irradiated Si and was able to identify both di-interstitial and di-vacancy chains running through the foil.

Benzene confined in MCM-41 below its melting point : A proton NMR study

2000 ◽  
Vol 10 (PR7) ◽  
pp. Pr7-99-Pr7-102 ◽  
Author(s):  
G. Dosseh ◽  
D. Morineau ◽  
C. Alba-Simionesco
Keyword(s):  
Melting Point ◽  
Proton Nmr ◽  
Nmr Study ◽  
Mcm 41

ELLIPSOMETRIC STUDY OF THE ICE SURFACE STRUCTURE JUST BELOW THE MELTING POINT

1987 ◽  
Vol 48 (C1) ◽  
pp. C1-495-C1-501 ◽  
Author(s):  
Y. FURUKAWA ◽  
M. YAMAMOTO ◽  
T. KURODA
Keyword(s):  
Melting Point ◽  
Surface Structure ◽  
Ice Surface ◽  
Ellipsometric Study

EINE CHEMISCHE METHODE ZUR BESTIMMUNG VON 16-EPI-ÖSTRIOL IM URIN DES MENSCHEN

1963 ◽  
Vol 44 (1) ◽  
pp. 47-66 ◽  
Author(s):  
W. Nocke ◽  
H. Breuer
Keyword(s):  
Melting Point ◽  
Phosphoric Acid ◽  
Aqueous Alkali ◽  
Percentage Error ◽  
Organic Layer ◽  
Maximum Percentage ◽  
Chemical Determination ◽  
Routine Assay ◽  
Hydrolysis Of

ABSTRACT A method for the chemical determination of 16-epi-oestriol in the urine of nonpregnant women with a qualitative sensitivity of less than 0.5 μg/24 h is described. The separation of 16-epi-oestriol and oestriol is accomplished by converting 16-epi-oestriol into its acetonide, a reaction which is stereoselective for cis-glycols and therefore not undergone by oestriol as a trans-glycol. Following partition between chloroform and aqueous alkali, the acetonide of 16-epi-oestriol is completely separated with the organic layer whereas oestriol as a strong phenol remains in the alkaline phase. 16-epi-oestriol is chromatographed on alumina as the acetonide and determined as a Kober chromogen. This procedure can easily be incorporated into the method of Brown et al. (1957 b) thus making possible the simultaneous routine assay of oestradiol-17β, oestrone, oestriol and 16-epi-oestriol from one sample of urine. The specificity of the method was established by separation of 16-epi-oestriol from nonpregnancy urine as the acetonide, hydrolysis of the acetonide by phosphoric acid, isolation of the free compound by microsublimation and identification by micro melting point, colour reactions and chromatography. The accuracy of the method is given by a mean recovery of 64% for pure crystalline 16-epi-oestriol when added to hydrolysed urine in 5–10 μg amounts. The precision is given by s = 0.24 μg/24 h. For the duplicate determination of 16-epi-oestriol the qualitative sensitivity is 0.44 μg/24 h, the maximum percentage error being ± 100% The quantitative sensitivity (±25% error) is 1.7 μg/24 h.

Effect of aluminum content on structure, transport and mechanical properties of Sn-Zn eutectic lead free solder alloy rapidly solidified from melt.

2015 ◽  
Vol 10 (1) ◽  
pp. 2641-2648
Author(s):  
Rizk Mostafa Shalaby ◽  
Mohamed Munther ◽  
Abu-Bakr Al-Bidawi ◽  
Mustafa Kamal
Keyword(s):  
Mechanical Properties ◽  
Melting Point ◽  
Lead Free ◽  
Al Alloy ◽  
Lead Free Solder ◽  
Pronounced Increase ◽  
Mass Unit ◽  
Size Refinement ◽  
Free Solder ◽  
Lead Free Solders

The greatest advantage of Sn-Zn eutectic is its low melting point (198 oC) which is close to the melting point. of Sn-Pb eutectic solder (183 oC), as well as its low price per mass unit compared with Sn-Ag and Sn-Ag-Cu solders. In this paper, the effect of 0.0, 1.0, 2.0, 3.0, 4.0, and 5.0 wt. % Al as ternary additions on melting temperature, microstructure, microhardness and mechanical properties of the Sn-9Zn lead-free solders were investigated. It is shown that the alloying additions of Al at 4 wt. % to the Sn-Zn binary system lead to lower of the melting point to 195.72 ˚C.  From x-ray diffraction analysis, an aluminium phase, designated α-Al is detected for 4 and 5 wt. % Al compositions. The formation of an aluminium phase causes a pronounced increase in the electrical resistivity and microhardness. The ternary Sn-9Zn-2 wt.%Al exhibits micro hardness superior to Sn-9Zn binary alloy. The better Vickers hardness and melting points of the ternary alloy is attributed to solid solution effect, grain size refinement and precipitation of Al and Zn in the Sn matrix.  The Sn-9%Zn-4%Al alloy is a lead-free solder designed for possible drop-in replacement of Pb-Sn solders.  

CERROTRU Alloy

Alloy Digest ◽  
1979 ◽  
Vol 28 (12) ◽  
Keyword(s):  
Melting Point ◽  
Liquid Metal ◽  
Physical Properties ◽  
Tensile Properties ◽  
Eutectic Alloy ◽  
Heat Treating ◽  
Tube Bending ◽  
Metal Products

Abstract CERROTRU Alloy is a bismuth-base eutectic alloy that melts at 281 F (138 C). It has the highest melting point of the bismuth-base alloys commonly used in industry. It provides production engineers with an easily castable material that is ready for use soon after it freezes. The alloy can be recovered easily and recycled into new uses any number of times. Cerrotru alloy has many uses including anchoring, molds for plastics, filler for tube bending and liquid metal in heat treating. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on casting, heat treating, and machining. Filing Code: Bi-15. Producer or source: Cerro Metal Products.

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