Thermal Stability Index Research Articles

Effect of the fibre-forming material structure and silica nanoparticles

The paper discusses the thermal properties of alginate fibres made from alginic acid or sodium alginate and from alginates substituted with divalent metal ions during the fibre-forming stage. Alginate fibres with an addition of silica nanoparticles have also been examined. The selection of fibre-forming parameters was intended to obtain the best either sorption or strength properties depending on the specific fibre application. Thermal curves of the fibres under investigations obtained by under air atmosphere and differential scanning calorimetry (DSC) under neutral gas atmosphere have been interpreted from the view of physical and chemical changes in the fibre-forming material. Based on thermogravimetric curves, the fibre thermal stability indices have been determined. It has been found that the addition of silica nanoparticles exerts a positive influence on the thermal properties of the examined fibres.

Structure and Thermal Stability of Novel Fluorophosphate Glasses.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Sol–gel derived organic–inorganic hybrid from trialkoxysilane-capped acrylic resin and titania: effects of preparation conditions on the structure and properties

Homogeneous organic–inorganic hybrid materials with high performance were successfully prepared by mixing (3-methacryloxypropyl)trimethoxysilane (MPMS) capped acrylic resin with titania synthesized by sol–gel approaches. The effects of the titania content, the amount of water and nature of catalysts in the sol–gel as well as the ratios of mixed solvents of butyl acetate and ethanol on the structures and properties of the hybrid materials were studied. Higher titania content, larger amount of water and base catalysis in the sol–gel process, as well as the solvent with higher ratio of butyl acetate to ethanol for the hybrids caused larger size and less open structure of titania phase. The hardness, elastic modulus, thermal stability and refractive index for the hybrid materials improved dramatically with increasing titania content. In general, better prosperities, especially mechanical properties, were achieved for the hybrid prepared under lower water content, pH values (such as acid catalysis) and m B/ m E ratio.

Structure and thermal stability of novel fluorophosphate glasses

A systematic investigation on glass formation in the PbF 2–InF 3–BaHPO 4 ternary system has been carried out. These glasses have characterized by IR spectra, Raman spectra and differential thermal analysis. The results show that the structure of these glasses is mainly affected by BaHPO 4 and InF 3 contents. With decreasing BaHPO 4 content, the glass structure gradually transforms from metaphosphate to polyphosphate. When InF 3 content is low, it mainly acts as network modifier, when its content is high; it enters glass matrix and forms In(O,F) 6 groups connecting the polymerized phosphorus oxygen species. PbF 2 mainly acts as network modifier in this system. Systematic variations of the glass transition temperature and the thermal stability index agree well with these results. The most stable glass with Δ T = 230 °C and S = 21.79 K is obtained.

Hyphenated techniques of thermal analysis for characterisation of soil humic substances

AbstractOur aim was to investigate the thermal behaviour of humic substances extracted from temperate and tropical soils by means of hyphenated techniques of thermal analysis (e. g. simultaneous thermal analysis DSC/TG coupled with mass spectrometry, MS, for the analysis of evolved gas, EGA) in order (i) to verify whether the chemical composition of isolated humic substances also reflected the differences in microbial parameters previously measured in related soil samples and (ii) to identify suitable indices of thermal stability. Our results show that the investigation of humic substances by thermal methods can provide information on soil organic matter dynamics. Differences in thermal behaviour between the two groups of soils were found. The indices of thermal stability here proposed, IR (index of thermal recalcitrance), and ID (index of thermal decomposability) clearly showed that in humic substances from tropical soils the thermally recalcitrant organic fraction dominated, whilst in temperate humic substances the opposite held. This agrees with previous results on the microbial dynamics and organic matter turnover of the respective soils and indicates that these indices of thermal stability could represent a useful tool in soil environmental quality investigations.

Wlasciwosci termiczne kauczukow butadienowo-akrylonitrylowych

The results of assessment of thermal characteristic (temp. up to 800°C in the air) of two grades of butadiene-acrylonitrile rubbers, differing in AN content (18% and 39%), were presented. Derivatography and thermogravimetry coupled with infrared spectroscopy (TG-FT-IR) methods (Fig. 1 and 4) have been applied in the investigations. DTA curves have been interpreted on the basis of additional measurements such as determination of crosslinking density and value of limiting viscosity number, elemental analysis and FT-IR spectroscopy. Activation energy of destruction and indices of thermal stability of elastomers investigated (Table 1) have been determined. In the rubbers investigated, after heating to 160°C, thermooxidative processes occur leading to hydroperoxide groups formation, decomposition of which initiates degradation as well as crosslinking processes [equations (1) - (5)]. In these rubbers mainly the processes of thermal crosslinking, as a result of butadiene mers polymerization, occur. So the lower AN content in the copolymer the higher thermal crosslinking efficiency. It has been stated that acrylonitrile mers' content also influences significantly the rate of thermal decomposition of elastomers and their activation energy, while does not influence the initial decomposition temperature. Products of the thermal decomposition of the polymers mentioned are following: butadiene, methane, carbon monoxide and carbon dioxide, other aliphatic hydrocarbons and also nitrogen compounds such as ammonia and hydrogen cyanide.

THERMAL PROPERTIES OF FIBRES FROM A NEW POLYMER OF THE POLYIMIDEAMIDE GROUP

The paper presents the thermal properties of fibres made of a modified polyimideamide. The effects of as-spun draw ratio and deformation during the fibre drawing stage on the structure, thermal properties, moisture absorption and tenacity of the obtained fibres have been determined. Based on the findings obtained by the DTA and DSC methods, it has been found that the modification of the polymer under investigation causes its glass transition temperature to decrease through the increase of molecular mobility. At the same time, the heat-resistant fibres with the amorphous oriented structure are characterized by a tenacity of 16 cN/tex, good absorption properties and increased porosity. The thermal stability indices of the examined fibres have been determined on the basis of thermogravimetric curves obtained both under air and inert gas.

IR transmitting glasses in the YF 3–PbF 2–CdF 2–AlF 3 system

Glasses have been synthesised in the four component YF 3–PbF 2–CdF 2–AlF 3 system using conventional melt quench route. Several glasses have been prepared by varying YF 3 and CdF 2 content. Glasses exhibit up to 65–70% transmission and extended cutoff up to nearly 9.5 μm. The glass transition temperature in these four component fluoride glasses ranged from 311°C to 364°C and the thermal stability index ( T x − T g) was close to 113°C for an optimised composition. Chemical durability studies in de-ionised water showed an excellent resistance to water attack. Excellent IR behavior, which compares well with ZrF 4 and AlF 3 based glasses, coupled with thermal and chemical stability, make these glasses promising for optical component design and fabrication.

Organic compound destruction and removal efficiency (DRE) for plasma incinerator off-gases using an electrically heated secondary combustion chamber

The United States Department of Energy (DOE) sponsored a series pilot-scale plasma incineration tests of simulated mixed wastes at the MSE Technology Applications, Inc. technology development test facility in Butte, MT. One of the objectives of the test series was to assess the ability of an electrically heated afterburner to destroy organic compounds that may be present in the off-gases resulting from plasma incineration of mixed wastes. The anticipated benefit of an electrically heated afterburner was to decrease total off-gas volume by 50% or more, relative to fossil fuel-fired afterburners. For the present test series, feeds of interest to the DOE Mixed Waste Focus Area (MWFA) were processed in a plasma centrifugal furnace while metering selected organic compounds upstream of the electrically heated afterburner. The plasma furnace was equipped with a transferred-mode torch and was operated under oxidizing conditions (10–15% oxygen at the stack). Feeds consisted of various mixtures of soil, plastics, Portland cement, silicate fines, diesel fuel, and scrap metals. Benzene, chloroform, and 1,1,1-trichloroethane were selected for injection as simulates of organics likely to be present in DOE mixed wastes, and because of their relative rankings on the US Environmental Protection Agency (EPA) thermal stability index. The organic compounds were injected into the off-gas system at a nominal concentration of 2000 ppmv. The afterburner outlet gas stream was periodically sampled, and analyzed by gas chromatography/mass spectrometry. For the electrically heated afterburner, at operating temperatures of 1800–1980°F (982–1082°C), organic compound destruction and removal efficiencies (DREs) for benzene, chloroform, and 1,1,1-trichloroethane were found to be >99.99%. The electrically heated afterburner was also operated at temperatures well below the design operating temperature, in order to assess the sensitivity of the afterburner to temperature swings. At 1300–1320°F (704–716°C) DREs for benzene and 1,1,1-trichloroethane were still >99.99%, while the DRE for chloroform was slightly degraded to 99.977%. At 820–850°F (438–454°C) the DRE for 1,1,1-trichloroethane remained >99.99%, while the DREs for benzene and chloroform were substantially degraded, in the order expected from the EPA thermal stability index. For comparison, analogous tests were performed using a conventional natural gas fired afterburner, with similar results. The natural gas fired afterburner yielded DREs greater than 99.99% for 1,1,1-trichloroethane, chloroform, and benzene, when operated at 1600–1820°F (871–993°C) and ∼1350°F (∼732°C). Similarly to the electrically heated afterburner, at ∼850°F (∼454°C) DREs were substantially degraded for chloroform and benzene. At normal operating temperatures both the electrically heated afterburner and the natural gas fired afterburner gave acceptable DREs (>99.99%), for the three injected organic compounds. DREs remained acceptable for both units even when operated at substantially reduced temperatures.

Thermal aging of silicone oil aromatic polyamide insulation systems

The thermal degradation behavior of silicone oil/aromatic polyamide insulation system was studied. It was found that the flash and fire points decreased due to the formation of low molecular weight by-products of such cyclic siloxane oligomers as D/sub 3/, D/sub 4/ and D/sub 5/. The gel permeation chromatography (GPC) and high performance liquid chromatography (HPLC) analysis clarified that the depolymerization of siloxane molecules happened during the thermal aging, resulting in the high- and low- molecular by-products formation. The thermal stability index (TGI) index obtained by the thermogravity (TG) measurements and cyclic oligomer detection could be used for the insulation diagnosis.

Affinities and Historical Zoogeography of the New Zealand Short-Tailed Bat, Mystacina tuberculata Gray 1843, Inferred from DNA-Hybridization Comparisons

We carried out DNA-hybridization comparisons among representatives of the major groups of Chiroptera to determine the phylogenetic position of the New Zealand short-tailed bat, Mystacina tuberculata. All analyses confirmed the noctilionoid affinity of this species suggested by an earlier serological study, with support from taxon jackknifing and at bootstrap levels of 98% or higher. However, a specific association with Noctilio was not found in more than 13% of the bootstrapped trees. The most precise of the thermal-stability indices employed (Tm, the median melting temperature of hybridized sequences) demonstrated a sister-group relationship of Mystacina to all noctilionoids, with Noctilio the first branch within Noctilionoidea but separated from the Mystacina lineage by a very short internode. Our determination of the timing of the divergence of Mystacina from noctilionoids is 54 myrbp. This estimate is based on independent indications that extant bat lineages began to diversify in the latest Cretaceous and is much earlier than the tentative estimate of 35 myrbp inferred from serology. Even if the diversification of all living bats occurred as early as 83 myrbp, as some authors have suggested, separation of Mystacinidae—on that basis, at 66 myrbp—could not have taken place soon enough for this taxon to be isolated on New Zealand before New Zealand separated from the rest of Gondwanaland. However, any of these dates would allow for the distribution of the noctilionoid–mystacinid common ancestor in South America, Australia, and Antarctica before the final sundering of Australia from Antarctica and for the divergence of Mystacinidae as a possible result of that event. This hypothesis is supported by the presence of fossil mystacinids in early and mid-Miocene deposits at Bullock Creek and Riversleigh, Queensland, showing that Mystacinidae had been resident in Australia from at least 25–20 myrbp. The most obvious scenario explaining the presence of Mystacinidae in New Zealand is therefore fortuitous dispersal from Australia across the Tasman Sea.

Effect oftrans-polyoctenamer on thermal stability of rubbers determined by thermal analysis

An effect of a cyclic low molecular-weight polymertrans-polyoctenamer rubber (TOR) on the thermal stability of diene rubbers and their vulcanizates was investigated. The investigation was carried out in the air and nitrogen atmospheres using thermogravimetry, DSC and simultaneous thermoanalytical methods. The thermal stability indexes:T 5,T max and activation energy of degradation (δE), as well asT g andT m values, have been determined. It was found thattrans-polyoctenamer (TOR) increases of the thermal stability indices of raw diene rubbers and their vulcanizates. The results show that the thermal degradation of diene rubbers occurred at higher temperature if they were blended with TOR. In our opinion, intermolecular structures formed between the cyclic low-molecular weight polymer and some linear rubber molecules may be the reason for the higher thermal stability of these rubber blends.

The physical and chemical properties of synthetic and natural jadeite for jewellery

Jadeite was synthesized from its glass of stoichiometric composition NaAlSi2O6, and a colouring agent Cr2O3 (0.3–0.6 wt%) was added to achieve the emerald colour. The conditions employed were a pressure range of 3.0–5.0 GPa and a temperature range of 1150–1750 °C, for periods of 1–480 min. The physical and chemical properties of synthetic jadeite, such as microstructure, unit cell parameters, melting point, thermal stability, hardness, density and refractive index, etc., were compared with those of natural jadeite. The optimum crystallizing conditions for the synthesis of jadeite for jewellery were above 4.5 GPa, 1450 °C and 60 min. The synthetic jadeite was emerald in colour, translucent, 12 mm diameter and 6 mm thick.

Experimental analysis of variance for DNA hybridization: II. Precision

Using DNAs from the Virginia opossum (Didelphis virginiana), we estimated the variance components for two classes of replicate hybrids: different drivers matched to the same tracer and different homoduplexes made from tracers matched to identical drivers. A nested analysis of variance (ANOVA) was used to partition total variance among four levels: Individuals, extracts, preparations, and different aliquots from the same preparation. The variance contributed by these levels depended on the kind of hybrid replicate (driver or tracer) and on the index of thermal stability (Tmode, Tm, T50H, or Normalized Percentage Hybridization). For replicate drivers, significant variance contributions were made by (1) individuals to Tm, (2) extracts to Tmode and NPH but not Tm, and (3) different preparations to NPH. The composite T50H measure calculated from both Tm and NPH revealed effects from both constituent indices. For replicate tracers, preparation error was the single most consistent effect across all indices, followed by extract effects for those indices that incorporated a measure of percent hybridization (T50H NPH). Total variance of the four indices was qualitatively similar for both drivers and tracers: Tmode ranked lowest, followed in order by Tm, T50H, and NPH, with the variance of NPH being as much as 100 times greater than for Tmode. These results provide guidelines for the design of experiments to generate DNA hybridization-based phylogenies and to assess their robustness with bootstrapping. Replicate drivers for a distance matrix based on Tm should use different individuals, whereas one based on Tmode could minimally use different extracts from the same individual. Thus, Tmode may be the index of choice for DNA hybridization experiments when material, time, and money are limited.

DNA/DNA hybridization studies of carnivorous marsupials. III. Relationships among species ofDidelphis (Didelphidae)

We report three sets of DNA hybridization experiments conducted to determine relationships among species ofDidelphis (D. albiventris, D. marsupialis, D. virginiana). The 1989 and 1991 sets had fewer replicates per cell than the 1990 series (3.4 and 5.4 vs 9), but in 1991 we distinguished two populations ofD. marsupialis and utilized several individuals for each heterologous comparison. BothPhilander opossum andLutreolina crassicaudata were used as outgroups in 1989, but onlyLutreolina was included in subsequent sets. For each set, we calculated all four standard indices of thermal stability (Tmode,Tm,T50H, and NPH) and constructed trees by least-squares (FITCH) and neighbor-joining methods, both before and after correction for asymmetric reciprocal cell values. Subsets of the 1989 data lacking eitherPhilander orLutreolina were analyzed similarly. To explore measurement imprecision, the corrected and uncorrected matrices for each of the four indices were bootstrapped 100 times for the 1989 set and subsets and 1000 times for the 1990 and 1991 sets. Again, for the 1990 and 1991 data, an additional 100 bootstrapped distances were fitted to user trees representing the three possible pairings ofDidelphis spp. to determine the significance of the FITCH branch lengths. The successive experimental sets generated increasingly consistent evidence for pairingD. marsupialis withD. albiventris. The 1989 experiments involved just 85 comparisons, and only ΔTmode's pairedD. marsupialis withD. albiventris (at bootstrap percentages of 70% or above), but did so whetherPhilander orLutreolina or both were included as the outgroup(s). FITCH and neighbor-joining trees had identical topologies for ΔTmode's but sometimes differed for the other measures. In contrast, all but one of the corresponding FITCH and neighborjoining trees matched for the 1990 and 1991 data, and three of the four distance measures (ΔTmode, ΔTm, and ΔT50H) unitedD. marsupialis withD. albiventris at bootstrap percentages averaging 81%; ΔNPH gave a different result for 1990, associatingD. marsupialis withD. virginiana. Further, all but 2 of the 16 matrices for 1990 and 1991 gave mean bootstrapped branch lengths for a consensus pairing that were positive and at least one standard deviation from zero, despite the very short internodes recovered. These results illustrate that the potential of DNA hybridization for resolving very close relationships depends on both the index and the experimental design employed. We conclude that of the three species,D. albiventris andD. marsupialis shared a more recent common ancestor and estimate thatDidelphis spp. have diverged at about 0.39% in nucleotide sequence per myr.

Properties and crystallization behaviors of TeO 2LiNbO 3 glasses

(100− x)TeO 2− xLiNbO 3 ( x = 10−60) glasses were prepared by using a conventional melt-quenching method, and some properties such as thermal stability, density and refractive index and crystallization behaviors of glasses were measured. The thermal stability of the glasses with x = 20 and 30 was high. The density of glasses decreased monotonically with increasing LiNbO 3 content from 5.50 g/cm 3 to 4.58 g/cm 3. The values of the refractive index of glasses were 2.04-2.11 and showed an anomalous compositional dependence. It was found from Raman scattering spectra that the structure of glasses was composed of the structural units of TeO 4 trigonal bipyramid, TeO 3 trigonal pyramid and NbO 6 octahedra. In the glasses with x = 10 and 20, α-TeO 2 (paratellurite) crystals were precipitated by heat treatment above 450°C. In the glasses with x ≧ 40, LiNbO 3 crystals were formed through the transformation of a metastable pyrochlore-type compound at temperatures above 500°C. From the present study, it is proposed that the fabrication of transparent TeO 2-based glasses containing ferroelectric LiNbO 3 microcrystallites may be possible.

Degradation of polymers by thermal gravimetric techniques

AbstractThe techniques involved in dynamic thermal gravimetric analysis are reviewed. Methods of studying overall kinetics of degradation, especially with respect to evaluation of order of reaction and overall activation energy, are outlined. Some applications to polymers such as Teflon and epoxide resins are described. Since the use of thermal gravimetric results for evaluating thermal stability raises the problem of a suitable standard for describing decomposition, some indices of thermal stability of polymers are discussed.

Thermal stability indices for polymeric materials based on energy considerations

AbstractAnalysis of thermogravimetric weight loss data from the literature indicated correlations between the overall energietics of decomposition and characteristics of the thermogravimetric curves for measurements made under nitrogen. Such correlations provide a means for comparing relative thermal stabilities of polymers from easily obtained weight loss data.