Temperature Modulated DSC (TMDSC) Applications and Limits of Phase Information, cp Determination and Effect Separation

The ADSC (Alternating DSC [1]) technique superimposes upon the conventional constant heating rate a periodically varying modulation [2–8]. The modulation creates high instantaneous heating rates which increases sensitivity. The low underlying constant heating rate is used to get better resolution. With ADSC it is possible to separate overlapping thermal effects without loss of sensitivity and to determine heat capacities under quasi-isothermal conditions. It has been reported that there are also some limitations for the use of the modulation techniques, i.e. that the accuracy of c_p determination is reduced at higher modulation frequencies due also to thermal diffusivity within the sample itself [9, 10]. In this contribution, the limitations given by the measuring system itself will be discussed. A key value is the limit frequency of the sensor arrangement. In the Mettler Toledo DSC821^c this frequency is approximately 1/3 Hz. From these findings the following recommendations amongst others can be given: for light mass crucibles, 30 s periods are reasonable with amplitudes not exceeding the heating/cooling rates possible. A blank and a calibration measurement will eliminate cell asymmetry and will enhance the accuracy of c_p measurements even at higher modulation frequencies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Description of the O2pressure influence on the oxidation time of motor oils

A characteristic index for the oxidation stability this is the oxidation induction time (OIT) which is defined by the time between the start of oxygen exposure and the onset of oxidation. Pressure DSC is required to increase oxygen concentration in order to achieve faster reactions at lower temperatures. OIT measurements of reference engine oils have been used to study the influence of oxygen pressure in the range from 0.1 to 10 MPa. A power law relationship was derived to describe this correlation between OIT and oxygen pressure. From this a quantitation factor is proposed to represent the influence of stabilizer. The exponent describes the sensitivity of the oxidation reaction of the oil towards the oxygen pressure and the term 'inherent stability' is proposed for that.. This relationship characterizes in more details the oxidation behavior. Extrapolation to higher pressures indicates, that the stabilization effects of additives can be overcome by the inherent stability. This signifies, that the ranking of the oils can be affected by the oxygen pressure.     

The new mettler toledo ultramicro thermobalance TGA850

A thermogravimetric unit is described having horizontal furnace arrangement, a temperature range of up to 1100°C and unsurpassed dynamic weighing range from 0 to 2 g at 0.1 μg resolution. Options of the system are sample robot, gas controller, high temperature furnace and hyphenated EGA techniques. In addition to the TG, the SDTA^TM curve allows the detection of endo-or exothermal effects (analogous to DTA or DSC) to a resolution of 5 mK.     

Metal Complexes with Macrocyclic Ligands. Part XL. Syntheses and silver(I) complexes of mono- and disubstituted dithiadiazamacrocycles

A series of N₂S₂-macrocycles with ring sizes varying between 12 and 16, as well as two 12-membered N₂S₂-rings with a pendant carboxylic and amino group, respectively, were synthesized. Their complexation properties towards Ag⁺ were studied by pH titrations and by potentiometry with a silver electrode. The observation that 1:1 ([AgLH₂]³⁺, [AgLH]²⁺, [AgL]⁺) and 1:2 species ([AgL₂H₂]³⁺, [AgL₂H]²⁺, [AgL₂]⁺) were formed is interpreted by postulating that Ag⁺ can bind either to the S-donors only, or to both the N- and S-atoms. The most stable complex [AgL]⁺ in the series of the nonfunctionalized macrocycles was found for the 12-membered N₂S₂-ring 3 . The stability of it increased when an additional donor group was introduced into the side chain. The highest formation constant (logβ₁₁₀ = 14.43(1)) was obtained with the 12-membered ring 12 carrying the ethanamine side chain. In view of a radiochemical application, all Ag⁺ complexes were tested in blood serum for their stability, but were not stable enough against transmetallation.     

1,1,3,3-Tetraethylurea as a solvent for conductance studies

1,1,3,3-Tetraethylurea (TEU), a solvent of relatively low dielectric constant, 14.4, was evaluated as a medium for conductance studies of a series of alkali metal salts and organic acids. Conductance data for KSCN, NaSCN, NaI, NaClO₄, and NaBPh₄ in TEU were analyzed by the Fuoss-Shedlovsky, Fouss-Onsager, and expanded Pitts equations. The behavior of these salts in TEU was compared with that of the same salt series in the previously studied tetramethylurea. Tetraethylurea also was used successfully as a solvent for conductometric titrations of several carboxylic acids and phenols.     

Metal complexes of macrocyclic ligands. Part XXIII. Synthesis,properties, and structures of mononuclear complexes with 12- and 14-membered tetraazamacrocycle-N,N′,N″,N‴-tetraacetic Acids

The two tetraazamacrocycle-N,N′,N″,N?-tetraacetic acids H₄dota and H₄teta form with Ni²⁺, Cu²⁺, and Zn²⁺ (M²⁺) mononuclear complexes MLH₂ and M′[ML], M′ being an alkaline earth ion. The structures of Ni(H₂dota) and Cu(H₂dota) have been solved by X-ray structure analysis. The metal ions are in a distorted octahedral geometry coordinated by four amino N-atoms and two carboxylates. In the case of Cu²⁺, the distortions are more pronounced than for Ni²⁺ indicating that the Jahn-Teller effect is operating. Starting from these two structures, the coordination geometry of the other complexes is discussed using VIS and IR spectra.     

Ca-Oxalate films and microbiological investigations of the influence of ancient pigments on the growth of lichens

Simultaneous thermogravimetry and thermomicroscopy were performed on Ca-oxalates which play an important role in the appearance of oxalate films connected with lichens superficially growing on human artefacts. Ca-oxalate exists in two well-described modifications: as the more stable monoclinic monohydrate whewellite and the less stable tetragonal dihydrate weddelite. Weddelite serves for lichens as a water absorbing and accumulating substrate which transforms to whewellite when humidity drops. To follow these morphological changes optically and the water loss gravimetrically at the same time, a combination of thermomicroscopy and thermogravimétric analysis was constructed, The reflection light microscope was connected to a video camera and computer so that the morphological changes and the thermogravimetric curves could be shown simultaneously on the screen as function of time and temperature.Lichens — double organisms composed of algae and fungi — form surface layers not only on natural organic and inorganic material but also on human artefacts. In calcareous artefacts such as the famous Chinese terracotta soldiers or Egyptian epigraphs they lead to a destruction of the surface by forming Ca-oxalate layers and thus to a deterioration of the historian work of art. But in places where the surface is covered by some blue colours (Egyptian and Chinese Blue, Chinese Purple) the growth of lichens is inhibited and the artefacts are well preserved. The copper ion contained in the pigments is responsible for this effect since copper is a strong poison for microorganism.As lichens exhibit an extremely slow growth under natural and laboratory conditions the two lichen components: algae and fungi were investigated separately. The three mentioned ancient pigments have very low solubility products and thus do not act on the quickly growing fungi. But under special experimental conditions Egyptian Blue formed clear halos on the growth plates of the algaeChlorella minutissima andTrebouxia glomerata. These halos were compared with those of the easily soluble copper sulphate as a standard.We are deeply indebted to Mrs. R. Daum for skilled assistance in handling the microbial strains and to Prof. Dr. G. Marx and Dr. H. Bischoff for the determination of the solubility products.     

Probing the electronic structures of coordination compounds by transient spectral hole-burning. Applications to specifically deuterated [Ru(bpy)3]2+ complexes

Transient spectral hole-burning (THB), a powerful technique for probing the electronic structures of coordination compounds, is applied to the lowest excited 3MLCT states of specifically deuterated [Ru(bpy)3]2+ complexes doped into crystals of racemic [Zn(bpy)3](ClO4)2. Results are consistent with and complementary to conclusions reached from excitation-line-narrowing experiments. Two sets of 3MLCT transitions are observed in conventional spectroscopy of [Ru(bpy-d(n))(3-x)(bpy-d(m))x]2+ (x = 1, 2; n = 0, 2; m = 2, 8; n not = m) complexes doped into [Zn(bpy)3](ClO4)2. The two sets coincide with the 3MLCT transitions observed for the homoleptic [Ru(bpy-d(m))3]2+ and [Ru(bpy-d(n))3]2+ complexes and can thus be assigned to localized 3MLCT transitions to the bpy-d(m) and bpy-d(n) ligands. The THB experiments presented in this paper exclude a two-site hypothesis. When spectral holes are burnt at 1.8 K into 3MLCT transitions associated with the bpy and bpy-d2 ligands in [Ru(bpy)(bpy-d8)2]2+, [Ru(bpy)2(bpy-d8)]2+, and [Ru(bpy-d2)2(bpy-d8)]2+, side holes appear in the 3MLCT transitions associated with the bpy-d8 ligands approximately 40 and approximately 30 cm(-1) higher in energy. Since energy transfer to sites 40 or 30 cm(-1) higher in energy cannot occur at 1.8 K, the experiments unequivocally establish that the two sets of 3MLCT transitions observed for [Ru(bpy-d(n))(3-x)(bpy-d(m))x]2+ (x = 1, 2) complexes in [Zn(bpy)3](ClO4)2 occur on one molecular cation.     

Dispersion equalisation in few-mode fibres

Dispersion equalisation of the modes of cylindrically symmetric few-mode optical fibres is investigated using equivalent planar waveguide representations. A numerical analysis based on the Characteristic Matrix Method has identified what we believe to be the first practical three-mode fibre with zero intermodal dispersion. This implies that the group velocities of each of the fibre??s three linearly polarized modes are equivalent. Dispersion equalisation is also confirmed in a power-law profile, as well as a novel two-mode fibre which operates within the third telecommunications windows. These few-mode fibres could potentially be used for long-haul telecommunications data links. In the case where the modes are not distinguished and are equally excited, the few-mode fibres could be used as larger core-radius alternatives to traditional single-mode fibres. If the modes are distinguished, each mode could in theory be considered an independent data channel. All modal data channels would be equivalent for such dispersion-free few-mode fibres, notwithstanding differences in intramodal dispersion and mode crosstalk.