High-temperature IR Research Articles

Spectroscopic Investigations of M(CO)5-C60 (M = W, MO) Complexes: Precursors for Metal Fullerides

Photochemical reactions of M(CO)6 (M = W, Mo) with C60 in solution yield η:2-complexes of M(CO)5 with C60. The complexes have been characterised by IR, UV/VIS, NMR and DSC. They do not show any orientational ordering down to 12 K and all the infrared bandwidths remain the same down to this temperature. The complexes can be decomposed thermally or photochemically yielding metal fullerides, which show characteristic reduction in peak width in the variable temperature IR spectra due to orientational ordering. Transitions are manifested in calorimetric studies also. Metal → C60 charge-transfer is observed in IR and XPS. A high temperature IR study of the C60-W(CO)5 complex reveals sequential elimination of the carbonyls yielding MC60. The study shows that carbonyl complexes can be used as precursors to make transition metal fullerides.

Natural titanite and malayaite: Structural investigations and the 500 K anomaly

Titanite, CaTiSiOS, and malayaite, CaSnSiOs, are isostructural. Both minerals exhibit a thermal anomaly near 500 K but diffuse reflections only occur in titanite. Titanite crystals from Rauris, Austria (Fe 1.8%, A1 3.8%) were studied using synchrotron X-ray diffraction, IR spectroscopy and high-resolution transmission electron microscopy (HRTEM). The phase transformation near 500 K is smeared out by impurities. The diffuse scattering disappears above 830 K. No antiphase boundaries were found in natural titanite. High-temperature X-ray diffraction and IR spectroscopy were used to study the thermal anomaly in malayaite. Structure determinations of malayaite at different temperatures reveal a discontinuity in the evolution of the anisotropic Debye-Waller factors of the Ca atoms near 500K. At this point IR spectra show a break in the temperature dependence of the intensity of the 533cm−1mode and the peak positions of the 499cm−1mode and the Si-0 stretching mode near 908cm−1.

Measuring absolute infrared spectral radiance with correlated visible photons: technique verification and measurement uncertainty

An experimental system in which correlated photons for radiometric measurements were used has been set up at the National Institute of Standards and Technology. We use visible-IR pairs of correlated photons produced by means of optical parametric downconversion to measure the radiance of a high-temperature IR source at 3.415 and 4.772 mum in an intrinsically absolute manner (i.e., without requiring any externally calibrated radiometric standard). To our knowledge, this is the only radiometric method with which one measures radiance directly, instead of using radiant power and aperture geometry measurements to deduce radiance indirectly. This technique has an additional unusual characteristic: It allows absolute radiometric measurements of IR radiation to be made with high-quality visible detectors. We compare measurements made with this technique with radiance measurements made with conventional means tied to existing radiometric standards. These comparisons show an average agreement to within ~3% between the two methods. The results demonstrate an accuracy consistent with the estimated uncertainty of the currentmeasurements. This is the first time to our knowledge that this method has been used to provide absolute radiance measurements of a source that has been calibrated conventionally, revealing unexpected systematic effects and allowing estimates of the ultimate accuracy of this method. In addition, these measurements are further into the IR than any previous measurements of this process and have produced the highest thermally stimulated downconversion signal yet seen.

Comparative study of the structures of some basic iron(III) sulfates

IR and EXAFS spectroscopies were used to study the products of the hydrolysis of iron(III) sulfate. A hypothesis for the structure of amorphous basic iron sulfate is made from a comparison of its IR spectra and radial atomic distribution curves with the corresponding data for jarosite. Analysis of the interatomic distances and manifestations of the sulfate ion in the low- and high-temperature IR spectra shows that in the amorphous product of the hydrolysis, unlike in the jarosite, the sulfate ion is not involved in the first coordination sphere of the iron atoms, but is held in the structure by hydrogen bonds. Reasons for the high catalyzing ability of the amorphous basic iron sulfate are suggested.

Thermal changes in synthetic deuterioxyapatite.

Deuterioxyapatite (Ca10(PO4)6(OD)2, DAp) was prepared from CaO, P2O5, and D2O in H2O and CO2 free air at 298K. The obtained DAp was identified as apatite single phase by a powder XRD technique. The deuterioxyl group was found by IR and MAS-NMR techniques, but hydroxyl group was not. Further, MAS-NMR measurement suggested the DAp had no tightly-bonded OD group. The deuterioxyl group was not substituted with hydroxyl group at 298K by stirring in distilled water for 7 days. From TG-MS measurement, dried DAp powder released deuterium in two rapid steps and in a slow step up to 873K. High-temperature XRD measurement showed large thermal expansion for DAp due to lattice defect led by heating. High-temperature IR spectra showed release of deuterioxyl group without substitution by hydroxyl group above 333K. Deuterioxyl group in DAp was easily released by heating, and DAp changed into oxyapatite.

Thermal, spectroscopic and XRD studies on nitroaminoguanidine (NAG)

Nitroaminoguanidine (NAG) has been investigated as regards its thermal decomposition characteristics using simultaneous thermal analysis, infrared spectroscopy, X-ray diffraction and polarising microscopy. XRD studies show thatNAG crystal belongs to the tetragonal system. The crystal structure parameters are found to be:a=17.063±0.005A,b=17.063±0.005A,c=5.155±0.005A andc/a axial ratio=0.302. Under non-isothermal conditions,NAG decomposed apparently in one stage with a loss in weight of 80%. But the thermal decomposition ofNAG in the solid phase under isothermal conditions proceeded through three stages. Both the first and the second stages obeyed theA-E (Avrami Erofee'v) equation forn=1. The 3rd stage is too slow and kinetics has not been attempted. The rate parameters for the first and second stages have been evaluated. Gaseous decomposition products detected using the IR gas cell are NH3, NO2, HCN, N2O, CO and CO2. High temperature IR studies indicate preferential deamination reaction initially indicating breaking of N−NH2 and C−NH2 bonds leading to NH2 radical formation. Addition of diphenylamine, a known chain inhibitor, decelerated the thermal decomposition, supporting a radical chain reaction.

Thermochromism in nickel(II) complexes: thermal, IR spectroscopic, solid-state 1H NMR and single crystal X-ray analysis of diaqua-bis(2,2-dimethyl-1,3-propanediamine) nickel(II) nitrate

The newly synthesized complex [Ni(dmtn) 2(H 2O) 2](NO 3) 2 (dmtn = 2,2-dimethyl-1,3-propanediamine) undergoes a reversible thermochromic phase transition in the range of 180–202°C ( ΔH = 10.4kJ mol −1) on heating after dehydration (dehydration temperature range 43–102°C). The complex has been characterized by X-ray crystallography at room temperature. The crystals are monoclinic, space group C2 m , a = 20.385(2), b = 6.9004(4), c = 6.9552(3) A ̊ , β = 102.60(5)°, V = 954.8(1) A ̊ 3 , Z = 2 and R = 0.046. The geometry of the nickel atom in the complex is tetragonally distorted octahedral with two H 2O molecules coordinated at the trans position. The diamine chelate rings are in the trans chair-chair conformations. The broad-line 1H NMR of partially deuterated [Ni(dmtn- d 4) 2(NO 3) 2] (deuterated amine protons) indicates the onset of dynamic disorder of the diamine chelate rings at the phase transition temperature. The high temperature IR spectral measurement shows the complex retains its trans configuration after dehydration and phase transition with NO − 3 ions coordinated as a monodentate ligand.

Spectral characteristics of high temperature IR photodetectors with electromagnetic carrier depletion

The work presents the numerically calculated spectral characteristics of the recently proposed new type of infrared photodetector utilizing electromagnetic carrier depletion (EMCD). The detector was optimized for CO 2 laser radiation (10.6 μm). The results are given for high-quality (Hg, Cd)Te material at 225 K.

Morphological characterization of autoclave and tubular LDPE by high temperature IR spectroscopy

High temperature IR spectroscopy is a rapid tool to identify morphological features,, at least qualitatively. This technique has been used in present work to study phase transitions, mesomorphous crystallinity, effect of branching, and effect of telogens, in both tubular and autoclave LDPE resins. With increasing temperature, most samples undergo transition from a semicrystalline state to amorphous state but samples having a very high initial crystallinity (e.g., Lotrene) become semi-crystalline at high temperatures. Autoclave LDPE samples having long-chain branching show interesting intensity changes in the triplet at 1300–1400 cm −1, when taken to high temperatures. High temperature IR spectra can be used to locate the α-relaxation temperature, (possibly T g) as indicated by the formation of a singlet at 720 cm −1. They can also be used to distinguish autoclave LDPE from tubular LDPE in commercial samples.

Synthesis and characterization of two isomers of Os 3(CO) 10(C 5H 4N-2-C(H) [dbnd]N [sbnd]R) and the conversion to ortho-metallated HOs 3(C 5H 3N-2-C(H) [dbnd]N [sbnd]R)(CO) 9. Part III. X-ray Structure of HOs 3(C 5H 3N-2-C(H) [dbnd]N [sbnd]i-Pr)(CO) 9

Os 3(CO) 10(MeCN) 2 reacts at room temperature in MeCN or toluene with R-Pyca† to yield two isomers of Os 3(CO) 10(R-Pyca) that differ in the bonding of the R-Pyca ligand to the Os 3(CO) 10 unit. In all cases Os 3(CO) 10(R-Pyca(4e)) (isomer A; 4a: R = c-Pr, 4b: R = i-Pr, 4c: R = neo-Pent, 4d: R = t-Bu), containing a chelating 4e donating R-Pyca ligand and three Os S bonds, could be isolated. In the case of R = c-Pr and R = i-Pr Os 3(CO) 10(R-Pyca(6e)) (isomer B; 5a: R = c-Pr, 5b: R = i-Pr), in which only two Os S bonds are present and the R-Pyca ligand is bonded as a 6e donating ligand bridging two non-bonded Os atoms, could be isolated as a minor product. At 70 °C Os 3(CO) 10(R-Pyca(4e)) (4b and 4d) loses one carbonyl and the pyridine moiety of the R-Pyca ligand is ortho-metallated to form HOs 3(C 5H 3N-2-C(H) N R)(CO) 9 (6b: R = i-Pr and 6d: R = t-Bu). Under the same conditions Os 3(CO) 10(i-Pr-Pyca(6e)) (5b) reacts to Os 2(CO) 6(6e)) (7b) containing a bridging 6e donating ligands. The latter two reactions were followed with FT-IR spectroscopy in a high temperature IR cell. The structure of the complexes in solution have been studied by 1H and 1C NMR and IR spectroscopy. The stoichiometries of 4a and 5a were determined by FAB-mass spectrometry while an exact mass determination was carried out for 4a. The crystal structure of 6b has been determined. Crystal of 6b are monoclinic, space group P2 1/ n, with a = 7.808(2), b = 17.613(3), c = 16.400(8)Å, β = 94.09(3)° and Z = 4. The structure was refined to R = 0.039. The molecule contains a triangular array of osmium atoms [Os(1) Os(2) = 2.898(2)Å, Os(1) Os(3) = 2.886(2)Åand Os(2) O(3) = 2.911(2)Å] and nine terminally bonded carbonyl ligands. The C 5H 3N-2-C(H) N-i-Pr ligand is chelate bonded to Os(2) with the pyridine and imine nitrogens atoms axially and equatorially coordinated respectively [Os(2) N(1) = 2.00(2)Åand Os(2) N(2) = 2.11(2)Å]. The i-Pr-Pyca ligand is ortho-metallated at C(1) and forms a four membered ring containing Os(2), Os(3), C(1) and N(1), the Os(3) C(1) distance being 2.12(2)Å. The hydride, which could not be located unequivocally from a difference Fourier map is proposed to bridge the Os(2) (3) bond on the basis of stereochemical considerations.

IR spectroscopic studies of surface acrolein and acrylic acid compounds in conditions of catalytic oxidation of acrolein on V−Mo−Si−O catalyst

Three surface complexes of acrolein have been identified by high-temperature IR spectroscopic method. Their extinction coefficients have been decermined.

Dimerization of Carboxylic Acids in Solution up to High Pressures and Temperatures. 2. Benzoic Acid

Benzoic acid in dilute solution of n-heptane and of CCl4 is studied via high-pressure hightemperature IR spectroscopy on the C = O and O - H stretching fundamentals. Lambert-Beer’s law is shown to be valid for the C = O modes of the acid monomer and of the hydrogen-bonded cyclic dimer, which enables the quantitative measurement of the dimerization equilibrium to a maximum pressure of 2 kbar and up to 175 °C. At identical pressure and temperature the dimerization equilibrium constant is larger in n-heptane than in CCl4. From the monomer-cyclic dimer equilibrium constants the pressure dependence of the dimerization enthalpy is determined and compared with direct information on both species as derived from their O - H fundamental mode absorption. Toward lower temperature the dimerization volume is decreasingly negative and, in CCl4 solution, ΔV even changes sign around 40 °C. Increasing pressure thus favours the dissociation of the hydrogen-bonded dimer into benzoic acid monomer molecules at ambient temperature.

Energy characteristics of a high-temperature ir radiator

Results are presented on the temperatures of the heated body and fused-silica envelope for a high-temperature IR emitter of new design based on a halogen filament lamp.

Strength of aprotic acidic centers estimated from the IR spectra of adsorbed acetonitrile

Isosteric adsorption heats of acetonitrile on Ca-, Mn-, Co-, Ni- and CrY zeolites have been estimated using high-temperature IR spectroscopy. As the coverage was increased, the adsorption heat decreased from 120–170 kJ/mol to 45–80 kJ/mol whereas υCN remained constant for each type of cations. It is concluded that υCN cannot be used as a criterion for the estimation of the strength of aprotic centers.

Model for the calculation of the complex heat transfer in high-temperature IR emitters

A mathematical model of the complex heat transfer in high-temperature IR emitters is proposed, together with a procedure for its numerical realization.

Determination of the strength of Lewis acid centers via IR spectroscopic measurement of adsorbed pyridine

According to high-temperature IR spectroscopic studies, the isosteric heats of pyridine adsorption on the Lewis centers of Al2 O3, ZrO2 and zeolite HNaY have been estimated. The dependence between the frequency υ8a (1580–1630 cm−1) and the adsorption heat is shown to take place only for centers formed by cations of the same metal.

Thermal considerations in the design of a dynamic IR target

The control of time-dependent temperature distribution of a dynamic high temperature IR target critically affects its radiance distribution. Two methods of controlling the target temperature through appropriate power generation and deposition are discussed. The application of the thermal analysis to a resolved, unresolved, and striped high temperature dynamic target is shown.

Preparation and Solid-phase Thermal cis-α↔cis-β Isomerization of the Chromium(III) Triethylenetetramine Complexes

Abstract Heating of a mixture of CrCl3·6H2O and triethylenetetramine (trien) produced violet products which gave cis-α-[Cr2(OH)2trien2]X4·2H2O and cis-α-[Cr(OH)(H2O)trien]X2·H2O (X=Cl, Br or I) on treatment with aqueous NaX solutions. cis-α-[CrCl2trien]Cl·2H2O were obtained in the presence of a trace amount of water. Absolutely dry conditions are necessary for the preparation of cis-β-[CrCl2trien]Cl. The thermally induced reversible cis-α↔cis-β isomerization was detected in the complexes cis-α-[Cr(OH)(H2O)trien]Cl2·H2O and cis-β-[CrCl2-trien]Cl by means of derivatography and high-temperature IR spectroscopy. The former cis-α-hydroxoaqua complex was found to be converted irreversibly into cis-β-form above 225 °C in the solid-phase. The cis-β-form obtained readily isomerized to cis-α-form in aqueous media. The dimeric cis-α-[Cr2(OH)2trien2]4+ was converted gradually into the monomeric cis-α-[Cr(OH)(H2O)trien]2+ in water.

Crystallization of Calcium Phosphate Glass Having Short Chain Structure

Crystallization characteristics of the glass having the molar ratio, CaO/P2O5=1.22 and/or (CaO+H2O)/P2O5=1.28, of which average chain length (Pn) was estimated to be 7, were studied by means of high temperature microscopy, high temperature X-ray diffraction technique and IR absorption spectroscopy.1. Crystalline phases formed in the glass below ca. 650°C consisted of tromelite and trace of β-calcium metaphosphate.2. Crystal growth rate, G (μ/min), of tromelite in the blown film sample at 680°-740°C was represented by the following equation: logG=25.6-25.0×103/T.3. The overall isothermal crystallization curves of the glass powder in size from 44 to 74μ at 600°-650°C were coincided with the Kolmogorow-Avrami equation, where Avrami exponent (m) had different two values depending on the crystallinity (V), and no induction period for the crystallization was found in all the curves.4. In the range V 0.6, the crystallization was found to contain the thermal nucleation and the three-dimensional growth.5. The activation energy for the growth was approximately in accordance with the energy for the crystallization, the values, 110-130kcal/mole, being comparable with P-O-P bond energy.6. The crystallization of the glass seemed reasonable to be in part accompanied by the polycondensation resulted from evolution of OH-radicals from P-O-P chain ends.

Infrared Kinetic Study of High‐Temperature Reactions of Synthetic Kaolinite

An infrared frequency shift method was used to follow the kinetics of conversion of dehydroxylated synthetic kaolinite to mullite. Comparison of the kinetic and activation thermodynamic data for natural and synthetic kaolinite suggests that the mechanism of high‐temperature reaction is similar, although the activation energy of synthetic kaolinite is larger than that of natural kaolinite because of the lack of nucleation‐promoting impurity cations in the former. The high‐temperature ir data indicate that there is little or no difference in the cation coordination of the phases intermediate to metakaolinite and mullite, but that the principal high‐temperature coordination change (probably the accommodation of aluminum in well‐defined tetrahedral sites) occurs during the later stages of mullite formation.