Dilatometric studies on structural phase transitions in (NH4)2 SnBr6 crystal

Thermal expansion along several directions was measured in the temperature range including the two transition temperatures. The orientation of the domain walls in two lower temperature phases was examined with a polarizing microscope. The results, together with the experiments so far reported, suggest the possibility that the symmetry of the phase between -116 °C and -129 °C is trigonal, in contrast to being tetragonal as previously conjectured.     

Influence of potassium sodium tartrate on the initial stage of silver electrodeposition

The nucleation and growth of silver from dilute aqueous solutions of AgNO₃ was studied in the absence and in the presence of potassium sodium tartrate in the electrolyte. In both cases data were obtained for the rate of nucleation and growth of silver crystals at constant overpotential.     

The solubility of sodium and potassium soaps and the phase diagrams of aqueous potassium soaps

Summary Solubility data are provided and collected for the pure sodium and potassium soaps. Hydrolysis obscures the temperatures of solution but is obviated by the presence of a small excess of alkali. Each sodium soap has a large range of temperature between fair and high solubility, whereas the potassium soaps go abruptly into solution, at almost the same temperature and concentration of each soap. The only soaps that are even moderately soluble at room temperature are potassium laurate, myristate, and oleate, the potassium salt of acids from coconut oil, and the sodium oleate. The other sodium and potassium soaps of the saturated fatty acids require elevated temperatures for solution. Phase diagrams for the five commonest potassium soaps are developed and recorded. This work was the basis of a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, Stanford University, 1947.     

Dilatometric studies of pure triglycerides and mixtures

Summary The melting dilations and the coefficients of expansion of the solid and liquid states have been reported for five symmetrical mixed triglycerides and three simple triglyceride . The melting dilations were found to decrease with increasing proportions of oleic acid in the triglyceride molecule. In some simple mixtures the melting dilations of the several phases were found to occur discretely, but in the more complex systems there was an extension and overlapping of the melting ranges. In the mixtures of triolein with more saturated triglycerides, the melting point of triolein was found to be generally unaffected, but the melting points of the more saturated glycerides were lowered by the presence of triolein. Calculations of the solid-to-liquid ratios from dilatometric data were found to be impossible in the more complex mixtures due to wide variations in the melting dilations of the several phases and to the overlapping of their melting ranges. Approximate calculations of solid-to-liquid ratios in simple systems in which melting dilations occur discretely can be accomplished if the melting dilations of the individual triglycerides are known. Paper No. 2703 of the Scientific Journal Series. Minnesota Agricultural Experiment Station, and Hormel Institute publication No. 73. Submitted as part of Ph.D. Thesis by B. M. Craig, University of Minnesota, 1950. Presented at meeting of the American Oil Chemists Society, San Francisco, Calif., September, 1950.     

Dilatometric studies of ammonium hydrogen selenate crystals

Capacitance method is used to measure the linear thermal expansion coefficient in NH₄HSeO₄ crystal along the crystallographic axes in the crystallographic range 245-408 K. Anomalies are observed at phase transition temperature to superionic phase and at Curie temperature.     

Study of the phase transitions to the incommensurate phase in (NH4)2BeF4 (AFB) crystals

Specific heat high resolution data for AFB crystals are presented. The effect of SO₄²-ions impurities and γ-irradiation upon the hysteresis phenomena in AFB crystals is discussed.     

Dilatometric and thermomechanical studies of aromatic polyamide fibres

The deformation of SVM aromatic polyamide fibres in the temperature range from room temperature to 400°C was investigated by thermomechanical analysis and dilatometry. In the first heating, fibres which had not been thermally drawn were characterized by self-elongation along the axis of orientation and transverse shrinkage, while thermally drawn fibres were characterized by shrinkage in two directions at temperatures below 200°C and self-elongation at higher temperatures. Self-elongation and transverse expansion were observed on repeated heating for both types of fibres in the investigated temperature region.Translated from Khimicheskie Volokna, No. 1, pp. 38–40, January–February, 1995.     

Thermal analysis, X-ray and electron diffraction studies on crystalline phase transitions in solvent-treated poly(hexamethylene terephthalate)

The crystal polymorphism, transformation, and morphologies in chloroform solvent-cast poly(hexamethylene terephthalate) (PHT) were examined by using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and temperature in situ transmission electron microscopy (TEM). Solvent-induced crystallization of PHT at room temperature yielded an initial crystal of γ-form, as confirmed by WAXD. Upon DSC scanning, the original γ-form in PHT exhibited three endothermic peaks, whose origins and association were carefully analyzed. The first peak, much smaller than the other two, is in the temperature range of ca. 100-120 °C. It was found that the solvent-induced γ-form was transformed to β-form at 125 °C via a solid-to-solid transformation mechanism. In addition, WAXD showed that γ- and β-forms co-existed in the temperature range of 100-125 °C. These mixed crystal forms were further identified using TEM, and the selected-area electron diffraction (ED) patterns revealed that both γ- and β-form crystals co-existed and were packed within the same spherulite. Solid-solid transformation from the solvent-induced γ-form to β-form in PHT upon heat scanning was presented with evidence and discussed.     

Raman scattering investigation of the phase transitions in (NH4)2ZnBr4

Results of Raman spectroscopic studies of (NH₄)₂ZnBr₄ crystal in the spectral range from 20-250 cm^-1 and over a range of temperature from 90K to 440K covering the low temperature ferroelectric and high temperature incommensurate phases are presented. The plots of the integrated areas and peak heights of the strong Raman lines versus temperature show anomalous behaviour near the two phase transitions.     

Investigations on the phase stability of Na-conducting sodium dysprosium (phospho) silicates

Na⁺-conducting sodium dysprosium (phospho) silicates with the compositions Na₅DySi₄O₁₂, Na_3.9Dy_0.6P_0.3Si_2.7O₉ and Na_3.9Dy_0.6Si₃O_8.85 were synthesized by solid state route. The phase evolution in the three systems was studied as a function of heat treatment temperature from 600 °C to 1000 °C by X-ray diffraction technique. It was possible to achieve a NASICON Na₅DySi₄O₁₂-type single phase with the compositions Na_3.9Dy_0.6P_0.3Si_2.7O₉ and Na_3.9Dy_0.6Si₃O_8.85 at 800 °C. Heat treatment at a higher temperature (>850 °C) resulted in the formation of a less conductive Na₉DySi₆O₁₈-type phase. Conventional and microwave sintering were carried out on Na_3.9Dy_0.6P_0.3Si_2.7O₉ sample at 800 °C and the ionic conductivities were measured as a function of temperature from 75 °C to 325 °C. The microwave sintered sample exhibited better Na⁺ ionic conductivity of 0.42 × 10⁻² S/cm when compared to that of conventionally sintered sample which was 0.43 × 10⁻³ S/cm at 325 °C.     

Characteristics of phase transitions in poly[bis(trifluoroethoxy)phosphazene]

The data on phase transitions in bis(trifluoroethoxy)phosphazene were examined and generalized. Their nature was determined and the mechanism of the transitions was described. Schemes were proposed for the phase transitions that take into account the conditions of fabrication and thermal history of the samples. Translated from Khimicheskie Volokna, No. 5, pp. 24–27, September–October, 1998.     

Dilatometric studies of phase transition in NaNH4SeO4·2H2O single crystal

Thermal expansion of NaNH₄SeO₄SeO₄2H₂O crystal was measured by means of dilatometric method along three crystallographic axes in the temperature range of 300-140 K. Anomalies of relative expansion and thermal expansion coefficients related to ferroelectric phase transition were observed and confirmed its continuous character.     

DSC studies on the transitions in poly(vinylidenefluoride) and some related copolymers

Summary The transition properties of poly(vinylidenefluoride) and of some related copolymers, either semicrystalline or amorphous, were studied by differential scanning calorimetry in the temperature range from 200 K to 500 K. The amorphous copolymers exhibit a single glass transition. Melting endotherms and a lower glass transition [Tg(L)] are systematically observed in the semi-crystalline materials as well as an upper glass transition [Tg(U)] for certain thermal and mechanical histories of the samples. Conditions for [Tg(U)] existence are related to solid state morphology of the macromolecules and loop length in the folded chains.     

Low-temperature solution processing route for potassium sodium niobate (KNN) thin films

A major challenge for integration of functional oxides, such as ferroelectrics, into microelectronics and flexible electronics is the reduction of their processing temperature, which needs to be lower than the degradation temperature of silicon and flexible plastic substrates. Aiming that, attention has been given to low-temperature processing of oxide films by chemical solution deposition (CSD). In the field of ferroelectrics, potassium sodium niobate ((K_1−xNa_x)NbO₃, KNN) has aroused a special interest due to its eco-friendliness, despite the high crystallization temperature. In this work, polycrystalline KNN thin films have been fabricated for the first time at a temperature as low as 400 °C using a modified CSD process, the Seeded Photosensitive Precursor Method (SPPM). Despite this low processing temperature, monophasic and stoichiometric films with appreciable values of remnant polarization, P_r ∼ 10.8 μC/cm², and hysteretic piezoresponse are obtained. These results open a window to the direct integration of KNN films into the high-performance electronic devices.     

Defect-induced phase transitions in YAl 3 (BO 3 ) 4 :Nd (NYAB) crystals

Besides the traditional borate materials, β-BaB 2 O 4 [1] and LiB 3 O 5 (LBO) [2] such crystals as Li 2 B 4 O 7 (LTBO) [3], CsLiB 6 O 10 (CLBO) [4], YAl 3 (BO 3 ) 4 (YAB) [5], Ca 4 GdO(BO 3 ) 3 (GdCBO) [6] and Ca 4 YO(BO 3 ) 3 (YCOB) [7] are currently being intensively investigated for non-linear optical applications. These materials typically have high viscosity and very often melt non-congruently. These properties create technological problems that can be resolved by applying very precise devices for operating the growth conditions. Another important problem that appears in the borates is an existence of vacancy-induced phase transitions [8]. The occusence of phase transitions in the vacancy-induced YAB crystals is because they possess cationic subsystems formed by ions of different weights. In order to stimulate the vacancy-bearing process, we have doped the crystals with the Nd ions. The defectiveness of the crystals was determined using light scattering similarly to the method described in Ref. [9]. The dimensionless parameter D was introduced as a ratio of the integral light scattering intensity in defective crystals to the same intensity in perfect crystals.     

Thermal decomposition kinetics of sodium perborate tetrahydrate to sodium metaborate by using model-fitting and model-free methods

Model-free and model-fitting methods have been applied to data for nonisothermal and isothermal decomposition of sodium perborate tetrahydrate to sodium metaborate. The kinetic triplet (f(a), A and E) of sodium perborate tetrahydrate was found by model fitting method defined with a single step reaction, which has an excellent fit for nonisothermal data and obeys different kinetic models and yields highly uncertain values of Arrhenius parameters. The isothermal and nonisothermal data for thermal decomposition of sodium perborate tetrahydrate to sodium perborate monohydrate and sodium metaborate were evaluated by model-free isoconversional method. The complex nature of multi-step process of sodium perborate tetrahydrate to sodium metaborate was more easily indicated by using wide temperature range in nonisothermal isoconversional method.     

Infrared studies of cryogenic transitions in poly(ethylene terephthalate) and polystyrene

Infrared absorbance measurements as a function of temperature down to 13°K have been made on poly(ethylene terephthalate) and polystyrene. Transition temperatures are assigned to the temperatures where there are abrupt changes in the absorbance or integrated band intensities. Bands of known structural origin arising from either crystal-line or amorphous phases are studied to probe the structure basis and environment effect for each transition. Transitions are found around 50, 120, 180, and 220°K for PET and around 50° and 235°K for polystyrene.     

Sharpening polycrystalline phase boundary for potassium sodium niobate ceramics with MnF2 modification

The influence of anion on structure and performance is unclear in potassium sodium niobate ((K,Na)NbO₃; KNN)-based ceramics, while cation doping has been widely researched. Here, the phase structure and electrical properties are explored in MnF₂-doped KNN ceramics. Significantly, sharp rhombohedral–orthorhombic (R–O) and orthorhombic–tetragonal (O–T) phase boundary as well as reduced diffusion degree is exhibited in the ceramics along with little changed phase transition temperatures due to the optimized F⁻ content at O site, which is different from that of cation replacement for A and B sites. Notably, the domain wall motion is facilitated due to the increased A vacancy and decreased O vacancy along with strengthened polarity, originating from the higher valence state and electronegativity of F⁻ with respect to O²⁻. And then, enhanced ferroelectricity is realized via MnF₂ modification, the piezoelectricity is elevated in turn. This work presents a new idea of anion doping for controlling structure and properties in perovskite materials.     

湿法磷酸介质中氟硅酸钾（钠）结晶动力学研究

运用粒数平衡方程,在MSMPR结晶器中研究了氟硅酸钾（钠）在湿法磷酸中的结晶动力学,建立了成核速率－晶体生长速率及成核速率－晶体生长速率－悬浮密度的动力学模型。     

Grafting of methyl methacrylate onto sodium alginate initiated by potassium ditelluratoargentate(III)

Sodium alginate (SA) was graft‐copolymerized with methyl methacrylate in an alkali aqueous solution with potassium ditelluratoargentate(III) (DTA) as the initiator. Graft copolymers with both a high grafting efficiency (>90%) and a high percentage of grafting were obtained, which indicated that the DTA–SA redox pair was an efficient initiator for this grafting. The grafting parameters, including total conversion, grafting efficiency, and percentage grafting, were evaluated comparatively. The dependence of these parameters on temperature and time, monomer concentration, initiator concentration, and SA backbone concentration was also investigated. The overall activation energy of this grafting was calculated as 37.50 kJ/mol. Proof of grafting was obtained from gravimetric analysis and IR spectra. A tentative mechanism involving a two‐step, single‐electron‐transfer process of DTA is proposed to explain the generation of radicals and the initiation of grafting. Some basic properties of the grafted copolymer were studied by instrumental analyses, including thermogravimetry, X‐ray diffraction, and scanning electron microscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1688–1694, 2005