• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.1
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• pp.151-162
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• 1997

The suitability of pivalic acid was confirmed as a secondary temperature standard material. Triple-point cells of pivalic acid were obtained by using combined process of vacuum distillation with zone refining. A detailed description of the purification process was given. The melting curves were used as criteria for determination of purities of pivalic acid. Triple points of these cells with purity of 99.9997% were measured to be $35.956\pm 0.003^{\circ}C$ by using the melting plateau curves. Thus the triple point cells of pivalic acid appear to be able to use for the calibration of thermistor thermometers with moderate precision.

• Journal of Korea Foundry Society
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• v.31 no.4
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• pp.191-197
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• 2011

Transparent organic materials have been frequently used as an analog of the solidifying metallic materials, because their transparency permits an in-situ observation of the microstructural development during solidification through optical microscopy. Pivalic acid (PVA)-ethanol system showing an anisotropic property in solid-liquid interfacial energy and interface kinetics was adopted in the present experiment, and the detailed experiments performed are as follows: (1) variation of dendrite tip temperature with growth velocity, (2) correlation between primary dendrite arm spacing (${\lambda}_1$) and the growth orientation away from the heat flow direction (tilt angle: ${\theta}$), (3) variation of dendrite tip radius (R) with growth velocity (V), (4) dendrite tip stability parameter (${\sigma}^*$) and its dependence on the concentration. Concerning the correlation between the dendrite tip temperature and growth velocity the present result is well suited to Hunt-Lu equation. As the tilt angle increases, the average primary dendrite spacing tends to increase.

• Journal of the Korean Chemical Society
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• v.19 no.3
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• pp.149-155
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• 1975

Pivalic acid, which has a globular shape and is a plastic crystal, has been examined by means of temperature-dependent with-line proton magnetic resonance spectroscopy. Results of temperature-dependent line width, second moment, and spin-lattice relaxation time studies of pivalic acid were interpreted in terms of dynamic behavior and hydrogen bonding. The dynamic behavior consists of superimposed reorientation of the methyl groups about their three-fold axes$(C_3) and of the molecule about the central C-C bond(C_3'),$ general molecular reorientation about the center of gravity, and molecular self-diffusion. Activation energies for the motional processes have been obtained from line width measurements using the modified Bloembergen, Purcell, and Pound theory and from spin-lattice relaxation time measurements. The results were compared with the Pople-Karasz theory of fusion and the agreement was found to be poor. The discrepancy was interpreted in terms of hydrogen bonding in this molecule.

• Korean Journal of Metals and Materials
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• v.49 no.7
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• pp.570-576
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• 2011

The shape of a dendrite tip has long been approximated by a paraboloid of revolution, but many attempts have been made as well to more accurately match the dendrite tip profile using other mathematical functions: power function, 4th order polynomial, and hyperbolic function. In the present work, dendrite tip shapes were matched by parabolic function. The differences between the dendrite tip shapes of pivalic acid(PVA)-ethanol(Eth) and succinonitrile(SCN)-salol systems, characterized by anisotropic and isotropic solid-liquid interfacial properties, respectively, were quantitatively treated using shape parameters. The PVA-Eth system showed a slightly higher Z/R value than the SCN-salol system, their Z/R values lying in the range 2-4. (Z is the distance from the tip beyond which the parabolic fit starts to deviate from the profile, and R the tip radius.) ${\lambda}_P$ is the distance from the tip beyond which side branching starts to appear, and is larger in the PVA-Eth system than the SCNsalol system. ${\lambda}_P$ is different for both sides of the 2-dimensional dendrite profile. The difference of ${\lambda}_P$ between both sides of the dendrite is larger for PVA-Eth system than for SCN-salol, implying that the dendrite of PVA-Eth is less symmetric than that of SCN-salol.

• Korean Journal of Materials Research
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• v.26 no.11
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• pp.644-648
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• 2016

In order to examine how the solid-liquid interface responds to temperature variation depending on the materials characteristics, i.e. faceted phase or nonfaceted phase, the moving solid-liquid interface of transparent organic material, as a model substance for metallic materials (pivalic acid, camphene, salol, and camphor-50wt% naphthalene) was observed in-situ. Plots of the interface movement distance against time were obtained. The solid-liquid interface of the nonfaceted phase is atomically rough; it migrates in continuous mode, giving smooth curves of the distance-time plot. This is the case for pivalic acid and camphene. It was expected that the faceted phases would show different types of curves of the distance-time plot because of the atomically smooth solid-liquid interface. However, salol (faceted phase) shows a curve of the distance-time plot as smooth as that of the nonfaceted phases. This indicates that the solid-liquid interface of salol migrates as continuously as that of the nonfaceted phases. This is in contrast with the case of naphthalene, one of the faceted phases, for which the solid-liquid interface migrates in "stop and go" mode, giving a stepwise curve of the distance-time plot.

• Journal of The Korean Society of Inherited Metabolic disease
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• v.16 no.2
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• pp.57-61
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• 2016

Isovaleric acidemia (IVA) is an autosomal recessively inherited organic acid disorder due to a defect of the enzyme isovaleryl-CoA dehydrogenase in the leucine metabolic pathway. Deficiency of this enzyme results in the accumulation of derivatives of isovaleryl-CoA. In acute illness in IVA, isovaleric acid and its derivatives accumulate and profound metabolic acidosis with ketosis, characteristic pungent body odor, hypoglycemia, and hyperammonemia can be developed. Additionally, recurrent vomiting, failure to thrive, developmental delay, epilepsy and mental retardation are chronic presenting symptoms and signs for IVA. On the result of newborn screening for inherited metabolic disorders, increased levels of isovalerylcarnitine (C5) are shown. However, C5 elevation can be accompanied with short/branched-chain acyl-CoA dehydrogenase (SBCAD) and therapy with certain antibiotics containing pivalic acid. Quantitative measurement of organic acids in urine and acylcarnitine profiles in plasma are necessary to differential diagnosis. Molecular genetic analysis of the IVD gene for IVA and ACADSB is also helpful to confirm IVA and SBCAD deficiency, respectively. Considering that IVA can be associated with significant morbidity and mortality at acute presentation of metabolic crisis, early diagnosis prior to the onset of symptoms by newborn screening enable to introduction of early treatment and prevention of acute and chronic complications.

• Journal of Powder Materials
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• v.25 no.4
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• pp.336-339
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• 2018

A unique porous material with controlled pore characteristics can be fabricated by the freeze-drying process, which uses the slurry of organic material as the sublimable vehicle mixed with powders. The essential feature in this process is that during the solidification of the slurry, the dendrites of the organic material should repel the dispersed particles into the interdendritic region. In the present work, a model experiment is attempted using some transparent organic materials mixed with glass powders, which enable in-situ observation. The organic materials used are camphor-naphthalene mixture (hypo- and hypereutectic composition), salol, camphene, and pivalic acid. Among these materials, the constituent phases in camphor-naphthalene system, i.e. naphthalene plate, camphor dendrite, and camphor-naphthalene eutectic exclusively repel the glass powders. This result suggests that the control of organic material composition in the binary system is useful for producing a porous body with the required pore structure.