Mutual solubility and metastable zone width of NH4H2PO4KH2PO4 mixed solutions and growth of mixed crystals

Self Cite

Mixed crystals of ammonium dihydrogen phosphate and potassium dihydrogen phosphate K 1-x (NH 4 ) x H 2 PO 4 were grown from aqueous solutions with x = 0. 06, 0.09, 0.15, 0.32, 0.42, 0.51, 0.63, 0.70, 0.76, 0.78, 0.84, 0.88, 0.89 and 0.91. The crystal composition that differs from solution was estimated by X-ray method. Morphology of the crystals changes from tetragonal prism to needles when the incorporation of either of the two components into the other; which also affects the growth rate along the prominent growth directions significantly. Growth along the [001] decreases initially with composition and reached the maximum when x = 0.5; whereas growth along the [100] always showed a decreasing trend with composition and attained a minimum value when x = 0.5. Crystal length along the [001] and [100] and aspect ratio are also compositional dependent. Unit cell parameters determined by X-ray powder and single crystal analyses revealed that the 'a' parameter shows only a small and linear variation but the 'c' parameter changes significantly with ADP incorporation because of the difference in the effective ionic radius of K + and NH 4 + ions and also the possibility of NH 4 + ion to form two different kinds of hydrogen bonds in the system. The existence of a pseudo-cubic cell at the mixing composition x = 0.78 was also revealed.

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Compositional dependence of morphology and lattice parameters during growth of K_1‐x(NH₄)_xH₂PO₄ mixed crystals

Srinivasan¹,

Cantoni²,

Bocelli³

2010

Self Cite

“…Effect of crystal morphology on proportional relationship It is believed that many factors can affect the crystal morphology during crystallization process [12,13]. Some crystallization products with different crystal morphologies are obtained and so as phosphoric acid crystallization process.…”

Section: Resultsmentioning

confidence: 99%

Study of phosphoric acid crystallization using a focused beam reflectance measurement method

Chen¹,

Wu²,

Zhu³

et al. 2010

A way for restoring the crystal size distributions (CSD) from measured chord length distributions (CLD) was reported in this paper. The kinetics of phosphoric acid crystallization process was investigated in cooling mode using focused beam reflectance measurement (FBRM) and digital photo technique. In order to restore the CSD from measured CLD and verify the reliability of FBRM data, digital photo technique in real time and optical microscope were applied in large crystal size and small range, respectively. Results indicated a converting constant A existed between CLD and CSD when crystal growth follows size-independent growth (Mcabe's ΔL law) law. It was verified by Malvern particles size analysis method. The converting constant A varied with crystal morphology. The crystal growth order increased with the stirring increasing speed during phosphoric acid crystallization process. The trend was especially notable at higher speed situations. It can illustrate that the state of phosphoric acid hemihydrate crystal growth was controlled by both diffusion and surface-integration with the increasing stirring speed.

“…Specifically, some literature reported the solubility, solution stability and defects of KADP crystals [6][7][8]. By preparing small crystals using slow evaporation technique, D. L. Xu et al [5,9] put forward that the competing growth of NH 4+ and K + decreased the growth rate along a axis, and the stress along c axis easily lead to cracking during crystal growth due to different bond strength between K-O and H N -O. S. Sen Gupta [10] and C. S. Tu [11] measured the dielectric constant of KADP crystals grown by slow evaporation technique, respectively.…”

Section: Introductionmentioning

confidence: 99%

Structural, optical and dielectric studies on K_1‐x(NH₄)_xH₂PO₄ mixed crystals grown from z‐cut seeds

Zhong

Teng

et al. 2010

Mixed crystals of K 1-x (NH 4 ) x H 2 PO 4 (KADP) were grown from KDP (KH 2 PO 4 ) dominated mixed solutions with varying molar proportion of ADP (NH 4 H 2 PO 4 ) addition. It was found that, as the increase of ADP molar concentration, the growth rate along z-axis of KADP crystal decreased rapidly. The structure of KADP crystals was investigated by powder XRD and the lattice parameter was calculated. The results showed that the lattice parameter c of KADP crystal increased with the molar concentration of ADP. The optical homogeneity of grown KADP crystals was determined with a differential phase-shifting interferometry. Frequency dependences of the dielectric constant and dielectric loss of KADP crystals were measured at room temperature (290 K). The dielectric constants of KADP crystals were almost invariant with the increase of frequency. In the region of 10 2 -10 4 Hz, the values of the dielectric loss reduced with the increase of frequency. The piezo-resonance coupling effect still exists in KADP crystals at room temperature, but shifted to low frequency band.