One of the first places among the synthetic minerals which can be applied in technology and industry belongs to the synthetic quartz due to its good piezoelectric and optical properties.
Synthetic types of piezoquartz raw materials are the indispensable crystalline materials for the production of unique perspective devices. The most common application of piezoelectric quartz is a piezoelectric resonator which is used as the basic element of the support technology products (Variable-frequency (VFO), temperature-compensated (TCXO), voltage-controlled (VCO), temperature-controlled (TCXO) oscillators, etc.). ZY-cut crystals are the most common crystals for use in the manufacture of quartz resonators and filters. ZX-cut crystals are used for the fabrication of surface acoustic wave delay lines on the basis of the large-scale ST-plates (300 mm in diameter). Piezoelectric quartz quality is determined by the International (IEC 758), Japanese (JIS C-6704) and Russian (OST 41-07-274-87) standards.
We produce a new modification of synthetic r/r-rod piezoquartz (r-bar) grown on the r/r-oriented seeds. The main features of this material compared to the previously known types are:
1. r-bar is mainly represented by the single monopyramid.
2. The predominant amount of graft r-bar material does not contain the dislocations that are inherited from the seed crystal. It allows to use this material for the manufacture of piezo elements using the plasma and chemical etching methods (crystal components with the inverse mesostructure for the high frequency quartz resonators).
3. Individual dislocations are located along the planes of the piezo element major cuts that do not lead to the through-etching of the piezoelectric elements.
Synthetic optical quartz is a unique optical medium suitable for manufacture of lenses and prisms (Wollaston, Rochon, Sénarmont prisms etc.), polarizers, compensators and various other parts of spectroscopic, interferometric, polarization and modulating devices. Spectropolarimeters with the shortwave work limit of about 180 nm, the lens and the wafers for the ultraviolet devices, wedges, precision etalon optical devices, interference-polarizing filters (IPF) for the solar activity investigations are manufactured on the basis of optical synthetic quartz. X-cut quartz wafers having a birefringence and no effect of rotation of the polarization plane have been used in optical devices. In this case, it is optimal to cut such wafers from XZ- or XY- crystals.
Synthetic quartz is produced by the hydrothermal synthesis. «Mineral» company has a variety of autoclaves with capacity from 24 to 4000 litres. Quartz single crystals are grown using such equipment at temperatures up to 400 °C and pressures up to 1500 atm.
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Fig. 1. Commercial varieties of synthetic piezoelectric quartz:
ZY-, ZX-, XZ- and XY-cuts (a, b);
rX-and rY’-cuts (c); r / r-cut (d).
«Mineral» company can supply right- and left-handed synthetic optical quartz. Synthetic optical quartz is divided into four sub-types for the Z-crystals and into six sub-types for X — crystals in accordance with the absorption coefficient, the unstriae value, the content of active acsessory minerals, defect-free area and solid inclusions.
Crystal type is characterized primarily in terms of the absorption coefficient at a wavelength of 190 nm (M-1, not more) — 1.0 — 7.0.
Crystal type is divided into two categories in terms of the unstriae value.
Synthetic optical quartz is produced in the form of right- and left-handed Z- and X- single crystal blocks with thickness up to 35-40 mm.
In main physical and optical characteristics (in particular, birefringence, refractive index, optical transmission over a wide range of wavelengths etc.) these crystals are identical to the best natural optical crystals. In transparency to ultra violet (UV) radiation (More than 90% at 220 nm) synthetic crystals are much better compared with natural (50-75%) ones.
«Mineral» company owns the technological processes providing the growth of optical quartz crystals resistant to γ-radiation dose of 105-106 R (while the natural optical quartz becomes opaque when exposed to ionizing radiation dose of 10-104 R).
Yield of synthetic optical quartz monoblocks is 90-95% due to high uniformity and absence of defects, while the yield of material received from unique natural crystals is less than 50% and is typically 30-45%.
«Mineral» company supplies quartz products (piezo- and optical quartz) to Russian and foreign companies (Japan, China, Taiwan, etc.).
Synthetic quartz dyed in various colors (blue, green, smoky, brown, citrine and amethyst) has been successfully used as semi-precious raw materials in the jewelry industry.
Blue and dark blue synthetic quartz crystals have no natural analogues. A wide range of brown quartz crystals (from light brown to reddish-brown) was obtained by hydrothermal method using the industrial environment.
Jewelry industry needs are completely met through the synthetic quartz with citrine color — from light lemon-yellow to orange and reddish-brown (thick tea) color.
For the first time synthetic amethyst has been obtained in Russia. In terms of jewelry characteristics synthetic amethyst is the full analogue of the best natural amethyst, in particular, of the so-called «Ural» ones and of other ones with various natural shades.
The main physical characteristics (such as hardness, refractive index, specific gravity etc.) of the grown amethyst crystals are almost identical to the same characteristics of natural ones. Absorption spectra of these crystals are also completely identical.
Synthetic amethysts possess a pronounced effect of anomalous color pleochroism which accompanied by the changes in tone color from reddish-purple to purple-blue when the crystal orientation is changed with respect to the angle of view.
Coloration of synthetic amethyst has high thermal and color stability.
Synthetic ametrine is the analogue of natural mineral Bolivianite. Ametrine is a bicolor (two colors) variety of quartz containing both purple (Amethyst) and golden-yellow (Citrine) colors. Violet color is concentrated in the R-sectors, while the r-sectors are painted yellow Citrine color.
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Druze of coloured quartz. We have the ability to produce the restoration of nature druzes in the conditions of the hydrothermal synthesis of industrial quartz. Nature takes hundreds of years to make druzes restoration; we can now do it in a few months. Crystal heals its wounds, regenerates the structure of faces, forms the new peaks, and enriches the color of natural material. Druzes can be painted in different colors depending on the crystals grown in this autoclave.
Fig. Druzes