N. V. Chukanov

I.r. spectroscopy characterization of various types of structural irregularities in pyrolytic boron nitride

Samples of pyrolytic BN ceramics were produced by CVD from BCl3-NH3-N2 mixtures at temperatures of 1300–2100°C, pressures 1–20 torr and varying partial pressures of the components. A theoretical analysis of the dependences of i.r. spectral band frequencies on interlayer distance and crystal block size is given. Five BN structure modifications have been found in BN ceramics from i.r. band shape analysis: hexagonal graphite-like, partially ordered, turbostratic, dense amorphous and highly dispersed amorphous, whose relative content strongly depends on the synthesis conditions.

Comparative Investigation of Thermal Decomposition of Various Modifications of Hexanitrohexaazaisowurtzitane (CL-20)

The thermal decomposition kinetics of different polymorphs of CL-20 (α, γ and e) has been investigated by thermogravimetry, IR spectroscopy and optical and electronic microscopy. The reactions proceed with self-acceleration and can be described by a kinetic law of first order with autocatalysis. Already at the earliest stages of decomposition (≤1%) phase transitions take place from αγ and from eγ. For this reason the observed decomposition is related to the decomposition of γ-CL-20. On the other hand, the kinetics of decomposition depends on the initial polymorphic state, so that the thermal decomposition increases in the series: α<γ<e. Experiments with different samples of α-CL-20 demonstrate that different rates of decomposition are observed for the same polymorph depending on the mean size and the size distribution of the crystals and their morphological features. In some cases the thermal stability of α-CL-20 can be increased by previous annealing. It is concluded that the thermal decomposition of CL-20 is purely a solid-state process. Microscopical and spectroscopical analysis of the condensed CL-20 decomposition product (formed after prolonged heating at high temperature) show that it has a network structure and consists mainly of carbon and nitrogen.

Kinetics of thermal decomposition of hexanitrohexaazaisowurtzitane

Thermal decomposition of hexanitrohexaazaisowurtzitane (HNIW) in the solid state and in solution was studied by thermogravimetry, manometry, optical microscopy, and IR spectroscopy. The kinetics of the reaction in the solid state is described by the first-order equation of autocatalysis. The rate constants and activation parameters of HNIW thermal decomposition in the solid state and solution were determined. The content of N2 amounts to approximately half of the gaseous products of HNIW thermolysis. The thermolysis of HNIW and its burning are accompanied by the formation of a condensed residue. During these processes, five of six nitro groups of the HNIW molecule are removed, and one NO2 group remains in the residue, which contains amino groups and no C−H bonds.

Regularities of pyrolytic boron nitride coating formation on a graphite matrix

The kinetics and structure of chemical vapour-phase deposition of boron nitride ceramics on a graphite matrix from the mixture BCl3/NH3/N2 have been investigated for a wide range of conditions (temperature 1300–2100°C, pressure 130–2600 Pa, at varying partial pressures of the components). The growth-rate was found to vary non-linearly with the consumption rates of the reagents. The content of hexagonal components in the BN-ceramics rose, while the turbostrate microphase content diminished with temperature. The dependences of the concentrations of hexagonal, turbostratic and amorphous fractions in BN-ceramics on the reaction mixture composition and total pressure have been determined.

Surkhobite: revalidation and redefinition with the new formula, (Ba, K)2CaNa(Mn, Fe2+, Fe3+)8Ti4(Si2O7)4O4(F, OH, O)6

Surkhobite, a new mineral related to the members of the jinshajiangite-perraultite series, was approved in 2002 (IMA No. 2002-037) and later discredited (IMA decision 06-E). It is redefined here with a new formula and revalidated with the original name (IMA 07-A). It occurs as platy crystals up to 1 mm and grains up to 2 × 1 × 0.4 cm in the association with aegirine, microcline, albite, quartz, amphibole, annite, bafertisite, astrophyllite, zircon, fluorite, polylithionite, stillwelite, sogdianite, tadjikite in alkaline pegmatite at the massif Dara-i-Pioz, Tajikistan. Surkhobite is translucent, brownish-red, lustre vitreous, streak white, cleavage perfect on {001}; hardness is anisotropic: the minimum value H 1 = 250 kg/mm 2 , the maximum value H 2 = 482 kg/mm 2 ; Mohs’ hardness is 4½. Biaxial, negative, β= 1.858(10), γ= 1.888(10); 2 V = 65(5)°; α= 1.790 (calculated from 2 V ). Optical orientation: X = b , Z ∧ a = 34°. Dispersion is strong, r . Pleochroism: Y (orange) > Z (bright-yellow) ≥ X (yellow). Microtwinning on (001) is observed. D calc = 3.98 g/cm 3 ; D meas = 3.84(10) g/cm 3 . IR and Mossbauer spectra are given. Chemical composition is (electron microprobe combined with Mossbauer data, wt.%): Na 2 O 2.27, K 2 O 1.87, CaO 2.53, SrO 0.26, BaO 11.16, MgO 0.13, MnO 16.32, FeO 13.92, Fe 2 O 3 2.11, Al 2 O 3 0.02, SiO 2 27.17, TiO 2 16.14, Nb 2 O 5 2.14, ZrO 2 0.34, F 2.94, H 2 O (by Penfield method) 1.17, -O=F 2 –1.24, total 99.25. The empirical formula is ( Z = 2): Na 2.60 K 1.41 Ca 1.60 Sr 0.09 Ba 2.58 (Mn 8.17 Fe 2+ 6.88 Fe 3+ 0.94 Mg0. 115 Al 0.01 ) ∑16.115 (Ti 7.17 Nb 0.57 Zr 0.10 ) ∑7.84 Si 16.06 H 4.61 F 5.49 O 70.51 . The simplified formula, taking into account the crystal structure, is ( Z = 2): KBa 3 Ca 2 Na 2 (Mn, Fe 2+ , Fe 3+ ) 16 Ti 8 (Si 2 O 7 ) 8 O 8 (OH) 4 (F,O,OH) 8 . The crystal structure was refined on a single crystal to R = 0.043 with 3686 independent reflections ( F > 2σ). Surkhobite is monoclinic, C 2, a = 10.723(1), b = 13.826(2), c = 20.791(4) A, β = 95.00(1)°. Surkhobite is the Mn-dominant analogue of jinshajiangite and differs from perraultite in that Ca is ordered onto and is dominant in the site A (6). The strongest lines of the powder difraction pattern [ d , A ( I , %) ( hkl )] are: 10.39 (20) (002), 3.454 (100) (006), 3.186 (15) (321), 2.862 (15) (225), 2.592 (70) (008), 2.074 (40) (048).

Shirokshinite, K(NaMg2)Si4O10F2, a new mica with octahedral Na from Khibiny massif, Kola Peninsula: descriptive data and structural disorder

Shirokshinite, K(NaMg 2 )Si 4 O 10 F 2 , is the analogue of tainiolite, K(LiMg 2 )Si 4 O 10 F 2 , with the M 1 octahedron fully occupied by Na instead of Li. It was found in the Kirovskii underground apatite mine (Kukisvumchorr Mountain, Khibiny massif, Kola Peninsula, Russia) as a late hydrothermal mineral in a small hyperalkaline pegmatite embedded in ristschorrite. Shirokshinite is associated with microcline, kupletskite, aegirine, natrolite, lorenzenite, calcite, remondite-(Ce), donnayite-(Y), mckelveyite-(Y) and galena. Crystals are usually skeletal and coarse hexagonal [001] prismatic. Shirokshinite is transparent to translucent, colourless to pale greyish, hardness Mohs9 ∼2.5; D(calc) = 2.922 g/cm 3 . Optically biaxial (-), α = 1.526(1), β = 1.553(2), γ = 1.553(2); 2V meas = −5(5)°, 2V calc = −0°; Y = b , Z ∼ a , Xc = 3(2)°. The IR spectrum of shirokshinite is unique even if close to that of tainiolite: in particular, the presence of Na + instead of Li + shifts some bands towards low-frequencies. Single-crystal diffraction data (Mo K α-radiation) gave a = 5.269(2), b = 9.092(9), c = 10.198(3) A, β = 100.12(7)°, Z = 2, 1 M -polytype, space group C 2/ m. Structure anisotropic refinement converged R = 0.13 for 715 observed reflections. Evidence of stacking faults in the structure is discussed and compared with the so called Ďurovic effect. The very little ditrigonal distortion in spite of the large dimension of the Na octahedron is discussed in comparison with tainiolite. A critical revision of old published data indicating octahedral Na in micas shows that this hypothesis was biased by the low quality of the chemical analyses.

Fukalite: An example of an OD structure with two-dimensional disorder

Abstract The real crystal structure of fukalite, Ca4Si2O6(OH)2(CO3), was solved by means of the application of order-disorder (OD) theory and was refined through synchrotron radiation diffraction data from a single crystal. The examined sample came from the Gumeshevsk skarn copper porphyry deposit in the Central Urals, Russia. The selected crystal displays diffraction patterns characterized by strong reflections, which pointed to an orthorhombic sub-structure (the “family structure” in the OD terminology), and additional weaker reflections that correspond to a monoclinic real structure. The refined cell parameters are a = 7.573(3), b = 23.364(5), c = 11.544(4) Å, β = 109.15(1)°, space group P21/c. This unit cell corresponds to one of the six possible maximum degree of order (MDO) polytypes, as obtained by applying the OD procedure. The derivation of the six MDO polytypes is presented in the Appendix1. The intensity data were collected at the Elettra synchrotron facility (Trieste, Italy); the structure refinement converged to R = 0.0342 for 1848 reflections with I > 2σ(I) and 0.0352 for all 1958 data. The structure of fukalite may be described as formed by distinct structural modules: a calcium polyhedral framework, formed by tobermorite-type polyhedral layers alternating along b with tilleyitetype zigzag polyhedral layers; silicate chains with repeat every fifth tetrahedron, running along a and linked to the calcium polyhedral layers on opposite sides; and finally rows of CO3 groups parallel to (100) and stacked along a.

Fluorcalciobritholite, Ca,REE)5[(Si,P)O4]3F, a new mineral: description and crystal chemistry

The new mineral fluorcalciobritholite, ideally Ca 3 Ce 2 (SiO 4 ) 2 (PO 4 )F, has been found at Mount Kukisvumchorr, Khibiny alkaline complex, Kola Peninsula, Russia, in veinlets which contains aggregates of orthoclase, nepheline, sodalite and biotite in association with grains of fayalite, gadolinite-(Ce), zircon, monazite-(Ce), zirconolite (“polymignite”), fluorapatite, fluorite, molybdenite, lollingite and graphite. Fluorcalciobritholite forms long-prismatic hexagonal crystals up to 0.5 x 10 mm; the main crystal form is the hexagonal prism {10–10}. The mineral is transparent, with a pale pinkish to brown colour and a white streak. The hardness (Mohs) is 5.5, and the observed density is 4.2(1) g/cm 3 . Optically, it is uniaxial (−) with ω 1.735(5), e 1.730(5). Electron microprobe gave the following empirical formula based on [Si+P+S] = 3 apfu : [Ca 2.80 (Ce 0.93 La 0.54 Nd 0.26 Y 0.18 Pr 0.08 Sm 0.03 Gd 0.03 Dy 0.02 Yb 0.02 Er 0.01 ) ∑2.12 Th 0.04 Mn 0.03 Sr 0.02 ] ∑4.99 [(Si 1.94 P 1.06 ) ∑3 O 12 ] [F 0.76 O 0.22 Cl 0.01 ] ∑0.99 (Z = 2). The IR spectrum of metamict fluorcalciobritholite from Siberia showed a marked similarity with those of hydroxylbritholite-(Ce) and hydroxylbritholite-(Y). The strongest lines of the X-ray powder pattern [ d in A ( I ) ( hkl )] are: 3.51 (45) 002, 3.15 (70) 102, 2.85 (100) 211, 121, 2.78 (60) 300. The mineral is hexagonal, space group P 6 3 / m , with a = 9.580(7), c = 6.985(4) A, V = 555.2(7) A 3 . The crystal structure was refined from single-crystal X-ray diffraction data to R F = 0.029. Fluorcalciobritholite, whose simplified formula is (Ca,REE) 5 [(Si,P)O 4 ] 3 F, differs from fluorbritholite in having Ca > ∑REE, and differs from fluorapatite in having Si > P. Its compositional field falls within the limits Ca 2.5 REE 2.5 (SiO 4 ) 2.5 (PO 4 ) 0.5 F (boundary with fluorbritholite) and Ca 3.5 REE 1.5 (SiO 4 ) 1.5 (PO 4 ) 1.5 F (boundary with fluorapatite). Both the mineral and its name have been approved by the IMA Commission on New Minerals and Mineral Names.

Lileyite, Ba2(Na,Fe,Ca)3MgTi2(Si2O7)2O2F2, a new lamprophyllite-group mineral from the Eifel volcanic area, Germany

The new Mg- and F-dominant lamprophyllite-group mineral lileyite (IMA 2011-021) was found at the Lohley quarry, Udersdorf, near Daun, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany, and named for the old name of the type locality, Liley. Associated minerals are nepheline, leucite, augite, magnetite, fluorapatite, perovskite, gotzenite. Lileyite is brown, translucent; streak is white. It forms platy crystals up to 0.1 × 0.3 × 0.5 mm in size and their clusters up to 1 mm across on the walls of cavities in an alkaline basalt. Lileyite is brittle, with Mohs hardness of 3–4 and perfect cleavage on (001). D calc is 3.776 g/cm 3 . The new mineral is biaxial (+), α = 1.718(5), β = 1.735(5), γ = 1.755(5), 2V (meas.) = 75(15)°, 2V (calc.) = 86°. The IR spectrum is given. The chemical composition is (EDS-mode electron microprobe, mean of 5 analyses, wt%): SiO 2 28.05, BaO 26.39, TiO 2 18.53, Na 2 O 6.75, MgO 4.58, FeO 4.48, CaO 2.30, SrO 2.23, MnO 1.44, K 2 O 1.41, Nb 2 O 5 0.95, F 3.88, –O=F 2 -1.63; total 99.36. The empirical formula based on 18 anions is: Ba 1.50 Sr 0.19 K 0.26 Na 1.89 Ca 0.36 Mn 0.18 Mg 0.99 Fe 0.54 Ti 2.01 Nb 0.06 Si 4.06 O 16.23 F 1.77 . The simplified formula is: Ba 2 (Na,Fe,Ca) 3 MgTi 2 (Si 2 O 7 ) 2 O 2 F 2 . The crystal structure was solved using single-crystal X-ray diffraction data ( R = 0.024). Lileyite is monoclinic, space group C 2/ m , a = 19.905(1), b = 7.098(1), c = 5.405(1) A, β = 96.349(5)°, V = 758.93(6) A 3 , Z = 2. The strongest lines of the powder diffraction pattern [ d , A ( I , %) ( hkl )] are: 3.749 (45) (31–1), 3.464 (76) (510, 311, 401), 3.045 (37) (51–1), 2.792 (100) (221, 511), 2.672 (54) (002, 601, 20-2), 2.624 (43) (710, 42–1). Type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia, registration number 4106/1.

The crystal structure and refined formula of mountainite, KNa2Ca2[Si8O19(OH)] · 6 H2O

Abstract Mountainite was described as a new mineral in 1957 with formula (Ca,Na2,K2)16Si32O80 · 24 H2O; its crystal structure was not solved up to now. We studied the structure of mountainite from the Yubileinaya pegmatite, Lovozero alkaline complex, Kola Peninsula, Russia. Mountainite is monoclinic, P2/c, a = 13.704(2), b = 6.5760(10), c = 13.751(2) Å, β = 105.752(10)°, V = 1192.7(3) Å3, Z = 2, Dcalc = 2.28 g/cm3. The crystal structure was solved by direct methods and refined to R(F) = 0.0639 for 1186 unique reflections with I > 3σ(I). Rietveld refinement on powder data completely confirmed the model obtained using a single crystal. Mountainite is a phyllosilicate, representative of a new structure type. The most specific feature of the mountainite structure is a TOT block formed by two SiO-layers [Si8O18(O,OH)2] (T-layers) and zig-zag columns of edge-sharing CaO5(H2O) octahedra sandwiched between them (O-layer). K cations occupy 10-fold polyhedra and are located between the columns of Ca-centered octahedra. The interlayer space between the neighboring TOT blocks is filled by Na cations and H2O molecules. The crystal-chemical formula is: KNa2Ca2{Si8O18[O(OH)]} · 6 H2O, the simplified formula is: KNa2Ca2Si8O19(OH) · 6 H2O.