Synthetic Crystalline Materials Research Articles

Economical routes to size-specific assembly of self-closing structures.

Programmable self-assembly has seen an explosion in the diversity of synthetic crystalline materials, but developing strategies that target "self-limiting" assemblies has remained a challenge. Among these, self-closing structures, in which the local curvature defines the finite global size, are prone to polymorphism due to thermal bending fluctuations, a problem that worsens with increasing target size. Here, we show that assembly complexity can be used to eliminate this source of polymorphism in the assembly of tubules. Using many distinct components, we prune the local density of off-target geometries, increasing the selectivity of the tubule width and helicity to nearly 100%. We further show that by reducing the design constraints to target either the pitch or the width alone, fewer components are needed to reach complete selectivity. Combining experiments with theory, we reveal an economical limit, which determines the minimum number of components required to create arbitrary assembly sizes with full selectivity.

Measurements of elastic properties of langatate at liquid helium temperatures for design of ultra low loss mechanical systems

We present full characterisation of acoustic wave devices based on the fully synthetic crystalline material at the liquid helium temperature range required for the design of ultra low loss mechanical systems in many areas of research, including frequency control and fundamental measurements. Temperature coefficients of the effective elastic tensor of Langatate (LGT) in Lagrangian representation are determined for the temperature range of 3.8–15 K. The Lagrangian formalism is mandatory in the analysed situation since the expansion coefficients of the LGT are still unknown at these temperatures. The measurement method involves a set of high-quality resonators of various cut angles and uses measurements of frequency-temperature relations to extract the temperature coefficients of the elastic tensor. In addition, power sensitivity of LGT resonators at cryogenic temperatures is determined and dominant loss mechanism is identified.

Phosphating of Calcium Carbonate for Obtaining Hydroxyapatite from the Ostrich Egg Shell

The Hydroxyapatite (HA), the major component of the inorganic portion of bones, may be obtained from different sources for use as biomaterial in the reconstruction of critical bone defects. Among these resources, the eggshell appears as a promising alternative since it is a waste material which may be reused as a source of calcium carbonate after adequate treatment, giving rise to mineral hydroxyapatite. After morphological and physicochemical adjustments allowing its standardization and utilization, hydroxyapatite (HA) may turn into a potentially useful biomaterial for different experimental purposes. This paper aims to present a viable method for obtaining a hydroxyapatite from Ostrich eggshell by wet precipitation process. This phosphating technique with emphasis on the issue of sustainable reuse of disposable materials allows the production of a synthetic crystalline material with characteristics similar to those of bone and tooth. The structural characterization was performed by X-Ray diffraction and scanning electron microscopy with field emission gun and energy dispersive X-ray in the Military Institute of Engineering.

On the nature of tincalconite

An examination of synthetic crystalline material by single crystal X-ray diffractometry reveals a unit-cell dimension that was previously ascribed to tincalconite. However, the best fit to the reflection data obtained at 291(2) K is obtained with composition Na 6 [B 4 O 5 (OH) 4 )] 3 ·8H 2 O. This formula is different from the Na 2 [B 4 O 5 (OH) 4 )]·3H 2 O previously assigned to tincalconite from an earlier crystallographic study. Additionally, our model fits best with non-crystallographic measurements and agrees with the analysis from a more recent low temperature crystallographic analysis. Tincalconite is best formulated as Na 6 [B 4 O 5 (OH) 4 )] 3 ·8H 2 O. It is trigonal, R32, a = 11.1402 (11), c = 21.207 (3) Å, Z = 3, R = 0.020 for 512 F o > 4σ (F o ) and 0.021 for all 529 data at 291(2) K.

Studies of sorbent/ion-exchange materials for the removal of radioactive strontium from liquid radioactive waste and high hardness groundwaters

Different sorbents were studied in terms of their full-scale applicability for radioactive strontium removal in low-level liquid radioactive waste (LLRW) management. The following types of sorbent/ion-exchange materials were investigated: natural zeolite–clinoptilolite, modified natural clinoptilolite, synthetic zeolites, new synthetic crystalline materials selective to strontium, ion-exchange resins, and modified fiber sorbents. Simulated solutions for experimental tests were prepared according to the composition of one of the facilities at the Hanford nuclear site (Richland, WA, USA). The following experiments were performed at different concentrations of strontium and competing elements (calcium, on the first hand): batch tests for determination of strontium distribution coefficients, sorbent/ion-exchanger selectivity to strontium in the presence of calcium, and kinetic measurements of strontium uptake. Modifications of Amberlite and Duolite ion-exchange resins (Rohm and Haas, USA) and new synthetic crystalline materials — silicotitanate IE-911 (UOP, USA) and sodium titanate (Allied Signal, USA) — showed the highest distribution coefficients of strontium ( K d∼ 2×10 4–4×10 5 ml/g). For all materials, the K d decreased significantly with increased calcium concentration. On the other hand, each of these sorbents showed poor selectivity to strontium in the presence of calcium. Newly developed sorbents (Institute of Chemistry, Vladivostok, Russia) based on a fiber matrix (FM and FP) showed the best relative selectivity to strontium followed by the natural zeolite (clinoptilolite extracted and produced in the USA). Synthetic zeolites (IE-96, TIE-96) had moderate values of both parameters (distribution coefficient and selectivity). Fiber sorption materials were also absolute leaders in kinetic measurements removing 40% to 60% of the strontium from solution within a few minutes.

Bubbles in ceramic systems: Invited Review Paper

The genesis and properties of bubbles are discussed, with ceramic examples selected from aqueous suspensions and pastes, dried bodies, molten and congealed glasses, glazes and vitreous bonds, natural and synthetic crystalline materials, and fluidized beds. Bubbles influence ceramic behavior before, during and after firing, sometimes desirably, but often adversely. Most develop by heterogeneous nucleation or by the entrapment of gases. Their expansion and mobility, or the mobility of their surfaces, induce flow in ambient liquids which may, for instance, accelerate the corrosion of refractories or produce glaze defects. Corrosion is accelerated also by the enhanced chemical reactivity and material transport at bubble surfaces.