Effect of additives, ball milling and isotopic exchange in porous magnesium borohydride.

Magnesium borohydride (Mg(BH4)2) is a promising material for solid state hydrogen storage. However, the predicted reversible hydrogen sorption properties at moderate temperatures have not been reached due to sluggish hydrogen sorption kinetics. Hydrogen (H) → deuterium (D) exchange experiments can contribute to the understanding of the stability of the BH4 - anion. Pure γ-Mg(BH4)2, ball milled Mg(BH4)2 and composites with the additives nickel triboride (Ni3B) and diniobium pentaoxide (Nb2O5) have been investigated. In situ Raman analysis demonstrated that in pure γ-Mg(BH4)2 the isotopic exchange reaction during continuous heating started at ∼80 °C, while the ball milled sample did not show any exchange at 3 bar D2. However, during ex situ exchange reactions investigated by infrared (IR) and thermogravimetric (TG) analyses a comparable H → D exchange during long exposures (23 h) to deuterium atmosphere was observed for as received, ball milled and γ-Mg(BH4)2 + Nb2O5, while the Ni3B additive hindered isotopic exchange. The specific surface areas (SSA) were shown to be very different for as received γ-Mg(BH4)2, BET area = 900 m2 g-1, and ball milled Mg(BH4)2, BET area = 30 m2 g-1, respectively, and this explains why no gas-solid H(D) diffusion was observed for the ball milled (amorphous) Mg(BH4)2 during the short time frames of in situ Raman measurements. The heat treated ball milled sample partially regained the porous γ-Mg(BH4)2 structure (BET area = 560 m2 g-1). This in combination with the long reaction times allowing for the reaction to approach equilibrium explains the observed gas-solid H(D) diffusion during long exposure. We have also demonstrated that a small amount of D can be substituted in both high surface area and low surface area samples at room temperature proving that the B-H bonds in Mg(BH4)2 can be challenged at these mild conditions.

Pd-Cu-M (M = Y, Ti, Zr, V, Nb, and Ni) Alloys for the Hydrogen Separation Membrane.

Self-supported fcc Pd-Cu-M (M = Y, Ti, Zr, V, Nb, and Ni) alloys were studied as potential hydrogen purification membranes. The effects of small additions (1-2.6 at. %) of these elements on the structure, hydrogen solubility, diffusivity, and permeability were examined. Structural analyses by X-ray diffraction (XRD) showed the fcc phase for all alloys with induced textures from cold rolling. Heat treatment at 650 °C for 96 h led to the reorientation in all alloys except the Pd-Cu-Zr alloy, exhibiting the possibility to enhance the structural stability by Zr addition. Hydrogen solubility was almost doubled in the ternary alloys containing Y and Zr compared to Pd65.1Cu34.9 alloy at 300 °C. It was noted that hydrogen diffusivity is decreased upon additions of these elements compared to the Pd65.1Cu34.9 alloy, with the Pd-Cu-Zr alloy showing the lowest hydrogen diffusivity. However, the comparable hydrogen permeability of the Pd-Cu-Zr alloy with the corresponding binary alloy, as well as its highest hydrogen permeability among the studied ternary alloys at temperatures higher than 300 °C, suggested that hydrogen permeation of these alloys within the fcc phase is mainly dominated by hydrogen solubility. Hydrogen flux variations of all ternary alloys were studied and compared with the Pd65.1Cu34.9 alloy under 1000 ppm of H2S + H2 feed gas. Pd-Cu-Zr alloy showed superior resistance to the sulfur poisoning probably due to the less favorable H2S-surface interaction and more importantly slower rate of bulk sulfidation as a result of improved structural stability upon Zr addition. Therefore, Pd-Cu-Zr alloys may offer new potential hydrogen purification membranes with improved chemical stability and hydrogen permeation compared to the binary fcc Pd-Cu alloys.

High-Pressure Raman and Calorimetry Studies of Vanadium(III) Alkyl Hydrides for Kubas-Type Hydrogen Storage.

Reversible hydrogen storage under ambient conditions has been identified as a major bottleneck in enabling a future hydrogen economy. Herein, we report an amorphous vanadium(III) alkyl hydride gel that binds hydrogen through the Kubas interaction. The material possesses a gravimetric adsorption capacity of 5.42 wt % H2 at 120 bar and 298 K reversibly at saturation with no loss of capacity after ten cycles. This corresponds to a volumetric capacity of 75.4 kgH2 m(-3) . Raman experiments at 100 bar confirm that Kubas binding is involved in the adsorption mechanism. The material possesses an enthalpy of H2 adsorption of +0.52 kJ mol(-1) H2 , as measured directly by calorimetry, and this is practical for use in a vehicles without a complex heat management system.

Thermodynamically neutral Kubas-type hydrogen storage using amorphous Cr(III) alkyl hydride gels.

In this paper we present amorphous chromium(III) hydride gels that show promise as reversible room temperature hydrogen storage materials with potential for exploitation in mobile applications. The material uses hydride ligands as a light weight structural feature to link chromium(III) metal centres together which act as binding sites for further dihydrogen molecules via the Kubas interaction, the mode of hydrogen binding confirmed by high pressure Raman spectroscopy. The best material possesses a reversible gravimetric storage of 5.08 wt% at 160 bar and 25 °C while the volumetric density of 78 kgH2 m(-3) compares favourably to the DOE ultimate system goal of 70 kg m(-3). The enthalpy of hydrogen adsorption is +0.37 kJ mol(-1) H2 as measured directly at 40 °C using an isothermal calorimeter coupled directly to a Sieverts gas sorption apparatus. These data support a mechanism confirmed by computations in which the deformation enthalpy required to open up binding sites is almost exactly equal and opposite to the enthalpy of hydrogen binding to the Kubas sites, and suggests that this material can be used in on-board applications without a heat management system.

Characterisation of porous hydrogen storage materials: carbons, zeolites, MOFs and PIMs.

Porous materials adsorb H2 through physisorption, a process which typically has a rather low enthalpy of adsorption (e.g. ca. 4 to 7 kJ mol(-1) for MOFs), thus requiring cryogenic temperatures for hydrogen storage. In this paper, we consider some of the issues associated with the accurate characterisation of the hydrogen adsorption properties of microporous materials. We present comparative gravimetric hydrogen sorption data over a range of temperatures for different microporous materials including an activated carbon, a zeolite, two MOFs and a microporous organic polymer. Hydrogen adsorption isotherms were used to calculate the enthalpy of adsorption as a function of hydrogen uptake, and to monitor the temperature dependence of the uptake of hydrogen. Under the conditions investigated, it was found that the Tóth equation provided better fits to the absolute isotherms compared to the Sips (Langmuir-Freundlich) equation at low pressures, whereas it appeared to overestimate the maximum saturation capacity. The isosteric enthalpy of adsorption was calculated by either: fitting the Sips and Tóth equations to the adsorption isotherms and then applying the Clausius-Clapeyron equation; or by using a multiparameter Virial-type adsorption isotherm equation. It was found that the calculated enthalpy of adsorption depended strongly upon the method employed and the temperature and pressure range used. It is shown that a usable capacity can be calculated from the variable temperature isotherms for all materials by defining a working pressure range (e.g. 2 to 15 bar) over which the material will be used.

Nitrogen and hydrogen adsorption by an organic microporous crystal.

Quick on the uptake: Following its identification during a targeted search, the intriguing crystal structure of 3,3',4,4'-tetra(trimethylsilylethynyl)biphenyl was investigated. Simple removal of the included solvent provides an organic crystal with an open microporous structure that has a striking similarity to that of zeolite A (see picture). Reversible adsorption of nitrogen and hydrogen gases at 77 K confirms that the microporosity is permanent.

The potential of organic polymer-based hydrogen storage materials.

The challenge of storing hydrogen at high volumetric and gravimetric density for automotive applications has prompted investigations into the potential of cryo-adsorption on the internal surface area of microporous organic polymers. A range of Polymers of Intrinsic Microporosity (PIMs) has been studied, the best PIM to date (a network-PIM incorporating a triptycene subunit) taking up 2.7% H(2) by mass at 10 bar/77 K. HyperCrosslinked Polymers (HCPs) also show promising performance as H(2) storage materials, particularly at pressures >10 bar. The N(2) and H(2) adsorption behaviour at 77 K of six PIMs and a HCP are compared. Surface areas based on Langmuir plots of H(2) adsorption at high pressure are shown to provide a useful guide to hydrogen capacity, but Langmuir plots based on low pressure data underestimate the potential H(2) uptake. The micropore distribution influences the form of the H(2) isotherm, a higher concentration of ultramicropores (pore size <0.7 nm) being associated with enhanced low pressure adsorption.

A triptycene-based polymer of intrinsic microposity that displays enhanced surface area and hydrogen adsorption.

A novel triptycene-based polymer of intrinsic microporosity (Trip-PIM) displays enhanced surface area (1065 m2 g(-1)) and reversibly adsorbs 1.65% hydrogen by mass at 1 bar/77 K and 2.71% at 10 bar/77 K.

Chemical activation of MgH2; a new route to superior hydrogen storage materials.

We report the discovery of a new, chemical route for 'activating' the hydrogen store MgH2, that results in highly effective hydrogen uptake/release characteristics, comparable to those obtained from mechanically-milled material.

Office-based lower airway endoscopy in pediatric patients.

BACKGROUND: Office-based evaluation of the lower airway in adults with only topical anesthetics has been well documented. This study was performed to assess the feasibility of performing office-based lower airway endoscopy in a pediatric population. DESIGN: One hundred five consecutive pediatric patients requiring flexible laryngoscopy were studied. All received only a topical anesthetic-decongestant applied nasally. After flexible laryngoscopy, the endoscope was passed below the vocal folds to visualize the subglottis, trachea, and carina. All evaluations were videotaped for later review. SETTING: Academic pediatric otolaryngology practice. MAIN OUTCOME MEASURES: All 105 patients were studied for complications and agreement between office endoscopy and operative endoscopy when necessary (performed in 20 patients). A subset of 24 consecutive patients were studied for ease of performing the lower airway evaluation, rated on a 3-point scale: 1, unable to perform; 2, performed with some difficulty; and 3, performed without difficulty. The ability to view the subglottis, trachea, and carina were also rated on a 3-point scale. RESULTS: There were no complications for any of the procedures. Office endoscopy correlated with operative endoscopy in all cases. In the subset of 24 patients, the mean score for ease of endoscopy was 2.83. The mean scores for visualizing the lower airway were 2.91 for the subglottis, 2.80 for the trachea, and 2.24 for the carina. CONCLUSION: With the use of only topical anesthesia, flexible endoscopy of the lower airway in children can be performed in the office setting and can be used effectively to evaluate abnormalities of the lower airway.

Quality of life assessment in nasal airway obstruction.

OBJECTIVES/HYPOTHESIS: Quality of life (QOL) assessment of patients with nasal obstruction has not been well studied. The objectives of the study were to determine the QOL of patients with nasal obstruction, to identify baseline variables predictive of patients' QOL, and to examine the relationship of QOL scores with patient assessment of nasal obstruction. STUDY DESIGN: Preliminary, cross-sectional study of a larger, prospective investigation. METHODS: Forty individuals met the criteria for inclusion. Participants were required to have a surgically treatable diagnosis of septal deviation, nasal valve collapse, and/or turbinate hypertrophy. Quality of life assessment was performed using the Rhinoconjunctivitis Quality of Life Questionnaire and the Rhinosinusitis Disability Index. Demographic data, along with patient assessment of nasal obstruction with a visual analogue scale, were recorded. RESULTS: Both instruments demonstrated good inter-item correlation as measured by Cronbach's alpha. Demographic variables, previous nasal surgeries, and comorbid conditions were not significantly correlated with QOL scores with either instrument. Correlations between visual analogue scale scores and the Rhinoconjunctivitis Quality of Life Questionnaire "sleep" (correlation coefficient [r] = 0.35, P =.02) and "nasal symptom" (r = 0.36, P =.02) domains demonstrated a trend toward significance. Patients with nasal valve collapse reported higher visual analogue scale scores for nasal obstruction compared with those with septal deviation alone (P <.01). CONCLUSIONS: Patients with nasal valve collapse demonstrated greater perception of nasal obstruction than those with septal deviation alone. The Rhinoconjunctivitis Quality of Life Questionnaire appears to be a more sensitive instrument than the Rhinosinusitis Disability Index for patients with nasal obstruction. However, existing measures may lack sensitivity in estimating the QOL of patients with nasal obstruction. A disease-specific instrument for nasal obstruction may be necessary to further evaluate this disease process.

Chronic sinonasal disease in patients with inflammatory bowel disease.

BACKGROUND: The objective of this study was to explore the possible relationship between inflammatory bowel disease (IBD) and chronic sinonasal disease. METHODS: A cross-sectional study was undertaken of 241 patients with Crohn's disease (CD) or ulcerative colitis from a tertiary medical center IBD clinic. Patient demographic data and information regarding IBD diagnosis and management, sinonasal disease diagnosis and management, and complications related to these diagnoses were gathered by retrospective chart review and a standardized patient survey. RESULTS: One hundred sixty surveys (67%) were returned and analyzed. Overall 48% of patients with IBD reported chronic sinonasal disease symptoms. Patients with CD had a higher prevalence of sinonasal disease than patients with ulcerative colitis (53% versus 32%; p < 0.02). The subgroup of CD patients with obstructive bowel complications had the highest prevalence of sinonasal disease (68% versus 27%; p = < 0.001), with 23% reporting chronic rhinosinusitis, 13% reporting chronic rhinitis, and an additional 32% reporting chronic nasal or sinus symptoms. CONCLUSION: The prevalence of chronic sinonasal disease is elevated in patients with IBD, occurring in approximately one-half of patients followed at a tertiary IBD center. Patients with CD experiencing obstructive complications had significantly increased rates of sinonasal disease. The relationship between chronic sinonasal disease and obstructive CD is not defined, but several hypotheses are generated.

Plastic bronchitis: an unusual bronchoscopic challenge associated with congenital heart disease repair.

Plastic bronchitis is a rare disorder characterized by the formation of branching mucoid bronchial casts. Several pathophysiologic conditions are associated with development of these intrabronchial casts, including congenital heart defects. The management of plastic bronchitis presents an unusual and interesting bronchoscopic challenge. We describe a patient who underwent a Fontan procedure for correction of a congenital heart defect and subsequently developed respiratory distress secondary to plastic bronchitis on two occasions. In both cases, endoscopic intervention was required to remove these casts. A review of the literature, including the proposed etiologies, diagnosis, and current medical and surgical management, is also undertaken.

Perspectives in laryngopharyngeal reflux: an international survey.

OBJECTIVES: Although data exists to support the relationship between laryngopharyngeal reflux (LPR) and laryngitis, there is variability among otolaryngologists regarding the methods and criteria used to make the diagnosis. This study was undertaken to discern the current attitudes and practices of a select cohort of otolaryngologists in regards to LPR. METHODS: Four hundred fifteen surveys were mailed to members of the American Broncho-Esophagological Association. Survey recipients were asked to rate patient symptomatology and physical examination findings in terms of their relationship to LPR and their preferred laryngeal visualization procedure in terms of clinical use and diagnostic accuracy. The role and validity of adjunctive diagnostic tests were also surveyed. RESULTS: Survey response rate was 38%. Symptoms felt to be most related to reflux were: throat clearing (98.3%), persistent cough (96.6%), heartburn/dyspepsia (95.7%), globus sensation (94.9%), and voice quality change (94.9%). The physical examination findings felt to be most related to reflux included: arytenoid erythema (97.5%), vocal cord erythema (95.7%) and edema (95.7%), posterior commissure hypertrophy (94.9%), and arytenoid edema (94.0%). Fiberoptic laryngoscopy was the most commonly performed diagnostic visualization procedure (75.7%) and was also considered to be most sensitive and specific (45.0%). The most commonly ordered adjunctive test was a double pH probe (37.2%), which was also felt to be the most sensitive and specific adjunctive test (75.9%). CONCLUSION: A polling of a select group of otolaryngologists demonstrated agreement in the criteria used to diagnose reflux laryngitis, although some variability exists. The development of objective guidelines for the diagnosis of LPR is a critical initial step toward evaluating the manifestations and therapeutic interventions for this disease process.