Distribution by Scientific Domains

Terms modified by AlN

  • aln buffer layer
  • aln film
  • aln layer
  • aln powder
  • aln thin film

  • Selected Abstracts

    Osteoporosis management: a perspective based on bisphosphonate data from randomised clinical trials and observational databases

    S. Boonen
    Summary Aims:, The efficacy of treatments for osteoporosis can be evaluated using a variety of study designs. This article aims to comprehensively review the evidence for bisphosphonate anti-fracture efficacy in postmenopausal women, discussing the strengths and limitations associated with each study method. Methods:, Literature analysis included English-language publications reporting results of randomised controlled trials (RCTs), post hoc analyses, meta analyses and observational studies evaluating the efficacy of alendronate (ALN), ibandronate (IBN), risedronate (RIS) and zoledronate (ZOL), with an initial sample size , 100 patients, and follow-up data for at least 1 year. Results:, Primary and secondary analyses of RCT data suggest differences among bisphosphonates with regard to site-specific anti-fracture efficacy and onset of fracture risk reduction. While some observational studies indicate differences in clinical outcomes among these agents, others report similar effectiveness. ALN and RIS data demonstrate sustained fracture protection for up to 10 and 7 years of treatment respectively. The efficacy of IBN and ZOL has been evaluated for up to 3 and 5 years respectively. Conclusions:, Understanding of the benefits of bisphosphonate treatment can be maximised by evaluating complementary data from RCTs and observational database studies. Fracture risk reduction with bisphosphonates is shown in RCTs and in real-world clinical settings. [source]

    Biological characteristics of breast cancer at the primary tumour and the involved lymph nodes

    E. Dikicioglu
    Summary Diminished oestrogen receptor (ER) expression in the involved axillary lymph nodes (ALN) in breast cancer compared with the primary tumour has been reported in previous studies. We have assessed a wider spectrum of tumour markers (ER, progesterone receptor (PgR), p53, Ki-67 and HER-2/neu) and compared extent and staining intensities at the primary tumour and the involved ALN on specimens of 22 cases with invasive ductal breast cancer. At the involved ALN, both the quantity of positive staining cells and the staining intensities for ER and PgR were decreased (p < 0.001 and p = 0.003, respectively). In contrast, the quantity of positive staining cells (p < 0.004) and the staining intensities for Ki-67 were increased. The differences for HER-2/neu and p53 staining at both sites were insignificant. The immunohistochemical staining properties of both the primary tumour and the ALN metastases showed no correlation with the number of involved ALN (p > 0.05). This study suggested that ALN metastasis might indicate a more unfavourable expression pattern of ER, PgR and Ki-67 in invasive ductal breast cancer. [source]

    Recovery of Trabecular and Cortical Bone Turnover After Discontinuation of Risedronate and Alendronate Therapy in Ovariectomized Rats

    Robyn K Fuchs
    Abstract Alendronate (ALN) and risedronate (RIS) are bisphosphonates effective in reducing bone loss and fractures associated with postmenopausal osteoporosis. However, it is uncertain how long it takes bone turnover to be re-established after treatment withdrawal, and whether this differs between the two drugs. The objective of this study was to determine the time required to re-establish normal bone turnover after the discontinuation of ALN and RIS treatment in an animal model of estrogen-deficiency osteoporosis. Two hundred ten, 6-mo-old female Sprague-Dawley rats were ovariectomized and 6 wk later were randomized into baseline controls (n = 10) and four treatment groups (n = 50/group): vehicle-treated controls (CON; 0.3 ml sterile water), ALN (2.4 ,g/kg), low-dose RIS (RIS low; 1.2 ,g/kg), and high-dose RIS (RIS high; 2.4 ,g/kg). Treatments were administered 3 times/wk by subcutaneous injection. Baseline controls were killed at the initiation of treatment. Other groups were treated for 8 wk, and subgroups (n = 10/ treatment group) were killed 0, 4, 8, 12, and 16 wk after treatment was withdrawn. Static and dynamic histological analyses were performed for cortical (tibial diaphysis) and trabecular (proximal tibia and L4 vertebrae) bone. DXA and mechanical testing was performed on the L5 vertebra. After 8 wk of treatment, trabecular bone turnover rates were significantly suppressed in all drug-treated animals. Trabecular bone formation rate (BFR/BS) remained significantly lower than vehicle in bisphosphonate-treated animals through 12 wk. Sixteen weeks after treatment withdrawal, trabecular BFR/BS in the proximal tibia was re-established in animals treated with RIS but not in animals treated with ALN compared with controls. BMD of the fifth lumbar vertebra remained significantly higher than controls 16 wk after treatment withdrawal in ALN-treated animals but not in RIS-treated animals. Despite reductions in BMD and increases in bone turnover, ultimate force of the fifth lumbar vertebra remained significantly higher in all drug-treated animals through 16 wk after withdrawal. [source]

    Effects of PTH and Alendronate on Type I Collagen Isomerization in Postmenopausal Women With Osteoporosis: The PaTH Study,,

    Patrick Garnero
    Abstract Fracture efficacy of PTH and alendronate (ALN) is only partly explained by changes in BMD, and bone collagen properties have been suggested to play a role. We analyzed the effects of PTH(1,84) and ALN on urinary ,,/,, CTX ratio, a marker of type I collagen isomerization and maturation in postmenopausal women with osteoporosis. In the first year of the previously published PaTH study, postmenopausal women with osteoporosis were assigned to PTH(1,84) (100 ,g/d; n = 119), ALN (10 mg/d; n = 60), or PTH and ALN together (n = 59). We analyzed patients on ALN alone (n = 60) and a similar number of patients assigned to PTH alone (n = 63). During the second year, women on PTH in the first year were reallocated to placebo (n = 31) or ALN (n = 32) and women with ALN continued on ALN. During the first year, there was no significant change in ,,/,, CTX ratio with PTH or ALN. At 24 mo, there was a marked increase of the ,,/,, CTX ratio in women who had received PTH during the first year, followed by a second year of placebo (median: +45.5, p < 0.001) or ALN (+55.2%, p < 0.001). Conversely, the ,,/,, CTX ratio only slightly increased (+16%, p < 0.05) after 2 yr of continued ALN. In conclusion, treatment with PTH(1,84) for 1 yr followed by 1 yr of placebo or ALN may be associated with decreased type I collagen isomerization. The influence of these biochemical changes of type I collagen on bone fracture resistance remains to be studied. [source]

    Pretreatment Levels of Bone Turnover and the Antifracture Efficacy of Alendronate: The Fracture Intervention Trial

    Douglas C Bauer MD
    Abstract The influence of pretreatment bone turnover on alendronate efficacy is not known. In the FIT, we examined the effect of pretreatment bone turnover on the antifracture efficacy of daily alendronate given to postmenopausal women. The nonspine fracture efficacy of alendronate was significantly greater among both osteoporotic and nonosteoporotic women with higher baseline levels of the bone formation marker PINP. Introduction: Previous trials have shown that high bone turnover is associated with greater increases in BMD among bisphosphonate-treated women. The influence of pretreatment bone turnover levels on antifracture efficacy has not been well studied. Materials and Methods: We randomized women 55,80 years of age with femoral neck BMD T scores , ,1.6 to alendronate (ALN), 5,10 mg/day (n = 3105), or placebo (PBO; n = 3081). At baseline, 3495 women were osteoporotic (femoral neck BMD T score , ,2.5 or prevalent vertebral fracture), and 2689 were not osteoporotic (BMD T score > ,2.5 and no prevalent vertebral fracture). Pretreatment levels of bone-specific alkaline phosphatase (BSALP), N-terminal propeptide of type 1 collagen (PINP), and C-terminal cross-linked telopeptide of type 1 collagen (sCTx) were measured in all participants using archived serum (20% fasting). The risk of incident spine and nonspine fracture was compared in ALN- and PBO-treated subjects stratified into tertiles of baseline bone marker level. Results and Conclusions: During a mean follow-up of 3.2 years, 492 nonspine and 294 morphometric vertebral fractures were documented. Compared with placebo, the reduction in nonspine fractures with ALN treatment differed significantly among those with low, intermediate, and high pretreatment levels of PINP levels (p = 0.03 for trend). For example, among osteoporotic women in the lowest tertile of pretreatment PINP (<41.6 ng/ml), the ALN versus PBO relative hazard for nonspine fracture was 0.88 (95% CI: 0.65, 1.21) compared with a relative hazard of 0.54 (95% CI: 0.39, 0.74) among those in the highest tertile of PINP (>56.8 ng/ml). Results were similar among women without osteoporosis at baseline. Although they did not reach statistical significance, similar trends were observed with baseline levels of BSALP. Conversely, spine fracture treatment efficacy among osteoporotic women did not differ significantly according to pretreatment marker levels. Spine fracture treatment efficacy among nonosteoporotic women was related to baseline BSALP (p = 0.05 for trend). In summary, alendronate nonspine fracture efficacy is greater among both osteoporotic and nonosteoporotic women with high pretreatment PINP. If confirmed in other studies, these findings suggest that bisphosphonate treatment may be most effective in women with elevated bone turnover. [source]

    Suppressed Bone Turnover by Bisphosphonates Increases Microdamage Accumulation and Reduces Some Biomechanical Properties in Dog Rib

    Tasuku Mashiba
    Abstract It has been hypothesized that suppression of bone remodeling allows microdamage to accumulate, leading to increased bone fragility. This study evaluated the effects of reduced bone turnover produced by bisphosphonates on microdamage accumulation and biomechanical properties of cortical bone in the dog rib. Thirty-six female beagles, 1,2 years old, were divided into three groups. The control group (CNT) was treated daily for 12 months with saline vehicle. The remaining two groups were treated daily with risedronate (RIS) at a dose of 0.5 mg/kg per day or alendronate (ALN) at 1.0 mg/kg per day orally. After sacrifice, the right ninth rib was assigned to cortical histomorphometry or microdamage analysis. The left ninth rib was tested to failure in three-point bending. Total cross-sectional bone area was significantly increased in both RIS and ALN compared with CNT, whereas cortical area did not differ significantly among groups. One-year treatment with RIS or ALN significantly suppressed intracortical remodeling (RIS, 53%; ALN, 68%) without impairment of mineralization and significantly increased microdamage accumulation in both RIS (155%) and ALN (322%) compared with CNT. Although bone strength and stiffness were not significantly affected by the treatments, bone toughness declined significantly in ALN (20%). Regression analysis showed a significant nonlinear relationship between suppressed intracortical bone remodeling and microdamage accumulation as well as a significant linear relationship between microdamage accumulation and reduced toughness. This study showed that suppression of bone turnover by high doses of bisphosphonates is associated with microdamage accumulation and reduced some mechanical properties of bone. [source]

    Feasibility of Using Peroneal Nerve Recordings for Deriving Stimulation Timing in a Foot Drop Correction System

    NEUROMODULATION, Issue 1 2003
    Morten Hansen
    Abstract The objective of this research was to demonstrate the potential of using peroneal nerve activity to derive timing control for stimulation in foot drop correction and to attempt recording and stimulation through the same electrode. Two subjects were implanted with cuff electrodes on the peroneal nerve. An input domain was derived from the recorded electroneurogram (ENG) and fed to a detection algorithm based on an Adaptive Logic Network (ALN) for predicting stimulation timing. A switching circuit was furthermore built for switching between stimulator and recorder for combined use of the cuff electrode. The detection was successful, but the accuracy depended on the signal to noise ratio of the recorded ENG. The switching circuit successfully allowed for simultaneous recording and stimulation through the same cuff electrode. We conclude that the peroneal nerve can potentially be used to record sensory information for derivation of a stimulator control signal in a foot drop application, while at the same time being stimulated to activate foot dorsiflexors. [source]

    Real Time Foot Drop Correction using Machine Learning and Natural Sensors

    NEUROMODULATION, Issue 1 2002
    Morten Hansen MScEE
    Abstract The objective of this study was to investigate and test a real time system implemented for Functional Electrical Stimulation (FES) assisted foot drop correction, deriving control timing from signals recorded from a peripheral sensory nerve. A hemiplegic participant was attached with a cuff electrode on the sural nerve connected to a telemetry controlled implanted neural amplifier, and a stimulation cuff electrode on the peroneal nerve connected to an implanted stimulator. An input domain was derived from the recorded electroneurogram (ENG) and fed to a detection algorithm based on an Adaptive Logic Network (ALN) for controlling the timing of the peroneal stimulation. The detection system was tested in real time over a period of 392 days, covering a variety of walking tasks. The detection system's ability to detect heel strike and foot lift without errors and to detect the difference between walking and standing proved to be stable for the duration of the study. We conclude that using ALNs and natural sensors provide a stable and accurate control signal for FES foot drop correction. [source]

    Abomasal lymph node responses to Haemonchus contortus intestinal antigens established in kid goats by infection or immunization with intestinal antigens

    Douglas P. Jasmer
    SUMMARY Immune responses to Haemonchus contortus intestinal antigens were evaluated using abomasal lymph node (ALN) lymphocytes from kid goats protected against challenge infection by immunization with parasite intestinal antigen, and from kids that were challenged after immunization with ovalbumin. ALN lymphocytes from the intestinal antigen-immunized group produced significantly higher antibody levels against intestinal antigens than the ovalbumin group, supporting the theory that immunization contributed to that ALN response. In contrast, intestinal lysates and membrane enriched preparations from intestinal cells stimulated significant proliferation of ALN lymphocytes in both groups. The proliferation was antigen-dependent, since intestinal antigens failed to stimulate proliferation in ALN lymphocytes from unimmunized and uninfected kids. For both the intestinal antigen and ovalbumin immunized groups, CD4+ T lymphocytes predominated in ALN lymphocytes that were stimulated to proliferate by intestinal antigens. The results indicate that H. contortus infection alone can induce ALN lymphocyte responses to intestinal antigens. In contrast to ALN lymphocyte responses, serum antibody against intestinal antigens was generally low to undetectable in ovalbumin-immunized kids following infection. Abomasal mucus from an H. contortus infected lamb was probed with a monoclonal antibody that binds to a periodate sensitive determinant on numerous H. contortus intestinal membrane and secreted proteins. Numerous bands of reactivity were detected, indicating that multiple parasite intestinal antigens were released into abomasal mucus during infection. The results, challenge the general concept that H. contortus intestinal antigens are ,hidden' from the host immune system during an infection. On the contrary, parasite intestinal proteins may be relatively abundant antigens presented to the host during infection. In addition, ALN T lymphocytes appear to provide a more sensitive measure than serum antibody to detect presentation of these antigens to the host immune system. [source]

    Alcoholic neuropathy is clinicopathologically distinct from thiamine-deficiency neuropathy

    ANNALS OF NEUROLOGY, Issue 1 2003
    Haruki Koike MD
    Characteristics of alcoholic neuropathy have been obscured by difficulty in isolating them from features of thiamine-deficiency neuropathy. We assessed 64 patients with alcoholic neuropathy including subgroups without (ALN) and with (ALN-TD) coexisting thiamine deficiency. Thirty-two patients with nonalcoholic thiamine-deficiency neuropathy (TDN) also were investigated for comparison. In ALN, clinical symptoms were sensory-dominant and slowly progressive, predominantly impairing superficial sensation (especially nociception) with pain or painful burning sensation. In TDN, most cases manifested a motor-dominant and acutely progressive pattern, with impairment of both superficial and deep sensation. Small-fiber-predominant axonal loss in sural nerve specimens was characteristic of ALN, especially with a short history of neuropathy; long history was associated with regenerating small fibers. Large-fiber-predominant axonal loss predominated in TDN. Subperineurial edema was more prominent in TDN, whereas segmental de/remyelination resulting from widening of consecutive nodes of Ranvier was more frequent in ALN. Myelin irregularity was greater in ALN. ALN-TD showed a variable mixture of these features in ALN and TDN. We concluded that pure-form of alcoholic neuropathy (ALN) was distinct from pure-form of thiamine-deficiency neuropathy (TDN), supporting the view that alcoholic neuropathy can be caused by direct toxic effect of ethanol or its metabolites. However, features of alcoholic neuropathy is influenced by concomitant thiamine-deficiency state, having so far caused the obscure clinicopathological entity of alcoholic neuropathy. Ann Neurol 2003 [source]

    Language and reading abilities of children with autism spectrum disorders and specific language impairment and their first-degree relatives

    AUTISM RESEARCH, Issue 1 2009
    Kristen A. Lindgren
    Abstract Autism spectrum disorder (ASD) and specific language impairment (SLI) are developmental disorders exhibiting language deficits, but it is unclear whether they arise from similar etiologies. Language impairments have been described in family members of children with ASD and SLI, but few studies have quantified them. In this study, we examined IQ, language, and reading abilities of ASD and SLI children and their first-degree relatives to address whether the language difficulties observed in some children with ASD are familial and to better understand the degree of overlap between these disorders and their broader phenotypes. Participants were 52 autistic children, 36 children with SLI, their siblings, and their parents. The ASD group was divided into those with (ALI, n=32) and without (ALN, n=20) language impairment. Relationships between ASD severity and language performance were also examined in the ASD probands. ALI and SLI probands performed similarly on most measures while ALN probands scored higher. ALN and ALI probands' language scores were not related to Autism Diagnostic Interview,Revised and Autism Diagnostic Observation Schedule algorithm scores. SLI relatives scored lowest on all measures, and while scores were not in the impaired range, relatives of ALI children scored lower than relatives of ALN children on some measures, though not those showing highest heritability in SLI. Given that ALI relatives performed better than SLI relatives across the language measures, the hypothesis that ALI and SLI families share similar genetic loading for language is not strongly supported. [source]

    Dietary fibre on cell proliferation in large bowel mucosal crypts near or away from lymphoid nodules and on mineral bioavailability

    CELL PROLIFERATION, Issue 6 2000
    I. L. Cameron
    The effect of consumption for 24 weeks of different amounts (0%, 5% or 10% w/w) of fermentable (pectin and guar gum) or nonfermentable (cellulose and lignin) dietary fibres on cell proliferation and other parameters in large bowel mucosal crypts was studied in rats. In all 12 dietary groups, the crypts located over the distal aggregate of lymphoid nodules (ALN) had more colchicine arrested metaphase figures per midaxial crypt section (MC) and a longer crypt column height than crypts located three to four cm away from this ALN. These differences are attributed to the tropic influence of nodular cells in the ALN. Consumption of fermentable fibre decreased pH in the lumen of the caecum, and glucose, Zn and Cu in serum but increased Ca and Mg in serum. The decrease in caecal pH and serum glucose was significantly correlated with a decrease in MC. Increased intake of the nonfermentable fibre types increased faecal bulk but had no significant correlation with the other measured crypt parameters. Multiple regression analyses was used to model the relationships between the mucosal crypt criterion variables and the two measured predictor variables, caecal pH and serum glucose. Relationships between dietary fibre, ALN, MC, bioavailability of dietary minerals and risk of colorectal cancer are discussed. [source]

    Effect of AlN doping on the growth morphology of SiC

    N. B. Singh
    Abstract AlN doped SiC films were deposited on on-axis Si-face 4H-SiC (0001) substrates by the physical vapor transport (PVT) method. Thick film in the range of 20 ,m range was grown and morphology was characterized. Films were grown by physical vapor deposition (PVD) in a vertical geometry in the nitrogen atmosphere. We observed that nucleation occurred in the form of discs and growth occurred in hexagonal geometry. The X-ray studies showed (001) orientation and full width of half maxima (FWHM) was less than 0.1 indicating good crystallinity. We also observed that film deposited on the carbon crucible had long needles with anisotropic growth very similar to that of pure AlN. Some of the needles grew up to sizes of 200 ,m in length and 40 to 50 ,m in width. It is clear that annealing of SiC-AlN powder or high temperature physical vapor deposition produces similar crystal structure for producing AlN-SiC solid solution. SEM studies indicated that facetted hexagons grew on the top of each other and coarsened and merged to form cm size grains on the substrate. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Beneficial Effects of AlN as Sintering Aid on Microstructure and Mechanical Properties of Hot-pressed ZrB2,

    F. Monteverde
    Higher density of ZrB2 ceramics than with the pure material is achieved when 4.6,% of aluminum nitride are added before hot-pressing as a sintering aid. AlN supports densification and prevents grain coarsening, mainly by virtue of its ability to remove the boron oxide layer that otherwise covers ZrB2 particles. The new material (see Figure for an SEM image of a polished section) has outstanding mechanical properties, e.g. strength values of 600 and 200 MPa at 25 and 1500,C. [source]

    Heat-Transport Mechanisms in Superlattices

    Yee Kan Koh
    Abstract The heat transport mechanisms in superlattices are identified from the cross-plane thermal conductivity , of (AlN)x,(GaN)y superlattices measured by time-domain thermoreflectance. For (AlN)4.1 nm,(GaN)55,nm superlattices grown under different conditions, , varies by a factor of two; this is attributed to differences in the roughness of the AlN/GaN interfaces. Under the growth condition that gives the lowest ,, , of (AlN)4 nm,(GaN)y superlattices decreases monotonically as y decreases, ,,=,6.35,W m,1 K,1 at y,=,2.2,nm, 35 times smaller than , of bulk GaN. For long-period superlattices (y,>,40,nm), the mean thermal conductance G of AlN/GaN interfaces is independent of y, G,,,620 MW m,2 K,1. For y,<,40,nm, the apparent value of G increases with decreasing y, reaching G,,,2 GW m,2 K,1 at y,<,3,nm. MeV ion bombardment is used to help determine which phonons are responsible for heat transport in short period superlattices. The thermal conductivity of an (AlN)4.1 nm,(GaN)4.9,nm superlattice irradiated by 2.3 MeV Ar ions to a dose of 2,,1014 ions cm,2 is reduced by <35%, suggesting that heat transport in these short-period superlattices is dominated by long-wavelength acoustic phonons. Calculations using a Debye-Callaway model and the assumption of a boundary scattering rate that varies with phonon-wavelength successfully capture the temperature, period, and ion-dose dependence of ,. [source]

    Preparation of Oriented Aluminum Nitride Thin Films on Polyimide Films and Piezoelectric Response with High Thermal Stability and Flexibility

    M. Akiyama
    Abstract c -Axis oriented aluminum nitride (AlN) thin films are successfully prepared on amorphous polyimide films by radiofrequency magnetron reactive sputtering at room temperature. Structural analysis shows that the AlN films have a wurtzite structure and consist of c -axis oriented columnar grains about 100,nm wide. The full width at half maximum of the X-ray diffraction rocking curves and piezoelectric coefficient d33 of the AlN films are 8.3 and 0.56,pC,N,1, respectively. The AlN films exhibit a piezoelectric response over a wide temperature range, from ,196 to 300,C, and can measure pressure within a wide range, from pulse waves of hundreds of pascals to 40,MPa. Moreover, the sensitivity of the AlN films increases with the number of times it was folded, suggesting that we can control the sensitivity of the AlN films by changing the geometric form. These results were achieved by a combination of preparing the oriented AlN thin films on polyimide films, and sandwiching the AlN and polymer films between top and bottom electrodes, such as Pt/AlN/polyimide/Pt. They are thin (less than 10,,m), self powered, adaptable to complex contours, and available in a variety of configurations. Although AlN is a piezoelectric ceramic, the AlN films are flexible and excellent in mechanical shock resistance. [source]

    Controlled Growth of High-Quality ZnO-Based Films and Fabrication of Visible-Blind and Solar-Blind Ultra-Violet Detectors

    ADVANCED MATERIALS, Issue 45 2009
    Xiaolong Du
    Abstract ZnO is a wide-bandgap (3.37,eV at room temperature) oxide semiconductor that is attractive for its great potential in short-wavelength optoelectronic devices, in which high quality films and heterostructures are essential for high performance. In this study, controlled growth of ZnO-based thin films and heterostructures by molecular beam epitaxy (MBE) is demonstrated on different substrates with emphasis on interface engineering. It is revealed that ultrathin AlN or MgO interfacial layers play a key role in establishing structural and chemical compatibility between ZnO and substrates. Furthermore, a quasi-homo buffer is introduced prior to growth of a wurtzite MgZnO epilayer to suppress the phase segregation of rock-salt MgO, achieving wide-range bandgap tuning from 3.3 to 4.55,eV. Finally, a visible-blind UV detector exploiting a double heterojunction of n-ZnO/insulator-MgO/p-Si and a solar-blind UV detector using MgZnO as an active layer are fabricated by using the growth techniques discussed here. [source]

    A Chemical Solution Approach to Epitaxial Metal Nitride Thin Films,

    ADVANCED MATERIALS, Issue 2 2009
    Hongmei Luo
    Epitaxial metal nitride films are prepared using a general chemical solution approach. A polymer-assisted deposition to prepare epitaxial cubic TiN, metastable AlN, and ternary nitride Ti1,xAlxN films is demonstrated. The structural, optical and electrical properties of the films are investigated, and may be of interest for many technological applications. [source]

    Preparation and Thermal Ablation Behavior of HfB2,SiC-Based Ultra-High-Temperature Ceramics Under Severe Heat Conditions

    Xinghong Zhang
    HfB2,SiC-based ultra-high-temperature ceramics with aluminum nitride (AlN) as a sintering aid were hot pressed at 1850C. The sinterability and mechanical properties were investigated and compared with the composite without a sintering aid. It was shown that the addition of AlN greatly improved the powder sinterability and enabled the production of a nearly full-dense composite. The mechanical properties, especially the flexural strength, were enhanced remarkably through the improvement in the sinterability and microstructure. The oxidation resistance of a composite doped with 10 vol% AlN was evaluated by a plasma arc heater and the ablation mechanism was discussed. [source]

    Near-Net Shape ,-Si4Al2O2N6 Parts by Hydrolysis Induced Aqueous Gelcasting Process

    Ibram Ganesh
    In this paper, a new net-shaping process, an hydrolysis-induced aqueous gelcasting (GC) (GCHAS) has been reported for consolidation of ,-Si4Al2O2N6 ceramics from aqueous slurries containing 48,50 vol%,-Si3N4, ,-Al2O3, AlN, and Y2O3 powders mixture. Dense ceramics of same composition were also consolidated by aqueous GC and hydrolysis assisted solidification routes. Among three techniques used, the GCHAS process was found to be superior for fabricating defect-free thin wall ,-Si4Al2O2N6 crucibles and tubes. Before use, the as purchased AlN powder was passivated against hydrolysis. The sintered ,-Si4Al2O2N6 ceramics exhibited comparable properties with those reported for similar materials in the literature. [source]

    Water-Based Method for Processing Aluminum Oxynitride (AlON)

    Lior Miller
    A water-based method for producing aluminum oxynitride (AlON) green bodies with a relatively high density is described. While alcohol is usually the medium for ball milling, this approach utilizes water to form a rigid network of aluminum hydroxide in Al2O3,AlN preforms. Al2O3,AlN preforms were prepared by four different routes based either on alcohol or water-based slips, and underwent identical sintering procedures. Samples prepared using the water-based method and pressure filtration reached a green density of 67%, compared with 52% and 47% for samples prepared from alcohol-based slips and formed using pressure filtration and dry pressing, respectively. [source]

    Blue-emitting AlN:Eu2+ Powder Phosphor Prepared by Spark Plasma Sintering

    Hyoung-SeoK Do
    Blue-emitting AlN:Eu2+ powder phosphor was synthesized by spark plasma sintering (SPS) using AlN, Si3N4, and Eu2O3 as the starting materials, and its luminescence properties were investigated. A single-phase Eu- and Si-co-doped AlN powder was successfully fabricated by SPS in the range of 1650,1800C for 5 min. The AlN:Eu2+ obtained exhibited a strong blue emission at 480 nm under the excitation of ,exc=340 nm and an electron beam. The highest photoluminescence intensity was observed in the phosphor sintered at 1700C, which was comparable to that of the phosphor prepared by gas pressure sintering at 1750C for 4 h. [source]

    Thermal Shock Resistance of an AlN,BN,SiC Ceramic

    Andrew A. Buchheit
    Mechanical and thermal properties of AlN,BN,SiC (ABS) ceramics were used to calculate the R, R,, and R,, thermal shock parameters. The R parameter values ranged from ,400 to 450C. Specimens were thermal shocked by water quenching and the critical quench temperatures (,TC) were compared with those of a baseline SiC composition. The behavior of the ABS was predicted by R parameter calculations while the behavior of the baseline material was predicted by the R, calculations due to its higher thermal conductivity (87 W(mK) -1) as compared with the ABS materials (,30 W(mK),1). The highest critical quench temperature for ABS was ,415C with the lowest at 360C, while the critical quench temperature for the baseline material was 450C. Using temperature dependent data over an appropriate temperature range (room temperature to the predicted ,TC), the R parameters of the ABS materials were within 15C of predictions. The baseline material was ,1.7 times higher than predicted and this was attributed to the high-thermal conductivity of the material resulting in soft thermal shock during quench testing. [source]

    Aqueous Colloidal Processing of ZTA Composites

    Susana M. Olhero
    Two different zirconia-alumina composites, ZTA-30 (70 wt% Al2O3+30 wt% ZrO2) and ZTA-60 (40 wt% Al2O3+60 wt% ZrO2), with potential for orthopedic applications, were processed in aqueous media and consolidated by slip casting (SC), hydrolysis-assisted solidification (HAS), and gelcasting (GC) from suspensions containing 50 vol% solids loading. For comparison purposes, the same ceramic compositions were also consolidated by die pressing of freeze-dried granules (FG). In the HAS process, 5 wt% of Al2O3 in the precursor mixture was replaced by equivalent amounts of AlN to promote the consolidation of the suspensions. Ceramics consolidated via GC exhibited higher green (three-point bend) strengths (,17 MPa) than those consolidated by other techniques. Further, these ceramics also exhibited superior fracture toughness and flexural strength properties after sintering for 1 h at 1600C in comparison with those consolidated by other techniques, including conventional die pressing (FG). [source]

    Thermodynamic Studies on the AlN Sintering Powders Treated With Phosphate Species

    Susana Maria Olhero
    The processing of aluminum nitride (AlN) ceramics in aqueous media requires the use of a surface layer to protect the surface of the particles against hydrolysis. This surface layer might influence the densification, affecting the reactions between AlN and sintering additives. The present paper describes a thermodynamic and experimental approach to evaluate the effects of a phosphate-based protecting surface layer on the densification of AlN in the presence of YF3,CaF2 as sintering aids, and to predict the densification behavior during sintering using thermodynamic assessments. Based on thermodynamic calculations and the measured weight loss of the samples during heating to sintering temperature, the chemical reactions occurring during firing were proposed. The proposed reactions were related to the experimental results as well as the final properties of the AlN samples, namely, thermal conductivity, microstructure, secondary phases, and density. [source]

    Novel Fabrication Route to Al2O3,TiN Nanocomposites Via Spark Plasma Sintering

    Lianjun Wang
    A novel method for the preparation of Al2O3,TiN nanocomposites was developed. A mixture of TiO2, AlN, and Ti powder was used as the starting material to synthesize the Al2O3,TiN nanocomposite under 60 MPa at 1400C for 6 min using spark plasma sintering. X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy were used for detailed microstructural analysis. Dense (up to 99%) nanostructured Al2O3,TiN composites were successfully fabricated, the average grain size being less than 400 nm. The fracture toughness (KIC) and bending strength (,b) of the nanostructured Al2O3,TiN composites reached 4.220.20 MPam1/2 and 74628 MPa, respectively. [source]

    Preparation and Properties of Porous Aluminum Nitride,Silicon Carbide Composite Ceramics

    Eirik Hagen
    Microporous two-phase AlN,SiC composites were prepared using Al4C3 and either Si (N2 atmosphere) or Si3N4 (Ar atmosphere) as precursors. The reaction mechanisms of the two synthesis routes and the effect of processing conditions on reaction rate and the material microstructures were demonstrated. The exothermic reaction between Si and Al4C3 under N2 atmosphere was shown to be a simple processing route for the preparation of porous two-phase AlN,SiC materials. The homogeneous two-phase AlN,SiC composites had a grain size in the range of 1,5 ,m, and the porosity varied in the range of 36%,45%. The bending strength was 50,60 MPa, in accordance with the high porosity. [source]

    Photoluminescence of Cerium-Doped ,-SiAlON Materials

    Rong-Jun Xie
    Cerium-doped ,-SiAlON (MxSi12,(m+n)Alm+nOnN16,n) materials have been prepared by gas-pressure sintering and post-hot-isostatic-press (HIP) annealing, using four powder mixtures of ,-Si3N4, AlN, and either (i) CeO2, (ii) CeO2+ Y-,-SiAlON seed, (iii) CeO2+ Y2O3, or (iv) CeO2+ CaO. Cerium-containing CeAl(Si6,zAlz)(N10,zOz) (JEM) phase, rather than Ce-,-SiAlON phase, forms in the sample with only CeO2, whereas a single-phase ,-SiAlON generates in samples with dual doping (CeO2+ Y2O3 and CeO2+ CaO). On ultraviolet-light excitation, JEM gives one broad emission band with maximum at 465 nm and a shoulder at 498 nm; ,-SiAlON shows an intense and broad emission band that peaks at 500 nm. The unusual long-wavelength emissions in JEM and ,-SiAlON are due to increases in the nephelauxetic effect and the ligand-field splitting of the 5d band, because the coordination of Ce3+ in JEM and ,-SiAlON is nitrogen enriched. [source]

    Effect of Controlling Parameters on the Reaction Sequences of Formation of Nitrogen-Containing Magnesium Aluminate Spinel from MgO, Al2O3, and AlN

    Siddhartha Bandyopadhyay
    The reaction sequences of the formation of nitrogen-containing magnesium aluminate spinel from MgO, Al2O3, and AlN were investigated as a function of temperature through dilatometric study and as a function of time through isothermal heat treatments. The natures of reactions are described through the appearance of phases in conjunction with densification behavior and the change in lattice parameter of the spinel phase. Although the dilatometric study provides the detail insights of the formation sequence, the isothermal runs reveal new information about the differential rate of reactivity of the reacting species that suggested a tentative controlling mechanism. Through the initial formation of magnesium aluminate, oxygen-rich solid solution (MgAlON) forms, which ultimately reacts with the rest of AlN to reach its nominal composition. Nitrogen diffusion through MgAlON lattice seems to be rate controlling. [source]

    A New Aluminum Coordination Site in Si-C-Al-N-(O) Ceramics

    Xudong Li
    A variety of Si-C-Al-N-(O) ceramics with different AlN and SiC contents were prepared by pyrolysis of Si-Al-C-O precursors at 1700C in nitrogen. In those ceramics containing small amounts of aluminum, a new 27Al MAS NMR peak at 134.3 ppm was found. The existence of this peak is discussed in relation to recent findings in aluminum-containing complex ceramic systems. [source]