A comparison of product yields and inorganic content in process streams following thermal hydrolysis and hydrothermal processing of microalgae, manure and digestate.

Thermal hydrolysis and hydrothermal processing show promise for converting biomass into higher energy density fuels. Both approaches facilitate the extraction of inorganics into the aqueous product. This study compares the behaviour of microalgae, digestate, swine and chicken manure by thermal hydrolysis and hydrothermal processing at increasing process severity. Thermal hydrolysis was performed at 170°C, hydrothermal carbonisation (HTC) was performed at 250°C, hydrothermal liquefaction (HTL) was performed at 350°C and supercritical water gasification (SCWG) was performed at 500°C. The level of nitrogen, phosphorus and potassium in the product streams was measured for each feedstock. Nitrogen is present in the aqueous phase as organic-N and NH3-N. The proportion of organic-N is higher at lower temperatures. Extraction of phosphorus is linked to the presence of inorganics such as Ca, Mg and Fe in the feedstock. Microalgae and chicken manure release phosphorus more easily than other feedstocks.

Effect of process conditions on the steam reforming of ethanol with a nano-Ni/SiO2 catalyst.

In this paper, a nano-Ni/SiO2 catalyst was prepared by a sol-gel method and tested for hydrogen production from ethanol steam reforming using a two-stage fixed-bed reaction system. The reaction conditions, such as reaction temperature, water/ethanol ratio and sample feeding rate, were investigated with the prepared nano-Ni/SiO2 catalyst. Brunauer-Emmett-Teller surface area and porosity, temperature-programmed oxidation, X-ray diffraction and focused ion beam (FIB)/scanning electron microscopy were used in this work to analysis the fresh and/or reacted catalysts. An extended catalyst stability test for ethanol steam reforming with the Ni/SiO2 catalyst was carried out at a reaction temperature of 600 degrees C, when the water/ethanol ratio was kept at 3.5 and sample feeding rate was 4.74 g h(-1). The results showed that a stabilized gas and hydrogen production was obtained with a potential H2 production of about 40 wt.%. Increasing the reaction temperature during ethanol steam reforming with the Ni/SiO2 catalyst resulted in an increase of gas and hydrogen production. The gas yield was slightly reduced when the water/ethanol ratio was increased from 2.0 to 3.5. However, the potential H2 production was increased. The investigation of the sample feeding rate showed that the gas production per hour was increased due to the higher sample feeding rate, but the potential H2 production was reduced.

Two stages catalytic pyrolysis of refuse derived fuel: production of biofuel via syncrude.

Thermo-catalytic pyrolysis of refuse derived fuels with different catalysts had been conducted in a two stages process due to its important potential value as fuel. The first stage was a pure thermal pyrolysis in a horizontal tubular reactor with feed rate of 0.5kg hourly. The second stage was a semi-batch process in the presence of catalysts. Results showed that the tested catalysts significantly have affected the quantity of products. E.g. gas yield could be increased with 350% related to the catalyst free case using ZSM-5, while that of pyrolytic oil was 115% over Y-zeolite. Gases consisted of mainly CO and CO(2) obtained from the tubular reactor, while dominantly hydrocarbons from the second stage. Ni-Mo-catalyst and Co-Mo-catalyst had shown activity in pyrolytic oil upgrading via in-situ hydrogenation-dehydrogenation reactions. Sulphur, nitrogen and chlorine level in pyrolytic oils could be significantly declined by using of catalysts.

Association between walking distance and percentiles of body mass index in older and younger men.

OBJECTIVE: To assess the association of weekly walking distance to body weight and waist circumference in elderly (age > or =75 years), senior (55< or = age <75 years), middle-aged (35< or = age <55 years), and younger men (18< or = age <35 years old). DESIGN: Cross-sectional analyses of baseline questionnaires from 7082 male participants of the National Walkers' Health Study. RESULTS: Standard regression analyses showed that body mass index (BMI) was inversely and significantly associated with walking distance (kg/m(2) per km/week) in elderly (slope (SE): -0.032 (0.008)), senior (-0.045 (0.005)) and middle-aged men (-0.037 (0.007)), as were their waist circumferences (-0.090 (0.025), -0.122 (0.012) and -0.091 (0.015) cm per km/week, respectively), and that these slopes remained significant when adjusted statistically for reported weekly servings of meat, fish, fruit and alcohol. However, percentile regression analyses showed that the declines in BMI per km/week walked were greater at the higher than the lower percentiles of the BMI distribution. In men > or =74 years old the decline per km walked was 4.9-fold greater among the heaviest men (that is, 90th BMI percentile; -0.076 kg/m(2) per km/week) than among the leanest men (that is, 10th BMI percentile; -0.015 kg/m(2) per km/week). The differences in slope at the 90th compared to the 10th BMI percentile were 5.4-fold among men 55-74 years old and sixfold among men 35-54 years old. Per km/week walked, the declines at the 90th percentile of waist circumference were also greater than at its 10th percentile, and intermediate for percentiles in between. Whereas standard regression analyses suggest that the average declines in BMI per km/week walked reported here are consistent with those reported previously per km/week run in male runners 35-54 years old (-0.036 (0.001) kg/m(2) per km/week) and > or =50 years old (-0.038 (0.001) kg/m(2) per km/week), percentile regression analyses showed that when adjusted to the leaner body weights of the runners the declines per km walked were between 49% and 59% less for walkers than runners. CONCLUSIONS: Declines in BMI and waist circumferences with walking distance depend upon the percentile of the BMI distribution, with the decline per km walked being significantly greater among heavier men.

Pyrolysis of waste electrical and electronic equipment: effect of antinomy trioxide on the pyrolysis of styrenic polymers.

This work has investigated the effect that antimony trioxide has on the pyrolysis of styrenic polymers and the effect that different types of brominated flame retardants used in plastics have on the composition of the pyrolysis products. Brominated high impact polystyrene (Br-HIPS) which contained either 5% or 0% antimony trioxide and either decabromodiphenyl oxide (DDO) or decabromodiphenyl ethane (DDE) was pyrolysed in a fixed bed reactor at 430 degrees C. Some experiments on the fixed bed reactor involved mixing the Br-HIPS with polystyrene. The gaseous products were analysed by GC-FID and GC-TCD and it was found that antimony trioxide caused an increase in the proportion of ethane and ethene and suppressed the proportion of butane and butene. When DDE was the flame retardant increased proportions of ethane and ethene were found in the pyrolysis gas compared to when DDO used. When polystyrene was mixed with the Br-HIPS it suppressed the trends observed in the gas composition during the pyrolysis of Br-HIPS. The pyrolysis oils were characterised using FT-IR, GC-MS, GC-FID, and GC-ECD. It was found that the plastic which did not contain antimony trioxide pyrolysed to form mainly toluene, ethylbenzene, styrene, cumene, and alpha-methylstyrene. The oils produced from the pyrolysis of the plastic that contained antimony trioxide did not contain any styrene or alpha-methylstyrene, but instead contained greater concentrations of ethylbenzene and cumene. The absence of styrene and alpha-methylstyrene from the pyrolysis oil occurred even when the Br-HIPS was mixed with polystyrene. GC-ECD analysis of the oils showed that the plastics which did not contain antimony trioxide pyrolysed to form (1-bromoethyl)benzene, which was totally absent from the pyrolysis oils when antimony trioxide was present in the plastic.

Self-selection contributes significantly to the lower adiposity of faster, longer-distanced, male and female walkers.

OBJECTIVE: Cross-sectional studies show that active individuals are leaner than their sedentary counterparts. The purpose of this paper is to determine the extent that this is due to self-selection bias, specifically to initially leaner men and women choosing to exercise longer and more intensely. METHODS: Walking quantity (weekly distance) and intensity (speed) were compared to current body mass index (BMI) (BMI(current)) and BMI at the start of walking (BMI(starting)) in 20,353 women and 5174 men who on average had walked regularly for exercise for 7.2 and 10.6 years, respectively. RESULTS: The relationships of both BMI(current) and BMI(starting) to both distance and intensity were nonlinear (convex). On average, BMI(starting) explained >70% of the association between BMI(current) and intensity, and 40 and 17% of the associations between BMI(current) and distance in women and men, respectively. Although the declines in BMI(current) with distance and intensity were greater among fatter individuals than leaner individuals, the portions attributable to BMI(starting) remained relatively constant regardless of fatness. Thus, self-selection bias accounted for most of the decline in BMI with walking intensity and smaller, albeit significant, proportions of the decline with distance. CONCLUSION: Although walking intensity and walking distance are both strongly associated with greater leanness, intensity is less likely to be causally related to leanness than is distance, and the latter should be encouraged for reversing or preventing weight gain.

Destruction of environmental organic pollutants by supercritical water oxidation.

The supercritical water oxidation of two environmental pollutants in the form of diesel fuel and two waste landfill leachate samples have been examined in relation to sub-critical and supercritical water oxidation conditions. Supercritical water oxidation involves reactions in an aqueous fluid phase under conditions below and around the critical point of water (T(c) = 374 degrees C, P(c) = 22.1 MPa). Experiments were carried out using a batch autoclave reactor at temperatures between 300 degrees C and 380 degrees C corresponding to pressures between 10.5 MPa and 22.8 MPa. The oxidative decomposition of the diesel fuel, which was loaded onto a sand matrix to simulate a contaminated land sample, was determined in relation to process conditions. The results showed that almost complete destruction of the components of the diesel fuel could be achieved. In addition, intermediate oxygenated compounds were formed and identified. The level of loading of the diesel fuel onto the sand matrix influenced the level of compound decomposition and the amount of intermediate oxygenated compounds formed. The characteristics of the waste landfill leachates were determined and were shown to be highly chemically complex. The high chloride concentration of the leachate resulted in significant corrosion of the reactor. However, almost complete oxidation of the organic components of the leachate could be achieved under supercritical water oxidation conditions.

Experience-dependent amelioration of motor impairments in adulthood following neonatal medial frontal cortex injury in rats is accompanied by motor map expansion.

One of the most common, and disruptive, neurological symptoms following neonatal brain injury is a motor impairment. Neonatal medial frontal cortical lesions in rats produce enduring motor impairments, and it is thought that lesion-induced abnormal cortical morphology and connectivity may underlie the motor deficits. In order to investigate the functional consequences of the lesion-induced anatomical abnormalities in adulthood, we used intracortical microstimulation to determine the neurophysiologic organization of motor maps within the lesion hemisphere. In addition, groups of neonatal lesion rats were given reach training or complex housing rehabilitation in adulthood and then mapped with intracortical microstimulation. The results demonstrate that neonatal medial frontal cortex lesions produce motor deficits in adulthood that are associated with abnormal motor maps. Further, adult behavioral treatment promoted partial recovery that was supported by reorganization of the motor maps whereby there were increases in the size of the forelimb motor maps. The experience-induced expansion of the forelimb motor maps in adulthood provides a neural mechanism for the experience-dependent improvements in motor performance.

Investigation of SO2, HCl and NOx, control from waste incinerators using a novel additive in a pilot scale reactor.

A pilot scale experimental investigation of the use of a novel additive, calcium magnesium acetate, for the simultaneous control of SO2, HCl and NOx has been carried out. The pilot scale reactor simulated the furnace and flue gas conditions of a typical large scale waste incinerator and was a vertical 4m high reactor operated at 80 kW. The calcium magnesium acetate was added as a wet spray to the reactor at temperatures above 750 degrees C. The influence of the calcium magnesium acetate dose rate was investigated on the simultaneous removal of SO2, HCl and NOx. Maximum reductions were achieved at a Ca/S ratio (or Ca/Cl ratio) of 2.5 and were, 70% for SO2, 45% for HCl and 18% for NOx for each of the pollutant gases respectively.

Long-term potentiation is associated with changes in synaptic ultrastructure in the rat neocortex.

Long-term potentiation (LTP) in the sensorimotor cortex of freely moving rats has been associated with changes in dendritic morphology and dendritic spine density. The current research examined changes in synaptic number and ultrastructure associated with LTP in this cortical region. LTP was induced over a 1 h period and the animals were sacrificed 2 h after the initial stimulation of the LTP group. Synapses within the terminal area of the apical dendrites from layer III pyramidal neurons were quantified by determining the total number of synapses per neuron, the number of excitatory and inhibitory contacts, number of synapses with different curvature subtypes, number of perforated synapses, and synaptic length. Several changes in synaptic morphology of excitatory synapses were revealed but no overall increase in the number of synapses per neuron was evident. Specifically, the induction of LTP was associated with an increased number of excitatory perforated and concave shaped synapses. Increased numbers of perforated concave synapses were also found to be significantly correlated with the degree of potentiation in the LTP animals. These and previous results suggest similar synaptic changes in both the cortex and hippocampus during the early phases of LTP maintenance and distinct synaptic changes during later phases of LTP maintenance.

The effects of changing exercise levels on weight and age-related weight gain.

OBJECTIVE: To determine prospectively whether physical activity can prevent age-related weight gain and whether changing levels of activity affect body weight. DESIGN/SUBJECTS: The study consisted of 8,080 male and 4,871 female runners who completed two questionnaires an average (+/-standard deviation (s.d.)) of 3.20+/-2.30 and 2.59+/-2.17 years apart, respectively, as part of the National Runners' Health Study. RESULTS: Changes in running distance were inversely related to changes in men's and women's body mass indices (BMIs) (slope+/-standard error (s.e.): -0.015+/-0.001 and -0.009+/-0.001 kg/m(2) per Deltakm/week, respectively), waist circumferences (-0.030+/-0.002 and -0.022+/-0.005 cm per Deltakm/week, respectively) and percent changes in body weight (-0.062+/-0.003 and -0.041+/-0.003% per Deltakm/week, respectively, all P<0.0001). The regression slopes were significantly steeper (more negative) in men than women for DeltaBMI and Delta%body weight (P<0.0001). A longer history of running diminished the impact of changing running distance on men's weights. When adjusted for Deltakm/week, years of aging in men and years of aging in women were associated with increases of 0.066+/-0.005 and 0.056+/-0.006 kg/m(2) in BMI, respectively, increases of 0.294+/-0.019 and 0.279+/-0.028% in Delta%body weight, respectively, and increases of 0.203+/-0.016 and 0.271+/-0.033 cm in waist circumference, respectively (all P<0.0001). These regression slopes suggest that vigorous exercise may need to increase 4.4 km/week annually in men and 6.2 km/week annually in women to compensate for the expected gain in weight associated with aging (2.7 and 3.9 km/week annually when correct for the attenuation due to measurement error). CONCLUSIONS: Age-related weight gain occurs even among the most active individuals when exercise is constant. Theoretically, vigorous exercise must increase significantly with age to compensate for the expected gain in weight associated with aging.

Middle cerebral artery (MCA) stroke produces dysfunction in adjacent motor cortex as detected by intracortical microstimulation in rats.

Middle cerebral artery (MCA) stroke in the rat produces impairments in skilled movements. The lesion damages lateral neocortex but spares primary motor cortex (M1), raising the question of the origin of skilled movement deficits. Here, the behavioral deficits of MCA stroke were identified and then M1 was examined neurophysiologically and neuroanatomically. Rats were trained on a food skilled reaching task then the lateral frontal cortex was damaged by unilateral MCA electrocoagulation contralateral to the reaching forelimb. Reach testing and training on two tasks was conducted over 30 post-surgical days. Later, M1 and the corticospinal tract were investigated using intracortical microstimulation (ICMS), anterograde and retrograde axon tracing. A skilled reaching impairment was observed post-surgery, which partly recovered with time and training. ICMS revealed a diminished forelimb movement representation in MCA rats, but a face representation comparable in size to sham rats. Anterograde and retrograde tract tracing suggest that M1 efferents were intact. Although M1 appears to be in the main anatomically spared after MCA stroke its function as assessed electrophysiologically and behaviorally is disrupted.

Pyrolysis of flame retardant brominated polyester composites.

A series of three flame retardant, thermoset polyester/styrene composite wastes were pyrolysed in a static-bed reactor. The wastes contained different proportions of brominated polyester resin. Higher char and gas yields were observed on the pyrolysis of the brominated samples than for a similar non-brominated sample. The pyrolysis gas composition showed a small, but significant influence of pyrolysis temperature and by the use of brominated resin. In all cases, over 95wt % of the bromine originally present in the composite ended up in the condensable products. Thermo-gravimetric analysis indicated that the presence of brominated polyester resins decreased the temperatures at which the main decomposition region started and the maximum rate of weight loss was observed. The global apparent activation energy of decomposition was between 83 and 97kJ mol(-1).

Vigorous exercise and the population distribution of body weight.

BACKGROUND: While the benefits of vigorous exercise on body weight and regional adiposity are well established, whether these benefits affect equally the highest and lowest portions of the weight distribution have not been previously reported. The impact of exercise on the more extreme body weights and body circumferences is clinically important because these values represent individuals at greatest health risk. METHOD: Self-reported weights and body circumferences from a cross-sectional sample of 7288 male and 2326 female runners were divided into five strata, according to the distances run per week and within each stratum the 5th, 10th, 25th, 50th, 75th, 90th and 95th percentiles were determined. Least-squares regression was then employed at each percentile to determine the dose-response relationship between running distance and adiposity as determined by body mass index (BMI) and self-reported circumferences of the waist, hip and chest. RESULTS: Per kilometer run per week, the associated decline for BMI was three-fold greater at the 95th than at the 5th percentile in men, and six-fold greater at the 95th than the 5th percentile in women (all P<0.001). Reported waist circumference also declined more sharply at the 95th percentile than at the 5th percentile in men (-0.13 +/- 0.02 vs -0.06 +/- 0.01 cm per km/week) and women (-0.18 +/- 0.04 vs -0.05 +/- 0.01 cm per km/week). In women, both hip and chest circumferences declined more sharply per kilometer run at the 95th percentile than at the 5th percentile. CONCLUSIONS: These results are consistent with the hypothesis that running promotes the greatest weight loss specifically in those individuals who have the most to gain from losing weight. Comparisons based on average BMI or average body circumferences are likely to underestimate the health benefits of running because of the J-shaped relationship between adiposity and mortality. Whether the observed cross-sectional associations are primarily due to exercise-induced weight loss or self-selection remains to be determined.

Fluidised bed pyrolysis and catalytic pyrolysis of scrap tyres.

Pyrolysis of scrap tyres was undertaken in a semi-continuous fluidised bed reactor in relation to the temperature of the fluidised bed. Subsequently, a fixed bed of Zeolite catalyst was placed in the freeboard of the reactor. The catalyst temperature was held constant at 500 degrees C and the influence of the temperature of the fluidised bed over the same temperature range as the uncatalysed pyrolysis examined. Two Zeolite catalysts were examined, a Y-type Zeolite catalyst and Zeolite ZSM-5 catalyst of differing pore size and surface activity. The main aim of the work was to examine the production of certain single ring aromatic compounds in the derived pyrolysis oil which are known to be of commercial value. The oils were therefore analysed in detail to determine the concentration of benzene, toluene, xylenes and limonene. In addition, detailed analyses of the derived gases under pyrolysis and catalytic pyrolysis conditions were determined. The influence of the temperature of pyrolysis was to increase the yield of benzene, toluene and xylenes but decrease the yield of limonene. In the presence of the catalyst, the yield of oil was reduced with a consequent increase in the gas yield. Benzene, toluene and xylenes present in the oils showed a significant increase in the presence of both of the catalysts. The two catalysts used, although of differing surface acidities and selective pore sizes, produced similar concentrations of benzene, toluene, xylene and limonene.

Pyrolysis of composite plastic waste.

Several different composite plastics were pyrolysed in a fixed bed reactor at final temperatures between 350 and 800 degrees C. The composites studied were polyester, phenolic, epoxy, vinylester, polypropylene and PET resins, reinforced with glass and/or carbon fibre. The product yields of oil gas and solid residue were determined together with a detailed composition of the derived gases. There was evidence to suggest that calcium carbonate filler, present in the polyester and phenolic composites, decomposed to form carbon dioxide at 800 degrees C, which was subsequently involved in char gasification reactions. Polyester, phenolic and epoxy composites generated highly aromatic, oxygenated condensable products. There was no noticeable correlation between the composition of these products and the final pyrolysis temperature. The tensile strength of recovered glass fibre was lower than that of virgin fibre and decreased markedly as the final pyrolysis temperature increased from 650 to 800 degrees C.

The effect of prolonged packing on the surface hardness of posterior composites.

This study evaluated the effect of four different packing times on the Knoop Hardness Number of three composites (Surefil, Z100 and Spectrum TPH). Ten samples of each composite were prepared for each packing time and 10 readings were made on each sample to produce the KHN. Photomicrographs were made of 147 indentations to determine whether the indentations had routinely been made on porosity-free sites. Statistical analysis was made using two-way ANOVA and least square means. Generally, as the packing time increased, the KHN decreased,and although the indentations appeared to have been made in porosity-free composite, the potential effect of porosities was not discounted. Increasing the packing time for clinical composites may result in a lower KHN and increased clinical wear, which would further increase if also associated with porosities within the composite.

Health effects resulting from exercise versus those from body fat loss.

OBJECTIVE: The purpose of this review was to assess whether body weight confounds the relationships between physical activity and its health benefits. METHODS: The review includes 80 reports from population-based studies (Evidence Category C) of physical activity or fitness and cardiovascular disease (CVD) or coronary heart disease (CHD). RESULTS: Eleven of 64 reports on activity found no relationship between physical activity and disease. Of the remaining 53 reports, 11 did not address the possible confounding effects of body weight, nine cited reasons that weight differences should not explain their observed associations, and 33 statistically adjusted for weight (as required). Only three of these changed their associations from significant to nonsignificant when adjusted. Ten of 16 reports on cardiorespiratory fitness and CHD or CVD used statistical adjustment, and none of these changed their findings to nonsignificant. Population studies show that vigorously active individuals also have higher high-density lipoprotein (HDL)-cholesterol concentration, a major risk factor for CHD and CVD, than sedentary individuals when statistically adjusted for weight. In contrast, intervention studies, which relate dynamic changes in weight and HDL, suggest that adjustment for weight loss largely eliminates the increase in HDL-cholesterol in sedentary men who begin exercising vigorously. Adjusting the cross-sectional HDL-cholesterol differences for the dynamic effects of weight loss eliminates most of the HDL-cholesterol difference between active and sedentary men. CONCLUSION: Population studies show that the lower incidence of CHD and CVD and higher HDL of fit, active individuals are not because of lean, healthy individuals choosing to be active (i.e., self-selection bias). Nevertheless, metabolic processed associated weight loss may be primarily responsible for the HDL differences between active and sedentary men, and possibly also their differences in CHD and CVD.

Physical fitness and activity as separate heart disease risk factors: a meta-analysis.

OBJECTIVE: Public health policies for physical activity presume that the greatest health benefits are achieved by increasing physical activity among the least active. This presumption is based largely on studies of cardiorespiratory fitness. To assess whether studies of cardiorespiratory fitness are germane to physical activity guidelines, we compared the dose-response relationships between cardiovascular disease endpoints with leisure-time physical activity and fitness from published studies. DATA SOURCES: Twenty-three sex-specific cohorts of physical activity or fitness (representing 1,325,004 person-years of follow-up), cited in Tables 4-1 and 4-2 of the Surgeon General's Report. DATA SYNTHESIS: Relative risks were plotted as a function of the cumulative percentages of the samples when ranked from least fit or active, to most fit or active. To combine study results, a weighted average of the relative risks over the 16 physical activity or seven fitness cohorts was computed at every 5th percentile between 5 and 100%. The analyses show that the risks of coronary heart disease or cardiovascular disease decrease linearly in association with increasing percentiles of physical activity. In contrast, there is a precipitous drop in risk occurring before the 25th percentile of the fitness distribution. As a consequence of this drop, there is a significant difference in the risk reduction associated with being more physically active or physically fit (P < or = 0.04). CONCLUSIONS: Being unfit warrants consideration as a risk factor, distinctly from inactivity, and worthy of screening and intervention. Formulating physical activity recommendations on the basis of fitness studies may inappropriately demote the status of physical fitness as a risk factor while exaggerating the public health benefits of moderate amounts of physical activity.

Shear strengths of a gallium alloy bonded to human enamel following nine different surface treatments.

OBJECTIVE: Gallium and indium-containing alloys have demonstrated an ability to wet and bond to many types of materials including enamel. The purpose of this study was to evaluate and compare the bond strengths of a gallium-and-indium-containing alloy and a dental amalgam to human enamel surfaces. METHOD: A flat enamel bonding surface was created by slicing recently extracted human molars with a 180-grit diamond wheel. Cylinders of amalgam or a gallium-indium alloy were bonded to the as-cut surfaces or to as-cut surfaces that had been pumiced, air-abraded or acid-etched for various times. Before testing, samples were stored under different conditions (100% humidity, immersed in water, thermocycled). The shear-bond strength was determined using a crosshead speed of 0.1 mm x min(-1). Sample size was 10. Data was subjected to ANOVA and a post-hoc Tukey's test. RESULTS: The bond strength of amalgam to enamel was zero. The bond strength of the gallium-indium alloy ranged between 6.5 MPa (10s etch with 10% phosphoric acid) and 4.2 MPa (pumiced enamel). Acid-etching significantly increased the bond strength (P>0.0001) The bond strength was not significantly affected by the type of mechanical surface preparation, storage conditions, thermocycling, etching times or acid concentrations. SIGNIFICANCE: Bonding, particularly chemical bonding, suggests a greater potential for better wetting and therefore better sealing of a cavity. Since microleakage of restorations is one of the principal causes of restoration failure, materials that can bond may in turn posses enhanced resistance to microleakage and ultimately, resistance to restoration failure. The gallium-indium alloy evaluated in this study may be such an alloy.