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1.
Clin Psychol Psychother ; 31(3): e2993, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38723656

RESUMO

INTRODUCTION: Visual hallucinations (VH) are more common than previously thought and are linked to higher levels of distress and disability in people with a psychotic illness. Despite this, scant attention has been given to VHs in the clinical literature, and the few therapy case series of cognitive behavioural therapy (CBT) published to date have not demonstrated reliable change. In other areas of clinical research, problematic mental imagery has been found to be more strongly related to negative affect in psychological disorders than negative linguistic thinking, and imagery focused techniques have commonly been found to improve the outcomes in CBT trials. Given VHs have many similarities with visual mental imagery and many of the distressing beliefs associated with VHs targeted in CBT are maintained by accompanying mental imagery (i.e., imaging a hallucinated figure attacking them), it seems plausible that an imagery-focused approach to treating VHs may be most effective. METHODS: The current study is a multiple baseline case series (N = 11) of a 10-session imagery-focused therapy for VH in a transdiagnostic sample. RESULTS: The study had good attendance and feedback, no adverse events and only one [seemly unrelated] drop-out, suggesting good feasibility, safety and acceptability. The majority of clients reported reduction on both full-scale measures (administered at 3 baselines, midtherapy, posttherapy and 3-month follow-up) and weekly measures of VH severity and distress, ranging from medium to large effect sizes. CONCLUSIONS: The case series suggests that an imagery-focused approach to treating VHs may be beneficial, with a recommendation for more rigorous clinical trials to follow.


Assuntos
Alucinações , Imagens, Psicoterapia , Humanos , Alucinações/terapia , Alucinações/psicologia , Feminino , Masculino , Adulto , Imagens, Psicoterapia/métodos , Pessoa de Meia-Idade , Resultado do Tratamento , Transtornos Psicóticos/terapia , Transtornos Psicóticos/psicologia , Transtornos Psicóticos/complicações
2.
Artigo em Inglês | MEDLINE | ID: mdl-37905563

RESUMO

It is unknown to what extent mental imagery and auditory verbal hallucinations (AVHs) are related. Trials evaluating this issue used both emotional and non-emotional mental imagery tools, thereby complicating outcomes comparisons. Therefore, the present study aimed to systematically review the literature on mental imagery in individuals with AVHs to (1) inventory imagery assessment tools used in this population, (2) to collect information on the relation between emotional and non-emotional mental imagery in all sensory domains and AVHs and (3) to integrate the outcomes of this systematic review in a model of different mental imagery domains and related assessment tools. We conducted a systematic literature search in the PubMed Database. After full-text screening, 17 papers were included. Findings showed that a variety of assessment methods have been used to assess various aspects of mental imagery in people with AVHs, suggesting that there is a lack of agreed theoretical conceptualization of mental imagery and AVHs. In addition, the studies confirmed as was expected that non-emotional mental imagery seemed unrelated to AVHs whereas emotional mental imagery was related to AVHs. Lastly, we proposed a model of mental imagery domains and corresponding assessment methods distinguishing between emotional and non-emotional mental imagery.

4.
Pilot Feasibility Stud ; 9(1): 117, 2023 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-37422659

RESUMO

BACKGROUND: A high proportion of patients diagnosed with schizophrenia-spectrum disorders will at some point in their lives be assessed as not having the capacity to make their own decisions about pharmacological treatment or inpatient care ('capacity'). Few will be helped to regain it before these interventions proceed. This is partly because effective and safe methods to do so are lacking. Our aim is to accelerate their development by testing, for the first time in mental healthcare, the feasibility, acceptability and safety of running an 'Umbrella' trial. This involves running, concurrently and under one multi-site infrastructure, multiple assessor-blind randomised controlled trials, each of which is designed to examine the effect on capacity of improving a single psychological mechanism ('mechanism'). Our primary objectives are to demonstrate feasibility of (i) recruitment and (ii) data retention on the MacArthur Competence Assessment Tool-Treatment (MacCAT-T; planned primary outcome for a future trial) at end-of-treatment. We selected three mechanisms to test: 'self-stigma', low self-esteem and the 'jumping to conclusions' bias. Each is highly prevalent in psychosis, responsive to psychological intervention, and hypothesised to contribute to impaired capacity. METHODS: Sixty participants with schizophrenia-spectrum diagnoses, impaired capacity and one or more mechanism(s) will be recruited from outpatient and inpatient mental health services in three UK sites (Lothian, Scotland; Lancashire and Pennine; North West England). Those lacking capacity to consent to research could take part if the key criteria were met, including either proxy consent (Scotland) or favourable Consultee advice (England). They will be allocated to one of three randomised controlled trials, depending on which mechanism(s) they have. They will then be randomised to receive, over an 8-week period and in addition to treatment as usual (TAU), 6 sessions of either a psychological intervention which targets the mechanism, or 6 sessions of assessment of the causes of their incapacity (control condition). Participants are assessed at 0 (baseline), 8 (end-of-treatment) and 24 (follow-up) weeks post-randomisation using measures of capacity (MacCAT-T), mechanism, adverse events, psychotic symptoms, subjective recovery, quality of life, service use, anxiety, core schemata and depression. Two nested qualitative studies will be conducted; one to understand participant and clinician experiences and one to investigate the validity of MacCAT-T appreciation ratings. DISCUSSION: This will be the first Umbrella trial in mental healthcare. It will produce the first 3 single-blind randomised controlled trials of psychological interventions to support treatment decision-making in schizophrenia-spectrum disorder. Demonstrating feasibility will have significant implications not only for those seeking to support capacity in psychosis, but also for those who wish to accelerate the development of psychological interventions for other conditions. TRIAL REGISTRATION: ClinicalTrials.gov NCT04309435 . Pre-registered on 16 March 2020.

5.
Br J Clin Psychol ; 62(3): 621-641, 2023 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-37357531

RESUMO

OBJECTIVES: The experience of psychosis and its sequelae (including treatment experiences) can be traumatic and affect feelings of safety and security. Until relatively recently, trauma therapy has been avoided with psychosis populations due to concerns about additional harm. Intervention-based research is growing, but focus on psychosis-related trauma is limited. Engendering psychological safety may support engagement with trauma-focused therapy, for which attachment theory provides a strong foundation. Imagery can enhance felt security and is an effective modality for working with trauma. Therefore, this study aimed to examine feasibility and preliminary outcomes of a novel attachment-focused imagery therapy (A-iMAPS) addressing psychosis-related trauma. METHODS: A multiple baseline case series: Participants received between two and five baseline assessments then engaged in the six-session A-iMAPS intervention. Participants completed weekly measures of trauma symptoms and felt security. Further measures were completed pre- and post-intervention. RESULTS: Twelve clinical participants were recruited from NHS services in Northwest England and eight retained through baseline and intervention to the end-of-therapy assessment (attending all sessions). A significant improvement was seen for felt security between baseline and intervention phases. Other measures of trauma symptoms, core schemas, paranoia and attachment varied in change from baseline to end of therapy, but some promising preliminary results were seen. CONCLUSIONS: This study shows that a brief attachment-focused imagery therapy is a promising intervention for targeting psychosis-related trauma, for which there are currently no other specific intervention studies. Utilizing an attachment-informed framework when working with trauma in psychosis should be considered in future intervention studies.


Assuntos
Imagens, Psicoterapia , Transtornos Psicóticos , Humanos , Transtornos Psicóticos/terapia , Transtornos Psicóticos/psicologia , Transtornos Paranoides , Psicoterapia , Emoções
6.
Psychol Psychother ; 96(3): 678-696, 2023 09.
Artigo em Inglês | MEDLINE | ID: mdl-37002818

RESUMO

OBJECTIVES: To examine the feasibility and acceptability of a novel telehealth (video-conferencing software and telephone calls) imagery-based therapeutic intervention for people experiencing persecutory delusions. Utilising a multiple baseline case series design and exploring imagery-focused therapy for psychosis (iMAPS). DESIGN: A non-concurrent A-B multiple baseline design was used. METHODS: Participants experiencing persecutory delusions and self-reporting a psychosis or schizophrenia-spectrum diagnosis were recruited through online adverts. On completion of assessments, participants were randomly assigned to multiple baseline assessments, of between three and five sessions. Six therapy sessions followed, consisting of imagery formulation, safe-place imagery creation, compassionate imagery, imagery manipulation and rescripting. Participants completed pre- and post-measures and sessional measures via an online survey software or in semi-structured interviews. Two weeks post-intervention, a final measure was completed exploring any potential adverse effects of psychotherapy. RESULTS: Five female participants completed all baseline and therapeutic sessions, suggesting the therapy was and mode of delivery was feasible and acceptable. Results indicate strong effect sizes across PANSS positive subscale and mood, as well as participants reporting a clinically significant change in at least one measure, for example, PSYRATS. All participants reported a reduction in the realness and compelling nature of distressing imagery. CONCLUSIONS: Results suggest delivering a telehealth imagery-focused therapy is acceptable and feasibly delivered via telehealth. A control group and blinding of assessments would strengthen the methodological limitations present.


Assuntos
Transtornos Psicóticos , Esquizofrenia , Telemedicina , Humanos , Feminino , Imagens, Psicoterapia , Transtornos Psicóticos/terapia , Esquizofrenia/terapia , Delusões/terapia
7.
Psychiatry Res ; 323: 115163, 2023 05.
Artigo em Inglês | MEDLINE | ID: mdl-36948019

RESUMO

Traumatic events play a key role in the development and course of psychosis. Psychotic symptoms themselves and coercive treatment practices can be inherently traumatic. Hence, reliable and valid methods of assessing trauma and its impact (i.e., Post-Traumatic Stress Disorder (PTSD) symptomology) are essential for use with people with psychosis. Many measures are available to select from, but this is the first review to appraise the psychometric properties of trauma measures to guide decision making regarding instrument use. The review was prospectively registered on Prospero (CRD42022306100). Evaluation of methodological and psychometric quality followed Consensus-based Standards for the selection of health Measurement Instruments (COSMIN) guidance. Twenty-four articles were eligible, with sixteen trauma measures evaluated. Childhood Trauma Questionnaire- Short Form demonstrated the most robust evidence for assessing experience of trauma. The Trauma and Life Experience (TALE) checklist was the only measure to include specific psychosis and iatrogenic harm items. For PTSD measures, the Symptoms of Trauma Scale and PTSD Symptom Scale- Self Report had the highest quality evidence. Psychometric strengths and weaknesses of various trauma measures are comprehensively evaluated, highlighting future research directions to strengthen the evidence base with emphasis on further evaluation of the TALE, which integrates trauma specific to psychosis.


Assuntos
Comportamento Problema , Transtornos Psicóticos , Transtornos de Estresse Pós-Traumáticos , Humanos , Psicometria , Transtornos Psicóticos/diagnóstico , Transtornos de Estresse Pós-Traumáticos/diagnóstico , Transtornos de Estresse Pós-Traumáticos/terapia , Autorrelato
8.
Child Adolesc Ment Health ; 27(3): 246-249, 2022 09.
Artigo em Inglês | MEDLINE | ID: mdl-35869030

RESUMO

BACKGROUND: There is a wealth of evidence to suggest that the Borderline Personality Disorder (BPD, or similar Emotionally Unstable Personality Disorder, EUPD) construct is harmful. We provide a commentary on the ideas expressed in the May Debate issue, highlighting both concerns and alternatives. METHOD: We bring together lived experience, clinical and research expertise. This commentary was written collaboratively drawing on all these sources of evidence. RESULTS: We outline evidence that the BPD construct is invalid, harmful, not necessary for effective treatment and a potential block to the development and evaluation of alternatives. CONCLUSIONS: We ask readers to consider these concerns, perspectives and ideas.


Assuntos
Transtorno da Personalidade Borderline , Transtornos da Personalidade , Adolescente , Transtorno da Personalidade Borderline/diagnóstico , Humanos , Transtornos da Personalidade/diagnóstico , Transtornos da Personalidade/tratamento farmacológico
9.
Front Psychiatry ; 12: 789418, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34925112

RESUMO

Background: Discharge from acute mental health inpatient units is often a vulnerable period for patients. Multiple professionals and agencies are involved and processes and procedures are not standardized, often resulting in communication delays and co-ordination failures. Early and appropriate discharge planning and standardization of procedures could make inpatient care safer. Aim: To inform the development of a multi-component best practice guidance for discharge planning (including the 6 component SAFER patient flow bundle) to support safer patient transition from mental health hospitals to the community. Methods: Using the RAND/UCLA Appropriateness method, a panel of 10 professional stakeholders (psychiatrists, psychiatric nurses, clinical psychologists, pharmacists, academics, and policy makers) rated evidence-based statements. Six hundred and sixty-eight statements corresponding to 10 potential components of discharge planning best practice were rated on a 9-point integer scale for clarity, appropriateness and feasibility (median ≥ 7-9) using an online questionnaire then remote online face-to-face meetings. Results: Five of the six "SAFER" patient flow bundle components were appropriate and feasible for inpatient mental health. One component, "Early Flow," was rated inappropriate as mental health settings require more flexibility. Overall, 285 statements were rated as appropriate and feasible. Forty-four statements were considered appropriate but not feasible to implement. Discussion: This consensus study has identified components of a best practice guidance/intervention for discharge planning for UK mental health settings. Although some components describe processes that already happen in everyday clinical interactions (i.e., review by a senior clinician), standardizing such processes could have important safety benefits alongside a tailored and timely approach to post-discharge care.

10.
BMJ Open ; 11(11): e046755, 2021 11 16.
Artigo em Inglês | MEDLINE | ID: mdl-34785541

RESUMO

OBJECTIVES: The aim of the project was to examine the acceptability and feasibility of a mobile phone application-based intervention 'TechCare', for individuals with psychosis in the North West of England. The main objectives were to determine whether appropriate individuals could be identified and recruited to the study and whether the TechCare App would be an acceptable intervention for individuals with psychosis. METHODS: This was a mixed methods feasibility study, consisting of a test-run and feasibility evaluation of the TechCare App intervention. SETTING: Early Intervention Services (EIS) for psychosis, within an NHS Trust in the North West of England. PARTICIPANTS: Sixteen participants (test-run n=4, feasibility study n=12) aged between 18 and 65 years recruited from the East, Central and North Lancashire EIS. INTERVENTION: A 6-week intervention, with the TechCare App assessing participants' symptoms and responses in real-time and providing a personalised-guided self-help-based psychological intervention based on the principles of Cognitive Behaviorual Therapy (CBT). RESULTS: A total of 83.33% (n=10) of participants completed the 6-week feasibility study, with 70% of completers achieving the set compliance threshold of ≥33% engagement with the TechCare App system. Analysis of the qualitative data suggested that participants held the view that the TechCare was both an acceptable and feasible means of delivering interventions in real-time. CONCLUSION: Innovative digital clinical technologies, such as the TechCare App, have the potential to increase access to psychological interventions, reduce health inequality and promote self-management with a real-time intervention, through enabling access to mental health resources in a stigma-free, evidence-based and time-independent manner. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov Identifier: NCT02439619.


Assuntos
Aplicativos Móveis , Transtornos Psicóticos , Autogestão , Adolescente , Adulto , Idoso , Estudos de Viabilidade , Disparidades nos Níveis de Saúde , Humanos , Pessoa de Meia-Idade , Transtornos Psicóticos/terapia , Adulto Jovem
11.
Chem Rev ; 121(20): 12327-12383, 2021 10 27.
Artigo em Inglês | MEDLINE | ID: mdl-34259500

RESUMO

High-level radioactive waste is accumulating at temporary storage locations around the world and will eventually be placed in deep geological repositories. The waste forms and containers will be constructed from glass, crystalline ceramic, and metallic materials, which will eventually come into contact with water, considering that the period of performance required to allow sufficient decay of dangerous radionuclides is on the order of 105-106 years. Corrosion of the containers and waste forms in the aqueous repository environment is therefore a concern. This Review describes the recent advances of the field of materials corrosion that are relevant to fundamental materials science issues associated with the long-term performance assessment and the design of materials with improved performance, where performance is defined as resistance to aqueous corrosion. Glass, crystalline ceramics, and metals are discussed separately, and the near-field interactions of these different material classes are also briefly addressed. Finally, recommendations for future directions of study are provided.


Assuntos
Resíduos Radioativos , Corrosão , Resíduos Radioativos/análise
12.
Sci Data ; 8(1): 58, 2021 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-33574339

RESUMO

Corrosion is an electrochemical phenomenon. It can occur via different modes of attack, each having its own mechanisms, and therefore there are multiple metrics for evaluating corrosion resistance. In corrosion resistant alloys (CRAs), the rate of localized corrosion can exceed that of uniform corrosion by orders of magnitude. Therefore, instead of uniform corrosion rate, more complex electrochemical parameters are required to capture the salient features of corrosion phenomena. Here, we collect a database with an emphasis on metrics related to localized corrosion. The six sections of the database include data on various metal alloys with measurements of (1) pitting potential, Epit, (2) repassivation potential, Erp, (3) crevice corrosion potential, Ecrev, (4) pitting temperature, Tpit, (5) crevice corrosion temperature, Tcrev, and (6) corrosion potential, Ecorr, corrosion current density, icorr, passivation current density, ipass, and corrosion rate. The experimental data were collected from 85 publications and include Al- and Fe-based alloys, high entropy alloys (HEAs), and a Ni-Cr-Mo ternary system. This dataset could be used in the design of highly corrosion resistant alloys.

13.
Behav Cogn Psychother ; 48(5): 530-545, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32264985

RESUMO

BACKGROUND: Many people with psychosis experience persecutory delusions and report negative schematic beliefs and intrusive mental images which may be maintaining factors for psychotic symptoms. AIMS: This study examined the feasibility and acceptability of a new psychological therapy targeting schemas and images (iMAPS therapy). METHOD: The study used a randomised multiple baseline design. Participants with first episode psychosis were randomised using a multiple baseline design with 2-5 assessments. Six sessions of therapy, consisting of a combination of imagery techniques and imagery rescripting techniques, was used. In each session, participants completed a Mental Imagery in Psychosis Questionnaire (MIPQ) and imagery interview. Mood and delusional beliefs (PSYRATS) were also measured at each session. RESULTS: Five participants with first episode psychosis completed the baseline visits and attended all therapy sessions. One participant declined the final assessment. Results demonstrated significant reductions in negative schematic beliefs, delusions, imagery distress and other measures of schema (YSQ, SMI). Although multiple baseline randomisation strengthens the study, it lacked a control arm and blind assessments. CONCLUSIONS: iMAPS appears a feasible and acceptable treatment for psychosis, and further evaluation is indicated.


Assuntos
Delusões , Imagens, Psicoterapia , Transtornos Psicóticos , Delusões/terapia , Humanos , Transtornos Psicóticos/terapia , Projetos de Pesquisa
14.
Behav Cogn Psychother ; 48(1): 67-81, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30957739

RESUMO

BACKGROUND: Cognitive behavioural treatments are recommended for people with psychosis. Core beliefs regarding the self and others are a key part of the models underpinning cognitive behavioural therapy but detailed understanding of these putative beliefs in people with psychosis are limited. A greater understanding of these mechanisms is necessary to improve and refine treatments. AIMS: This study utilized a qualitative approach to explore core schematic beliefs in psychosis (strongly held positive and negative beliefs about the self and others) and their relation to hallucinations and delusions. METHOD: Twenty individuals with psychosis participated in individual semi-structured interviews. Inductive thematic analysis was used to analyse the interviews. RESULTS: Four emergent themes were identified: (i) the solidity and permanency of core beliefs, (ii) the causes and development of core beliefs, (iii) a synergistic relationship between core beliefs and symptoms, and (iv) core beliefs associated with images and their influence on psychotic symptoms. CONCLUSIONS: This study provides new insights into the range and character of core beliefs in psychosis and provides important data to guide ongoing and future development of treatment approaches for psychosis.


Assuntos
Cultura , Delusões/diagnóstico , Delusões/psicologia , Transtornos Psicóticos/diagnóstico , Transtornos Psicóticos/psicologia , Esquizofrenia/diagnóstico , Psicologia do Esquizofrênico , Adolescente , Adulto , Terapia Cognitivo-Comportamental/métodos , Delusões/terapia , Feminino , Alucinações/diagnóstico , Alucinações/psicologia , Humanos , Imaginação , Entrevista Psicológica , Masculino , Pessoa de Meia-Idade , Transtornos Psicóticos/terapia , Pesquisa Qualitativa , Esquizofrenia/terapia , Adulto Jovem
15.
J Ment Health ; 27(4): 336-344, 2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-29271276

RESUMO

BACKGROUND: Clinical guidelines recommend cognitive behaviour therapy (CBT) for people with psychosis, however, implementation is poor and not everyone wishes to engage with therapy. Understanding service user (SU) preferences for receiving such treatments is a priority for services. AIMS: To explore SU preferences and outcomes of different methods of delivering CBT for psychosis. METHOD: SUs experiencing psychosis could choose between treatment as usual (TAU); TAU plus telephone-delivered CBT with self-help, CBT recovery manual (TS); high support CBT (HS - TAU plus TS plus group sessions) or randomisation. Participants received their option of choice and were followed-up on several outcomes over 9 and 15 months. RESULTS: Of 89 people recruited, three chose to be randomised and 86 expressed a treatment preference (32 chose TAU, 34 chose TS, 23 chose HS). There were few differences between those who chose therapy compared to those who chose TAU. Those who had more positive impacts from their symptoms were significantly more likely to choose TAU. CONCLUSIONS: Most people had strong preferences about treatment delivery and a substantial number did not wish to receive additional therapy. These findings have to be considered when planning and allocating resources for people with psychosis.


Assuntos
Terapia Cognitivo-Comportamental , Preferência do Paciente , Transtornos Psicóticos/psicologia , Transtornos Psicóticos/terapia , Adolescente , Adulto , Idoso , Atenção à Saúde , Humanos , Pessoa de Meia-Idade , Resultado do Tratamento , Adulto Jovem
16.
Psychol Psychother ; 90(3): 456-479, 2017 09.
Artigo em Inglês | MEDLINE | ID: mdl-28035734

RESUMO

PURPOSE: Schema therapy was first applied to individuals with borderline personality disorder (BPD) over 20 years ago, and more recent work has suggested efficacy across a range of disorders. The present review aimed to systematically synthesize evidence for the efficacy and effectiveness of schema therapy in reducing early maladaptive schema (EMS) and improving symptoms as applied to a range of mental health disorders in adults including BPD, other personality disorders, eating disorders, anxiety disorders, and post-traumatic stress disorder. METHODS: Studies were identified through electronic searches (EMBASE, PsycINFO, MEDLINE from 1990 to January 2016). RESULTS: The search produced 835 titles, of which 12 studies were found to meet inclusion criteria. A significant number of studies of schema therapy treatment were excluded as they failed to include a measure of schema change. The Clinical Trial Assessment Measure was used to rate the methodological quality of studies. Schema change and disorder-specific symptom change was found in 11 of the 12 studies. CONCLUSIONS: Schema therapy has demonstrated initial significant results in terms of reducing EMS and improving symptoms for personality disorders, but formal mediation analytical studies are lacking and rigorous evidence for other mental health disorders is currently sparse. PRACTITIONER POINTS: First review to investigate whether schema therapy leads to reduced maladaptive schemas and symptoms across mental health disorders. Limited evidence for schema change with schema therapy in borderline personality disorder (BPD), with only three studies conducting correlational analyses. Evidence for schema and symptom change in other mental health disorders is sparse, and so use of schema therapy for disorders other than BPD should be based on service user/patient preference and clinical expertise and/or that the theoretical underpinnings of schema therapy justify the use of it therapeutically. Further work is needed to develop the evidence base for schema therapy for other disorders.


Assuntos
Transtornos Mentais/terapia , Avaliação de Resultados em Cuidados de Saúde , Psicoterapia/métodos , Humanos
17.
Environ Sci Technol ; 50(10): 5216-24, 2016 05 17.
Artigo em Inglês | MEDLINE | ID: mdl-27049925

RESUMO

Iron oxides and oxyhydroxides play an important role in minimizing the mobility of redox-sensitive elements in engineered and natural environments. For the radionuclide technetium-99 (Tc), these phases hold promise as primary hosts for increasing Tc loading into glass waste form matrices, or as secondary sinks during the long-term storage of nuclear materials. Recent experiments show that the inverse spinel, magnetite [Fe(II)Fe(III)2O4], can incorporate Tc(IV) into its octahedral sublattice. In that same class of materials, trevorite [Ni(II)Fe(III)2O4] is also being investigated for its ability to host Tc(IV). However, questions remain regarding the most energetically favorable charge-compensation mechanism for Tc(IV) incorporation in each structure, which will affect Tc behavior under changing waste processing or storage conditions. Here, quantum-mechanical methods were used to evaluate incorporation energies and optimized lattice bonding environments for three different, charge-balanced Tc(IV) incorporation mechanisms in magnetite and trevorite (∼5 wt % Tc). For both phases, the removal of two octahedral Fe(II) or Ni(II) ions upon the addition of Tc(IV) in an octahedral site is the most stable mechanism, relative to the creation of octahedral Fe(III) defects or increasing octahedral Fe(II) content. Following hydration-energy corrections, Tc(IV) incorporation into magnetite is energetically favorable while an energy barrier exists for trevorite.


Assuntos
Compostos Férricos/química , Tecnécio/química , Óxido Ferroso-Férrico/química , Oxirredução
18.
Environ Sci Technol ; 49(22): 13699-707, 2015 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-26513333

RESUMO

During the processing of low-activity radioactive waste to generate solid waste forms (e.g., glass), technetium-99 (Tc) is of concern because of its volatility. A variety of materials are under consideration to capture Tc from waste streams, including the iron oxyhydroxide, goethite (α-FeOOH), which was experimentally shown to sequester Tc(IV). This material could ultimately be incorporated into glass or alternative low-temperature waste form matrices. However, questions remain regarding the incorporation mechanism for Tc(IV) in goethite, which has implications for predicting the long-term stability of Tc in waste forms under changing conditions. Here, quantum-mechanical calculations were used to evaluate the energy of five different charge-compensated Tc(IV) incorporation scenarios in goethite. The two most stable incorporation mechanisms involve direct substitution of Tc(IV) onto Fe(III) lattice sites and charge balancing either by removing one nearby H(+) (i.e., within 5 Å) or by creating an Fe(III) vacancy when substituting 3 Tc(IV) for 4 Fe(III), with the former being preferred over the latter relative to gas-phase ions. When corrections for hydrated references phases are applied, the Fe(III)-vacancy mechanism becomes more energetically competitive. Calculated incorporation energies and optimized bond lengths are presented. Proton movement is observed to satisfy undercoordinated bonds surrounding Fe(III)-vacancies in the goethite structure.


Assuntos
Compostos de Ferro/química , Minerais/química , Resíduos Radioativos , Tecnécio/química , Compostos Férricos/química , Modelos Teóricos , Oxirredução , Prótons , Teoria Quântica , Temperatura
20.
Sci Rep ; 5: 9286, 2015 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-25788358

RESUMO

We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O2 bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H2O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date.

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